Binary oxo catalysts using chromium, molybdenum, or tungsten

Abstract

Hydroformylation catalysis of olefins was extended to include group 6 metal carbonyls of chromium, molybdenum, and tungsten. Hydroformylation activity and selectivity for pure M(CO)e catalysts were both low, whereas organophosphine complexes of the type M(CO),(PR,) exhibited good selectivity but still showed low catalytic activity. By the introduction of trace amounts of a second metal carbonyl such as cobalt, a binary metal catalyst system could be "custom tailored" to yield excellent catalytic activity and good selectivity. Catalytic activity was lower than a pure cobalt carbonyl-trialkylphosphine catalyst used in high concentration, and linear product formation was not as high for the binary catalyst systems. An unexpected synergistic effect was observed in these binary metal systems which contained a "major" catalyst M(CO),(PBu,) and a "minor" catalyst HCo(CO),PBu3. The active catalytic species exhibited the most desirable features of each individual metal catalyst. Binary catalysts of Cr/Co, Mo/Co, and W/Co all performed equally effectively as oxo catalysts when hydroformylating terminal or internal straight chain olefins. Mononuclear complexes of the type M(CO)5(FBu3) showed exceptionally high thermal stabilii. Parametric studies were performed to determine optimum operating conditions for these unique catalyst systems. In trod uctionCommercial oxo processes which once used pure cobalt carbonyl catalysts exclusively now include organophosphine-complexed cobalt or rhodium carbonyl catalysts. While cobalt and rhodium catalysts are excellent for hydroformylating olefins to alcohols, both are based on strategic metals which must be imported from abroad. Any major long-term disruption in availability of these metals could lead to serious consequences for oxo alcohol producers. Several years ago cobalt availability was a cause for concern, although major shortages did not materialize. Rhodium availability has not posed any serious threats to date. However, since the producer's price for this metal has approached $800 per troy ounce since its commercial use in low-pressure oxonation, high rhodium recovery is essential to achieve high process efficiency. To maximize catalyst efficiency, i.e., the cost of catalyst per pound of product produced, a rhodium-triphenylphosphine catalyst is best applicable in propene oxonation rather than higher olefin oxonation since the product/catalyst separation step facilitates high rhodium recovery.Several major concerns prompted the investigation of metal systems other than cobalt or rhodium as potential hydroformylation catalysts. To lessen the chance of strategic metal shortages, the oxo catalyst had to be based principally on metals produced in the U.S. The producer's price for such metals had to be more in line with base metals rather than precious metals. To favor process economics, the oxo catalyst had to possess exceptionally high thermal stability to facilitate an efficient direct separation of high molecular weight oxo products from the catalyst. Finally, catalyst activity...

Metal-organic frameworks as kinetic modulators for branched selectivity in hydroformylation

“…The inactivity of MIL-101 and zeolite-Y might be explained by an electronic interaction between the metal open sites in the MOF and the Co catalyst. The detrimental effect of Al/amines and of Cr to the activity in Co-catalysed hydroformylation is described in the literature 34,35 .…”