Catalytic oxidations using ruthenium porphyrins - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 48

Addition of increases the turnover numbers by
factors of 2-6, depending on the substrate, while addition of aq. KOH or
NaOH increases turnovers by a further factor of up to 6. Thus addition of
KOH increases turnovers for isopropanol and benzylalcohol by factors of 5-
6. Maximum turnovers over 24 h of ~200 (100% yield) were achieved for 2-,
3-, or 4-MeO substituted benzyl alcohols, and the catalyst still remains
active. Oxidation of primary alcohols (such as 1-butanol) to the aldehyde
was less efficient, with turnovers of up to 40 being noted over 24 h, with no
formation of carboxylic acids. The use of rather than air did not increase

the oxidation rates 65,167,168 .
In general, use of instead of for the
aerobic oxidations made little difference, i.e. the activities were similar over
24 h, but the TDCPP analogue was more susceptible to deactivation via a
decarbonylation process that generated the Ru(CO) derivative 168 . For the
oxidation of benzhydrols, the perchloro derivative
exhibited activity similar to that of
The stoichiometric reaction between and the alcohols (2-

propanol, and under Ar conforms to that shown in

eq. 33 or Ph(H)), as evidenced by NMR. The

paramagnetic bis(alkoxy)ruthenium(IV) complexes were isolated and fully
characterized by NMR, UV-vis and IR spectroscopies, magnetic moment
data (2 unpaired electrons), and X-ray structures for
and

The

NMR spectra show upfield, paramagnetic shifts for the
hydrogens to the to -34 region (vs. 8 - 9 for diamagnetic or
complexes), consistent with Ru(IV) species possessing symmetry 49,170 .
Detailed kinetic studies on the stoichiometric oxidation of 2-PrOH,
benzyl alcohol and several benzhydrols by have
led to the mechanism outlined in Figure 25; the rapid pre-equilibrium ( K ) to
give a Ru-dioxo-alcohol intermediate ( 25 ), followed by a rate-determining
( k ) hydride transfer from the conforms to the measured saturation
kinetic behaviour and the rate-law given in eq. 34 169 . The reactions were

monitored by NMR and UV-Vis spectroscopies but even at higher
[ROH], when the rate is zero-order in ROH and ( 25 ) should be fully formed,