Bent Metallocenes of Germanium, Tin, and Lead with Aminoboratabenzene Ligands − Crystal Structures of E[3,5-Me2C5H3BN(SiMe3)2]2 (E = Ge, Sn, and Pb)



The reaction of GeI2, SnCl2, or PbCl2 with two equivalents of lithium aminoboratabenzenes in diethyl ether affords the new sandwich compounds Pb(3,5-Me2C5H3BNMe2)2 (4) and E[3,5-Me2C5H3BN(SiMe3)2]2 (5: E = Ge, 6: E = Sn, 7: E = Pb). While compound 4 undergoes a redox ligand coupling reaction at ambient temperature to give lead black and ligand dimers, the bis(trimethylsilyl)amino compounds 57 are thermally stable, and coupling products are only detected under the conditions of mass spectrometry. This difference in stability can be attributed to the different perturbation effects which the B-amino groups exert on the electronic properties of the boratabenzene rings. Crystal structure determinations reveal that the compounds 57 possess a monomeric bent-sandwich geometry in the solid state with facially bonded boratabenzenes. The E−C distances span rather large ranges [5: 2.320−2.939(4) Å; 6: 2.519−3.033(9) Å; 7: 2.632−3.054(7) Å]; the central element E is always particularly close to one of the two α-C atoms and displays intermediate E−B distances.