Additives complexation with

This has been explained by the formation of additional complexes with e-doner, which increases the rate of reaction with stabilization of incipient osmium cations,... 

In Chapter 3, it was mentioned that positive ions can form addition complexes with 7T systems. Since the initial step of electrophilic substitution involves attack by a positive ion on an aromatic ring, it has been suggested that such a complex, called a % complex (represented as 10), is formed first and then is converted to the arenium ion 11. Stable solutions of arenium ions or 7t complexes (e.g., with Br2, l2> picric... 

The two component form an addition complex with diethyl ether, which exploded violently after partial desiccation an ether-free complex is also unstable. 

The ions Sm+, Eu+, Tm+, and Yb+ form addition complexes with 1,3,5-tri-ferf-butylbenzene (130), whereas other lanthanide ions form dehydrogenation products (see Section III.A.2). 

Theory The assay of cholesterol is solely based on the fact that practically all 3 (3-hydroxysterols e.g., cholesterol, readily produces an insoluble molecular addition complex with pure digitonin (1 1)—a steroidal saponin isolated from either Digitalis purpurea or Digitalis lanata. The complex thus obtained is crystalline in nature, fairly stable and possesses very low solubilities. 

Salts of substituted biguanides with N-acylsulphonamides, of general structure [RS0zN-C0R ] [R NH2C( NH)NH-C( NH)NH2] have been prepared (JSO), as have addition complexes with 2-hydroxy-4,6-dimethylpyrimidine (477). 

It is evident, however, that this problem can be much more comphcated than either the wetted wall column or the catalytic wall reactor, because it combines the complexities of both. In fact, there are numerous additional complexities with this reactor beyond those simplified cases. 

Chemical vapor infiltration (CVl) is similar to CVD in that gaseous reactants are used to form solid products on a substrate, but it is more specialized in that the substrate is generally porous, instead of a more uniform, nominally flat surface, as in CVD. The porous substrate introduces an additional complexity with regard to transport of the reactants to the surface, which can play an important role in the reaction as illustrated earlier with CVD reactions. The reactants can be introduced into the porous substrate by either a diffusive or convective process prior to the deposition step. As infiltration proceeds, the deposit (matrix) becomes thicker, eventually (in the ideal situation) filling the pores and producing a dense composite. 

Aluminum chloride loses its activity when dissolved in excess methanol but yields a catalyst when converted to its monomethanolate (AICI3—CH3OH). On the other hand, the dimethanolate has no catalytic activity. Nitroalkanes (such as nitromethane) form 1 1 addition complexes with aluminum chloride that modify its reactivity and are used for more selective alkylations.90... 

A few calcium complexes having nitrogen ligands are known. Calcium halides form addition complexes with NH3 such as CaCl2wNH3 (n = 2,4,8) and CaBr2fiNH3 (n = 2,4,6,8). Hexaammine calcium [12133-31 -2], Ca(NH3)6, is formed by reaction of calcium metal and anhydrous NH3 (11) (see... 

Significantly, however, if the C02 is introduced into the solution after formation of the oxidative addition complex with acetonitrile, C02 insertion does not proceed. This is positive evidence that the mechanism of insertion in this particular reaction does not involve direct insertion into the metal-carbon bond. 

Air. Like all other ethers, dioxane forms explosive peroxides on exposure to air and these may be hazardous if the dioxane is distilled. Since dioxane is miscible with water, peroxides should be removed by passing the liquid through a column of activated alumina. The alumina should be washed with water or methanol before being discarded.4 Nickel. Dioxane reacts almost explosively with Raney nickel above 210°C.5 Sulfur Trioxide. The addition complex with sulfur trioxide decomposes violently on storage.6... 

Section 3.4.6—which, by the way, referred to Sharpless epoxidations—you learned that catalytic asymmetric syntheses are among the most elegant asymmetric syntheses and that they can rely on a substrate reacting (exclusively) with an enantiomerically pure reagent that is formed in situ from an achiral precursor molecule and a catalytic amount of an enantiomerically pure additive. It was emphasized that an exclusive reaction of this precursor molecule/additive complex with the substrate takes place if it is much more reactive than the achiral precursor molecule without the enantiomerically pure additive. If under these circumstances additive control of stereoselectivity occurs, this principle even allows recovery of the enantiomerically pure additive after the conversion, which is more convenient than if it could only be released from the product via a chemical reaction. 

Compared to diazonium salts, diazo compounds are generally much less reactive towards nucleophiles than towards electrophiles. As a result of this azo coupling reactions of diazo compounds are the exception rather than the rule. Electron withdrawing substituents on the diazo carbon increase the reactivity towards nucleophiles. Consequently the ability to undergo azo coupling reactions increases from diazomethane to diazocarbonyl- and 2-diazo-l, 3-dicarbonyl compounds. Among the earliest reactions known were those with cyanide and sulfite ions Tertiary phosphines, as opposed to amines, can form stable addition complexes with diazoalkanes probably due to the ability of phosphorus to stabilize the betaine with its empty d orbitals (6). 

Cationic phosphine/phosphite -allyliron complexes are more rare. Aside from the previously mentioned report of the preparation of (139a), complex (139b) has been made from the reaction of allyl halides and Fe[P(OMe)3]5. Additionally, complexes with mixed CO/phosphine ligands (139c) have been prepared by the reaction of either (135 X = Br) or [( -allyl)Fe(CO)3]2 with two equivalents of phosphine, followed by NaBPlu addition. ... 

The reaction of Os3(CO)i2 with H2 at 110°C. produces a reactive, unsaturated hydrido cluster Os3(/u.-H)2(CO)io. This dark purple complex is analogous to diborane and has the two hydrides bridging a very short Os s bond. It can add phosphines, phosphites, arsines, pyridine, and isocyanides to form Os3H2(CO)ioL (Scheme 25). The hydrido cluster adds alkenes and alkynes. Initially, an addition complex with a r-bonded alkene or alkyne is formed. Hydride addition to the unsaturated ligand follows. 

The poly(vinyl alcohol)-iodine charge transfer complexes have been the subject of many investigations " Water-soluble iodine complexes with ix)ly(l-vinyl-pyrrolidone) are commercially available as disinfecting agents PoIy(N-vinyl car-bazole) polyamides and poly(ethylene oxide) are also found to form molecular addition complexes with iodine and iodine compounds. An account of the different types of molecular complexes formed with various polymers has been published ... 

I Dinitrogen tetroxide can give additional complexes with compounds possess- l an ether bond. They were examined by Shechter et al. and described in his jflvlew paper [48]. 

T- Urbariski (Vol. ILpp. 167, 169) and later VViunowski I2 have shown by way of thermal analysis that some f7-miro cotnpounds such aso-mamiiud hc a-nilrate and erythrilol tetranitrate can form additional complexes with aromatic iiitro compounds. 

Codeine is unaffected by Grignard reagents [374], but codeine methyl ether forms simple addition complexes with ethyl- and phenyl-magnesium halides these are readily decomposed with liberation of the unchanged base [375]. 

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