6533b827fe1ef96bd1286518

RESEARCH PRODUCT

Unusual stability of reaction intermediates in ortho-metalation reactions of dicyclohexylphenylphosphane with dirhodium(II) tetraacetate

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Abstract Reaction of dirhodium(II) tetraacetate with 1 molar equivalent of dicyclohexylphenylphosphane afforded the complex [Rh 2 (μ-O 2 CCH 3 ) 3 {μ-(C 6 H 4 )PCy 2 }(CH 3 COOH) 2 ] ( 1 ) in which the phosphane ligand is coordinated to the rhodium atoms in a bridging ortho -metalated mode. As a second product, [Rh 2 (μ-O 2 CCH 3 ) 3 {μ-(C 6 H 4 )PCy 2 }(CH 3 COOH)(PhPCy 2 )] ( 2 ) was isolated from the same reaction. 2 proved to be unusually stable toward further reaction to a doubly ortho -metalated complex which has been accessible in the reaction of dirhodium(II) tetraacetate with other phosphane ligands. However, doubly ortho -metalated [Rh 2 (μ-O 2 CCH 3 ) 2 {μ-(C 6 H 4 )PCy 2 } 2 (CH 3 COOH) 2 ] ( 4 ) was isolated in low yield after a prolonged thermal reaction between dirhodium(II) tetraacetate and 2 equivalents of PhPCy 2 . Exchange of the bridging acetate ligands in 1 and 4 by trifluoroacetate ligands afforded [Rh 2 (μ-O 2 CCF 3 ) 3 {μ-(C 6 H 4 )PCy 2 }(CF 3 COOH) 2 ] ( 5 ) and [Rh 2 (μ-O 2 CCF 3 ) 2 {μ-(C 6 H 4 )PCy 2 } 2 (CF 3 COOH) 2 ] ( 7a ). Complex 7a without axial ligands, [Rh 2 (μ-O 2 CCF 3 ) 2 {μ-(C 6 H 4 )PCy 2 } 2 ] ( 7b ) was isolated, as well. The crystal structure of complex 5 was determined showing consequences of the bulky cyclohexyl groups on several structural parameters.