Phosphine ligands nucleophilic substitution

Berry turnstile pseudorotation mechanism. Interestingly, with an excess of less sterically demanding nucleophiles such as PMe3, PPh3, or P(OMe)3, only one of the phosphine ligands is substituted, yielding 67 when the nucleophile is carbon monoxide, probably by a dissociative mechanism [293],... 

Recently, the scope of the allylic substitution has been extended to sulfinate salts 84 to obtain allylic sulfones 85. Due to solubility problems of both nucleophile 84 and carbonate leaving group, a polar solvent mixture of DMF and 2-methoxyethanol had to be employed, which limits the reaction to the use of a phosphine ligand. Thus, various aryl sulfinates 84 and functionalized carbonates 81 could be converted to the corresponding allylic sulfones 85 with good to excellent yields and regioselectivites and complete retention of stereochemistry (eq. 2 in Scheme 20) [65]. 

The protocol of the allylic alkylation, which proceeds most likely via a c-allyl-Fe-intermediate, could be further improved by replacing the phosphine ligand with an M-heterocyclic carbene (NHC) (Scheme 21) [66]. The addition of a ferf-butyl-substituted NHC ligand 86 allowed for full conversion in the exact stoichiometric reaction between allyl carbonate and pronucleophile. Various C-nucleophiles were allylated in good to excellent regioselectivities conserving the 71 bond geometry of enantiomerically enriched ( )- and (Z)-carbonates 87. Even chirality and prochirality transfer was observed (Scheme 21) [67]. 

Asymmetric allylation of carbon nucleophiles has been carried out extensively using Pd catalysts coordinated by various chiral phosphine ligands and even with nitrogen ligands, and ee > 90% has been achieved in several cases. However, in most cases, a high ee has been achieved only with the 1,3-diaryl-substituted allylic compounds 217, and the synthetic usefulness of the reaction is limited, Therefore, only references are cited[24,133],... 

Non-activated aryl bromides (but not fluorides) can be used as substrates for palla-dium(0)-catalyzed aromatic nucleophilic substitutions with aliphatic or aromatic amines. These reactions require sodium alcoholates or cesium carbonate as a base, and sterically demanding phosphines as ligands. Moreover, high reaction temperatures are often necessary to achieve complete conversion (Entries 7 and 8, Table 10.4 Experimental Procedure 10.1). Unfortunately, the choice of substituents on the amine... 

Fluoroarene-Cr(CO)2L complexes 33p [L = CO, PPh3, P(OPh)3, P(pyrrolyl)3, P(pyrolyl)2 (NMeBn)], where L is a potential linker ligand for solid-phase synthesis, have been evaluated with regard to the rates of nucleophilic substitution by amines [35]. The preparative and kinetic results indicate that SNAr reactions on tris(pyrrolyl)phosphine-modified fluoroar-enechromium complexes proceed rapidly and with high efficiency, and are thus appropriate for the development of solid-phase versions for use in combinatorial synthesis (Scheme 18). 

The organic chemistry of phosphorus is scattered about the book with important reactions in Chapters 14 and 31 (the Wlttig reaction). 17 (various nucleophilic substitutions), 23 (conjugate addition of phosphines), and 41 (mechanisms involving phosphorus), in Chapter 46 you will see how important phosphorus compounds are as ligands for transition metals. 

The coordination chemistry of diphosphine and diarsine ligands has been intensively investigated in recent years.i Very much less work has been carried out on the corresponding mixed ligands, the intermediate arsine-phosphine bidentates, owing to a considerable extent to the lack, until recently, of suitable synthetic routes to such ligands. Two routes are now available the nucleophilic substitution of organohalogen compounds, two examples of which... 

In the allylic substitution of racemic 2-propenyl acetates or related substrates with the same substituents at 1 and 3 positions, the jt-allylpalladium intermediate containing a meso type 7r-allyl group is formed from both enantiomers of the allylic substrate. Two jt-allyl carbons at the 1- and 3-positions are diastereotopic on coordination of a chiral phosphine ligand to palladium. The asymmetric induction arises from preferential attack by the nucleophile on either of the two diastereotopic TT-allyl carbon atoms (Scheme 2-28). 

Allylic ethers and alcohols have long been known to react with Grignard reagents in the presence of an appropriate Ni-based complex containing phosphine ligands [26]. These reactions are related to the well-studied Pd-catalyzed allylic substitution reactions that utilize soft nucleophiles [27], and a number of important mechanistic studies on the stereochemical outcome of this class of transformations have been carried out [28]. 

---