Syntheses and structures of the trinuclear ruthenium complexes [RuCl 2(PAd2Bu)]3 and [RuCl2(P tBu2Cy)]3

Article abstract of DOI:10.1021/om050649i

The trinuclear ruthenium complexes [RuCl₂-(PAd ₂Bu)]₃ and [RuCl₂(P^tBu ₂Cy)]₃ have been obtained by reaction of [(cymene)RuCl₂]₂ with 2 equiv of the respecti

Full text of DOI:10.1021/om050649i

5792
Organometallics 2005, 24, 5792-5794
Syntheses and Structures of the Trinuclear Ruthenium
Complexes [RuCl2(PAd2Bu)]3 and [RuCl2(PtBu2Cy)]3
Se´bastien Gauthier, Rosario Scopelliti, and Kay Severin*
Institut des Sciences et Inge´nierie Chimiques, EÄ cole Polytechnique Fe´de´rale de Lausanne
(EPFL), CH-1015 Lausanne, Switzerland
Received July 29, 2005
Scheme 1
Summary: The trinuclear ruthenium complexes [RuCl2-
(PAd2Bu)]3 and [RuCl2(PtBu2Cy)]3 have been obtained
by reaction of [(cymene)RuCl2]2 with 2 equiv of the
respective phosphine. Crystallographic analyses show
that the three metal fragments are connected by strong
Ru-Ru bonds and bridging chloro ligands.
Neutral ruthenium(II) chloro complexes with mono-
dentate phosphine ligands are key starting materials
in organometallic synthesis1,2 and catalysis.2,3 With
small phosphine ligands such as PMe3,4 PMe2(CH2Ph),5
and PMe2Ph,6 electronically saturated complexes of the
formula [RuCl2L4] (L ) PR3, PR2R′) (A) can be obtained
(Scheme 1). The 16-electron complexes [RuCl2L3] (C) are
formed with sterically more demanding ligands such as
PPh3,2 P(p-C6H4CH3)3,7 and PEtPh2.6 In solution, com-
plexes with the latter ligand are in equilibrium with the
dimer [Ru2Cl4(PEtPh2)5] (B).6 Complexes of the formula
RuCl2L2 (D) tend to dimerize via chloro bridges.8 Using
the ortho-methyl-substituted phosphine ligand PPh2-
(2,6-Me2C6H3), however, it was possible to stabilize a
monomeric 14-electron complex of type D.9 In this case,
two agostic interactions between the methyl groups and
the ruthenium center were observed. The formal re-
moval of another phosphine ligand would lead to the
hypothetical 12-electron complexes RuCl2L (E). These
complexes are expected to form aggregates in order to
increase the coordination number of the metal, but to
the best of our knowledge, complexes of the type
[RuCl2L]n have not been described so far. In the follow-
ing, we report the synthesis and the structures of two
first examples of this class of compounds.
When sterically demanding phosphine ligands are em-
ployed, the arene π-ligand can subsequently be cleaved
off by photochemical or thermal activation. The result-
ing ruthenium complexes have been employed as cata-
lysts for ring-closing11 and ring-opening olefin meta-
thesis reactions12 as well as for atom transfer radical
addition13 and polymerization reactions.14 So far, there
is only very limited knowledge about what type of
complexes are formed after cleavage of the π-ligand.
When 1 equiv of PCy3 was employed with respect to the
dimer [(arene)RuCl2]2, only a partial replacement of the
arene was observed and binuclear complexes of the
formula [(arene)Ru(µ-Cl)3RuCl(L)(PCy3)] (L ) µ-N2 or
η2-C2H4) were obtained.13,14a
In continuation of these studies, we have investi-
gated the reaction of [(cymene)RuCl2]215 with the steri-
cally very demanding phosphine ligands PAd2Bu and
PtBu2Cy. These ligands are commercially available16
The chloro-bridged complexes [(arene)RuCl2]2 are
known to react with PR3 ligands to give monomeric
adducts of the general formula [(arene)RuCl2(PR3)].10
(10) Bennett, M. A.; Smith, A. K. J. Chem. Soc., Dalton Trans. 1974,
233-241.
(11) (a) Fu¨rstner, A.; Mu¨ller, T. J. Am. Chem. Soc. 1999, 121, 7814-
7821. (b) Fu¨rstner, A.; Ackermann, L. Chem. Commun. 1999, 95-96.
