Effect of a κ1‑Bonded-M-1,2,3-triazole (M = Co, Ru) on the Structure and Reactivity of Group 6 Alkoxy (Fischer) Carbenes

The [3 + 2] cycloaddition of two different metal-bound azides, [(Me4cyclam)­CoII(N3)]­ClO4 and (η5-C5H5)­(dppe)­RuII(N3), (dppe = Ph2PCH2CH2PPh2) with Cr(0) and W(0) (ethoxy)­(alkynyl) Fischer carbenes has been efficiently used for the preparation of polymetallic metal-carbene complexes. The presence of the κ1-bonded metal triazole causes a significant influence on the electronic properties, structure, and reactivity of this new class of Fischer alkoxycarbenes. For the Ru­(II) derivatives, their chemical behavior is considerably influenced by the interaction of the (η5-C5H5)­(dppe)­RuII-triazole moiety with the empty p-carbene orbital that provokes a noticeable decrease in the electrophilicity of the MC carbon (manifested by the shielding of the 13C NMR chemical shifts). In turn, in the Co­(II) derivatives, the incorporation of the (Me4cyclam)­CoII moiety diminishes the aromaticity of the triazole ring and has a marked effect on the energy and distribution of the LUSO orbital, mostly resident on the Co­(II) fragment. The almost negligible participation of the carbene moiety in the LUSO makes this position unable to react with nucleophiles. The reactions reported in this work constitute the first examples of [3 + 2] cycloaddition of azides and alkynyl Fischer carbene complexes in solution.