Synthesis and transformations of triosmium carbonyl cluster complexes containing bridging aryl ligands

Article abstract of DOI:10.1021/om300235n

The reaction of Os₃(CO)₁₀(NCMe)₂ (1) with C₆H₅Au(PPh₃) has yielded the complex Os ₃(CO)₁₀(ν, η¹-C₆H ₅)(ν-AuPPh₃) (2), which

Full text of DOI:10.1021/om300235n

Communication
pubs.acs.org/Organometallics
Synthesis and Transformations of Triosmium Carbonyl Cluster
Complexes Containing Bridging Aryl Ligands
Richard D. Adams,* Vitaly Rassolov,* and Qiang Zhang
Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208, United States
S
* Supporting Information
ABSTRACT: The reaction of Os3(CO)10(NCMe)2 (1) with C6H5Au(PPh3) has
yielded the complex Os3(CO)10(μ,η1-C6H5)(μ-AuPPh3) (2), which contains an
bridging η1-phenyl ligand and a Au(PPh3) group that bridges the same unsaturated
Os−Os bond in the 46-electron cluster complex. When it was heated to reflux in an
octane solution (125 °C), compound 2 was decarbonylated and converted to the
complex Os3(CO)9(μ3-C6H4)(μ-AuPPh3)(μ-H) (3), which contains a triply
bridging benzyne ligand by a CH cleavage on the bridging phenyl ring. The
reaction of Os3(CO)10(NCMe)2 with (1-C10H7)Au(PPh3) (1-C10H7 = 1-naphthyl)
yielded the complex Os3(CO)10(μ-2-C10H7)(μ-AuPPh3) (4), which exists as two
isomeric forms in the solid state. A 1,2-hydrogen shift in the naphthyl ligand
occurred in the formation of 4. The green isomer 4a is structurally similar to 2 and
contains a bridging η1-2-naphthyl ligand and a bridging Au(PPh3) group and is
electronically unsaturated overall. The pink isomer 4b contains a bridging η2-2-
naphthyl ligand and a bridging Au(PPh3) group and is electronically saturated. The pink isomer is found in hexane solution and
was converted to the complex Os3(CO)9(μ3-C10H6)(μ-AuPPh3)(μ-H) (5) when heated to reflux in octane (125 °C) for 30 min.
Compound 5 contains a triply bridging 1,2-naphthyne ligand.
ears ago Johnson and Lewis showed that the triosmium
carbonyl complex Os3(CO)10(NCMe)2 (1) reacts with
by elimination of the two NCMe ligands and an oxidative
addition of the Au−C bond of the C6H5Au(PPh3) to the
Os3(CO)10 group to give the complex Os3(CO)10(μ-C6H5)(μ-
AuPPh3) (2) in 47% yield. The structure of 2 was established
crystallographically, and an ORTEP diagram of its molecular
structure is shown in Figure 1. The molecule contains a
triangular cluster of three osmium atoms with a η1-bridging
phenyl ligand and a bridging AuPPh3 group across the Os1−
Os2 bond. The bond distances to the carbon atom C(1) of the
bridging phenyl group, Os1−C1 = 2.191(13) Å and Os2−C1 =
2.236(11) Å, are shorter (on the average) than those found in
two previously reported triosmium cluster complexes contain-
ing bridging phenyl ligands: Os3(CO)8(μ3-Se2)(μ-Ph)(μ-
PhCO)10 (2.24(2) and 2.51(2) Å) and Os3(CO)8(μ-
PPh2)(μ-Ph)(μ-PPhC6H4)2a (2.19 and 2.39 Å). The doubly
bridged Os1−Os2 bond in 2 is significantly shorter (2.7521(6)
Å) than the two other Os−Os bonds (Os1−Os3 = 2.8785(5)
Å, Os2−Os3 = 2.8746(5) Å) in 2. Assuming that the phenyl
ligand and the Au(PPh3) group are both 1-electron donors,
then compound 2 contains a total of 46 electrons at the metal
atoms and the cluster is formally unsaturated. Compound 2 is
electronically similar to the 46-electron triosmium cluster
complexes Os3(CO)10(μ-H)2,11 Os3(CO)10(μ-AuPEt3)2,12 and
Os3(CO)10(μ-AuPPh3)(μ-H),13 whose doubly bridged Os−Os
bonds (2.683(1),11b 2.684(1),12 and 2.699(1) Å,13 respectively)
are also significantly shorter than the unbridged Os−Os bonds.
