Carbene complexes. Part 15. The synthesis and properties of electron-rich olefin-derived mono-and oligo-carbenenitrosyl-ruthenium, -osmium, and -nickel complexes

Abstract

An electron-rich olefin [:[graphics omitted]R]₂(L^R₂; R = Me, Et, or CH₂Ph) readily reduces [RuCl₃(NO)(PPh₃)₂] to [RuCl(NO)(PPh₃)₂] which then (a)(R = Me) reacts with an excess of olefin to give the dioxygen- and water-sensitive [Ru(L^ME)₄(NO)]Cl (1), or (b)(R = CH₂Ph) yields [RuCl(L^CH3PH)₂(NO)](3). Complex (1) is readily oxidised by Ag⁺ to give trans-[RuCl(L^ME)₄(NO)]X₂(X =[BF₄] or [ClO₄]) and reacts with CO to afford trans-[Ru(CO)Cl(L^ME)₄]Cl. In contrast, complex (3) is oxidised by Mel or PhCH₂Cl to give [RuMe(Cl)I(L^CH3PH)₂(NO)](8) or [RuCl₃(L^CH3PH)₂(NO)](9) respectively, and with CO gives [Ru(CO)Cl(L^CH3PH)₂(NO)]. Complex (3) also undergoes oxidative addition with a heavy dihalogen to give [Ru(Cl)I₂(L^CH3PH)₂(NO)] or [RuBr₂Cl(L^CH3PH)₂(NO)] which differ in configuration from (8) or (9). The complex [OsCl₃(NO)(PPh₃)₂] is only sluggishly reduced by L^ME₂, finally affording the exceptionally air- water-, or dissolution-sensitive [OS(L^ME)₄(NO)]Cl(2). and L^CH₂Ph₂ does not effect reduction but yields [OsCl₂(L^ME₂Ph)₃(NO)] Cl and trans-[OsCl (L^CH₂ph)₄(NO)] Cl₂. Complex (2) is easily oxidised: with Ag[BF₄] or CH₂Cl₂ it forms trans-[OsCl(L^ME)₄(NO)][BF₄]₂ or trans-[OsCl(L^ME)₄(NO)]Cl₂ respectively. Whereas only one PPh₃ is lost from [Ru(NO)₂(PPh₃)₂] and L^Et₂ yielding [RuL^Et(NO)₂PPh₃], both are displaced from [Ni(NO)(PPh₃)₂X] to give [Ni(L^R)₂(NO)X](X = Cl, R = Et; X = Br, R = CH₂Ph). Spectro-scopic data (¹H and ¹³C n m.r. and i.r.) of the new complexes are reported. Many of the complexes exhibit com-plicated ¹H n.m.r. spectra because of the inequivalence of N–CH₂Ph protons or N–CH₃ groups, caused by restricted rotation [ΔG‡(rotation) >25 kcal mol^–1 about M–C^carb, bonds]. Several trends are noted: as the metal charge increases (neutral < unipositive < dipositive)(i)v(CN₂) increases, (ii)δ(¹³C_carb.) becomes more shielded, (iii) the barrier to Ru-C_carb. rotation increases, and (iv) complex stability increases, which are compatible with the pro-gressively increased amidinium nature of the carbene ligand.