Cooperative bond activation and catalytic reduction of carbon dioxide at a group 13 metal center

Article abstract of DOI:10.1002/anie.201500570

A single-component ambiphilic system capable of the cooperative activation of protic, hydridic and apolar H-X bonds across a Group 13 metal/activated β-diketiminato (Nacnac) ligand framework is reported. The hydride complex derived from the activation of H₂ is shown to be a competent catalyst for the highly selective reduction of CO₂ to a methanol derivative. To our knowledge, this process represents the first example of a reduction process of this type catalyzed by a molecular gallium complex. A single-component ambiphilic Group 13 system has been developed, capable of the cooperative activation of protic, hydridic, and apolar H-X bonds. The hydride complex derived from the activation of H₂ catalyzes the selective transformation of CO₂ to a methanol derivative, representing the first example of such a reduction process catalyzed by a molecular gallium complex.

Full text of DOI:10.1002/anie.201500570

Angewandte
Chemie
DOI: 10.1002/anie.201500570
Group 13 Metal Catalysis
Hot Paper
Cooperative Bond Activation and Catalytic Reduction of Carbon
Dioxide at a Group 13 Metal Center**
Joseph A. B. Abdalla, Ian M. Riddlestone, Rꢀmi Tirfoin, and Simon Aldridge*
Abstract: A single-component ambiphilic system capable of
À
the cooperative activation of protic, hydridic and apolar H X
bonds across a Group 13 metal/activated b-diketiminato
(Nacnac) ligand framework is reported. The hydride complex
derived from the activation of H2 is shown to be a competent
catalyst for the highly selective reduction of CO2 to a methanol
derivative. To our knowledge, this process represents the first
example of a reduction process of this type catalyzed by
À
Scheme 1. Cooperative H X bond activation using target ambiphilic
systems I (M=group 13 metal).
a molecular gallium complex.
À
H
X bond activation processes represent key mechanistic
steps in numerous catalytic reactions of critical industrial
importance.[1] Classically such activation is brought about by
oxidative addition utilizing the readily accessible n/n + 2
redox states of “noble” transition metals.[1] Recently however,
economic and environmental imperatives have driven the
development of alternative catalyst systems, including
a number based on cooperative metal–ligand activation
processes.[2–4] The implication of metal centers in a single
fixed oxidation state, for example in the pincer systems of
Milstein,[4] suggests that such bond activation processes might
also be viable using complexes of the lighter main group
metals.
The deprotonation of an aluminium-bound Nacnac ligand
at the backbone methyl position has previously been accom-
plished by the use of an amide base in THF.[8] The use of
a donor solvent, however, necessarily generates a tetra-
coordinate, base-stabilized metal center. In order to circum-
vent this problem we envisaged carrying out deprotonation in
more weakly coordinating media. However, in either diethyl
ether or benzene the reactions of the dichloroaluminum and
-gallium systems [(Dipp2Nacnac)MCl2] (1: M = Al; 2: M =
Ga)[10] with lithium or potassium alkyls exclusively generate
1
“ate” complexes (Scheme 2). H and 13C NMR data for the
products 5a/b and 6 reveal the characteristic patterns of the
A key feature of many complexes capable of such
deprotonated diene (Nacnac’) backbone,[6–9] but X-ray crys-
À
cooperative H X bond activation is the availability of
a ligand site with appreciable Lewis basicity.[4] As such, H
À
X cleavage takes place by ligand (re)protonation, with the
formally anionic XÀ component sequestered by the metal
center. b-Diketiminato (“Nacnac”) ligand systems have
proved to be highly effective in the stabilization of a range
of low-valent/low-coordinate main group metal centers.[5]
Moreover, the backbone methyl groups of such ligands are
amenable to deprotonation, thereby generating a pendant
alkene function (with appreciable nucleophilic character at
the terminal carbon), and converting the monoanionic imino-
amide ligand into a dianionic diamide.[6–9] With this in mind,
we wondered if such a backbone activated system might be
partnered with a Lewis acidic three-coordinate Group 13
center to generate an ambiphilic system (e.g. I, Scheme 1)
À
capable of the cooperative activation of H X bonds.
