Tris -phosphine

The first polyphosphino maeroeyeles designed speeifieally for use as transition metal binders were reported in 1977 in back-to-baek eommunications by Rosen and Kyba and their eoworkers. The maeroeyeles reported in these papers were quite similar in some respeets, but the synthetic approaches were markedly different. DelDonno and Rosen began with bis-phosphinate 18. Treatment of the latter with Vitride reducing agent and phosphinate 19, led to the tris-phosphine,20. Formation of the nickel (II) complex of 20 followed by double alkylation (cyclization) and then removal of Ni by treatment of the complex with cyanide, led to 21 as illustrated in Eq. (6.15). The overall yield for this sequence is about 10%. 

All the reported methods suffer from drawbacks, being either multistep processes that are time-consuming or affording difficult-to-separate mixtures of bis- and tris(phosphane) complexes.13 Moreover, they usually require an excess of phosphane or the cumbersome preparation of sophisticated starting materials, ultimately leading to low overall yields. It is noteworthy that the tris(phosphine) complexes cannot be prepared by substitution of CO by phosphine in the well-known and easily prepared bis(phosphine) complexes.14... 

In the low-temperature region, the P-31 spectra of all of the solutions exhibited the doublet arising from the triphenylphosphine coordinated with rhodium. This doublet has a chemical-shift value of + 39.8 ppm (relative to 85% H3P04) and a coupling constant,/P Rh, of 155 Hz. As such, it arises undoubtedly from triphenylphosphine bound to rhodium in a trigonal bipyramidal complex, (Ph3P)3Rh(CO)H. None of the spectra showed any indication of the trans-bisphosphine complex that is formed by dissociation of the tris-phosphine complex. The equilibrium concentration of (Ph3P)2Rh(CO)H was too low for detection by NMR under all of the experimental conditions used in the present studies. 

Introducing a chiral center in the amide functionality renders all 32 potential isomers diastereomeric and thus discernable (in principle) by NMR spectroscopy. In practice, the lanthanide complexes formed (Eu, Gd and Tb) with macrocyclic monoamide tris(phosphinate) ligands bearing a chiral center on the amide group exist as only two non-interconverting diastereomers in a ratio of 2 1 and 4 1 for the a-phenylethyl and a-l-napthylethyl derivatives, respectively (DOTMP-MPMeA and DOTMP-MNaphMeA) [114]. The configuration at... 

In Figure 1, the observed reactions are indicated in the context of a proposed catalytic scheme for terminal hydroformy-lation. The reaction pathway involving the alkyl phosphine intermediate (VIII) is the most likely. Overall, the results of the NMR studies provide consistent explanations for the process parameters of selective hydroformylation, particularly of the low pressure continuous product flashoff process (.5,15). it was shown that, in contrast to prior indications (3), the tris-phosphine complex (I) is a remarkably stable and favored species in the presence of excess phosphine and H2. This complex (I) is postulated to have a key role in the reversible generation and... 

The mechanism of the oxidative addition of aryl bromides to the bis-P(o-tolyl)3 Pd(0) complex 3 was surprising [196]. It has been well established that aryl halides undergo oxidative addition to L2Pd fragments [197 -200] thus, one would expect oxidative addition of the aryl halide to occur directly to 3 and ligand dissociation and dimerization to occur subsequently. Instead, the addition of aryl halide to [Pd[P(o-tolyl)3]2] occurs after phosphine dissociation, as shown by an inverse first-order dependence of the reaction rate on phosphine concentration and the absence of any tris-phosphine complex in solution [196]. 

II) occurs readily at room temperature even in nonpolar solvents. Various tripodal tris-phosphine ligands have also been shown to attach all three phosphorus atoms providing [Ir(COD)P3]+ compounds. ... 

The uptake of Hj by RhClLj is reversible at 25°C, as is the uptake by L Rh Cl. The two siloxyphosphine complexes catalyze the hydrogenation of styrene. The hydrogenation rate is higher for the tris(phosphine) than for the tetrakis(phosphine) complex. 

One major advantage offered by the dppf ligand in Rh-catalyzed olefin hydroformylation is exemplified in its higher linear aldehyde selectivity when present in a dppf Rh ratio of 1.5 or higher [37,242]. This result leads to the proposed key intermediate of a Rh dimer with both chelating and bridging phosphine in the catalytic cycle. It also confirms the significance of the tris (phosphine) moieties at the point when the aldehyde selectivity is determined, i.e., the step in which the hydride is inserted into the M-olefin bond. This involvement of a dinuclear or tris (phosphine) intermediate appears to differ from the intermediate RhH(CO)(PR 3)z (olefin) (which is converted into the square planar Rh(R)(CO)(PR 3)2 by hydride insertion) commonly accepted for hydroformylation catalyzed by monophosphine complexes. P NMR studies also established the existence of the equilibrium in which the disphosphine can be... 

Donor-r acceptor (D-rA) interactions. The combination of donor and acceptor sites raises the possibility of D A interactions (intramolecular and intermolecular). In most systems, such D A interactions are prevented by the steric demand of the substituents (steric frustration) and/or the nature of the organic linker (geometric frustration). Noticeable exceptions are illustrated in Scheme 1 (i) the Cj-bridged phosphine-alane 3 adopts a head-to-tail dimeric structure and is usually reacted in the presence of an additional Lewis base to displace the A1 interactions " (ii) the di- and tri-phosphine boranes 7 and 8 equilibrate in solution between open and closed forms which were unambiguously identified in the solid state by X-ray diffraction analyses (iii) the pyridine-borane 2 exists in solution as a mixture of closed monomeric form and head-to-tail dimeric structure, but N B interactions are readily cleaved upon coordination to Ru. ... 

The bridging coordination of M—X bonds represents a preliminary stage in their intramolecular activation and may ultimately lead to zwitterionic complexes upon heterolytic cleavage. Such a process has been observed and unambiguously authenticated with simple phosphine-boranes of type 4 as well as di- and tri-phosphine derivatives of the heavier group 13 elements 7 and 8. 

Trialkyl- and triaryl-phosphines, -arsines and -stibines are all good donors toward rf-group transition metals and chelating di- and tri-phosphines and -arsines have been especially widely used as 7r-acid ligands (Section 22-13). The oxides, R3MO, also form many complexes, but they function simply as donors. Trialkyl- and triaryl-phosphines, -arsines and -stibines generally react with alkyl and aryl halides to form quaternary salts ... 

A common way to generate a chiral catalyst involves a modification of Wilkinson s catalyst (340) in which an optically active tertiary phosphine, bis- or tris-phosphines are used as ligands in place of triphenyl-phosphine. If the phosphorous atom of the added phosphine is the stereogenic center, the optical yields are usually 4-22%, as in the conversion of atropic acid (447) to hydratropic acid (448) with 22% ee." " " An example of this type of phosphine is (-)-methylpropylphenylphosphine. bis(Phosphines) are commonly used, including 449 (called dipamp)" " and 450 (called R-camp)." " ... 

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