Large phosphine

The industrial process requires a large phosphine excess ([P]/[Rh] = 21 1) which can be easily provided by the extremely water-soluble TPPTS. However, the reactants are insoluble in such an aqueous phase, therefore the reaction is mn in the presence of co-solvents, usually alcohols. (Less soluble TPPMS performs better at [P]/[Rh] = 3, probably its surfactant properties help in solubilizing the diene and methyl acetoacetate.) The organic products are easily separated from the aqueous catalyst solution which can be recycled. 

With the knowledge that 14 can activate aldehydes in 1, the role of 1 in the reaction was explored further. Specifically, the relative rates of C—H bond activation and guest ejection, and the possibility of ion association with 1, were investigated. The hydrophobic nature of 14 could allow for ion association on the exterior of 1, which would be both cn t h al pi cal I y favorable due to the cation-it interaction, and entropically favorable due to the partial desolvation of 14. To explore these questions, 14 was irreversibly trapped in solution by a large phosphine, which coordinates to the iridium complex and thereby inhibits encapsulation. Two different trapping phosphines were used. The first, triphenylphosphine tris-sulfonate sodium salt (TPPTS), is a trianionic water-soluble phosphine and should not be able to approach the highly anionic 1, thereby only trapping the iridium complex that has diffused away from 1. The second phosphine, l,3,5-triaza-7-phosphaadamantane (PTA), is a water-soluble neutral phosphine that should be able to intercept an ion-associated iridium complex. 

In order to examine the stereochemical implications in the synthesis of (largely) phosphinic acids (but also tertiary phosphine oxides), Inch and coworkers " employed carbohydrate frameworks as chiral templates. As primary substrates, the cyclic phospho-rochloridate 161 and the corresponding phosphorofluoridate 162 were prepared from methyl 1,2,3-di-O-methyl-a-D-glucopyranoside, each phosphoryl halide being obtained as a mixture of diastereoisomers, anomeric at phosphorus, and from which, in each case, the major component (thought to have an equatorial P=0 bond) was isolated. Configurations in both substrates and reaction products were assigned with the aid of proton and NMR... 

Trigold oxonium cations consist of three Au-phosphine units boimd to an oxygen center in a pyramidal geometry (Fig. 6). This compound had been synthesized from dilferent phosphine ligands of varying steric bulk. For large phosphine ligands,... 

Intrusion of gas phase probes metal carbonyl clusters internal or external location of metal carbonyl cluster in zeolite Large phosphine molecule cannot diffuse through zeolite aperture into the zeolite cages to react with encaged carbonyl dusters effective for highly reactive carbonyl clusters. 

The problem of the synthesis of highly substituted olefins from ketones according to this principle was solved by D.H.R. Barton. The ketones are first connected to azines by hydrazine and secondly treated with hydrogen sulfide to yield 1,3,4-thiadiazolidines. In this heterocycle the substituents of the prospective olefin are too far from each other to produce problems. Mild oxidation of the hydrazine nitrogens produces d -l,3,4-thiadiazolines. The decisive step of carbon-carbon bond formation is achieved in a thermal reaction a nitrogen molecule is cleaved off and the biradical formed recombines immediately since its two reactive centers are hold together by the sulfur atom. The thiirane (episulfide) can be finally desulfurized by phosphines or phosphites, and the desired olefin is formed. With very large substituents the 1,3,4-thiadiazolidines do not form with hydrazine. In such cases, however, direct thiadiazoline formation from thiones and diazo compounds is often possible, or a thermal reaction between alkylideneazinophosphoranes and thiones may be successful (D.H.R. Barton, 1972, 1974, 1975). 

The search for catalyst systems which could effect the 0x0 reaction under milder conditions and produce higher yields of the desired aldehyde resulted in processes utilizing rhodium. Oxo capacity built since the mid-1970s, both in the United States and elsewhere, has largely employed tertiary phosphine-modified rhodium catalysts. For example, over 50% of the world s butyraldehyde (qv) is produced by the LP Oxo process, technology Hcensed by Union Carbide Corporation and Davy Process Technology. 

Two processes have been used to manufacture gaseous phosphine on a large scale. These are commonly known as the alkaline (1) and acid processes (2). 

Solvent Extraction Reagents. Solvent extraction is a solution purification process that is used extensively in the metallurgical and chemical industries. Both inorganic (34,35) and organic (36) solutes are recovered. The large commercial uses of phosphine derivatives in this area involve the separation of cobalt [7440-48-4] from nickel [7440-02-0] and the recovery of acetic acid [61-19-7] and uranium [7440-61-1]. 

In the presence of a large excess of PH, primary phosphines, RPH2, are formed predominantiy. Secondary phosphines, R2PH, must be either isolated from mixtures with primary and tertiary products or made in special multistep procedures. Certain secondary phosphines can be produced if steric factors preclude conversion to a tertiary product. Both primary and secondary phosphines can be substituted with olefins. After the proper selection of substituents, mixed phosphines of the type RRTH or RR R T can be made. 

Homogeneous rhodium-catalyzed hydroformylation (135,136) of propene to -butyraldehyde (qv) was commercialized in 1976. -Butyraldehyde is a key intermediate in the synthesis of 2-ethyIhexanol, an important plasticizer alcohol. Hydroformylation is carried out at <2 MPa (<290 psi) at 100°C. A large excess of triphenyl phosphine contributes to catalyst life and high selectivity for -butyraldehyde (>10 1) yielding few side products (137). Normally, product separation from the catalyst [Rh(P(C2H2)3)3(CO)H] [17185-29-4] is achieved by distillation. 

The reaction of a large number of other nucleophiles with iminium salts will at least be mentioned in this section. Among the nucleophiles which react with iminium salts are cyanide 48,115-119), mercaptide 48), alkoxide 48), amine 120), azide 44), phosphine 44), and phosphate ester 44). One can say with little reservation that almost all nucleophiles will react... 

The crystal structure of the K(18-crown-6) salt shows a fac-octahedral structure (Ru—H 1.59-1.71 A, Ru—P 2.312-2.331 A) with a large distortion from regular octahedral geometry (H-Ru-H 70-88° P-Ru-P 102-111°) owing to the disparate steric demands of the hydride and tertiary phosphine ligands [95]. 

The long Rh—P bonds in the tertiary phosphine adducts show little dependence upon the tertiary phosphine and are interpreted in terms of a largely cr-component in the Rh-P bond they are also affected by the strong trans-influence of the Rh-Rh bond. 

The PMe2Ph complexes have been studied in particular detail [163-165], since their 1H NMR spectra lend themselves to assigning the stereochemistry of the complexes. Figure 2.88 shows the relationships between a large number of these complexes, which are in general typical of iridium(III) phosphine complexes. 

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