Scheme 2. Reactions of b-diketiminato (Nacnac)-stabilized aluminium
and gallium halides with strong Brønsted bases: formation of “ate”
complexes and halide-free systems. Key reagents and conditions:
i) (for 5a) tBuLi (1.5 equiv), Et2O, À788C to RT, 12 h 39%, (for 5b, 6)
K[CH(SiMe3)2] (1.1 equiv), benzene, RT, 12 h, then 18-crown-6, 87%
(for 5b), 46% (for 6); ii) K[CH(SiMe3)2] (1.3 equiv), benzene, 30 min,
RT, >95% conversion by NMR (the 10% isolated yield of 8b reflects
very high solubility in hydrocarbon media); iii) K[CH(SiMe3)2]
(1.5 equiv), benzene, 30 min, RT, 45%.
[*] J. A. B. Abdalla, Dr. I. M. Riddlestone, R. Tirfoin, Prof. S. Aldridge
Inorganic Chemistry Laboratory, Department of Chemistry
University of Oxford, South Parks Road, Oxford, OX1 3QR (UK)
E-mail: Simon.Aldridge@chem.ox.ac.uk
[**] EPSRC (studentship: J.A.B.A.; NMSF, Swansea University; EP/
L025000/1 and EP/K014714/1).
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201500570.
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Figure 1. Molecular structures of 6 (left) and 7 (right) determined by
X-ray crystallography. Most H atoms omitted, and selected C atoms
shown in wireframe format for clarity; thermal ellipsoids at 50%
probability level. Key bond lengths [ꢀ] and angles [8]: (for 6) Ga(1)–
N(4) 1.874(3), Ga(1)–N(18) 1.871(3), Ga(1)–Cl(2) 2.198(1), Ga(1)–
Cl(3) 2.210(1), Cl(2)–K(33) 3.285(1), Cl(3)–K(33) 3.425(1); (for 7)
Al(3)–N(4) 1.869(3), Al(3)–N(8) 1.856(3), Al(3)–Cl(2) 2.292(1), K(1)–
Cl(2) 3.160(2), K(1’)–Cl(2) 3.292(1).
Figure 2. Molecular structure of 8b determined by X-ray crystallogra-
phy. Most H atoms omitted, and selected C atoms shown in wireframe
format for clarity; thermal ellipsoids at 50% probability level. Key bond
lengths [ꢀ] and angles [8]: Ga(1)–N(2) 1.854(2), Ga(1)–N(6) 1.849(2),
Ga(1)–C(33) 1.988(2), N(2)–C(3) 1.397(3), N(6)–C(5) 1.409(3), C(3)–
C(4) 1.372(3), C(4)–C(5) 1.440(3), C(3)–C(20) 1.484(4), C(5)–C(19)
1.375(3); N(2)-Ga(1)-N(6) 104.5(1), N(2)-Ga(1)-C(33) 126.5(1), N(6)-
Ga(1)-C(33) 129.0(1). DFT calculated HOMO (left, À3.72 eV) and
LUMO (right, À1.59 eV) for 8a.
tallography shows that the alkali metal chloride is retained
even when a potassium base is used (Figure 1 and Supporting
Information). The Group 13 metal center therefore remains
À
4-coordinate, with minimal M Cl elongation, and with the
lithium/potassium cation bridging the two chloride substitu-
ents of the dichloroaluminate/gallate fragment.
=
À
ized C C double and C C single bonds across the Nacnac’
À
With this in mind, we hypothesized that replacement of
one of the aluminium/gallium-bound chlorides with a steri-
cally bulky, weakly bridging substituent (e.g. tBu) might
promote KCl loss. Accordingly, the reaction of
[(Dipp2Nacnac)Al(tBu)Cl] (3) with K[CH(SiMe3)2] was
investigated; the product so generated (after recrystallization
from toluene) also shows the desired backbone deprotona-
tion, but KCl is again retained within an overall dimeric
backbone. In addition, the C N [1.397(3), 1.409(3) ꢀ] and
À
Ga N contacts [1.849(2), 1.854(2) ꢀ] are consistent with
a diamido ligand description,[8] and the sum of the N-Ga-N
and N-Ga-C angles [360.0(3)8] confirms the presence of
a trigonal planar gallium center.
