Phosphanes methylene

Alkylidene-phosphapyrazolines 98-101 are much more thermally stable than their relatives 88, which do not possess the exo-methylene substitution. Dediazo-niation of 98 required heating in toluene at 110°C and gave one or more of the following products, probably via intermediate diphenylmethylene(vinylidene)phos-phoranes methylenephosphiranes, (2-siloxyvinyl)phosphanes, 2//-l,3-oxaphos-pholes, and l-alkylidene-2,3-dihydro-l//-benzo[c]phospholes (169). Thermolysis of 100 ( R = t-Bu, 1-adamantyl) afforded isolable 2-phosphabutadienes (169). The photochemical elimination of N2 from 98 generated cyclic azomethine imine dipoles 104 (Scheme 8.24), which rearrange to compounds 105 and 106 that could be further trapped with DMAD to form 107 (170). 

A number of compounds having the P(II)=C-P(III) backbone structure (phosphino methylene phosphanes) have recently ( 1, 2) been prepared by our group via condensation and migration of tri-methysilyl groups at low temperatures. 

The phosphino methylene phosphanes so formed occur as yellow oils with little or no tendency towards crystallization. In order to obtain suitable materials for x-ray structure studies, we converted two compounds to convenient derivatives. 

Analoge Verbindungen erhalt man auch bei der Alkylierung von Phosphan-phosphano-imiden und bei der Protonierung von Trimethylphosphan-(dimethyl-methylen-phosphor-anylimid)746 747 z.B. ... 

In certain cases the process analogous to the isonitrile synthesis for the preparation of phosphaalkenes, showing proton- and halogene-substituted C-bridged atoms, is a successful one. 2,4,6-tri-i-butylphenyl-phosphane can be transferred to the phosphaalkene using a strong alkaline solution of chloroform [Eq. (7)] or methylene chloride [Eq. (8)]. A carbene addition mechanism is involved in this reaction (36, 37). 

Phosphaalkene complexes of type A show shifts that differ less from the free phosphane phosphorus, but this time more to the higher field. Herein, the n system prevails, as can be seen from the 13C NMR signal of the methylene carbon atom. The signals for it and the tjl-coordinated species are detected in the area of sp2-hybridized C atoms. 

Naturally, it is possible to synthesise a similar ligand system without central chirality and in fact without the unnecessary methylene linker unit. A suitable synthesis starts with planar chiral ferrocenyl aldehyde acetal (see Figure 5.30). Hydrolysis and oxidation of the acetal yields the corresponding carboxylic acid that is transformed into the azide and subsequently turned into the respective primary amine functionalised planar chiral ferrocene. A rather complex reaction sequence involving 5-triazine, bromoacetal-dehyde diethylacetal and boron trifluoride etherate eventually yields the desired doubly ferrocenyl substituted imidazolium salt that can be deprotonated with the usual potassium tert-butylate to the free carbene. The ligand was used to form a variety of palladium(II) carbene complexes with pyridine or a phosphane as coligand. 

Methylene transfer from isopropylidenetriphenyl-l -phosphane to a,/i-unsaturated esters allows the preparation of gew-dimethyl-substituted cyclopropyl ketones, e.g. The ketones... 

A P-C bond was also formed on treatment of cyclopropyltrimethylphosphonium bromide (3) with sodium amide to give cyclopropyl(dimethyl)methylene-A -phosphane (4). When a large excess of amide was used, cyclopropyl[cyclopropyldimethyl-A -phosphanylideneamino]-(methyl)methylene-2 -phosphane also occurred. " ... 

Treatment of [(cyclopropyl)(methoxycarbonyl)methylene]triphenyl-i -phosphane with aqueous sodium hydroxide at reflux afforded, after acidification, cyclopropylacetic acid in 70% yield. 

Most remarkably, no codimerization involving the unsaturated ester molecule is observed, even though nickel compounds such as the acrylonitrile complex are efficient catalysts for such codimerization reactions vide infra). An additional homodimer, l,3-bis(methylene)cy-clohexane (6), is formed as a minor product with phosphane-modified nickel catalysts. Only trace amounts of product 6 are obtained with maleic anhydride as cocatalyst. 

