Platinum Participation in the Hydrogenation of Phenylacetylene by Ru 5(CO)15(C)[Pt(PBut3)]

Article abstract of DOI:10.1021/ja049955y

The hydride and PhC₂H complexes, Ru₅(CO)₁₄(μ₆-C)[Pt(PBu^t₃)](μ-H)₂, 2, and Ru₅(CO)₁₃(μ₅-C)(PhC₂H)[Pt(PBu^t₃)], 3,

Full text of DOI:10.1021/ja049955y

Published on Web 02/21/2004
Platinum Participation in the Hydrogenation of Phenylacetylene by
Ru5(CO)15(C)[Pt(PBut3)]
Richard D. Adams,* Burjor Captain, and Lei Zhu
Department of Chemistry and Biochemistry, UniVersity of South Carolina, Columbia, South Carolina 29208
Received January 4, 2004; E-mail: adams@mail.chem.sc.edu
Recent studies have shown that bimetallic cluster complexes are
excellent precursors for highly active nanocluster hydrogenation
catalysts when placed on mesoporous supports.1 In certain cases,
these bimetallic catalysts exhibit evidence for strong synergistic
effects.1,2 Platinum- and palladium-ruthenium carbonyl cluster
complexes are among the most effective precursors for these
catalysts.2 In our previous studies of bimetallic clusters in homo-
geneous catalysis, we observed promotional effects of platinum,
but no evidence for its direct participation in the process.3
We have recently prepared the tri-tert-butylphosphine complex
Ru5(CO)15(C)[Pt(PBut3)], 1, and have shown that it exists in solution
as a mixture of rapidly interconverting isomers having closed (1a)
and open (1b) structures for the metal cluster, eq 1.4 We have now
investigated the reactions of 1 with hydrogen and phenylacetylene,
PhC2H, and have found evidence for catalytic hydrogenation activity
in solutions. We have also isolated bimetallic complexes that show
heteronuclear coordination of both of these reagents.
Figure 1. An ORTEP diagram of Ru5(CO)14(µ6-C)[Pt(PBut3)](µ-H)2, 2,
showing 40% probability thermal ellipsoids. Selected interatomic distances
(Å) are: Pt(1)-Ru(4) ) 2.8336(3), Pt(1)-Ru(2) ) 2.8497(3), Pt(1)-Ru(3)
) 2.9969(3), Pt(1)-Ru(1) ) 3.1189(3), Pt(1)-H(1) ) 1.67(4), Pt(1)-H(2)
) 1.71(4), Pt(1)-P(1) ) 2.3248(9).
The dihydride complex Ru5(CO)14(µ6-C)[Pt(PBut3)](µ-H)2, 2, was
obtained in 68% yield from the reaction of 1 with hydrogen in a
heptane solution at reflux.5 Compound 2 was characterized crys-
tallographically, and an ORTEP diagram of its molecular structure
is shown in Figure 1.6 The molecule consists of an octahedral cluster
of six metal atoms, PtRu5, with a carbido ligand in the center. A
PBut3 ligand is coordinated to the platinum atom, and there are
two hydride ligands (refined crystallographically) that bridge two
of the Pt-Ru bonds. In contrast to most hydride bridges, these
hydride-bridged Pt-Ru bonds, Pt(1)-Ru(4) ) 2.8336(3) Å, Pt(1)-
Ru(2) ) 2.8497(3) Å, are significantly shorter than the unbridged
Pt-Ru bonds, Pt(1)-Ru(3) ) 2.9969(3) Å, Pt(1)-Ru(1) )
3.1189(3) Å.7 This could be due to influences of the interstitial
carbido ligand.8 The hydride ligands show strong one-bond coupling
Figure 2. An ORTEP diagram of Ru5(CO)13(µ5-C)(PhC2H)[Pt(PBut3)], 3.
Selected interatomic distances (Å) are: Pt(1)-C(3) ) 1.980(7), Pt(1)-
P(1) ) 2.3122(19), Pt(1)-Ru(1) ) 2.6787(6), Pt(1)-Ru(2) ) 2.8476(6),
Pt(1)-Ru(3) ) 2.9979(5), Ru(1)-Ru(5) ) 2.7705(8), Ru(1)-Ru(4) )
2.7949(8), Ru(1)-Ru(2) ) 2.9856(7), Ru(1)-Ru(3) ) 3.0018(7), Ru(2)-
Ru(3) ) 2.6666(7), Ru(2)-Ru(5) ) 2.8926(7), Ru(3)-Ru(4) ) 2.9037(7),
Ru(4)-Ru(5) ) 2.8898(8), Ru(2)-C(3) ) 2.210(7), Ru(2)-C(2) )
2.214(6), C(2)-C(3) ) 1.369(10).
