Phosphites electronic effects

Several new spirophosphoranes (e.g. 82) have been derived from a further study of the reactions of phosphites (e,g. 80) with isatin (SI)46. The compounds were characterised by analysis, i.r. and 31P n.m.r. spectra and the course and rates of reaction depend substantially on the steric and electronic effects of the substituents on phosphorus. 

More sterically demanding ligands will favour the formation of species containing a low number of ligands L and therefore more CO ligands. A high proportion of CO ligands also leads to electron poor rhodium species and thus to enhanced dissociation of CO. For phosphites this effect has been clearly observed [40] as will be discussed in section 8.4. 

As discussed for biphenol-based phosphites, phosphites derived from ClMeO-biphenol should also be sterically more demanding and have an increased ring size as compared to catechol-based phosphites. Moreover, by comparing the catalytic results of biphenol- and ClMeO-biphenol-based ligands, conclusions on the influence of the substitution pattern and resulting electronic effects on the activity and selectivity in the hydroformylation can be drawn. Therefore, ClMeO-biphenol-based phosphites with PEG side chains consisting of one to three ethylene glycol units were included in the present study. 

In order to assess steric and electronic effects on the bond enthalpies of reaction of phosphine and phosphite ligands to platinum(II), the enthalpies (AH) of reaction of these ligands L on reaction with [PtMe(PPhMe2)2(THF)]PF6 have been measured (equation 412). These authors measured the enthalpies of 34 ligands, and correlated the measured enthalpy with the ligand cone angles.1342,1343 Representative data are shown in Table 8. 

Steric and Electronic Effects in Cobaloxime Complexes of Phosphines and Phosphites... 

Ogata and Yamashita have studied the kinetics of the reaction of phosphites with aliphatic a-diketones and with benzils to give the adducts (48). In all cases the reaction was second-order, first-order in phosphite and ketone. For symmetrical diketones steric effects appear to control the rate, while in unsymmetrical examples electronic effects are much more important. In cyclic diketones the rate constant decreases... 

S. E. Lyubimov, V. N. Kalinin, A. A. Tyutyunov, V. A. Olshevskaya, Y. V. Dutikova, C. S. Cheong, P. V. Petrovskii, A. S. Safronov, V. A. Davankov, Chiral phosphites derived from carboranes Electronic effect in catalytic asymmetric hydrogenation, Ghirality 2009, 21, 2. 

A nickel-catalyzed route to the formation of arylphosphonates starting from aryl halides and secondary phosphites has been reported (Scheme 4.243) [336]. While some of the methods described previously added nickel salts such as NiCl to the reaction mixture along with a ligand to solubilize/stabilize the metal center, the authors opted to use a preformed nickel complex. A significant electronic effect was observed in this... 

The authors rationalized the selectivity on the basis of electronic effects. With the n-acidic phosphite, Au-C backdonation is limited thus, the gold carbenoid reacts as a carbocation. With the strongly o-donating NHC, Au-C backdonation is more efficient and the gold carbenoid behaves as a carbene. Other theoretical studies on [(NHC)Au]-stabilized carbocations, including non-classical ones, have been reported, yet no specific role of the NHC was highlighted. ... 

The roles of phosphines are not clearly understood and are unpredictable. Therefore, in surveying optimum conditions of catalytic reactions, it is advisable to test the activity of all these important types of phosphines and phosphites. which have different steric effects and electron-donating properties. 

Vanadium compounds in a low oxidation state are known to be effective for inducing one-electron reduction. The highly stereoselective monodebromination of gem-dibromocyclopropanes proceeds with the help of a low-valent vanadium species generated from vanadium(III) chloride and zinc in dimethoxyethane in cooperation with diethyl phosphonate or triethyl phosphite... 

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