Influence of the cone angles and the π-acceptor properties of phosphorus-containing ligands in the chemistry of dihydrogen complexes of ruthenium

Article abstract of DOI:10.1021/om000371o

A series of new dicationic dihydrogen complexes of ruthenium of the type trans-[(dppe)₂Ru-(η²-H₂)(L′)] [BF₄]₂ (dppe = Ph₂PCH₂CH₂PPh₂; L′ = PF(OMe)₂, PF(OEt)₂, PF(OⁱPr)₂) have been prepared by protonating the precursor hydride complexes trans-[(dppe)₂Ru(H)(L′)][BF₄] using HBF₄·Et₂O. The precursor hydride complexes have been obtained from trans-[(dppe)₂Ru-(H)(L)][BF₄] (L = P(OMe)₃, P(OEt)₃, P(OⁱPr)₃) via the substitution of a -OR group on the trans phosphorus ligand with a fluoride in the presence of HBF₄·Et₂O. Coupling of the dihydrogen ligand with the trans phosphorus moiety has been observed. In addition to the complexes bearing trans phosphite groups, the precursor hydrides containing trans phosphine ligands, viz., PMe₃ and PMe₂Ph, have also been prepared and characterized. It was found that the binding ability of the trans phosphorus ligand in both the hydride and dihydrogen complexes decreases with an increase in the steric congestion of the trans phosphorus moiety. This indicates that the stability of this series of complexes depends on the cone angles of the trans phosphorus ligand. The protonation reactions of the hydride precursors trans-[(dppe)₂Ru(H)(L)][BF₄] (L = P(OMe)₃, P(OEt)₃, P(OEt)₃, P(OⁱPr)₃) (under certain experimental conditions in the case of P(O_iPr)₃) result in mixtures of the new hydride complexes trans-[(dppe)₂Ru(H)(L′)][BF₄] (L′ = PF(OMe)₂, PF(OEt)₂, PF(OⁱPr)₂) and the trans-[(dppe)₂Ru(η²-H₂)(L′)] [BF₄]₂ derivatives. There is a strong dependence on the quantity of the acid used for the isolation of either the new hydrides or the corresponding dihydrogen complexes. Both dihydrogen and the new hydride complexes have been isolated and characterized. On the other hand, the protonation reactions of the starting hydrides that have trans-PMe₃, PMe₂Ph, or P(OⁱR)₃ (under certain experimental conditions) ligands gave a hydride dihydrogen complex, the structure formulation of which could not be established with certainty. The roles of the steric as well as the π-accepting properties of the trans phosphorus ligands in this series of complexes are discussed.

Full text of DOI:10.1021/om000371o

4506
Organometallics 2000, 19, 4506-4517
In flu en ce of th e Con e An gles a n d th e π-Accep tor
P r op er ties of P h osp h or u s-Con ta in in g Liga n d s in th e
Ch em istr y of Dih yd r ogen Com p lexes of Ru th en iu m
Nisha Mathew and Balaji R. J agirdar*
Department of Inorganic & Physical Chemistry, Indian Institute of Science,
Bangalore 560 012, India
R. Srinivasa Gopalan and G. U. Kulkarni
Chemistry and Physics of Materials Unit, J awaharlal Nehru Centre for
Advanced Scientific Research, J akkur, Bangalore 560 064, India
Received May 1, 2000
A series of new dicationic dihydrogen complexes of ruthenium of the type trans-[(dppe)2Ru-
(η2-H2)(L′)][BF4]2 (dppe ) Ph2PCH2CH2PPh2; L′ ) PF(OMe)2, PF(OEt)2, PF(OiPr)2) have been
prepared by protonating the precursor hydride complexes trans-[(dppe)2Ru(H)(L′)][BF4] using
HBF4‚Et2O. The precursor hydride complexes have been obtained from trans-[(dppe)2Ru-
(H)(L)][BF4] (L ) P(OMe)3, P(OEt)3, P(OiPr)3) via the substitution of a -OR group on the
trans phosphorus ligand with a fluoride in the presence of HBF4‚Et2O. Coupling of the
dihydrogen ligand with the trans phosphorus moiety has been observed. In addition to the
complexes bearing trans phosphite groups, the precursor hydrides containing trans phosphine
ligands, viz., PMe3 and PMe2Ph, have also been prepared and characterized. It was found
that the binding ability of the trans phosphorus ligand in both the hydride and dihydrogen
complexes decreases with an increase in the steric congestion of the trans phosphorus moiety.
This indicates that the stability of this series of complexes depends on the cone angles of
the trans phosphorus ligand. The protonation reactions of the hydride precursors trans-
[(dppe)2Ru(H)(L)][BF4] (L ) P(OMe)3, P(OEt)3, P(OiPr)3) (under certain experimental
conditions in the case of P(OiPr)3) result in mixtures of the new hydride complexes trans-
[(dppe)2Ru(H)(L′)][BF4] (L′ ) PF(OMe)2, PF(OEt)2, PF(OiPr)2) and the trans-[(dppe)2Ru(η2-
H2)(L′)][BF4]2 derivatives. There is a strong dependence on the quantity of the acid used for
the isolation of either the new hydrides or the corresponding dihydrogen complexes. Both
dihydrogen and the new hydride complexes have been isolated and characterized. On the
other hand, the protonation reactions of the starting hydrides that have trans-PMe3, PMe2Ph,
or P(OiR)3 (under certain experimental conditions) ligands gave a hydride dihydrogen
complex, the structure formulation of which could not be established with certainty. The
roles of the steric as well as the π-accepting properties of the trans phosphorus ligands in
this series of complexes are discussed. X-ray crystal structures of trans-[(dppe)2Ru(H)-
(P(OMe)3)][BF4], trans-[(dppe)2Ru(H)(PF(OMe)2)][BF4], and trans-[(dppe)2Ru(η2-H2)(PF-
(OEt)2)][BF4]2 have been determined. trans-[(dppe)2Ru(H)(L)][BF4] (L ) PMe3, PMe2Ph,
P(OiPr)3) undergoes substitution of the trans phosphorus ligand with H2 to give trans-
[(dppe)2Ru(H)(η2-H2)][BF4] reversibly under very mild conditions.
In tr od u ction
dihydride, whereas heterolysis provides a metal hydride
and a proton equivalent.
The activation of molecular hydrogen by transition-
metal complexes is the central theme in catalytic
hydrogenation reactions.1 There have been numerous
reports on the nature of the interaction of H2 with a
metal center: that is, either as η2-H2 (“side-on”) or as
the oxidatively added species, the dihydride. It has been
found earlier that the nature of the metal center and
the ancillary ligands play very important roles in
dictating the equilibrium between these two species.2,3
The homolytic activation of dihydrogen generates a
Transition-metal centers that are quite electrophilic
in nature have been found to greatly promote the
activation of dihydrogen toward heterolytic cleavage.2c,d,4
(2) (a) Kubas, G. J . Acc. Chem. Res. 1988, 21, 120. (b) Crabtree, R.
H. Acc. Chem. Res. 1990, 23, 95. (c) J essop, P. G.; Morris, R. H. Coord.
Chem. Rev. 1992, 121, 155. (d) Heinekey, D. M.; Oldham, W. J ., J r.
Chem. Rev. 1993, 93, 913. (e) Crabtree, R. H. Angew. Chem., Int. Ed.
Engl. 1993, 32, 789. (f) Morris, R. H. Can. J . Chem. 1996, 74, 1907.
(3) Burdett, J . K.; Eisenstein, O.; J ackson, S. A. In Transition Metal
Hydrides: Recent Advances in Theory and Experiment; Dedieu, A., Ed.;
VCH: New York, 1991; p 149.
(1) (a) J ames, B. R. Homogeneous Hydrogenation; Wiley: New York,
1973. (b) Chaloner, P. A.; Esteruelas, M. A.; J oo´, F.; Oro, L. A.
Homogeneous Hydrogenation; Kluwer Academic: Boston, MA, 1994.
(4) (a) Rocchini, E.; Mezzetti, A.; Ru¨egger, H.; Burckhardt, U.;
Gramlich, V.; Del Zotto, A. D.; Martinuzzi, P.; Rigo, P. Inorg. Chem.
1997, 36, 711. (b) Brothers, P. J . Prog. Inorg. Chem. 1981, 28, 1.
10.1021/om000371o CCC: $19.00 © 2000 American Chemical Society
Publication on Web 09/23/2000

Dihydrogen Complexes of Ruthenium
Organometallics, Vol. 19, No. 22, 2000 4507
Lau and co-workers5a reported dicationic dihydrogen
complexes of ruthenium bearing triazacyclononane,
trimethyltriazacyclononane, and hydrotris(pyrazolyl)-
borate as ancillary ligands. They found the dicationic
species to be more acidic than the monocationic hydro-
tris(pyrazolyl)borate and cyclopentadienyl counterparts.
