Phosphine/halide complexes, osmium

Organometallic reagents and catalysts continue to be of considerable importance, as illustrated in several procedures CAR-BENE GENERATION BY a-ELIMINATION WITH LITHIUM 2,2,6,6-TETRAMETHYLPIPERIDIDE l-ETHOXY-2-p-TOL-YLCYCLOPROPANE CATALYTIC OSMIUM TETROXIDE OXIDATION OF OLEFINS PREPARATION OF cis-1,2-CYCLOHEXANEDIOL COPPER CATALYZED ARYLA-TION OF /3-DICARBONYL COMPOUNDS 2-(l-ACETYL-2-OXOPROPYL)BENZOIC ACID and PHOSPHINE-NICKEL COMPLEX CATALYZED CROSS-COUPLING OF GRIG-NARD REAGENTS WITH ARYL AND ALKENYL HALIDES 1,2-DIBUTYLBENZENE. 

Osmium pentacarbonyl is a convenient precursor to other osmium carbonyl complexes. Hydrogenation gives the dihydride OsH2(CO)4. This hydride is not acidic with a p/fa of 18.5 but it can be deprotonated by strong bases to give [OsH(CO)4] and reduced by sodium (Scheme 23). Substitution of CO on Os(CO)5 by trialkyl or triarylphosphines, arsines, or stibenes gives Os(CO)4L or Os(CO)3L2. Other carbonyl phosphine complexes result from the reduction of osmium halides by alcohols in the presence of the tertiary phosphine. 

A process for the coproduction of acetic anhydride and acetic acid, which has been operated by BP Chemicals since 1988, uses a quaternary ammonium iodide salt in a role similar to that of Lil [8]. Beneficial effects on rhodium-complex-catalyzed methanol carbonylation have also been found for other additives. For example, phosphine oxides such as Ph3PO enable high catalyst rates at low water concentrations without compromising catalyst stability [40—42]. Similarly, iodocarbonyl complexes of ruthenium and osmium (as used to promote iridium systems, Section 3) are found to enhance the activity of a rhodium catalyst at low water concentrations [43,44]. Other compounds reported to have beneficial effects include phosphate salts [45], transition metal halide salts [46], and oxoacids and heteropolyacids and their salts [47]. 

The metal will react readily with oxygen, chlorine, or fluorine to yield the respective products. The metal will also react slowly with nitric acid to give OSO4. Osmium(O) compounds involve several carbonyls, as well as phosphine, amine, arene, diene complexes, and the well-studied osmium clusters. The compounds are usually prepared by reducing an osmium salt in the presence of the appropriate ligand and, if necessary, a halide acceptor such as copper, silver, or zinc salts. 

Osmium(III), d, compounds consist of the halide salts, except fluoride, and complexes involving halides, amines, and acetylacetonate, as well as some mixed ligand species involving phosphines and arsines. These complexes are... 

Ruthenium(III), d, is ruthenium s most stable oxidation state and resembles rhodium(III) and iridium(III) more than osmium(III). The salts inelude the halides, hydroxides, and oxides RuCls SHaO is most important because it is a good starting material for other compounds and reacts readily with olefins and phosphines. Complexes of this oxidation state are known with water, eyanide, oxygenated organies, sueh as diketones and earboxylates, pyridines, earbonyls, ey-elopentadienyls, phosphine, and arsine ligands. A notable differenee between ruthenium(II) and ruthenium(III) is the absenee of ruthenium(III) nitrosyl complexes. 

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