| Vaska's Complex |
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Information AboutVaska's Complex |
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Vaska's complex is the common name for '''''trans''-chlorocarbonylbis(triphenylphosphine)iridium(I)''': ''trans''-IrCl(CO) {Link without Title} 2. It is a Square Planar Diamagnetic Organometallic complex consisting of a central Iridium atom bound to two mutually trans- Triphenylphosphine Ligand s, Carbon Monoxide , and chloride. The complex was prepared and analyzed by Di Luzio and Vaska in 1961. Vaska's complex can undergo Oxidative Addition s and is notable for its ability to bind to O2 reversibly. It is isolated as a pale yellow Crystalline solid. PREPARATION OF VASKA'S COMPLEX The synthesis involves heating an iridium salt with P(C6H5)3 with a CO source. The most popular method uses Dimethylformamide (DMF) as a solvent, which decomposes to give CO. Sometimes Aniline is added to accelerate the reaction. The reaction typically is conducted under nitrogen. In the synthesis, triphenylphosphine serves as both a ligand and a reductant, and the Carbonyl Ligand is derived by decomposition of dimethylformamide probably via a deinsertion of an intermediate Ir-C(O)H species. The following is a possible balanced equation for this complicated reaction. :H2IrCl6 + 3.5P(C6H5)3 + HCON(CH3)2 + 4C6H5NH2 + 1.5H2O → IrCl(CO) {Link without Title} 2 + (CH3)2NH2+Cl- + 1.5 OP(C6H5)3 Typical sources of iridium used in this preparation are IrCl3.''x''H2O and H2IrCl6. REACTIONS OF VASKA'S COMPLEX Vaska's complex is the prototypical compound exhibiting patterns of reactivity that provided a conceptual framework for Homogeneous Catalysis . Vaska's complex, with 16 valence electrons, is considered "unsaturated" and can thus bind to one two-electron or two one-electron ligands to become electronically saturated with 18 valence electrons. The addition of two one-electron ligands is called Oxidative Addition . Upon oxidative addition, the oxidation state of the iridium increases from Ir(I) to Ir(III). The four-coordinated square planar arrangement in the starting complex converts to an Octahedral , six-coordinate product. Vaska's complex undergoes oxidative addition with conventional oxidants such as halogens, strong acids such as HCl, and other molecules known to react as Electrophile s, such as Iodomethane (CH3I). An interesting characteristic of Vaska's complex is that it binds O2 reversibly. :IrCl(CO) + O2 ↔ IrCl(CO)[P(C6H5)3 2O2 The dioxygen ligand is bonded to Ir(I) via both oxygen atoms, so-called side-on bonding. In myoglobin and hemoglobin, O2 binds "end-on," attaching to the metal via only one of the two oxygen atoms. The oxygenation reaction is carried out simply by bubbling O2 through a solution of Vaska's complex in toluene. The resulting dioxgen adduct reverts to the parent complex upon heating in boiling benzene solution. SPECTROSCOPY |
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