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)Å, 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–CO_t 1.889, Fe–CO_t 1.729, Ir–CO_b 2.154, and Fe–CO_b 1.887 Å(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)Å, 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–CO_t 1.863, Fe–CO_t 1.722, Ir–CO_b 2.142, and Fe–CO_b 1.947 Å. 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)Å, 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–CO_t 1.845, Fe–CO_t 1.776, Ir–CO_b 2.113, and Fe–CO_b 1.996 Å.