Divergent Pathways Involving 1,3-Dipolar Addition and N−N Bond Splitting of an Organic Azide across a Zirconium Methylidene

Abstract

The zirconium methylidene (PNP)Zr=CH2(OAr) (1) reacts with N3Ad to give two products (PNP)Zr=NAd(OAr) (2) and (PNP)Zr(η2-N=NAd)(N=CH2)(OAr) (3), both resulting from a common cycloaddition intermediate (PNP)Zr(CH2N3Ad)(OAr) (A). Using a series of control experiments in combination with DFT calculations, it was found that 2 results from a nitrene by a carbene metathesis reaction in which N2 acts as a delivery vehicle and forms N2CH2 as a side product. In the case of 3, N−N bond splitting of the azide at the α-position allowed the isolation of a rare example of a parent ketimide complex of zirconium. Isotopic labeling studies and solid-state X-ray analysis are presented for 2 and 3, in addition to an independent synthesis for the former.