Reaction of (S)-BINAP with H4Ru4(CO)12. The first example of face-bridging BINAP coordination and 100% stereoselectivity in formation of a chiral tetranuclear cluster framework

Article abstract of DOI:10.1021/om034288n

The reaction of H₄Ru₄(CO)₁₂ with (S)-BINAP in the presence of Me₃NO affords the cluster H₄Ru₄(CO)₁₀(μ-(S)-BINAP) (2) in good yield. Gentle heating of a benzene-ethanol solution of 2 results in the dissociation of CO and coordination of a naphthyl fragment of BINAP to give H₄Ru₄(CO)₉(μ₃-(S)-BINAP) (3) with face-bridging coordination of the diphosphine ligand. The solid-state structures of both clusters have been determined by X-ray crystallography. Their structures in solution and some details of ligand sphere dynamics have been elucidated using 1D variable-temperature ¹ and ³¹P NMR spectroscopy together with selective decoupling measurements and ¹H COSY and NOESY experiments. The difference ¹H nuclear Overhauser effect (NOE) spectra provide additional support for the structural models suggested by visualization of important intramolecular nonbonding contacts in the molecules under study. The metal frameworks in 2 and 3 are chiral, due to the chemical difference of the ruthenium atoms induced by asymmetry of their ligand environments. The chemical reactions, which result in the formation of 2 and 3, display exceptional stereoselectivity to give a unique S,S configuration of the two ((S)-BINAP and cluster framework) stereogenic centers in the both compounds. The NMR and CD spectroscopic studies indicated that the S,S configuration observed in the solid state remains unchanged in solution. The cluster 3, containing face-bridging BINAP, demonstrates exceptional thermal stability and does not undergo metal framework racemization up to 343 K.

Full text of DOI:10.1021/om034288n

568
Organometallics 2004, 23, 568-579
Rea ction of (S)-BINAP w ith H4Ru 4(CO)12. Th e F ir st
Exa m p le of F a ce-Br id gin g BINAP Coor d in a tion a n d 100%
Ster eoselectivity in F or m a tion of a Ch ir a l Tetr a n u clea r
Clu ster F r a m ew or k
Sergey P. Tunik,*,† Tatiana S. Pilyugina,† Igor O. Koshevoy,†
Stanislav I. Selivanov,† Matti Haukka,‡ and Tapani A. Pakkanen‡
Department of Chemistry, St. Petersburg University, Universitetskii pr., 26,
St. Petersburg 198504, Russian Federation, and Department of Chemistry,
University of J oensuu, P.O. Box 111, FIN-80101 J oensuu, Finland
Received November 10, 2003
The reaction of H4Ru4(CO)12 with (S)-BINAP in the presence of Me3NO affords the cluster
H4Ru4(CO)10(µ-(S)-BINAP) (2) in good yield. Gentle heating of a benzene-ethanol solution
of 2 results in the dissociation of CO and coordination of a naphthyl fragment of BINAP to
give H4Ru4(CO)9(µ3-(S)-BINAP) (3) with face-bridging coordination of the diphosphine ligand.
The solid-state structures of both clusters have been determined by X-ray crystallography.
Their structures in solution and some details of ligand sphere dynamics have been elucidated
using 1D variable-temperature 1H and 31P NMR spectroscopy together with selective
1
decoupling measurements and H COSY and NOESY experiments. The difference 1H nuclear
Overhauser effect (NOE) spectra provide additional support for the structural models
suggested by visualization of important intramolecular nonbonding contacts in the molecules
under study. The metal frameworks in 2 and 3 are chiral, due to the chemical difference of
the ruthenium atoms induced by asymmetry of their ligand environments. The chemical
reactions, which result in the formation of 2 and 3, display exceptional stereoselectivity to
give a unique S,S configuration of the two ((S)-BINAP and cluster framework) stereogenic
centers in the both compounds. The NMR and CD spectroscopic studies indicated that the
S,S configuration observed in the solid state remains unchanged in solution. The cluster 3,
containing face-bridging BINAP, demonstrates exceptional thermal stability and does not
undergo metal framework racemization up to 343 K.
In tr od u ction
to both chelating and bridging coordination modes,
making this chemistry more diverse and potentially
providing other ways for the transfer of chiral induction
in these complexes. It is worth noting that chiral
induction in the BINAP-containing polynuclear com-
plexes may be enhanced and modified by asymmetry of
the other chiral elements, such as asymmetric metal
frameworks, which are chiral due to the difference in
ligand environment of each metal center.5-8 These
additional opportunities make the coordination chem-
istry of BINAP in transition-metal clusters especially
interesting and promising from the viewpoint of directed
chiral pocket design. This also means that investigation
of the structure and dynamic properties of these com-
pounds may shed light on the nature of chiral induction
in related catalytic reactions. However, at present this
chemistry has not received sufficient attention. Very few
examples of synthetic and structural studies of BINAP-
containing transition-metal clusters have been pub-
Asymmetric induction of a wide range of mononuclear
transition-metal complexes containing the ligand 2,2′-
bis(diphenylphosphino)-1,1′-binaphthyl (BINAP) in vari-
ous catalytic reactions is well documented.1-4 The de-
gree of induction and, consequently, enantiomeric excess
of the reaction products are dictated by the properties
of the chiral pocket formed by BINAP in the coordina-
tion sphere of a catalyst, which in turn is determined
by the ligand coordination mode and by location of the
vacancies available for coordination of catalytic sub-
strates. The chelating coordination of BINAP is a com-
mon structural motif for mononuclear complexes, and
the corresponding coordination and catalytic chemistry
has been studied in detail. Bonding of BINAP in tran-
sition-metal clusters may give rise, at least in principle,
* To whom correspondence should be addressed. E-mail: stunik@
chem.spbu.ru.
† St. Petersburg University.
‡ University of J oensuu.
(1) Noyori, R. Asymmetric Catalysis in Organic Synthesis; Wiley:
New York, 1994.
(2) Noyori, R. In Stereocontrolled Organic Synthesis; Trost, B., Ed.;
Blackwell: Oxford, U.K., 1994; p 1.
(5) Bruce, M. I.; Nicholson, B. K.; Patrick, J . M.; White, A. H. J .
Organomet. Chem. 1983, 254, 361-9.
(6) Collin, J .; J ossart, C.; Balavoine, G. Organometallics 1986, 5,
203-208.
(3) Akutagawa, S. In Asymmetric Synthesis by Ru-BINAP; Scaros,
M. G., Prunier, M. L., Eds.; Marcel Dekker: New York, 1995; p 135.
(4) Procter, G. Asymmetric Synthesis; Oxford University Press:
Oxford, U.K., 1996.
(7) Deeming, A. J .; Stchedroff, M. J .; Whittaker, C.; Arce, A. J .; De
Sanctis, Y.; Steed, J . W. J . Chem. Soc., Dalton Trans. 1999, 3289.
(8) Tunik, S. P.; Koshevoy, I. O.; Poe, A. J .; Farrar, D. H.; Nord-
lander, E.; Haukka, M.; Pakkanen, T. A. Dalton 2003, 2457.
10.1021/om034288n CCC: $27.50 © 2004 American Chemical Society
Publication on Web 01/07/2004

