Unsaturated platinum-rhenium cluster complexes. synthesis, structures and reactivity

Article abstract of DOI:10.1021/ja070773o

Two new compounds PtRe₃(CO)₁₂(PBu^t ₃)(μ-H)₃, 9, and PtRe₂(CO) ₉(PBu^t₃)(μ-H)₂, 10, were obtained from the reaction of Pt(PBu^t₃)₂ with Re ₃(CO)₁₂(μ-H₃), 8, at room temperature. Compound 9 contains a butterfly cluster of four metals formed by the insertion of the platinum atom from a Pt(PBu^t₃) group into one of the hydride-bridged metal-metal bonds of 8. The three hydrido ligands are bridging ligands across each of three new Pt-Re bonds. Compound 10 contains a triangular PtRe₂ cluster with two hydrido ligands; one bridges a Pt-Re bond, and the other bridges the Re-Re bond. The new compound Pt ₂Re₂(CO)₇(PBu^t₃) ₂(μ-H)₂, 11, was obtained from the reaction of 8 with Pt(PBu^t₃)₂ in hexane at reflux. Compound 11 was also obtained from 10 by reaction with an additional quantity of Pt(PBu ^t₃)₂. Compound 11 contains a tetrahedral cluster of four metal atoms with two dynamically active hydrido ligands. A CO ligand on one of the two platinum atoms also exchanges between the two platinum atoms rapidly on the NMR time scale. Compound 11 is electronically unsaturated and was found to add hydrogen at room temperature to form the tetrahydrido cluster complex, Pt₂Re₂(CO)₇(PBu ^t₃)₂(μ-H)₄, 12. Compound 12 has a structure similar to 11 but contains one triply bridging hydrido ligand, two edge bridging hydrido ligands, and one terminal hydrido ligand on one of the two platinum atoms. A kinetic isotope effect D/H of 1.5(1) was determined for the addition of H₂ to 11. Hydrogen can be eliminated from 12 by heating to 97°C or by the application of UV-vis irradiation at room temperature. Compound 12 adds CO at room temperature to yield the complex Pt ₂Re₂(CO)₈(PBu^t₃) ₂(μ-H)₄, 13, which contains a planar cluster of four metal atoms with a Pt-Pt bond and four edge bridging hydrido ligands. Compounds 11 and 12 react with Pt(PBu^t₃)₂ to yield the known five metal cluster complexes Pt₃Re₂(CO) ₆(PBu^t₃)₃(μ-H)₂, 14, and Pt₃Re₂(CO)₆(PBu^t ₃)₃(μ-H)₄, 15, respectively. Density functional calculations confirm the hydride positions in the lowest energy structural isomers of 11 and 12 and suggest a mechanism for H₂ addition to 11 that occurs on the Pt atom with the lower coordination number.

Full text of DOI:10.1021/ja070773o

Published on Web 04/18/2007
Unsaturated Platinum-Rhenium Cluster Complexes.
Synthesis, Structures and Reactivity
Richard D. Adams,*,† Burjor Captain, Mark D. Smith, Chad Beddie, and
†
†
‡
,
‡
Michael B. Hall*
Contribution from the Department of Chemistry and Biochemistry, UniVersity of South Carolina,
Columbia, South Carolina 29208, and Department of Chemistry, Texas A&M UniVersity,
College Station, Texas 77843-3255
Received February 2, 2007; E-mail: adams@mail.chem.sc.edu
Abstract: Two new compounds PtRe
3
(CO)12(PBut
with Re (CO)12(µ-H
3
)(µ-H)
3
, 9, and PtRe
2
(CO)
9
(PBut
3
2
)(µ-H) , 10, were
t
obtained from the reaction of Pt(PBu
)
3 2
3
3
), 8, at room temperature. Compound 9 contains
t
a butterfly cluster of four metals formed by the insertion of the platinum atom from a Pt(PBu
3
) group into
one of the hydride-bridged metal-metal bonds of 8. The three hydrido ligands are bridging ligands across
each of three new Pt-Re bonds. Compound 10 contains a triangular PtRe cluster with two hydrido ligands;
one bridges a Pt-Re bond, and the other bridges the Re-Re bond. The new compound Pt Re (CO)
2
2
2
7
-
t
t
(PBu
3 2
) (µ-H)
2
, 11, was obtained from the reaction of 8 with Pt(PBu
3
)
2
in hexane at reflux. Compound 11
t
was also obtained from 10 by reaction with an additional quantity of Pt(PBu
3 2
) . Compound 11 contains a
tetrahedral cluster of four metal atoms with two dynamically active hydrido ligands. A CO ligand on one of
the two platinum atoms also exchanges between the two platinum atoms rapidly on the NMR time scale.
Compound 11 is electronically unsaturated and was found to add hydrogen at room temperature to form
t
the tetrahydrido cluster complex, Pt
2 2
Re (CO)
7
(PBu
3
)
2 4
(µ-H) , 12. Compound 12 has a structure similar to
1
1 but contains one triply bridging hydrido ligand, two edge bridging hydrido ligands, and one terminal
hydrido ligand on one of the two platinum atoms. A kinetic isotope effect D/H of 1.5(1) was determined for
the addition of H to 11. Hydrogen can be eliminated from 12 by heating to 97 °C or by the application of
2
UV-vis irradiation at room temperature. Compound 12 adds CO at room temperature to yield the complex
t
Pt
2 2
Re (CO)
8
(PBu
3
)
2
(µ-H)
4
, 13, which contains a planar cluster of four metal atoms with a Pt-Pt bond and
t
four edge bridging hydrido ligands. Compounds 11 and 12 react with Pt(PBu
metal cluster complexes Pt
3
)
2
to yield the known five
t
(PBut
3
Re
2
(CO)
6
(PBu
3 3
) (µ-H)
2
, 14, and Pt
3 2
Re (CO)
6
3
)
3
(µ-H) , 15, respectively.
4
Density functional calculations confirm the hydride positions in the lowest energy structural isomers of 11
and 12 and suggest a mechanism for H addition to 11 that occurs on the Pt atom with the lower coordination
2
number.
Introduction
In recent studies we have shown that metal containing
t
groupings M(PBu 3), M ) Pd and Pt, obtained from the
t
precursors M(PBu 3)2, M ) Pd and Pt, are readily added to the
metal-metal bonds of polynuclear metal carbonyl cluster com-
plexes to form electron-deficient adducts containing bridging
t
t
M(PBu 3) groups. For example, the reaction of M(PBu 3)2, M )
t
Pd and Pt, with Ru3(CO)12 and Os3(CO)12 yield tri-M(PBu 3)
adducts: Ru3(CO)12[Pd(PBu 3)]3, 1, and Os3(CO)12[Pt(PBu 3)]3, 2.
t
1
t
2
interconvert rapidly on the NMR time scale at room tempera-
t
t
3
t
t
Pd(PBu 3)2 and Pt(PBu 3)2 also react with Ru5(CO)15(µ5-C)
to afford the adducts Ru5(CO)15(C)[M(PBu 3)], 3, M ) Pd, and
3 2 4 12 3
ture. Pt(PBu ) reacts with Ir (CO) to yield the di-Pt(PBu )
t
t
4
2 4 12 3 2
adduct Pt Ir (CO) (PBu ) , 5.
4
, M ) Pt. Compounds 3 and 4 both exist in solution as a
Platinum-rhenium bimetallic catalysts have attracted great
interest because of their superior properties for the important
process of petroleum reforming. Recent studies have shown
mixture of open and closed isomers (e.g., 4a and 4b) that
5
†
University of South Carolina.
Texas A&M University.
‡
(3) (a) Adams, R. D.; Captain, B.; Fu, W.; Pellechia, P. J.; Smith, M. D. Angew.
Chem., Int. Ed. 2002, 41, 1951-1953. (b) Adams, R. D.; Captain, B.;
Fu, W.; Pellechia, P. J.; Smith, M. D. Inorg. Chem. 2003, 42, 2094-
2101.
(4) Adams, R. D.; Captain, B.; Hall, M. B.; Smith, J. L., Jr.; Webster, C. E. J.
Am. Chem. Soc. 2005, 127, 1007-1014.
(
1) (a) Adams, R. D.; Captain, B.; Fu, W.; Hall, M. B.; Manson, J.; Smith, M.
D.; Webster, C. E. J. Am. Chem. Soc. 2004, 126, 5253-5267. (b) Adams,
R. D.; Captain, B.; Fu, W.; Smith, M. D. J. Am. Chem. Soc. 2002, 124,
5
628-5629.
(
2) Adams, R. D.; Captain, B.; Zhu, L. Inorg. Chem. 2006, 45, 430-436.
10.1021/ja070773o CCC: $37.00 © 2007 American Chemical Society
J. AM. CHEM. SOC. 2007, 129, 5981-5991
9
5981

A R T I C L E S
Adams et al.
Experimental Section
General Data. Reagent grade solvents were dried by the standard
procedures and were freshly distilled prior to use. Infrared spectra were
recorded on a Thermo Nicolet Avatar 360 FT-IR spectrophotometer.
1
31
1
H NMR and P{ H} NMR were recorded on a Varian Mercury 400
1
spectrometer operating at 400.1 and 161.9 MHz, respectively. H NMR
and 31P{ H} NMR spectra of 11 and 12 were recorded on a Varian
Inova 500 spectrometer operating at 500.2 and 202.5 MHz, respectively.
