Deuteriation complexes

The nmr spectrum of the cyclooctenyl complex [80-H] shows five resonances in the ratio of 1 2 2 2 1. If the fast exchange process (66), which renders the two endo hydrogen atoms adjacent to the n-allyl unit equivalent, could be frozen out, each of the peaks with the relative intensity 2 would be split into two. In the mono-deuteriated complex [80] the three averaged peaks C-l/C-5, C-2/C-4 and C-6/C-8 show isotopic perturbation. 

The anomalously fast base hydrolysis of the rra//s-[Co(en)2Cl2] and trans-[Co(ddn)Cl2]+ions (ddn = /J,5-2,3,2-tet = / ,5 -l,9-diamino-3,7-diazanonane)has been shown to arise mainly from the unusually high lability of their conjugate bases. Using deuteriated complexes the extent of replacement of the labelled amine protons... 

In Group VA alkylidenes, one of the major mechanistic problems concerns the existence of the a-H elimination from alkyls. The transformation shown in equation (23), which occurs also for the analogous deuteriated complex) offered... 

The addition of tetrabutylammonium chloride to H solutions of [68] and [69] in deuteriated acetonitrile resulted in remarkable nmr shifts of the respective proton signals of both receptors. Of particular note were the substantial downfield shifts of the amide protons (AS = 1.28 ppm for [68] and 1.52 ppm for [69]) on addition of one equivalent of chloride. These results suggest that a significant —CO—NH-Cr hydrogen-bonding interaction contributes to the overall anion complexation process. Subsequent nmr titration curves suggesting 1 1 stoichiometry with anion complexes of [68] and [69] were found in all cases. Negligible shifts were observed under identi-... 

Perdeuteriated isopropyl, t-butyl, and t-pentyl fluorides were prepared from the corresponding deuteriated alkyl chlorides (bromides) by halogen exchange. The perdeuteriated alkyl fluorides were then used in the formation of the deuteriated carbonium ions under similar conditions as those for the protium complexes. The resonance spectra were obtained at 9 2 Mc/s and the data are summarized in Table 7... 

In another study a sudden spectral change and a reduction in x( Li) from 360 kHz at 213 K to 85 kHz at RT was observed for the LDA-THF complex (26, Scheme 4, Table 9) between 282 and 286 K. Again, this result can be associated with dynamic processes which involve, according to C and H NMR investigations of partially deuteriated species, the THF ligands. 

Temperature-dependent lineshape changes were observed in an early study of the fluo-renyllithium(TMEDA) complex. A detailed study by lineshape analysis, which was also applied to the TMEDA complex of 2,3-benzofluorenyllithium(TMEDA) (Figure 29f, yielded barriers AG (298) of 44.4 and 41.9 kJmoD for the 180° ring flip in these systems, respectively . A second dynamic process, which was detected via the temperature dependence of, the spin-lattice relaxation time in the rotating frame, is characterized by barriers of 35.1 and 37.6 kJmoD, respectively, and may be ascribed to the ring inversion process. For the fluorenyl complex, a barrier AG (298) of 15.9 kJmoD for the methyl rotation in the TMEDA hgand was determined from temperature-dependent NMR spectra of the deuteriated system. 

As for LiC2H2, the authors have shown spectroscopically by using partial asymmetrical deuteriation [Li (CH2CD2)m] that lithium bridged symmetrically the carbon-carbon bond . Possible structures for the Li(C2H4) , n = 1, 2, and 3 complexes are depicted in Scheme 4. 

A problem with (—)-sparteine 362 is its lack of availability in both enantiomeric forms. Reversed selectivity in the generation of planar chirality has been achieved by second lithiations (see Schemes 163 and 171) and a remarkable modification of this strategy works with arenechromium tricarbonyls. By using excess BuLi (sometimes f-BuLi is required) in the presence of sparteine 362, a doubly lithiated species 450 may be formed from 448. The formation of the doubly lithiated species may be confirmed by double deuteriation with excess D2O. However, other electrophiles react selectively only once and give products of opposite absolute stereochemistry from those formed after monolithiation, if in rather low yield. Presumably, the first lithiation, which is directed by (—)-sparteine, produce an organolithium 448 whose complexation with (—)-sparteine remains favourable. The second lithiation must produce a less stable organolithium—one which cannot form a... 

Reaction of butyllithium with VBE tetrahydroisoquinolyl formamidine proceeds as shown in Scheme 56. The lack of a kinetic isotope effect in deuteriated substrates revealed that the slow step in the sequence is the complexation of the BuLi with the formamidine, followed by selective removal of the a proton as shown. A rationale for this selectivity is that the butyl group is oriented trans to the isopropyl of the 5-membered... 

The treatment of the deuteriated cis oxirane 32 by EDA in HMPA yields exclusively the nondeuteriated alcohol 33. Indeed, complexation of the lithium cation by HMPA prevents the formation of the six-center transition state. The isomerization thus follows a more common E2 process, i.e. anti -elimination. 

At -107°C, reaction of hexafluoroacetone-complexed pyridine with LiTMP followed by MeOD as the electrophile gave 90% C-2 deuteriation, whereas at -78°C, C-2 (48%) and C-4 (28%) deuterium incorporation was observed. 

The reduction of tosylhydrazones by complex metal hydrides has been used very effectively to prepare saturated steroid hydrocarbons in high yields.317 In certain cases this reduction (with lithium aluminum hydride) takes a different course, and olefins are formed.318 The effect is dependent on both the reagent concentration and the steric environment of the hydrazone.319 Dilute reagent and hindered hydrazone favor olefins borohydride gives the saturated hydrocarbon. The hydrogen picked up in olefin formation comes from solvent, and in full reduction one comes from hydride and the other from solvent. This was shown by deuteriation experiments with the hydrazone (150) 319... 

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