FULL PAPER DOI: 10.1002/chem.201301928

Reactivity of Bridged Pentelidene Complexes with Isonitriles: A New Way to Pentel-Containing Heterocycles Michael Seidl,[a] Michael Schiffer,[a] Michael Bodensteiner,[a] Alexey Y. Timoshkin,[b] and Manfred Scheer*[a] Abstract: The reaction of [Cp*E{W(CO)5}2] (E = P (1 a), As (1 b); Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl) with isonitriles RNC (R = tBu, cyclohexyl (Cy), nBu) depends on the steric demand of the substituent at the isonitrile as well as on the stoichiometry of the starting materials. With tBuNC only the Lewis acid/base adducts [Cp*E{W(CO)5}2ACHTUNGRE(CNtBu)] (E = P (2 a), As (2 b)) are formed. The use of Cy and n-butylisonitrile leads first to the formation of the Lewis acid/base adduct, but only at low temperatures. At ambient temperatures, a rearrangement occurs and bicycloACHTUNGRE[3.2.0]heptane derivatives of the type [{C(Me)CACHTUNGRE(CH2)C(Me)C(Me)C(Me)}C(NR)E{W(CO)5}2] (E = P, As; R = Cy, nBu) (3 a-Cy, 3 b-Cy, 3 a-nBu and 3 b-nBu)

are obtained. The use of a further equivalent of isonitrile results in products revealing two new structural motifs, the four-membered ring derivatives [CACHTUNGRE(Cp*)N(R)C(NR)E{W(CO)5}2] (4: E = P, As; R = Cy, nBu) and the bicyclic complexes [[{C(Me)CACHTUNGRE(CH2)C(Me)C(Me)C(Me)}C(NR)2E{W(CO)5}2] (5: E = As; R = Cy). The reaction pathway depends on the substituent at the isonitrile. By treatment of 1 a with two equivalents of CyNC only a 2H-1,3-azaphosphet complex 4 a-Cy (E = P; R = Cy) is formed. Treatment of 1 b with two equivalents of Keywords: arsenic · heterocycles · isonitriles · pentelidenes · phosphorus · X-ray diffraction

Introduction Carbene complexes of transition metals are widely used compounds in organic synthesis and catalysis.[1] Their Group 15 relatives, the pentelidene complexes bearing a PR unit, represent for terminal coordinated complexes an established class of compounds.[2] In comparison the area of bridged complexes with a delocalized MEM bond is rather underdeveloped; in the past, different types of compounds have been synthesized,[3, 5] although their reactivity was not the focus of interest. This has been changed by recent contributions of the Ruiz group[4] and by us.[6–12] Our special interest is dedicated to the reactivity of Cp*-containing bridged pentelidene complexes of the formulae [a] M. Seidl, Dr. M. Schiffer, Dr. M. Bodensteiner, Prof. Dr. M. Scheer Institut fr Anorganische Chemie der Universitt Regensburg 93040 Regensburg (Germany) Fax: (+ 49) 941-943-4439 E-mail: [email protected] [b] Prof. Dr. A. Y. Timoshkin Department of Chemistry St. Petersburg State University 198504 Old Peterhoff, St. Petersburg (Russia)

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CyNC exclusively leads to the complex 5 b-Cy (E = As; R = Cy). Treatment of 1 a with two equivalents of nBuNC results in a mixture of complexes, the 2H-1,3-azaphosphet 4 a-nBu (E = P; R = nBu) and the bicyclic complex 5 a-nBu (E = P; R = nBu). For the arsenidene complex 1 b a mixture of the 2H-1,3-azarsete complex 4 b-nBu (E = As; R = nBu) and the bicyclic complex 5 b-nBu (E = P, As; R = Cy, nBu) is obtained. Complex 4 b-nBu is the first example of a 2H-1,3-azarsete complex. All products have been characterized by using mass spectrometry, NMR spectroscopy, and X-ray diffraction analysis.

[Cp*E{W(CO)5}2] (E = P (1 a), As (1 b); Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl),[5] which show an extremely versatile reactivity pattern. The labile bound-Cp* group shifts easily to the metal atom after thermal activation leading to an intermediate containing a pentel–tungsten triple bond,[6] which can be trapped by alkynes,[7] phosphaalkynes,[8] and triply bound dimetallic complexes.[9] Photolysis of the pentelidene complexes induces a Cp* radical elimination resulting in the presence of diphosphenes to triphospha- or arsadiphosphaallyl radicals.[10] Notable in the reaction with nitriles, Cp* migration of the phosphinidene complex occurs yielding new P-containing heterocycles.[11] Interestingly, along with a Cp* ring expansion initiated by MesCP[8] (Mes = 2,4,6Me3C6H2) and the hydrophosphination reaction to give transient diphospha- and arsaphosphanorbornene derivatives,[12] for these bridged compounds no formation of heterocycles has been observed so far. However, this direction attracts our interest and we started to evaluate the potential of these compounds for the design of heterocycles featuring different main group elements in one system. The mentioned hydrophosphination reaction of a primary phosphine starts with a nucleophilic attack at the maingroup-element center E of the pentelidene complexes [Cp*E{W(CO)5}2] (E = P, As). Thus, the use of appropriate

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nucleophiles, which can open additional reactions channels, was of interest. So, isonitriles[13] came into the focus of our interest, which are known to be good donors, revealing a carbene-like character with additional functions caused by their zwitterionic nature.[14] Because of their unique properties, isonitriles have become indispensable building-blocks for organic synthesis, especially for the synthesis of heterocycles.[15] In the following we report on the reactions of the bridged-pentelidene complexes with isonitriles resulting in a variety of new heterocyclic compounds. These reactions can be controlled by the steric demand of the organic substituent at the isonitrile as well as by the stoichiometry of the starting materials. In most cases, an activation and conversion of the Cp* substituent occurred for which very few examples are known in the literature.[8, 12, 16]

bulky tert-butyl group at the isonitrile, no subsequent reactions occur (see below) and also with an excess of this nitrile no other reactions proceed. For 2 a, dissociation into the starting materials takes place after heating the solution to 110 8C for some minutes, whereas 2 b decomposes under these conditions into unidentified materials. If the sterically less-demanding CyNC (Cy = cyclohexyl) is used in a 1:1 reaction with 1 a/b, the bicyclic complexes 3 a-Cy and 3 b-Cy (Scheme 1) are formed. The reaction proceeds already at 78 8C monitored by a color change after the addition of the isonitrile. This indicates the formation of the initially formed Lewis base adducts (2 a/b-like). On warming the reaction mixture to room temperature, the transformation to 3 a-Cy and 3 b-Cy, respectively, occurs. The temperature range between 78 and 27 8C has been monitored by using 31P{1H} NMR spectroscopy for the reaction of the P-containing starting material 1 a with CyNC. From 78 to 0 8C only one singlet at d = 73.7 ppm with 1 Results and Discussion JACHTUNGRE(P,W) = 164 Hz is observed. This chemical shift is almost identical to that of 2 a (d = 73.1 ppm), which proves the The sequence of the reaction of the pentelidene complexes first occurrence of the Lewis acid/base adduct 2 a-Cy. At [Cp*E{W(CO)5}2] (1: E = P (a), As (b)) with isonitriles is il0 8C, the signal of 3 a-Cy appears at d = 25.4 ppm (1JACHTUNGRE(P,W) = 143 Hz; 156 Hz). By further reducing the steric bulk of the substituent at the isonitrile and the use of nBuNC in a 1:1 stoichiometric reaction with 1 a/b the complexes with the structural motif of 3 are obtained. By using this method 3 a-nBu was isolated in good yields, for which the single-crystal X-ray structural analysis shows that only the Z isomer of 3 a-nBu exists (Scheme 2). The 1 H and 31P NMR spectra on the other hand reveal two sets of signals, which suggested the presence of two isomers of 3 a-nBu in solution. Isolated crystals of 3 a-nBu were dissolved in C6D6 and the 1H and 31 P NMR spectra were measured, which show also two sets of signals, one for each isomer. The 31P NMR spectrum showed Scheme 1. Sequence of the reaction between [Cp*E{W(CO)5}2] (E = P, As) and isonitriles. two singlets, one at d = 1 24.5 ppm, with JACHTUNGRE(P,W) = lustrated in Scheme 1 and shows a strong dependency from the steric demand of the substituent at the nitrile and the stoichiometric ratio of the starting materials. Thus, immediately after tBuNC was added into the dark-blue solution of the pentelidene complexes 1 a/b, the color changes to yellow, which indicates the nucleophilic attack at the pentel atom by degradation of the initial 3c–4e bonding mode of the WPW system.[3a] The Lewis acid/base adducts 2 a/b (Scheme 1) were isolated in very good yields. Due to the Scheme 2. Equilibrium between the two isomers of 3 a-nBu in solution.

