Tetrairon Cluster Cp3Fe4(CO)4(C5H4PPh2) as a P–O Chelating Agent to Bind Palladium(II) and Copper(I) Ions through Phosphine and μ3-Carbonyl Groups

The complex cis-[Pd(Cp3Fe4(CO)4(C5H4PPh2))2](BF4)2 (2) has been prepared by treating [Pd(NCMe)4](BF4)2 with Cp3Fe4(CO)4(C5H4PPh2) (1) through coordination of the phosphine group and the oxygen atom of one μ3-CO ligand. Compound 2 reacts with [PNN]NO2 to produce trans-Pd(Cp3Fe4(CO)4(C5H4PPh2))2(NO2)2 (3), where the hemilabile O ligation is displaced by a nitrite ligand. Further reaction of 3 and [Cu(dppf)(NCMe)2]BF4 (dppf = (C5H4PPh2)2Fe) gives the mixed-metal complex trans-[Pd(Cp3Fe4(CO)4(C5H4PPh2))2(NO2Cu(dppf))2](BF4)2 (4), the nitrite ligands of which are likely coordinated to the Pd(II) ion in an N-monodentate fashion and to the Cu(I) ions in an O,O-bidentate mode. The analogous reaction of 1 with [Cu(NCMe)4]BF4 affords [Cu(Cp3Fe4(CO)4(C5H4PPh2))2]BF4 (5), which shows no reactivity toward [PNN]NO2. The structures of 2·3CH2Cl2, 3·2CH3CN, and 5·2CH2Cl2 have been determined by an X-ray diffraction study. Compounds 2 and 5 contain uncommon η2,μ4-carbonyl ligands.