PHASE-DEPENDENT DIAGONAL AND LATERAL ISOMERISM OF THE RHENIUM COMPLEXES (ETA(5)-C(5)H(4)ME)RE(CO)(2)BR-2

The new diagonal and lateral monosubstituted cyclopentadienyl dibromod icarbonylrhenium complexes (eta(5)-C(5)H(4)R)Re(CO)(2)Br-2 (R = Me, Et , tBu, Si(CH3)(3), C6H11) have been synthesized and fully characterize d by elemental analysis and IR and NMR spectroscopy. All the lateral c omplexes are completely converted to the corresponding diagonal isomer s upon refluxing in toluene. Interestingly, diag-(eta(5)-C(5)H(4)Me)Re (CO)(2)Br-2 isomerizes to the corresponding lateral isomer in almost q uantitative yield upon heating at 106-110 degrees C in the solid state . A DSC study of diag-(eta(5)-C(5)H(4)Me)Re(CO)(2)Br-2 shows that the solid state diag to lat isomerization proceeds exothermically. This is the first example of an organometallic complex that undergoes a phase -dependent reversible isomerization reaction under only thermal condit ions.