Revisiting the Preparation and Catalytic Performance of a Phosphine-Modified Co(II) Hydroformylation Precatalyst.

In light of recent conflicting reports regarding the hydroformylation catalytic activity derived from cationic Co(II) precatalysts of the form [Co(acac)(bis(phosphine))]BF 4 , the synthetic procedures and characterization of [Co(acac)(dppBz)]BF 4 , 1 , are evaluated. Leveraging calibrated ESI-TOF MS methodologies, substantial quantities of Co(acac) 2 (dppBz), 2 , were observed within samples of 1 . The source of the impurity, 2 , is determined to derive from incomplete protonolysis of the Co(acac) 2 precursor and ligand scrambling occurring during the synthesis of 1 . Revised synthetic procedures using lower temperature conditions and longer reaction times afford analytically pure samples of 1 based on ESI-TOF MS and NMR spectroscopic analysis. Complex 1 is demonstrated to act as a hydroformylation precatalyst for the conversion of 1-hexene to 1-heptanal under relatively mild conditions at 51.7 bar and 140 °C. The presence of impurity 2 is shown to dramatically decrease the catalytic performance derived from 1 .