Alkenylphosphines

Considerable effort has been expended on using cyclopentadienylphosphines as templates for the assembly of bimetallic complexes. The central problem here is that effective strategies have yet to be devised for connecting two different reactive metals. For this reason, one metallic component of cyclopentadienylphosphine complexes is generally chemically dormant. This gives rise to the all too familiar situation of structurally novel compounds that are chemically inert. Clearly the challenge of the coming years will be the preparation of reactive heterobimetallic complexes which are constructed in such a way that both metals can interact in a concerted manner with the substrates. 

Perhaps the most versatile approach to substituted cyclopentadienyl phosphines has been described in a series of reports by Kauffmann et aL concerning the chemistry of a spiro-cycloheptadiene. This derivative, which apparently can be easily prepared from cyclopentadiene and ethy-lenedibromide, reacts with a range of lithiated ligand precursors. This route provides access to a wide range of relatively complex hybrid ligands. 

---

NMR monitoring of the reaction of the palladium complex with 1-octyne suggested that the alkyne inserts into the Pd-H bond. Further heating produced a mixture of the two regioisomeric alkenylphosphine oxides, the anti-Markovnikov adduct being the favored product (54 46, 65% yield). 

The alkenylphosphine oxide Ph2P(0)H reacts with [Pt(PEt)3] at room temperature to give cis-[PtH(P(0)Ph2)(P(0H)Ph2)(PEt3)] (9), the crystal structure of which reveals a novel intramolecular hydrogen bond.65... 

Veits, Y.A., Karlstedt, N.B., and Beletskaya, I.P, Cross-coupling of silylphos-phines with substituted vinyl halides as a method of 2-alkenylphosphine synthesis, Zh. Org. Khim., 30, 66, 1994. 

Polyphosphoric acid (PPA) (115%) has been used in a very convenient preparation of phosphindoline 1-oxides and phosphinoline 1-oxides by cyclization of various alkenylphosphine oxides (12).14 Isophosphindole oxide (13) has been pre-... 

Table 11 Synthesis of optically active alkenylphosphinates via palladium-catalyzed H-P addition of (-)-menthyl phenylphosphinate...

Scheme 10.1 Intramolecular reactions with alkenylphosphines proceed smoothly [18].

One of the fascinating aspects of organophosphorus chemistry is the extent to which stereochemical and electronic factors control the rate and also the nature of the products of nucleophilic displacements at tetrahedral phosphorus. Our original goal in this work was to design a synthesis of diethylphosphonomethyl-alkenylphosphinates III. Unfortunately the condensation of I with aldehydes occurred primarily by path A (Scheme I) to give II... 

Nucleophilic substitution of a,/3-epoxysilanes followed by the Peterson elimination is valuable for the stereoselective synthesis of alkenes.3 The reactions with lithium phenylsulfide and diphenylphosphide form alkenyl sulfides and alkenylphosphines, respectively, in a stereospecific manner. 7-Metallo-a,/ -epoxysilanes are isomerized to a-siloxyallylmetals by anionic ring opening and subsequent Brook rearrangement (Equation... 

The inteimolecular hydrophosphination of phenylacetylene (76, equation 20) with di-phenylphosphine using Ni(acac)2 (47) and (Et0)2P(0)H has been reported to give aUcenyl-phosphine (77) in high yields . Alkenylphosphines are an important class of ligands whose applications have been limited by the lack of a simple and convenient synthetic procedure. This reaction gave the corresponding iyn-addition products with a mixture of a- and / -adducts. Selectivities could be fine-tuned by judicious choice of catalyst precursor used to facilitate this reaction. 

Magnesium gives an alkenylphosphine-complex 8 [22], calcium and strontium produce / ,/T-bis(trimethylsilyl)phospholides 9 and 10 [11], and barium gives a dissymmetric phospholide bearing an enyne group 11 [22]. In every case... 

Whereas the direct reaction of a-substituted alkenylzirconocene reagents with chlorophosphines does not lead to the related alkenylphosphines, two groups have now shown that if the reactions are carried out in the presence of copper(I) chloride the desired phosphines are obtained, initially as copper-complexes, from which they can be liberated by treatment with appropriate reagents. It is thought that alkenylcopper reagents are involved in these reactions, and, using this approach, new alkenylphosphines have been prepared, e.g., (41)," and the diphosphines (42)." ... 

