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 N3 Ad 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(CH2 N3 Ad)(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 N2 CH2 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.