Lithium Di-­‐ and Trimethyl Dimolybdenum(II) Complexes with Mo-­‐Mo Quadruple Bonds and Bridging Methyl Groups

摘要

New dimolybdenum complexes of composition [Mo2{μ-Me}2Li(S)}(μ-\udX)(μ-N^N)2] (3a−3c), where S = THF or Et2O and N^N represents a bidentate\udaminopyridinate or amidinate ligand that bridges the quadruply bonded molybdenum\udatoms, were prepared from the reaction of the appropriate [Mo2{μ-O2CMe}2(μ-N^N)2]\udprecursors and LiMe. For complex 3a, X = MeCO2, while in 3b and 3c, X = Me. Solution\udNMR studies in C6D6 solvent support formulation of the complexes as contact ion pairs\udwith weak agostic Mo−CH3···Li interactions, which were also evidenced by X-ray\udcrystallography in the solid-state structures of the molecules of 3a and 3b. Samples of 3c\udenriched in 13C (99%) at the metal-bonded methyl sites were also prepared and\udinvestigated by NMR spectroscopy employing C6D6 and THF-d8 solvents. Crystallization of\ud3c from toluene:tetrahydrofuran mixtures provided single crystals of the solvent separated\udion pair complex [Li(THF)4] [Mo2(Me)2(μ-Me){μ-HC(NDipp)2}2] (4c), where Dipp\udstands for 2,6-iPr2C6H3. A computational analysis of the Mo2(μ-Me)2Li core of complexes 3a and 3b has been developed, which\udis consistent with a small but non-negligible electron-density sharing between the C and Li atoms of the mainly ionic CH3···Li interactions.