Reaction studies on heterodinuclear alkanediyl complexes: some examples of metalloselectivity

Abstract

The reactions of some heterobimetallic alkanediyl complexes of the type [(η-C₅R₅)(OC)₂Fe(C_nH_2n)ML_y][R = H, n= 3–6, ML_y= Mo(CO)₃(cp), W(CO)₃(cp), Ru(CO)₂(cp) or Re(CO)₅; R = Me, n= 3, ML_y= Ru(CO)₂(cp); cp =η-C₅H₅] with tertiary phosphines, trityl hexafluorophosphate (Ph₃CPF₆) and halogens were investigated. The reactions of [(cp)(CO)₂Fe(C₃H₆)ML_y] with PPh₃ were metalloselective, with the phosphine always attacking the expected metal site, which could be predicted from the reactivities of the corresponding monometallic alkyl or homodinuclear alkanediyl species. The alkanediyl chain length was found not to influence the site of nucleophilic attack. The reactions of [(cp)(OC)₂Fe(C₃H₆)ML_y][ML_y= Ru(CO)₂(cp), Mo(CO)₃(cp) or W(CO)₃(cp)] with Ph₃CPF₆ gave the complexes [(cp)(OC)₂Fe(C₃H₅)ML_y]PF₆, where the β-CH unit is believed to be weakly bonded to both metal centres. The reaction of [(cp)(OC)₂Fe(C_nH_2n)Ru(CO)₂(cp)](n= 4 or 6) with the trityl salt was not metalloselective, and gave a mixture of equal amounts of [(cp)(OC)₂Fe{CH₂CH(CH₂)_n–2}Ru(CO)₂(cp)]PF₆ and [(cp)(OC)₂Fe{(CH₂)_n–2CHCH₂}Ru(CO)₂(cp)]PF₆. In contrast, [(cp)(OC)₂Fe(C₄H₈)W(CO)₃(cp)] gave only [(cp)(OC)₂Fe{CH₂CH(CH₂)₂}W(CO)₃(cp)]PF₆. Metalloselectivity was observed for the reaction of [(cp)(OC)₂Fe(C₆H₁₂)W(CO)₃(cp)] with HCl, which gave cleavage of the W–C bond. In contrast, the reaction of [(cp)(OC)₂Fe(C₅H₁₀)Ru(CO)₂(cp)] with I₂ resulted in cleavage of both metal–alkyl bonds. The reactions of [(cp)(OC)₃Mo(C₄H₈)Mo(CO)₃(cp)] with PPh₃ to give [(cp)(OC)₂-(Ph₃P)Mo{C(O)(CH₂)₄}Mo(CO)₃(cp)] and [(cp)(OC)₂(Ph₃P)Mo{C(O)(CH₂)₄C(O)}Mo(PPh₃)(CO)₂-(cp)] are also reported.