Of hydride complexes

FIGURE 5. Syntheses of hydride complexes from germyl complexes. Reprinted with permission from Reference 42. Copyright (1991) American Chemical Society... 

Hydrido-carbonyl and -phosphine complexes. A series of hydride complexes [IrHCl(PPh3)2(RCOO)] (R = Me, Et, Pr, H, Ph, CF3, MeCHCl, or P-NO2-CgH4) (44) have been prepared via the protonation of [Ir(N2)Cl(PPh3)2] w ith... 

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]. 

Crystals of the dinuclear hydride may be obtained by layering hexane onto a concentrated methanol solution of hydride complex. 

TYPES OF HYDRIDE COMPLEX 19.2.1 With Molecular Hydrogen... 

The main methods for the synthesis of hydride complexes are sufficiently well discussed, their procedure features are interaction of complex compounds with hydrogen, oxidative addition of hydrogen-containing molecules, formation of hydride complexes resulting from cleavage of the C — H bond, and protonation of the central atom of certain complexes [18a,28], Various physical and chemical meth-... 

The main synthetic methods used in the preparation of the coordination compounds mentioned above are reactions of coordinatively unsaturated complexes with hydrogen, protonation of hydride complexes, and formation of complexes containing molecular hydrogen by a synthesis reaction under reducing conditions. 

Hydride is also one of the highest Trans Effect and Trans Influence ligands. Structures of hydride complexes often show rather long M L bond lengths trans to H. H2 is a low trans effect ligand, however, and a trans H M (H2) arrangement is found in many nonclassical hydrides. 

The very rapid substitution reactions of hydride complexes H2pe(CO)4 and H2Ru(CO)4 at -70 °C are interpreted in terms of hydride migration. ... 

L, used in this mechanism, is a ligand which can stabilize the intermediate palladium complexes and satisfy a coordination number of the palladium whatever it is. L, for example, can be carbon monoxide, phosphines, solvents, or another molecule of palladium. Formation of hydride complexes by the oxidative addition of hydrogen chloride or hydrogen to a metal complex is well known (9, 27), as is formation of alkyl metal complexes by addition of metal hydrides to olefins. 

Scheme 20.4 shows a set of dynamics involving the binding and splitting of H2 that essentially represent the reaction coordinate for homolytic H-H bond cleavage or in the reverse process, the formation of H2 from a dihydride species. Remarkably these can be equilibrium processes in certain cases. Solutions of the complex W(CO)3(PTr3)2(H2) were observed by NMR spectroscopy to contain about a 4 1 ratio of dihydrogen to dihydride complex, proving that side-on bonded H2 complexes were the first step in formation of hydride complexes (Eq. (20.1) P = PiPrj) [lb, 2]. 

Dziegielewski et al. [43] recently reported the reduction of molecular nitrogen by hydrogen in a 1 1 THF-cyclohexane solution of hydride complexes of tungsten(IV) with diphenylalkylphosphines ([WH4(P(C2H5)Ph2)4] and [WH4(P(CH3)Ph2)4]) in a field of gamma radiation. The products of the reaction were ammonia, hydrazine, and some amines. 

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