Generation, Thermodynamics, and Chemistry of the Diphenylcarbene Anion Radical (Ph2C.-)

Article abstract of DOI:10.1021/ja00258a015

Dissociative electron attachment with Ph2C=N produced Ph2C^.- (m/z 166).The reactions of Ph2C^.- with potential proton donors of known gas-phase acidity were used to bracket PA(Ph2C^.-) = 380 +/- 2 kcal mol^-1 from which ΔH_f⁰(Ph2C^.-) = 81.8 +/- 2 kcal mol^-1 was calculated.The reactions of Ph2C^.- with CH3OH and C2H5OH proceeded with major and minor amounts, respectively, of a H2^.+-transfer channel, forming Ph2CH2, RCHO, and an electron.The kinetic nucleophilicity of Ph2C^.- in S_N2 displacement reactions with CH3X and C2H5X molecules was shown to be medium, which requires a significant intrinsic barrier in these reaction.The reactions of Ph2C^.- with various aldehydes, ketones, and esters were fast and established two principal product-forming channels: (1) H⁺ transfer if the neutral reactant contains activated C-H bonds and (2) carbonyl addition followed by radical β-fragmentation of one of the groups originally attached to the carbonyl carbon.The order for the ease of radical β-fragmentation in the tetrahedral intermediates was RO > alkyl >> H, and CO2CH3 > CH3.Since the reactions of Ph2C^.- with the simple esters HCO2CH3 and CH3CO2CH3 were fast, it should now be possible to examine the reactions of carbonyl-containing organic molecules, which are expected to react slower than these esters and obtain their relative reactivities.