Early-late heterobimetallic complexes with a Ta-Ir multiple bond: Bimetallic oxidative additions of C-H, N-H, and O-H bonds

Article abstract of DOI:10.1021/om300429u

A heterobinuclear transition metal complex with a Ta-Ir multiple bond, Cp*(Me₃SiCH₂)₂Ta-IrCp*(H) ₂ (1), was synthesized using a salt elimination reaction. The isolable complex was characterized by NMR, IR, UV-vis spectroscopy, and X-ray crystallography. Compound 1 features an exceptionally short intermetallic distance (Ta-Ir 2.4457(3) A). DFT calculation for 1 revealed the presence of a highly covalent bonding nature in spite of the involvement of such disparate d elements. Oxidative additions of C-H, N-H, and O-H bonds to 1 were also investigated.

Full text of DOI:10.1021/om300429u

Communication
pubs.acs.org/Organometallics
Early−Late Heterobimetallic Complexes with a Ta−Ir Multiple Bond:
Bimetallic Oxidative Additions of C−H, N−H, and O−H Bonds
Masataka Oishi,† Masashi Kino,† Masayuki Saso,† Masato Oshima,‡ and Hiroharu Suzuki*,†
†Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro-ku, Tokyo 152-8552,
Japan
‡School of Engineering, Tokyo Polytechnic University, 1583 Iiyama, Atsugi-shi, Kanagawa 243-0297, Japan
S
* Supporting Information
ABSTRACT: A heterobinuclear transition metal complex
with a Ta−Ir multiple bond, Cp*(Me3SiCH2)2Ta−IrCp*(H)2
(1), was synthesized using a salt elimination reaction. The
isolable complex was characterized by NMR, IR, UV−vis
spectroscopy, and X-ray crystallography. Compound 1 features
an exceptionally short intermetallic distance (Ta−Ir 2.4457(3)
Å). DFT calculation for 1 revealed the presence of a highly
covalent bonding nature in spite of the involvement of such
disparate d elements. Oxidative additions of C−H, N−H, and O−H bonds to 1 were also investigated.
tudies of the electronic structures and properties of metal−
equimolar amount of powdery Li[Cp*IrH3] at 25 °C. The
resulting slurry was then stirred for 15 h. After workup, a crude
product was obtained as a brown solid (ca. 90% yield),8 which
was purified by recrystallization from pentane at −30 °C, giving
reddish-brown crystals of [{Cp*Ta(CH2SiMe3)2}(Cp*IrH2)]
(1) (Scheme 1).
S
metal bonds are of particular importance in fundamental
chemistry.1 Among a number of directly metal−metal-bonded
complexes, early−late heterobimetallic compounds have
attracted considerable attention with regard to synergetic
effects in their reactivity.2 Much effort has also been devoted
to studying higher bond orders (especially, higher than triple
bonds) of homobinuclear complexes such as K2[Re2Cl8]·H2O3
and [ArCrCrAr] (Ar = C6H3-2,6(C6H3-2,6-iPr2)2),4 but there
are still few studies of heterobinuclear analogues, and such
studies are limited to direct bonds between transition metals
close to each other in the d block2b,d or complexes stabilized
using rigid hard−soft spectator ligand linkages.5,6 An example
of the latter case is the report by Wolczanski’s group on the
heterobimetallic complex [Ti(μ:η1,η1-OCMe2CH2PPh2)3Rh],
which possesses a cylindrically symmetric triple bond that is
suggested to arise from one Ti(dσ)−Rh(dσ) and two dative
Rh(dπ)→Ti(d/pπ) interactions.5b Very recently, Thomas and
co-workers investigated [ClZr(μ:η1,η1-NR′PR2)3CoI] and its
application in redox chemistry and catalysis.6b,c
We have previously reported that [(L2ZrPh)(Cp*Ir)(μ-H)3]
(L  Cp derivative) enables aromatic C−H(D) activation.7
Reversible ligand exchange is thought to proceed through a
transient Zr−Ir-bonded intermediate [(L2Zr)(Cp*IrH2)],
which ultimately results in dimerization to
[(L2Zr)2(Cp*Ir)2(μ3−H)4] as stable and isolable complexes.
