Establishing Indium in Frustrated Lewis Pair Chemistry: From Synthesis to Catalytic Applications

In contrast to the vast majority of known frustrated Lewis pair (FLP) systems, which are based on “hard” (hard–soft acid–base, HSAB) boron‐based compounds, this work is on systems containing the “soft” indium Lewis acid functions. The geminal intramolecular indium FLP t Bu 2 InCH 2 P t Bu 2 ( 1 ) was prepared from t Bu 2 InCl and LiCH 2 P t Bu 2 , and its pyridine adduct t Bu 2 In(py)CH 2 P t Bu 2 ( 4 ) was prepared from t Bu 2 InCl(py) and LiCH 2 P t Bu 2 . Both systems are unreactive toward H 2 but show FLP‐typical reactivity toward CO 2 and CS 2 . The cyclic CO 2 and CS 2 adducts of 1 are stable at room temperature, and the CO 2 in the adduct can be replaced by CS 2 , showing that the CO 2 adduct formation is reversible. The catalytic activity of 4 toward CO 2 reduction with pinacolborane to MeOBPin was tested. While 4 shows decent turnover numbers, the turnover frequencies (TOFs) are low due to a long incubation period after the first reduction step. The formaldehyde‐adduct of FLP 1 proved to be an efficient catalyst, reaching TOFs of up to 41.3 h –1 , thus surpassing a previous FLP‐held record of 21 h –1 using pinacolborane as a reducing agent.