Polypyrazolylborate complexes

Although some polypyrazolylborate complexes of chromium(II) have been reported to undergo oxidation on exposure to air,115 the resulting chromium(III) complexes have not been investigated. 

Complexes of molybdenum form the largest set of any of the transition metals. Many of these compounds display spectroscopic properties, isomerism and structural features that illustrate the coordination chemistry of polypyrazolylborate complexes. In addition, this system illustrates that trispyrazolylborate ligands are more bulky than their formal analogue C5H5. 

CO)3] (R = H or Pz) complexes via carbonylation of [Rh(RBPz3](L L)] (L-L = C2H4 cyclo-octa-1,5-diene) substrates.146 Oxidation of this product with iodine in dichloromethane yielded the deep red Rh111 derivative [Rh(RBPz3)I2(CO)], which n.m.r. evidence showed to be an (i3-polypyrazolylborate complex. 

Poly(l-pyrazolyl)borates ( scorpionates ) are well-established, versatile, and easily accessible ligands in coordination chemistry, which have found widespread applications ranging from analytical chemistry to homogeneous catalysis and materials science . Table 5 shows many of the polypyrazolylborate complexes with different metals published in the last decade. 

A good illustration of geometric and conformational stereoisomerism in bidentate polypyrazolylborate complexes is provided by the stable,... 

Polypyrazolylborates metal complexes, 2, 87,245-257 bidcntatc. 2,246 biological applications, 2.255 preparation. 2, 246 tridentate, 2,247 Polypyrazolylgallates... 

Thorium complexes, 3, 1131-1215 groundwaters geochemistry, 6. 852 polypyrazolylborates, 2. 255 Thorium(IV) complexes cupferron, 2, 512 peptides... 

Ytterbium, trinitratotris(dimethyl sulfoxide)-structure, 1, 97 Ytterbium, tris(acetylacetone)(4-ammo-3-penten-stereochemistry, 1,81 Ytterbium complexes acetylacetone, 2,373 dipositive oxidation state hydrated ions, 3,1109 polypyrazolylborates, 2,255 Ytterbium(III) complexes ethyl glycinate, diacetate... 

Complexes with polypyrazolylborates and related tripodal ligands 300... 

On the addition of anhydrous CrBr2 dissolved in warm ethanol to a warm solution of the [NEt4]+ salt of the appropriate polypyrazolylborate (17) in the same solvent, crystals of the complexes [Cr H B(pz)4 2] (n = 0, 1 or 2 appear) (Table 19).115 These are moderately air-stable, and the ethyl derivative [Cr Et2B(pz)2 2]2, which was obtained from [Cr2(02CMe2)4] and Na Et2B(pz)2 in THF on which hexane was layered to induce crystallization, is stable to air.116 An indazole (a 4,5-substituted pyrazole) derivative [Cr(H2B 4,5-(5-N02benzo)pz 2)2] is also known (Table 19). The isolation of [Cr HB(pz)3 2] and [Cr B(pz)4 2] from aqueous solution117 could not be repeated.115... 

Despite the vast interest shown by coordination chemists in polypyrazolylborate ligands (17) since their discovery in 1966 few complexes of chromium(III) with these ligands have been mentioned in the literature. The complex [ B(pz)4 2Cr]PF6 (147) may be prepared by either of the routes outlined in Scheme 89.657... 

Selected nickel(II) complexes with polypyrazolylborate and related ligands are reported in Table 56. 

Table 56 Selected Complexes with Polypyrazolylborates and Related Ligands...

By far the most common synthesis technique is to introduce polypyrazolylborate ligands by replacing halide groups. As might be expected this leads to a great variety of complexes. In some... 

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