1
31
1
P{ H} NMR spectra were externally referenced against 85% ortho-
PO . Electrospray mass spectrometric measurements were obtained
H
3
4
on a MicroMass Q-Tof spectrometer. Elemental analyses were per-
formed by Desert Analytics (Tucson, AZ). Bis(tri-tert-butyl phosphine)-
t
platinum(0), Pt(PBu
3 2
)
, was obtained from STREM and was used
(CO)12(µ-H) was prepared according
without further purification. Re
3
3
9
to the published procedure. Product separations were performed by
TLC in air on Analtech 0.25 and 0.5 mm silica gel 60 Å F254 glass
plates.
with Pt(PBut
(CO)12(µ-H) ) at Room Temper-
3 3 2
ature. Pt(PBu ) (36.2 mg, 0.060 mmol) was added to a solution of
Reaction of Re
3
t
that unsaturated polynuclear metal complexes containing bulky
phosphine ligands can absorb relatively large amounts of
hydrogen under mild conditions. We have recently prepared
3
2
Re
3
3 2 2
(CO)12(µ-H) (18.0 mg, 0.020 mmol) in 30 mL of CH Cl . The
6
reaction mixture was stirred at room temperature for 14 h. The solvent
was removed in Vacuo, and the products were then isolated by TLC
by using a 5:1 hexane/methylene chloride solvent mixture to yield in
the new highly unsaturated platinum-rhenium complex Pt3Re2-
t
(
CO)6(PBu 3)2, 6, that readily adds 3 equiv of hydrogen at room
2
order of elution the following: 2.9 mg (14% yield) of yellow PtRe -
temperature to yield the hexahydrido complex Pt3Re2(CO)6-
t
(
(
(
(
CO)
PBu
9
t
(PBu
3
)(µ-H)
3
2
3
, 10, and 5.1 mg (20% yield) of purple PtRe (CO)12-
t
7
(
PBu 3)3(µ-H)6, 7, eq 1.
-1
3
)(µ-H) , 9. Spectral data for 9: IR νCO (cm in hexane) 2104
w), 2080 (m), 2046 (m), 2014 (vs), 2004 (s), 1989 (s), 1961 (m), 1949
sh, w), 1935 (m); H NMR (400 MHz, CDCl , rt, TMS) δ ) 1.49 (d,
1
3
3
2
2
J
)
)
7 H, CH
3
, J(P,H) ) 13 Hz), -9.17 (d, 2H, hydride, J -H ) 6 Hz,
P
1
2
1
Pt-H ) 756 Hz), -11.39 (d, 1H, hydride, J(P,H) ) 9 Hz, J(Pt,H)
118 Hz); 31P{ H} NMR (162 MHz, CDCl
1
, rt, 85% ortho-H
3
3
4
PO ) δ
1
+
99.85 (s, 1 P, J(Pt,P) ) 2856 Hz). Mass Spec. ES /MS calcd for
t
+
[
M + CH
3
CN + H], [PtRe
3
(CO)12(PBu
3
)(µ-H)
3
+ CH CN + H] ,
3
1
-
1
338; found, 1338. Spectral data for 10: IR νCO (cm in hexane):
2
101 (m), 2070 (s), 2008 (vs), 1991 (m), 1982 (m), 1972 (m), 1958
1
3
(s), 1950(m). H NMR (400 MHz, CDCl
3
, rt, TMS) δ ) 1.53 (d, J(P,
2
1
H) ) 13 Hz, 27 H, CH
3
), -7.19 (d, J(P,H) ) 14 Hz, J(Pt, H) ) 538
2
31
t
Hz, 1H, hydride), -15.41 (s, J(Pt, H) ) 31 Hz, 1H, hydride); P-
We have now investigated the reaction of Pt(PBu 3)2 with
Re3(CO)12(µ-H)3, 8, and have obtained three new compounds:
1
{
1
H} NMR (162 MHz, CDCl
3
, rt, 85% ortho-H
J(Pt,P) ) 2936 Hz, 1 P). Elemental analysis (%) calcd: 24.63, C;
.76, H. Found: 25.31, C; 2.85, H.
Reaction of Re (CO)12(µ-H)
with Pt(PBut
30.0 mg, 0.050 mmol) and Re (CO)12(µ-H) (23.0 mg, 0.026 mmol)
3 4
PO ) δ ) 110.6 (s,
t
t
PtRe3(CO)12(PBu 3)(µ-H)3, 9, PtRe2(CO)9(PBu 3)(µ-H)2, 10, Pt2-
2
t
t
Re2(CO)7(PBu 3)2(µ-H)2, 11. Compound 9 is a Pt(PBu 3) adduct
of 8, but unlike the Pt(PBu 3) adduct of its isoelectronic neighbor
Os3(CO)12, the platinum atom from the Pt(PBu 3) group in 9
3
3
3 2 3 2
) )
at 68 °C. Pt(PBut
t
(
3
3
t
were dissolved in 40 mL of hexane. After the mixture was heated to
reflux for 2 h, the solvent was removed in Vacuo, and the products
were separated by TLC (silica gel) using a 3:1 hexane/methylene
has been inserted into the metal-metal bond to which it was
2
added. The unsaturated compound 11 adds H2 reversibly to
t
form the new compound Pt2Re2(CO)7(PBu 3)2(µ-H)4, 12. Com-
chloride solvent mixture. This yielded in order of elution the follow-
t
pound 12 adds CO to form the new open cluster compound
ing: 9.2 mg (35% yield) of yellow PtRe
2
t
(CO)
9
(PBu
3
2
)(µ-H) , 10, 1.8
t
mg (5% yield) of purple PtRe (CO) (PBu )(µ-H) , 9, and 8.4 mg (24%
Pt2Re2(CO)8(PBu 3)2(µ-H)4, 13. The synthesis and characteriza-
3
12
3
3
t
yield) of red Pt
2
Re
2
(CO)
7
(PBu
)
3 2
2
(µ-H) , 11. Spectral data for 11: IR
) 2035 (w), 2015 (m), 1994 (vs), 1916 (m, sh),
, -40 °C, TMS) δ ) 1.20
3
broad, 27 H, CH ), -0.87 (s, 1H, hydride), -2.05 (dd, J(P,H) ) 6
tions of the new platinum-rhenium compounds 9-13 are
reported here. A preliminary report of a portion of this work
has been published.8
-
1
ν
CO (cm in CH
2
Cl
2
1
1
900 (s, br). H NMR (500 MHz, toluene-d
8
2
(
2
1
31
1
Hz, J(P,H) ) 11 Hz, J(Pt,H) ) 621 Hz, 1H, hydride). P{ H} NMR
(202.5 MHz, toluene-d , -25 °C, 85% ortho-H PO ): δ ) 85.5 (d,
J(P,P) ) 82 Hz, J(Pt,P) ) 3880 Hz, 1 P), 112.7 (d, J(P-P) ) 82
(
5) (a) Xiao, J.; Puddephatt, R. J. Coord. Chem. ReV. 1995, 143, 457-500.
(
b) Augustine, S. M.; Sachtler, W. M. H. J. Catal. 1989, 116, 184-194.
8
3
4
(
c) Nacheff, M. S.; Kraus, L. S.; Ichikawa, M.; Hoffman, B. M.; Butt, J.;
3
1
3
Sachtler, W. M. H. J. Catal. 1987, 106, 263-272.
1
+
+
(
6) (a) Dyson, P. J.; McIndoe, J. S. Angew. Chem., Int. Ed. 2005, 44, 2.
2
Hz, J(Pt,P) ) 2435 Hz, 1 P). Mass Spec. ES /MS calcd for M , [Pt -
(
b) Brayshaw, S. K.; Ingleson, M. J.; Green, J. C.; McIndoe, J. S.;
t
+
2
(µ-H) ] , 1365; found, 1365. Elemental analysis (%)
Re
calcd: 27.27, C; 4.14, H. Found: 27.27, C; 3.90, H.
Reaction of 9 with PBut . An excess amount of PBut
mmol) was added to a solution of 9 (7.0 mg, 0.005 mmol) in 15 mL
of CH Cl . The reaction mixture was stirred at room temperature for
2
(CO)
7
(PBu
3
)
2
Raithby, P. R.; Kociok-K o¨ hn, G.; Weller, A. S. J. Am. Chem. Soc.
2
006, 128, 6247-6263. (c) Brayshaw, S. K.; Ingleson, M. J.; Green,
J. C.; Raithby, P. R.; Kociok-K o¨ hn, G.; McIndoe, J. S.; Weller, A. S. Angew.
Chem., Int. Ed. 2005, 44, 6875-6878. (d) Ingleson, M. J.; Mahon,
M. F.; Raithby, P. R.; Weller, A. S. J. Am. Chem. Soc. 2004, 126, 4784-
(13 µL, 0.052
3
3
4
785.
2
2
(
7) (a) Adams, R. D.; Captain, B.; Beddie, C.; Hall, M. B. J. Am. Chem. Soc.
approx 1.25 h during which time the purple colored solution turned
2
007, 129, 986-1000. (b) Adams, R. D.; Captain, B. Angew. Chem., Int.
Ed. 2005, 44, 2531-2533.
(
8) Adams, R. D.; Captain, B.; Smith, M. D. Angew. Chem., Int. Ed. 2006, 45,
(9) Kaesz, H. D.; Knox, S. A. R.; Koepke, J. W.; Saillant, R. B. Chem.
Commun. 1971, 477.
1
109-1112.
