The square pyramidal hydride cation [RuH(dcpe)2]+, dcpe = Bis(dicyclohexylphosphino)ethane. Structures of [RuH(dcpe)2]+[BPh4]- and of the zwitterionic {(η6-C6H5)BPh3}RuH(dcpe)

Article abstract of DOI:10.1021/ic970583m

Two hydrido ruthenium complexes could be isolated from the reaction between RuCl₂(DMSO)₄ (DMSO = dimethyl sulfoxide) and the chelating 1,2-bis(dicyclohexylphosphino)ethane (dcpe) and [BPh₄]^-. These are [RuH-(dcpe)₂]⁺[BPh₄]^- with a five-coordinate, 16 valence electron cation and the neutral zwitterionic 18 valence electron compound {(η⁶-C₅H₅)BPh₃}RuH(dcpe). The relative amounts of these products depend on the reaction conditions. If NaBPh₄ is replaced by NH₄PF₆ or added after the reaction with the diphosphine has gone to completion, the 16 valence electron species [RuH(dcpe)₂]⁺ is the only product. Reducing the size of the diphosphine chelate to 1,1-bis(dicyclohexylphosphino)methane (dcpm) has a large effect on the reaction course. Either trans-RuHCl-(dcpm)₂ or trans-RuCl₂(dcpm)₂ is formed, depending on the conditions. X-ray structures of [RuH(dcpe)₂]⁺[BPh₄]^- (monoclinic, P2/c, a = 24.936(5) A?, b = 12.633(3) A?, c = 25.801(5) A?, β= 102.86(3)°, V = 7924(3) A?³, Z = 4, R = 0.062, R_w = 0.1694) and {(η⁶-C₆H₅)BPh₃}RuH(dcPe) (monoclinic, P2₁/n, a = 14.321(5) A?, b = 19.716-(7) A?, c = 17.100(5) A?, β = 107.60°, V = 4602(3) A?³, Z = 4, R = 0.0648, R_w = 0.1873) have been determined. A nearly planar arrangement of the four P atoms exists around Ru in the five-coordinate cation, implying a distorted square pyramid. This structural motif has not been observed previously for a d⁶ RuL₅ system with a P₄X donor set. {(η⁶-C₆H₅)BPh₃}RuH(dcpe) represents an example for the noninnocent behavior of the noncoordinating [BPh₄)]^- anion. The coordinated six-membered ring displays a boatlike distortion with the BPb₃ substituent and the para-carbon of the coordinated ring displaced away from the metal.

Full text of DOI:10.1021/ic970583m

Inorg. Chem. 1997, 36, 6197-6204
6197
The Square Pyramidal Hydride Cation [RuH(dcpe)2]+, dcpe )
Bis(dicyclohexylphosphino)ethane. Structures of [RuH(dcpe)2]+[BPh4]- and of the
Zwitterionic {(η6-C6H5)BPh3}RuH(dcpe)
Rainer F. Winter* and Fridmann M. Hornung
Institut fu¨r Anorganische Chemie der Universita¨t Stuttgart, Pfaffenwaldring 55,
D-70569 Stuttgart, Germany
ReceiVed May 15, 1997X
Two hydrido ruthenium complexes could be isolated from the reaction between RuCl2(DMSO)4 (DMSO ) dimethyl
sulfoxide) and the chelating 1,2-bis(dicyclohexylphosphino)ethane (dcpe) and [BPh4]-. These are [RuH-
(dcpe)2]+[BPh4]- with a five-coordinate, 16 valence electron cation and the neutral zwitterionic 18 valence electron
compound {(η6-C6H5)BPh3}RuH(dcpe). The relative amounts of these products depend on the reaction conditions.
If NaBPh4 is replaced by NH4PF6 or added after the reaction with the diphosphine has gone to completion, the
16 valence electron species [RuH(dcpe)2]+ is the only product. Reducing the size of the diphosphine chelate to
1,1-bis(dicyclohexylphosphino)methane (dcpm) has a large effect on the reaction course. Either trans-RuHCl-
(dcpm)2 or trans-RuCl2(dcpm)2 is formed, depending on the conditions. X-ray structures of [RuH(dcpe)2]+[BPh4]-
(monoclinic, P2/c, a ) 24.936(5) Å, b ) 12.633(3) Å, c ) 25.801(5) Å, â ) 102.86(3)°, V ) 7924(3) Å3, Z )
4, R ) 0.062, Rw ) 0.1694) and {(η6-C6H5)BPh3}RuH(dcpe) (monoclinic, P21/n, a ) 14.321(5) Å, b ) 19.716-
(7) Å, c ) 17.100(5) Å, â ) 107.60°, V ) 4602(3) Å3, Z ) 4, R ) 0.0648, Rw ) 0.1873) have been determined.
A nearly planar arrangement of the four P atoms exists around Ru in the five-coordinate cation, implying a
distorted square pyramid. This structural motif has not been observed previously for a d6 RuL5 system with a
P4X donor set. {(η6-C6H5)BPh3}RuH(dcpe) represents an example for the noninnocent behavior of the
“noncoordinating” [BPh4]- anion. The coordinated six-membered ring displays a boatlike distortion with the
BPh3 “substituent” and the para-carbon of the coordinated ring displaced away from the metal.
Introduction
comparable number of examples of [MX(L2)2]+ are known,
where L2 represents a chelating diphosphine and X a unidentate
There has been a long-standing interest in the structures of
five-coordinate complexes and the factors governing the prefer-
ence of either the trigonal bipyramidal (tbp) or the square
pyramidal (sqp) structure type. While the tbp coordination mode
should be generally favored for steric reasons, the specific
requirements of the ligands and/or electronic effects arising from
the metal d electron configuration or the ligand properties may
stabilize the sqp structure type.1,2 The balance between these
isomeric forms is often quite delicate, as exemplified by the
occasional observation of both configurations present in the
same solid state material3 or the dependence of the preferred
structure type on the counterion4 and even the solvent of
crystallization.5
monoanionic ligand.10-17 They possess a P4X donor set around
the metal center and are frequently generated by dissociation
of an anionic ligand Y- from saturated six-coordinate precursors.
The readiness with which MXY(L2)2 complexes undergo such
a ligand dissociation was found to depend on several factors
such as the steric bulk and the electronic properties of the
chelating diphosphine and the ligand X-, the ring size of the
chelate formed, the solvent employed, or which of the two
possible isomers (cis or trans) of the starting material is
used. To only briefly illustrate some of these points, trans-
RuCl2(Ph2P(CH2)3PPh2)2 was reported to react with NaBPh4 or
NaPF6 in ethanol to give [RuCl(Ph2P(CH2)3PPh2)2]+, while the
methyl substituted derivative trans-RuCl2(Me2P(CH2)3PMe2)
does not.10,11,14 Likewise, RuBr2(dcpe)2 (dcpe ) bis(dicyclo-
hexylphosphino)ethane) spontaneously dissociates a bromide ion
upon dissolution in dichloromethane, whereas the dichloro
derivative requires refluxing of the starting material in ethanol
in the presence of a noncoordinating counterion.12 The effect
of the chelate ring size may be inferred from the fact that trans-
Special attention has been paid to five-coordinate complexes
with a d6 configuration of the metal center, particularly in view
of their high reactivity arising from electronic and steric
unsaturation. While ruthenium complexes of the type Ru(PR3)3-
XY are relatively common,6-9 it is only recently that a
X Abstract published in AdVance ACS Abstracts, December 15, 1997.
(1) (a) Rossi, A. R.; Hoffmann, R. Inorg. Chem. 1975, 14, 365. (b) Elian,
M.; Hoffmann, R. Inorg. Chem. 1975, 14, 1058.
(2) Idrissi, I. L.; Eisenstein, O.; Jean, Y. New J. Chem. 1990, 14, 671.
(3) Raymond, K. N.; Corfield, P. W. R.; Ibers J. A. Inorg. Chem. 1968,
7, 1362.
(4) Terzis, A.; Raymond, K. N.; Spiro, T. G. Inorg. Chem. 1970, 9, 2415.
(5) Stalick, J. K.; Corfield, P. W. R.; Meek, D. W. Inorg. Chem. 1973,
12, 1668.
(10) Bressan, M.; Rigo, P. Inorg. Chem. 1975, 14, 2286.
(11) Briggs, J. C.; McAuliffe, C. A.; Dyer, G. J. Chem. Soc., Dalton Trans.
1984, 423.
(12) Mezzetti, A.; Del Zotto, A.; Rigo, P.; Pahor R. B. J. Chem. Soc., Dalton
Trans. 1989, 1045.
