Rhodium carbonyl complexes catalysts

In SILP carbonylation we have introduced a new methanol carbonylation SILP Monsanto catalyst, which is different from present catalytic alcohol carbonylation technologies, by using an ionic liquid as reaction medium and by offering an efficient use of the dispersed ionic liquid-based rhodium-iodide complex catalyst phase. In perspective the introduced fixed-bed SILP carbonylation process design requires a smaller reactor size than existing technology in order to obtain the same productivity, which makes the SILP carbonylation concept potentially interesting for technical applications. 

Facile formation of metal carbonyl complexes makes rhodium a very useful catalyst for both the hydroformylation of multiple bonds and the decarbonylation of the aldehydes. Two groups have independently utilized rhodium carbonyl complex obtained from decarbonylation of aldehydes in PKR (Scheme 5). 

Prior to these investigations by HCC the promotional effect of iodide on the oxidative addition of Mel was investigated by others [9, 39, 40]. Foster demonstrated that the rate enhancement of this reaction in anhydrous medium was attributable to increased nucleophilicity of the rhodium catalyst with added iodide. The rationale for this observation was the generation of an anionic rhodium carbonyl complex, [Rh(CO)2l(L)]. Generation of this species was observed only with iodide added to certain neutral Rh species. No rate enhancement occurred with iodide added to the anionic complex, [Rh(CO)2l2] [39]. Similarly, in solvents with a high water concentration, iodide salts exhibited no rate enhancement in the presence of [Rh(CO)2l2] [11]. Maitlis and co-workers, in more recent investigations, reported a promotional effect of iodide in aprotic solvents on the oxidative addition of CH3I on [Rh(CO)2l2] [9a, 9c]. 

Rhodium carbonyl complexes are used as catalyst precursors in the hydroformyla-tion reaction Since rhodium catalysts are two to four orders of magnitude more efficient than cobalt-based ones, they are used to carry out hydroformylation of kineti-cally inert olefins, such as styrene and nitroalkenes. ... 

Catalytic processes that take place in a uniform gas or liquid phase are classified as homogeneous catalysis. Homogeneous catalysts are generally well-defined chemical compounds or coordination complexes, which, together with the reactants, are molecularly dispersed in the reaction medium. Examples of homogeneous catalysts include mineral acids and transition metal compounds (e. g., rhodium carbonyl complexes in 0X0 synthesis). 

This reaction has been modified using a group VIB metal complex as catalyst in combination with trace amounts of cobalt or rhodium carbonyl complex." ... 

Rhodium catalysts are known to be effective in the hydroformylation of unsaturated bonds and also in the decarbonylation of aldehydes. This efficacy arises from facile formation of rhodium carbonyl complexes from either carbon... 

System 1 A variety of monometallic rhodium complexes and heterobimetahic cobalt-rhodium carbonyl complexes were used as catalyst precursors for the room... 

In addition to dimerization and clustering to multinuclear rhodium carbonyl complexes, active catalyst can also be removed from the reaction mixture by orthometallation. Several reports have appeared on orthometallation of rhodium triphenyl phosphite complexes in literature but... 

Probably the most important industrial application of a transition-metal nucleophile is the Monsanto process for carbonylating methanol, using soluble rhodium-carbonyl complexes in the presence of iodide. The catalyst is in fact [Rhl2(CO)2] (Forster 1979, and references therein), and the catalytic cycle is shown in Scheme 21. The substrate for the rhodium catalyst is methyl iodide, which oxidatively adds to yield [Rh(Me)(I)3(CO)2] . 

In general, rhodium-catalyzed hydroformylation of alkynes proceeds much slower than the reaction with olefins. It should be remembered that homogeneously catalyzed hydroformylation of olefins with unmodified rhodium catalysts can be irreversibly poisoned by the presence of even trace quantities of alkynes. As Liu and Garland [94, 95] found by means of in situ IR spectroscopy, the reason is likely the formation of dinuclear rhodium-carbonyl complexes I, which are stable even in the presence of hydrogen (Scheme 4.17). Therefore, alternative pathways for the production of a,P-unsaturated aldehydes have been suggested, consisting of Ni-catalyzed hydrocyanation followed by chemoselective hydrogenation [96]. 

Similar activation takes place in the carbonylation of dimethyl ether to methyl acetate in superacidic solution. Whereas acetic acid and acetates are made nearly exclusively using Wilkinson s rhodium catalyst, a sensitive system necessitating carefully controlled conditions and use of large amounts of the expensive rhodium triphenylphosphine complex, ready superacidic carbonylation of dimethyl ether has significant advantages. 

Polymer-supported catalysts incorporating organometaUic complexes also behave in much the same way as their soluble analogues (28). Extensive research has been done in attempts to develop supported rhodium complex catalysts for olefin hydroformylation and methanol carbonylation, but the effort has not been commercially successful. The difficulty is that the polymer-supported catalysts are not sufftciendy stable the valuable metal is continuously leached into the product stream (28). Consequendy, the soHd catalysts fail to eliminate the problems of corrosion and catalyst recovery and recycle that are characteristic of solution catalysis. 

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