(12) (a) Baran, J.; Bogdanska, I.; Jan, D.; Delaude, L.; Demonceau,
A.; Noels, A. F. J. Mol. Catal. A 2002, 190, 109-116. (b) Jan, D.;
Delaude, L.; Simal, F.; Demonceau, A.; Noels, A. F. J. Organomet.
Chem. 2000, 606, 55-64. (c) Hafner, A.; Mu¨hlebach, A.; van der Schaaf,
P. A. Angew. Chem., Int. Ed. Engl. 1997, 36, 2121-2124. (d) Demon-
ceau, A.; Stumpf, A. W.; Saive, E.; Noels, A. F. Macromolecules 1997,
30, 3127-3136. (e) Stumpf, A. W.; Saive, E.; Demonceau, A.; Noels, A.
F. J. Chem. Soc., Chem. Commun. 1995, 1127-1128. (f) Demonceau,
A.; Noels, A. F.; Saive, E.; Hubert, A. J. J. Mol. Catal. 1992, 76, 123-
132.
(1) Schro¨der, M.; Stephenson, T. A. In Comprehensive Coordination
Chemistry; Wilkinson, G., Gillard, R. D., McCleverty, J. A., Eds.;
Pergamon Press: Oxford, 1987; Vol. 4, p 377.
(2) Jardine, F. H. Prog. Inorg. Chem. 1984, 31, 265-370.
(3) (a) Naota, T.; Takaya, H.; Murahashi, S.-I. Chem. Rev. 1998, 98,
2599-2660. (b) Bennett, M. A.; Matheson, T. W. In Comprehensive
Organometallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W.,
Eds.; Pergamon Press: Oxford, 1982; Vol. 4, p 931.
(4) (a) Holmes, N. J.; Levason, W.; Webster, M. J. Chem. Soc., Dalton
Trans. 1997, 4223-4229. (b) Jones, R. A.; Real, F. M.; Wilkinson, G.;
Galas, A. M.; Hursthouse, M. B.; Malik, K. M. A. J. Chem. Soc., Dalton
Trans. 1980, 511-518. (c) Singer, H.; Hademer, E.; Oehmichen, U.;
Dixneuf, P. J. Organomet. Chem. 1979, 178, C13-C16.
(5) Bennett, R. L.; Bruce, M. I.; Stone, F. G. A. J. Organomet. Chem.
1972, 38, 325-334.
(13) Quebatte, L.; Solari, E.; Scopelliti, R.; Severin, K. Organome-
tallics 2005, 24, 1404-1406.
(14) (a) Quebatte, L.; Haas, M.; Solari, E.; Scopelliti, R.; Nguyen,
Q. T.; Severin K. Angew. Chem., Int. Ed. 2005, 44, 1084-1088. (b)
Simal, F.; Jan, D.; Delaude, L.; Demonceau, A.; Spirlet, M.-R.; Noels,
A. F. Can. J. Chem. 2001, 79, 529-535. (c) Simal, F.; Sebille, S.; Hallet,
L.; Demonceau, A.; Noels, A. F. Macromol. Symp. 2000, 161, 73-85.
(d) Simal, F.; Jan, D.; Demonceau, A.; Noels A. F. In Controlled/Living
Radical Polymerization; Matyjaszwski, K., Ed.; ACS Symposium Series
768; ACS: Washington, 2000; Chapter 16. (e) Simal, F.; Demonceau,
A.; Noels, A. F. Angew. Chem., Int. Ed. 1999, 38, 538-540.
(15) Bennett, M. A.; Huang, T.-N.; Matheson, T. W.; Smith, A. K.
Inorg. Synth. 1982, 21, 74-78.
(6) Armit, P. W.; Boyd, A. S. F.; Stephenson, T. A. J. Chem. Soc.,
Dalton Trans. 1975, 1663-1672.
(7) Knoth, W. H. J. Am. Chem. Soc. 1972, 94, 104-109.
(8) Hoffman, P. R.; Caulton, K. G. J. Am. Chem. Soc. 1975, 97,
4221-4228.
(9) Baratta, W.; Herdtweck, E.; Rigo, P. Angew. Chem., Int. Ed.
1999, 38, 1629-1631.
