Copper(I) Alkoxides and Aryloxides
Copper(I) alkoxides and aryloxides have been prepared from mesitylcopper(I) and alcohols or phenols. The solid state structures of the alkoxides and aryloxides are .my.2- and/or .my.3-OR bridged Cun clusters (R: (C6H5)2C, CH2=CHCH2C6H4, (C6H5)2C6H3, n = 4; (CH3)3C, n = 8; H2C=CH(CH3)2C, n = 6), containing two-, three- or four-coordinated copper(I) centres, with Cu-O bond distances ranging from 1.834(7) to 2.785(6) Å.
The reaction between mesitylcopper(I) and alcohols or phenols in a carbon monoxide atmosphere resulted in carbonyl complexes of copper(I) alkoxides or copper(I) aryloxides, in which a single CO binds to copper. A decrease of the aggregation number, and, in general, an appreciable lengthening of the Cu-O bond distance is observed. The terminally bonded CO is labile and the Cu-C bond is judged to be predominantly of s character, with minimal metal - ligand .pi.* contribution. Nevertheless, carbon monoxide can be used to isolate derivatives of copper(I) aryloxides which otherwise defy isolation.
Methylbutenoxocopper(I) [Cu6(OC(CH3)2C(H)=CH2)6 ] and o-allylphenoxocopper(I) [Cu4(OC6H4CH2C(H)=CH2 )4], contain copper(I) centres .pi.-coordinated by the intramolecular allylic group. In solution the copper(I)-alkene bond in methylbutenoxocopper(I) is broken, while it remains intact in o-allylphenoxocopper(I). Contrary to methylbutenoxocopper(I), o-allylphenoxocopper(I) does not react with carbon monoxide and is unusually stable at ambient atmosphere, both in the solid state and in contact with non-coordinating solvent.
Reaction of triphenylphosphine and copper(I) phenoxide in a molar ratio of PPh3:Cu of 1:1 resulted in a tetrameric m3-phenoxide complex, with a cubane-type Cu4O4 core and four-coordinated copper(I). Changing the PPh3:Cu ratio to 1.5:1 gave a dimeric .my.2-phenoxide complex in which one copper(I) centre is four-coordinated by two phenoxide and two PPh3 ligands, while the other is coordinated by a single PPh3 ligand and thus three-coordinated.