Arylimido complexes of ruthenium(IV) porphyrins

Treatment of [Ru(tbpp)O-2] [H(2)tbpp = 5,10,15,20-tetrakis(p-tert-butylphenyl)porphyrin] with SiMe(3)Cl gave [Ru(tbpp)Cl-2] in good yield. Reaction of [Ru(tbpp)Cl-2] with para-substituted anilines NRH(2) (R = p-XC(6)H(4) where X = Me, H, Cl or I) afforded the first arylimidoruthenium(IV) complexes [Ru(tbpp)(NR)]. These are paramagnetic with mu(eff) ca. 2.8 mu(B) and display H-1 NMR spectra that are typical for paramagnetic ruthenium(IV) porphyrins. The cyclic voltammograms of [Ru(tbpp)(NR)] exhibit reversible Ru-V-Ru-IV and Ru-IV-R(III) couples. Treatment of [Ru(tbpp)(NR)] with Ag-I or Ce-IV afforded 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=PR(3)'. The reduction of [Ru(tbpp)(NR)] by PMe(2)Ph shows saturation kinetics, in which the rate is first order in [Ru-IV]. The mechanism proposed for the Ru-mediated imido transfer involves reversible binding of phosphine to Ru-IV and rate-limiting intramolecular imido-group transfer. The first-order rate constant (k(1)) and phosphine binding constant (K) and for the reduction of [Ru(tbpp)(NC(6)H(4)Me-p)] by PMe(2)Ph at 25.0 degrees C in toluene solution were determined to be (6.86 +/- 0.19) x 10(-4) s(-1) and (23.6 +/- 6.5) x 10(3) mol dm(-3), respectively. The activation enthalpy (Delta H-double dagger) and entropy (Delta S-double dagger) for the above reaction are 125 +/- 1 kJ mol(-1) and 113 +/- 21 J K-1 mol(-1), respectively. For the reduction of para-X-substituted arylimido complexes [Ru(tbpp)(NC(6)H(4)X-p)] by tertiary PMe(2)Ph the rate decreases in the order X = I > H approximate to Cl > Me. The imido transfer from [Ru-V(tbpp)(NC(6)H(4)Me-p)](+) to PMe(2)Ph is about 60 times faster than that from [Ru-IV(tbpp)(NC(6)H(4)Me-p)].