The rhodium and iridium complexes
ClRhH2(P⌒O)(P∼O) (2a,b)
and ClIrH2(P⌒O)(P∼O)
(3a) (P⌒O = η2(P,O) coordination,
P∼O = η1(P) coordination of
Cy2PCH2CH2OCH3
(a) and
Cy2PCH2C4H7O
(b); C4H7O = tetrahydrofuranyl)
were subjected to dynamic NMR studies.
They exhibit a fast fluxional behavior both of the two ether
oxygen donors and of the two cis
hydrides at room temperature. The exchange of the hydrides is
assisted by the fact that
one of the ether moieties simulates an external solvent. The
complexes 2a,b show the same
behavior as is suggested for the coordinatively unsaturated species
ClRhH2(PPh3)2,
which
is generally postulated to be an active intermediate in the catalytic
hydrogenation of olefins.
In the course of the formation of 3a from its
ortho-metalated
(4a;
=
η2(P,CH2) coordination of
Cy2PCH2CH2OCH2)
and dihydrogen, one C−H bond
of the methoxy group and an additional Ir−H bond were formed.
This was confirmed by
the corresponding reaction of 4a with D2 to give
the analogous dideuterium complex 3a‘.
The opposite behavior was observed when 4a was treated
with DCl: one C−D and one Ir−Cl bond were formed in the complex
Cl2IrH(P⌒O)(P∼O) (5a; one
Cy2PCH2CH2OCH2D
ligand)
while the hydride remained at the metal. The
103Rh chemical shift has been determined
for
compound 2b.
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