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Cite this: Chem. Commun., 2014, 50, 5382 Received 16th October 2013, Accepted 2nd December 2013 DOI: 10.1039/c3cc47912a
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Pyridine-2-thiolate bridged tin–palladium complexes with Sn(PdN2Cl2), Sn(PdN2S2), Sn(PdN2C2) and Sn(Pd2N4) skeletons†‡ Erik Wa¨chtler,a Robert Gericke,a Lyuben Zhechkov,b Thomas Heine,b c a Thorsten Langer,c Birgit Gerke,c Rainer Po ¨ ttgen and Jo ¨ rg Wagler*
www.rsc.org/chemcomm
Reactions of tin(IV) complexes of the type Sn(PyS)2X2 (X = Cl, PyS, Ph; PyS = pyridine-2-thiolate) with Pd(PPh3)4 provide easy access to novel heterometallic complexes with Pd–Sn bonds. Electronic characteristics of this connection were analysed by X-ray crystallography, 119
Sn Mo ¨ssbauer spectroscopy and quantum chemical analyses.
The chemistry of heterodinuclear complexes with the TM-E bonding situation (TM = transition metal, E = main group metal or metalloid) is currently being explored across the periodic table, and a great variety of novel complexes with transition metal s-donors in the coordination sphere of a main group metal (or metalloid) have been reported in the past few years. The well-explored group of metallaboratranes (i.e., compounds featuring TM-B bonds)1 has been joined by complexes with TM-E (E = Be,2 Al,3 Ga,4 In,5 Si,6 Sn,7 Sb,8 Bi,9 Te10) bonds, just to name a selection. Recently, we have shown that even in complexes with a formal TM’E bonding situation (e.g., in a stannylene complex, Sn acts as a lone pair s-donor), significant contributions of the reverse bonding mode TM-E (upon formal change of the oxidation numbers of metal and metalloid elements) may add to the bonding situation (Scheme 1, I).11 The same findings have been reported by Jambor et al. (for compound II).12 a
¨r Anorganische Chemie, TU Bergakademie Freiberg, D-09596 Freiberg, Institut fu Germany. E-mail: [email protected]; Fax: +49 3731 39 4058 b School of Engineering and Science, Theoretical Physics – Theoretical Materials Science, Jacobs University Bremen gGmbH, D-28759 Bremen, Germany c ¨r Anorganische und Analytische Chemie, Universita ¨t Mu ¨nster, Institut fu ¨nster, Germany Corrensstrasse 30, D-48149 Mu † This article is part of the ChemComm ‘Emerging Investigators 2014’ themed issue. ‡ Electronic supplementary information (ESI) available: Detailed syntheses and char¨ssbauer spectroscopy, CHNS microanalyses), tables acterisation (NMR and 119Sn Mo with parameters of data collection and structure refinement of the crystal structures reported in this paper and CIF. CCDC 963362 ([Pd(PyS)2(PPh3)2]), 963363 (1, modification 1), 963364 (1, modification 2), 963365 (1(CHCl3)2), 963366 (2(CHCl3)2), 963367 (3(THF)), 963368 (4), 963369 (5(THF)2) and details of quantum chemical analyses. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/ c3cc47912a
5382 | Chem. Commun., 2014, 50, 5382--5384
Scheme 1
Our further investigations addressed the elucidation of the currently ‘‘pure formalism’’ with respect to usability of this general principle in synthetic approaches and with regard to the influence of the further metalloid coordination sphere on the directionality of the formally dative bonding mode, i.e., on the TM’E vs. TM-E competition. The (N,S)-bidentate pyridine-2-thiolato ligand (PyS), which is a constituent of compound II (and related to the methimazolyl ligand in compound I), was a helpful tool for our study, as the desired precursor compounds III–VI (Scheme 1) were already known from the literature,13 and the mesomerism of this anion serves the purpose of our investigation. Whereas compound I was prepared in a one-pot synthesis from tin(II) and palladium(II) precursors,11 we now aim at synthesis using a combination of different starting materials with different ligand combinations and with palladium and tin in different oxidation states (Scheme 2). Thus, routes A, C and D start from tin(II) precursors and may involve a formal tin(III) intermediate (the stannyl complex 2 in route D). The utilisation of tin(IV) precursors opens further access routes (B) to such complexes. We must stress that this is particularly important
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Scheme 2