The palladium-catalyzed reactions of the substituted MCP, 1-methylene-2-vinylcyclopropane (22), have been investigated in great detail.In addition to the product variability resulting from the formation of different regioisomers, isomers with respect to the configuration at the double bonds are formed in this reaction. Thus, a rearrangement product 3-methylenecyclopen-tene (23), together with five major dimerization products 24-26, result from the palladium/ phosphane-catalyzed reaction. 

Whereas palladium(0)-catalyzed reactions of dialkyl fumarate and dialkyl maleate yield reaction products identical to those obtained from the phosphane-modified nickel-catalyzed reactions (vide supra), analogous palladium(0)-catalyzed reactions with ( )-but-2-enoic or (E)-cinnamic acid derivatives lead to different products to the nickel-catalyzed reactions, i.e. in the palladium-catalyzed reactions formal distal cleavage of but-2-enoic MCP occurs to provide methyl tra i-2-methyl-4-methylenecyclopentanecarboxylate (12, R = Me) and methyl trans-4-methylene-2-phenylcyclopentanecarboxylate (12, R = Ph), respectively." Yields and stereoselectivities are slightly higher with palladium(O) catalysts. When R = Me, 7.4% of the C-C double bond isomerization product, methyl traM -2,4-dimethylcyclopent-3-enecarboxylate (13, R = Me), is additionally obtained, raising the combined yield of cyclocodimers to 49.9%. With methyl (jE )-cinnamate, analogous isomerization only occurs upon workup, i.e. distillation of the crude product. 

Reaction of cyanobenzylidenetriphenyl-l -phosphane with cyclopropenones in toluene at 110°C for 7 hours gave azacyclopentadienones 15, which reacted with a second molecule of cyclopropenone to give 7-oxo-3-[phenyl(triphenylphosphonio)methylene]-7,7a-dihydro-3//-pyrrolizin-2-olates 16. ... 

Reaction of tris(2-pyridyl)phosphane (8) with chlorine in methylene dichloride or acetonitrile gave chlorotris(2-pyridyl)phosphonium chloride or its covalent isomer tris(2-pyridyl)phosphonium dichloride (20). Treatment of the dichloride derivative with dilute HCl afforded the coupling product, 2,2 -bipyridine (16), whereas tris(2-pyridyl)phosphine oxide (9) was isolated from the reaction with sodium hydroxide. 

FIGURE 25. He(I) PE spectra of [bis(trimethylsilyl)methylene]chlorophosphane, the thermal elimination of R3SiCl (hatched) and trimethylsilylmethylidine phosphane obtained by subtraction of the digitalized R3SiCl ionization pattern from that of the 1300 K pyrolysis mixture50... 

A rhodium complex with chiral phosphane ligand was also intercalated into sodium hectorite by cation exchange (Sento et al. ). The intercalated compound was characterized by FTIR, XRD, and TEM and the basal spacing of the compound was estimated to be 2.29 nm. This novel het-erogenized eatalyst exhibited a characteristic chiral as well as size recognition of the substrate molecule (like the "Tailor-made compounds" method used earlier by Balandin in the hydrogenation of tripticene derivatives over Ni) and was used in enantioselective hydrogenation of the itaconates (methylene-succinic acid esters). 

At least three names are available for the compound H3P=CH2. These are phosphine methylene, methylene phosphonium ylid and phosphonium methylide moreover, the compound can be classed as a phosphorane The compound PhjP Rj may be called triphenylphosphonium methylide, tri-phenylphosphonium methanide or triphenyl-methylenephosphorane. The pyridine analogue, C5H5P, has been known variously as phosphobenzene, phosphabenzene, phosphorin, and most recently, phosphinine. The term phosphane for (1) in Table 1.4 and its derivatives is the most recent and the most systematic, but it is difficult to see how the more widespread and firmly rooted term phosphine will ever be replaced. In addition, adoption of the term phosphane would put it in line with such little-used terms as carborane for CH4, nitrane for NH3 and oxane for HjO. 

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