Tetrakis borate complexes

Asslani et al.ul have described the synthesis of the tetrakis(pyrazolyl)borate complexes [ZrCl2(BPz4)2], [ZrBr2(BPz4)2] and [Zr(BPz4)4]. Analytical and H NMR data were reported for these compounds, but Reger and Tarquini115 have been unable to reproduce the NMR data. 

Asslani et have describeci the synthesis of the tetrakis(pyrazolyl)borate complexes... 

A further anomaly of the reactions between CpCo(Rf)(CO)I (Rf=C2Fs, "C3F7, CsFv) and KB(pz)4, is that the major products were not the respective tetrakis(pyrazolyl)borate complexes. Rather, these materials were formulated as CpCo(Rf)(pz2H) (Chart 2), on the basis of their monomeric and diamagnetic nature, and NMR spectroscopic data. 

There is a continuous search for new superacid catalysts. The kinetics of ROP of D3 and D4 initiated by protic borate complex (tetrakis(pentafluorophenyl)boric add hydrate), HB (C6Fs)4-3H2O, revealed that the reaction is first-order in monomer and first-order in initiator. The formation of cydic oligomers typical for CROP of cydosiloxanes initiated by protic acids was observed. 

The cyclopalladated complexes of hydrotiis(pyrazol-l-yl)borate and tetrakis (pyrazol- l-yl)borate have a common feature of bidentacy of the pyrazol- 1-ylborate... 

The monocation tris(diethylether) ethylzinc is formed from diethyl zinc as a tetrakis(penta-fluorophenyl)borate salt.85 Longer-chain linear and cyclic ether complexes (2) of zinc alkyls have also been observed. The reaction between zinc dialkyls and primary amines gives a number of structurally diverse products dependent on the reaction conditions and the amine.86 The... 

Homoleptic complexes have been obtained also with tetrakis(l-pyrazolyl)borates, e.g., [ B(pz)4 2Cd] and [ B(3-Mepz)4 2Cd] (both P2 jc, Z = 2) in both compounds structure analyses the ligands have been shown to coordinate trihapto, i.e., with one pz ring free. In both cases Cd has a distorted octahedral environment, with averaged structural data very similar to those for the tris(l-pyrazolylhydridoborate complexes.201 Variable-temperature 3H NMR studies of these and of mixed complexes with tris- and bis(l-pyrazolylhydridoborates indicate fluxional behavior (coalescence temperatures and barriers for the dynamic processes are given). 

This complex is not the actual catalyst for the hydrovinylation, but needs to be activated in the presence of a suitable co-catalyst. The role of this additive is to abstract the chloride ion from the nickel centre to generate a cationic allyl complex that further converts to the catalytically active nickel hydride species. In conventional solvents this is typically achieved using strong Lewis acids such as Et2AlCl. Alternatively, sodium or lithium salts of non-coordinating anions such as tetrakis-[3,5-bis(trifluoromethyl)phenyl]borate (BARF) can be used to activate hydrovinylation... 

A very reactive Lewis acid is obtained when the complex [(EBTHI)Zr(Me)2] is converted in situ to a dicationic species by protonation with the acid H-BARF (BARF = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) in the presence of the Diels—Alder substrate oxazolidi-none [88] (Scheme 8.48). The dicationic species is stabilized through coordination by the oxazolidinone and by diethyl ether (derived from the acid etherate employed). The catalyst loading in the Diels—Alder reaction could be lowered to 1 mol% (Zr) and the reaction still... 

An iridium(I) complex with the l,2-bis(tcrt-butylmethylphosphino)ethane (4) and tetrakis(3,5-bis(trifluoromethyl)phenyl)borate as the counter anion catalyzes the hydrogenation of several acyclic aromatic Ai-arylimines under atmospheric hydrogen pressure at room temperature, giving the desired chiral amines with high-to-excellent enantioselectivities (up to 99%, Fig. 6) [19]. The authors also tested (S )-BINAP (Fig. 1) and (/ )-Ph-PHOX (PHOX = 2-[2-(diphenylphosphino) phenyl]-4,5-dihydrooxazole) hgands with lower enantioselectivities [19]. Both steric and electronic properties of the ligand and the combination with the BArF anion are in the base of the efficacy of this catalytic system. On the other hand, attempted hydrogenations of Ai-(2,2,2-trifluoro-l-phenylethylidene)aniline and M-(l,2,2-trimethyl-propylidene)aniline under the same conditions resulted in... 

After extensive experimentation, a simple solution for avoiding catalyst deactivation was discovered, when testing an Ir-PHOX catalyst with tetrakis[3,5-bis (trifluoromethyl)phenyl]borate (BArp ) as counterion [5]. Iridium complexes with this bulky, apolar, and extremely weakly coordinating anion [18] did not suffer from deactivation, and full conversion could be routinely obtained with catalyst loadings as low as 0.02 mol% [19]. In addition, the BArp salts proved to be much less sensitive to moisture than the corresponding hexafluorophosphates. Tetrakis (pentafluorophenyl)borate and tetrakis(perfluoro-tert-butoxy)aluminate were equally effective with very high turnover frequency, whereas catalysts with hexafluorophosphate and tetrafluoroborate gave only low conversion while reactions with triflate were completely ineffective (Fig. 1). 

Neutral [Re03L] complexes are formed with monoanionic tripodal ligands such as hydrotris-(pyrazolyl)borate (HB(pz)3 ) (17), tetrakis(pyrazolyl)borate (B(pz)4 ) (18), and the phosphite-based Kldui ligand ([cpCo PO(OR)2 3] ) (19) and their derivatives. 

The analogous coordination behavior of hydridotris(pyrazolyl)borate and tetrakis(pyrazolyl)-borate has been demonstrated by numerous reactions. Reduction of the rhenium(VII) complex [Re03 B(pz)4] with PPh3 in THF gives a reactive dimeric intermediate which reacted with monodentate and bidentate protic substrates to yield products with tridentate B(pz)4 ligands... 

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