Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Titanium hydrosilylation

While it is beyond the scope of this chapter to cover the asymmetric hydrosilylation of ketones and imines in any detail, a number of the more catalytically active ML combinations will be mentioned here. A full review of the area has recently appeared.138 Asymmetric hydrosilylation of carbonyl groups is usually performed with rhodium or titanium catalysts bearing chelating N- or P-based ligands. Representative results for some of the most active Rh/L combinations (Scheme 32) for addition of Si H to acetophenone are given in Table 11. [Pg.288]

Among titanium compounds, many sit on the border of being organometallic/coordination compounds. One which is of interest in relation to the enhancing effects of F (see Section 9.5.5.2) is the titanium fluoride complex (52), which is highly active for the hydrosilylation of imines (Scheme 33).143... [Pg.288]

The enantioselective hydrosilylation of 2-pentylcyclopentenone is effected with PMHS and an active catalyst derived from (R.R)-ethylenebis(tetrahydro-indenyl)titanium difluoride and phenylsilane (EBTHI)Ti (Eq. 3 50).587 The use of diphenylsilane, a rhodium catalyst, and (W, / )-(. ,.S )-BuTRAP as the chiral ligand gives similar results.576 Other related approaches give greatly inferior enantioselectivies, 592 594... [Pg.108]

For a review encompassing titanium-catalyzed hydrosilylation of alkenes and carbonyl compounds, see Harrod, J. F. Coord. Chem. Rev. 2000, 206-207, 493-531. [Pg.535]

Particularly noteworthy is the discovery of a new type of the active catalyst 99,103,104 a crystalline, air-stable yellow-orange solid, which can serve as a highly enantioselective tool in the titanium-catalyzed hydrosilylation of imines. The reaction can be highly stereoselective for both acyclic and cyclic imines under a wide range of hydrogen pressures (Scheme 6-46). [Pg.374]

Other metal complexes such as titanium or ruthenium complexes can also be used to catalyze the olefin hydrosilylation reactions. Further information is provided elsewhere.30... [Pg.460]

Buchwald has reported the titanium-catalyzed cyclization/hydrosilylation of 6-hepten-2-ones and 5-heptenals to form silylated cyclopentanols4 As an example, reaction of 6-hepten-2-one and diphenylsilane catalyzed by Gp2Ti(PMe3)2 in the presence of PMes (O.bequiv.) in toluene at —20°C followed by acidic workup gave... [Pg.390]

Titanium-catalyzed cyclization/hydrosilylation of 6-hepten-2-one was proposed to occur via / -migratory insertion of the G=G bond into the titanium-carbon bond of the 77 -ketone olefin complex c/iatr-lj to form titanacycle cis-ll] (Scheme 16). cr-Bond metathesis of the Ti-O bond of cis- iij with the Si-H bond of the silane followed by G-H reductive elimination would release the silylated cyclopentanol and regenerate the Ti(0) catalyst. Under stoichiometric conditions, each of the steps that converts the enone to the titanacycle is reversible, leading to selective formation of the more stable m-fused metallacycle." For this reason, the diastereoselective cyclization of 6-hepten-2-one under catalytic conditions was proposed to occur via non-selective, reversible formation of 77 -ketotitanium olefin complexes chair-1) and boat-1), followed by preferential cyclization of chair-1) to form cis-11) (Scheme 16). [Pg.391]

An interesting example of the highly enantioselective hydrosilylation of imines has been reported by Buchwald and co-workers. A titanium fluoride complex, (5,5)-(EBTHI)TiF2, catalyzes the formation of silylamines in high yields, with good tolerance of functional groups [Eq. (75)].187... [Pg.256]

ASYMMETRIC HYDROSILYLATION OF KETONES AND IMINES WITH TITANIUM CATALYSTS... [Pg.124]

TABLE 2.3. Asymmetric Hydrosilylation of Ketones with Titanium Catalysts ... [Pg.129]

Bis(oxazolinyl)phenylrhodium complex, in styrene asymmetric hydrosilylation, 10, 821 Bis(pentadienyl) complexes preparation and properties, 5, 336 with titanium(II), 4, 265... [Pg.66]

Dimethyl bis-benzamidinato complex, with Ti(IV), 4, 344 Dimethyl carboranes, with tantalum, 5, 163 Dimethyl complexes with cadmium, 2, 464 with nickel, 8, 58-59 with platinum(II), 8, 460 with titanium(IV), 4, 331, 4, 343 Dimethyl diallylmalonate, cyclization-hydrosilylation, 11, 385 Dimethyl diamido complexes, with Ti(IV), 4, 332... [Pg.97]

