Homogeneous catalysis

Homogeneous catalysis

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R.X+[M.]R.'[Pd]R.R '+[M.]X

After catalyst formation (formation of a palladium (0) complex), the formation of R-R 'occurs through oxidative addition of R-X, metathesis (sometimes also referred to as transmetalation) and reductive elimination of R-R', which is irreversible.

In most cases this is the speed determining step metathesis(double conversion, transmetalation). If R contains a β-H atom, the Organyl (halogeno) palladium complex decompose in a rapid reaction with β-H elimination. Therefore, most cross-couplings are restricted to organyl halides R-X that do not contain a β-H atom. This restriction does not apply to R'-X, since reductive eliminations of R-R 'from diorganyl-palladium complexes.

In principle, a "carbonylating coupling" is possible in the presence of CO, because CO insertions into a Pd-C bondexpire quickly. The product is then not the hydrocarbon R-R ', but a ketone R-C (O) -R'.

Video: Difference Between Homogeneous Catalysis and Heterogeneous Catalysis - Surface Chemistry (May 2022).