Synthesis of the sterically crowded cycloheptatrienyl complexes [M(CO)(PPh 3) 2(η-C 7H 7)] + (M = Mo or W): X-ray crystal structures of [W(CO)(PPh 3) 2(η-C 7H 7)][BF 4] and [W(CO) 2(PPh 3)(η-C 7H 7)][BF 4] · CH 2Cl 2

Abstract

The first examples of complexes of the sterically crowded, bis(triphenylphosphine) auxiliary M(PPh 3) 2(η-C 7H 7) (M = Mo or W) have been synthesised. [Mo(CO)(PPh 3) 2(η-C 7H 7)][PF 6] ( 1) was obtained by low-temperature reaction of [MoMe(CO)(PPh 3)(η-C 7H 7)] with [Ph 3C][PF 6] in the presence of PPh 3. The tungsten analogue [W(CO)(PPh 3) 2(η-C 7H 7)][BF 4] ( 3) was formed by reaction of [WI(CO)(PPh 3)(η-C 7H 7)] with Ag[BF 4] in acetone followed by addition of PPh 3. An X-ray crystallographic structural comparison of complex 3 with its mono-phosphine counterpart, [W(CO) 2(PPh 3)(η-C 7H 7)][BF 4] · CH 2Cl 2 ( 4) reveals that the principal structural differences between 3 and 4 resulting from replacement of a carbonyl ligand by PPh 3 are: (i) an increase in the sum of the angles between the tripodal ligands and (ii) an elongation of the W–PPh 3 bond length (from 2.4950(12) Å in 4 to 2.5360(6) and 2.5496(6) Å in the bis(phosphine) complex 3).