Transition complexes, silica-based

The fl and values are shown in Table 3.1. Higher values of H are related to transitions occurring mainly by dynamic coupling. The differing values of free and silica-based complexes indicate that in the free complexes the chemical environment is most polarizable, in comparison with the silica-based complexes. Furthermore, the differing values between free and silica-based complexes could be associated with a decrease of the metal-ligand bond energies for the sUica-based species. 

Silica (s. a. Copper-silica, Ozone/silica) 28, 175s32 Silica-based s. Transition metal complexes, -Silica gel 6, 572s31 29, 98s31 ... 

Selective oxidation of hydrocarbons/terpenes in the liquid phase was studied using three types of zeolite- and mesoporous silica-based catalysts (1) transition metal complexes... 

In hydrogenation, early transition-metal catalysts are mainly based on metallocene complexes, and particularly the Group IV metallocenes. Nonetheless, Group III, lanthanide and even actinide complexes as well as later metals (Groups V-VII) have also been used. The active species can be stabilized by other bulky ligands such as those derived from 2,6-disubstituted phenols (aryl-oxy) or silica (siloxy) (vide infra). Moreover, the catalytic activity of these systems is not limited to the hydrogenation of alkenes, but can be used for the hydrogenation of aromatics, alkynes and imines. These systems have also been developed very successfully into their enantioselective versions. 

The base matrices are divided into two groups. The inorganic matrices are based on silica or zirconia, on which the transition metal ion is complexed with the ligand bonded on the matrix. The inorganic sorbents have high column efficiency but low capacity and low chemical stability. The hgand can also be coated prior to, or during, the experiment, on the octadecylated silica (ODS) reversed phase, which presents the most inexpensive but efficient and selective sorbent for CLEC. 

Emissions from both the and the previously unreported lli states of the IF molecule have been observed in the gas-phase reaction of L with F2 at low pressure a four-centre complex has been proposed as the reaction intermediate. A combined theoretical-experimental programme has been conducted to establish techniques for the study of excited-state transitions in Ij and IC1. Experimental techniques based on two-step excitation using two synchronized, tunable lasers have been developed, and successfully applied to excited-state fluorescence measurements on ICl. lodine(i) chloride adsorbed on silica gives the same Raman spectrum as that obtained from adsorbed l2. ... 

A wide range of catalyst systems are based on phosphine complexes of transition metals. Figure 35 shows P CP-MAS spectra of samples prepared by derivatization of silica with (Cf,H5)2PCH2CH2SiO(CH2CH3)3 [66]. The samples for which spectra are shown correspond to the situations before and after... 

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