Web Release Date: February 14,
Ligand Exchange and Oxidative Addition on a Silica-Supported
Rhodium Complex, trans-[(
SiO)Rh(PMe3)2(CO)]
Contribution from the Department of Chemistry, University of Ottawa, 10 Marie Curie, Ottawa, Ontario, Canada K1N 6N5
Received September 10, 1997
Abstract:
The surface organometallic fragment
[RhI(P(CH3)3)2(CO)],
1, was prepared by the reaction of
trans-[CH3Rh(P(CH3)3)2(CO)]
with partially dehydroxylated silica. 1 is attached to
the silica surface by a covalent
bond to oxygen. The reactions of 1 with organic and
inorganic substrates were followed by transmission
infrared and solid-state NMR spectroscopies. Ligand exchange
reactions were observed when 1 was treated
with 13CO and
P(CH(CH3)2)3. In the
presence of excess PR3 (R is methyl or isopropyl), cationic
[Rh(PR3)3CO]+ was formed. In the presence of HCl/DCl,
Cl2, CCl3Br, CH3I, and
CH2=CHCH2Cl, 1 underwent
oxidative
addition to give Rh(III) surface species, characterized by a shift
of the 
(CO) modes ca. 100 cm-1 to
higher
frequency and displacement of the 31P chemical shifts to
lower field. In the case of HCl/DCl,
(Rh-H/D)
modes were also observed. Oxidative addition of CH3I
to 1 occurs without CO insertion, but the
formation
of acyl complexes was induced by addition of excess
P(CH3)3 or CO. The reaction of
1 with
CH2=CHCH2Cl
exhibits biphasic kinetic behavior, implying consecutive elementary
reactions of oxidative addition followed
by spontaneous CO insertion into the metal-carbon bond. The
demonstration of these reactions on an oxide
surface supports the idea that, under carefully controlled conditions,
surface reactivity can be interpreted by
using concepts from organometallic chemistry.
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