A highly acidic and stable dicationic dihydrogen com-
plex, trans-[(dppe)2Ru(η2-H2)(CNH)]2+, was recently
reported by Morris et al.5b They found that this complex
was only stable with respect to the loss of protons or
H2 under strongly acidic conditions (excess triflic acid).
However, it should not be implied that the dicationic
dihydrogen complexes would be stronger acids than the
monocationic derivatives. Harman and Taube6 found the
dicationic osmium complex [Os(H2)(NH3)5]2+ to be a
weak acid that was stable toward moderately strong
bases such as NaOMe. Recently, Kubas and co-workers7
reported a highly electrophilic rhenium monocationic
species, [Re(CO)4(PR3)]+, that was found to bring about
activation of H2 heterolytically. Their aim was to
synthesize certain cationic systems that are extremely
electrophilic, containing mainly π-acceptor ligands that
enhance σ-donation from H2 to the metal at the cost of
back-donation, thus enhancing the tendency of H2 to
undergo heterolysis.
The coordination of molecular hydrogen to a metal
center has been achieved in the presence of a large
number of different coligands, e.g., phosphines, car-
bonyls, tris(pyrazolyl)borate, and mixed-ligand systems
such as cyclopentadienyl and carbonyl or phosphine and
phosphine and nitrogen or oxygen donors, etc. Amendola
et al.8 reported the synthesis of molecular hydrogen
complexes of the type [MH(η2-H2)P4]+ of the iron triad
containing monodentate phosphite ligands. Bianchini
and co-workers9,10 reported cationic rhodium and cobalt
complexes, [(PP)3Rh(H2)]+ and [(PP)3Co(H2)]+ ((PP)3 )
P(CH2CH2PPh2)3), respectively. Both of these species
were formulated as complexes having intact H-H
bonds. However, Heinekey et al.11 showed that in both
the complexes the H2 ligand was in fact oxidatively
added rather than being intact. As yet, there are no
reports in the literature on dicationic dihydrogen com-
plexes of transition metals where the ancillary ligands
are exclusively phosphorus-based ones.
moiety. In addition, we intend to build systems that are
capable of activating H2 in a heterolytic fashion. Since
phosphines and especially phosphites are good π-accep-
tors, one could achieve high electrophilicity on the metal
center by having such phosphorus ligands trans to the
η2-H2 ligand. In the current work, we have attempted
to employ certain phosphites, P(OMe)3 (cone angle θ )
107°), P(OEt)3 (θ ) 109°), and P(OiPr)3 (θ ) 130°), and
phosphines, PMe3 (θ ) 118°), PMe2Ph (θ ) 122°), PBu3
(θ ) 132°), PPh3 (θ ) 145°), and PCy3 (θ ) 170°),12 as
the trans ligands. However, it was found that the
starting hydride complexes trans-[(dppe)2Ru(H)(L)][BF4]
(L ) P(OMe)3, P(OEt)3, P(OiPr)3), in the presence of
HBF4‚Et2O, undergo substitution of an -OR group of
-
the phosphite ligand with F- (from the BF4 anion) to
provide a series of new hydride derivatives with a trans
fluorophosphite ligand of the type PF(OR)2. During the
preparation of this manuscript, Kubo et al.13 reported
the preparation of certain iron-fluorophosphorane com-
plexes. The fluorophosphorane moiety was formed via
a nucleophilic attack of F- toward a trivalent phospho-
rus atom that is coordinated to the metal center. It has
been reported earlier that a bound dihydrogen ligand
often lacks observable coupling to adjacent bound
phosphines.2c,d During this study we have observed
substantial coupling of the dihydrogen ligand with the
trans phosphorus which ranges from 49 to 51 Hz.14 The
trans phosphorus ligand in trans-[(dppe)2Ru(H)(L)][BF4]
(L ) PMe3, PMe2Ph, or P(OiPr)3) undergoes substitution
with molecular hydrogen to give trans-[(dppe)2Ru(H)-
(η2-H2)][BF4] in a reversible fashion under very mild
conditions.
Exp er im en ta l Section
Gen er a l P r oced u r es. All reactions were carried out under
N2 or Ar at room temperature using standard Schlenk15 and
inert-atmosphere techniques unless otherwise specified. Sol-
vents for the reactions that involved the synthesis of dihydro-
gen complexes were thoroughly saturated with either Ar or
H2 just before use.
1
The H and 31P NMR spectral data were obtained using an
AMX Bruker 400 MHz instrument. All shifts are reported on
the δ scale. The shift of the residual protons of the deuterated
solvent was used as an internal reference. Variable-temper-
ature proton T1 measurements were carried out at 400 MHz
using the inversion recovery method (180°-τ-90° pulse se-
quence at each temperature).16 The observed and the calcu-
The objective of this work is the synthesis of isostruc-
tural dihydrogen complexes of ruthenium consisting of
only phosphorus-based ligands of the type trans-
[(dppe)2Ru(η2-H2)(P)][BF4]2 (dppe ) Ph2PCH2CH2PPh2;
P ) phosphite, phosphine), to study how sensitive the
properties of the dihydrogen complexes would be to the
changes in the steric as well as the π-accepting abilities
of the phosphorus ligand that is trans to the dihydrogen
(12) Tolman, C. A. Chem. Rev. 1977, 77, 313.
(13) Kubo, K.; Bansho, K.; Nakazawa, H.; Miyoshi, K. Organo-
metallics 1999, 18, 4311.
(14) Previously reported H2-P couplings are as follows. (a) [(η2-
HD)(dppb)Ru(µ-Cl)3Ru(Cl)(dppb)], 2J (HHD,P) ) 7.5 Hz: J oshi, A. M.;
J ames, B. R. J . Chem. Soc., Chem. Commun. 1989, 1785. (b) [(PP)3Ru-
(H)(η2-HD)]+, 2J (HHD,P) ) 29.7 Hz: Bianchini, C.; Perez, P. J .;
Peruzzini, M.; Zanobini, F.; Vacca, A. Inorg. Chem. 1991, 30, 279. (c)
[(PP3Cy)Ru(H)(η2-HD)][BPh4], 2J (HHD,P) ) 32 Hz: J ia, G.; Drouin, S.
D.; J essop, P. G.; Lough, A. J .; Morris, R. H. Organometallics 1993,
12, 906. (d) [(triphos)Re(CO)2(η2-HD)]+, 2J (HHD,Ptrans) ) 12.7 Hz,
2J (HHD,Pcis) ) 2.3 Hz: Bianchini, C.; Marchi, A.; Marvelli, L.; Peruzzini,
M.; Romerosa, A.; Rossi, R.; Vacca, A. Organometallics 1995, 14, 3203.
(e) [(triphos)Ir(H)2(η2-H2)]+, average 2J (H2,P) ) 20 Hz observed at -120
°C: Bianchini, C.; Moneti, S.; Peruzzini, M.; Vizza, F. Inorg. Chem.
1997, 36, 5818. (f) Mathew, N.; J agirdar, B. R. Inorg. Chem., in
press.
(5) (a) Ng, S. M.; Fang, Y. Q.; Lau, C. P.; Wong, W. T.; J ia, G.
Organometallics 1998, 17, 2052. (b) Fong, T. P.; Forde, C. E.; Lough,
A. J .; Morris, R. H.; Rigo, P.; Rocchini, E.; Stephan, T. J . Chem. Soc.,
Dalton Trans. 1999, 4475.
(6) Harman, W. D.; Taube, H. J . Am. Chem. Soc. 1990, 112, 2261.
(7) Huhmann-Vincent, J .; Scott, B. L.; Kubas, G. J . J . Am. Chem.
Soc. 1998, 120, 6808.
(8) Amendola, P.; Antoniutti, S.; Albertin, G.; Bordignon, E. Inorg.
Chem. 1990, 29, 318.
(9) Bianchini, C.; Mealli, C.; Peruzzini, M.; Zanobini, F. J . Am.
Chem. Soc. 1987, 109, 5548.
(10) Bianchini, C.; Mealli, C.; Meli, A.; Peruzzini, M.; Zanobini, F.
J . Am. Chem. Soc. 1988, 110, 8725.
(11) (a) Heinekey, D. M.; Liegeois, A.; van Roon, M. J . Am. Chem.
Soc. 1994, 116, 8388. (b) Heinekey, D. M.; van Roon, M. J . Am. Chem.
Soc. 1996, 118, 12134.