However, isolation and characterization of such highly reactive
intermediates with interactions between vastly different metal
centers have not been successful. Here we describe the
synthesis of a multiply bonded Ta−Ir complex and bimetallic
oxidative addition of C−H(D), N−H, and O−H bonds.
In a glovebox, to a toluene solution of [Cp*Ta(Cl)-
(CH2SiMe3)(CHSiMe3)], which was prepared from a 1:3
mixture of [Cp*TaCl4] and LiCH2SiMe3, was added an
Scheme 1. Synthesis of 1
Structure of diamagnetic 1 was identified by both spectros-
1
copy and crystallography. The H NMR spectrum in C6D6
solvent shows the characteristic upfield resonance of Ir-bound
hydride at δ = −9.68 ppm as well as signals for other
hydrocarbyl ligands in typical chemical shift region. The spin−
lattice relaxation time (T1) for the Ir−H resonance in 1 (T1 min
= 0.30 s) suggests that 1 is a classical hydrido complex.
Furthermore, the IR spectrum of 1 shows a distinct absorption
at 2154 cm−1, which is assignable to the terminal Ir−H
stretching vibration.9
As seen in Figure 1, single-crystal X-ray analysis of 1 shows a
three-legged piano stool geometry for both Ta and Ir centers.
The intermetallic distance (2.4457(3) Å)10 is exceptionally
short in comparison to those in other known complexes with a
Ta−Ir single bond, e.g., [(indenyl)(Cp)Ta(μ-CH2)2Ir(CO)2]
(2.858(1) Å),11a,b [Cp2Ta(μ-CH2)2Ir(CO)2(PEt3)] (2.881(1)
Received: May 18, 2012
© XXXX American Chemical Society
A
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Communication
between the two metal atomic orbitals but also antibonding
interactions between the Ir orbital and p-orbitals of the three
Cp*-ring carbon atoms. The former bonding interaction might
reflect less restricted Ta−Ir bond rotation, as suggested by the
variable temperature NMR result.
The NBO orbital can account for the metal orbital
contributions in more detail (Ta: 37%, Ir: 63%), and Ta has
a higher d character in the hybridized orbital than does Ir (Ta:
sd6.47, Ir: sd2). The UV−vis spectra of 1 have an absorption
band as a shoulder in the visible-light region (λmax = 503 nm, ε
= 729 mol−1 L cm−1), which is obviously of much smaller
energy than the ground state HOMO−LUMO gap of
optimized-1 (3.74 eV). A time-dependent DFT calculation on
1 was therefore carried out, and the HOMO−LUMO transition
was found to be the major component (90.4%) of the least
energetic excitement (2.85 eV, i.e. 436 nm) with an oscillator
strength (f) = 0.0137. This estimation has better consistency
with the experimental data.
It is intriguing to explore the reactivities of M−M′ multiple
bonds. Complex 1 is air- and moisture-sensitive and reacts
readily with excess H2O,14 affording the oxo complex
[{Cp*Ta(O)(CH2SiMe3)}(Cp*Ir)(μ-H)3] (2).15 The terminal
Ta oxo structure was confirmed by NMR, X-ray, and IR
analyses.16−18 Treatment of 1 with D2O yielded a mixture of
isotopomers [{Cp*Ta(O)(CH2SiMe3)}(Cp*Ir)(μ-D)n(μ-
H)3−n] (2-dn) in a ratio of d0/d1/d2/d3 = 6:26:63:4 (∼55%
total D incorporation) and Me3SiCH2.7D0.3. The ratio was
independent of both the reaction time and the amount of D2O
employed. It therefore seems reasonable to suggest that the
formation of 2 does not proceed simply via σ-bond metathesis
on the Ta side alone but involves initial bimetallic oxidative
addition of H2O into the Ta−Ir double bond, followed by
reductive elimination of Me4Si from an intermediate, i.e.,
[{Cp*Ta(OH)(CH2SiMe3)2}(Cp*Ir)(μ-H)3].15a
Figure 1. X-ray structure of 1 (hydrogen atoms except for IrH are
omitted for clarity; thermal ellipsoids are drawn at 50% probability
level). Selected bond distances (Å) and angles (deg): Ta1−Ir1
2.4457(3), Ta1−C11 2.194(5), Ta1−C15 2.173(5), Ta1−Ir1−Cp*-
(cent) 163.7, C11−Ta1−C15 103.2(2), Cp*(cent)−Ta1−Ir1−Cp*-
(cent) 71.0.
