Pentamethylcyclopentadienyl molybdenum and tungsten carbene complexes. X-Ray crystal structures of cis- and trans-[Mol(CO)2{C(CH2)3O}(η-C5Me5)]

Abstract

Treatment of [M(CO)₃(η-C₅Me₅)]^–(M = Mo or W) with Br[CH₂]₃ Br gives the metallapropanes [M{(CH₂)₃Br}(CO)₃(η-C₅Me₅)]. Reaction of [Mo{(CH₂)₃Br}(CO)₃(η-C₅Me₅)] with I^– provides cis and trans carbenes [MoI(CO)₂{[graphic omitted]}(η-C₅Me₅)]. Crystallisation of the mixture gives two crystal forms, one of which consists of pure trans isomer while the second consists of a mixture of predominantly two cis components (68.5 and 7.1%) with some trans isomer (24.4%) incorporated in the crystal. For the trans isomer, orthorhombic, a= 15.38(6), b= 15.65(8), c= 14.78(6)Å, R 0.0665 for 1 335 independent reflections. For the cis isomer, monoclinic, a= 12.73(4), b= 9.26(3), c= 16.09(4)Å, β= 108.68(9)°, R 0.0908 for 974 independent reflections. In tetrahydrofuran solution the two isomers slowly interconvert at ambient temperature. The reaction of Br^– with [Mo{(CH₂)₃Br}(CO)₃(η-C₅Me₅)] gives the carbene [MoBr(CO)₂{[graphic omitted]}(η-C₅Me₅)] as predominantly the cis isomer. The reaction of CN^– with [Mo{(CH₂)₃Br}(CO)₃(η-C₅Me₅)] gives the trans carbene [Mo(CN)(CO)₂{[graphic omitted]}(η-C₅Me₅)] while reaction with SCN^– gives the cis carbene [Mo(NCS)(CO)₂{[graphic omitted]}(η-C₅Me₅)]. Reaction of [W{(CH₂)₃Br}(CO)₃(η-C₅Me₅)] with I^– affords the iodo carbene [WI(CO)₂{[graphic omitted]}(η-C₅Me₅)] as predominantly the trans isomer. Reaction of [Mo{(CH₂)₃Br}(CO)(η-C₅Me₅)] with [Fe(CO)₂(η-C₅H₅)]^– results in elimination of Br^– and formation of the heterodimetalla-alkane species [(η-C₅Me)(OC)₃Mo(CH₂)₃Fe(CO)(η-C₅H₅)].