Osmium(III) complexes with POP pincer ligands: Preparation from commercially available OsCl3 · 3H2O their X-ray structures

Article abstract of DOI:10.1021/ic101498h

Complexes OsCl₃{dbf(PⁱPr₂)₂} [1; dbf(PⁱPr₂)₂ = 4,6-bis(diisopropylphosphino) dibenzofuran], OsCl₃{xant(PⁱPr₂)₂} [2; xant(Pⁱ

Full text of DOI:10.1021/ic101498h

Inorg. Chem. 2010, 49, 8665–8667 8665
DOI: 10.1021/ic101498h
Osmium(III) Complexes with POP Pincer Ligands: Preparation from
Commercially Available OsCl3 3H2O and Their X-ray Structures
3
,†
†
,‡
†
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Gregorio Asensio,* Ana B. Cuenca, Miguel A. Esteruelas,* Mercedes Medio-Simon,
‡
‡
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Montserrat Olivan, and Marta Valencia
†
´
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Departamento de Quımica Organica, Universidad de Valencia, 46100 Valencia, Spain, and
‡
´
ꢀ
ꢀ
Departamento de Quımica Inorganica, Instituto de Ciencia de Materiales de Aragon,
Universidad de Zaragoza, CSIC, 50009 Zaragoza, Spain
Received July 27, 2010
Complexes OsCl3{dbf(PiPr2)2} [1; dbf(PiPr2)2 = 4,6-bis(diisopropyl-
phosphino)dibenzofuran], OsCl3{xant(PiPr2)2} [2;xant(PiPr2)2 =9,9-
dimethyl-4,5-bis(diisopropylphosphino)xanthene], and OsCl3{xant-
(PPh2)2} [3; xant(PPh2)2 = 9,9-dimethyl-4,5-bis(diphenylphosphino)-
xanthene] have been obtained in high yield by the reaction of the
no practical use in catalysis because it is more reducing than
ruthenium and prefers to be saturated by coordination and
redox isomers with more metal-carbon bonds.1 As a con-
sequence of this extended skepticism, very scarce effort to
find starting materials from OsCl3 3H2O or related salts has
3
corresponding diphosphine with OsCl3 3H2O. The ruthenium(III)
been done.2 However, we have proven that osmium can be a
promising alternative to the classical metal catalysts.3
3
counterparts RuCl3{dbf(PiPr2)2} (4), RuCl3{xant(PiPr2)2} (5), and
RuCl3{xant(PPh2)2} (6) are similarly obtained from RuCl3 3H2O in
Pincer ligands are having a tremendous impact in organo-
metallics and homogeneous catalysts.4 As a consequence of
the disposition of their donor atoms, they develop marked
abilities to stabilize less common metal oxidation states5 and
afford metal complexes capable of activating inert bonds.6
The most commonly encountered linker groups consist of
either a metalated aryl ring in anionic PCP ligands or
uncharged PNP pyridines or neutral POP ethers. Among
the latter, the xanthene-based systems occupy a prominent
place.7 The influence of coordinating parameters, such as the
separation between the phosphorus atoms, the flexibility
3
moderate yields. The X-ray structures of dbf(PiPr2)2 and complexes
1-3 are also reported.
The number of complexes obtained in high yield directly
from commercially available inorganic salts determines the
development of the chemistry of a transition metal, in par-
ticular for those of the platinum group. Success in ruthenium
chemistry during the past decade has been, in part, due to the
ready accessibility of a wide range of these types of starting
materials. In contrast to ruthenium, osmium is considered of
(4) (a) Albrecht, M.; van Koten, G. Angew. Chem., Int. Ed. 2001, 40, 3750.
(b) van der Boom, M. E.; Milstein, D. Chem. Rev. 2003, 103, 1759. (c) Singleton,
J. T. Tetrahedron 2003, 59, 1837. (d) Benito-Garagorri, D.; Kirchner, K. Acc.
Chem. Res. 2008, 41, 201.