for metalloid compounds which appear to be less stable in the case of lower oxidation numbers of the metalloid (e.g., significantly lower stability of SnPh2 relative to SnCl2). All four routes shown in Scheme 2 proved to be suitable to access compound 1, however routes A, B and C produced similar yields (>70%), whereas route D proved to be less efficient (see ESI‡). (Note: the intermediate and starting materials 2 and [Pd(PyS)2(PPh3)2],14 respectively, the crystal structures of which have not been reported so far, were characterized by X-ray crystallography, see ESI.‡) Thus, route B was chosen to access related compounds 3, 4 and 5 through suitable tin(IV) starting materials (Scheme 3). As shown by X-ray crystallography (Fig. 1), compounds 1, 3 and 4 exhibit similar molecular architectures, i.e., distorted trigonal-bipyramidal coordination of tin with two axial Sn–N bonds as a fundamental motif, t15 = 0.66, 0.57 and 0.75, respectively. (Three different crystal structures of 1, i.e., two solvent free modifications and a chloroform solvate, were determined, see ESI.‡ In the discussion we refer to the solvent free modification which was obtained along the synthesis.) Noteworthily, the monodentate (PyS) ligands in 3 are S-bound to tin, while their N atoms (N3 and N4) cap two of the equatorial edges with Sn N separations of 2.95 and 3.03 Å, respectively, thus making the Sn atom [5+2]-coordinate in a rather pseudo-pentagonal-bipyramidal fashion. As a result, the sharp S3–Sn1–S4 angle arises (85.98(7)1), whereas the related Cl–Sn–Cl (in 1) and C–Sn–C (in 4) angles are 104.48(2)1 and 107.71(7)1, respectively. The Sn–Pd bonds slightly increase from 1 via 3 to 4
Scheme 3
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Fig. 1 Molecular structures of 1, 3 and 4 in the crystal structures of 1, 3THF and 4. Selected atoms are labelled, displacement ellipsoids show 50% probability, H atoms are omitted for clarity and PPh3 groups are simplified as a stick model.
(2.5052(2), 2.5328(2) and 2.5370(2) Å, respectively), and the Sn–N bonds (2.287(2), 2.292(2) (1); 2.335(2), 2.386(2) (3); 2.347(2), 2.387(2) Å (4)) exhibit the same trend and reflect response to the lowering of the Lewis acidity of the tin atom upon substitution of Cl for (PyS) for Ph. Similar behaviour (i.e., elongation of axial Sn–Cl bonds upon substitution of Sn bound equatorial Cl atoms for Ph groups) has been observed with pentacoordinate stannates [SnCl5] and [SnCl3Ph2] .16 Except for the Sn–Pd bonds, the Pd coordination spheres do not exhibit any noteworthy response to the different Sn coordination spheres, i.e., the Pd–S bonds range from 2.297 to 2.312 Å, and the Pd–P bond lengths (2.3751(4), 2.3531(5) and 2.3786(5) Å in 1, 3 and 4, respectively) do not exhibit systematic changes with respect to the features observed in the Sn coordination spheres. In general, the Pd atoms are housed in nearly square-planar coordination spheres. Despite the seemingly low influence of the Sn coordination sphere on Pd, the electronic situation along the Sn–Pd–P axis still varies significantly, as reflected by the different 2J(119Sn,31P) couplings in solution (4311, 4598 and 2677 Hz for 1, 3 and 4, respectively). Further differences were revealed by Natural Bonding Orbital (NBO) analyses. Addition of a second equivalent of [Pd(PPh3)4] to 3 furnishes 5 with a change from the Sn–S to Sn–N coordination mode of the dangling (PyS) ligands of 3 and insertion of PdPPh3 into the S2-clamp. As shown by crystallography (Fig. 2), the tin coordination sphere in 5 is distorted octahedral with trans Pd–Sn bonds. The four Sn–N bonds exhibit slightly different lengths, i.e., short and long Sn–N bonds oppose each other, and the average Sn–N bond length exceeds those observed in compounds 1, 3 and 4. With respect to the again nearly squareplanar Pd coordination spheres, the Pd–S bonds are similar to those of compounds 1, 3 and 4, but the Pd–Sn bonds are significantly longer (by up to 0.09 Å) as well as the Pd–P bonds
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Fig. 2 Molecular structure of 5 in the crystal structure of 5(THF)2. Selected atoms are labelled, displacement ellipsoids show 50% probability, H atoms are omitted for clarity and PPh3 groups are simplified as a stick model. Selected bond lengths [Å]: Pd1 P1 2.4139(5), Pd2 P2 2.4033(5), Pd1 S1 2.3085(5), Pd1 S2 2.2969(6), Pd2 S3 2.2989(5), Pd2 S4 2.3017(6), Pd1 Sn1 2.5946(2), Pd2 Sn1 2.5945(2), Sn1 N1 2.464(2), Sn1 N2 2.361(2), Sn1 N3 2.397(2), Sn1 N4 2.457(2).
