Synthesis, Characterization, and Reactivity Study of a Chromium(VI) Neopentylidene Complex

The bis(arylimido)chromium(VI) dineopentyl complex, (ArN) 2 Cr(CH 2 t Bu) 2 (Ar = 2,6-diisopropylphenyl), undergoes α-hydrogen abstraction to generate a coordinatively unsaturated neopentylidene intermediate, which can be trapped by a σ-donor ligand (tetramethylurea) to afford the corresponding adduct (ArN) 2 Cr(═CH t Bu)[OC(NMe 2 ) 2 ]. Due to its high reactivity, the neopentylidene intermediate subsequently reacts with t BuCN to generate a tris(imido)chromium(VI) complex (ArN) 2 Cr[═N–C( t Bu)═CH t Bu](NC t Bu). The N-bonded t BuCN can be replaced by a strong σ-donor PPh 3, making a phosphine adduct (ArN) 2 Cr[═N–C( t Bu)═CH t Bu](PPh 3 ). Additionally, the neopentylidene intermediate can react with t BuNCO via cycloaddition, ring-opening metathesis, and cycloaddition to yield a biuret complex (ArN) 2 Cr{[ t BuNC(O)] 2 N t Bu}. It also reacts with cyclohexene in a [2 + 2] cycloaddition to afford the chromacyclobutane derivative (ArN) 2 Cr(C 11 H 20 ). In addition to cycloaddition, 1,2-addition is a typical reactivity pattern of the neopentylidene intermediate. The neopentylidene intermediate can react with dimethyl carbonate and t BuNH 2 to afford complexes (ArN) 2 Cr(OMe)[C(COOMe)H t Bu] and (ArN) 2 Cr(CH 2 t Bu)(NH t Bu), respectively.