Å),11b and [Cp2Ta(μ-CH2)2Ir(Cp*)(H)] (2.776(1) Å).11c The
bitetrahedral Ta and Ir centers in 1 are twisted with respect to
each other (torsion angle Cp*(cent)−Ta1−Ir1− Cp*(cent) =
71.0°). Although this solid-state structure shows the two alkyl
groups on the Ta and the two hydride ligands as nonequivalent,
1
variable temperature H NMR measurements at 163−298 K
indicated that each ligand set is equivalent in solution, implying
a weak secondary Ta−Ir bonding interaction.
We performed a DFT calculation at the B3LYP level on the
geometrical and electronic structures of 1. The DFT-optimized
structure of 1 has good agreement with the experimental data,
especially in terms of the Ta−Ir distance (2.4303 Å), Ta−Ir−
Cp*(cent) angle (158.3°), and Cp*(cent)−Ta−Ir−Cp*(cent)
torsion angle (75.2°). According to the calculated M−H and
H−H distances (Ta−H = 2.21, 2.47 Å; Ir−H = 1.62, 1.63 Å,
H−H = 2.23 Å), 1 can best be described as having a terminal
dihydride structure.12 NBO analysis indicated a positively
charged Ta center (natural charge = +1.273) but a less
polarized Ta−Ir bonding interaction [Cp*Ta(CH2SiMe3)2
fragment = +0.254, Cp*IrH2 fragment = −0.254]. In addition,
the Wiberg index, Ta−Ir = 1.210, is decisive evidence of a
relatively high covalent bonding interaction between Ta and Ir
although it is still less than that for a formal covalent double
bond.13 Molecular orbitals 130 (HOMO) and 121 (HOMO-9)
are depicted in Figure 2. The energetically low-lying HOMO-9
explicitly represents the Ta(dσ)−Ir(dσ) bonding interaction,
while the HOMO includes not only an indistinct π-interaction
With the above finding in hand, we investigated the oxidative
addition of various substrates to complex 1. Thermolysis of 1 in
C6D6 solvent at 60−80 °C was reluctant to eliminate or
exchange the hydrocarbyl ligands but slowly promoted H/D
exchange of the methylene and methyl protons of the
Me3SiCH2 group as well as of Ir-bound hydrides with C6D6
(80 °C, 24 h; D incorporations into IrH2, TaCH2, and SiMe3
were 25%, 33%, and <4%, respectively). As shown in Scheme 2
Scheme 2. Formation of 1-dn and 3 through Possible
Oxidative Addition Intermediate A
Figure 2. Depictions of the molecular orbitals 130 (HOMO) and 121
(HOMO-9) of DFT-optimized 1 (left) and schematic metal atomic
orbital interactions (right).