Å, Ru(2)-C(3) ) 2.210(7) Å, Ru(2)-C(2) ) 2.214(6) Å, C(2)-
C(3) ) 1.369(10) Å.
When compound 3 was treated with hydrogen (30 psi) in the
presence of a 50-fold excess PhC2H at 80 °C, styrene was obtained
catalytically at a rate of 20(2) turnovers/h.10 From these solutions,
we have isolated the new platinum-ruthenium cluster complex,
Ru5(CO)12(µ5-C)[PtPBut3](PhC2H)(µ-H)2, 4.11 An ORTEP diagram
of the structure of 4 is shown in Figure 3. Like 3, compound 4
contains a platinum-capped Ru3 triangle of a Ru5 cluster, but the
Ru5 cluster is not a square-pyramidal cluster as in 3. Instead, one
of the Ru-Ru bonds in the Ru5 cluster has been eliminated, Ru(1)-
Ru(3) ) 3.6574(5) Å in 4 versus 3.0018(7) Å in 3.12 One CO ligand
was eliminated in going from 3 to 4, and 1 equiv of H2 was added.
The hydrogen exists in the form of two hydride ligands, H(1) and
H(2), that bridge the Pt(1)-Ru(1) and Ru(1)-Ru(5) metal-metal
1
1
to 195Pt in the H NMR spectrum: δ ) -13.86 (d, JPt-H ) 774
2
Hz, JP-H ) 8 Hz).
The alkyne complex Ru5(CO)13(µ5-C)(PhC2H)[Pt(PBut3)], 3, was
obtained in 41% yield from the reaction of 1 with PhC2H in a
CH2Cl2 solution at reflux.9 Compound 3 was characterized crys-
tallographically, and an ORTEP diagram of its molecular struc-
ture is shown in Figure 2. This molecule consists of a platinum-
capped square-pyramidal pentaruthenium cluster of six metal
atoms with a carbido ligand in the center of the Ru5 cluster. A
PBut3 ligand is coordinated to the platinum atom, and a PhC2H
ligand bridges one of the PtRu2 triangles, Pt(1)-C(3) ) 1.980(7)
9
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J. AM. CHEM. SOC. 2004, 126, 3042-3043
10.1021/ja049955y CCC: $27.50 © 2004 American Chemical Society

C O MMU N I C A T I O N S
synergistic effects observed by these bimetallic clusters when they
are used as catalysts on supports.1,2
Acknowledgment. These studies were supported by the Office
of Basic Energy Sciences of the U.S. Department of Energy, Grant
No. DE-FG02-00ER14980.
Supporting Information Available: Details of the synthesis and
characterizations of the products (PDF), and CIF files for the structural
analyses. This material is available free of charge via the Internet at
http://pubs.acs.org.
References
Figure 3. An ORTEP diagram of Ru5(CO)12(µ5-C)[PtPBut3](PhC2H)(µ-
H)2, 4, showing 40% probability thermal ellipsoids. Selected interatomic
distances (Å) are: Pt(1)-C(3) ) 1.991(4), Pt(1)-P(1) ) 2.3146(11), Pt(1)-
Ru(1) ) 2.6793(4), Pt(1)-Ru(2) ) 2.7045(4), Pt(1)-Ru(3) ) 2.8143(4),
Pt(1)-H(1) ) 1.79(5), Ru(1)-Ru(5) ) 2.8161(5), Ru(1)-Ru(4) )
2.8609(5), Ru(1)-Ru(2) ) 2.9208(5), Ru(1)-Ru(3) ) 3.6574(5), Ru(1)-
H(1) ) 1.79(5), Ru(1)-H(2) ) 1.73(5), Ru(2)-C(3) ) 2.230(4), Ru(2)-
C(2) ) 2.289(4), Ru(2)-Ru(3) ) 2.6694(5), Ru(2)-Ru(5) ) 2.8906(5),
Ru(3)-C(2) ) 2.050(4), Ru(3)-Ru(4) ) 2.9747(6), Ru(4)-Ru(5) )
2.8939(6), Ru(5)-H(2) ) 1.79(5), C(2)-C(3) ) 1.395(5).
