Titanium complexes organic reactions

Bis(cyclopentadienyl)titanium(II) dicarbonyl complexes, preparation and reactivity, 4, 250 Bis(cyclopentadienyl)titanium(II) dinitrogen complexes, preparation and reactivity, 4, 250 Bis(cyclopentadienyl)titanium halides ligand metathesis reactions, 4, 537 olefin polymerization, 4, 538 organic reactions, 4, 540 properties, 4, 530 reductions, 4, 532 synthesis, 4, 510... 

Mukaiyama Aldol Condensation. As expected, the chiral titanium complex is also effective for a variety of carbon-carbon bond forming processes such as the aldol and the Diels-Alder reactions. The aldol process constitutes one of the most fundamental bond constructions in organic synthesis. Therefore the development of chiral catalysts that promote asymmetic aldol reactions in a highly stereocontrolled and truly catalytic fashion has attracted much attention, for which the silyl enol ethers of ketones or esters have been used as a storable enolate component (Mukaiyama aldol condensation). The BINOL-derived titanium complex BINOL-TiCl2 can be used as an efficient catalyst for the Mukaiyama-ty pe aldol reaction of not only ketone si ly 1 enol ethers but also ester silyl enol ethers with control of absolute and relative stereochemistry (eq 11). ... 

Asymmetric [2 + 2] cycloaddition reaction affords a practical means of synthesis of optically active cyclobutanes, which can be used as useful intermediates in organic synthesis [138]. Narasaka reported that asymmetric [2 -i- 2] cycloaddition between acryloyl oxazolidinone derivatives and bis(methylthio)ethylene proceeded with high enantios-electivity when catalyzed by TADDOL-derived titanium complex (Sch. 58) [139]. The cyclobutane product was transformed into carbocyclic oxetanocin analogs or (-n)-grand-isol [140]... 

Redox and metathetical reactions are covered in this section. Some of these reactions lead to specific complexes with Ti-O, Ti-N, and Ti-G bonds which could be alternatively collected in subsequent sections. Comments on the applications of the bis-Cp dihalo titanium complexes as olefin polymerization pre-catalysts and reagents in organic... 

The extensive use of Cp -titanium complexes in the development of organic synthetic methodology is beyond the scope of this chapter. We include here some examples of the various reaction types in which titanium(iv) derivatives are used as reagents in organic synthesis, although no attempt has been made to cover this subject comprehensively. Section 4.05.8 covers additionally an overview of the applications of titanium complexes in stoichiometric and catalytic organic reactions. 

The use of bis-Cp titanium complexes as catalytic systems for reductive transformations via one-electron transfer in organic reaction has been reviewed.1... 

The chemistry of bis(alkynyl) metal complexes, including the titanium derivatives, focusing on the synthesis, chemical behavior, structure, and bonding of different type of mononuclear and heterometallic molecules has been discussed in a review.1280 A review focusing the preparation and the reactivity of compounds of the type Cp 2Ti-(ct-C=CR)2 (Cp = Cp, Gp ) has appeared which summarizes special aspects of C-C coupling and cleavage processes in organic reactions.1281... 

Titanium enolato complexes have been used as important synthetic carbon nucleophiles in stereoselective organic reactions. However, synthetic, structural, and characterization aspects of this type of complexes are rather scarce, because they are generally used in situ rather than in isolated form. 

The racemo-pair of a new ansa-titanium complex (Scheme 636) is obtained by the reaction of the lithium salt of the corresponding substituted cyclopentadienyl organic molecule with TiCl3 in diethyl ether/toluene followed by oxidation with HC1. One of the racemo-forms was isolated as a pure substance and its structure determined by X-ray diffraction.1650... 

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... 

A bimetallic titanium complex of BINOL derivative can be used to catalyze the asymmetric carbonyl-ene reaction [46]. Insoluble polymeric catalyst 74 was prepared from a self-assembly of Ti(OiPr)4 and non-crosshnked copolymers with (R)-binaphthol pendant groups (Scheme 3.22) [47]. The self-assembled polymeric Ti complex is insoluble in organic solvent and catalyzed the carbonyl-ene reaction of glyoxylate 75 and a-methylstyrene 76. When the reaction of 75 and 76 was carried out with 20mol% of 74 in Gl pCf at room temperature, an 85% yield of the product with 88% ee was obtained. Following its recovery by filtration, this catalyst was reused five times with full retenhon of its activity and enantioselectivity, without further treatment... 

Alkyl complexes of titanium have been extensively studied both from the point of view of the nature of the metal-carbon bond as well as their application as alkylating reagents in organic reactions [4-6,20,21], The simplest methyl complex, MeTiCl3 (8), is readily obtained by the reaction of TiCl4 with half an equivalent of ZnMe2 [22,23]. An ether adduct of 8 is synthesized by treatment of TiCl with an ethereal solution of MeLi [24]. Alkoxy substitution on titanium stabilizes the methyl complexes. Reaction of TiCl(0 Pr)3 (9) with MeLi affords MeTi(O Pr)3(10), which is thermally very stable and can be distilled under reduced pressure (48-53 °C/0.01 mmHg) [25], The phenyl derivative 11 is prepared by the similar reaction of 9 with PhLi. 

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