Reduction of CO₂ and Related Compounds with a Low‐Valent Ca^I Synthon

The reduction of CO 2 with low‐valent s ‐block metal complexes is limited to Mg I reducing agents. Herein, the reduction of a series of CX 2 reagents (X = O, S, N i Pr) with the Ca I synthon [(BDI)Ca(THP)] 2 (N 2 ) ( VI ) is described, which is a Ca II complex that reacts like the hypothetical Ca I complex (BDI)CaCa(BDI); BDI = HC[(Me)‐N(DIPeP)] 2 , DIPeP = 2,6‐Et 2 CH‐phenyl, THP = tetrahydropyran. Reaction of VI with excess CO 2 led to crystallization of a carbonate complex with a Ca 4 (CO 3 ) 2 4+ core. The stabilizing BDI ligands also react by nucleophilic addition of CO 2 at the backbone γ ‐C atom. Reaction with only two equivalents of CO 2 gave the presumed carbonite (CO 2 2 − ) intermediate, but this could not be confirmed by X‐ray diffraction. Reaction with CS 2 gave the first unique s ‐block metal complex with a CS 2 2 − anion. This anion bridges between two (BDI)Ca + cations by CaC and CaS bonding. The reduction of i PrN=C=N i Pr with VI gave C–C coupling to a [( i PrN) 2 C–C(N i Pr) 2 ] 2 − dianion. An intermediate with a C(N i Pr) 2 2 − dianion could not be isolated.