Reaction of (S)-BINAP with H4Ru4(CO)12
Organometallics, Vol. 23, No. 3, 2004 569
lished.9-14 It is interesting that even the limited number
of complexes obtained demonstrated an unusual diver-
sity of BINAP coordination modes to give chelate,11,14
bridging,9,12 and monodentate11 bonding of the ligand
to polynuclear metal frameworks.
BINAP (Aldrich) and reagent grade solventssdichloromethane,
hexane, benzene, ethanol, and methanol (Vekton)swere dried
over appropriate drying agents and distilled prior to use. All
manipulations of the starting materials and reaction mixtures
were carried out under an atmosphere of argon using standard
Schlenk techniques. The products were purified by column
chromatography on silica (5-40 mesh) in air. Fast atom
bombardment (FAB+) mass spectra were obtained on a J EOL
SX-102 instrument; 3-nitrobenzyl alcohol was used as a matrix
and CsI as a calibrant. The observed isotopic distribution
patterns fit completely to the calculated ones. The IR spectra
were recorded on Nicolet 550 Magna FTIR and Specord M80
spectrometers. Microanalyses were carried out in the Analyti-
cal Laboratory of the University of J oensuu.
NMR Mea su r em en ts. The 1H, 13C, and 31P NMR spectra
were recorded on Bruker DPX 300 and Bruker AM 500
spectrometers operating at the proton nominal frequency of
300 and 500 MHz. The chemical shifts were referenced to
residual solvent resonances and external 85% H3PO4 in 1H,
13C, and 31P spectra, respectively. All data were acquired,
processed, and displayed using Bruker XWINNMR software
and standard pulse-sequence library. The 2D COSY spectra
were recorded using the magnitude mode, and NOESY data
were acquired in the phase-sensitive mode at a mixing time
of 0.5 s. The accuracy of the temperature measurements in
the variable-temperature (VT) experiments was (1.0 °C.
The well-known catalytic activity of H4Ru4(CO)12 and
its derivatives in various organic reactions15-21 makes
this cluster very attractive for the investigation of its
reactions with chiral ligands to obtain asymmetric
catalysts with different and modifiable properties. A few
synthetic and catalytic studies in this area have already
been carried out,22-25 including the synthesis of the
cluster H4Ru4(CO)10(1,1-BINAP) (1),14 where the diphos-
phine occupies a chelating position at a ruthenium atom
of the tetranuclear framework. However, extremely
forcing conditions used in this synthesis (150 °C, 150
atm of H2) and low product yield motivated us to
reinvestigate this reaction. Two new compounds, H4Ru4-
(CO)10(µ-(S)-BINAP) (2) and H4Ru4(CO)9(µ3-(S)-BINAP)
(3), have been obtained under relatively mild conditions
using a modified synthetic procedure. In the present
paper we report the synthesis and X-ray structural
characterization of 2 and 3 together with the NMR
study of their solution structure and stereochemical
nonrigidity of the hydride ligands. In both cases incor-
poration of BINAP into the coordination sphere of
H4Ru4(CO)12 demonstrated a unique (100%) stereose-
lectivity in formation of the chiral “S-Ru4” framework,
which is asymmetric due to different ligand environ-
ments at each Ru atom of the tetrahedral skeleton. The
chiral framework configuration in 3 proved to be unex-
pectedly stable. It remains intact throughout a wide
temperature range, which is indicative of the cluster
potential in possible catalytic applications. Absolute
configurations of chiral elements in 2 and 3 has been
determined in the solid state by X-ray crystallography
and confirmed in solution by multinuclear NMR and CD
measurements.
Syn th esis of H4Ru 4(CO)10(µ2-(S)-BINAP ) (2). H4Ru4-
(CO)12 (102 mg, 0.137 mmol) and (S)-BINAP (86 mg, 0.138
mmol) were suspended in degassed benzene (12 cm3) under
an argon atmosphere, and a degassed solution of Me3NO‚2H2O
(32 mg, 0.288 mmol) in methanol (5 cm3) was added dropwise
with vigorous stirring. Addition of Me3NO results in immediate
formation of a transparent red solution.
A. A Schlenk tube containing the reaction mixture was
placed into an oil bath (55 °C) and heated with stirring for
20-30 min. By this time the solution had darkened and a TLC
spot test (eluant CH2Cl2-hexane (2/5 v/v)) showed the presence
of two main products, 1 (orange band) and 2 (red-brown band).
The solvents were then removed in vacuo. The remaining solid
was dissolved in 1.5 cm3 of dichloromethane and this solution
diluted with 3 cm3 of hexane, leaving some insoluble orange
crystalline material. The solution was then purged (ca. 2 min)
with CO and transferred onto a chromatographic column (2.5
× 10 cm). Careful separation of the sample (Rf parameters of
1 and 2 are very close to each other) using a CH2Cl2-hexane
(2/5 v/v) mixture gave a bright orange band of H4Ru4(CO)10-
(1,1-(S)-BINAP) (1; 55 mg, 31%) and a wide red-brown band
of H4Ru4(CO)10(µ-(S)-BINAP) (2; 105 mg, 59%).
B. The reaction mixture was left under argon at room
temperature overnight, yielding a dark red solution and some
amorphous precipitate. A TLC spot test (eluant CH2Cl2-
hexane (2/5 v/v)) showed the presence of 1 and 2. The solvents
were removed in vacuo. The remaining solid was dissolved in
1.5 cm3 of dichloromethane, and this solution was diluted with
3 cm3 of hexane (leaving some insoluble orange crystalline
material). The solution was purged (for ca. 2 min) with CO
and transferred onto a chromatographic column (2.5 × 10 cm).
Elution with a CH2Cl2-hexane mixture (2/5 v/v) gave a bright
orange band of 1 (20 mg, 11%) and a wide red-brown band of
2 (128 mg, 71%).
Exp er im en ta l Section
Gen er a l Com m en t s. The starting complex H4Ru4(CO)12
was prepared according to the published procedure.26 (S)-
(9) Derdau, V.; Laschat, S.; Dix, I.; J ones, P. G. Organometallics
1999, 18, 3859.
(10) Casado, M. A.; Perez-Torrente, J . J .; Ciriano, M. A.; Oro, L. A.;
Orejon, A.; Claver, C. Organometallics 1999, 18, 3035.
(11) Deeming, A. J .; Stchedroff, M. J . Chem. Soc., Dalton Trans.
1998, 3819.
(12) Deeming, A. J .; Speel, D. M.; Stchedroff, M. Organometallics
1997, 16, 6004.
(13) Prestopino, F.; Persson, R.; Monari, M.; Focci, N.; Nordlander,
E. Inorg. Chem. Commun. 1998, 1, 302.
(14) Braga, D.; Matteoli, U.; Sabatino, P.; Scrivanti, A. J . Chem.
Soc., Dalton Trans. 1995, 419.
(15) Bianchi, M.; Menchi, G.; Francalanci, F.; Piacenti, F.; Matteoli,
U.; Frediani, P.; Botteghi, C. J . Organomet. Chem. 1980, 188, 109.
(16) Doi, Y.; Tamura, S.; Koshizuka, K. J . Mol. Catal. 1983, 19, 213.
(17) Schmidt, G. F.; Reiner, J .; Suss-Fink, G. J . Organomet. Chem.
1988, 355, 379.
(18) Bhaduri, S.; Sharma, K.; Mukesh, D. J . Chem. Soc., Dalton
Trans. 1992, 77.
Spectroscopic characteristics are as follows.
1. IR (ν(CO)/cm-1; hexane): 2075 m, 2045 s, 2025 s, 2004
m, 1994 w, 1985 w, 1975 w. 1H NMR (δ/ppm (J , Hz); CDCl3, T
) 253 K): hydride signals, -16.6 (s), -16.8 (dd, J (H-P) )
32.6 and 17.3), -17.1 (t, J (H-P) ) 8.3), -17.7 (dd, J (H-P) )
(19) Adams, R. D.; Falloon, S. B. Organometallics 1995, 14, 4594.
(20) Castiglioni, M.; Giordano, R.; Sappa, E. J . Organomet. Chem.
1995, 491, 111.
(21) Ellis, D. J .; Dyson, P. J .; Parker, D. G.; Welton, T. J . Mol. Catal.
A: Chem. 1999, 150, 71.
(22) Homanen, P.; Persson, R.; Haukka, M.; Pakkanen, T. A.;
Nordlander, E. Organometallics 2000, 19, 5568.
(23) Salvini, A.; Frediani, P.; Bianchi, M.; Piacenti, F.; Pistolesi, L.;
Rosi, L. J . Organomet. Chem. 1999, 582, 218.
(24) Matteoli, U.; Beghetto, V.; Scrivanti, A. J . Mol. Catal. A: Chem.
1996, 109, 45.
(25) Scarpi, D.; Menchi, G.; Occhiato, E. G.; Guarna, A. J . Mol. Catal.
A: Chem. 1996, 110, 129.
(26) Knox, S. A. R.; Koepke, J . W.; Andrews, M. A.; Kaesz, H. D. J .
Am. Chem. Soc. 1975, 97, 3942.

