The reaction of [WI 2 (CO) 3 (NCMe) 2 ] with an excess of FcCH 2 PH 2 [Fc ) Fe(η 5 -C 5 H 5 )(η 5 -C 5 H 4 )] in THF leads to formation of the seVen-coordinate pentanuclear complex salt [WI(CO) 2 (PH 2 CH 2 Fc) 4 ]I (1), while other compounds of the type [MI(CO) 2 L 4 ]I (with M ) Mo, W and L ) PH 2 Fc, PH 2 CH 2 Fc) could not be obtained. The obserVation of this exceptional behaVior was supported by quantum chemical calculations. Compound 1 is stable in the solid state, while an equilibrium between 1, [WI 2 (CO) 2 (PH 2 CH 2 Fc) 3 ], and FcCH 2 PH 2 is ob-serVed in solution. The structure of the cation [WI(CO) 2 (PH 2 -CH 2 Fc) 4 ] + is an almost ideal trapezoidal octahedron, with the two CO ligands sharing one octahedral position.