(13) Batista, A. A.; Cordeiro, L. A. C.; Oliva, G. Inorg. Chim. Acta 1993,
203, 185.
(6) (a) Stephenson, T. A.; Wilkinson, G. J. Inorg. Nucl. Chem. 1966, 28,
945. (b) Hallmann, P. S.; Mc Garvey, B. R.; Wilkinson, G. J. Chem.
Soc. A 1968, 3143.
(7) Hoffmann, P. R.; Caulton, K. G. J. Am. Chem. Soc. 1975, 97, 4221.
(8) Cotton, F. A.; Matusz, M. Inorg. Chim. Acta 1987, 131, 213.
(9) (a) La Placa, S. A.; Ibers, J. A. Inorg. Chem. 1965, 4, 778. (b) Skapski,
A. C.; Troughton P. G. H. Chem. Comm. 1968, 1230.
(14) Bressan, M.; Morvillo, A. Inorg. Chim. Acta 1987, 132, 1.
(15) Chin, B.; Lough, A. J.; Morris, R. H.; Schweitzer C. T.; D’Agostino,
C. Inorg. Chem. 1994, 33, 6278.
(16) Polam, J. R.; Porter, C. L. J. Coord. Chem. 1993, 29, 109.
(17) (a) Bianchini, C.; Peruzzini, M.; Zanello, P. Gazz. Chim. Ital. 1994,
124, 372. (b) Bianchini, C.; Peruzzini, M.; Ceccanti, A.; Laschi, F.;
Zanello, P. Inorg. Chim. Acta 1997, 259, 61.
S0020-1669(97)00583-1 CCC: $14.00 © 1997 American Chemical Society

6198 Inorganic Chemistry, Vol. 36, No. 27, 1997
Winter and Hornung
RuCl2(Ph2P(CH2)nPPh2)2 reacts with NaPF6 in refluxing ethanol
to yield five-coordinate compounds when n ) 3,10,13 whereas
no such reaction is observed for n ) 2.15 The more reactive
cis-isomer of the latter complex, however, dissociates a chloride
anion under the above reaction conditions.15
of the dissociatively more inert six-coordinate complexes trans-
RuCl2(dcpm)2 (4) and trans-RuHCl(dcpm)2 (3) (dcpm ) bis-
(dicyclohexylphosphino)methane).
Experimental Section
As far as their structures in the solid state are concerned, the
five-coordinate d6 ruthenium complexes fall into two distinct
categories. Those with a P3XY donor set around the metal adopt
a sqp structure with one P atom at the apical position. The
basal plane accommodates the two remaining P atoms as well
as X and Y which are mutually trans to each other.8,9 In the
case of a P4X donor set the structures were predicted to depend
on the electronic properties of the ligand X.2 For X ) Cl- (or
any other σ acceptor/π donor) the antibonding interaction
between the filled π orbital of the ligand and the dxy orbital on
the metal renders a tbp structure with Cl- in the equatorial plane
and an acute angle between the two remaining equatorial ligands
as the energy minimum. This arrangement was indeed found
for all examples hitherto known12,13,16 with the notable exception
of [RuPP3Cl]+ (PP3 ) P(C2H4PPh2)3), which possesses a sqp
structure with the Cl- ligand in a basal position.17a Most
interestingly, the Os analogue of this latter compound is reported
to be isostructural, whereas the corresponding Fe complex is
trigonal bipyramidal with two unpaired electrons.17b In ref 13
the authors have communicated the structure of [RuCl-
(Ph2P(CH2)3PPh2)2] as square pyramidal, but a closer inspection
and a comparison with the other known structures reveals that
a distorted trigonal bipyramidal structure is in much better
agreement with the actual data. For X ) H-, both the tbp and
the sqp structures were calculated to be true minima, the latter
being favored by about 29 kJ/mol.2 Although some hydrides
of this type (X ) H) were prepared,12,15,18-20 no X-ray structures
have been available. Their spectroscopic data suggest a sqp
structure in solution for [RuH(BINAP)2]+ (BINAP ) R-bis-
(diphenylphosphino)-1,1′-binaphthyl)19a but rather a tbp structure
for the corresponding complex with dcpe (dcpe ) bis(dicyclo-
hexylphosphino)ethane).12
General Procedures. All manipulations were performed by standard
Schlenk techniques under an atmosphere of dry argon. Dichloro-
methane was dried by disitillation from CaH2, and ethanol was predried
with Mg and freshly distilled from CaH2 before use. All solvents were
degassed by either at least three freeze-pump-thaw cycles or saturation
with argon prior to use. RuCl2(DMSO)4 (DMSO ) dimethylsulfoxide)
was prepared according to a literature method.23 1,2-Bis(dicyclohexy-
lphosphino)ethane (dcpe) and 1,1-bis(dicyclohexylphosphino)methane
(dcpm) were obtained from Strem Chemicals and the deuterated solvents
from Aldrich. All commercial materials were used as received.
Infrared spectra were obtained on a Perkin-Elmer Paragon 1000 PC
FT-IR instrument; 1H (250.13 MHz), 13C (62.90 MHz), and 31P-NMR
spectra (101.26 MHz) were recorded on a Bruker AC 250 spectrometer
at 303 K (unless stated otherwise) in the solvent indicated. The spectra
were referenced to the residual protonated solvent (1H), the solvent
signal itself (13C), or external H3PO4 (31P). If necessary, the assignement
of 13C NMR spectra was aided by appropriate DEPT experiments
(DEPT ) distortionless enhancement by polarization transfer). The
assignments of the IR bands are based upon comparison of the IR
spectra of complexes 2a and 2b and a comparison with the IR data of
-
the respective diphosphine and those of BPh4 salts.24 The spectral
changes of the spectrum of complex 2b in the visible region upon
addition of CH3CN were monitored by adding increasing amounts of
degassed CH3CN to a 0.83 mM solution of complex 2b in CH2Cl2 in
a gas-tight UV/vis cuvette under argon and recording the spectra after
each addition. Elemental analyses (C, H, N) were performed at in-
house facilities.
Synthesis of {(η6-C6H5)BPh3}RuH(dcpe) (1) and [RuH(dcpe)2]-
[BPh4] (2a). Method 1. RuCl2(DMSO)4 (0.484 g, 1.0 mmol), dcpe
(0.845 g, 2.0 mmol), and NaBPh4 (3.422 g, 10.0 mmol) were suspended
in 30 mL of ethanol, and the mixture was warmed to a gentle reflux
under stirring. Within minutes the suspension cleared to a yellow
solution which soon precipitated a pale orange solid. Upon further
heating, this solid slowly turned dark yellow and finally orange. After
90 min, the solid was allowed to settle and the mother liquor was
removed by cannula filtration. The orange residue was washed three
times with 5 mL portions of ethanol by warming the mixture to a gentle
reflux, allowing the solids to settle, and filtering hot as above. The
resulting orange powder was dried in vacuo and extracted into CH2Cl2
(2 × 10 mL). The extracts were filtered by cannula to remove residual
NaBPh4 and were crystallized by layering the concentrated solution
with ethanol. Several batches were obtained by further concentration
of the respective mother liquors. The initial fractions were enriched
with the white {(η6-C6H5)BPh3}RuH(dcpe), whereas the later ones were
found to contain a higher proportion of the orange-red [RuH-
(dcpe)2]+[BPh4]- salt. The crystals were sorted manually as far as
possible, and the inseparable mixtures (partly lumps of the two different
compounds baked together) recrystallized again. This procedure was
repeated until further recrystallizations did only yield inseparable
mixtures. Yields: [RuH(dcpe)2]+[BPh4]-‚3CH2Cl2, 0.627g, 41% based
on Ru; {(η6-C6H5)BPh3}RuH(dcpe)‚0.5CH2Cl2, 0.097 g, 11% based on
Ru.
The high reactivity of these systems is of considerable interest.
