Anions [Fe2(CO)8]2– and [Fe2(CO)6(µ-CO)(µ-PPh2)]– as building blocks for the synthesis of mixed-metal clusters. Crystal structure of [Fe2(CO)6(µ-CO)(µ-PPh2){µ-Cu(PPh3)}]

Abstract

Treatment of the salt [NEt₄]₂[Fe₂(CO)₈] with a tetrahydrofuran solution of the complex [Cul(PPh₃)] gives an anionic orange-red cluster [NEt₄][Fe₂(CO)₆(µ-CO)₂{µ-Cu(PPh₃)}]1 which is air- and thermally unstable. When [NEt₄][Fe₂(CO)₆(µ-CO)(µ-PPh₂] and [MX(PPh₃)](M = Cu, Ag or Au) are allowed to react in the presence of TIBF₄, the new neutral clusters [Fe₂(CO)₆(µ-CO)(µ-PPh₂)-{µ-M(PPh₃)}](M = Cu, 2; Ag, 3; or Au, 4) are obtained in ca. 80% yield. These relatively air-stable clusters have been characterized by IR and ³¹P NMR spectroscopy and the structure of 2 has been established by single-crystal X-ray diffraction studies: triclinic, space group P, with a= 11.081(3), b= 12.190(3), c= 15.808(4)Å, α= 76.41(2), β= 87.03(2), γ= 80.48(2)°, Z= 2 and R= 0.05. The basic skeleton consists of the first example of a Fe₂Cu triangle. In this, the iŕon–iron bond is bridged by a phosphido and a carbonyl group.