Synthesis and reactivity of the cycloheptatrienyl-bridged bimetallic complexes [M(CO)3(μ-η6: Η1-C7H7)M'(CO)2(η-C 5R5)](M = Cr, Mo or W; M' = Fe or Ru; R = H or Me)

Article abstract of DOI:10.1016/S0022-328X(96)06235-3

The cycloheptatrienyl-bridged bimetallics [M(CO)₃(μ-η⁶:η¹-C₇H ₇)M'(CO)₂ (η-C₅R₅)] (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(η-C₇H₇)]⁺ with [M'(CO)₂(η-C₅R₅)]^- in THF. ¹H and ¹³C NMR studies on complexes 2 to 5 indicate the operation of a dynamic process involving a 1,2 shift of the η¹-bound M' metal group around the cycloheptatrienyl ring. Complex 5 undergoes ready fission of the Fe-C₇H₇ bond to yield the homobimetallic products [Fe₂(CO)₄(η-C₅Me₅)₂] and [Mo₂(CO)₆(μ-η⁶:η⁶-C ₁₄H₁₄)], and infrared data indicate the intermediacy of unstable [Mo(CO)₃(μ-η⁶:η¹-C₇H ₇Fe(CO)₂Cp]6 in the formation of analogous homobimetallics from the reaction of [Mo(CO)₃(η-C₇H₇)][PF₆] with Na[Fe (CO)₂Cp]. Thermolysis of 2, 3 and 4 gives, in addition to homobimetallic products, the heterobimetallic, metal-metal bonded complexes [Ru(CO)₂(η-C₅R₅)M(CO) ₂(η-C₇H₇)] (M = Mo, R = H or Me; M = W, R = H). A heterobimetallic complex [Mo(CO)₂(η-C₇H₇) Re(CO)₅] 8 is also generated by thermolysis of [Mo(CO)₃(η-η⁶:η¹-C ₇H₇)Re(CO)₅] 7 together with Re₂(CO)₁₀ and [Re(CO)₃ (η⁵-C₇ H₇)]. Stirring 4 or 7 in NCMe at room temperature results in detachment of the η⁶- bound Mo(CO)₃ group and the respective formation of [Ru(η¹-C₇H₇)(CO)₂(η-C ₅Me₅)] 9 and [Re(η¹-C₇H₇)(CO)₅].