Exchange couplings and hydrogen dynamics in ruthenium trihydride adducts with coinage-metal cations †
1997
The reactions of AgBF
4
and
[Au(tht)
2
]PF
6
with
[Ru(η-C
5
Me
5
)H
3
{P(C
6
H
11
)
3
}] 1
(tht = tetrahydrothiophene) led to the adducts
[{Ru(η-C
5
Me
5
)H
3
[P(C
6
H
11
)
3
]}
2
M]X
(M = Ag, X = BF
4
3;
M = Au, X = PF
6
4) similar to the
previously reported
[{Ru(η-C
5
Me
5
)H
3
[P(C
6
H
11
)
3
]}
2
Cu]PF
6
2.
Variable-temperature 1
H NMR experiments were performed on
2–4 dissolved in organic liquids down to 130 K which complement
previous experiments on 1. Like 1 and 2, 3 and 4 display at low
temperatures exchange couplings between proton pairs in the trihydride
sites which increase with temperature and which depend on the molecular
structure. At higher temperatures a classical exchange between the
hydride protons occurred the rate constants for which determined by
lineshape analysis. As the coinage metal lowers the symmetry of the
trihydride spin systems from the AB
2
type in 1 to the ABC
type in 2–4, the 1
H NMR spectra also give information
about the rate constants of an intramolecular metal transfer leading to
an effective AB
2
symmetry of the trihydride spins. The
results indicate (i) the absence of kinetic hydrogen/deuterium
isotope effects on the classical hydrogen-exchange processes within the
margin of error in the temperature interval covered, (ii) only
small effects of the presence of Lewis-acidic cation on the classical
exchange dynamics, but (iii) important effects of these cations
on the quantum-mechanical exchange couplings. In particular, these
couplings increase with increasing electronegativity of the coinage
metal by favouring dihydrogen configurations.
Keywords:
- Correction
- Source
- Cite
- Save
- Machine Reading By IdeaReader
20
References
14
Citations
NaN
KQI