REACTIONS OF THE CYCLOHEPTATRIENYL COMPLEXES [MX(CO)(2)(ETA-C7H7)] (M= MO, X = BR, M = W, X = I) WITH CNBUT - X-RAY CRYSTAL-STRUCTURE OF [WI(CO)(2)(CNBUT)(2)(ETA(3)-C7H7)]

Reaction of [MX(CO)(2)(eta(7)-C7H7)] (M = Mo, X = Br; M = W, X = I) wi th two equivalents of CNBut in toluene affords the trihapto-bonded cyc loheptatrienyl complexes [MX(CO)(2)(CNBut)(2)(eta(3)-C7H7)] (1, M = Mo , X = Br; 2, M = W, X = I). The X-ray crystal structure of 2 reveals a pseudo-octahedral molecular geometry with an asymmetric ligand arrang ement at tungsten in which one CNBut is located trans to the eta(3)-C7 H7 ring. Treatment of 2 with tetracyanoethene results in 1,4-cycloaddi tion at the eta(3)-C7H7 ring to give [WI(CO)(2)(CNBut)(2){eta(3)-C9H7( CN)(4)}], 3. The principal reaction type of the molybdenum complex 1 i s loss of carbonyl and bromide ligands to afford substituted products [MoBr(CNBut)(2)(eta(7)-C7H7)] 4 or [Mo(CO)(CNBut)(2)(eta(7)-C7H7)]Br. Reaction of [MoBr(CO)(2)(eta(7)-C7H7)] with one equivalent of CNBut in toluene at 60 degrees C affords [MoBr(CO)(CNBut)(eta(7)-C7H7)], 5, wh ich is a precursor to [Mo(CO)(CNBut)(NCMe)(eta(7)-C7H7)][BF4], 6, by r eaction with Ag[BF4] in acetonitrile. In contrast with the parent dica rbonyl systems [MoX(CO)(2)(eta(7)-C7H7)], complexes of the Mo(CO)(CNBu t)(eta(7)-C7H7) auxiliary, 5 and 6, do not afford observable eta(3)-C7 H7 products by ligand addition at the molybdenum centre. (C) 1998 Else vier Science S.A. All rights reserved.