Transformation of cyclohexadiene on an Fe3P frame: cluster complexes with hexadiene, cyclohexadiene and arene ligands

UV photolysis of the phosphinidine-bridged cluster complex [Fe3(CO)9(H)2(PtBu)] (9) in the presence of 1,3-cyclohexadiene gives the complex [Fe3(CO)8(η4-1,3-cyclohexadiene)(μ3-PtBu)] (13) in 20% yield. As a side-reaction, hydrogenolysis of cyclohexadiene occurs to give the complexes [Fe3(CO)8(2-5-η-2,4-hexadiene)(μ3-PtBu)] (14) and [Fe3(CO)8(1-4-η-1,3-hexadiene)(μ3-PtBu)] (15) in about 5% yield each. The crystal and molecular structures of 13, 14 and 15 were determined. The (cyclo)hexadiene ligands are bonded to the Fe3P clusters in the apical coordination mode; of the carbonyl ligands two are semi-bridging. The composition [Fe3(μ2-H)(CO)7(μ-1-3-η:4,5-hexadienyl)(μ3-PtBu)] (16) is tentatively assigned to a fourth product (2% yield), based on IR and NMR spectroscopic data. On heating to 80°C, a mixture of the complexes 14 and 15 is quantitatively converted into 16. Complex 13 is also formed in lower yield (15%) from [Fe3(CO)10(PtBu)] (10) and 1,3-cyclohexadiene in a thermal reaction. UV irradiation of complex 13 in benzene solution gives [Fe3(CO)7(η-C6H6)(μ3-PtBu)] (18a) in low yield. In toluene, a 3:7 mixture of 18a and [Fe3(CO)7(η-C6H5Me)(μ3-PtBu)] (18b) is obtained, proving the dehydrogenation of the cyclohexadiene ligand in 13 to give an η6-benzene. The apical (η6-) coordination of the toluene ligand in 18b is confirmed by a crystal structure analysis, which also shows the presence of a face-capping carbonyl ligand.