Cobalt Phosphino-α-Iminopyridine-Catalyzed Hydrofunctionalization of Alkenes: Catalyst Development and Mechanistic Analysis

A family of CoCl2(PNpy) complexes were prepared, where PNpy = 2-iminopyridyl-phosphine ligands derived from aminoalkyl and aminoaryl phosphines and 2-keto- and 2-formylpyridines. Reduction of CoCl2(PNpy) complexes in the presence of PPh3 gave CoH(PNpy)(PPh3) and CoMe(PNpy)(PPh3), which were active for hydrofunctionalization of alkenes. According to DFT calculations, the CoMe(PNpy)(PPh3) complexes are best described as Co(II) derivatives of the anion [PNpy]−, with a labile PPh3 coligand. Metalation of Na[Ph2PC2NHpy] gave the dimers [CoCl(Ph2PC2NHpy)]2. Monomeric complexes catalyze hydrosilylation of 1-octene with Ph2SiH2, with the CoCl2(iPr2PC3NHpy)/2NaBEt3H system exhibiting the highest rate and selectivity for anti-Markovnikov product. In situ NMR studies established the following: (i) silanes protonolyze catalyst precursors to give the Co-silyl complexes Co(SiR3)(Ph2PC6H4NPhpy)(PPh3), (ii) alkenes compete with PPh3 to give Co(SiHPh2)(Ph2PC6H4NPhpy)(η2-alkene), (iii) ethylene inserts into the Co–Si bond to give Co(CH2CH2SiR3)(Ph2PC6H4NPhpy)(PPh3).