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 monoamidinate (CPAM) group 6 complexes of the general formula Cp*­[N­(iPr)­C­(Me)­N­(iPr)]­M­(CO)­(L) (II), where Cp* = η5-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(iPr)­C­(Me)­N­(iPr)]­W}2(μ-η1:η1-N2) (3) with excess NCMe under a CO atmosphere produced the ditungsten bridging diimido complex {Cp*­[N­(iPr)­C­(Me)­N­(iPr)]­W}2[μ-η1:η1-NC­(Me)C­(Me)­N] (4). Photolysis of Cp*­[N­(iPr)­C­(Me)­N­(iPr)]­M­(CO)2, where M = Mo (6), W (7), or treatment of Cp*­[N­(iPr)­C­(Me)­N­(iPr)]­Mo­(CO)­(NCMe) (1a) with excess alkene provided Cp*­[N­(iPr)­C­(Me)­N­(iPr)]­M­(CO)­(L) for M = Mo and L = η2-ethene (8), M = W and L = η2-ethene (9), M = Mo and L = η2-norbornene (10), M = W and L = η2-norbornene (11), M = W and L = η2-cyclopentene (12), M = Mo and L = η2-cyclopentene (13), and M = Mo and L = η2-styrene (14). When isobutene was employed as the alkene, C–H bond activation occurred to produce Cp*­[N­(iPr)­C­(Me)­N­(iPr)]­W­(H)­(η3-C4H7) (15). Photolysis of 7 in the presence of SMe2 provided Cp*­[N­(iPr)­C­(Me)­N­(iPr)]­W­[κ-C,O-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 1a with propylene oxide (C3H6O) provided the 16-electron complex Cp*­[N­(iPr)­C­(Me)­N­(iPr)]­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. Under a CO atmosphere, 19 is converted to the 18-electron complex Cp*­[N­(iPr)­C­(Me)­N­(iPr)]­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.