(15) (a) Shriver, D. F.; Drezdon, M. A. The Manipulation of Air-
Sensitive Compounds, 2nd ed.; Wiley: New York, 1986. (b) Herzog,
S.; Dehnert, J .; Luhder, K. In Techniques of Inorganic Chemistry;
J ohnassen, H. B., Ed.; Interscience: New York, 1969; Vol. VII.
(16) Hamilton, D. G.; Crabtree, R. H. J . Am. Chem. Soc. 1988, 110,
4126.

4508 Organometallics, Vol. 19, No. 22, 2000
Mathew et al.
Ta ble 1. 1H NMR Sp ectr a l Da ta (δ) of tr a n s-[(d p p e)2Ru (H)(L)][BF 4] Com p lexes in CD2Cl2
L (compd no.)
δ(Ru-H)
J (H,Ptrans), Hz
J (H,Pcis), Hz
δ(CH2-CH2)
δ(L)
δ(Ph)
P(OMe)3 (1)
-9.27 (d qnt, 1H)
120
20.4
2.67 (m, 4H)
2.23 (m, 4H)
2.62 (m, 4H)
2.23 (m, 4H)
2.72 (m, 4H)
2.47 (m, 4H)
2.55 (m, 4H)
2.24 (m, 4H)
2.40 (m, 4H)
2.11 (m, 4H)
2.76 (d, 9H)
6.71-7.29 (m, 40H)
P(OEt)3 (2)
P(OiPr)3 (3)
PMe3 (4)
-9.63 (d qnt,1H)
-11.07 (d qnt, 1H)
-10.81 (d qnt, 1H)
-11.86 (d qnt, 1H)
120
120
60
20.4
22.4
20.7
21.6
2.99 (q, 6H)
0.73 (t, 9H)
4.13 (m, 3 H)
0.84 (d, 18H)
0.34 (d, 9H)
6.95-7.39 (m, 40H)
6.67-7.49 (m, 40H)
6.86-7.63 (m, 40H)
6.56-7.71 (m, 45H)
PMe2Ph (5)
64
0.58 (d, 6H)
Ta ble 2. 31P {1H} NMR Sp ectr a l Da ta (δ) of
P r ep a r a tion of tr a n s-[(d p p e)2Ru (H)(P Me3)][BF 4] (4).
This complex was prepared in the same manner as for complex
1, except that the workup procedure was carried out exclu-
sively under an atmosphere of H2. Upon workup, a cream-
colored product was obtained, which was crystallized from a
tr a n s-[(d p p e)2Ru (H)(L)][BF 4] Com p lexes in CD2Cl2
δ(P)
compd no.
L
dppe
J (P,P), Hz
1
2
3
4
5
133 (qnt, 1P)
61.89 (d, 4P)
61.25 (d, 4P)
59.99 (d, 4P)
60.11 (d, 4P)
58.63 (d, 4P)
32.2
32.4
32.4
21.4
17.5
CH2Cl2-Et2O mixture. Yield: 85%. Anal. Calcd for C55H58-
132.23 (qnt, 1P)
127.7 (qnt, 1P)
-37.75 (qnt, 1P)
-25.75 (qnt, 1P)
BF4P5Ru‚0.5CH2Cl2: C, 60.36; H, 5.38. Found: C, 60.53; H,
5.15. The NMR spectral data are summarized in Tables 1 and
2.
P r epar ation of tr a n s-[(dppe)2Ru (H)(P Me2P h )][BF4] (5).
This complex was also prepared using a procedure similar to
the one employed for the preparation of 4. A cream-colored
product resulted upon workup of the reaction mixture. Yield:
80%. Anal. Calcd for C60H60BF4P5Ru‚3CH2Cl2: C, 54.83; H,
4.82. Found: C, 55.32; H, 4.40. The NMR spectral data are
summarized in Tables 1 and 2.
lated T1 data for the complexes are summarized in Table 7.
All 31P NMR spectra were proton-decoupled, unless otherwise
stated. 31P NMR chemical shifts have been measured relative
to 85% H3PO4 in CD2Cl2. 19F NMR spectra were recorded with
respect to CFCl3 in CD2Cl2. Elemental analyses were carried
out at the National Chemical Laboratory, Pune, India. 1,2-
Bis(diphenylphosphino)ethane17 (dppe) and trans-[(dppe)2Ru-
(H)(η2-H2)][BF4]18 were prepared according to literature pro-
cedures.
P r ep a r a tion of tr a n s-[(d p p e)2Ru (H)(P (OMe)3)][BF 4]
(1). trans-[(dppe)2Ru(H)(η2-H2)][BF4] (0.25 g, 0.25 mmol) was
dissolved in 7 mL of CH2Cl2 under 1 atm of H2. Then P(OMe)3
(0.09 mL, 0.5 mmol) was added dropwise using a syringe over
a period of 1 min with stirring. The reaction mixture turned
color from bright orange to pale yellow soon after the addition
was over. This solution was stirred at room temperature
overnight under a hydrogen atmosphere, after which time it
was filtered through a Celite pad on a filter frit under an
atmosphere of nitrogen. The volume of the filtrate was reduced
to ca. 1 mL. Addition of excess diethyl ether caused the
precipitation of a colorless solid that was washed with diethyl
ether (10 × 5 mL) and dried in vacuo. Yield: 0.29 g, 81%. Anal.
Calcd for C55H58BF4RuP5‚CH2Cl2: C, 56.29; H, 5.06. Found:
C, 56.88; H, 5.41. The NMR spectral data are summarized in
Tables 1 and 2.
Attem p t To P r ep a r e tr a n s-[(d p p e)2Ru (H)(P Bu 3)][BF 4].
A procedure similar to that employed for the preparation of 1
was used for the synthesis of this complex. Upon workup of
the reaction mixture, a yellow powder resulted whose spec-
troscopic properties were similar to the compound of the
formula trans-[(dppe)2Ru(H)Cl] (6) reported earlier.19
Attem p ts To P r ep a r e tr a n s-[(d p p e)2Ru (H)(P P h 3)][BF 4]
a n d tr a n s-[(d p p e)2Ru (H)(P Cy3)][BF 4]. A 5 mm NMR tube
was charged with 20 mg (0.02 mmol) of trans-[(dppe)2Ru(H)-
(η2-H2)][BF4], which was dissolved in 0.7 mL of CD2Cl2 under
1 atm of argon. The tube was maintained under argon
pressure, using an inlet needle through a septum. Then 1 equiv
(0.02 mmol) of PPh3/PCy3 was added to the tube by briefly
removing the septum under argon pressure. The tube was then
1
capped and the H NMR spectrum recorded. No change from
the starting spectrum took place. The tube was then shaken
continuously, and at regular intervals of time, 1H NMR spectra
were recorded. Substitution of the dihydrogen ligand with the
phosphine did not take place even after 48 h at room temper-
ature.
P r ep a r a tion of tr a n s-[(d p p e)2Ru (H)(P (OEt)3)][BF 4] (2).
This complex was prepared using a procedure similar to the
one that was employed for 1. The yield of the colorless product
obtained was 82%. Anal. Calcd for C58H64BF4RuP5: C, 60.47;
H, 5.6. Found: C, 59.96; H, 5.72. The NMR spectral data are
summarized in Tables 1 and 2.
P r ep a r a tion of tr a n s-[(d p p e)2Ru (H)(P (OiP r )3)][BF 4]
(3). A procedure similar to the one that was used for 1 was
employed for the preparation of compound 3, except that after
the reaction mixture was stirred for a period of 30 min under
a hydrogen atmosphere, nitrogen was introduced and the
stirring was continued overnight. A cream-colored product was
obtained upon workup of the reaction mixture. Yield: 80%.
The product always contained certain impurities, and purifica-
tion procedures resulted in partial decomposition of the
product. Anal. Calcd for C61H70BF4RuP5‚CH2Cl2: C, 58.22; H,
5.67. Found: C, 59.28; H, 5.82. The NMR spectral data are
summarized in Tables 1 and 2.
P r oton a tion Rea ction of tr a n s-[(d p p e)2Ru (H)(L)][BF 4]
(L ) P (OEt)3). A 20 mg portion (0.017 mmol) of trans-
[(dppe)2Ru(H)(P(OEt)3)][BF4] was dissolved in 0.7 mL of
CD2Cl2 in a 5 mm NMR tube that was capped with a septum.
