Discrete Mixed-Valence Metal Chains: Iridium Pyridonate Blues

Abstract

Discrete chains of metal atoms are of current interest from both theoretical and practical points of view. One synthetic approach to this type of compounds is based on ligandassisted reactions using polydentate ligands, which is exemplified by several families of metal string complexes supported by oligo-a-pyridylamido ligands. [1] A second approximation involves the formation of metal ± metal bonds between partially oxidized d 8 square-planar complexes, for which the platinum blues are the most representative examples. [2] Most of the reported platinum blues have been prepared from disymmetric square-planar dinuclear complexes with two amidate N-C-O-type ligands as bridges, and it has been claimed [2a±c] that the head-to-head (HH) configurations are essential to achieve the tetrametallic platinum chains. Moreover, it has been argued that the head-to-tail (HT) structures do not dimerize for steric reasons. In fact, all the reported structures of platinum blues are based on HH dimers. Other metals, for which square-planar complexes are common, such as rhodium, iridium, and gold, are suitable for forming such metallic chains, but few examples for these metals are known. [3] Herein we describe two new tetrametallic mixedvalence iridium compounds, which substantiate that dinuclear complexes with HT configurations are actually able to participate in metallic chains, while those with HH configurations generate the thermodynamically stable compounds.An appropriate precursor for the formation of iridium pyridonate blues is the binuclear complex [{Ir(m-OPy)-(CO) 2 } 2 ] (Opy 2-pyridonate (1)). It was prepared, as purple microcrystals with metallic luster, by bubbling carbon monoxide through a solution of the complex [{Ir(m-OPy)(cod)} 2 ] (cod 1,5-cyclooctadiene) in toluene. [4] While the HT configuration of the a-pyridonate ligands was found in the solid state and in solution for the diolefinic complex, a bridging ligand rearrangement occurs on carbonylation. Thus, complex 1 was found to be a 1:1 mixture of the HH and the HT isomers in solution (Scheme 1). Noteworthy, these configurational isomers were found to be in a chemical equilibrium, as shown by the 1 H two-dimensional exchange (EXSY) spectrum.Oxidation of a solution of 1 in toluene with diiodine (in a 2:1 molar ratio) at 50 8C gives immediately an EPR-silent purple solution from which a crystalline blue solid (2) was isolated in excellent yield (95 %) on addition of hexane. [5] This acetal 2, [a] 20 D À 21.7 (c 0.67 in CHCl 3 ), was spectroscopically identical to that prepared previously [3] ([a] 20 D À 22.2 (c 1.15 in CHCl 3 ) [3] ). The sense of asymmetric induction was the same as those observed in kinetic resolutions of terminal epoxides under similar reaction conditions. The enantiomeric excess of the desymmetrized product 14 was determined by chiral HPLC analysis of the corresponding benzoate 16; comparison of 16 with a sample of low enantiomeric excess (prepared by mixing 16 with its enantiomer ent-16, also synthesized by desymmetrization of 3) showed t...

Synthesis and structure of solution-stable one-dimensional palladium wires

“…blues [7][8][9][10][11][12] , or closed-shell 1-D stacks organized by metallophilic interactions that are typically not considered formal metal-metal bonds 13,14 . There are a few examples of infinite 1-D chains in the solid state with metal-metal bonds, one of the oldest being the family of partially-oxidized tetracyanoplatinates-Krogmann salts-formed by bulk oxidation of crystalline samples of Pt(II) complexes 15 .…”

A Hexanuclear Iridium Chain

“…With this methodology there are, in principle, no limitations to the chain length other than the thermodynamic stability of the compound, provided that the steric encumbrance between the links is kept at minimum. To date, this method has allowed the isolation of only two rare 1D rhodium-chain compounds [3] and the platinum, [4] rhodium, [5] and iridium [6] blues, which typically consist of tetrametallic chains. [7] Between both situations only a remarkable octanuclear platinum chain, reported by Matsumoto and co-workers, is known.…”

“…[7a] In particular, the incorporation of different metals may enhance the catalytic properties of the coordination polymers. By using this approach, we now report the syntheses and crystal structures of three 3D lanthanide±transition metal coordination polymers of the form [{M 2 (Cu 3 (iminodiacetate) 6 …”

P066: Prenatal sonographic measurement of the fetal iliac angle in trisomy 21, 18 and 13

“…Oxidation of a toluene solution of the dinuclear complex [Ir 2 (μ‐OPy) 2 (CO) 4 ]6a ( 1 ; Opy=2‐pyridonate) with diiodine (in a 3:1 molar ratio) at 0 °C immediately gave an EPR‐silent, dark‐blue solution from which a crystalline solid having a copper‐like aspect ( 2 ) was isolated in good yield (75 %) on addition of hexanes 9. The crystal structure of 2 10 (Figure 1), revealed the hexametallic chain formed by an almost linear array in which two HH‐[Ir 2 (μ‐OPy) 2 (I)(CO) 4 ] units sandwich an HT‐[Ir 2 (μ‐OPy) 2 (CO) 4 ] complex.…”