Phosphines, alkylation oxides

The possible role of oxygen atom transfer in molybdenum enzyme catalysis was recognized in the early 1970s (190-194). In the ensuing years, a wealth of chemistry has established molybdenum as the premier exponent of such reactions (7, 195). Importantly, related dioxo-Mo(VI) and oxo-Mo(IV) complexes are interconverted by oxygen atom transfer reactions (Eq. (13)). These reactions are effected by reductants (X) such as tertiary alkyl and aryl compounds of the group 15 elements (especially phosphines) and oxidants (XO) such as S- and N-oxides. In many cases, however, the Mo(VI) and Mo(IV) compounds participate in a comproportionation reaction yielding dinuclear Mo(V) complexes (Eq. (15)). 

Various strategies exist for the preparation of alkyl- or aryl-substituted tertiary phosphines. Direct oxidation of alkyl-substituted phosphines by exposure to air is not practical since side products with P—O—C bonds might be formed.3 A few illustrative examples highlight the different routes that may be used. Arylphosphine oxides (e.g., (140)) can be made using aqueous H202 in diethylether as solvent (Equation (35)).302 The same procedure (aq. H202, THF, 0°C) can be used to prepare (141) (Scheme 10) in 49% yield the dioxide (142) can easily be separated from (141) by virtue of its poor solubility in THF.303... 

Upon warming, alkylpalladium complex 4 underwent P-hydride elimination to generate allylbenzene and Pd(P(t-Bu)2Me)2HBr. This process was inhibited by the presence of excess P(t-Bu)2Me, consistent with a pathway that involves initial dissociation of a phosphine [45]. Oxidative-addition adduct 4 reacted with one equivalent of o-tolylboronic acid to generate the coupling product in 94% yield in addition, it served as a competent catalyst for cross-couplings of alkyl bromides and arylboronic acids. 

The described reaction proceeds slowly for aryl-thiolate DNICs and is fast for alkyl-thiolate complexes. Trapping of the elemental sulfur atoms by phosphine inhibits oxidation [137]. The fate of the sulfide ligands in reactions of biological iron-sulfur clusters with NO remains unknown, although analogically it is expected that sulfur by-products must be sequestered from the vicinity of the iron atoms in order for the DNICs to remain stable. It was shown that the cluster reassembly... 

Synthesis. The first hiUy alkyl/aryl-substituted polymers were reported in 1980 via a condensation—polymeri2ation route. The method involves, first, the synthesis of organophosphine-containing alkyl or aryl substituents, followed by the ready oxidation of the phosphine to a phosphorane with leaving groups suitable for a 1,2-elimination reaction. This phosphorane is then thermally condensed to polymers in which all phosphoms atoms bear alkyl or aryl substituents. This condensation synthesis is depicted in Eigure 2 (5—7,64). 

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. 

Phosphine oxides having higher alkyl substituents are also prepared industrially using Grignard reagents. 

Alkyl- and aryl-pyridazines can be prepared by cross-coupling reactions between chloropyridazines and Grignard reagents in the presence of nickel-phosphine complexes as catalysts. Dichloro[l,2-bis(diphenylphosphino)propane]nickel is used for alkylation and dichloro[l,2-bis(diphenylphosphino)ethane]nickel for arylation (78CPB2550). 3-Alkynyl-pyridazines and their A-oxides are prepared from 3-chloropyridazines and their A-oxides and alkynes using a Pd(PPh3)Cl2-Cu complex and triethylamine (78H(9)1397). 

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. 

Under similar conditions, perfluoroalkyl iodides react with alkyl phosphates to give fluorinated phosphine oxides, phosphinates, and phosphines [54 (equation 49) The product formed depends upon the stoichiometry and type of iodide used. When sodium alkyl trithiocarbonates are used as substrates, perfluoroalkyl tri-thiocarbonates ate formed [55]. 

Most common is the preparation of alkyl phosphonic acid esters (phospho-nates) 4 (Z,Z = OR) from phosphorous acid esters (phosphites) 1 (Z,Z = OR). The preparation of phosphinic acid esters (Z = R, Z = OR) from phosphonous acid esters, as well as phosphine oxides (Z,Z = R) from phosphinous acid esters is also possible. 

Important and widely used variants of the Wittig reaction are based on carbanionic organophosphorus reagents, and are known as the Wadsworth-Emmons reaction, Wittig-Horner reaction or Horner-Wadsworth-Emmons reaction. As first reported by Horner, carbanionic phosphine oxides can be used today carbanions from alkyl phosphonates 13 are most often used. The latter are easily prepared by application of the Arbuzov reaction. The reactive carbanionic species—e.g. 14 —is generated by treatment of the appropriate phosphonate with base, e.g. with sodium hydride ... 

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-... 

While the chemistry of alkyl and allylic sulfoxide anions is similar to that of phosphine oxides, phosphinates and sulfone stabilized anions (Sections 1.5.2.2.1 -2), the situation is further complicated by the additional stereogenic center at sulfur. Therefore in all cases, asymmetric induction may arise from the stereocenter at sulfur. 

Phosphine complexes like OsN(PMe3)2(R2)Cl (R = CH2SiMe3) with chloride tram to nitride, and frans-phosphines and iraras-alkyls, have been made [191]. Me3NO (but not Ph3PO or C5H5NO) oxidizes a nitride group into a nitrosyl... 

The most important of the tertiary phosphine complexes of platinum(IV) are Pt(QR3)2X4, generally prepared by halogen oxidation [174] of cis- or trans-Pt(QR3)2X2 (Q = P, As, R = alkyl Q = Sb, R = Me), since direct reaction of the platinum(IV) halides with the ligands leads to reduction. Once made, the platinum(IV) compounds are stable to reduction ... 

The use of this phosphine facilitates assignment of configuration as virtual coupling is observed when the phosphines are trans (section 2.9.5).) Syntheses follow established routes using methyllithium as an alkylating agent the platinum(iV) complexes can be made by direct alkylation of platinum(IV) compounds or by oxidative addition to platinum(II) species. 

A wide variety of high-performance polymeric materials have been synthesized by incorporating thermally stable moieties such as sulfone, ketone, or aryl or alkyl phosphine oxide in addition to the ether linkage in poly(arylene ether)s. 

In 6.5.2.1 it is shown that BF3 and BCI3 add to phosphine Pt complexes without cleaving the B—X bond. In contrast, aryl and alkyl boron halides are added oxidatively with phosphine Pt complexes - ... 

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