Metal-Induced Coordination Inversion and Carbon−Nitrogen Bond Rearrangement. Structurally Characterized Phenyl Isocyanate Inserted into Aluminum Methyl Compounds and O- and N-Bound Aluminum Compounds

Abstract

[C4H3N(CH2NMe2)-2]AlMe2 (1) is prepared in 88% yield by the reaction of substituted pyrrole [C4H4N(CH2NMe2)-2] with 1 equiv of AlMe3 in methylene chloride. Reaction of compound 1 with 1 equiv of phenyl isocyanate in toluene generates a seven-membered cycloaluminum compound {C4H3N[CH2NPh(CONMe2)]-2}AlMe2 (2). The phenyl isocyanate was inserted into the aluminum and dimethylamino nitrogen bond and induced an unusual rearrangement which results in C−N bond breaking and formation. A control experiment shows that the reaction of substituted pyrrole [C4H4N(CH2NMe2)-2] with 1 equiv of phenyl isocyanate in diethyl ether yields a pyrrolyl attached urea derivative {C4H3N(CH2NMe2)-2-[C(O)NHPh]-1} (3). The demethanation reaction of AlMe3 with 1 equiv of 3 in methylene chloride at 0 °C afforded O-bounded and N-bounded aluminum dimethyl compounds {C4H3N(CH2NMe2)-2-[C(O)NPh]-1}AlMe2 (4a) and {C4H3N(CH2NMe2)-2-[CO(NPh)]-1}AlMe2 (4b) in a total 78% yield after recrystallization. Both 4a and 4b are observed in 1H NMR spectra; however, the relative ratio of 4a and 4b depends on the solvent used. Two equivalents of AlMe3 was reacted with 3 in methylene chloride to yield a dinuclear aluminum compound AlMe3{C4H3N(CH2NMe2)-2-[C(O)NPh]-1}AlMe2 (5). Reaction of 5 with another equivalent of ligand 3 results in the re-formation of compounds 4a and 4b