Hemilabile Phosphonate−Phosphane−Rh Catalysts for Homogeneous and Heterogeneous Carbonylation

Abstract

New rhodium complexes with phosphonate-phosphane ligands (RO) 2 P(O)-X-PPh 2 (1a-d), a, X ) CH 2 ; b, X ) (CH 2 ) 2 ; c, X ) (CH 2 ) 3 ; d, X ) p-C 6 H 4 , have been synthesized and characterized. Both, open-chain structures [ClRh(cod)PPh 2 -X-P(O)(OR) 2 ] (2a-d) and cyclic complexes [(cod)-Rh(PPh 2 -X-P(O)(OR) 2 )]A (3a-c, A ) BF 4 , PF 6 ) were isolated after stoichiometric reactions at mild conditions. FTIR investigations of 2b supported on silica at temperatures between 150 and 250 °C suggest that the phosphonate-phosphane ligand stabilizes rhodium monocarbonyl species and allows also the formation of free coordination sites to form dicarbonyl species, which is in accord with the proposed hemilabile behavior of the complexes in methanol carbonylation. During the catalytic cycle, the phosphane group is assumed to be strongly coordinated to the rhodium, while the phosphoryl oxygen of the phosphonate group is supposed to change between a free and a coordinated state, thus vacating or occupying a coordination site. This is supported by the findings that the activation enthalpies for the open-chained catalyst precursors 2a-d increased significantly with growing distance between the phosphonate and phosphane groups. The new rhodium-phosphonate-phosphane complexes 2a and 2b afforded also heterogeneous catalysts with enhanced activity in vapor-phase carbonylation. Activated carbon has been found to be a suitable support for hemilabile rhodium complexes, but normal diffusion of reactants begins to limit the high intrinsic carbonylation rate over the supported catalysts. Experimental SectionMaterials. Methanol, methyl iodide, and methyl acetate (Merck) were used as received. Dichloromethane was dried

Structural and Theoretical Studies ofortho-Substituted Triphenylphosphane Ligands and Their Rhodium(I) Complexes

“…[6] With the possible hemilabile character of these ligands, a more weakly coordinated donor site may appear between the coordinated/uncoordinated equilibrium, allowing an interesting setup for catalytic reactions. Hemilabile character has earlier been reported for several mixed heteroatom-phosphorus ligands, including ether-phosphanes, [7] hydroxyphenyl phosphanes, [8] phosphonate-phosphanes, [9] and amido-diphosphanes. [10] The fluxional behavior of this type of ligand around the metal center is considered to activate CO and H 2 molecules, thus improving the oxo-reactions such as carbonylation and hydroformylation.…”

Synthesis and coordination properties of palladium(II) and platinum(II) complexes with phosphonated triphenylphosphine derivatives

“…Ambitions to use various ''field-proven'' homogeneous catalysts under aqueous and biphasic conditions made for the synthesis of a vast amount of phosphines modified by hydrophilic groups such as ammonium and phosphonium (cationic), sulfonate, phosphonate and carboxylate (anionic) or alcohol and polyether chain (neutral) [1]. Phosphines modified by phosphonate moiety [2] have been attracting attention as alternatives to well-established sulfonates [1]; several examples of their use in biphasic catalysis have been mentioned in literature [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] (e.g., Pd-catalysed electrochemical reduction of CO 2 [3], Rh-catalysed carbon-carbon double bond hydrogenation or hydroformylation [4,5], Pd-catalysed benzyl halide carbonylation [6] and Suzuki coupling [7]). A great advantage (compared with other hydrophilic moieties) is the possibility to bind the phosphonated ligand to an inert oxide surface (e.g., Al 2 O 3 ) [8], onto activated carbon surface [9] or into a layered framework, e.g., zirconium phosphonate [10,12] or zirconium phosphite/phosphonate hybrid material [13].…”

“…Phosphines modified by phosphonate moiety [2] have been attracting attention as alternatives to well-established sulfonates [1]; several examples of their use in biphasic catalysis have been mentioned in literature [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] (e.g., Pd-catalysed electrochemical reduction of CO 2 [3], Rh-catalysed carbon-carbon double bond hydrogenation or hydroformylation [4,5], Pd-catalysed benzyl halide carbonylation [6] and Suzuki coupling [7]). A great advantage (compared with other hydrophilic moieties) is the possibility to bind the phosphonated ligand to an inert oxide surface (e.g., Al 2 O 3 ) [8], onto activated carbon surface [9] or into a layered framework, e.g., zirconium phosphonate [10,12] or zirconium phosphite/phosphonate hybrid material [13]. Such supported catalysts have been successfully tested in Rhcatalysed alkene hydroformylation [12,14], Rh-catalysed methanol carbonylation [9,15], Ru-catalysed asymmetric b-keto ester hydrogenation [4,11] or Heck reaction [13].…”

“…A great advantage (compared with other hydrophilic moieties) is the possibility to bind the phosphonated ligand to an inert oxide surface (e.g., Al 2 O 3 ) [8], onto activated carbon surface [9] or into a layered framework, e.g., zirconium phosphonate [10,12] or zirconium phosphite/phosphonate hybrid material [13]. Such supported catalysts have been successfully tested in Rhcatalysed alkene hydroformylation [12,14], Rh-catalysed methanol carbonylation [9,15], Ru-catalysed asymmetric b-keto ester hydrogenation [4,11] or Heck reaction [13]. Several tests were also performed in organic solvents under homogeneous conditions (e.g., Pt/Sn-catalysed alkene hydroformylation [11], Rh-catalysed methanol carbonylation [16] and Rh-catalysed styrene hydroformylation [17]).…”

Bridged Hemilabile Allylphosphonate Ligand: Synthesis and Crystal Structure of a New Binuclear Rhodium Complex

“…Olefinic phosphines and olefinic amines have been shown to give rise to such chelate complexes; meanwhile, no study of the potential hemilability of these bidentate ligands has been reported. New hemilabile rhodium complexes with phosphonate−phosphine ligands (RO) 2 P(O)(CH 2 ) n PPh 2 have been recently shown as promising catalyst precursors because of the easy ring opening of the chelate structure by decoordination of the phosphonate moiety …”