THERMAL SOLID-STATE DIAG-LAT ISOMERIZATION STUDIES OF (ETA(5)-C5H4R)RE(CO)(L)BR-2 - DSC AND THERMOMICROSCOPY STUDIES

The thermal solid-state diag-lat isomerisation of (eta(5)-C5H4R)Re(CO) (L)Br-2 (R=Me, tBu and SiMe3; L=CO, CNC6H3Me2, P(OMe)(3) and P(OPh)(3) ) has been studied by DSC, and thermomicroscopy. In all instances, whe re isomerisation of (eta(5)-C5H4R)Re(CO)(L)Br-2 (1) was observed, the diagonal (trans) isomer converted to the lateral (cis) isomer in an ex othermic reaction. The effects of heating rate and crystal size on the isomerisation reaction involving (1) (R=Me, L=CO) has been studied. M icroscopic studies on 1, (R=Me, L=CO and P(OPh)(3); R=tBu, L=CNC6H3Me2 ) showed that the solid-state isomerisation reactions proceeded via a nuclear formation and growth mechanism.. Interestingly, no crystal cra cking was observed when (1) (R=Me, L=P(OPh)(3)) underwent a thermal so lid-state isomerisation reaction. (C) 1998 Elsevier Science B.V.