[NBu4][ReNCl4]: Facile synthesis, structure, electron paramagnetic resonance spectroscopy and reactions

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Abstract
The compound [NBu4][ReNCl4] has been found to be easily accessible by the reaction of [NBu4][ReO4] with sodium azide and HCl gas in ethanol and represents an excellent precursor for the synthesis of further rhenium nitrido complexes. It has been studied by X-ray crystallography. Rhenium(VI) compounds of the general formula [ReNX4(5)]–,2– (X = Br or NCS) were obtained when [NBu4][ReNCl4] reacts with HBr or KSCN. The products as well as mixed-ligand intermediates which are formed during the ligand exchange have been studied by EPR spectroscopy. The EPR parameters of the individual mixed-ligand compounds are clearly correlated to the composition of the co-ordination sphere and can be used to characterize the mixed-ligand species unambiguously. This is shown by a nearly linear dependence of g0, g||, a0 Re and A|| Re on the spin–orbit coupling constants of the equatorial donors. Reactions of [NBu4][ReNCl4] with most organic ligands yielded rhenium(V) compounds. A number of phosphine complexes and chelates with sulfur-containing ligands have been prepared and spectroscopically characterized. A crystallographic study on [ReN(Hdetcb)2] (Hdetcb– = N 2-diethylthiocarbamoylbenzamidinate) shows cis co-ordination for the chelating S,N-donor ligands. Weak intermolecular hydrogen bridges have been found between the co-ordinated nitrogen atoms and the lone pair of the nitrido nitrogen. A comparison between the crystal structural data of [NBu4]2[ReN(mnt)2] (mnt2– = 1,2-dicyanoethene-1,2-dithiolate), prepared from [NBu4][ReNCl4] and Na2mnt, and [NBu4][ReO(mnt)2] shows longer Re–S bonds in the nitrido anion but markedly higher O–Re–S bond angles indicating higher steric requirements of the oxo ligand compared with ‘N3–’.

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