that they are close in energy, although such complexes are
unknown (38,39). Since the CuO 2 Cu fragment should be quite
oxidizing it is not unexpected that it undergoes an oxygen trans-
fer to a phosphine in agreement with our observation. It is well
known that a variety of oxygen transfer agents are able to con-
vert phosphines to phosphine oxides.
B. SPLITTING OFALKYLCARBONATESPHOTOCATALYZED BYCOPPER
HYDROTRISPYRAZOLYLBORATECOMPLEXES
While indeed a clean photoreduction of CO 32 to CO in the
complex (prophos)CuI(CO 3 )CuI(prophos) was observed the con-
comitant oxidation did not yield oxygen or hydrogen peroxide
but phosphine oxide( 30 ). In order to prevent this dead end, pho-
sphines have to be replaced by ligands that do not act as oxygen
atom acceptors. For this purpose we selected the tridentate
ligand hydrotris (3,5-dimethyl-1-pyrazolyl)borate (Tp) as a suit-
able ligand ( 40 ). Various Cu(I) and Cu(II) complexes of Tp or
other Tp derivatives have been prepared and characterized
( 41 – 45 ). Unfortunately, we were not able to obtain simple car-
bonate complexes of the CuITp moiety (Structure 1). In the pres-
ence of CO 32 , CuITp underwent a decomposition.
HBN NN NNN Cu
IHowever, CuITp* ( 41 – 45 ) can be dissolved in an aqueous solution
of carbonic acid esters CO(OR) 2 with R¼CH 3 ,C 2 H 5 , and
½CH 2 CH 2 without decomposition. The photolysis of these sol-
utions smoothly proceeds according to Eq. (5).
PHOTOCHEMICAL ACTIVATION AND SPLITTING OF H 2 O 357