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143 Hz, 151 Hz, and the other one at d = 27.1 ppm, with 1 JACHTUNGRE(P,W) = 144 Hz, in the ratio 82 to 18. It was possible to assign the signal sets to the corresponding isomers, by applying rotating frame nuclear Overhauser effect NMR spectroscopy (ROESY) in which only the Z isomer showed a coupling between the proton at the nitrogen atom and a methyl group at the Cp* fragment. These results prove that a transformation of the Z isomer into the E isomer takes place. The Z isomer is still the main component, which is consistent with theoretical calculations predicting the Z isomer to be marginally more stable (by 2 kJ mol1) than the E isomer. The treatment of the arsenic derivative 1 b with nBuNC leads to 3 b-nBu. It was possible to isolate crystals of 3 b-nBu at low temperatures, but in contrast to the isostructural 3 b-Cy this complex rearranges slowly in solution at room temperature into the educts, which is shown by the blue color of free 1 b. However, the free nBuNC reacts further with other 3 b-nBu to form the more stable compound 5 b-nBu (Scheme 1), which was detected by using 1H NMR spectroscopy. This finding reveals already the possibility of subsequent reactions if an excess of isonitrile is used, for which two different reaction channels have been found. Treatment of the phosphinidene complex [Cp*P{W(CO)5}2] (1 a) with two equivalents of CyNC leads to the new 2,3-dihydro-1,3-azaphosphete complex 4 a-Cy (Scheme 1). During this process the Cp* ligand rearranges and migrates from the phosphorus to the carbon atom of one isonitrile. Complex 4 a-Cy can be described as a zwitterionic-like four-membered heterocycle, which is composed of two isonitriles and the phosphorus atom of the phosphinidene complex. Only two other examples of such a structural motif are mentioned in the literature; Roques et al. reported the reaction of a phosphenium cation with isonitriles, which led to a 1-aza-3-phosphetine cation, as they proposed by spectroscopic data.[17] This reveals the similarities of electron-deficient phosphenium cations and the electrophilic phosphinidene complex. The other example was found by Streubel et al., which involved the treatment of a 2H-azaphosphirene with CyNC in the presence of trifluoromethansulfonic acid and triethylamine.[18] Contrary to the reaction of the phosphinidene complex 1 a with two equivalents of CyNC, the reaction with the arsenidene complex 1 b results in the formation of the constitutional isomer 5 b-Cy, a bicyclic system composed of two five-membered rings (Scheme 1). The complex 3 b-Cy can be transformed into 5 b-Cy by the insertion of a second isonitrile into an AsC bond. This insertion is favored by the reduction of the ring strain, going from a four-membered- to a five-membered-ring system. For example, insertion reactions of isonitriles into a BB bond have been reported.[19] However, to the best of our knowledge, there is no example of an insertion of an isonitrile into an AsC bond. To determine if this insertion reaction occurred, compound 3 b-Cy was treated with one equivalent of the isonitrile and after a period of time signals for 5 b-Cy could be monitored in the 1 H NMR spectrum. Moreover, the corresponding treatment of the phosphorus derivative 3 a-Cy gave no evidence for

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the formation of 5 a-Cy; only the signals for 4 a-Cy were found in the 31P NMR spectrum, indicating that no insertion into the PC bond took place. In contrast, for the reaction with nBuNC both products 4 a-nBu and 5 a-nBu were formed in a ratio of 70 to 30, and they can be separated by using column chromatography. The 31P NMR spectrum of 4 a-nBu shows a singlet at d = 58.5 ppm, which is shifted to low-field relative to 4 a-Cy (d = 48.0 ppm; 1JACHTUNGRE(P,W) = 160 Hz). For 5 a-nBu a singlet at d = 101.2 ppm can be observed. For the subsequent reactions of 3 with different substituted isonitriles, see the Supporting Information. If the arsenidene complex 1 b is treated with two equivalents of nBuNC, two compounds are formed, 4 b-nBu and 5 b-nBu. However, compound 5 b-nBu is the main product with a ratio of 72 to 28 % of 4 b-nBu. We were able to isolate crystals of 4 b-nBu accompanied by crystals of 5 b-nBu. Unfortunately, attempts to separate both products by using column chromatography were unsuccessful (due to the decomposition of 4 b-nBu). Whereas 5 b represents a new bicyclic heterocycle of arsenic, product 4 b-nBu is the first example of a 4-membered 2,3-dihydro-1,3-azarsete complex. The structures of all products were confirmed by using X-ray crystallography. The molecular structures of the complexes 2 a/b are shown in Figure 1. The coordination geome-

Figure 1. Molecular structure of 2 a/b. Hydrogen atoms are omitted for clarity. Selected bond lengths [] and angles [8]: Compound 2 a: W1P1 2.6129(12), W2P1 2.5778(13), P1C11 1.922(5), P1C21 1.796(6), N1 C21 1.140(7); W1-P1-W2 120.3(1), W1-P1-C11 117.7(2), W1-P1-C21 94.4 (2), W2-P1-C11 116.1(2), W2-P1-C21 102.9 (2), C11-P1-C21 97.3(2), C21N1-C22 178.2(6). Compound 2 b: W1As1 2.6769(5), W2As1 2.6464(6), As1C11 2.035(5), As1C21 1.960(6), N1C21 1.147(7); W1-As1-W2 121.94(2), W1-As1-C11 116.88(15), W1-As1-C21 94.45(14), W2-As1-C11 116.19(15), W2-As1-C21 102.03(13), C11-As1-C21 95.8(2), C21-N1-C22 176.8(5).

try of the pentel atom changed from trigonal-planar at the pentelidene in complexes 1 a/b to a slightly distorted tetraACHTUNGREgonal coordination. With the change of the coordination geometry also an elongation of the EW bonds occurs.[11] The newly formed PC and AsC bonds are 1.796(6) and 1.960(6)  and hence in the normal range of single bonds. The molecular structures of 3 a/b-Cy and 3 a/b-nBu are shown in Figure 2. The complexes can be described as a zwitterionic bicyclic system formed by the five-membered ring of the Cp* ligand and a four-membered ring. The four-

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Figure 2. Molecular structures of 3 a/b-Cy (left) and 3 a/b-nBu (right). All hydrogen atoms except the ones bond to N1 and C18 have been omitted for clarity. Selected bond lengths [] and angles [8]: Compound 3 a-Cy: W1P1 2.6119(7), W2P1 2.6070(7), P1C11 1.958(3), P1C21 1.815(3), C11C12 1.574(4), C12C21 1.517(4), C13C18 1.336(5), C14C15 1.347(5), N1C21 1.291(4); W1-P1-W2 116.99(3), C11-P1-C21 74.90(14), P1-C11-C12 90.70(19), C11-C12-C21 96.0(2), P1-C21-C12 98.21(19). Compound 3 b-Cy: W1As1 2.6841(5), W2As1 2.6722(6), As1C11 2.082(5), As1C21 1.965(4), C11C12 1.569(6), C12C21 1.514(7), N1 C21 1.265(5); W1-As1-W2 118.76(2), C11-As1-C21 71.2(2), As1-C11-C12 91.2(3), C11-C12-C21 99.7(3), As1-C21-C12 97.5(2). Compound 3 anBu: W1P1 2.6183(14), W2P1 2.6140(14), P1C11 1.966(5) P1C21 1.823(6), C11C12 1.572(9), C12C21 1.503(7), C14C15 1.356(10), C13 C18 1.330(10), N1C21 1.286(7); W1-P1-W2 120.02(5), C11-P1-C21 74.0(3), P1-C11-C12 90.9(3), C11-C12-C21 95.8(4), P1-C21-C12 98.9(4). Compound 3 b-nBu: W1As1 2.6854(6), W2As1 2.6806(6), As1C11 2.080(5) As1C21 1.957(6), C11C12 1.563(8), C12C21 1.511(10), C13 C18 1.327(10), C14C15 1.336(10), N1C21 1.277(8); W1-As1-W2 122.32(2), C11-As1-C21 70.6(3), As1-C11-C12 91.9(4), C11-C12-C21 98.7(5), As1-C21-C12 98.4(4).

