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Photochemical reaction of Ru(PP3)H2 (PP3 = P(CH2CH2PPh2)3) in THF under a rigorously inert atmosphere yields the cyclometalated complex Ru[(Ph2PCH2CH2)2P(CH2CH2PPhC6H4)]H. The latter is converted back to Ru(PP3)H2 under H2 and reacts even with traces of N2 to yield Ru(PP3)(N2). The dinitrogen complex may be synthesized directly by a number of methods. NMR spectroscopy shows that photolysis of Ru(PP3)H2 under C2H4 and CO yields Ru(PP3)(C2H4) and Ru(PP3)(CO), respectively. Photolysis of Ru(PP3)H2 with HSiEt3 in THF yields Ru(PP3)(SiEt3)H, while photolysis in mixtures of THF and benzene at low temperature yields Ru(PP3)(Ph)H. The latter is also generated by reduction of Ru(PP3)Cl2 in the presence of benzene. Os(PP3)(Ph)H is formed either by photolysis of Os(PP3)H2 or by reduction of Os(PP3)Cl2 in the presence of benzene. Irradiation of Os(PP3)H2 in THF or THF/hexane mixtures initially yields the THF C−H activation product, Os(PP3)(2-C4H7O)H. This complex is also generated by reduction of Os(PP3)Cl2 with sodium naphthalenide under N2 in the presence of THF. Os(PP3)(2-C4H7O)H is converted to the cyclometalated complex, Os[(Ph2PCH2CH2)2P(CH2CH2PPhC6H4)]H, on irradiation in THF and to Os(PP3)(Ph)H on irradiation in benzene. Reaction of Os(PP3)H2 with CH3OTf (Tf = triflate) yields Os(PP3)(OTf)H, which is converted to the labile Os(PP3)(CH3)H on reaction with methyllithium. Laser flash photolysis of Ru(PP3)H2 in cyclohexane (laser wavelength 308 nm) yields transient Ru(PP3) with an absorption maximum at 395 nm. The transient reacts with H2, C6H6, HSiEt3, CO, N2, C2H4, and THF with little discrimination; the second-order rate constants for these reactions lie in the range 5 × 105−2 × 106 dm3 mol-1 s-1 at 295 K. Kinetic isotope effects have been determined for the reaction with benzene and THF, as 1.5 (0.2) and 1.1 (0.2), respectively. Activation parameters for reaction of Ru(PP3) are as follows:  with HSiEt3 ΔH ⧧ = 35 (2) kJ mol-1, ΔS ⧧ = −18 (6) J K-1 mol-1; with C6H6 ΔH ⧧ = 39 (4) kJ mol-1, ΔS ⧧ ≈ 0 J K-1 mol-1. The reaction with THF yields a short-lived adduct, probably bound through oxygen, which is rapidly converted to the cyclometalated product. Laser flash photolysis of Os(PP3)H2 generates transient Os(PP3) (λmax = 390 nm). The transient kinetics of Os(PP3) are substantially different from its ruthenium analogue. It reacts with alkanes and shows different behavior toward THF but is unaffected by addition of H2. Rate constants in the range 6 × 104−6 × 105 dm3 mol-1 s-1 (295 K) are presented for reaction with C6H6, THF, HSiEt3, CO, C2H4, N2, and several alkanes. Kinetic isotope effects have been determined for the reactions with methylcyclohexane and benzene as 5.6 (1.5) and 0.6 (0.1), respectively. The rate constants for reaction with alkanes rise in the order, methylcyclohexane < pentane < heptane < methane. The rate constants for reaction with methane and benzene are insignificantly different. Following reaction of Os(PP3) with THF to form Os(PP3)(THF), C−H insertion occurs with a first-order rate constant of 4.2 (...