570 Organometallics, Vol. 23, No. 3, 2004
Tunik et al.
1
Ta ble 1. Cr ysta l Da ta for H4Ru 4(CO)10((S)-BINAP )
(2) a n d H4Ru 4(CO)9((S)-BINAP )‚C6H14 (3)
30.7 and 19.2). These data fit completely the IR and H NMR
spectroscopic data obtained earlier for H4Ru4(CO)10(1,1-(S)-
BINAP).14
2
3
2. IR (ν(CO)/cm-1; hexane): 2072 s, 2049 m, 2033 s, 2026
sh, 2010 m, 2003 w, 1989 w, 1980 w, 1966 w. 1H NMR (δ/ppm
(J , Hz); CDCl3, T ) 258 K): phenyl and naphthyl signals, 8.2-
5.2, -16.5 (2H, d, J (H-P) ) 11.7 and dd, J (H-P) ) 23.5 and
11.5), -16.3 (d, J (H-P) ) 32.3) -17.2 (dq, J (H-P) ) 10.3,
J (H-H) ) ca. 2). 31P{1H} NMR (δ/ppm; CDCl3, T ) 283 K):
42.9, 28.4. FAB-MS (m/z): 1311 [M+] (calcd 1311), [M+ - nCO],
n ) 1-10. Anal. Calcd for C54H36O10P2Ru4: C, 49.47; H, 2.77.
Found: C, 49.46; H, 2.99.
empirical formula
fw
temp (K)
λ (Å)
cryst syst
space group
a (Å)
C
54H36O10P2Ru4
C
59H50O9P2Ru4
1311.05
100(2)
1369.21
120(2)
0.710 73
orthorhombic
P212121
14.0399(2)
22.1665(3)
47.2933(6)
14718.4(3)
12
1.775
1.333
0.0320
0.0683
0.710 73
orthorhombic
P212121
13.5301(2)
19.7539(4)
20.7708(4)
5551.5(2)
4
1.638
1.180
0.0514
0.0866
b (Å)
c (Å)
V (Å3)
Single crystals of 2 suitable for X-ray analysis were obtained
by slow diffusion of hexane vapor into a CH3OH-CH2Cl2
solution under an argon atmosphere.
Z
F
calcd (Mg/m3)
µ(Mo KR) (mm-1
R1a (I g 2σ)
)
Syn th esis of H4Ru 4(CO)9(µ3-(S)-BINAP ) (3). A 100 cm3
Schlenk tube was charged with H4Ru4(CO)10(µ2-(S)-BINAP) (92
mg, 0.07 mmol), benzene (20 cm3), and absolute ethanol (15
cm3). The resulting red solution was purged with argon for
3-5 min and evacuated. The Schlenk tube was then placed in
an oil bath (80 °C) and stirred for 40 h. During this time
evacuation was repeated periodically until a TLC spot test
(eluant CH2Cl2-hexane (2/3 v/v)) showed complete consump-
tion of the starting cluster. The TLC spot test also showed the
presence of the new complex 3 along with trace amounts of 1.
The reaction mixture was reduced in volume in vacuo to ca.
15 cm3 and diluted with degassed 2-propanol (10 cm3). Further
removal of the solvent, addition of octane (10 cm3), and final
reduction in volume to 10 cm3 gave a red crystalline precipi-
tate. The mixture was left for 30 min to complete precipitation.
The pale mother liquor was decanted, and the remaining solid
was successively washed with a degassed 2-propanol-heptane
mixture (1/2 v/v; 5 cm3) and heptane (2 × 5 cm3) and dried in
vacuo to give 72 mg (80%) of H4Ru4(CO)9(µ3-(S)-BINAP) (3).
IR (ν/cm-1; hexane): 2070 w, 2060 s, 2040 s, 2009 s, 1997 m,
wR2b (I g 2σ)
R1 ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) [∑[w(Fo2 - Fc2)2]/∑[w(Fo2)2]]1/2
.
a
hexanemolecule in the asymmetric unit. Hexane carbons were
refined with equal anisotropic displacement parameters. The
structure of poorly diffracting 2 was solved in the chiral space
group P212121. The asymmetric unit consists of three inde-
pendent H4Ru4(CO)10(BINAP) molecules, due to the presence
of two isomers. The ratio of the isomers is thus 2:1. Positions
of hydrides were estimated by the XHYDEX33 program. All
other hydrogens were placed in idealized positions and con-
strained to ride on their parent atom. The crystallographic
data are summarized in Table 1. Selected bond lengths and
angles are shown in Table 2.
Resu lts a n d Discu ssion
Syn th eses a n d Solid -Sta te Str u ctu r es of 2 a n d
3. Reaction of H4Ru4(CO)12 with (S)-BINAP in the
presence of Me3NO gives two isomers, 1 and 2, of the
H4Ru4(CO)10(BINAP) stoichiometry in a very good (90%)
total yield. Careful chromatographic separation of the
reaction mixture affords both compounds in a pure state.
It seems that the harsh conditions employed in the
previously reported reaction of H4Ru4(CO)12 and (S)-
BINAP14 prevented formation and isolation of 2, which
proved to be the major product in the synthesis de-
scribed above. Single-crystal X-ray structural charac-
terization of 114 revealed that the cluster contains (S)-
BINAP coordinated to a ruthenium atom in a chelating
manner. In contrast, 2 displays a bridging coordination
mode of the BINAP ligand, which spans an edge of the
closed ruthenium tetrahedron. Gentle heating of 2 in a
benzene/ethanol solution results in nearly quantitative
elimination of CO and formation of H4Ru4(CO)9(µ3-(S)-
BINAP) (3), where the diphosphine occupies a face-
bridging position over a ruthenium triangle. Coordina-
tion of BINAP to the third ruthenium atom in an η2
mode occurs through an aromatic ring of the ligand
naphthyl system. The solid-state structures of 2 and 3
have been determined using single-crystal X-ray dif-
fraction; selected bond lengths and angles are given in
Table 2, and molecular structures are shown in Figures
1 and 2, respectively.
1
1970 w. H NMR (δ/ppm (J , Hz); CDCl3, 214 K): phenyl and
naphthyl signals, 8.3-5.0, -15.3 (dm, 2J (P-H) ) 38.1), -15.7
(dd, 2J (P-H) ) 25.6 and 10.9), -16.5 (d, 2J (P-H) ) 14), -17.8
2
(br m). The last signal displays J (P-H) ) ca. 10 Hz at 210 K
in CD2Cl2. 31P{1H} NMR (δ/ppm (J , Hz); CDCl3, 293 K): 49.5
(d, 1P, J (P-P) ) 2.8), 27.4 (d, 1P, J (P-P) ) 2.8). FAB-MS
(m/z): 1283 [M+] (calcd 1283), [M+ - nCO], n ) 1-9. Anal.
Calcd for C53H36O9P2Ru4: C, 49.61; H, 2.83. Found: C, 49.20;
H, 3.03.
Single crystals of 3 suitable for X-ray analysis were obtained
by slow diffusion of methanol into a dichloromethane solution
of 3 at room temperature.
X-r a y Str u ctu r e Deter m in a tion s. The crystals were
immersed in perfluoropolyether, mounted in a cryo loop, and
measured at a temperature of 100 K or 120 K. The X-ray
diffraction data were collected with a Nonius KappaCCD
diffractometer using Mo KR radiation (λ ) 0.710 73 Å). The
Denzo-Scalepack27 program package was used for cell refine-
ments and data reduction. All structures were solved by direct
methods using the SHELXS-97 program and the WinGX
graphical user interface.28,29 A multiscan absorption correction
based on equivalent reflections (XPREP in SHELXTL v. 6.12)30
was applied to structure 2 (Tmin/Tmax ) 0.123 72/0.169 17).
Structural refinements were carried out with SHELXH-9731
for 2 and with SHELXL-9732 for 3. Structure 3 contained a
(27) Otwinowski, Z.; Minor, W. Macromolecular Crystallography;
Methods in Enzymology 276; Carter, J . C. W., Sweet, R. M., Eds.;
Academic Press: New York, 1997; Part A, p 307.
(28) Sheldrick, G. M. SHELXS97, Program for Crystal Structure
Determination; University of Gottingen, Gottingen, Germany, 1997.
(29) Farrugia, L. J . J . Appl. Crystallogr. 1999, 32, 837.
(30) Sheldrick, G. M. SHELXTL Version 5.1; Bruker Analytical
X-ray Systems, Madison, WI, 1998.
Str u ctu r e of 2. Three independent molecules have
been found in the unit cell of 2; two of them (A and B)
are essentially similar and display only minor variations
in bond lengths and angles. The third molecule (C) can
be considered as a conformer of the A,B structure with
(31) Sheldrick, G. M. SHELXH-97; University of Gottingen, Got-
tingen, Germany, 1997.
(32) Sheldrick, G. M. SHELXL97, Program for Crystal Structure
Refinement; University of Gottingen, Gottingen, Germany, 1997.
(33) Orpen, A. G.; XHYDEX. J . Chem. Soc., Dalton Trans. 1980,
2509.