membered heterocycle consists of the carbon atom of the isonitrile, two carbon atoms of the Cp* ligand, and the pentel atom. The angle between the two planes, formed by the ring systems, is 114 8 (for 3 a-Cy/-nBu) and 113 8 (for 3 b-Cy/-nBu). The distances for C14–C15, C13–C18, and C21–N1 are similar in all four compounds (1.320–1.342, 1.336–1.355, and 1.265–1.291 , respectively) and in the range of CC and CN double bonds. With values of 1.815(3) and 1.823(6)  for 3 a-Cy/-nBu, the P1C21 distances represent PC single bonds. In comparison, the P1C11 bond lengths are elongated at 1.958(3) and 1.966(5) , most likely caused by the steric demands of the tungsten-pentacarbonyl fragment and the methyl groups at the Cp* ligand. The longer bond lengths also indicate that this P1-C11 bond is the weakest bond in this four-membered ring system and thus, should be first cleaved as can be seen in the subsequent reactions to 4 and 5, respectively. The same bonding situation is observed for 3 b-Cy/-nBu (As1–C21 1.965(4) / 1.957(6) ; As1–C11 2.082(5) /2.080(5) ). The angles in the four-membered ring are between 90 and 98 8, except the angle C11-E-C21 (E = P, As), which is 74.9/74.0 8 for 3 a-Cy/-nBu and 71.2/70.6 8 for 3 b-Cy/-nBu. The central feature of 4 a-Cy/-nBu and 4 b-nBu (Figure 3) is the four-membered ring system that is built from the pentel atom, one C atom of each isonitrile, and the N atom of one isonitrile. All distances are in the range of single bonds except for the distance between the C11 and N1 atom, which lies between a single and double bond. The two

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Figure 3. Molecular structure of 4 a/b-nBu (left) and 4 a-Cy (right). All hydrogen atoms have been omitted for clarity. Selected bond lengths [] and angles [8]: 4 a-Cy: W1P1 2.5803(11), W2P1 2.5686(12), P1C11 1.865(5), P1C12 1.902(5), N1C11 1.315(5), N1C12 1.462(6), N2C12 1.245(5); W1-P1-W2 125.04(5), C11-P1-C12 69.8(2), P1-C11-N1 97.5(3), C11-N1-C12 101.7(4), P1-C12-N1 91.0(3), P1-C12-N2 145.5(4), N1-C12N2 123.6(4). Compound 4 a-nBu: W1P1 2.5776(9), W2P1 2.5766(9), P1C11 1.880(4), P1C12 1.896(5), N1C11 1.317(6), N1C12 1.446(5), N2C12 1.251(6); W1-P1-W2 126.17(4), C11-P1-C12 69.7(2), P1-C11-N1 96.4(3), C11-N1-C12 102.6(3), P1-C12-N1 91.4(3), P1-C12-N2 148.6(3), N1-C12-N2 120.1(4). Compound 4 b-nBu: W1As1 2.6483(6), W2As1 2.6505(6), As1C11 2.010(5), As1C12 2.018(6), N1C11 1.342(7), N1 C12 1.447(7), N2C12 1.245(8); W1-As1-W2 128.19(3), C11-As1-C12 66.5(2), As1-C11-N1 96.4(3), C11-N1-C12 104.5(5), As1-C12-N1 92.7(4), As1-C12-N2 148.1(4), N1-C12-N2 119.3(5).

Scheme 3. Two resonance structures of the complexes 4 a/b-nBu and 4 a-Cy.

resonance structures of the complexes are shown in Scheme 3. Of note is the small angle between C11-E-C12 for these compounds (69.7(2) and 66.5(2)) 8, since it is even more strained than in 3. The structure of 5 a/b-nBu and 5 b-Cy (Figure 4) is characterized by the bicyclic system of two five-membered rings. The angle between the two planes formed by the ring systems is for 5 b-Cy/-nBu 110.5 8 and for 5 a-nBu 111.1 8. This is about 3 8 less than in the corresponding compounds 3 a/b. All bonds in the new-formed five-membered ring are in the range of single bonds. A proposed reaction pathway for the reaction of the pentelidene complexes with isonitriles is depicted in Scheme 4. The first step is the nucleophilic attack of the isonitrile at the pentel atom and the formation of the Lewis acid/base adduct 2. For tBuNC, this is the final product since the additional formation of a new CC bond is not possible due to the steric demands of the substituent at the isonitrile. For the other isonitriles a rearrangement occurs and a new CC bond is formed in the product 3. Finally, a deprotonation of the methyl group at the Cp* substituent proceeds by the nitrogen atom of the isonitrile, which alternatively could also

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FULL PAPER isonitrile into the EC bond to form 5 after some rearrangements. Another possible reaction pathway leads to the formation of 4 and includes the protonation of the CH2 group at the Cp* substituent by the proton of the iminium fragment. The attack of a second isonitrile at the pentel atom causes the migration of the Cp* substituent to the carbon atom of the first isonitrile, by cleaving the EC bond. Afterwards, the four-membered ring is closed by the formation of a new CN bond of 4.

Figure 4. Molecular structure of 5 a/b-nBu (left) and 5 b-Cy (right). All hydrogen atoms except the ones bond to N1 and C19 have been omitted for clarity. Selected bond lengths [] and angles [8]: Compound 5 b-Cy: W1As1 2.7122(3), W2As1 2.7160(3), As1C11 1.953(3), As1C17 2.011(3), C11C12 1.533(4), C12C16 1.546(4), C16C17 1.528(5), N1 C11 1.290(4), N2C17 1.258(5), C13C19 1.335(5), C14C15 1.334(5); W1-As1-W2 125.95(1), C11-As1-C17 85.48(14), As1-C11-C12 115.2(2), C11-C12-C16 108.2(2), C12-C16-C17 111.5(3), As1-C17-C16 112.0(2). Compound 5 a-nBu: W1P1 2.6258(16), W2P1 2.6246(16), P1C11 1.826(8), P1C17 1.857(7), C11C12 1.536(11), C12C16 1.559(10), C16 C17 1.537(11), N1C11 1.289(8), N2C17 1.281(8); W1-P1-W2 125.93(7), C11-P1-C17 88.6(3), P1-C11-C12 115.8(4), C11-C12-C16 105.8(6), C12C16-C17 108.5(6), P1-C17-C16 113.5(4). Compound 5 b-nBu: W1As1 2.6959(4), W2As1 2.6927(4), As1C11 1.950(4), As1C17 1.993(4), C11C12 1.536(6), C12C16 1.552(6), C16C17 1.525(7), N1C11 1.283(5), N2C17 1.261(5); W1-As1-W2 127.82(2), C11-As1-C17 85.07(17), As1-C11-C12 115.5(3), C11-C12-C16 107.0(4), C12-C16-C17 110.9(4), As1-C17-C16 112.7(3).

DFT calculations: Gas-phase reaction energetic profiles based on density functional theory (DFT) calculations are schematically presented in Figure 5, and thermodynamic parameters for the considered reactions are given in Table 1. Optimized structures of all compounds are given in the Supporting Information. All reactions with isonitriles are predicted to be exothermic. The nature of the substituent (nBu vs. Cy) plays a minor role on reaction energetics. Phosphorus-containing compounds react with isonitriles slightly more exothermically than arsenic-containing compounds, but the difference in reactivity is small (below 20 kJ mol1). Slightly weaker AsC versus PC bonds are expected on the basis of larger atomic radii of As. Energetically, reactions with a second isonitrile are very exothermic both for the formation of 4 and 5. Notably, compounds 5 a/5 b are the most energetically favorable products in the gas phase both for nBu and Cy substituents (including mixed compounds). Thus, formation of 4 a/4 b is rather kinetically controlled, whereas 5 a/5 b are thermodynamically controlled products. Although all computations have been performed for the gas phase, it is expected that the reaction energy trends will also hold in toluene solution. To check this assumption, reaction energies in toluene solution have been estimated by using the polarizable continuum model (PCM). Results show (Table 1), that gas-phase and solution reaction energies are close; the maximal difference does not exceed 12 kJ mol1.

