Phosphines and halides

Prolonged standing in a THF solution results in its decomposition as outlined above however, by brief warming in THF followed by slow cooling, single crystals of the compound have been obtained. Its molecular stereochemistry is meridional in the solid state.9 Substitution reactions of the THF ligand by phosphine and halide ligands have been described.9,15... 

Since the discovery of catalysts 2 and 3 containing one NHC ligand, the attractive family of NHC-ruthenium complexes has been rapidly expanded. In the following section, the different structural modifications of complexes 2 and 3 reported in the literature will be presented (phosphine and halide ligands, benzylidene ligand, NHC ligand). 

Studies of complexes with different phosphine and halide ligands led to the observation that there is no Unear correlation between the basicity of the phosphine and catalyst initiation (dissociation of the phosphine), since the steric properties of the phosphine also affect the activity of the catalyst. Higher activity was reported for chloride complexes than the corresponding bromide or iodide complexes [50]. 

RT, the protonation equilibrium constant is 203 M for RhCKCOCAsPhj) it is 75 M. Similar K values are found for Ir and Rh complexes with phosphine and halide ligands. Finally, ruthenocene is half-protonated in H SO with an acidity function, Hg, of —5.7, whereas half-protonation of ferrocene requires an Hg of —7.7. 

Crystal structures of the L2X2Ru=CHR carbene complexes reveal that they have a distorted square pyramidal geometry with the alkylidene in the axial position and the trans phosphines and halides in the equatorial plane.R. H. Grubbs and co-workers have conducted extensive kinetic studies on L2X2Ru=CHR complexes and proposed a mechanism that is consistent with the observed activity trends. There are two possible mechanistic pathways (I II) ... 

Platinum(i).—Substitution of the dinuclear [(MeNC)gM2] cation (M2 = Pd2, PdPt, or Pt2) with isocyanides, phosphines, and halide has been examined (seep. 348). Electrochemical reduction of [M S2C2(CN)2 2] (M = Pd or Pt) in MeCN gives M complexes (see p. 348). Two reversible reductions and a one-electron oxidation were also observed for the Pt complexes [Pt (NH)2C2(CN)2 2] -The enthalpy of reaction (IS) has been determined and the results show that the C C... 

An interesting example of both phosphine and halide exchange is observed when a 1 1 mixture of RuCl2(PPh3)3 and cw-RuCl2(PF3)2(PPh3)2 is refluxed in acetone (49). Three geometric isomers of 13 are isolated. 

Tertiary phosphines and primary and secondary phosphines can be oxidized by elemental halogen to halophosphine halides. 

Notable examples of general synthetic procedures in Volume 47 include the synthesis of aromatic aldehydes (from dichloro-methyl methyl ether), aliphatic aldehydes (from alkyl halides and trimethylamine oxide and by oxidation of alcohols using dimethyl sulfoxide, dicyclohexylcarbodiimide, and pyridinum trifluoro-acetate the latter method is particularly useful since the conditions are so mild), carbethoxycycloalkanones (from sodium hydride, diethyl carbonate, and the cycloalkanone), m-dialkylbenzenes (from the />-isomer by isomerization with hydrogen fluoride and boron trifluoride), and the deamination of amines (by conversion to the nitrosoamide and thermolysis to the ester). Other general methods are represented by the synthesis of 1 J-difluoroolefins (from sodium chlorodifluoroacetate, triphenyl phosphine, and an aldehyde or ketone), the nitration of aromatic rings (with ni-tronium tetrafluoroborate), the reductive methylation of aromatic nitro compounds (with formaldehyde and hydrogen), the synthesis of dialkyl ketones (from carboxylic acids and iron powder), and the preparation of 1-substituted cyclopropanols (from the condensation of a 1,3-dichloro-2-propanol derivative and ethyl-... 

In the Wittig reaction an aldehyde or ketone is treated with a phosphorus ylid (also called a phosphorane) to give an alkene. Phosphorus ylids are usually prepared by treatment of a phosphonium salt with a base, and phosphonium salts are usually prepared from the phosphine and an alkyl halide (10-44) ... 

The THT ligand in [AuRX2(THT)] and in other complexes can be displaced easily for other neutral or anionic ligands (e.g., phosphine, amines, halide, etc.), and a wide variety of derivatives... 

Furthermore, a series of mixed diphenyl cyclopropenone complexes was obtained282), in which olefins, phosphines, CO, and halide ion served as additional ligands. 

These reactions may be considered to be a method of obtaining 1,3,2,5-dioxaborataphosphoniarinanes with different substituents at carbon and phosphorus atoms of the ring. Comparing the properties of cyclic oxyalkyl-phosphines and boryloxyalkylphosphines, it should be noted that in both cases the reaction with alkyl halides results in the formation of a tertiary phosphonium salt. The reaction with electrophilic reagents such as diphe-nylchlorophosphine and diphenylchloroborane proceeded quite differently [Eq. (100)]. 

Oxidative addition occurs readily with allylic halides. Donor ligands (tertiary phosphines, bipyridyl, halide ions) and anionic complexes are required for activation of aromatic and vinyl halides (4, 70). Certain aliphatic halides are also reactive. The intermediate species R—Ni—X... 

I, Table X) requires tertiary phosphine-nickel halide or tertiary phosphine-nickel carbonyl complexes at 140-170°C. This implies oxidative addition of aromatic halides to nickel, replacement of the halide with amines, and reductive elimination. 

Rauhut, M.M. and Semsel, A.M., Reactions of elemental phosphorus with organometallic compounds and alkyl halides. The direct synthesis of tertiary phosphines and cyclotetraphosphines, J. Org. Chem., 28, 473, 1963. 

The reaction of phosphines and alkyl halides presents an alternative way to generate phosphonium electrophiles (Scheme 3.8). In particular, the combination of a phosphine and carbon tetrabromide (the Appel reaction) allows for in situ formation of a phosphonium dibromide salt (48, X = Br). Treatment of a hemiacetal donor 1 with the phosphonium halide 48 initially provides the oxophosphonium intermediate 38 (X = Br). However, the oxophosphonium intermediate 38 can react with bromide ion to form the anomeric bromide intermediate 49 (X = Br) with concomitant generation of phosphine oxide. With the aid of bromide ion catalysis (i.e. reversible, catalytic formation of the more reactive P-anomeric bromide 50) [98], the nucleophile displaces the anomeric bromide to form the desired glycoside product 3. The hydrobromic add by-product is typically buffered by the presence of tetramethyl urea (TMU). 

---