Reaction of (S)-BINAP with H4Ru4(CO)12
Organometallics, Vol. 23, No. 3, 2004 571
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles (d eg) for H4Ru 4(CO)10((S)-BINAP ) (2) a n d
H4Ru 4(CO)9((S)-BINAP ) (3)
Bond Lengths
2A
2C
3
2A
2C
3
C(1)-Ru(1)
C(2)-Ru(1)
C(3)-Ru(2)
C(4)-Ru(2)
C(5)-Ru(3)
C(6)-Ru(3)
C(7)-Ru(3)
C(8)-Ru(4)
C(9)-Ru(4)
C(10)-Ru(4)
C(12)-C(13)
C(12)-P(2)
C(13)-C(14)
C(14)-C(20)
C(15)-C(16)
C(15)-C(20)
C(16)-C(17)
C(17)-C(18)
C(18)-C(19)
C(19)-C(20)
C(21)-C(22)
1.844(11)
1.878(10)
1.917(12)
1.896(9)
1.924(11)
1.915(11)
1.880(9)
1.890(10)
1.895(9)
1.941(10)
1.432(11)
1.830(8)
1.349(12)
1.406(12)
1.382(12)
1.428(11)
1.411(13)
1.344(12)
1.428(11)
1.415(12)
1.393(11)
1.862(9)
1.885(11)
1.892(9)
1.889(10)
1.933(9)
1.914(11)
1.908(9)
1.881(8)
1.870(8)
1.885(9)
1.888(10)
1.933(9)
1.887(8)
1.875(8)
1.849(8)
1.879(10)
-
1.468(9)
1.834(8)
1.369(10)
1.413(11)
1.351(12)
1.420(11)
1.395(12)
1.379(11)
1.422(10)
1.400(10)
1.403(10)
C(21)-C(29)
C(22)-C(23)
C(22)-P(1)
1.438(11)
1.418(11)
1.873(8)
1.441(11)
1.435(11)
1.851(8)
1.453(9)
1.387(10)
1.873(7)
C(23)-C(24)
C(24)-C(30)
C(25)-C(26)
C(25)-C(30)
C(26)-C(27)
C(27)-C(28)
C(28)-C(29)
C(29)-C(30)
P(1)-Ru(1)
P(2)-Ru(2)
Ru(1)-Ru(3)
Ru(1)-Ru(4)
Ru(1)-Ru(2)
Ru(2)-Ru(4)
Ru(2)-Ru(3)
Ru(3)-Ru(4)
C(13)-Ru(4)
1.360(11)
1.408(12)
1.315(12)
1.415(12)
1.403(12)
1.383(11)
1.419(11)
1.424(12)
2.392(2)
1.337(11)
1.430(11)
1.372(12)
1.430(11)
1.393(12)
1.364(11)
1.429(11)
1.413(12
1.380(10)
1.388(11)
1.379(12)
1.415(10)
1.410(11)
1.361(10)
1.416(10)
1.416(10)
2.3652(19)
2.3554(19)
2.7548(8)
2.9487(8)
2.9617(9)
3.0516(9)
2.9530(9)
2.7384(9)
2.469(7)
1.888(9)
1.913(10)
1.906(12)
1.389(12)
1.867(9)
1.358(11)
1.404(11)
1.378(12)
1.437(11)
1.376(13)
1.373(12)
1.421(11)
1.410(11)
1.397(11)
2.370(2)
2.375(2)
2.353(2)
2.7935(9)
2.9294(10)
2.9765(10)
2.9592(10)
2.9733(9)
2.7891(10)
2.7523(9)
2.9546(10)
2.9639(10)
2.9905(10)
3.0196(9)
2.7598(10)
Bond Angles
2A
2C
3
2A
2C
3
C(37)-P(1)-Ru(1)
C(31)-P(1)-Ru(1)
C(22)-P(1)-Ru(1)
C(49)-P(2)-Ru(2)
C(43)-P(2)-Ru(2)
C(12)-P(2)-Ru(2)
P(1)-Ru(1)-Ru(3)
P(1)-Ru(1)-Ru(4)
Ru(3)-Ru(1)-Ru(4)
P(1)-Ru(1)-Ru(2)
Ru(3)-Ru(1)-Ru(2)
Ru(4)-Ru(1)-Ru(2)
C(4)-Ru(2)-P(2)
C(3)-Ru(2)-P(2)
C(4)-Ru(2)-Ru(4)
C(3)-Ru(2)-Ru(4)
P(2)-Ru(2)-Ru(4)
C(4)-Ru(2)-Ru(3)
C(3)-Ru(2)-Ru(3)
P(2)-Ru(2)-Ru(3)
Ru(4)-Ru(2)-Ru(3)
C(4)-Ru(2)-Ru(1)
C(3)-Ru(2)-Ru(1)
P(2)-Ru(2)-Ru(1)
Ru(4)-Ru(2)-Ru(1)
Ru(3)-Ru(2)-Ru(1)
C(7)-Ru(3)-C(6)
C(7)-Ru(3)-C(5)
C(6)-Ru(3)-C(5)
C(7)-Ru(3)-Ru(4)
C(6)-Ru(3)-Ru(4)
119.6(3)
102.3(3)
125.9(3)
115.8(3)
113.9(3)
111.0(3)
176.06(7)
125.08(7)
58.28(2)
117.21(6)
61.94(2)
60.13(2)
97.7(3)
121.2(3)
115.0(2)
105.4(2)
126.0(2)
117.6(2)
118.3(2)
104.6(2)
174.77(6)
118.00(5)
57.27(2)
118.62(5)
62.08(2)
62.17(2)
98.3(3)
C(5)-Ru(3)-Ru(4)
C(7)-Ru(3)-Ru(1)
C(6)-Ru(3)-Ru(1)
C(5)-Ru(3)-Ru(1)
Ru(4)-Ru(3)-Ru(1)
C(7)-Ru(3)-Ru(2)
C(6)-Ru(3)-Ru(2)
C(5)-Ru(3)-Ru(2)
Ru(4)-Ru(3)-Ru(2)
Ru(1)-Ru(3)-Ru(2)
C(8)-Ru(4)-Ru(3)
C(9)-Ru(4)-Ru(3)
C(10)-Ru(4)-Ru(3)
C(8)-Ru(4)-Ru(1)
C(9)-Ru(4)-Ru(1)
C(10)-Ru(4)-Ru(1)
Ru(3)-Ru(4)-Ru(1)
C(8)-Ru(4)-Ru(2)
C(9)-Ru(4)-Ru(2)
C(10)-Ru(4)-Ru(2)
Ru(3)-Ru(4)-Ru(2)
Ru(1)-Ru(4)-Ru(2)
C(13)-Ru(4)-Ru(1)
C(13)-C(14)-C(20)
C(14)-C(13)-C(12)
C(14)-C(13)-Ru(4)
C(12)-C(13)-Ru(4)
C(11)-C(12)-C(13)
C(11)-C(12)-P(2)
C(13)-C(12)-P(2)
97.1(3)
89.2(3)
96.8(3)
92.7(3)
103.6(3)
94.4(2)
96.7(3)
163.3(3)
64.93(2)
145.5(2)
111.2(2)
102.3(3)
64.72(2)
62.40(2)
88.7(3)
104.5(3)
-
117.1(3)
103.7(3)
115.9(3)
105.8(3)
126.4(3)
166.53(6)
119.89(7)
57.71(2)
103.21(6)
63.65(2)
60.70(2)
97.0(3)
104.6(3)
160.1(3)
63.30(2)
151.1(3)
95.7(3)
113.4(3)
61.70(2)
62.05(2)
89.3(3)
100.3(2)
161.4(3)
64.83(3)
152.3(3)
100.8(2)
108.7(3)
62.13(2)
61.59(2)
88.7(3)
78.2(3)
81.0(3)
175.7(3)
143.8(3)
93.6(3)
119.6(3)
58.42(2)
91.1(3)
139.8(3)
120.7(3)
62.21(2)
60.72(2)
173.8(3)
140.4(3)
100.2(3)
119.0(3)
57.46(2)
88.0(3)
144.1(3)
120.3(3)
63.20(2)
59.80(2)
95.2(3)
99.8(3)
86.1(3)
97.4(2)
146.5(3)
98.5(2)
144.5(3)
100.5(3)
112.76(6)
93.3(3)
100.9(3)
166.33(7)
54.67(2)
90.8(3)
154.0(3)
115.89(6)
59.50(2)
54.76(2)
93.6(4)
103.8(3)
158.9(3)
90.14(5)
100.2(3)
112.8(2)
142.87(6)
54.23(2)
154.9(3)
100.5(3)
99.47(5)
58.71(2)
55.52(2)
95.8(4)
147.0(3)
111.49(6)
102.9(3)
92.0(2)
157.42(6)
56.09(2)
155.5(3)
97.8(3)
101.75(6)
59.14(2)
56.01(2)
94.6(4)
57.80(2)
106.0(3)
157.1(3)
61.05(2)
59.12(2)
104.27(16)
120.8(7)
120.6(7)
81.4(4)
104.5(4)
118.7(7)
128.7(5)
111.6(6)
120.3(9)
122.3(8)
119.6(8)
123.0(8)
92.5(4)
95.0(4)
104.1(3)
157.2(3)
92.8(4)
97.1(4)
98.9(3)
160.9(2)
96.1(4)
95.0(4)
82.8(2)
161.3(3)
118.7(8)
128.2(6)
113.0(6)
119.2(8)
122.6(7)
117.8(6)
a different orientation of the BINAP binaphthyl frag-
ment relative to the Ru(1)Ru(2)Ru(4) face (see Figure
1). In the A,B structural pattern one of the naphthyl
moieties is brought to close proximity to the metal
triangle due to the particular mode of phosphorus atom
coordination to the Ru(1)-Ru(2) edge. We believe that
this coordination mode is dictated by a weak but
naphthyl moiety. As shown below by nuclear Over-
hauser effect (NOE) NMR measurements, the A,B
conformation of 2 dominates in solution, and we believe
that the presence of the C conformer in the crystal cell
is a result of lattice packing effects. Because of this,
essential structural features of the A,B conformer only
will be discussed here in detail. The molecule consists
of a ruthenium tetrahedron surrounded by 10 terminal
COs, 4 bridging hydrides, and (S)-BINAP coordinated
in the bridging position between Ru(1) and Ru(2). The
electron count for 2 gives 60 electrons, which fits
important interaction (so-called dihydrogen bonding34-37
)
of a hydride ligand with the protons of the adjacent
(34) Richardson, T. B.; Koetzle, T. F.; Crabtree, R. H. Inorg. Chim.
Acta 1996, 250, 69.
(35) Custelcean, R.; J ackson, J . E. Chem. Rev. 2001, 101, 1963.
(36) Xu, W.; Lough, A. J .; Morris, R. H. Can. J . Chem. 1997, 75,
475.
(37) Abramov, Y. A.; Brummer, L.; Klooster, W. T.; Bullock, R. M.
Inorg. Chem. 1998, 37, 6317.

572 Organometallics, Vol. 23, No. 3, 2004
Tunik et al.
F igu r e 1. ORTEP plot of the molecular structure of H4Ru4(CO)10(µ2-BINAP) (2). Thermal ellipsoids are drawn at the
50% level.
ometry of the ruthenium tetrahedron is highly asym-
metric as well. The four Ru-Ru bonds spanned by the
hydride ligands are substantially longer (lav ) 2.9596
Å) compared to the other metal-metal distances (lav
)
2.7913 Å). This trend is typical for the diphosphine-
substituted H4Ru4(CO)12 derivatives, and a very similar
elongation of the Ru-Ru bonds bridged by the hydride
ligands was observed in the other H4Ru4(CO)10(µ-PP)
clusters.22,38,39 Bridging coordination of the diphosphine
gives an eight-membered ligand containing the dimet-
allacycle, where the conformation of the BINAP back-
bone is substantially distorted compared to that of the
free ligand. This distortion stems from the disparity
between the ligand bite angle and available vacancies
at adjacent ruthenium atoms and causes a strain in this
cyclic molecular fragment because of the BINAP back-
bone rigidity. This strain is partially relieved through
asymmetric coordination of the ligand: for example, the
P(1)-Ru(1)-Ru(2) and P(2)-Ru(2)-Ru(1) angles in 2
are 117.2 and 101.8°, respectively. In the other H4Ru4-
(CO)10(µ-PP) clusters where diphosphines (dppm,40
dppe,39 and dppp40) form five-, six-, and seven-membered
dimetallacycles containing relatively flexible hydrocar-
bon backbones, the angular distortions are substantially
lower and variations in P-Ru-Ru bonding angles
around the phosphorus atoms are at most 4.5° (H4Ru4-
(CO)10(µ-dppe)). It is interesting that two other com-
pounds containing bridging BINAP, ((3,3-dimethylbu-
F igu r e 2. ORTEP plot of the molecular structure of
H4Ru4(CO)9(µ3-BINAP) (3). Thermal ellipsoids are drawn
at the 50% level.
precisely with a closed configuration of the tetraruthen-
ium core. Three of the bridging hydrides, H(01), H(02),
and H(04), symmetrically surround the Ru(1)Ru(2)-
Ru(4) triangle to occupy cis positions with respect to the
phosphorus atoms of BINAP, whereas H(03) bridges the
Ru(2)-Ru(3) edge in the position trans to P(2). This
configuration of the hydride ligands is evidently a
potential sink for the clusters of this sort, as the same
ligand arrangement has been found in the other H4Ru4-
(CO)10(µ-PP) clusters22,38,39 containing various diphos-
phines. The disposition of the four hydride bridges and
two phosphorus atoms around the ruthenium tetrahe-
dron makes it asymmetric (chiral), and all three mol-
ecules presented in the unit cell display identical
stereoconfigurations of the metal framework. The ge-
9
tyne)(µ-(R)-BINAP)Co2(CO)4 and Ru3(µ-OH)2(CO)8(µ-
(R)-BINAP)12) display substantially different structural
behavior: in the dicobalt complex the Co-Co-P angles
equal 100.8 and 117.0°, whereas coordination of BINAP
in the triruthenium cluster is essentially symmetric to
give nearly equal P-Ru-Ru angles, 109.9 and 110.8°.
Metal-metal bond distances in these complexes, 2.501
and 3.031 Å, respectively, may control the coordination
geometry and related strain of the ligand bonding.
However, the Ru(1)-Ru(2) bond length in 2 (2.9765(10)
Å) is closer to the value in the trinuclear ruthenium
(38) Bruce, M. I.; Horn, E.; Bin Shawkataly, O.; Snow, M. R.;
Tiekink, E. R. T.; Williams, M. L. J . Organomet. Chem. 1986, 316,
187.
(39) Churchill, M. A.; Lashewicz, R. A.; Shapley, J . R.; Richter, S.
I. Inorg. Chem. 1980, 19, 1277.
(40) Puga, J .; Arce, A.; Braga, D.; Centritto, N.; Grepioni, F.; Castillo,
R.; Ascanio, J . Inorg. Chem. 1987, 26, 867.