This point is evident from their fast reactions with anionic or
neutral ligands such as CO or H2 to yield six-coordinate 18
valence electron complexes trans-[RuX(L2)2L′]+,10-12,15,18,19
their propensity for CH activation, and their potential for
synthetic applications18 or as hydrogenation catalysts.21 As to
CH activation processes, the hydrides (X ) H-) are probably
the most powerful among the [RuX(L2)2]+ derivatives. They
may form strong agostic interactions with the hydrocarbon
chelate bridges of the diphosphine ligands, provided the chelate
ring is large enough to allow the alkyl chains to approach the
vacant coordination site.20,22
In this paper we give an account of the synthesis of
-
-
[RuH(dcpe)2]+[A-] (A- ) BPh4 (2a), PF6 (2b)) and the
identification of the {(η6-C6H5)BPh3}RuH(dcpe) zwitterion and
Method 2. RuCl2(DMSO)4 (0.096 g, 0.20 mmol), dcpe (0.079 g,
0.187 mmol), and NaBPh4 (0.638 g, 1.86 mmol) were suspended in 8
mL of ethanol, and the mixture was warmed to a gentle reflux under
stirring. Within minutes the suspension cleared to a pale orange
solution. Soon an almost white solid precipitated which gradually
turned pale orange. After 60 min, the solid was allowed to settle and
the solvent was removed by filter cannula. The resulting crude product
was washed with another 4 mL portion of hot ethanol, vacuum dried,
and extracted into CH2Cl2 (5 mL). After drying in vacuo 0.093 g of
a pale orange solid was obtained, which was found to contain
(18) Ashworth, T. V.; Singleton, E. J. Chem. Soc., Chem. Commun. 1976,
705.
(19) (a) Tsukahara, T.; Kawano, H.; Ishii, Y.; Takahashi, T.; Saburi, M.;
Uchida, Y.; Akutagawa, S. Chem. Lett. 1988, 2055. (b) Saburi, M.;
Aoyagi, K.; Takahashi, T.; Uchida, Y. Chem. Lett. 1990, 601.
(20) Ogasawara, M.; Saburi, M. Organometallics 1994, 13, 1911.
(21) (a) Saburi, M.; Hiroyuki, K.; Youichi, I.; Yasuzo, U. Kenkyu
HokokusAsahi Garasu Kogyo Gijutsu Shoreikai 1987, 50, 225; CAS
No., 109: 109958p. (b) Muramatsu, H.; Kawano, H.; Ishii, Y.; Saburi,
M.; Uchida, Y. J. Chem. Soc., Chem. Commun. 1989, 769. (c) Saburi,
M.; Ohnuki, M.; Ogasawara, M.; Takahashi, T.; Uchida, Y. Tetrahe-
dron Lett. 1992, 33, 5783. (d) Saburi, M.; Takeuchi, H.; Ogasawara,
M.; Tsukahara, T.; Ishii, Y.; Ikariya, T.; Takahashi, T.; Uchida, Y. J.
Organomet. Chem. 1992, 428, 155.
(23) Spencer, I. P.; Wilkinson G. J. Chem. Soc., Dalton Trans. 1973, 204.
(24) (a) Chatten, L. G.; Pernarowski, M.; Levi, L. J. Am. Pharm. Assoc.
1959, 48, 276. (b) Costa, G.; Camus, A.; Gatti, L. J. Organomet. Chem.
1967, 8, 339.
(22) Ogasawara, M.; Aoyagi, K.; Saburi, M. Organometallics 1993, 12,
3393.

Square Pyramidal Hydride Cation [RuH(dcpe)2]+
Inorganic Chemistry, Vol. 36, No. 27, 1997 6199
[RuH(dcpe)2]+[BPh4]- and {(η6-C6H5)BPh3}RuH(dcpe) in an ap-
proximate 2:3 ratio. After two recrystallizations and sorting the crystals
as above [RuH(dcpe)2]+[BPh4]-‚3CH2Cl2 (0.035 g, 25% based on dcpe)
and {(η6-C6H5)BPh3}RuH(dcpe)‚0.5CH2Cl2 (0.049 g, 30% based on
dcpe) were obtained.
Synthesis of trans-RuHCl(dcpm)2 (3). Method 1. RuCl2(DMSO)4
(0.160 g, 0.33 mmol) and bis(dicyclohexylphosphino)methane (dcpm)
(0.271 g, 0.663 mmol) were suspended in 12.5 mL of ethanol, and 1
mL of NEt3 was added. The pale yellow suspension was stirred under
warming to a gentle reflux. Within minutes all solids dissolved to give
a yellow-orange, clear solution to which NaSbF6 (0.521 g, 2.0 mmol)
was added as a solid. This caused an immediate color change to red-
orange, and a purple precipitate appeared. The mixture was then kept
at a gentle reflux for 3 h during which time the precipitate gradually
turned pale orange. The volume of the reaction mixture was reduced
to ca. 4 mL, and the solid collected by filtration. After drying in vacuo,
the solid residue was extracted into 2 × 7 mL of CH2Cl2. The combined
extracts were cautiously layered with 3 mL of pentane. An almost
white precipitate formed overnight, which was isolated by filtration
and found to contain predominantly RuHCl(dcpm)2 (3) besides little
trans-RuCl2(dcpm)2 (4). The mother liquor was further concentrated
until new solids formed on the wall of the Schlenk tube and were
allowed to crystallize overnight. After filtration the remaining solution
contained only the product which was isolated by evaporating the
solvents as a pale yellow, microcrystalline solid. The mixture obtained
in the first crystallization step was dissolved in the minimum amount
of hot benzene. Upon cooling, the dichloride precipitated as an orange,
microcrystalline powder which was separated by cautiously syringing
off the mother liquor which was in turn evaporated to yield a further
crop of complex 3. Combined yields: 0.194 g (62%) of complex 3
and 0.028g (9%) of complex 4.
Spectral and Analytical Data. Complex 1. 1H-NMR (CDCl3):
3
δ 7.37, (2,6-H (BPh3), d, JH-H ) 7.07 Hz, 6H), 7.08 (3,5-H (BPh3),
vt, NH-H ) 7.32 Hz, 6H), 6.95 (4-H, (BPh3), t, 3JH-H ) 7.32 Hz, 3H),
3
5.83 (2,6-H (η6-Ph), d, JH-H ) 5.47 Hz, 2H), 5.60 (3,5-H (η6-Ph), t,
3
NH-H ) 5.50 Hz, 2H), 5.38 (4-H, (η6-Ph), t, JH-H ) 5.50 Hz, 1H),
1.18-1.79 (C6H11, m, 44H), 0.88 (PCH2, m, 2H), 0.64 (PCH2, m, 2H),
-11.59 (RuH, t, 2JP-C ) 36.5 Hz, 1H). 13C-NMR (CD2Cl2): δ 160.85
(ipso-C, BPh3, non-binomial quart, JB-C ) 60 Hz), 136.1, 125.8, 122.8
(o, m, p-C (BPh3)), 92.9, 91.7, 88.9 (o, m, p-C (η6-Ph)), 38.5 (ipso-C,
(dcpe), vt, NP-C ) 10.3 Hz), 37.0 (ipso-C, (dcpe), m, NP-C ) 16.2
Hz), 29.2, 28.0, 27.4 (CH2 (dcpe), all s), 27.3 (CH2 (dcpe), vt, NP-C
3.2 Hz), 27.1 (CH2 (dcpe), s), 26.9 (CH2 (dcpe), vt, NP-C ) 4.2 Hz),
26.3 (CH2 (dcpe), vt, NP-C ) 1.4 Hz), 26.1 (CH2 (dcpe), vt, NP-C
)
)
4.4 Hz), 25.3 (CH2 (dcpe), s), 20.9 (PCH2 (dcpe), vt, NP-C ) 20.0
Hz); the resonance of the ipso-C atom of the coordinated phenyl ring
could not be observed. 31P{1H}-NMR (CDCl3): δ 97.2 (s). 31P-NMR
2
(CDCl3): δ 97.2 (d, JP-H ) 36 Hz). IR (KBr, cm-1): 3057, 3037,
3001, 2984 (arene CH (BPh4-)), 2925, 2851 (CH2, CH (dcpe)), 2001
(RuH), 1582, 1562, 1495, 1481 (arene CC (BPh4-)), 1445, 1425 (CH2
(dcpe)), 1263 (dcpe), 852, 739, 732, 703 (ω(BPh4-)), 661, 532. Anal.
Calcd for C50H69BP2Ru‚0.5CH2Cl2: C, 68.43; H, 7.96. Found: C,
68.27; H, 7.94.
Method 2. RuCl2(DMSO)4 (0.091 g, 0.19 mmol), dcpm (0.147 g,
0.38 mmol), and NaSbF6 (0.301 g, 1.16 mmol) were suspended in a
solution of Na (0.16 g, 7 mmol) in EtOH (7.5 mL) and heated to a
gentle reflux for 3 h. After the solids were allowed to settle and the
solvent was removed by cannula filtration, the pale orange residue was
washed with 2 portions of warm EtOH (2 mL each) and dried in vacuo.
