On the mechanism of the copper(II) catalysis of the formation of urethanesfrom alcohols and isocyanates

The ability of a range of opper(II) complexes to catalyse the formation of a urethane from butanol and phenyl isocyanate in chloroform at 25 degreesC has been investigated. Nine of the complexes were of P-dicarbonyl compounds , RCOCH2COR ', where R = alkyl, and R ' = alkyl or O-alkyl, and it was foun d that the catalytic activity of these complexes increases as the electron- donating properties of the R and R ' groups increases. It is shown that thi s is consistent with the active species in the catalytic cycle being the di meric copper(II) alkoxide which is formed by alcoholysis of the starting co mplex, and whose structure is directly analogous to that of the alkoxide wh ich has been proposed as the active species in the tin(IV)-catalysed format ion of urethanes. Further support for the catalytic role of this copper alk oxide is provided by the very high catalytic activity of the alkoxide prepa red from the most active of the P-dicarbonyl complexes, i.e. that of dipiva loylmethane, and of a cationic methoxy-bridged bis(bipyridyl) complex. (C) 2000 Elsevier Science B.V. All rights reserved.