TPPTS metal complexes

Importantly, the Pd(tppts)3 catalyst, generated in situ by complexation of PdCl2 with tppts in H20 followed by reduction of the resulting [PdCl(tppts)3]+ complex with CO,448 451 was stable under hydrocarboxylation conditions 452 In contrast, the Pd/PPh3 system in organic solvents is not completely stable with respect to palladium metal formation. 

This is a rare example of efficient organometallic catalysis in aqueous media which exhibits higher rates than conventional transition metal complexes in organic solvents. Other such examples are the Pd/tppts catalysed hydrocarboxy-lation of propene (cf. Section 4) and the (SAP) Rh/tppts catalysed hydroformy-lation of methyl acrylate (cf. Sections 3.5 and 11). 

Complexes of ruthenium, [HRu(CO)Cl(tppms)3] 2H20 and [HRu(CO) Cl(tppts)3], were reported to be catalysts for the same hydrogenation reaction (92). The metal complexes were not pure rather, they were used in the presence of the free sulfonated phosphanes and their respective oxides. 

The lifetime of the rhodium precatalyst depends on the rate at which the metal complex HRh(CO)(TPPTS)3 and the excess ligand TPPTS undergo decomposition. The catalyst lifetime is considerably increased by occasional addition of extra ligand. In general an increase in the reaction temperature and/or CO pressure results in a decrease in the catalyst lifetime. 

Anionic metal complexes, for example [Rh(CO)2l2], can be exchanged onto the anion-exchange resin Dowex 1-X8. The supported rhodium carbonyl iodide complex functions as an immobilized methanol Carbonylation catalyst. Metal complexes of the water-soluble phosphine TPPTS and its monosulfonated analog have also been exchanged onto anion-exchange resins. The pendant sulfonate groups provide the electrostatic attraction to the support. 

Metal complexes of TPPMS and TPPTS have amphophilic character because of the presence of both hydrophilic sulfonate groups and hydro-phobic phenyl groups in the ligand structure. This feature allows the complex to transfer readily between the aqueous and organic phases in a biphasic system. Furthermore, these complexes can aggregate to form micelles, or surface-active compounds. This property may be a particularly important one when the properties and selectivities of catalysts formed by such phosphines are being considered (130). 

More recently, the application scope of thermoregulated phase-separable transition metal complex with nonionic phosphine ligand has been expanded from hy-droformylation to hydrogenation, and the central metal varied from Rh to Ru. The first experimental study is the hydrogenation of styrene catalyzed by thermoregulated phase-separable Ru3(CO)12/PETPP complex catalyst. Under the conditions of Ph2 = 2.0 MPa, T=90°C, catalyst/substrate (mol/mol) = 1/1000, 3 hours, the Ru3(CO)12/PETPP complex catalyst exhibited good activity (Table 5). Compared with other catalysts, Ru3(CO)12/PETPP complex showed the same catalytic activity compared to the lipophilic Ru3(CO)9(TPP)3, while the hydrophilic Ru3(CO)9-(TPPTS)3 and Ru3(CO)9(TPPMS)3 are less active (Table 6). 

The isolation of water-soluble palladium(O) complexes was achieved by Herrmann and co-workers by gel-permeation chromatography for Pd(TPPTS)3 [5], An X-ray determination was reported by Casalnuovo and Calabrese for Pd(TPPMS), [6] this is the first published structure of a transition metal complex containing a sulfonated phosphine. 

As water is immiscible with most organic substrates, most reactions involving water are done with liquid-liquid biphasic systems. The use of biphasic organometallic catalysts to catalyze aqueous-phase reactions is a novel method to address this issue. The catalyst in such reactions is a water-soluble transition metal complex with substrates that are partially water-soluble. The Ruhrchemie-Rhone-Poulenc process, which involves hydrofor-mylation of propylene to n-butanol, is an example of biphasic organometallic catalysts being used on an industrial scale (Comils and Kuntz, 1995). The catalyst employed is a water-soluble Rhodium (I) complex of trisulfonated triphenylphosphine (tppts) (see Fig. 5.3). 

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