Single-step, highly active, and highly selective nanoparticle catalysts for the hydrogenation of key organic compounds

Article abstract of DOI:10.1002/1521-3773(20011217)40:24<4638::AID-ANIE4638>3.0.CO;2-W

Pores for cluster catalysts: Nanoparticles of both Ru₅Pt and Ru₁₀Pt₂, uniformly distributed along the inner walls of mesoporous silica, exhibit high catalytic performance in the single-step hydrogenation of dimethyl terephthalate (DMT, to 1,4-cyclohexanedimethanol (CHDM); see scheme), of benzoic acid (to cyclohexane carboxylic acid), and of naphthalene (in the presence of sulfur) to cisdecalin.

Full text of DOI:10.1002/1521-3773(20011217)40:24<4638::AID-ANIE4638>3.0.CO;2-W

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[26] The data were collected on a Nonius CAD4 diffractometer; CuKa; l ˆ
1.54184 ä; w2q scan; 293(2) K; the structure was solved by the
application of direct methods and refined using SHELX97(G. M.
Sheldrick, Acta Crystallogr. Sect. A 1990, 46, 467 473); the refine-
ments were against jF2 j , the data were reduced using XCAD4 (K.
Harms, S. Wocadlo, University of Marburg), all programs included in
the WinGX package (L. J. Farrugia, J. Appl. Crystallogr. 1999, 32,
837 838); the H atoms were geometrically placed.
[27] Crystallographic data (excluding structure factors) for the structures
reported in this paper have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication
no. CCDC-164579 (1), -164580 (4), and -164581 (5). Copies of the
data can be obtained free of charge on application to CCDC, 12 Union
Road, Cambridge CB21EZ, UK (fax: (‡44)1223-336-033; e-mail:
deposit@ccdc.cam.ac.uk).
[28] Y. A. Ovchinnikov, V. T. Ivanov, Tetrahedron 1974, 30, 1871 1890.
[29] Crystal data for 4 (colorless): Dimensions 0.05 Â 0.05 Â 0.48 mm,
monoclinic, P21/a, a ˆ 9.434(14), b ˆ 10.338(4), c ˆ 11.393(7) ä, b ˆ
111.22(6)8, Vˆ 1035.8 ä3, Z ˆ 2; 1calcd ˆ 1.246 gcmÀ3; 2qmax ˆ 1308;
1810 reflections (1725 independent, 967 with F > 2.0sF, 1725 used in
refinement); 167parameters were refined; the max. and min. electron
density map were 0.366 and À0.217eä À3; the final residues were
R(F) ˆ 0.0814, and Rw(F 2) ˆ 0.2358, GoF ˆ 0.931.
aggregate as bundles. Since all the strong columnar dipoles
are oriented in the same direction, intense anisotropy exists
that can in principle expand to macroscopic levels. Growing
monocrystals of such materials is now possible. We will soon
be in a position to find out if highly polarized nanotubes can
be used in devices to rectify current or display unexpected
properties.[11] Our approach allows us to control precisely the
internal diameter of the tube simply by modifying the
positions and number of alkenes inside the monomers. We
have prepared the higher C3 symmetric lactam homologue,
which incorporates conjugated dienes rather than simple
conjugated alkenes; its crystal structure should yield further
information about the capacity of conjugation to provide
adequate rigidity to the tube units.
Received: June 11, 2001
Revised: October 15, 2001 [Z17261]
[30] Crystal data for
5
(colorless): dimensions 0.08 Â 0.17 Â 0.45 mm,
trigonal, R3, a ˆ 17.299(5), b ˆ 17.299(5), c ˆ 4.819(5) ä, Vˆ
1248.9 ä3, Z ˆ 3; 1calcd ˆ 1.162 gcmÀ3; 2qmax ˆ 1308; 988 reflections
(878 independent, 518 with F > 2.0sF, 878 used in refinement); 65
parameters were refined; the max. and min. electron density map
were 0.237and À0.202 eäÀ3; the final residues were R(F) ˆ 0.0937,
and Rw(F 2) ˆ 0.2556, GoF ˆ 0.991.
