Bis(η-pentamethylcyclopentadienyl) complexes of molybdenum, tungsten and rhenium via metal vapour synthesis

Abstract

Co-condensation of molybdenum or tungsten atoms with 1,2,3,4,5-pentamethylcyclopenta-1,3-diene (C₅HMe₅) affords the decamethylmetallocene dihydrides [M(η-C₅Me₅)₂H₂](M = Mo or W). UV photolysis of the latter results in the sequential formation of the ‘tucked-in’ compounds [M(η-C₅Me₅)(η⁶-C₅Me₄CH₂)H] and [M(η-C₅Me₅){η⁷-C₅Me₃(CH₂)₂}](M = Mo or W). For the tungsten analogue, deuterium labelling studies show that the latter reaction proceeds via the decamethylmetallocene followed by intramolecular oxidative addition to a ring methyl group. Treatment of [W(η-C₅Me₅)₂H₂] with CCl₄ yields [W(η-C₅Me₅)₂Cl₂], which reacts with ZnMe₂ to afford [W(η-C₅Me₅)₂Me₂] and with LiCH₂Bu^t to afford [W(η-C₅Me₅)(η⁶-C₅Me₄CH₂)Cl]. Reduction of [W(η-C₅Me₅)₂Cl₂] with sodium amalgam gives [W(η-C₅Me₅)(η⁶-C₅Me₄CH₂)H]; reduction of the latter with potassium affords an intermediate anion, which reacts with water or iodomethane to give [W(η-C₅Me₅)₂H₂] or [W(η-C₅Me₅)₂Me₂] respectively. [Mo(η-C₅Me₅)₂H₂] reacts with 1,2-diiodoethane to give [Mo(η-C₅Me₅)₂I₂], which is reduced by sodium amalgam to [Mo(η-C₅Me₅)(η⁶-C₅Me₄CH₂)H]; there is no evidence for the formation of [{Mo(η-C₅Me₅)₂}₂]. Co-condensation of rhenium atoms with C₅HMe₅ yields [Re(η-C₅Me₅)₂H] and [Re(η-C₅Me₅)(η⁶-C₅Me₄CH₂)], both of which can be reversibly protonated to give [Re(η-C₅Me₅)₂H₂]⁺ and [Re(η-C₅Me₅)(η⁶-C₅Me₄CH₂)H]⁺ respectively. UV photolysis of [Re(η-C₅Me₅)₂H] gives the stable 17-electron metallocene [Re(η-C₅Me₅)₂], which reacts with nitric oxide to afford the bent nitrosyl derivative, [Re(η-C₅Me₅)₂(NO)]. [Re(η-C₅Me₅)₂] may be reduced to the diamagnetic anion [Re(η-C₅Me₅)₂]^– with potassium; the latter reacts with iodomethane to afford [Re(η-C₅Me₅)₂CH₃], but the analogous reaction with chloro- or iodo-methyl ether results in the unexpected formation of [Re(η-C₅Me₅){η-C₅Me₄(CH₂OMe)}Me]. Oxidation of [Re(η-C₅Me₅)₂] with AgBF₄ gives the ‘tucked-in’ cation [Re(η-C₅Me₅)(η⁶-C₅Me₄CH₂)H]⁺, which is also obtained from the reaction of [Re(η-C₅Me₅)₂H] with chlorocarbons. UV photolysis of [Re(η-C₅Me₅)(η⁶-C₅Me₄CH₂)H]⁺ gives the double ‘tucked-in’ cation [Re(η-C₅Me₅){η⁷-C₅Me₃(CH₂)₂}]⁺; photolysis of [Re(η-C₅Me₅)₂H₂]⁺ also results in the stepwise formation of [Re(η-C₅Me₅)(η⁶-C₅Me₄CH₂)H]⁺ and [Re(η-C₅Me₅){η⁷-C₅Me₃(CH₂)₂}]⁺.