Synthesis and reactivity of the cycloheptatrienyl-bridged bimetallic complexes [M(CO)(3)(mu-eta(6):eta(1)-C7H7)M'(CO)(2)(eta-C(5)R(5))] (M=Cr, Mo or W; M'=Fe or Ru; R=H or Me)

The cycloheptatrienyl-bridged bimetallics [M(CO)(3)(mu-eta(6):eta(1)-C7H7)M'(CO)(2)(eta-C(5)R(5))] (R = H, M' = Ru: 1, M = Cr, 2, M = Mo; 3, M = W; R = Me, M = Mo: 4, M' = Ru; 5, M' = Fe) have been synthesised by reaction of [M(CO)(3)(eta-C7H7)](+) with [M'(CO)(2)(eta-C(5)R(5))](-) in THF. H-1 and C-13 NMR studies on complexes 2 to 5 indicate the operation of a dynamic process involving a 1,2 shift of the eta(1)-bound M' metal group around the cycloheptatrienyl ring. Complex 5 undergoes ready fission of the Fe-C7H7 bond to yield the homobimetallic products [Fe-2(CO)(4)(eta-C(5)Me(5))(2)] and [Mo-2(CO)(6)(mu-eta(6):eta(6)-C14H14)], and infrared data indicate the intermediacy of unstable [Mo(CO)(3)(mu-eta(6):eta(1)-C7H7)Fe(CO)(2)Cp] 6 in the formation of analogous homobimetallics from the reaction of [Mo(CO)(3)(eta-C7H7)][PF6] with Na[Fe(CO)(2)Cp]. Thermolysis of 2, 3 and 4 gives, in addition to homobimetallic products, the heterobimetallic, metal-metal bonded complexes [Ru(CO)(2)(eta-C(5)R(5))M(CO)(2)(eta-C7H7)] (M = Mo, R = H or Me; M = W, R = H). A heterobimetallic complex [Mo(CO)(2)(eta-C7H7)Re(CO)(5)] 8 is also generated by thermolysis of [Mo(CO)(3)(mu-eta(6):eta(1)-C7H7)Re(CO)(5)] 7 together with Re-2(CO)(10) and [Re(CO)(3)(eta(5)-C7H7)]. Stirring 4 or 7 in NCMe at room temperature results in detachment of the eta(6)-bound Mo(CO)(3) group and the respective formation of [Ru(eta(1)-C7H7)(CO)(2)(eta-C(5)Me(5))] 9 and [Re(eta(1)-C7H7)(CO)(5)].