Transition phosphonate

Multilayers of Diphosphates. One way to find surface reactions that may lead to the formation of SAMs is to look for reactions that result in an insoluble salt. This is the case for phosphate monolayers, based on their highly insoluble salts with tetravalent transition metal ions. In these salts, the phosphates form layer stmctures, one OH group sticking to either side. Thus, replacing the OH with an alkyl chain to form the alkyl phosphonic acid was expected to result in a bilayer stmcture with alkyl chains extending from both sides of the metal phosphate sheet (335). When zirconium (TV) is used the distance between next neighbor alkyl chains is - 0.53 nm, which forces either chain disorder or chain tilt so that VDW attractive interactions can be reestablished. 

The cyclic phosphonate ester analog of the cyclic transition state. Antibodies raised against this phosphonate ester act as enzymes they are catalysts that markedly accelerate the rate of ester hydrolysis. 

Dialkyl dimethyl phosphoramidites (16) react with j8-propiolactone to give the phosphoramidate (17) and the phosphonate (18), A kinetic study suggests a mechanism involving initial attack of phosphorus at saturated carbon to give (17), while a four-centred transition state (19) is invoked to explain the formation of (18). 

The discussion of the activation of bonds containing a group 15 element is continued in chapter five. D.K. Wicht and D.S. Glueck discuss the addition of phosphines, R2P-H, phosphites, (R0)2P(=0)H, and phosphine oxides R2P(=0)H to unsaturated substrates. Although the addition of P-H bonds can be sometimes achieved directly, the transition metal-catalyzed reaction is usually faster and may proceed with a different stereochemistry. As in hydrosilylations, palladium and platinum complexes are frequently employed as catalyst precursors for P-H additions to unsaturated hydrocarbons, but (chiral) lanthanide complexes were used with great success for the (enantioselective) addition to heteropolar double bond systems, such as aldehydes and imines whereby pharmaceutically valuable a-hydroxy or a-amino phosphonates were obtained efficiently. 

Zn -PDF, 37 pM versus E. coli Fe -PDF), it was successfully used to provide co-crystals bound in the active site of both Co - and Zn -E. coli PDF [58], These structures reveal that the H-phosphonate binds to the metal in a monodentate fashion, adopting a tetrahedral coordination state similar to that of the native resting state of the enzyme. This is in contrast to later co-crystal structures obtained with more potent hydroxamic acid or reverse hydroxamate inhibitors, which bind to the metal in a bidentate fashion vide infra). Presumably these bidentate inhibitors mimic the true transition state of the enzyme, in which the metal centre slips to a penta-coordinate geometry in order to activate the Wformyl carbonyl of the substrate [56, 67]. 

Aldol addition and related reactions of enolates and enolate equivalents are the subject of the first part of Chapter 2. These reactions provide powerful methods for controlling the stereochemistry in reactions that form hydroxyl- and methyl-substituted structures, such as those found in many antibiotics. We will see how the choice of the nucleophile, the other reagents (such as Lewis acids), and adjustment of reaction conditions can be used to control stereochemistry. We discuss the role of open, cyclic, and chelated transition structures in determining stereochemistry, and will also see how chiral auxiliaries and chiral catalysts can control the enantiose-lectivity of these reactions. Intramolecular aldol reactions, including the Robinson annulation are discussed. Other reactions included in Chapter 2 include Mannich, carbon acylation, and olefination reactions. The reactivity of other carbon nucleophiles including phosphonium ylides, phosphonate carbanions, sulfone anions, sulfonium ylides, and sulfoxonium ylides are also considered. 

Guilbault GG, Das J. 1969. Chemisorption reactions of diisopropylmethyl phosphonate with transition metal salts. Journal of Physical Chemistry 73(7) 2243-2247. 

Although transition metal-mediated P-H addition across ordinary alkenes proceeds well only with five-membered cyclic hydrogen phosphonates, addition across the olefinic linkage of a,P-unsaturated compounds occurs readily with a range of phosphorus species and catalytic agents. Of particular note are the reaction systems involving platinum,96-107 palladium,108-115 and the lanthanides.116-122... 

A photoinitiated reaction has been reported of trialkyl phosphite with an electron-deficient vinylic halide for which an olefinic carbon is covalently bound to a metallic center (Figure 6.24).92 Unfortunately, only low yields of the target phosphonate are obtained. In another report involving a transition metal bound to carbon, an acetylenic carbon covalently bound to an iron center has been found to undergo... 

Enantioselective synthesis of a-hydroxy phosphonates can also be achieved by asymmetric oxidation with camphorsulfonyl oxaziridines (Scheme 2-60).156 Reasonable yields can usually be obtained. (+)-147a or (+)-147b favors formation of the (S )-product, as would be expected, because these oxidations proceed via a transition state that parallels that previously discussed for the stereoselectivity observed with ketones.157... 

An example of esterase behaviour is provided by a catalytic antibody developed by Tramontano et al. (1988), using a phosphonate transition state analogue [53] as the hapten. The antibody cleaves the carboxylic ester [54, R = Me] with enzyme-like efficiency (kc/ku = 6.25 X 106 = 1.5 mM ... 

Use transition metal sequestrants such as phosphonates or nitrilotriacetic acid in the formulation containing peroxygen bleaches, since transition metals can catalyze the decomposition of peroxide. 

Transition states of this tetrahedral nature have now been mimicked effectively by a range of stable analogues, including phosphonic acids, phosphonate esters, a-difluoroketones, and hydroxymethylene functional groups (Jacobs, 1991). Lerner s group elicited antibodies to a tetrahedral anionic phosphonate hapten [3] (Appendix entry 2.9)2 whilst Schultz s group isolated a protein with high affinity for p-nitrophenyl cholyl phosphate [4] (Fig. 4) (Appendix entry 3.2). 

Clearly, the oxyanion hole is now as significant a feature of the binding site of such acyl transfer abzymes as it is already for esterases and peptidases — and not without good reason. Knossow has analysed the structures of three esterase-like catalytic antibodies, each elicited in response to the same phosphonate TSA hapten (Charbonnier et al., 1997). Catalysis for all three is accounted for by transition state stabilization and in each case there is an... 

In order to generate antibodies which catalyse the hydrolysis of carbonates (6, 10), carboxylic esters (9) and amides with a certain degree of specificity, the phosphates (7a. lOai and phosphonates 9a were used as haptens that mimic the tetrahedral negatively charged transition state of the spontaneous hydrolysis reaction (see Scheme 11.3) [27] [29]. 

Transition Metal-Catalyzed Addition of Hydrogen Phosphonate. 36... 

Hydrogen phosphonates [(R0)2P(0)H] and secondary phosphine oxides R2P(0)H exist in equilibrium with their P(III) tautomers, (RO)2P(OH) and R2P(0H), respectively, the P(V) tautomers being more favored under ambient conditions. As ligands, they coordinate, like tertiary phosphines, to transition metals to form complexes, which have been used as catalysts for organic reactions. However, catalytic addition reactions of P(V)-H bonds have not been scrutinized until recently. 

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