Radical Cations of Bis(diphenylphosphino) Derivatives (Ph2P-R-PPh2): The Formation of Localized, Cyclic, and Dimeric Configurations. An ESR and Quantum Chemical Study

Article abstract of DOI:10.1021/j100176a042

A matrix ESR study on radiogenic radical cations of Ph2P-R-PPh2 derivatives with various linkers (R) is presented.The experiments show that in a frozen dichloromethane solution the radical cations can adopt localized (Ph2PR*+), cyclic <*>, and dimeric (Ph2RP*-PRPh2+) configurations, depending on the nature of the linker.The cyclic and dimeric products are formed in the reaction of a localized cation with a second free-electron pair, resulting in an intra- or intermolecular three-electron P-P ?* bond, respectively.The formation of the cyclic structure, with a strongly bent P-P ?* bond, requires a specific proximate position of the two phosphine moieties in the precursor molecule.The mutual orientation of the two free-electron pairs of the precursors is assessed by NMR via the ⁿJ_PP spin-spin coupling constant.Ab initio UHF quantum chemical calculations at the 3-21G*/SCF level support the assignments.