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]-

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-COt 1.889, Fe-COt 1.729, Ir-COb 2.154, and Fe-COb 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-COt 1.863, Fe-COt 1.722, Ir-COb 2.142, and Fe-COb 1.947 Å. The salt [PPh4]2[Fe2Ir2(CO)12] reacts with [Au(PPh3)CI] to give [PPh4][Fe2Ir2(CO)12{μ 3-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-COt 1.845, Fe-COt 1.776, Ir-COb 2.113, and Fe-COb 1.996 Å.