The bis(pentadentate) ligand tmpdtne binds two Co(II) cente
rs, and the entity is
readily oxidized to the dicobalt(III)de
rivative [Co
2(tmpdtne)Cl
2]
4+ which has been sepa
rated into two isome
ric fo
rms. NMR studies establish these asmeso and
rac isome
rs a
rising f
rom the diffe
rent o
r same absolute configu
rations fo
r the asym configu
ration abouteach Co(III) cente
r. Each dinuclea
r ion base hyd
rolyses to the dihyd
roxo de
rivative [Co
2(tmpdtne)(OH)
2]
4+ with
retained asym configu
rations about each metal ion and also
retained
rac o
r meso configu
rations. The kinetics fo
rthe stepwise loss of the two Cl
- ligands is uniphasic, and data a
re p
resented to show that the loss of the fi
rstchlo
ride is
rate dete
rmining and is followed by ve
ry
rapid int
ramolecula
r and loss of the second Cl
- via a hyd
roxo-b
ridged species to yield the obse
rved dihyd
roxo de
rivative. Meso and
rac fo
rms of the latte
r have been c
rystallized.The X-
ray c
rystal st
ructu
re of the
rac-dihyd
roxo complex is
repo
rted, and it establishes the configu
rations of all thecomplexes
repo
rted. The
1H NMR spect
ra fo
r the hyd
roxo ions show ve
ry high field Co-OH
resonances (ca.
![](/images/gifcha<font color=)
rs/delta.gif" BORDER=0 >-0.5 ppm) not obse
rved p
reviously fo
r such ions, and this
result is discussed in the context of published
1H NMRdata fo
r b
ridged Co-OH-Co species. The base hyd
rolysis kinetics fo
r the dichlo
ro ions a
re fi
rst o
rde
r in [OH
-],and dep
rotonation at an
![](/images/gifcha<font color=)
rs/alpha.gif" BORDER=0>-CH
2 cente
r (
![](/images/gifcha<font color=)
rs/alpha.gif" BORDER=0> to a py
ridyl) is identified as the sou
rce of the catalysis, since the
re is noNH cente
r available fo
r dep
rotonation on the ligand. These data fu
rthe
r suppo
rt the new pseudoaminate basehyd
rolysis mechanism fi
rst
repo
rted in 2003. The values of
kOH fo
r the second-o
rde
r base-catalyzed
reaction a
reca. 4.0 M
-1 s
-1 fo
r both the
rac and meso isome
rs, and these
results a
re discussed in te
rms of the inc
reasedacidities of these 4+ cations compa
red to thei
r 2+ ion counte
rpa
rts.