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

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Abstract
An electron-rich olefin [:[graphics omitted]R]2(LR 2; 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(LME)4(NO)]Cl (1), or (b)(R = CH2Ph) yields [RuCl(LCH3PH)2(NO)](3). Complex (1) is readily oxidised by Ag+ to give trans-[RuCl(LME)4(NO)]X2(X =[BF4] or [ClO4]) and reacts with CO to afford trans-[Ru(CO)Cl(LME)4]Cl. In contrast, complex (3) is oxidised by Mel or PhCH2Cl to give [RuMe(Cl)I(LCH3PH)2(NO)](8) or [RuCl3(LCH3PH)2(NO)](9) respectively, and with CO gives [Ru(CO)Cl(LCH3PH)2(NO)]. Complex (3) also undergoes oxidative addition with a heavy dihalogen to give [Ru(Cl)I2(LCH3PH)2(NO)] or [RuBr2Cl(LCH3PH)2(NO)] which differ in configuration from (8) or (9). The complex [OsCl3(NO)(PPh3)2] is only sluggishly reduced by LME 2, finally affording the exceptionally air- water-, or dissolution-sensitive [OS(LME)4(NO)]Cl(2). and LCH2Ph2 does not effect reduction but yields [OsCl2(LME 2Ph)3(NO)] Cl and trans-[OsCl (LCH2ph)4(NO)] Cl2. Complex (2) is easily oxidised: with Ag[BF4] or CH2Cl2 it forms trans-[OsCl(LME)4(NO)][BF4]2 or trans-[OsCl(LME)4(NO)]Cl2 respectively. Whereas only one PPh3 is lost from [Ru(NO)2(PPh3)2] and LEt 2 yielding [RuLEt(NO)2PPh3], both are displaced from [Ni(NO)(PPh3)2X] to give [Ni(LR)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–Ccarb, bonds]. Several trends are noted: as the metal charge increases (neutral < unipositive < dipositive)(i)v(CN2) increases, (ii)δ(13Ccarb.) becomes more shielded, (iii) the barrier to Ru-Ccarb. rotation increases, and (iv) complex stability increases, which are compatible with the pro-gressively increased amidinium nature of the carbene ligand.

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