ТЕТРАКИС(ТРИФЕНИЛАЦЕТАТО) ДИРОДИЙ (II)

Description

Tetrakis(triphenylacetato)dyrhodium(II) is a dinuclear carboxylate complex of rhodium(II), in which two rhodium atoms are connected by a rhodium-rhodium bond and bridges from four triphenylacetic acid ligands. Formula C80H60O8Rh2, CAS 68803-79-2, molecular weight 1355.14. It belongs to the class of organometallic catalysts based on binuclear rhodium(II) carboxylates, structurally related to rhodium(II) acetate, but with bulky triphenylacetate ligands, giving the center increased steric protection and selectivity.

Basic Attributes

• CAS No: 68803-79-2
• Chemical formula: C80H60O8Rh2
• Molecular weight: 1355.14

Physical characteristics

• Appearance: green crystalline powder

Data on melting and boiling points, density and other physical constants are not published in open sources by manufacturers; the substance is supplied as a high-purity research reagent.

Scope of application

The compound is used as a homogeneous catalyst in fine organic synthesis, primarily for carbene transfer reactions from diazo compounds: asymmetric cyclopropanation of alkenes, C–H functionalization and related transformations, where sterically bulky triphenylacetate ligands on a binuclear rhodium center provide high chemo- and stereoselectivity. Such catalysts are used in the synthesis of pharmaceutical substances and chiral building blocks, where control of the optical purity of the product is required. In addition to preparative use, the complex serves as an object of research in the field of rhodium-organic chemistry - studying the structure, reactivity of binuclear carboxylates and the development of new catalytic systems.

Mechanism of action

Like other rhodium(II) carboxylates, the catalyst activates the diazo compound by eliminating molecular nitrogen and forming an electrophilic metallocarbenoid on the rhodium center. This intermediate then transfers the carbene moiety to a substrate—an alkene double bond (cyclopropanation), a C–H bond (insertion), a heteroatom with a lone pair (ylide formation), or an aromatic ring. The volume and electronic properties of the carboxylate ligand directly determine which of these conversion pathways predominates and with which stereochemistry the reaction proceeds; switching from compact acetate to bulky triphenylacetate is one way to tune such selectivity without changing the metal center itself.

Handling and storage

Like other rhodium coordination complexes, it is sensitive to light and moisture; store in an airtight container, in a cool, dry place, protected from direct light, away from strong reducing agents and acids that can destroy carboxylate bridges. Reactions involving a catalyst are usually carried out under an inert atmosphere and in the presence of dried solvents, since trace amounts of moisture and oxygen can reduce the activity and selectivity of the rhodium center. The catalyst loading is usually maintained at a fraction of a percent of the substrate weight, which is typical for rhodium carbene catalysts and significantly reduces the cost of large preparative synthesis batches.