H+ AUPPH3+ EXCHANGE FOR THE HYDRIDE COMPLEXES CPMOH(CO)(2)(L) (L=PME3, PPH3, CO) - FORMATION AND STRUCTURE OF [CP(CO)(2)(PME3)MO(AUPPH3)(2)](+)[BF4](-)/

The reaction of CpMoH(CO)(2)L with AuPPh3+BF4- in THF at -40 degrees C proceeds directly to the MoAu2 cluster compounds [CpMo(CO)(2)L(AuPPh3 )(2)]+BF4- (L = PMe3 (1), PPh3 (2)) with release of protons. A 1:1 rea ction leaves 50% of the starting hydride unreacted. At lower temperatu re, however, the formation of a [CpMo(CO)(2)-(PMe3)(mu-H)(AuPPh3)](+) intermediate is observed. This compound evolves to the cation of 1 and CpMoH(CO)(2)-(PMe3) upon warming and is deprotonated by 2,6-lutidine to afford CpMo(CO)(2)(PMe3)(AuPPh3). The X-ray structure of 1 can be d escribed as a four-legged piano stool with the PMe3 and the ''eta(2)-( AuPPh3)(2)'' ligands occupying relative trans positions. [Cp(CO)(2)(PM e3)Mo(AuPPh3)(2)](+) (M-r = 1298.41): monoclinic, space group P2(1)/n, a = 18.457(13) Angstrom, c = 26.096(2) Angstrom, beta = 105.086(5)deg rees, V = 4472.0(5) Angstrom(3), Z = 4. The reaction of CpMoH(CO)(2)(P Me3) with 3 equiv of AuPPh3+ affords a MoAu3 cluster, [CpMo(CO)(2)(PMe 3)-(AuPPh3)(3)](2+) (3), in good yields under kinetically controlled c onditions. Under thermodynamically controlled conditions, 3 dissociate s extensively into 1 and free AuPPh3+. It is proposed that the hydride ligand helps build higher nuclearity Mo-Au clusters. The difference i n reaction pathways for the interaction of AuPPh3+ with CpMoH(CO)(2)L when L = PR3 or CO and for the interaction of CpMoH(CO)(2)(PMe3) with E+ when E = H, Ph3C or AuPPh3 is discussed. The lower acidity and grea ter aurophilicity of the [CpMo(CO)(2)L(mu-H)(AuPPh3)](+) intermediate when L = PMe3 favor attack by AuPPh3+ before deprotonation.