B
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Communication
(top), this observation would imply occurrence of inter- and
intramolecular C−H(D) cleavages via oxidative addition
followed by α-elimination (A → B) and successive deuteride
shifts to the alkylidene α-carbon. The related intramolecular
exchange between the bridging CH2 proton and Ir-bound D in
[Cp2Ta(μ-CH2)2Ir(Cp*)(D)] has been reported.11c In an
attempted preparation of [{Cp*Ta(CH2SiMe3)(CHDSiMe3)}-
(Cp*IrD2)] (1-d3) using Li[Cp*IrD3] (>99% D-enriched),
faster intramolecular H/D exchange took place at 25 °C,
resulting in lower D incorporation on the Ir and higher D
incorporation into Ta methylene moieties than would be
expected based on the starting materials. On the other hand,
exposure of 1 to 1 atm of H2 caused elimination of Me4Si (2
equiv), leading to clean formation of a tetranuclear complex
[(Cp*TaH)2(Cp*IrH)2] (3) (>99% NMR yield, 62% isolated
yield), presumably through intermediates A and C (bottom of
Scheme 2).19,20
In other words, intramolecular bimetallic oxidative addition and
reductive elimination of the N−H bond take place in the Ta−Ir
system.
Bimetallic oxidative additions of alcohols to [{Ti(NMe2)3}-
{CpRu(CO)2}] and [(Cp2Zr)(Cp*Ir)(μ-NtBu)] have been
reported.24,25 The entire regioselective scission of the Mearly
−
t
Mlate direct bond to MearlyOR (R = Bu, aryl) and MlateH is
apparently the result of the high oxophilicity of group IV metals
and basicities of the d-electron-rich late metals. The attempted
i
alcoholysis of 1 with MeOH and PrOH (excess) disappoint-
ingly brought about disruption of the Ta−Ir bimetallic
t
Activation of the ammonia N−H bond is challenging because
the presence of the nitrogen lone pair usually enables facile
formation of Lewis acid−base adducts for the majority of
transition metal complexes, and the N−H bond has a relatively
structure, whereas BuOH reacted with 1 at 25 °C in the
presence of H2 (1 atm), giving rise to a monoalkoxide
[{Cp*Ta(OtBu)(CH2SiMe3)}(Cp*IrH2)] (6) and unreacted
tBuOH, leaving the Ta−Ir bond intact (Ta−Ir = 2.450(1) Å).
Unlike the reaction of 1 with amines and the bulky alcohol,
reaction with 2 equiv of a phenol does not necessarily require
H2, leading to selective formation of [{Cp*Ta(OR)2}-
(Cp*IrH2)] (7) (Scheme 4). The Ta−Ir distance in the
solid-state structure of 7b still shows the presence of a direct
Ta−Ir bond (Ta−Ir (av) = 2.456 Å).
high bond dissociation energy (108.2
0.3 kcal mol−1).21,22
We therefore examined reactions between 1 and primary
amines as well as ammonia. These results are summarized in
Scheme 3. The reactions with the primary amines were greatly
Scheme 3. NMR-Scale Reaction of 1 with Ammines
Scheme 4. NMR-Scale Reaction of 1 with Phenols
The mechanism of hydrocarbyl/aryloxy ligand exchange was
preliminarily studied by a labeling experiment using 1 and
4-tBuC6H4OD (∼2 equiv), resulting in 55% D incorporation
into the Ir hydride moiety of 7a-dn (91% conversion of 1, 86%
yield of 7a-dn: d0/d1/d2 = 24:42:34). This observation rules out
a mechanism via σ-bond metathesis on the Ta center only, but
reasonably supports occurrence of oxidative addition/reductive
elimination sequences.26 More importantly, oxidative addition
of a third equivalent of a phenol to the Ta−Ir bond in 7
proceeded to afford triaryloxides [{Cp*Ta(OR)3}(Cp*Ir)(μ-
H)3] (8). Furthermore, treatment of 8a with Me3SiCH2Li or
KN(TMS)2 as a base smoothly regenerated 7a in 70% and 85%
yields, respectively. Therefore, thanks to the multiple
interactions, the Ta−Ir species appeared to be stable during
the course of the oxidative addition and reductive eliminations
of phenols.