(5) For example, see: (a) Conner, D.; Jayaprakash, K. N.; Cundari, T. R.;
Gunnoe, T. B. Organometallics 2004, 23, 2724. (b) Ingleson, M. J.; Pink, M.;
Caulton, K. G. J. Am. Chem. Soc. 2006, 128, 4248. (c) Ingleson, M. J.; Pink, M.;
Fan, H.; Caulton, K. G. J. Am. Chem. Soc. 2008, 130, 4262. (d) Hebden, T. J.;
Denney, M. C.; Pons, V.; Piccoli, P. M. B.; Koetzle, T. F.; Schultz, A. J.; Kaminsky,
W.; Goldberg, K. I.; Heinekey, D. M. J. Am. Chem. Soc. 2008, 130, 10812.
(e) Segawa, Y.; Yamashita, M.; Nozaki, K. J. Am. Chem. Soc. 2009, 131, 9201.
(6) For example, see: (a) Ghosh, R.; Zhang, X.; Achord, P.; Emge, T. J.;
Krogh-Jespersen, K.; Goldman, A. S. J. Am. Chem. Soc. 2007, 129, 853.
(b) Prechtl, M. H. G.; Ben-David, Y.; Giunta, D.; Busch, S.; Taniguchi, Y.;
*To whom correspondence should be addressed. E-mail: gregorio.asensio@
uv.es (G.A.), maester@unizar.es (M.A.E.).
(1) (a) Caulton, K. G. J. Organomet. Chem. 2001, 617-618, 56. (b)
Esteruelas, M. A.; Oro, L. A. Adv. Organomet. Chem. 2001, 47, 1. (c) Esteruelas,
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M. A.; Lopez, A. M. Organometallics 2005, 24, 3584. (d) Esteruelas, M. A.;
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Lopez, A. M.; Olivan, M. Coord. Chem. Rev. 2007, 251, 795.
(2) For relevant osmium starting materials, see: (a) Vaska, L.; Diluzio,
J. W. J. Am. Chem. Soc. 1961, 83, 1262. (b) Hoffman, P. R.; Caulton, K. G.
J. Am. Chem. Soc. 1975, 97, 4221. (c) Esteruelas, M. A.; Werner, H. J. Organomet.
Chem. 1986, 303, 221. (d) Werner, H.; Zenkert, K. J. Organomet. Chem. 1988,
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345, 151. (e) Aracama, M.; Esteruelas, M. A.; Lahoz, F. J.; Lopez, J. A.; Meyer,
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U.; Oro, L. A.; Werner, H. Inorg. Chem. 1991, 30, 288. (f) Dickinson, P. W.;
Girolami, G. J. Inorg. Chem. 2006, 45, 5215. (g) Esteruelas, M. A.; García-Yebra,
Wisniewski, W.; Gorls, H.; Mynott, R. J.; Theyssen, N.; Milstein, D.; Leitner, W.
Chem.—Eur. J. 2007, 13, 1539. (c) Gunanathan, C.; Ben-David, Y.; Milstein, D.
Science 2007, 317, 790. (d) Bernskoetter, W. H.; Hanson, S. K.; Buzak, S. K.;
Davis, Z.; White, P. S.; Swartz, R.; Goldberg, K. I.; Brookhart, M. J. Am. Chem.
Soc. 2009, 131, 8603. (e) Kohl, S. W.; Weiner, L.; Schwartsburd, L.; Konstanti-
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2009, 324, 74.
(7) For example, see: (a) van Leeuwen, P. W. N. N.; Kamer, P. C. J.; Reek,
J. N. H.; Dierkes, P. Chem. Rev. 2000, 100, 2741. (b) Freixa, Z.; van Leeuwen,
P. W. N. N. Dalton Trans. 2003, 1890. (c) Birkhold, M.-N.; Freixa, Z.; van
Leeuwen, P. W. N. M. Chem. Soc. Rev. 2009, 38, 1099. (d) Ledger, A. E. W.;
Moreno, A.; Ellul, C. E.; Mahon, M. F.; Pregosin, P. S.; Whittlesey, M. K.;
Williams, J. M. J. Inorg. Chem. 2010, 49, 7244and references cited therein.
