Zinc hydrides

Zinc hydride can be isolated from the reaction of LiH with ZnBr2 or NaH with Znl2 ... 

The zinc hydride complex [TpBut]ZnH, the first metal hydride derivative of the type [Tp1 ]MH to be prepared, is readily synthesized by metathesis of ZnH2 with Tl[TpBut] [Eq. (28)] 80,138). 

Fig. 38. ORTEP drawing of [TpBu ]ZnH (the zinc hydride ligand was not located, but is illustrated in the expected axial position). Reprinted with permission from Ref. (80). Copyright 1995 American Chemical Society.

There has been an increasing number of reports of the utilization of zinc hydride complexes as precursors in organic transformations and as reducing agents. Zinc hydrides have been less well investigated than the other group 13 hydrides due to the formation of polymeric and oligomeric species that are difficult to characterize. 

Zinc hydride, 4492 Zirconium hydride , 4493 See COMPLEX HYDRIDES, pyrophoric materials See entry LANTHANIDE-TRANSITION METAL ALLOY HYDRIDES... 

Recently, de Koning et a/.157 have found that hydride transfer takes place exclusively to the 4-position of pyridine, using zinc hydride and magnesium hydride. The reaction is fairly slow and eventually is completed to yield the pyridine complex of bis(l,4-dihydro-l-pyridyI)zinc and its magnesium analog, Zn(NR2)2-2py and Mg(NR2)2-2py, where NR2 is the 1,4-dihydropyridyl residue. H- and 13C-NMR spectral data give consistent answers in agreement with the proposed structures 112 and 113. 

Magnesium—nickel hydride, 4458 Plutonium(III) hydride, 4504 Poly(germanium dihydride), 4409 Poly(germanium monohydride), 4407 Potassium hydride, 4421 Rubidium hydride, 4444 Sodium hydride, 4438 f Stibine, 4505 Thorium dihydride, 4483 Thorium hydride, 4535 Titanium dihydride, 4484 Titanium—zirconium hydride, 4485 Trigermane, 4415 Uranium(III) hydride, 4506 Uranium(IV) hydride, 4536 Zinc hydride, 4486 Zirconium hydride , 4487 See COMPLEX HYDRIDES, PYROPHORIC MATERIALS See entry LANTHANIDE—TRANSITION METAL ALLOY HYDRIDES... 

One route to Zn—H bonds involves metathesis of a hydride with Zn—X or Zn—R (R = alkyl) bonds.1 A second route, used in the preparation of anionic zinc hydride complexes, involves donor-acceptor interaction between H- and diorganozinc.2 For example3... 

Sodium trihydridozincate( 1 —) is air- and moisture-sensitive, but can be stored at room temperature under vacuum or an inert atmosphere. Because of this stability Na[ZnH3] is a promising compound for the preparation of zinc hydride derivatives. The infrared spectrum and x-ray powder pattern of Na[ZnH3] are reported,4 and an alternate preparation has been mentioned.8... 

Zinc hydride, a moderately stable sohd slowly decomposed by water, may be prepared by the reaction of LiH, NaH, or LiAlH4 on a zinc halide snch as the bromide or iodide. If organometallic derivatives of zinc of the type Li ZnR +2 are treated with LiAlHi, complex hydrides snch as LiZnHs, Li2ZnH4, and LisZnHs may be prepared. 

In a first step Li2Zn(CH3)4 was prepared from methyl lithium and dimethyl zinc. Reduction of this compound with LLAIH4 produces the complex zinc hydride in... 

Deprotonation of the zinc alcohol complexes shown in Fig. 12 to produce zinc alkoxide species has not been reported. Instead, mononuclear, tetrahedral zinc alkoxide complexes, supported by hydrotris(pyrazolyl)borate ligands, ([TpBut,Me or Tpph,Me, Scheme 8), have been generated via treatment of zinc hydride precursor complexes with aliphatic alcohols.68-70 A zinc ethoxide complex, [TpBut,Me]Zn-OEt, was also prepared via decarboxylation of the ethyl carbonate complex, [TpBut,Me]Zn-0C(0)0Et.49 X-ray crystallographic studies of [Tpph Me] Zn-OCH3 and [TpBut,Me]Zn-OEt revealed Zn-O bond lengths of 1.874(2) and 1.826(2) A, respectively.68,71 These bond distances are 0.1 A shorter than found for the alcohol complexes shown in Fig. 12. 

Scheme 8 Equilibrium formation of tetrahedral zinc-alkoxide and aryloxide complexes. The alkoxide complexes can be independently prepared via treatment of a zinc hydride precursor complex with the appropriate alcohol. Experimental methods for the determination of Kk (300 K) are given in reference 69.

Zinc hydride is made by reaction 21.108 (or from LiH and ZnBr2) and is a fairly stable solid at 298 K. 

---