The fundamental basis for ambiphilic reactivity in 8a/8b
was probed by a combination of experimental and quantum
chemical studies. DFT calculations (Figure 2 and Supporting
Information) accurately reproduce the key geometric param-
eters and reveal a HOMO which has significant amplitude at
the terminal carbon of the exocyclic alkene function, and
a LUMO which is dominated by Ga 4pz character. Such
observations are also borne out experimentally: 8a reacts
with 4-(N,N-dimethylamino)pyridine (DMAP) through coor-
dination at gallium, and with B(C6F5)3 to give a zwitterionic
structure,
[{(Dipp2NacNac’)Al(tBu)ClK(toluene)}2]
(7,
Figure 1). 7 nonetheless features a markedly lengthened
À
Al Cl contact compared to 3 [2.292(1) ꢀ vs. 2.168(1) ꢀ], and
the less halophilic nature of gallium (vs. aluminum)[11]
suggested to us that similar chemistry might be successful
with gallium, especially if carried out in conjunction with
a weaker metal–halogen bond. Thus, the deprotonation of
[(Dipp2Nacnac)Ga(tBu)Br] (4a) with K[CH(SiMe3)2] was
1
investigated (Scheme 2). In this case, the H and 13C NMR
spectra are also consistent with backbone deprotonation [for
example, signals at dH = 1.52, 3.23/3.93 and 5.29 ppm, corre-
sponding to the CH3, two distinct alkene CH, and g-CH
protons, respectively],[8] but in contrast to 7, the pattern of
resonances for the Dipp groups (two methine septets, four
methyl doublets) is indicative of a plane of symmetry within
the molecule. While the oily nature of this compound (8a)
prevented definitive structural characterization, analogous
chemistry using the tert-amyl substituent (tAm, -CMe2Et)
allowed for crystallization of [(Dipp2Nacnac’)Ga(tAm)] (8b).
With the exception of the tAm/tBu signals, the 1H and
13C NMR spectra of 8a and 8b are essentially indistinguish-
able, and in the latter case the formation of a three-coordinate
gallium center could be confirmed crystallographically
(Figure 2).
Scheme 3. Reactivity of 8a towards external Lewis acids/bases. Key
reagents and conditions: i) DMAP (1.0 equiv), benzene, RT, 15 min,
66%; ii) B(C6F5)3 (1.0 equiv), benzene, RT, 1 h, 71%. Molecular struc-
tures of 9 (right) and 10 (left) determined by X-ray crystallography.
Most H atoms omitted, and selected C atoms shown in wireframe
format for clarity; thermal ellipsoids at 50% probability level.
The molecular structure of 8b features disparate endo-
À
cyclic [1.372(3), 1.440(3) ꢀ] and exocyclic C C distances
[1.375(3), 1.484(4) ꢀ], consistent with the presence of local-
2
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À
system featuring a borate-appended Nacnac ligand (Scheme 3
and Supporting Information). 8a therefore possesses both
Lewis basic and Lewis acidic character, and the fact that it
does not undergo intermolecular aggregation is attributed to
the high steric loading around the gallane center.
visible in the crystallographic difference Fourier map at a Ga
H distance of 1.44(3) ꢀ.
While the ready reactivity of 8a towards both acidic and
hydridic H X bonds can be rationalized on the basis of the
À
strongly polarized electron distribution in 8a, this system
remarkably also possesses the ability to heterolytically cleave
non-polar molecules such as dihydrogen. In this case, the
reaction requires more forcing conditions (12 h at 708C), but
the product so generated [(Dipp2Nacnac)Ga(tBu)H] (13;
Scheme 4) has been unambiguously characterized both spec-
troscopically and crystallographically, and synthesized inde-
pendently from 4a and K[BEt3H] (Supporting Information).
In the case of protic substrates such as ammonia, it can be
shown that pre-coordination at gallium, followed by inter-
molecular deprotonation is a feasible reaction pathway.[14,15]
In the case of H2, however, we hypothesized that concerted
activation was more likely: Sicilia and co-workers, for
example, have examined computationally the possibility for
Confirmation that this system might be regarded as single-
component frustrated Lewis pair,[12] led us to investigate its
À
À
reactivity towards a range of H X bonds. Thus, protic H X
bonds, such as those found in ammonia and hydrogen sulfide
are cleaved rapidly at room temperature,[13] leading to
protonation of the Nacnac’ backbone and to the assimilation
of the NH2 /SHÀ conjugate base at the gallium center
À
(Scheme 4 and Supporting Information). In each case,
À
direct 1,4-addition of an H X bond across a single (Nacnac’)E
molecule (E = Si, Ge).[16] Monitoring the conversion of 8a to
13 (and the corresponding reaction of 8a with D2) by in situ
1H NMR spectroscopy, however, reveals 1) the formation of
several long-lived intermediate species characterized by
Nacnac g-CH signals in the region dH = 4.89-5.27 ppm;
À
2) the appearance of a broad Ga H resonance at dH =
5.44 ppm showing similar concentration–time behavior.