5982 J. AM. CHEM. SOC.
9
VOL. 129, NO. 18, 2007

Unsaturated Platinum
−
Rhenium Cluster Complexes
A R T I C L E S
Table 2. Crystallographic Data for Compounds 12-13
Table 1. Crystallographic Data for Compounds 9-11
compound
9
10
11
compound
12
13
empirical formula
formula weight
crystal system
lattice parameters
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
PtRe3PO12C24H30 PtRe2PO9C21H29 Pt2Re2P2O7C31H54
empirical formula
Pt Re P O C H ‚
8 32 58
Pt Re P O C H
2
2
2
7
31 56
2
2
2
1295.14
1023.90
1363.26
1
/
2CH2Cl2
monoclinic
monoclinic
orthorhombic
formula weight
crystal system
lattice parameters
a (Å)
b (Å)
c (Å)
1409.76
monoclinic
1395.30
triclinic
9.0366(5)
17.4393(9)
11.3378(6)
90
27.395(3)
14.3333(16)
19.087(2)
90
15.2359(14)
15.2464(14)
50.847(5)
90
14.7121(9)
17.2332(11)
17.1146(11)
90
105.002(1)
90
9.0728(4)
10.2568(5)
11.5861(6)
95.204(1)
97.889(1)
101.259(1)
1039.73(9)
P 1h (#2)
1
2.228
12.627
294
56.6
4668
225
1.078
0.001
0.0200; 0.0497
multiscan
1.000/0.621
0.614
109.701(1)
90
130.348(2)
90
90.0
90
γ (deg)
γ (deg)
3
â (deg)
V (Å )
1682.16(16)
P21/m (#11)
2
5711.9(11)
C2/c (# 15)
8
11811.3(19)
P212121 (#19)
12
γ (deg)
space group
3
Z value
V (Å )
4191.3(5)
3
space group
P2 /c (#14)
Fcalcd (g/cm )
2.560
2.38
2.30
1
µ (Mo KR) (mm-1)
15.00
13.44
13.44
Z value
4
3
temperature (K)
296
294
100
Fcalcd (g/cm )
2.23
12.59
294
56.6
9236
449
1.001
0.000
0.0198; 0.0493
multiscan
1.000/0.655
0.97
µ (Mo KR) (mm-1)
2
Θmax (deg)
52.0
56.4
50.0
no. obsd (I > 2σ(I))
2869
182
6066
324
17760
620
temperature (K)
no. parameters
2Θmax (deg)
goodness of fit (GOF)a 1.062
1.024
1.056
no. obsd (I > 2σ(I))
max shift final cycle
0.000
0.002
0.002
no. parameters
Residuals*: R1; wR2 0.0400; 0.0864
absorption correction, multiscan
max/min
0.0385; 0.0988 0.0734; 0.1747
goodness of fit (GOF)a
multiscan
multiscan
max shift final cycle
1.000/0.650
1.47
1.000/0.473
1.000/0.474
a
residuals: R1; wR2
largest peak in final
2.27
10.17
-
3
absorption correction,
max/min
largest peak in final diff
map (e-/Å3)
diff. map (e /Å )
a
2
R ) Σhkl(||Fobsd| - |Fcalcd||)/Σhkl|Fobsd|; Rw ) [Σhklw(|Fobsd| - |Fcalcd|) /
2
1/2
2
2
ΣhklwFobsd ] , w ) 1/σ (Fobsd); GOF ) [Σhklw(|Fobsd| - |Fcalcd|) /(ndata -
1
/2
nvari)]
.
a
2
R ) Σhkl(||Fobsd| - |Fcalcd||)/Σhkl|Fobsd|; Rw ) [Σhklw(|Fobsd| - |Fcalcd|) /
2
1/2
2
2
light yellow/colorless. The solvent was removed in Vacuo, and the
product was then isolated by TLC by using pure CH Cl solvent to
yield 3.7 mg (76%) of colorless Re (CO)12(µ-H)
Reaction of 10 with Pt(PBut . Pt(PBut
(30.0 mg, 0.050 mmol)
was added to a solution of 10 (10.4 mg, 0.010 mmol) in 25 mL of
hexane. The reaction mixture was heated to reflux for 8 h, after which
the solvent was removed in Vacuo. The products were separated by
TLC (silica gel) using a 3:1 hexane/methylene chloride solvent mixture
ΣhklwFobsd ] , w ) 1/σ (Fobsd); GOF ) [Σhklw(|Fobsd| - |Fcalcd|) /(ndata -
nvari)]1
/2
.
2
2
3
3
.
(PBut
pink Pt
2
Re
2
(CO)
8
)
3 2
4
(µ-H) , 13, and 2.1 mg of unreacted 12.
3
)
2
3 2
)
Spectral data for 13: IR νCO (cm- in hexane) 2083 (vw), 2062 (m),
1
1
2
028 (vw), 1993 (m), 1974 (s), 1934 (s), 1903 (vw). H NMR (400
3
MHz, toluene-d , rt, TMS) δ ) 1.34 ppm (d, J(P,H) ) 12 Hz, 54 H,
8
1
2
CH
3
1
), -6.27 ppm (t, J(Pt,H) ) 683 Hz, J(P,H) ) 7 Hz, 2H, hydride).
3
1
P{ H} NMR (162 MHz, toluene-d
8
, rt, 85% ortho-H
3
PO
4
): 98.9 ppm
to yield in order of elution the following: 6.0 mg (58% yield) of
3
1
2
(
s, J(P,P) ) 301 Hz, J(Pt,P) ) 2554 Hz, J(Pt,P) ) 2253 Hz, 1P).
t
starting yellow 10 and 3.0 mg (22% yield) of red Pt
µ-H) , 11.
Addition of H
2 2 7
Re (CO) (PBu
3 2
) -
+
+
t
+
4
(µ-H) ] , 1395;
Mass Spec. ES /MS calcd for M , [Pt
found, 1395. NOTE: When CO gas was bubbled though a solution of
2 in hexane, the color changed from orange to yellow within 1 min.
An IR spectrum of the reaction mixture indicated formation of
2
Re
2
(CO)
8
(PBu
3
)
2
(
2
2
to 11. Compound 11 (16.1 mg, 0.012 mmol) was
1
dissolved in 30 mL of heptane. With stirring, hydrogen gas was passed
through the solution at room temperature for 12 h. The heptane solvent
was then removed in Vacuo, and the product was isolated by TLC (silica
t
10
compound 10 and Pt
Reaction of 11 with Pt(PBu
and 11 (6.1 mg, 0.0045 mmol) in 10 mL of octane were refluxed for
.5 h. An IR spectrum of the reaction mixture at this time showed
3 3 3 3
(PBu ) (CO) .
t
t
3 2 3 2
) . Pt(PBu ) (5.1 mg, 0.0085 mmol)
gel) using a 3:1 hexane/methylene chloride solvent mixture to yield
t
1
1.5 mg of bright-orange Pt
2
Re
2
(CO)
7
(PBu
3
2 4
) (µ-H) , 12 (71% yield).
1
Spectral data for 12: IR νCO (cm- in hexane) 2041 (m), 2028 (s),
1
t
almost complete conversion to Pt
3
Re
2
(CO)
6
(PBu
3
)
3
2
(µ-H) , 14. Due to
1
2
006 (vs), 1936 (s), 1927 (vs), 1918 (m, sh). H NMR (400 MHz,
the instability of 14,7a this compound was not isolated in this work.
3
toluene-d
8
, rt, TMS) δ ) 1.29 ppm (d, J(P,H) ) 13 Hz, 27 H, CH
3
),
Reaction of 12 with Pt(PBut
t
)
3 2
(6.5 mg, 0.011 mmol)
3 2
) . Pt(PBu
3
2
1
3
.27 ppm (d, J(P,H) ) 13 Hz, 27 H, CH
7 Hz, 1H, hydride), -2.34 ppm (d, J(Pt,H) ) 588 Hz, J(P,H) ) 12
3
), -2.13 ppm (s, J(Pt,H) )
and 12 (7.5 mg, 0.0055 mmol) were dissolved in 15 mL of heptane.
After the mixture heated to reflux for 20 min, the solvent was removed
in Vacuo, and the products were separated by TLC (silica gel) using a
1
2
1
2
Hz, 1H, hydride), -6.10 ppm (dd, J(Pt,H) ) 801 Hz, J(Pt,H) ) 43
2
3
31
1
Hz, J(P,H) ) 10 Hz, J(P,H) ) 3 Hz, 2H, hydride). P{ H} NMR
4
:1 hexane/methylene chloride solvent mixture. This yielded in order
of elution the following: a trace amount of yellow PtRe (CO) )-
(PBut
, 10, a trace amount of pink 13, 6.2 mg (65% yield) of brown
3
(
162 MHz, toluene-d
62 Hz, J(Pt,P) ) 3388 Hz, J(Pt,P) ) 197 Hz, 1P), 108.14 ppm (d,
8
, 25 °C, 85% ortho-H
3
PO
4
) 95.75 ppm (d, J(P,P)
2
9
3
1
2
)
(
µ-H)
Pt Re
3
2
2
3
1
2
J(P,P) ) 62 Hz, J(Pt,P) ) 2720 Hz, J(Pt,P) ) 296 Hz, 1P). Mass
t
(CO)
6
(PBu
3
)
3
4
(µ-H) , 15, 0.9 mg of unreacted 12, and 1.0 mg
+
+
(PBut
+
4
(µ-H) ] , 1367;
Spec. ES /MS calcd for M , [Pt
2
Re
2
(CO)
7
3
)
2
(
13% yield) of 11.