(1) Thomas, J. M.; Johnson, B. F. G.; Raja, R.; Sankar, G.; Midgley, P. A.
Acc. Chem. Res. 2003, 36, 20.
(2) (a) Raja, R.; Sankar, G.; Hermans, S.; Shepard, D. S.; Bromley, S.;
Thomas, J. M. Chem. Commun. 1999, 1571. (b) Raja, R.; Khimyak, T.;
Thomas, J. M.; Hermans, S.; Johnson, B. F. G. Angew. Chem., Int. Ed.
2001, 40, 4638. (c) Thomas, J. M.; Raja, R.; Johnson, B. F. G.; O’Connell,
T. J.; Sankar, G.; Khimyak, T. Chem. Commun. 2003, 1126. (d) Hermans,
S.; Raja, R.; Thomas, J. M.; Johnson, B. F. G.; Sankar, G.; Gleeson, D.
Angew. Chem., Int. Ed. 2001, 40, 1211.
(3) (a) Adams, R. D. J. Organomet. Chem. 2000, 600, 1. (b) Adams, R. D.;
Barnard, T. S.; Li, Z.; Wu, W.; Yamamoto, J. J. Am. Chem. Soc. 1994,
116, 9103. (c) Adams, R. D.; Barnard, T. S. Organometallics 1998, 17,
2567.
Scheme 1
(4) (a) Adams, R. D.; Captain, B.; Fu, W.; Pellechia, P. J.; Smith, M. D.
Inorg. Chem. 2003, 42, 2094. (b) Adams, R. D.; Captain, B.; Fu, W.;
Pellechia, P. J.; Smith, M. D. Angew. Chem., Int. Ed. 2002, 41, 1951.
(5) Here, 9.3 mg of 1 (0.0070 mmol) in 10 mL of heptane was heated to
reflux under a slow purge with hydrogen for 1.5 h. Separation by TLC
(4:1 hexane-methylene chloride solvent) yielded 6.3 mg (68%) of dark
gray Ru5(CO)14(µ6-C)[PtPBut3](µ-H)2, 2. Spectral data for 2, IR νCO (cm-1
in CH2Cl2): 2087 (m), 2052 (s), 2015 (s), 1971 (w, sh), 1821 (w, br). 1H
3
NMR (in toluene-d8): δ ) 1.22 (d, 27H, CH3, JP-H ) 13 Hz), -13.86
(d, 2H, JPt-H ) 774 Hz, JP-H ) 8 Hz). 31P{1H} NMR (in toluene-d8):
1
2
1
δ ) 85.3 (s, 1P, JPt-P ) 4739 Hz). Anal. Calcd: C, 24.77; H, 2.22.
Found: C, 25.13; H, 2.50. Crystal data for 2: orthorhombic, space group
) Pccn, a ) 20.5414(9) Å, b ) 21.3611(9) Å, c ) 18.4550(8) Å, Z ) 8.
For 8493 reflections, R1 ) 0.0241, wR2 ) 0.0556.
(6) Diffraction data were collected on a Bruker APEX diffractometer using
Mo KR radiation. The structure was solved by direct methods and refined
on F 2 by using the SHELXTL structure solving program library and was
corrected for absorption by using SADABS.
(7) Teller, R. G.; Bau, R. Struct. Bonding 1981, 41, 1.
(8) In the presence of additional bridging ligands, the bond lengthening effects
of bridging hydride ligands are often not observed.7
(9) Here, 16 mg of 1 (0.012 mmol) was dissolved in 20 mL of CH2Cl2.
Phenylacetylene (0.010 mL, 0.090 mmol) was added and then heated to
reflux for 1 h. Separation by TLC (6:1 hexane-methylene chloride solvent)
yielded 6.8 mg of a Ru5(CO)13(µ5-C)(PhC2H)[PtPBut3], 3 (41%). Spectral
data for 3, IR νCO (cm-1 in CH2Cl2): 2076 (vs), 2044 (vs), 2027 (s),
bonds. The resonances of the hydride ligands in the 1H NMR
spectrum are consistent with the solid-state structure.11 Compound
4 contains a PhC2H that bridges a PtRu2 triangle similarly to that
in 3. Interestingly, 4 can be obtained independently in a better yield
simply by treating 3 with hydrogen and the decarbonylation agent
Me3NO at 40 °C.13
1
2014 (vs), 1985 (w, sh), 1955 (vw, sh). H NMR (in CDCl3): δ ) 8.58
3
(d, 1H, CH, JP-H ) 16 Hz), 7.3-7.4 (m, 5H, Ph), 1.50 (d, 27H, CH3,
1
3JP-H ) 13 Hz). 31P{1H} NMR (in CDCl3): δ ) 113.4 (s, 1P, JPt-P
)