Reaction of (S)-BINAP with H4Ru4(CO)12
Organometallics, Vol. 23, No. 3, 2004 573
cluster, whereas the distortions observed resemble those
in the dicobalt complex. These observations suggest that
the asymmetry of bridging BINAP coordination cannot
be completely assigned to the effect of different metal-
metal distances spanned by the diphosphine, and the
disparity between the ligand bite angle and the geom-
etry of coordination vacancies at the corresponding
ruthenium atoms seems to play a key role in the
asymmetric coordination of BINAP in 2.
requirements in 3 result in coordination of the C3-C4
(C(13)-C(14)) bond to give the structure shown in
Figure 2. This molecule consists of a closed ruthenium
tetrahedron, in agreement with the 60-electron count,
provided that the naphthyl group donates an electron
pair to the Ru(4) atom. The position of the BINAP
phosphorus atoms and four bridging hydride ligands
around the tetrahedron is completely analogous to that
found in 2. Similarly to 2, the four longest Ru-Ru bonds
are spanned by hydrides; the average difference between
two nonbridged (short) and hydride-bridged (long) bonds
is about 0.2 Å. The loss of the C(10)O ligand did not
result in a rearrangement of the other nine carbonyls,
as they were found in their regular positions: two at
each phosphorus-substituted Ru atom, two at the naph-
thyl-bonded Ru(4), and three at the unsubstituted
Ru(3) atom. The average bond lengths for these carbonyl
groups, (Ru-C)av ) 1.883 Å and (C-O)av ) 1.445 Å, are
in very good agreement with the values found for the
corresponding ligands in 2. Coordination of the naphthyl
fragment in 3 does not substantially affect the structural
parameters of the aromatic system. Both naphthyl
fragments remain nearly planar, and the bond lengths
in the coordinated six-membered ring are only slightly
elongated: (C-C)av ) 1.414 Å (cf. 1.408 Å for the
corresponding noncoordinated naphthyl group in 2). The
coordinated C(13)-C(14) bond in 3 is even shortened
compared to the same bond length in 2. These observa-
tions point to an effective but complicated mechanism
to dissipate the excitation inside the conjugated aro-
matic system caused by its bonding to a metal atom.
As pointed out above, three bridging hydrides in 2 form
a nearly symmetric “crown” around the Ru(1)Ru(2)-
Ru(4) triangle, whereas coordination of the naphthyl
group to Ru(4) in 3 results in folding of H(04) out of the
plane to form a 174.5° angle between the ruthenium
triangle and the Ru(2)H(04)Ru(4) bridge: cf. 120.3°
revealed in 2. The H(01) and H(02) hydride bridges keep
an undistorted configuration, with the corresponding
angles equal to 117.4 and 121.9°, respectively. Similarly
to 2, coordination of the BINAP phosphorus atoms in 3
is highly asymmetric, as shown by the angular param-
eters of this molecule: P(1)-Ru(1)-Ru(2) and P(2)-
Ru(2)-Ru(1) are 118.6 and 99.5°, and Ru(1)-P(1) and
Ru(2)-P(2) are 2.392(2) Å and 2.353(2) Å, respectively.
The different ligand environment at each ruthenium
atom makes the “Ru4” tetrahedron chiral, and the
asymmetry of the cluster framework found in the solid
state remains unchanged in solution, which has been
confirmed by a combination of NMR and circular dichro-
ism (CD) measurements and will be discussed below.
The positions of 10 terminal CO ligands in 2 are very
similar to those found in the other H4Ru4(CO)10(µ-PP)
clusters.22,38-40 Three CO ligands are bonded to unsub-
stituted Ru(3) and Ru(4), and two CO groups together
with the phosphorus atoms of BINAP are bonded to
Ru(1) and Ru(2). The Ru-C and C-O distances for the
carbonyl ligands are also typical for these complexes and
do not display any irregularities compared to analogous
tetraruthenium clusters.22,38-40 However, insertion of
the sterically demanding BINAP into the coordination
sphere of 2 results in rather short nonbonding contacts
of C(10)O with C(13) and C(14) atoms of the naphthyl
fragment: 3.305, 3.402, 3.488, and 3.160 Å, respectively.
This interaction, in turn, bends the carbonyl ligand out
of the Ru(1)Ru(2)Ru(4) triangle to increase the Ru(2)-
Ru(4)-C(10) and Ru(1)-Ru(4)-C(10) angles up to 119.6
and 120.6°, respectively: cf. the average Ru-Ru-C cis
angle (95.3(7.9)°) for the other carbonyl groups in 2. This
strain gives rise to easily predictable chemical conse-
quences, which consist of labilization of C(10)O and
spontaneous substitution of this ligand by the adjacent
naphthyl group of BINAP to give 3. As the reaction
slowly occurs at room temperature, gentle heating of a
benzene-ethanol solution of 2 is a convenient synthetic
route to 3.
Figure 2 shows the ORTEP plot of 3. This is the first
example of BINAP face-bridging coordination, where a
naphthyl fragment serves as an additional two-electron-
donor functionality. In an earlier study11 it was shown
that refluxing the Os3(CO)12 and (R)-BINAP mixture in
octane eventually forces ortho metalation of a BINAP
phenyl ring to give a face-bridging triosmium hydride
cluster, which, however, differs substantially from the
structural pattern shown in Figure 2. Coordination of
the naphthyl fragments through a pseudo “double bond”
of the aromatic system is well-known in organometallic
chemistry, including a few examples of ruthenium and
palladium BINAP complexes with the binaphthyl moi-
ety coordination to the metal centers.41-45 In the ru-
thenium complexes41-45 BINAP donates an additional
electron pair from a naphthyl fragment to relieve
electronic unsaturation of the metal atom to form a
stable 18-electron species. Geometry of the metal orbit-
als available for the interaction with the naphthyl
fragment in these mononuclear complexes evidently
dictates involvement of the C1-C2 bond in the coordina-
tion to the ruthenium center. In contrast, geometrical
Solu tion Str u ctu r es of 2 a n d 3. The idealized
structure of “Ru4(CO)x” (x ) 9, 10) fragment in both
clusters is not asymmetric because of a mirror plane
through Ru(3), Ru(4), and the center of the Ru(1)-Ru-
(2) bond. Although insertion of the asymmetric diphos-
phine into this structural pattern makes the phosphorus
atoms and the phosphorus-bound ruthenium atoms
diastereotopic, the carbonyl environment and “Ru4(µ-PP)-
(CO)x” fragment are still achiral. Therefore, in the
following discussion we will focus on the structure and
dynamic behavior of the “H4Ru4(µ-PP)” fragment, since
its stereochemistry is of crucial importance for the
asymmetry of the molecules as a whole. Most of the
(41) Pathak, D. D.; Adams, H.; Bailey, N. A.; King, P. J .; White, C.
J . Organomet. Chem. 1994, 479, 237.
(42) Kocovsky, V.; Vyskocil, S.; Cisarova, I.; Sejbal, V.; Tislerova,
I.; Smrcina, M.; Lloyd-J ones, G. C.; Stephen, S. C.; Butts, C. P.; Murray,
M.; Langer, V. J . Am. Chem. Soc. 1999, 121, 7714.
(43) Geldbach, T. J .; Pregosin, P. S.; Albinati, A. Organometallics
2003, 22, 1443.
(44) den Reijer, C. J .; Dotta, P.; Pregosin, P. S.; Albinati, A. Can. J .
Chem. 2001, 79, 693.
(45) Cyr, P. W.; Rettig, S. J .; Patrick, B. O.; J ames, B. R. Organo-
metallics 2002, 21, 4672.

