An alpha-diiminato germylene family: syntheses, structures, and reactivity towards C-C coupled digermylene and digermylene oxide

The synthesis and reactivity of a rigid alpha-diiminate ligand supported chlorogermylene 2 were demonstrated. The reaction of 2 with hydride donor K[BH(Bu-s)(3)] yielded a hydride addition product, a five-membered 6 pi-aromatic germylene 3. A nonaromatic germylene 4 was produced by dehydrochlorination of 2 with KN((SiBuMe2)-Bu-t)(2). Halide abstraction with AlCl3 from 2 afforded a cationic germylene 5, and the reduction of 2 with potassium led to a C-C coupled digermylene 6 via a radical coupling pathway. Hydrolysis of 2 in the presence of NHC ((Bu-t-NCH)(2)C:) gave digermylene oxide 7. DFT investigations of central GeII-rings in molecules 3-5 provided the details of frontier molecular orbitals. The energy level of the lone pair on the Ge atom in 3 is slightly higher than that in 4, indicating that 3 is the stronger sigma-donor than 4. Digermylene 6 and its diastereoisomer 6a feature trans-bent and gauche-bent configurations along their axially chiral C-C bonds, respectively. The conformational and cis-trans isomerism was observed by the isolation of crystal structures 7 and 7a because of intramolecular steric hindrance.