Cocondensation reactions

Conventional cocondensation reactions involving ionic precursors in the presence of cationic or nonionic surfactant led to the formation of surface-functionalized ionosilicas featuring typical MCM-41 and SBA-15 architectures [98]. Similar to classical reaction involving organic trialkoxysilylated precursors, the use of ionic liquid precursors has shown to disturb the self-assembly of the 

Further works in the field of nanostructured silica starting from SDA-CSDA ion pairs concern the formation of materials containing tethered anions. The formation of this type of material involves inverse ion pairs with respect to the synthesis of AMS mesophases, that is, anionic costructure-directing agent and cationic surfactant [78,106,107], 

In conclusion, various types of ionically modified surface-functionalized silicas displaying high structiu-al regularities are accessible via template-directed hydrolysis-cocondensation methods. These methods involve the use of ionic 

The use of ionic precursors in template-directed hydrolysis-polycondensation reactions clearly indicated a strong contribution of the precursor toward the formation of structured mesophases, based on ionic precursor-surfactant interactions. The work of Che and coworkers beautifully illustrates that templating methods involving surfactant-precursor ion pairs allow accessing highly structured siuface-functionalized silica materials. However, this work exclusively focused on the use of monosilylated costructure-directing agents and the formation of siuface-fimctionalized mesoporous silica phases. 

A number of unstable and transient species have been synthesized via matrix cocondensation reactions, and their structure and bonding have been studied by vibrational spectroscopy. The principle of the method is to cocondense two solute vapors (atom, salt, or molecule) diluted by an inert gas on an IR window (IR spectroscopy) or a metal plate (Raman spectroscopy) that is cooled to low temperature by a cryocooler. Solid compounds can be vaporized by conventional heating (Knudsen cell), laser ablation, or other techniques, and mixed with inert gases at proper ratios [128]. In general, the spectra of the cocondensation products thus obtained exhibit many peaks as a result of the mixed species produced. In order to make band assignments, the effects of changing the temperature, concentration (dilution ratios), and isotope substitution on the spectra must be studied. In some cases, theoretical calculations (Sec. 1.24) must be carried out to determine the structure and to make band assignments. Vibrational frequencies of many molecules and ions obtained by matrix cocondensation reactions are listed in Chapter 2. 

Matrix cocondensation reactions are classified into the following five types  

Salt-Molecule Reaction. Tevault and Nakamoto [131] carried out matrix cocondensation reactions of metal salts such as PbF2 with L(CO, NO and N2) in Ar, and confirmed the formation of PbF2-L adducts by observing the shifts of IR bands of both components. These spectra are shown in Fig. 3.67 (of Sec. 3.18.6). 

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Fig. 19. The optical spectrum of the products of a Ag Kr — 1 10 cocondensation reaction, (A) after deposition at 10-12 K, and (B) after 60-min, narrow-band (8 nm), 325-nin continuous irradiation from an Oriel 500-W xenon lamp-Schoeffel monochromator assembly (152).

It has, however, proved possible to synthesize the following chromium complexes via a 77 K, Cr-atom, cocondensation reaction with 2,-... 

This general method either involves low-molar-mass azo compounds having additional functionality, which can be used to start a polymerization of a vinyl monomer selectively, or a ring-opening addition but also to participate in cocondensation reactions. 

Laboratory in Oxford, and Geoffrey Ozin at the University of Toronto in the early 1970s. With the metal atom cocondensation technique (which as described in Chaps. 6 and 7 was also used to prepare a series of zerovalent arene and olefin metal complexes), they reported simultaneously that the elusive palladium and platinum tetracarbonyls, Pd(CO)4 and Pt(CO)4, as well as the coordinatively unsaturated fragments M(CO)3, M(CO)2, and M(CO) (M = Pd, Pt) were formed by cocondensation reactions of Pd and Pt atoms with CO in inert gas matrices at 4-10 K [119-122]. The comparison of the CO bond stretching force constants for Pd(CO)ra and Pt(CO)ra (n - 1-4) revealed that, in analogy to Ni(CO) , the most stable compounds were the tetracarbonyls. In a xenon matrix, Pd(CO)4 existed up to about 80 K [120]. Ozin s group as well as others... 

Scheme 5.5 Preparation of bis(pyridine)chromium 15 via the ring-substituted derivative 14, which is obtained by a metal atom/ligand vapour cocondensation reaction...

The following procedure is representative of a metal-templated [2+2] cocondensation reaction of an aromatic dialdehyde with an acyclic diamine.26... 

The chemistry of dichlorosilylene can be studied by either gas-phase or cocondensation reactions (17, 62, 103, 104). In most cases, dichlorosilylene generated by pyrolysis of perchloropolysilanes was used in the gas-phase reactions whereas thermal reduction was used for cocondensation experiments. 

It has been reported that the 29Si NMR spectrum of the soluble part of the polymer, which accounted for 70% of the total products in the cocondensation reaction of SiF2 and propene, was consistent with the structure [ C(CH3)—CH2SiF2—This is strong evidence supporting the silirane mechanism (110). 

The true competitive preference of insertion vs. addition is shown in the cocondensation reactions of SiF2 with cis- and (rarcs-CHCl=CHCl. 

When the cocondensation reactions are carried out at — 196°C, the kinetic competition of the radical species among various reaction pathways becomes a controlling factor. It is therefore quite reasonable to observe the various relative yields of trans and cis products in these cocondensation reactions (Table II). 

While compound (3) obtained in the cocondensation reaction may still be formed through the contribution from the silirane mechanism, just as it is formed in the gas phase, the formation of (4) and (5) cannot be rationalized with the same reaction mechanism. The fact that compound (4) was found to be the major product in the cocondensation reaction strongly indicates that the reaction proceeds via the diradical mechanism shown in Scheme 12. Compounds (3) and (4) are both thermally stable. It is interesting to note that compound (4) can be converted into compound (3) in n-hexane solution by UV irradiation. 

Roh, J. K., Higuchi, M., and Sakata, I., Curing behaviour and bonding properties of thermosetting resin adhesives. V. Cocondensation reaction of phenol with melamine, Mokuzai Gakkaishi. 36, 42, 1990 Chem. Abstr., 113, 41891, 1990. 

As expected, many of these compounds are prepared from the cocondensation reactions of cyclopropenones or cyclopropenyl salts. For example, methylenecyclopropene (75) can... 

The complex Mo205(Me)2-2MeOH was detected (56) as a condensation product of Mo03 vapor with methanol, water, and THF at - 196°C. Such cocondensation reactions in the vapor phase again appear to have considerable potential as a novel synthetic route. 

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