Coordinatively unsaturated ruthenium phosphine half-sandwich complexes: Correlations to structure and reactivity

Article abstract of DOI:10.1021/om020359r

A number of 16e two-legged piano-stool complexes [Cp*Ru(PP)] [BA?₄] have been prepared by reaction of NaBA?₄ with either [Cp*RuCl(PP)] (PP = (PEt₃)₂, ⁱPr₂PCH₂CH₂PⁱPr₂ (dippe), (PPh₃)₂) or [Cp*RuCl(PR₃)] plus PR₃ (PR₃ = PMeⁱPr₂, PPhⁱPr₂) in fluorobenzene under argon. The complexes [Cp*Ru(PEt₃)₂][BA?₄], [Cp*Ru(dippe)][BA?₄], and [Cp*Ru(PMeⁱPr₂)₂] [BA?₄] have been structurally characterized by X-ray crystallography. Attempts to isolate analogous species containing other phosphine ligands such as PⁱPr₃, PCy₃, and PMe₃ led to the sandwich derivative [Cp*Ru(η⁶-FPh)] [BA?₄], which was also structurally characterized. Both [Cp*Ru(PPh₃)₂] [BA?₄] and [Cp*Ru(PPhⁱPr₂)₂] [BA?₄] are unstable and rearrange to the 18e sandwich species [Cp*Ru(η⁶-C₆H₅PR₂)] [BA?₄] and to [Cp*Ru(η⁶-C₆H₅POR₂)] [BA?₄] (R = Ph, ⁱPr) under trace amounts of oxygen. The geometry of the 16e complexes as well as their affinity for an additional ligand depend on the substituents on the phosphorus. The reactivity with respect to the addition of N₂, PR₃, O₂, H₂, and HCl to form 18e derivatives has been studied. Some model systems have been analyzed using density functional theory (DFT) calculations. Also included are comparative studies on the NN counterparts. The moieties [CpRu(PP)]⁺ (PP = (PH₃)₂, H₂PCH₂CH₂PH₂) adopt typically pyramidal structures (i.e. in the absence of bulky and rigid substituents on P) versus planar structures of [CpRu(NN)]⁺ (NN = (NH₃)₂, H_2- NCH₂CH₂NH₂). [Cp*Ru(PP)]⁺ is more stable but has nevertheless a higher affinity of adding a σ ligand than [Cp*Ru(NN)⁺.

Full text of DOI:10.1021/om020359r

5334
Organometallics 2002, 21, 5334-5346
Coor d in a tively Un sa tu r a ted Ru th en iu m P h osp h in e
Ha lf-Sa n d w ich Com p lexes: Cor r ela tion s to Str u ctu r e
a n d Rea ctivity
Halikhedkar Aneetha, Manuel J ime´nez-Tenorio, M. Carmen Puerta, and
Pedro Valerga*
Departamento de Ciencia de Materiales e Ingenier´ıa Metalu´rgica y Quı´mica Inorga´nica,
Facultad de Ciencias, Universidad de Ca´diz, 11510 Puerto Real, Ca´diz, Spain
Valentin N. Sapunov, Roland Schmid, and Karl Kirchner
Institute of Applied Synthetic Chemistry, Vienna University of Technology,
Getreidemarkt 9/ 153, A-1060 Vienna, Austria
Kurt Mereiter
Institute of Chemical Technologies and Analytics, Vienna University of Technology,
Getreidemarkt 9, A-1060 Vienna, Austria
Received May 6, 2002
A number of 16e two-legged piano-stool complexes [Cp*Ru(PP)][BAr′4] have been prepared
by reaction of NaBAr′4 with either [Cp*RuCl(PP)] (PP ) (PEt3)2, iPr2PCH2CH2PiPr2 (dippe),
(PPh3)2) or [Cp*RuCl(PR3)] plus PR3 (PR3 ) PMeiPr2, PPhiPr2) in fluorobenzene under argon.
The complexes [Cp*Ru(PEt3)2][BAr′4], [Cp*Ru(dippe)][BAr′4], and [Cp*Ru(PMeiPr2)2][BAr′4]
have been structurally characterized by X-ray crystallography. Attempts to isolate analogous
species containing other phosphine ligands such as PiPr3, PCy3, and PMe3 led to the sandwich
derivative [Cp*Ru(η6-FPh)][BAr′4], which was also structurally characterized. Both [Cp*Ru-
(PPh3)2][BAr′4] and [Cp*Ru(PPhiPr2)2][BAr′4] are unstable and rearrange to the 18e sandwich
species [Cp*Ru(η6-C6H5PR2)][BAr′4] and to [Cp*Ru(η6-C6H5POR2)][BAr′4] (R ) Ph, iPr) under
trace amounts of oxygen. The geometry of the 16e complexes as well as their affinity for an
additional ligand depend on the substituents on the phosphorus. The reactivity with respect
to the addition of N2, PR3, O2, H2, and HCl to form 18e derivatives has been studied. Some
model systems have been analyzed using density functional theory (DFT) calculations. Also
included are comparative studies on the NN counterparts. The moieties [CpRu(PP)]+ (PP )
(PH3)2, H2PCH2CH2PH2) adopt typically pyramidal structures (i.e. in the absence of bulky
and rigid substituents on P) versus planar structures of [CpRu(NN)]+ (NN ) (NH3)2, H2-
NCH2CH2NH2). [CpRu(PP)]+ is more stable but has nevertheless a higher affinity of adding
a σ ligand than [Cp*Ru(NN)]+.
In tr od u ction
These features are nicely reproduced by DFT calcula-
tions by Costuas and Saillard5 in terms of both small
HOMO-LUMO gap and weak HOMO-LUMO overlap
(rendering the J ahn-Teller instability of the pseudo-
Half-sandwich d6 complexes of the group 8 elements
Fe, Ru, and Os, ubiquitous in organometallic chemistry,
typically adhere to the 18e rule. There is, however, a
small but growing number of relatively stable “genuine”
16e complexes.1 Since such unsaturated compounds are
potential catalysts, it is highly desirable to understand
in more detail the parameters that are related to
stability, reactivity, and structure. This goal will be
achieved by the synergistic use of experiment and
theory.
C
2v geometry insignificant). It is interesting to note that,
if a singlet ground state (S ) 0) is assumed, the
pyramidal structure would be favored. Furthermore,
pyramidalization of the metal center is favored by strong
π-acceptor ligands, especially if they are also strong
σ-donors. Thus, with the weak π-acceptor phosphine
ligands, the triplet state is the ground state, while with
the strong π-acceptor CO ligand, the singlet state is
more stable. The configurational stability of pyramidal
vs planar 16e complexes depending on the electronic
For the iron case, five unsaturated complexes of the
type [η5-Cp′Fe(PP)]+ (Cp′ ) Cp, Cp*, pentadienyl; PP
) Ph2PCH2CH2PPh2 (dppe), Pri PCH2CH2PPri2 (dippe),
2
2 PEt3) have so far been isolated and structurally
characterized.2-4 All of them have a planar (C2v) ground-
state structure (i.e., the Cp plane is perpendicular to
the P-Fe-P plane) and are paramagnetic (S ) 1).
(2) Hamon, P.; Toupet, L.; Hamon, J .-R.; Lapinte, C. Organometal-
lics 1996, 15, 10.
(3) de la J ara Leal, A.; Tenorio, M. J .; Puerta, M. C.; Valerga, P.
Organometallics 1995, 14, 3839.
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Y. J . Am. Chem. Soc. 1990, 112, 6539.
(1) Poli, R. Chem. Rev. 1996, 96, 2135.
(5) Costuas, K.; Saillard, J .-Y. Organometallics 1999, 18, 2505.
10.1021/om020359r CCC: $22.00 © 2002 American Chemical Society
Publication on Web 10/26/2002