10.1021/om050649i CCC: $30.25 © 2005 American Chemical Society
Publication on Web 10/27/2005

Communications
Organometallics, Vol. 24, No. 24, 2005 5793
Scheme 2
and have mainly been used in Pd-catalyzed reac-
tions.17,18 The organometallic chemistry in connection
with ruthenium, on the other hand, has just started to
be explored.19 As the solvent for our reactions, we
decided to use fluorobenzene, which is chemically inert
and has a low tendency to form π-complexes. When a
solution of [(cymene)RuCl2]2 and 2 equiv of the re-
spective phosphine was heated for 3 h at 80 °C, the
complexes 1 and 2 were formed in excellent yield
(Scheme 2). The PAd2Bu complex 1 precipitates from
solution, whereas the PtBu2Cy complex 2 is obtained
after evaporation of the solvent and washing with
pentane.
Figure 1. Graphic representation of the molecular struc-
ture of 1 in the crystal. The solvent molecules (CHCl3,
C5H12) are not shown for clarity. Selected bond lengths [Å]
and angles [deg]: Ru1-Cl1 2.376(3), Ru1-Cl2 2.432(3),
Ru1-Cl4 2.361(3), Ru1-Cl3 2.354(3), Ru1-P1 2.463(4),
Ru1-Ru2 2.5716(14), Ru2-Ru3 2.5834(14), Ru1-Ru3
2.5649(14); Cl1-Ru1-Cl2 82.56(12), Cl4-Ru1-Cl2
154.15(13), Cl2-Ru1-P1 96.20(12).
The complexes were analyzed by 1H, 13C, and 31P
NMR spectroscopy. The data confirmed that the cymene
ligand has been cleaved off. A single peak in the 31P
NMR spectra was observed. The elemental analysis was
in agreement with structures of the formula [RuCl2-
(PR2R′)]n. This was confirmed by the results of single-
crystal X-ray analyses.20,21
Both complexes have trinuclear structures, in which
the three RuCl2(PR2R′) fragments are connected by
Ru-Ru bonds and by bridging chloro ligands (Figures
1 and 2). The Ru-Ru distances (Ru-Ru ) 2.56-2.58
Å) are indicative of very strong metal-metal interac-
tions. The Ru-Ru bonds in trinuclear hydrido com-
plexes of the general formula [Ru3H3(O)(arene)3]+, for
example, are approximately 0.2 Å longer (Ru-Ru )
2.74-2.81 Å),22 and the unsupported Ru-Ru bonds in
[Ru3(CO)12] have an average distance of 2.8515(4) Å.23
As expected for such a compact Ru3 core, the Ru-Cl
(16) The ligands are available from Strem.
(17) For catalytic applications of PAd2Bu see: (a) Tewari, A.; Hein,
M.; Zapf, A.; Beller, M. Synthesis 2004, 935-941. (b) Ehrentraut, A.;
Zapf, A.; Beller, M. Adv. Synth. Catal. 2002, 344, 209-217. (c) Zapf,
A.; Ehrentraut, A.; Beller, M. Angew. Chem., Int. Ed. 2000, 39, 4153-
4155. (d) Ehrentraut, A.; Zapf, A.; Beller, M. Synlett 2000, 1589-1592.
(e) Ehrentraut, A.; Zapf, A.; Beller, M. J. Mol. Catal. 2002, 182-183,
515-523.
Figure 2. Graphic representation of the molecular struc-
ture of 2 in the crystal. The solvent molecule (C5H12) and
the hydrogen atoms are not shown for clarity. Selected bond
lengths [Å] and angles [deg]: Ru1-Cl1 2.3980(12),
Ru1-Cl2 2.3531(12), Ru1-Cl1B 2.3681(12), Ru1-Cl2B
2.4080(12), Ru1-P1 2.5028(13), Ru1-Ru1B 2.5693(7);
Cl1-Ru1-Cl2 84.15(4), Cl1B-Ru1-Cl2 157.09(5),
Cl2-Ru1-P1 102.78(4).
(18) For catalytic applications of PtBu2Cy see: (a) Roy, A. H.;
Hartwig, J. F. Organometallics 2004, 23, 1533-1541. (b) Galardon,
E.; Ramdeehul, S.; Brown, J. M.; Cowley, A.; Hii, K. K.; Jutand, A.
Angew. Chem., Int. Ed. 2002, 41, 1760-1763.
(19) Junge, H.; Beller, M. Tetrahedron Lett. 2005, 46, 1031-1034.
(20) Crystal data for complex 1 × CHCl3 × C5H12: C78H130Cl9P3Ru3,
M ) 1782.99, orthorhombic, a ) 35.121(6) Å, b ) 23.608(3) Å, c )
19.039(3) Å, V ) 15786(4) Å3, T ) 140(2) K, space group Aba2, Z ) 8,
µ ) 0.975 mm-1, 44 821 reflections collected, 13 468 independent
reflections, Rint ) 0.1198, R1 [I > 2σ(I)] ) 0.0790, wR2 (all data) )
0.2234.