Y
arenes to yield the complexes Os3(CO)10(μ3-C6H2R1R2)(μ-H)2
(R1, R2: H, H; H, Me; H, Prn; H, CHCHPh; H, Cl; Me, Me),
which contain triply bridging aryne ligands.1 Over the years, a
variety of triosmium and triruthenium aryne complexes have
also been obtained from the reactions of Os3(CO)12 and
Ru3(CO)12 with aryl-substituted phosphines,2,3 arsines,3
stibines,4 thioethers,5 etc. at elevated temperatures. To date,
very little has actually been established with regard to the
mechanism(s) of the formation of the aryne ligands in these
reactions. Presumably, they begin with the loss of a ligand(s)
from the cluster, which is followed by a series of two CH
cleavages from the arene or a cleavage of an aryl group from an
aryl-substituted group V or VI donor and a cleavage of one CH
bond from the aryl ligand. Hartwig et al. have investigated the
transformation of a σ-phenyl ligand into an η2-benzyne ligand
in a mononuclear ruthenium complex.6 Johnson et al. showed
that the triply bridging η6-C6H6 ligand in the complex
Os3(CO)9(μ3-C6H6) was converted into a benzyne ligand in
the complex Os3(CO)9(μ3-C6H4)(μ-H)2 under irradiation.7
Herein we report the first examples of the formation of triply
bridging arynes directly from bridging aryl ligands in stable
unsaturated triosmium complexes generated from reactions of
Os3(CO)10(NCMe)2 with the gold complexes ArylAu(PPh3)
(Aryl = phenyl, naphthyl (C10H7)). The compound C6H5Au-
(PPh3)8 can be regarded as a close relative of C6H6 itself; the
Au(PPh3) is isolobal with H and also contains one odd electron
for bonding to the carbon atom of the C6H5 group.9
Compound 1 reacts with C6H5Au(PPh3) in CH2Cl2 at 40 °C
Received: March 21, 2012
Published: April 11, 2012
© 2012 American Chemical Society
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Figure 3. ORTEP diagram of the molecular structure of Os3(CO)9(μ3-
C6H4)(μ-AuPPh3)(μ-H) (3), with thermal ellipsoids given at the 30%
probability level. The hydrogen atoms are omitted for clarity. Selected
interatomic bond distances (Å): Os1−Os2 = 2.8902(6), Os1−Os3
=3.0229(7), Os2−Os3 = 2.7560(6), Au1−Os1 =2.7507(6), Au1−Os2
= 2.8131(6), Os1−C1 = 2.085(10), Os3−C6 = 2.097(10), Os2−C1 =
2.285(10), Os2−C6 = 2.374(10), Os1−H1 = 1.69(9), Os3−H1 =
1.99(9), C1−C6 = 1.429(14).
Figure 1. ORTEP diagram of the molecular structure of Os3(CO)10(μ-
C6H5)(μ-AuPPh3) (2), with thermal ellipsoids given at the 30%
probability level. The hydrogen atoms are omitted for clarity. Selected
interatomic bond distances (Å) and angles (deg): Os1−Os2 =
2.7521(6), Os1−Os3 = 2.8785(5), Os2−Os3 = 2.8746(5), Os1−C1 =
2.191(13), Au1−Os1 = 2.7621(5), Au1−Os2 = 2.7668(5), Os2−C1 =
2.236(11); Os1−C1−Os2 = 76.9(4).
C6H4)(μ-H)2 except for the presence of the bridging AuPPh3 in
the place of one of the bridging hydride ligands.1 The benzyne
C−C bond distance C1−C2 = 1.429(14) Å is typical of those
of other benzyne ligands.2−5 Compound 3 was formed by the
loss of a CO ligand from the Os(CO)4 group and the activation
of one of the ortho-positioned CH bonds in the bridging
phenyl ligand in 2. It is an electronically saturated 48-electron
complex.