Ruthenium Phosphine Half-Sandwich Complexes
Organometallics, Vol. 21, No. 24, 2002 5335
properties of the ligands for diamagnetic systems has
been analyzed in detail by the Hofmann6 and Eisen-
stein7 groups. As a result, the relative stability of the
above iron complexes may be traced to the energetically
unfavorable change in spin state, preventing the un-
saturated complex from adding nucleophiles. This point
of view has been put forward by Poli.1 An unusual case
of a neutral 14e half-sandwich complex, [Cp*Fe{N(Si-
Me3)2}], adopting a so-called “pogo-stick” structure, has
been reported recently by Siemeling.8 The solid-state
structure of the diamagnetic complex is unprecedented
in the chemistry of open-shell organometallics.
cationic complex, or even dinitrogen. The introduction
of a salt of the bulky, noncoordinating anion [BAr′4]-
(Ar′ ) 3,5-(CF3)2C6H3))20 and its use as a halide scav-
enger in combination with fluorobenzene as the solvent
open up new possibilities to generate and stabilize
cationic, highly electrophilic, coordinatively unsaturated
species. An example is the successful isolation of [(η5-
Cp′)Ru(NN)][BAr′4].17,18 However, the resulting 16e
species generated in this way are potentially so reactive
so as to scavenge trace amounts of dinitrogen present
even in high-purity argon, giving dinitrogen-bridged
complexes. This is what happens in the course of the
reaction of [CpRu(P)2Cl] ((P)2 ) dippe, (PEt3)2, (PMei-
Pr2)2) with NaBAr′4 in fluorobenzene under argon,
which yields [{CpRu(P)2}2(µ-N2)][BAr′4]2.21 Alterna-
tively, familiar ligands such as PPh3 may be forced to
adopt a rare η3-coordination mode, allowing the metal
to attain the 18e configuration in [CpRu(η3-PPh3)(PMe-
iPr2)][BAr′4].21
For the Ru situation, spin state arguments are not
particularly relevant, owing to the larger HOMO-
LUMO gap compared to that in the iron congeners. The
stability of open-shell Ru complexes is enhanced on
using strong π-donor ligands X, as in [Cp*Ru(PR3)X] (R
i
) Cy, Pr, tBu, X ) halide, alkoxide, amide)9-14 or
[Cp*Ru(carbene)X] (carbene ) 1,3-R2-imidazol-2-yli-
denes).15 A very recent example of a π-stabilized 16e
complex is [Cp*Ru(RNCR′NR)] (R ) tBu, Cy), in which
the amidinate ligand is acting both as a σ- and π-donor
to avoid unsaturation.16
We have found that halide abstraction from certain
Cp*Ru complexes containing bulky phosphines having
good σ-electron-donor capabilities leads to cationic 16e
species of the type [Cp*Ru(PP)]+. Such species are
amenable to isolation in high yields and were unequivo-
cally characterized by spectral techniques and occasion-
ally single-crystal X-ray structure analysis. The present
paper describes the outcome of our efforts to synthesize
and characterize a number of coordinatively unsatur-
ated species [Cp*Ru(PP)][BAr′4]. Furthermore, their
structural and chemical properties will be compared
with theoretical treatments using density functional
theory (DFT). Specifically, we compare the electronic
structures of coordinatively unsaturated half-sandwich
ruthenium complexes containing N and P donor coli-
gands and their reactivities toward simple ligands. Part
of the work has appeared as a preliminary communica-
In the course of our efforts to synthesize and charac-
terize coordinatively unsaturated ruthenium complexes,
we recently switched over to hard nitrogen donors. In
this way the first genuine cationic 16e ruthenium
complexes [Cp*Ru(Me2NCH2CH2NR2)]+ (R ) Me, iBu)17
and [CpRu(Me2NCH2CH2NMe2)]+18 became available.
The nearly C2v symmetric complexes are remarkably
stable, particularly those of Cp*, and show surprisingly
little affinity toward the simple ligands N2, H2, and
ethylene despite the absence of π-donor stabilization,
bulky ligands,19 and spin state changes. Analogous [(η5-
Cp′)Ru(PP)]+ complexes remain unknown so far, being
obviously too reactive to be isolated. Such species, when
generated in situ by halide (X) abstraction from the
halide complex [(η5-Cp′)Ru(PP)X], react readily with any
suitable source of electrons to achieve the 18e configu-
ration, be it solvent molecules, the counterion of the
tion.22
Exp er im en ta l Section
All synthetic operations were performed under a dry argon
atmosphere, using conventional Schlenk techniques. Tetrahy-
drofuran, diethyl ether, and petroleum ether (boiling point
range 40-60 °C) were distilled from the appropriate drying
agents. All solvents were deoxygenated immediately before
use. The complexes [Cp*RuCl(PR3)2] (R ) Et, Ph, Me),23,24
[Cp*RuCl(dippe)],25 and [Cp*RuCl(PR3)] (PR3 ) PMeiPr2, PPhi-
Pr2, PiPr3, PCy3)9,11,13,26 as well as Na[BAr′4]20 were prepared
according to reported procedures. IR spectra were recorded in
Nujol mulls on a Perkin-Elmer FTIR Spectrum 1000 spectro-
photometer. UV-vis spectra were measured on a Milton Roy
Spectronic 3000 Diode Array instrument. NMR spectra were
taken on a Varian Unity 400 MHz or Varian Gemini 200 MHz
instrument at 298 K unless otherwise stated. Chemical shifts
are given in ppm from SiMe4 (1H and 13C{1H}) or 85% H3PO4
(31P{1H}). Microanalysis were performed by the Serveis Cien-
t´ıfico-Te`cnics, University of Barcelona.
(6) Ward, T. R.; Schafer, O.; Daul, C.; Hofmann, P. Organometallics
1997, 16, 3207.
(7) J ohnson, T. J .; Folting, K.; Streib, W. E.; Martin, J . D.; Huffman,
J . C.; J ackson, S. A.; Eisenstein, O.; Caulton, K. G. Inorg. Chem. 1995,
34, 488.
(8) Siemeling, U.; Vorfeld, U.; Neumann, B.; Stammler, H.-G.
Organometallics 1998, 17, 483.
(9) Campion, B. K.; Heyn, R. H.; Tilley, T. D. J . Chem. Soc., Chem.
Commun. 1988, 278.
(10) (a) Ko¨lle, U.; Kossakowski, J .; Raabe, G. Angew. Chem., Int.
Ed. Engl. 1990, 29, 773. (b) Ko¨lle, U.; Rietmann, C.; Raabe, G.
Organometallics 1997, 16, 3273.
(11) Arliguie, T.; Border, C.; Chaudret, B.; Devillers, J .; Poilblanc,
R. Organometallics 1989, 8, 1308.
(12) Lindner, E.; Haustein, M.; Mayer, H. A.; Gierling, K.; Fawzi,
R.; Steinmann, M. Organometallics 1995, 14, 2246.
(13) (a) J ohnson, T. J .; Huffman, J . C.; Caulton, K. G. J . Am. Chem.
Soc. 1992, 114, 2725. (b) Bickford, C. C.; J ohnson, T. J .; Davidson, E.
R.; Caulton, K. G. Inorg. Chem. 1994, 33, 1080.
(14) Braun, T.; Laubender, M.; Gevert, O.; Werner, H. Chem. Ber./
Recl. 1997, 130, 559.
(20) Brookhart, M.; Grant, B.; Volpe, A. F., J r. Organometallics 1992,
11, 3920.
(21) Aneetha, H.; J imenez-Tenorio, M.; Puerta, M. C.; Valerga, P.;
Mereiter, K. Organometallics 2002, 21, 628.
(22) J ime´nez-Tenorio, M.; Puerta, M. C.; Valerga, P.; Mereiter, K.
J . Am. Chem. Soc. 2000, 122, 11230.
(23) Coto, A.; J ime´nez-Tenorio, M.; Puerta, M. C.; Valerga, P.
Organometallics 1998, 17, 4392.
(24) Fagan, P. J .; Mahoney, W. S.; Calabrese, J . C.; Williams, I. D.
Organometallics 1990, 9, 1843.
(25) de los R´ıos, I.; J ime´nez-Tenorio, M.; Padilla, J .; Puerta, M. C.;
Valerga, P. J . Chem. Soc., Dalton Trans. 1996, 377.
(26) J ime´nez-Tenorio, M.; Puerta, M. C.; Valerga, P. J . Organomet.
Chem. 2000, 609, 161.
(15) (a) Huang, J .; Schanz, H.-J .; Stevens, E. D.; Nolan, S. P.
Organometallics 1999, 18, 2370. (b) Huang, J .; Stevens, E. D.; Nolan,
S. P.; Petersen, J . L. J . Am. Chem. Soc. 1999, 121, 2674.
(16) Yamaguchi, Y.; Nagashima, H. Organometallics 2000, 19, 725.
(17) (a) Gemel, C.; Mereiter, K.; Schmid, R.; Kirchner, K. Organo-
metallics 1997, 16, 5601. (b) Gemel, C.; Sapunov, V. N.; Mereiter, K.;
Ferencic, M.; Schmid, R.; Kirchner, K. Inorg. Chim. Acta 1999, 286,
114.
(18) Gemel, C.; Huffman, J . C.; Caulton, K. G.; Mauthner, K.;
Kirchner, K. J . Organomet. Chem. 2000, 593-594, 342.
(19) Caulton, K. G. New J . Chem., 1994, 18, 25.