The resulting pale yellow solid was extracted into CH2Cl2 (2 × 5 mL)
and dried. The crude product contained predominantly complex 3 along
with ca. 12% of a second monohydrido complex (31P{1H}-NMR
Complex 2a. 1H-NMR (CDCl3): δ 7.43 (3,5-H (BPh4-), m, 8H),
7.06 (2,6-H (BPh4-) , vt, NH-H ) 7.32 Hz, 8H), 6.89 (4-H, (BPh4-), t,
3JH-H ) 7.32 Hz, 4H), 2.15 (ipso-CH (dcpe), vt, NH-H ) 2.18 Hz,
4H), 1.19-1.88 (C6H11, m, 84H), 0.88 (PCH2, m, 4H), 0.77 (PCH2, m,
4H), -32.06 (RuH, quint, 2JP-C ) 19.2 Hz, 1H). 13C-NMR (CD2Cl2):
δ 164.5 (ipso-C, BPh4-, nonbinomial quart, JB-C ) 50 Hz), 136.3, 125.9
(nonbinomial quart, 3JB-C ) 2.7 Hz), 122.0 (p, o, m-C (BPh4-)), 40.8
(ipso-C, (dcpe), vquint, NP-C ) 4.5 Hz), 40.3 (ipso-C, (dcpe), vquint,
NP-C ) 6.0 Hz), 30.4, 30.3, 29.0, 28.7, 28.2, 28.0, 27.6, 26.7, 26.6
(CH2 (dcpe), all s), 20.7 (PCH2 (dcpe), vquint, NP-C ) 10.9 Hz).
31P{H}-NMR (CDCl3): 74.2 (s), 74.0 (s). IR (KBr, cm-1): 3054, 3033,
2997 (arene CH, BPh4-), 2928, 2850 (CH2, CH (dcpe)), 2236 (RuH),
1579, 1481 (arene CC (BPh4-)), 1446, 1424 (CH2 (dcpe)), 1263 (dcpe),
3
(CDCl3), δ 4.0 (s); 31P, (CDCl3), δ 4.0 (d, JP-H ) 16.2 Hz)). The
latter was removed by dissolving the residue in the minimum amount
of CH2Cl2, layering the solution with an approximately equal amount
of pentane, and allowing it to stand at ambient temperature overnight.
The remaining solution was separated from the precipitate and put to
dryness to yield 0.088 g of pure complex 3 (0.092 mmol, 48%).
Spectral and Analytical Data for Complex 3. 1H-NMR (C6D6):
850, 731, 703 (ω(BPh4-)), 613, 533. UV/vis (CH2Cl2; λmax, nm (ꢀmax
,
M-1 cm-1): 411 (2180). Anal. Calcd for C76H117BP4Ru‚3CH2Cl2: C,
62.37; H, 8.15 Found: C, 62.71; H, 8.20.
2
2
δ 3.33 (PCH2P (dcpm), dt, JH-H ) 14.50 Hz, JP-H ) 2.20 Hz, 2H),
2
2
Synthesis of [RuH(dcpe]2[A-] (A- ) BPh4- (2a), PF6- (2b)). The
procedure is given for the synthesis of the [PF6]- salt 2b; the analogous
[BPh4]- salt is, however, obtained in essentially the same yield by
replacing NH4PF6 by NaBPh4. RuCl2(DMSO)4 (0.175 g, 0.361 mmol)
and dcpe (0.305 g, 0.721 mmol) were suspended in 9 mL of ethanol to
which 1 mL of NHiPr2 had been added. This mixture was warmed to
reflux for 3 h, and a clear orange solution formed. A solution of 0.587
g of NH4PF6 (3.6 mmol) in 4 mL of hot ethanol was added, and an
orange precipitate immediately formed. This mixture was allowed to
stir for 30 min and then filtered via a paper tipped cannula. The residue
was washed with an additional 4 mL portion of hot ethanol, dried in
vacuo, and extracted into 7 mL of CH2Cl2. The orange-red air-sensitive
solution was taken to dryness and gave the analytically pure product.
Large, blocklike crystals were obtained by slow concentration of a
solution in CH2Cl2. Yield: 0.351 g, 90%.
3.05 (PCH2P (dcpm), dt, JH-H ) 14.50 Hz, JP-H ) 3.48 Hz, 2H),
2.98 (t, br ipso-CH (dcpm), 2JH-H ) 10.5 Hz, 4H), 2.50 (m, 4H), 2.33
(m, 4H), 2.08 (m, 8H), 1.20-1.91 (m, 68H, all CH2 (dcpm)), -17.44
(RuH, quint, 2JP-H ) 18.71 Hz). 13C-NMR (C6D6): δ 39.1 (ipso-CH,
(dcpm), vquint, NP-C ) 4.9 Hz), 36.2 (ipso-CH, (dcpm), vquint, NP-C
) 3.4 Hz), 34.0 (PCH2, (dcpm), vquint, NP-C ) 8.8 Hz), 30.6, 30.0,
29.9, 29.2, 28.1, 28.0, 26.9, 26.4 (all CH2 (dcpm), all s). 31P{1H}-
NMR (C6D6): δ 6.9 (s). 31P-NMR (C6D6): δ 6.9 (d, 3JP-H ) 18 Hz).
IR (KBr, cm-1): 2922, 2843 (CH2, CH (dcpm)), 1947 (RuH), 1445,
1261, 1172, 1094, 1025, 803, 748 (dcpm). UV/vis (CH2Cl2; λmax, nm
(ꢀmax, M-1 cm-1): 381 (sh), 353 (880), 343 (1060), 315 (1090). Anal.
Calcd for C50H93ClP4Ru‚CH2Cl2: C, 58.92; H, 9.21. Found: C, 58.44;
H, 9.60.
Synthesis of trans-RuCl2(dcpm)2 (4). RuCl2(DMSO)4 (0.085 g,
0.137 mmol) and dcpm (0.143 g, 0.35 mmol) were refluxed in ethanol
for 1 h. A yellow solution and some yellow precipitate formed. The
solvent was evaporated and the tarry residue recrystallized by slowly
cooling a hot, concentrated solution in a 1:1 ethanol/chlorobenzene
mixture. Well-shaped pale orange transparent crystals formed overnight
which were isolated by filtration. Another batch was obtained by further
concentration of the mother liquor. The combined crystal fractions
were washed with cold ethanol and dried in vacuo. Yield: 0.126 g,
94%.
Spectral and Analytical Data for Complex 2b. The spectral data
of this compound are identical to those of the [BPh4]- salt 2a (Vide
supra) besides the absence of the signals due to the [BPh4]- counterion
1
in the H-NMR and IR spectra and the presence of the heptet of the
[PF6]- ion in the 31P-NMR spectra as well as the two characteristic
-
bands of PF6 at 838 and 557 cm-1 in the IR. Anal. Calcd for
C52H97F6P5Ru: C, 57.18; H, 8.95 Found: C, 57.20; H, 8.97.
Synthesis of [RuD(dcpe)2]+[PF6]- (2c). The synthesis was per-
formed as given above, but by replacing ethanol with C2H5OD and
starting from 0.115 g (0.238 mmol) of RuCl2(DMSO)4, 0.200 g of dcpe
(0.475 mmol), 0.6 mL of NHiPr2, and 6 mL of C2H5OD. Yield: 0.212
g, 88%. The spectral data for this compound were identical to those
of the pure hydride, but the hydride resonance integrated to only ca.
0.5 H.
Spectral and Analytical Data for Complex 4. 1H-NMR (C6D6):
δ 3.54 (PCH2 (dcpm), vquint, 2JP-H ) 3.65 Hz, 4H), 2.70 (vt, br. ipso-
2
CH (dcpm), JH-H ) 10.9 Hz, 8H), 2.51 (m, 8H), 2.05 (d, br, JH-H
)
13.2 Hz, 8H), 1.22-1.85 (m, 64H, all CH2 (dcpm)). 13C-NMR
(C6D6): δ 36.2 (ipso-C (dcpm), vquint, NP-C ) 4.0 Hz), 33.6 (m, PCH2P
(dcpm)), 30.8, 30.2, 30.1, 29.5, 28.4, 27.0 (C6H11 (dcpm), all s). 31P-

6200 Inorganic Chemistry, Vol. 36, No. 27, 1997
Winter and Hornung
Table 1. Crystallographic Data and Data Collection Parameters for
Complexes 1 and 2a
complex 1. The spectroscopic data of complex 2a suggested a
rather high cation symmetry. In its 31P-NMR spectrum at 303
K two sharp singlets with almost identical chemical shifts at δ
) 74.2 and 74.0 ppm are observed. The presence of the
characteristic [BPh4]- resonances in the 13C- and 1H-NMR
spectra and a quintet hydride signal in the H-NMR spectrum
at δ ) -32.06 ppm integrating as one proton confirmed the
product identity.