(by up to 0.06 Å). We attribute this bond lengthening along the P–Pd–Sn axis to the now trans-disposed Pd–Sn bonds. In contrast to other tin compounds with more than one transition metal in the Sn coordination sphere, which could be interpreted as bridging stannylene or stannide complexes,17 the tin atom in 5 cannot exhibit directional s-lone-pair donation due to the opposing Pd–Sn bonds. Currently, 5 reveals the widest TM–Sn–TM angle observed in such heterometallic complexes (175.15(1)1), which is much larger than the related angle observed in compound VII18 (151.71). To elucidate differences in the Pd–Sn bonding situations of 1, 3, 4 and 5, NBO analyses were performed (see ESI‡). The electronic populations of the Pd–Sn NBOs are similar (1.79, 1.71, 1.69 and 1.67 electrons for 1, 3, 4 and 5, respectively). The tin contributions to these NBOs are 57, 54, 52 and 48% in the same order, reflecting a decrease of s-donor action of tin (transition towards a s-lone-pair acceptor) along this series. The natural charges of Pd (ca. 0.6 in 1, 3 and 4; 0.7 in 5) underline the pronounced role of Pd as the lone pair donor in 5 (i.e., pronounced Pd0-SnIV’Pd0 characteristics). The hybrid orbital contribution of Pd to the Pd–Sn NBO is always close to sp2d. In sharp contrast, the Sn hybrid orbital contribution to the same NBO lacks significant d character and it strongly depends on the Sn coordination sphere (%s, %p = 73, 27; 51, 49; 40, 60 and 50, 50 for 1, 3, 4 and 5, respectively). Whereas the sp hybrid contribution of tin within the linear Pd–Sn–Pd coordination in 5 appears plausible, the striking shift from predominant s to p orbital contributions along the series 1, 3, 4 signals a decrease in stannylene character in the same direction. 119 ¨ssbauer data (isomer shifts in mm s 1 for 1, 3, 4 Sn Mo and 5 are 1.63(1), 1.81(1), 1.54(1) and 2.05(1), respectively) indicate varying 5s level populations in the tin atoms of these compounds, which are in good agreement with the calculated 5s populations (1.05, 1.11, 0.94 and 1.09 electrons in the same order). Thus, the electronic population of the Sn atom in these
5384 | Chem. Commun., 2014, 50, 5382--5384
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compounds is intermediate between tin(II) and tin(IV), but closer to tin(IV) (isomer shifts of III, IV and V are 3.17(1)/ 3.15(1), 0.7913c and 0.8213c mm s 1, respectively). In the context of the transition metal rich coordination sphere, even the isomer shift of 5 (2.05(1) mm s 1) is still characteristic of tin(IV), because compounds Sn[Fe(CO)2C5H5]4 and PhSn[Fe(CO)2C5H5]3, which are considered tin(IV) compounds, exhibit similar isomer shifts (of 2.14 and 2.00 mm s 1, respectively).19 In conclusion, we have shown that the TM-E coordination mode is relevant in a great variety of ‘‘stannylene’’ complexes and that these compounds can be easily accessed from tin(IV) precursors by coordination of a palladium(0) complex moiety. In this course, compound 5 revealed a novel coordination pattern, i.e., with two trans-disposed TM donor moieties in the octahedral tin coordination sphere.
