Phosphines, alkylation formation

The gas-phase reactivity of proton-bound NHC-H-PCyj has been investigated. NHCs are shown to be more basic than PCyj, accounting for the [Ru]-NHC complexes to be more efficient than their PCy3 counterpart. Collision-induced dissociation was shown to result in phosphine alkylation, formation of methylimidazole, and elimination of cyclohexene. Activation of Hj by aminocarbenes has been studied computationally. The energy of every elementary chemical event of the process has been determined, with special attention given to substituent effects on the energy barriers. 

The first polyphosphino maeroeyeles designed speeifieally for use as transition metal binders were reported in 1977 in back-to-baek eommunications by Rosen and Kyba and their eoworkers. The maeroeyeles reported in these papers were quite similar in some respeets, but the synthetic approaches were markedly different. DelDonno and Rosen began with bis-phosphinate 18. Treatment of the latter with Vitride reducing agent and phosphinate 19, led to the tris-phosphine,20. Formation of the nickel (II) complex of 20 followed by double alkylation (cyclization) and then removal of Ni by treatment of the complex with cyanide, led to 21 as illustrated in Eq. (6.15). The overall yield for this sequence is about 10%. 

Several groups have been successful at the catalytic conversion of carbon dioxide, hydrogen, and alcohols into alkyl formate esters using neutral metal - phosphine complexes in conjunction with a Lewis acid or base (109). Denise and Sneeden (110) have recently investigated various copper and palladium systems for the product of ethyl formate and ethyl formamide. Their results are summarized in Table II. Of the mononuclear palladium complexes, the most active system for ethyl formate production was found to be the Pd(0) complex, Pd(dpm)2, which generated 10/imol HCOOEt per /rniol metal complex per day. It was anticipated that complexes containing more than one metal center might aid in the formation of C2 products however, none of the multinuclear complexes produced substantial quantities of diethyl oxalate. 

In 1970 the transition metal catalyzed formation of alkyl formates from CO2, H2, and alcohols was first described. Phosphine complexes of Group 8 to Group 10 transition metals and carbonyl metallates of Groups 6 and 8 show catalytic activity (TON 6-60) and in most cases a positive effect by addition of amines or other basic additives [26 a, 54-58]. A more effective catalytic system has been found when carrying out the reaction in the supercritical phase (TON 3500) [54 a]. Similarly to the synthesis of formic acid, the synthesis of methyl formate in SCCO2 is successful in the presence of methanol and ruthenium(II) catalyst systems [54 b]. 

More recently, an improved protocol for palladium-catalyzed alkoxycarbony-lation of aryl chlorides with alkyl formates was developed by Beller and colleagues [225]. In the presence of palladium(II) acetate/n-butylbis(l-adamantyl)phosphine, and l,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as a base, for the first time non-activated chloroarenes could be conveniently carbonylated in good yields (Scheme 2.28). In this report, it has been shown that the catalyst system presented does not need the presence of ruthenium co-catalysts. 

The influence of the conditions on the product distribution is the same as for ethyl acrylate (see Figure 29). High temperatures and low pressures give linear product (up to l b=3 1), and low temperatures and high pressures lead to branched products (l b=l 99). For carbonyl based catalysts, phosphite based catalysts, and phosphine based catalysts this has been weU documented (Chapters 2, 3, and 4). The reversibility of the branched alkyl formation is also accounted for. 

Garbodiimide Formation. Carbodiimide formation has commercial significance in the manufacture of Hquid MDI. Heating of MDI in the presence of catalytic amounts of phosphine oxides or alkyl phosphates leads to partial conversion of isocyanate into carbodiimide (95). The carbodiimide (39) species reacts with excess isocyanate to form a 2 + 2cycloaddition product. The presence of this product in MDI leads to a melting point depression and thus a mixture which is Hquid at room temperature. 

Examples are given of common operations such as absorption of ammonia to make fertihzers and of carbon dioxide to make soda ash. Also of recoveiy of phosphine from offgases of phosphorous plants recoveiy of HE oxidation, halogenation, and hydrogenation of various organics hydration of olefins to alcohols oxo reaction for higher aldehydes and alcohols ozonolysis of oleic acid absorption of carbon monoxide to make sodium formate alkylation of acetic acid with isobutylene to make teti-h ty acetate, absorption of olefins to make various products HCl and HBr plus higher alcohols to make alkyl hahdes and so on. 

