부산대학교 도서관

Endothermichalogen elimination reactions, in which molecular halogen photoproductsare generated in the absence of chemical traps, are rare. Inspiredby the proclivity of mononuclear Ni(III) complexes to participatein challenging bond-forming reactions in organometallic chemistry,we targeted Ni(III) trihalide complexes as platforms to explore halogenphotoelimination. A suite of Ni(III) trihalide complexes supportedby bidentate phosphine ligands has been synthesized and characterized.Multinuclear NMR, EPR, and electronic absorption spectroscopies, aswell as single-crystal X-ray diffraction, have been utilized to characterizethis suite of complexes as distorted square pyramidal, S= 1/2 mononuclear Ni(III) complexes. All complexes participate inclean halogen photoelimination in solution and in the solid state.Evolved halogen has been characterized by mass spectrometry and quantifiedchemically. Energy storage via halogen elimination was establishedby solution-phase calorimetry measurements; in all cases, halogenelimination is substantially endothermic. Time-resolved photochemicalexperiments have revealed a relatively long-lived photointermediate,which we assign to be a Ni(II) complex in which the photoextrudedchlorine radical interacts with a ligand-based aryl group. Computationalstudies suggest that the observed intermediate arises from a dissociativeLMCT excited state. The participation of secondary coordination sphereinteractions to suppress back-reactions is an attractive design elementin the development of energy-storing halogen photoelimination involvingfirst-row transition metal complexes. [ABSTRACT FROM AUTHOR]