Thermal Elimination of Hydrogen from 12 at 97 °C. Compound
2 (12.8 mg, 0.009 mmol) was dissolved in 60 mL of heptane in a 100
mL three-neck flask equipped with a reflux condenser and a gas inlet.
A slow stream of nitrogen (flow rate ∼27 mL/min) was allowed to
flow through the flask while refluxing this solution for 4 h. The progress
of this reaction can be monitored by IR. The heptane solvent was then
removed in Vacuo, and the products were separated by TLC (silica
gel) using a 3:1 hexane/methylene chloride solvent mixture to yield in
found, 1367. Elemental analysis (%) calcd: 27.23, C; 4.28, H. Found:
2
7.64, C; 3.99, H.
1
Controlled Addition of CO to 12. Compound 12 (13.5 mg, 0.010
mmol) was dissolved in 7 mL of heptane in a 10 mL Schlenk tube.
The Schlenk tube was then evacuated and filled with nitrogen three
times and finally evacuated partially on the last filling. Carbon
monoxide gas (CO) (215 µL, 0.009 mmol) was added to the partially
evacuated Schlenk tube by using a syringe. The reaction was stirred at
room temperature for 2 h. The solvent was then removed in Vacuo,
and the product was isolated by TLC (silica gel) using a 4:1 hexane/
methylene chloride solvent mixture to yield 10.0 mg (73% yield) of
(
10) Goel, R. G.; Ogini, W. O.; Srivastava, R. C. J. Organomet. Chem. 1981,
214, 405-417.
J. AM. CHEM. SOC.
9
VOL. 129, NO. 18, 2007 5983

A R T I C L E S
Adams et al.
order of elution the following: 0.7 mg (5% yield) of starting orange
The crystals of compound 9 belong to the monoclinic crystal system.
The systematic absences in the intensity data for these crystals were
consistent with either of the space groups P2 and P2 /m. The structure
1 1
t
Pt
Re
2
Re
(CO)
Photoelimination of Hydrogen from 12. Compound 12 (12.8 mg,
.009 mmol) was dissolved in 60 mL of hexane in a 100 mL three-
2
(CO)
7
(PBu
3
)
2
(µ-H)
4
, 12, and 11.5 mg (90% yield) of red Pt
2
-
(PBut
(µ-H)
, 11.
2
7
3
)
2
2
could be solved only in the latter space group. The three hydrido ligands
were located but could not be refined and were included finally as fixed
contributions where they were located in the diff. Fourier maps. The
quaternary carbons on the tri-tert-butyl phosphine ligand were disor-
dered over two orientations and were refined in the ratio 50/50. The
carbon atoms of the tri-tert-butyl phosphine ligand were refined with
isotropic displacement parameters.
For compound 10 the systematic absences in the data indicated two
possible space groups, C2/c or Cc. The former was attempted first and
confirmed by the successful solution and refinement of the structure.
The two hydrido ligands were located and refined successfully with
isotropic thermal parameters.
0
neck flask equipped with a reflux condenser and a gas inlet. A slow
stream of nitrogen (flow rate ∼27 mL/min) was allowed to flow through
the flask while irradiating this solution for 4 h using a medium-pressure
mercury UV lamp (1000 W). The progress of this reaction can be
monitored by IR. The hexane solvent was then removed in Vacuo, and
the products were separated by TLC (silica gel) using a 3:1 hexane/
methylene chloride solvent mixture to yield in order of elution the
t
following: trace amounts (<0.5 mg) of pink Pt
2
Re
Re
2
(CO)
(CO)
8
(PBu
(PBu
3
)
)
2
(µ-
(µ-
t
4
H) , 13, trace amounts (<0.5 mg) of orange Pt
3
2
6
3
3
6
H) , 7, trace amounts (<0.5 mg) of brown 15, 1.0 mg (8% yield) of
starting orange 12, and 10.6 mg (83% yield) of red 11.
Detection of Hydrogen Elimination by H NMR. A 6.0 mg amount
Compound 11 crystallized in the orthorhombic crystal system. The
space group P2 P2 P2 was identified on the basis of the patterns of
1 1 1
1
of 12 was dissolved in 0.6 mL of toluene-d
8
in a 5 mm NMR tube.
systematic absences in the data. The compound crystallizes with three
independent molecules in the crystallographic asymmetric unit. The
structure is disordered. The disorder is evident from the presence of
several large residual electron density peaks in the vicinity of the metal
atoms. Various twinning and disorder models were attempted but were
unsuccessful. Careful examination of the diffraction pattern showed
no indication of a different unit cell. Several attempts were made to
crystallize this compound from different solvent mixtures and different
crystallization conditions; however, beautiful pristine looking red single
crystals were always obtained with the same unit cell dimensions. Only
the platinum, rhenium, and phosphorus atoms were refined with
anisotropic thermal parameters. The two hydrido ligands could not be
located.
The NMR tube was evacuated and filled with nitrogen five times. The
NMR tube was then evacuated partially. The partially evacuated NMR
tube was placed in an oil bath maintained at 100 °C for 3 h. After
this period of time the NMR tube was taken out of the oil bath and
1
kept cold (ice-water bath) while proceeding to acquire the H NMR
1
spectrum. The H NMR spectrum of this solution showed a singlet
at δ ) 4.51 indicating the presence of H
was also detected by irradiating a sample of 12 in toluene-d
in an NMR tube for 4 h using a medium-pressure mercury UV lamp
2
in solution. Similarly, H
2
8
solvent
(1000 W).
Determination of the Kinetic Isotope Effect (KIE) for the
Addition of H to 11. In a 100 mL Schlenk flask, 10.0 mg of 11 in 40
2
Compound 12 crystallized in the monoclinic crystal system. The
space group P2 /c was identified on the basis of the patterns of
1
mL of hexane were stirred overnight at room temperature to ensure
that 11 had completely dissolved. The flask was then evacuated and
filled with deuterium gas three times. The flask was stirred at room
temperature under the deuterium atmosphere. During this time, samples
were removed periodically via syringe, and IR spectra in the CO region
were recorded. Under identical conditions, 10.0 mg of 11 in 40 mL of
hexane were stirred at room temperature under a hydrogen atmosphere,
and IR spectra were recorded periodically. At certain times the IR
spectra of the two samples appeared to be virtually the same. The KIE
was determined to be the ratio of the reaction times D/H for the two
reactions when the spectra appeared to be identical. For example, the
systematic absences in the data. Each of the four hydrido ligands were
located and refined successfully with isotropic thermal parameters. One-
half of a molecule of methylene chloride from the crystallization solvent
cocrystallized with the complex. The solvent molecule was included
in the analysis and was satisfactorily refined with anisotropic thermal
parameters.
Compound 13 crystallized in the triclinic crystal system. The space
group P 1h was assumed and confirmed by the successful refinement
and solution of the structure. With Z ) 1, the molecule is crystallo-
graphically centrosymmetrical and thus contains only one-half of the
formula equivalent of the molecule in the asymmetric crystal unit. Both
independent hydrido ligands were located and refined successfully with
isotropic thermal parameters.
IR spectrum for the D
the same as the IR spectrum after 1.5 h for the H
thus the D /H isotope effect was determined to be 1.5(1).
2
addition reaction after 2.25 h was approximately
2
addition reaction,
2
2
Crystallographic Analyses. Single crystals of 9, 10, 11, 12, and
3 suitable for X-ray diffractions were obtained by slow evaporation
Details of the Computational Treatments. All calculations were
performed using the Gaussian 03 suite of programs.13 The computational
1
of solvent from solutions in methylene chloride/hexane solvent mixtures
at -20 °C. Each data crystal was glued onto the end of a thin glass
fiber. X-ray intensity data were measured by using a Bruker SMART
APEX CCD-based diffractometer using Mo KR radiation (λ ) 0.710 73
Å). The raw data frames were integrated with the SAINT+ program
by using a narrow-frame integration algorithm. Correction for Lorentz
and polarization effects were also applied with SAINT+. An empirical
absorption correction based on the multiple measurement of equivalent
reflections was applied using the program SADABS. All structures
were solved by a combination of direct methods and difference Fourier
model of the experimental system was constructed with PMe
3
ligands
in place of P(t-Bu) ligands to reduce the computational demands of
3
the system. Optimized gas-phase geometries were obtained by using
the B3PW91 DFT method.1 The basis set (BS1) used for geometry
optimizations and energy calculations was implemented as follows: for
4,15
1
1
1
6
rhenium and platinum, the valence double-ú LANL2DZ basis sets
(
13) All calculations were conducted using the Gaussian03 suite of programs:
Frisch, M. J., et al. Gaussian 03, revision B.4; Gaussian, Inc.: Pittsburgh,
PA, 2003.
2
(14) Becke, A. D. J. Chem. Phys. 1993, 98, 5648-5652.
syntheses and refined by full-matrix least-squares on F , using the
(
15) (a) Burke, K.; Perdew, J. P.; Wang, Y. In Electronic Density Functional
Theory: Recent Progress and New Directions; Dobson, J. F., Vignale, G.,
Das, M. P., Eds.; Plenum: New York, 1998; pp 81-111. (b) Perdew, J. P.