1
2a
formula
fw
temp, K
cryst syst
space group
a, Å
C50H69BP2Ru‚0.5CH2Cl2 C76H117BP4Ru‚3CH2Cl2
886.34
1521.33
188(3)
1
188(3)
monoclinic
P21/n (No. 14)
14.321(5)
19.716(6)
17.100(5)
107.6
monoclinic
P2/c (No. 13)
24.936(5)
12.633(3)
25.801(5)
102.86(3)
7924(3)
With chelates that are too small to allow for agostic
interactions between the vacant coordination site and the (CH2)n
bridges of the diphosphine ligands, rather high-field-shifted
hydride resonances are generally found.20a We also note that
such a high-field shift is not without precedence for five-
coordinate hydride complexes of group 8 metals.27 The P-H
coupling constant of 19 Hz is in the usual range.20a,21 As such,
the 31P-NMR data are in much better agreement with a slightly
distorted, square pyramidal (sqp) structure than with a trigonal
bipyramidal (tbp) one. Considerably larger differences between
the chemical shifts of the axial and the equatorial sites (the shift
difference ∆δ is usually in the range of some 15-43 ppm) are
to be expected in the latter case.11,12,14,16 The fact that two
narrowly spaced singlet signals with no apparent coupling rather
than only one singlet are observed in the 31P-NMR spectra of
complexes 2a,b most probably arises from dynamic processes.
The X-ray structure of complex 2a (Vide infra) indicates that
two of the P atoms are displaced out of the best plane RuP4
toward the hydride, whereas the remaining two point away from
this ligand. This might render the two pairs of P atoms slightly
inequivalent. As the possibility of a fast exchange between the
different sites of a tbp structure could not be ruled out, we
performed a low-temperature NMR study. Upon cooling a
broadening of the two signals was observed, and at T ) 215 K
they merged into one broad resonance. (See Note Added in
Proof.) Further cooling to 190 K resulted in the appearance of
two broad peaks of different heights and half-widths that were
located at δ ) 77.6 (W1/2 ) 168 Hz) and δ ) 74.6 ppm (W1/2
) 99 Hz). Likewise, below 215 K the hydride signal appeared
as a broad resonance at δ ) -32.42 ppm. The electronic
spectrum shows an intense absorption band at λmax ) 411 nm
that can be regarded as characteristic for five-coordinate d6
systems. In accordance with the higher ligand field strength
of the hydride this band exhibits a hypsochromic shift of about
50-80 nm with respect to the corresponding [RuX(L2)2]+ (X
) halogen).10,12 To our surprise our spectroscopic data did not
match those reported by Rigo for a compound of identical
composition,12 the most prominent difference being the shift of
the hydride ligand (see Note Added in Proof). Therefore it
seemed desirable to confirm the identity of complex 2a by
performing an X-ray analysis. This was also of significance in
a different context: [RuH(L2)2]+ are excellent precursors to
powerful hydrogenation catalysts,21 and many attempts have
been made to characterize one of these five-coordinate mono-
hydrides by crystallography. None of them has been successful
until now. In part this is due to their high reactivity. Thus,
crystallization of [RuH(Me-DuPhos)2]+ (Me-DuPhos ) 1,2-bis-
((2R,5R)-2,5-dimethylphospholano)benzene) under N2 has led
to the isolation of the dinitrogen addition product.28 The crystal
structure of complex 2a (Vide infra) confirmed an sqp config-
uration of the cation.
b, Å
c, Å
â, deg
V, Å3
4602(3)
F
calc, g cm-3
wavelength, Å 0.710 73, Mo KR
1.279
1.275
0.710 73, Mo KR
4
Z
4
µ, mm-1
0.501
0.522
0.0620
final Ra indices 0.0648
[I > 2σ(I)]
Rwa indices
0.1873
0.1694
(all data)
2
2
a R ) (∑||Fo| - |Fc||)/∑|Fo|. Rw ) {∑[w(|Fo| - |Fc| )2]/
4
∑[w(Fo )]}1/2
.
{1H}-NMR (C6D6): δ -6.5 (s). IR (KBr, cm-1): 2923, 2847 (CH2,
CH (dcpm)), 1444, 1262, 1171, 1129, 1101, 1023, 1005, 898, 891,
849, 802, 768, 742, 700 (dcpm). UV/vis (chlorobenzene; λmax, nm (ꢀmax
,
M-1 cm-1): 500 (30), 426 (60), 329 (sh).
Crystallographic Studies. Single crystals of compound 1 were
obtained by slow evaporation of a CH2Cl2 solution at room temperature,
whereas single crystals of compound 2a formed upon diffusion of
ethanol into a CH2Cl2 solution at 4 °C. Crystal, data collection, and
refinement parameters are given in Table 1. The single crystals were
taken from the mother liquors, separated under nujol, and sealed in a
glass capillary. The data collection was performed on a Siemens-P4
four-circle diffractometer. The structures of 1 and 2a were solved by
direct methods, using the SHELXTL-Plus25 package. Refinement was
carried out with SHELXL-93,26 employing full-matrix least squares
methods. Anisotropic thermal parameters were refined for all non-
hydrogen atoms. All hydrogen atoms were constrained using a riding
model with isotropic thermal parameters fixed at 20% greater than that
of the bonded atom. The crystallographic data have been deposited at
the Cambridge Crystallographic Data Centre. They can be ordered
free of charge from the following: The Director, CCDC, 12 Union
Road, Cambridge CB2 1EZ, GB (telefax, +44 1223/336-033; e-mail,
teched@chemcrys.cam.ac.uk).
Results
Synthesis of {(η6-C6H5)BPh3}RuH(dcpe)] (1) and [RuH-
-
-
(dcpe)2]+[A]- (A- ) BPh4 (2a), PF6 (2b)). In 1989 Rigo
and co-workers reported the synthesis of [RuCl(dcpe)2]+
[BPh4]- (dcpe ) bis(dicyclohexylphosphino)ethane).12 Our
initial experiments to reproduce their results, however, yielded
a mixture of two different products which were isolated as white
and dark orange crystals, respectively, and subsequently char-
acterized as the zwitterionic arene complex {(η6-C6H5)BPh3}-
RuH(dcpe) (1) and the five-coordinate hydride [RuH-
(dcpe)2]+[BPh4]- (2a). As one might expect from their different
composition, the relative amounts in which these two products
are formed depend on the reaction stoichiometry. Thus, if 2
equiv of the chelate ligand is present, the five-coordinate cation
2a constitutes the major product, whereas the use of only 1 equiv
of the diphosphine leads to a higher proportion of the arene
The second product of this reaction is the arene coordinated
{(η6-C6H5)BPh3}RuH(dcpe) (1). This species is characterized
(25) Sheldrick, G. M. SHELXTL-Plus: An Integrated System for SolVing,
Refining and Displaying Crystal Structures from Diffraction Data;
Siemens Analytical X-Ray Instruments Inc.: Madison, WI, 1989.
(26) Sheldrick, G. M. SHELXL-93, Program for Crystal Structure Deter-
mination; Universita¨t Go¨ttingen: Go¨ttingen, Germany, 1993.
(27) Esteruelas, M. A.; Werner, H. J. Organomet. Chem. 1986, 303, 221.
(28) Schlaf, M.; Lough, A. J.; Morris, R. H. Organometallics 1997, 16,
1253.

Square Pyramidal Hydride Cation [RuH(dcpe)2]+
Inorganic Chemistry, Vol. 36, No. 27, 1997 6201
by two distinct sets of phenyl protons and carbons, integrating
to 3:1 in the 1H-NMR spectrum. At 303 K, the less intense of
these two subsets is comprised of two well-resolved triplets at
δ ) 5.60 and 5.38 ppm and a doublet at δ ) 5.83 ppm with
relative intensities of 2:1:2. As a consequence of the metal
coordination these signals are shifted by approximately 1.3-
1.5 ppm to higher field with respect to the protons of the
uncoordinated phenyl rings. In the hydride region a triplet signal
is detected at δ ) -11.59 ppm with a 36.5 Hz coupling constant
to two identical P atoms. Likewise, the sharp singlet in the
31P-NMR spectrum at δ ) 97.2 ppm splits into a doublet with
a 36 Hz coupling constant in the proton coupled spectrum. Upon
a decrease in the temperature, the 31P resonance broadens
considerably and almost vanishes but no decoalescence is
observed down to 190 K. Larger effects are, however, observed
however, does not compete with the diphosphine chelate, and
complex 2b is formed in high yields irrespective of the time at
which the anion is added.
