Claude Chuit

Intramolecular coordination at phosphorus: donor-acceptor interaction in three- and four-coordinated phosphorus compounds

Abstract The phosphorus derivatives P(X)(O2C6H4−1,2)2[C6H4(CH2NMe2)2−2] (9–11) undergo ready extension of coordination by N → P intramolecular donor-acceptor interaction as shown by 31P NMR and dynamic 1H NMR spectroscopy. This extension of coordination does not occur with P(X)(OEt)2[C6H4(CH2NMe2)2−2] (7 and 8). The ΔG≡ of pseudo-rotation was calculated by dynamic 1H NMR spectroscopy to be 57–58 kJ mol−1 for the three compounds P(X)O2C64−1,2)2[C10H6(NMe2−8)] (19–21).

Reactivity of hypervalent species of silicon: cleavage of the allyl-silicon bond

Abstract The reactivities of the silicon-allyl bonds in two kinds of pentacoordinated silicon species CH2CHCH2Si(o-O2C6H4)2 −NMe4+ (1) and CH2CHCH2- Si(OCH2CH2)3N (2) has been compared. In the allyl transfer to carbonyl compounds under nucleophilic conditions (NaOMe, KF or Bu4NF) and electrophilic conditions (TiCl4, AlCl3, BF3) these two species show quite different behaviour. Complex 1 is activated by nucleophiles, while for 2 transfer occurs under electrophilic conditions. These results indicate that the reactivity of these species is a function of their overall charge and geometry.

Preparation and characterization of new organic-inorganic hybrid materials incorporating phosphorus centres

The reaction of p-bromo(triisopropyloxysilyl)benzene 2 with magnesium led to stable THF solutions of the corresponding Grignard reagent. The reaction of this latter with PCl3 or PhPCl2 allowed the preparation of phosphines 4 and 5 respectively. LiAlH4 reduction of 4 afforded phosphine 6. Compounds 4 and 6 have been transformed into phosphorus derivatives including BH3, W(CO)5, platinum and palladium complexes, all of them bearing three hydrolysable groups. Hydrolysis and condensation of these phosphorus derivatives in the presence of an acid catalyst result in the formation of new hybrid organic-inorganic silica gels incorporating phosphorus centres. Solid state 13C, 29Si, 31P NMR spectroscopies were used to evaluate the integrity of the organic moiety and to determine the degrees of hydrolysis and condensation in the network materials. It was shown that during the sol-gel process there is no alteration around the phosphorus centre. The xerogels are amorphous microporous materials with specific surface areas lying between less than 10m2g1 and 800m2g1 depending on the experimental conditions. In contrast with these results, complete cleavage of the SiC bonds was observed during the hydrolysis and polycondensation of the tris-(triisopropyloxysilylmethyl)phosphine 7 and of tris(trihydrosilylmethyl)phosphine 8.

Organic-inorganic hybrid materials. Preparation and properties of dibenzo-18-crown-6 ether-bridged polysilsesquioxanes

Dibenzo-18-crown-6 ether derivatives bearing two (1, 2) or four (3) hydrolysable Si(OR)3 groups have been synthesised. Their hydrolysis and polycondensation gave rise to new hybrid organic–inorganic materials incorporating dibenzo-18-crown-6 ether moieties covalently linked to silica by two or four Si–C bonds. The complexation of alkali metal cations (Na+ and/or K+) by these materials was investigated. A survey of the uptake of cations showed that four types of chelating sites exist within these materials, the ratio of which depends on the nature of the precursor (flexibility of the spacers between the benzene rings and the silicon centres and number of hydrolysable Si(OR)3 groups) and also on the degree of condensation σ of the polysiloxane network. Furthermore, the complexation of K+ by the precursors 1, 2 and 3 and of Na+ by 1 were performed quantitatively. During the sol–gel polymerisation of these complexes it was shown that about 95% of the alkali cations were retained within the xerogel. This study proves that the two routes of incorporation of salts within these hybrid materials are not equivalent.

On the nucleophilic activation of silyl enol ethers and esters; a survey and mechanistic interpretation

Abstract Two distinct mechanisms of nucleophilic activation of silyl enol ethers and esters which have been put forward in the literature are described. The first involves the formation of a “naked” enolate aniion and the second involves hypervalent silicon intermediates. A unified approach accounting for the various experimental results is proposed. The first step is common to both, and involves the formation of a pentacoordinate species whatever the catalyst. Subsequently two competing processes can take place, depending on the fluoride anion source, both involving nucleophilic attack on the pentacoordinate silicon species: with “naked” fluoride anion a free enolate is formed, whereas with the less reactive fluoride anion the silicon is further coordinated by the substrate (carbonyl compound) to give a hexacoordinate silicon itnermediate.

