Mono titanium complexes

We were particularly interested to see whether a regio- and stereoselective hy-droxyalkylation and amrnoalkylation of 1 and 2 with aldehydes and imino esters, perhaps by choice of the substituent X at the Ti atom, with formation of the corresponding sulfonimidoyl-substituted homoallyl alcohols 4-7 and the homoallyl amines 8-11 (Fig. 1.3.3) could be achieved. Reggelin et al. had already demonstrated that the sulfonimidoyl-substituted mono(allyl)titanium complexes 3, the... 

The lithiation of the T-configured acyclic allyl sulfoximines T-13 with n-BuLi gave the corresponding lithiated allyl sulfoximines -15 [15] which upon treatment with 1.1 equiv ofClTi(OiPr)3 at-78 to 0 °C in THF furnished the bis (allyl) titanium complexes -16, admixed with equimolar amounts of Ti(OiPr)4, in practically quantitative yields (Scheme 1.3.5) [14, 16]. Surprisingly the bis (allyl) titanium complexes -16 together with Ti(OiPr)4 and not the corresponding mono (allyl) titanium complexes were formed. 

Reaction of the bis(allyl) titanium complexes 16 and 18 with aldehydes occurs in a step-wise fashion with intermediate formation of the corresponding mono (allyl) titanium complex containing the alcoholate derived from 4 and 5 as a ligand at the Ti atom. Then the mono(allyl)titanium complexes combine with a second molecule of the aldehyde. Both the bis (allyl) titanium complexes and the mixed mono(allyl)titanium complexes react with the aldehydes at low temperatures with high regio- and diastereoselectivities. Interestingly, control experiments revealed that for the reaction of the bis (allyl) titanium complexes with the aldehyde to occur the presence of Ti(OiPr)4 is required, and for that of the intermediate mono(allyl)titanium complexes the addition of ClTi(OiPr)3 is mandatory (vide infra). 

The treatment of the lithiated allyl sulfoximines E-15 with 1.1-1.2 equiv of ClTi(NEt2)3 at -78 to 0°C in THF or ether afforded the corresponding mono (allyl) titanium complexes E-19 in practically quantitative yields (Scheme 1.3.7) [14, 16]. Similarly the Z-configured complexes Z-19 were obtained from the Z-configured allyl sulfoximines Z-15. Reaction of the titanium complexes E-19 with aldehydes at -78 °C took place at the a-position and gave the corresponding homoallyl alcohols 6 with >98% diastereoselectivity in medium to good yields (Scheme 1.3.8) [14, 16]. 

However, a more detailed study of the reaction of the mono(allyl)titanium complexes -19 carrying different alkyl groups at the double bond with different aldehydes revealed in some cases the highly diastereoselective (>98%) formation of significant amounts of the isomeric homoallyl alcohols 4 besides 6 (Table 1.3.1). 

Scheme 1.3.7 Synthesis of chiral sulfonimidoyl-substituted mono(allyl)titanium complexes.

Table 1.3.1 Reaction of the acyclic mono(allyl)titanium complexes -19 with aldehydes.

Table 1.3.3 Reaction of the cyclic mono(allyl)titanium complexes 20 (n = 1) with aldehydes.

Surprisingly, the mono (allyl) titanium complexes 19 reacted with the imino ester 23c also at the y-position with high diastereoselectivities and gave the unsaturated... 

Amidocarbonylation aldehydes, 11, 512 enamides, 11, 514 overview, 11, 511-555 Amido complexes with bis-Cp titanium, 4, 579 Group 4, surface chemistry on oxides, 12, 515 Group 5, surface chemistry on oxides, 12, 524 with molybdenum mono-Cp, 5, 556 with mono-Cp titanium(IV) alkane elimination, 4, 446 amine elimination, 4, 442 characteristics, 4, 413 via dehalosilylation reactions, 4, 448 HCL elimination, 4, 446 metathesis reactions, 4, 438 miscellaneous reactions, 4, 448 properties, 4, 437... 

