Organolutetium vinyl and tuck-over complexes via C-H bond activation

Article abstract of DOI:10.1021/ja065788l

The vinyl C-H bond of tetramethylfulvene is activated in the presence of [(C₅Me₅)₂LuH]_x, 1, to form a vinyl organolutetium complex, (C₅Me₅)₂Lu(CH=C₅Me₄), 2. Also formed in the reaction is the tuck-over complex, (C₅Me₅)₂Lu(μ-H)(μ-η¹:η⁵-CH₂C₅Me₄)Lu(C₅Me₅), 3, containing a (CH₂C₅Me₄)^2- moiety long postulated to exist in organolutetium chemistry but never crystallographically characterized. Evidence for these C-H bond activations by a (C₅Me₅)₃Lu intermediate, 4, is presented. Complex 3 can also be made in high yield by thermolysis of 1. Under H₂, 1 catalytically hydrogenates TMF to C₅Me₅H. Copyright

Full text of DOI:10.1021/ja065788l

Published on Web 10/13/2006
Organolutetium Vinyl and Tuck-Over Complexes via C-H Bond Activation
William J. Evans,* Timothy M. Champagne, and Joseph W. Ziller
Department of Chemistry, UniVersity of California, IrVine, California 92697-2025.
Received August 17, 2006; E-mail: wevans@uci.edu
Scandium, yttrium, and lanthanide methyl and hydride metal-
locenes of formula [(C5Me5)2MMe]x and [(C5Me5)2MH]x are highly
reactive organometallic reagents for C-H bond activation.1-12 The
specific reactivity is variable and depends upon the precise metal/
ligand combination involved. Recent studies of the sterically
crowded tris(pentamethylcyclopentadienyl) lanthanide complexes,
(C5Me5)3Ln,13,14 have shown that when Ln is small enough, even
(C5Me5)1- complexes can engage in C-H bond activation of arenes,
eq 1.15 To develop further this (C5Me5)1--based C-H bond
Figure 1. Thermal ellipsoid plot of (C5Me5)2Lu(CHdC5Me4), 2, drawn at
the 40% level.
activation chemistry, the reaction of [(C5Me5)2LuH]x,3 1, with
tetramethylfulvene (TMF) was examined to determine if
(C5Me5)3Lu would form as was observed with (C5Me5)3Y, eq 2.15
(C5Me5)3Lu would be the most crowded of the (C5Me5)3Ln
lanthanide complexes and could be more reactive for C-H bond
activation than (C5Me5)3Y. We report here that C-H bond
activation did occur, but surprisingly with the vinylic C-H bond
of tetramethylfulvene.
Figure 2. Thermal ellipsoid plot of (C5Me5)2Lu(µ-H)(µ-η1:η5-CH2C5-
Me4)Lu(C5Me5), 3, drawn at the 50% level.
CH2dCHMe, and CH2dCHC6H4X (X ) CF3, OMe, Me).5 These
NMR data also showed vinyl rather than allyl C-H bond activation.
Previous studies of [(C5Me5)2LnR]x and [(C5Me5)2LnH]x have
Addition of TMF to 1 in methylcyclohexane generates two
metalation products, (C5Me5)2Lu(CHdC5Me4), 2, a rare example
shown that specific σ-bond metathesis reactivity depends on a
variety of factors.1-12 For example, in comparison with eq 3, C-H
bond activation of TMF was not observed under comparable
conditions with the highly reactive [(C5Me5)2LuMe]x3,12 and [(C5-
Me5)2YMe]x.4
of a lanthanide vinyl complex, and the “tuck-over”6,10,16 complex
(C5Me5)2Lu(µ-H)(µ-η1:η5-CH2C5Me4)Lu(C5Me5), 3, eq 3, in ap-
proximately a 2:1 ratio along with C5Me5H. The compounds were
The structure of 2 contains a vinyl carbon, C(26), at a distance
of 2.422(5) Å from Lu in a [(C5Me5)2Lu]1+ metallocene unit
displaying conventional metrical parameters. No Lu-C(sp2) dis-
tances are in the Cambridge Crystallographic Database for com-
parison, but this Lu-C length is similar to the 2.423(3) Å Lu-C
(terminal-Me) distance observed in (C5Me5)2MeLu(µ-Me)Lu(C5-
Me5)2.12 The Lu-C(26) distance is surprisingly close to the 2.468-
(10) Å Sm-C(CHdCH2) distance in the samarium calyx-pyrrole
complex cited above17 considering that Sm3+ is approximately 0.1
separated by crystallization and fully characterized by X-ray
crystallography, Figures 1 and 2. If 1 is added slowly to a stirred
solution of TMF in methylcyclohexane, then 2 can be isolated free
from 3. Complex 3 can be independently synthesized in 88% yield
by heating 1 to 70 °C for 24 h.
C-H bond activation at the vinyl position in TMF instead of at
an allylic methyl position was unexpected. The only other structur-
ally characterized vinyl lanthanide in the literature is (Et8-calix-
pyrrole)(CHdCH2)Sm(µ3-Cl)[Li(THF)]2[Li(THF)2].17 The closest
data in the literature on the activation of vinyl C-H bonds are the
NMR studies of (C5Me5)2ScMe with MeCHdCMe2, CH2dCMe2,
Å larger than Lu3+ 18
In 2, the methyl group involving C(27) is
.
also oriented toward lutetium, but the 2.933(7) Å Lu-C(27)
distance is quite long.
Complex 3 is similar in structure, but not isomorphous with the
Ln ) La16, Sm10, and Y6 analogs prepared from [(C5Me5)2LnH]x.
The 2.01(5) and 2.09(5) Å Lu-H distances are reasonable based
on X-ray data on other lanthanide hydrides,6,10,16 but as is typical
with these distances, the error limits are high. The “(C5Me5)(C5-
9
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10.1021/ja065788l CCC: $33.50 © 2006 American Chemical Society