The resulting solution was subjected to three cycles of freeze-
pump-thaw degassing. One atmosphere of argon gas was then
introduced into the tube. Two equivalents (0.03 mmol) of 54%
HBF4‚Et2O was added to this solution and the 1H NMR
spectrum recorded. Thereafter, the concentration of the acid
added was increased in increments of 2 equiv each time. The
new hydride complex trans-[(dppe)2Ru(H)(L′)][BF4] (L′ )
PF(OEt)2) was observed soon after 2 equiv of the acid was
added. In the presence of excess acid, the dihydrogen complex
trans-[(dppe)2Ru(η2-H2)(L′)][BF4]2 was obtained. Complete con-
version of the hydride complex to the dihydrogen complex took
place after the addition of ca. 30 equiv of the acid.
P r ep a r a tion of tr a n s-[(d p p e)2Ru (H)(L′)][BF 4] (L′ )
P F (OMe)2 (7), P F (OEt)2 (8)). Similar procedures were em-
ployed for the preparation of both these complexes. As a
(17) Chatt, J .; Hart, F. A. J . Chem. Soc. 1960, 1378.
(18) Bautista, M. T.; Cappellani, E. P.; Drouin, S. D.; Morris, R. H.;
Schweitzer, C. T.; Sella, A.; Zubkowski, J . J . Am. Chem. Soc. 1991,
113, 4876.
(19) (a) Chatt, J .; Hayter, R. G. J . Chem. Soc. 1961, 2605. (b) Chin,
B.; Lough, A. J .; Morris, R. H.; Schweitzer, C. T.; D’Agostino, C. Inorg.
Chem. 1994, 33, 6278.

Dihydrogen Complexes of Ruthenium
Organometallics, Vol. 19, No. 22, 2000 4509
Ta ble 3. 1H NMR Sp ectr a l Da ta (δ) of tr a n s-[(d p p e)2Ru (H)(L′)][BF 4] Com p lexes in CD2Cl2
L′ (compd no.)
PF(OMe)2 (7)
δ(Ru-H)
J (H,Ptrans),Hz J (H,Pcis), Hz J (H,F), Hz
δ(CH2CH2)
δ(L′)
δ(Ph)
-8.3 (d sex, 1H)
136.0
136.0
132.0
20
24
2.63 (m, 4H) 2.79 (d, 6H)
2.25 (m, 4H)
2.62 (m, 4H) 3.17 (m, 4H)
2.25 (m, 4H) 0.54 (t, 6H)
2.66 (m, 4H) 4.02 (m, 2H)
2.30 (m, 4H) 0.78 (d, 12H)
6.66-7.22 (m, 40H)
PF(OEt)2 (8)
PF(OiPr)2 (9)
-8.24 (d sex, 1H)
-8.78 (d sex, 1H)
20.6
21.2
24
6.70-7.28 (m, 40H)
6.79-7.25 (m, 40H)
21.5
Ta ble 4. 31P {1H} a n d 19F NMR Sp ectr a l Da ta (δ) of tr a n s-[(d p p e)2Ru (H)(L′)][BF 4] Com p lexes in CD2Cl2
δ(P) δ(F)
compd no.
dppe
L′
J (P,P), Hz
BF4
L′
J (P,F), Hz
7
8
9
62.28 (d, 4P)
61.86 (d, 4P)
61.42 (d, 4P)
134.22 (d qnt, 1P)
134.75 (d qnt, 1P)
134.85 (d qnt, 1P)
32.9
32.4
32.2
-33.85 (s, 4F)
-33.97 (s, 4F)
-31.41 (s, 4F)
71.70 (d, 1F)
76.08 (d, 1F)
86.78 (d, 1F)
1158.2
1142
1140.3
Ta ble 5. 1H NMR Sp ectr a l Da ta (δ) of tr a n s-[(d p p e)2Ru (η2-H2)(L′)][BF 4]2 Com p lexes in CD2Cl2
L′ (compd no.)
PF(OMe)2 (10)a
δ(Ru(η2-H2))
J (H,Ptrans), Hz
δ(CH2CH2)
δ(L′)
δ(Ph)
-5.12 (d, 2H)
50.4
3.04 (m, 4H)
2.75 (m, 4H)
3.07 (m, 4H)
2.79 (m, 4H)
2.84 (m, 4H)
3.13 (m, 4H)
3.23 (d, 6H)
6.27-7.31 (m, 40H)
PF(OEt)2 (11)
PF(OiPr)2 (12)
-5.24 (d, 2H)
-5.63 (d, 2H)
50.9
49.5
3.64 (m, 4H)
0.76 (t, 6H)
4.41 (m, 2H)
0.94 (d, 12H)
6.7-7.74 (m, 40H)
6.78-7.45 (m, 40H)
a
From ref 14f.
Ta ble 6. 31P {1H} a n d 19F NMR Sp ectr a l Da ta (δ) of tr a n s-[(d p p e)2Ru (η2-H2)(L′)][BF 4]2 Com p lexes in CD2Cl2
δ(P) δ(F)
compd no.
L′
dppe
J (P,P), Hz
L′
J (P,F), Hz
BF4
10a
11
12
125.29 (d qnt, 1P)
124.94 (d qnt, 1P)
123.14 (d qnt, 1P)
48.56 (d, 4P)
48.04 (d, 4P)
47.54 (d, 4P)
43.3
42.8
42.4
73.97 (d, 1F)
79.36 (d, 1F)
91.24 (d, 1F)
1158.2
1148.4
1153.3
-29.67 (br s, 8F)
-28.91 (br s, 8F)
-27.17 (br s, 8F)
a
From ref 14f.
representative example, the preparation of trans-[(dppe)2Ru-
(H)(PF(OMe)2)][BF4] will be described here. trans-[(dppe)2Ru-
(H)(P(OMe)3)][BF4] (0.2 g, 1.8 mmol) was dissolved in CH2Cl2
(6 mL) under 1 atm of argon. To this solution was added 5
equiv (9 mmol) of 54% HBF4‚Et2O dropwise using a syringe.
The addition of HBF4‚Et2O led to a color change of the solution
from colorless to yellow. The reaction mixture was stirred for
a period of 4 h, after which time nitrogen was introduced. The
solution was stirred under these conditions overnight. The
yellow solution was then filtered through a Celite pad on a
filter frit, and the filtrate was concentrated to ca. 1 mL.
Addition of excess diethyl ether caused the precipitation of a
pale yellow solid that was washed several times with diethyl
ether to remove the excess HBF4‚Et2O, and the product was
dried in vacuo. The sample was crystallized from a CH2Cl2
solution via slow diffusion of Et2O at room temperature for
several days. Yield: 81%. Anal. Calcd for C54H55BF5O2P5Ru‚
0.5CH2Cl2 (7): C, 57.4; H, 4.95. Found: C, 57.63; H, 5.12. Calcd
P r ep a r a tion of tr a n s-[(d p p e)2Ru (η2-H2)(L′)][BF 4]2 (L′
) P F (OMe)2 (10), P F (OEt)2 (11), P F (OiP r )2 (12)). Similar
procedures were employed for the preparation of all of these
complexes. A 20 mg portion of trans-[(dppe)2Ru(H)(L′)][BF4]
was dissolved in 0.7 mL of CD2Cl2 in a 5 mm NMR tube
provided with a septum. It was then subjected to three freeze-
pump-thaw cycles, after which argon gas was introduced.
Then ca. 10 equiv of 54% HBF4‚Et2O was added. The dihy-
drogen complexes formed were characterized using NMR
spectroscopy. The NMR spectral data are summarized in
Tables 5 and 6.
The same reactions were carried out on a preparative scale
in order to attempt the isolation of the dihydrogen complexes.
As a representative example, the isolation of the PF(OEt)2
complex will be described. Upon addition of a large excess (ca.
40 equiv) of 54% HBF4‚Et2O to a solution of trans-[(dppe)2Ru-
(H)(PF(OEt)2)][BF4] (0.15 g, 0.13 mmol) in CH2Cl2 under 1 atm
of argon, a reddish orange solution resulted. The product was
allowed to crystallize from the reaction mixture by slow
diffusion of diethyl ether at room temperature over a period
of several days. Red crystals were obtained that were handled
under an atmosphere of argon and were found to be extremely
sensitive with respect to loss of H2.
for
C56H59BF5O2P5Ru‚0.5CH2Cl2 (8): C, 58.08; H, 5.18.
Found: C, 57.35; H, 4.80.
The NMR spectral data of these two derivatives are sum-
marized in Tables 3 and 4.
