Neutral oxo and nitrido complexes of technetium(V) and rhenium(V) with an unsaturated tetradentate (N2S2) ligand. Crystal structure of [N,N′-ethylenebis(thioacetylacetonylideneiminato](2–)S,S′,N,N′) nitridotechnetium(V)

Abstract

Ligand-exchange reactions of the tetradentate unsaturated N2S2Schiff-base ligand N,N′-ethylenebis (thioacetylacetonylideneimine)(H2L) with labile monooxo-technetium(V) and -rhenium(V) compounds ([NBu4][TcOCl4]; [NBu4][ReOCl4] or [ReOCl3(PPh3)2]) gave two types of neutral six-co-ordinated species [MO(L)Cl] and [{MO(L)}2O](M = Tc or Re). The monooxo monomeric complexes rearrange to the µ-oxo dimeric species via a charged labile intermediate in wet organic solvents or when solution are kept in contact with air. Reaction of H2L with [NBu4][TcVINCl4] follows a reduction–substitution route to give another neutral, but five-co-ordinated species, [TcN(L)] which contains the [TcVN]2+ nitride core. All complexes have been characterized by means of standard spectroscopic techniques. The influence of the metal on ligand 1H NMR chemical shifts is discussed. The technetium centre shifts all the ligand protons more downfield than does rhenium. This behaviour is in general agrement with the stronger acidity of the [TcO]3+ core with respect to [ReO]3+. The five-co-ordination of the nitrido complex [TcN(L)] is confirmed by its X-ray structure determination: monoclinic, space group P21/n, a= 14.654(7), b= 12.62(5), c= 7.819(4)A, β= 92.60(3)° and Z= 4. The co-ordination sphere around the Tc centre is nearly square pyramidal with an apical multiply bonded nitrogen atom [TcN 1.621(8)A].