N → P intramolecular stabilization of phosphenium ions and preparation of hypercoordinated phosphanes with unusual properties

The reaction of ArLi 1 (Ar = [C6H3(CH2NMe2)2-2,6]) with Ph2PCl affords the phosphane 2 which, on treatment with HCl, gives rise to the monoprotonated ammonium salt 3, even in the presence of an excess of HCl. 2 reacts with MeI to give exclusively the phosphonium salt 4. Reaction of 1 with PhPCl2 gives the stabilized phosphenium ion [ArPPh]+Cl−6. This ion is reduced by LiAlH4 in ArPHPh 9, which undergoes hydride abstraction on treatment with trityl cation, giving the same ionic phosphorus species. This unusual reaction is an example of increased reactivity of a PH bond resulting from hypercoordination at the phosphorus atom.

MORE INFORMATION ABOUT THE EXISTENCE OF SILICONIUM IONS

Abstract We confirm that compounds 2 bearing a SiH bond are siliconium ions. In contrast we show that the non-functional cationic compounds 4–7 exist as silylammonium ions or siliconium ions depending on the counteranion and on the solvent.

Evidences for intramolecular N →P coordination in (8-dimethylamino-1-naphthyl) diphenylphosphane and derivatives

Abstract An extension of coordination by intramolecular N → P donor-aceptor interaction in (8-dimethylamino-1-naphthyl)diphenylphosphane 1 has been shown by X-ray structure determination. In addition, a very easy intramolecular isomerisation process around the phosphorus atom at room temperature was revealed by dynamic NMR studies. Isomerisation also occurs in the corresponding oxide 2, sulfide 3, and phosphonium salts 4 and 5, but with slightly higher activation energies.

Pentacoordinate silicon compounds. Reactions of silatranes with nucleophiles

Abstract The reactions of hydro, organyl and halosilatranes with nucleophiles have been studied. Substitution involving cleavage of equatorial SiO bonds is always observed. Silatranes exhibit reactivity quite different from that of analogous trialkoxysilanes or anionic pentacoordinate silicon compounds.

Preparation And Structure Of Phosphonium Ions With Intramolecular P N Coordination; Novel Diphosphonium Salts And Ionomer Containing Backbone Hypervalent Phosphorus

Starting from R′R2P (R′ = 8-dimethylamino-1-naphthyl) containing a donor dimethylamino group, the new phosphonium salts [R′R2P(CH2Ph)]+Br– [R = Me (9) or Ph (10)] and [R′R2P(p-CH2C6H4CH2)PR2R′]2+[2Br]2– [R = Ph (12)] have been prepared. An interaction between the N and P atoms is evident from the X-ray crystal structure of 10 the N–P distance being less than the sum of the van der Waals radii of the 2 atoms. The geometry of 10 is that of a monocapped tetrahedron whereas the X-ray crystal structure determination shows essentially regular tetrahedral geometry for the analogous compound without the donor amino group, [(1-Np)Ph2P(CH2Ph)]+Br– (11). Treatment of 1,5-bis(dimethylamino)-2,6-dilithionaphthalene with chlorodiphenylphosphane gave 1,5-bis(dimethylamino)-2,6-bis(diphenylphosphanyl)naphthalene (8) which in the presence of methyl iodide afforded the diphosphonium salt [1,5-bis(dimethylamino)-2,6-bis(diphenylmethylphosphonium)naphthalene]2+[2I]2– (13). Similarly, treatment of 8 with 1 equivalent of benzyl bromide gave the monophosphonium salt [1,5-bis(dimethylamino)-2diphenylbenzylphosphonium-6-diphenylphosphanyl-naphthalene]+[Br]– (14) whereas in the presence of 2 equivalents of the same reagent [1,5-bis(dimethylamino)-2,6-bis(diphenylbenzylphosphonium)naphthalene]2+[2 Br]2– (15) was obtained. The ionomer poly([(1,5-bis{dimethylamino}2,6-bis{diphenylphosphonium}naphthalene)-(P,P-p-xylylene)]2+[2 Br]2–) (16), soluble in liquid SO2, was prepared by treatment of 8 with α,α′-dibromo-p-xylene.