The rhodium diformate complex [Rh III (tacn)(HCOO) 2 ](OTf) ( 2, tacn = 1,4,7-triazacyclononane, OTf - = CF 3 SO 3 - ) reacts with HCOONa at pH 6−7 at 80 °C in water to form a rhodium dihydride CO complex, [Rh III (tacn)(H) 2 (CO)](OTf) ( 5 ), with H 2 evolution from the formato ligands of 2 . This is the first example of H 2 evolution from hydrogen atoms of formato ligands of a metal diformate complex. Complex 2 was synthesized from the reaction of a rhodium aqua complex, [Rh III (tacn)(H 2 O) 3 ](OTf) 3 ( 1 ), with HCOONa in water. Recrystallization of 2 with HCOONa in water gave crystals of a rhodium triformate complex, [Rh III (tacn)(HCOO) 3 ] ( 3 ), whose structure was unequivocally determined by X-ray analysis. The key intermediate in the transformation from 2 to 5 is a rhodium hydride formate complex, [Rh III (tacn)H(HCOO)](OTf) ( 4 ), which was obtained by heating of an aqueous solution of the rhodium diformate complex 2 with 10 equiv of dimethyl sulfoxide (DMSO) at pH 6−7 in water. Complex 4 was well characterized by isotopic labeling measurements of 1 H NMR, electrospray ionization mass spectrometry (ESI-MS), and GC.
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Ogo et al. (2005) studied this question.
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