Phosphines dehalogenation

The present reaction may be reasonably explained by the smooth oxidative addition of aryl halides to metallic nickel to give aryl nickel halides, followed by disproportionation to bisarylnickels, which upon reductive elimination afford the dehalogenative coupled products. Providing strong support for this mechanism, the intermediates, arylnickel halide and bisarylnickel (Ar=C F ), were isolated as the phosphine complexes. 

The novel, low-melting-point salt [N-pentylpyridinium][cJoso-CB11H12] has been used as solvent in several dehalogenations of mono- and polychlorides and -bromides, catalyzed by several Pd phosphine complexes [69]. The debromina-tion of hexabromo- and 1,2,4,5-tetrabromobenzene was accomplished quite rapidly, whereas the dechlorination of 1,2,4-trichlorobenzene proceeded more slowly, but with excellent selectivity to 1,2-dichlorobenzene. The system could be recycled at least seven times without noticeable decrease of activity. 

The rates of dehalogenation of a-bromo- and a-iodo-m-cyanobenzylphenyl-sulphones (89) by a number of sterically hindered phosphines in aqueous DMF have... 

All the other half-sandwich complexes in this section derive from the chemistry of ReCp Os and ReCp Cl4 (136). Complex (136) forms an octahedral adduct ReCp Cl4(PMe3), but excess phosphine reduces it to ReCp Cl2(PMe3)2. Hydrolysis and aminolysis form ReCp OCl2and ReCp (NR)Cl2 respectively. Stepwise reductive dehalogenation with Al/HgCl2... 

Although many nucleophiles dehalogenate a-halocarbonyl compounds, the most generally used have been halides, especially iodide ion, thiols and other nucleophilic sulfur species, and phosphines. All of these are effective by themselves, but all benefit by addition of an electrophile to the medium to assist cleavage by coordination to the carbonyl (equation 11). 

Although silylenes have been known for a long time as transient intermediates in thermal, photochemical or dehalogenation reactions, stable species have become available only recently. Si(II) compounds with coordination number larger than two have already been isolated in the late eighties, i.e., decamethylsilicocene prepared by Jutzi et al [1] and the tetracoordinated phosphine derivative obtained by Karsch et al [2]. 

Pd/C also catalyzes the PTC reduction of aryl and heteroaryl halides with sodium formate [52]. The reductive dehalogenation of allyl and benzyl halides with HCOOK can be carried out in a heptane/water system in the presence of water-soluble complexes of type PdCl2(sulfonated phosphine)2 and a PT agent... 

Rate data for the triphenylphosphine-promoted dehalogenation of meso-l, -dibromo-l,2-diarylethanes to form ranj-stilbene in DMF are consistent with a concerted unti-elimination mechanism involving the attack of phosphine on bromine. Attack of triphenylphosphine on halogen also occurs in its reaction with the A chIoropyrroiidine-2,5-diones (82), leading eventually to the betaines (83). The... 

Chloro-l-phenylpropene (cinnamyl chloride) was reductively dehalogenated in water/n-heptane biphasic systems by hydrogen transfer from formates using Pd(II) complexes with sulfonated phosphine ligands of the type 21 (Scheme 3.38) [271], Addition of polyether detergents increased the rate of hydrogenolysis and supressed the formation of alcohol... 

Perchloro ketones can be similarly dehalogenated by trialkyl phosphites or triphenyl-phosphine.73... 

Oxophosphines have been generated by pyrolysis of cyclic phosphine oxides, e.g. r rr-butyloxophosphine (equation 102) and oxophenylphosphine (equation 103) The thermally stable dihydrophosphole 38 gave oxophenylphosphine upon irradiation (equation 104) ". Another route to oxophosphines is the dehalogenation of phosphonic dihalides with magnesium, e.g. oxophenylphosphine from phenylphosphonic dichloride... 

Several possible reactions may give rise to impurities in the preparation of phosphonic or phosphinic acid esters by the Michaelis-Arbuzov reaction, and it is possible that, in some cases, such reactions become preponderant. Triethyl phosphite, for instance, has been successfully used as a dehalogenating agent, in particular, for debrominations. Isomerization of allylic groups may occur through S T-type processes (reaction 5) or be induced thermally (reactions 6 and 7) 25,126... 

Cuprous chloride tends to form water-soluble complexes with lower olefins and acts as an IPTC catalyst, e.g., in the two-phase hydrolysis of alkyl chlorides to alcohols with sodium carboxylate solution [10,151] and in the Prins reactions between 1-alkenes and aqueous formaldehyde in the presence of HCl to form 1,3-glycols [10]. Similarly, water-soluble rhodium-based catalysts (4-diphenylphosphinobenzoic acid and tri-Cs-io-alkylmethylam-monium chlorides) were used as IPTC catalysts for the hydroformylation of hexene, dodecene, and hexadecene to produce aldehydes for the fine chemicals market [152]. Palladium diphenyl(potassium sulfonatobenzyl)phosphine and its oxide complexes catalyzed the IPTC dehalogenation reactions of allyl and benzyl halides [153]. Allylic substrates such as cinnamyl ethyl carbonate and nucleophiles such as ethyl acetoactate and acetyl acetone catalyzed by a water-soluble bis(dibenzylideneacetone)palladium or palladium complex of sulfonated triphenylphosphine gave regio- and stereo-specific alkylation products in quantitative yields [154]. Ito et al. used a self-assembled nanocage as an IPTC catalyst for the Wacker oxidation of styrene catalyzed by (en)Pd(N03) [155]. 

---