Lithium-palladium complex supported by phosphonatophosphine and chloride ligands

Article abstract of DOI:10.1021/ic800355m

The reaction of the phosphonatophosphine ligand Ph₂PCH(SiMe ₃)P(O)(OEt)₂ with [PdCl₂(COD)] in the presence of LiCl afforded the neutral, mixed-metal complex [LiPd₂CI ₅{μ-Ph₂PCH

Full text of DOI:10.1021/ic800355m

Inorg. Chem. 2008, 47, 3934-3936
Lithium-Palladium Complex Supported by Phosphonatophosphine and
Chloride Ligands
Adel Hamada and Pierre Braunstein*
Laboratoire de Chimie de Coordination, Institut de Chimie (UMR 7177 CNRS), UniVersite´ Louis
Pasteur, 4 rue Blaise Pascal, F-67070 Strasbourg Ce´dex, France
Received February 26, 2008
Scheme 1
The reaction of the phosphonatophosphine ligand Ph2PCH-
(SiMe3)P(O)(OEt)2 with [PdCl2(COD)] in the presence of LiCl
afforded the neutral, mixed-metal complex [LiPd2CI5{µ-Ph2PCH2-
P(O)(OEt)2}2] in which the Li+ cation is tetrahedrally coordinated
by the PdO bonds and two Pd-bound Cl atoms.
The highly electropositive nature of the alkali metals
accounts for the polar nature of their bonds to other elements.
A considerable number of structures have been reported for
lithium complexes and aggregates whose diversity results
from the range of alkali-metal-ligand interactions available.1
Lithium derivatives play a considerable role in organome-
tallic and organic synthesis, and mixed complexes or
aggregates, such as the lithium cuprates, possess a reactivity
very different from that of the corresponding homometallic
systems.2 It is also known that some reactions work better
in the presence of added salts, e.g., LiCl, although their exact
role is not always fully understood, and that the nature of
the bonding interactions in organometallic complexes may
strongly depend on the retention of an alkali metal in the
structure.3
In the course of our studies on heterofunctional P,O ligands
and the reactivity of their metal complexes,4 we noticed that,
among the huge diversity of heterofunctional ligands, phos-
phines containing a phosphoryl function, i.e., phosphonate,
phosphinate, or phosphate, have received relatively little atten-
tion, although it is established that the PdO group can
coordinate to a metal center via the O atom.5,6 The hemilabile
nature of the latter interaction4b may play an important role
during a catalytic cycle, as shown with methanol carbonylation
catalysts based on rhodium phosphine-phosphonate com-
plexes.7 We have thus prepared new enolphosphato- and
phosphonatophosphine ligands that associate PIII and PV
centers.6a,b
* To whom correspondence should be addressed. E-mail: braunstein@
chimie.u-strasbg.fr. Fax: +33 390 241 322.
(1) (a) For example, see: Setzer, W. N.; von Rague´ Schleyer, P. AdV.
Organomet. Chem. 1985, 24, 353. (b) Gregory, K.; von Rague´
Schleyer, P.; Snaith, R. AdV. Inorg. Chem. 1992, 37, 47. (c) Hoffmann,
D.; Dorigo, A.; von Rague´ Schleyer, P.; Reif, H.; Stalke, D.; Sheldrick,
G. M.; Weiss, E.; Geissler, M. Inorg. Chem. 1995, 34, 262. (d) Pratt,
L. M.; Streitwieser, A. J. Org. Chem. 2003, 68, 2830. (e) Hanusa,
T. P. In ComprehensiVe Coordination Chemistry II; McCleverty, J. A.,
Meyer, T. J., Eds.; Elsevier: Oxford, U.K., 2004; Vol. 3, pp 1-92.
(2) (a) For example, see: Volhardt, K. P. C. Organic Chemistry; Freemann,
W. H. and Co.: New York, 1987. (b) Power, P. P. In Progress in
Inorganic Chemistry; Lippard, S. J. , Eds.; Wiley: New York, 1991;
Vol. 39, p 75. (c) Rossiter, B. E.; Swingle, N. M. Chem. ReV. 1992,
92, 771. (d) Holloway, C. E.; Melnik, M. ReV. Inorg. Chem 1993, 13,
233. (e) Nakamura, E.; Yamanaka, M.; Mori, S. J. Am. Chem. Soc.
2000, 122, 1826. (f) Eaborn, C.; El-Hamruni, S. M.; Hill, M. S.;
Hitchcock, P. B.; Hopman, M.; Le Gouic, A.; Smith, J. D. J.
