Ethylenebis titanium

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... 

The first isolable alkenetitanium complex, the bis(pentamethylcyclopentadienyl)-titanium—ethylene complex 5, was prepared by Bercaw et al. by reduction of bis(penta-methylcyclopentadienyl)titanium dichloride in toluene with sodium amalgam under an atmosphere of ethylene (ca. 700 Torr) or from ( (n-C5Mc5)2Ti 2(fJ-N2)2 by treatment with ethylene [42], X-ray crystal structure analyses of 5 and of the ethylenebis(aryloxy)trimethyl-phosphanyltitanium complex 6 [53] revealed that the coordination of ethylene causes a substantial increase in the carbon—carbon double bond length from 1.337(2) A in free ethylene to 1.438(5) A and 1.425(3) A, respectively. Considerable bending of the hydrogen atoms out of the plane of the ethylene molecule is also observed. By comparison with structural data for other ethylene complexes and three-membered heterocyclic compounds, the structures of 5 and 6 would appear to be intermediate along the continuum between a Ti(11)-ethylene (4A) and a Ti(IV)-metallacyclopropane (4B) (Scheme 11.1) as... 

The hypothesis of stereochemical control linked to catalyst chirality was recently confirmed by Ewen (410) who used a soluble chiral catalyst of known configuration. Ethylenebis(l-indenyl)titanium dichloride exists in two diaste-reoisomeric forms with (meso, 103) and C2 (104) symmetry, both active as catalysts in the presence of methylalumoxanes and trimethylaluminum. Polymerization was carried out with a mixture of the two isomers in a 44/56 ratio. The polymer consists of two fractions, their formation being ascribed to the two catalysts a pentane-soluble fraction, which is atactic and derives from the meso catalyst, and an insoluble crystalline fraction, obtained from the racemic catalyst, which is isotactic and contains a defect distribution analogous to that observed in conventional polypropylenes obtained with heterogeneous catalysts. The failure of the meso catalyst in controlling the polymer stereochemistry was attributed to its mirror symmetry in its turn, the racemic compound is able to exert an asymmetric induction on the growing chains due to its intrinsic chirality. 

Employing silyated quadridentate Schiff bases, e.g. 0,0 -bis(trimethylsilyl)-JV,JV -ethylenebis(salicylideneimine),105 a range of titanium(IV) complexes Ti(j/5-C5H5)(salen)L (25 L = Cl, OMe, SMe, NMe2, SnPh3, acac) have been prepared. 

Collins and coworkers have developed two synthetic routes for the preparation of chiral [l,2-ethylenebis(jj -3-alkylcyclopentadienyl)]titanium dichlorides (R = Me, Et, i-Pr, r-Bu) in 80 85% yields as a nuxture of racemic and meso-titanocene dichlorides. In more recent work, the addition of a methyl group to the cyclopentadienyl rings has allowed Collins and coworkers to prepare a series of [1,2-ethylene-l,T-bis(4-R-2-methylcyclopentadienyl)] titanium dichlorides (R = Me, j-Pr, r-Bu) stereoselectively to give the racemic isomers. ... 

Preparative Methods this reagent is an intermediate for the preparation of optically pure ethylenebis(tetrahydro-l-ind-enyl)zirconium dichloride. That is, according to the procedure described for the kinetic resolution of ethylenebis(tetrahydro-1 -indenyl)titanium dichloride with (/ ,/ )- or (S. Sf-binaphtholate, 1 equiv of racemic ethylenebis(tetrahydro- l-indenyl)zirconium dichloride can be resolved with 0.5 equiv of (/ ,7 )-binaphthol in the presence of sodium metal in toluene to yield the optically active (5, 5)-ethylenebis(tetrahydro-l-indenyl)zirconium dichloride and the (—)-[ethylenebis(tetrahydro-l(7 )-indenyl]-zirconium (/ )-binaphtholate. The separated optically pure (—)- [ethy lenebis( tetrahydro-1 (7 )-indenyl]zirconium (7 )-bi-... 

Related Reagents. (/ ,/ )-[Ethylene-l,2-bis(i -4,5,6,7-tetra-hydro-l-indenyl)]titanium (/ )- ,l -Bi-2,2 -naphtholate ( )-1, l -Ethylenebis(4,5,6,7-tetrahydro-l-indenyl)zirconium Dichloride. 