(21) Crystal data for complex 2 × C5H12
8530.1(14) Å3, T ) 140(2) K, space group R3c, Z ) 6, µ ) 1.183 mm-1
16 012 reflections collected, 3343 independent reflections, Rint ) 0.0537,
R1 [I > 2σ(I)] ) 0.0323, wR2 (all data) ) 0.0698.
: C47H99Cl6P3Ru3, M )
bonds are relatively short (Ru-Cl ) 2.35-2.43 Å).
Dinuclear complexes with the common M(µ-Cl)3Ru
binding motif, for comparison, show Ru-(µ-Cl) distances
in the range of 2.50 ( 0.05 Å.24 The Ru-P bonds in 1
and 2, on the other hand, are relatively long: with an
average length of 2.49 Å, they are longer than what is
1273.08, rhombohedral, a ) b ) 14.9378(12) Å, c ) 44.142(5) Å, V )
,
(22) (a) Vieille-Petit, L.; Therrien, B.; Buryak, A.; Severin, K.; Su¨ss-
Fink, G. Acta Crystallogr. 2004, E60, m1909-m1911. (b) Vieille-Petit,
L.; Therrien, B.; Su¨ss-Fink, G. Inorg. Chim. Acta 2003, 355, 394-398.
(c) Vieille-Petit, L.; Therrien, B.; Su¨ss-Fink, G.; Ward, T. R. J.
Organomet. Chem. 2003, 684, 117-123. (d) Faure, M.; Jahncke, M.;
Neels, A.; Stoeckli-Evans, H.; Su¨ss-Fink, G. Polyhedron 1999, 18,
2679-2685.
(23) Churchill, M. R.; Hollander, F. J.; Hutchinson, J. P. Inorg.
Chem. 1977, 16, 2655-2659.

5794 Organometallics, Vol. 24, No. 24, 2005
Communications
typically found for Ru(II) complexes with sterically
demanding PCy3 or PiPr3 ligands (Ru-P ) 2.40 (
0.05 Å).25
was most likely due to its low solubility. For the arene
complex [(1,3,5-C6H3 Pr3)RuCl2]2, on the other hand, an
i
explanation could be the unfavorable formation of
i
Trinuclear ruthenium complexes, which contain ex-
clusively chloro and phosphine ligands, have been
characterized before.26 These cationic complexes have
the formula [Ru3Cl5(PPh3)6]+ or [Ru3Cl5(L-L)3]+ (L-L
) BINAP, (Ph2P)2C6H4). But contrary to what is ob-
served for 1 and 2, they possess a Ru3(µ2-Cl)3(µ3-Cl)2 core
with two face-capped µ3-chloride atoms and Ru-Ru
distances of more than 3.21 Å.
putative intermediate [(1,3,5-C6H3 Pr3)RuCl2(PAd2Bu)]
due to steric congestion between the sterically demand-
ing ligands C6H3 Pr3 and PAd2Bu.29
i
The complexes 1 and 2 are remarkably stable. Heat-
ing solutions of 1 or 2 with 3 equiv of the ligand PPh3,
PCy3, or 1,3-diaminopropane in toluene at 70 °C for 1 h
did not lead to any significant decomposition of the
trinuclear structure as evidenced by 31P NMR spectros-
copy. Upon addition of bis(diphenylphosphino)ethane
(dppe), however, the formation of [RuCl2(dppe)2] was
observed, regardless of the stoichiometry. When toluene
solutions of 1 and 2 were heated for 1 h to 70 °C under
an atmosphere of CO, the PAd2Bu complex 1 was found
to be largely inert, whereas for the PtBu2Cy complex 2,
a number of unidentified new peaks were observed in
the 31P NMR spectrum together with a dominant peak
for the starting material 2. The nature of these products
was not investigated further.
In summary, we have described the syntheses and the
structures of two complexes of the general formula
[RuCl2(PR2R′)]3. The trimers are composed of 12-
electron RuCl2(PR2R′) fragments, which aggregate by
formation of Ru-Ru bonds and µ-Cl bridges. The
resulting clusters are remarkably stable, as evidenced
by attempted addition reactions with P- and N-donor
ligands and with carbon monoxide. [(Arene)RuCl2]2
complexes in combination with sterically demanding
phosphine ligands are frequently used for the in-situ
generation of electronically unsaturated Ru-cata-
lysts.11-14,19 So far, there is only very limited knowledge
about what kind of complexes are formed after cleavage
of the arene ligand. The possibility that chemically inert
complexes of type [RuCl2(PR2R′)]3 can be generated in
such reactions should be considered in future investiga-
tions.