Conclusion Scheme 4. Proposed pathways for the reactions of 1 a/b with isonitriles.

be the initial step before the CC bond-formation continues. If a second equivalent of isonitrile is present (1:2 ratio of the starting materials) two different paths are possible to react further with 3. One way is the insertion of a second

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The results have shown that the reactions of the pentelidene complexes with isonitriles leads to a series of new heterocycles containing Group 15 elements. Each reaction step of the reaction sequences was evidenced through isolated and structurally characterized compounds; it includes sequential

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steric demand of the substituent at the isonitrile and its stoichiometric ratio. Moreover, a first example of the insertion of an isonitrile into an AsC bond was found by the formation of 5 b as well as the first 2,3-diACHTUNGREhydro-1,3-azarsete complex 4 b.

Experimental Section Figure 5. Gas-phase energetic reaction profile for the reactivity of 1 a/1 b with isonitriles.







Table 1. Reaction energies DE0 , standard enthalpies DH298 and Gibbs energies DG298 in kJ mol1, standard en tropies DS298 in J mol1 K1, equilibrium constants K298 at 298.15 K for the gas-phase processes and PCM reac tion energies in toluene solution DE0 (solv), kJ mol1. B3LYP/6-31G* (LANL2DZ ECP on W) level of theory. 

1 a + nBuNC!2 a-nBu 1 a + CyNC!2 a-Cy 1 b + nBuNC!2 a-nBu 1 b + CyNC!2 b-Cy 2 a-nBu + nBuNC!4 a-nBu 2 a-Cy + CyNC!4 a-Cy 2 b-nBu + nBuNC!4 b-nBu 2 b-Cy + CyNC!4 b-Cy 2 a-nBu!(Z)-3 a-nBu 2 a-Cy!3 a-Cy 2 b-nBu!(Z)-3 b-nBu 2 b-Cy!3 b-Cy (Z)-3 a-nBu + nBuNC!5 a-nBu 3 a-Cy + CyNC!5 a-Cy (Z)-3 b-nBu + nBuNC!5 b-nBu 3 b-Cy + CyNC!5 b-Cy (Z)-3 a-nBu + CyNC!5 a-nBuCy 3 a-Cy + nBuNC!5 a-Cy/-nBu (Z)-3 b-nBu + CyNC!5 b-nBu/-Cy 3 b-Cy + nBuNC!5 b-Cy/-nBu (Z)-3 a-nBu + nBuNC!4 a-nBu 3 a-Cy + CyNC!4 a-Cy (Z)-3 b-nBu + nBuNC!4 b-nBu 3 b-Cy + CyNC!4 b-Cy 5 a-nBu!4 a-nBu 5 a-Cy!4 a-Cy 5 b-nBu!4 b-nBu 5 b-Cy!4 b-Cy Z-3 a-nBu + CyNC!4 a-nBu/-Cy 3 a-Cy + nBuNC!4 a-Cy/-nBu (Z)-3 b-nBu + CyNC!4 b-nBu/-Cy 3 b-Cy + nBuNC!4 b-Cy/-nBu 5 a-nBu/-Cy!5 a-Cy/-nBu 5 b-nBu/-Cy!5 b-Cy/-nBu 4 a-nBu/-Cy!4 b-Cy/-nBu 4 b-nBu/-Cy!4 b-Cy/-nBu







DE0 ACHTUNGRE(solv)

DH298

DS298

DG298

K298

90.0 95.8 78.1 84.5 137.2 120.5 128.9 114.5 21.6 9.8 14.7 5.2 146.8 122.9 143.3 119.3 140.5 144.1 134.8 136.8 115.6 110.7 114.2 109.4 29.3 12.2 21.9 9.9 78.6 61.3 54.3 23.3 2.4 1.1 23.3 34.2

90.8 95.8 79.1 84.2 127.6 111.0 118.8 104.6 23.8 12.7 16.7 8.4 136.0 111.6 132.3 107.8 128.9 133.0 123.2 125.8 103.7 98.2 102.1 96.3 29.7 13.4 22.7 11.5 66.5 50.2 43.0 11.3 2.1 0.8 22.4 35.0

81.2 87.1 72.9 76.2 124.5 107.8 113.4 101.4 17.2 5.7 7.8 0.7 137.3 111.6 133.3 107.8 129.7 134.0 124.2 126.8 107.3 102.1 105.7 100.7 27.4 9.5 20.1 7.2 70.6 52.2 45.3 17.1 1.4 1.1 24.0 31.9

187.6 194.6 205.7 193.9 219.8 209.0 201.8 220.8 47.1 39.1 27.0 44.3 219.4 216.0 214.3 216.2 219.5 210.0 216.2 207.2 172.7 169.9 174.7 176.4 41.5 46.0 33.9 39.8 189.6 199.6 183.6 209.5 10.4 3.5 9.0 31.3

25.2 29.0 11.6 18.4 59.0 45.5 53.3 35.6 3.2 5.9 0.3 12.5 71.9 47.3 69.4 43.3 64.3 71.4 59.8 65.0 55.8 51.4 53.6 48.1 15.1 4.2 10.0 4.7 14.1 7.3 9.4 45.3 1.7 0.0 26.7 41.2

2.63  104 1.22  105 1.06  102 1.68  103 2.19  1010 9.46  107 2.16  109 1.72  106 3.62 9.17  102 0.89 6.53  103 3.91  1012 1.90  108 1.45  1012 3.93  107 1.85  1011 3.18  1012 2.94  1010 2.46  1011 6.1  109 1.03  109 2.43  109 2.63  108 2.29  103 5.42 1.78  102 6.69 2.93  102 5.17  102 2.22  102 1.14  108 2.0 9.85  101 2.08  105 6.05  108

nucleophilic attacks of the isonitriles at the electrophilic pentel atom, rearrangements under Cp* migration, and the formation of condensed heterocycles. Activation of the Cp* substituent, a rare process so far, is a general feature of the formed heterocycles. The reactions are controlled by the

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DE0

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General remarks: All reactions are performed under an atmosphere of dry nitrogen with standard vacuum, Schlenk, and glovebox techniques. Solvents are purified and degassed by standard procedures. Commercialgrade chemicals are used without ACHTUNGREfurther purification. and [Cp*P{W(CO)5}2][5, 6a, 20] [Cp*As{W(CO)5}2][8] were prepared according to literature methods. NMR spectra were recorded at 27 8C on a Bruker Avance 400 (1H: 400.132 MHz, 31 P: standard tetramethylsilane, 161.976 MHz; standard 85 % H3PO4, 13 C: 100.627 MHz, standard tetramethylsilane) or on a Bruker Avance III 600 (1H: 600.253 MHz, standard tetramethylsilane, 31P: 242.986 MHz; standard 85 % H3PO4, 13C: 150.950 MHz, standard tetramethylsilane). IR spectra were obtained on a Varian FTS 800 spectrometer and mass spectra were recorded on a Finnigan MAT SSQ 710 A (EI/FD). The elemental analyses were performed with an Elementar Vario EL III. General procedure for the reactions of the pentelidene complexes with isonitriles: The reactions of the pentelidene complexes with isonitriles have generally been carried out under the following conditions (variations of this procedure are mentioned in the synthesis of the specific compound). The pentelidene complex was dissolved in toluene and cooled to 78 8C. The isonitrile was dissolved in toluene (10 mL) and added to the cooled solution. The reaction mixture was then warmed up to room temperature and stirred overnight. The solvent is reduced under vacuum to 5 mL and then stored at 28 8C.