Like gold, silver readily forms insoluble (yellow) thiolates [Ag(SR)] primary alkylthiolates are thought to have non-molecular structures but with bulky tertiary alkyls (n = 8), probably having a cyclic structure. Addition of excess thiolate leads to the formation of clusters like Ag6(SPh)g, Ag5(SPh)7 and Ag5(SBu )6 (phosphine adducts are known, too). 

Examples of the intermolecular C-P bond formation by means of radical phosphonation and phosphination have been achieved by reaction of aryl halides with trialkyl phosphites and chlorodiphenylphosphine, respectively, in the presence of (TMSlsSiH under standard radical conditions. The phosphonation reaction (Reaction 71) worked well either under UV irradiation at room temperature or in refluxing toluene. The radical phosphina-tion (Reaction 72) required pyridine in boiling benzene for 20 h. Phosphinated products were handled as phosphine sulfides. Scheme 15 shows the reaction mechanism for the phosphination procedure that involves in situ formation of tetraphenylbiphosphine. This approach has also been extended to the phosphination of alkyl halides and sequential radical cyclization/phosphination reaction. ... 

Other cyclizations at phosphorus have been observed when certain phosphinates were used in the acid-catalyzed Mannich reaction. As observed previously with various phosphonous acid derivatives, reaction of aliphatic phosphinic acids with primary amines favored the formation of 2 1 adducts (73). Thus, glycine and other a-amino acids reacted under the typical conditions with excess formaldehyde and alkyl phosphonous acids to give the bis-phosphinylmethyl adducts 125. 

NH-Phosphinous amides are also alkylated at phosphorus by electrophilic olefins, such as acrylonitrile and acrylamide, with concomitant formation of a... 

Wittig reactions are versatile and useful for preparing alkenes, under mild conditions, where the position of the double bond is known unambiguously. The reaction involves the facile formation of a phosphonium salt from an alkyl halide and a phosphine. In the presence of base this loses HX to form an ylide (Scheme 1.15). This highly polar ylide reacts with a carbonyl compound to give an alkene and a stoichiometric amount of a phosphine oxide, usually triphenylphosphine oxide. 

A. Preparation.—Halogen displacement reactions have been used to prepare a number of new aminofluorophosphines. Aminodifluorophos-phine (1) has been prepared for the first time, from either bromodifluoro-phosphine or chlorodifluorophosphine, and ammonia. Studies of its n.m.r. spectrum have been made (see Chapter 11). The related NN-difluoroaminodifluorophosphine (2) has been prepared, from difluoroiodo-phosphine, and found to be explosive. Two syntheses of A-alkyl-amino-difluorophosphines have been reported, one of which was complicated by the subsequent formation of the phosphorane (3) and the bis-(A-alkylamino)fluorophosphine (4). 

Diphosphenes stabilised by bulky groups, e.g. (157, R = 2,4,6-tri-t-butylphenyl), can be isolated in high yield from the reactions of alkyl- or aryl-(trichlorogermyl)phosphines with an excess of the base DBU. The formation of less sterically crowded systems, e.g. (157, R = t-butyl), is also possible by this route,... 

Photolysis of the first known cyclic a-diazo-p-oxophosphine oxide 49 is unsuccessful with regard to phosphene formation. There is no evidence for a P/C-phenyl shift, which should lead to 51, nor for a P/C-alkyl shift, which would afford 52 via ring contraction, since none of the expected phosphinic esters could be isolated in methanolM). 

Benzannulated NHPs are straightforwardly accessible from AUV-disubsti luted o-phenylenediamines either via base-induced condensation with substituted dichlorophosphines [25] or PC13 [26], or via transamination with tris(dialkylamino) phosphines [13, 14, 27], respectively. An analogous NH-substituted derivative was obtained in low yield via transamination of o-phcnylcncdiaminc with ethoxy-bis(diethylamino)phosphine [28], and condensation of o-phenylenediamine with excess tris(diethylamino)phosphine furnished a l,3-bis(phosphino)-substituted heterocycle [29], Intermediates with one or two NH functions were detectable by spectroscopy but could not be isolated in pure form under these conditions. However, 2-chloro-benzo-l,3,2-diazaphospholene and the corresponding 1-phenyl derivative were prepared in acceptable yield via condensation of PC13 with o-phenylenediamine under microwave irradiation [30], or with A-phenyl-o-phenylenediamine under reflux [27], respectively, in the absence of additional base. The formation of tetrameric benzo-NHPs during transamination of A-alkyl-o-phenylenediamines with P(NMe2)3 has already been mentioned (cf. the section entitled 1,3,2-Diazaphospholes and 1,3,2-Diazaphospholides ). 

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)]. 

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