[1] J.-M. Lehn, Pure Appl. Chem. 1978, 50, 871 892.
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1319.
[3] K. M¸ller-Dethlefs, P. Hobza, Chem. Rev. 2000, 100, 143 167.
[4] B. Eisenberg, Acc. Chem. Res. 1998, 31, 117 123.
[5] G. W. Gokel, O. Murillo, Acc. Chem. Res. 1996, 29, 425 432.
[6] M. R. Ghadiri, J. R. Granja, L. K. Buehler, Nature 1994, 369, 301
304.
[7] T. D. Clark, L. K. Buehler, M. R. Ghadiri, J. Am. Chem. Soc. 1998,
120, 651 656.
[8] D. Ranganathan, V. Haridas, C. S. Sundari, D. Balasubramanian, K. P.
Madhusudanan, R. Roy, I. L. Karle, J. Org. Chem. 1999, 64, 9230
9240.
[9] D. Ranganathan, C. Lakshmi, I. L. Karle, J. Am. Chem. Soc. 1999, 121,
6103 6107.
[10] D. T. Bong, T. D. Clark, J. R. Granja, M. R. Ghadiri, Angew. Chem.
2001, 113, 1016 1041; Angew. Chem. Int. Ed. 2001, 40, 988 1011.
[11] P. K. Kienker, W. F. DeGrado, J. D. Lear, Proc. Natl. Acad. Sci. USA
1994, 91, 4859 4863.
[12] T. D. Clark, J. M. Buriak, K. Kobayashi, M. P. Isler, D. E. McRee,
M. R. Ghadiri, J. Am. Chem. Soc. 1998, 120, 8949 8962.
[13] L. Tomasic, G. P. Lorenzi, Helv. Chim. Acta 1987, 70, 1012 1016.
[14] D. Seebach, J. L. Matthews, A. Meden, T. Wessels, C. Baerlocher, L. B.
McCusher, Helv. Chim. Acta 1997, 80, 173 182.
Single-Step, Highly Active, and Highly
Selective Nanoparticle Catalysts for the
Hydrogenation of Key Organic Compounds**
Robert Raja, Tetyana Khimyak, John Meurig Thomas,*
Sophie Hermans, and Brian F. G. Johnson*
More than three quarters of the organic molecular products
that are manufactured industrially entail the processes of
either hydrogenation or oxidation; and with the impending
arrival of the so-called hydrogen economy and the parallel
drive towards clean technology this fraction will inevitably
rise in the near future, the most desirable agents of conversion
[15] J. L. Matthews, K. Gademann, B. Jaun, D. Seebach, J. Chem. Soc.
Perkin Trans. 1 1998, 3331 3340.
[16] M. R. Ghadiri, J. R. Granja, R. A. Milligan, D. E. McRee, N.
Khazanovich, Nature 1993, 366, 324 327.
[17] J. D. Hartgerink, J. R. Granja, R. A. Milligan, M. R. Ghadiri, J. Am.
Chem. Soc. 1996, 118, 43 50.
[18] V. Pavone, E. Benedetti, B. DiBlasio, A. Lombardi, C. Pedone, L.
Tomasic, G. P. Lorenzi, Biopolymers 1989, 28, 215 223.
[19] J. Lowbridge, E. Mtetwa, R. J. Ridge, C. N. C. Drey, J. Chem. Soc.
Perkin Trans. 1 1986, 155 156.
[*] Prof. Sir J. M. Thomas, Dr. R. Raja
The Royal Institution of Great Britain
Davy Faraday Research Laboratory
21 Albemarle Street, London W1S 4BS (UK)
Fax : (‡44)1223-339200
[20] D. N. J. White, C. Morrow, P. J. Cox, C. N. C. Drey, J. Lowbridge, J.