Synthesis of [Cp*P{W(CO)5}2CNtBu] (2 a): [Cp*P{W(CO)5}2] (1 a) (0.19 g, 0.23 mmol) was dissolved in toluene (40 mL) and tBuNC (0.019 g, 0.23 mmol) was added at room temperature. The solution was stirred for two hours at room temperature and then the solvent was reduced under vacuum to 5 mL. Crystals of 2 a suitable for X-ray analysis were obtained after storage at + 4 8C. (Yield: 0.198 g, 0.21 mmol, 96 %). 1H NMR (400 MHz, C6D6, 27 8C, TMS): d = 0.94 (s; 9 H; CH3) 1.33 (d, 3JACHTUNGRE(P,H) = 15 Hz, 3 H; CH3), 1.66 (m, 6 H; CH3), 1.81 ppm (m, 6 H; CH3);

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Pentel-Containing Heterocycles

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P{1H} NMR (162 MHz, C6D6, 27 8C, 85 % H3PO4): d = 73.1 ppm (s; JACHTUNGRE(P,W) = 173 Hz); 13C NMR (100 MHz, C6D6, 27 8C, TMS): d = 11.7 (s; CH3), 12.4 (s; CH3), 23.6 (s; CH3), 28.3 (s; CH3), 55.6 (s; C), 62.7 (s; CH), 141.0 (s; C), 141.1 (s; C), 199.2 ppm (s; CO); IR (KBr): n˜ = 2212 (vs), 2071 (s), 2059 (s), 1985 (sh), 1908 cm1 (br); MS (EI, 70 eV): m/z (%): 897 (1) [M + ], 677 (45) [M + ACHTUNGRE(C5Me5CACHTUNGRE(CH3)3CN], 649 (60) [M + ACHTUNGRE(C5Me5CACHTUNGRE(CH3)3CNCO], 352 (14) [W(CO)6], 135 (60) [C5Me5 + ]; elemental analysis calcd (%) for C25H24NO10PW2 : C 33.49, H 2.70, N 1.56; found: C 33.65, H 3.20, N 1.75. 1

Synthesis of [Cp*As{W(CO)5}2CNtBu] (2 b): [Cp*As{W(CO)5}2] (1 b) (0.172 g, 0.2 mmol) in toluene (20 mL) tBuNC (0.045 mL, 0.4 mmol) were added at room temperature. The solution was stirred for two hours at room temperature and then the volume of the solvent was reduced to 5 mL under vacuum. Crystals of 2 b suitable for X-ray analysis were obtained after storage at + 4 8C. (Yield: 0.062 g, 0.065 mmol, 32 %). 1 H NMR (400 MHz, C6D6, 27 8C, TMS): d = 1.72 (s, 9 H; CH3), 1.86 ppm (s, 15 H; CH3); 13C NMR (100 MHz, C6D6, 27 8C, TMS): d = 12.1 (s, CH3), 29.5 (s, CH3), 63.7 (s, CH3), 116.6 (s, CN),136.3 (s, C), 140.8 (s, C), 199.1 (s, CO), 200.3 ppm (s, CO); IR (KBr): n˜ = 2215 (w), 2071 (s), 2059 (s), 1977 (sh), 1938 cm1 (br); MS (FD): m/z (%): 941 (2) [M + ], 858 (100) [M + CNCACHTUNGRE(CH3)3], 723 (36) [M + ACHTUNGRE(C5Me5CACHTUNGRE(CH3)3CN]; elemental analysis calcd (%) for C25H24NO10AsW2 : C 31.9, H 2.56, N 1.5; found: C 31.86, H 2.41, N 1.36. Synthesis of 3 a-Cy: [Cp*P{W(CO)5}2] (1 a) (240 mg, 0.30 mmol) was treated with CyNC (0.031 mL, 0.027 g, 0.25 mmol). A change of the color from dark-blue to yellow was observed. Crystals of 3 a suitable for X-ray analysis were obtained after storage at + 4 8C (Yield: 0.120 g, 0.13 mmol, 52 %). 1H NMR (400 MHz, C6D6, 27 8C, TMS): d = 0.6–0.19 (m, 10 H; CH2 Cy), 0.91 (s; 3 H; CH3), 1.31 (d, 3JACHTUNGRE(P,H) = 15.4 Hz, 3 H; CH3), 1.53 (m, 3 H; CH3), 1.57 (m, 3 H; CH3), 3.70 (m, 1 H; CH), 4.17 (s, 1 H; CH2), 4.72 (s, 1 H; CH2), 7.25 ppm (br, 1 H; NH); 31P{1H} NMR (162 MHz, C6D6, 27 8C, 85 % H3PO4): d = 27.2 ppm (s, 1JACHTUNGRE(P,W) = 143 Hz, 1JACHTUNGRE(P,W) = 156 Hz); 13C NMR (100 MHz, C6D6, 27 8C, TMS): d = 11.1 (s, CH3), 13.1 (s, CH3), 18.9 (s, CH3), 22.7 (s, CH3), 23.4 (s, CH2), 24.5 (s, CH2), 30.7 (s, CH2), 30.8 (s, CH2), 31.5 (s, CH2), 57.8 (s, CH Cy), 63.2 (s, C), 131.4 (s, C), 139.2 (s, C), 152.2 (s, C), 200.3 ppm (s; CO); IR (KBr): n˜ = 3271 (s), 2071 (s), 2058 (s), 1985 (sh), 1939 (vs), 1916 (br), 1857 (s), 1845 (s), 1622 cm1 (w); MS (EI, 15 eV): m/z (%): 923 (3) [M + ], 895 (10) [M + CO], 867 (6) [M + 2CO], 679 (70) [M + C5Me5C6H11CN)], 651 (49) [M + C5Me5ACHTUNGRE(C6H11CN)(CO)], 599 (100) [M + C5Me5C6H11CN)ACHTUNGRE3(CO)]; elemental analysis calcd (%) for C27H26NO10PW2 : C 35.13, H 2.84, N 1.52; found: C 34.79, H 3.10, N 1.41. Synthesis of 3 b-Cy: [Cp*As{W(CO)5}2] (1 b) (343 mg, 0.40 mmol) was treated with CyNC (0.043 mL, 0.038 g, 0.35 mmol). Crystals of 3 b suitable for X-ray analysis were obtained after storage at + 4 8C. (Yield: 0.110 g, 0.11 mmol, 31 %). 1H NMR (400 MHz, CD2Cl2, 27 8C, TMS): d = 1.10–2.30 (m, 10 H; CH2 Cy), 1.38 (s, 3 H; CH3), 1.64 (s, 3 H; CH3), 1.79 (s, 3 H; CH3), 1.82 (s, 3 H; CH3), 3.70 (m, 1 H; CH), 4.65 (s, 1 H; CH2), 5.05 (s, 1 H; CH2), 8.80 ppm (br, 1 H; NH); 13C NMR (100 MHz, CD2Cl2, 27 8C, TMS): d = 11.4 (s, CH3), 13.1 (s, CH3), 19.5 (s, CH3), 20.8 (s, CH3), 23.4 (s, CH2), 24.0 (s, CH2), 24.8 (s, CH2), 31.9 (s, CH2), 32.1 (s, CH2), 60.3 (s, CH Cy), 67.1 (s, C), 101.7 (s, C=CH2), 134.8 (s, C), 141.1 (s, C), 151.6 (s, C), 157.3 (s, C), 199.6 (s, CO), 199.7 (s, CO), 199.9 (s, CO); 229 ppm (s, C); IR (KBr): n˜ = 3258 (s), 2071 (s), 2058 (s), 1980 (sh), 1940 (vs), 1919 (br), 1847 (s), 1622 cm1 (w); MS (EI, 15 eV): m/z (%): 967 (8) [M + ], 939 (3) [M + CO], 911 (2) [M + 2CO], 883 (2) [M + 3CO], 723 695 (32) [M + C5Me5 (100) [M + C5Me5ACHTUNGRE(C6H11CN)], + ACHTUNGRE(C6H11CN)(CO)], 667 (20) [M C5Me5C6H11CN)2(CO)]; elemental analysis calcd (%) for C27H26NO10AsW2 : C 33.53, H 2.71, N 1.45; found: C 33.69, H2.76, N 1.28. Synthesis of 3 a-nBu: [Cp*P{W(CO)5}2] (1 a) (163 mg, 0.20 mmol) was treated with nBuNC (0.015 mL, 12.5 mg, 0.15 mmol) and a change in the color of the solution occurred from blue to yellow-brown. The crystallization started at room temperature and yellow crystals suitable for X-ray analysis could be obtained. To improve the yield the solution was stored at 28 8C. Yield: 64 mg, 0.07 mmol, 48 %. Isomer 1 (Z): Yield: 82.5 %. 1H NMR (600 MHz, C6D6, 25 8C, TMS): d = 0.68 (t, JACHTUNGRE(H,H) = 7.4 Hz, 3 H; CH3 nBu); 0.90 (s, 3 H; CH3); 0.94–1.08 (m,

