CO2/13CO2 Dynamic Exchange in the Formate Complex [(2,9‑( t Bu)2‑phen)Cu(O2CH)] and Its Catalytic Activity in the Dehydrogenation of Formic Acid

Monometallic formate complexes of copper­(I) are rare. We report here the synthesis, characterization, and crystal structure of the simple tricoordinate [(phen*)­CuI(κ1-O2CH)] (1) supported with the bulky phenanthroline ligand 2,9-diterbutyl-1,10-phenanthroline (phen*). Complex 1 decarboxylates at 100 °C to give H2 and Cu(0) deposit with free phen*. To trap the hypothetical hydride [(phen*)­CuH], Lewis acidic boron BR3 compounds (R = C6F5, Et) or organic scavengers have been introduced in the solution. In most cases, degradation occurs except with B­(C6F5)3 that gives the cationic complex [{(phen*)­Cu}2(μ-HCO2)]­[(HCO2)­B­(C6F5)3] (2) which has been crystallized. While 1 does not react with CS2, it undergoes under 1 atm of 13CO2, a dynamic decarboxylation/carboxylation process that indicates transient formation of the hydride. The catalytic activity of complex 1 in the dehydrogenation of formic acid is revealed.