Synthesis and Calorimetric, Spectroscopic, and Structural Characterization of Isocyanide Complexes of Trialkylaluminum and Tri-tert-butylgallium
ABSTRACT Addition of tert-butylisocyanide or 2,6-dimethylphenylisocyanide to a solution of trialkylaluminum or trialkylgallium results in formation of complexes R(3)M·C≡N(t)Bu (M = Al, R = Me (1), Et (2), (i)Bu (3), (t)Bu (4); M = Ga, R = (t)Bu (9)) or R(3)M·C≡N(2,6-Me(2)C(6)H(3)) (M = Al, R = Me (5), Et (6), (i)Bu (7), (t)Bu (8); M = Ga, R = (t)Bu (10)), respectively. Complexes 1, 4, 5, and 8-10 are isolated as solids, whereas the triethylaluminum and triisobutylaluminum adducts 2, 3, 6, and 7 are viscous oils. Complexes 1-10 were characterized by NMR ((1)H, (13)C) and IR spectroscopies, and the molecular structures of 4, 5, and 8-10 were also determined by X-ray crystallography. The frequency of the C≡N stretch of the isocyanide increased by 58-91 cm(-1) upon complexation, consistent with coordination of the isocyanide as a σ donor. Enthalpies of complex formation for 1-10 were determined by isothermal titration calorimetry. Enthalpy data suggest the following order of decreasing Lewis acidity: (t)Bu(3)Al ≫ (i)Bu(3)Al ≥ Me(3)Al ≈ Et(3)Al ≫ (t)Bu(3)Ga. In the absence of oxygen and protic reagents, the reported complexes do not undergo insertion or elimination reactions upon heating their benzene-d(6) solutions to 80 °C.
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ABSTRACT: Complexes [PhBP(Ph)3]RuH(η(3)-H2SiRR') (R,R' = Me,Ph, 1a; RR' = Ph2, 1b) react with XylNC (Xyl = 2,6-dimethylphenyl) to form Fischer carbene complexes [PhBP(Ph)3]Ru(H)═[C(H)(N(Xyl)(η(2)-H-SiRR'))] (2a,b) that feature a γ-agostic Si-H bond. The ruthenium isocyanide complexes [PhBP(Ph)3]Ru(H)(CNXyl)(η(2)-HSiHRR') (6a,b) are not intermediates as they do not convert to 2a,b. Experimental and theoretical investigations indicate that XylNC is activated by initial coordination to the silicon center in 1a,b, followed by 1,1-insertion into an Si-H bond of the coordinated silane and then rearrangement to 2a,b.Journal of the American Chemical Society 07/2013; 135(28). DOI:10.1021/ja404910h · 11.44 Impact Factor