Chem. Eur. J. 2013, 00, 0 – 0

4 H; CH2); 1.29 (d, 3JACHTUNGRE(P,H) = 16 Hz; 3 H; CH3); 1.51 (d, 4JACHTUNGRE(P,H) = 2 Hz, 3 H; CH3); 1.52 (d, 4JACHTUNGRE(P,H) = 5 Hz, 3 H; CH3); 3.10 (m, 2 H; CH2); 4.11 (s, 1 H; CH2); 4.67 (s, 1 H; CH2); 7.28 ppm (br, 1 H; NH); 31P{1H} NMR (162 MHz, C6D6, 27 8C, 85 % H3PO4): d = 24.5 ppm (s,1JACHTUNGRE(P,W) = 143, 1 JACHTUNGRE(P,W) = 151 Hz), 13C NMR (151 MHz, C6D6, 25 8C, TMS): d = 11.1 (d, 4 JACHTUNGRE(P,C) = 2.3 Hz; CH3); 13.0 (d, 3JACHTUNGRE(P,C) = 1.4 Hz; CH3); 13.5 (s; CH3); 18.9 (d, 3JACHTUNGRE(P,C) = 1.4 Hz; CH3); 19.6 (s; CH2); 20.5 (d, 2JACHTUNGRE(P,C) = 9 Hz; CH3); 29.8 (s; CH2); 50.0 (s; CH2); 54.4 (d, 1JACHTUNGRE(P,C) = 19 Hz, C); 63.2 (d, 2 JACHTUNGRE(P,C) = 4 Hz; C); 100.6 (d, 4JACHTUNGRE(P,C) = 3 Hz; CH2); 135.0 (d, 3JACHTUNGRE(P,C) = 8 Hz; C); 151.7 (s, C); 157.9 (s; C); 199.6 (m; CO); 199.9 ppm (s; CO). Isomer 2 (E): Yield: 18.5 %. 1H NMR (600 MHz, C6D6, 25 8C, TMS): d = 0.59 (t, JACHTUNGRE(H,H) = 7.3 Hz, 3 H; CH3 nBu); 0.83–1.08 (m, 4 H; CH2); 1.10 (s, 3 H; CH3); 1.23 (d, 3JACHTUNGRE(P,H) = 16 Hz, 3 H; CH3); 1.46 (d, 4JACHTUNGRE(P,H) = 2.4 Hz, 3 H; CH3); 1.55 (d, 4JACHTUNGRE(P,H) = 5 Hz, 3 H; CH3); 2.97 (m, 2 H; CH2); 4.39 (s, 1 H; CH2); 4.81 (s, 1 H; CH2); 7.88 ppm (br, 1 H; NH); 31P{1H} NMR (162 MHz, C6D6, 27 8C, 85 % H3PO4): d = 27.1 ppm (s,1JACHTUNGRE(P,W) = 144 Hz); 13 C NMR (151 MHz, C6D6, 25 8C, TMS): d = 10.9 (d, 4JACHTUNGRE(P,C) = 2.3 Hz; CH3); 12,9 (d, 3JACHTUNGRE(P,C) = 1.7 Hz; CH3); 13.1 (s, CH3); 18.6 (s, CH3); 19.4 (s, CH2); 20.1 (d, 2JACHTUNGRE(P,C) = 10 Hz; CH3); 30.6 (s, CH2); 50.6 (s, CH2); 52.1 (d, 1 JACHTUNGRE(P,C) = 20 Hz; CH3); 63.5 (s, C); 103.5 (s, CH2); 134.5 (s, C); 150.3 (s, C); 156.1 (s, C); 200 (m; CO); 200.2 (s, CO); 200.4 ppm (s, CO); IR (KBr): n˜ = 3283 (w), 2071 (s), 2057 (s), 1981 (sh), 1953 (sh), 1939 (sh), 1921 (vs), 1908 (vs), 1857 (s), 1853 (s), 1626 cm1 (w); MS (EI, 70 eV): m/z (%): 897 (2) [M + ], 868 (6) [M + CO], 841 (3) [M + 2 CO], 813 (1) [M + 3 CO], 785 (4) [M + 4 CO], 757 (3) [M + 5(CO)], 729 (6) [M + 6 CO], 701 (14) [M + 7 CO]; elemental analysis calcd (%) for C25H24NO10PW2 : C 33.47, H 2.70, N 1.56; found: C 33.47, H 2.72, N 1.54. Synthesis of 3 b-nBu: [Cp*As{W(CO)5}2] (1 b) (171 mg, 0.20 mmol) was treated with nBuNC (0.015 mL, 12.5 mg, 0.15 mmol). After warming to room temperature and stirring for 16 h the solution kept its blue color. The solvent was reduced to 5 mL and stored at 28 8C. After one day, yellow crystals suitable for X-ray analysis were obtained. (Yield: 28 mg, 0.03 mmol, 20 %). 1H NMR (400 MHz, C6D6, 27 8C, TMS): d = 0.67 (t, 3 JACHTUNGRE(H,H) = 7 Hz, 3 H; CH3 nBu), 0.82 (s, 3 H; CH3), 0.95–1.12 (m, 4 H; CH2 nBu), 1.35 (s, 3 H; CH3), 1.46 (s, 3 H; CH3), 1.56 (s, 3 H; CH3), 3.10 (s, 2 H; CH2 nBu), 4.04 (s, 1 H; CH2), 4.71 (s, 1 H; CH2), 7.73 ppm (br, 1 H; NH); IR (KBr): n˜ = 3273 (s), 2070 (s), 2057 (s), 1981 (sh), 1938 (sh), 1919 (vs), 1852 (s), 1628 cm1 (w); MS (EI, 70 eV): m/z (%): 941 (10) [M + ], 885 (5) [M + 2 CO], 857 (5) [M + 3 CO], 773 (8) [M + 6 CO], 745 (20) [M + 7 CO], 722 (46) [M + C5Me5ACHTUNGRE(C4H9CN)]. Synthesis of 4 a-Cy: [Cp*P{W(CO)5}2] (1 a) (160 mg, 0.20 mmol) was treated with CyNC (0.05 mL, 0.044 g, 0.4 mmol) at room temperature. A color change from dark-blue to orange was observed. The solvent was reduced to 5 mL and the solution cooled to + 4 8C and stored until orange crystals suitable for X-ray analysis were obtained. (Yield: 68 mg, 0.06 mmol, 30 %). 1H NMR (400 MHz, C6D6, 27 8C, TMS): d = 0.52–3.04 (m, 20 H; CH2 Cy), 1.37 (d, 3JACHTUNGRE(H,H) = 1 Hz, 6 H; C5ACHTUNGRE(CH3)5), 1.52 (s, 3 H; C5ACHTUNGRE(CH3)5), 1.87 (d, 3JACHTUNGRE(H,H) = 1 Hz, 6 H; C5ACHTUNGRE(CH3)5), 4.02 ppm (m, 2 H; CH); 31P{1H} NMR (162 MHz, C6D6, 27 8C, 85 % H3PO4): d = 48.0 ppm (s, 1 JACHTUNGRE(P,W) = 160 Hz); 13C NMR (100 MHz, C6D6, 27 8C, TMS): d = 11.1 (s, CH3), 12.4 (s, CH3), 18.6 (s, CH3), 23.2 (s, CH2), 25.0 (s, CH2), 25.7 (s, CH2), 26.3 (s, CH2), 31.3 (s, CH2), 33.4 (s, CH2), 58.5 (s, CH), 64.4 (s, CH), 139.9 (s, CH), 140.6 (s, CH), 154.4 (s, CH), 199.3 (s, CO), 200.0 (s, CO), 230.0 ppm (s, C); IR (KBr): n˜ = 2074 (s), 2060 (s), 1980 (sh), 1932 (vs), 1686 (w), 1636 cm1 (w); MS (EI, 20 eV): m/z (%): 1032 (28) [M + ], 1004 (16) [M + CO], 976 (100) [M + 2 CO], 948 (5) [M + 3 CO]; elemental analysis calcd (%) for C34H37N2O10PW2 : C 39.5, H 3.6, N 2.7; found: C 39.30, H 3.65, N 2.62. Synthesis of 4 a-nBu and 5a-nBu: [Cp*P{W(CO)5}2] (1 a) (240 mg, 0.30 mmol) were treated with nBuNC (0.065 mL, 0.052 g, 0.62 mmol); a change of color from dark-blue to orange can be immediately observed. After a chromatographic workup two fractions can be isolated. The first fraction obtained was orange (n-hexane/toluene = 2:1) and the second fraction was yellow (CH2Cl2). The solvent in both fractions was reduced and the solutions were stored at + 4 8C. In the first fraction, orange crystals of 4a-nBu (yield: 83 mg, 0.08 mmol, 26 %) were obtained and in the second fraction yellow crystals of 5a-nBu (yield: 34 mg, 0.035 mmol, 12 %).

