Syntheses, Structures, and Bonding Analyses of Carbene-Stabilized Stibinidenes

Reactions of two equivalents of LGa {L = HC[C(Me)NAr](2); Ar = 2,6-iPr(2)-C6H3} with SbX3 (X = Cl, Br) yield double-inserted products (LGaX)(2)SbX (X = Cl 1, Br 2), which were isolated at -40 degrees C. Warming solutions of 1 and 2 to ambient temperature results in intramolecular elimination of LGaX2 and formation of Ga-substituted stibinidenes L(X)GaSb as reaction intermediates, which were stabilized by coordination of strong sigma-donating carbenes. Four carbene-stabilized stibinidenes (Me)CAAC-SbGa(X)L {(Me)CAAC = [H2C(CMe2)(2)NAr]C, Ar = 2,6-iPr(2)-C6H3, X = Cl 3, Br 4} and IDipp-SbGa(X)L {IDipp = 1,3-bis(2,6-diisopropylphenyl)-imidazol-2-ylidene, X = Cl 5, Br 6} were characterized by single-crystal X-ray diffraction and the nature of the bonding in 3-6 was further investigated by quantum chemical methods. The studies reveal substantial Sb-C-carbene pi-backbonding contributions in 3 and 4, whereas the IDipp-stabilized derivatives 5 and 6 exhibit Sb-C-carbene single bonds. DFT computations with and without dispersion corrections reveal that dispersion interactions mainly from the bulky aryl groups decisively contribute to the stability of 3-6.