The complexes (C5Me5)Rh(PMe3)(3,5-C6H3R2)H for R = C(CH3)3, CH(CH3)2, Si(CH3)3, CH3, and CF3 (lc-g) have been prepared both by irradiation of (C5Me5)Rh(PMe3)(C2H4) in neat arene and by thermolysis of (C5Me5)Rh(PMe3)(Ph)H (la) in neat arene. Quenching the hydride species with CHBr3 allowed isolation of the corresponding bromide complexes (CsMe5)Rh(PMe3)(3,5-C6H3R2)Br (2c-g). Rates of reductive elimination of arene for the series of disubstituted aryl hydride complexes were measured at various temperatures and activation parameters AH* and AS* obtained and compared with those of (C5Mes)-Rh(PMe3)(Ph)H (la) and (C5Me5)Rh(PMe3)(tolyl)H (lb). AH* values range from +35 to +18 kcal/mol, and AS* values range from +16.4 to -19 cal/mol K. Laser flash photolysis experiments using (C5Me5)Rh(PMe3)(C2H4) in neat toluene at various temperatures allowed the determination of activation parameters AH* and AS* for intramolecular C-H bond oxidative addition of the //2-arene complex 3b. Equilibrium measurements allowed determination of AG°values for several of the disubstituted aryl hydride complexes versus the parent phenyl hydride complex. A kinetic isotope effect of &h/&d = 1.0 ± 0.1 was measured for the reaction of (CsMe5)Rh(PMe3)(C2H4) with a 1:1 mixture of 5-deuterio-l,3-di-£ertbutylbenzene and l,3-di-/er£-butylbenzene. The equilibrium isotope effect for the same reaction Keq = 2.27(1) favors the aryl hydride and free deuterated arene.

Photolysis of [(PP3)RuH2] (PP3 = P(CH2CH2PPh2)3) (1) in THF at 23 °C under an inert atmosphere (N2, Ar, or He) in the presence of thiophene (T) or ethyl 2-thiophenecarboxylate (2-CO2EtT) gives the (hydride)2-thienyl complexes [(PP3)Ru(H)(2-Tyl)] (5) (Tyl = C4H3S) and [(PP3)Ru(H)(2-CO2EtTyl)] (7) (CO2EtTyl = C4H2(CO2Et)S), respectively. The C−H insertion products 5 and 7 are also selectively obtained by the thermal reaction of the Ru(0) dinitrogen complex [(PP3)Ru(N2)] (4) in THF with T or 2-CO2EtT. Complexes 5 and 7 are both photochemically and thermally stable. Under comparable conditions, the photolysis of the Os derivative [(PP3)OsH2] in THF in the presence of T exclusively yields the C−H insertion product [(PP3)Os(H)(2-Tyl)]. Photolysis of 1 at 23 °C under nitrogen and in the presence of 2,5-dimethylthiophene (2,5-Me2 T) gives the complex [(PP3)Ru(η1-S-2,5-Me2 T)] (8) containing an S-bound thiophene molecule. Complex 8 is also obtained by reaction of isolated 4 with 2,5-Me2 T. The Ru(0) transient, [(PP3)Ru], generated by laser flash photolysis in either cyclohexane or THF solution, has been detected and characterized by UV−vis spectroscopy. [(PP3)Ru] reacts with T (k 2 = (1.4 ± 0.2) × 106 dm3 mol-1 s-1), yielding an adduct [(PP3)Ru(T)]. In cyclohexane, [(PP3)Ru(T)] decays to the C−H insertion product 5 with first-order kinetics (k = 20 ± 1 s-1 at 296 K). In THF, the 16 e- Ru(0) transient forms with THF a short-lived adduct, probably bound through oxygen, [(PP3)Ru(THF)], which reacts with T to give [(PP3)Ru(T)] (k obs = 680 s-1, [T] = 0.3 mol dm-3 under Ar). This T adduct decays to [(PP3)Ru(2-Tyl)H] with first-order kinetics (k = 18 ± 1 s-1). Similar measurements with 2,5-Me2 T yield a rate constant for [(PP3)Ru] + 2,5-Me2 T in cyclohexane of (1.0 ± 0.3) × 106 dm3 mol-1 s-1. The resulting [(PP3)Ru(2,5-Me2 T)] is kinetically stable. Flash photolysis of [(PP3)OsH2] in cyclohexane with added T yields rate constants for [(PP3)Os] + T and for isomerization of [(PP3)Os(T)] of (3.7 ± 0.1) × 105 dm3 mol-1 s-1 and 8 ± 1 s-1, respectively.