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Abstract: The first examples of complexes of the sterically crowded, bis(triphenylphosphine) auxiliary M(PPh3)2(η-C7H7) (M=Mo or W) have been synthesised. [Mo(CO)(PPh3)2(η-C7H7)][PF6] (1) was obtained by low-temperature reaction of [MoMe(CO)(PPh3)(η-C7H7)] with [Ph3C][PF6] in the presence of PPh3. The tungsten analogue [W(CO)(PPh3)2(η-C7H7)][BF4] (3) was formed by reaction of [WI(CO)(PPh3)(η-C7H7)] with Ag[BF4] in acetone followed by addition of PPh3. An X-ray crystallographic structural comparison of complex 3 with its mono-phosphine counterpart, [W(CO)2(PPh3)(η-C7H7)][BF4]·CH2Cl2 (4) reveals that the principal structural differences between 3 and 4 resulting from replacement of a carbonyl ligand by PPh3 are: (i) an increase in the sum of the angles between the tripodal ligands and (ii) an elongation of the W–PPh3 bond length (from 2.4950(12)Å in 4 to 2.5360(6) and 2.5496(6)Å in the bis(phosphine) complex 3). [Copyright &y& Elsevier]