Arylimido complexes of ruthenium(IV) porphyrins

Treatment of [Ru(tbpp)O2] [H2tbpp = 5,10,15,20-tetrakis(p-tert-butylphenyl)porphyrin] with SiMe3Cl gave [Ru(tbpp)Cl2] in good yield. Reaction of [Ru(tbpp)Cl2] with para-substituted anilines NRH2(R = p-XC6H4where X = Me, H, Cl or I) afforded the first arylimidoruthenium(IV) complexes [Ru(tbpp)(NR)]. These are paramagnetic with μeffca. 2.8 μBand display1H NMR spectra that are typical for paramagnetic ruthenium(IV) porphyrins. The cyclic voltammograms of [Ru(tbpp)(NR)] exhibit reversible RuV-RuIVand RuIV-RuIIIcouples. Treatment of [Ru(tbpp)(NR)] with AgIor CeIVafforded the imidoruthenium(V) complex [Ru(tbpp)(NR)]+. The complexes [Ru(tbpp)(NR)] underwent imido-group transfer reactions with tertiary phosphines to give [Ru(tbpp)-(PR′3)2] and RN=PR3′. The reduction of [Ru(tbpp)(NR)] by PMe2Ph shows saturation kinetics, in which the rate is first order in [RuIV]. The mechanism proposed for the Ru-mediated imido transfer involves reversible binding of phosphine to RuIVand rate-limiting intramolecular imido-group transfer. The first-order rate constant (k1) and phosphine binding constant (K) and for the reduction of [Ru(tbpp)(NC6H4Me-p)] by PMe2Ph at 25.0°C in toluene solution were determined to be (6.86 ± 0.19) × 10-4s-1and (23.6 ± 6.5) × 103mol dm-3, respectively. The activation enthalpy (ΔH‡) and entropy (ΔS‡) for the above reaction are 125 ± 1 kJ mol-1and 113 ± 21 J K-1mol-1, respectively. For the reduction of para-X-substituted arylimido complexes [Ru(tbpp)(NC6H4X-p)] by tertiary PMe2Ph the rate decreases in the order X = I > H ≈ Cl > Me. The imido transfer from [RuV(tbpp)-(NC6H4Me-p)]+to PMe2Ph is about 60 times faster than that from [RuIV(tbpp)(NC6H4Me-p)].