Reactivity Differences of Pt⁰ Phosphine Complexes in C−C Bond Activation of Asymmetric Acetylenes

Carbon−carbon bond activation reactions of asymmetric acetylene derivatives of the type L2Pt(PhCCR) were studied with 1,2-bis(diisopropylphosphino)ethane (dippe), 1,2-bis(di-tert-butylphosphino)ethane (dtbpe), and 1-diisopropylphosphino-2-dimethylaminoethane (dippdmae) chelates. (dippe)Pt(η2-PhCCCH3) (1a), (dippe)Pt(η2-PhCCCF3) (1b), and (dippe)Pt(η2-PhCCC(CH3)3) (1c) showed no thermal reactivity at 160 °C, but 1b showed evidence for C−C cleavage to form (dippe)Pt(Ph)(CCCF3) upon irradiation with UV light (>300 nm). In comparison, dtbpe analogues of these metal complexes, (dtbpe)Pt(η2-PhCCCH3) (2a), (dtbpe)Pt(η2-PhCCCF3) (2b), and (dtbpe)Pt(η2-PhCCC(CH3)3) (2c), showed either C−H or C−C activation products upon photolysis. 2b produced (dtbpe)Pt(Ph)(CCCF3), but 2a or 2c showed the formation of (dtbpe)Pt(D)(C6D5) (2D) by activation of the C6D6 solvent. Compounds 2a−c showed no thermal reactivity at 160 °C. Two complexes with the hemilabile chelate dippdmae were synthesized and fully characterized, (dippdmae)Pt(η2-PhCCCF3) (3b) and (dippdmae)Pt(η2-PhCCC(CH3)3) (3c). C−C cleavage products of the type (L2)Pt(Ph)(CCCF3) were observed only upon photolysis of compounds 1b, 2b, and 3b.