Small-Molecule Activation within the Group 6 Complexes (η5-C5Me5)[N(iPr)C(Me)N(iPr]M(CO)(L) for M = Mo, W and L = N2, NCMe, η2-Alkene, SMe2, C3H6O

A series of midvalent monocyclopentadienyl monoamidiriate (CPAM) group 6 complexes of the general formula Cp*[N(Pr-i)C(Me)N(Pr-i)]M(CO)(L) (II), where Cp* = eta(5)-C5Me5 and M = Mo, W, have been prepared, and most of them have been structurally characterized. Treatment of the ditungsten "end-on-bridged" dinitrogen complex {Cp* [N(Pr-i)C(Me)N(Pr-i)]W}(2) (mu-eta(1):eta(1)-N-2) (3) with excess NCMe under a CO atmosphere produced the ditungsten bridging diimido complex {Cp*[N(Pr-i)C(Me)N(Pr-i)]W}(2){mu-eta(1):eta(1)-NC(Me)=C(Me)N] (4). Photolysis of Cp*[N(Pr-i)C-(Me)N(Pr-i)]M(CO)(2), where M = Mo (6), W (7), or treatment of Cp*[N(Pr-i)C(Me)N(Pr-i)]Mo(CO)(NCMe) (1a) with excess alkene provided Cp*[N(Pr-i)C(Me)N(Pr-i)]-M(CO)(L) for M = Mo and L = eta(2)-ethene (8), M = W and L = eta(2)-ethene (9), M = Mo and L = eta(2)-norbomene (10), M = W and L = eta(2)-norbomene (11), M = W and L = eta(2)-cyclopentene (12), M = Mo and L = eta(2)-cyclopentene (13), and M = Mo and L = eta(2)-styrene (14). When isobutene was employed as the alkene, C-H bond activation occurred to produce Cp*[N(Pr-i)C(Me)-N(Pr-i)]W(H)(eta(3)-C4H7) (15). Photolysis of 7 in the presence of SMe2 provided Cp*[N(Pr-i)C(Me)N(Pr-i)]W[kappa-C,Omicron-C(O)Me](SMe) (16) through oxidative C-S bond activation of a coordinated SMe2, followed by 1,1-carbonyl migratory insertion into the new W-C bond. Finally, reaction of la with propylene oxide (C3H6O) provided the 16-electron complex Cp*[N(Pr-i)C(Me)N(Pr-i)]Mo[C(O)CH(Me)CH2O] (19) via similar oxidative C-O bond activation of coordinated C3H6O, followed by 1,1-carbonyl migratory insertion into the Mo-C bond of an intermediate metallaoxetane. Undera CO atmosphere, 19 is converted to the 18-electron complex Cp*[N(Pr-i)C(Me)N(Pr-i)]Mo[C(O)CH(Me)CH2O]CO) (20). These results provide additional support for the development of new stoichiometric and catalytic transformations that are mediated by CPAM group 6 metal complexes and that are relevant to the goal of small-molecule fixation.