Anomalous hydrogen-1 and carbon-13 spectra of some new N-acyl-N′-aryldiazene complexes of osmium

Abstract

The complex [OsCl₃O(PPh₃)₂] reacts with the hydrazides 4-RC₆H₄NHNHCOR′(R = MeO, Me, H, Cl, or NO₂; R′= H, Me, Et, Prⁿ, Bu^t or CH₂Ph) to give the N-acyl-N′-aryldiazene complexes [OsCl₂(4-RC₆H₄·N₂·COR′)(PPh₃)₂]. Although apparently diamagnetic, their ¹H and ¹³C n.m.r. spectra show shifts of a pattern and magnitude characteristic of paramagnetic species. Moreover these shifts are restricted to certain protons and carbon atoms of the diazene ligand, and the tertiary phosphine protons and carbon atoms show no anomalies. The magnitude of the shifts is highly dependent on the nature of the substituents in the diazene N-phenyl group, and there is an approximately linear relation between the shifts and Hammett σ constants for the substituent. Variable-temperature ¹H n.m.r. spectra suggest that a second-order paramagnetic effect may be responsible for the shifts.