P r ep a r a tion of tr a n s-[(d p p e)2Ru (H)(P F (OiP r )2)][BF 4]
(9). To a solution of trans-[(dppe)2Ru(H)(η2-H2)][BF4] (0.2 g,
0.2 mmol) in CH2Cl2 (6 mL) under 1 atm of H2 were added
excesses of both 54% HBF4‚Et2O and P(OiPr)3. The reaction
mixture was then stirred under an atmosphere of H2 for a
period of 12 h, after which time nitrogen was introduced for
the workup procedure. trans-[(dppe)2Ru(H)(PF(OiPr)2)][BF4] (9)
was obtained as a cream-colored product in a yield of 82%,
Note: In the preparation of trans-[(dppe)2Ru(η2-H2)(PF-
(OiPr)2)][BF4]2, a very large excess of the protonating agent
was used.
P r ot on a t ion R ea ct ion s of tr a n s-[(d p p e)2R u (H)(L)]-
[BF 4] (L ) P Me3, P Me2P h , P (OiP r )3). A 5 mm NMR tube
was charged with 20 mg of trans-[(dppe)2Ru(H)(L)][BF4], which
was dissolved in 0.7 mL of CD2Cl2. The resulting solution was
subjected to three cycles of freeze-pump-thaw degassing. One
atmosphere of argon gas was then introduced into the tube.
About 1 equiv of 54% HBF4‚Et2O was added to this solution,
and the 1H NMR spectrum was recorded, which gave an
which was crystallized from
a CH2Cl2 solution via slow
diffusion of Et2O at room temperature over a period of several
days. Anal. Calcd for C58H63BF5O2P5Ru‚0.5CH2Cl2: C, 58.72;
H, 5.39. Found: C, 59.08; H, 5.99. The NMR spectral data of
this complex are given in Tables 3 and 4.

4510 Organometallics, Vol. 19, No. 22, 2000
Mathew et al.
Ta ble 8. Cr ysta llogr a p h ic Da ta for
tr a n s-[(d p p e)2Ru (H)(P (OMe)3)][BF 4] (1) a n d
tr a n s-[(d p p e)2Ru (H)(P F (OMe)2)][BF 4] (7)
Ta ble 7. Obser ved a n d Ca lcu la ted Sp in -La ttice
Rela xa tion Tim es (T1, m s; 400 MHz) of th e
Dih yd r ogen Liga n d in th e Com p lexes
tr a n s-[(d p p e)2Ru (η2-H2)(L′)][BF 4]2 (L′ ) P F (OMe)2
1
7
a
(10), P F (OEt)2 (11), P F (OiP r )2 (12)) in CD2Cl2
formula
fw
C
56H59BCl2F4O5P5Ru
C54.40H54BF5O2.40P5Ru
1107.91
monoclinic
P21/n (No. 14)
12.4134(1)
23.4229(1)
19.0126(3)
90
T1(10)b
T1(11)
T1(12)
1225.66
orthorhombic
Fdd2 (No. 43)
36.134(7)
52.258(14)
12.951(2)
90
cryst syst
space group
a, Å
T, K
obsd
calcd
obsd
calcd
obsd
calcd
305
302
298
283
268
253
243
233
223
213
203
19.19
18.61
17.60
17.03
17.89
19.05
21.36
24.53
30.88
42.13
18.86
18.52
18.12
17.20
17.35
18.95
21.20
24.89
30.75
39.97
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
18.04
17.32
16.6
18.04
18.76
20.92
24.53
28.86
36.07
18
18.33
17.75
16.74
18.47
19.05
21.36
24.10
30.30
35.35
18.31
17.44
17.25
17.98
19.17
21.15
24.27
29.08
36.43
17.12
16.94
17.68
18.88
20.88
24.04
28.91
36.39
90
90
106.384(1)
90
24455.8(89)
16
1.332
5303.58(10)
4
1.388
Z
D
calcd, g/cm3
T, K
λ, Å
298
130
0.710 73
0.530
0.710 73
0.505
µ, mm-1
a
b
Italicized data indicate T1 minima. From ref 14f.
Ra
Rw
0.0625
0.1592
0.0654
0.1416
a
indication of the formation of a hydride dihydrogen complex
(13).20 Upon further addition of HBF4‚Et2O in increments of 1
equiv each time, the 1H NMR spectrum indicated the presence
of another dihydrogen complex; the structure formulations of
these two species could not be established with certainty.
Formation of the dihydrogen complex trans-[(dppe)2Ru(η2-H2)-
(L)][BF4]2 (L ) PMe3, PMe2Ph, P(OiPr)3) was not observed.
Obser vation of th e H-D Isotopom er s of tr a n s-[(dppe)2-
Ru (η2-H2)(L′)][BF 4]2 (L′ ) P F (OMe)2 (14), P F (OEt)2 (15),
P F (OiP r )2 (16)). D2 gas was purged through a solution
containing a mixture of trans-[(dppe)2Ru(η2-H2)(L′)][BF4]2
(major) and trans-[(dppe)2Ru(H)(L′)][BF4]2 in CD2Cl2 in a 5 mm
NMR tube for ca. 10 min. The H-D isotopomer formed was
observed by 1H NMR spectroscopy. The J (H,D) values obtained
for the complexes 14-16 are respectively 29, 28, and 27 Hz.
X-r a y St r u ct u r e Det er m in a t ion of tr a n s-[(d p p e)2-
Ru (H)(P (OMe)3)][BF 4] (1) a n d tr a n s-[(d p p e)2Ru (H)(P F -
(OMe)2)][BF 4] (7). High-quality crystals of the complexes 1
and 7 were chosen after examination under an optical micro-
scope and coated with epoxy before mounting. X-ray diffraction
intensities were measured by ω scans using a Siemens three-
circle diffractometer attached to a CCD area detector and a
graphite monochromator for the Mo KR radiation (50 kV, 40
mA). The crystal of 7 was cooled to 130 K on the diffractometer
using a stream of cold nitrogen gas from a vertical nozzle, and
this temperature was maintained throughout the data collec-
tion. In the case of 1, the data collection was carried out at
room temperature. The unit cell parameters and the orienta-
tion matrix of the crystal were initially determined using ca.
60 reflections from 25 frames collected over a small ω scan of
7.5° sliced at 0.3° interval. A hemisphere of reciprocal space
was then collected using the SMART software21 with 2θ setting
of the detector at 28°. Data reduction was performed using
the SAINT program,21 and the orientation matrix along with
the detector and the cell parameters were refined for every
40 frames on all the measured reflections. The crystal data
parameters are listed in Table 8. An empirical absorption
correction based on symmetry-equivalent reflections was ap-
plied using the SADABS program,22 taking the merged reflec-
tion file obtained from SAINT as the input. The correct Laue
group of the crystal was chosen for the absorption correction.
The Rint values before and after the absorption corrections were
0.1312 and 0.0597 and 0.1143 and 0.1096 for the complexes 1
and 7, respectively.
a
2
R ) ∑(|Fo| - |Fc|)/∑|Fo|; Rw ) [∑w(|Fo| - |Fc|)2/∑w|Fo| ]1/2 (based
on reflections with I > 2σ(I)).
The phase problem was solved by the Patterson method,
and the non-hydrogen atoms were refined anisotropically, by
means of full-matrix least-squares procedures using the
SHELXTL program.23 Hydrogen atoms other than those on
ruthenium were fixed and were refined isotropically.
X-r a y Str u ctu r e Deter m in a tion of tr a n s-[(d p p e)2Ru -
(η2-H2)(P F (OEt)2)][BF 4]2 (11). We experienced certain dif-
ficulties in this case during data collection and analysis. The
main problem was that the crystals had cracks in them and
were found to be quite unstable with respect to decomposition.
Therefore, it was necessary to coat them with polyacrylate
adhesive before mounting. A small portion possibly devoid of
cracks was cut from a crystal and mounted on a glass fiber.
The data were collected at 130 K in order to bring down any
thermal disorder in the BF4- counterion. Although the hydro-
gen atoms could not be located, the presence of two BF4- anions
indicates that the complex is a dicationic dihydrogen complex.
Some residual density (peak, 2.172 e Å-3; hole, -1.282 e Å-3
)
near BF4- exists which could not be identified with certainty.
The crystal data parameters, atomic coordinates, bond dis-
tances and angles, anisotropic displacement parameters, and
hydrogen atom coordinates for this complex have been depos-
ited in the Supporting Information.
