Zirconium borohydrides

Many borohydrides are highly unstable and have to be used as freshly prepared ethereal solutions. However there are instances where the polymer-supported versions are more stable e. g. an Amberlyst anion exchange resin supported borohydride and cyanoborohydride [61], polyvinylpyridine supported zinc borohydride [62] and the corresponding zirconium borohydride [63]. Such compounds, in their labeled forms, should turn out to be very useful. 

Zirconium Borohydride (Zirconium Tetrahydro-borate). Zr(BH4)4 mw 150.5 volatile pyrophoric cryst mp 28.7° bp 123° (extrapolated) d l.l3g/cc. Prepn is by reacting Zr tetrachloride with Li borohydride — the yield is 77%. Accdg to Gaylord (Ref 4) the compd is spontaneously flammable in air... 

The AS4 and CH4 molecules are clear-cut examples of the two distinctly different arrangements. However, these distinctions are not always so unambiguous. Two independent studies reported the structure of zirconium borohydride, Zr(BH4)4. Both described its geometry by the same polyhedral configuration, while they differed in the assignment of the chemical bonds (Figure 3-17). The most important... 

Figure 3-17. The molecular configuration of zirconium borohydride, Zr(BH4)4, in two interpretations but described by the same polyhedral shape. Left, the zirconium atom is directly bonded to the four tetrahedrally arranged boron atoms [28] Right the zirconium and the tetrahedrally arranged boron atoms are not bonded direcdy their linkage is established by four times three hydrogen bridges [29].

V. P. Spiridonov, G. I. Mamaeva, Study of the Zirconium Borohydride Molecule by Electron Diffraction by Gases. Zh. Strukt. Khim. 1969, 10, 132-135. 

The 7t-cyclopentadienyl zirconium borohydride (14) has a chemical shift of +32-5 p.p.m. from trimethyl borate and is a quintet with a coupling constant of 86 c./sec. In contrast to this,... 

Sodium or potassium borohydride was not successful in this synthesis. Zirconium borohydride in ether reacts with an ether solution of lithium aluminum hydride to give a white precipitate of Zr(AlH4)4 that decomposes at room temperature to give a black pyrophoric solid of unknown composition. 

Reduction.—/8-(3 -Methyl-2 -butyl)-9-borabicyclo[3,3,l]nonane and the 9-borabicyclo[3,3,l]nonane-pyridine complex are mild chemoselective reducing agents for aldehydes. Tri-n-butyltin hydride on dried silica gel reduces aldehydes rapidly and unhindered ketones relatively slowly yielding the corresponding alcohols in high yields. Sodium borohydride adsorbed on to alumina and the zirconium borohydride (9) reduce aldehydes and ketones to alcohols in aprotic... 

These methods deal with specific cases. The list of examples is not exhaustive. The low-T (200-300°C) decomposition of the transition-metal borohydrides M(BH4> , e.g., leads to titanium, zirconium, halfnium, uranium and thorium borides . Alternatively, the uranium diboride may be obtained by reacting uranium hydride with diborane in hydrogen at 200-400°C. 

The binary borohydride species Zr( III 11)4 and U(BH4)4 have been investigated by quantum mechanical techniques and, for the zirconium case, also by gas-phase electron diffraction. All confirm that these simple molecules have a staggered conformation of borohydride ligands.15 In a related study, the hafnium analog Hf(BH4)4 has also been analyzed and is essentially isostructural.16 These studies show the molecules to possess tetrahedral symmetry with all of the BH4 ligands triply (i.e., if) bridging. Photoelectron spectra [He(i)] of the half and bent metallocene complexes Zr(7]S-CsHs)(BH4)4, M(7]S-CsHs)2(BH4)2 (M = Zr, Hf), and Ta(7]S-CsHs)2(BH4) have been determined.17... 

Dicyclopentadienyldihydrido-zirconium, 108 Sodium borohydride, 278 Sodium dithionite, 281 to carbonyl compounds Arene(tricarbonyl)chromium com-... 

Applications The most important application sectors for metallic sodium in the USA are in the production of sodium borohydride (ca. 38%), which is used as a reducing agent, and in the manufacture of herbicides (ca. 25%). A further important sector accounting for 20% of the consumption of sodium, is the production of metals which are difficult to reduce such as uranium, thorium, zirconium, tantalum and titanium. Its utilization in the production of titanium has, however, declined of late. Tetramethyl- and tetraethyl lead... 

CHROMIC ACID, STRONTIUM SALT (7789-06-2) SrCrO A strong oxidizer accelerates the burning of combustible materials. Violent reaction with reducing agents active metals, cyanides, esters, and thiocyanates. Incongjatible with acids, bases, water, fluorine, hydrazine, zirconium dusts, potassiiun iodide, sodium tetraborate, sodium tetraborate decahydrate, sodium borohydride. 

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