Notes and references 1 H. Braunschweig and R. D. Dewhurst, Dalton Trans., 2011, 549. 2 H. Braunschweig, K. Gruss and K. Radacki, Angew. Chem., Int. Ed., 2009, 48, 4239. 3 H. Braunschweig, K. Gruss and K. Radacki, Angew. Chem., Int. Ed., 2007, 46, 7782. 4 H. Braunschweig, K. Gruss and K. Radacki, Inorg. Chem., 2008, 47, 8595. 5 E. J. Derrah, M. Sircoglou, M. Mercy, S. Ladeira, G. Bouhadir, K. Miqueu, L. Maron and D. Bourissou, Organometallics, 2011, 30, 657. 6 J. Wagler and E. Brendler, Angew. Chem., Int. Ed., 2010, 49, 624. 7 J. Wagler, A. F. Hill and T. Heine, Eur. J. Inorg. Chem., 2008, 4225. ´rez and F. P. Gabbaı¨, Angew. Chem., 8 T.-P. Lin, C. R. Wade, L. M. Pe Int. Ed., 2010, 49, 6357. 9 T.-P. Lin, I.-S. Ke and F. P. Gabbaı¨, Angew. Chem., Int. Ed., 2012, 51, 4985; C. Tschersich, C. Limberg, S. Roggan, C. Herwig, N. Ernsting, S. Kovalenko and S. Mebs, Angew. Chem., Int. Ed., 2012, 51, 4989. 10 T.-P. Lin and F. P. Gabbaı¨, Angew. Chem., Int. Ed., 2013, 52, 3864. ¨chtler, T. Heine, L. Zhechkov, T. Langer, 11 E. Brendler, E. Wa ¨ttgen, A. F. Hill and J. Wagler, Angew. Chem., Int. Ed., 2011, R. Po 50, 4696. ´, L. Dosta ´l, S. Herres-Pawlis, A. Ru ˚ˇ 12 J. Martincova zicˇka and R. Jambor, Chem.–Eur. J., 2011, 17, 7423. 13 (a) J. Ichikawa and T. Mukaiyama, Chem. Lett., 1985, 1009; (b) M. Masaki and S. Matsunami, Bull. Chem. Soc. Jpn., 1976, ¨rmann, R. Barbieri, 49, 3274; (c) F. Huber, R. Schmiedgen, M. Schu G. Ruisi and A. Silvestri, Appl. Organomet. Chem., 1997, 11, 869; ˆlam, J. Meunier-Piret, M. Biesemans, R. Willem and (d) M. Boua ¨chtler, M. Gielen, Inorg. Chim. Acta, 1992, 198–200, 249; (e) E. Wa R. Gericke, S. Kutter, E. Brendler and J. Wagler, Main Group Met. Chem., 2013, 36, 181. 14 Y. Nakatsu, Y. Nakamura, K. Matsumoto and S. Ooi, Inorg. Chim. Acta, 1992, 196, 81. 15 A. W. Addison, T. N. Rao, J. Reedijk, J. van Rijn and G. C. Verschoor, J. Chem. Soc., Dalton Trans., 1984, 1349. ¨ller, J. Siekmann and G. Frenzen, Acta Crystallogr., Sect. C: 16 (a) U. Mu Cryst. Struct. Commun., 1996, 52, 330; (b) D. Weber, S. H. Hausner, ¨ber-Pabst, S. Yun, J. A. Krause-Bauer and H. Zimmer, A. Eisengra Inorg. Chim. Acta, 2004, 357, 125. 17 (a) R. D. Ball and D. Hall, J. Organomet. Chem., 1973, 56, 209; (b) E. Simon-Manso and C. P. Kubiak, Angew. Chem., Int. Ed., 2005, 44, 1125. 18 A. Balch, H. Hope and F. E. Wood, J. Am. Chem. Soc., 1985, 107, 6936. 19 V. I. Gol’danskii, B. V. Borshagovskii, E. F. Makarov, R. A. Stukan, K. N. Anisimov, N. E. Kolobova and V. V. Skripkin, Teor. Eksp. Khim., 1967, 3, 478.
