Molecular diol complexation

At low temperatures in inert solvents (such as methylene dichloride) a controlled polymerization can be effected using various acids and alkylating agents. These initiators include boron trifluoride etherate, triethylaluminum, trityl hexachloroantimonate, triethylam-monium hexachloroantimonate, diethyloxonium hexafluoroantimonate, p-toluenesulfonic acid and diethylzinc or cadmium-1,2-diol complexes. Crystalline, high molecular weight... 

The l,T-binaphthalene-2,2 -diol complexes of Lewis acids have received considerably more attention. Mikami hrst reported the apphcation of BtNOL/ri(IV) complexes for enantioselective allylations of glyoxylates.ii Keck" and Umani-Ronchi/Tagliavinin independently devised allylation procedures with (/ )-BtN0L/Ti(0-iPr)4 and (5)-BIN0L/Ti(0-iPr)2Cl2, respectively (Scheme 5.2.83). The use of molecular sieves is essential for high reactivity and stereoselectivity. 

Bertheas O., Metzger P, Largeau C. (1999) A high molecular weight complex lipid, aliphatic polyaldehyde tetraterpene-diol polyacetal from Botryococcus braunii (L race). Phytochem. 50, 85-96. 

The system has been used as an analytical tool (4), because the complex formed shows greater conductivity than the sum of the conductivities of the boric acid and the diol compound. Favorably situated diols have a pronounced effect in increasing the conductivity. cis-l,2-Diols fixed in position by molecular structure—e.g., o-dihydroxyphenols and cis-dicyclic polyols—are favorable structures. The reaction is depicted in Figure 2. 

The monoketone bis(2,2, /V,/V -bipyridyl)ketone forms a [CoinL2]+ complex on reaction with [Co(NH3)4(C03)]+ in water.981 As reported for a quite different Co11 complex, the ketone is hydrated to form the gem diol which binds as a monodeprotonated O-donor along with the two pyridine groups in a tridentate chelate, with very little distortion from octahedral observed in the complex. This appears to represent a facile route for this type of inherently poor donor to achieve coordination. Chelated /3-diketonate anions are long-studied examples of O-donor chelates, and continue to be examined. A simple example is the m-[Co(acac)2(NH 3)2]1 (acac = 2,4-pentane-dionate), structurally characterized and utilized to produce molecular mechanics force field parameters for /3-diketones bound to Co111.982... 

ABA triblock copolymers, where A was PBd and B either PS or PMMA were prepared by the combination of ROMP and ATRP techniques [122], The PBd middle blocks were obtained through the ROMP of cyclooctadi-ene in the presence of l,4-chloro-2-butene or cis-2-butene-l,4-diol bis(2-bromo)propionate using a Ru complex as the catalyst. The end allyl chloride or 2-bromopropionyl ester groups were subsequently used for the ATRP of either styrene or MMA using CuX/bpy (X = Cl or Br) as the catalytic system (Scheme 50). Quantitative yields but rather broad molecular weight distributions (Mw/Mn higher than 1.4) were obtained. 

A related enantiomerically pure zinc amide initiator, (340), has also been described.966 This complex catalyzes the alternating copolymerization of CHO and C02 to yield isotactic material (RR SS = 86 14). Similar enantiomeric excesses have been achieved using a mixture of Et2Zn and the chiral amino alcohol (341).967 Molecular weight distributions are much broader than using catalyst (340), but this protocol is still a convenient way to prepare optically pure diols (Scheme 23). 

A theoretical analysis is presented for the binding of the four dia-stereoisomers of benzo[a]pyrene diol epoxides (BPDEs) to N2(g), N6(a), 06(G) and NU(c). Molecular models for binding and stereoselectivity involving intercalation, intercalative covalently and externally bound forms are presented. Molecular mechanics calculations provide the energetics which suggest possible structures for the formation of each of the principal DNA-BPDE complexes. Stereographic projections are used to illustrate the molecular structures and steric fits. The results of previous calculations on intercalation and adduct formation of BPDE l(+) in kinked DNA (37) are summarized and extended to include the four diastereoisomers l( ) and II( ). The theoretical model is consistent with the observed experimental data. 

The catalyst was prepared from the corresponding chiral diol and TiCl2(OPr-/)2 at room temperature in the presence of 4 A molecular sieves. Without molecular sieves, stoichiometric amounts of the titanium complex were required to obtain an equally high enantioselectivity. A remarkable solvent effect was observed. Various cycloadducts were only obtained with high optical yields when non-polar solvents were employed252,253. For example, 4-substituted 4-cyclohexene-1,2-dicarboxylate derivatives 408 were obtained with ee values ranging from 91 to 94% in the reactions of 91a, 399 and 407 with 17b in toluene/... 

Halogens are frequently used as oxidation agents and, under two-phase conditions, they can either be employed as ammonium complex halide salts [3], or in the molecular state with or without an added quaternary ammonium catalyst [4]. Stoichiometric amounts of tetra-n-butylammonium tribromide under pH controlled conditions oxidize primary alcohols and low-molecular-weight alkyl ethers to esters, a,cyclic ethers produce lactones [3], and secondary alcohols yield ketones. Benzoins are oxidized to the corresponding benzils (80-90%) by the tribromide salts in acetonitrile in the presence of benzoyl peroxide [5]. 

The key to a controlled molecular weight build-up, which leads to the control of product properties such as glass transition temperature and melt viscosity, is the use of a molar excess of diisopropanolamine as a chain stopper. Thus, as a first step in the synthesis process, the cyclic anhydride is dosed slowly to an excess of amine to accommodate the exothermic reaction and prevent unwanted side reactions such as double acylation of diisopropanolamine. HPLC analysis has shown that the reaction mixture after the exothermic reaction is quite complex. Although the main component is the expected acid-diol, unreacted amine and amine salts are still present and small oligomers already formed. In the absence of any catalyst, a further increase of reaction temperature to 140-180°C leads to a rapid polycondensation. The expected amount of water is distilled (under vacuum, if required) from the hot polymer melt in approximately 2-6 h depending on the anhydride used. At the end of the synthesis the concentration of carboxylic acid groups value reaches the desired low level. 

To overcome this issue Kureshy et al. [55, 56] reported dimeric form of Jacobsen s catalysts 3, 4. They used the concept of solubility modification by altering the molecular weight of the catalyst so that in a post catalytic work-up procedure the catalyst is precipitated, filtered and used for subsequent catalytic runs. The complexes 3, 4 (0.2 mol % of Co(lll)-salen unit) (Figure 2) were effectively used for HKR of racemic epoxides, e.g., styrene oxide, epichlorohydrin, 1,2-epoxypropane, 1,2-epoxyhexane, 1,2-epoxyoctane, and 1,2-epoxydodecane to achieve corresponding epoxides and 1,2-diols in high optical purity and isolated yields. In this process, once the catalytic reaction is complete the product epoxides were collected by reduced pressure distillation. Addition of diethylether to the residue precipitated the catalyst which was removed by filtration. However, the recovered catalyst was required to be reactivated by its treatment with acetic acid in air. The catalysts were reused 4 times with complete retention of its performance. 

As for the Cg oses molecular models for Cg oses show that the proposed coordination is also favoured for arabitol but not for xylitol. The arabitol complex has the same configuration as mannitol, but the 3-C, 4-C bond cleavage gives 1 Cg and 1 Cg instead of 2 Cg molecules. Therefore the yield of 1,2-propane diol and glycerol is lower for arabitol than for mannitol. 

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