EQUILIBRIUM STUDIES OF THE DISPLACEMENT OF ETA-1(S)-THIOPHENES (TH) FROM CP(CO)(PPH3)RU(ETA-1(S)-TH)+

The reactions of Cp(CO)(PPh3)RuCl (Cp = eta(5)-C5H5) with Ag+ and thiophenes (Th) produce the stable sulfur-bound (eta(1)(S) thiophene complexes Cp(CO)(PPh3)Ru(eta(1)(S)-Th)+ (Th = T, 2-MeT, 3-MeT, 2,5-Me2T, Me4T, BT, and DBT). Equilibrium constants (K') for the displacement of thiophene (T) by methyl-substituted thiophenes, benzo[b]thiophene (BT), and dibenzothiophene (DBT), Cp(CO)(PPh3)Ru(eta(1)(S)-T)+ + Th' reversible Cp(CO)(PPh3)Ru(eta(1)(S)-Th')+ + T, increase in the following order: T (1) < 2,5-Me2T (2.76) < 2-MeT (4.11) < 3-MeT (6.30) < BT (29.9) < Me4T (57.4) < DBT (74.1). In general, methyl groups on thiophene increase K', but alpha-methyl groups reduce the stabilities of complexes with 2-MeT, 2,5-Me2T, and Me4T ligands due to a steric interaction with the PPh3 group. The ligands tetrahydrothiophene (THT) and MeCN have K' values (> 7.1 x 10(6)) which are much higher than any of the thiophenes, while MeI (K' = 2.0) is a slightly better ligand than T. An X-ray structure determination of [Cp(CO)(PPh3)Ru(2-MeT)BF4 is also reported.