PHOTOCHEMISTRY OF BIS-(CHLORO(DICARBONYL)RHODIUM) IN LOW-TEMPERATURE FROZEN GAS MATRICES AT 12 K AND IN NUJOL MULLS AT 77 K - INFRARED AND ELECTRONIC SPECTROSCOPIC EVIDENCE FOR RETENTION OF THE BIS-((CHLORO)RHODIUM) BRIDGING UNIT BUT PHOTOEJECTION OF TERMINAL CARBONYL LIGANDS

Infrared and electronic spectroscopic evidence is presented in relatio n to the photochemical reactions of {(Cl)(CO)(2)Rh}(2), whose bent str ucture has been confirmed by Fourier transform Raman spectroscopy. Pho tolysis in Ar, CH4 and N-2 gas matrices at ca. 12 K and in Nujol mulls at ca. 77 K leads to facile and reversible ejection of the terminal C O ligands but retention of the {(Cl)Rh}(2) bridging unit. The primary species formed were Rh-2(Cl)(2)(CO)(3) in Ar, CH4 and Nujol media and Rh-2(Cl)(2)(CO)(3)(N-2) in N-2 matrices. Further reversible CO loss af forded {Rh(Cl)(CO)}(2) and {Rh(Cl)(CO)(N-2)}(2), respectively. In CO m atrices the modest photoreaction was interpreted in terms of CO additi on to give an 18 electron dimeric species {Rh(Cl)(CO)(3)}(2) rather th an bridge cleavage to give the 16 electron species Rh(Cl)(CO)(3). In v iew of the facility of the CO ejection/recombination processes it is s uggested that such reaction pathways could be important in the substit ution reactions of {Rh(Cl)(CO)(2)}(2) and could aid the interpretation of the kinetic data. (C) 1998 Elsevier Science S.A.