Synthesis and Reactivity of low-valent group 15 compounds


Tetraalkyldistibines R4Sb2 such as Me4Sb2 and Et4Sb2 are long known low-valent organoantimony compounds. Me4Sb2 for instance was synthesized for the first time almost eighty years ago by reaction of an Sb-mirror with methyl radicals.[1,2] Since then, alternative synthetic pathways were established and their structures were investigated, in detail.[3]

Distibines Sb2R4 and dibismuthines R4Bi2 tend to form intermolecular interactions in the solid state, yielding chain-like structures with E···E bond lengths below the sum of the van-der-Waals radii (4.12 Å).[4]. The formation of intermolecular interactions is typically observed for compounds containing small organic substituents, whereas sterically demanding substituents hamper the formation of intermolecular contacts.

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Scheme 1: Intermolecular interactions in Me4Sb2.

These interactions are rather weak and are often interrupted upon melting, resulting in a bathochromic shift between fluid and solid phases, the so-called ''thermochromic'' behavior.[5] For instance, Me4Sb2 is yellow in the solid state in liquid nitrogen, red close to its melting point of 17 °C, again yellow in the fluid state but colourless in the gas phase.[6] We recently studied the solid state structures of Et4Sb2 and Et4Bi2.[7]

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Figure 1: Molecular structures of Et4Sb2 and Et4Bi2

The crystals were obtained by in situ crystallization on the diffractometer using an IR laser-asssited technique. Et4Sb2 forms endless chains via short intermolecular Sb···Sb contacts of 3.688(1) Å between two distibine units, which agrees very well with values of reported for Me4Sb2 (3.645, 3.678 Å) and [(HC=CMe)2]2Sb2 (3.63 Å). In contrast, Et4Bi2 doesn't form isolated Bi chains but exists as rather isolated molecules and the closest intermolecular Bi···Bi distance of 4.4598(4) Å is longer than the sum of the van-der-Waals radii (4.14 Å).

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Figure 2: Intermolecular interactions in Et4Sb2 and Et4Bi2

According to these structural findings, it isn't surprising that Et4Sb2 shows thermochromic behavior, while Et4Bi2 only shows an intensification of the red color to a deep red color upon cooling to -103° C.

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Figure 3: Color change of Et4Sb2 upon cooling.


[1] For a historical review see: D. Seyferth, Organometallics 2001, 20, 1488.

[2] a) F. A. Paneth, Trans. Faraday Soc. 1934, 30, 179; b) F. A. Paneth, H. Loleit, J. Chem. Soc. 1935, 366.

[3] For review articles see: a) H. J. Breunig, R. Rössler, Coord. Chem. Rev. 1997, 163, 33; b) C. Silvestru, H. J. Breunig, H. Althaus, Chem. Rev. 1999, 99, 3277; c) H. J. Breunig, R. Rössler, Chem. Soc. Rev. 2000, 29, 403; d) Y. Matano, T. Ikegami, in Organobismuth Chemistry, ed. H. Suzuki, Y. Matano, Elsevier, Amsterdam, 2001, p. 107ff; e) G. Balázs, H. J. Breunig, in Unusual Structures and Physical properties in organometallic Chemistry, ed. M. Gielen, R. Willem, B. Wrackmeyer, J. Wiley & Sons, West Sussex (GB), 2002, p. 387ff; f) L. Balázs, H. J. Breunig, Coord. Chem. Rev. 2004, 248, 603; g) H. J. Breunig, Z. Anorg. Allg. Chem. 2005, 631, 621.

[4] Mantina, M.; Chamberlin, A. C.; Valero, R.; Cramer, C. J.; Truhlar, D. G. J. Phys. Chem. A 2009, 113, 5806.

[5] a) Ashe, III, A. J.; Ludwig Jr., E. G.; Oleksyszyn, J.; Huffman J. C. Organometallics 1984, 3, 337; b) Mundt, O.; Riffel, H.; Becker, G.; Simon, A. Z. Naturforsch. 1984, 39b, 317; c) Mundt, 0.; Riffel, H.; Becker, G.; Simon, A. Z. Naturforsch. 1988, 43b, 952; d) Breunig, H. J. Z. Anorg. Allg. Chem. 2005, 631, 621; e) Breunig, H. J.; Lork, E.; Moldovan, O.; Rat, C. I. J. Organomet. Chem. 2008, 693, 2527; f) Monakhov, K. Y.; Zessin, T.; Linti G., Eur. J. Inorg. Chem. 2010, 322.

[6] A. J. Ashe, III, E. G. Ludwig, Jr., J. Oleksyszyn, J. C. Huffman Organometallics 1984, 3, 337.

[7] a) Kuczkowski, A.; Heimann, S.; Weber, A.; Schulz, S.; Bläser, D.; Wölper, C. Organometallics 2011, 30, 4730; b) Schulz, S.; Heimann, S.; Kuczkowski, A.; Wölper, C.; Bläser, D. Organometallics 2013, 32, 3391.