Iron–iridium mixed-metal carbonyl clusters. Part 2. Synthesis and chemical behaviour of the tetranuclear complexes [FeIr3(CO)12]–, [Fe2Ir2(CO)12]2–, [Fe2Ir2H(CO)12]–, and [Fe3Ir(CO)13]–. Solid-state structures of [N(PPh3)2][FeIr3(CO)12], [NEt4]2[Fe2Ir2(CO)12], and [PPh4][Fe2Ir2(CO)12-{µ3-Au(PPh3)}

Abstract

The compound [FeIr3(CO)12]– can be obtained by degradation of [FeIr4(CO)15]2– under a carbon monoxide atmosphere as well as by reduction of an equimolar mixture of [Fe(CO)5] and [Ir4(CO)12] in alcoholic NaOH under 1 atm (101 325 Pa) of carbon monoxide. The salt [N(PPh3)2][FeIr3(CO)12](1) crystallizes in the monoclinic space group P21/c with unit-cell dimensions a= 14.968(2), b= 19.892(2), c= 16.610(2)A, β= 96.10(2)°, and Z= 4. The molecular structure of the anion consists of a tetrahedron of metal atoms surrounded by twelve carbonyl groups: nine are terminally bound whereas three are bridging the edges of the FeIr2 basal face. Average bond distances are Ir–Ir 2.696, Ir–Fe 2.682, Ir–COt 1.889, Fe–COt 1.729, Ir–COb 2.154, and Fe–COb 1.887 A(b = bridging, t = terminal). The dianion [Fe2Ir2(CO)12]2–(2) was obtained by several different ways, the most selective being the condensation of [Fe2(CO)9] with [Ir(CO)4]–. The salt [NEt4]2[Fe2Ir2(CO)12](2) crystallizes in the monoclinic space group P21 with a= 9.072(5), b= 19.910(5), c= 10.094(3)A, β= 91.92(3)°, and Z= 2. The molecular structure of the dianion is based on a tetrahedral cluster of metal atoms and consists of an apical Ir(CO)3 group co-ordinated by three metal–metal bonds to a basal Fe2Ir(CO)9 fragment containing two Fe(CO)2 units and one Ir(CO)2 group linked to each other by a metal–metal bond and bridging carbonyl groups. Selected distances are: Ir–Ir 2.734(1), Fe–Fe 2.581(2), and averages Ir–Fe 2.683, Ir–COt 1.863, Fe–COt 1.722, Ir–COb 2.142, and Fe–COb 1.947 A. The salt [PPh4]2[Fe2Ir2(CO)12] reacts with [Au(PPh3)CI] to give [PPh4][Fe2Ir2(CO)12{µ3-Au(PPh3)}](3) which crystallizes in the monoclinic space group P21/c with a= 10.990(3), b= 13.693(2), c= 35.883(3)A, β= 97.39(2)°, and Z= 4. The metal framework of the anion is a trigonal bipyramid with the Au(PPh3) moiety in one of the apical positions, the other being occupied by a Fe(CO)3 group. Each edge of the equatorial triangle, formed by one iron and two iridium atoms, is spanned by a bridging carbonyl ligand, and two terminal CO groups are attached to each metal of this triangle. Selected bond distances are: Ir–Ir 2.758(1), and averages Ir–Fe 2.710, Ir–Au 2.786, Fe–Au 2.806(1), Ir–COt 1.845, Fe–COt 1.776, Ir–COb 2.113, and Fe–COb 1.996 A.