In summary, we have demonstrated that the new hydride 1
with a direct multiple bond between Ta and Ir can be formed
via the salt elimination route. In oxidative addition reactions,
the bonding nature of the Ta−Ir system was found to alter,
depending, in principle, on the facility of the early metal−ligand
multiple bonds, i.e., H2O and primary amines prefer oxo and
imide trihydride structures with no direct metal−metal covalent
bond [formal shortness ratio (FSR) = 1.022 (2) and 1.025−
1.033 (4)], whereas two hydrocarbyl or alkoxy ligands on the
Ta preserve multiple bonds between disparate d elements (1, 6,
accelerated upon addition of H2 (1 atm) under mild conditions,
yielding yellow imido complexes 4a−d, whose structures were
identified using NMR and X-ray analyses. As shown in Figure
S4 (Supporting Information) (R  C6H4-4-Br), the preferred
imido structure of 4d, with sp2 → sp hybridization of a π-
donating nitrogen, features Ta(V) Lewis acid, even with an
electron-deficient substituent (Ta−N (av) = 1.808 Å, Ta−N−
C(Aripso) (av) = 165.7°).23 When excess ammonia was reacted
with 1 in the presence of H2, imide 4e and amide 5e were
formed. The structure of 5e was identified on the basis of the
similarity of the NMR and IR spectral data to those of 1 (see
Supporting Information). 4e and 5e are analogous to structures
B and C (Scheme 1), respectively.
To demonstrate equilibrium between 4e and 5e, we carried
out a spin-saturation transfer (SST) experiment. Although the
ratio of [5e]/[4e] did not greatly change in the temperature
range 298−353 K ([5e]/[4e] = 0.97
0.07), irradiation of
hydride resonance of 4e (δ = −13.18 ppm) at 353 K
substantially decreased the hydride integration of 5e (47%
decrease at δ = −10.85 ppm). The observed SST process
unequivocally indicates hydride-assisted interconversion be-
tween Ta−N and Ta−Ir multiple bonds, as described by eq 1.
C
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comparison, see Burckhardt, U.; Casty, G. L.; Tilley, T. D.; Woo, T.
K.; Rothlisberger, U. Organometallics 2000, 19, 3830.
(13) Theoretical estimation of bond orders between early and late
transition elements usually gives smaller values than expected, most
probably because of the significant contribution of their ionic
character. See ref 2b.
and 7). Furthermore, the present Ta−Ir system gave reversible
reactions of 7 and phenols without extensive decomposition of
the bimetallic complex. Applications of these fundamental but
unique M−M′−ligand conjugations and bimetallic oxidative
additions of protic substrates are currently under investigation.
(14) A recent review on oxidative addition of H2O to transition metal
complexes: Ozerov, O. V. Chem. Soc. Rev. 2009, 38, 83.
(15) (a) Parkin, G.; van Asselt, A.; Leahy, D. J.; Whinnery, L.; Hua,
N. G.; Quan, R. W.; Henling, L. M.; Schaefer, W. P.; Santarsiero, B. D.;
Bercaw, J. E. Inorg. Chem. 1992, 31, 82. (b) Gouzyr, A. I.; Wessel, H.;
ASSOCIATED CONTENT
■
S
* Supporting Information
Experimental and computational details of new complexes as
well as X-ray crystallographic files (CIF) for [Cp*Ta(Cl)-
(CH2SiMe3)(CHSiMe3)], 1−3, 4a, 4c, 4d, 6, and 7b. This
material is available free of charge via the Internet at http://
pubs.acs.org.
Barnes, C. E.; Roesky, H. W.; Teichert, M.; Uson
́
, I. Inorg. Chem. 1997,
36, 3392.
(16) The mean Ta−Ir distance of 2 (2.665 Å) from X-ray analysis is
considered to result from a typical three-centered two-electron (3c−
2e) bonding interaction among Ta, H, and Ir atoms.
AUTHOR INFORMATION
(17) The observed TaO distance in 2 (1.748(11) Å) is in the
range reported for the terminal TaO length (1.73−1.76 Å) with the
́
ez, M.;
■
Corresponding Author
*E-mail: hiroharu@o.cc.titech.ac.jp.