574 Organometallics, Vol. 23, No. 3, 2004
Tunik et al.
Ch a r t 1. Dia gr a m s of Sp in -Sp in Cou p lin gs in 2
a n d 3
F igu r e 3. 500 MHz variable-temperature 1H NMR spectra
of 2 in the hydride region: (A) in CDCl3; (B) in CD2Cl2.
The spectrum recorded at 260 K is shown separately along
with a schematic assignment of the hydride resonances.
NMR spectroscopic data obtained are available as Sup-
porting Information; the numbers of the corresponding
figures bear an “S” prefix. Only some indicative spectra
related to the discussion are given in the main body of
the text.
Clu ster 2. The proton NMR measurements showed
that at room temperature the molecule is stereochemi-
cally nonrigid. The signals of four hydrides (Figure 3)
and the resonances of two inequivalent phosphorus
atoms in the 31P NMR spectrum are substantially
broadened. This is evidently a result of intramolecular
hydride exchange that has also been verified by 1H
NOESY measurements (Figure S1A), which showed
scrambling of all hydrides between four available bridg-
ing positions. However, the dynamic process is frozen
at 258 K, where one can observe a few fairly narrow
resonances of inequivalent hydrides between -16.0 and
-17.3 ppm in the proton NMR spectrum (Figure 3). It
is worth noting that the NOESY spectrum (Figure S1B,
258 K) displays very weak exchange (positive) cross-
peaks along with weak NOE (negative) signals. The
weak exchange signals point to the slow rate of the
hydride dynamics, whereas the NOE responses show the
ability of the routine to detect the presence of adjacent
hydrides.
in complete agreement with the structure of the
“H4Ru4(µ-PP)” pattern found in the solid state, where
H(03), H(04), and H(01) hydrides are in the vicinity of
P(2) and P(1), respectively, and the “Ru(1)-Ru(2)”
bridging position of H(02) allows two-bond coupling of
this hydride to both phosphorus nuclei. Additionally,
coupling of H(03) to P(2) shows the highest 2J (P-H)
value (32 Hz), which is consistent with the trans
position of the intervening nuclei about Ru(2).
The other P-H coupling constants are about 10 Hz,
2
except for J (P(2)-H(02)), which is more than 2 times
larger (25 Hz) than that of this hydride to P(1). This
could be explained in terms of the H(02) semibridging
position on the Ru(1)-Ru(2) edge. On the basis of the
data obtained, it is hardly possible to ascribe this effect
either to angular dependence of the two-bond coupling
or to a difference in the H(02) to Ru(1) and Ru(2)
distances. However, the asymmetry of the hydride
bridging coordination with respect to the phosphorus
1
atoms is clearly evident. The H COSY spectrum in the
The lowest field resonance, which looks like a slightly
distorted quartet of double intensity, is in fact a
combination of two overlapped signals (d and dd, as
hydride area together with selective 1H{1H} decoupling
experiments showed all possible pairwise interactions
between the hydrides (2J (H-H) equal to ca. 2 Hz each),
except that of H(01)-H(03). The latter observation is
completely in line with the remote disposition of these
two ligands on the tetraruthenium framework, in
contrast to the other pairs of hydrides. The results of
the proton NMR studies given above clearly point to an
asymmetric location of the hydrides around the ruthe-
nium tetrahedron and indicate that the structure of the
“H4Ru4(PP)” fragment found in the solid state remains
unchanged in solution at the low-temperature limit. It
has to be mentioned that at temperatures below 258 K
the signals of hydrides start to broaden (Figure 3), which
is an indication of a dynamic process that affects the
form of the lines observed in the temperature range
165-250 K. One of the possibilities is exchange between
two forms of the molecule: for example, for the A,B T
C conformers found in the solid state. This suggestion
1
shown in Figure 3), distinguished by selective H{31P}
1
and 31P{1H} decoupling measurements together with H
COSY experiments (Figure S2). The NMR data men-
tioned above also made it possible to construct a detailed
diagram of two-bond 1H-31P and 1H-1H spin-spin
couplings, shown in Chart 1, which allows complete
assignment of the hydride signals schematically repre-
sented in the upper part of Figure 3. On the basis of
this diagram, the low-field signal (49.5 ppm) in the 31P
spectrum of 2 coupled to three bridging hydrides should
be associated with P(2), whereas the high-field reso-
nance (27.4 ppm), which interacts with only two hydride
ligands, should be associated with P(1). Of the four
hydride resonances, three signals are coupled to a
unique phosphorus nucleus, either P(1) or P(2), and only
one displays coupling to both. These observations are

Reaction of (S)-BINAP with H4Ru4(CO)12
Organometallics, Vol. 23, No. 3, 2004 575
F igu r e 5. 1H NMR spectrum of 2 in the aromatic region
1
(in CD2Cl2, 260 K). The inset shows a part of the H-1H
COSY spectrum related to H(13) and H(14) proton signals.
sons. First of all, there are no physical reasons for
acceleration of the intramolecular hydride scrambling
(which was nearly completely frozen at 258 K) with the
decrease of temperature. Second, the NOE enhance-
ments between “averaged” hydride signals of two forms
were observed in the NOESY spectrum at 258 K (Figure
S1B) as a few weak negative signals. The emergence of
the positive NOE responses for the major form at 183
K can be explained by the well-known inversion of the
NOE effect sign at the ω0τc ) 1.12 point while the
temperature decreases (ω0 is the Larmor frequency and
τc is the correlation time of diffusion motion). The
change of the NOE signal sign is also in line with the
anisotropy of the overall diffusive motion for highly
asymmetric molecules such as the cluster 2.
1
F igu r e 4. 300 MHz H EXSY spectrum of 2 (in CD2Cl2,
193 K). 1D projections of the spectrum are enlarged 12
times to clearly show the signals of minor form of 2, marked
with a “+” symbol; “m” denotes the multiplets of the major
form. The signals of an admixture are marked with
asterisks. Major/minor form exchange cross-peaks are
denoted “m/+”.
1
is supported by the low-temperature H NOESY spec-
trum of this system recorded at 183 K.
The spectrum clearly demonstrates the presence of
another minor form of the cluster, which accounts for
about 5% of the total amount under these conditions.
Four cross-peaks (m/+) between the signals of major and
minor forms clearly point to the presence of the ex-
change between these species at 183 K. The exchange
is evidently responsible for the low-temperature broad-
ening of the well-resolved signals observed in the spec-
trum recorded at 258 K (Figure 3). Thus, this spectrum
represents averaged spectroscopic properties of the
major and minor forms of 2 in solution. The essential
feature of this spectrum consists of frozen intramolecu-
lar scrambling of the hydrides with simultaneous fast
exchange between two species. These observations point
to a very low kinetic barrier of the species interconver-
sion, which is consistent with the exchange between
structurally similar A,B and C conformers. It is worth-
while to stress at this point that the hydride to phos-
phorus and hydride to hydride spin-spin couplings in
both conformers are essentially similar and the differ-
ence in binaphthyl moiety orientation in A,B and C does
not affect the conclusions about the structure of the
“H4Ru4(PP)” fragment drawn above. The low content of
the minor form together with the poor solubility of the
complex and high viscosity of the solution at 183 K
prevented full characterization of this species. Never-
theless, the general structure of the signals observed
in the hydride region points to the similarity of the
hydride environment in both exchanging clusters and
agrees well with assignment of these species to the pair
of A,B and C conformers. The spectrum shown in Figure
4 also displays the cross-peaks between the signals of
the major form, marked “NOE”. We assign these cross-
peaks to NOE enhancement due to the following rea-
To assign the dominating form to one of the structural
patterns observed in the solid state, it is important to
find out an essential difference in these structures,
which may allow discrimination of two structural hy-
potheses. It has been mentioned above that the A,B
and C conformers differ in the distance between
Ru(1)Ru(2)Ru(4) triangle and adjacent naphthyl moiety
of BINAP. In particular, the close proximity of the metal
triangle and the naphthyl moiety in the A,B conformer
results in short contacts (2.34 Å) between the H(04)
hydride and the H(13) proton. None of the binaphthyl
protons in the conformer C display a similar short
nonbonding distance to the hydride ligands. It is evident
that 1H difference nuclear Overhauser effect (NOE)
measurements, which are highly sensitive to the dis-
tance between the intervening nuclei, can serve as a tool
to distinguish the structures under question. The key
point in the NOE study was unambiguous assignment
of the protons in the naphthyl fragments, which has
1
been made on the basis of H-1H COSY experiments
(193 and 258 K, Figures S3 and S4) and selective
1H{31P} decoupling measurements. It is also worth
noting that analysis of the low-temperature 1H-1H
COSY spectrum in the aromatic area also points to the
dominance of one major form of 2 in solution. It has been
found that the dd signal at 7.78 ppm can be unambigu-
ously assigned to H(13) because of its coupling both to
P(2) and to only one (H(14)) proton (7.92 ppm) of the
naphthyl fragment (Figure 5). This spectroscopic pat-
tern can be generated by the interaction of H(13), H(14),
and P(2) only, and no other protons in the BINAP bridge
match this particular feature.