Highly enantioselective hydrosilylation of the imine 144 was achieved using (S,S)-(ebthi)titanium difluoride as a catalyst precursor to give the optically active benzylamine 145 with 99% ee in 95% after acidic workup [85],... [Pg.413]

The utilization of allyl alcohol as the nucleophilic reagent to prepare dendritic carbo-siloxanes was also reported by Lang and Brilning134,135. Using a second generation allyl-terminated carbosiloxane dendrimer, they were able to attach titanium moieties via a simple hydrosilylation reaction (equation 12)134. Lang and coworkers were also successful in binding cobalt moieties to ethynyl-terminated carbosiloxane dendrimers (e.g. equation 13)136,137. [Pg.774]

Furthermore, over the past 15 years, it has also been demonstrated that titanium(m) complexes can be used as catalysts in organic transformations. Complexes containing a Ti(m) center have been shown to be active catalysts for the hydrosilylation of lactones, esters, and ketones and have also been used to reduce both aryl and alkyl halides, ketones, aldehydes, aromatic azo compounds, and epoxides. These organic applications of titanium(m) complexes are beyond the scope of this chapter. [Pg.282]

The titanium complexes bearing <9-phosphinophenoxo ligands shown in Scheme 380 are prepared by metallation of the corresponding phenol followed by reaction with CpTiCl3. The complexes were found to be fluxional by H NMR analysis at low temperature. The X-ray structure shows that in the solid state the molecule is chiral at the metal center. These complexes are effective catalysts for olefin hydrogenation and imine hydrosilylation.911... [Pg.487]

Hydrosilylation of unsaturated organic molecules is an attractive organic reaction. Asymmetric hydrosilylation of prochiral ketones or imines provides effective routes to optically active secondary alcohols or chiral amines (Scheme 756). These asymmetric processes can be catalyzed by titanium derivatives. The ( A ebthi difluoro titanium complex has been synthesized from the corresponding chloro compound.1659 This compound results in a very active system for the highly enantioselective hydrosilylation of acyclic and cyclic imines and asymmetric hydrosilylation reactions of ketones including aromatic ketones.1661,1666,1926-1929 An analogous l,l -binaphth-2,2 -diolato complex catalyzes the enantioselective hydrosilylation of ketones.1... [Pg.658]

Equation 11.14. Titanium catalyzed tandem hydroamination/hydrosilylation of aminoalkynes [133]. [Pg.369]

In the case of the hydrosilylation of C=N bonds, extremely high levels of enantioselectivity were dramatically realized by use of the (tetrahydroinde-nyl)titanium(IV) fluoride T4 (Fig. 12) by Buchwald in 1996 [55]. The in situ catalyst uniquely derived by mixing the titanocene fluoride T4 (1.0-0.02 mol %) with phenylsilane PhSiHj (1.5 eq referred to ketone) as hydrogen atom donor reduces the imines 13-17 (Fig. 13) to the amines A3-A7 in 80-96% yields (Table 3). An alternative activation method for the titanocene by addition of methanol and pyrrolidine was also described. In this case, the imine from acetophenone and methylamine, 13, was converted at room temperature to 35 °C to give the corresponding secondary amine in 94-95% yield with 97-99% ees (S). Moreover, alkylimines were also reduced in 92-99% ees. [Pg.285]

Table 3. Asymmetric hydrosilylation of imines with the chiral titanium catalyst (S,S)-(EBT-HI)Tip2 (T4)... Table 3. Asymmetric hydrosilylation of imines with the chiral titanium catalyst (S,S)-(EBT-HI)Tip2 (T4)...

See other pages where Titanium hydrosilylation is mentioned: [Pg.327]    [Pg.517]    [Pg.206]    [Pg.391]    [Pg.125]    [Pg.125]    [Pg.821]    [Pg.130]    [Pg.184]    [Pg.260]    [Pg.490]    [Pg.497]    [Pg.541]    [Pg.610]    [Pg.618]    [Pg.80]    [Pg.120]    [Pg.269]    [Pg.284]    [Pg.284]    [Pg.169]    [Pg.108]    [Pg.284]   
See also in sourсe #XX -- [ Pg.99 , Pg.464 ]




SEARCH



Hydrosilylation titanium catalysed

© 2024 chempedia.info