Complexes of chromium(II) halides with weak donor ligands.

Investigations have been carried out to find suitable chromium(II) salts for preparative reactions in non-aqueous solvents, since the presence of water can lead to oxidation, even under nitrogen, and to failure to complex with weak donor ligands. All the chromium(II) compounds have had to be handled under nitrogen or in vacuo, and apparatus previously used by others has been modified to overcome difficulties caused by attack of solvents on greased taps and joints. Although insoluble in acetone alone, anhydrous chromium(II) chloride and bromide have been found to dissolve in acetone in the presence of small quantities of methanol. Another new way of preparing a non-hydroxylic solution of chromium(II) chloride which has been developed is to dissolve chromium metal directly in tetrahydro-furan through which gaseous hydrogen chloride is being passed. A number of new complexes of chromium(II) halides with urea, N-methylurea, biuret, methanol, tetrahydrofuran, thiourea, N,N'-ethylenethiourea and N,N'-dicyclohexylthiourea have been prepared using these solutions, and their properties investigated by spectroscopic (35,000 - 70 cm[-1]) and magnetic techniques. Colour changes suggested that triphenylphosphine and 1,2-bis(diphenyl-phosphino)ethane coordinate weakly with chromium(II), but no complexes could be isolated. It has not been possible to conclude with certainty whether two complexes, CrBr[2.] 5N,N'-ethylenethiourea and CrBr[2]. 5N,N'-dicyclo-hexylthiourea, are five or six coordinate, but all the others are six coordinate with monomeric or polymeric structures. Infra-red results indicate that all the complexes contain either metal-oxygen or metal-sulphur bonds, but some of the substituted thiourea complexes may also contain metal-nitrogen bonds. An investigation of the action of tri(isobutyl)aluminium on solutions of chromium(II) chloride and acetylacetonate in the presence of substituted phosphine and gaseous nitrogen failed to produce any isolable products. Reduction appeared to have taken place, but extensive obscuring of the visible region of the spectrum by charge-transfer bands made deductions inconclusive