Reactions of a tungsten alkylidyne complex with mono-dentate phosphines: Thermodynamic and theoretical studies

Addition of mono-dentate phosphines PMe3 and PMe2Ph to the W(VI) alkyl alkylidyne complex W(CH2SiMe3)3(CSiMe3) (1) is reversible, each reaching equilibrium. Thermodynamic studies of the equilibria have been conducted, giving ΔH° = −10.0(1.1) kcal/mol and ΔS° = −23(4) eu for the addition of PMe3 and ΔH°′ = −3.0 (0.7) kcal mol−1 and ΔS°′ = −6(3) eu for the addition of PMe2Ph, indicating that the addition is exothermic. The experimental measurement allows a benchmarking study to select a proper DFT method to describe the current system. Of the DFT methods tested, M06 has demonstrated superior performance in calculating binding energy of a bimolecular reaction. The calculated reaction pathways show that W(CH2SiMe3)3(CSiMe3) (1) reacts with PR3 to form W(CH2SiMe3)3(CSiMe3)(PR3) (PR3 = PMe3, 3a; PMe2Ph, 3b), and the adduct then undergoes α-H migration to form W(CH2SiMe3)2(CHSiMe3)2(PR3) (4a, 4b). 4a and 4b are found to be thermodynamically and kinetically stable intermediates. The calculations also suggest a pathway in the formation of the alkyl alkylidene alkylidyne complex W(CH2SiMe3)-(CHSiMe3)(CSiMe3)(PR3)2 (5a).

Thermodynamic studies of the addition of mono-dentate phosphines PMe3 and PMe2Ph to the W(VI) alkyl alkylidyne complex W(CH2SiMe3)3(CSiMe3) (1) have been conducted. DFT calculations reveal the details of the transformations involved in the equilibria.Figure optionsDownload as PowerPoint slide