THE SYNTHESIS AND SOLID-STATE STUDY OF THE DISUBSTITUTED CYCLOPENTADIENYL RHENIUM COMPLEXES, (ETA(5)-C5H3R1R2) RE(CO)(2)BR-2 (R-1, R-2 = ME, SIME3, TBU)

Deprotonation of (eta(5)-C5H4R1)Re(CC)(3) (R-1 = Me, tBu) with two equ ivalents of n-butyllithium in tetrahydrofuran (THF) and subsequent tre atment of the lithium derivatives with trimethylchlorosilane gave the disubstituted cyclopentadienyl tricarbonyl rhenium complexes (eta(5)-C 5H3R1R2)Re(CO)(3) (1) (R-2 = SiMe3) in 60 to 70% yield. Interestingly, [eta(5)-1,3-C5H3(SiMe3)(2)]Re(CO)(3), was formed (14% yield) in one s tep by the reaction of (eta(5)-C5H5)Re(CO)(3) with three equivalents o f n-butyllithium followed by addition of trimethylchlorosilane. For R- 1 = tBu, SiMe3; R-2 = SiMe3, only the 1,3-disubstituted product (1) wa s produced, while for R-1 = Me; R-2 = SiMe3, both the 1,2- and 1,3-dis ubstituted compounds were obtained. Bromination of (1) in CHCl3 yielde d diag- and lat-(eta(5)-C5H3R1R2)Re(CO)(2)Br-2 (2) (R-1 = Me, tBu, SiM e3; R-2 = SiMe3). Reaction of both the diag and laf isomers of (2) (R- 1 = R-2 = SiMe3) with P(OPh)(3) in the presence of NMe3O gave only dia g-(eta(5)-C5H3R1R2)Re(CO)P(OPh)(3)Br-2. The detailed investigation of the solution and solid-state isomerisation reaction of (2) (R-1, R-2= SiMe3) revealed that (i) in solution the lat isomer converted to the d iag isomer, (ii) the crystalline material did not isomerise and (iii) the photolysis of the diag isomer adsorbed on SiO2 yielded the lat iso mer. Thus in the solid state, molecule-molecule interactions control t he mobility of the ligands bound to the metal centre.