The unsaturation in 2 results in delocalized bonding across the
Os(1), Os(2), and C(1) atoms. The nature of this delocalized
bonding can be seen in the DFT calculated molecular orbitals
HOMO-3, HOMO-5, and HOMO-9 of 2, which are shown in
Figure 2.14 As a result of a small HOMO/LUMO gap of 1.52
There have been no previous reports of naphthyne ligands;
therefore, for comparison, we also investigated the reaction of 1
with 1-NpAu(PPh3)15 (1-Np = 1-naphthyl = 1-C10H7). The
reaction of 1-NpAu(PPh3) with 1 provided a product having
the formula Os3(CO)10(2-Np)(μ-AuPPh3) (4) in 58% yield.
Unlike 2, the color of 4 is pink in solution. Interestingly,
however, crystals grown from hexane solutions at room
temperature are green and are similar in color to those of 2,
but crystals of 4 grown from hexane at −25 °C are pink, like the
solutions. The molecular structures of 4 in both crystal
modifications were established crystallographically. The struc-
ture found in the green crystals will be called 4a and the
isomeric structure found in the pink crystals will be called 4b.
An ORTEP diagram of the molecular structure of 4a is
shown in Figure 4. The structure of 4a is similar to that of 2
except that it contains an η1-2-Np ligand that bridges the
AuPPh3-bridged Os−Os bond (Os1−C1 = 2.313(11) Å and
Os2−C1 = 2.332(11) Å). The plane of the C10 ring is virtually
perpendicular (86.1(2)°) to the plane of the Os3 triangle. A 1,2-
hydrogen shift in the naphthyl ligand must have occurred in the
formation of 4a. If the 2-Np ligand and the AuPPh3 group both
serve as 1-electron donors, then the cluster of 4a contains 46
electrons and is unsaturated just like 2. Accordingly, the Os1−
Os2 bond is short (2.7484(6) Å) compared to the other Os−
Os bonds (Os1−Os3 = 2.8745(6) Å, Os2−Os3 = 2.8668(6)
Å).
Figure 2. Contour diagrams of the LUMO, HOMO, HOMO-3,
HOMO-5, and HOMO-9 with calculated energies showing the
bonding of the η1-bridging phenyl ligand to the osmium atoms in 2.
eV (see Figure 2) there is a strong absorption at λ 632 nm (ε =
560 M−1.cm−1) in the visible region of the spectrum, which is
responsible for the bright green color of the complex.14
When a solution of 2 was heated to reflux in octane solvent,
it was decarbonylated and transformed into the benzyne
compound Os3(CO)9(μ3-C6H4)(μ-AuPPh3)(μ-H) (3) in 94%
yield. Compound 3 was characterized crystallographically, and
an ORTEP diagram of its molecular structure is shown in
Figure 3. The structure of 3 is similar to that of Os3(CO)9(μ3-
An ORTEP diagram of the molecular structure of 4b is
shown in Figure 5. This structure is an isomer of 4a, and it
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planar C10 ring is not perpendicular to the Os3 triangle but is
49.27(0.27)° from the Os3 plane. The C1−C6 distance is
1.380(14) Å. In this molecule the 2-Np ligand serves as a 3-
electron donor and the AuPPh3 group serves as a 1-electron
donor; thus, the osmium atoms in the pink isomer 4b contain a
total of 48 electrons. The triosmium cluster in 4b is
electronically saturated, and as a result, there are no unusually
short Os−Os bonds. The doubly bridged Os1−Os2 bond
(2.8538(6) Å) is nearly as long as the other two Os−Os bonds
(Os1−Os3 = 2.8997(6) Å, Os2−Os3 = 2.8899(7) Å). As a
result, the HOMO/LUMO gap in 4b is larger than that in 2
and the absorption in the visible spectrum lies at higher energy
(λ 518 nm, ε = 3009 cm−1 M−1),14 which accounts for its pink
color. Compound 4b must obviously convert to 4a when
crystals are grown at room temperature. Conversely, when the
green crystals of 4a are dissolved in hexane, the solutions are
pink, indicating a facile and apparently complete transformation
from 4a back to 4b. We have not yet obtained any
spectroscopic evidence for the presence of significant amounts
of isomer 4a in solutions at room temperature and at low
temperature.18 Further investigations of the 4a−4b trans-
formation are in progress.
