Temperature dependence, *H NMR spectroscopy

Examples come from Hahn et al. [491] who synthesised the pincer imidazolium salt from a,a -dibromolutidine and A-alkyl-benzimidazole using a standard protocol. Synthesis of the palladium(ll) complex was then achieved with palladium(ll) acetate in DMSO. The structure is similar to that of the palladium(II) pincer carbene complexes with nonannulated pincer ligands. Temperature dependant H-NMR spectroscopy... 

However, Kammerer showed later by temperature-dependent H NMR spectroscopy of what was definitely a cyclic tetramer, that the nonequivalent protons of the bridging methylene groups at room temperature, became equivalent at 60 °C. This was first interpreted by Kammerer in terms of conversion of two of the Comforth s diastereoisomers but a few years later [19] correctly interpreted as the mirror image conformational interconversion of the cone structure (Fig. 1.5). In 1985 Gutsche et al. [20] proved that the HBC fraction of Comforth was the cyclic octamer. 

As in the case of carbon-bridged calixarenes, conformational behaviors of azacalixarenes in solution have been investigated by means of temperature dependent H NMR spectroscopy. It was reported that azacalixarenes 4a-f, 7b-d, 7f, 7g, 8a, 20b, and 20f were conformationally flexible in solution [17-19,24,25]. Gong et al. pointed out from their NMR studies of compounds 7b, 7f, 20b, and 20f that the lack of steric hindrance and intramolecular hydrogen bonds were responsible for their high conformational mobihty in solution, as compared to carbon-bridged calixarenes [24]. 

At high pH, the stability of the cyclometalated iridium complexes 21 and 23 is limited, because they gradually decomposed when heated in 1 M NaOH at 80 °C for 24 hours. At room temperature, the stability was higher and the complexes were partly deuterated when dissolved in 1M NaOH. Time-dependent H NMR spectroscopy allowed the sequence of deuteration to be monitored, thus providing access to selectivity patterns (Figure 3.2). 

K, in CD3COCD3 at 240 K), sometimes at different temperature (in CDCI3 at 216-303 K) by h NMR spectroscopy. The h NMR spectra are dependent markedly on solution conditions, and suggest that there are different equilibrium mixtures of accessible conformers (97MI12). 

The restricted rotation about exocyclic partial double bonds in some 3-azapyrylium salts was investigated by temperature-dependent C- and H-NMR spectroscopy (87MRC688). 

Long et al. [87] have studied the association of PS-polymers bearing adenine- and thymine endgroups, prepared via Michael-type addition. The association was followed by H-NMR spectroscopy, relying on the temperature dependency of the imide-protons and revealed strong effects in solution. The formation of 1 1 complexes was proven and extended to other polymers such as poly(acrylates) and their respective melt viscosities [88]. Similar results have been reported for PS-b-Pl [89] and polyisoprenes [90]. hi... 

H NMR spectroscopy combined with different techniques (see Section 4.05.3.6) has been used to perform the dynamic characterization of fananserin 35, an anxiolytic drug which can be crystallized as four different polymorphs. The dynamics were monitored by measuring the spin-lattice relaxation and line-shape evolution temperature dependence <2006MI798>. 

Methyl 3-(imidazolyl)acrylate (3) prepared earlier in a two step procedure" can be obtained in high yield from imidazole (1) and methyl propiolate (2) at ambient temperature. The presence of KIO montmorillonite speeds up the reaction but does not alter the E Z isomer ratio determined by H-NMR spectroscopy. The distribution of the addition products (3 and 4) depends on the molar ratio of the reactants. Double Michael addition is favored by the use of excess imidazole leading to alkyl 3,3-bis(l-imidazolyl)propionate (4) (Table 1). Remarkable acceleration can be achieved in the reaction of benzimidazoles (5) (R = H, Ph) with propiolic esters (2) by the use of KIO montmorillonite the reaction time can be decreased from 5-7 days to 1-7 hours (Table 2). 

Table 3 summarizes the results at low temperatures in this solvent mixture. These data show the hydration numbers n to be markedly sensitive to the type and the concentration of the anion, Low estimates of n were attributed to either replacement of water in the primary coordination sphere by the CIO4 or NO3 ions or to changes in water activity in solution as a result of hydrogen bonding between water and acetone (Brucher et al. 1985). Such hydrogen bonding has been detected by H-NMR spectroscopy in water-acetone mixtures at very low water content (Takahashi and Li 1966) and could involve either A. . . HOH or A. .. HOH. .. A species, depending on the relative concentrations of water and acetone. 

The Cr-N02 complexes reported to date do not appear to isomerize under photolysis conditions, but can decompose with release of NO when irradiated with light (88). However, the complex CpCr(N0)2(N02) (Cp = cyclopentadiene) prepared by metathesis of CpCr(NO)2Cl with NaN02 in methanol, exists in both the nitro and nitrito forms in solution (Figure 8), with the nitrito isomer favored both in solution and in the solid state (89). The equilibrium is temperature dependent as determined by H NMR spectroscopy, with the nitrito isomer favored at higher temperatures (AHeq = 1.8(3)kcalmol AS=9.3(9) eu) (89). In addition, H NMR and... 

Figure 10.2 Mobility of the atoms in the ionic liquid phase indicated by the temperature dependence of the line width of the proton signals of Pd/IEMIMJTf/SiOj in solid-state H NMR spectroscopy. The encircled data point is the line width of the parent supported ionic liquid [EMIMjTf/SiOj [52). (With permission of ACS.)...

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