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4 a-nBu: 1H NMR (400 MHz, C6D6, 27 8C, TMS): d = 0.52 (t, 3JACHTUNGRE(H,H) = 7.3 Hz, 3 H; CH3 nBu), 0.81 (sext, 3JACHTUNGRE(H,H) = 7.3 Hz, 2 H; CH2 nBu), 0.88 (t, 3JACHTUNGRE(H,H) = 7.3 Hz, 3 H; CH3 nBu), 1.30 (m, 2 H; CH2 nBu), 1.32 (s, 3 H; C5ACHTUNGRE(CH3)5), 1.44 (sext, 3JACHTUNGRE(H,H) = 7.4 Hz, 2 H; CH2 nBu), 1.53 (s, 3 H; C5ACHTUNGRE(CH3)5), 1.71 (m, 2 H; CH2 nBu), 1.79 (s, 6 H; C5ACHTUNGRE(CH3)5), 3.00 (m, 2 H; CH2 nBu), 3.85 ppm (t, 3JACHTUNGRE(H,H) = 7.3 Hz, 3 H; CH3 nBu); 31P{1H} NMR (162 MHz, C6D6, 27 8C, 85 % H3PO4): d = 58.5 ppm (s, 1JACHTUNGRE(P,W) = 160 Hz); 13 C NMR (100 MHz, C6D6, 27 8C, TMS): d = 11.1 (s; C5ACHTUNGRE(CH3)5), 12.2 (s; C5ACHTUNGRE(CH3)5), 13.1 (s; CH3 nBu), 13.9 (s; CH3 nBu), 18.7 (s; C5ACHTUNGRE(CH3)5), 20.4 (s; CH2 nBu), 20.6 (s; CH2 nBu), 30.4 (s; CH2 nBu), 33.0 (s; CH2 nBu), 46.8 (s; CH2 nBu), 51.2 (s; CH2 nBu), 64.4 (s; C5ACHTUNGRE(CH3)5), 139.3 (s; C), 140.3 (s; C), 199.1 (s; CO), 199.2 ppm (s; CO); IR (KBr): n˜ = 2075 (s), 2060 (s), 1982 (sh), 1942 (vs), 1923 (vs), 1911 (vs), 1701 (w), 1636 cm1 (w); MS (EI, 70 eV): m/z (%): 980 (2) [M + ], 952 (2) [M + CO], 924 (2) [M + 2 CO], 896 (2) [M + 3 CO], 868 (2) [M + 4 CO], 218.3 (100) [nBuNCACHTUNGRE(C5Me5) + ], 135 (100) [C5Me5 + ]; elemental analysis calcd (%) for C30H33N2O10PW2 : C 36.76, H 3.39, N 2.86; found: C 36.54, H 3.40, N 2.73. 5 a-nBu: 1H NMR (400 MHz, C6D6, 27 8C, TMS): d = 0.68 (t, 3JACHTUNGRE(H,H) = 7 Hz, 3 H; CH3), 1.03 (t, 3JACHTUNGRE(H,H) = 7 Hz, 3 H; CH3), 1.10 (m, 2 H; CH2), 1.15 (s, 3 H; CH3),1.27 (m, 2 H; CH2), 1.30 (s, 3 H; CH3),1.38 (s, 3 H; CH3), 1.68(m, 2 H; CH2), 1.70(s, 3 H; CH3), 2.02 (m, 2 H; CH2), 3.31 (m, 1 H; CH2), 3.47 (m, 1 H; CH2), 3.97 (m, 2 H; CH2), 4.19 (s, 1 H; CH2), 4.67 (s, 1 H; CH2), 8.40 ppm (br, 1 H; NH); 31P{1H} NMR (162 MHz, C6D6, 27 8C, 85 % H3PO4): d = 101.2 ppm (s, 1JACHTUNGRE(P,W) = 155 Hz, 1JACHTUNGRE(P,W) = 138 Hz); 31P NMR (162 MHz, C6D6, 27 8C, 85 % H3PO4): d = 101.2 ppm (d, 3JACHTUNGRE(P,H) = 10 Hz, 1JACHTUNGRE(P,W) = 155 Hz, 1JACHTUNGRE(P,W) = 138 Hz); 13C NMR (100 MHz, C6D6, 27 8C, TMS): d = 10.4 (s, CH2), 11.0 (s, CH3), 13.5 (s, CH3), 14.3 (s, CH3), 19.9 (s, CH2), 20.5 (s, CH3), 21.2 (s, CH2), 23.8 (s, CH3), 29.6 (s, CH2), 33.9 (s, CH2), 52.3 (s, CH2), 58.7 (s, CH2), 64.6 (s, C), 68.1 (s, C), 101.5 (s, CH2), 132.8 (s, C), 150.7 (s, C), 158.5 (s, C), 198.6 (s, CO), 198;7 (s, CO), 198.8 (s, CO), 198.9 ppm (s; CO); IR (KBr): n˜ = 3251 (w), 2073 (s), 2061 (s), 1990 (sh),1975 (sh), 1937 (vs), 1626 (w), 1595 cm1 (w); MS (EI, 70 eV): m/z (%): 980 (7) [M + ], 952 (2) [M + CO], 924 (12) [M + 2 CO], 896 (7) [M + 3 CO], 868 (4) [M + 4 CO], 840 (3) [M + 5 CO], 812 (5) [M + 6 CO], 784 (5) [M + 7 CO], 756 (8) [M + 8 CO], 218.3 (74) [nBuNCACHTUNGRE(C5Me5) + ], 135 (60) [C5Me5 + ]. Synthesis of 4 b-nBu and 5 b-nBu: [Cp*As{W(CO)5}2] (1 b) (171 mg, 0.20 mmol) was treated with nBuNC (0.042 mL, 0.033 g, 0.4 mmol); a change of the color from dark-blue to orange can be immediately observed. Compound 4 b-nBu started to crystallize as orange plates and compound 5 b-nBu crystalized as yellow plates. A separation of both compounds was not successful because of the decomposition of compound 4 b-nBu during the column chromatography. Only compound 5 b-nBu could be obtained analytically pure (yield: 42 mg, 0.041 mmol, 21 %). 4 b-nBu: 1H NMR (400 MHz, C6D6, 27 8C, TMS): d = 0.55 (t, 3JACHTUNGRE(H,H) = 7 Hz, 3 H; CH3), 0.83 (m, 2 H; CH2), 0.89 (t, 3JACHTUNGRE(H,H) = 7 Hz, 3 H; CH3), 1.25–1.75 (m, 8 H; CH2), 1.38 (s, 6 H; CH3), 1.49 (s, 3 H; CH3), 1.78 (s, 6 H; CH3), 2.98 (m, 2 H; CH2), 3.74 ppm (t, 3JACHTUNGRE(H,H) = 7 Hz, 2 H; CH2). 5 b-nBu: 1H NMR (400 MHz, C6D6, 27 8C, TMS): d = 0.70 (t, 3JACHTUNGRE(H,H) = 7 Hz, 3 H; CH3), 1.01 (t, 3JACHTUNGRE(H,H) = 7 Hz, 3 H; CH3), 1.09 (m, 2 H; CH2), 1.15 (s, 3 H; CH3), 1.24 (s, 3 H; CH3), 1.30 (m, 2 H; CH2), 1.37 (s, 3 H; CH3), 1.65 (m, 2 H; CH2), 1.69 (s, 3 H; CH3), 2.99 (m, 2 H; CH2), 3.35 (m, 1 H; CH2), 3.48 (m, 1 H; CH2), 3.85 (m, 2 H; CH2), 4.20 (s, 1 H; CH2), 4.72 (s, 1 H; CH2), 8.89 ppm (br, 1 H; NH); 13C NMR (100 MHz, C6D6, 27 8C, TMS): d = 10.4 (s, CH2), 11.0 (s, CH3), 13.5 (s, CH3), 14.2 (s, CH3), 19.9 (s, CH2), 21.0 (s, CH3), 21.1 (s, CH2), 22.1 (s, CH3), 29.4 (s; CH2), 33.6 (s; CH2), 53.3 (s; CH2), 60.2 (s; CH2), 66.7 (s; C), 70.1 (s, C), 101.7 (s, CH2), 133.3 (s, C), 150.5 (s; C), 157.2 (s; C), 178.0 (s; C), 198.9 (s, 1 JACHTUNGRE(W,C) = 126 Hz; CO), 199.0 (s, 1JACHTUNGRE(W,C) = 126 Hz; CO), 199.4 (s, CO), 199.6 (s, CO), 232.4 ppm (s, C); IR (KBr): n˜ = 3301 (w), 2072 (s), 2060 (s), 1990 (sh) 1974 (sh),1933 (vs),1919 (vs), 1626 (w), 1599 cm1 (w); MS (EI, 70 eV): m/z (%): 1024 (2) [M + ], 700.2 (4) [M + W(CO)5], 644.2 (5) [M + 2 COW(CO)5], 616.3 (9) [M + 3 COW(CO)5], 376.4 (22) [M + 2 W(CO)5], 135 (34) [C5Me5 + ]; elemental analysis calcd (%) for C30H33AsN2O10W2 : C 35.18, H 3.25, N 2.74; found: C 35.68, H 3.59, N 2.44.

