6084
J. Am. Chem. Soc. 1999, 121, 6084-6085
Scheme 1
Hydrogenolysis of Aliphatic Carbon-Fluorine Bonds
in Fluoroalkyl-Iridium Complexes to Give
Hydrofluorocarbons
Russell P. Hughes* and Jeremy M. Smith
Department of Chemistry
6128 Burke Laboratory, Dartmouth College
HanoVer, New Hampshire 03755
ReceiVed February 16, 1999
The chemical inertness of saturated perfluorocarbons (PFCs)
arises in large part from the strength of the aliphatic C-F bond,
the strongest single bond formed by carbon.1 The stoichiometric
and catalytic activation of these normally inert C-F bonds has
been the subject of considerable interest among transition metal
chemists.2-4 In contrast to aromatic fluorocarbons for which a
variety of functionalization reactions have been reported,3,5-7 the
aliphatic C-F bonds in saturated PFCs have no strong binding
site for interaction with a metal center. It is not surprising that
reports of their activation reactions with transition-metal centers
almost invariably involve the metal acting as a reductant or a
catalytic electron shuttle.8-10 Other strongly reducing conditions
using ammonia, alkali metals, metal oxalate salts, and elemental
carbon have been reported.11-14 Nonreducing conditions involving
abstraction of fluorine by lanthanide and actinide complexes have
also been reported.15,16 In all of these reactions, the thermodynamic
driving force is usually provided by formation of strong metal-
fluorine bonds or high lattice energy metal fluorides.4,13
exogenous protic acids,27-30 or protons from intramolecular
water31,32 as fluoride acceptors; subsequent hydrolysis of the R-CF2
to a ketone or CO occurs, with strong HF and CO bonds providing
thermodynamic compensation for breaking the strong CF bonds.
Here we report the first examples of hydrogenolysis of the R-CF2
groups in some iridium fluoroalkyls using dihydrogen under
ambient conditions.
The cationic (aqua)(fluoroalkyl)iridium complexes 1 and 233
can be prepared from the corresponding iodides as previously
described for rhodium analogues.31 Treating methylene chloride
solutions of 1 or 2 with dihydrogen results in clean and rapid
formation of the known iridium trihydride 3, whose 1H, 19F, and
31P NMR data are consistent with those previously reported34,35
and that of an independently prepared sample. The fate of the
fluoroalkyl ligand was an approximately 1:1 mixture of two
hydrofluorocarbon (HFC) compounds, identified as RFCFH2 and
RFCH3 (RF ) CF3, CF3CF2) by 19F NMR spectroscopy.36 No trace
of the monohydrogenated species, CF3CF2H or CF3CF2CF2H were
observed. Similarly treatment of the corresponding perfluoroiso-
propyl complex 433 with H2 affords only 3 and CF3CH2CF3 with
no observable trace of CF3CFHCF3 (Scheme 1). These observa-
tions represent, to our knowledge, the first examples of the
hydrogenolysis of aliphatic CF bonds in the coordination sphere
of a transition metal. Furthermore, the reaction is selective for
H2, with no observable hydrolysis of the fluoroalkyl group, even
in the presence of the water originally present in the coordination
While organometallics bearing aliphatic fluoroalkyl groups have
been known since the early days of organotransition-metal
chemistry,17-21 the saturated fluoroalkyl chains in these complexes
are usually inert. However, the R-fluorines in such compounds
are unusually reactive in the presence of strong Lewis acids,22-26
(1) Smart, B. E. In Chemistry of Functional Groups, Supplement D; Patai,
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(33) 1; IR (KBr), υOH ) 3422 cm-1 1H NMR (CDCl3) δ 1.70 (s, 15H,
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C5Me5); 1.68 (d, JPH ) 11 Hz, 9H, PMe3); 19F NMR (CDCl3), δ -82.29 (s,
3F, CF3); -82.22 (d, JAB ) 303, 1F, CRFA); -90.10 (d, JAB ) 303, 1F, CRFB);
-150.33 (s, 4F, BF4); 31P{1H}NMR (CDCl3), δ -23.48 (dd, JPF ) 16.0, JPF
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T. M.; Schwarz, H. Angew. Chem., Int. Ed. Engl. 1995, 34, 213-217.
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1
) 8.0, PMe3). 2; IR (KBr), υOH ) 3340 cm-1; H NMR (CDCl3) δ 1.71 (d,
JHH ) 2 Hz, 15H, C5Me5); 1.70 (d, JPH ) 11 Hz, 9H, PMe3); 19F NMR (CD2-
Cl2), δ -79.32 (t, JFF ) 12, 3F, CF3); -71.96 (m, JAB ) 261, 1F, CRFA);
-94.96 (m, JAB ) 261, 1F, CRFB); -116.40 (m, 2F, CâF2); -149.67 (s, 4F,
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BF4); 31P{1H}NMR (CD2Cl2), δ -21.71 (br s, PMe3). 4; IR (KBr), υOH
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1
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PMe3); 1.61 (d, JPH ) 2 Hz, 15H, C5Me5). 19F NMR (CD2Cl2), δ -69.91 (s,
6F, CF3); -149.56 (s, 4F, BF4); -180.50 (s, 1F, CF). 31P{1H}NMR (CD2-
Cl2), δ -69.90 (br s, PMe3) Satisfactory microanalysis data were obtained
for all new compounds.
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10.1021/ja990490z CCC: $18.00 © 1999 American Chemical Society
Published on Web 06/10/1999