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 found that the catalytic activity of these complexes increases as the electron-donating properties of the R and R ' groups increases. It is shown that this is consistent with the active species in the catalytic cycle being the dimeric copper(II) alkoxide which is formed by alcoholysis of the starting complex, and whose structure is directly analogous to that of the alkoxide which has been proposed as the active species in the tin(IV)-catalysed formation of urethanes. Further support for the catalytic role of this copper alkoxide is provided by the very high catalytic activity of the alkoxide prepared from the most active of the P-dicarbonyl complexes, i.e. that of dipivaloylmethane, and of a cationic methoxy-bridged bis(bipyridyl) complex.