Carbon-nitrogen bond formation via the reaction of terminal alkynes with a dinuclear side-on dinitrogen complex

The dinuclear dinitrogen complex ([P2N2]Zr)2(mu-eta2:eta2-N2) reacts with terminal aryl alkynes to generate a new species in which the dinitrogen unit has been functionalized. The products formed have the general formula ([P2N2]Zr)2(mu-eta2:eta2-N2CCAr)(mu-CCAr) and display a styryl-hydrazido unit bridging the two Zr centers along with a bridging arylalkynide. The crystal structures of three of these products are reported. A mechanism is proposed for this process that involves cycloaddition of the alkyne to the side-on dinitrogen unit followed by protonation of the Zr-C bond by a second equivalent of terminal alkyne. A fluxional process is operative in solution that equilibrates the phosphorus nuclei at high temperature; in the slow exchange limit, the two [P2N2]Zr ends of complex are inequivalent as evidenced by four resonances in the 31P NMR spectrum for the inequivalent phosphorus donors. This C-N bond-forming reaction is unique in that an activated dinitrogen fragment undergoes a reaction with an alkyne.