Phosphines, alkylation silyl

For a long time, the only coordination mode known for these complexes was the SBP. The group VI (Cr, Mo, W) pentacarbonyl complexes were the first to be observed, and many others with this geometry were later characterized with different metals (Ru(II), Rh(III), Ir(III), etc) and very varied ligands (alkyl, silyl, phosphine, halide, etc.). In all these complexes, the angle between two basal transoid ligands lies between 160° and 180° three examples are shown in 4-28. 

The relatively stable (arylsulfonylmethyl)iodonium salts 763 (Section 2.1.9.5) are efficient electrophilic alkylating reagents towards various organic nucleophiles (thiophenolate anion, amines, pyridine, triphenyl phosphine and silyl enol ethers). All these reactions proceed under mild conditions and selectively afforded the appropriate product of alkylation along with iodobenzene as the by-product (Scheme 3.299) [1016]. 

On the other hand, with alkyl silyl ketones or w ith acylgermanes, only the normal Wittig products, alkene and phosphine oxide, were obtained in good yield. 

The stable P-unsubstituted phosphinous amide H2PN(SiMe3)2 has been shown to suffer the nucleophilic displacement of the disilazane moiety by the action of thiols R-SH giving the phosphinous thioesters R-S-PH2 [13]. For the sake of brevity we shall not comment on other relevant reactions of AT-silyl phosphinous amides, such as the anionic P-silylation [115] and P-alkylation [22], the consecutive dialkylation of PH derivatives [18] and the fluorodesily-lation of P-fluoro-JV-silyl derivatives [140]. 

In a related strategy, ethynylphosphines (81) have been prepared with a view to synthesising polyphosphacyclopolyyne materials such as (82) (Scheme 24) [70]. Interaction between the phosphorus lone pairs and the organic 71-systems is supported by the fact that the phosphorus atoms of mono- and di-silyl-capped analogues of bis(arylphosphine) derivative (81) exhibit an unusually low inversion barrier (65 kj mol versus 130-140 kj mol for classical alkyl-or aryl-phosphines). Indeed, the rings (82) exhibit values of at ca. 300 nm, consistent with this assumption. 

Derivatization reactions. In addition to changing the substituents in the primary precursor phosphines, (MegSi)2NPRR , two other approaches have been used to prepare polymers with more complex substituents attached to the backbone by direct P-C linkages. These are (a) alteration of R and R in the immediate N-silylphosphoranimine precursors, MegSiN=P(OOUCFo)RR , and (b) alteration of R and R in the preformed poly(alkyl/aryl-phosphazenes), (RR P=N]n. Some examples of the former method are described below and in other papers (21-23), while the use of the latter approach to prepare several silylated poly(alkyl/arylphosphazenes) has been recently reported. (20)... 

Catalytic asymmetric hydrosilylation of prochiral olefins has become an interesting area in synthetic organic chemistry since the first successful conversion of alkyl-substituted terminal olefins to optically active secondary alcohols (>94% ee) by palladium-catalyzed asymmetric hydrosilylation in the presence of chiral monodentate phosphine ligand (MOP, 20). The introduced silyl group can be converted to alcohol via oxidative cleavage of the carbon-silicon bond (Scheme 8-8).27... 

The most common method for the synthesis of phosphinopeptides is the addition of a nucleophilic, trivalent phosphorus species to a carbon electrophile, including conjugated double bonds, alkylating agents, imines, and carbonyl compounds. By analogy with the phosphite ester additions described above, the nucleophilic form of a phosphinic acid is the trivalent species, generated from the more stable, pentavalent PH derivative by deprotonation or by silylation (cf. Scheme 2). 

The 1,4-disilylation of a,/3-unsaturated ketones has been reported by Ito and co-workers.172 Unsymmetrically substituted disilanes, PhCl2SiSiMe3 and Cl3SiSiMe3, undergo reaction in the presence of catalytic amounts of palladium complexes with tertiary alkyl phosphine or bidentate phosphine ligands to yield /3-silyl ketones [Eq. (64)]. 

Me3SiPPh2 assists in the insertion of CO into the Mn-R bond or RMn(CO)5 (R = alkyl or aryl) followed by silyl migration to oxygen. With Mn(CO)5H, however, only cis-substitution by the phosphine occurs, while with the cyclopentadienyl metal tricarbonyl hydrides, silylation occurs at the metal (Scheme 23)92. 

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