| Summary: | The rhenium dithiodiolate, Hydrido-tris-(3 ,5-dimethyl- 1 -pyrazol yl)
borato(ethane- 1 ,2-dithiodiolato)(oxo)rheni um(V), and Hydrido-tris-(3 ,5-dimethyl-
1 -pyrazolyl)borato(phenylethanedithiodiolato)(oxo)rhenium(V), were synthesized
by reductive cyclocondensation of alkane-1,2-dithiols with Tp'Re0��� in a one pot
fashion. The rhemium monothiodiolate, Hydrido-tris-(3 ,5-dimethyl- 1 -pyrazolyl)
borato(ethane- 1 ,2-monothiodiolato)(oxo)rhenium(V), and Hydrido-tris-(3 ,5-
dimethyl- 1 -pyrazolyl)borato(propanemonothiodiolato)(oxo)rhenium(V), were also
synthesized by using the same procedure. The syn and anti isomers of rhenium
phenylethanedithiodiolate and rhenium propanemonothiodiolate were characterized
by using COSY, nOe, and HSQC experiments. An X-ray crystal structure of the
rhenium ethanedithiodiolate was obtained, and an unusually small dihedral angle
(S-C-C-S) of about 12�� was observed. The solution conformation of these
compounds was investigated by using a Karplus relationship between vicinal
coupling constants and dihedral angle. The dihedral angle for the
ethanedithiodiolate appeared to be 38�� indicating a staggered geometry for the ring.
All of these complexes failed to cyclorevert to any detectable extent at
120��C after 7 days. This observation reflects the thermal stability of rhenium
dithiodiolate and monothiodiolate complexes. Energetics of ethylene addition to
tetrathioperrhenate anion (ReS������) and addition of hydrogen sulfide to the alkene
adduct were calculated by DFT calculation using LACVP** basis set with B3LYP
functionals. The heat of reaction of ethylene addition to ReS������ was 15.4 kcal/mol,
and 111.1 kcal/mol for addition of hydrogen sulfide to the alkene adduct. These
results are consistent with the stability of the dithiodiolate complex toward
cycloreversion reaction.
Reaction of Tp'Re0��� and ethylene sulfide led to the rhenium
ethanedithiolate complex both with and without acid catalysis. This observation led
to a proposed multi step mechanism. === Graduation date: 2002
|
|---|