Organomet. Chem. 2000, 597, 3. (g) Smith, M. B., March, J. AdVanced
Organic Chemistry, 5th ed.; John Wiley: New York, 2001.
The new silyl-substituted ꢀ-phosphonatophosphine ligand
1 was prepared according to Scheme 1, via the intermediacy
(4) (a) Braunstein, P. Chem. ReV. 2006, 106, 134. (b) Braunstein, P.; Naud,
F. Angew. Chem., Int. Ed. 2001, 40, 680.
(5) (a) DeBolster, M. W. G.; Goeneveld, W. L. In Topics in Phosphorus
Chemistry; Griffith, E. J., Grayson, M., Eds.; Wiley: New York, 1976;
Vol. 8, p 273. and references cited therein. (b) Gahagan, M.; Mackie,
R. K.; Cole-Hamilton, D. J.; Cupertino, D. C.; Harman, M.; Hurst-
house, M. B. J. Chem. Soc., Dalton Trans. 1990, 2195. (c) Weis, K.;
Rombach, M.; Vahrenkamp, H. Inorg. Chem. 1998, 37, 2470. (d)
Kingsley, S.; Chandrasekhar, V.; Incarvito, C. D.; Lam, M. K.;
Rheingold, A. L. Inorg. Chem. 2001, 40, 5890.
(3) (a) For example, see: Hao, S.; Song, J.-I.; Berno, P.; Gambarotta, S.
Organometallics 1994, 13, 1326. (b) Karet, G. B.; Castro, S. L.;
Folting, K.; Bollinger, J. C.; Heintz, R. A.; Christou, G. J. Chem.
Soc., Dalton Trans. 1998, 67. (c) Ganesan, M.; Be´rube´, C. D.;
Gambarotta, S.; Yap, G. P. A. Organometallics 2002, 21, 1707. (d)
Fagnou, K.; Lautens, M. Angew. Chem., Int. Ed. 2002, 41, 26. (e)
Mund, G.; Vidovic, D.; Batchelor, R. J.; Britten, J. F.; Sharma, R. D.;
Jones, C. H. W.; Leznoff, D. B. Chem.sEur. J. 2003, 9, 4757. (f)
Vela, J.; Vaddadi, S.; Kingsley, S.; Flaschenriem, C. J.; Lachicotte,
R. J.; Cundari, T. R.; Holland, P. L. Angew. Chem., Int. Ed 2006, 45,
1607.
(6) (a) Morise, X.; Braunstein, P.; Welter, R. Inorg. Chem. 2003, 42, 7752.
(b) Morise, X.; Braunstein, P.; Welter, R. C.R. Chim. 2003, 6, 91. (c)
Schull, T. L.; Knight, D. A. Coord. Chem. ReV. 2005, 249, 1269. (d)
Reisinger, C. M.; Nowack, R. J.; Volkmer, D.; Rieger, B. Dalton
Trans. 2007, 272.
3934 Inorganic Chemistry, Vol. 47, No. 10, 2008
10.1021/ic800355m CCC: $40.75  2008 American Chemical Society
Published on Web 04/17/2008

COMMUNICATION
structure of this complex in 3 · 3CH2Cl2; see below.10)
Obviously, the LiCl present in this complex originated
adventitiously from the ligand synthesis. The SiMe3 group
has been eliminated and the masked carbanion protonated,
owing to the presence of traces of H2O. We noted that when
the reaction of 1 with [PdCl2(COD)] was stopped after 10
min, additional 1H NMR signals were observed, which could
be consistent with the initial formation of 2b (31P{1H} NMR
(CDCl3) δ 19.1 (d, 2+3J(P,P) ) 20.0 Hz, PPh2), 23.1 (d,
2+3J(P,P) ) 20.0 Hz, PO), which progressively loses its silyl
group to give 2a. We have also noticed by 31P{1H} NMR
monitoring that the hydrolysis of 2b to give 2a is significantly
faster than that of the uncoordinated ligand 1.