These observations imply that a simple concerted bimolecular
process is unlikely, a finding in line with the crystallograph-
ically determined 1,4 Ga···C separation of ca. 4.14 ꢀ for 8b.[17]
By contrast, the observation of discrete GaH-containing
intermediates is not inconsistent with initial activation of H2
À
by 8a in 1,2 fashion across the Ga N bond(s), and computa-
À
À
tional evaluation of the regioisomeric Ga N/H H activation
products is energetically consistent with their potential
intermediacy in the 8a/H2 reaction.[18,19] Moreover, precedent
for 1,2-activation of H2 within a strongly Lewis acidic Group
13 heterocycle comes from the work of Piers and co-workers
on pentaarylboroles.[20]
À
Ga H bonds have previously been shown 1) to be capable
=
of inserting unsaturated substrates featuring C E multiple
Scheme 4. Differing regioselectivities in the activation of protic and
À
hydridic H X bonds by 8a. Key reagents and conditions: i) (for 11/12)
À
bonds, and 2) to be generated from Ga X bonds by meta-
excess NH3/H2S gas, benzene, RT, 30 min (decolorization in <2 min),
60–75%; (for 13) H2 (ca. 4 atm), benzene, 708C, 7 h, 54%; ii) SiH4
(1 atm), benzene, RT, 1 h, 62%. Molecular structures of 11 (upper), 13
(lower right) and 14 (lower left) determined by X-ray crystallography
(see Supporting Information for 12). Most H atoms omitted, and
selected C atoms shown in wireframe format for clarity; thermal
ellipsoids at 50% probability level.
thesis reactions utilizing silanes or boranes as the hydride
source.[21] Thus, we hypothesized that the catalytic reduction
=
of C O double bonds might be possible using either 8a or 13
as an entry point into an appropriate cycle. In particular, we
were interested in the catalytic reduction of CO2, since such
chemistry has little precedent among single-site main group
systems. In the event, although CO2 reacts with 8a to give an
intractable mixture of products, the corresponding reaction
regeneration of the b-diketiminato backbone is reflected in
with
13
cleanly
yields
the
formate
complex
a heterocycle geometry featuring equivalent internal C C
[(Dipp2Nacnac)Ga(tBu){k1-OC(O)H}] (15) which has been
characterized by standard spectroscopic and crystallographic
techniques (Scheme 5 and Supporting Information).[22] More-
over, 15 can be shown to react with pinacolborane (HBpin,
pin = OCMe2CMe2O) in benzene to yield 13 and MeOB-
pin.[23] Such observations imply that 13 could act as a catalyst
for the reduction of CO2 to MeOBpin using HBpin. Thus, in
benzene solution at 608C, (using excess CO2) complete
(highly selective) conversion of HBpin to MeOBpin (and
À
À
distances [1.400(1) ꢀ for 11], and C N bonds which are
shortened compared to the formal single bonds found in the
diamido Nacnac’ ligand in 8b [1.332(1) ꢀ for 11 cf. 1.397(3),
À
1.409(3) ꢀ]. Activation of hydridic H X bonds proceeds in
the opposite sense, with SiH4, for example, giving rise to
a backbone appended SiH3 moiety and a gallium bound
1
hydride (Scheme 4). The latter is signaled in the H NMR
spectrum of 14 by a broad resonance at dH = 5.43 ppm and is
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paper. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
Received: January 20, 2015
Published online: && &&, &&&&
Scheme 5. Stoichiometric uptake of CO2 by [(NacnacDipp)Ga(tBu)H]
(13). Key reagents and conditions: i) CO2 gas (ca. 1 atm), toluene, RT,
12 h, 66%. Molecular structure of 15 determined by X-ray crystallog-
raphy. Most H atoms omitted, and selected C atoms shown in
wireframe format for clarity; thermal ellipsoids set at the 50%
probability level.
