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UV photolysis of the phosphinidine-bridged cluster complex [Fe 3 (CO) 9 (H) 2 (P t Bu)] ( 9 ) in the presence of 1,3-cyclohexadiene gives the complex [Fe 3 (CO) 8 (η 4 -1,3-cyclohexadiene)(μ 3 -P t Bu)] ( 13 ) in 20% yield. As a side-reaction, hydrogenolysis of cyclohexadiene occurs to give the complexes [Fe 3 (CO) 8 (2-5-η-2,4-hexadiene)(μ 3 -P t Bu)] ( 14 ) and [Fe 3 (CO) 8 (1-4-η-1,3-hexadiene)(μ 3 -P t Bu)] ( 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 Fe 3 P clusters in the apical coordination mode; of the carbonyl ligands two are semi-bridging. The composition [Fe 3 (μ 2 -H)(CO) 7 (μ-1-3-η:4,5-hexadienyl)(μ 3 -P t Bu)] ( 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 [Fe 3 (CO) 10 (P t Bu)] ( 10 ) and 1,3-cyclohexadiene in a thermal reaction. UV irradiation of complex 13 in benzene solution gives [Fe 3 (CO) 7 (η-C 6 H 6 )(μ 3 -P t Bu)] ( 18a ) in low yield. In toluene, a 3:7 mixture of 18a and [Fe 3 (CO) 7 (η-C 6 H 5 Me)(μ 3 -P t Bu)] ( 18b ) is obtained, proving the dehydrogenation of the cyclohexadiene ligand in 13 to give an η 6 -benzene. The apical (η 6 -) 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. |
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