Addition Reactions of Me3SiCN with Aldehydes Catalyzed by Aluminum Complexes Containing in their Coordination Sphere O, S, and N Ligands

The reaction of one equivalent of LAlH2 (1; L=HC(CMeNAr)2, Ar=2,6‐iPr2C6H3, β‐diketiminate ligand) with two equivalents of 2‐mercapto‐4,6‐dimethylpyrimidine hydrate resulted in LAl[(μ‐S)(m‐C4N2H)(CH2)2]2 (2) in good yield. Similarly, when N‐2‐pyridylsalicylideneamine, N‐(2,6‐diisopropylphenyl)salicylaldimine, and ethyl 3‐amino‐4,5,6,7‐tetrahydrobenzo[b]thiophene‐2‐carboxylate were used as starting materials, the corresponding products LAl[(μ‐O)(o‐C6H4)CN(C5NH4)]2 (3), LAlH[(μ‐O)(o‐C4H4)CN(2,6‐iPr2C6H3)] (4), and LAl[(μ‐NH)(o‐C8SH8)(COOC2H5)]2 (5) were isolated. Compounds 2–5 were characterized by 1H and 13C NMR spectroscopy as well as by single‐crystal X‐ray structural analysis. Surprisingly, compounds 2–5 exhibit good catalytic activity in addition reactions of aldehydes with trimethylsilyl cyanide (TMSCN). Four Lewis acidic aluminum compounds, LAl[(μ‐S)(m‐C4N2H)(CH2)2]2 (2), LAl[(μ‐O)(o‐C6H4)CN(C5NH4)]2 (3), LAlH[(μ‐O)(o‐C4H4)CN(2,6‐iPr2C6H3)] (4), and LAl[(μ‐NH)(o‐C8SH8)(COOC2H5)]2 (5), were synthesized and fully characterized. They efficiently catalyze the addition reactions of trimethylsilyl cyanide to aldehydes. DFT studies reveal that the reaction proceeds through a stepwise mechanism where the C1−Si bond in the coordinated TMSCN is lengthened as a result of adequate charge separation between the C1 and Si atoms.