5336 Organometallics, Vol. 21, No. 24, 2002
Aneetha et al.
[Cp *Ru (P Et3)2][BAr ′4] (1). To a solution of [Cp*RuCl-
(PEt3)2] (0.25 g, 0.5 mmol) in fluorobenzene (15 mL) was added
solid NaBAr′4 (0.44 g, 0.5 mmol). The mixture was stirred for
15 min at room temperature. The initial orange solution was
rapidly converted to a deep blue suspension. Sodium chloride
was removed by filtration through Celite. The resulting
solution was layered with petroleum ether and left standing
undisturbed at room temperature. Well-formed blue crystals
were obtained by slow diffusion of the petroleum ether into
the fluorobenzene solution. These crystals were isolated by
cannulating off the supernatant liquor and dried under an
argon stream. Yield: 0.38 g, 57%. Anal. Calcd for C54H57BF24P2-
Ru: C, 48.5; H, 4.27. Found: C, 48.2; H, 4.12. Spectral data
for 1 are as follows. 1H NMR (400 MHz, CD2Cl2, 213 K): δ
1.11 (br, P(CH2CH3)3), 1.30 (s, C5(CH3)5), 1.91 (m, P(CH2CH3)3).
31P{1H} NMR (161.89 MHz, CD2Cl2, 213 K): δ 20.4. The
exceeding instability of this complex in solution prevented the
recording of its 13C{1H} NMR spectrum.
Yield: 0.66 g, 55%. Complex 5 is unstable and gradually turns
into a yellow oily material, which consists of a mixture of the
sandwich derivatives [Cp*Ru(η6-C6H5PPh2)][BAr′4] (5a ) and
[Cp*Ru(η6-C6H5POPh2)][BAr′4] (5b). For this reason, it was not
analyzed. Spectral data for 5 are as follows. 1H NMR (400
MHz, CD2Cl2): δ 1.11 (s, C5(CH3)5), 7.05, 7.35, 7.41 (m br,
P(C6H5)3). 31P{1H} NMR (161.89 MHz, CD2Cl2): δ 33.8. 13C-
{1H} NMR (100.58 MHz, CD2Cl2): δ 10.1 (s, C5(CH3)5), 82.3
(s, C5(CH3)5), 128.7, 130.9, 133.5 (P(C6H5)3). Selected spectral
1
data for [Cp*Ru(η6 -C6H5PPh2)][BAr′4] (5a ) are as follows. H
NMR (400 MHz, CD2Cl2): δ 1.99 (s, C5(CH3)5), 5.42, 5.52, 5.66
(m br, η6-PC6H5), 7.1-7.7 (m, PC6H5). 31P{1H} NMR (161.89
MHz, CD2Cl2): δ -13.6. Selected spectral data for [Cp*Ru(η6-
C6H5POPh2)][BAr′4] (5b) are as follows. 1H NMR (400 MHz,
CD2Cl2): δ 1.99 (s, C5(CH3)5), 5.77, 5.98 (η6-POC6H5), 7.2-7.7
(POC6H5). 31P{1H} NMR (161.89 MHz, CD2Cl2): δ 31.3.
[Cp *Ru (P P h iP r 2)2][BAr ′4] (6). This compound was ob-
tained in a fashion analogous to that for 3, starting from
[Cp*RuCl(PPhiPr2)] (0.15 g, 0.33 mmol), PPhiPr2 (0.1 mL,
excess), and NaBAr′4 (0.3 g, 0.33 mmol) in fluorobenzene.
Yield: 0.34 g, 69%. As is the case for compound 5, complex 6
is also unstable, and it was not analyzed. It gradually turns
into a yellow-brown oily material, which consists of a mixture
of the sandwich derivatives [Cp*Ru(η6-C6H5PiPr2)][BAr′4] (6a )
and [Cp*Ru(η6-C6H5POiPr2)][BAr′4] (6b). Spectral data for 6
[Cp *Ru (d ip p e)][BAr ′4] (2). This compound was obtained
in a fashion analogous to that for 1, starting from [Cp*RuCl-
(dippe)] (0.27 g, 0.5 mmol) and NaBAr′4 (0.44 g, 0.5 mmol) in
fluorobenzene (15 mL). Yield: 0.46 g, 68%. Anal. Calcd for
C
56H59BF24P2Ru: C, 49.4; H, 4.34. Found: C, 49.3; H, 4.40.
Spectral data for 2 are as follows. 1H NMR (400 MHz, CD2-
Cl2, 193 K): δ -4.94 (1 H, br, Ru-H-CH2), 0.60, 0.84 (m br,
P(CH(CH3)2)2), 1.43 (s, C5(CH3)5), 1.60 (d, PCH2), 2.43 (m br,
P(CH(CH3)2)2). 31P{1H} NMR (161.89 MHz, CD2Cl2, 193 K): δ
81.3. 13C{1H} NMR (100.58 MHz, CD2Cl2, 193 K): δ 10.8 (s,
C5(CH3)5), 16.6, 17.2 (s, P(CH(CH3)2)2), 18.1 (m, PCH2), 26.2
(m, P(CH(CH3)2)2), 83.2 (s, C5(CH3)5).
1
are as follows. H NMR (400 MHz, CD2Cl2, 198 K): δ 1.06 (s,
C5(CH3)5), 1.25 (m br, P(CH(CH3)2)2), 2.63 (m br, P(CH(CH3)2)2),
6.93, 7.26, 7.43 (m, P(C6H5)). 31P{1H} NMR (161.89 MHz, CD2-
Cl2): δ 39.6. 13C{1H} NMR (100.58 MHz, CD2Cl2): δ 11.1 (s,
C5(CH3)5), 18.9, 20.0 (s, P(CH(CH3)2)2), 28,1 (m, P(CH(CH3)2)2),
79.7 (s, C5(CH3)5), 128.2, 131.9, 135.0 (P(C6H5)). Selected
spectral data for [Cp*Ru(η6-C6H5PiPr2)][BAr′4] (6a ) are as
follows. 1H NMR (400 MHz, CD2Cl2): δ 1.98 (s, C5(CH3)5), 1.18,
1.21 (m, P(CH(CH3)2)2), 2.19 (m, P(CH(CH3)2)2), 5.35, 5.66 (m,
η6 - PC6H5). 31P{1H} NMR (161.89 MHz, CD2Cl2): δ 12.1.
Selected spectral data for [Cp*Ru(η6-C6H5POiPr2)][BAr′4] (6b):
δ 1.98 (s, C5(CH3)5), 1.04, 1.09, 1.25 (m, PO(CH(CH3)2)2), 2.12,
2.40 (m, PO(CH(CH3)2)2), 5.72 (m, η6-POC6H5). 31P{1H} NMR
(161.89 MHz, CD2Cl2): δ 52.8.
[Cp *Ru (P R3)3][BAr ′4] (R ) Et (7), Me (8)). To a solution
of [Cp*RuCl(PR3)2] (0.2 mmol) in fluorobenzene were added
PR3 (R ) Et for 7 and R -) Me for 8; 0.05 mL, excess) and
NaBAr′4 (0.18 g, ca. 0.2 mmol). The resulting yellow solution
was stirred for 10 min at room temperature, filtered through
Celite, and layered with petroleum ether. The resulting well-
formed yellow crystals were separated from the mother liquor,
washed with petroleum ether, and dried in vacuo. Data for 7
[Cp *Ru (P MeiP r 2)2][BAr ′4] (3). A solution of [Cp*RuCl-
(PMeiPr2)] (0.2 g, 0.5 mmol) in fluorobenzene (15 mL) was
treated with a slight excess over the stoichiometric amount of
PMeiPr2 (0.1 mL). When the mixture was stirred for a few
minutes at room temperature, NaBAr′4 (0.44 g, 0.5 mmol) was
added. A color change to deep blue was observed. The mixture
was stirred for 15 min. Sodium chloride was removed by
filtration through Celite. The filtrate was layered with petro-
leum ether and left undisturbed at room temperature. Blue
crystals were obtained by slow diffusion of petroleum ether
into the fluorobenzene, were separated from the supernatant
liquor, and were dried under an argon stream. Yield: 0.45 g,
66%. Anal. Calcd for
C
56H61BF24P2Ru: C, 49.3; H, 4.48.
Found: C, 49.5; H, 4.42. Spectral data for 3 are as follows. 1H
NMR (400 MHz, CD2Cl2, 198 K): δ 0.67, 1.10 (m br, P(CH-
(CH3)2)2), 1.34 (s, C5(CH3)5), 1.48 (m, PCH3), 2.13 (m br,
P(CH(CH3)2)2). 31P{1H} NMR (161.89 MHz, CD2Cl2, 198 K): δ
26.7. 13C{1H} NMR (100.58 MHz, CD2Cl2, 198 K): δ 3.27 (m,
PCH3), 11.0 (s, C5(CH3)5), 17.6, 19.1 (s, P(CH(CH3)2)2), 26.9 (d,
J (C,P) ) 22 Hz, P(CH(CH3)2)2), 79.9 (s, C5(CH3)5).
are as follows. Yield: 0.25 g, 87%. Anal. Calcd for C60H72
-
BF24P3Ru: C, 49.6; H, 4.96. Found: C, 49.4; H, 5.03. Spectral
1
data for 7 are as follows. H NMR (400 MHz, CD3COCD3): δ
1.23 (m, PCH2CH3), 1.74 (s, C5(CH3)5), 2.01 (m, PCH2CH3). 31P-
{1H} NMR (161.89 MHz, CD3COCD3): δ 21.33. 13C{1H} NMR
(100.58 MHz, CD3COCD3): δ 11.30 (m, PCH2CH3), 11.48 (C5-
(CH3)5), 25.24 (m, PCH2CH3), 95.33 (C5(CH3)5). Data for 8 are
as follows. Yield: 0.24 g, 88%. Anal. Calcd for C51H54BF24P3-
Ru: C, 46.1; H, 4.07. Found: C, 45.8; H, 3.99. Spectral data
for 8 are as follows. 1H NMR (400 MHz, CDCl3): δ 1.37 (m,
PCH3), 1.70 (s, C5(CH3)5). 31P{1H} NMR (161.89 MHz, CDCl3):
δ 2.26. 13C{1H} NMR (100.58 MHz, CDCl3): δ 11.50 (C5(CH3)5),
22.68 (m, PCH3), 95.82 (C5(CH3)5).
The complexes 7 and 8 can be also isolated as BPh4- salts,
by treatment of [Cp*RuCl(PR3)2] with 1 equiv of either PEt3
or PMe3 and an excess of NaBPh4 in MeOH. The resulting
yellow precipitate is filtered, washed with EtOH and petro-
leum ether, and dried in vacuo. The complexes can be
recrystallized from acetone/EtOH.
[Cp *Ru (η6-C6H5F )][BAr ′4] (4). Compound 4 was often
formed either as the final product or as a byproduct of the
reaction of Cp*Ru phosphine halo complexes with NaBAr′4 in
fluorobenzene. It can be efficiently prepared by addition of
NaBAr′4 (0.89 g, 1 mmol) to [{Cp*RuCl}4] (0.27 g, 0.25 mmol)
in fluorobenzene (15 mL). The mixture was stirred at room
temperature for 15 min. Then, it was filtered through Celite,
layered with petroleum ether, and allowed to stand at room
temperature. Large colorless crystals were obtained by slow
diffusion of petroleum ether into the fluorobenzene solution.
The crystals were separated from the mother liquor, washed
with petroleum ether, and dried in vacuo. Yield: 0.76 g, 63%.
Anal. Calcd for C48H32BF25Ru: C, 48.2; H, 2.68. Found: C,
47.9; H, 2.55. Spectral data for 4 are as follows. 1H NMR (400
MHz, CD2Cl2): δ 1.43 (s, C5(CH3)5), 6.03, 6.21, 6.47(m, C6H5F).
13C{1H} NMR (100.58 MHz, CD2Cl2): δ 10.5 (s, C5(CH3)5); 79.5,
87.6, 87.5 (C6H5F); 98.61 (s, C5(CH3)5).
[Cp *Ru H2(P P h iP r 2)2][BAr ′4] (9). To [{Cp*RuCl}4] (0.12 g,
0.11 mmol) in fluorobenzene (10 mL) was added PPhiPr2 (0.2
mL, 0.9 mmol). To this purple solution, under a hydrogen
atmosphere, was added NaBAr′4 (0.39 g, 0.44 mmol). The
reaction mixture slowly becomes pale. It was stirred for 30
[Cp *Ru (P P h 3)2][BAr ′4] (5). This compound was obtained
in the form of a sticky blue solid, following a procedure
analogous to that for 1, starting from [Cp*RuCl(PPh3)2] (0.79
g, 0.5 mmol) and NaBAr′4 (0.44 g, 0.5 mmol) in fluorobenzene.

