Work

Time-Resolved Ultraviolet–Infrared Experiments Suggest Fe–Cu Dinuclear Arene Borylation Catalyst Can Be Photoactivated

Year: 2021

Type: article

Abstract: Heterodinuclear complexes with a direct metal–metal bond offer the possibility of unique mechanisms and intermediates. The Cp(CO) 2 Fe–Cu(IPr) (IPr = N, N -bis(2,6-diisopropylphenyl)imidazol-2-ylidene) heterodinuclear complex 1 was reported to photochemically catalyze arene borylation. To examine possible initial steps of photoinitiated catalysis, we synthesized a triethylsilyl-substituted Fe–Cu catalyst derivative 5 that provided cyclohexane solubility to conduct time-resolved UV–IR studies. Time-resolved vibrational spectroscopic measurements suggest that photolysis of 5 stimulates CO dissociation without Fe–Cu metal–metal bond cleavage. UV–IR measurements of 5 with added pinacolborane (HBPin) showed a very similar set of IR bleaches and a new monocarbonyl IR absorbance, and HBPin appears to stabilize the monocarbonyl species. This suggests that arene borylation catalysis may begin with a photochemical step rather than a relatively endothermic thermal-induced cleavage of the Fe–Cu bond, and therefore a new possible catalytic cycle is proposed.

Source: Organometallics

DOI: 10.1021/acs.organomet.1c00136