Our initial guess as to why this reaction gave a totally
different result in our hands (i.e. [RuH(dcpe)2]+ and not [RuCl-
(dcpe)2]+)12 was the different procedure employed in drying the
ethanol solvent. This was, however, found to have no effect
on the product distribution. More specifically, ethanol itself is
the most likely hydride source. We note that Ogasawara and
Saburi have already suggested that ethanol is involved in the
slow transformation of the monohydride cations [RuH(L2)2]+
to their respective dihydrides (eq 1).20
[RuH(L2)2]+ + CH3CH2OH f RuH2(L2)2 + CH3CHO +
H+ (1)
1
in the H-NMR spectrum, where at 213 K the two low-field
proton signals of the coordinated phenyl ring at δ ) 5.78 and
5.67 ppm (CD2Cl2) merge into one broad resonance at δ ) 5.61
ppm, presumably as a consequence of a hindered rotation of
the metal fragment with respect to the bulky arene substituent.
At still lower temperatures down to 200 K this signal sharpens,
while no coalescence with the remaining proton is found and
all proton couplings within the coordinated ring are lost.
The PPh3 derivative of complex 1, {(η6-C6H5)BPh3}RuH-
(PPh3)2, has briefly been mentioned in the literature, but no
spectroscopic data were provided,29 and the related [{(η6-C6H5)-
PPh2}RuH(PPh3)2]+[BF4]- has been obtained by thermolysis
of RuH(CO2Me)(PPh3)3 in methanol and its structure determined
by X-ray analysis.30 Complex 1 may also be compared to the
cationic arene complexes [(η6-arene)RuH(PR3)2]+ which were
first synthesized by Werner31 only that in the case of complex
1 the anionic nature of the arene substituent renders the molecule
neutral. The isoelectronic and isostructural compounds CpR-
RuH(PR3)2 are also well documented.32,33 The formation of
complex 1 can be rationalized from the competitive attack of a
[BPh4]- nucleophile on the RuCl2(DMSO)4 starting material
or a partially substituted coordinatively unsaturated derivative
thereof. Compound 1 represents one more example for the
noninnocent behavior of the “noncoordinating” [BPh4]- anion,34
and a growing number of such structures are reported in the
literature.34b Complex 1 is only formed if the tetraphenylborate
salt is added at the beginning of the reaction. Thus, complex
2a may be isolated in high yields and without any contamination
by complex 1 if the tetraphenylborate salt is added after first
allowing RuCl2(DMSO)4 to react with 2 equiv of the diphos-
phine for 3 h under reflux. Moreover, complex 1 seems to
prevail in the early stages of the reaction since the precipitates
are initially only lightly colored and become more and more
intense orange with time. In separate experiments we showed
that both products, once formed, are stable and do not
interconvert under the reaction conditions employed. We found
that complex 1 does not react to complex 2a in the presence of
excess dcpe and there is no complex 1 formed when complex
2a is refluxed in ethanol with equimolar amounts of RuCl2-
(DMSO)4, NaBPh4, and excess NEt3. The [PF6]- anion,
While no such complication was encountered in our case,
the above reaction suggested to us that the monohydride might
be formed by an analogous reaction via a coordinatively
unsaturated intermediate. We do not know whether this
intermediate is the respective chloro compound [RuCl(dcpe)2]+
that we were unable to obtain under our reaction conditions.
Our results with the dcpm ligand (dcpm ) (C6H11)2PCH2P-
(C6H11)2, Vide infra), however, make it more likely that the
hydride is transferred at an earlier stage of this reaction.
Irrespective of the detailed reaction sequence, the net conversion
can be formulated as shown in eq 2.
RuCl2(DMSO)4 + 2dcpe + NHiPr2 + C2H5OH +
NaBPh4 f [RuH(dcpe)2]+[BPh4]- + NaCl + NH2 Pr2Cl +
i
CH3CHO (2)
We have no direct evidence for the formation of either
acetaldehyde or the quaternary ammonium salt, but there are
several observations which support the above reaction scheme.
Thus, the presence of the amine is a necessary prerequisite in
order to achieve good yields of complexes 2a,b. In its absence
the yields of isolated complexes 2a,b dropped to typically 30-
35%, while the replacement of diisopropylamine by triethyl-
amine has no effect. The function of the amine is then to trap
the protons formed upon heterolytic dissociation of H+ from
ethanol, thus preventing a detrimental protonation of the
phosphine ligands. Even stronger evidence comes from the
observation that the reaction run in C2H5OD yields an ap-
proximately 1:1 mixture of the deuterated analogue [RuD-
(dcpe)2]+ and the corresponding hydride. The roughly 50%
incorporation of deuteride into the final product may indicate
that the hydride originates statistically from the ethanol OH
function and the methylene CH2 group. We can, however, at
present not exclude a H/D exchange reaction between the
deuterated alcohol and the basic amine and/or D transfer to
complex 2a,b from any deuterated species present with subse-
quent competitive loss of a hydride or deuteride.
Description of the Structures. The X-ray crystal structure
of complex 2a reveals the presence of two crystallographically
independent cations. Both possess a crystallographic 2-fold axis
of symmetry through the metal center. The cations and the
crystallographically unique anion pack as discrete units within
the crystal lattice with no short intermolecular contacts. No
unusual features are found for the [BPh4]- anion, which warrants
no further discussion. The structure of one of the cations is
given in Figure 1. Crystallographic data collection parameters
and selected bond distances and angles for the cations are given
in Tables 1 and 2. Both exhibit a distorted square planar
arrangement of the four P atoms around Ru which points to a
(29) Hough, J. J.; Singleton, E. J. Chem. Soc., Chem. Commun. 1972, 371.
(30) McConway, J. C.; Skapski, A. C.; Phillips, L.; Young, R. J.; Wilkinson,
G. J. Chem. Soc., Chem. Commun. 1974, 327.
(31) Werner, H.; Werner, R. Angew. Chem., Int. Ed. Engl. 1978, 17, 683.
(32) (a) Chinn, M. S.; Heinekey, D. M. J. Am. Chem. Soc. 1990, 112, 5166.
(b) Jia, G.; Morris, R. H. J. Am. Chem. Soc. 1991, 113, 875. (c) Jia,
G.; Lough, A. J.; Morris, R. H. Organometallics 1992, 11, 161. (d)
Lemke, F. R. J. Am. Chem. Soc. 1994, 116, 11183.
(33) (a) Lemke, F. R.; Brammer, L. Organometallics 1995, 14, 3980. (b)-
Brammer, L.; Klooster, W. T.; Lemke, F. R. Organometallics 1996,
15, 1721.
(34) (a) Seppelt, K. Angew. Chem., Int. Ed. Engl. 1993, 32, 1025. (b)
Strauss, S. H. Chem. ReV. 1993, 93, 927.

6202 Inorganic Chemistry, Vol. 36, No. 27, 1997
Winter and Hornung
Figure 1. ORTEP diagram of the cation of complex 2a at a 50%
probability level. Hydrogen atoms are omitted for clarity. Only one of
the two crystallographically unique cations is shown.
Figure 2. Perspective drawing of complex 1.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
Complexes 1 and 2a (Two Independent Cations)
Complex 1
Ru-C(51)
2.374(4)
2.288(4)
2.272(4)
1.418(6)
1.411(6)
1.400(7)
2.280(1)
1.42(5)
1.641(6)
1.653(7)
83.95(5)
80(2)
Ru-C(54)
Ru-C(55)
Ru-C(56)
C(54)-C(55)
C(55)-C(56)
C(51)-C(56)
Ru-P(2)
2.301(4)
2.234(4)
2.253(4)
1.419(7)
1.406(6)
1.419(6)
2.286(2)
1.661(6)
1.644(7)
Ru-C(52)
Ru-C(53)
C(51)-C(52)
C(52)-C(53)
C(53)-C(54)
Ru-P(1)
Ru-H(1)
B-C(51)
B-C(61)
B-C(71)
B-C(81)
P(1)-Ru-P(2)
H-Ru-P(2)
centra-Ru-P(2)
H-Ru-P(1)
79(2)
134.5
122.6
centra-Ru-P(1)
centra-Ru-H
135.1
Complex 2a
Ru(1)-P(11)
2.353(2) Ru(2)-P(21)
2.346(2) Ru(2)-P(22)
1.847(6) P(21)-C(21)
1.815(13) P(21)-C(211)
1.867(5) P(21)-C(221)
1.844(6) P(22)-C(22)
1.870(5) P(22)-C(231)
2.340(2)
2.341(2)
1.853(9)
1.856(6)
1.743(11)
1.838(6)
1.863(6)
1.805(13)
97.90(6)
Ru(1)-P(12)
P(11)-C(11)
P(11)-C(111)
P(11)-C(121)
P(12)-C(12)
P(12)-C(131)
P(12)-C(141)
P(12)-Ru(1)-P(11)
Figure 3. ORTEP diagram of a side view of complex 1 at a 50%
probability level showing the boatlike distortion of the coordinated
phenyl ring. The cyclohexyl substituents are omitted for clarity.
