78328-97-9Relevant academic research and scientific papers
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 (1981)
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.