C O M M U N I C A T I O N S
Scheme 1
To claim the existence of a new (C5Me5)3M complex, crystal-
lographic data are generally required.13-15,19 Hence, more data are
desirable to support the explanation invoking “(C5Me5)3Lu” as an
intermediate. However, the following experiments support the
assignment of 4 as (C5Me5)3Lu. In analogy to eq 1, addition of
TMF to 1 in benzene and toluene generates the metalated products,
[(C5Me5)2LuPh]x and [(C5Me5)2Lu(CH2Ph)]x much faster than 1
alone. Attempts to trap (C5Me5)3Lu from the reaction of 1 with
TMF in methylcyclohexane at -78 °C gave a mixture of 2 and 3
analogous to room-temperature reaction, but a new singlet in the
1H NMR spectrum was observed at δ1.97 ppm that is close to the
resonances of the other diamagnetic La22 and Y15 (C5Me5)3Ln
complexes. The addition of TMF to this NMR sample caused the
1.97 ppm signal to disappear and the amount of 2 to increase.
In summary, these results suggest that even with the smallest
lanthanide, Lu, the reactivity of (C5Me5)3Lu complexes is accessible.
The C-H bond activation of TMF to make 2 by this route
demonstrates that new and selective C-H bond activation pathways
are still accessible with the proper combination of metal and ligand.
If (C5Me5)3Lu is indeed the species that is catalytically hydrogenat-
ing TMF, this suggests it could be effective in selective catalytic
hydrogenation of double bonds with different steric demands in a
system with multiple unsaturation.
Scheme 2
Me4CH2)Lu” fragment of 3 has previously been invoked as a “tuck-
in” intermediate in lutetium-based C-H bond activation chemistry
arising from [(C5Me5)2LuMe]x.1,3,4
Acknowledgment. We thank the Chemical Sciences, Geo-
sciences, and Biosciences Division of the Office of Basic Energy
Sciences of the Department of Energy for support.
The formation of the “tuck-over” complex 3 from the hydride 1
and TMF is unusual in that C5Me5H and not H2 is the byproduct.
This suggests that 3 is formed by an undetected intermediate. This
is further supported by the fact that 2 and 3 do not interconvert or
react with each other and the tuckover complex 3 does not metalate
TMF to make 2. The fact that order of addition affects the product
ratio suggests that 2 and 3 are formed by competitive pathways.
These observations can be rationalized by assuming that the first
step in this C-H bond activation system is a reaction between 1
and TMF that is analogous to eq 2. This would make, as a transient
intermediate, a tris(pentamethylcyclopentadienyl) complex of com-
position “(C10H15)3Lu,” 4, Scheme 1. This complex could adopt
an (η5-C5Me5)3Lu structure like its yttrium analog,15 or two possible
alkyl structures (η5-C5Me5)2Lu(η1-C5Me5) or (η5-C5Me5)2Lu(CH2-
CHC4Me4), depending on the nature of the Lu-H addition. As soon
as 4 is formed, it could then metalate the abundant TMF present to
make 2. Activation of the vinyl C-H bond could be explained
because it is the most sterically accessible if 4 is very crowded. If
the order of addition is reversed and TMF is added to 1, the intially
formed 4 could also activate a methyl C-H bond of the excess
[(C5Me5)2LuH]x initially present to make the (C5Me4CH2)2- ion in
3.
Supporting Information Available: Synthetic, spectroscopic, and
X-ray diffraction details (PDF, CIF). This material is available free of
charge via the Internet at http://pubs.acs.org.
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