Keywords: b-diketiminate · bond activation · carbon dioxide ·
cooperative reactivity · gallium
.
[1] See, for example: Organotransition Metal Chemistry: From
Bonding to Catalysis (Ed.: J. F. Hartwig), University Science
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[2] Main group systems in small-molecule activation: a) P. P. Power,
Nature 2010, 463, 171 – 177; b) D. Martin, M. Soleilhavoup, G.
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[3] See, for example: a) P. J. Chirik, K. Wieghardt, Science 2010, 327,
794 – 795. For approaches to hydrogenation using “non-pre-
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Chem. Soc. 2006, 128, 9628 – 9629; b) S. Yao, Y. Xiong, M. Driess,
Organometallics 2011, 30, 1748 – 1767.
Scheme 6. Reduction of CO2 to MeOBpin by HBpin catalyzed by
gallium hydride 13.
[8] a) S. P. Sarish, H. Roesky, M. John, A. Ringe, J. Magull, Chem.
Commun. 2009, 2390 – 2392; b) S. P. Sarish, B. Nekoueishahraki,
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[11] The Group 13 Metals Aluminium, Gallium, Indium and Thal-
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Downs), Wiley, Chichester, 2011.
pinBOBpin) occurs over 4 h at 10 mol% loading (Scheme 6).
Catalytic reduction of CO2 in this fashion by non-transition
metal systems is very rare,[24] with previous examples of
single-site main group metal catalysts requiring the use of
a strong Lewis acid co-catalyst. The activity of 13 can thus be
compared to B(C6F5)3-activated magnesium and calcium
hydride systems reported by Hill and co-workers (complete
conversion over 6 d (Mg) or 4 d (Ca) at 608C using 10 mol%
loading).[24h] The derived turnover frequencies (2.5 vs. 0.07/
0.1 hÀ1) therefore imply that 13 is 1–2 orders of magnitude
more active for this selective reduction process.
[12] D. W. Stephan, G. Erker, Angew. Chem. Int. Ed. 2010, 49, 46 – 76;
Angew. Chem. 2010, 122, 50 – 81.
[13] Previous examples of 1,4-activation of ammonia and hydrogen
sulfide by Group 14 Nacnac’ systems: a) A. Jana, I. Objartel,
H. W. Roesky, D. Stalke, Inorg. Chem. 2009, 48, 798 – 800; b) A.
Meltzer, S. Inoue, C. Prꢂsang, M. Driess, J. Am. Chem. Soc. 2010,
132, 3038 – 3046. For the oxidative activation of NH3 at gallium,
see: c) Z. Zhu, X. Wang, Y. Peng, H. Lei, J. C. Fettinger, E.
Rivard, P. P. Power, Angew. Chem. Int. Ed. 2009, 48, 2031 – 2034;
Angew. Chem. 2009, 121, 2065 – 2068.
[14] The 1:1 ammonia adduct of 10 has been synthesized by direct
combination with NH3 (and structurally characterized, see the
Supporting Information) and its reaction with 8a shown to
proceed through a proton transfer to the alkenic backbone
function of the latter to generate [(Nacnac)Ga(tBu)]+.
In conclusion, we report the synthesis of a single-compo-
nent ambiphilic system capable of the cooperative activation
À
of protic, hydridic and apolar H X bonds across a gallium/
activated Nacnac ligand framework. Moreover, the hydride
complex derived from the activation of H2 is a competent
catalyst for the selective reduction of CO2 to a methoxy
derivative using HBpin. Although gallium hydrides have
previously been reported to act a radical initiators in a similar
fashion to Bu3SnH,[25] the process we describe represents, to
our knowledge the first example of such a reduction process
catalyzed by a molecular gallium species. Further studies
aimed at extension to the corresponding alanes are ongoing.
À
[15] For an example of the coordination of a less polar E H bond at
a Group 13 center see: A. Y. Houghton, J. Hurmalainen, A.
Mansikkamꢂki, W. E. Piers, H. M. Tuononen, Nat. Chem. 2014,
6, 983 – 988.
[16] M. E. Alberto, N. Russo, E. Sicilia, Chem. Eur. J. 2013, 19, 7835 –
7846.
