T complex

These studies at the same time aroused my interest in the mechanistic aspects of the reaetions, including the complexes of RCOF and RF with BF3 (and eventually with other Lewis acid fluorides) as well as the complexes they formed with aromatics. 1 isolated for the first time at low temperatures arenium tetrafluoroborates (the elusive (T-complexes of aromatic substitutions), although I had no means to pursue their structural study. Thus my long fascination with the chemistry of car-bocationic complexes began. 

The solubility of hydrogen chloride in solutions of aromatic hydrocarbons in toluene and in w-heptane at —78-51 °C has been measured, and equilibrium constants for Tr-complex formation evaluated. Substituent effects follow the pattern outlined above (table 6.2). In contrast to (T-complexes, these 7r-complexes are colourless and non-conducting, and do not take part in hydrogen exchange. 

M.o. theory and the transition state treatment In 1942 Wheland proposed a simple model for the transition state of electrophilic substitution in which a pair of electrons is localised at the site of substitution, and the carbon atom at that site has changed from the sp to the sp state of hybridisation. Such a structure, originally proposed as a model for the transition state is now known to describe the (T-complexes which are intermediates in electrophilic substitutions... 

The most common oxidatiou states and corresponding electronic configurations of rhodium are +1 which is usually square planar although some five coordinate complexes are known, and +3 (t7 ) which is usually octahedral. Dimeric rhodium carboxylates are +2 (t/) complexes. Compounds iu oxidatiou states —1 to +6 (t5 ) exist. Significant iudustrial appHcatious iuclude rhodium-catalyzed carbouylatiou of methanol to acetic acid and acetic anhydride, and hydroformylation of propene to -butyraldehyde. Enantioselective catalytic reduction has also been demonstrated. 

Formation of the n-complex can be reversible. The partitioning of the n-complex forward to product or back to reactants depends on the ease with which the electrophile can be eliminated relative to a proton. For most electrophiles, it is easier to eliminate the proton, in which case the formation of the n-complex is essentially irreversible. Formation of the (T-complex is least likely to be reversible for the electrophiles in group A in Scheme 10.1, whereas those in group C are most likely to undergo reversible n-complex formation. Formation of the n-complex is usually, but not always, the rate-determining step in... 

A similar quantitative treatment of sulphoxides as hydrogen bonding acceptors has been obtained by comparing the IR frequency shift AvOH of the C—I bond in an acetylenic iodide such as IC=CI (Avc j) due to formation of a C—T complex with phenol in various bases. This investigation suggests that sulphoxides belong to the same family as carbonyls, phosphine oxides, arsine oxides and their derivatives90. 

Self-Test 16.9A What change in magnetic properties can be expected when NOz ligands in an octahedral complex are replaced by Cl" ligands in (a) a (t complex ... 

Palladium can be the leaving atom if the substrate is a Jt-allylpalladium complex (an T complex). Ions of ZCHZ compounds react with such complexes in the presence of triphenylphosphine, for example. 

In acidic media the /i-eriodide anions or periodide complexes these — like the iodide anion — are appreciably less reactive than the iodine cation [13]. 

Slii.ErTED Data for Struciurai.ly Characterized Cohai.t Complexes... 

Because Me3SiI (TIS) 17 is relatively expensive and very sensitive to light, air, and humidity, it is usually prepared in situ from TCS 14 and Nal in acetonitrile [1-6], although other solvents such as CH2CI2, DMF, benzene, or hexane have also been used [5, 6] (Scheme 12.1). It is assumed that TIS 17 forms, in situ, with MeCN, a (T-complex 1733 [2, 3-6], yet Me3SiI 17 can also be prepared by treatment of hex-amethyldisilane 857 with iodine in organic solvents [4-6]. The chemistry of TIS 17 has been reviewed [4—6]. 

All these oxidants form t-complexes by accepting electrons from olefinic bonds, a property which has been widely discussed Oxidations by these species are not, however, restricted to olefinic compounds and there is considerable evidence that they are not totally restricted to two-equivalent action. Kinetic data on their oxidations, once rare, has become profuse in the last decade both for aqueous and non-aqueous media. 

Coopersmith C. and Lenington S. (1998). Pregnancy block in house mice (Mus domesticus) as a function of t-complex genotype examination of the mate choice and male infanticide hypotheses. J Comp Psychol 112, 82-91. 

The very nucleophilic C=S function of 1,3,4,5-tetramethylimidazolium-2-dithiocarboxylate gives a molecular 1 1 C.T. complex with iodine, but with... 

Synthetic organic chemistry applications employing alkane C-H functionalizations are now well established. For example, alkanes can be oxidized to alkyl halides and alcohols by the Shilov system employing electrophilic platinum salts. Much of the Pt(ll)/Pt(rv) alkane activation chemistry discussed earlier has been based on Shilov chemistry. The mechanism has been investigated and is thought to involve the formation of a platinum(ll) alkyl complex, possibly via a (T-complex. The Pt(ll) complex is oxidized to Pt(iv) by electron transfer, and nucleophilic attack on the Pt(iv) intermediate yields the alkyl chloride or alcohol as well as regenerates the Pt(n) catalyst. This process is catalytic in Pt(ll), although a stoichiometric Pt(rv) oxidant is often required (Scheme 6).27,27l 2711... 

Reactions between di-iodine and the thioamides (l)-(5) lead to the formation of charge transfer (c.t.) complexes with the so called spoke or extended spoke stractures (DS I or DS I - Ij) according to the general reaction shown in Scheme 13.1 [10]. 

The S-I-I gronp has a linear structure with an angle of almost 180°. The N-C-S-I torsion angle is also fonnd almost equal to 180° indicating an almost co-planar arrangement of the I towards >C=S bond except the case of [(PTU) complex, where it is fonnd to be -95.93°. In fact [(PTU)IJ complex is the first c.t. complex with perpendicnlar arrangement of I towards >C=S characterized by X-ray ciystal-lography [3],... 

Onr resnlts strongly indicate that the antithyroid drugs PTU (2) and N-Methyl-2-mercapto-imidazoline (MMI) have a different way of action. Thns, (2) together with NMBZT (4) forming weak S-I c.t. complexes (Table 13.1) may interfere either by inhibiting TPO activity or by inhibiting Deiodinase (ID-1) enzyme which is responsible for the formation of T3 from T4 hormone. 

In conclusion, while 6-alkyl-2-selenouracil compounds (RSeU) are stable in various solvents, including water and other polar or non-polar solvents, spoke c.t. complexes of formnlae [(RSeU)IJ are formed in dichloromethane solutions, but are unstable in methanol/acetonitrile and/or acetone solntions. [(RSeU)IJ is transformed to 6-alkyl-2-nracil in methanolic/acetonitrile solntions. Upon re-crystallization in acetone the diselenides are formed possibly throngh the formation of a substituted selenouracil as indicated by H, NMR spectra and ESI-MS spectra. The whole process may be hydrolytic (Scheme 13.5). 

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