Reactions of the cycloheptatrienyl complexes [MX(CO) 2( η-C 7H 7)] (M=Mo, X=Br; M=W, X=I) with CNBu t: X-ray crystal structure of [WI(CO) 2(CNBu t) 2( η3-C 7H 7)

Abstract

Reaction of [MX(CO) 2( η 7-C 7H 7)] (M=Mo, X=Br; M=W, X=I) with two equivalents of CNBu t in toluene affords the trihapto-bonded cycloheptatrienyl complexes [MX(CO) 2(CNBu t ) 2( η 3-C 7H 7)] ( 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 arrangement at tungsten in which one CNBu t is located trans to the η 3-C 7H 7 ring. Treatment of 2 with tetracyanoethene results in 1,4-cycloaddition at the η 3-C 7H 7 ring to give [WI(CO) 2(CNBu t ) 2{ η 3-C 9H 7(CN) 4}], 3. The principal reaction type of the molybdenum complex 1 is loss of carbonyl and bromide ligands to afford substituted products [MoBr(CNBu t ) 2( η 7-C 7H 7)] 4 or [Mo(CO)(CNBu t ) 2( η 7-C 7H 7)]Br. Reaction of [MoBr(CO) 2( η 7-C 7H 7)] with one equivalent of CNBu t in toluene at 60°C affords [MoBr(CO)(CNBu t )( η 7-C 7H 7)], 5, which is a precursor to [Mo(CO)(CNBu t )(NCMe)( η 7-C 7H 7)][BF 4], 6, by reaction with Ag[BF 4] in acetonitrile. In contrast with the parent dicarbonyl systems [MoX(CO) 2( η 7-C 7H 7)], complexes of the Mo(CO)(CNBu t )( η 7-C 7H 7) auxiliary, 5 and 6, do not afford observable η 3-C 7H 7 products by ligand addition at the molybdenum centre.