To investigate in more detail the parameters that are
of importance for the formation of complex 1, we have
performed a number of additional experiments. When
the temperature of the reaction was reduced from 80 to
60 °C, no precipitation was observed after 3 h, indicating
that the thermal activation is essential. Complex 1
remained the dominant reaction product when the
stoichiometry between PAd2Bu and [(cymene)RuCl2]2
was increased to P:Ru ) 2:1. Using substoichiometric
amounts of phosphine (P:Ru ) 0.5), however, the
precipitation of an unidentified compound of low solu-
bility was observed. To determine whether other pre-
cursors for the “RuCl2” fragment could be used to
synthesize 1, we have investigated the reaction of
i
27
[(1,3,5-C6H3 Pr3)RuCl2]2 and [(cod)RuCl2]n (cod ) cy-
cloocta-1,5-diene)28 with PAd2Bu (C6H5F, P:Ru ) 1.25,
80 °C, 3 h). Neither of the two starting materials gave
significant amounts of complex 1. For [(cod)RuCl2]n, this
(24) For some selected examples see: (a) Gauthier, S.; Scopelliti,
R.; Severin, K. Helv. Chim. Acta 2005, 88, 435-446. (b) Gauthier, S.;
Quebatte, L.; Scopelliti, R.; Severin, K. Chem. Eur. J. 2004, 10, 2811-
2821. (c) Amaroso, D.; Yap, G. P. A.; Fogg, D. E. Organometallics 2002,
21, 3335-3343. (d) Amaroso, D.; Yap, G. P. A.; Fogg, D. E. Can. J.
Chem. 2001, 79, 958-963.
(25) For some selected examples see: (a) Jung, S.; Ilg, K.; Brandt,
C. D.; Wolf, J.; Werner, H. Eur. J. Inorg. Chem. 2004, 469-480. (b)
Louie, J.; Grubbs, R. H. Organometallics 2002, 21, 2153-2164. (c)
Fu¨rstner, A.; Ackermann, L.; Gabor, B.; Goddard, R.; Lehmann, C. W.;
Mynott, R.; Stelzer, F.; Thiel, O. R. Chem. Eur. J. 2001, 7, 3236-3253.
(d) Coalter, J. N., III; Bollinger, J. C.; Huffman, J. C.; Werner-
Zwanziger, U.; Caulton, K. G.; Davidson, E. R.; Ge´rard, H.; Clot, E.;
Eisenstein, O. New J. Chem. 2000, 24, 9-26.
(26) (a) Liu, S. H.; Yang, S.-Y.; Lo, S. T.; Xu, Z.; Ng, W. S.; Wen, T.
B.; Zhou, Z. Y.; Lin, Z.; Lau, C. P.; Jia, G. Organometallics 2001, 20,
4161-4169. (b) Mashima, K.; Komura, N.; Yamagata, T.; Tani, K.;
Haga, M.-a. Inorg. Chem. 1997, 36, 2908-2912. (c) Mashima, K.; Hino,
T.; Takaya, H. J. Chem. Soc., Dalton Trans. 1992, 2099-2107. (d)
Mashima, K.; Hino, T.; Takaya, H. Tetrahedron Lett. 1991, 32, 3101-
3104.
Supporting Information Available: Synthetic proce-
dures and analytical data for the complexes 1 and 2 as well
as crystallographic data in CIF format. This material is
available free of charge on the Internet at http://pubs.acs.org.
OM050649I
i
(29) When the complex [(1,3,5-C6H3 Pr3)RuCl2]2 was dissolved to-
(27) Hull, J. W., Jr.; Gladfelter, W. L. Organometallics 1984, 3, 605-
613.
(28) Albers, M. O.; Ashworth, T. V.; Oosthuizen, H. E.; Singleton E.
Inorg. Synth. 1989, 26, 68-69.
gether with 2 equiv of PAd2Bu in CH2Cl2 at room temperature, the
i
formation of the monomeric adduct [(1,3,5-C6H3 Pr3)RuCl2(PAd2Bu)]
could not be observed by 31P NMR spectroscopy. This is in contrast to
what was found for [(cymene)RuCl2]2.