Thermolysis of tungsten dialkyl compounds leads to the formation of the transient alkylidene complexes Cp*W(NO)(=CHR) (R = t-Bu, Ph). These are the first alkylidene compounds capable of activating CH bonds of both arenes and alkanes, and we are in the midst of delineating the scope and selectivity of this activation chemistry, including cases where functionalization of the substrate occurs after the initial C-H activation event. For example, the allyl products are subject to further modification, including C-C bond-forming reactions with alkenes. We have also observed similar coupling of organic fragments after multiple C-H activations with a related tungsten alkyne system.

The carbonyl (CO) ligand frequently undergoes reactivity at the metal centre, such as the well-known migratory insertion reaction. In contrast, examples of the related nitrosyl ligand displaying such reactivity are exceedingly rare – nitrosyls act almost exclusively as inert, "spectator" ligands. However, a number of nitrosyl complexes discovered in our group rearrange to an oxo-imide configuration, effecting both N-C bond-formation and N-O bond cleavage. We hope to establish the mechanism of this exciting transformation and to define the scope of groups with which the NO ligand will combine.

Early invesitigations into chemistry of the CpCr(NO) fragment showed a dissimilarity to the Mo and W congeners; while the various Cp'M(NO)X₂ compounds were isolable as diamagnetic 16e complexes (Cp' = Cp, Cp*; M = Mo, W; X = hydrocarbyl, halide), species such as CpCr(NO)Cl₂ were stable only as paramagnetic 17e anions, not as 16e neutral compounds. However, recent synthetic efforts have afforded tetrahedral diamagnetic Cr(II) nitrosyl compunds without a Cp ligand and with a formal valence electron count of only fourteen. We wish to establish the characteristic reactivity of this highly unsaturated class of compounds, including the potential of thermally generating intermediates capable of activating CH bonds, in analogy to the tungsten complexes above.

The first NO complexes of niobium and tantalum, and the first alkyl nitrosyls of vanadium, have recently been prepared in our laboratory, employing the tridentate phosphine ligand Me₃CSi(CH₂PMe₂)₃. Both saturated 18e carbonyl and unsaturated 16e halide and alkyl derivatives have been developed. Although similar to the Group 6 Cp derivatives, these Group 5 complexes have much more electron-rich metal centres and so much weaker N-O bonds. We expect this to lead to a greater scope of reactivity for the NO ligand, potentially allowing it to act as an organic synthon for N-containing heterocycles. Finally, we are attempting to extend nitrosyl chemistry to the Group 4 metals as well.