Synthesis and reactivity of the cycloheptatrienyl-bridged bimetallic complexes [M(CO) 3(μ-η 6: η 1-C 7H 7)M'(CO) 2(η-C 5R 5)](M = Cr, Mo or W; M' = Fe or Ru; R = H or Me)

Abstract

The cycloheptatrienyl-bridged bimetallics [M(CO) 3(μ-η 6:η 1-C 7H 7)M'(CO) 2 (η-C 5R 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(η-C 7H 7)] + with [M'(CO) 2(η-C 5R 5)] − 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 η 1-bound M' metal group around the cycloheptatrienyl ring. Complex 5 undergoes ready fission of the Fe-C 7H 7 bond to yield the homobimetallic products [Fe 2(CO) 4(η-C 5Me 5) 2] and [Mo 2(CO) 6(μ-η 6:η 6-C 14H 14)], and infrared data indicate the intermediacy of unstable [Mo(CO) 3(μ-η 6:η 1-C 7H 7Fe(CO) 2Cp] 6 in the formation of analogous homobimetallics from the reaction of [Mo(CO) 3(η-C 7H 7)][PF 6] 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-C 5R 5)M(CO) 2(η-C 7H 7)] (M = Mo, R = H or Me; M = W, R = H). A heterobimetallic complex [Mo(CO) 2(η-C 7H 7) Re(CO) 5] 8 is also generated by thermolysis of [Mo(CO) 3(η-η 6:η 1-C 7H 7)Re(CO) 5] 7 together with Re 2(CO) 10 and [Re(CO) 3 (η 5-C 7 H 7)]. Stirring 4 or 7 in NCMe at room temperature results in detachment of the η 6- bound Mo(CO) 3 group and the respective formation of [Ru(η 1-C 7H 7)(CO) 2(η-C 5Me 5)] 9 and [Re(η 1-C 7H 7)(CO) 5].