A Glimpse Into the Chemical Reactivity of the Unsaturated Hydride [MoWCp2(H)(μ-PCy2)(CO)2]

Abstract The unsaturated hydride [MoWCp2(H)(μ-PCy2)(CO)2] (1) reacted rapidly with stoichiometric amounts of different isocyanides at room temperature to give two types of formimidoyl derivatives: the symmetrically bridged complexes [MoWCp2(μ-η2:η2-CHNR)(μ-PCy2)(CO)2] [R = tBu (2a), 4-C6H4OMe (2b)], and the asymmetrically bridged complex [MoWCp2(μ-1κC:2κN-HCNR)(μ-PCy2)(CO)2] [R = Xyl (3)], with the latter compound undergoing slow rearrangement above 293 K to give the aminocarbyne isomer [MoWCp2{μ-CNH(Xyl)}(μ-PCy2)(CO)2] (4). The reaction of 1 with excess CNtBu led to the double addition product [MoWCp2(μ-H)(μ-PCy2)(1κ-CNtBu)(2κ-CNtBu)(1κ-CO)(2κ-CO)] (5), whereas the reaction with excess CN(4-C6H4OMe) at room temperature gave a mixture of two complexes having 5-electron donor aminocarbene-iminoacyl ligands: [MoWCp2(μ-1η2:2κC,κC´-HCN(4-C6H4OMe)C{N(4-C6H4OMe)})(μ-PCy2)(CO)2] (6) and [MoWCp2(μ-1κC,κC´:2η2-HCN(4-C6H4OMe)C{N(4-C6H4OMe)})(μ-PCy2){2κ-CN(4-C6H4OMe)}(1κ-CO)] (7) following from formimidoyl-isocyanide coupling. The title hydride reacted with N2CH(SiMe3) to give the addition product [MoWCp2(1κ-H)(μ-PCy2)(2κ-CO)2{1κ-N2CH(SiMe3)}] (8c), in which the coordinated diazoalkane acts formally as an imido-like four-electron donor group. Reaction with N2CPh2 led instead to a mixture of four products derived from the addition of either one molecule of diazoalkane: [MoWCp2(1κ-H)(μ-PCy2)(2κ-CO)2(1κ-N2CPh2)] (8d-W) and [MoWCp2(2κ-H)(μ-PCy2)(1κ-CO)2(2κ-N2CPh2)] (8d-Mo), or two molecules of the reagent: [MoWCp2(2κ-H)(μ-PCy2)(2κ-CO)2(1κ-N2CPh2)2] (9d-Mo) and [MoWCp2(1κ-H)(μ-PCy2)(1κ-CO)2(2κ-N2CPh2)2] (9d-W). These latter products lack of a metal−metal bond due to a dissimilar electron donation from the diazoalkane ligands, which act as 2- and 4-electron donors, respectively. Reaction of 1 with excess (p-tol)C(O)H (p-tol = 4-C6H4Me) in refluxing toluene gave the oxoacyl complex [MoWCp2{μ-1κC:2η2-C(O)CH2(p-tol)}(1κ-O)(μ-PCy2)(2κ-CO)] (10) as the unique product, following from C–O bond cleavage of the incoming reagent. Finally, compound 1 reacted with HC2(p-tol) at room temperature to give a mixture of the α-substituted alkenyls trans-[MoWCp2{μ-κ:η2-C(p-tol)CH2}(μ-PCy2)(CO)2] (trans-11) and cis-[MoWCp2{μ-1κ:2η2-C(p-tol)CH2}(μ-PCy2)(CO)2] (cis-11) in a ratio ca. 7/1, whereas the reaction in refluxing toluene led to mixtures of the β-substituted alkenyls trans-[MoWCp2{μ-1κ:2η2-CHCH(p-tol)}(μ-PCy2)(CO)2] (trans-12) and cis-[MoWCp2{μ-κ:η2-CHCH(p-tol)}(μ-PCy2)(CO)2] (cis-12) in a ratio ca. 10/1, with the former α-substituted complexes fully rearranging into the β-substituted alkenyls rapidly at 363 K, as shown by independent experiments.