A series of base-stabilized silylium species were synthesized and their reactivity toward CO 2 explored, yielding the characterization of a novel N/ Si + FLP-CO 2 adduct. These silicon species are active catalysts in the hydroboration of CO 2 to the methoxide level with 9-BBN, catecholborane (catBH), and pinacolborane (pinBH). Both experiments and DFT calculations highlight the role of the FLP-CO 2 adduct in the catalysis. Depending on the nature of the hydroborane reductant, two distinct mechanisms have been unveiled. While 9-BBN and catBH are able to reduce an intermediate FLP-CO 2 adduct, the hydroboration of CO 2 with pinBH follows a different and novel path where the B−H bond is activated by the silicon-based Lewis acid catalyst. In these mechanisms, the formation of a highly stabilized FLP-CO 2 adduct is found detrimental to the kinetics of the reaction.

The kinetics of the oxidative additions of haloheteroarenes HetX (X=I, Br, Cl) to [Pd(0) (PPh3 )2 ] (generated from [Pd(0) (PPh3 )4 ]) have been investigated in THF and DMF and the rate constants have been determined. In contrast to the generally accepted concerted mechanism, Hammett plots obtained for substituted 2-halopyridines and solvent effects reveal a reaction mechanism dependent on the halide X of HetX: an unprecedented SN Ar-type mechanism for X=Br or Cl and a classical concerted mechanism for X=I. These results are supported by DFT studies.