Stable Copper I Carbonyl Complexes

The poly(pyrazolyl)borate ligands were developed by Trofimenko and have been used by him and others as cyclopentadienyl-like ligands which are capable of forming complexes that are often more stable than the analogous tj -cyclo-pentadienyl complexes. We have used this property to prepare a series of isolable, relatively stable copper(I) carbonyl complexes. The detailed syntheses of three complexes of this type, Cu(CO)[(pz)3BH), Cu(CO)[(Me2pz)3BH] (Mejpz = 3,5-dimethyl-l-pyrazolyl), and Cu(CO)((pz)4B], are described below. 

The reaction is carried out in a Schlenk tube. Fig. 1. Acetone (10 mL) is cooled in an ice bath and saturated with carbon monoxide by passing in a brisk stream of the gas for 10 minutes. Potassium hydrotiis(pyrazolato)borate (252 mg, 1.0 mmole) and copper(I) chloride (99 mg, 1 mmole) are added to the acetone, and the mixture is stirred for 30 minutes while continuing to pass a slow stream of carbon monoxide. At the end of this period, the white suspension is filtered, using the Schlenk-type apparatus illustrated, Fig. 2, keeping the whole under an atmosphere of CO. The clear colorless filtrate is evaporated to dryness, and the cream-colored residue is extracted with 10 mL ligjit petroleum (boiling range 40-60°, saturated with CO) and filtered. Evaporation of the solvent from the filtrate affords a white powder of Cu(CO)[(pz)3BH] (156 mg, 51%). 

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These early successes with carbonyl complexes of rhenium encouraged me to undertake systematic research on the carbon monoxide chemistry of the heavy transition metals at our Munich Institute during the period 1939-45, oriented towards purely scientific objectives. The ideas of W. Manchot, whereby in general only dicarbonyl halides of divalent platinum metals should exist, were soon proved inadequate. In addition to the compounds [Ru(CO)2X2] (70), we were able to prepare, especially from osmium, numerous di- and monohalide complexes with two to four molecules of CO per metal atom (29). From rhodium and iridium (28) we obtained the very stable rhodium(I) complexes [Rh(CO)2X]2, as well as the series Ir(CO)2X2, Ir(CO)3X, [Ir(CO)3]j (see Section VII,A). With this work the characterization of carbonyl halides of most of the transition metals, including those of the copper group, was completed. 

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