Figure 1. View of the molecular structure of 3 in 3·3CH2Cl2. H atoms
are omitted for clarity, except on the PCP carbons. Selected bond distances
[Å] and angles [deg]: Pd1-P1 2.2323(10), Pd1-Cl1 2.2868(9), Pd1-Cl2
2.3327(9), Pd1-Cl3 2.4095(10), Pd2-P3 2.2214(10), Pd2-Cl3 2.3999(10),
Pd2-Cl4 2.2967(9), Pd2-Cl5 2.3178(9), Li-O1 1.864(7), O1-P2 1.476(3),
Li-O4 1.880(7), O4-P4 1.474(3), Li-Cl2 2.403(7), Li-Cl5 2.397(7);
Cl1-Pd1-Cl2 175.41(4), Pd1-Cl2-Li 89.72(16), Cl4-Pd2-Cl5 173.98(4),
Pd2-Cl5-Li 91.84(16), Pd1-Cl3-Pd2 106.21(4), P2-O1-Li 139.2(3),
P4-O4-Li 127.3(3), O1-Li-Cl2 101.6(3), O1-Li-Cl5 114.0(3),
O1-Li-O4 116.2(4), O4-Li-Cl2 118.9(3), O4-Li-Cl5 100.2(3),
Cl2-Li-Cl5 106.0(3).
of Me3SiCH2P(O)(OEt)2 (see the Supporting Information),8,9
and it was reacted with [PdCl2(COD)] to give after 1 h
mainly complex 2a, with a small amount of another complex,
3 (see below).9 The 31P{1H} NMR spectrum (CDCl3) of 2a
consists of two singlets at δ 9.7 and 23.8 for the PPh2 and
Having identified the nature of the unusual complex 3,
we performed the reaction of eq 1 in the presence of excess
LiCl and obtained 3 in ca. 54% isolated yield, with the water
responsible for the hydrolysis of the silyl group coming from
the hygroscopic LiCl.
Single crystals of 3 · 3CH2Cl2 were obtained, and the
structure of the complex, determined by X-ray diffraction,
is almost identical with that of 3 · CHCl3 (Figure 1).10 The
molecule possesses almost a C2 symmetry axis passing
through the atoms Li and Cl3. Each PdII center has a square-
planar coordination geometry [the sum of the angles around
Pd1 and Pd2 is 360.3(2) and 360.0(7)°, respectively], and
the bridging chloride Cl3 is trans to the phosphine donors
P1 and P3. The phosphonate PdO atoms are bonded to the
Li+ cation [Li-O1 1.864(7) Å; Li-O4 1.880(7) Å], which
1
phosphonate groups, respectively. The H NMR spectrum
is consistent with the structure shown for 2a.9 The second,
minor compound formed in this reaction (ca. 15% yield)
could be crystallized as 3 · CHCl3 and was shown by X-ray
diffraction to be an anionic dinuclear PdII complex with a
Li+ cation encapsulated, resulting in the neutral molecule
[LiPd2CI5{µ-Ph2PCH2P(O)(OEt)2}2] (3). (Figure 1 shows the
(7) Bischoff, S.; Weigt, A.; Miessner, H.; Lu¨cke, B. J. Mol. Catal. A:
Chemical 1996, 107, 339.
(8) (a) Savignac, P.; Teulade, M. P.; Collignon, N. J. Organomet. Chem.
1987, 323, 135. (b) Aboujaoude, E. E.; Lie´te´, S.; Collignon, N.;
Teulade, M. P.; Savignac, P. Synthesis 1986, 934.
(9) Selected data. Me3SiCH2P(O)(OEt)2:8b yield 80%. 1H NMR (CDCl3):
(10) Crystal data for 3·CHCl3: Owing to strong disorder of the OEt groups
on P2 and of one of the CHCl3 molecules of solvation, a squeeze
procedure (PLATON) was applied and only one molecule of CHCl3
was considered. Analytical data are consistent, with a total of four
molecules of CHCl3 being present. C34H44Cl5LiO6P4Pd2 ·CHCl3, M
) 1188.93, monoclinic, C2/c, a ) 34.6944(3) Å, b ) 13.0287(2) Å,
c ) 23.0410(2) Å, ꢀ ) 90.557(1)°, V ) 10414.6 Å3, Z ) 8, Dc )
1.517 g cm-3, µ(Mo KR) ) 1.261 mm-1, F(000) ) 4752. A Nonius-
Kappa CCD diffractometer was employed for the collection of 11 896
unique reflections (Mo KR, λ ) 0.710 73 Å, T ) 173 K).16 The
structure was solved by direct methods and refined by a full-matrix
least-squares technique based on F2 (SHELX9717). The final R1 and
wR2 are 0.0399 and 0.1157, respectively, for 511 parameters and 9517
reflections [I > 2σ(I)]. CCDC no. 669910. Crystal data for 3·3CH2Cl2:
2
δ 0.14 (s, 9H, SiCH3), 1.12 (2H, d, J(P,H) ) 22 Hz, PCH2Si), 1.28
(6H, t, 3J(H,H) ) 5.0 Hz, OCH2CH3), 4.04 (m, 4H, OCH2CH3).
