Benzamidinate complexes

While ytterbium(II) benzamidinate complexes have been known for many years/ the synthesis of the first divalent samarium bis(amidinate) required the use of a sterically hindered amidinate ligand, [HC(NDipp)2l (Dipp = C6H3Pr2-2,6)/ As illustrated in Scheme 54, the dark green compound Sm(DippForm)2(THF)2 (DippForm = [HC(NDipp)2] ) can be prepared by three different synthetic routes. Structural data indicated that hexacoordinated... 

In general, Group 4 benzamidinates show poor activities as olefin polymerization catalysts.158-162 However, bis(benzamidinate) complex (52) affords isotactic PP (>95% mmmm) at >7 atm propylene pressure 163 at ambient pressure atactic PP is produced.164 An unsymmetrical tris (benzamidinate) zirconium complex has also been shown to afford highly isotactic PP.165... 

One of the most critical technical issues regarding LIE type of calculations seems to be the treatment of electrostatic interactions, at least for charged ligands. These problems were discussed in Ref. 19 using the trypsin-benzamidine complex as an illustration. The starting point was then that one should expect, or require, that the electrostatic free energies calculated with the LIE method have some physical meaning, even in... 

Using this approach, Bizzozero and Zweifel (9) and Bizzozero and Dutler (10) have constructed molecular models of two intermediates (an enzyme-substrate complex and a tetrahedral intermediate) by appropriate modification of the models of stable enzyme-species. The stable enzyme-species used (15, 16) are trypsin-benzamidine complex (TR-B) (17), trypsin-pancreatic trypsin inhibitor complex (TR-PTI) (18, 19) and tosyl-chymotrypsin (Tos-CHT) (20) which are related to enzyme substrate complex, tetrahedral intermediate and acyl-enzyme respectively. 

Monoaromatic acetylenes, polymerization, 11, 566—568 Monoaryloxo complexes, with mono-Cp Ti(IV), 4, 474 Mono(benzamidinate) complexes, in ethylene polymerization, 4, 1139-1141... 

Abstract The synthesis and X-ray structure of various octahedral zirconium complexes and their catalytic properties in the polymerization of a-olefins are described. Benzamidinate, amido, allylic, and phosphinoamide moieties comprise the study ligations. For the benzamidinate complexes, a comparison study between homogeneous and heterogeneous complexes is presented. For the phosphinoamide complex, we show that the dynamic symmetry change of the complex from C2 to C2v allows the formation of elastomeric polymers. By controlling the reaction conditions of the polymerization process, highly stereoregular, elastomeric, or atactic polypropylenes can be produced. The formation of the elastomeric polymers was found to be the result of the epimerization of the last inserted monomer to the polymer chain. 

This obviously minimizes repulsion between the bulky isopropyl groups. The torsion angles between the phenyl rings and the ZrCN2 planes are 89.3°, which is the highest value for any metal benzamidinate complex. 

It is important to point out that the zirconium benzamidinate complexes 1 and 5 have lower catalytic activity in the a-olefin polymerizations than the corresponding metallocene systems (lxlO7 and 6xl06 g polymer-mol Zr -h 1 for ethylene and propylene, respectively [70]). The difference in activity can be rationalized by the structural environment of the metal (Zr) center. In the metallocenes, the cone angle is normally the key feature for unsaturation, whereas in the octahedral complexes the groups at the N-moiety may induce an electronic unsaturation at the metal center. Thus, the lower polymerization activities of the complexes 1 and 5 may be a consequence of the partial saturation at the metal orbitals as compared to the metallocenes [71-73]. 

Fig. 12a-c AFM pictures of different polypropylenes, a Isotactic polymer from Table 2, entry 4 b elastomeric polymer obtained with Ti benzamidinate complex [41 ] c atactic polymer fraction from Table 2, entry 8... 

Group 4 benzamidinate complexes were found to be active catalytic precursors, in the presence of MAO, for the isomerization of aliphatic olefins and the disproportionation (see Disproportionation) of 1,4- and 1,3-cyclohexadienes (Scheme 50). The active species is the cationic hydride complex obtained for aliphatic olefins by the insertion of the methyl ligand with concomitant /3-hydrogen elimination, and for the alicyclic dienes by an activation of the allylic hydrogen and subsequent elimination of methane. 

Scandium (and similar yttrium) benzamidinate complexes [ RC6H4C(NSiMe3)2 2ScCl(THF)] (R = H, MeO) have been reported and are believed to have octahedral structures (1). 

J. W. Essex, D. L. Severance, J. Tirado-Rives, and W. L. Jorgensen, /. Phys. Chem. B, 101, 9663 (1997). Monte Carlo Simulations for Proteins Binding Affinities for Trypsin-Benzamidine Complexes Via Free-Energy Perturbations. 

Volkis, V NeUcenbaum, E. Lisovskii, A. Hasson, G Semiat, R. Kapon, M. Botoshansky, M. Eishen, Y. Eisen, M. S. Group 4 octahedral benzamidinate complexes Syntheses, structures, and catalytic activities in the polymerization of propylene modulated by pressure. J. Am. Chem. Soc. 2003, 125, 2179-2194. 

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