Trityl tetrakis borate

The authors conducted a similar investigation of precatalysts 7 and 11 using TiBA and trityl tetrakis(pentafluorophenyl)borate as the cocatalyst. They concluded that this material contained no fraction that could be characterized as blocky. It was therefore proposed that reversible chain transfer occurred only with MAO or TMA and not with TiBA. This stands in contrast to the work of Chien et al. [20] and Przybyla and Fink [22] (vida supra), who claim reversible chain transfer with TiBA in similar catalyst systems. Lieber and Brintzinger also investigated a mixture of isospecific 11 and syndiospecific 12 in attempts to prepare iPP/sPP block copolymers. Extraction of such similar polymers was acknowledged to be difficult and even preparative temperature rising elution fractionation (TREF) [26, 27] was only partially successful. 

Rieger et al. described a heteroatom-containing C, symmetric metallocene 13 whose stereoselectivity depended on the activator [28, 29], The resulting PP contained fewer stereoerrors when activated with a combination of TiBA and trityl tetrakis(pentafluorophenyl)borate than with MAO. In addition, the molecular weight was lower with MAO. To explain this, it was proposed that some of the stereoerrors arise by reversible chain transfer to aluminum. 

Indeed, a variety of Lewis acids have been shown to effed glycosylation with hemiacetal donors. Ernst and coworkers have used 5mol% of [Rh(III)(MeCN)3 (triphos)] tris(triflate) with 4 A molecular sieves to prepare glycoconjugates 18 and 19 [26]. Mukaiyama s group has used trityl tetrakis(pentafluorophenyl)borate (3-5 mol%) with Drierite in the preparation of disaccharides 20 and 21 [27,28]. In the synthesis of 21, the a-seledivity was shown to arise from in situ anomerization of the (1-pyranoside over time. 

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. 

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]. 

Benzylic silyl ethers couple with allylsilanes in the presence of trityl tetrakis [3,5-bis(trifluoromethyl)phenyl]borate (TFPB) catalyst leading to carbon-carbon bond formation (equation 77). The corresponding Z11CI2-catalyzed reactions with an allyl silyl ether lead to a mixture of regioisomers145,146. 

Takeuchi K, Tamura T, Mukaiyama T. The trityl tetrakis(penta-fluorophenyl)borate catalyzed stereoselective glycosylation using new glycosyl donor, 3,4,6-tri-0-benzyl-2-0-/j-toluoyl-beta-D-glucopyranosyl phenylcarbonate. Chem. Lett. 2000 2 122-123. 

Takeuchi, K, Mukaiyama, T, Trityl tetrakis(pentafluorophenyl)borate catalyzed stereoselective glycosylation using glycopyranosyl fluoride as a glycosyl donor, Chem. Lett, 555-556, 1998. 

Jona, H, Takeuchi, K, Saitoh, T, Mukaiyama, T, Effective activation of armed thioglycoside with a new combination of trityl tetrakis(pentafluorophenyl)borate [TrB(C6p5)4] and iV-(ethylthio)phtha-limide (PhthNSEt), Chem. Lett., 1178-1179, 2000. 

Uchiro, H, Mukaiyama, T, An efficient method for catalytic and stereoselective glycosylation with thioglycosides promoted by trityl tetrakis(pentafluorophenyl)borate and sodium periodate, Chem. 

Shortly thereafter (1994), Kira, Sakurai, and coworkers reported a very similar reaction of tributhyltin hydride with trityl tetrakis[3,5-di(trifluoromethyl)phenyl]borate in CD2Cl2. The resulting species, which they called a trivalent tin cation, had a chemical shift of 5 356 at —20 °C. The material decomposed above this temperature and reacted with ethyl ether at —70 °C to give a more solvated species [ Bu3Sn(Et20)+ ] with a chemical shift of 5 165 at —20 °C. 

Cations 1, with different substituents X, can be synthesized by hydride transfer reactions [3] from 2,5-disilaheptanes 2. The reaction of 2 with one equivalent trityl tetrakis(pentafluorophenyl) borate (TPFPB) in benzene at room temperature yields the trivalent silylium ions 3 and triphenylmethane (Scheme 1). The silylium ions 3 are only transient species and undergo intramolecular cyclization which yield the cations 1. 

In addition to differences in polymer microstructures caused by cocatalyst (activation with MAO versus borate activation), some specific particularities are noticed with regards to the influence of additional parameters on polymerization results using different cocatalysts. For the 5,6-ethoxy-substituted indenyl zirconium complexes 10a and 10b (Figure 9.9), where 10a is activated with MAO and 10b with trityl tetrakis(pentafluorophenyl)borate, [Ph3C]+[B(C6F5)4] , it has been found that the mmmm pentad concentration of the polymer products varies over a broad range (33-56%) depending on temperature and monomer concentration but is independent of the Al/Zr ratio (Table 9.i).99,i00,i03... 

The first carbene-stabilized phosphorus mononitride was also synthesized using CAAC A [222], Reaction of SIPr=N-PCl2 with CAAC A, followed by reduction with magnesium metal, afforded the phosphorus mononitride adduct stabilized by one SIPr NHC and one CAAC A (Figure 15.54). This molecule features a P-N distance of 1.7085(16) A as measured by X-ray crystallography. Oxidation using trityl tetrakis(pentafluorophenyl)borate gave the radical cation as a dark-brown-colored microcrystalline solid. EPR spectroscopy in fluorobenzene... 

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