31P{1H} NMR (CDCl3): δ 34.2 (s, PO). IR (CH2Cl2): ν(PdO) 1244 s
cm-1. Ph2PCH(SiMe3)P(O)(OEt)2 (1): yield 78%. 1H NMR (CD2Cl2):
δ 0.05 (s, 9H, SiMe3), 1.07 (t, 3H, 3J(H,H) ) 7.0 Hz, CH2CH3), 1.15
3
2
(t, 3H, J(H,H) ) 7.0 Hz, CH2CH3), 2.46 (dd, 1H, PCHP, J(PO,H)
) 21.6 Hz, 2J(P,H) ) 1.1 Hz, PCHP), 3.69 (m, 1H, OCH2), 3.83 (m,
1H, OCH2CH3), 3.87 (m, 2H, OCH2CH3), 7.34-7.86 (m, 10H,
aromatics). 31P{1H} NMR (CD2Cl2): δ -16.5 (d, 2J(P,P) ) 21.0 Hz,
PPh2), 29.8 (d, 2J(P,P) ) 21.0 Hz, PO). IR: ν(PdO) 1229 s cm-1
.
[PdCl2{Ph2PCH2P(O)(OEt)2}-P,O] (2a): yield 78%. 1H NMR (CDCl3):
δ 1.09 (t, 6H, 3J(HH) ) 6.7 Hz, OCH2CH3), 3.18 (dd, 2H, 2J(PO,H)
2
) 20.6, J(P,H) ) 4.0 Hz, PCH2P), 3.92-4.05 (m, 4H, OCH2CH3),
7.26-7.90 (m, 10H, aromatics). 31P{1H} NMR (CDCl3): δ 9.7 (s,
PPh2), 23.8 (s, PO). IR (KBr): 1236 s, 1166 m cm-1. [LiPd2CI5{µ-
Ph2PCH2P(O)(OEt)2}2] (3): yield 54% based on Pd. 1H NMR
(CD2Cl2): δ 1.15 (t, 12H, 3J(H,H) ) 7.0 Hz, OCH2CH3), 3.18 (dd,
C34H44Cl5LiO6P4Pd2 ·3CH2Cl2, M ) 1324.34, triclinic, P1, a )
j
11.1497(5) Å, b ) 15.5662(6) Å, c ) 16.6267(8) Å, R ) 110.906(2)°,
ꢀ ) 95.971(2)°, γ ) 91.575(2)°, V ) 2674.6(2) Å3, Z ) 2, Dc )
1.644 g cm-3, µ(Mo KR) ) 1.381 mm-1, F(000) ) 1324. A Nonius-
Kappa CCD diffractometer was employed for the collection of 12 149
unique reflections (Mo KR, λ ) 0.710 73 Å, T ) 173 K).16 The
structure was solved by direct methods and refined by a full-matrix
least-squares technique based on F2 (SHELX9717). The final R1 and
wR2 are 0.0466 and 0.1036, respectively, for 554 parameters and 8525
reflections [I > 2σ(I)]. CCDC no. 669909.
2
2
4H, J(PO,H) ) 20.7 Hz, J(P,H) ) 14.5 Hz, PCH2P), 3.86 (m, 4H,
OCH2CH3), 3.96 (m, 4H, OCH2CH3), 7.49-7.97 (m, 20H, aromatics).
31P{1H} NMR (CD2Cl2): δ 16.3 (s, PPh2), 24.7 (s, PO). 7Li NMR
(ref LiCl 1 M/D2O): δ 0.15 (s). IR (pure): 1172 s, 1233 s cm-1. IR
(KBr): 1173 s, 1251 s cm-1. Mass spectrum (MALDI-TOF+): m/z
1030.91 [M - Cl].
Inorganic Chemistry, Vol. 47, No. 10, 2008 3935

COMMUNICATION
has a tetrahedral coordination geometry, completed by the
chloride ligands Cl2 and Cl5 [Li-Cl2 2.403(7) Å; Li-Cl5
2.397(7) Å]. The angles at the bridging chlorides are
Pd1-Cl2-Li 89.72(16)° and Pd2-Cl5-Li 91.84(16)°. Some
intramolecular nonclassical hydrogen bonds are present
between the PCH2 protons and the bridging chlorides,
whereas intermolecular nonclassical hydrogen bonds involve
the solvent molecules.9
Preliminary catalytic experiments have shown that 3 cata-
lyzes the oligomerization of ethylene (296 K, 10 bar, C2H4,
4 × 10-5 mol of complex, 6 equiv of EtAlCl2, total volume
of toluene 15 mL)15 with a poor activity [TOF ) 90 mol of
C2H4/(g pf Pd) h] but an interesting selectivity of 76% for
decenes. When methylaluminoxane was used as a cocatalyst
(similar conditions, 200 equiv, total volume of toluene 20
mL), the activity remained low [TOF ) 340 mol of C2H4/(g
of Pd) h] but decenes were again the major products
(selectivity of 50%). These preliminary observations require
further investigations.
