One-electron activation of CO by a Rhodium(II) porphyrin bimetalloradical complex and concerted reactions of two (RhCO) units

A rhodium(LI) porphyrin bimetalloradical complex, Rh-.(CH2)(6)Rh-. (1) reacts with CO and ethene to form an ethanedionyl reductive coupling product, Rh(CH2)(6)Rh(mu-C(O)C(O)) (2), and an ethylene-bridged complex, Rh(CH2)(6)Rh(mu-CH2CH2) (4), respectively. Reaction of 1 with 1,3-butadiene proceeds by a 1,4-addition to yield a four-carbon-bridged complex, Rh(CH2)(6)Rh(mu-CH2CH=CHCH2) (5). H-1 NMR spectra of 2 and 4 manifest the inherent chirality of two-carbon-bridged tethered diporphyrin complexes. Solutions of 1 and CO react with H2O, CH3CH2OH, and H-2 to produce multifunctionalized formyl complexes H-Rh(CH2)(6)Rh-CHO (6), H(O)C-Rh(CH2)(6)Rh-C(O)OCH2CH3 (7), and H(O)C-Rh(CH2)(6)Rh-CHO (8), respectively, but fail to react to an observable extent with methane. Reactivity studies indicate that solutions of 1 and CO function as a source of a species that contains two carbonyl groups ((.)[OCRh(CH2)(6)RhCO](.)) (3) that are activated toward one-electron reactions at the carbonyl carbon. Reactions of 3 with substrates (H2O, C2H5OH, H-2) are discussed in terms of a proposed pathway where two metalloformyl radicals ([MCO](.)) and the substrate occur in a four-centered transition state (Rh-C(O)(.)... A ... B ...(.)(O)C-Rb).