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Cite this: Chem. Commun., 2014, 50, 5382 Received 16th October 2013, Accepted 2nd December 2013 DOI: 10.1039/c3cc47912a
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Pyridine-2-thiolate bridged tin–palladium complexes with Sn(PdN2Cl2), Sn(PdN2S2), Sn(PdN2C2) and Sn(Pd2N4) skeletons†‡ Erik Wa¨chtler,a Robert Gericke,a Lyuben Zhechkov,b Thomas Heine,b c a Thorsten Langer,c Birgit Gerke,c Rainer Po ¨ ttgen and Jo ¨ rg Wagler*
www.rsc.org/chemcomm
Reactions of tin(IV) complexes of the type Sn(PyS)2X2 (X = Cl, PyS, Ph; PyS = pyridine-2-thiolate) with Pd(PPh3)4 provide easy access to novel heterometallic complexes with Pd–Sn bonds. Electronic characteristics of this connection were analysed by X-ray crystallography, 119
Sn Mo ¨ssbauer spectroscopy and quantum chemical analyses.
The chemistry of heterodinuclear complexes with the TM-E bonding situation (TM = transition metal, E = main group metal or metalloid) is currently being explored across the periodic table, and a great variety of novel complexes with transition metal s-donors in the coordination sphere of a main group metal (or metalloid) have been reported in the past few years. The well-explored group of metallaboratranes (i.e., compounds featuring TM-B bonds)1 has been joined by complexes with TM-E (E = Be,2 Al,3 Ga,4 In,5 Si,6 Sn,7 Sb,8 Bi,9 Te10) bonds, just to name a selection. Recently, we have shown that even in complexes with a formal TM’E bonding situation (e.g., in a stannylene complex, Sn acts as a lone pair s-donor), significant contributions of the reverse bonding mode TM-E (upon formal change of the oxidation numbers of metal and metalloid elements) may add to the bonding situation (Scheme 1, I).11 The same findings have been reported by Jambor et al. (for compound II).12 a
¨r Anorganische Chemie, TU Bergakademie Freiberg, D-09596 Freiberg, Institut fu Germany. E-mail: [email protected]; Fax: +49 3731 39 4058 b School of Engineering and Science, Theoretical Physics – Theoretical Materials Science, Jacobs University Bremen gGmbH, D-28759 Bremen, Germany c ¨r Anorganische und Analytische Chemie, Universita ¨t Mu ¨nster, Institut fu ¨nster, Germany Corrensstrasse 30, D-48149 Mu † This article is part of the ChemComm ‘Emerging Investigators 2014’ themed issue. ‡ Electronic supplementary information (ESI) available: Detailed syntheses and char¨ssbauer spectroscopy, CHNS microanalyses), tables acterisation (NMR and 119Sn Mo with parameters of data collection and structure refinement of the crystal structures reported in this paper and CIF. CCDC 963362 ([Pd(PyS)2(PPh3)2]), 963363 (1, modification 1), 963364 (1, modification 2), 963365 (1(CHCl3)2), 963366 (2(CHCl3)2), 963367 (3(THF)), 963368 (4), 963369 (5(THF)2) and details of quantum chemical analyses. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/ c3cc47912a
5382 | Chem. Commun., 2014, 50, 5382--5384
Scheme 1
Our further investigations addressed the elucidation of the currently ‘‘pure formalism’’ with respect to usability of this general principle in synthetic approaches and with regard to the influence of the further metalloid coordination sphere on the directionality of the formally dative bonding mode, i.e., on the TM’E vs. TM-E competition. The (N,S)-bidentate pyridine-2-thiolato ligand (PyS), which is a constituent of compound II (and related to the methimazolyl ligand in compound I), was a helpful tool for our study, as the desired precursor compounds III–VI (Scheme 1) were already known from the literature,13 and the mesomerism of this anion serves the purpose of our investigation. Whereas compound I was prepared in a one-pot synthesis from tin(II) and palladium(II) precursors,11 we now aim at synthesis using a combination of different starting materials with different ligand combinations and with palladium and tin in different oxidation states (Scheme 2). Thus, routes A, C and D start from tin(II) precursors and may involve a formal tin(III) intermediate (the stannyl complex 2 in route D). The utilisation of tin(IV) precursors opens further access routes (B) to such complexes. We must stress that this is particularly important
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Scheme 2
