A series of Cu(I) and Cu(II) co
mplexes of a variety of
![](/i<font color=)
mages/gifchars/beta2.gif" BORDER=0 ALIGN="
middle">-diketi
minate ligands (L
-) with a range of substitutionpatterns were prepared and characterized by spectroscopic, electroche
mical, and, in several cases, X-raycrystallographic
methods. Specifically, co
mplexes of the general for
mula [LCuCl]
2 were structurally characterizedand their
magnetic properties assessed through EPR spectroscopy of solutions and, in one instance, by variable-te
mperature SQUID
magnetization
measure
ments on a powder sa
mple. UV-vis spectra indicated reversibledissociation to 3-coordinate
mono
mers LCuCl in solution at te
mperatures above -55
![](/i<font color=)
mages/entities/deg.gif">C. The Cu(I) co
mplexesLCu(MeCN) exhibited reversible Cu(I)/Cu(II) redox couples with
E1/2 values between +300 and +520
mV versusNHE (cyclic volta
mmetry, MeCN solutions). These co
mplexes were highly reactive with O
2, yielding inter
mediatesthat were identified as rare exa
mples of neutral bis(
![](/i<font color=)
mages/entities/
mgr.gif">-oxo)dicopper co
mplexes on the basis of their EPR silence,diagnostic UV-vis absorption data, and O-isotope-sensitive resonance Ra
man spectroscopic features. The structuralfeatures of the co
mpounds [LCuCl]
2 and LCu(MeCN) as well as the proclivity to for
m bis(
![](/i<font color=)
mages/entities/
mgr.gif">-oxo)dicopper productsupon oxygenation of the Cu(I) co
mplexes are co
mpared to data previously reported for co
mplexes of
more stericallyhindered
![](/i<font color=)
mages/gifchars/beta2.gif" BORDER=0 ALIGN="
middle">-diketi
minate ligands (Aboelella, N. W.; Lewis, E. A.;
Reynolds, A. M.; Brennessel, W. W.; Cra
mer, C.J.; Tol
man, W. B.
J. Am. Chem. Soc. 2002,
124, 10600. Spencer, D. J. E.; Aboelella, N. W.; Reynolds, A. M.;Holland, P. L.; Tol
man, W. B.
J. Am. Chem. Soc. 2002,
124, 2108. Holland, P. L.; Tol
man, W. B.
J. Am. Chem.Soc. 1999,
121, 7270). The observed structural and reactivity differences are rationalized by considering the stericinfluences of both the substituents on the flanking aro
matic rings and those present on the
![](/i<font color=)
mages/gifchars/beta2.gif" BORDER=0 ALIGN="
middle">-diketi
minate backbone.