Stabilized terphenyl-substituted digermene derivatives of simple organic groups and their halide precursors: Preference for symmetrically bonded structures

The reaction of 1 equi ir of MeMgBr, EtMgBr, or LiPh with Ge(Cl)C6H3-2,6-Tr ip(2) (1; Trip = C6H2-2,4,6-i-Pr-3) in diethyl ether solution afforded the dimers {Ge(R)C6H3-2,6-Trip(2)}(2) (R = Me (2), Et (3), Ph (4)), which have trans-bent Ge-Ge-bonded structures that are maintained in solution. The com pounds 2 and 3 are rare examples of "digermene" species having alkyl substi tuents. The previously described halide precursor 1 was found to crystalliz e simultaneously as both a V-shaped monomer and weakly Ge-Ge-bonded dimer { Ge(Cl)C6H3-2,6-Trip(2)}(2) (5), which dissociated readily to monomers in hy drocarbon solution. This species reacted readily with pyridine (py) to form the monomeric 1:1 adduct py . Ge-(Cl)C6H3-2,6-Trip(2) (7), which has pyram idal coordination at germanium. The dimeric structures found for 2-4 were i n sharp contrast with recently published results for their tin and lead ana logues, which displayed either unsymmetric dimeric structures as in 2,6-Tri p(2)H(3)C(6)(Me)(2)SnSnC6H3-2,6-Trip(2) or monomeric structures as in Pb(Me )C6H3-2,6-Trip(2). The chloro derivatives {Ge(Cl)C6H3-2,6-Trip(2)}(n) (n = 1, 2; i.e. 1 and 5) also differed from their tin congeners in that the corr esponding tin dimer is associated through chloride bridging, whereas 5, and the related dimer {Ge(Cl)C6H3-2,6-Mes(2)}(2) (6), are associated through w eak element-element bonding. The experimental results are in general agreem ent 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 struct ure for tin.