Cationic binuclear trihydride complexes of platinum. A fluxional behavior for bridging and terminal hydrido ligands. Crystal and molecular structure of [Pt₂H₃{(t-Bu)₂P(CH₂)₃P(t-Bu)₂}₂][B(C₆H₅)₄]

A series of complexes of bis(diphosphine)trihydridodiplatinum(II) cations have been prepared from the corresponding mononuclear cis-(diphosphine)dihydridoplatinum(II) or dimeric bis(diphosphine)diplatinum(0) compexes. These complexes are very stable. While their IR spectra are consistent with the presence of both terminal and bridging hydrido ligands, the NMR spectra are consistent with only one form of hydride coordination and show equivalence within the sets of H, P, and Pt atoms. These results suggest a rapid exchange of bridging and terminal hydrido ligands. The static molecular structure is proposed to involve one bridging and two terminal hydrido ligands. The complex [Pt₂H₃{(t-Bu)₂P-(CH₂)₃P(t-Bu)₂)₂] [B(C₆H₅)₄] crystallizes in space group C_2h ⁵-P2₁/c with four formula units in a cell of dimensions a = 19.41 (1) Å, b = 18.03 (1) Å, c = 21.51 (1) Å, and β = 120.57 (3)°. The complex is sensitive to X radiation as evidenced by its progressive decomposition during data collection. Three data subsets on different crystals were acquired and merged to yield a total of 3468 unique reflections having F_o ²> 3σ(F_o ²). Least-squares refinement, including anisotropic thermal parameters for Pt and P atoms but isotropic parameters for the other nonhydrogen atoms, led to final conventional agreement indices (on F) of R = 0.081 and R_w= 0.101. The hydrido ligands were not located, but their positions are inferred from the coordination geometries of the Pt atoms. The Pt-Pt separation is 2.768 (2) Å and the dihedral angle between the two P-Pt-P coordination planes is 89°. The spectral and structural details, as well as those of the fluxional process, are discussed and related to those of similar mono-and binuclear platinum complexes.