Ruthenium Phosphine Half-Sandwich Complexes
Organometallics, Vol. 21, No. 24, 2002 5337
P(CH(CH3)2)2). 31P{1H} NMR (161.89 MHz, CD3COCD3):
min and filtered through Celite. Evaporation of solvent to
dryness gave a white crystalline solid. It was washed with
petroleum ether and dried. Yield: 0.13 g, 80%. Anal. Calcd
for C66H67BF24P2Ru: C, 53.2; H, 4.50. Found: C, 53.2; H, 4.46.
Spectral data for 9 are as follows. 1H NMR (400 MHz, CD3-
COCD3): δ -8.77 (t, 2J (H,P) ) 28.4 Hz, RuH2), 1.56 (s, C5-
(CH3)5), 1.25 (m, P(CH(CH3)2)2), 2.38 (m, P(CH(CH3)2)2), 7.52,
7.54, 7.59 (m, PC6H5). 1H NMR (400 MHz, CD2Cl2, 193 K):
major isomer, δ -9.43 (t, 2J (HA,P) ) 33.9 Hz, RuHAHB), -9.19
(t, 2J (HB,P) ) 23.8 Hz, RuHAHB); minor isomer, δ -9.03 (t,
2J (H,P) ) 30.2 Hz, RuH2). 31P{1H} NMR (161.89 MHz, CD3-
COCD3): δ 70.27. 31P{1H} NMR (161.89 MHz, CD2Cl2, 193
K): major isomer (83% at 193 K), δ 64.3 (d, J (PA,PB) ) 22 Hz,
PA), 70.9 (d, J (PA,PB) ) 22 Hz, PB); minor isomer (17% at 193
K), δ 62.4 (d, J (PA,PB) ) 19.5 Hz, PA), 71.9 (d, J (PA,PB) ) 19.5,
PB). 13C{1H} NMR (100.58 MHz, CDCl3): δ 10.35 (s, C5(CH3)5),
18.92, 20.32 (s, P(CH(CH3)2)2), 27.47 (m, P(CH(CH3)2)2), 100.72
(s, C5(CH3)5), 128.30, 130.65, 132.32 (PC6H5).
δ
71.64. 13C{1H} NMR (100.58 MHz, CD3COCD3): δ 10.89 (s,
C5(CH3)5), 19.06, 19.21, 19.30, 21.09 (s, P(CH(CH3)2)2), 21.17
(m, PCH2), 26.35 (m, P(CH(CH3)2)2), 104.02 (s, C5(CH3)5).
[Cp *Ru HCl(P MeiP r 2)2][BAr ′4] (14). To a solution of 3
(0.14 g, ca. 0.1 mmol) in 5 mL of dichloromethane was added
1 drop of concentrated hydrochloric acid. The color changed
immediately to yellow-orange. Concentration and addition of
petroleum ether gave a yellow-orange solid, which was washed
with petroleum ether and dried. Yield: 0.14 g, quantitative.
Anal. Calcd for C56H62BClF24P2Ru: C, 48.0; H, 4.43. Found:
1
C, 47.8; H, 4.36. Spectral data for 14 are as follows. H NMR
2
(400 MHz, CD3COCD3): δ -9.24 (t, J (H,P) ) 30.3 Hz), 1.28
(m, P(CH(CH3)2)2), 1.42 (d, PCH3),1.89 (s, C5(CH3)5), 2.30 (m,
P(CH(CH3)2)2). 31P{1H} NMR (161.89 MHz, CD3COCD3):
δ
39.17. 13C{1H} NMR (100.58 MHz, CD3COCD3): δ 6.78 (d,
J (C,P) ) 27.4 Hz, PCH3), 10.72 (s, C5(CH3)5), 19.08, 19.35,
20.03, 20.51 (s, P(CH(CH3)2)2), 29.24 (t, J (C,P) ) 29.6 Hz,
P(CH(CH3)2)2), 104.02 (s, C5(CH3)5).
[Cp *Ru H(P P h iP r 2)2] (10). A THF solution of [Cp*RuH2-
(PPhiPr2)2][BAr′4] was treated with an excess of solid KOtBu.
The reaction mixture was stirred at room temperature for 1
h. Then the solvent was removed in vacuo. The residue was
extracted with petroleum ether, and the extracts were filtered
through Celite. Concentration and cooling to -20 °C gave a
pale yellow residue. Yield: 60-70%. Anal. Calcd for C34H54P2-
Ru: C, 65.3; H, 8.64. Found: C, 64.9; H, 8.40. Spectral data
X-r a y Str u ctu r e Deter m in a tion s. Crystals of 1-4, 7, and
9 were obtained by slow diffusion of petroleum ether into
fluorobenzene solutions. Crystal data and experimental details
are given in Table 1. X-ray data were collected on a Bruker
AXS Smart CCD area detector diffractometer (graphite-
monochromated Mo KR radiation, λ ) 0.710 73 Å, 0.3° ω-scan
frames covering complete spheres of the reciprocal space).
Corrections for Lorentz and polarization effects, for crystal
decay, and for absorption were applied. All structures were
solved by direct methods using the program SHELXS97.27a
Structure refinement on F2 was carried out with the program
SHELXL9727b for 1-3, 7, and 9 and SHELXH9727c for 4. All
non-hydrogen atoms were refined anisotropically. Hydrogen
atoms were inserted in idealized positions and were refined
riding with the atoms to which they were bonded.
Com p u ta tion a l Deta ils. All calculations were performed
using the Gaussian9828 software package on the Silicon
Graphics Power Challenge of the Vienna University of Tech-
nology. To reduce computational effort, [Cp*Ru(PEt3)2]+,
[Cp*Ru(dippe)]+, or [Cp*Ru(PMeiPr2)2]+ and related diamine
complexes such as [Cp*Ru(Me2NCH2CH2NR2)]+ (R ) Me, iBu)
were modeled by the smaller entities [CpRu(PH3)2]+, [CpRu-
(H2PCH2CH2PH2)]+, [CpRu(H2NCH2CH2NH2)]+, and [CpRu-
(NH3)2]+. The geometry and energy of the 16e complexes as
well as the 18e complexes trans-[CpRu(H2PCH2CH2PH2)(H)2]+,
[CpRu(H2PCH2CH2PH2)(η2-H2)]+, trans-[CpRu(PH3)2(H)2]+, and
[CpRu(PH3)2(η2-H2)]+ were optimized at the B3LYP level29 with
the Stuttgart/Dresden ECP (SDD) basis set30 to describe the
electrons of the ruthenium atom. For all other atoms the
1
for 10 are as follows. H NMR (400 MHz, C6D6): δ -13.78 (t,
2J (H,P) ) 36 Hz), 1.48 (s, C5(CH3)5), 1.26, 1.11, 0.96 (m, P(CH-
(CH3)2)2), 2.04 (m, br, P(CH(CH3)2)2), 7.58, 7.60, 7.69 (m,
PC6H5). 31P{1H} NMR (161.89 MHz, C6D6): δ 77.03. 13C{1H}
NMR (100.58 MHz, C6D6): δ 12.05 (s, C5(CH3)5), 19.64, 20.69,
21.20, 22.58 (s, P(CH(CH3)2)2), 27.70, 29.27 (m, P(CH(CH3)2)2),
90.64 (s, C5(CH3)5), 126.54, 131.09, 131.96, 133.92 (PC6H5).
[Cp *Ru H2(P P h 3)2][BAr ′4] (11). To [Cp*RuCl(PPh3)2] (0.12
g, 0.15 mmol) in fluorobenzene (10 mL) was added NaBAr′4
(0.133 g, 0.15 mmol) under a hydrogen atmosphere. The
reaction mixture slowly became pale. It was stirred for 30 min
and filtered through Celite. Evaporation of solvent to dryness
gave a pale yellow glassy solid which crystallized on cooling.
It was washed with petroleum ether and dried. Yield: 0.17 g,
70%. Anal. Calcd for
C78H59BF24P2Ru: C, 57.6; H, 3.63.
Found: C, 57.7; H, 3.56. Selected spectral data for 11 are as
follows. 1H NMR (400 MHz, CD2Cl2): δ -7.28 (t, 2J (H,P) )
26.4 Hz), 1.36 (s, C5(CH3)5), 7.30, 7.35, 7.48 (m, PC6H5). 31P-
{1H} NMR (161.89 MHz, CD2Cl2): δ 63.20. 13C{1H} NMR
(100.58 MHz, CD2Cl2): δ 9.94 (C5(CH3)5), 101.67 (C5(CH3)5),
128.72, 131.03, 133.99, 135.19 (PC6H5).
[Cp *Ru HCl(P Et3)2][BAr ′4] (12). To a solution of [Cp*RuCl-
(PEt3)2] (0.1 g, ca. 0.2 mmol) in 5 mL of fluorobenzene were
added a 5 mL ether solution containing anhydrous HCl (ca.
0.4 mmol, generated by reaction of 25 µL of SiCl(CH3)3 with 6
µL of MeOH) and NaBAr′4 (0.17 g, 0.196 mmol). The reaction
mixture is yellow. It was stirred for 30 min and filtered
through Celite. Evaporation of solvent gave a yellow-orange
solid. It was washed with petroleum ether and dried. Yield:
0.19 g, 70%. Anal. Calcd for C54H58BClF24P2Ru: C, 47.3; H,
4.23. Found: C, 47.0; H, 4.15. Spectral data for 12 are as
(27) (a) SHELXS97, Program for Crystal Structure Solution; Uni-
versity of Go¨ttingen, Go¨ttingen, Germany, 1990. (b) SHELXL97,
Program for Crystal Structure Refinement; University of Go¨ttingen,
Go¨ttingen, Germany, 1997. (c) SHELXH97, Special Version of
SHELXL97 for the Refinement of Very Large Structures; University
of Go¨ttingen, Go¨ttingen, Germany, 1997.
(28) Frisch, M. J .; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J . R.; Zakrzewski, V. G.; Montgomery, J . A.,
J r.; Stratmann, R. E.; Burant, J . C.; Dapprich, S.; Millam, J . M.;
Daniels, A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J .;
Barone, V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo,
C.; Clifford, S.; Ochterski, J .; Petersson, G. A.; Ayala, P. Y.; Cui, Q.;
Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.;
Foresman, J . B.; Cioslowski, J .; Ortiz, J . V.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R. L.;
Fox, D. J .; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.;
Gonzalez, C.; Challacombe, M.; Gill, P. M. W.; J ohnson, B. G.; Chen,
W.; Wong, M. W.; Andres, J . L.; Head-Gordon, M.; Replogle, E. S.;
Pople, J . A. Gaussian 98, revision A.5; Gaussian, Inc.: Pittsburgh, PA,
1998.
1
2
follows. H NMR (400 MHz, CD3COCD3): δ -9.68 (t, J (H,P)
) 31.2 Hz), 1.24 (m, PCH2CH3), 1.89 (s, C5(CH3)5), 2.16, 2.00
(m, PCH2CH3). 31P{1H} NMR (161.89 MHz, CD3COCD3): δ
33.31. 13C{1H} NMR (100.58 MHz, CD3COCD3): δ 9.27
(PCH2CH3), 10.21 (s, C5(CH3)5), 20.11, 20.42 (m, PCH2CH3),
104.21 (s, C5(CH3)5).
[Cp *Ru HCl(d ip p e)][BAr ′4] (13). This compound was ob-
tained in a fashion analogous to that for 12, starting from
[Cp*RuCl(dippe)]. Alternatively, it can be prepared by direct
reaction of 2 with anhydrous HCl in diethyl ether. Yield:
quantitative. Anal. Calcd for C56H60BClF24P2Ru: C, 48.1; H,
4.29. Found: C, 48.2; H, 4.08. Spectral data for 13 are as
(29) Becke, A. D. J . Chem. Phys. 1993, 98, 5648. Miehlich, B.; Savin,
A.; Stoll, H.; Preuss, H. Chem. Phys. Lett. 1989, 157, 200. Lee, C.; Yang,
W.; Parr, G. Phys. Rev. B 1988, 37, 785.
(30) (a) Haeusermann, U.; Dolg, M.; Stoll, H.; Preuss, H. Mol. Phys.
1993, 78, 1211. (b) Kuechle, W.; Dolg, M.; Stoll, H.; Preuss, H. J . Chem.
Phys. 1994, 100, 7535. (c) Leininger, T.; Nicklass, A.; Stoll, H.; Dolg,
M.; Schwerdtfeger, P. J . Chem. Phys. 1996, 105, 1052.
1
2
follows. H NMR (400 MHz, CD3COCD3): δ -9.95 (t, J (H,P)
) 30.3 Hz), 1.97 (s, C5(CH3)5), 2.09 (m, PCH2), 2.45, 3.11 (m,

