Facile O-atom insertion into C C and C H bonds by a trinuclear copper complex designed to harness a singlet oxene

doi:10.1073/pnas.0707119104

Facile O-atom insertion into CC and CH bonds by a trinuclear copper complex designed to harness a singlet oxene

Institute of Chemistry, Academia Sinica, Nankang, Taipei, Taiwan 115, Republic of China

Communicated by Harry B. Gray, California Institute of Technology, Pasadena, CA, July 31, 2007 (received for review March 30, 2007)

Abstract

Two trinuclear copper [Cu^ICu^ICu^I(L)]¹⁺ complexes have been prepared with the multidentate ligands (L) 3,3′-(1,4-diazepane-1,4-diyl)bis(1-((2-(dimethylamino)ethyl)(methyl)amino)propan-2-ol) (7-Me) and (3,3′-(1,4-diazepane-1,4-diyl)bis(1-((2-(diethylamino) ethyl)(ethyl) amino)propan-2-ol) (7-Et) as models for the active site of the particulate methane monooxygenase (pMMO). The ligands were designed to form the proper spatial and electronic geometry to harness a “singlet oxene,” according to the mechanism previously suggested by our laboratory. Consistent with the design strategy, both [Cu^ICu^ICu^I(L)]¹⁺ reacted with dioxygen to form a putative bis(μ₃-oxo)Cu^IICu^IICu^III species, capable of facile O-atom insertion across the central CC bond of benzil and 2,3-butanedione at ambient temperature and pressure. These complexes also catalyze facile O-atom transfer to the CH bond of CH₃CN to form glycolonitrile. These results, together with our recent biochemical studies on pMMO, provide support for our hypothesis that the hydroxylation site of pMMO contains a trinuclear copper cluster that mediates CH bond activation by a singlet oxene mechanism.

Footnotes

^†To whom correspondence should be sent at the present address:
Institute of Chemistry, Academia Sinica, 128 Sec. 2, Academia Road, Taipei 115, Taiwan, Republic of China.
E-mail: chans{at}chem.sinica.edu.tw
Author contributions: P.P.-Y.C., R.B.-G.Y., and J.C.-M.L. performed research; S.I.C. designed research; S.I.C. contributed new reagents/analytic tools; P.P.-Y.C. and S.I.C. analyzed data; and P.P.-Y.C. and S.I.C. wrote the paper.
The authors declare no conflict of interest.
This article contains supporting information online at www.pnas.org/cgi/content/full/0707119104/DC1.
Abbreviations:

MMO,

methane monooxygenase;

pMMO,

particulate MMO;

sMMO,

soluble MMO;

DFT,

density functional theory;

7-Me,

3,3′-(1,4-diazepane-1,4-diyl)bis(1-((2-(dimethylamino)ethyl)(methyl)amino)propan-2-ol);

7-Et,

3,3′-(1,4-diazepane-1,4-diyl)bis(1-((2-(diethylamino)ethyl)(ethyl)amino)propan-2-ol;

ESI,

electrospray ionization;

amu,

atomic mass unit.