CONTROL OF THE BRIDGEHEAD DONOR ATOM IN THE TRIPODAL LIGAND OVER OXIDATIVE ADDITION OF AU(PPH(3))(+) TO [X(CH(2)CH(2)PPH(2))(3)RHH] (X=N, P) - X-RAY-DIFFRACTION AND MULTINUCLEAR (RH-103, P-31, H-1) NMR-STUDIES

The electrophilic fragment Au(PPh(3))(+) reacts in tetrahydrofuran with the monohydrides [(NP3)RhH] and [(PP3)RhH] to give the mixed-metal adducts [(NP3)Rh(H){Au(PPh(3))}](+) and [(PP3)Rh(mu-H){Au(PPh(3))}](+), respectively [NP3 = N(CH(2)CH(2)PPh(2))(3); PP3 = P(CH(2)CH(2)PPh(2))(3)]. The structures of [(NP3)Rh(H){Au(PPh(3))}]PF6.0.5C(4)H(8)O (4) and of [(PP3)Rh(mu-H){Au(PPh(3))}]BPh(4).0.5C(2)H(5)OH (3b) have been determined by X-ray diffraction analyses. Compound 4 crystallizes in monoclinic space group P21/c (No. 14) with a = 11.132(4) Angstrom, b = 20.779(4) Angstrom, c = = 26.647(5) Angstrom, beta = 97.63(1)Angstrom, Z = 4, and V = 6105.71 Angstrom(3). The rhodium(III) center is coordinated in a distorted octahedral geometry by the nitrogen and the three phosphorus atoms of NP3, by a gold atom from Au(PPh(3)), trans to nitrogen, and by a terminal; hydride ligand. The Rh-Au distance in 4 [2.531(1) Angstrom] is the shortest ever reported. Compound 3b crystallizes in monoclinic space group P21/a (No. 14) with a = 14.775(4) Angstrom, b = 35.627(4) Angstrom, c = 14.113(4) Angstrom, beta = 95.94(5)degrees, Z = 4, and V = 7389.04 Angstrom(3). The geometry of the coordination polyhedron around rhodium approximates a trigonal bipyramid with the bridgehead phosphorus and an intact HAu(PPh(3)) group transoid to each other. All the mixed rhodium-gold hydrides have been studied in solution by means of NMR techniques, including Rh-103 spectra obtained from inverse H-1, {Rh-103} experiments. These studies confirm that, also in solution, the presence of nitrogen in the tripodal ligand results in oxidative addition of Au(PPh(3))(+) to the metal, whereas formal oxidation of the terminal hydride occurs when the bridgehead donor atom is phosphorus.