5338 Organometallics, Vol. 21, No. 24, 2002
Ta ble 1. Su m m a r y of Cr ysta llogr a p h ic F iles for Com p ou n d s 2-4, 7, a n d 9
Aneetha et al.
2
3
4
7
9
formula
fw
T (K)
C
56H59BF24P2Ru
C56H61BF24P2Ru
1363.87
223(2)
C48H32BF25Ru
1195.62
223(2)
C60H72BF24P3Ru
1453.97
223(2)
C66H67BF24P2Ru
1490.02
173(2)
1361.85
213(2)
cryst size (mm)
cryst syst
space group
cell params
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
0.70 × 0.70 × 0.70 0.80 × 0.70 × 0.70 0.80 × 0.40 × 0.30 0.70 × 0.65 × 0.60 0.72 × 0.40 × 0.40
triclinic
monoclinic
monoclinic
monoclinic
monoclinic
P1h (No. 2)
P21 (No. 4)
P21/c (No. 14)
P21/c (No. 14)
P21/n (No. 14)
12.597(6)
12.946(6)
18.967(9)
95.40(2)
99.62(2)
92.78(2)
3030(2)
2
12.474(5)
18.974(8)
13.003(5)
12.830(12)
58.17(6)
20.348(19)
19.447(5)
13.750(4)
26.068(6)
12.284(3)
15.105(4)
36.404(9)
92.68(2)
104.71(2)
107.42(2)
99.14(1)
3074(2)
2
14688(25)
12
6651(3)
4
6669(3)
4
Z
Fcalcd (g cm-3
)
1.493
1.473
1.622
1.452
1.484
λ(Mo KR) (Å)
µ(Mo KR) (cm-1
F(000)
0.71073
4.21
0.71073
4.15
0.71073
4.50
0.71073
4.12
0.71073
3.90
)
1380
1384
7128
2968
3032
max and min transmissn factors 0.80-0.72
0.83-0.76
1.9-30.0
67 375
17 644 (0.021)
15 719
1.00-0.87
2.0-24.0
135 060
22 779 (0.038)
19 241
1.00-0.88
1.7-30.0
69 930
19 015 (0.031)
13 862
1.00-0.92
2.2-30.0
93 030
19 071 (0.027)
15 788
θ range for data collection (deg) 1.8-30.0
no. of rflns collected
44 116
no. of unique rflns (Rint
no. of obsd reflections (I > 2σI)
no. of params
)
17 192 (0.021)
14 100
816
758
2055
874
926
final R1, wR2 values (I > 2σI)
final R1, wR2 values (all data)
goodness of fit on F2
0.0538, 0.1433
0.0665, 0.1566
1.027
0.0605, 0.1684
0.0679, 0.1789
1.022
0.0643, 0.1433
0.0756, 0.1496
1.049
0.0443, 0.1071
0.0677, 0.1252
1.023
0.0445, 0.1029
0.0573, 0.1105
1.056
residual electron density
+1.03/-0.70
+1.36/-1.04
+0.961/-0.53
+0.58/-0.62
+0.67/-0.60
peaks (e Å-3
)
6-31G** basis set was employed.31 Frequency calculations were
performed to confirm the nature of the stationary points,
yielding no imaginary frequency for the minima. All geom-
etries were optimized without constraints (C1 symmetry), and
the energies were zero point corrected.
host the cations arranged in a zigzag-like fashion (cf.
Figure S3 of the Supporting Information). The cations
show two-legged piano-stool structures with significant
differences in the orientation of the P-bonded alkyl
groups relative to the Cp* moieties. In the case of 1,
the [BAr′4]- anion and the Cp*Ru moiety are reasonably
ordered, but the PEt3 ligands were found to be heavily
disordered around the ruthenium atom. Attempts to
model the disorder were made by considering two
complex cations with a relative occupancy factor of 0.5
each and different positions of the phosphorus atoms
and ethyl groups of the PEt3 ligands. Unfortunately, the
structural disorder prohibited the determination of
accurate bond lengths and angles. All relevant X-ray
data, including figures, have been deposited as Sup-
porting Information for reference. In sum, the raw
molecular skeleton obtained from diffraction experi-
ments points in the case of 1 to a genuine 16-electron
species possibly stabilized by an agostic interaction. An
important structural parameter is the degree of pyra-
midalization of the 16e complex, measurable by the
angle of pyramidalization R, defined as the angle formed
by the centroid of the Cp* ring, the ruthenium atom,
and the centroid of the triangle defined by the atoms
Ru, P(1), and P(2). For complex 1, R is estimated to be
ca. 170°. Solutions of 1 in fluorobenzene or dichlo-
romethane are unstable, since the initially dark blue
solutions gradually turn green and finally yellow. This
suggests a steady conversion of the 16e cation into
several more stable 18e species, namely [Cp*Ru(O2)-
(PEt3)2]+,26 [Cp*Ru(N2)(PEt3)2]+,26 and [Cp*Ru(PEt3)3]+
(5; see Reactivity of the 16e Complexes). Therefore,
crystallization of 1 was only achieved from concentrated
solutions in a rather short period of time and the mother
liquor was discarded, which usually becomes greenish.
The instability in solution prevented clean NMR spectra
Resu lts a n d Discu ssion
Syn th esis a n d Str u ctu r e of 16e Com p lexes. The
complexes [Cp*RuCl(PEt3)2] and [Cp*RuCl(dippe)] react
with NaBAr′4 in fluorobenzene under argon to give the
cationic 16e complexes [Cp*Ru(PEt3)2][BAr′4] (1) and
[Cp*Ru(dippe)][BAr′4] (2). In an analogous fashion,
coordinatively unsaturated [Cp*Ru(PMeiPr2)2][BAr′4] (3)
was obtained by treatment of [Cp*RuCl(PMeiPr2)] with
PMeiPr2 (1 equiv) and NaBAr′4 in fluorobenzene under
argon. Attempts to obtain mixed-phosphine complexes
such as [Cp*Ru(PMeiPr2)(PEt3)][BAr′4] proved so far to
be unsuccessful. Compounds 1-3 are very air sensitive,
diamagnetic, deep blue materials. The color arises from
a strong band in the visible spectrum (CH2Cl2 solution)
between 600 and 700 nm, characteristic of 16e half-
sandwich ruthenium complexes.9-18
The X-ray crystal structures of 1-3 consist of closely
related packings of complex cations and [BAr′4]- anions
separated by van der Waals contacts, without interac-
tion with the metal centers. The [BAr′4]- ions form in
principle three-dimensional lattices with approximately
quadratic channels (dimensions of the squarelike grids
of about 12.5-13.2 Å with a mutual angle of 93-94°,
translation period along the channel about 19 Å), which
(31) (a) McClean, A. D.; Chandler, G. S. J . Chem. Phys. 1980, 72,
5639. (b) Krishnan, R.; Binkley, J . S.; Seeger, R.; Pople, J . A. J . Chem.
Phys. 1980, 72, 650. (c) Wachters, A. H. Chem. Phys. 1970, 52, 1033.
(d) Hay, P. J . J . Chem. Phys. 1977, 66, 4377. (e) Raghavachari, K.;
Trucks, G. W. J . Chem. Phys. 1989, 91, 1062. (f) Binning, R. C.; Curtiss,
L. A. J . Comput. Chem. 1995, 103, 6104. (g) McGrath, M. P.; Radom,
L. J . Chem. Phys. 1991, 94, 511.

Ruthenium Phosphine Half-Sandwich Complexes
Organometallics, Vol. 21, No. 24, 2002 5339
F igu r e 1. ORTEP drawing (50% thermal ellipsoids) of the
cation [Cp*Ru(dippe)]+ in complex 2. Hydrogen atoms,
except H(25a) have been omitted. Selected bond lengths
(Å) and angles (deg) with estimated standard deviations
in parentheses: Ru-C(1), 2.179(3); Ru-C(2), 2.235(3); Ru-
C(3), 2.211(3); Ru-C(4), 2.205(3); Ru-C(5), 2.203(3); Ru-
P(1), 2.331(1); Ru-P(2), 2.356(1); Ru‚‚‚C(25), 2.953(4); Ru‚
‚‚H(25a), 2.262 (calculated); P(1)-Ru-P(2), 83.13(4); Ru-
P(2)-C(24), 99.46(12).
F igu r e 2. ORTEP drawing (50% thermal ellipsoids) of the
cation [Cp*Ru(PMeiPr2)2]+ in complex 3. Hydrogen atoms
have been omitted. Selected bond lengths (Å) and angles
(deg) with estimated standard deviations in parentheses.
Ru-C(1), 2.198(4); Ru-C(2), 2.205(5); Ru-C(3), 2.175(6);
Ru-C(4), 2.206(5); Ru-C(5), 2.126(5); Ru-P(1), 2.395(1);
Ru-P(2), 2.393(1); P(1)-Ru-P(2), 101.43(5).
simple, just as expected for a compound of C2v sym-
metry. The cation [Cp*Ru(PMeiPr2)2]+ (Figure 2) dis-
plays a pseudo-C2v structure, similar to that of [Cp*RuX-
(PR3)], [Cp*Ru(TMEDA)][BAr′4],17,18 or [Cp*Ru(amidin-
ate)].16 Since the isopropyl groups are all directed away
from the region perpendicular to the RuP2 plane, agostic
donation is absent. The shortest contact between Ru and
the isopropyl carbon atoms is Ru‚‚‚C(17) at 3.303(13) Å
(shortest calculated R-H distance 2.67 Å to H(17a)), too
far for agostic donation. The degree of pyramidalization
for [Cp*Ru(PMeiPr2)2]+ is minimal (R ) 171°).
(CD2Cl2) from being obtained. The resonances attribut-
able to 1 were always deteriorated by signals stemming
from follow-up products. Although the 31P{1H} NMR
spectrum of 1 consists of one singlet, agostic interactions
cannot be ruled out.
1
In fact, the H NMR spectrum of 2 in CD2Cl2 at 193
K displays one broad resonance at -4.94 ppm, which
clearly points to the presence of an agostic interaction
in this particular case. The 31P{1H} NMR spectrum
consists of one singlet at this temperature, and no
decoalescence is observed. This suggests that there is
rapid hydrogen scrambling with all of the isopropyl
protons of the dippe ligand, rendering the phosphorus
atoms equivalent in the NMR time scale. Also the X-ray
structure of [Cp*Ru(dippe)]+ reveals an agostic interac-
tion with a hydrogen atom of an isopropyl group (Figure
1). The observed Ru‚‚‚C(25) separation is 2.953(4) Å
(calculated Ru-H(25a) bond distance 2.262 Å). The Ru‚
‚‚C(25) distance is only slightly longer than the average
Ru‚‚‚C value of 2.875 Å observed for [RuPh(CO)(PMet-
Bu2)2][BAr′4],33 which contains two strong agostic in-
Attempts to prepare [Cp*Ru(PR3)2][BAr′4] (PR3 ) Pi-
Pr3, PCy3) were unsuccessful. Halide abstraction from
the corresponding neutral derivative [Cp*RuCl(PR3)] in
the presence of PiPr3 or PCy3, using Na[BAr′4] in
fluorobenzene as halide scavenger, did not yield any
blue material, in contrast to 1-3. Instead, large color-
less chunky crystals were obtained, which contained no
phosphorus, as inferred from the 31P{1H} NMR spectra.
Furthermore, the isolated materials from both reactions
turned out to be the same compound: viz., the 18e
sandwich derivative [Cp*Ru(η6-C6H5F)][BAr′4] (4). De-
spite the poor coordinating abilities of halobenzenes,35
the formation of π-complexes is a possibility to be
considered when Na[BAr′4] in combination with fluo-
robenzene is used for the generation of highly reactive
species. In fact, Cp*Ru π-complexes of highly fluorinated
arenes are known, such as the series of derivatives
[Cp*Ru(η6-C6F6-n(OMe)n)][CF3SO3] (n ) 0-2).36 In our
particular case, halide abstraction from either [Cp*RuCl-
(PiPr3)] or [Cp*RuCl(PCy3)] takes place with simulta-
neous phosphine loss and generation of the fragment
{[Cp*Ru]+}, which is trapped by fluorobenzene, furnish-
ing the sandwich complex 4. The latter can alternatively
be obtained in high yield by direct reaction of the
tetramer [{Cp*Ru(µ-Cl)}4] with Na[BAr′4] in fluoroben-
t
teractions of the Bu groups of the two phosphines. A
shorter Ru‚‚‚C distance of 2.651 Å (average) has been
reported for [RuCl2{PPh2(C6H3Me2)}2], showing two
agostic Ru‚‚‚H-C interactions of the methyl groups.34
The Ru-P(2)-C(24) angle in 2 is 99.45°, in contrast to
117-124° in the case of nonagostic isopropyl groups.
The [Cp*RuP2]+ moiety adopts a bent (pyramidalized)
conformation with R ) 160°.
No evidence of agostic interactions can be detected
in the NMR spectra of 3. Indeed, the spectra are very
(32) J ohnson, C. K. ORTEP, A Thermal Ellipsoid Plotting Program;
Oak Ridge National Laboratory, Oak Ridge, TN, 1965.
(33) (a) Huang, D.; Streib, W. E.; Eisenstein, O.; Caulton, K. G.
Angew. Chem., Int. Ed. 1997, 36, 2005. (b) Huang, D.; Streib, W. E.;
Bollinger, J . C.; Caulton, K. G.; Winter, R. F.; Scheiring, T. J . Am.
Chem. Soc. 1999, 121, 8087.
(35) Dembek, A. A.; Fagan, P. J . Organometallics 1995, 14, 3741.
(36) Koelle, U.; Hornig, A.; Englert, U. Organometallics 1994, 13,
4064.
(34) Baratta, W.; Herdtweck, E.; Rigo, P. Angew. Chem., Int. Ed.
1999, 38, 1629.