for metalloid compounds which appear to be less stable in the case of lower oxidation numbers of the metalloid (e.g., significantly lower stability of SnPh2 relative to SnCl2). All four routes shown in Scheme 2 proved to be suitable to access compound 1, however routes A, B and C produced similar yields (>70%), whereas route D proved to be less efficient (see ESI‡). (Note: the intermediate and starting materials 2 and [Pd(PyS)2(PPh3)2],14 respectively, the crystal structures of which have not been reported so far, were characterized by X-ray crystallography, see ESI.‡) Thus, route B was chosen to access related compounds 3, 4 and 5 through suitable tin(IV) starting materials (Scheme 3). As shown by X-ray crystallography (Fig. 1), compounds 1, 3 and 4 exhibit similar molecular architectures, i.e., distorted trigonal-bipyramidal coordination of tin with two axial Sn–N bonds as a fundamental motif, t15 = 0.66, 0.57 and 0.75, respectively. (Three different crystal structures of 1, i.e., two solvent free modifications and a chloroform solvate, were determined, see ESI.‡ In the discussion we refer to the solvent free modification which was obtained along the synthesis.) Noteworthily, the monodentate (PyS) ligands in 3 are S-bound to tin, while their N atoms (N3 and N4) cap two of the equatorial edges with Sn N separations of 2.95 and 3.03 Å, respectively, thus making the Sn atom [5+2]-coordinate in a rather pseudo-pentagonal-bipyramidal fashion. As a result, the sharp S3–Sn1–S4 angle arises (85.98(7)1), whereas the related Cl–Sn–Cl (in 1) and C–Sn–C (in 4) angles are 104.48(2)1 and 107.71(7)1, respectively. The Sn–Pd bonds slightly increase from 1 via 3 to 4
Scheme 3
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Fig. 1 Molecular structures of 1, 3 and 4 in the crystal structures of 1, 3THF and 4. Selected atoms are labelled, displacement ellipsoids show 50% probability, H atoms are omitted for clarity and PPh3 groups are simplified as a stick model.
(2.5052(2), 2.5328(2) and 2.5370(2) Å, respectively), and the Sn–N bonds (2.287(2), 2.292(2) (1); 2.335(2), 2.386(2) (3); 2.347(2), 2.387(2) Å (4)) exhibit the same trend and reflect response to the lowering of the Lewis acidity of the tin atom upon substitution of Cl for (PyS) for Ph. Similar behaviour (i.e., elongation of axial Sn–Cl bonds upon substitution of Sn bound equatorial Cl atoms for Ph groups) has been observed with pentacoordinate stannates [SnCl5] and [SnCl3Ph2] .16 Except for the Sn–Pd bonds, the Pd coordination spheres do not exhibit any noteworthy response to the different Sn coordination spheres, i.e., the Pd–S bonds range from 2.297 to 2.312 Å, and the Pd–P bond lengths (2.3751(4), 2.3531(5) and 2.3786(5) Å in 1, 3 and 4, respectively) do not exhibit systematic changes with respect to the features observed in the Sn coordination spheres. In general, the Pd atoms are housed in nearly square-planar coordination spheres. Despite the seemingly low influence of the Sn coordination sphere on Pd, the electronic situation along the Sn–Pd–P axis still varies significantly, as reflected by the different 2J(119Sn,31P) couplings in solution (4311, 4598 and 2677 Hz for 1, 3 and 4, respectively). Further differences were revealed by Natural Bonding Orbital (NBO) analyses. Addition of a second equivalent of [Pd(PPh3)4] to 3 furnishes 5 with a change from the Sn–S to Sn–N coordination mode of the dangling (PyS) ligands of 3 and insertion of PdPPh3 into the S2-clamp. As shown by crystallography (Fig. 2), the tin coordination sphere in 5 is distorted octahedral with trans Pd–Sn bonds. The four Sn–N bonds exhibit slightly different lengths, i.e., short and long Sn–N bonds oppose each other, and the average Sn–N bond length exceeds those observed in compounds 1, 3 and 4. With respect to the again nearly squareplanar Pd coordination spheres, the Pd–S bonds are similar to those of compounds 1, 3 and 4, but the Pd–Sn bonds are significantly longer (by up to 0.09 Å) as well as the Pd–P bonds
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Fig. 2 Molecular structure of 5 in the crystal structure of 5(THF)2. Selected atoms are labelled, displacement ellipsoids show 50% probability, H atoms are omitted for clarity and PPh3 groups are simplified as a stick model. Selected bond lengths [Å]: Pd1 P1 2.4139(5), Pd2 P2 2.4033(5), Pd1 S1 2.3085(5), Pd1 S2 2.2969(6), Pd2 S3 2.2989(5), Pd2 S4 2.3017(6), Pd1 Sn1 2.5946(2), Pd2 Sn1 2.5945(2), Sn1 N1 2.464(2), Sn1 N2 2.361(2), Sn1 N3 2.397(2), Sn1 N4 2.457(2).
