Tert-Butoxide ligand

The dominant Ti(tartrate) species is a dimer (Fig. 1.18a), as deduced on the basis of FTIR and NMR measurements [490]. The hydroperoxide is coordinated to Ti in r 2 bidentate fashion (Fig. 1.18b) [492] as indicated by the observation that Kgq for TBHP is less than 1.0 with both Ti(DlPT)(O-z-Pr)2 and Ti(DlPT)(O-f-Bu)2, and supported by DFT calculations [493,494] (DIPT = diisopropyltartrate). This implies that TBHP is sterically more demanding than zso-propoxide or tert-butoxide ligands, unlikely unless bidentate coordination of the alkyl peroxide were important [489]. 

Stereoblock copolymers comprised of a sequence of high-trans poly(2,3-(CF3)2NBD) followed by a sequence of high-cis poly(2,3-(CF3)2NBD) are obtained when ROMP is carried out initially with 16a and the tert-butoxide ligands are subsequently replaced by hexafluoro-tm-butoxide before... 

Di-tert,-butylphosphino)-biphenyl has been used by Buchwald [5] et al. as the most efficient ligand in the Pd-catalyzed amination of aryl chlorides. 2-Chloro-4-methyl-toluene can be aminated with pyrrolidine in 98% yield using sodium-tert.-butoxide [eq. (e)]. 

The bulky ligands PPh3 and AsPh3 add to the unsubstituted end of 31 (180,181). The resulting phosphonium salt (32) is deprotonated by butyllith-ium at — 78°C to yield an ylid (33) which reacts with aldehydes in a Wittig reaction. Deprotonation with potassium tert-butoxide followed by addition of aldehyde 34 gives the E isomer (35) only [Eq. (20)] (182). Trimethylphosphite... 

The Buchwald-Hartwig reaction was performed under a variety of conditions starting with the model compounds and leading up to target substrate. The results are shown in Table 3. There was a 70 % yield obtained in the reaction of triflate 35 with the cyclic secondary amine morpholine using condition A (entry l),32 however the reaction fails with diphenethylamine (entry 2). Changing the base to sodium tert-butoxide (condition B) or the catalyst to Pd2(dba)3 and ligand (condition C) also resulted in no reaction (entries 3 and 4). 

For the case of tri(o-tolyl)phosphine-ligated catalysts, the upper pathway appears to predominate. Oxidative addition occurs first via loss of a ligand from the bisphosphine precursor to form the oxidative adduct, which exists as a dimer bridged through the halogen atoms (equation 33). This dimer is broken up by amine, the coordination of which to palladium renders its proton acidic. Subsequent deprotonation by base leads to the amido complex, which can then reductively eliminate to form the product. When tert-butoxide is used as the base, the rate is limited by formation of and reductive elimination from the amido complex, while for the stronger hexamethyldisilazide, the rate-determining step appears to be oxidative addition. ... 

Zim and Buchwald synthesized the palladacyclic phosphine complex 44 based on their ligand P(Bu-f)2(o-biphenyl) 13 (equation 46)157. This air- and moisture-stable palladium complex is a convenient one-component precatalyst for animation of aryl chlorides when combined with sodium tert-butoxide or sodium methoxide. For coupling of anilines, the addition of NEt3, which is possibly acting as the reducing agent to produce Pd(0), is necessary. 

By far the most frequently used method is the deprotonation with potassium tert-butoxide, which gives the potassium salts in nearly quantitative yields. The method seems to be usable for any bis(chalcogenophosphinyl and -phosphoryl)imide and has been employed for a broad diversity of derivatives, regardless of the nature of the chalcogen.2,26,30,33,36-38,49,89,91,99 If the salts are needed for further use in reactions with metal halides to form complexes, the potassium salt can be used in situ, without isolation, e.g., with zinc(II) chloride or palladium and platinum chloro complexes.41,43 Potassium metal in THF also forms the salt K[SPh2PNPPh2S] in 82% yield, 38 but the method is not practical for preparative purposes. Potassium-crown ether complexes, [K(18-crown-6)][Q1Ph2PNPPh2Q1] with Q1 = O,92 Q1 = S,93 and Q1 = Se,98 have been prepared by direct complexation of the potassium salt with the macrocyclic ligand. 

As can be seen from Table 1 sodium tert-butoxide gives similar results compared to lithium amides as base (entries 1 and 2). Both are superior to lithium tcrt-butoxide (entries 3 and 4). Since NaOtBu is easier to handle it seems to be the base of choice for this reaction. With tri-o-tolylphosphine as ligand the procedure is limited to secondary amines. Nevertheless, some application of this new method - mainly from industrial... 

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