Phosphines complex stability

The chemistry of technetium(II) and rhenium(II) is meagre and mainly confined to arsine and phosphine complexes. The best known of these are [MCl2(diars)2], obtained by reduction with hypophosphite and Sn respectively from the corresponding Tc and Re complexes, and in which the low oxidation state is presumably stabilized by n donation to the ligands. This oxidation state, however, is really best typified by manganese for which it is the most thoroughly studied and, in aqueous solution, by far the most... 

Within the osmium complexes in oxidation states (II-IV) [11,12] the stability of the +4 oxidation state becomes more important. Ammine and tertiary phosphine complexes have been selected for detailed examination. 

The reactivity of (367) and (368) towards phosphine complexes of Ni11 has been investigated. Depending on the nature of the phosphine and the dithiocarbamate used, different complexes were obtained 974 The stability constants for the Ni11 complexes of (369), (370), and (371) have been determined in aqueous solution. Both 1 1 and 1 2 complexes were observed.975... 

The chemistry of platinum(0) is overwhelmingly dominated by phosphine complexes with the general formula [Pt(PR3) ] (n = 2-4). These complexes undergo various types of oxidative addition reactions, activating a wide variety of bonds. The stability of the complexes depends on the steric... 

Mixed silver telluride-tellurolate complexes have been prepared in a similar manner to those of selenium. The reactions of a silver salt with RTeTMS in the presence of phosphines as stabilizing agents are reported in Scheme 9 1043-1046... 

Amine complexes stabilized with phosphine ligands of the type [AuL(PR3)]+ have been obtained for L = bipy,2310 phen,2310,231 quinoline,23 1 acridine,2311 benzo[h]quinoline,2311 naphthyr-idine (388)2311 2,2 -biquinoline,2311 di-2-pyridyl-ketone,2311 di-2-pyridylamine,2311 2-(2-pyridyl)-benzimidazole, 2311 ferrocenylpyridine, 2-nitroaniline,2312 4-methoxyaniline,2312 NHPh2, 2 NHEt2,2312 NMe3,2312 quinuclidine,2313 NEt3,2314 2-aminothiazoline,2315 histidine,2316... 

Electron spin resonance (ESR) signals, detected from phosphinated polystyrene-supported cationic rhodium catalysts both before and after use (for olefinic and ketonic substrates), have been attributed to the presence of rhodium(II) species (348). The extent of catalysis by such species generally is uncertain, although the activity of one system involving RhCls /phosphinated polystyrene has been attributed to rho-dium(II) (349). Rhodium(II) phosphine complexes have been stabilized by steric effects (350), which could pertain to the polymer alternatively (351), disproportionation of rhodium(I) could lead to rhodium(II) [Eq. (61)]. The accompanying isolated metal atoms in this case offer a potential source of ESR signals as well as the catalysis. 

Phosphine complexes, osmium, 19 642 Phosphine coordination complexes, of uranium, 25 436 Phosphine derivatives, 19 28 Phosphine oxide(s), 11 495-496 19 66 predicted deviations from Raoult s law based on hydrogen-bonding interactions, 8 814t in salicylic acid manufacture, 22 8 Phosphine oxide diols/triols, 11 501 Phosphine selenides, 22 90 Phosphinic acid, 19 20, 54-55 Phosphinic anhydride, 11 499 Phosphinothricin acetyltransferase (PAT) proteins, 13 360 Phosphite esters, 19 20 Phosphites, in VDC polymer stabilization, 25 720... 

As a result of the higher stability the process can be (and must be ) operated at lower pressure (25-100 bar versus 200-300 bar for HCo(CO)4). The higher stability can be explained by the electron donation of the phosphine to the electron deficient cobalt carbonyl thus strengthening the Co-CO bonds. The phosphine complex is less active than the tetracarbonyl complex and therefore the reaction is carried out at higher temperatures (170 °C versus 140 °C). The temperature is "dictated" by the rate required the high pressures in the tetracarbonyl system are needed to prevent decomposition of the carbonyls to metal and CO. 

Even in an excess of ligands capable of stabilizing low oxidation state transition metal ions in aqueous systems, one may often observe the reduction of the central ion of a catalyst complex to the metallic state. In many cases this leads to a loss of catalytic activity, however, in certain systems an active and selective catalyst mixture is formed. Such is the case when a solution of RhCU in water methanol = 1 1 is refluxed in the presence of three equivalents of TPPTS. Evaporation to dryness gives a brown solid which is an active catalyst for the hydrogenation of a wide range of olefins in aqueous solution or in two-phase reaction systems. This solid contains a mixture of Rh(I)-phosphine complexes, TPPTS oxide and colloidal rhodium. Patin and co-workers developed a preparative scale method for biphasic hydrogenation of olefins [61], some of the substrates and products are shown on Scheme 3.3. The reaction is strongly influenced by steric effects. 

When heated under reflux in benzene or methanol, in the absence of hydrogen, isomerisation of the terminal olefin of the pent-4-enyl phosphine n=3) is completed in less than 5 hours to yield the cis-pent-3-enyl phosphine complex. For the but-3-enyl complex ( =2) the isomerisation to the but-2-enyl phosphine complex is incomplete even after 88 hours. The mechanism involves a i-allyl hydride intermediate, whose stability, as in the case of the hydrogenation studies, is controlled by the... 

The effect of tin compounds, especially tetra-alkyl and tetra-aryl tin compounds, is similar to that of phosphine, though lower temperature and pressure are required for the catalyst s optimum activity. Tin can promote the activity of the nickel catalyst to a level that matches that of rhodium under mild conditions of system pressure and temperature e.g. 400 psig at 160 C. The tin-nickel complex is less stable than the phosphine containing catalyst. In the absence of carbon monoxide and at high temperature, as in carbonyl-ation effluent processing, the tin catalyst did not demonstrate the high stability of the phosphine complex. As in the case of phosphine, addition of tin in amounts larger than required to maintain catalyst stability has no effect on reaction activity. 

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