576 Organometallics, Vol. 23, No. 3, 2004
Ch a r t 2. Sch em a tic Str u ctu r e a n d Dia gr a m of Non bon d in g Con ta cts in 2 a n d 3
Tunik et al.
The NOE measurements (258 K, Figure S5) show that
it is the A,B conformer that dominates in solution under
these conditions. In accordance with the remote location
of the H(03) hydride with respect to the BINAP aromatic
protons, no related signals have been found in the
corresponding NOE difference spectrum. In contrast, the
other three hydrides display strong connectivities with
the protons of the binaphthyl fragment and phenyl rings
of BINAP. Irradiation of the H(04) hydride resonance
led to NOE enhancement of the proton (dd) signal at
7.78 ppm, which has been assigned to H(13), and the
emergence of the NOE difference signal points to the
close proximity of these two nuclei in solution, as was
found in the solid state. It is worth noting at this point
that none of the hydrides in the structural pattern C
display short (less than 3.0 Å) nonbonding contacts with
the naphthyl protons. The shortest distances are about
4.2 Å, which is far beyond the limiting value expectable
for a nonzero NOE response. These observations indi-
cate the proximity of the naphthyl fragment to the
ruthenium tetrahedron in the major form of 2 presented
in solution at this temperature. This is completely
compatible with the dominance of the A,B conformer
in solution under these conditions. The solid-state
structure of the A,B conformer also displays short
intramolecular contacts of H(01) with H(42) (2.32 Å) and
of H(02) with H(48) (2.15 Å) (see Chart 2). These
contacts most likely account for the signals in the NOE
spectrum generated by irradiation of H(01)/H(02) fre-
quencies, separate irradiations of which are impossible
due to nearly identical positions of the hydride reso-
nances.
These NOE responses (multiplet at 7.25 ppm and two
broadened signals at 5.8 and 7.8 ppm) can be assigned
to ortho phenyl protons on the basis of their connectivi-
ties observed in the 1H COSY spectrum (Figures S3 and
S4) and their couplings to P(1) and P(2). Broadening of
the resonances at 5.8 and 7.8 ppm is evidently a result
of hindered rotation of the corresponding phenyl ring
about the phosphorus-carbon bond, because both sig-
nals narrow down to well-resolved multiplets at lower
temperature. A similar hindered rotation of the two
phenyl rings in bridging BINAP has been found earlier
in Ru3(CO)8(µ-OH)2(µ-(R)-BINAP).12 The authors as-
signed the hindrances to parallel alignment of the
corresponding naphthyl and phenyl fragments, which
is also observed in 2 for the Ph(1) and Ph(2) rings (see
Chart 2). The phenyl ring rotation in this case may only
occur through a transient state with a perpendicular
orientation of these fragments, which results in emer-
gence of a potential barrier for this rotation. In the
triruthenium cluster symmetric coordination of BINAP
made the phenyl rings and the corresponding barriers
equivalent. In the cluster 2 asymmetric coordination of
the phosphorus atoms of the diphosphine together with
the interaction of the ortho protons of Ph(1) and Ph(2)
rings with H(01) and H(02) makes the corresponding
barriers different, which results in different dynamic
behavior of the phenyl moieties.
Thus, the NMR data obtained for 2 showed that below
258 K the location of the hydride ligands around the
tetraruthenium skeleton matches well the structural
pattern found in the solid state. The NOE measure-
ments provided clear indication that the A,B conforma-
tion dominates in solution in the temperature range
studied. The A,B and C conformers do not display
substantial differences in structural parameters (bond
lengths and angles, Table 2) normally used in discrimi-
native analysis of molecular conformations. The varia-
tions observed can hardly discriminate the energy of
A,B and C to provide domination of the former structure
in solution. However, one can notice that these two
forms of 2 are distinguished by left and right rocking of
BINAP with respect to the Ru(1)-Ru(2) edge, ac-
companied by the shift of the binaphthyl moiety to and
from the metal framework in A,B and C, respectively.
It seems very probable that the short contact of the
hydride and binaphthyl proton in the A,B conformer
discussed above can be considered as “dihydrogen
bonding”,34-37 which compensates fpr the van der Waals
repulsion of BINAP and other ligands to “organize” 2
into the A,B structure. This type of bonding is now
recognized34-37 as an important structural factor in
transition-metal hydrides. Retention of these contacts
in solution is well documented by the 1H-1H NOE
measurements carried out for 2. This is an important
indication of the role this weak interaction may play in
the determination of subtle structural features of the
cluster hydrides.
Monitoring of the 1H and 31P NMR spectra in the
temperature range 300-350 K in d8-toluene showed
substantial decomposition of the sample, which pre-
vented a detailed characterization of the intramolecular
dynamic processes that occur in 2 above 300 K. How-

Reaction of (S)-BINAP with H4Ru4(CO)12
Organometallics, Vol. 23, No. 3, 2004 577
naphthyl proton signal (6.4 ppm), together with a weak
response of H(14), whereas irradiation of H(01) and
H(02) generates NOE responses related to H(42) (6.42
ppm) and H(48) (7.5 ppm) phenyl protons, respectively.
It is relevant to note that the H(13) signal in 3 (dd due
to H-H and P-H couplings) is substantially upfield
shifted (6.4 ppm) compared to the signal of the same
proton in 2 (dd, 7.8 ppm). This observation is completely
in line with a regular high-field shift of the proton
signals of coordinated double bonds and aromatic rings
and suggests that coordination of the naphthyl fragment
is maintained in solution.
1
Variable-temperature H NMR measurements (Fig-
ure 6) showed essentially different dynamic behavior
of 3 compared to 2. In the temperature range 195-300
K, the hydride signals corresponding to H(01) and H(02)
do not display any broadening, whereas those of H(04)
and H(03) successively broaden, degrade to the baseline,
and eventually collapse into a doublet at -16.5 ppm
(J (P-H) ) 15 Hz). In contrast to the hydride dynamics
observed in 2, where the scrambling process starts at
255 K and makes them all equivalent above 300 K, the
H(04)-H(03) pairwise exchange in 3 starts at substan-
tially lower temperature and does not involve two other
hydrides in the whole temperature range studied. A
plausible explanation of the early onset of the H(04) T
H(03) exchange observed in 3 may be derived from the
changes in the H(04) coordination geometry caused by
a ligand interaction with the adjacent naphthyl frag-
ment. This interaction results in a shift of the bridging
ligand away from the Ru(1)Ru(2)Ru(3) triangle (see
Figure 2 and Table 2). One of the possible mechanisms
of two µ2-bridging ligand exchange is a (µ2,µ2) T (µ3,t)
T (µ2,µ2) sequence with a transition state including face-
bridging and terminal hydrides. The shift of H(04)
mentioned above brings it into close proximity to the
position it has to occupy in the µ3 transition state over
the Ru(2)Ru(3)Ru(4) triangle, thus lowering the poten-
tial barrier of the exchange. It has to be stressed that
H(03) T H(04) exchange does not wipe out the asym-
metry of the “H4Ru4(PP)” fragment. The VT 31P NMR
measurements showed two fairly narrow doublets cor-
responding to the strongly inequivalent phosphorus
atoms of BINAP in the temperature range 190-343 K
(Figure S8), which confirms that the cluster framework
retains its chiral configuration despite the H(03) T
H(04) exchange. In contrast to 2, no broadening of the
31P signals was observed above 300 K; moreover, no
decomposition of the sample was detected during the
NMR experiments.
F igu r e 6. 1H NMR spectrum of 3 in the hydride region
(in CDCl3, 214 K). The assignment of the hydride reso-
nances is schematically shown at the top of the spectrum.
ever, extrapolation of the trends observed at lower
temperatures most likely points to (a) complete scram-
bling of the hydride environment over the tetraruthe-
nium skeleton and (b) oscillation of the BINAP binaph-
thyl system from one ruthenium triangle to another, to
give the achiral “H4Ru4(µ-PP)” pattern, as has been
suggested earlier for other H4Ru4(CO)12 derivatives
containing asymmetric diphosphines.22,40
Clu ster 3. The 1H NMR spectrum of 3 features
stereochemical nonrigidity of the hydride ligands above
200 K (Figure 6). In the limiting low-temperature
spectrum shown in Figure 6, four well-resolved hy-
dride resonances are observed between -15 and -18
ppm that points, similarly to 2, to an asymmetric struc-
1
ture of the “H4Ru4(µ-PP)” fragment. Selective H{1H},
1H{31P}, and 31P{1H} decoupling measurements re-
vealed the spin-spin coupling pattern shown in Chart
1. This allowed complete assignment of the proton NMR
spectrum in the hydride region, which is shown at the
top of Figure 6. The coupling diagram is essentially the
same as that found for 2, which testifies in favor of
essentially similar locations of the hydrides around the
tetraruthenium framework. This diagram also confirms
the structure of the hydride environment suggested for
3 on the basis of X-ray crystallographic analysis. In
agreement with this structure, the 31P NMR spectrum
also displays two doublets at 50.29 and 28.18 ppm
(3J (P-P) ) 2.8 Hz). The highest value of 2J (P-H)
observed for H(03) and P(2) testifies in favor of their
trans position around Ru(2), and asymmetric coupling
of H(02) with the phosphorus nuclei (25.6 and 10.9 Hz)
most likely points to the semibridging location of this
hydride over the Ru(1)-Ru(2) edge.
Thus, the NMR study of the cluster 3 clearly demon-
strates its high stability in the temperature range
covering possible conditions of hydrogenation catalysis.
The data obtained prove that the asymmetric structure
of this cluster revealed in the solid state remains
unchanged in solution and the dynamics of the hydride
ligands does not erase the chemical difference between
the four ruthenium atoms of the cluster framework.
Circular dichroism (CD) measurements discussed below
reinforce this observation and confirm that the molecule
bears chirality not only in the BINAP binaphthyl system
but also in the asymmetric cluster core.
Completely analogous to 2, the 1H NOE measure-
ments for 3 (CDCl3, 215 K, Figure S7) were very
indicative in elucidation of the cluster molecular struc-
ture in solution. The short nonbonding contacts H(04)-
H(13) (2.02 Å), H(01)-H(42) (2.44 Å), and H(02)-H(48)
(2.19 Å) result in enhancement of the corresponding
signals in the aromatic area upon selective irradiation
of associated hydrides, whereas H(03) did not give a
NOE response in the aromatic region because of its
remote location with respect to the naphthyl fragments
and phenyl rings of BINAP. Thus, irradiation into the
H(04) frequency gives strong enhancement of the H(13)
Ster eoch em istr y of 2 a n d 3. The metal framework
in tetrahedral clusters is a potentially chiral structural