[17] A termolecular process involving the concerted activation of H2,
with one molecule of 8a acting as a Lewis acid and a second
acting as a Lewis base (as is postulated for certain FLP
systems)[12] is also conceivable. However, the g-CH 1H NMR
Experimental Section
Synthetic, spectroscopic and crystallographic data for all new com-
pounds, details of the DFT calculations (including run files), and all
CIFs are included in the Supporting Information. CCDC 1038748–
1038762 contain the supplementary crystallographic data for this
4
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Angewandte
Chemie
resonance for [(Nacnac) Ga(tBu)]+ (as would be generated in
such a reaction by protonation of 8a) is found at very low field
(dH = 6.41 ppm in C6D5Br). As such, it is unlikely that
[(Nacnac)Ga(tBu)]+ corresponds to one of the intermediate
species found in the 8a/H2 reaction by in situ 1H NMR
monitoring.
under catalytic conditions.[24h] If the reduction of CO2 by HBpin
catalyzed by 10 mol% 13 is carried out in THF, the reaction
proceeds more slowly and the predominant reduction product
after 16 h is HC(O)OBpin.
[24] For catalytic CO2 reduction by non-transition metal systems, see:
a) L. Gu, Y. Zhang, J. Am. Chem. Soc. 2010, 132, 914 – 915;
b) S. N. Riduan, Y. Zhang, J. Y. Ying, Angew. Chem. Int. Ed.
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10027; d) A. Berkefeld, W. E. Piers, M. Parvez, J. Am. Chem.
Soc. 2010, 132, 10660 – 10661; e) M. J. Sgro, D. W. Stephan,
Angew. Chem. Int. Ed. 2012, 51, 11343 – 11345; Angew. Chem.
2012, 124, 11505 – 11507; f) R. Dobrovetsky, D. W. Stephan,
Angew. Chem. Int. Ed. 2013, 52, 2516 – 2519; Angew. Chem.
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L. Maron, F.-G. Fontaine, J. Am. Chem. Soc. 2013, 135, 9326 –
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[18] The presence in the reaction mixture of appreciable concen-
trations of the regioisomeric products resulting from addition of
À
H2 across either of the Ga N bonds in 8a is consistent with
preliminary DFT calculations which show that these two systems
lie within 1.0 kcalmolÀ1 energetically of 8a + H2 (see Supporting
Information).
À
À
[19] For an example of E H bond activation across an Al N bond
see: T. W. Myers, L. A. Berben, J. Am. Chem. Soc. 2013, 135,
9988 – 9990.
[20] a) C. Fan, L. G. Mercier, W. E. Piers, H. M. Tuononen, M.
Parvez, J. Am. Chem. Soc. 2010, 132, 9604 – 9608.
[21] a) A. J. Downs, C. R. Pulham, Chem. Soc. Rev. 1994, 23, 175 –
184; b) S. Aldridge, A. J. Downs, Chem. Rev. 2001, 101, 3305 –
3366.
[22] For insertion of CO2 into a Nacnac-stabilized Ge hydride, see: A.
ˇ
Jana, G. Tavcar, H. W. Roesky, M. John, Dalton Trans. 2010, 39,
[25] See, for example: M. Satoshi, K. Fujita, T. Nakamira, H.
Yorimitsu, H. Shinokubo, S. Matsubara, K. Oshima, Org. Lett.
2001, 3, 1853 – 1855.
À
9487 – 9489. For related insertion into an Al H bond, see:
b) T. W. Myers, L. A. Berben, Chem. Sci. 2014, 5, 2771 – 2777.
[23] MeOBpin has previously been shown to result from the further
reaction of the formate ester HC(O)OBpin with excess HBpin
Angew. Chem. Int. Ed. 2015, 54, 1 – 6
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
5
These are not the final page numbers!

.
Angewandte
Communications
Communications
Group 13 Metal Catalysis
J. A. B. Abdalla, I. M. Riddlestone,
R. Tirfoin, S. Aldridge*
&&& — &&&
Cooperative Bond Activation and
Catalytic Reduction of Carbon Dioxide at
a Group 13 Metal Center
A single-component ambiphilic Group 13
system has been developed, capable of
the cooperative activation of protic,
tion of H2 catalyzes the selective trans-
formation of CO2 to a methanol deriva-
tive, representing the first example of
such a reduction process catalyzed by
a molecular gallium complex.
À
hydridic and apolar H X bonds. The
hydride complex derived from the activa-
6
www.angewandte.org
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2015, 54, 1 – 6
These are not the final page numbers!