A particularly interesting example of CO displacement involves the photochemical reaction of the early transition metal complexes [M(>/5-C5H5)2(CO)2] (M = Ti, Zr, Hf) with PF3 (Scheme 10). In the case of (M = Hf) this complex represented the first hafnocene-phosphine complex to be reported. A slightly better synthetic route to the mono(trifluorophosphine)titanium(II) complex involves displacement of PEt3 from [Ti( /5-C5H5)2(CO)(PEt3)]. 

Mono-Cp titanium derivatives show reactivity as catalyst precursors for olefin polymerizations, particularly for the polymerization of styrene and functionalized monomers. A review highlighting the developments in the design and applications of non-metallocene complexes, including mono-Cp derivatives, as catalyst systems for a-olefin polymerization has appeared.440 Titanium complexes bearing Cp in addition to chloro ligands and activated by aluminum... 

DFT calculations combined with molecular mechanics methods have been used to study the first (R = Me) and the second (R = propyl) insertion of the ethylene monomer into the Ti-R bond of (CpSiMe2NBut)(R)Ti(/t-Me)B(C6F5)3. The influence of the counterion and the solvent effects on the energetic profile of the polymerization have been evaluated. Theoretical investigations have also been directed at mechanistic aspects of olefin polymerizations catalyzed by mono-Cp titanium complexes. The chain propagation mechanism, the chain termination and... 

Scheme 350 shows the structures of a number of mono-Cp titanium complexes with more elaborately substituted aryloxo ligands. The compounds are formed by the reaction of Cp TiCl3 with 1 equiv. of the substituted phenol in the presence of an excess of pyridine or by treatment of the lithium phenoxide with Cp TiCl3 some of them have been... 

The synthesis and characterization of the indenyl species (l-MeInd)TiCl2(OR) (R = Me, Et, Pr1, Bu, cyclo-C Hu) have been reported. They have been applied as catalysts for the syndiotactic polymerization of styrene.878 Binuclear mono-Ind titanium(iv) complexes have been synthesized by reaction of TiCl(OPr )3 with the lithium salt of the bis-indene reagent. [(-CH2-l-Ind)Ti(OPr )3]2 is obtained as a 1 1 rac- and meso-mixture (Scheme 184 Section 4.05.3.1.l.(vii)).417... 

Mono-Cp titanium binuclear complexes with trisiloxane bridges have been synthesized. In the presence of MMAO, these complexes initiate the polymerizations of ethylene and styrene.938... 

Macrocyclic mono-Cp titanium(iv) complexes with peptide-derived ligands coordinated to the titanium atom have been described by the reaction of the pseudo-nonapeptide with 3 equiv. of NaOMe in CH2C12 and subsequent reaction with Cp TiCl3 (Cp = Cp, Cp ) (Scheme 395). The molecular structure of the Cp derivative has been determined by X-ray diffraction and shows a distorted pseudo-octahedral titanium environment.939... 

Ethane- and propane-1,2-dithiolato Cp titanium derivatives have been reported. They are reduced by boron and tin hydrides.1013,1014 Mono-Cp titanium(iv) sulfido complexes have been made by treatment of CpTiCl3 with dithiols in the presence of donor ligands such as imidazole or PMe3 under different reaction conditions (Scheme 418).1015 The structures of the compounds have been reported. Electrochemical studies suggest that these compounds are formed through a radical mechanism.1016... 

A more recent and in-depth polymerization study of a tight bite angle A,0-chelated early transition metal being utilized for alkene polymerization was presented by Sun s group [10b] in 2010. A set of bis(chloro)mono(cyclopentadienyl)mono(amidate) titanium complexes, in a half-sandwich configuration, were synthesized. Electronic... 

Reduction of the group 4 M(IV) center by MAO or trialkylaluminum to lower-valent species is a common phenomenon, especially for titanium complexes and sometimes for zirconium complexes as These reductive processes are not considered to be deactivation but rather part of generating the true catalytically active species in the case of mono-Cp titanium complexes for syndiospe-cific styrene polymerization (vide supra). Addition of a monomer to an active catalytic system often surprisingly increases the quantity of Ti(III) ° or Zr-... 

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