Tethered η 2 -B,C Borataalkene Cerium Complexes

Abstract

Abstract: The synthesis and complexation of borataalkenes are of burgeoning interests, owing to their isoelectronic structures to alkenes and potential applications in catalysis. Nevertheless, borataalkene lanthanide complexes are significantly underdeveloped to date, which presumably can be attributed to the mismatch between soft π(B=C) donor and hard lanthanide ions. We herein illustrate several tethered borataalkene cerium complexes. Treatment of cerium diylide 1 with excess BEt3 generated complex 2, featuring a 6-membered NBCPCSi ring. Subsequent reactions between 2 and excess KC8 lead to dearylation and ortho-metalation, affording complex [3•K2(Et2O)3]2. Control experiments imply that dearylation likely happened prior to ortho-metalation in the formation of complex [3•K2(Et2O)3]2, as suggested by the isolation of complex 4•K(Et2O)2. In these complexes, the atomic distances between B and C range from 1.461(14)-1.517(16) Å, demonstrating the presence of borataalkene moieties. Quantum chemical calculations elucidate their electronic structures, revealing the η2-B,C-cerium interactions are predominately electrostatic in nature with distinct ligand-to-metal π donations and without significant π backbonding contributions. These findings may open an avenue to other borataalkene f-block complexes and novel catalytic transformations mediated by them.