Synthesis of Cationic Silaamidinate Germylenes and Stannylenes and the Catalytic Application for Hydroboration of Pyridines.

The N-heterocyclic germylenes and stannylenes LSi(NAr)2EX (L = PhC(NtBu)2, Ar = 2,6-iPr2C6H3; E = Ge, Sn; X = Cl, CF3SO3, BPh4) supported by the bulky silaamidinate ligand [LSi(NAr)2]- have been synthesized and fully characterized. The germylene triflate LSi(NAr)2GeOTf (3b) and dimeric borate [LSi(NAr)2Ge]2ClBPh4 (3a) enabled highly regio- and chemoselective catalytic hydroboration of pyridines and may represent the most active catalytic system for the transformation. DFT calculations disclosed that the cationic germylene [LSi(NAr)2Ge]+ with a low-lying LUMO energy initiated the catalytic process. In contrast, the analogous amidinate germylene triflates are almost inactive, indicating the silaamidinate ligand is essential for the stabilization of cationic species.