Poly pyrazolyl borate Complexes

Solution Studies of Poly(pyrazolyl)borate Complexes. 116... 

Recently, Lipton et al. [25] have used zinc-67 NMR to investigate [Zn(HB(3,5-(CH3)2pz)3)2] complexes which have been doped with traces of paramagnetic [Fe(HB(3,4,5-(CH3)3pz)3)2]. The low-temperature Boltzmann enhanced cross polarization between XH and 67Zn has shown that the paramagnetic iron(II) dopant reduces the proton spin-lattice relaxation time, Tj, of the zinc complexes without changing the proton spin-lattice relaxation time in the Tip rotating time frame. This approach and the resulting structural information has proven very useful in the study of various four-coordinate and six-coordinate zinc(II) poly(pyrazolyl)borate complexes that are useful as enzymatic models. 

Although the poly(pyrazolyl)borate complexes of iron(II) have been well known for many years, [1] it is only recently that the complexes with the tris(l-pyrazolylmethane ligand, HC(pz)3, [45-48] have been studied in detail. It should be noted that poly(pyrazolyl)methane ligands, such as the tris(l-pyrazolylmethane ligand, are neutral, whereas the poly(pyrazolyl)bo-rate ligands, such as the tris(l-pyrazolyl)borate ligand, HB(pz)3", are monoanions. As a consequence, the metal(II) poly(pyrazolyl)methane complexes are dications and often have quite different properties from those of the analogous metal(II) poly(pyrazolyl)borate molecular complexes. But, in spite of these differences there are often very close structural similarities between the dicationic complexes and the neutral complexes. Therefore the study of the pyrazolylmethane complexes will parallel that of the borate complexes discussed above. 

The first silver(I) poly(pyrazolyl)borate complexes were reported in 1975.150 Since then, a number of silver complexes of the type Ag(L)(R B(pz)4 ) have been isolated and characterized.151,152 They were prepared by the reaction of the poly(pyrazolyl)borate anions with silver(I) salts, usually the nitrate, in the presence of donor ligands, L, and were isolated as white, thermally stable compounds. In most cases they were either insoluble, or at best only sparingly soluble, in common organic solvents. 

The Organometallic Chemistry of Group 10 Poly(pyrazolyl) borate Complexes... 

It is perhaps unsurprising that the role of phosphane ligands in group 10 poly(pyrazolyl)borate complexes can often be summarized as "spectator-ial," and in many instances is incidental in respect of chemistry. Indeed, the dominant utility of these ligands is as donors with which to trap or stabilize coordinately unsaturated materials. 

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