Carbon—phosphorus dimers

The lithium salt of a substituted cyclopentadienyl anion has been used in reaction with phosphorus trichloride for carbon-phosphorus bond formation.70 The resultant simple displacement product ultimately undergoes dimerization and loss of four (from the dimer) equivalents of HC1 (Equation 4.25). 

A series of four-membered Si- or P-containing heterocycles was produced in various yields by electrocyclization or [2-t-2]-dimerization of compounds with multiple carbon-silicon or carbon-phosphorus bonds. These unsaturated species are formed under photolysis of diazo compounds containing a P or Si atom in an a position with respect to the diazo group, following a [l,2]-sigmatropic shift in the intermediate carbene. 

Carbon-phosphorus double bonds also participate in the Diels-Alder reaction and are a source of a variety of tetrahydrophosphinine derivatives. The C=P unit has a relatively short history the first compounds were not isolated until 1976. Special characteristics must be present to give stable compounds that resist dimerization or polymerization. Strongly electron-attracting groups or large bulky groups that provide steric retardation of the dimerization or polymerization are required. The former type are the more useful in the Diels-Alder reaction, because steric effects from the bulky substituents can also reduce the reactivity of the C=P unit to additions. An example of a successful cycloaddition is given in Scheme 5.17 (where TMS is MesSi). The literature on Diels-Alder reactions of C=P compounds is the subject of a 2008 review. ... 

M dppm)] with Ph2PCH=CH2 gives [Fe2(CO)s(M-Ph2PCH=CH2)(M dppm)] which on heating results in carbon-phosphorus bond cleavage to afford [Fe2(CO)4(p-CH=CH2)(M PPh2)(M-dppm)] . The synthesis and X-ray crystal structure of the bis(allyl) dimer... 

The stepwise formation of tropones upon insertion of GO into alkyne dimers coordinated to diiron centers is a commonly found process in iron carbonyl chemistry no triiron complexes are isolated during these processes (e.g., see Refs 14 and 14a). Finally, GO insertion is observed when diiron dimers linked by diacetylene moieties are reacted with diethylamine to give the complexes 6 and 7 (Figure 2) these complexes also contain iron-carbon-nitrogen and iron-carbon-phosphorus bonds. 

If the reaction temperature is raised to 430 K and the carbon monoxide pressure to 3 atm, coordination of the metal atom in the rearranged product occurs via the phosphorus site, as in 159 (M = Cr, Mo, W) [84JOM(263)55]. Along with this product (M = W) at 420 K, formation of the dimer of 5-phenyl-3,4-dimethyl-2//-phosphole, 160 (the a complex), is possible as a consequence of [4 - - 2] cycloaddition reactions. Chromium hexacarbonyl in turn forms phospholido-bridged TiyP)-coordinatedcomplex 161. At 420 K in excess 2,3-dimethylbutadiene, a transformation 162 163 takes place (82JA4484). 

Phosphorus ylids react with carbon dioxide to give the isolable salts (48), which can be hydrolyzed to the carboxylic acids (49) (thus achieving the conversion RR CHX RR CHCOOH) or (if neither R nor R is hydrogen) dimerized to... 

Usually, C-mercury substituted phosphorus ylides are monomers and in order to stabilize these complexes the presence of a second substituent on the carbon is necessary to balance the electron-donating effect of the metal. However a dimeric complex 85 has been obtained by the reaction of mercuric halides HgX2... 

Its molecular structure (Figure 37) consists of a centrosymmetric dimer with a bridging H2Al(OR)( U-OR)2Al(OR)H2 entity. The Ta atoms are approximately square pyramidal, with the four phosphorus atoms forming the basal plane (Ta lies 0.64 A out of it). The relatively short Ta—A1 distances are comparable to those found in other transition metal aluminum complexes (Ta—Al 2.79-3.13 A). The hydrogen atoms have not been located, but were evidenced by chemical and spectroscopic techniques (IR 1605, 1540 cm 1 HNMR 16.30p.p.m.). The Ta—(ju-H2)A1 unit is relatively stable, and (54) is inert to carbon monoxide or trimethylamine. It is a poor catalyst in the isomerization of 1-pentene. Formation of complexes analogous to (54) may explain the low yields often obtained from alkoxoaluminohy-drides and metal halides. 

Wittig-type olefinations can also be performed using selenoaldehydes. Phosphorus ylides initially attack the carbon atom of the selenocarbonyl functionality.405 Aromatic selenoketones undergo reductive dimerization with organo-lithium reagents probably via an electron transfer mechanism.406 Also the addition of organolithium reagents takes... 

Carbene carbon. Carbonyl carbon. COD = 1.5-cyclooctadiene. CioHja = cyclopen tad iene dimer. Carbon trans to phosphorus or arsenic. Carbon trans to halogen or methyl. Phenyl carbon. Cyanide carbon. 

Trichlorophosphoraneimines, CbP NR, are the most accessible compounds of this class. They can be prepared by reacting phosphorus pentachloride with primary amines or their hydrochlorides, usually in carbon tetrachloride as solvent. The intermediate aminotetrachlorophosphorane CLtP-NHR is seldom isolated. With aromatic amines the products are monomeric only when the aromatic amine is weakly basic, otherwise the phosphoraneimine will dimerize to cyclic dimers [Cl3PNR]2 (see Section 5.4). ... 

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