578 Organometallics, Vol. 23, No. 3, 2004
Tunik et al.
To the best of our knowledge, the only example of the
Cotton effect at longer wavelengths was observed for
the [Pd(BINAP)H2O]2+ complex,51 where an optical
rotation band appears at about 400 nm. This makes it
possible to assign the 220-400 nm features observed
in the CD spectrum of 3 to binaphthyl-related, intrali-
gand π-π*, and MLCT electronic transitions. Longer
wavelength absorptions in the electronic spectra of the
cluster compounds are normally attributed to metal core
based transitions, and a broad positive band observed
between 400 and 500 nm can be assigned to the
asymmetry of the “Ru4” stereogenic center. The CD
spectra obtained for the “chiral-in-framework” diaster-
eomers of the (µ-H)Os3(CO)10(µ-XY) (XY ) (R)-(4-(1-
hydroxyethyl)-2-pyridinyl), (S)-3-(N-methyl-2-pyrrolid-
inyl)-2-pyridinyl)) clusters7 have been interpreted in a
similar way. The Cotton effects observed in the 230-
500 nm range have been considered characteristic of the
M3(µ-XY) framework asymmetry, because chiral organic
auxiliaries do not display electronic transitions in this
interval. In the case of these triosmium clusters nearly
no “synthetic” stereoresolution was observed and sepa-
ration of the diastereomers was achieved using HPLC.
In contrast, 3, as well as 2, have been synthesized as
unique diastereoisomers according to the NMR and CD
data.
This unique situation is completely determined by
specific features of the BINAP stereochemistry. The
structural patterns given in Chart 2 clearly show that
as soon as the (S)-BINAP forms a “PP” bridge over a
ruthenium-ruthenium edge, there is only one way for
the binaphthyl system to occupy a µ3-bridging position,
namely, to use its “left hand” (P(2)-bound naphthyl
fragment) in this bonding. This particular mode of the
BINAP face-bridging coordination also determines the
asymmetry of the hydride ligand design around the
ruthenium tetrahedron, which does not disappear even
under fast regime exchange of H(03) and H0(4).
Clu ster 2. In the structural pattern shown in Chart
2, the “(CO)10Ru4(BINAP)” fragment in 2 is not chiral
because the two “Ru(CO)2P” centers are not stere-
ochemically different but only diastereotopic. The tet-
rahedron becomes chiral, due to the asymmetry of the
hydride ligand coordination to afford the S configuration
of the ruthenium tetrahedron in the solid state. Simi-
larly to 3, no evidence for the presence of another R,S
diastereomer has been observed, either in the solid state
or in solution. However, 2 is substantially less stereo-
chemically rigid compared to 3. As mentioned above,
decomposition of 2 upon heating above 300 K prevents
a detailed characterization of the high-temperature
dynamics in this cluster. Nevertheless, it is possible (fast
heating, fast acquisition) to observe total scrambling of
all hydrides over the tetraruthenium skeleton. This
process together with rocking of the diphosphine relative
to the Ru(1)-Ru(2) edge eventually results in the onset
of a symmetry plane onto the “H4Ru4(PP)” fragment to
give degradation of both phosphorus resonances into the
baseline above 350 K. The racemization dynamics of this
F igu r e 7. Circular dichroism spectrum of 3 (25 °C, in
dichloromethane).
unit, the asymmetry of which emerges from the differ-
ence in chemical nature of the tetrahedron vertexes.
Directed design of the differences in metal atom ligand
environments is a way to induce chirality into a homo-
nuclear M4 cluster framework. The potential of a chiral
molecule to act as an asymmetric catalyst depends
strongly on its stereochemical stability, which is deter-
mined by the potential barrier for racemization pro-
cesses. It has been shown earlier46,47 that stereopure
heteronuclear tetrahedral clusters easily racemize un-
der catalytic conditions to give an effective but nondis-
criminating catalyst. As a rule, the stability of config-
uration of the chiral ligands is substantially higher than
that of the cluster framework, which results in pre-
dominant use of the “chiral-in-ligand” cluster catalysts
where stereoinduction is dictated by the ligand asym-
metry only.14,22-25 Nevertheless, it is quite evident that
a combination of the stereoinduction from the chiral
ligand and from a stable asymmetric metal framework
may give rise to enhanced stereoresolution of the
catalyst, which was one of the driving forces for the
present synthetic project.
The solid-state structure of 3 (Figure 2) clearly shows
asymmetry of the ruthenium tetrahedron, in which all
ruthenium atoms are distinguished by the difference in
their ligand environment. On the basis of CIP rules,48
one can assign the S stereoconfiguration to the “Ru4”
framework, treating it as an analogue of a tetrahedral
carbon atom. The combination of two chiral elements
in 3 ((S)-BINAP and (S)-“Ru4”) gives the S,S configu-
ration of the diastereomeric molecule. The NMR spec-
troscopic study of 3 indicated that this absolute config-
uration remains unchanged in solution and showed
unusually high thermal stability of the chiral framework
in a fairly wide temperature range.
The presence of the tetraruthenium framework in its
stereopure configuration is also supported by the CD
spectrum of 3, shown in Figure 7. The spectrum exhibits
optical activity in the interval 220-500 nm. Analysis
of the literature data shows that mononuclear com-
plexes containing BINAP and its derivatives49,50 nor-
mally display a CD response at the wavelengths below
350 nm.
(49) Evans, O. R.; Manke, D. R.; Lin, W. Chem. Mater. 2002, 14,
3866.
(50) Mikami, K.; Yusa, Y.; Aikawa, K.; Hatano, M. Chirality 2003,
15, 105.
(51) Muller, C.; Whiteford, J . A.; Stang, P. J . J . Am. Chem. Soc.
1998, 120, 9827.
(46) Richter, F.; Vahrenkamp, H. Chem. Ber. 1982, 115, 3243.
(47) Vahrenkamp, H. J . Organomet. Chem. 1989, 370, 65.
(48) Pure Appl. Chem. 1976, 45, 11.

Reaction of (S)-BINAP with H4Ru4(CO)12
Organometallics, Vol. 23, No. 3, 2004 579
occurring through the “double bonds” of the ligand
naphthyl fragment. The structures of both clusters in
the solid state have been established using X-ray
crystallography. The solution structure of 2 and 3 and
the dynamic behavior of the hydride ligands were
elucidated using a wide range of NMR spectroscopic
techniques.
2. The tetrahedral metal frameworks in 2 and 3 are
chiral, due to the asymmetry of the ligand environment
at each ruthenium atom. Syntheses of both clusters
display extremely high (100%) stereoselectivity to give
an S(BINAP),S(Ru4) diastereoconfiguration of these
molecules.
3. The cluster 3 demonstrates unusually high thermal
stability, retaining stereoconfiguration of the metal
framework intact up to 80 °C.
F in a l Rem a r k . It has been discovered that 3 is not
chemically inert. The cluster exhibits hemilability of the
coordinated naphthyl fragment. Two-electron donors
such as CO, acetonitrile, and 1-hexene can be easily
added to 3 to restore the edge-bridging coordination of
BINAP. The room-temperature reaction with CO im-
mediately and quantitatively regenerates the starting
H4Ru4(CO)10(µ2-BINAP) cluster. The products of reac-
tions with the other ligands mentioned above have been
isolated, and the study of their structure and properties
is now in progress. These results also point to the
promising catalytic potential of 3, which is now under
investigation.
F igu r e 8. Circular dichroism spectrum of 2 (25 °C, in
hexane).
sort may very likely account for the moderate chiral
discrimination obtained with H4Ru4(CO)12 derivatives
containing asymmetric bridging diphosphines,22 as com-
pared to related mononuclear complexes. In the case of
these tetranuclear ruthenium catalysts, which undergo
metal framework racemization, the coordination and
transformation of a substrate in a remote part of the
molecule may be only slightly affected by the presence
of the asymmetric diphosphine ligands.
Nevertheless, similar to the case for 3, the room-
temperature CD spectrum of 2 (Figure 8) displays
optical activity in a relatively broad wavelength range.
Positive and negative absorption bands in the 400-550
nm interval may be assigned to the “Ru4” stereogenic
center, which points to incomplete racemization of 2 at
or below room temperature.
Ack n ow led gm en t. Financial support provided by
the Russian Foundation for Basic Research (Grant 02-
03-32792), the Nordic Council of Ministers (T.S.P. and
S.P.T.), and the Academy of Finland (M.H.) is gratefully
acknowledged. We thank Pavel Tsitovich for CD spectra
recording and Drs. I. S. Podkorytov and P. S. Lobanov
for fruitful discussions of related NMR and stereochem-
ical problems.
In conclusion, we have found the following.
1. The reaction of (S)-BINAP with H4Ru4(CO)12 in the
presence of trimethylamine N-oxide affords the substi-
tuted cluster H4Ru4(CO)10(µ-(S)-BINAP) (2), containing
the diphosphine ligand coordinated in a bridging mode.
Further gentle heating of 2 gives an unusual face-
bridging coordination of BINAP in H4Ru4(CO)9(µ3-(S)-
BINAP) (3), additional bonding of the diphosphine
Su p p or tin g In for m a tion Ava ila ble: Tables giving crys-
tallographic data and figures giving 1H COSY, EXSY, and
difference NOE NMR spectra of the clusters 2 and 3; crystal-
lographic data are also available as CIF files. This material is
available free of charge via the Internet at http://pubs.acs.org.
OM034288N