Chem. Soc. Perkin Trans. 2 1982, 239 243.
E-mail: has22@cam.ac.uk
Prof. Sir J. M. Thomas
Department of Materials Science and Metallurgy
New Museums Site
[21] I. L. Karle, J. Karle, Acta Crystallogr. 1963, 16, 969 975.
[22] M. Dobler, J. D. Dunitz, J. Krajewski, J. Mol. Biol. 1969, 42, 603 606.
[23] L. Zhang, J. P. Tam, Tetrahedron Lett. 1997, 38, 4375 4378.
[24] R. D. Allan, H. W. Dickenson, G. A. R. Johnston, R. Kazlauskas,
H. W. Tran, Aust. J. Chem. 1985, 38, 1651 1656.
Pembroke Street, Cambridge CB2 3QZ (UK)
Prof. B. F. G. Johnson, Dr. R. Raja, T. Khimyak, Dr. S. Hermans
Department of Chemistry, University of Cambridge, Lensfield Road,
Cambridge CB2 1EW (UK)
Fax : (‡44)1223-339200
[25] Crystal data for
1
(colorless): dimensions 0.15 Â 0.15 Â 0.30 mm,
triclinic, P1, a ˆ 4.726(2), b ˆ 7.709,c ˆ 11.054(2) ä, a ˆ 72.97(1), b ˆ
77.78(1), g ˆ 88.55(1)8, Vˆ 306.1 ä3, Z ˆ 1; 1calcd ˆ 1.286 gcmÀ3
;
[**] We gratefully acknowledge the support (by a rolling grant to J.M.T.
and an award to B.F.G.J.) of EPSRC (UK), of the Cambridge Overseas
Trust (Schlumberger research), and ICI (for T.K.), and the award of a
research fellowship (for S.H.) from Newnham College, Cambridge.
2qmax ˆ 1408; 1353 reflections (1353 independent, 1193 with F >
2.0sF, 1353 used in refinement); 198 parameters were refined; the
max. and min. electron density map were 0.241 and À0.207eä À3; the
final residues were R(F) ˆ 0.0509, and Rw(F 2) ˆ 0.1382, GoF ˆ 1.042.
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being molecular hydrogen and air (or oxygen). But increasing
use of these agents requires the further development of
robust, new, highly active and selective catalysts that, ideally,
should effect single-step conversions under relatively mild
and solvent-free conditions.[1] Here we describe the promising
performance of two, related new bimetallic nanocatalysts for
the hydrogenation of:
1) benzoic acid to cyclohexane carboxylic acid (1);
2) dimethyl terephthalate (DMT) to 1,4-cyclohexanedime-
thanol (CHDM) (2);
3) naphthalene in a highly selective manner to cis-decalin (3).
It is relevant to note that 1, upon treatment with NOHSO4
in the presence of strong acid (such as oleum) yields
caprolactam,[2] the precursor of nylon; that 2 is preferred
over ethylene glycol[3] as a stepping stone in the production of
polyester fibers for extensive use in photography, antifogging
agents, and in other applications involving polycarbonates and
polyurethanes;[4] and that 3 is a useful source (and storage
medium) for hydrogen. The hydrogenation of only the
benzene ring in benzoic acid has scarcely been described.[5]
Likewise, the hydrogenation of DMT to dimethyl hexahy-
droterephthalate (DMHT, Scheme 1) has been achieved to
date only with a rhodium complex tethered on silica-
supported palladium.[6]
Figure 1. A) Structure of the anion in [Ph4P]2[Ru5PtC(CO)15] (4).[18]
B) Structure of the anion in [PPN]2[Ru10Pt2C2(CO)28] (5; PPN ˆ
‡
ˆ ˆ
[(C6H5)3P N P(C6H5)3] ), prepared and fully described as reported
elsewhere.[19]
Scheme 1. Hydrogenation of dimethyl terephthalate (DMT).
accessible to all the reactant and product molecules of this
investigation.