4545 Hz). Anal. Calcd: C, 29.57; H, 2.39. Found: C, 28.47; H, 2.15.
Crystal data for 3: triclinic, space group ) P-1, a ) 12.6218(5) Å, b )
13.3776(5) Å, c ) 14.3654(5) Å, R ) 92.6780(10)°, â ) 91.0510(10)°,
γ ) 109.9580(10)°, Z ) 2. For 9150 reflections, R1 ) 0.0454, wR2 )
0.1139.
When 4 was treated with CO at 25 °C, both hydrides and the
PhC2H ligand were eliminated in the form of styrene, and compound
1 was formed. When solutions of 4 were treated with hydrogen
and an excess of PhC2H, styrene was formed catalytically, 21(2)
turnovers/h. Interestingly, when Ru6(CO)17(µ6-C) was treated with
hydrogen and PhC2H under similar conditions, no styrene was
produced. A summary of these reactions is shown in Scheme 1.
Further studies to establish the mechanism of the catalytic process
are in progress, but certain notable features are already apparent:
(1) the bimetallic complex 1 is capable of activating both hydrogen
and PhC2H separately and in combination; (2) PhC2H can be
hydrogenated to styrene catalytically, and (3) in all of the species
characterized so far, 2-4, the platinum atom is directly involved
in bonding to either the hydride ligands, the PhC2H ligand, or both.
This demonstrates that the platinum atom plays a direct role in the
activation of the reagents. This could also help to explain the
(10) For comparison, the nine-metal cluster H2Pt3Ru6(CO)20(µ3-PhC2Ph) was
shown to catalyze the hydrogenation of diphenylacetylene to (Z)-stilbene
at a rate of 47 turnovers/h at 50 °C.3b
(11) For 4, IR νCO (cm-1 in CH2Cl2): 2083 (s), 2047 (s), 2023 (vs), 2004 (w,
sh), 1977 (w, sh), 1948 (vw, sh). 1H NMR (in toluene-d8): δ ) 9.76 (dd,
3
3
2
1H, CH, JH-H ) 1.5 Hz, JP-H ) 4 Hz, JPt-H ) 42 Hz), 7.72 (d, 2H,
Ph-H), 7.18 (t, 2H, Ph-H), 7.05 (t, 1H, Ph-H), 0.99 (d, 27H, CH3,3JP-H
) 13 Hz), -9.56 (ddd, 1H, hydride on Pt, 2JP-H ) 1.5 Hz, 2JH-H ) 4 Hz,
3JH-H ) 1.5 Hz, JPt-H ) 641 Hz), -18.55 (d, hydride on Ru, JH-H
)
1
2
4 Hz). 31P{1H} NMR (in toluene-d8): δ ) 124.0 (s, 1P, JPt-P ) 3839
Hz). Anal. Calcd: C, 29.27; H, 2.61. Found: C, 29.63; H, 2.44. Crystal
data for 4: triclinic, space group ) P-1, a ) 12.3991(9) Å, b )
12.6807(10) Å, c ) 16.5292(12) Å, R ) 105.157(2)°, â ) 104.028(2)°,
γ ) 94.753(2)°, Z ) 2. For 9934 reflections, R1 ) 0.0335, wR2 ) 0.0741.
(12) Compounds 3 and 4 have the same number of valence electrons; however,
4 is unsaturated because it has one less Ru-Ru bond than 3.
1
(13) Here, 22.5 mg of 3 (0.016 mmol) was dissolved in 25 mL of CH2Cl2.
Under a purge with H2, 5.4 mg of Me3NO‚2H2O (0.049 mmol) was added,
and the solution was then heated to reflux for 1 h. Separation by TLC
(4:1 hexane-methylene chloride solvent) yielded 4.2 mg of dark gray
Ru5(CO)12(µ5-C)[PtPBut3](PhC2H)(µ-H)2, 4 (19%).
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