Reactions of Iso(thio)cyanates with Dialanes: Cycloaddition, Reductive Coupling, or Cleavage of the C═S or C═O Bond.

The dialanes [(dpp-Bian)Al-Al(dpp-Bian)] () and [(dpp-dad)Al(THF)-(THF)Al(dpp-dad)] () (dpp-Bian = 1,2-[(2,6-PrCH)NC]CH, dpp-dad = [(2,6-PrCH)NC(CH)]) react with some isothiocyanates, isocyanates, and diphenylketene via [2 + 4] cycloaddition of the C═O or C═S bond across the C═C-N-Al fragment to afford complexes [L(X═C-Y)Al-Al(X═C-Y)L] with an intact Al-Al single bond (, L = dpp-Bian, X = PhN, Y = O; , L = dpp-Bian, X = PhC, Y = O; , L = dpp-dad, X = BnN, Y = S; , L = dpp-dad, X = BuN, Y = O; , L = dpp-dad, X = PrN, Y = S; and , L = dpp-dad, X = CyN, Y = S). A mixed C═N and C═O mode cycloadduct, [(dpp-Bian)(TosN═C-O)Al-Al(TosN-C═O)(dpp-Bian)] , was obtained in the reaction of with tosylisocyanate. Heating the solution of resulted in a thermal transformation and a change of the cycloaddition mode from C═O to C═N to give the product [(dpp-Bian)(PhN-C═O)Al(O)Al(PhN-C═O)(dpp-Bian)] . The reduction of and with Na yielded the products [Na(THF)][(dpp-dad)(X═C-Y)Al] (, X = PrN, Y = S, = 2 and , X = BuN, Y = O, = 3) in which one of the methyl groups of the backbone of the initial dpp-dad ligand was dehydrogenated. When was reacted with the bulky adamantyl isocyanate AdNCO, the C-C coupling of two substrates occurred to form [(dpp-dad)Al(O═C-NAd)Al(dpp-dad)] in which the coupled dianionic oxamide ligand bridged two Al atoms in a μ,η-N,O/N,O mode. Moreover, in the presence of 2.0 equiv of Na metal, precursor reacts with BuNCS, -TolylNCS, or MeSiNCO, possibly through the reduced Al intermediate, to yield the sulfur- or oxygen-bridged dimer [Na(solv)][(dpp-dad)Al(μ-E)] (, E = S, solv = THF, = 3 and , E = O, solv = DME, = 2) upon C═S or C═O bond cleavage. Dialane reacts with dimethylsulfone to give a Lewis adduct [(dpp-Bian)(MeSO)Al] (), which releases dimethylsulfone upon heating. The diamagnetic compounds - and - were characterized by NMR and IR spectroscopy. The molecular structures of - were established by single-crystal X-ray diffraction analysis. Electronic structures of the compounds and possible isomers have been examined by DFT calculations.