Tetrakis -borate salts

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... 

Another important bioanalytical application of voltammetric ISEs is the detection of polyions (see also above). A technique using cyclic voltammetry on micropipette electrodes filled with the organic electrolyte solutions in 1,2-dichloroethane was successfully applied for the detection of protamine [65] in saline solution and heparin in undiluted sheep plasma samples [66]. Protamine transport was facilitated with dino-nylnaphthalenesulfonic acid (DNNS). As a heparin-selective component the tetrakis-(4-chlorophenyl)borate salt of trimethyloctadecyl ammonium was used. 

The catalytic activity of the oxoisoindolium salt 54 and 55 was compared to that of trityl tetrakis[pentafluorophenyl]borate salts in the addition reaction of enol acetate to benzaldehyde and glycosylation reaction (Scheme 59) [151, 152]. 

The silicon analogs of carbocations have been reported a number of times [131], but there is only one confirmed sighting to date, the highly hindered trimesitylsilicenium ion as its tetrakis(pentafluorophenyl)borate salt [132] ... 

Dialkyl metallocenes and other dialkyl Group 4 transition metal complexes are useful as precatalysts in combination with co-catalysts such as tris(perfluoro-aryl)boranes or tetrakis(periluoroaryl)borate salts [18]. Recently, an expedient procedure for the production of dimethyl metallocenes and Cp-amido dimethyl metal complexes in high yields and purity has been reported. The direct synthesis of Group 4 dimethylmetallocenes [19] consists of the one-pot reaction between the r-ligand, a 2-fold excess of MeLi, and MtCU. This simple method produces the dimethylated complexes in higher overall yield, and saves on reaction time and solvents, compared to the classic two-step route, which consists in the synthesis of the metallocene dichloride followed by its methylation with 2 equiv. MeLi. 

Fig. 8. Profiles of percentage conversion vs time for various illumination times for photopolymerizations of phenyl glycidyl ether initiated using 8.86 xnM of iodonium tetrakis pentafluorophenyl borate salt at 50°C and light intensity of 25 mW cm (see reference 150). Full illumination — 90-s illumination — 60-s illumination ----30-s...

From dihydrobis(l-imidazolyl)borate or tetrakis(l-imidazolyl)borate and silver salts the interesting mixed tetrametallic macrocycles 24 and 25 (Fig. 8) are prepared in high yields (40-60%) [36]. 

Suitable electrolytes for the aqueous phase (w) comprise, for example, LiCl, HCl, MgCl2, MgS04, while suitable electrolytes for the organic phase (o) comprise salts of, for example, tetrabutylammonium, tetraphenylarsonium, or bis(triphenyl-phosphoranylidene)ammonium cations with tetraphenylborate, tertrakis(4-chloro-phenyl)borate, or tetrakis[3,5-bis(trifluoromethyl)phenyl]borate anion. 

These rod-shaped ligands share a sterically efficient terminal N-donor and their divalent Co chemistry is well established. They will be discussed here only with selected examples. [Co (NCMe)6](TFPB)2 (TFPB- = tetrakis(3,5-bis(trifhioromethyl)phenyl)borate)) has been synthesized and characterized in the solid state along with a number of other divalent transition metal analogs.357 As a result of the extremely poor coordinating ability of the anion and facile loss of MeCN ligands from the cation, the salt is an excellent source of naked Co2+ ions. Thermolysis up to 100 °C leads to the loss of one MeCN and formation of a r -bound nitrile, whereas above 130 °C decomposition occurs with loss of MeCN and abstraction of fluoride from the anion to form CoF2. 

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... 

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). 

In 1998 the groups of Jprgensen and Helmchen reported the preparation of the chiral silyl cationic salt 2 (Scheme 3) [30]. This was the first time that a chiral silyl cation was used as a catalyst in an enantioselective reaction, hi order to ensure that the silyl salt had a high reactivity, the almost chemically inert and non-coordinating anions tetrakis[pentafluorophenyl]borate [TPFPB] and tetrakis[3,5-bis (trifluor-omethyl)phenyl]borate [TFPB] were chosen as counter anions. 

Since silyl cations are highly reactive and moisture sensitive, the salts (S)-2a and (S)-2b were prepared in situ from the air and moisture stable precursor (S)-5 via a hydride transfer [34, 35] with trityl tetrakis[3,5-bis(trifluoromethyl)phenyl]borate [Tr][TFPB] or trityl tetrakis[pentafluorophenyl]borate [Tr][TPFPB], The authors showed by Si-NMR studies that the desired salts were formed. The silyl salt (5)-2a was then tested in the Diels-Alder reaction as shown in Scheme 5. A good reactivity was found, and the product was obtained in 95% yield with higher than 95% endo selectivity at -40 °C in 1 h. However, only 10% ee was achieved. 

BF24NaC32Hi2, Borate, tetrakis(3,5-bis(trifluor-omethyl)phenyl)-, sodium salt, 34 5... 

C30H24O4P2W, Tungsten(O), tetracarbonyl 1,2-bis(diphenylphosphino)ethane -, 34 108 C32Hi2BF24Na, Borate, tetrakis(3,5-bis(trifluoro-methyl)phenyl)-, sodium salt, 34 5 C32H29FeNP2, Iron(II), cyano( ) -cyclopentadie-nyl)-l,2-bis(diphenylphosphino)ethane-, 34 161... 

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