Resu lts a n d Discu ssion
Syn t h esis a n d Ch a r a ct er iza t ion of t h e New
Ru th en iu m Hyd r id e Com p lexes. The new ruthe-
nium hydride complexes trans-[(dppe)2Ru(H)(L)][BF4] (L
) P(OMe)3, P(OEt)3, P(OiPr)3, PMe3, PMe2Ph) were
prepared from trans-[(dppe)2Ru(H)(η2-H2)][BF4] by sub-
stituting the dihydrogen ligand with a phosphite or the
phosphine ligand, analogous to the preparation of trans-
[(dppe)2Os(H)(CH3CN)][BF4] reported by Schlaf et al.24
(eq 1). All the reactions provide the products in good
yields. The products are all colorless to pink solids. The
compounds have been purified by crystallization from
CH2Cl2-Et2O solutions in the presence of a small excess
of the appropriate phosphite or phosphine in the crys-
tallization solution. We have observed that the phos-
(20) 1H NMR spectral data (CD2Cl2) for (13): δ -10.26 (q, 1H, Ru-
H, J (H,Pcis) ) 18 Hz), -4.90 (br s, 2H, η2-H2), 2.32 (m, 4H, CH2CH2),
2.83 (m, 4H, CH2CH2), 6.46-7.77 (m, 40H, PPh2). (a) T1 (400 MHz,
CD2Cl2, 298 K): hydride, 310 ms; dihydrogen ligand, 27 ms. (b) T1-
(min) (240 K): dihydrogen ligand, 18.04 ms; J (H,D) ) 27 Hz.
(21) Siemens Analytical X-ray Instruments, Inc., Madison, WI, 1995.
(22) Sheldrick, G. M. SADABS User Guide; University of Go¨ttin-
gen: Go¨ttingen, Germany, 1993.
(23) SHELXTL (SGI version); Siemens Analytical X-ray Instru-
ments, Inc., Madison, WI, 1995.
(24) Schlaf, M.; Lough, A. J .; Maltby, P. A.; Morris, R. H. Organo-
metallics 1996, 15, 2270.

Dihydrogen Complexes of Ruthenium
Organometallics, Vol. 19, No. 22, 2000 4511
phite or the phosphine ligand in the hydride phosphite/
phosphine complex to be quite labile, and in the absence
of an excess phosphite or phosphine in the crystalliza-
tion mixture, the hydride complex undergoes loss of the
phosphorus ligand, yielding intractable products.
In the preparation of the triisopropyl phosphite hy-
dride complex we always obtained mixtures of trans-
[(dppe)2Ru(H)(P(OiPr)3)][BF4] and trans-[(dppe)2Ru(H)-
(PF(OiPr)2)][BF4] (mechanism of the formation of this
compound is elucidated in the later sections). When
appropriate reaction conditions are employed, either one
of the products can be obtained exclusively, as men-
tioned in the Experimental Section.
F igu r e 1. ORTEP view of the trans-[(dppe)2Ru(H)-
(P(OMe)3)]+ (1) cation at the 50% probability level.
phite ligand with molecular hydrogen under very mild
conditions (see the following sections). We were unable
to isolate the PBu3 hydride derivative. The phosphine
in this case is quite labile toward substitution. A
complex of the formula trans-[(dppe)2Ru(H)Cl] that has
been previously reported19 only was obtained in an
attempt to isolate the PBu3 hydride. The solvent CH2Cl2
is the source of the chloride in this case. However,
attempts to prepare the PPh3 and PCy3 hydride deriva-
tives failed and the starting hydride-dihydrogen com-
plex only was left behind. This is due to the greater
steric crowding (cone angles of 145 and 170°, respec-
tively) in the resulting complexes. Therefore, we sought
to examine the crystal structure of one of the hydride
complexes, trans-[(dppe)2Ru(H)(P(OMe)3)][BF4], in order
to obtain some insight regarding the cavity formed by
the sterically encumbered [(dppe)2Ru(H)]+ fragment
which eventually will help us in choosing the appropri-
ate ligands for the preparation of the dihydrogen
complexes with desired properties.
1
The H NMR spectra of the complexes show doublet
of quintets for the hydride ligand, confirming the
coupling of the hydride with trans phosphorus (phos-
phite or phosphine) and the cis phosphorus (dppe)
ligands. Whereas the trans coupling with the phospho-
rus has been found to be on the order of 120 Hz for the
complexes containing phosphite ligands, the J (H,Ptrans
)
values are considerably reduced, 60 and 64 Hz in the
cases of PMe3 and PMe2Ph hydride complexes, respec-
tively. Phosphites, in general, have been found to exhibit
larger couplings to other nuclei than phosphines in
metal complexes.25 This has been attributed to an
increase in the “s” character of the bonding orbitals in
phosphite complexes compared to that in phosphines.
On the other hand, the J (H,P) values for the cis
phosphorus atoms range from 20 to 22 Hz. The 31P{1H}
NMR spectra consist of only one doublet (J (P,P) ranging
from 17 to 32 Hz) for the dppe phosphorus nuclei,
indicating all four phosphorus nuclei to be equivalent
and split by the phosphite/phosphine ligand, and a
quintet corresponding to the phosphite or the phosphine
ligand coupled to the four dppe phosphorus nuclei.
We have found that the phosphorus ligand in the case
of trans-[(dppe)2Ru(H)(L)][BF4] (L ) PMe3, PMe2Ph,
P(OiPr)3, PBu3) (cone angles of 118, 122, 130, and 132°,
respectively), is relatively loosely bound in comparison
to the complexes where L ) P(OMe)3, P(OEt)3 (cone
angles of 107 and 109°, respectively). In fact, the trans-
[(dppe)2Ru(H)(L)][BF4] (L ) PMe3, PMe2Ph, P(OiPr)3)
complexes undergo substitution of the phosphine/phos-
Str u ctu r e of tr a n s-[(dppe)2Ru (H)(P (OMe)3)][BF4]
(1). The structure of the cation is shown in Figure 1. It
consists of a square pyramid defined by the four dppe
phosphorus atoms and the P(OMe)3 moiety with certain
deviations from an ideal square-pyramidal geometry. In
-
addition to a discrete BF4 counterion a molecule of
CH2Cl2 and two water molecules (this compound was
found to be stable toward air and moisture; therefore,
adequate precautions were not taken to exclude mois-
ture from the solvent, which could be the source of water
molecules) are also present. The hydride ligand that
completes the sixth coordination site on the ruthenium
center was not located; however, 1H NMR spectroscopy
provides evidence of its presence. The four phosphorus
atoms of the dppe ligand define a square plane with a
small mean deviation of 0.02°. The ruthenium atom is
slightly displaced from this plane by 0.241 Å and is
closer to the phosphite phosphorus atom. The dppe bite
angles P(1)-Ru(1)-P(2) and P(3)-Ru(1)-P(4) are
78.07(7) and 84.59(7)°, respectively. The Ru-P (of dppe)
bond distances vary between 2.351(2) and 2.381(2) Å,
and the Ru-P distance (of P(OMe)3) is 2.337(2) Å. The
(25) (a) Berger, S.; Braun, S.; Kalinowski, H.-O. NMR Spectroscopy
of the Non-Metallic Elements; Wiley: Chichester, U.K., 1996; pp 895-
981, and references therein. For comparative phosphite-X and phos-
phine-X couplings in transition metal complexes, see: (b) George, T.
A.; Sterner, C. D. Inorg. Chem. 1976, 15, 165. (c) Garrou, P. E.;
Hartwell, G. E. Inorg. Chem. 1976, 15, 646. (d) Tau, K. D.; Meek, D.
W. Inorg. Chem. 1979, 18, 3574. (e) Guesmi, S.; Taylor, N. J .; Dixneuf,
P. H.; Carty, A. J . Organometallics 1986, 5, 1964.

4512 Organometallics, Vol. 19, No. 22, 2000
Mathew et al.
Ta ble 9. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for tr a n s-[(d p p e)2Ru (H)(P (OMe)3)][BF 4] (1)
Ru(1)-P(5)
Ru(1)-P(4)
Ru(1)-P(3)
Ru(1)-P(2)
Ru(1)-P(1)
2.337(2)
2.351(2)
2.370(2)
2.374(2)
2.381(2)
P(5)-O(1)
P(5)-O(2)
P(5)-O(3)
O(1)-C(53)
O(2)-C(54)
O(3)-C(55)
1.577(7)
1.606(7)
1.629(8)
1.454(13)
1.416(10)
1.373(13)
P(5)-Ru(1)-P(4)
P(5)-Ru(1)-P(3)
P(4)-Ru(1)-P(3)
P(5)-Ru(1)-P(2)
P(4)-Ru(1)-P(2)
P(3)-Ru(1)-P(2)
P(5)-Ru(1)-P(1)
P(4)-Ru(1)-P(1)
97.50(7)
P(3)-Ru(1)-P(1)
P(2)-Ru(1)-P(1)
O(1)-P(5)-O(2)
O(1)-P(5)-O(3)
O(2)-P(5)-O(3)
O(1)-P(5)-Ru(1)
O(2)-P(5)-Ru(1)
O(3)-P(5)-Ru(1)
98.31(8)
78.07(7)
105.9(4)
102.0(4)
92.3(4)
114.7(3)
113.5(2)
125.1(3)
97.38(9)
84.59(7)
93.41(8)
96.55(7)
168.91(8)
95.37(9)
166.33(8)
phosphorus-oxygen bond distances of the phosphite
moiety fall in the range 1.577(7)-1.629(8) Å. The
phosphite ligand is not perfectly perpendicular to the
square plane defined by the four dppe phosphorus
atoms; it is somewhat tilted toward P(2). However, the
tilt is not really very appreciable. There are large
deviations from an idealized tetrahedral geometry
around the phosphite P atom. The selected bond lengths
and angles have been summarized in Table 9.
