Pyrazolylborate complexes, activation

Synthesis, structure, and hydrothiolation activity of rhodium pyrazolylborate complexes Rt>R N—N pph, / / 3 Rh y/ / Xpph N—N PPh3 3... 

Many Ni alkyl or aryl complexes containing bidentate nitrogen donors, among them compound 177, have been used as moderately active catalysts for olefin polymerization. The pyrazolylborate complexes 178 and 179 catalyze the co-polymerization of ethylene and GO, and, in contrast to other Ni catalysts, do not require preactivation with ethylene. The N-N- and N-O-ligated complexes 180 and 181 are even more efficient and the latter can be used in supercritical C02. ... 

Pyrazolylborate complexes of titanium [12] have been studied for SPS polymerization. Similarities between the cyclopentadienyl ligand and the hydridotris(pyrazolyl)borate ligand have been noted for transition metal complexes. But the catalytic activities of pyrazolylborate complexes are much lower than those of the analogous pentamethylcyclopentadienyl complexes. This ligand may donate too much electron density to the titanium. 

A series of ionic liquids have been tested for the polymerisation of phenylacetylene with the pyrazolylborate rhodium complexes 46 and 47, shown in Scheme 8.13.[701 Complex 46 afforded higher molecular weights and lower polydispersity at comparable activity in the ionic liquid relative to dichloromethane. The addition of small amounts of methanol to the ionic liquid was found to have a positive effect on the catalytic activity. With complex 47 best results were obtained in [C4Ciim]Cl, giving 64% yield after 2 hours at 65°C. Molecular weights were usually lower with 46 than those obtained with either 47a or 47b as catalyst. 

Synthesis and structural chemistry of non-cyclopentadienyl organolanthanide complexes have been reviewed by Edelmann and Schumann et /.13,13a 24 Marques et al. have published a review on the chemistry of the lanthanide using pyrazolylborate ligands.36 Theoretical investigations on lanthanide alkyls have been published by Eisenstein et al. under the title Lanthanide complexes electronic structure and H—H, C-H, and Si-H bond activation from a DFT perspective. ... 

Recently. Alvarado et al. reported a related set of active catalysts for quinoline hydrogenation, formed in situ by addition of pyrazolylborate ligands Tp, hydrotris(pyrazolyl)borate and Tp. hydrotris(3,5-dimethylpyrazolyl)borate -which are isolectronic with cyclopentadienyl ligands- to [M(COD)C1]2 (M = Rh, Ir, COD = 1,5-cyclooctadiene), [Ir(COE)Cll2 (COE = cyclooctenc), and RuCl2(NCMe)4. Again, rhodium turned out to be the most efficient metal, and the activity was related with the ease of formation of Tp or Tp complexes. No mechanistic details were provided [101]. 

Pettinari R, Pettinari C, Marchetti F, Monari M, Mosconi E, De Angelis F. Boron functionalization and unusual B-C bond activation in rhodium(III) and iridium(III) complexes with diphenylbis(pyrazolylborate) ligands Ph2Bp. OrganometaUics. 2013 32 3895-3902. 

C-H activation reactions [35]. Rhodium pyrazolylborates, as highly electron-rich metal complexes, are found to be useful catalysts for the Markovnikov-type addition of thiols to alkynes. In particular, Tp Rh(PPh3)2 (Tp = hydrotris (3,5-dimethylpyrazolyl)borate) exhibits an excellent catalytic activity toward the regioselective hydrothiolation of a range of alkynes with both arene- and alkanethiols (Scheme 11) [36 0]. A variety of functional groups are well tolerated, and both sterically encumbered alkynes and thiols are successful in hydrothiolation. Electron-rich alkynes react more rapidly than electron-deficient alkynes. 

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