Phosphine titanium complex

We reported a catalytic enantioselective cyanosUylation of ketones that produces chiral tetrasubstituted carbons from a wide range of substrate ketones [Eq. (13.31)]. The catalyst is a titanium complex of a D-glucose-derived ligand 47. It was proposed that the reaction proceeds through a dual activation of substrate ketone by the titanium and TMSCN by the phosphine oxide (51), thus producing (l )-ketone cyanohydrins ... 

For several of these bidentate phosphine assemblies crystal structures were obtained. Figure 10.13 (Table 10.8) shows the crystal structure of octahedrally coordinated titanium complex 39. 

To date, the hydrofunctionalization route has mainly been used to prepare PBs. Both conceivable strategies, namely the hydroboration of unsaturated phosphines and the hydrophosphination of unsaturated boranes have been reported (Scheme 25). With dialkyl and diarylboranes, the reactions proceed spontaneously under mild conditions, while the addition of boronates HB(OR)2 is catalyzed by a titanium complex, and the... 

The present interest in asymmetric catalysis was demonstrated by awarding Nobel prizes to three winners W. S. Knowles (USA) for elaboration of rhodium complex catalysts effective in asymmetric synthesis of anti-Parkinson medicine, R. Noyori (Japan) for elaboration of a new catalytic system based on chiral ruthenium-phosphine complex catalysts that are very effective in hydrogenation reactions, and B. Sharpless (USA) for elaboration of epoxidation and other reactions under the action of chiral titanium complexes. 

Amines and nitriles facilitate the complexation of metals such as Fe, Ti, W, and Ru. In this work, functionalized phenols are attached to the ring, followed by metal complexation. Titanium complexes (36) and (37) are examples. Similar binding chemistry employing Mn is accomplished through a phenyl phosphine moiety in place of the nitrile. Metals also can add to unsaturated bonds yielding new complexes. For example, a... 

C10H15N, Benzenemethanamine, N,N,4-trimethyl-, lithium complex, 26 152 C10H15P, Phosphine, diethylphenyl-, nickel complex, 28 101 platinum complex, 28 135 CioHigAsi, Arsine, 1,2-phenylenebis(dimethyl-, gold complex, 26 89 nickel complex, 28 103 CioHie, 1,3-Cyclopentadiene, 1,2,3,4,5-pen-tamethyl-, 28 317 chromium complex, 27 69 cobalt complexes, 28 273, 275 iridium complex, 27 19 samarium complex, 27 155 titanium complex, 27 62 ytterbium complex, 27 148 CioH,gBrN04S, Bicyclo[2.2.1]heptane-7-methanesulfonate, 3-bromo-1,7-di-methyl-2-oxo-, U.IRHENDO, ANTPi]-, ammonium, 26 24... 

An unsymmetrical salen ligand bearing a Lewis base catalyses Ti(OPr-i)4-promoted addition of TMSCN to benzaldehyde with as little as 0.05 mol% loading, quantitative conversion is achieved in 10 min at ambient temperature. Another salen catalyst - a bifunctional salen-phosphine oxide-Ti(IV) combination - promotes enantioselective cyanosilylation of aldehydes. Fine tweaking of the structure of another series of bifunctional chiral salen-Ti(IV) complexes allows the enantioselectivity to be reversed. Biaryl-bridged salen-titanium complexes are also highly efficient catalysts, one example giving 87% ee at room temperature. ... 

While the majority of group 4B metal carbonyl complexes contain 7r-bonded hydrocarbon ligands, most notably 17-cyclopentadienyl, recent studies by Wreford and co-workers have led to the identification and isolation of three novel phosphine-stabilized titanium carbonyl complexes (12,13). 

Treatment of 4 with either PF3 or 13CO results in CO substitution believed to proceed via a dissociative process yielding Ti(CO)2(PF3)-(dmpe)2 (6) and Ti(13CO)3(dmpe)2. Structural characterization of 6 showed it also to be monomeric, but possessing a monocapped trigonal prismatic geometry. Complexes 4, 5, and 6 may be considered phosphine-substituted derivatives of the as yet unisolated Ti(CO)7, thus representing the only isolable titanium carbonyl complexes where the titanium atom is in the zero oxidation state. 

The IR and XH-NMR spectral data for the various titanocene mono-carbonyl-phosphine complexes are compiled in Table III. Examination of the carbonyl stretching frequencies (Table III) nicely demonstrates the enhanced 7r-backbonding of the titanium center to CO as the -accepting ability of the phosphine ligand decreases. 

A major advantage that nonenzymic chiral catalysts might have over enzymes, then, is their potential ability to accept substrates of different structures by contrast, an enzyme will select only its substrate from a mixture. Striking examples are the chiral phosphine-rhodium catalysts, which catalyze die hydrogenation of double bonds to produce chiral amino acids (10-12), and the titanium isopropoxide-tartrate complex of Sharpless (11,13,14), which catalyzes the epoxidation of numerous allylic alcohols. Since the enantiomeric purities of the products from these reactions are exceedingly high (>90%), we might conclude... 

Diaminocarbene complexes were reported as early as 1968 [152], Preparation and applications of such complexes have been reviewed [153], Because of 7t-electron donation by both nitrogen atoms, diaminocarbenes are very weak tt-acceptors and have binding properties towards low-valent transition metals similar to those of phosphines or pyridines [18,153]. For this reason diaminocarbenes form complexes with a broad range of different metals, including those of the titanium group. Titanium does not usually form stable donor-substituted carbene complexes, but rather ylide-like, nucleophilic carbene complexes with non-heteroatom-substituted carbenes (Chapter 3). 

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