N-allylpyrazole as a ligand : IV. Preparation and characterization of the N-olefin chelate complexes with group VI metal(0) carbonyls

Abstract

Reaction of 1-allyl-3,5-dimethylpyrazole (ADMP) with Group VI metal hexacarbonyls, M(CO) 6 (M = Cr, Mo, W), under photoirradiation yielded novel mono-olefin complexes of the general formula M(CO) 4(ADMP), in which both pyrazolyl- N and the olefinic part of the allyl group are coordinated to the metal in a cis-configuration. The coordinated olefinic group showed 1H NMR upfield shifts, a decrease of the CC vibration frequencies from those of the free ligand. The ligand N-allylpyrazole coordinated to Cr and Mo was found to be easily displaced by other donor ligands such as tertiary phosphines. The displacement reactions provided a convenient route for the preparation of the cis- or trans-disubstituted tetracarbonyl complexes of these metals.