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

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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 LiCH2But 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}]+.

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