SYNTHESIS AND CHARACTERIZATION OF A SERIES OF TRIETHYLPHOSPHINE-LIGATED PT-AU CLUSTER COMPOUNDS - X-RAY CRYSTAL AND MOLECULAR-STRUCTURE OF [PT(AUPET(3))(9)](NO3)(3)

The first triethylphosphine-stabilized Pt-Au cluster compounds, [Pt(Au PEt(3))(10)](2+) (2) and [Pt(AuPEt(3))(9)](3+) (3), were prepared by t he direct reaction of Pt(PEt(3))(3) with AuPEt(3)NO(3) under a dihydro gen atmosphere. Cluster 2 is the highest-nuclearity homoleptic Pt(AuPR (3))(n) cluster yet prepared. The reactivity and structures of these c lusters are in agreement with the well-established electron-counting a rguments. The 18-electron cluster 2 was converted into the 16-electron cluster 3 by oxidation with 2 equiv of ferricinium ion [Fe(eta(5)-C5H 5)(2)](+). Cluster 3 was converted into 2 by reduction with Hz in the presence of [AuPEt(3)](+). Cluster 3 was also observed to cleanly add the 2-electron donors CO and PEt(3) to form the 18-electron clusters [ (CO)Pt(AuPEt(3))(9)](3+) (4) and [(PEt(3))Pt(AuPEt(3))(9)](3+) (5), re spectively. Single-crystal X-ray diffraction results show that 3 has a flattened, toroidal structure in which the PtAu9 framework has a Pt-c entered, tricapped trigonal prismatic geometry. Crystal data for [Pt(A uPEt(3))(9)](NO3)(3) is as follows: hexagonal P6(3)/m, a = 15.134(5) A ngstrom, c = 23.48(1) Angstrom, V = 4657 Angstrom(3), Z = 2, residuals R = 0.056, and R(w) = 0.053 for 1489 observed reflections and 81 vari ables, Mo K alpha radiation. Compound 3 was found to reversibly add H- 2 in solution to form the dihydride cluster [(H)(2)Pt(AuPEt(3))(9)](3) (6). The equilibrium constant for this addition reaction is 1.1 x 10 (3) M(-1) (CD2Cl2 solution, 25 degrees C), slightly smaller than that for [Pt(AuPPh(3))(8)](2+). The rate of the addition is also slower tha n that with [Pt(AuPPh(3))(8)](2+). Cluster 3 is an excellent homogeneo us catalyst for H-2-D-2 equilibration giving a turnover rate for HD pr oduction of 0.13 s(-1) (nitrobenzene solvent, 30 degrees C, 1 atm). Th e PEt(3)-containing clusters give similar rates and follow the same ge neral trends previously observed with PPh(3)-ligated clusters. The che mistry of these new clusters is explained by consideration of the ster ic and electronic properties of the PEt(3) ligand. These new compounds will be useful as models for hydrogen activation by Pt-Au clusters an d as precursors for supported Pt-Au catalysts.