2CuITpþCO ORðÞ 2 þ2H 2 O!TpCuIIðÞmOH 2
CuIITpþCOþ2ROHð 28 ÞThe photoreduction to CO was also observed when CO(OR) 2 was
replaced by urea. A detailed analysis was carried out for the pho-
tolysis in the presence of dimethyl carbonate. The irradiation of
CuITp (lmax¼279 nm;e¼16,180M^1 cm^1 andlmax¼227 nm
(sh);e¼8600 M^1 cm^1 ) in a water/dimethylcarbonate mixture
was accompanied by spectral changes (Fig. 4) that indicated a
clean conversion to TpCuII(OH) 2 CuIITp. The spectrum of an
authentical sample of this complex ( 42 ) shows absorptions at
lmax¼260 nm, e¼6800 and lmax¼653 nm, e¼120 M^1 cm^1.
Moreover, a gas was formed that already in the beginning
becomes visible as bubbles. This gas is not CO 2 but apparently
CO. The quantitative determination of the gas was carried out
by measuring the volume with a gas burette. The stoichiometric
ratio of TpCuII(OH) 2 CuIITp to CO was found to be roughly 1:1
confirming the product ratio in Eq. (5). The quantum yield for the
disappearance of CuITp wasf¼1.5 10 ^3 5% (lirr¼313 nm).
At later stages of the photolysis, secondary reactions took place
as indicated by the irregular pattern of the spectral changes
and the loss of the isosbestic points at 230 and 440 nm.
1.0A abb0.5200 300 400 500
l (nm)600 7000.0FIG. 4. Spectral changes during the photolysis of 6.89 10 ^5 M
CuITp* in a water/dimethylcarbonate mixture under argon at room
temperature after 0 min (a), 40, 80, and 160 min (b) irradiation times
withlirr>290 nm, 1-cm cell, spectral region 450–800 nm with 10-fold
extension of absorbance.
358 ARND VOGLER AND HORST KUNKELY