5340 Organometallics, Vol. 21, No. 24, 2002
Aneetha et al.
the phosphine is small (i.e. PMe3), isolation is not
feasible, since the metal center is not shielded against
side reactions tending to attain the 18e configuration.
On the other hand, overly bulky phosphines, such as
PiPr3 and PCy3, obviously do not form stable [Cp*Ru-
(PP)]+ cations. The increased steric pressure generated
when two bulky phosphines are bound to a single Cp*Ru
moiety may force longer metal-phosphorus separations.
Consequently, the phosphine ligands are replaced by
other donor molecules: i.e., arenes. This hypothesis is
consistent with the sequence of relative Ru-PR3 binding
energies measured by Nolan and co-workers, confirming
the lability of both PiPr3 and PCy3 bound to the Cp*Ru
moiety.40
Halide abstraction from [Cp*RuCl(PPh3)2] and [Cp*-
RuCl(PPhiPr2)] in the presence of PPhiPr2 using Na-
BAr′4 in fluorobenzene gave, in both cases, deep blue
solutions, from which blue solids could be isolated.
However, the 16e complexes [Cp*Ru(PPh3)2][BAr′4] (5)
and [Cp*Ru(PPhiPr2)2][BAr′4] (6) could not be crystal-
lized (in contrast to 1-3) but decomposed to oily, yellow
F igu r e 3. ORTEP drawing (50% thermal ellipsoids) of one
of the three independent cations [Cp*Ru(η6-C6H5F)]+ in
complex 4. Hydrogen atoms have been omitted. Selected
bond lengths (Å) with estimated standard deviations in
parentheses: Ru(1)-C(1), 2.171(5); Ru(1)-C(2), 2.181(5);
Ru(1)-C(3), 2.167(6); Ru(1)-C(4), 2.178(5); Ru(1)-C(5),
2.179(5); Ru(1)-C(11), 2.174(6); Ru(1)-C(12), 2.198(6); Ru-
(1)-C(13), 2.217(6); Ru(1)-C(14), 2.241(6); Ru(1)-C(15),
2.210(6); Ru(1)-C(16), 2.207(6); C(11)-F(1), 1.301(9).
1
materials. The H and 31P{1H} NMR spectra of freshly
prepared solutions in CD2Cl2 are consistent with the 16e
cations [Cp*Ru(PPh3)2]+ and [Cp*Ru(PPhiPr2)2]+. No
evidence for agostic interactions was found. On stand-
ing, signals corresponding to at least two different η6-
1
C6H5 groups appear in the H NMR spectrum, whereas
zene. This underlines the high affinity of the moiety
{[Cp*Ru]+} for aromatic systems.35-38
the 31P{1H} NMR spectrum displays new resonances
arising at -13.6 and 31.3 ppm in the case of 5 and 12.1
and 52.8 ppm in the case of 6. The high-field signals
suggest the presence of PPh3 and PPhiPr2 groups that
were not coordinated through the phosphorus atom to
the metal, whereas the resonances at lower fields
suggest the presence of POPh3 and POPhiPr2 groups,
also not coordinated through phosphorus. We interpret
these observations in terms of the rearrangement of the
16e into the 18e sandwich derivatives [Cp*Ru(η6-C6H5-
PPh2)]+ (5a ) and [Cp*Ru(η6-C6H5PiPr2)]+ (6a ) plus free
phosphine (Scheme 1). Trace amounts of oxygen caused
metal-mediated phosphine oxidation, yielding the cor-
responding phosphine oxide. We and other authors have
previously reported the formation of phosphine oxides
in reactions of half-sandwich ruthenium complexes.26,41-43
Furthermore, the system [CpRuCl(PPh3)2]/NaClO4 acts
as a catalyst for the oxidation of PPh3 to POPh3 in
refluxing MeOH.42 In addition, POPh3 is known to
coordinate to ruthenium in an η6 fashion, as in [CpRu-
(η6-C6H5POPh2)][ClO4].42 In the present case both
POPh3 and POPhiPr2 may behave in this way, furnish-
ing [Cp*Ru(η6-C6H5POPh2)]+ (5b) and [Cp*Ru(η6-C6H5-
POiPr2)]+ (6b) (Scheme 1). These species may well be
responsible for the additional set of coordinated arene
The reaction of [Cp*RuCl(PMe3)2] with NaBAr′4 also
failed to give the 16e compound [Cp*Ru(PMe3)2]+.
Instead, a yellow-orange solution was obtained as a
mixture of colorless crystals of the fluorobenzene sand-
wich complex 4 and yellow crystals of the tris(phos-
phine) derivative [Cp*Ru(PMe3)3][BAr′4] (6). Hence,
halide abstraction from [Cp*RuCl(PMe3)2] results in
ligand redistribution:
The crystal structure of 4 contains an asymmetric
unit of three independent cation complexes and three
[BAr′4]- anions. One cationic complex is disordered in
two possible orientations with fractional occupation
factors of 0.69 and 0.31, respectively. The ORTEP32 view
in Figure 3 shows a sandwich structure with a planar
π-complexed C6H5F ring. The dimension of coordinated
fluorobenzene is similar to that found in other η6-C6H5F
complexes.39 Also, the closely related complex [(η5-C5-
Me4Et)Ru(η6-C6F5OH)][CF3SO3] may be noted.36 The
ruthenium-fluorobenzene carbon bond distances in the
latter compare well with the average value of 2.225 Å
found in 4. Furthermore, all Ru-C separations in 4 are
in the range found for other RuCp(arene) cations.21,37,38
It would appear that the stability of the 16e complexes
of the type [Cp*Ru(PP)][BAr′4] is critically dependent
on the steric requirements of the phosphine ligands. If
1
resonances observed in the H NMR spectra. On stand-
(39) Khaleel, A.; Klabunde, K. J . Inorg. Chem. 1996, 35, 3223.
J agirdar, B. R.; Palmer, R.; Klabunde, K. J .; Radonovich, L. J . Inorg.
Chem. 1995, 34, 278. Prout, K.; Gourdon, A.; Couldwell, C.; Meunier,
B.; Miao, F. M.; Woolcock, J . Acta Crystallogr., Sect. B 1982, 38, 456.
Batsanov, A. S.; Struchkov, Yu. T.; Zaitseva, N. N.; Yur’eva, L. P.;
Kravtsov, D. N. Metalloorg. Khim. (Organomet. Chem. USSR) 1989,
2, 586.
(40) Luo, L.; Nolan, S. P. Organometallics 1994, 13, 4781.
(41) de los R´ıos, I.; J ime´nez-Tenorio, M.; Padilla, J .; Puerta, M. C.;
Valerga, P. Organometallics 1996, 15, 4565.
(42) Uson, R.; Oro, L. A.; Ciriano, M. A.; Naval, M. M.; Apreda, M.
C.; Foces-Foces, C.; Cano. F. H.; Garc´ıa-Blanco, S. J . Organomet. Chem.
1983, 256, 331.
(43) J ia, G.; Ng, W. S.; Chu, H. S.; Wong, W.-T.; Yu, N.-T.; Williams,
I. D. Organometallics 1999, 18, 3597.
(37) Fagan, P. J .; Ward, M. D.; Calabrese, J . C. J . Am. Chem. Soc.
1989, 111, 1698. Ward, M. D.; Fagan, P. J .; Calabrese, J . C.; J ohnson,
D. C. J . Am. Chem. Soc. 1989, 111, 1719.
(38) Gemel, C.; Kirchner, K.; Schmid, R.; Mereiter, K. Organome-
tallics 1996, 15, 532. Kriesel, J . W.; Konig, S.; Freitas, M. A.; Marshall,
A. G.; Leary, J . A.; Tilley, T. D. J . Am. Chem. Soc. 1998, 120, 12207.

Ruthenium Phosphine Half-Sandwich Complexes
Organometallics, Vol. 21, No. 24, 2002 5341
Sch em e 1. Rea ction Sequ en ce for th e F or m a tion a n d Degr a d a tion of Com p ou n d s 7 a n d 8
Ta ble 2. Exp er im en ta l a n d Op tim ized Str u ctu r a l Da ta for Va r iou s [Ru Cp L2]+ Com p lexesa
[(C5R5)RuL2]+
av M-C5 (Å)
M-L (Å)
L-M-L (deg)
R (deg)a
[CpRu(NN)]+ Complexes
[CpRu(H2NCH2CH2NH2)]+
[CpRu(NH3)2]+
2.165
2.196
2.218, 2.217
78
171
179
180
179
168
2.202, 2.192
91
[CpRu(Me2NCH2CH2NMe2)]+
[Cp*Ru(Me2NCH2CH2NMe2)]+
[Cp*Ru(Me2NCH2CH2N(Bui)2)]+
2.09(1)
2.142(7)
2.13(1)
2.142(6), 2.163(8)
2.183(7), 2.180(6)
2.18(1), 2.21(1)
80.9(1)
80.3(3)
78.1(5)
[CpRu(PP)]+ Complexes
[CpRu(H2PCH2CH2PH2)]+
[CpRu(PH3)2]+
2.248
2.346
83
149
152
170
160
171
2.241
2.355, 2.357
2.275, 2.355
2.331(1), 2.356(1)
2.393(1), 2.395(1)
96
[Cp*Ru(PEt3)2]+
2.201
99.3
83.13(4)
101.4(1)
[Cp*Ru (dippe)]+
2.206(3)
2.182(5)
[RuCp*(PMePri2)2]+
a
R ) C5 ring(centroid)-Ru-L2(centroid).
ing in fluorobenzene, [Cp*Ru(PPhiPr2)2][BAr′4] con-
verted to mixtures of [Cp*Ru(η6-C6H5PiPr2)][BAr′4] and
[Cp*Ru(η6-C6H5POiPr2)][BAr′4] and finally yielded [Cp*-
Ru(η6-C6H5F)][BAr′4] (4) plus variable relative amounts
of free PPhiPr2 and POPhiPr2 (Scheme 1). This process
is not observed in the case of the PPh3 derivatives under
otherwise identical conditions.
between the ideally planar (180°) and the pyramidal
(149°) geometry. In contrast, the related amine com-
plexes adopt the C2v structure. The optimized geometry
of [CpRu(H2NCH2CH2NH2)]+ is close to the experimen-
tal molecular structures of [Cp*Ru(Me2NCH2CH2NR2)]+
(R ) Me, iBu)18 and [CpRu(Me2NCH2CH2NMe2)]+,17 the
angle R varying from 168 to 180°. In other words, amine
ligands participate much less in the LUMO than phos-
phine ligands. This participation in the LUMO is further
increased on bending. However, bending is hampered
by bulky L2 ligands, and the reactivity is modified
accordingly.
The reactivity of the unsaturated CpML2 complexes
is, of course, mainly given by their acceptor propensity,
which in turn depend on the energy and the spatial
orientation of the LUMO. This feature is reflected by
the agostic interaction between the hydrogen atoms of
an isopropyl group and ruthenium in [Cp*Ru(dippe)]+
or the addition of σ-donors, such as dinitrogen and PR3.
Furthermore, the combination of the σ-accepting and
π-donating properties of Cp′ML2 creates the conditions
for the η2-mode addition of not only unsaturated com-
pounds but also the simple σ-bond of dihydrogen.
It may be mentioned that even the Ru-C5 distances
as well as the 13C NMR resonances of the ring carbon
atoms of the Cp* ligand can be used as criteria to
distinguish preliminarily between 16e and 18e com-
plexes, as shown in Figure 5.
In summation, all coordinatively unsaturated ruthe-
nium phosphine half-sandwich complexes considered
here have bent or pseudo-bent (pseudo-C2v) geometries,
with the pyramidal distortion depending on the size of
the phosphine. The free space available through bending
allows agostic interactions to occur between the alkyl
hydrogens and the ruthenium center. Thereby the
coordinatively unsaturated character is partially com-
pensated. In contrast, there is no agostic interaction in
the pseudo-planar complex [Cp*Ru(PMeiPr2)2]+. Thus,
bending actually activates the metal acceptor ability.
The ground-state structures of model 16e complexes
[CpRu(EH3)2]+ and [CpRu(H2ECH2CH2EH2)]+, where E
) P, N, have been determined by means of DFT
calculations. Table 2 summarizes the results of the DFT-
optimized geometries, revealing that they are in good
agreement with comparable experimental data. Relative
B3LYP energies of optimized [CpRu(H2ECH2CH2EH2)]+
at various angles R ) Cp(centroid)-Ru-L2(centroid) are
depicted in Figure 4. The ground-state structure of the
phosphine complex is strongly pyramidalized, with R )
149° close to the ideal pseudo-octahedral ML5 coordina-
tion, and the energy differing by about 6 kcal/mol
Rea ctivity of th e 16e Com p lexes. Before, the
reactivity of [Cp*Ru(PEt3)2]+ 23,26,44 and [Cp*Ru-

