摘要：

Reduction of CO2 with catecholborane (HBcat)is knownto be catalyzed by nickel hydride complexes supported by a bis(phosphinite)-basedor POCOP-type pincer ligand. The objective of this research is toexamine how changing the metal center from nickel to palladium wouldimpact the outcome of CO2 reduction. Stoichiometric studiesshow that the palladium hydride complexes react rapidly with CO2, although the resulting palladium formate complexes can loseCO(2) under reduced pressure or in chloroform. In the presenceof HBcat, the formate complexes are converted back to the palladiumhydride species while the formate group is reduced to CH(3)OBcat. This process is also accompanied by the formation of palladiumbis(catecholato)borate complexes, which diverts some of the HBcatto yield B-2(cat)(3) and B2H6. For palladium hydrides stabilized by a POCOP-pincer ligand withrelatively small phosphorus substituents (e.g., isopropyl or cyclopentylgroups), HBcat cleaves the P-O bonds in the ligand backboneto degrade the catalysts to secondary phosphine complexes. WithoutCO(2), HBcat also undergoes H-2 elimination withthe Pd-H moiety to form palladium boryl complexes. These sidereactions with HBcat and the palladium pincer complexes play profoundroles in the catalytic reduction of CO2 with the borane.

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