Titanium complexes theoretical studies

The work of Davis was, however, unable to distinguish which oxygen was attacked on the titanium peroxo complex when the alkene co-ordinates. Therefore, Neurock and Manzer conducted a theoretical study of the mechanism of alkene epoxidation using TS-1 with aqueous hydrogen peroxide.32 The workers concluded that their calculations to predict both the structure and relative bands in the IR spectra for TS-1 were in good agreement with experimental data. The calculations indicated that the oxygen closest to the titanium centre was the active site for alkene attack. The result was the direct formation of... 

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... 

Several complexes combining q2 and q3 - BH4 ligands in the coordination sphere have been reported with TP, TET, TBP and OCT geometries (Scheme 9). It is worth comparing the tetrahydrobrate coordination modes found in a series of M(BH4)3L2 (M = Sc, Ti, V) complexes. Despite the three compounds exhibiting TBP structures, vanadium shows the three BH4 coordinated q2, scandium prefers two q3 and one q2, and titanium prefers two q2 and one q3-BH4 ligands. These series have been theoretically studied in order to discuss the importance of electronic effects as a main factor... 

Kulinkovich himself proposed that the dialkoxytitanacyclopropanes as the key intermediate in the Kulinkovich cyclopropanation. Extensive theoretical study on mechanism was published in 2001. Eisch also provided detailed exploration of the mechanism for the Kulinkovich reaction in 2003. In 2007, Kulinkovich proposed a modified ate complex mechanism for titanium-mediated cyclopropanation of carboxylic esters with Grignard reagents. 

From both the experimental and theoretical points of view, the most thoroughly studied catalytic systems are undoubtedly allylnickel(II) systems and monocyclopentadienyl titanium complexes. In the case of the nickel systems, chain growth proceeding by BD insertion into the allyl-transition metal bond was proven directly by NMR spectroscopy for both 1,4-trans- and 1,4-cis-regulating catalysts. In this case, the proposed mechanism for stereoregulation suggests that the cis-trans... 

Kholdeeva, O., Trubitsina, T, Maksimovskaya, R., et al. (2004). First Isolated Active Titanium Peroxo Complex Characterization and Theoretical Study, Inorg. Chem., 43, pp. 2284-2292. 

Herrmann and co-workers synthesized [Os(0)(Me)4] from 0s04 and dimethylzinc or methyltris(isopropoxy)titanium (180). An alternative route is by methylation of the glycolate osmium(VI) complex [0=0s(0CH2CH26)2] with dimethylzinc (180). The thermally labile ethyl derivative [Os(0)(Et)4] has also been prepared (180). [Os(0)(Me)4] is an orange, air-stable, volatile, crystalline compound that melts at 74°C without decomposition. The gas-phase average molecular structure of [Os(0)(Me)4], determined by electron diffraction techniques, is consistent with a theoretical model of C4 symmetry with d(Os—C) = 2.096(3) A, d(0s=0) = 1.681(4) A, and ZO—Os—C = 112.2(5)° (180). Cyclic voltammetric studies showed that [Os(0)(Me)4] undergoes reversible reduction at - 1.58 V and an irreversible oxidation at -f 2.2 V vs Ag/AgCl in MeCN. 

Recent progresses in the development of the titanium-phosphinimido complexes and their application as olefin polymerization pre-catalysts have been reviewed - and related computational studies have been reported. Based on these theoretical results, the synthesis of a family of pre-catalysts of general formula Cp TiX2[NP(NR2)3] (X = C1, Me) (Scheme 234) containing the tris(amino)phosphinimido ligand has been described.638... 

In many catalytic processes and transition metal mediated reactions, a-bor-ane complexes have been shown to be intermediates. The bis(borane) complex Cp2Ti( 72-HBcat/)2 (HBcaT = HBcat-4-f-Bu) is a highly active catalyst for the hydroboration of vinylarenes [37]. A mechanism, shown in Scheme 3, has been proposed for the Ti-catalyzed hydroboration on the basis of a detailed mechanistic study [37]. Theoretical calculations provided further support to the proposed reaction mechanism and showed that the reductive elimination step, giving the product molecules, is rate-determining [38]. In the Cp2Ti(CO)2 catalyzed hydroboration of alkynes [36,37], the proposed reaction mechanism (Scheme 4) also involves a a-borane complex similar to 11 and 14. In the titanium-catalyzed decaborane-olefin hydroborations [47,48], a-borane complexes were also considered as intermediates. In the Cp2MH (M = Nb, Ta) mediated hydroboration reactions of olefins [39,41], Smith and his coworkers observed several interesting cr-borane complexes, such as 21-23 discussed above. 

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