Antiferromagnetic complexes with metal-metal bonds. X. Synthesis and molecular structure of an antiferromagnetic bis[cyclopentadienyl(t-butoxy)-chromium]iron tetracarbonyl cluster containing a Cr2Fe metallacycle

Photochemical reaction of Fe(CO)5 with the Cp2Cr2(OR)2 (I) complex (Cp = π-C5H5, R = CMe3) in toluene gives brown-black prisms of the CpCr(μ-OR)2CrCp · Fe(CO)4 (II) cluster. An X-ray analysis of II shows that the metal atoms form an almost equilateral Cr2Fe triangle with normal CrFe bonds (2.707(1) and 2.691(1) A) and the short CrCr bond (2.635(1) A) supplemented by two bridged OR groups. Each Cr atom is coordinated by a planar π-C5H5 ligand while the Fe atom coordinates four terminal CO groups. A qualitative MO diagram gives an explanation of the CrCr bond length in II which is the same as in the starting complex I, although the antiferromagnetic exchange parameter −2J is simultaneously increased from 246 cm− in I to 304 cm− in II.