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Synthesis of 5b-Cy: [Cp*As{W(CO)5}2] (1 b) (171 mg, 0.20 mmol) was treated with CyNC (44 mg, 0.4 mmol, 0.05 mL) and a change of the color from blue to yellow was observed. The solution was then stirred for 2 h at room temperature. The volume of the solvent was reduced to 5 mL and the solution was stored at 28 8C. After one day yellow crystals of 5 b-Cy suitable for X-ray analysis were obtained (yield: 108 mg, 0.1 mmol, 50 %). 1H NMR (400 MHz, CD2Cl2, 27 8C, TMS): d = 1.27–2,45 (m, 20 H; CH2), 1.22 (s, 3 H; CH3), 1.64 (s, 3 H; CH3), 1.69 (s, 3 H; CH3), 1.82 (s, 3 H; CH3), 3.54 (tt,3JACHTUNGRE(H,H) = 8.8 Hz, 3JACHTUNGRE(H,H) = 4.2 Hz, 1 H; CH), 4.22 (m, 1 H; CH), 4.96 (s, 1 H; CH2), 5.28 (s, 1 H; CH2), 9.42 ppm (br, 1 H; NH); 13C NMR (100 MHz, CD2Cl2, 27 8C, TMS): d = 10.8 (s, CH3), 11.3 (s, CH3), 21.3 (s, CH3), 23.3 (s, CH3), 23.5 (s, CH2), 23.8 (s, CH2), 23.8 (s, CH2), 24.3 (s, CH2), 25.0 (s, CH2), 26.2 (s, CH2), 30.7 (s, CH2), 31.67 (s, CH2), 33.4 (s; CH2), 33.4 (s, CH2), 34.0 (s, CH2), 61.8 (s, CH), 66.7 (s,; CH), 67.2 (s, C), 70.2 (s, C), 102.9 (s, CH2), 134.0 (s, C), 150.8 (s, C), 158.5 (s, C), 176.0 (s, C), 191.9 (s, C), 199.6 (s, CO), 199.8 (s, CO), 200.4 ppm (s, CO); IR (KBr): n˜ = 3206 (w), 2072 (s), 2060 (s), 2000 (sh), 1982 (sh), 1924 (vs), 1882 (vs), 1630 (w), 1586 cm1 (w); MS (FD): m/z (%): 1076 (100) [M + ], 752 (66) [M + W(CO)5], 429 (44) [M + 2 W(CO)5]; elemental analysis calcd (%) for C34H37AsN2O10W2 : C 37.94, H 3.47, N 2.60; found: C 37.97, H 3.45, N 2.56. Crystal structure analysis: Machine parameters, crystal data, and data collection parameters are summarized in Table 1 in the Supporting Information. The crystal samples were processed at an Agilent Technologies (formerly Oxford Diffraction), Gemini R Ultra, and SuperNova diffractometer, respectively. Either a semi-empirical multi-scan absorption correction from equivalents[21] or an analytical absorption correction from crystal faces[22] was applied. The structures were solved by SIR-92[23] or SuperFlip[24] and a least-square refinement on F2 was carried out with SHELXL.[25] Hydrogen atoms at the carbon atoms were located in idealized positions and refined isotropically according to the riding model. The hydrogen positions at the nitrogen sites were located from the difference Fourier map and refined without constrains in the case of 3 a-nBu, 3 b-nBu, 5 a-nBu, and 5 b-nBu, all others were constrained and refined according to the riding model with fixed distances (0.88  NH). In 5 a-nBu and 5 b-nBu one n-butyl group is disordered over two positions (for 5 a-nBu in a ratio of 54(2):46(2) and for 5 b-nBu in a ratio of 64(1):36(1). In 5 b-Cy one cyclohexyl group is disordered over two positions in a ratio of 61(1):39(1). In addition to this disorder, the structure of 5 b-Cy contains a solvent toluene molecule. The large residual density reported in the cif file of 2 a is located close to the tungsten atoms. The large second parameter of the weighting factor of 3 a-nBu originates from the crystal size being rather large for the beam size. CCDC-939672 (2 a), CCDC-939673 (2 b), CCDC-939674 (3 a-Cy), CCDC939675 (3 a-nBu), CCDC-939676 (3 b-Cy), CCDC-939677 (3 b-nBu), CCDC-939678 (4 a-Cy), CCDC-939679 (4 a-nBu), CCDC-939680 ACHTUNGRE(4 b-nBu), CCDC-939681 (5 a-nBu), CCDC-939682 (5 b-Cy), and CCDC939683 (5 b-nBu) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Theoretical calculations: The geometries of the compounds have been fully optimized with gradient-corrected density functional theory (DFT) in form of Beckes three-parameter hybrid method B3LYP[26] with standard 6-31G* all-electron basis set as implemented in Gaussian 03 program package.[27] ECP basis set of Hay and Wadt was used for W.[28] All structures correspond to minima on their respective potential energy surfaces.

Acknowledgements This work was supported by the Deutsche Forschungsgemeinschaft and the Alexander von Humboldt Foundation (A.Y.T.). The authors are grateful to COST action CM0802 (PhoSciNet) for general support.

[1] Recent reviews on carbene chemistry: a) J. W. Herndon, Coord. Chem. Rev. 2011, 255, 3; b) A. J. Arduengo, G. Bertrand, Chem.

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Heterocycles M. Seidl, M. Schiffer, M. Bodensteiner, A. Y. Timoshkin, M. Scheer* . . . . . . . . . . . . . . . . . . . . &&&&—&&&& Reactivity of Bridged Pentelidene Complexes with Isonitriles: A New Way to Pentel-Containing Heterocycles Bridging the gap: The treatment of pentelidene complexes with isonitriles led to a series of new heterocycles containing Group 15 elements. Each step of the reaction sequences was evidenced through isolated and structurally characterized compounds. The activation of the 1,2,3,4,5-pentamethyl-

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cyclopentadienyl (Cp*) substituent, which is so far a rare process, is a general feature of the formed heterocycles. The reactions are controlled by the steric demand of the substituent at the isonitrile and its stoichiometric ratio (see scheme).

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