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C.; Olivan, M.; Onate, E. Inorg. Chem. 2006, 45, 10162. (h) Gross, C. L.;
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(3) (a) Esteruelas, M. A.; Herrero, J.; Lopez, A. M.; Olivan, M. Organo-
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metallics 2001, 20, 3202. (b) Cobo, N.; Esteruelas, M. A.; Gonzalez, F.; Herrero,
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J.; Lopez, A. M.; Lucio, P.; Olivan, M. J. Catal. 2004, 223, 319. (c) Castarlenas,
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M. A.; García-Yebra, C.; Onate, E. Organometallics 2008, 27, 3029. (e) Castarlenas,
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M. A.; García-Yebra, C.; Olivan, M.; Onate, E.; Valencia, M. Organometallics
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r
2010 American Chemical Society
Published on Web 09/09/2010
pubs.acs.org/IC

8666 Inorganic Chemistry, Vol. 49, No. 19, 2010
Asensio et al.
Scheme 2
Figure 1. Molecular structure of dbf(PiPr2)2.
Scheme 1
ortho to the ether bridge.10 The reactions of the correspond-
ing dilithiated species with chlorodiisopropylphosphine afford
dbf(PiPr2)2 and xant(PiPr2)2, which are isolated as a white
solid in 84% yield and a yellow oil in 88% yield, respectively.
The diphosphine dbf(PiPr2)2 has been characterized by
X-ray diffraction analysis. The structure (Figure 1) reveals that
range, or the natural bite angle, on the selectivity and activity
of precursors containing these types of ligands in some
catalytic processes has been discussed.7a-c In contrast to
the remaining platinum group metals, osmium-pincer chem-
istry is a little studied field,8 in particular that of POP ligands.
In the search for osmium-pincer starting materials, we have
˚
the separation between the phosphorus atoms of 6.192(2) A is
˚
significantly longer, about 2.2 A, than that in 9,9-dimethyl-4,5-
investigated the reactions of OsCl3 3H2O with xanthene-type
bis(diphenylphosphino)xanthene [xant(PPh2)2; 4.08011 and
3
12
˚
˚
ligands. In this Communication, we report the synthesis of
4,6-bis(diisopropylphosphino)dibenzofuran [dbf(PiPr2)2] and
9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene [xant-
(PiPr2)2] and the preparation and X-ray structures of novel9
OsIIIPOP compounds.
4.155(1) A ] and between 0.4 and 0.2 A longer than those
calculated for 4,6-bis(diphenylphosphino)dibenzofuran [dbf-
˚
˚
(PPh2)2; 5.760 A by MM calculations and 5.956 A by PM3
calculations].11 The most noticeable spectroscopic feature of
dbf(PiPr2)2 is a singlet at 9.2 ppm in the 31P{1H} NMR
spectrum in dichloromethane at room temperature. In con-
trast to dbf(PiPr2)2, the spectrum of xant(PiPr2)2 at room
temperature shows a broad signal, which is converted into a
singlet at 248 K, δ -12.2.
