Tris borato ligands

Poly(pyrazolyl)borato ligands offer a variety of coordination modes according to their degree of substitution. Bis and tris(pyrazolyl)hydro-borato derivatives tend to adopt bidentate and tridentate coordination modes almost exclusively (5), while the tetrakis(pyrazolyl)borato ligand... 

Bis and tris(pyrazolyl)hydroborato ligands are generally prepared as the potassium derivatives by the direct reaction of KBH4 with the appropriate pyrazole (RR pzH), as illustrated in Scheme 1 for the parent system (13). The reaction is extremely general and has been applied to a number of different derivatives, which have included the incorporation of chiral (14, 15) and tethered (16) substituents. However, if the alkyl substituents of the pyrazole are inequivalent (i.e., R + R ), a potential problem may be encountered with the formation of isomeric products, in which either of the R and R substituents may occupy the 3-position of the poly(pyrazolyl)borato ligand. Nevertheless, if the difference in steric demands of R and R is large, there is a strong... 

Kinetics studies have demonstrated that the isomerization is a first-order process, characterized by the activation parameters AH% = 34.5(8) kcal mol-1 and A St = 6(2) e.u. Such rearrangements of poly-(pyrazolyl)borato ligands are not uncommon, and have also been observed for Cu and Co complexes of the tris(3-isopropylpyrazolyl)hydro-borato ligand system, i.e., [T73-HB(3-Pr pz)3]M — [T73-HB(3-Pr1pz)2(5-Pr pz)]M (32). 

A wide series of ferrocenyl-molybdenum complexes of known redox properties bear the tris(3,5-dimethylpyrazolyl)borato ligand or the N,iV, N"-trimethyl-l,4,7-triazacyclononane ligand. They are illustrated in Scheme 7-7 [55 — 59]. 

Synthesis, crystal structure, and reactivity of a four-coordinate iron(II) chloride complex bearing the sterically demanding tert-butyl-tris (3 -isopropylpyrazolyl) borato ligand... 

The active site in CAII has been modelled using a tris(pyrazolyl)hydroborato ligand (28.22) to mimic the three histidine residues that bind Zn in the metalloenzyme. Because Zn is a metal ion, it tolerates a range of coordination geometries. However, tris(pyrazolyl)hydro-borato ligands are tripodal (see Section 19.7) and can force tetrahedral coordination in a complex of type [Zn(28.22)X]. The hydroxo complex 28.23 is one of a series... 

Bis- and tris(pyrazolyl)borato ligands have been widely used to stabilize a variety of alkylmetal complexes among which several alkylzinc derivatives. Stable monomeric three-coordinate alkylzinc complexes, B (3-... 

Jove FA, Pariya C, Scoblete M, Yap GPA, Theopold KH. A family of four-coordinate iron(II) complexes bearing the stericaUy hindered tris(pyrazolyl)borato ligand Tp . Chem EmJ. 2011 17 1310-1318. 

Silver(I) complexes are known with the tris(pyrazolyl)borate [HB(pz)3] and the methyl, phenyl, bromo, or trifluoromethyl-substituted derivatives. The structure of the silver tri(pyrazolyl)borato species has been a puzzle since it was first reported.385,386 It was suggested that the structure could be oligomeric, but recently the crystal structure of the compound [Ag HB(3,5-Me2pz)3 ]2 shows that it has a dimeric structure387 where the silver(I) centers are tricoordinated by a bidentate arm of one ligand and a monodentate arm of the other ligand (29). The related complexes [Ag HB(4-Brpz)3 ]2, [Ag HB(4-Mepz)3 ]2, [Ag HB(3,5-Me2pz)3 ]2, [Ag HB(3-Mepz)3 ] , [Ag B(pz)4 ], and... 

The X-ray structure of the unsubstituted tris(pyrazolyl)borato zinc nitrate has been solved showing a unidentate coordination mode for nitrate, in contrast with the t-butyl substituted ligand, which shows anisobidentate nitrate coordination due to the steric effects.232 A partial explanation of the reduced activity of cadmium-substituted carbonic anhydrase is offered by Parkin on the basis of the comparison of nitrate coordination to cadmium and zinc trispyrazo-lylborate moieties. A contributing factor may be the bidentate coordination supported by the cadmium that does not allow the facile access to a unidentate bicarbonate intermediate, which could be highly important to carbonic anhydrase activity.233... 

Group III Donors. Boron donor ligands. The unusual tris(pyrazolyl)borato-complex [RuL3(CO)2X] [X = Cl, Br, or I L = (16a)] has been prepared ... 

Tris(pyrazolyl)borato and Related Triaza Ligand Complexes... 

Tris(pyrazolyl)borato and related cyclic triaza ligand complexes of the general class [Mo(NO)Tp XY], in which the metal adopts a formal oxidation state of 0,1, or II, have been described above in Section 5.6. 

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