In Electronic Structure of Solids ’91; Ziesche, P., Eschrig, H., Eds.;
Akademie Verlag: Berlin, 1991; p 11. (c) Perdew, J. P.; Chevary, J. A.;
Vosko, S. H.; Jackson, K. A.; Pederson, M. R.; Singh, D. J.; Fiolhais, C.
Phys. ReV. B 1992, 46, 6671-6687. (d) Perdew, J. P.; Chevary, J. A.;
Vosko, S. H.; Jackson, K. A.; Pederson, M. R.; Singh, D. J.; Fiolhais, C.
Phys. ReV. B 1993, 48, 4978. (e) Perdew, J. P.; Burke, K.; Wang, Y. Phys.
ReV. B 1996, 54, 16533-16539.
1
2
SHELXTL software package. All non-hydrogen atoms were refined
with anisotropic thermal parameters. Hydrogen atoms were placed in
geometrically idealized positions and included as standard riding atoms
during the least-squares refinements. Crystal data, data collection
parameters, and results of the refinements are listed in Tables 1 and 2.
(
11) SAINT+, version 6.2a; Bruker Analytical X-ray System, Inc.: Madison,
Wisconsin, U.S.A., 2001.
(16) (a) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 270-283. (b) Wadt,
W. R.; Hay, P. J. J. Chem. Phys. 1985, 82, 284-298. (c) Hay, P. J.; Wadt,
W. R. J. Chem. Phys. 1985, 82, 299-310.
(12) Sheldrick, G. M. SHELXTL, version 6.1; Bruker Analytical X-ray Systems,
Inc.: Madison, Wisconsin, U.S.A., 1997.
5984 J. AM. CHEM. SOC.
9
VOL. 129, NO. 18, 2007

Unsaturated Platinum−Rhenium Cluster Complexes
A R T I C L E S
were supplemented with sets of 6p functions for transition metals
17
developed by Couty and Hall; for phosphorus, the LANL2DZdp basis
1
6,18,19
for carbon and oxygen, the 6-31G(d′)20 basis sets
set was used;
were used; for the hydrogen atoms attached to carbon, the 6-31G basis
2
0
set was used; while, for dihydrogen and for the hydrogen atoms that
bonded to the platinum and rhenium, the 6-31G++(d′,p′) basis set was
2
0
used. All structures were calculated in singlet spin states using the
restricted B3PW91 method. Calculating the harmonic vibrational
frequencies and noting the number of imaginary frequencies confirmed
the nature of all intermediates (NImag ) 0) and transition state
structures (NImag ) 1).
Fenske-Hall Molecular Orbital Calculations. A single-point
molecular orbital calculation on 11 was performed on the molecular
structure as derived from the single-crystal X-ray diffraction analysis.
PH
ligands were calculated using the program XHYDEX in the WINGX
was used in place of PBut
in these calculations. The two hydride
3 3
2
1
suit of programs. The molecular orbital calculations reported herein
were performed by using the Fenske-Hall method.22 Contracted
Figure 1. An ORTEP diagram of the molecular structure of PtRe3(CO)12-
t
(
PBu 3)(µ-H)3, 9, showing 40% probability thermal ellipsoids. Selected
double-ú basis sets were used for the Re 5d, Pt 5d, P 3p, and C and O
interatomic distances (Å) and angles (deg) are as follows: Pt(1)-Re(1) )
2
2
p atomic orbitals. The Fenske-Hall molecular orbital method is an
.9280(5); Pt(1)-Re(2) ) 2.9532(7); Pt(1)-P(1) ) 2.312(3); Re(1)-Re-
approximate self-consistent-field (SCF) nonempirical method that is
capable of calculating molecular orbitals for very large transition metal
systems and has built-in fragment analysis routines that allow one to
assemble transition metal cluster structures from the ligand-containing
fragments.
(
2) ) 3.0476(5); Re(1)-Pt(1)-Re(1*) ) 119.41(2); Re(1)-Pt(1)-Re(2)
) 62.420(12).
2.9280(5) Å, Pt(1)-Re(2) ) 2.9532(7) Å. The two equivalent
Re-Re distances Re(1)-Re(2) ) Re(1*)-Re(2) ) 3.0476(5)
Å are not significantly different from the Re-Re distance in
Results and Discussion
2
3
Re2(CO)10 [3.042(1) Å] but are significantly shorter than the
t
24
Two new compounds PtRe3(CO)12(PBu 3)(µ-H)3, 9, and
hydride bridged Re-Re distances, 3.241(2) Å, found in 8.
t
PtRe2(CO)9(PBu 3)(µ-H)2, 10, were obtained from the reaction
Hydride bridged metal-metal bonds are usually longer than the
t
25
of Pt(PBu 3)2 with Re3(CO)12(µ-H3), 8, at room temperature in
corresponding bonds that do not have bridging hydride ligands.
the yields 20% and 14%, respectively. Both products were
1
31
characterized by IR, H and P NMR, single-crystal X-ray
diffraction, and elemental analyses. An ORTEP diagram of the
molecular structure of 9 is shown in Figure 1. The compound
consists of a butterfly tetrahedral cluster of four metal atoms,
three of rhenium and one of platinum. In the solid state, the
molecular structure of compound 9 contains reflection symmetry
in the crystal with the platinum atom, the rhenium atom Re(2),
and the phosphorus atom of the phosphine ligand lying on the
reflection plane. There are 12 carbonyl ligands, four terminal
COs on each rhenium atom. The platinum atom is bonded to
all three rhenium atoms: Pt(1)-Re(1) ) Pt(1)-Re(1*) )
The metal cluster is structurally similar to the platinum-
rhenium dianion, [PtRe3(CO)13(µ-H)] , 16, obtained by Ber-
2
-
(
17) Couty, M.; Hall, M. B. J. Comput. Chem. 1996, 17, 1359-1370.
18) Basis sets were obtained from the Extensible Computational Chemistry
Environment Basis Set Database, Version 02/25/04, as developed
and distributed by the Molecular Science Computing Facility, Environ-
mental and Molecular Sciences Laboratory which is part of the
Pacific Northwest Laboratory, P.O. Box 999, Richland, Washington
(
2-
inghelli et al. from the reaction of [{Pt3(CO)6}n]
with
-
26
[Re2(CO)8H2(µ-H)] . The hydride bridged Pt-Re bond in 16
is 2.799(1) Å in length. The Pt-Re bonds in 16 that do not
have bridging hydride ligands are 2.706(1) Å and 2.798(2) Å.
The Re-Re distances in 16 are 3.046(1) Å and 3.091(1) Å.
9
9352, U.S.A., and funded by the U.S. Department of Energy. The Pacific
Northwest Laboratory is multiprogram laboratory operated by
a
Battelle Memorial Institute for the U.S. Department of Energy under
Contract DE-AC06-76RLO 1830. Contact Karen Schuchardt for further
information.
t
Compound 9 contains one PBu 3 ligand that is coordinated to
the platinum atom, Pt(1)-P(1) ) 2.312(3) Å. There are three
hydrido ligands. They were located in the structural analysis
but were not refined. One bridges each of the three Pt-Re
bonds. They appear only as two resonances in a 2/1 ratio in the
(
19) Check, C. E.; Faust, T. O.; Bailey, J. M.; Wright, B. J.; Gilbert, T. M.;
Sunderlin, L. S.; J. Phys. Chem. A 2001, 105, 8111-8116.
20) (a) Ditchfield, R.; Hehre, W. J.; Pople, J. A. J. Chem. Phys. 1971, 54,
(
7
1
1
1
24-728. (b) Hehre, W. J.; Ditchfield, R.; Pople, J. A. J. Chem. Phys.
972, 56, 2257-2261. (c) Hariharan, P. C.; Pople, J. A. Theor. Chim. Acta
973, 28, 213-222. (d) Petersson, G. A.; Al-Laham, M. A. J. Chem. Phys.
991, 94, 6081-6090. (e) Petersson, G. A.; Bennett, A.; Tensfeldt, T. G.;
1
2
H NMR spectrum, δ ) - 9.17 (d, 2H, hydride, JP-H ) 6
Al-Laham, M. A.; Shirley, W. A.; Mantzaris, J. J. Chem. Phys. 1988, 89,
1
2
Hz, JPt-H ) 756 Hz), -11.39 (d, 1H, hydride, J(P,H) ) 9
2
193-2218. (f) Foresman, J. B.; Frisch, Æ. Exploring Chemistry with
1
Electronic Structure Methods, 2nd ed.; Gaussian, Inc.: Pittsburgh, PA; p
Hz, J(Pt,H) ) 118 Hz), because two of them are equivalent.
1
10. The 6-31G(d′,p′) basis set has the d polarization functions for C, N,
Both resonances show one bond coupling to platinum. Two bond
O, and F taken from the 6-311G(d) basis set, instead of those which use
the exponent with an original arbitrarily assigned value of 0.8 used in the
6
-31G(d) basis set.
(23) Churchill, M. R.; Amoh, K. N.; Wasserman, H. J. Inorg. Chem. 1981, 20,
1609-1611.
(
21) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837-838. http://www.chem.g-
la.ac.uk/∼louis/wingx.
(24) Masciocchi, N.; Sironi, A.; D’Alfonso, G. J. Am. Chem. Soc. 1990, 112,
9395-9397.
(
22) Hall, M. B.; Fenske, R. F. Inorg. Chem. 1972, 11, 768-779; Manson, J.;
Webster, C. E.; Perez, L. M.; Hall, M. B. http://www.chem.tamu.edu/jimp2/
index.html.
