Introduction

Low-valent main and transition metal compounds are an exciting research field in the area of organometallic chemistry. Cluster compounds have structural and chemical properties that make them interesting from a technological point of view as well as from the perspective of a basic researcher. Oligomeric metal clusters, which are connected by metal-metal bonds and kinetically stabilized by an organic ligand shell, are intermediates between the molecular world and the "bulk" material. The interesting question is: How many metal atoms are needed (or how large must be a cluster) to model the properties of the "bulk" material.

In the range of the low-valent main group element compounds, the compounds especially of the group 13 (Al, Ga) and 14 (Si, Ge) were investigated in the past. The cluster [Al₇₇(N(SiMe₃)₂)₂₀]^2- and [Ga₈₄(NTMS₂)₂₀]^x- (x = 3, 4) synthesized by the Schnöckel group are among the largest structurally characterized metalloid cluster compounds.[1,2] In addition to such large cluster compounds, low-valent compounds containing much less metal atoms, were synthesized, in particular neutral M^I and M^II of the type [MR]_x and R₂M-MR₂.[3] These compounds are not only interesting target compounds, but are also expected to show a diverse chemistry.[4]

In the last decade, base-stabilized molecules have received agrowing interest. In particular N-heterocyclic carbenes (NHC) were found to stabilize unforeseen compounds such as (NHC)₂Si₂, formally containing a Si₂ molecule with Si=Si double bond andSi atoms in the formal oxidation state 0.[5] Since this initial report, several interesting main group element compounds of this type with interesting bonding properties have been reported.[6]

We are interested for some time in the synthesis, structure and reactivity of low-valent group 12 (Zn), low-valent group 13 (Al, Ga, In) and low-valent group 15-compounds (Sb, Bi).

References

[1] Ecker, A.; Weckert, E.; Schnöckel, H. Nature 1997, 387, 379

[2] (a) Schnepf, A.; Schnöckel, H. Angew. Chem. Int. Ed. 2001, 40, 712; (b) Schnepf, A.; Jee, B.; Schnöckel, H.; Weckert, E.; Meents, A.; Lubbert, D.; Herrling, E.; Pilawa, B. Inorg. Chem. 2003, 42, 7731.

[3] (a) G. Linti, H. Schnöckel, Coord. Chem. Rev. 2000, 206–207, 285. (b) W. Uhl, Chem. Soc. Rev. 2000, 259; (c) S. Schulz in Comprehensive Organometallic Chemistry III, Chapter 03.07; Ed. R. H. Crabtree, D. M. P. Mingos, 287. (d) H. Schnöckel, Chem. Rev. 2010, 110, 4125

[4] (a) W. Uhl, Adv. Organomet. Chem. 2004, 51, 53. (b) S. Nagendran, H. W. Roesky, Organometallics 2008, 27, 457. (c) P. P. Power, Nature 2010, 463, 171. (d) C. A. Caputo, P. P. Power, Organometallics 2013, 32, 2278

[5] Y. Wang, Y. Xie, P. Wei, R. B. King, H. F. Schaefer III, P. von R. Schleyer, G. H. Robinson, Science 2008, 321, 1069.

[6] a) Y. Wang, G. H. Robinson Dalton Trans. 2012, 41, 337. (b) D. J. D. Wilson, J. L. Dutton, Chem. Eur. J. 2013, 19, 13626.