SYNTHESIS AND EVALUATION OF THE BONDING PROPERTIES OF 2,5-BIS(2-(DIPHENYLPHOSPHINO)ETHYL)THIOPHENE - A NEW POTENTIALLY TRIDENTATE LIGAND

The new ligand 2,5-bis(2-(diphenylphosphino)ethyl)thiophene(1) has bee n synthesized in four steps from thiophene, and its bonding capabiliti es have been evaluated. Compound 1 displaces the cycloheptatriene liga nd in Mo(CO)(3)-(cycloheptatriene) to give [fac-Mo(CO)(3)(1)] (2), but the complex slowly converts in solution to [mer-Mo(CO)(3)(1)] (3). Th e structure of 2 has been established by an X-ray structure determinat ion. Crystallographic data for 2: monoclinic C-2h(5)-P2(1)/n,a = 10.29 4(1) Angstrom, b = 16.470(1) Angstrom, c = 18.878(2) Angstrom, beta = 93.62(1)degrees, V = 3194 Angstrom(3), Z = 4; R = 0.032, R(w) = 0.043 for 4124 observations and 379 variable parameters. Ligand 1 is tripoda l, bonded through the two phosphorus atoms and sulfur atom. With cobal t, the complex [Co(CO)(3)(1)][BPh(4)] (4) has been isolated. In this c omplex, ligand 1 is bidentate, with the two phosphorus atoms trans. In refluxing butanone, the bonding of the sulfur atom is achieved by CO displacement, giving the complex [Co(CO)(2)(1)][BPh(4)] (5), which has been isolated and characterized. With (COD)Rh(acac) in the presence o f perchloric acid, the complex [(COD)Rh-(1)][ClO4] (6) is obtained, in which ligand 1 is bidentate. 1,5-Cyclooctadiene in this complex can b e displaced by CO, leading to the two complexes [(CO)(2)Rh(1)][ClO4] ( 7) and [(CO)Rh(1)][ClO4] (8), which are in equilibrium, depending on t he partial pressure of CO. In the two complexes, ligand 1 is tridentat e, and the structure of 8 has been established by an X-ray structure d etermination. Crystallographic data for 8: triclinic C-i(1)-<P(1)over bar>, a = 10.940(3) Angstrom, b = 16.215(3) Angstrom, c = 9.548(2) Ang strom, alpha = 97.93(2)degrees, beta = 107.76(2)degrees, gamma = 89.29 (2)degrees, V = 1613 Angstrom(3), Z = 2; R = 0.040, R(w) = 0.042 for 4 021 observations and 220 variable parameters.