The first chiral bridged zirconocene synthesized in 1984 by Brintzinger and used as an isospecific polymerization catalyst was racemic ethylenebis-(4,5,6,7-tetrahydro-l-indenyl)zirconium dichloride (see Structure 9) [45]. Ewen showed that the analogous ethylenebis(l-indenyl)titanium dichloride (a mixture of the meso form and the racemate) produces a mixture of isotactic and atactic polypropylene [46]. The chiral titanocene as well as the zirconocene were shown to work by enantiomorphic site control in the case of the titanocene, the achiral meso structure causes the formation of atactic polymer. 

The hydrogenation of [ethylenebis(2-indenyl)] titanium dichloride with Pt02 has also been described (Scheme 648).1670... 

Ethylenebis(pentamethylcyclopentadienyl)titanium reacted with methylenecyclopropane or 1-methylene-2-phenylcyclopropane in hexane to give the corresponding 5-titanaspiro[2.4]heptane 6 in 65 and 83% yield, respectively. These organometallic compounds are stable, but can... 

Reduction of dichloro-NN -ethylenebis(salicylideneiminato)titanium(rv) by BH4 gives a compound which analyses as [Ci6Hi N202Ti(BH3)2]2. The crystal structure of this showed the presence of amine-boranes as donor groups, and the novel unit (19) in the complex. ... 

The basic compound of Brintzinger s ansa-titanocene complexes is ethylenebis-(tetrahydroindenyl)titanium dichloride, (EBTHI)TiCl2. Further analogues ((EBTHI)TiH, (EBTHI)Ti(Me)2, and (EBTHI)Ti(CO)2) have been wddely used for asymmetric hydrogenation, hydrosilylation, and Pauson-Khand reaction (121). Novel optically active titanium complexes containing a linked amido-cyclopentadienyl ligand have been developed and used for asymmetric hydrogenation (122). 

Chemical composition distribution Biscyclopentadienyl titanium dichloiide Biscydopentadienyl zirconium dichloride Ethylenebis(indenyl)zirconium dichloride Ethylenebis(tetrahydroindenyl)zirconium dichloride Ethylidene(l-tetramethylcyclopentadienylKindenyl) titanium dichloride... 

With these C2-symmetric homogeneous catalysts at hand, the groups of John Ewen at Exxon and Walter Kaminsky at the University of Hamburg almost simultaneously published revolutionary studies on the formation of isotactic polypropylene upon activation of chiral flni fl-metallocenes with Ewen used a 56 44 mixture of rac- and meso-ethylenebis(indenyl)titanium... 

Both (RJi) and (S,S) enantiomers of ethylenebis(rf-tetrahydroindenyl)titanium difluoride (EBTHI)TiF2, were developed by Buchwald et al. and used in many efficient enantioselective hydrogenations of ketones [15] and imines [16]. The utility of this process was demonstrated in the enantio- and diastereo-selective preparation of sertraline according to Scheme 7.2. The enantioselectivity and yield in this reaction ranged between 90 and 96% e.e. and 40-50%, respectively. The yield is based on the racemic 5, and amounts to 76-96% when based on the (4S)-enantiomer. Workup in this reaction requires chromatographic separation of (15,45 )-1, from the (4i )-ketone 4. Later, in Sect. 7.5.4, we shall discuss an independent research project that resulted in the efficient recycling of the wrong enantiomer of this ketone. 

C2 5H2 aCoNftOa, Dioxygen(N,N -(2-(2 -pyridyl)ethyl)ethylenebis(sali-cylideneiminato))cobalt acetonitrile solvate, 44B, 839 C2sH27ClN303Ti, N,N -Ethylenebis(salicylideneiminato)chloropyridine-titanium(III) tetrahydrofuran solvate, 44B, 840 C2 5H2 7C0N3O3, N,N -(2-(2 -Pyridyl)ethyl)ethylenebis(salicylideneim-inato)cobalt(II) ethanol solvate, 44B, 839 C2 5H3oBr2C02Nft03, (Bis(propane-1,3-diyl)-di(5-methylphalaldimin-2- olato))bis(bromocobalt(II)) methanol solvate, 41B, 976 C2 sHi8ClFeN202S2, Chloro(bis(salicylideniminephenyl)disulfido)iron-... 

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