Dynamic 15N NMR studies of iron phosphine complexes containing coordinated dinitrogen

The N-15-labelled iron dinitrogen complexes trans-[FeH(N-2)(PP)(2)](+)[BPh4](-) (PP=dppe, depe, dmpe) and cis-[FeH(N-2)(PP3)](+)[BPh4](-) were prepared in situ by exchange of unlabelled coordinated dinitrogen with N-15(2). N-15 NMR chemical shifts and coupling constants are reported. The N-15 spectra exhibit separate signals for the metal-bound and terminal nitrogen atoms of the coordinated N-2. The N-15 resonances display N-15, N-15 coupling as well as P-31, N-15 coupling and long-range N-15,H-1 coupling when there is a metal-bound hydrido ligand. Exchange between free and coordinated dinitrogen was monitored by magnetization transfer between N-15-labelled sites using an inversion-transfer-recovery experiment. Exchange between the metal-bound and terminal nitrogen atoms of coordinated N-2 was also monitored by magnetization transfer and this could proceed by N-2 dissociation or by an intramolecular process. Copyright (C) 2003 John Wiley Sons, Ltd.