μ-Borole triple-decker complexes as catalysts for oxidative coupling of benzoic acid with alkynes. Structure of a hybrid rhodacyclopentadienyl/borole triple-decker complex

Abstract Reaction of dimethylamine adduct of 1-methyl-3-borolene with [(C 2 H 4 ) 2 RhCl] 2 gives the triple-decker complex (η-C 4 H 4 BMe)Rh(μ-η:η-C 4 H 4 BMe)Rh(η-C 4 H 4 BMe) ( 1a ) in 62% yield and trace amount ( 4 H 4 BMe)Rh(μ-η:η-C 4 H 4 Rh{(μ-η:η-C 4 H 4 BMe)Rh(η-C 4 H 4 BMe)})Rh(η-C 4 H 4 BMe) ( 2 ). The structure of 2 was determined by X-ray diffraction. In the presence of Cu(OAc) 2 , 1a and (η-C 4 H 4 BPh)Rh(μ-η:η-C 4 H 4 BPh)Rh(η-C 4 H 4 BPh) ( 1b ) catalyze the oxidative coupling of benzoic acid with diphenylacetylene selectively giving 1,2,3,4-tetraphenylnaphtalene in 50–90% yields. Analogous reactions of benzoic acid with 1-phenyl-1-butyne catalyzed by 1a and [CpRhI 2 ] 2 regioselectively give 1,4-diethyl-2,3-diphenylnaphthalene. The related dicationic triple-decker complexes [(9-SMe 2 -7,8-C 2 B 9 H 10 )Rh(μ-η:η-C 4 H 4 BPh)Rh(9-SMe 2 -7,8-C 2 B 9 H 10 )] 2+ ( 3 ) and [Cp*Rh(μ-η:η-C 4 H 4 BPh)IrCp*] 2+ ( 4 ) were also tested as catalysts.