Analogous titanium complexes

Arylamido complexes of a general formula of Cp Zr[N(Ar)SiMe3]Cl2 can be obtained in a similar fashion. Thus, the reaction of Cp MCl3 with 1 equiv. of Li[N(Ar)SiMe3] produces complexes 31248 and 313.252 The difluoride 312 was prepared by metathesis reaction of the dichloride and Me3SnF. Upon activation with MAO, all complexes are active for polymerization of ethylene within complexes 312, the zirconium complexes are much more active than the analogous hafnium complexes, whereas within complexes 313, the zirconium complex exhibits poor activity as compared with the analogous titanium complex. 

The kinetics of polymerization are remarkably similar to those for the reaction initiated by the analogous titanium complexes 25 and 26 first-order in initiator, zero-order in monomer for the major part of the reaction, and activation energy of 105 kJ mol Propagation via tantalacyclobutane and tantalum carbene complexes is clearly implied. 

The trinuclear [ClCu Zr2(OPr )9 ] has the [CuZr(jU3-OPr )2(jU,-OPr )3] core similar to the analogous titanium complex. The homoleptic Cu(i)Zr(iv) complex has a different structure [Cu2Zr2(OPr )io] containing the confacial bi-octahedral Zr2(OPr )9 unit into which the Cu2(/u,-OPr ) group is inserted by the copper atoms bridging with terminal isopropoxo ligands on each Zr. The (/i-OPr ) Cu(/i-OPr ) system has a hnear O-Cu-0... 

A chiral titanium complex with 3-cinnamoyl-l,3-oxazolidin-2-one was isolated by Jagensen et al. from a mixture of TiCl 2(0-i-Pr)2 with (2R,31 )-2,3-0-isopropyli-dene-l,l,4,4-tetraphenyl-l,2,3,4-butanetetrol, which is an isopropylidene acetal analog of Narasaka s TADDOL [48]. The structure of this complex was determined by X-ray structure analysis. It has the isopropylidene diol and the cinnamoyloxazolidi-none in the equatorial plane, with the two chloride ligands in apical (trans) position as depicted in the structure A, It seems from this structure that a pseudo-axial phenyl group of the chiral ligand seems to block one face of the coordinated cinnamoyloxazolidinone. On the other hand, after an NMR study of the complex in solution, Di Mare et al, and Seebach et al, reported that the above trans di-chloro complex A is a major component in the solution but went on to propose another minor complex B, with the two chlorides cis to each other, as the most reactive intermediate in this chiral titanium-catalyzed reaction [41b, 49], It has not yet been clearly confirmed whether or not the trans and/or the cis complex are real reactive intermediates (Scheme 1.60). 

Thus it seems possible that analogous titanium-based complexes play a role in the activation of the catalyst with AlEts according to ... 

Using the same boratabenzene 68, Bazan and co-workers have formed titanium complex 70 and then studied its further reactions with acetylenes. Treatment of 70 with acetylene itself resulted in 71 as well as two ring-expanded products, 72 and 73 (Scheme 1) <2003AGE4510>. Formation of 72 was favored at low concentrations of acetylene in toluene solution whereas 73 becomes prevalent at high concentrations a mechanism involving initial coordination of acetylene to titanium was proposed. Similar reaction of 70 with (trimethylsilyl)acetylene gave a 79% yield of the product analogous to 72, the structure of which was determined by X-ray diffraction (see Section 7.14.3). 

A titanium complex with a pyrazolylborate ligand was studied by Campbell and Malanga [19]. Similarities between the cyclopentadienyl ligand and the hydridotris(pyrazolyl)borate ligand have been noted for transition metal complexes. Catalyst efficiencies are much lower than those of the analogous penta-methylcyclopentadienyl complexes. 

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]... 

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