The bimetallic nanoparticle catalysts reported here are
discrete anchored clusters, Ru5Pt and Ru10Pt2, prepared by
the gentle decarbonylation of the parent, mixed-metal
precursor anions, [Ru5PtC(CO)15]2À and [Ru10Pt2C2(CO)28]2À
(Figure 1), after first inserting them, along with their counter-
ions into mesoporous silica, in a manner closely akin to the
A preliminary test of the performance of these catalysts was
carried out using cyclohexene as the reactant. The results
(Table 1) leave little doubt that the catalytic activity and
selectivity of both Ru5Pt and Ru10Pt2 are exceptional. In the
hydrogenation of naphthalene again the performance of these
two catalysts is exceptional (Table 1): only the fully hydro-
genated naphthalenes (decalins) are formed, and the ratio of
the cis to the trans forms is high (ca. 5.5:1 to 8.6:1 depending
upon the precise conditions). Moreover, these catalysts are
unimpaired in their performance even when substantial
amounts of a well-known ™sulfur poison∫ is deliberately
introduced–in sharp contrast to the behavior of otherwise
good bimetallic nano-catalysts (Pd6Ru6, Ru6Sn, and Cu4Ru12)
previously tested by us.
[9]
preparation of anchored Ru6Sn,[7] Pd6Ru6,[8] and of Cu4Ru12,
nanoclusters described previously. The diameter of the
resulting, well-dispersed, isolated and anchored bimetallic
nanoparticles is in the range of approximately 10 20 ä[10, 11]
(see below).
A bright-field (BF) scanning transmission electron micro-
graph (Figure 2A) directly reveals the mesoporosity of the
silica (MCM-41) used as host to encapsulate the bimetallic
nanoparticle catalysts.[12, 13] And a bright field/high-angle-
annular dark field (BF/HAADF) pair (Figure 2B and C)
shows clearly the uniform size and distribution of the denuded
mixed-metal anion (in this case Ru10Pt2) within the meso-
pores. These anchored nanoparticle catalysts are readily
In the hydrogenation of benzoic acid the efficacy of the two
RuPt nanocatalysts again surpasses that of the three, quite
distinct bimetallic catalysts that we have previously described
(Figure 3).
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This, in turn, is converted at about 2008C and 40 bar (40 Â
105 Pa) H2 over a copper chromite catalyst, into the required
CHDM.[14] With our catalysts, one-step conversions of DMHT
into CHDM are effected in high yield even after a mere 4 h
contact time at 1008C, a pressure of 20 bar (20 Â 105 Pa) H2, in
ethanol as a benign solvent (Table 2). It is noteworthy that the
yield of CHDM passes through a maximum, there being cross-
linked products such as 4-methyloxymethlhydroxymethylcy-
clohexane and bis (4-hydroxymethylcyclohexyl) ether formed
during the conversion. Other bimetallic nano-catalysts that
are less efficient than Ru5Pt or Ru10Pt2 as straightforward
hydrogenation catalysts (see Table 1), species such as
Cu4Ru12, are especially effective in producing good yields of
CHDM (see Table 2). Kinetic studies (Figure 4 and Figure 5)
reveal the changes more explicitly. It is also noteworthy
that the cis:trans ratio of the CHDM formed is 80:20 for the
Cu4Ru12 catalyst, and 65:35 in the case of both the RuPt
catalysts. It augurs well here that, in the case of the
Cu4Ru12 catalyst, these values are extremely significant for
industrial processing (ideally 88:12).[15, 16] Notably, the
Pd6Ru6 catalyst produces a 50:50 mixture (cis:trans) of
CHDM.
Figure 2. A) BF scanning transmission electron micrograph[7, 12] of
a
typical group of crystallites of mesoporous silica (ca. 30 ä diameter) onto
the inner walls of which nanoparticle arrays have been anchored (not
clearly visible, see Figures 2B and C of Ru10Pt2 catalysts. B) and C) A BF/
HAADF pair of another region of the mesopore-encapsulated Ru10Pt2
nanocatalysts. Whereas in (B) many of the nanoparticles are just about
visible, in C) they all stand out very clearly and are seen to be aligned along
the mesopores (compare Figure 4 of ref. [7]).