5342 Organometallics, Vol. 21, No. 24, 2002
Aneetha et al.
F igu r e 4. B3LYP energies of optimized [CpRu(H2NCH2CH2NH2)]+ and [CpRu(H2PCH2CH2PH2)]+ at various angles R )
Cp(centroid)-Ru-L2(centroid).
F igu r e 5. Relationship between Ru-Cp* bond distances and the 13C NMR resonances of the ring carbon atoms of the
Cp* ligand in Cp*RuLn complexes.
(dippe)]+ 25,41,45-47 was explored in situ by starting from
suitable 18e precursors containing labile ligands. Now,
the complexes 1-3 as well as 5 and 6 offer the op-
portunity to carry out direct experimental studies on
the binding and activation of substrates by a coordina-
tively unsaturated ruthenium center. The transforma-
tion into the 18e configuration can be attained in three
different ways, namely (a) direct ligand addition, (b)
oxidative addition, and (c) degradation to other stable
18e species. Scheme 2 summarizes the reactivity of
compounds 1-3. It is worth noting that these complexes
exhibit different degrees of affinity for an additional
ligand.
Rea ction w ith N2. When exposed to a dinitrogen
atmosphere, both 1 and 2 form the respective dinitrogen
complexes [Cp*Ru(N2)(PEt3)2]+ and [Cp*Ru(N2)(dippe)]+,
which were characterized previously in the form of their
[BPh4]- salts.23,41 In contrast, 3 is unreactive toward
dinitrogen, and so is 5 and 6 (Schemes 1 and 2).
(44) Bustelo, E.; J ime´nez-Tenorio, M.; Puerta, M. C.; Valerga, P.
Organometallics 1999, 18, 4563.
(45) de los R´ıos, I.; J ime´nez-Tenorio, M.; Puerta, M. C.; Valerga, P.
J . Am. Chem. Soc. 1997, 119, 652.
(46) Coto, A.; de los R´ıos, I.; J ime´nez-Tenorio, M.; Puerta, M. C.;
Valerga, P. J . Chem. Soc., Dalton Trans. 1999, 4309.
(47) Bustelo, E.; J ime´nez-Tenorio, M.; Puerta, M. C.; Valerga, P. Eur.
J . Inorg. Chem. 2001, 2391. Bustelo, E.; J ime´nez-Tenorio, M.; Puerta,
M. C.; Valerga, P.; Mereiter, K. Organometallics 2002, 21, 1903.
(48) Gemel, C.; LaPensee, A.; Mauthner, K.; Mereiter, K.; Schmid,
R.; Kirchner, K. Monatsh. Chem. 1997, 128, 1189.
Rea ction w ith P R3. Complex 1 reacts with an excess
of phosphine to yield the 18e tris(phosphine) derivative
[Cp*Ru(PEt3)3][BAr′4] (7). An ORTEP view of 7 is
presented in Figure 6, showing a three-legged piano-
stool structure with the three phosphine ligands in a
fac disposition around ruthenium and slightly elongated
Ru-Cp* separations. This structure is very similar to
that of the cation of [CpRu(PMeiPr2)3][BAr′4], recently
reported by us.21 Thus, the ease of PEt3 dissociation
provides a pathway for the stabilization of electrophilic
(49) Mauthner, K.; Mereiter, K.; Schmid, R.; Kirchner, K. Inorg.
Chim. Acta 1995, 236, 95. Kirchner, K.; Mauthner, K.; Mereiter, K.;
Schmid, R. J . Chem. Soc., Chem. Commun. 1993, 892.

Ruthenium Phosphine Half-Sandwich Complexes
Organometallics, Vol. 21, No. 24, 2002 5343
Sch em e 2. Su m m a r y of th e Rea ctivity of
Com p ou n d s 1-3
F igu r e 6. ORTEP drawing (50% thermal ellipsoids) of the
cation [Cp*Ru(PEt3)3]+ in complex 7. Hydrogen atoms have
been omitted. Selected bond lengths (Å) and angles (deg)
with estimated standard deviations in parentheses: Ru-
C(1), 2.290(3); Ru-C(2), 2.283(3); Ru-C(3), 2.301(3); Ru-
C(4), 2.286(3); Ru-C(5), 2.270(3); Ru-P(1), 2.353(1); Ru-
P(2), 2.354(1); Ru-P(3), 2.355(1); P(1)-Ru-P(2), 96.84(3);
P(1)-Ru-P(3), 93.42(3); P(2)-Ru-P(3), 94.74(3).
species. This feature has already been noted in the
context of the formation of the zwitterionic alkynyl-
phosphonio species [Cp*Ru{CtCC(PEt3)Me2}(PEt3)2]-
[BPh4], resulting from nucleophilic attack of PEt3 at the
γ-carbon of the highly electrophilic allenylidene deriva-
tive [Cp*Ru{dCdCdCMe2}(PEt3)2][BPh4]. In this case
no external source of PEt3 is required.44 A similar
behavior was observed in connection with halide ab-
straction from [Cp*RuCl(PMe3)2], giving a mixture of 4
and the tris(phosphine) derivative [Cp*Ru(PMe3)3]-
[BAr′4] (8), as mentioned above. With an excess of
phosphine the compounds 3, 5, and 6 do not transform
into the 18e tris(phosphine) derivatives of the type
[Cp*Ru(PR3)3]+.
this compound toward O2 does not match that of its
congeners 1 and 2 or other Cp*Ru moieties capable of
forming stable dioxygen complexes, such as [Cp*Ru(O2)-
(dppm)]+ 43 and [Cp*Ru(O2)(dppe)]+.49
Rea ction w ith H2. The reactivity of the [(C5R5)Ru-
(PP)]+ systems toward dihydrogen has been the subject
of very detailed studies.27,41,50-52 The coordinatively
unsaturated complexes undergo oxidative addition of
H2, yielding the ruthenium(IV) dihydride complexes
[(C5R5)RuH2(PP)]+, which in some instances have been
shown to exist in equilibrium with their dihydrogen
tautomers [(C5R5)Ru(H2)(PP)]+. Metastable dihydrogen
complexes are also generated by protonation of neutral
monohydrides at low temperature and, in most cases,
rearrange irreversibly to their dihydride tautomers upon
raising the temperature. Thus, the reaction of H2 with
[CpRu(PH3)2]+ is calculated to be exothermic by 21.9
kcal/mol, respectively. In the dihydrogen complexes,
back-donation via dfσ*(H2) electron transfer is strong
and, therefore, the rotation of the η2-H2 ligand is
hindered. Lowering the σ*(H2) orbital energy can ulti-
mately complete the electron transfer to H2 toward
oxidative addition, giving the classic Ru(IV) dihydride
complexes. According to the DFT calculations both η2-
dihydrogen and classical dihydride complexes [CpRu-
(PH3)2(η2-H2)]+ and trans-[CpRu(PH3)2(H)2]+ as well as
[CpRu(H2PCH2CH2PH2)(η2-H2)]+ and [CpRu(H2PCH2-
CH2PH2)(H)2]+ are stable systems differing only slightly
in energy (Figure 7). While in the case of the monoden-
tate system the dihydride species is more stable by
Rea ction w ith O2. All compounds (1-3, 5, and 6)
react with oxygen, but in different ways. The species 1
and 2 bind O2 irreversibly, furnishing the dioxygen
complexes [Cp*Ru(O2)(PEt3)2]+ 26 and [Cp*Ru(O2)(dip-
pe)]+,25 which were isolated previously and character-
ized as the [BPh4]- salts. Exposure of solutions of 5 and
6 to oxygen, on the other hand, causes rapid decomposi-
tion of the complex with concomitant formation of the
respective phosphine oxides POPh3 and POPhiPr2. As
shown in Scheme 1, the phosphine oxides bind to the
Cp*Ru moieties in an η6 fashion, furnishing the cationic
sandwich complexes [Cp*Ru(η6-C6H5POR2)][BAr′4] (R )
i
Ph (5b), Pr (6b)). Fluorobenzene and dichloromethane
solutions of 3 gradually turn red-brown when exposed
to air. NMR monitoring (in CD2Cl2) indicates a slow
formation of paramagnetic species, with no evidence of
formation of a diamagnetic dioxygen complex: i.e.,
[Cp*Ru(O2)(PMeiPr2)2][BAr′4]. Attempts to isolate the
reaction product failedsa brown oil was the only result.
Trying to use another anion, we treated a solution of 3
in MeOH in the air with an excess of NaBPh4. After a
few minutes, a crystalline precipitate was formed, which
upon isolation turned out to be the sandwich derivative
[Cp*Ru(η6-C6H5BPh3)].48 Thus, the nature of the product
of the interaction of 3 with dioxygen remains unknown.
It can be stated though that the reactivity pattern of
(50) (a) J ia, G.; Lau, C. P. J . Organomet. Chem. 1998, 565, 37. (b)
Gelabert, R.; Moreno, M.; Lluch, J . M.; Lledo´s, A. J . Am. Chem. Soc.
1997, 119, 9840. (c) Chinn, M. S.; Heinekey, D. M. J . Am. Chem. Soc.
1990, 112, 5166.
(51) Klooster, W. T.; Koetzle, T. F.; J ia, G.; Fong, T. P.; Morris, R.
H.; Albinati, A. J . Am. Chem. Soc. 1994, 116, 7677. J ia, G.; Lough, A.
J .; Morris, R. H. Organometallics 1992, 11, 161. J ia, G.; Morris, R. H.
J . Am. Chem. Soc. 1991, 113, 875.
(52) Brammer, L.; Klooster, W. T.; Lemke, F. R. Organometallics
1996, 15, 1721.