The new ligands have been synthesized under an argon
atmosphere according to Scheme 1. Because of the presence
of the ether oxygen, the addition of 3.0 equiv of sec-butyl-
lithium to diethyl ether solutions of dibenzofuran and 9,9-
dimethylxanthane in the presence of tetramethylethylenedia-
mine produces dilithiation of the heterocycles at the positions
Ligands dbf(PiPr2)2, xant(PiPr2)2, and xant(PPh2)2 react
with OsCl3 3H2O in 2-propanol under reflux to provide after
3
60 h the osmium(III) derivatives OsCl3{dbf(PiPr2)2} (1),
OsCl3{xant(PiPr2)2} (2), and OsCl3{xant(PPh2)2} (3), which
are isolated as yellow solids in 98%, 70%, and 78% yield,
respectively, according to Scheme 2. Under the same condi-
(8) For relevant papers, see: (a) Gusev, D. G.; Dolgushin, F. M.; Antipin,
M. Y. Organometallics 2001, 20, 1001. (b) Gusev, D. G.; Maxwell, T.;
Dolgushin, F. M.; Lyssenko, M.; Lough, A. J. Organometallics 2002, 21,
1095. (c) Gusev, D. G.; Lough, A. J. Organometallics 2002, 21, 2601. (d) Liu,
S. H.; Lo, S. T.; Wen, T. B.; Williams, I. D.; Zhou, Z. Y.; Lau, C. P.; Jia, G. Inorg.
Chim. Acta 2002, 334, 122. (e) Wen, T. B.; Zhou, Z. Y.; Jia, G. Organometallics
2003, 22, 4947. (f) Gusev, D. G.; Fontaine, F.-G.; Lough, A. J.; Zargarian, D.
Angew. Chem., Int. Ed. 2003, 42, 216. (g) Lee, J.-H.; Pink, M.; Caulton, K. G.
tions, the reactions of these diphosphines with RuCl3 3H2O
3
led to the ruthenium counterparts RuCl3{dbf(PiPr2)2} (4),
RuCl3{xant(PiPr2)2} (5), and RuCl3{xant(PPh2)2} (6). How-
ever, they are obtained in moderate yields (30-60%), as red
(4) or orange (5 and 6) solids.
~
Organometallics 2006, 25, 802. (h) Castarlenas, R.; Esteruelas, M. A.; Onate, E.
Organometallics 2007, 26, 3082. (i) Gauvin, R. M.; Rozenberg, H.; Shimon,
L. J. W.; Ben-David, Y.; Milstein, D. Chem.—Eur. J. 2007, 13, 1382. (j)
Kuznetsov, V. F.; Gusev, D. G. Organometallics 2007, 26, 5661. (k) Lee, J.-H.;
Pink, M.; Tomaszewski, J.; Fan, H.; Caulton, K. G. J. Am. Chem. Soc. 2007, 129,
8706. (l) Lee, J.-H.; Fan, H.; Pink, M.; Caulton, K. G. New J. Chem. 2007, 31,
838. (m) Baratta, W.; Ballico, M.; Chelucci, G.; Siega, K.; Rigo, P. Angew.
Complexes 1-3 have been characterized by X-ray diffrac-
tion analysis. Figure 2 shows views of their molecular geo-
metries and summarizes some structural parameters. The
coordination polyhedron around the osmium atom in the
three compounds can be rationalized as being derived from a
distorted octahedron with the chloride ligands in a mer
disposition [Cl(1)-Os-Cl(3) = 171.60(3)° (1), 170.06(5)°
and 169.47(5)° (2), and 165.81(5)° (3)]. The structures reveal
ꢀ
Chem., Int. Ed. 2008, 47, 4362. (n) Esteruelas, M. A.; Masamunt, A. B.; Olivan,
~
M; Onate, E.; Valencia, M. J. Am. Chem. Soc. 2008, 130, 11612. (o) Betley, T. A.;
Qian, B. A.; Peters, J. C. Inorg. Chem. 2008, 47, 11570.
(9) The predominant coordination chemistry of group 15 donors with
ruthenium and osmium concerns metal oxidation states e2þ. For the 3þ
oxidation state, limited examples have been reported. See: Housecroft, C. E.
In Comprehensive Coordination Chemistry II: from biology to nanotechnology;
Constable, E. C., Dilworth, J. R., Eds.; Elsevier Ltd.: London, 2004; Vol. 5,
Chapter 5.5, p 555.
(11) Kranenburg, M.; van der Burgt, Y. E. M.; Kamer, P. C. J.; van
Leeuwen, P. W. N. M.; Goubitz, K.; Fraanje, J. Organometallics 1995, 14,
3081.
