Presentation Title

Photocatalysis with Copper

Presenter's Name(s)

Steven G. DannenbergFollow

Project Collaborators

Rory Waterman (Graduate Student Mentor)

Abstract

Bis(acetylacetonato)copper(II) (Cu(acac)2, 1), is a highly active catalyst for the hydrophosphination of alkenes and alkynes with primary and secondary phosphines. Typical hydrophosphination substrates, such as styrene, are converted to secondary phosphines with phenylphosphine in hours under thermal conditions and minutes under ambient temperature irradiation centered at 360 nm. This reactivity outpaces previous reports of hydrophosphination with air-stable salts in terms of speed and is on par with the best air-sensitive catalysts. The photocatalytic conditions are critical, and allow access to high conversions of rarely reported unactivated substrates within hours. These unactivated substrates have never been reported with an air-stable catalyst and only been utilized a few times with air-sensitive catalysts in more modest yields, with harsher conditions, and more difficult to synthesize catalysts. Initial mechanistic work does not suggest a radical mechanism, rather the formation of a copper(I) active species is indicated. Hammett analysis indicates that depending on the substrate, either a nucleophilic or insertion-based mechanism may be at work. Several experimental and literature results point to the in-situ formation of a copper phosphido species. Efforts continue to isolate catalytic intermediates to further elucidate the mechanism of catalysis. 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. Continued efforts are geared towards enantioselective hydrophosphination with copper(I) complexes under irradiation.

Primary Faculty Mentor Name

Rory Waterman

Status

Graduate

Student College

College of Arts and Sciences

Program/Major

Chemistry

Primary Research Category

Engineering & Physical Sciences

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Photocatalysis with Copper

Bis(acetylacetonato)copper(II) (Cu(acac)2, 1), is a highly active catalyst for the hydrophosphination of alkenes and alkynes with primary and secondary phosphines. Typical hydrophosphination substrates, such as styrene, are converted to secondary phosphines with phenylphosphine in hours under thermal conditions and minutes under ambient temperature irradiation centered at 360 nm. This reactivity outpaces previous reports of hydrophosphination with air-stable salts in terms of speed and is on par with the best air-sensitive catalysts. The photocatalytic conditions are critical, and allow access to high conversions of rarely reported unactivated substrates within hours. These unactivated substrates have never been reported with an air-stable catalyst and only been utilized a few times with air-sensitive catalysts in more modest yields, with harsher conditions, and more difficult to synthesize catalysts. Initial mechanistic work does not suggest a radical mechanism, rather the formation of a copper(I) active species is indicated. Hammett analysis indicates that depending on the substrate, either a nucleophilic or insertion-based mechanism may be at work. Several experimental and literature results point to the in-situ formation of a copper phosphido species. Efforts continue to isolate catalytic intermediates to further elucidate the mechanism of catalysis. 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. Continued efforts are geared towards enantioselective hydrophosphination with copper(I) complexes under irradiation.