Selective reductive coupling of carbon monoxide

Tetra-(3,5 dimethylphenyl)porphyrinato rhodium(II)dimer, [(TXP)Rh]2, reacts reversibly with CO to form a 1,2-ethanedionyl complex, (TXP)Rh–C(O)C(O)–Rh(TXP), which constitutes the first well-characterized example of reductive coupling of CO to form a dimetal α-diketone species.