€
(10) (a) Gschwend, H. W.; Rodriguez, H. R. Org. React. 1979, 26, 1. (b)
Schwartz, E. B.; Knobler, C. B.; Cram, D. J. J. Am. Chem. Soc. 1992, 114, 10775.
(12) Hillebrand, S.; Bruckmann, J.; Kruger, C.; Haenel, M. W. Tetra-
hedron Lett. 1995, 36, 75.

Communication
Inorganic Chemistry, Vol. 49, No. 19, 2010 8667
˚
Figure 2. Molecular structures of complexes 1-3 and selected angles (deg) and distances (A).
that the rigid polycyclic backbones do not have any signifi-
cant influence in the coordination of the diphosphines
because OsCl3 produces a leveling effect on the relevant
coordinating parameters of the ligands, such as the separa-
tion between the phosphorus atoms or the P-M-P bite
angle. Thus, although the separation between the phos-
phorus atoms in the free ligands is very sensitive to the
rigidity imposed by the central ring of the polycycle, the
sum of the Os-P bond lengths in the three compounds is
indicating an orthorhombic symmetry, and the spectra can be
described by taking into account only a Zeeman term de-
scribed by a g tensor with principal values of g1 = 2.63(2),
g2 = 2.54(3), and g3 = 2.03(3) for 1 and g1 = 2.51(2), g2 =
2.20(2), and g3 = 2.01(2) for 4.
In conclusion, diphosphineosmium(III) complexes can be
prepared in high yield, directly from OsCl3 3H2O, by the
3
reaction of the commercially available inorganic salt with
POP ligands such as dbf(PiPr2)2, xant(PiPr2)2, or xant(PPh2)2.
The comparison of the structures of the free ligands with those
of the resulting complexes OsCl3{dbf(PiPr2)2}, OsCl3{xant-
(PiPr2)2}, and OsCl3{xant(PPh2)2} reveals that the polycyclic
backbones of the diphosphines do not have any significant
influence on the structural parameters of the complexes
because the metal produces a leveling effect on the relevant
coordinating features of the ligands.
˚
˚
˚
similar [≈4.81 A (1), ≈4.70 A (2), and ≈4.65 A (3)]; i.e., OsCl3
˚
shortens, by about 1.4 A, the separation between the phos-
i
˚
phorus atoms of dbf(P Pr2)2, while it separates, by about 0.5 A,
the phosphorus atoms of xant(PiPr2)2 and xant(PPh2)2.13 The
differences between the P-Os-P angles and between the Os-O
distances are not significant. The P-Os-P angle in 1 is about 6°
smaller than those of 2 and 3, the same as the Cl(1)-Os-Cl(3)
angle of 3 with regard to those of 1 and 2, whereas the Os-O
˚
separation in 1 is about 0.1 A shorter than those in 2 and 3.
Acknowledgment. We thank Pablo J. Alonso for re-
cording the EPR spectra. Financial support was provided
by the Spanish MICINN (Projects CTQ2008-00810 and
CTQ2007-65720 and Consolider Ingenio 2010 CSD2007-
The electron paramagnetic resonance (EPR) spectra of the
dbf(PiPr2)2 complexes 1 and 4 in the solid state were recorded
in order to corroborate the paramagnetic character of these
species. The room temperature spectra of both compounds
consist of a broad featureless signal whose shape indicates an
anisotropic environment. Upon measurement at lower tem-
perature (namely, 15 K), three features are clearly resolved,
ꢀ
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00006), Diputacion General de Aragon (E35), and the
European Social Fund.
Supporting Information Available: Experimental details re-
garding the synthesis and characterization and crystallographic
data (CIF) for dbf(PiPr2)2 and 1-3. This material is available
free of charge via the Internet at http://pubs.acs.org.
(13) The separations between the phosphorus atoms in these compounds
˚
˚
˚
are 4.748(1) A for 1, 4.671(2) and 4.666(2) A for 2, and 4.620(2) A for 3.