1.93(2)
P(22)-C(241)
82.61(6)
P(21)-Ru(2)-P(22)
P(11)-Ru(1)-P(11a)b 98.40(8)
P(12)-Ru(1)-P(12a)b 96.94(8)
P(12)-Ru(1)-P(11a)b 174.37(5)
P(21)-Ru(2)-P(21b)b 82.52(9)
P(22)-Ru(2)-P(22b)b 82.63(8)
sents the only crystallographically characterized example of a
square pyramidal five-coordinate d6 ruthenium cation with a
P4X donor set besides [RuCl(PP3)]+,17a where this structural
motif is induced by the rigidity of the chelating PP3 ligand (PP3
) P(C2H4PPh2)3). All other representatives belong to the type
RuP3XY; the chlorine derivatives [RuClP4]+ are trigonal
bipyramidal.13-18 These observations are in complete agreement
with theoretical predictions.2 Moreover, complex 2a is the only
example within this whole series where the metal is part of the
pyramid base with trans pairs of basal P atoms displaced to
different sides from the best plane. This is most likely due to
the steric bulk of the cyclohexyl substituents and the small apical
hydride. In fact, any net pyramidalization of the Ru center (i.e.
all P atoms bending away from Ru in the same direction) would
cause unfavorably close contacts between the cyclohexyl rings.
The arene complex 1 crystallizes in the monoclinic space
group P21/n with Z ) 4 and 12 molecules of CH2Cl2 in the
unit cell. The individual molecules are well-separated, and there
are no intermolecular contacts shorter than the sum of the
corresponding van der Waals radii. Views of the molecule are
given in Figures 2-4, and the most important bond lengths and
angles are collected in Table 2 (for a listing of the crystal-
lographic data see Table 1). The most notable feature is the
P(21)-Ru-P(22b)b
172.68(6)
a Midpoint of the coordinated arene ring C(51)-C(56). b Symmetry
transformations to generate equivalent atoms: (a) -x, y, -z + 1/2; (b)
3
-x + 1, y, -z + /2.
square pyramidal structure type. The hydride was not localized
but is expected to reside in an apical position. For each cation
the two independent Ru-P bond lengths differ only slightly
from each other (data for the second cation are given in
parantheses). Their average of 2.350 (2.341) Å lies at the lower
limit of those values found for the basal P atoms in other five-
coordinate, square pyramidal, 16 valence electron ruthenium
compounds RuClX(PR3)3 (2.37 Å av).8,9 Owing to crystal-
lographic symmetry, the Ru atom is part of the best plane
through the basal P atoms which in turn exhibit rather large
displacements of 0.115 (0.150) Å out of the mean plane. As a
consequence the angle between the equivalent pairs of trans P
atoms is decreased to 174.37(5) (172.68(6))°. A further
distortion of the pyramid base arises from the diphosphine
chelate bite angles of 82.61(6) (82.52(9) and 82.63(8))°, being
considerably smaller than the remaining angles of 98.40(8)° and
96.94(8) (97.90(6))° between unbridged P atoms.
It is worth mentioning that the [RuH(dcpe)2]+ cation repre-

Square Pyramidal Hydride Cation [RuH(dcpe)2]+
Inorganic Chemistry, Vol. 36, No. 27, 1997 6203
B-C6,centr-Ru-H amounts to 9.2° (Figure 4; C6,centr refers to
the midpoint of the arene ring C(51)-C(56)). This rotameric
structure also represents a general energy minimum for [(η6-
arene)ML3] systems with monosubstituted arene rings if the ring
substituent is an electron donor.36
Synthesis of trans-RuHCl(dcpm)2 (3) and trans-RuCl2-
(dcpm)2 (4). We have already mentioned that the outcome of
the reaction between a chelating diphosphine and a substitution-
ally labile RuII precursor complex critically depends inter alia
on the chelate ring size. The relevant literature reveals the trend
of a decreasing aptitude toward chloride dissociation with
decreasing chelate ring size. Here we address this question with
the example of two congeners of the bis(dicyclohexylphosphi-
no)alkane (alkane ) (CH2)2 (dcpe), CH2 (dcpm)) series. If 2
equiv of the dcpm ligand are allowed to react with
RuCl2(DMSO)4 in the presence of excess NaSbF6 and NHiPr2
in refluxing ethanol, the mixed ruthenium hydrido chloride
RuHCl(dcpm)2 (3) constitutes the major product accompanied
by small amounts of the corresponding dichloride 4. Separation
of these products is readily achieved on the basis of their
different solubilities. Due to its dipole moment, the pale yellow,
18 valence electron monohydride 3 is much more soluble in
CH2Cl2 and aromatic solvents such as benzene, toluene, or
Figure 4. Top view of complex 1 showing the near ecliptic conforma-
tion of the hydride. Only the molecule skeleton is depicted.
boatlike distortion of the coordinated phenyl ring of the [BPh4]-
-
anion with the BPh3 substituted C atom C51 and the para C
atom C54 being 0.064(6) and 0.049(7) Å above the best plane
defined by the remaining four C atoms and being bent away
from the metal. This distortion is evident from a side view in
Figure 3 and is quantified by the interplanar angles between
C51,C52,C56 or C53,C54,C55 and the mean plane through the
almost coplanar C52,C53,C55,C56 of 4.8(1) and 3.9(1)°,
respectively. Out-of-plane deformations are not without pre-
cedence for the coordinated [BPh4]- anion,35 although several
other modes of distortion are known.36 As a consequence of
the metal coordination, the C-C bond lengths within the η6
bound phenyl ring are somewhat elongated with respect to those
of the free arene rings. The Ru atom is slightly shifted away
from the ring center. This effect is, however, rather small as is
evident from the 1.7° angle between the axis ring center Ru
and the normal to the mean plane C52,C53,C55,C56 and
compares well to the [BPh4]- salt of the [(η6-toluene)RuH-
(PPh3)2]+ cation.37 The Ru-P bond lengths of 2.286(2) and
2.288(2) Å are basically identical and somewhat short with
respect to the other crystallographically investigated [(η6-arene)-
RuH(PPh3)2]+ cations (2.311-2.332 Å)30,37 but somewhat longer
than those in the isoelectronic CpRuH(PR3)2 derivatives (2.238-
2.288 Å).33 We were able to localize the hydride ligand at a
distance of 1.42(5) Å away from the metal center but note that
terminal M-H bond lengths determined by X-ray diffraction
always fall short of the values determined by neutron diffraction
(compare the Ru-H distances of 1.36(8) and 1.630(4) Å
determined for CpRuH(PMe3)2 by X-ray and neutron diffraction,
respectively).33
chlorobenzene than the almost insoluble dichloride 4.
A
reviewer suggested that a more basic medium such as NaOEt
in EtOH should provide a more complete conversion to the
hydride complex. This is indeed the case since essentially no
complex 4 is found in the crude product obtained under these
conditions. However, another monohydrido species, possibly
the corresponding OEt complex which is difficult to separate
from complex 3, is formed as a byproduct, thus lowering the
yield of isolated complex 3. In its 31P spectrum complex 3
exhibits a sharp singlet at δ ) 6.9 ppm, indicative of an axial
symmetry. This singlet splits into a doublet with a coupling
constant of about 18 Hz in the proton coupled spectrum. The
corresponding hydride resonance is found as a quintet signal at
δ ) -17.44 ppm with a coupling constant of 18.7 Hz. In
addition, a weak band at 1947 cm-1 in the IR spectrum of this
compound can be assigned to the Ru-H stretching vibration.
From the observation of both the hydrido chloride 3 and the
dichloride 4 in the reaction mixture, one may assume that
complex 4 is the direct precursor of complex 3 and the latter is
being formed upon sodium assisted chloride dissociation and
the subsequent reaction of the coordinatively unsaturated
intermediate with ethanol as the hydride source (Vide supra).
In order to examine both of these points, we first investigated
the reaction of RuCl2(DMSO)4 with the diphosphine ligand
under conditions identical to those above, except for the shorter
reaction times and the absence of the sodium salt and the amine.
