Abstract
A variety of binuclear rhodium(I) complexes featuring two bridging dimethylphosphinate ligands ((CH3)(2)PO2-) have been prepared and tested in the alkoxycarbonylation of aromatic C-H bonds. The complex [Rh(mu-kappa O,O'-(CH3)(2)PO2)(cod)](2) has been prepared by a reaction of [Rh(mu-MeO)(cod)](2) with 2 equivalents of dimethylphosphinic acid. Binuclear complexes [Rh(mu-kappa O,O'-(CH3)(2)PO2)(CO)L](2) (L = PPh3, P(OMe)Ph-2 and P(OPh)(3)) were obtained by carbonylation of the related mononuclear complexes [Rh(kappa O-(CH3)(2)PO2)(cod)(L)], which were prepared in situ by the reaction of [Rh(mu-kappa O,O'-(CH3)(2)PO2)(cod)](2) with 2 equivalents of L. Conversely, if L = IPr, the reaction of [Rh(mu-kappa O,O'-(CH3)(2)PO2)(CO) L](2) with carbon monoxide affords the mononuclear complex [Rh(kappa O-(CH3)(2)PO2)(CO)(2)IPr]. The subsequent reaction with trimethylamine N-oxide gives the corresponding binuclear complex [Rh(mu-kappa O,O'-(CH3)(2)PO2)(CO)(IPr)](2) by abstraction of one of the carbonyl ligands. Complexes [Rh mu-kappa O,O'-(CH3)(2)PO2)(cod)](2) and [Rh(kappa O( CH3)(2)PO2)(cod)(L)] (L = IPr, PPh3, P(OMe) Ph-2, P(OPh)(3)) are active precatalysts in the alkoxycarbonylation of C-H bonds, with the ligand system playing a key role in the catalytic activity. The complexes that feature more labile Rh-L bonds give rise to better catalysts, probably due to the more straightforward substitution of L by a second carbonyl ligand, since a more electrophilic carbonyl carbon atom is more susceptible toward aryl migration. In fact, complexes [Rh(mu-kappa O,O'-(CH3)(2)PO2)(CO)(2)](2) and [Rh(mu-Cl)(CO)(2)](2), generated in situ from [Rh(mu-kappa O,O'-(CH3)(2)PO2)(cod)](2) and [Rh(mu-Cl)(cod)(2)](2), respectively, are the most active catalysts tested in this work.