RESTRICTED ROTATION AROUND THE P-C BOND IN METALATED PHOSPHONIUM SALTS - A VARIABLE-TEMPERATURE H-1-NMR STUDY - X-RAY CRYSTAL-STRUCTURES OF[(AUP(C6H11)(3))(2)(MU-C(PTO(3))(PY-2))]CLO4 AND AUPPH3)(2)(MU-(C(PPH3)(PY-2))(AUPPH3))](CF3SO3)(2)

A variable-temperature H-1 NMR study has been performed for the comple xes [(AuL)(2){mu-C(PTo(3))R}]ClO4 [To = C6H4Me-4; L = PPh3, R = C(O)NM e2, pyridyl-2 (py-2), C(O)Ph, C(O)C6H4OMe-4, C(O)C6H4NO2-4, CO2Me, CN; R = py-2, L = P(C6H4OMe-4)(3), P(C6H11)(3), PMe3], mu(2)-{C(PTo(3))(p y-2)}{Ag(eta(2)O(2)NO)(OClO3)}]. H2O, and h3)(2){mu(2)-{C(PTo(3))(py-2 )}(AuPPh3)}](ClO4)(2). The To(3)P-C(AuL)(2) rotation is shown to be re stricted at room or lower temperatures. The estimated values of Delta G for these processes lie in the range 67.3-42.2 kJ.mol(-1) and are a ttributed mainly to steric effects, although electronic effects could also be operative. The crystal structures of [{AuP(C6H11)(3)}(2){mu-C( PTo(3))(py-2)}]ClO4 (2c) and AuPPh3)(2){mu-{C(PPh3)(py-2)}(AuPPh3)}](C F3SO3)(2) (9'.2CH(2)Cl(2)) have been determined. 2c crystallizes in th e monoclinic system, space group P2(1)/n, with a = 14.056(3) Angstrom, b = 24.556(4) Angstrom, c = 19.110(3) Angstrom, beta = 111.00(2)degre es and, Z = 4. 9' crystallizes in the monoclinic system, space group P 2(1)/c, with a = 17.232(6) Angstrom, b = 25.800(7), c = 18.005(7) Angs trom, beta = 96.77(3)degrees, and Z = 4.