When a solution of 4 was heated to reflux in octane solvent,
it was decarbonylated and transformed into the naphthyne
compound Os3(CO)9(μ3-1,2-η2-C10H6)(μ-AuPPh3)(μ-H) (5)
in 63% yield. Compound 5 was also characterized crystallo-
graphically, and an ORTEP diagram of its molecular structure is
shown in Figure 6. The structure of 5 is similar to that of 3.
Compound 5 contains the first example of an unsubstituted
triply bridging naphthyne ligand. The naphthyne C−C bond
distance (C1−C6 = 1.435(16) Å) is similar in length to that
Figure 4. ORTEP diagram of the molecular structure of Os3(CO)10(μ-
2-Np)(μ-AuPPh3) (4a) obtained from the green crystals, with thermal
ellipsoids given at the 30% probability level. The hydrogen atoms are
omitted for clarity. Selected interatomic bond distances (Å): Os1−Os2
= 2.7484(6), Os1−Os3 = 2.8745(6), Os2−Os3 = 2.8668(6), Au1−
Os1 = 2.7424(6), Au1−Os2 = 2.7772(6), Os1−C1 = 2.313(11), Os2−
C1 = 2.332(11).
Figure 5. ORTEP diagram of the molecular structure of
Os3(CO)10(μ3-η2-2-Np)(μ-AuPPh3) (4b), with thermal ellipsoids
given at the 30% probability level. The hydrogen atoms are omitted
for clarity. Selected interatomic bond distances (Å): Os1−Os2 =
2.8538(6), Os1−Os3 = 2.8997(6), Os2−Os3 = 2.8899(7), Au1−Os1
= 2.7573(6), Au1−Os2 = 2.8146(6), Os1−C1 = 2.174(11), Os2−C1
= 2.369(10), Os2−C6 = 2.544(10), C1−C6 = 1.380(14).
Figure 6. ORTEP diagram of the molecular structure of Os3(CO)9(μ3-
1,2-η2-C10H6)(μ-AuPPh3)(μ-H) (5), with thermal ellipsoids given at
the 30% probability level. The hydrogen atoms are omitted for clarity.
Selected interatomic bond distances (Å): Os1−Os2 = 2.8950(6),
Os1−Os3 = 2.9882(7), Os2−Os3 = 2.7494(6), Os1−C1 = 2.123(11),
Os2−C1 = 2.298(11), Os2−C6 = 2.370(12), Os1−Au1 = 2.7395(7),
Os2−Au1 = 2.7923(7), Os3−C6 = 2.085(12), Au1−P1 = 2.284(3),
C1−C6 = 1.435(16).
contains a σ,π-coordinated η2-2-Np ligand that bridges the
AuPPh3-bridged Os−Os bond. Naphthyl atom C(1) is bonded
to both osmium atoms (Os1−C1 = 2.313(11) Å and Os2−C1
= 2.332(11) Å). Interestingly, naphthyl atom C(6) is also
bonded to Os(2) (Os2−C6 = 2.544(10) Å), although the
distance is slightly longer.16,17 As a result, the plane of the
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This work has demonstrated the multicenter conversion of
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Scheme 1
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ASSOCIATED CONTENT
2422. (c) Hoferkamp, L. A.; Rheinwald, G.; Stoeckli-Evans, H.; Suss-
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S
* Supporting Information
Text, figures, tables, and CIF files giving details of the synthesis
and characterizations of compounds 2−5, computational
analyses for 2, and data for each of the structural analyses.
This material is available free of charge via the Internet at
http://pubs.acs.org.
(NH ) C H ](μ-H); see: Cabeza, J. A.; Noth, H.; de Jesus Rosales-
̈
2
2
10
5
Hoz, M.; Sanchez-Cabrera, G. Eur. J. Inorg. Chem. 2000, 2327−2332.
(18) H NMR and 31P NMR spectra of solutions of 4 in toluene-d8
1
AUTHOR INFORMATION
solvent at room temperature and at −80 °C indicate the presence of
only one isomer, and on the basis of color, it is the pink isomer 4b.
■
Corresponding Author
*E-mail: Adamsrd@mailbox.sc.edu (R.D.A.).
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This research was supported by the following grants from the
National Science Foundation: CHE-1111496 and CHE-
1048629.
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