Synthesis and reactions of do imido aryl derivatives of chromium, molybdenum, and tungsten. Crystal structures of Cr(NBut)2(C6H2Me3-2,4,6)2, Mo(NBut)2(C6H3Me2-2,6)2, and Cr(NBut)2[C(C6H2Me3-2,4,6)NBut](C6H2Me3-2,4,6)

Abstract

The compounds M(NBu^t)₂R′₂(M = Cr, Mo, or W, R′= C₆H₂Me₃-2,4,6 or C₆H₃Me₂-2,6; M = Mo, R′= C₆H₄Me-o) have been prepared form M(NBu^t)₂(OSiR₃)₂(M = Cr or Mo, R = Me; M = W, R = Ph) and appropriate Grignard reagents. Cr(NBu^t)₂(C₆H₂Me₃-2,4,6)₂ reacts with CO to give a thermally unstable bis(acyl) complex Cr(NBu^t)₂(COC₆H₂Me₃-2,4,6)₂ which eliminates the amide HN(Bu^t)(COC₆H₂Me₃-2,4,6) possibly via acyl migration to the imido nitrogen. Cyclic voltammetry on Cr(NBu^t)₂(C₆H₂Me₃-2,4,6)₂ shows a quasi-reversible one-electron reduction, E_½^red=–1.31 V. Reaction of compounds M(NBu^t)₂R′₂(M = Cr, Mo, or W, R′= C₆H₂Me₃-2,4,6; M = Mo, R′= C₆H₃Me₂-2,6) with t-butyl isocyanide gives the corresponding η²-iminoacyls M(NBu^t)₂[C(R′)NBu^t]R′. The X-ray crystal structures of Cr(NBu^t)₂(C₆H₂Me₃-2,4,6)₂, Mo(NBu^t)₂(C₆H₃Me₂-2,6)₂, and Cr(NBu^t)₂[C(C₆H₂Me₃-2,4,6)NBu^t](C₆H₂Me₃-2,4,6) have been determined. The first two consist of monomeric distorted tetrahedra in which one o-methyl group on each aryl ligand is positioned close to the metal atom. In the latter compound the structure is best described in terms of a distorted tetrahedron, with the η²-iminoacyl occupying one split site.