Crystal structure of homodinuclear platinum complex containing a metal–metal bond bridged by hydride and phosphide ligands

The hydrido and phosphido ligands bridge the two PtII atoms to form the dinuclear complex, in which both PtII atoms are in a distorted square-planar arrangement.


Chemical context
Transition metal hydrides play a central role in many homogeneous catalytic reactions (Bertolasi et al., 1993;Clegg et al., 1996) and are very important in hydrogenation or hydroformylation. Their characterization is commonly carried out by NMR spectroscopy, X-ray analysis or neutron diffraction (Ciriano et al., 1978). Hydrides of Pt II are the most numerous of any transition metal hydride group (Leoni et al., 1995;Bachechi et al., 1993). In addition to the presence of the hydride ligand, the complexes invariably have a coordinated phosphine. Pure complexes are usually both air stable and kinetically inert (Roundhill, 1978).
We report here the synthesis and structural analysis of a new hydrido-bridged diplatinum complex, -diphenylphosphido--hydrido-bis[bromido(triphenylphosphane-P)platinum(II)] diethyl ether monosolvate. One of the attractive features of this dinuclear complex is that it is doubly bridged by hydrido and phosphido ligands in a trans fashion. The bridging of metal-metal-bonded homodinuclear complexes with a phosphido ligand allows the stabilization of the metalmetal bond. Many phosphido complexes (with and without a metal-metal bond) have been well documented and both their structural and reactivity features investigated (Stephan, 1989; Table 1 Selected geometric parameters (Å , ).

Figure 1
The asymmetric unit of title compound, showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.

NMR Spectroscopy
The 1 H NMR spectrum was recorded on a FT Bruker AVANCE III instrument at 296 K. The spectrum exhibits high field resonance, which unequivocally indicates the presence of a bridging hydride ligand absorbing at À4.5 ppm ( Fig. 4)

Database survey
A search of the Cambridge Structural Database (Version 5.38; Groom et al., 2016) gave 60 hits for a direct platinum platinum bond with a hydrido bridge. Only one contains the same core as the title compound with hydrido and phosphido bridges (Jans et al., 1983).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. The hydrido H atom was located in difference-Fourier maps and refined with a distance restraint of 1.7 Å using the command DFIX in SHELXL2014. C-bound H atoms were positioned geometrically and refined as riding atoms, with C-H = 0.95 (aromatic), 0.99 (CH 2 ) and 0.98 Å (CH 3 ) and with U iso (H) = 1.2U eq (C) or 1.5U eq (Cmethyl). Atom Br1 is disordered over two positions in a 0.92:0.08 ratio. Part of the 1 H NMR spectrum of the hydride bridging absorbing at À4.55 ppm.
Cg4, Cg5 and Cg7 are the centroids of the C13-C18, C19-C24 and C31-C36 rings, respectively.   Data collection: APEX2 (Bruker, 2006); cell refinement: SAINT (Bruker, 2006); data reduction: SAINT (Bruker, 2006); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009) and Mercury (Macrae et al., 2006).  Special details Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell esds are taken into account in the estimation of distances, angles and torsion angles Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 >2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.