The formation and structure of 3, through a combination
of serendipity and design, nicely illustrate the composition,
properties, and structural changes that can result from the
presence of LiCl in a reaction mixture. Preliminary experi-
ments indicate that complex 2a does not lead to 3 upon the
addition of LiCl. This could be explained by the lower kinetic
reactivity of the P,O chelate once formed toward ring
opening. It can be anticipated that reactivity studies will show
marked differences between 2a or 2b and 3, and this is under
study. Conversely, the typical solubility properties of LiCl
are completely different when it is complexed by the
dipalladium moiety.
An alternative description of this heterometallic complex
is to view it as constituted of a LiCl unit trapped by a neural
Pd2Cl4 moiety and the P,O ligands serving as bridges between
the Pd and Li centers. In contrast to other examples where
a Li cation is chelated by two M-Cl ligands,11 there is no
solvent molecule coordinated to Li (usually Et2O or THF).
Instead, intramolecular stabilization is achieved by bridging
interactions with a functional ligand. This molecule appears
to be of an unprecedented type, and we are aware of only
one other report on fully characterized Li-Pd complexes.12
A recent illustration of the enhanced catalytic properties
of a Li-containing dimetallic aggregate is provided by the
alkyl complex [(THF)4Li4Pd2Me8], which is very active and
selective in the Heck coupling of 4-bromoacetophenone
with n-butyl acrylate.12 A complex with a Fe-Cl-Li unit
stabilized by a bridging carboxylate ligand was recently
shown to be an interesting precursor to novel cubane-type
structures.13 During the synthesis of a lithiated titanium
phosphonate complex from (MeO)2P(O)CH2SiMe3, it was
found that traces of water also played an important role, but
complete removal of the silyl group was not oberved.14
Acknowledgment. This work was supported by the Centre
National de la Recherche Scientifique and the Ministe`re de
l’Enseignement Supe´rieur et de la Recherche. We are grateful
to Lydia Brelot and Prof. Richard Welter (ULP Strasbourg)
for the determination of the crystal structures of 3 and to
Dr. X. Morise for discussions.
(11) (a) For example, see: Hvoslef, J.; Hope, H.; Murray, B. D.; Power,
P. P. J. Chem. Soc., Chem. Commun. 1983, 1438. (b) Kasani, A.;
McDonald, R.; Cavell, R. G. Chem. Commun. 1999, 1993. (c)
Hitchcock, P.; Lappert, M. F.; Prashar, S. J. Organomet. Chem. 2000,
613, 105. (d) Smith, J. M.; Lachicotte, R. J.; Holland, P. L. Chem.
Commun. 2001, 1542. (e) Eckert, N. A.; Bones, E. M.; Lachicotte,
R. J.; Holland, P. L. Inorg. Chem. 2003, 42, 1720. (f) Kuo, P.-C., Jr.;
Chang, C.; Lee, W.-Y.; Lee, H. M.; Huang, J.-H. J. Organomet. Chem.
2005, 690, 4168. (g) Pi, C.; Zhang, Z.; Liu, R.; Weng, L.; Chen, Z.;
Zhou, X. Organometallics 2006, 25, 5165.
Supporting Information Available: Crystallographic details in
the form of a CIF file and experimental procedures. This material
is available free of charge via the Internet at http://pubs.acs.org.
IC800355M
(12) Lamm, K.; Stollenz, M.; Meier, M.; Go¨rls, H.; Walter, D. J.
Organomet. Chem. 2003, 681, 24.
(15) Speiser, F.; Braunstein, P.; Saussine, L. Acc. Chem. Res. 2005, 38,
784.
(13) Klein, D. P.; Young, V. G., Jr.; Tolman, W. B.; Que, L., Jr Inorg.
Chem. 2006, 45, 8006.
(16) Kappa CCD Reference Manual; Nonius BV: Delft, The Netherlands,
1997.
(14) Mu¨ller, J. F. K.; Kulicke, K. J.; Neuburger, M.; Spichty, M. Angew.
Chem., Int. Ed. 2001, 40, 2890.
(17) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure Refine-
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3936 Inorganic Chemistry, Vol. 47, No. 10, 2008