Clean Technologies Throughout Two-Phase Catalysis by Organometallic Complexes

Roberto Fernando de Souza*, Paulo Anselmo Ziani Suarez, Jairton Dupont

LMC/IQ/UFRGS, Av. Bento Gonçalves 9500, CEP91501-970, Porto Alegre, Brazil; rfds@if.ufrgs.br

Abstract

Two-phase catalysis has been largely studied as an improvement to homogeneous catalytic processes. Major benefits of these technologies are economics, basically associated with the recycle of the catalyst, and environmental, since in these process there is no organic solvents which generate the major quantity of industrial wastes enabling new clean technologies.

The introduction of methyl-butyl-imidazolium (MBI) based ionic liquids allows the transposition of homogeneous catalysts to liquid-liquid two-phase catalytic processes like olefins oligomerization and selective hydrogenation of olefins.

In the first part of this work we describe the use of MBI ionic liquids in butenes dimerization by nickel complexes, discussing the control of the activity and selectivity by modifiers like CS2PR3. Turnover frequencies higher than 7 cycles/second and selectivities up to 96% in dimers (with branching index of 1.3) has been obtained. The DIFASOL process (new two-phase version of the DIMERSOL IFP’s process) will be discussed as a clean technology improvement.

In the second part we describe the use of MBI ionic liquids (with anions like BF4, PF6 and ZnCl4) in the hydrogenation of olefins, diolefins and even unsaturated polymers. A large variety of organic substrates has been hydrogenated as showed in Table 1.

Table 1. Hydrogenation of unsaturated compounds with two-phase catalytic process

Substrate

Catalyst precursor/Ionic liquid

Product

RuCl2(PPh3)3/(BMI.Cl)2(ZnCl2)

RhCl(PPh3)3/MBI.PF6

Pd(acac)2/BMI.BF4

Pd(acac)2/BMI.BF4

Pd(acac)2/BMI.BF4

NBRa

RuHCl(CO)(PCy3)2/BMI.BF4

HNBRb

a) acrylonitrile-butadiene rubber; b) hydrogenated acrylonitrile-butadiene rubber.

The catalytic performance of classic palladium, rhodium and ruthenium complexes in homogeneous and two-phase medium are compared. The catalysts were reused up to 15 times with complete conservation of the catalytic activity and selectivity achieving a productivity of more than 15 kg of products per gram of metal.

In this work we will discuss these new technologies in view of the concept of "atomic economy" which means, new process with total recycle of the ionic liquid (solvent), transition metal catalyst and total conversion of reagents in high value products. In summary this new "biphasic" process are not only economically attractive and applicable to large-scale reactions, but also environmentally friendly.