(25) (a) Bau, R.; Drabnis, M. H. Inorg. Chim. Acta 1997, 259, 27-50. (b) Teller,
R. G.; Bau, R. Struct. Bonding (Berlin) 1981, 41, 1-82.
J. AM. CHEM. SOC.
9
VOL. 129, NO. 18, 2007 5985

A R T I C L E S
Adams et al.
distance (Å)
Table 3. Selected Intramolecular Distances and Angles for 11a
molecule 1
molecule 2
molecule 3
atom
atom
distance (Å)
atom
atom
distance (Å)
atom
atom
Pt(1)
Pt(1)
Pt(1)
Pt(2)
Pt(2)
Re(1)
Pt(2)
2.6665(16)
2.9100(15)
2.8648(16)
2.7259(15)
2.6119(15)
2.9419(13)
Pt(3)
Pt(3)
Pt(3)
Pt(4)
Pt(4)
Re(3)
Pt(4)
2.6738(16)
2.9152(16)
2.8662(15)
2.7019(16)
2.6144(15)
2.9388(14)
Pt(5)
Pt(5)
Pt(5)
Pt(6)
Pt(6)
Re(5)
Pt(6)
2.6646(17)
2.8972(18)
2.8674(18)
2.7116(18)
2.6139(18)
2.921(2)
Re(1)
Re(2)
Re(1)
Re(2)
Re(2)
Re(3)
Re(4)
Re(3)
Re(4)
Re(4)
Re(5)
Re(6)
Re(5)
Re(6)
Re(6)
a
Estimated standard deviations in the least significant figure are given in parentheses.
couplings to platinum are usually less than 40 Hz.27 Overall,
compound 9 has only 60 valence electrons; two less than the
amount 62 usually found for butterfly tetrahedral cluster
complexes. This can be explained by the presence of the
platinum atom that formally has only 16 valence electrons.
We showed previously that the reaction of Os3(CO)12, which
metal atoms, two of rhenium and one of platinum. There are
nine carbonyl ligands, four terminal COs on each rhenium atom
and one on the platinum atom. Compound 10 contains two
hydrido ligands that were located and refined in the structural
analysis. One bridges the Pt(1)-Re(1) bond, and the other
bridges the Re-Re bond, Re(1)-Re(2) ) 3.1726(4) Å. As
expected, the hydride bridged Pt-Re bond, Pt(1)-Re(1) )
2.9667(4) Å, is significantly longer than the unbridged Pt-Re
bond, Pt(1)-Re(2) ) 2.8133(4) Å. The two highly shielded
t
is isoelectronic with 8, with Pt(PBu 3)2 resulted in the formation
t
t
of PPBu 3 adducts of Os3(CO)12, Os3(CO)12[Pt(PBu 3)]n n ) 1-3
t
2
by the addition of Pt(PBu 3) groups across the Os-Os bonds.
There was no evidence for insertion of the Pt(PBu 3) group into
t
1
2
resonances in the H NMR spectrum, δ ) -7.19 (d, J(P,H) )
1
2
the metal-metal bond in these additions. In the reaction of 8
14 Hz, J(Pt, H) ) 538 Hz) and -15.41 (s, J(Pt, H) ) 31 Hz),
are attributed to the hydrido ligands. Compound 10 contains
t
t
with Pt(PBu 3)2, only one Pt(PBu 3) group was added to the
t
molecule of 8, and it was inserted into the Re-Re bond.
one PBu ligand that is coordinated to the platinum atom, Pt-
3
Since there was no loss of CO from the 8 in the formation of
(1)-P(1) 2.3837(15) Å. Compound 10 is structurally similar
t
9
, compound 9 could be viewed as a Pt(PBu 3) adduct of 8
t
formed by the insertion of the platinum atom from a Pt(PBu 3)
group into one of the hydride bridged metal-metal bonds. Two
of the hydrido ligands then migrated from Re-Re bonds to the
new Pt-Re bonds. These results demonstrate an interesting new
t
t
feature of the reactions of Pt(PBu 3)2, namely that the Pt(PBu 3)
group derived from it can actually be cleanly inserted into a
hydride bridged rhenium-rhenium bond without loss of a CO
ligand.
t
Interestingly, when 9 was treated with PBu 3, it was converted
back to 8 in 76% yield. The conversion of 9 back to 8
demonstrates that the insertion of the Pt(PBu 3) group into the
hydride bridged Re-Re bond is reversible.
An ORTEP diagram of the molecular structure of 10 is shown
to the platinum-rhenium compound PtRe2(CO)9(PPh3)2(µ-H)2,
7, obtained by Beringhelli et al. from the reaction of Re2(CO)8-
t
1
26
(µ-H)2 with Pt(PPh3)2(C2H4). The hydride-bridged Pt-Re bond
in 17 is 2.906(1) Å in length; the Pt-Re bond without a hydride
bridge is 2.788(1) Å. The hydride-bridged Re-Re length in 17
is 3.203(1) Å. Compound 10 has only 46 valence electrons;
two less than the 48 amount expected for electron precise
triangular metal cluster complexes. As in 9, this can be explained
by a 16 electron configuration at the platinum atom.
in Figure 2. This compound contains a triangular cluster of three
t
When the reaction of 8 with of Pt(PBu 3)2 was performed in
t
hexane at reflux, the new compound Pt2Re2(CO)7(PBu 3)2(µ-
H)2, 11, was obtained in 24% yield in addition to smaller
quantities of 9 (5%) and an increased quantity of 10 (35%). It
was subsequently shown that 11 is formed from 10 in 58% yield
t
by reaction with Pt(PBu 3)2 for 8 h at hexane reflux.
Compound 11 crystallizes with three independent molecules
in the crystallographic asymmetric unit. All three molecules are
structurally similar. An ORTEP diagram of the molecular
structure of one of the three molecules of 11 is shown in Figure
3
. Selected bond distances for the three molecules are listed in
Figure 2. An ORTEP diagram of the molecular structure of PtRe2(CO)9-
t
(PBu 3)(µ-H)2, 10, showing 40% probability thermal ellipsoids. Selected
Table 3. This compound consists of a cluster of four metal
interatomic distances (Å) and angles (deg) are as follows: Pt(1)-P(1)
.3837(15), Pt(1)-Re(2) ) 2.8133(4), Pt(1)-Re(1) ) 2.9667(4), Pt(1)-
H(1) ) 1.87(6), Re(1)-Re(2) ) 3.1726(4), Re(1)-H(1) ) 1.89(6),
Re(1)-H(2) 1.85(12), Re(2)-H(2) 1.87(12); Re(2)-Pt(1)-
Re(1) ) 66.52(1), Pt(1)-Re(1)-Re(2) ) 54.424(10), Pt(1)-Re(2)-Re(1)
59.056(8).
2
(
26) Beringhelli, T.; Ceriotti, A.; Ciani, G.; D’Alfonso, G.; Garlaschelli, L.;
Della Pergola, R.; Moret, M.; Sironi, A. J. Chem. Soc., Dalton Trans. 1993,
)
)
199-200.
(27) Adams, R. D.; Pompeo, M. P.; Wu, W. Inorg. Chem. 1991, 30, 2425-
)
2432.
5986 J. AM. CHEM. SOC.
9
VOL. 129, NO. 18, 2007

Unsaturated Platinum−Rhenium Cluster Complexes
A R T I C L E S
Figure 3. An ORTEP diagram of the molecular structure of one of the
three independent molecules in the unit cell of the crystal of Pt2Re2(CO)7-
t
(
PBu 3)2(µ-H)2, 11, showing 40% probability thermal ellipsoids.
atoms, two of rhenium and two of platinum, in the shape of a
tetrahedron. The molecule contains seven carbonyl ligands.
Three are located on each rhenium atom, and one is on one of
the two platinum atoms; see Pt(1) in Figure 3. Each platinum
t
atom contains one PBu 3 ligand. Compound 11 contains only
54 cluster valence electrons. This is six less than the 60 required
for a tetrahedral cluster in which all metal atoms have 18
electron configurations; see below. The platinum atom Pt(2)
has one less ligand than Pt(1). This could imply some electron
unsaturation at this atom. The two Pt-Re bonds to Pt(2), Pt-
(
(
2)-Re(1) ) 2.7259(15) [2.7019(16) Å, 2.7116(18) Å] and Pt-
2)-Re(2) ) 2.6119(15) Å [2.6144(15)Å, 2.6139(18) Å], are
Figure 4. 1H NMR spectra at 500 MHz of compound 11 at various
temperatures in toluene-d8 solvent.
much shorter than the unbridged Pt-Re bond in 10, 2.8133(4)
Å. The Pt-Pt bond is short but not unusually short, 2.6665(16)
Å [2.6738(16) Å and 2.6646(17) Å]. The molecular formula as
confirmed from the parent ion in its mass spectrum indicates
the presence of two hydrido ligands. This is supported by the
presented in Figure 4. Since 195Pt coupling to the hydride
resonance is observed in the dynamically averaged spectrum at
108 °C, the exchange mechanism must be an intramolecular
one. The most plausible mechanism for the interchange of the
hydrido ligands is by migratory shifts from one edge of the
1
H NMR spectrum recorded at -40 °C, which shows two highly
2
28
shielded resonances at δ ) -0.87 (s, 1H), -2.05 (dd, J(P,H)
cluster to another until site interchange is completed.
