Phosphines, tertiary, complex hydrides

Butadiene and ethylene are codimerized with a soluble rhodium-phosphine complex as the catalyst. Very little has been reported on the mechanistic evidence for this reaction. However, a catalytic cycle as shown in Fig. 7.9 involving a rhodium hydride seems likely. Reducing rhodium trichloride with ethanol in the presence of a tertiary phosphine generates the hydride complex 7.32. The 1,4-hydride attack on the coordinated butadiene gives an rf-allyl complex. This is shown by the conversion of 7.33 to 7.34. Ethylene coordination to 7.34 produces 7.35. 

In view of the chemical reactivity of the tertiary phosphine and nickel hydride complexes to air, all manipulations should be carried out in a nitrogen or argon atmosphere.6 All solvents should be distilled under a nitrogen or argon atmosphere. 

In the absence of strongly rr-bonding ligands such as tertiary phosphines, complex hydrides, e.g., [A1HJ and [BHJ react with Cu, Ag and Au halides to form metal-hydrogen compounds, usually of low thermal stability. Uncomplexed CuH is unstable, even at — 80 C. 

A. Complex Hydrides with Tertiary Phosphines and Related Ligands. 135... 

Complex hydrides with tertiary phosphines and related ligands... 

The A-frame hydride [Pt2H2(/i-H)(/i-dppm)2] undergoes reductive elimination of H2 in the presence of tertiary phosphine ligands, L, to give the platinum(I) dimer, [Pt2HL(//-dppm)2]. Hill and Puddephatt have shown that this occurs via the intermediate [Pt2II2(/i-H)L(//-dppm)2] (14).99 Carbon monoxide reacts rapidly and reversibly with [PtH(/r-PP)2Pt(CO)]+, PP = R2P-CH2-PR2, R = Et or Ph, to give [PtH(/i-PP)2Pt(CO)2]+ and [PtH(CO)(/u-PP)2Pt(CO)2]+, the first reported mixed valence, platinum(0)-platinum(ll) complexes.100... 

The electrosynthesis of hydride complexes directly from molecular hydrogen at atmospheric pressure by reduction of Mo(II) and W(II) tertiary phosphine precursors in moderate yield has been described as also the electrosynthesis of trihydride complexes of these metals by reduction of M(IV) dihydride precursors [101,102]. Hydrogen evolution at the active site of molybdenum nitrogenases [103] is intimately linked with biological nitrogen fixation and the electrochemistry of certain well-defined mononuclear molybdenum and tungsten hydrido species has been discussed in this context [104,105]. 

The procedures described below have consistently given stable, crystalline products for a number of tertiary phosphine copper hydride complexes. These complexes can be prepared by the careful reaction of lithium tetrahydrido-aluminate(l-) with tertiary phosphine copper halide complexes. The reactions are run in etheral solvents under an inert atmosphere. The resultant products are... 

Solvato complexes of platinum(II) of the type fraws-[PtY(solvent)L2]+ (Y = hydride, alkyl, or aryl solvent = alcohol or ketone L = tertiary phosphine or arsine) have been known since 1961.1 They are obtained by halogen abstraction from the corresponding halo complexes tran.s-[PtXYL2] in the presence of the desired solvent.2 The methanol complex is also rapidly and quantitatively formed when trans-[PtH(N03)(PEt3)2] is dissolved in this solvent.2... 

Compound ( -CsMes Zr (7) is formally a 16-electron complex and as such can be expected to add donors such as tertiary phosphines and CO. Accordingly, 7 absorbs PF3 (0.89 mol/mol of 7) at —80°C in toluene to yield the unstable, 18-electron complex (r75-C5Me5)2Zr(H)2(PF3)(18). On the basis of its lH NMR spectrum at —50°C (Table I), the structure of 8 appears to be analogous to (T75-C5H5)2TaH3, with PF3 occupying the central equatorial position mutually cis to both hydride ligands, i.e.,... 

This means that we use (a) P-31 NMR both qualitatively, for information on the orientation of the tertiary phosphine ligands, and analytically to determine the number of complexes in solution (this is a very receptive nucleus and 1-2% of impurities often are detected readily) (b) Sn-119 (I = i, natural abundance = 8.6%) NMR as a probe for the identity of the trichlorostannate moiety and (c) Pt-195 (I = i, natural abundance = 33.7%) NMR for multiplicity data concerned with the number of coordinated phosphines (and NMR spins in general). The value of H-l NMR in metal hydride chemistry is so well established (18) that no further justification is required here. 

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