A comparison of Cp*- and Tp-ruthenium carbyne complexes prepared via site selective electrophilic addition to neutral ruthenium vinylidenes

The synthesis and characterization of a series of ruthenium carbyne complexes supported by either pentamethylcyclopentadienyl (Cp*) or hydridotris(pyrazolyl)borate (Tp) ligands are discussed. Reacting the neutral ruthenium(II) vinylidenes [Cp*Cl(PPh3)Ru(CCHR)] (1) or [TpCl(PPh3)Ru(CCHR)] (2) with excess HBF4 · Et2O yields the ruthenium(IV) carbynes [Cp*Cl(PPh3)Ru(CCH2R)][BF4] (3: R = tBu, 3a; R = nBu, 3b; R = Ph, 3c), and [TpCl(PPh3)Ru(CCH2R)][BF4] (4: R = tBu, 4a; R = nBu, 4b; R = Ph, 4c). Complexes 3a and 3b are isolable solids, whereas 3c and 4a–c must be prepared and examined in solution at low temperatures using variable temperature NMR spectroscopy. In contrast, reactions of 1 or 2 (R = Ph) with MeOTf selectively yield the chloride abstracted products [Cp*(OTf)(PPh3)Ru(CCHPh)] (5) or [Tp(OTf)(PPh3)Ru(CCHPh)] (6), respectively, along with one equivalent of MeCl. When R = tBu or nBu, the reactions are much less selective. The relative stabilities of the complexes reported are compared and discussed.