(by up to 0.06 Å). We attribute this bond lengthening along the P–Pd–Sn axis to the now trans-disposed Pd–Sn bonds. In contrast to other tin compounds with more than one transition metal in the Sn coordination sphere, which could be interpreted as bridging stannylene or stannide complexes,17 the tin atom in 5 cannot exhibit directional s-lone-pair donation due to the opposing Pd–Sn bonds. Currently, 5 reveals the widest TM–Sn–TM angle observed in such heterometallic complexes (175.15(1)1), which is much larger than the related angle observed in compound VII18 (151.71). To elucidate differences in the Pd–Sn bonding situations of 1, 3, 4 and 5, NBO analyses were performed (see ESI‡). The electronic populations of the Pd–Sn NBOs are similar (1.79, 1.71, 1.69 and 1.67 electrons for 1, 3, 4 and 5, respectively). The tin contributions to these NBOs are 57, 54, 52 and 48% in the same order, reflecting a decrease of s-donor action of tin (transition towards a s-lone-pair acceptor) along this series. The natural charges of Pd (ca. 0.6 in 1, 3 and 4; 0.7 in 5) underline the pronounced role of Pd as the lone pair donor in 5 (i.e., pronounced Pd0-SnIV’Pd0 characteristics). The hybrid orbital contribution of Pd to the Pd–Sn NBO is always close to sp2d. In sharp contrast, the Sn hybrid orbital contribution to the same NBO lacks significant d character and it strongly depends on the Sn coordination sphere (%s, %p = 73, 27; 51, 49; 40, 60 and 50, 50 for 1, 3, 4 and 5, respectively). Whereas the sp hybrid contribution of tin within the linear Pd–Sn–Pd coordination in 5 appears plausible, the striking shift from predominant s to p orbital contributions along the series 1, 3, 4 signals a decrease in stannylene character in the same direction. 119 ¨ssbauer data (isomer shifts in mm s 1 for 1, 3, 4 Sn Mo and 5 are 1.63(1), 1.81(1), 1.54(1) and 2.05(1), respectively) indicate varying 5s level populations in the tin atoms of these compounds, which are in good agreement with the calculated 5s populations (1.05, 1.11, 0.94 and 1.09 electrons in the same order). Thus, the electronic population of the Sn atom in these
5384 | Chem. Commun., 2014, 50, 5382--5384
Communication
compounds is intermediate between tin(II) and tin(IV), but closer to tin(IV) (isomer shifts of III, IV and V are 3.17(1)/ 3.15(1), 0.7913c and 0.8213c mm s 1, respectively). In the context of the transition metal rich coordination sphere, even the isomer shift of 5 (2.05(1) mm s 1) is still characteristic of tin(IV), because compounds Sn[Fe(CO)2C5H5]4 and PhSn[Fe(CO)2C5H5]3, which are considered tin(IV) compounds, exhibit similar isomer shifts (of 2.14 and 2.00 mm s 1, respectively).19 In conclusion, we have shown that the TM-E coordination mode is relevant in a great variety of ‘‘stannylene’’ complexes and that these compounds can be easily accessed from tin(IV) precursors by coordination of a palladium(0) complex moiety. In this course, compound 5 revealed a novel coordination pattern, i.e., with two trans-disposed TM donor moieties in the octahedral tin coordination sphere.
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