86013-16-3Relevant academic research and scientific papers
Metal complex catalysts interlayered in smectite clay. Hydroformylation of 1-hexene with rhodium complexes ion exchanged into hectorite
Farzaneh, Faezeh,Pinnavaia, Thomas J.
, p. 2216 - 2220 (2008/10/08)
The cationic hydroformylation catalyst precursor Rh(COD)(PPh3)2+, where COD = 1,5-cyclooctadiene, readily intercalates into the swelling layered silicate clay mineral hectorite by replacement of Na+ ions initially present on the interlamellar surfaces. Under hydroformylation conditions, however, the active rhodium complex desorbs from the clay interlayers due to the formation of neutral RhH(CO)x(PPh3)2 (x = 1,2) species. Rhodium complexes containing the positively charged phosphinophosphonium ligand Ph2P(CH2)2+PPh2(CH 2Ph), abbreviated P-P+, are shown to be much more suitable for catalyst intercalation. [Rh(COD)Cl]2, [Rh(CO)2Cl]2, and Rh(COD)+ all form cationic complexes with P-P+ which bind to the clay interlayers and catalyze the hydroformylation of 1-hexene at 100°C and 600 psi CO/H2 when acetone is the solvating medium. Under these conditions, >95% of the 1-hexene is hydroformylated in the clay interlayers. The ratios of normal-to branched-chain aldehydes (n/b) are somewhat higher for the intercalated catalysts (2.4-3.0) than for the homogeneous catalysts under analogous conditions (1.5-2.1). In addition, the intercalated catalyst tends to lower the extent of 1-hexene isomerization relative to homogeneous solution. Spatial factors may influence the relative stabilities of primary and secondary metal alkyls formed as intermediates in the restricted interlayer regions of the layered silicate. The polarity of the solvating medium is important in promoting hydroformylation in the interlayer regions of the intercalated clay catalysts. No hydroformylation activity is observed for the intercalated catalyst in benzene, since this solvent fails to swell the hectorite interlayers and provide access to the metal centers. Solvation by DMF causes extensive dissociation of Rh-(P-P+) bonds in the clay interlayers and loss of a neutral rhodium carbonyl to solution.
