Phosphine, acid strength

Effects of acid strength and anion concentration have been studied as well as the effect of monodentate amines.564,565 Phosphines, in particular dppp, have been used as favorable ligands,566,567 but it has been shown that dppp is oxidized by nitrobenzene under the prevailing conditions.568 Giant clusters and heteropolyanions have been used.569,570 The role of nitroso... 

A variety of organophosphine transition-metal complexes have been used for the detection of SO2 [149]. Cook et al. used triphenyl- and tribenzyl phosphine compounds as ligands bound to Cu and Mn. Varying the ligand affects the Lewis acid strength of the metal complex, and hence, its ability to bind SO2. One complex (bis(tribenzylphosphine)copper(II) thiophenolate — [Cu(PBz3)2)SPh]) exhibited a reversible response to SO2 that was linear in the range of lO-KKK) mg/L. 

G. A. Kumar and M. A. McAllister, Theoretical investigation of the relationship between proton NMR chemical shift and hydrogen bond strength, J. Org. Chem. 63, 6968-6972 (1998). L. Gonzalez, O. Mo, M. Yanez, and J. Elguero, Very strong hydrogen bonds in neutral molecules the phosphinic acid dimers, J. Chem. Phys. 109, 2685-2693 (1998). 

Acid strengths are compared in Table 5.21. With given alkyl substituents, the acidity of a phosphinic acid is generally less than those of the corresponding phosphonic or phosphoric acids. For methyl derivatives the pA"j values lie in the order ... 

Other highly active palladium chloride-based catalysts include di-2-pyridylmethylamine-based paUadium, tr(WM-bidentate pyridine, and PdCl2/phosphinous acid complexes. Typical examples are shown in Scheme 2. This section is concerned with the coupling reactions of aryl chlorides using the above PdCh-based catalysts. Chloro arenes are cheap to manufacture and therefore play a vital role as intermediates in the chemical industry. The low reactivity of chlorides is usually attributed to the strength of the C-Cl bond. Remarkable progress has been achieved since 1998 in the development of palladium-based catalysts that can in fact accomplish cross-couplings and Heck reactions. ... 

With this last point in mind, the synthesis of mono-, bis- and tra-sulfonated triphenylphosphine will be described, but the same methodology can be applied to the preparation of other sulfonated arylphosphines. In general, these phosphines are made by direct sulfonation using fuming sulfuric acid (oleum) [21], The extent of sulfonation is determined by the SO3 strength, as well as factors such as the temperature and time of the reaction. The monosulfonated phosphine (tppms) is prepared using oleum of 20% SO3 strength, with typically 30% SO3 used... 

Fuming sulfuric acid (oleum) of 20% SO3 strength is suitable for preparation of monosulfonated products [1-3] while for multiple sulfonation 30% (or more) SO3 is required [4-10], The phosphine is dissolved in cold oleum with protonation of the phosphoms atom therefore in cases when the phenyl rings are directly attached to the phosphoms (e.g. triphenylphosphine or the bis(diphenylphosphino)alkanes) sulfonation takes place in the 3-position. 

The strength or coordinating power of different Lewis acids can vary widely against different Lewis bases. Thus, for example, in the case of boron trihalides, boron trifluoride coordinates best with fluorides, but not with chlorides, bromides, or iodides. In coordination with Lewis bases such as amines and phosphines, BF3 shows preference to the former (as determined by equilibrium constant measurements).66 The same set of bases behaves differently with the Ag+ ion. The Ag+ ion complexes phosphines much more strongly than amines. In the case of halides (F, CP, Br, and P), fluoride is the most effective base in protic acid solution. However, the order... 

The phosphonitrilic halides are weaker bases than are some related nonaromatic compounds, just as pyridine is a weaker base than piperidine. The bond type in the phosphonitrilic series is probably the same as in the phosphine-imines RaPrNR (80, 81) the stability of these compounds, too, increases with the electronegativity of the substituents on the phosphorus. Tetraphenylphosphine-imine is one of the most stable of these compounds, and forms a hydrochloride. Its base strength is therefore greater than those of the phosphonitrilic halides, presumably because the opportunities for electronic delocalization are less. The Af-ethyl ester of the trimeric phosphonitrilic acid, which has a cyclic structure, but in which resonance of the same type as in the phosphonitrilic halides cannot occur, also forms a hydrochloride ( 1). It is, therefore, a comparatively strong base, in spite of the inductive effect of the two oxygen atoms on the phosphorus. The extreme weakness of the phosphonitrilic halides as bases cannot therefore be wholly due to the inductive effect of the halogens. 

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