Tris borate derivatives

The pyrrolylphosphines and the tris-(pyrazolyl)borate derivative were investigated [48, 73] at square-planar tetra-coordinate Rh complexes for which the Lever model was then extended (see in the following). 

Figure 7.3 Analysis of the 4H four-way RNA junction of the human U1 snRNA by comparative gel electrophoresis (Duckett et al., 1995). The central sequence of the junction is shown. The A G pair at the center was retained in this analysis, although changing it to a Watson—Crick pair did not alter the global shape of the junction. The six long—short species can be considered to be derived from a junction with four arms of 40 bp. The central 20 bp comprises RNA, and the outer arms are DNA. The junction species were electrophoresed in an 8% polyacrylamide gel, in 90 mM Tris—borate (pH 8.3) and 1 mM Mg2+. The mobility pattern of the six species is slow, slow, fast, fast, slow, slow. The simplest interpretation (shown on the right-hand side) is that of a stacked structure based on A on D and B on C coaxial stacking, with the axes nearly perpendicular. The pattern would also be consistent with a rapid exchange between nearly equal populations of parallel and antiparallel forms. However, a recent crystal structure has found a perpendicular stacked structure for this RNA junction (Pomeranz-Krummel et al., 2009).

Besides bidentate ligands, tripyrazolylborates (Tp) (see Tris(pyrazolyl)borates) derivatives, which are of anionic tridentate in facial configuration, also afford octahedral... 

Tp = tris(pyrazolyl)borate derivative, L = bispyridine (X = NO) or bisphenolate (X = O) bridging ligands [68]. Because of the presence of only 25.5 % as hyperfine coupling-active nuclei Mo ( Mo with 15.9 % and Mo with 9.6 %, both with I = 5/2), the delocalization is evident from the approximately halved hyperfine coupling constants (as compared with mononuclear Mo species) and from the relative ESR intensities of lines corresponding to molecules with Mo- Mo, Mo-Mo and Mo-Mo isotope combinations [67, 68]. 

Bulky sulfur counterparts (see Figure 8) preceded the (phosphino)borates and are known for tri- 8a and bidentate 8b ligands. " These ligands are particularly noteworthy as thioether auxiliaries because neutral thioether donors commonly suffer from high ligand lability. Riordan s group has made use of these (thioether)borate derivatives, as well as pyrazolyl/thioether hybrid borates 8c and 8d, in the preparation of a suite of interesting late metal complexes. 

As the demand for new polymers increased, catalysts with two active sites per molecule were developed. It was found that tris-pentafluoropheityl-aluminium, (C6F5)3A1, could be used to replace the borate derivatives, and when used in conjunction with the typical transition metallocene catalyst precursors, a series of di-cationic derivatives of titanium and zirconium could be produced. Work in Dow showed that these di-cationic catalysts were up to 30 times more reactive than boron activated catalysts, while still producing polymers with the same molecular weight and melting point. ... 

Classic A/-heterocychc ligands, eg, bipyridyl (bipy), terpyridyl, imidazole, pyrazine, phenanthroline, piperazine (including alkyl- and aryl-substituted derivatives), and polypyrazol-l-yl-borates (bis, tris, and tetra), have all been found to coordinate Th(IV) chlorides, perchlorates, and nitrates. The tripodal hydrotris(pyrazolyl)borates, HBPz, have been used to stabilize organometaHic complexes (31). Bis-porphyrin Th(IV) "sandwich" complexes have been... 

It is noteworthy that carbene function may be manifested in the derivatives of tris(imidazol-l-yl)borate 44 (96AGE310). Its reaction first with n-butyllithium, then with iron(II) chloride, and finally with sodium tetraphenylborate gives the iron(III) carbene derivative 45. 

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... 

Recently, a somewhat different synthetic approach has been reported. Halcrow et al. (215) synthesized a series of five-coordinate copper(II) complexes comprising a tridentate tris(pyrazolyl)borate ligand and a bidentate phenol derivative. Neutral complexes [Cun(TpPh)(bidentate phenolate)] were synthesized and structurally characterized [Tpph] = hydrido-tris(3-phenylpyrazol-l-yl)borate. The species [Cun(TpPh)(2-hydroxy-5-methyl-3-methylsulfanylbenzaldehydato)] can electro-chemically be converted to the (phenoxyl)copper(II) monocation, which has been characterized in solution by UV-vis spectroscopy. It displays two intense absorption maxima at 907 nm (e = 1.2 x 103 M 1 cm-1), and 1037 (1.1 x 103 M l cm-1), resembling in this respect the radical cofactor in GO (Fig. 7). 

The successful utilization of alkoxo Zn- and Mg-tris(pyrazolyl) borate initiators in the lactide polymerization inspired the synthesis of sterically bulky B-diketiminates (BDls) (Fig. 5) and their zinc and magnesium derivatives [60-62]. Replacing the ancillary ligands resulted in the production of several mono- and dinuclear complexes of Mg" and Zn" 24-39 (Fig. 6), which demonstrated excellent catalytic activity for the polymerization of l- and rac-lactide [62-66]. 

Our attempts as well as those of C. C. Price to react 2.4.6-triphenylpyry-lium salts with phosphine, phenylphosphine or tris-hydroxymethyl-phosphine in the hope of isolating phosphorins or their P-substituted derivatives were unsuccessful. In contrast, MarM applying essentially the same principle but using pyridine as base and solvent, succeeded by heating 2.4.6-triphenylpyrylium-tetrafluoro-borate 21 with tris-hydroxymethyl-phosphine 5. He was able to isolate 2.4.6-triphenyl-X -pbosphorin 22, m. p. 171—172 C, as the first X -phosphorin in 20-25% yield. 

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