Notes
exception of ref 15a [Cp*2Ta(O)H] (1.69 Å). (a) Gom
́ ́ ́
Gomez-Sal, P.; Jimenez, G.; Martín, A.; Royo, P.; Sanchez-Nieves, J.
Organometallics 1996, 15, 3579. (b) Amini, M. M.; Tamizkar, T.;
Mirzaee, M.; Ng, S. W. Acta Crystallogr., Sect. E: Struct. Rep. Online
2005, E61, m1053. (c) Mullins, S. M.; Bergman, R. G.; Arnold, J.
Organometallics 1999, 18, 4465.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
(18) IR of complex 2 (KBr): ν(TaO) 888 cm−1. The typical Ta
O stretching vibration appears at 850−1000 cm−1 . Nugent, W. A.;
Mayer, J. M. Metal−Ligand Multiple Bonds; Wiley: New York, 1988.
(19) We have not been able to isolate any complex of type C, but our
1H NMR monitoring of the reaction of 1 to 3 in C6D6 solvent
suggested the presence of intermediate D (up to 7% yield) rather than
structure C. Assigned characteristic 1H NMR chemical shifts of D
(benzene-d6): δ 2.33 (15H, s, C5Me5), 1.68 (15H, s, C5Me5), −12.41
(3H, s, μ-H).
■
We thank the Japan Society for the Promotion of Science for
supporting this research through a Grant-in-Aid for Scientific
Research (S) (grant no. 18105002).
REFERENCES
■
(1) Cotton, F. A.; Murillo, L. A.; Walton, R. A. Multiple Bonds
Between Metal Atoms, 3rd ed.; Springer: New York, 2005.
(2) (a) Stephan, D. W. Coord. Chem. Rev. 1989, 95, 41. (b) Wheatley,
N.; Kalck, P. Chem. Rev. 1999, 99, 3379. (c) Gade, L. H. Angew. Chem.,
Int. Ed. 2000, 39, 2658. (d) Collman, J. P.; Boulatov, R. Angew. Chem.,
Int. Ed. 2002, 41, 3949.
(3) Cotton, F. A.; Curtis, N. F.; Harris, C. B.; Johnson, B. F. G.;
Lippard, S. J.; Mague, J. T.; Robinson, W. R.; Wood, J. S. Science 1964,
145, 1305.
(4) (a) Nguyen, T.; Sutton, A. D.; Brynda, M.; Fettinger, J. C.; Long,
G. J.; Power, P. P. Science 2005, 310, 844. (b) Kreisel, K. A.; Yap, G. P.
A.; Dmitrenko, O.; Landis, C. R.; Theopold, K. H. J. Am. Chem. Soc.
2007, 129, 14162. (c) Gagliardi, L.; Roos, B. O. Nature 2005, 433, 848.
(d) Nippe, M.; Goodman, S. M.; Fry, C. G.; Berry, J. F. J. Am. Chem.
Soc. 2011, 133, 2856.
(20) For characterization of 3 see Supporting Information and CIF
data. The Ta−Ir bonding nature will be discussed in due course.
(21) Luo, Y.-R.. Handbook of Bond Dissociation Energies in Organic
Compounds; CRC Press: Boca Raton, FL, 2003.
(22) Early metal-based NH3 activations (a) Ref 15a. (b) Freundlich,
J. S.; Schrock, R. R.; Davis, W. M. J. Am. Chem. Soc. 1996, 118, 3643.
(c) Aguado-Ullate, S.; Carbo, J. J.; Gonzalez-del Moral, O.; Martín, A.;
́ ́
Mena, M.; Poblet, J.-M.; Santammaría, C. Inorg. Chem. 2011, 50, 6269
and references cited therein..
(23) The Ta−N distance and Ta−N−C(Aripso) angle in 4 vary
slightly, depending on the nitrogen substituent. See CIF data in the
Supporting Information.
