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Photocatalytic Hydrophosphination with Air-Stable and Commercially Available Bis(acetylacetonato)copper(II) (Cu(acac)2)
preprintsubmitted on 29.06.2020, 17:53 and posted on 01.07.2020, 04:50 by Steven Dannenberg, Rory Waterman
Bis(acetylacetonato)copper(II) (Cu(acac)2, 1), is active for the hydrophosphination of alkenes and alkynes with primary and secondary phosphines. Under thermal conditions, the activity of 1 is comparable to some of the best literature catalysts, but 1 is unique in that set possessing air- and water-stability. However, under ambient temperature irradiation centered at 360 nm, the conversions are remarkable with some reactions complete in minutes and several rarely reported unactivated substrates achieving high conversions within hours. The photocatalytic conditions are critical, and comparison to literature catalysts has been made in which 1 demonstrates superior activity. Initial mechanistic work does not suggest a radical mechanism rather the formation of a copper(I) active species. Hammett analysis indicates that depending on the substrate, either a nucleophilic or insertion-based mechanism may be at work. The enhanced reactivity provided by light also appears to be generalizable to other copper(I) compounds under irradiation, representing a broader phenomenon in metal catalyzed P–C bond formation. This simple, bench-stable, and inexpensive catalyst is highly effective, placing hydrophosphination in the hands of many more synthetic chemists.