Given the sensitive time dependence of product yields in
the (one-step) hydrogenation of DMT there is abundant
scope here for the chemical engineer to optimize the
production of CHDM. Further work on the structure and
catalytic properties of the two compositionally identical, but
elementally different, bimetallic nanoparticles, is in progress.
The hydrogenation of DMT (see Scheme 1) to the valuable
product CHDM (2) is carried out industrially in two steps
using two reactors.[14] The first, which requires a temperature
in the range 160 1808C and a pressure of 30 48 MPa, uses a
supported Pd catalyst. This highly exothermic process yields
the intermediate, dimethyl hexahydroterephthalate (DMHT).
Experimental Section
[Ph4P]2[Ru5PtC(CO)15] (4): An excess of KOH (500 mg) was added to a
solution of [Ru5PtC(CO)16] (200 mg, 0.17mmol) in methanol. The mixture
was stirred at room temperature for 2 h after which an excess of Ph4PCl
(160 mg, 0.43 mmol) was added to yield 4 as dark red precipitate. The solid
was collected by filtration and washed with hexane, yield: 268 mg (87%).
Table 1. Hydrogenation of cyclohexene and naphthalene–comparison of catalysts.
[d]
Catalyst[a]
Substrate
t [h]
p H2 [bar][b]
T [K]
Conv [mol%]
TOF [hÀ1
]
Product distribution [mol%][e]
A
B
C
D
Ru5Pt/SiO2
Ru10Pt2/SiO2
Pd6Ru6/SiO2
Ru6Sn/SiO2
Cu4Ru12/SiO2
Ru5Pt/SiO2
Ru10Pt2/SiO2
Pd6Ru6/SiO2
Ru6Sn/SiO2
Cu4Ru12/SiO2
cyclohexene
cyclohexene
cyclohexene
cyclohexene
cyclohexene
naphthalene
naphthalene
naphthalene
naphthalene
naphthalene
1.5
3
1.5
2
1.5
3
1.5
3
10
1
8
353
353
353
52.5
96.9
75.2
98.0
31.3
55.0
1989
26.5
2015
21.71950
31.5
6860
6341
14530
14201
3250
3015
92
1734
89
80
100
100
100
100
100
100
0
15
10
17353
15
17353
15
8
732.0
6
6
14
19
12
18
19
18
15.2
11.5
11.5
11
85
14.7
1.5
3
20.2
8
373
373
373
373
373
792
84
15
8[c]
8
805
86.4
1660
1671
19
13.3
44.7
45.0
7.0
89.4
88.5
50
no reaction
48.2
no reaction
no reaction
no reaction
10.2
11.3
34
8[c]
8
15
8[c]
8
9.5
238
45
6.5
8[c]
8
8[c]
[a] The mesoporous SiO2 used here is of the MCM-41 type. Reaction conditions: cyclohexene ꢀ 50 g; naphthalene ꢀ 8 g (dissolved in 55 g of hexadecane);
catalyst ˆ 50 mg; H2 pressure ˆ 20 bar. [b] Residual H2 pressure in the reactor. [c] 200 ppm of sulfur was introduced (benzothiophene). [d] TOF ˆ
[(molsubstr)(molcluster
)
À1 hÀ1]. [e] A ˆ cyclohexane; B ˆ cis-decalin; C ˆ trans-decalin; D ˆ others.
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Figure 3. Bar chart of the relative performances and selectivity of the Ru5Pt and Ru10Pt2 catalysts compared to other bimetallic nanocatalysts, (used by us in
our previous studies[7 9]) for the hydrogenation of benzoic acid. Note that the Ru5Pt and Ru10Pt2 catalysts display a high degree of selectivity for the
cyclohexane carboxylic acid in marked contrast to the other bimetallic analogues. Reaction conditions: benzoic acid ꢀ2.5 g (dissolved in 75 mL of ethanol);
catalyst ˆ 50 mg, H2 pressure ˆ 20 bar, Tˆ 373 K; t ˆ 24 h.
