RHENIUM-PLATINUM MIXED-METAL CLUSTERS - CHARACTERIZATION IN SOLUTION AND DYNAMIC BEHAVIOR OF THE ISOMERS OF {[RE3PT(MU-H)3(CO)14] - AN EXAMPLE OF A LABILE METAL FRAGMENT THAT UNDERGOES INTERMOLECULAR EXCHANGE}
Articolo
Data di Pubblicazione:
1994
Citazione:
RHENIUM-PLATINUM MIXED-METAL CLUSTERS - CHARACTERIZATION IN SOLUTION AND
DYNAMIC BEHAVIOR OF THE ISOMERS OF {[RE3PT(MU-H)3(CO)14] - AN EXAMPLE
OF A LABILE METAL FRAGMENT THAT UNDERGOES INTERMOLECULAR EXCHANGE} / T. BERINGHELLI, G. D'ALFONSO, A. MINOJA. - In: ORGANOMETALLICS. - ISSN 0276-7333. - 13:2(1994), pp. 663-668.
Abstract:
The cluster (Re3Pt(mu-H)3(CO)14] (1), which contains a {[ReH(CO)5]
molecule bound to the Pt atom of a Re2Pt triangular cluster, exists in
solution at low temperature as two isomers, with a ratio of ca. 19:1.
The values of the H-1-Pt-195 coupling constants and the dynamic behavior
suggest that in both the species [ReH(CO)5] is bound to Pt, but with
different locations with respect to the H-bridged Re-Pt triangular edge:
cis in the major one (1a), as found in the solid state structure, and
trans in the minor isomer (1b). H-1 2D EXSY experiments at 180 K showed
the occurrence of two dynamic processes: one interconverts the two
isomers, while the other one leads to intermolecular exchange of the
[ReH(CO)5] fragment. The addition of [ReH-CO)5] caused a dramatic
increase of the rate of this exchange even at 180 K and showed that this
latter process is operative only in the major species 1a. The
isomerization rate, on the contrary, is insensitive to the addition of
[ReH(CO),5], indicating its intramolecular nature. The rate constants
of the two processes obtained at 180 K allowed the calculation of the
activation parameters DELTAG(double dagger)180 = 43.0 kJ/mol and
DELTAG(double dagger)180 = 41.9 kJ/mol for the isomerization and for
[ReH-CO)5] exchange, respectively. Several indirect thermodynamic and
kinetic evidences indicate that above 210 K one or more species, in fast
exchange with the two isomers, are present in solution. At 264 K, a H-1
2D EXSY experiment showed the onset of a new exchange process, implying
the cleavage of the H-Re bond of the [ReH(CO)5] fragment, likely via
oxidative addition of [ReH(CO)5] on Pt.}
Tipologia IRIS:
01 - Articolo su periodico
Elenco autori:
T. BERINGHELLI, G. D'ALFONSO, A. MINOJA
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