(24) General oxidative addition of alcohol and phenol O−H groups
to transition metal complexes (a) Sponsler, M. B.; Weiller, B. H.;
Stoutland, P. O.; Bergman, R. G. J. Am. Chem. Soc. 1989, 111, 6841.
(b) Ladio, F. T.; Kooti, M.; Merola, J. S. Inorg. Chem. 1993, 32, 1681.
(c) Blum, O.; Milstein, D. Angew. Chem., Int. Ed. Engl. 1995, 34, 229.
(d) Tani, K.; Iseki, A.; Yamagata, T. Angew. Chem., Int. Ed. 1998, 34,
3381. (e) Blum, O.; Milstein, D. J. Am. Chem. Soc. 2002, 124, 11456.
(f) Dorta, R.; Rozenberg, H.; Shimon, L. J. W.; Milstein, D. Eur. J.
Chem. 2003, 9, 5237. (g) Monaghan, P. K.; Puddephatt, R. J.
Organometallics 1984, 3, 444. (h) Grotjahn, D. B.; Gong, Y.;
DiPasquale, A. G.; Zakharov, L. N.; Rheingold, A. L. Organometallics
2006, 25, 5693. (i) Werner, H.; Michenfelder, A.; Schulz, M. Angew.
Chem., Int. Ed. Engl. 1991, 30, 596. (j) Weihong, S. L.; Wayland, B. B.
Chem. Commun. 2007, 4024.
(25) (a) Sartain, W. J.; Selegue, J. P. J. Am. Chem. Soc. 1985, 107,
5818. (b) Baranger, A. M.; Bergman, R. G. J. Am. Chem. Soc. 1994,
116, 3822.
(26) Estimated D incorporation into Ir hydride moiety of 7a for the
two mechanisms: 0% (via σ-bond metathesis) and 56% (via oxidative
addition/reductive elimination when KIE is unity).
́ ́
(5) (a) Ferguson, G. S.; Wolczanski, P. T.; Parkanyi, L.; Zonnevylle,
M. C. Organometallics 1988, 7, 1967. (b) Slaughter, L. M.; Wolczanski,
P. T. Chem. Commun. 1997, 2109.
(6) (a) Greenwood, B. P.; Forman, S. I.; Rowe, G. T.; Chen, C. -H.;
Foxman, B. M.; Thomas, C. M. Inorg. Chem. 2009, 48, 6251.
(b) Greenwood, B. P.; Rowe, G. T.; Chen, C. -H.; Foxman, B. M.;
Thomas, C. M. J. Am. Chem. Soc. 2010, 132, 44. (c) Zhou, W.;
Napoline, J. W.; Thomas, C. M. Eur. J. Inorg. Chem. 2011, 13, 2029.
(7) Oishi, M.; Suzuki, H. Inorg. Chem. 2009, 48, 2349.
(8) An NMR-scale reaction was carried out in C6D6 solvent under
identical conditions, yielding 1 quantitatively.
(9) [Cp*IrH4]: ν(Ir−H) (KBr) at 2150 cm−1. Gilbert, T. M.;
Bergman, R. G. Organometallics 1983, 2, 1458.
(10) The formal shortness ratio (FSR) of complex 1 is estimated to
be 0.938 [= 2.446 Å/(1.343 Å + 1.265 Å)] (a) Ref 1. (b) Pauling, L.
The Nature of the Chemical Bond, 3rd ed.; Cornell University Press:
Ithaca, 1960.
(11) (a) Hostetler, M. J.; Bergman, R. G. J. Am. Chem. Soc. 1990, 112,
8621. (b) Hostetler, M. J.; Butts, M. D.; Bergman, R. G. Inorg. Chim.
Acta 1992, 198, 377. (c) Butts, M. D.; Bergman, R. G. Organometallics
1994, 13, 2668.
(12) In spite of the low accuracies of the bridging Ta−H distances of
known bimetallic complexes (X-ray analysis), the calculated value, >2.2
Å, is too long for the bridging mode. For an experimental/theoretical
D
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