Table 2. Hydrogenation of dimethyl terephthalate (DMT)–comparison of catalysts.
[b]
Catalyst[a]
t [h]
Conv [mol%]
TOF [hÀ1
]
Product distribution [mol%][c]
A
B
C
D
Ru5Pt/SiO2
4
8
24
4
8
24
4
8
24
4
8
7.5
18.4
36.9
23.3
39.5
67.2
6.2
155
191
138
714
605
443
98
58.7
55.3
61.2
42.6
53.6
51.4
32.9
22.5
33.5
5.2
6.9
39.4
38.7
Ru10Pt2/SiO2
Pd6Ru6/SiO2
Ru6Sn/SiO2
Cu4Ru12/SiO2
52.3
9.0
37.1
48.5
51.1
74.2
16.8
4.2
15.5
23.764
125
18.2
81.5
5.3
8.0
54
2781.0
77.2
22.6
23.0
24
4
8
18.6
10.4
14.2
102
45
22.2
25.3
54.5
63.2
24
11.3
[a] The mesoporous SiO2 used here is of the MCM-41 type. Reaction conditions: DMTꢀ 2.5 g (dissolved in 75 mL ethanol); Tˆ 373 K; H2 pressure ˆ 20 bar;
catalyst ꢀ50 mg. [b] TOF ˆ [(molsubstr)(molcluster
)
À1 hÀ1]. [c] A ˆ dimethyl hexahydroterephthalate (DMHT); B ˆ 1,4-cyclohexanedimethanol (CHDM); C ˆ
mixture of 4-methyl-4-cyclohexane carboxylic acid methyl ester and 1-hydroxymethyl-4-methylcyclohexane; D ˆ mixture of 4-methyloxymethylhydroxy-
methylcyclohexane and bis(4-hydroxymethylcyclohexyl) ether.
Elemental analysis calcd (%) for C64H40O15P2PtRu5: C 42.44, H 2.23, P 3.42;
on a holey carbon film supported on a copper grid from a suspension in
hexane, as described in ref. [7].
found: C 40.62, H 2.27, P 3.42; IR (CH Cl2): nÄmax ˆ (CO) 1975s (br), 1911w
2
(sh), 1823w (br), 1771w (br) cmÀ1; 1H NMR (400 MHz, 300 K, CD2Cl2): d ˆ
The catalytic reactions were carried out in a high-pressure stainless steel
catalytic reactor lined with poly ether ether ketone (PEEK). Dry hydrogen
(20 bar (20 Â 105 Pa)) was pressurized into the reaction vessel and, using a
mini robot liquid-sampling valve, small aliquots of the sample were
removed to study the kinetics of the reaction, without perturbing the
pressure in the reactor.[17] The products were analyzed (using a suitable
internal standard)[7] by gas chromatography (GC, Varian, Model 3400 CX)
employing a HP-1 capillary column (25 m  0.32 mm) and flame ionization
detector. The identity of the products was confirmed by injecting
authenticated samples and further by liguid chromatography mass spec-
trometry (LC-MS; Shimadzu, QP 8000) employing a gamma-cyclodextrin
dialkyl column (Chiraldex, 20 m  0.25 mm).
7.92 7.60 (m, 20H, P(CH5)4); 13C NMR (400 MHz, 300 K, CD2Cl2): d ˆ
6
201.0 (m, CO), 136.0 117.37 (m, CH5); MS: m/z (%): 566 (100) [M2À/2],
6
552 (48) [M2À/2 À CO].
