Formation of the alkoxyalkyl complexes [M{CHMe(OMe)}(CO)2(η-C5H4R)](M = Mo, R = H; M = W, R = H or Me) and their transformations by loss of MeOH into η3-propenoyl or vinyl complexes. Crystal structures of [Mo{CHMe(PPh3)}(CO)2(PPh3)(η-C5H5)]BF4, [Mo(η3-CH2CHCO)(CO)(PPh3)(η-C5H5)] and [W(σ-CHCH2)(CO)2(PPh3)(η-C5H4Me)

Abstract

Addition of MeSO3F or [Me3O]BF4 followed by PPh3 to the aldehyde complex [Mo(MeCHO)(CO)2(η-C5H5)]– results in formation of the methoxyalkyl complex trans-[Mo{CHMe(OMe)}(CO)2(PPh3)(η-C5H5)] in a reaction that proceeds via the unstable [Mo{η2-CHMe(OMe)}(CO)2(η-C5H5)]. A by-product of this reaction is the ylide trans-[Mo{CHMe(PPh3)}(CO)2(PPh3)(η-C5H5)]X (X = BF4– or SO3F–), a species (X = BF4) better prepared by treatment of trans-[Mo{CHMe(OMe)}(CO)2(PPh3)(η-C5H5)] with HBF4 in the presence of PPh3. The crystalline ylide trans-[Mo{CHMe(PPh3)}(CO)2(PPh3)(η-C5H5)]BF4 is monoclinic, with a= 11.378(34), b= 18.903(35), c= 20.17(8)Å, β= 115.28(31)° and for the 3918 independent reflections with I/σ(I) > 3.0, R= 0.0510. In solution, trans-[Mo{CHMe(OMe)}(CO)2(PPh3)(η-C5H5)] either degrades to [MoH(CO)2(PPh3)(η-C5H5)] or loses MeOH to form the η3-propenoyl [Mo(η3-CH2CHCO)(CO)(PPh3)(η-C5H5)]. This molecule is monoclinic, with a= 17.231(50), b= 8.189(14), c= 16.727(36)Å, β= 106.79(22)° and for the 1654 independent reflections for which |F|/σ(|F|) > 4.0, R= 0.100. The proposed mechanism for its formation is based on isotopic tracking experiments and includes a vinyl to carbonyl migration. Treatment of [WMe(CO)3(η-C5H4R)](R = H or Me) with PPh3 in MeCN gives the acyl [W(σ-COMe)(CO)2(PPh3)(η-C5H4R)]. These react with [Me3O][BF4] to form the cationic carbenes [W{CMe(OMe)}(CO)2(PPh3)(η-C5H4R)]BF4, which in turn react with LiBHEt3 to give the alkoxyalkyls trans-[W{CHMe(OMe)}(CO)2(PPh3)(η-C5H4R)]. The alkoxyalkyls trans-[W{CHMe(OMe)}(CO)2(PPh3)(η-C5H4R)] react with traces of acid to form the σ-vinyls trans-[W(σ-CHCH2)(CO)2(PPh3)(η-C5H4R)], the methylcyclopentadienyl species of which is crystalline, monoclinic, with a= 36.952(40), b= 10.971(13), c= 25.148(23)Å and β= 103.60(8)°. For the 2542 independent reflections for which |F|/σ(|F|) > 5.0, R converged to 0.0750.