P r oton a tion Rea ction of th e Hyd r id e Com p lex
tr a n s-[(d p p e)2Ru (H)(L)][BF 4] (L ) P (OEt)3). The
protonation reaction of the hydride complex was carried
out in CD2Cl2 using excess HBF4‚Et2O under 1 atm of
F igu r e 2. Protonation reaction of trans-[(dppe)2Ru(H)-
(P(OEt)3)][BF4] (2) in CD2Cl2 showing the hydride region
of the 1H NMR spectrum. The number of equivalents of
HBF4‚Et2O added with respect to the starting hydride
complex is indicated on the left of each spectrum.
1
either dihydrogen or argon. The H NMR spectrum of
the hydride region showed two sets of signals consisting
of a doublet of sextets (that are further split; see text
later) and a broad doublet corresponding to a mixture
of two products in major amounts. In accordance with
the variable-temperature T1 relaxation times (400 MHz;
9 equiv of HBF4 added: see Table 7 for the T1 data),
the doublet of sextets has been assigned to a new
hydride complex (the T1 data for the PF(OR)2 hydrides
has been deposited in the Supporting Information),
whereas the broad doublet has been assigned to the
dihydrogen complex. A titration with an increasing
number of equivalents of HBF4‚Et2O was carried out.
Initially with 2 equiv of the acid, only the new hydride
(doublet of sextets centered at -8.24 ppm) was obtained
(Figure 2). However, a small amount of the dihydrogen
complex (a broad doublet centered at -5.20 ppm) begins
to emerge with an increase in the concentration of the
acid. In the presence of a large excess of HBF4‚Et2O,
the major product is the dihydrogen complex. Another
new overlapping doublet of quintets centered at -9.39
ppm that is further split (J ) 68.1 Hz) arises upon
addition of 2 equiv of the acid to the starting hydride
complex. The concentration of this species is small.
From the coupling constants it is clear that a phosphine
P atom is trans to the hydride, indicating an isomerized
hydride derivative in the presence of 2 equiv of the acid.
The origin of the isomerization reaction is not clear. This
hydride complex upon protonation gives rise to the
corresponding minor isomer of the dihydrogen complex
(-6.0 ppm, br d).
ppm) that is further split. The separation between these
1
two sextets corresponds to 136 Hz. The H{31P} NMR
spectrum gave a doublet centered at -8.24 ppm. A
doublet of quintets centered at 134.75 ppm was obtained
in the 31P{1H} NMR spectrum corresponding to the
phosphite phosphorus, in addition to the doublet cen-
tered at 61.86 ppm for the dppe phosphorus. The
separation between the two quintets is equal to 1142
Hz. We found that J (P,F) falls in the range of 900-1300
Hz for compounds having a direct P-F bond.26 The new
hydride complex, thus, can be formulated as having a
fluoride on the phosphite: that is, trans-[(dppe)2Ru(H)-
(L′)][BF4], where L′ ) PF(OEt)2. This formulation
seemed quite reasonable, and the coupling constants are
2
as follows: 2J (H,Ptrans) ) 136 Hz, J (H,Pcis) ) 20 Hz,
3
1J (P,F) ) 1142 Hz, and J (H,F) ) 24 Hz. Using an NMR
simulation program,27 the hydride region was simu-
lated, which matched the observed spectrum. The
coupling of the hydride with the fluorine is shown in
Figure 3. To prove this structure formulation, we sought
to obtain the X-ray crystal structure of one of these
complexes. And indeed, X-ray crystallography revealed
without any ambiguity that the new hydride com-
plex was trans-[(dppe)2Ru(H)(L′)][BF4], where L′ )
PF(OMe)2.
The protonation reaction of trans-[(dppe)2Ru(H)-
(P(OEt)3)][BF4] was carried out on a preparative scale
with 2 equiv of HBF4‚Et2O, and the major new hydride
complex was isolated as pale yellow crystals. The 1H
NMR spectrum of this species showed a doublet of
sextets pattern in the hydride region (centered at -8.24
(26) (a) Mathieu, R.; Poilblanc, R. Inorg. Chem. 1972, 11, 1858. (b)
Meakin, P.; Muetterties, E. L.; J esson, J . P. J . Am. Chem. Soc. 1972,
94, 5271. (c) Nixon, J . F. Adv. Inorg. Chem. Radiochem. 1970, 13, 363.
(d) Bystrov, V. F.; Neimysheva, A. A.; Stepanyants, A. U.; Knunyants,
I. L. Dokl. Akad. Nauk SSSR 1964, 156, 637; Chem. Abstr. 1964, 61,
6548c.
(27) Bruker WIN-DAISY 4.05 version.

Dihydrogen Complexes of Ruthenium
Organometallics, Vol. 19, No. 22, 2000 4513
Sch em e 1
Ta ble 10. Com p a r ison of th e Con e An gles (d eg) of
th e Tr a n s P h osp h or u s Liga n d s
ligand
cone angle (θ)a
ligand
cone angle (θ)b
PF3
104
107
109
118
122
130
132
145
170
P(OMe)3
P(OEt)3
PMe3
PMe2Ph
P(OiPr)3
PBu3
PF(OMe)2
PF(OEt)2
106
107
PF(OiPr)2
121
PPh3
PCy3
a
Entries in these columns have been taken from ref 12.
Entries in these columns have been computed.31
b
PF(OR)2 compounds have been prepared earlier28 by
treating PCl(OR)2 with a fluorinating agent such as
SbF3. Recently, Pregosin and co-workers29 found that
the P-C bond undergoes cleavage that is HBF4 induced
in certain chiral ruthenium MeO-Biphep (MeO-
Biphep ) 6,6′-dimethoxybiphenyl-2,2′-diylbis(diarylphos-
phine)) complexes. The P-C bond breaking process has
been shown to involve a monofluorophosphine interme-
diate possessing a P-F bond, the source of the fluoride
being BF4 anion. It has been earlier reported30 that
-
the transition-metal complex LnMX (X ) halide) reacts
with trialkyl phosphite, P(OR)3, resulting in the cationic
phosphite intermediate [LnM(P(OR)3)]X. The halide X-
then readily attacks an R-carbon atom in the OR group
of the phosphite to give the phosphonate complex [LnM-
(P(O)(OR)2)] and RX in an Arbuzov-like dealkylation
reaction. This has been observed by Kubo et al.13 in the
reaction of their iron phosphite complex with F-,
wherein the F- attacks the methyl carbon of the
phosphite ligand and not the phosphorus atom, result-
ing in a phosphonate complex. No phosphonate deriva-
tive has been obtained in our case.
The cone angles θ for the resulting fluorophosphite
ligands can be easily computed using the θ value of PF3,
which is 104° as a base value.31 These angles have been
summarized in Table 10.
Str u ctu r e of tr a n s-[(d p p e)2Ru (H)(P F (OMe)2)]-
[BF 4] (7). An ORTEP diagram of the [(dppe)2Ru(H)(PF-
(OMe)2)] cation is shown in Figure 4. The molecular
structure consists of discrete [(dppe)2Ru(H)(PF(OMe)2)]+
and the [BF4]- counterion together with one molecule
of CH3OH. The [BF4]- counterion as well as CH3OH are
1
F igu r e 3. (a) H NMR spectrum of the hydride region of
trans-[(dppe)2Ru(H)(PF(OEt)2)][BF4] (8) in CD2Cl2. (b)
1H{31P} NMR spectrum showing J (H,F).
A mechanism involving the reduction of the cone
angle of the trans phosphorus ligand induced by the
reaction with HBF4‚Et2O seems reasonable. During the
reaction, the -OR group on the phosphite phosphorus
is likely to get protonated followed by the elimination
-
of ROH. Consequently, one of the BF4 counterions
provides the F- for the phosphite (Scheme 1).