The catalytic materials were prepared by standard procedures.[7, 9] The
mesoporous silica was loaded with cluster 4 or 5 by making a slurry in
diethyl ether/dichloromethane. The mesopore-encapsulated clusters 4 and
5 were activated by heating at 1958C in vacuo for 2 h. As in earlier
preparations,[7] the FT-IR spectra recorded after activation showed no
residual peaks corresponding to the carbonyl stretching frequencies.
The electron microscopy characterizations were carried out on
a
VG HB501 field-emission STEM microscope, and the catalysts dispersed
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The Ru Pt catalysts have been re-used three times
without appreciable loss in catalytic activity or selectiv-
ity. Further, experiments, analogous those reported
earlier,[7] were carried out to rule out the possibility of
leaching, and analysis of the resulting filtrate at the end
of reaction (24 h, for DMT hydrogenation) by ICP
(ICP ˆ inductively charged plasma) and atomic absorp-
tion spectroscopy (AAS) revealed only trace amounts
(<5 ppb) of dissolved metal ions (Pt, Ru).
Received: August 13, 2001 [Z17719]
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J. M. Thomas, B. F. G. Johnson, T. Maschmeyer,
Chem. Commun. 1999, 2131.
[9] D. S. Shephard, T. Maschmeyer, G. Sankar, J. M.
Thomas, D. Ozkaya, B. F. G. Johnson, R. Raja,
R. D. Oldroyd, R. G. Bell, Chem. Eur. J. 1998, 4,
1214.
Figure 4. Kinetics of hydrogenation of DMT by using Ru10Pt2 (A). An expanded view of the
initial part of the reaction where the formation of CHDM, after 4 h, is clearly detected is shown
in (B). The CHDM further reacts in the presence of this catalyst to form coupling by-products
&
*
as elaborated in Table 2 and in the text. conversion of DMT; C (see Table 2 for details);
~
!
^
DMHT; CHDM; D (see Table 2 for details).
[10] J. M. Thomas, Angew. Chem. 1999, 111, 3800;
Angew. Chem. Int. Ed. 1999, 38, 3588.
[11] W. Zhou, J. M. Thomas, D. S. Shephard, B. F. G.
Johnson, D. Ozkaya, T. Maschmeyer, R. G. Bell, Q.
Ge, Science 1998, 280, 705.
[12] D. Ozkaya, W. Zhou, J. M. Thomas, P. A. Midgeley,
V. J. Keast, S. Hermans, Catal. Lett. 1999, 60, 113.
[13] J. M. Thomas, O. Terasaki, P. L. Gai, W. Zhou, J.
Gonzalez-Callet, Acc. Chem. Res. 2001, 34, 583.
[14] a) M. L. Schlossman (Tevco), US-A 4301046, 1981
[Chem. Abstr. 1982, 96, 24664c]; b) P. Appleton,
M. A. Wood (Eastman Chemical), US 5414159,
1993 [Chem. Abstr. 1995, 123, 170535d].
[15] P. Werle, M. Morawietz, Ullmanns Encyclopedia of
Industrial Chemistry, Wiley-VCH, Weinheim, Ger-
many, 2001.
[16] R. D. Adams, W. Wu, J. Cluster Sci. 1991, 2, 27 1
290.
[17] J. M. Thomas, R. Raja, G. Sankar, R. G. Bell, Acc.
Chem. Res. 2001, 34, 191.
[18] The single-crystal X-ray structure of 4 will be
reported elsewhere.
[19] B. F. G. Johnson, S. Hermans, T. Khimyak, Organo-
metallics 2001, submitted.
Figure 5. Kinetics of hydrogenation of DMT using Cu4Ru12 as the catalyst. Note that the
product distribution is markedly different (c.f. Figure 4) and the formation of by-products is
relatively suppressed. The synergistic role of the copper in driving the reaction further
(conversion of DMHT into CHDM) is clearly evident here, in stark contrast with what is
&
*
observed in Figure 4 using the Ru10Pt2 catalyst; conversion of DMT; C (see Table 2 for
~
!
^
details); DMHT; CHDM; D (see Table 2 for details).
4642
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