THIOPHENE COMPLEXES OF THE PLATINUM-GROUP METALS .2. PREPARATION AND CHARACTERIZATION OF CATIONIC THIOPHENE COMPLEXES OF [(CYCLOOCTADIENE)IR][BF4] AND [(NORBORNADIENE)RH][BF4] AND X-RAY CRYSTAL-STRUCTURE OF [(ETA(5)-2,5-DIMETHYLTHIOPHENE)(CYCLOOCTADIENE)RH][BF4]

Cleavage of chloro-bridged rhodium and iridium dimers, [(NBD)RhCl]2 and [(COD)IrCl]2, in methanol leads to the formation of cationic (COD)2Ir+ and (NBD)Rh+ monomers, respectively. Reaction of these cationic species with 2-methylthiophene and 2,5-dimethylthiophene results in the formation of complexes in which the thiophene coordinates in an eta5 manner. With benzothiophene and dibenzothiophene, complexes bearing a 1:1 metal:ligand stoichiometry are obtained with the ligand coordinating in an eta6 fashion using the six carbon atoms of the arene ring. Good yields of these Rh and Ir products are obtained with the exception of those of reactions involving thiophene, where only small amounts of product were obtained. A crystal structure determination of the cationic (cyclooctadiene)rhodium 2,5-dimethylthiophene complex shows that the thiophene ligand binds to the transition metal center in an eta5 manner. The S atom is displaced 0.1888 angstrom from the least-squares plane defined by the four carbon ring atoms and displays C-S bond lengths similar to those found in free thiophene. The structure crystallizes in the monoclinic space group P2(1)/n with lattice parameters a = 8.731(7) angstrom, b = 21.57(2) angstrom, c = 8.833(7) angstrom, beta = 104.43(6)-degrees, and V = 1611(2) angstrom3. Convergence to conventional R values of R = 0.0418 and R(w) = 0.0652 was obtained for 190 variable parameters and 2113 reflections with F > 0sigma(F).