The synthesis of primary alkenylphosphines has been accomplished utilizing the same rDA method that was used to synthesize primary enamines. The synthesis of primary alkenylphosphines had been an unsolved problem owing to the high reactivity of the phosphine group under acidic, basic and neutral conditions. The preparation of vinylphosphine (38a) and isopropenylphosphine (38b) by FVP of the apprc riate anthracene (37) or 1,3-diphenylbenzofuran (39) adduct has been accomplished as shown in equation (26). ( )-Prop-l-enylphosphine was synthesized by a similar rDA route. These phosphines were found to be surprisingly stable, with a half-life of approximately 8 d for (38a). 

Lithiated ( )- and (Z)-2-alkenylphosphine oxides and phosphonates react with cyclic enones in a 1,4-conjugate addition manner (Schemes 19 and 20). The ( )- and (Z)-allylic anions react in highly dia-stereoselective fashion to deliver respectively syn and anti vinylic phosphine oxides and phosphonates. Chiral allylphosphonyl anions undergo enantioselective 1,4-addition with cyclic enones of varying... 

Dipole Moments. - The polarity and conformation in solution of 2-thiophosphoryl-l,3-dithianes (100) has been studied by the dipole moment method and using IR spectral data. In solution, they exist mainly as an equilibrium of two chair-like conformers with axial orientation of the phosphorus-containing substituent. The polarity and conformations of alkenylphosphine oxides (115) and related acetates (116) have also been determined. ... 

Another interesting catalytic transformation involving alkynes is the hydro phosphinylation, which affords alkenylphosphine oxides [62]. The formation of hydride-phosphinito compounds is one of the key steps of the reaction. These species are formed by oxidative addition of the P-H bond of diphenylphosphine oxide to platinum(O) and palladium(O) complexes, which act as catalytic precursors. In this context, it should be mentioned that a novel method to prepare hydride-phosphinito compounds has been recently reported. The new strategy starts from 133 and involves the oxidative addition of the P-H bond of... 

The free-radical reaction of diphenylphosphine with terminal acetylenes 381 (R = Pr, -Bu or Ph) in the presence of the initiator azoisobutyronitrile or under UV irradiation furnishes the (Z)-alkenylphosphines 382. Hydrophosphorylation of propargyl alcohol 383 (R = HOCH2) and its derivatives 383 (R = BUOCH2, HOCMe2 or PhC02CH2) with Ph2POH results in the adducts 384, which may add a further molecule of the reagent to yield 385 62. 

Noble metals like Pd and Rh are not always required a Cul/ethylenediamine catalyst precursor promoted regioselective addition of diphenylphosphine oxide to terminal alkynes to yield -alkenylphosphine oxides (Scheme 8) [16]. When... 

Hydrophosphinylation of 1-octyne with diphenylphosphine oxide (105) afforded the alkenylphosphine oxide 106 by internal attack with high regioselectivity. However, addition of a small amount of Ph2P(0)OH changed the regioselectivity to provide the product 107 by terminal attack [32]. 

AlkenyIphosphonium salts and alkenylphosphine oxides are both of use in the synthesis of carbocyclic and heterocyclic systems, and new routes to these derivatives are of value. Cycloalkenes react... 

These organocopper intermediates were successfully trapped with electrophiles such as allyl bromide, acyl chlorides, and diphenylchlorophosphine, but not with benzaldehyde and methyl iodide. The resulting products were subjected to in situ oxidation with elemental sulfur to form stable alkenylphosphine sulfides 353 [103]. Owing to its synthetic potential, the regioselective carbometallation of substituted ynol ethers has recentiy witnessed a renaissance [91aj. Thus, the alkynyl ethers 354 were treated under different carbocupration conditions (Scheme 10.121). 

The basic pathways for the synthesis of phosphorus-containing macrocyclic substances are high dilution techniques and template reactions. The use of the template route enables the assembly of the triphosphine macrocyclic ligand L8, obtained as its complex with tricarbonylmolybdenum [3]. Cyclooligomerisations of molybdenum-coordinated alkenylphosphines [3] were also investigated [2], The synthesis of (CO)3Mo(L8) and (CO)3Mo(L1199) was carried out in 70-85% yield in a manner similar to that described earlier (Eq. 5.1) [3]. 

---