41267-B3
Electronic Structure, Molecular Structure, and Site of Bond Breaking in Facial- and Meridional-(Dihapto-[60]Fullerene)(Dihapto-Bidentate Ligand)Transition Metal(0) Complexes
Solvents such as benzene, chlorobenzene, cyclohexane, and toluene displace C60 from Ir(C60)(CO)(Cl)(PPh3)2 according to equation 1. Ir(CO)(PPh3)2(Cl)(C60) + solv ---> Ir(CO)(PPh3)2(Cl)(solv) (1) Two consecutive reactions are observed when the reaction is run a binary mixture of solvents (solvent1 and solvent2). The first reaction was identified as C60/solvents exchange producing non-equilibrium mixtures of Ir(CO)(PPh3)2(Cl)(solvent1) and Ir(CO)(PPh3)2(Cl)(solvent2) and the second reaction was identified as a solvent1/solvent2 exchange between Ir(CO)(PPh3)2(Cl)(solvent1) and Ir(CO)(PPh3)2(Cl)(solvent2) species. The experimental rate law for C60 dissociation from Ir(C60)(CO)(Cl)(PPh3)2 in binary mixtures of solvents is -d[Ir(C60)(CO)(Cl)(PPh3)2] /dt = kobsd [Ir(C60)(CO)(Cl)(PPh3)2] (2), Where kobsd = (ksolv1 [solv1]a + ksolv2 [solv2]b + C60 [C60]) (3). [C60]-independent kobsd values indicate that ksolv1 [solv1]a and ksolv2 [solv2]b >> kC60 [C60], and as consequence equation 3 becomes kobsd ≈ ksolv1 [solv1]a + ksolv2 [solv2]b (4). The corresponding experimental rate law for solvent exchange between Ir(solvent1)(CO)(Cl)(PPh3)2 and Ir(solvent2)(CO)(Cl)(PPh3)2 is -d[Ir(solv1)(CO)(Cl)(PPh3)2]/dt = k’obsd [Ir(solv1)(CO)(Cl)(PPh3)2] (5), where k’obsd = k’sov1 [solv1]c + k’solv2 [solv2]d (6). Linear plots of kobsd/[solv2] vs. [solv1]/[solv2] and linear plots of k’obsd/[solv2] vs. [solv1]/[solv2]as predicted by equations 7 and 8, respectively, indicate that the reactions are first order with respect to the solvents concentration (i.e. that a = b = c = d =1). kobsd/[solv2] = ksolv1 [solv1]/ [solv2] + ksolv2 (7) k’obsd/[solv2] = k’sov1 [solv1]/ [solv2] + k’solv2 (8) The rate constant values (ksolv1, ksolv2, and k ’sov1, and k’solv2) were estimated from the intercepts and slope values of these plots. Values of ksolvent for C60/solvent exchange on Ir(CO)(PPh3)2(Cl)(C60) at 22.0 ◦C are solvent-dependent (ktoluene > kchlorobenzene > kbenzene >> kcyclohexane). The corresponding values of k’solvent for the solvent/solvent exchange on Ir(CO)(PPh3)2(Cl)(solvent) are also solvent-dependent exhibiting the same pattern as kobsd values (k’toluene > k’chlorobenzene > k’benzene > k’cyclohexane). The trends observed for ksolvent and k’solvent values indicate the existence of some selectivity or discriminatory ability of Ir(CO)(PPh3)2(Cl)(C60) and Ir(CO)(PPh3)2(Cl)(solvent) for attack by incoming solvents. The rate constant values for solvent exchange on Ir(CO)(PPh3)2(Cl)(solvent) are nearly independent on the nature of the leaving solvent, suggesting a small Ir-solvent bond enthalpy. Moreover, the observed relative ksolvent/k’solvent ratios (i.e. kbenzene/k’benzene ≈ 10; kcyclohexane/k’cyclohexane ≈ 4; kchlorobenzene/k’cyclohexane ≈ 6; ktoluene/k’toluene ≈ 8) are in line with the expectation that Ir-C60 bond is stronger than Ir-solvent bonds. In conclusion the C60/solvent exchange on Ir(CO)(PPh3)2(Cl)(C60) and the solvent/solvent exchange on Ir(CO)(PPh3)2(Cl)(solvent) take place via a solvent-assisted C60 dissociation and via an associative solvent exchange, respectively. A small solvent-Ir bond enthalpy is deduced from the observation that k’benzene value at 22 ◦C is independent of the coordinated solvent in Ir(CO)(PPh3)2(Cl)(solvent) and a relatively large C60-Ir bond enthalpy is deduced from the observation that ksolvent >> k’solvent.