5344 Organometallics, Vol. 21, No. 24, 2002
Aneetha et al.
stable by 2.0 kcal/mol. It is interesting to note that
similar results have been found for the related com-
plexes [CpRu(H2PCH2PH2)(η2-H2)]+ and [CpRu(H2PCH2-
PH2)(H)2]+, where the first complex is slightly more
stable.50b This is in line with the experimental findings
that frequently both dihydrogen and trans-dihydride
Ru(IV) complexes can be observed in solution, at least
at lower temperatures. Attempts to optimize the geom-
etry of the cis-dihydride complex failed, resulting in
collapse of the structure to afford the dihydrogen
complex. This finding is in line with the fact that, to
date, no cis-dihydride complexes of the type [CpRu(PP)-
(H)2]+ have been isolated or spectroscopically detected.
Furthermore, it is interesting to note that we were
unable to locate a transition state directly connecting
the dihydrogen and the trans-dihydride complex.
For the systems in our hands both dihydride [Cp*-
RuH2(PP)]+ and dihydrogen [Cp*Ru(H2)(PP)]+ com-
plexes have previously been identified where PP )
(PEt3)2,26 dippe,41 (PPh3)2.50,51 All of the dihydride
structures have the transoid configuration.
F igu r e 7. B3LYP energies (kcal mol-1) of optimized dihy-
drogen and trans-dihydride complexes of [CpRu(PH3)2]+
and [CpRu(H2PCH2CH2PH2)]+.
The reaction of 3 with H2 in CD2Cl2 at -80 °C yielded
exclusively the dihydride complex [Cp*RuH2(PMei-
Pr2)2]+.26 The same product resulted from the protona-
tion of [Cp*RuH(PMeiPr2)2] with HBF4 at -80 °C,
whereas the dihydrogen tautomer [Cp*Ru(H2)(PMei-
merely 1.0 kcal/mol, the situation is reversed for the
chelate complex, where the dihydrogen complex is more
1
F igu r e 8. Variable-temperature H (hydride region) and 31P{1H} NMR spectra (CD2Cl2) of the dihydride complex 9.

Ruthenium Phosphine Half-Sandwich Complexes
Organometallics, Vol. 21, No. 24, 2002 5345
Ch a r t 1
Pr2)2]+ was not detected. In an analogous fashion, the
dihydride complex [Cp*RuH2(PPhiPr2)2][BAr′4] (9) was
obtained either by reaction of [Cp*RuCl(PPhiPr2)] with
H2 and NaBAr′4 in FPh in the presence of PPhiPr2 or
by protonation of the monohydride [Cp*RuH(PPhiPr2)2]
(10) at low temperature, with no evidence for the
presence of the dihydrogen isomer [Cp*Ru(H2)(PPhiPr2)2]-
[BAr′4].
The NMR spectra of 9 are found to change with
temperature (Figure 8). The hydride resonance appears
1
as one triplet in the H NMR spectrum at room tem-
perature. This signal broadens when the temperature
is lowered. Below 213 K, it decoalesces to several triplet
signals. The 31P{1H} NMR spectrum consists of one
singlet at room temperature but becomes featureless at
233 K, and new sets of resonances appear below 213 K.
These sets correspond to two AM spin systems, in the
ratio 83:17 in CD2Cl2 at 193 K. The (T1)min values
between 450 and 600 ms (CD3COCD3, 400 MHz, 183
K) for the hydride resonances indicate a classical
dihydride structure for 9. These features can be ratio-
nalized by assuming an equilibrium between rotamers
of the phosphine in a transoid dihydride. For each
rotational isomer, one group on each phosphine is
pointing away from Cp*, and the other two are to the
sides; hence, several possible rotamers are possible, as
shown in Chart 1.
F igu r e 9. ORTEP drawing (50% thermal ellipsoids) of the
cation [Cp*RuH2(PPhiPr2)2]+ in complex 9. Hydrogen at-
oms, except hydrides, have been omitted. Selected bond
lengths (Å) and angles (deg) with estimated standard
deviations in parentheses: Ru-H(1Ru), 1.50(3); Ru-
H(2Ru), 1.53(3); Ru-C(3), 2.255(2); Ru-C(4), 2.266(2); Ru-
C(2), 2.294(2); Ru-C(1), 2.309(2); Ru-C(5), 2.314(2); Ru-
P(1), 2.3454(7); Ru-P(2), 2.3514(7); H(1Ru)-Ru-H(2Ru),
124.5(17); P(1)-Ru-P(2), 107.96(2).
Sch em e 3. P r op osed Str u ctu r es for th e Rota m er ic
Isom er s of Com p ou n d 9 in Equ ilibr iu m
From NMR spectroscopy, it seems that there is one
major species having two inequivalent hydrides (each
2
a doublet of doublets of doublets with J (H,PA), 2J (H,PM),
and a small 2J (H,H′)) and inequivalent phosphorus. This
i
rotamer may well have one Ph and one Pr pointing
away from the Cp* (rotamer I), since the other combi-
nations (rotamers II and III) would have equivalent
phosphorus atoms. There is another minor rotamer with
inequivalent phosphorus atoms, associated with the
triplet at -9.03 ppm in the 1H NMR spectrum, although
another hydride multiplet corresponding to this rotamer
could be hidden in the hydride signal of the major
isomer. For this rotamer we can think of an arrange-
ment of phosphines in an alternated disposition, one
with the phenyl group pointing away from the Cp* and
another one with one Ph substituent pointing toward
the Cp* (i.e., like the disposition of PMeiPr2 found in
the X-ray structure of 3). Therefore, possible structures
of the rotamers observed at low temperature consistent
with NMR data should be those shown in Scheme 3.
The X-ray crystal structure of 9 was determined with
an ORTEP view of the complex cation shown in Figure
9. Consistent with the NMR data, the cation shows a
four-legged piano-stool structure with the hydrides in
a transoid disposition. The phosphine ligands are in-
equivalent, due to the orientations of the phenyl sub-
stituents, with a torsion angle C(11)-P(1)-P(2)-C(23)
of 83.9°. The plane P(1)-Ru-P(2) is almost perpendicu-
lar (87.3°) to the plane defined by the C5 ring of the Cp*.
The Ru-H(1Ru) and Ru-H(2Ru) separations of 1.50-
(3) and 1.53(3) Å compare well with the values of 1.599-
(8) and 1.604(9) Å obtained from the Ru-H bond lengths
in [Cp*RuH2(PMe3)2][BF4].52 Likewise, the H(1Ru)-
Ru-H(2Ru) and P(1)-Ru-P(2) angles of 124.5(17) and
107.96(2)°, respectively, are close to those in [Cp*RuH2-
(PMe3)2][BF4] (118.8(4) and 111.1(2)°).52 Therefore, the
X-ray structure is consistent with that of rotamer I; the
minor species observed in solution by NMR spectroscopy
may have slightly different orientations of the phenyl
groups resulting from the different torsion angle C(11)-

5346 Organometallics, Vol. 21, No. 24, 2002
Aneetha et al.
P(1)-P(2)-C(23). Rotation around the Ru-P bonds at
higher temperatures causes averaging between all pos-
sible rotamers, leading to equivalent hydride and phos-
phorus atoms. It is interesting to note that the dynamic
behavior exhibited by 9 is exceptional, not found with
the related dihydride complexes [Cp*RuH2(PMeiPr2)2]+ 26
and [Cp*RuH2(PMePh2)2]+.51
namics, and reactions of these species will be described
in detail in a forthcoming paper.
In summation, the properties of the coordinatively
unsaturated [CpRu(PP)]+ complexes appear to be con-
nected with the ease of bending of the ligands, since
species with bulky and rigid ligands are relatively inert.
Thus, the complexes 1 and 2 easily form 18e adducts
with σ-ligands, such as N2 and PR3, in contrast to
complex 3, most likely due to van der Waals repulsions
between Cp* and the PMeiPr2 pieces. Actually, interli-
gand interactions are being increasingly recognized as
an important factor in determining the coordination
geometry and reactivity of many metal complexes.53
Rea ction w ith HCl. The compounds 1-3 also un-
dergo oxidative addition of HCl, yielding the ruthenium-
(IV) chloro hydrido complexes [Cp*RuHCl(PEt3)2][BAr′4]
(12), [Cp*RuHCl(dippe)][BAr′4] (13), and [Cp*RuHCl-
(PMeiPr2)2][BAr′4] (14). Whereas 12 and 13 were readily
prepared by reaction of 1 or 2 with anhydrous HCl,
generated from Me3SiCl and MeOH in Et2O, in the case
of 3 the dihydride was obtained. However, 14 was
accessible by reaction of 3 with aqueous HCl. The
reaction of 5 with HCl was not clean, probably due to
phosphine dissociation further complicated by the pres-
ence of protons. The 1H NMR spectra of compounds 12-
14 display one triplet resonance in the hydride region,
as expected, whereas the 31P{1H} NMR spectra consist
of one singlet. No changes were observed on lowering
the temperature. Hence, a four-legged piano-stool struc-
ture can be proposed for these derivatives. Other
molecules such as H2S and 1-alkynes have been shown
to give oxidative addition reactions with the complexes
[Cp*Ru(PP)]+ (PP ) (PEt3)2, dippe), yielding the ruthe-
nium(IV) hydrido metallothiol [Cp*RuH(SH)(PP)]+ 25,48
and hydrido alkynyl derivatives [Cp*RuH(CtCR)-
(PP)]+.46,47,49 We have found that the reaction of 3 with
1-alkynes also leads to the hydrido alkynyl complex
[Cp*RuH(CtCR)(PMeiPr2)2][BAr′4]. The structure, dy-
Ack n ow led gm en t. We thank the Ministerio de
Educacio´n y Cultura of Spain (DGICYT, Project BQU-
2001-4046, Accion Integrada HU-2001-0020) for finan-
cial support, J ohnson Matthey plc for generous loans
of ruthenium trichloride, and the Royal Society of
Chemistry for the award of a grant for international
authors (to M.J .T.). Suggestions from Prof. Robert H.
Morris, University of Ontario (Toronto, Canada), are
also gratefully acknowledged.
Su p p or tin g In for m a tion Ava ila ble: Tables of X-ray
structural data, including data collection parameters, posi-
tional and thermal parameters, and bond distances and angles,
for complexes 1-4, 7, and 9. This material is available free of
charge via the Internet at http://pubs.acs.org.
OM020359R
(53) Sapunov, V. N.; Kirchner, K.; Schmid, R. Coord. Chem. Rev.
2001, 214, 143.