Stabilized Terphenyl-Substituted Digermene Derivatives of Simple Organic Groups and Their Halide Precursors: Preference for Symmetrically Bonded Structures

Abstract

The reaction of 1 equiv of MeMgBr, EtMgBr, or LiPh with Ge(Cl)C6H3-2,6-Trip2 (1; Trip = C6H2-2,4,6-i-Pr3) in diethyl ether solution afforded the dimers {Ge(R)C6H3-2,6-Trip2}2 (R = Me (2), Et (3), Ph (4)), which have trans-bent Ge−Ge-bonded structures that are maintained in solution. The compounds 2 and 3 are rare examples of “digermene” species having alkyl substituents. The previously described halide precursor 1 was found to crystallize simultaneously as both a V-shaped monomer and weakly Ge−Ge-bonded dimer {Ge(Cl)C6H3-2,6-Trip2}2 (5), which dissociated readily to monomers in hydrocarbon solution. This species reacted readily with pyridine (py) to form the monomeric 1:1 adduct py·Ge(Cl)C6H3-2,6-Trip2 (7), which has pyramidal coordination at germanium. The dimeric structures found for 2−4 were in sharp contrast with recently published results for their tin and lead analogues, which displayed either unsymmetric dimeric structures as in 2,6-Trip2H3C6(Me)2SnS̈nC6H3-2,6-Trip2 or monomeric structures as in Pb(Me)C6H3-2,6-Trip2. The chloro derivatives {Ge(Cl)C6H3-2,6-Trip2}n (n = 1, 2; i.e. 1 and 5) also differed from their tin congeners in that the corresponding tin dimer is associated through chloride bridging, whereas 5, and the related dimer {Ge(Cl)C6H3-2,6-Mes2}2 (6), are associated through weak element−element bonding. The experimental results are in general agreement with earlier theoretical data on the hypothetical M2H4 (M = Ge, Sn, Pb) model compounds which predicted a stable, symmetric, dimeric, Ge−Ge-bonded structure for germanium but an unsymmetric methylmethylene analogue structure for tin.