SYNTHESIS, X-RAY CRYSTAL-STRUCTURE AND PHOTOCHEMISTRY OF HYLCYCLOPENTADIENYL)(DICARBONYL)(DIHYDRIDO)RHENIUM IN CYCLOHEXANE AND LIQUID XENONSOLUTIONS AND IN LOW-TEMPERATURE MEDIA AT ABOUT 12 K

An improved synthesis of (eta(5)-C5Me5)Re(CO)(2)(H)(2) has been devise d (yield 88%) via (eta(5)-C5Me5)Re(CO)(3) and (eta(5)-C5Me5)Re(CO)(2)( Br)(2). An X-ray crystallographic determination has shown that the hyd ride ligands occupy trans positions, in confirmation of IR and NMR mea surements. The properties and reactions of trans-(eta(5)-C5Me5)Re(CO)2 (H)2 and related compounds (eta(5)-C5Me5)Re-(CO)(2)(X) (Y) (X = H, Me; Y = H, Me, Cl) are described. The solution photochemistry of trans-(e ta(5)-C5Me5)Re(CO)(2)(H)(2) in cyclohexane at 298 K and in liquid xeno n at 200 K, including studies under Dir indicate that the primary phot oproduct is the cis isomer and that trans to cis interconversion, whic h can be reversed thermally, is an intramolecular process. Photochemic al studies of (eta(5)-C5Me5)Re(CO)(2)(N-2) in Liquid Xe under H-2 and D-2 pressures at 200 K gave cis-(eta(5)-C5Me5)Re(CO)(2)(H)(2) and cis- (eta(5)-C5Me5)Re(CO)(2)(D)(2), respectively. Matrix isolation studies at about 12 K, including (CO)-C-13 labelling, confirmed that the photo isomerisation process is an intramolecular process since no ejected CO is observed and no (CO)-C-13 uptake occurred. Subsequent photolysis a ffords H-2 and CO ejection yielding (eta(5)-C5Me5)Re(CO)(2) and (eta(5 )-C5Me5)Re(CO)(H)(2), respectively. In N-2 and CO matrices the subsequ ent photolysis also yielded (eta(5)-C5Me5)Re(CO)(2)(N-2) and (eta(5)-C 5Me5)Re(CO)(3) but in CH4 matrices there was no evidence of C-H photoa ctivation to yield (eta(5)-C5Me5)Re(CO)(2)(CH3) (H) Reversal from cis to trans could not be observed for gas matrices but was observed at ne ar ambient temperatures for the cis isomer produced at about 12 K in N ujol mull media.