Indeed, the trans-dichloride 4 can be isolated in high yields by
crystallization from a hot chlorobenzene/ethanol solution as pale
orange, diamond or hexagonal shaped crystals or as a micro-
crystalline powder. The trans-stereochemistry is established by
the observation of a singlet in the 31P-NMR spectrum at δ )
-6.5 ppm. In accordance with other MCl2P4 derivatives of this
architecture the electronic spectrum of complex 4 exhibits only
weak bands in the visible region. The assumption that the trans-
dichloride 4 is a direct precursor of complex 3 was investigated
by treating isolated complex 4 with NaSbF6 in refluxing ethanol
to which excess NHiPr2 had been added. Essentially no
conversion of complex 4 to the trans-hydrido chloride 3 was,
however, observed. This leads us to believe that the incorpora-
tion of the hydride takes event at an earlier stage of this reaction
and that chloride dissociation occurs from an only partially
diphosphine substituted intermediate or the starting material
itself.
A feature common to the other [(η6-arene)RuH(PPh3)2]+
cations is the T-shaped arrangement of the phosphine ligands
with P-Ru-P angles of about 95-105°.30,37 This is not the
case for {(η6-C6H5)BPh3}RuH(dcpe) (PRuP ) 83.95(5)°) as the
five-membered chelate does not allow for such an opening of
this angle. The bulky cyclohexyl substituents lead to a rather
large 71.3° tilt of the plane P1,Ru,P2 with respect to the best
plane for the cooordinated arene ring. One more feature of this
structure deserves some further comment. This is the orientation
of the RuHP2 unit with respect to the arene substituent. NMR-
spectroscopic and crystallographic studies as well as EHMO
calculations on such systems have revealed two rotameric
minimum structures separated by only a small energy barrier.
In the solid state complex 1 adopts one of these minimum
-
structures with the hydride ligand nearly eccliptical to the BPh3
,
i.e. the donor substituted carbon atom. The dihedral angle
(35) (a) Nolte, M. J.; Gafner, G.; Haines, L. M. J. Chem. Soc., Chem.
Commun. 1969, 1406. (b) Ware, D. C.; Olmstead, M. M.; Wang, R.;
Taube, H. Inorg. Chem. 1996, 35, 2576.
(36) (a) Substituted and para C atoms are closer to the metal: Albano,
M.; Aresta, M.; Manassero, M. Inorg. Chem. 1980, 19, 1069. (b) Only
the BPh3 substituted carbon out of plane: de Carvalho, L. C. A.;
Dartiguenave, M.; Dartiguenave, Y.; Beauchamp, A. L. J. Am. Chem.
Soc. 1984, 106, 6848. (c) Planar arene ring: Kruger, G. J.; du Preez,
A. L.; Haines, R. J. J. Chem. Soc., Dalton Trans. 1974, 1302.
(37) Siedle, R. R.; Newmark, R. A.; Pignolet, L. H.; Wang, D. X.; Albright,
T. A. Organometallics 1986, 5, 38.

6204 Inorganic Chemistry, Vol. 36, No. 27, 1997
Winter and Hornung
Summary
In the present work we have reinvestigated the reaction
between RuCl2(DMSO)4 and dcpe in the presence of either NH4-
PF6 or NaBPh4 in refluxing ethanol and have shown that the
coordinatively unsaturated hydride cation [RuH(dcpe)2]+ is the
major and, upon slight modification of the reaction conditions,
the only product. An X-ray analysis of the [BPh4]- salt 2a
establishes this cation as belonging to the square pyramidal
structure type. Low-temperature NMR studies make it very
likely that this structure is also maintained in solution. In the
case of the [BPh4]- counterion we were able to identify the as
yet unnoticed zwitterionic {(η6-C6H5)BPh3}RuH(dcpe) as the
second product which was found by X-ray analysis to feature
a boat-shaped η6-coordinated phenyl ring. Further investigations
make it likely that the latter compound is formed by competitive
nucleophilic attack of the [BPh4]- anion on a coordinatively
unsaturated reaction intermediate, whereas the hydride 2a itself
is inert toward this anion. The coordinatively unsaturated
cations present in complexes 2a,b readily coordinate acetonitrile.
Reducing the size of the dcpe chelate by one CH2 unit renders
six-coordinate species dissociatively stable even in the presence
of a large excess of NaSbF6 in boiling ethanol. Depending on
the exact reaction conditions either trans-RuHCl(dcpm)2 (3) or
trans-RuCl2(dcpm)2 (4) are isolated in good to excellent yields.
We have shown that the dichloride 4 is no direct precursor to
the hydride 3 and that chloride abstraction and hydride addition
take place at an earlier stage of the reaction; i.e. they involve
intermediates that contain less than two chelating diphosphine
ligands.
Figure 5. Spectral changes upon consecutive addition of increasing
amounts of CH3CN to a solution of complex 2b in CH2Cl2. The overlay
displays the absorption band of complex 2b without added CH3CN
(upper trace) and after addition of approximately 150, 260, 370, 520,
730, 1000, 1250, and 2300 equiv of CH3CN (lower traces).
Reaction of [RuH(dcpe)2]+[A]- with CH3CN. The five-
coordinate, 16 valence electron cations [RuXP4]+ (X ) halogen,
H), irrespective of their structure, readily add neutral two-
electron donor ligands or halide anions to achieve electronic
saturation at the metal center. The stability of these adducts
varies with the size and the donor ability of the incoming
nucleophile, and frequently equilibria are obtained.12,15,19a Thus,
while CO forms stable six-coordinate cations, all attempts to
isolate solid samples of the acetonitrile or nitromethane solvates
have failed so far. [RuH(dcpe)2]+[A]- (A- ) [PF6]-, [BPh4]-)
seems to be a remarkable exception in that no reactions with
CH3CN, CO, or N2 have been observed12 (see, however, Note
Added in Proof). (Other [RuH(L2)2]+ cations are nevertheless
reported to be highly reactive toward CO, halogenide, and, most
notably, H2 and N2.)19,26 In our hands, however, rapid reactions
of both the [PF6]- and the [BPh4]- salts with acetonitrile were
found to occur. This process is conveniently monitored by UV/
vis spectroscopy. Addition of increasing amounts of CH3CN
to a CH2Cl2 solution of complexes 2a,b leads to a discoloration
of the orange solution to a very pale orange and a leaching of
Note Added in Proof. We only recently became aware of
previous work by M. C. Puerta and others describing the
synthesis and reactivity of [RuH(dippe)]+[BPh4]- (dippe )
bis(diisopropylphosphino)ethane),38 an analogue to the com-
plexes 2a,b discussed here. Not only did they establish the high
reactivity of this cation toward various nucleophiles but they
also found, in complete agreement with our results, that the
NMR data reported in ref 12 for the [RuH(dcpe)2]+ cation are
erroneous and originate instead from the dioxygen adduct
[RuH(η2-O2)(dcpe)2]+. This species is formed upon exposing
[RuH(dcpe)2]+ to air and was fully characterized. Moreover,
the dioxygen complex is substitutionally inert, which accounts
for the failure of the authors of ref 12 to observe any reactivity
of their samples of 2b toward CO and CH3CN.
the strong visible band of the five-coordinate cation at λmax
)
411 nm. In the near UV a new band is observed as a shoulder
near λ ) 300 nm. It increases in height as more acetonitrile is
added and is consequently attributed to a CH3CN containing
product (Figure 5). Even in the presence of a large excess of
CH3CN there is still some remainder of the original band of
the five-coordinate cation which shows that the equilibrium for
this process lies quite to the left. From the UV/vis changes an
equlibrium constant Kc of about 0.0023 mol-1 L-1 may be
derived. In accordance with the above observation solutions
of complexes 2a,b in CH3CN contain a strong band at 299 nm
(ꢀmax ) 1800 M-1 cm-1) as well as an even stronger band at
230 nm (ꢀmax ) 7000 M-1 cm-1) but do not exhibit any
absorption at 411 nm. The addition was found to be reversible
as pumping off the solvent in vacuo under heating to 60 °C
and redissolving the solid residue in CH2Cl2 regenerated the
original spectrum. This lets us assume that complexes 2a,b
are generally reactive toward neutral two-electron donor mol-
ecules. At present we are investigating their interaction with
terminal alkynes, and we will report our findings in due course.
Acknowledgment. We are indebted to the Fonds der
Chemischen Industrie, Frankfurt am Main, Germany, and to
Prof. W. Kaim for support of this work.
Supporting Information Available: X-ray crystallographic files,
in CIF format, for complexes 1 and 2a are available on the Internet
only. Access information is given on any current masthead page.
IC970583M
(38) Jime´nez-Tenorio, J.; Puerta, M. C.; Valerga, P. Inorg. Chem. 1994,
33, 3515.