Synthesis, X-ray crystal structure and photochemistry of ( η5-pentamethylcyclopentadienyl)(dicarbonyl)(dihydrido) rhenium in cyclohexane and liquid xenon solutions and in low temperature media at about 12 K

Abstract

An improved synthesis of ( η 5-C 5Me 5)Re(CO) 2(H) 2 has been devised (yield 88%) via ( η 5-C 5Me 5)Re CO) 3 and ( η 5-C 5Me 5)-Re(CO) 2(Br) 2. An X-ray crystallographic determination has shown that the hydrido ligands occupy trans positions, in confirmation of IR and NMR measurements. The properties and reactions of trans-( η 5-C 5Me 5)Re(CO) 2(H) 2 and related compounds ( η 5-C 5Me 5)Re-(CO) 2(X)(Y) (X  H, Me; Y  H, Me, Cl) are described. The solution photoctemistry of trans-( η 5-C 5Me 5)Re CO 2(H) 2) in cyclohexane at 298 K and in liquid xenon at 200 K, including studies under D 2, indicate that the primary photoproduct is the cis isomer and that trans to cis interconversion, which can be reversed thermally, is an intramolecular process. Photochemical studies of ( η 5-C 5Me 5)Re-(CO) 2N 2) in liquid Xe under H 2 and D 2 pressures at 200 K gave cis-( η 5-C 5Me 5)Re(CO) 2 and cis-( η 5-C 5Me 5)Re(CO) 2(D) 2, respectively. Matrix isolation studies at about 12 K, including 13CO labelling, confirmed that the photoisomerisation process is an intramolecular process since no ejected CO is observed and no 13CO uptake occurred. subsequent photolysis affords H2 and CO ejection yielding ( η 5-C 5Me 5)Re(CO) 2 and ( η 5-C 5Me 5)Re(CO)(H) 2, respectively. In N 2 and CO matrices the subsequent photolysis also yielded ( η 5-C 5Me 5)Re(CO) 2( N 2) and ( η 5-C 5Me 5)Re(CO) 3 but in CH 4 matrices there was no evidence of CH photoactivation to yield ( η 5-C 5Me 5)Re(CO) 2(CH 3)(H). Reversals from cis to trans could not be observed for gas matrices but was observed at near ambient temperatures for the cis isomer produced at about 12 K in Nujol mull media.