Other Phosphines

Water-soluble mono- and diphosphines represent the major class of phosphines used in aqueous-phase homogeneous catalysis. However, some new types of water-soluble phosphines have been developed, including phosphines containing sugar substructures [31] or phosphonate chains [32], and chiral sulfonated phosphines for the asymmetric hydrogenation of dehydropeptides [33] and phosphines with amino acid moieties [59]. 

Besides the well-known applications of water-soluble phosphines, e.g., in hydroformylation, water-soluble catalysts may have significant advantages for electrochemical processes in which the much lower resistance of aqueous solutions compared with that of organic solutions would improve the energy efficiency of the process. It is known that the electrochemical reduction of carbon dioxide to carbon 

Reagents (i) KOBu, thf (ii) LiAlH4, Et20 (iii) HCHO, EtOH. 

The following topics have not been considered in this section metal complexes of sulfonated 2,2 -bipyridine [43] and alizarin [44], water-soluble porphyrins and cy-dopentadienyl ligands [45], and metal complexes of sulfonated phenanthroline derivatives [46], Also P,N-bidentate phosphines [47], of which coordination properties await further study, have not been discussed here. 

Trinkhaus, R. Seleke, D. Heller, Tetrahedron Asymmetry 1995, 6, 1973. 

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Complexes with other phosphines can be prepared by the general route of refluxing IrCl3 or IrClg- in an alcohol that acts as the source of CO, then adding the phosphine. In certain cases, a displacement reaction can be used... 

Void-free phenolic-epoxy networks prepared from an excess of phenolic novolac resins and various diepoxides have been investigated by Tyberg et al. (Fig. 7.37).93 -95 The novolacs and diepoxides were cured at approximately 200°C in the presence of triphenylphosphine and other phosphine derivatives. Network densities were controlled by stoichiometric offsets between phenol and... 

Liicke et al. have prepared other phosphinated POSS compounds Tg[(CH2)2-PMe2]8 and Tg[(CH2)3-PMe2]8 by treating T8[CH = CH2]8 or T8[CH2-CH = CH2]8 with H-PMe2 under UV irradiation. The former compound has shown to have good coordination properties to carbonyl transition metal complexes such as CpMn(CO)3 (Table 15). 

Auranofin and Other Phosphine(Thiolato)Cold(l) Species... 

Recently, Y. Yamamoto reported a palladium-catalyzed hydroalkoxylation of methylene cyclopropanes (Scheme 6-25) [105]. Curiously, the catalysis proceeds under very specific conditions, i.e. only a 1 2 mixture of [Pd(PPh3)4] and P(o-tolyl)3 leads to an active system. Other combinations using Pd(0 or II) precursors with P(o-tolyl)3 or l,3-bis(diphenylphosphino)propane, the use of [Pd(PPh3)4] without P(o-tolyl)3 or with other phosphine ligands were all inefficient for the hydroalkoxylation. The authors assumed a mechanism in which oxidative addition of the alcohol to a Pd(0) center yields a hydrido(alkoxo) complex which is subsequently involved in hydropal-ladation of methylenecyclopropane. 

Various type (967) dinuclear complexes with phosphido bridges have been prepared, usually by reduction of [(R3P)2NiX2] with, for example, sodium.2372-237 The terminal phosphines can be exchanged by other phosphines or by CO, yielding (968) and (969) in the latter case.2373,2374 Diphenylphosphide Ni1 complexes have also been prepared electrochemically.2376... 

The most active palladium catalyst system developed for the asymmetric hydrosilylation of cyclopentadiene (Scheme 23) involves the use of the (/ )-MOP-phen ligand (38), which shows significant enhancement of enantioselectivity compared to (R)-MeO-MOP (80% ee from (38), 39% ee from (36a)).114 Other phosphine ligands that afford active palladium catalysts for the same transformation include the /3-7V-sulfonylaminoalkylphosphine (39) and phosphetane ligand (40) (Equation (13)).115-117 A comparison of the enantioselectivities of these ligands for the palladium-catalyzed hydrosilylation of cyclopentadiene is given in Table 8. 

Some other phosphine complexes with late transition metals such as Rh, Ir, Ni, Cu, and Co have been reported to act as active electrocatalysts for reduction of C02 into CO and/or 11 COO in anhydrous conditions.179-182... 

Other phosphines investigated include cyanoethylphosphine, benzylphosphine, and cyclopentyl-phosphine, but all suffered from a prereaction in the presence of metal alkyls.153... 

Functionally substituted phosphines play an important role as ligands in a great variety of phosphorus coordination compounds. They have some interesting features that distinguish them from other phosphine ligands, namely (a) the presence of other heteroatoms bearing lone electron pairs in addition to phosphorus (b) the presence of functional groups able to form bonds with a metal with the participation of its valence electrons ... 

The combination of [Rh(Cl(NBD)]2 and ligands 89, 90, 91, or 92 with diphenylsilane asymmetrically reduces aryl alkyl ketones, including acetophenones, in excellent yields and in 81 to 90% ee (Eq. 346).574 The best results are with ferrocene 91 and acetophenone in toluene.575 Other phosphine-substituted ferrocenes do not give comparable results. Rhodium(I) complexes of TADDOL-derived... 

Other phosphine systems have been reported in which four phenyl groups are oriented around a rhodium center (249-254). They all hydrogenate Z-enamides efficiently, and intermediates with a conformation of edge-face phenyls seem plausible in each case. The 2S,4S-4-diphenyl-... 

We conclude that only one phosphine attacks a ji-S group of 20. Indeed, the phosphine sulfide product from dmpm is Me2P(S)CH2PMe2, not a bis(sulfide).The other phosphine implicated by Eqs. (32) and (33), whether from a second PR3 or from a di-phosphine, adds as a Lewis base to rhenium. The basis for this is that a pyridine easily replaced one of the phosphines in the mechanism. This proposed mechanism should steer the reaction directly towards formation of 21, but owing to the dilemma posed in point (c), an intermediate likely intervenes. It can partition to the slowly-reacting 21 or to 23, the latter step requiring additional phosphine Scheme 13 shows the postulated mechanism. The dual role for phosphine and the use of Py in its place and the proposal for partitioning are shown in Scheme 14. 

One widely studied catalyst system for hydroformylation in organic solvents is Rh(CO)2(acac) combined with triphenylphosphine (or other phosphines) in varying ratios. The same catalyst has been shown to catalyse the hydroformylation of 1-pentene to n- and Ao-hexanal in [bmim][PFg] as shown in Scheme 8.10 [25],... 

Clearly, other phosphine ligands have a pronounced effect on the activity at the rhodium centre. Not only does the activity and percentage of the //-product increase, but the amount of phosphine that is required relative to the rhodium also... 

This reaction has been shown to be general for other phosphines with sp carbon atoms in the right positions for giving five — membered rings after cyclometala-tion ... 

The kinetics and mechanisms of the oxidation of various other phosphines by trans-[Ru (0)2(tpy)(H20)] " and tranx-[Ru (0)2(tpy)(MeCN)] " have also been investigated. ... 

Very little has been published on the structural properties of other phosphine complexes of nickel(O), but tetra(methyldichlorophosphine)-nickel is worthy of mention because it may be prepared by the direct action of the ligand on nickel metal 210). 

Green and coworkers19 prepared the title compound and other related monoalkyne complexes by reaction of the corresponding bis(alkyne) complex with triphenylphosphine (or other phosphines) in good yields. The method described here works for several alkynes, for example, 2-butyne or phenyl-acetylene, and also for phosphines, for example, PEt3 or P(OPh)3. 

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