2
1
31
1
)
6 Hz, J(P,H) ) 11 Hz, J(Pt,H) ) 621 Hz, 1H). Due to
The P{ H} NMR at -25 °C exhibits two resonances of
1
95
minor disorder the structural analysis was not high and therefore
equal intensity with mutual couplings and couplings to Pt, δ
31
3
1
the hydrido ligands could not be located. The absence of P-H
) 85.5 (d, 1 P, JP-P ) 82 Hz, JPt-P ) 3880 Hz), 112.7 (d,
195
3
1
and Pt-H couplings to the resonance at -0.87 ppm suggests
that this hydrido ligand probably bridges the Re-Re bond. The
resonance at -2.05 ppm exhibits one bond coupling to one Pt
1 P, JP-P ) 82 Hz, JPt-P ) 2435 Hz). This is consistent
with the structure as found in the solid state. The resonances
broaden and average as the temperature is raised, although the
fast exchange limit could not be obtained due to the onset of
decomposition of the compound at temperatures greater than
100 °C. This is indicative of yet another dynamical process
whereby the environments of the phosphine ligands are inter-
changed. The most simple mechanism for this would be a simple
shifting of the terminal CO ligand on atom Pt(1) to an equivalent
position on atom Pt(2). This shift will probably involve
traversing an intermediate in which the CO ligand is simulta-
neously bonded to both Pt atoms; see Scheme 1. Bridge-terminal
1
atom, J(Pt,H) ) 621 Hz, and small couplings to both
2
2
phosphorus atoms, J(P,H) ) 6 Hz and J(P,H) ) 11 Hz). This
could be consistent with a number of locations about the cluster,
but molecular orbital calculations described below strongly
indicate that it bridges the Pt(1)-Re(1) bond shown in Figure
3
. This is also supported by the long length of the Pt(1)-Re(1)
25
bond, Pt(1)-Re(1) ) 2.9100(15) Å.
The hydrido ligands in 11 are dynamically active on the NMR
1
time scale as shown in the variable temperature H NMR spectra
Scheme 1
J. AM. CHEM. SOC.
9
VOL. 129, NO. 18, 2007 5987

A R T I C L E S
Adams et al.
Figure 5. QM model optimized structures and relative energies for 11. Relative energies compared to the lowest energy structure, 11A (0.0 kcal/mol).
Platinum (green), rhenium (beige), phosphorus (purple), oxygen (red), carbon (gray), hydrogen (white).
coordination rearrangements of CO ligands have been known
for many years and are well-known to be facile.29 The hydrido
ligand that bridges the Pt-Re bond will also have to shift to a
symmetrically equivalent Pt-Re bond involving the other Pt
atom. The facile shifting of the hydrido ligands in 11 was
1
established by the H NMR spectra, Figure 4.
It is known that cluster complexes can have less than the
expected number of valence electrons in the presence of
platinum atoms because of the tendency of platinum to adopt
1
6 electron configurations. Tetrahedral Pt2M2 compounds often
30
have 58 valence electrons. However, a decrease to 54 electrons,
as found in 11, is very unusual and suggests a high degree of
electronic unsaturation. The unsaturation may be tied to the
t
presence of the bulky PBu 3 ligands which inhibits the addition
Figure 6. An ORTEP diagram of the molecular structure of 12 showing
40% probability thermal ellipsoids. Selected interatomic distances (Å) are
as follows: Pt(1)-Pt(2) ) 2.7025(2); Pt(1)-Re(1) ) 2.9732(2); Pt(1)-
Re(2) ) 2.8805(2); Pt(2)-Re(1) ) 2.9182(2); Pt(2)-Re(2) ) 2.7866(2);
Re(1)-Re(2) ) 2.8303(3); Pt(1)-H(3) ) 1.50(7); Pt(2)-H(2) ) 1.78(6),
Pt(2)-H(4) ) 1.51(5), Re(1)-H(1) ) 1.74(4), Re(1)-H(2) ) 2.03(6), Re-
of other ligands, such as CO, that would ordinarily provide
additional electrons to the metal atoms.
A number of geometry optimized structures were calculated
for 11 by using the B3PW91 DFT method by placing the
hydrido ligands in various bridging positions along the metal-
metal bonds. These results are shown in Figure 5. The most
stable structure is 11A which has two bridging hydrido
ligands: one along the Re-Re bond and one along the Re(1)-
Pt(1) bond as labeled in Figure 3. It is also worth noting that
the structure 11A is also the only optimized structure that
accurately reproduces the arrangement of the nonhydrogen
ligands for 11 as established by the crystal structure analysis.
It is therefore assumed that this structure has the correct
arrangement for the hydrido ligands.
(
1)-H(3) ) 2.02(7), Re(2)-H(1) ) 1.89(4); Re(2)-H(2) ) 1.95(6); Pt-
1)-P(1) ) 2.3909(10); Pt(2)-P(2) ) 2.2729(9).
(
1
1
2, in 71% isolated yield after a 12 h reaction period. Compound
2 was characterized by IR, H and P NMR spectroscopy,
1
31
mass spectrometry, and single-crystal X-ray diffraction analyses.
An ORTEP diagram of the molecular structure of 12 is shown
in Figure 6. The structure of the cluster 12 is very similar to
that of 11. The four metal atoms are arranged in the form of a
tetrahedron. The seven CO ligands are distributed among the
metal atoms similarly to those in 11, and as in 11 each platinum
Because of the unusually facile addition of hydrogen to the
t
atom contains one PBu 3 ligand.
7
unsaturated five metal cluster complex 6, we were prompted
to investigate the reactivity of 11 with hydrogen. Interestingly,
it was found that 11 reacts with hydrogen at room temperature
to yield the tetrahydrido complex Pt2Re2(CO)7(PBu 3)2(µ-H)4,
(28) Churchill, M. R.; Lashewycz, R. A.; Shapley, J. R.; Richter, S. I. Inorg.
Chem. 1980, 19, 1277-1285.
(
29) Adams, R. D.; Cotton, F. A. Dynamical Nuclear Magnetic Resonance
Spectroscopy; Academic Press: 1975.
t
5988 J. AM. CHEM. SOC.
9
VOL. 129, NO. 18, 2007

Unsaturated Platinum−Rhenium Cluster Complexes
A R T I C L E S
The presence of the four hydrido ligands was confirmed by
its mass spectrum, m/e ) 1367, and further supported by the
1
H NMR spectrum; see below. In addition, the structural analysis
of 12 was of much better quality than that of 11, and in this
analysis each of the four hydrido ligands was located and refined
crystallographically. Two of the hydrido ligands occupy posi-
tions similar to those proposed for 11; that is, one H(1) bridges
the Re-Re bond and one H(3) bridges the Pt(1)-Re(1) bond.
The other two hydrido ligands are associated with Pt(2). H(2)
is a triply bridging ligand that is bonded to Pt(2), Re(1), and
Re(2); Pt(2)-H(2) ) 1.78(6) Å, Re(1)-H(2) ) 2.03(6) Å, Re-
(2)-H(2) ) 1.95(6) Å. H(1) is terminally coordinated to Pt(2),
Pt(2)-H(4) ) 1.51(5) Å. As expected the Pt-H bond distance
of the terminally coordinated hydrido ligand is significantly
shorter than that for bridging hydrido ligands.25 The hydride
bridged metal-metal bonds in 12 are all significantly longer
than those in 11, Pt(2)-Re(1) ) 2.9182(2) Å; Pt(2)-Re(2) )
2
5
2
.7866(2) Å. The Pt(1)-Re(1) bond distance, 2.9732(2) Å, is
longer than that in 11, but the Re-Re distance is slightly shorter,
Re(1)-Re(2) ) 2.8303(3) Å. The Pt(1)-Re(2) bond in 12 is
slightly longer than that in 11, 2.8805(2) Å.
The 1H NMR spectrum of 12 exhibits three high field
resonances, -2.13, -2.34, and -6.10 ppm in a 1/1/2 ratio,
consistent with the presence of four hydrido ligands, but this
is not completely consistent with the solid-state structure which
shows four inequivalent hydrido ligands. Low temperature
1
measurements of the H NMR spectra of 12 showed a sub-
stantial broadening of the hydride resonance at -6.10 ppm
which suggests that this may be a dynamically averaged
resonance, but this could not be resolved into its components
at the lowest temperatures that we could achieve on our
spectrometer (-85 °C).
To test for the presence of a kinetic isotope effect in the
addition of hydrogen to 11, we compared the rates of addition
of H2 and D2 to 11 as a function of time. A significant isotope
effect, D/H isotope effect of 1.5(1), was determined by following
the rates of formation of 12 and 12-d2 from 11 by IR
spectroscopy. This suggests that the activation of H2 may occur
at or before the slow step of the reaction.
Figure 7. A contour plot of the Fenske-Hall lowest unoccupied molecular
orbital (LUMO) of 11 (top) and labeling diagram (bottom).
