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][Tc^VINCl₄] follows a reduction–substitution route to give another neutral, but five-co-ordinated species, [TcN(L)] which contains the [Tc^VN]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)Å, 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)Å].