78328-95-7Relevant academic research and scientific papers
Photochemical Substitution Reactions of Iron Tricarbonyl 1,4-Dimethyltetraazadiene and Related Complexes. Behavior Consistent with the Strong Coupling Limit
Johnson, Curtis E.,Trogler, William C.
, p. 6352 - 6358 (2007/10/02)
Photosubstitution of CO in Fe(CO)3 and Fe(CO)2 proceeds via a dissociative mechanism, in contrast to corresponding thermal reactions, which are of associative character.Syntheses of Fe(CO)3, Fe(CO)2L , Fe(CO)L2 2=dmpe> and Fe3 are reported.Quantum yields for CO substitution in the tricarbonyl complex increase exponentially as a function of excitation energy from 0.08 at 578 nm to 0.53 at 313 nm.The visible and near-ultraviolet absorptions in the electronic spectrum have been attributed to ?-->?* transitions of the FeN4 metallocycle.There is a little correlation between the detailed wavelength dependence of the quantum yields and either the absorption spectrum or the nature of the lowest excited electronic states.Since the quantum yield-wavelength dependence suggests that photodissociation competes with vibrational relaxation, a weak coupling description is inappropriate.Ramifications of the strong coupling limit are explored, and we propose that the amount by which the irradiation energy exceeds the treshold for Fe-CO bond cleavage accounts for the observed wavelength dependence.Carbon monoxide photosubstitution in Fe(CO)2 and Fe(CO)3 may also be explained in the strong coupling limit.Results for the latter complex further suggest a connection between the coordination environment about iron and the quantum efficiency of the photosubstitution process.
Kinetics and mechanism of ligand substitution in iron tricarbonyl 1,4-dimethyltetraazabutadiene
Chang, Chi-Yen,Johnson, Curtis E.,Richmond, Thomas G.,Chen, Yun-Ti,Trogler, William C.,Basolo, Fred
, p. 3167 - 3172 (2008/10/08)
Thermal carbon monoxide substitution in Fe(CO)3(N4Me2)2 proceeds readily to form monosubstituted products Fe(CO)2L(N4Me2) with L = PMe3, PMe2Ph, PBu3, PEt2Ph, P(OEt)3, P(OMe)3, PH2Ph, P(c-Hx)3, PPh3, AsMe3, AsEt3, AsMe2Ph, 4-CNpy, and Me3CNC. Bis- and trissubstituted products are also observed in the case of tert-butyl isocyanide. The substitution proceeds solely by a second-order process with a rate law that is first order in both Fe(CO)3(N4Me2) and entering ligand. In addition, the rate is strongly dependent on the nature of the ligand, particularly its size and basicity. Activation parameters further support the associative nature of the reaction in toluene: PMe3, ΔH? = 6.9 ± 0.2 kcal/mol, ΔS? = -31.4 ± 0.7 eu; PBu3, ΔH? = 7.3 ± 0.3 kcal/mol, ΔS? = -38.6 ± 1.1 eu; PEt2Ph, ΔH? = 7.3 ± 0.1 kcal/mol, ΔH? = -41.1 ± 0.2 eu; P(OMe)3, ΔH? = 11.0 ± 0.2 kcal/mol, ΔS? = -35.0 ± 0.6 eu; Me3CNC, ΔH? = 11.6 ± 0.5 kcal/mol, ΔS? = -34.9 ± 1.4 eu; AsMe3, ΔH? = 13.3 ± 0.3 kcal/mol, ΔS? = -34.3 ± 0.9 eu. Likewise in methanol: AsMe3, ΔH? = 9.8 ± 0.1 kcal/mol, ΔS? = -34.2 ± 0.2 eu; PPh3, ΔH? = 11.9 ± 0.8 kcal/mol, ΔS? = -38.8 ± 1.6 eu. The rate of reaction is increased in polar solvents and to a greater extent in alcohol solvents, which are capable of hydrogen bonding with the tetraazabutadiene nitrogens. In the presence of excess BF3, the rate of substitution is increased by a factor of 106. Factors which facilitate nucleophilic attack in Fe(CO)3(N4Me2) are discussed and contrasted with the dissociative mechanisms found for other iron carbonyls.