2
(
Figure 8d). From 11-η -H2, addition of dihydrogen proceeds
2
through the transition state, TS-η -H2 f 12B (Figure 8e),
to yield complex 12B (Figure 8f), in which the H-H distance
has increased to 1.571 Å. The structure and energy of TS-η -
2
H2 f 12B were estimated from the highest energy point
on a relaxed potential energy scan starting from 12B, from which
the H-H distance was reduced in increments of 0.05 Å. This
relaxed potential energy scan revealed the highest electronic
energy was obtained at a H-H distance of 1.421 Å, and thus,
Mechanism of Hydrogen Addition to 11. Molecular orbital
calculations were performed to try to shed some light on the
mechanism of the addition of H2 to 11. Figure 7 shows a contour
diagram of the Fenske-Hall LUMO of 11. It shows that a major
component of the orbital is found on the platinum atom Pt(2),
shown in Figure 3, which strongly suggests that this atom is a
likely site for the H2 addition. It is also the atom which is most
strongly associated with the two added hydrido ligands in the
product 12. Accordingly, optimized structures to test the mode
of addition of H2 to this atom were investigated by using the
B3PW91 DFT method and a computational model in which
PMe3 ligands were used in place of P(t-Bu)3 ligands. Figure 8
shows a pathway of geometry optimized structures for the
addition of H2 to the platinum atom Pt(2) in 11 to form 12.
The addition begins by coordination of dihydrogen to 11A to
2
this point was used as TS-η -H2 f 12B. However, it should
2
be noted that the electronic energy of TS-η -H2 f 12B is only
0
.05 kcal/mol higher than the electronic energy of 12B; thus,
1
2B is a very shallow minima on the potential energy surface.
The final product, 12A (Figure 8h), is generated from 12B via
the transition state TS-12B f 12A (Figure 8g). Nocera has
recently shown that hydrogen adds selectively to a single metal
31
site in some mixed valence diiridium complexes.
Interestingly, compound 12 readily eliminates 1 equiv of
hydrogen when heated to 97 °C to regenerate 11 in 90% isolated
yield. Similarly, the elimination of H2 from 12 to yield 11 can
be induced at room temperature by the application of UV-vis
irradiation to solutions of 12. The hydrogen that was eliminated
1
1
form an η -H2 complex, 11-η -H2 (Figure 8b). Next, the
1
dihydrogen ligand changes coordination modes via TS-η -H2
f η -H2 (Figure 8c) to form the η -H2 complex, 11-η -H2
1
was verified as H2 by its characteristic H NMR resonance at δ
2
2
2
)
4.51 observed in solutions of 12 that were heated to 100 °C
(
30) (a) Farrugia, L. J. AdV. Organomet. Chem. 1990, 31, 301-391. (b) Adams,
R. D.; Captain, B.; Fu, W.; Hall, M. B.; Smith, M. D.; Webster, C. E.
Inorg. Chem. 2004, 43, 3921-3929.
(31) (a) Gray, T. G.; Veige, A. S.; Nocera, D. G. J. Am. Chem. Soc. 2004, 126,
9760-9768. (b) Veige, A. S.; Gray, T. G.; Nocera, D. G. Inorg. Chem.
2005, 44, 17-26.
J. AM. CHEM. SOC.
9
VOL. 129, NO. 18, 2007 5989

A R T I C L E S
Adams et al.
1
Figure 8. QM optimized dihydrogen complexes, transition states for H2 activation, and resulting local minima for the 11 + H2 at Pt: (a) 11A, (b) 11-η -H2,
1
2
2
2
(
c) TS-η -H2 f η -H2, (d) 11-η -H2, (e) TS-η -H2 f 12B, (f) 12B, (g) TS-12B f 12A, and (h) 12. Relative energies of the 11-H2-Pt series (a-h) are
2
compared to the lowest energy 11 complex + separated H2 ) 0.0 kcal/mol. The structure and relative energy of (e) TS-η -H2 f 12B were estimated from
the highest energy structure of a relaxed potential energy scan starting from 12B, in which the H-H distance was decreased in increments of 0.05 Å. All
other structures were fully optimized. Platinum (green), rhenium (beige), phosphorus (purple), oxygen (red), carbon (gray), hydrogen (white).
or subjected to UV-vis irradiation at room temperature. The
mechanism for the thermal elimination of H2 from 12 is assumed
to be the microscopic reverse of the addition process shown in
Figure 8.
Because 12 is also electronically unsaturated, it was decided
to investigate its reaction with CO. Compound 12 was found
to react with CO in heptane solvent at room temperature to yield
t
the new compound Pt2Re2(CO)8(PBu 3)2(µ-H)4, 13, in 73% yield
1
31
within 2 h. Compound 13 was characterized by IR, H and
P
NMR spectroscopy, mass spectrometry, and single-crystal X-ray
diffraction analyses. An ORTEP diagram of the molecular
structure of 13 is shown in Figure 9. The molecule contains a
crystallographically imposed center of symmetry in the solid
state. The structure of 13 has a planar cluster of four metal
atoms, two of platinum and two of rhenium, in the shape of a
rhombus. There is a bond between the two diagonally positioned
platinum atoms, Pt(1)-Pt(1*) ) 2.7140(2) Å. Each rhenium
atom contains four linear terminal carbonyl ligands, and each
Figure 9. An ORTEP diagram of the molecular structure of 13 showing
40% probability thermal ellipsoids. Selected interatomic distances (Å) and
angles (deg) are as follows: Pt(1)-Pt(1*) ) 2.7140(2), Pt(1)-Re(1) )
t
platinum atom contains one PBu 3 ligand. Compound 13 contains
four hydrido ligands that bridge each of the four Pt-Re bonds
around the periphery of the cluster, Pt(1)-H(1) ) 1.59(4) Å,
2
.8801(2), Pt(1)-Re(1*) ) 2.8879(2), Pt(1)-H(1) ) 1.59(4), Pt(1)-H(2)
) 1.69(4), Re(1)-H(1) ) 1.88(4).
5990 J. AM. CHEM. SOC.
9
VOL. 129, NO. 18, 2007

Unsaturated Platinum−Rhenium Cluster Complexes
A R T I C L E S
Scheme 2
Pt(1)-H(2) ) 1.69(4) Å, Re(1)-H(1) ) 1.88(4) Å. These Pt-
Re bonds are similar in length to the hydride bridged Pt-Re
bonds in 11and 12, Pt(1)-Re(1) ) 2.8801(2) Å and Pt(1)-
Re(1*) ) 2.8879(2) Å. The hydrido ligands are all equivalent
and appear as a single resonance at -6.27 ppm with appropriate
coordination. Compound 12 which is also unsaturated was found
to add CO to yield the open cluster complex 13. Compound 11
and 12 add yet another platinum atom to yield the five metal
7
cluster complexes 14 and 15.
Recent studies have shown that heteronuclear metallic nano-
particles prepared from mixed metal carbonyl cluster complexes
containing platinum exhibit superior properties as hydrogenation
1
95
31
1
2
Pt and P couplings, J(Pt,H) ) 683 Hz, J(P,H) ) 7 Hz in
1
the H NMR spectrum. Compound 13 contains a total of 58
cluster valence electrons which is four less than that required
for such a structure in which all the metal atoms have 18 electron
configurations. This can be explained for 13 if the two platinum
atoms have 16 electron configurations.
3
2
catalysts. Our studies suggest that ligand deficient platinum
atoms are the preferred sites for hydrogen activation in unsatur-
ated mixed metal cluster complexes. They may also be prime
sites for hydrogen activation on platinum containing ligand-
free heteronuclear nanoparticles on supports.
When 11 and 12 were treated with additional quantities of
t
Pt(PBu 3)2, they were enlarged to yield the triplatinumdirhenium
t
Acknowledgment. This research was supported by the Office
of Basic Energy Sciences of the U.S. Department of Energy
under Grant No. DE-FG02-00ER14980 and the USC Nano-
center. We thank Dr. Perry J. Pellechia for assistance with the
variable temperature NMR measurements. Dedicated to the
memory of F. Albert Cotton, a true friend and leader.
complexes Pt3Re2(CO)6(PBu 3)3(µ-H)2, 14, and Pt3Re2(CO)6-
t
(
PBu 3)3(µ-H)4, 15, respectively. These unsaturated cluster
complexes, which also add hydrogen at room temperature, have
recently been described by us in another report and will not be
further described herein.7
a
Summary and Conclusions
Supporting Information Available: CIF files for each of the
structural analyses are available. Also complete citation for ref
3. This material is available free of charge via the Internet at
http://pubs.acs.org.
A summary of the reactions described in this report are shown
in Scheme 2. It has been shown for the first time that the Pt-
1
t
(
PBu 3) group can be inserted into the hydride-bridged Re-Re
bond of 8 to yield the adduct 9 as the first step in a metal
substitution process that leads to the trinuclear PtRe2 complex
JA070773O
t
1
0. Compound 10 reacts with Pt(PBu 3)2 to yield the highly
(
32) (a) Hungria, A. B.; Raja, R.; Adams, R. D.; Captain, B.; Thomas, J. M.;
Midgley, P. A.; Golvenko, V.; Johnson, B. F. G. Angew. Chem., Int. Ed.
2006, 45, 4782-4785. (b) Thomas, J. M.; Johnson, B. F. G.; Raja, R.;
Sankar, G.; Midgley, P. A. Acc. Chem. Res. 2003, 36, 20-30. (c) Hermans,
S.; Raja, R.; Thomas, J. M.; Johnson, B. F. G.; Sankar, G.; Gleeson, D.
Angew. Chem., Int. Ed. 2001, 40, 1211-1215.
unsaturated four metal Pt2Re2 complex 11 that adds hydrogen
reVersibly under mild conditions to yield the tetrahydrido Pt2-
Re2 complex 12. Molecular orbital calculations suggest that the
H2 addition occurs at the platinum atom with the lower
J. AM. CHEM. SOC.
9
VOL. 129, NO. 18, 2007 5991