Multinuclear magnetic resonance study of some imidovanadium complexes

Abstract

Abstract14N NMR studies were carried out for a series of mononuclear and dinuclear vanadium complexes with different types of nitrogen ligands (terminal and µ‐imido, amido, nitrido, amine). Some complexes containing ancillary phosphine moieties were also characterized by 31P NMR spectroscopy. The observed shieldings for terminal and bridging imido ligands are intermediate between those of nitrido and amido moieties, and the latter appear less shielded than coordinated tertiary amines. The ranges for individual ligand types are sufficiently resolved to allow the use of nitrogen chemical shifts as a structure assignment tool. The 14N NMR signals of terminal and bridging imido nitrogens displayed marked differences in their lineshapes which could be used as an additional criterion for signal assignment. Examination of substituent influences revealed the absence of a general parallelism between δ14N and δ51V, but gave evidence for parallel relationships between both quantities for complexes with formal 12VE and 16VE electron counts. Determination of 1J(51V,14N) and 1J(51V,31P) coupling constants in mononuclear complexes was feasible from simulation of 14N and 31P lineshapes and suggested that imido ligands exhibit generally greater couplings to vanadium than amido ligands. Analysis of the 31P {1H,14N} NMR spectrum allowed us to determine 2J(51V,31P) for the vanadacycle cyclo(tBuN—PC(tBu)—VCl3—). It was shown that both couplings can be employed for the acquisition of two‐dimensional 31P,51V shift correlations. Copyright © 2001 John Wiley & Sons, Ltd.