To Split or Not to Split: [AsCCAs]-Coordinated Mo, W, and Re Complexes and Their Reactivity toward Molecular Dinitrogen.

Molybdenum, tungsten, and rhenium halides bearing a 2,2'-(PrAs)-substituted diphenylacetylene ([AsCCAs], ) were prepared and reduced under an atmosphere of dinitrogen in order to activate the latter substrate. In the case of molybdenum, a diiodo () and a triiodo molybdenum precursor () were equally suited for reductive N splitting, which led to the isolation of [AsCCAs]Mo≡N(I) () in each case. For tungsten, [AsCCAs]WCl () was reduced under N to afford {[AsCCAs]WCl}(N) (), which is best described as a dinuclear πδ-configured μ-(η: η)-N-bridged dimer. Attempts to reductively cleave the N unit in did lead to the expected tungsten nitride (), which had to be prepared independently via the treatment of with sodium azide. To arrive at a πδ-configured N-bridged dimer in a tetragonally distorted ligand environment, [AsCCAs]ReCl () was reduced in the presence of N. As expected, a μ-(η: η)-N-bridged dirhenium species, namely, {[AsCCAs]ReCl}(N) (), was formed, but found to very quickly decompose (presumably via loss of N), not only under reduced pressure, but also upon irradiation or heating. Hence, an alternative synthetic route to the originally envisioned nitride, [AsCCAs]Re≡N(Cl) (), was developed. While all the aforementioned nitrides (, and ) were found to be fairly robust, significantly different stabilities were noticed for {[AsCCAs]MCl}(N) ( for = W, for = Re), which is ascribed to the electronically different MNM cores (πδ for δ for ) in these μ-(η: η)-N-bridged dimers.