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
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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.
