Synthesis and reactions of cycloheptadienyl and cyclooctadienyl tungsten complexes: X-ray crystal structure of [W(CO)2(PPh3)2(η5-C7H9)][BF4]

Protonation of the cycloheptatriene complex [W(CO)3(η6-C7H8)] with H[BF4] · Et2O in CH2Cl2 affords the cycloheptadienyl system [W(CO)3(η5-C7H9)][BF4] (1). Complex 1 reacts with NaI to yield [WI(CO)3(η5-C7H9)], which is a precursor to [W(CO)2(NCMe)3(η3-C7H9)][BF4], albeit in very low yield. The dicarbonyl derivatives [W(CO)2L2(η5-C7H9)]+ (L2=2PPh3, 4, or dppm, 5) were obtained, respectively, by H[BF4] · Et2O protonation of [W(CO)2(PPh3)(η6-C7H8)] in the presence of PPh3 and reaction of 1 with dppm. The X-ray crystal structure of 4 (as a 1/2 CH2Cl2 solvate) reveals that the two PPh3 ligands are mutually trans and are located beneath the central dienyl carbon and the centre of the edge bridge. The first examples of cyclooctadienyl tungsten complexes [WBr(CO)2(NCMe)2(1–3-η:5,6-C8H11)] (6) and [WBr(CO)2(NCMe)2(1–3-η:4,5-C8H11)] (7) were synthesised by reaction of [W(CO)3(NCR)3] (R=Me or Prn) with 3-Br-1,5-cod/6-Br-1,4-cod or 5-Br-1,3-cod/3-Br-1,4-cod (cod=cyclooctadiene), respectively. Complexes 6 and 7 are precursors to the pentahapto-bonded cyclooctadienyl tungsten species [W(CO)2(dppm)(1–3:5,6-η-C8H11)][BF4] and [W(CO)2(dppe)(1–5-η-C8H11)][BF4] · CH2Cl2.