We have carried out a reaction of trans-[(dppe)2Ru-
(H)(L)][BF4], L ) P(OR)3 with 1 equiv of DBF4‚Et2O
under an atmosphere of Ar in CD2Cl2 in a 5 mm NMR
tube. One could expect either isotope scrambling in the
hydride complex to yield a deuteride derivative or the
formation of ROD. We have not been able to observe
either of these species using NMR spectroscopy. How-
ever, X-ray crystallographic studies of trans-[(dppe)2Ru-
(H)(PF(OMe)2)][BF4] revealed a molecule of MeOH (see
description of the structure). A blank experiment was
also carried out by the addition of HBF4‚Et2O to a
solution of P(OR)3 in CH2Cl2, and then 19F NMR was
recorded. A small amount of the substituted product
PF(OR)2 was obtained, as indicated in the 19F NMR
spectrum.
(28) Soborovskii, L. Z.; Gololobov, Yu. G. Zh. Obshch. Khim. 1964,
34, 1141; Chem. Abstr. 1964, 61, 1747a.
(29) den Reijer, C. J .; Ru¨egger, H.; Pregosin, P. S. Organometallics
1998, 17, 5213.
(30) (a) Brill, T. B.; Landon, S. J . Chem. Rev. 1984, 84, 577 and
references therein. (b) Nakazawa, H.; Fujita, T.; Kubo, K.; Miyoshi,
K. J . Organomet. Chem. 1994, 473, 243.
(31) θ(PF(OR)2) ) 1/3[θ(PF3)] + 2/3[θ(P(OR)3)].12

4514 Organometallics, Vol. 19, No. 22, 2000
Mathew et al.
dihydrogen complexes trans-[(dppe)2Ru(η2-H2)(L′)][BF4]2
(L′ ) PF(OR)2) were obtained upon further addition of
HBF4‚Et2O to the new hydride complexes trans-[(dppe)2-
Ru(H)(L′)][BF4]. Protonation was complete upon addi-
1
tion of ca. 30 equiv of the acid. The H NMR spectrum
of the dihydrogen complex shows a broad doublet in the
hydride region corresponding to the coupling of the
dihydrogen with the trans phosphorus (2J (H,Ptrans) )
49-51 Hz). This has been proved beyond doubt by
carrying out selective decoupling experiments in both
1H and 31P NMR spectroscopy.14f Such a large coupling
of dihydrogen ligand with a heteronucleus is unprec-
edented, although coupling constants on the order of 32
Hz or less have been reported earlier.14a-e Since the line
broadening of the dihydrogen ligand is more than the
3J (H,F) value, coupling with the fluorine of the phos-
phite was not observed. The dihydrogen complex has
been isolated in the case of L′ ) PF(OEt)2, and the X-ray
crystal structure has been determined.
Str u ctu r e of tr a n s-[(d p p e)2Ru (η2-H2)(P F (OEt)2)]-
[BF 4]2 (11). Due to the difficulties experienced during
both data collection as well as analysis as described in
the Experimental Section, it was not possible to solve
the structure of 11 satisfactorily. However, the presence
of two BF4- counterions indicates the dicationic nature
of this species. Evidence for the existence of a dihydro-
gen ligand with an intact H-H bond was obtained from
NMR spectroscopy. The important parameter that is
useful in the context of the coupling of the dihydrogen
ligand with the trans phosphorus ligand is the Ru-P
(of phosphite) bond distance in this complex. The Ru-P
(of phosphite) bond length was found to be 2.173(4) Å,
which is much shorter than that in the P(OMe)3 hydride
complex (2.337(2) Å) and the hydride PF(OMe)2 deriva-
tive (2.263(2) Å).
F igu r e 4. ORTEP view of the trans-[(dppe)2Ru(H)(PF-
(OMe)2)]+ (7) cation at the 50% probability level.
Ta ble 11. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for tr a n s-[(d p p e)2Ru (H)(P F (OMe)2)][BF 4] (7)
Ru(1)-P(5)
Ru(1)-P(2)
Ru(1)-P(4)
Ru(1)-P(1)
Ru(1)-P(3)
2.264(2)
2.341(2)
2.364(2)
2.367(2)
2.388(2)
P(5)-O(2)
P(5)-O(1)
P(5)-F(5)
O(2)-C(54)
O(1)-C(53)
1.567(6)
1.568(6)
1.595(5)
1.438(9)
1.439(9)
P(5)-Ru(1)-P(2)
P(5)-Ru(1)-P(4)
P(2)-Ru(1)-P(4)
P(5)-Ru(1)-P(1)
P(2)-Ru(1)-P(1)
P(4)-Ru(1)-P(1)
P(5)-Ru(1)-P(3)
P(2)-Ru(1)-P(3)
97.05(8)
90.40(8)
97.55(8)
93.80(8)
84.30(8)
175.18(8)
98.41(8)
164.14(8)
P(4)-Ru(1)-P(3)
P(1)-Ru(1)-P(3)
O(2)-P(5)-O(1)
O(2)-P(5)-F(5)
O(1)-P(5)-F(5)
O(2)-P(5)-Ru(1)
O(1)-P(5)-Ru(1)
F(5)-P(5)-Ru(1)
78.87(8)
98.15(8)
106.1(3)
99.3(3)
99.7(3)
115.7(2)
116.5(2)
117.1(2)
not shown in the figure. The hydride hydrogen could
not be located. The cation can be described as a distorted
octahedron. The four phosphorus atoms of the dppe
ligand deviate from a square plane with a mean devia-
tion of 0.12°. P(1) and P(4) are below this square plane
and are relatively closer to the PF(OMe)2 phosphorus
atom, whereas P(2) and P(3) are above the plane and
pushed away slightly from the phosphite phosphorus
atom. The ruthenium atom sits approximately in the
center of the square plane and is displaced by 0.203 Å
toward the PF(OMe)2 moiety. The Ru-P (of dppe) bond
distances fall in the range 2.341(2)-2.388(2) Å. The
dppe bite angles P(1)-Ru(1)-P(2) and P(3)-Ru(1)-P(4)
are respectively 84.30(8) and 78.87(8)°. The significant
feature is the tightening of the fluorophosphite P(5)-
Ru(1) bond, which is 2.264(2) Å relative to the Ru(1)-P
(of dppe) bond distances. This distance is also shorter
compared to the Ru-P (of P(OMe)3) distance of 2.337(2)
Å in the case of trans-[(dppe)2Ru(H)(P(OMe)3)][BF4].
This reduction of the bond distance reflects a combined
effect of the decrease in the steric crowding: that is,
the reduction of the cone angle as well as the better
π-accepting nature of the PF(OMe)2 ligand. Appreciable
reduction in the P-O bond distances has also been
observed. The P-F bond distance has been found to be
1.595(5) Å. Pertinent bond distances and the angles are
collected in Table 11.
P r oton a tion Rea ction s of th e Hyd r id e Com -
p lexes tr a n s-[(d p p e)2Ru (H)(L)][BF 4] (L ) P Me3,
P Me2P h , P (OiP r )3). The protonation reactions of these
complexes have been carried out exclusively under an
atmosphere of Ar in a similar manner as in the cases of
the trimethyl phosphite and triethyl phosphite hydrides.
Upon protonation with HBF4‚Et2O, a hydride dihydro-
gen complex whose formulation is unclear resulted in
each case. NMR spectroscopy of this species evidenced
the absence of the trans phosphorus ligand originally
present in the starting hydride complex. This species
is moderately stable and can be observed in the presence
of a slight excess of acid. We have found the hydride
dihydrogen complex that finally results has spectro-
scopic properties which are different from another
hydride dihydrogen complex, trans-[(dppe)2Ru(H)(η2-
H2)][BF4], reported earlier.18 Currently, we are attempt-
ing to decipher the nature of this complex.
Attempts to prepare trans-[(dppe)2Ru(H)(PBu3)]-
[BF4] from trans-[(dppe)2Ru(H)(η2-H2)][BF4] and PBu3
in CH2Cl2 provided the previously reported trans-
[(dppe)2Ru(H)Cl].19 The reaction pathway leading to the
chloride complex is unclear at this time; however, it
perhaps goes through an intermediate phosphine com-
plex that is highly sterically congested. The phosphine
complex and the 5-coordinate species [(dppe)2Ru(H)] are
at equilibrium that is shifted far to the side of the
5-coordinate complex at room temperature. As a result
P r oton a tion Rea ction s of tr a n s-[(d p p e)2Ru (H)-
(L′)][BF 4] (L′ ) P F (OMe)2, P F (OEt)2, P F (OiP r )2). The

Dihydrogen Complexes of Ruthenium
Organometallics, Vol. 19, No. 22, 2000 4515
of the instability of this 17-electron complex (5-coordi-
nate species), it abstracts a chloride from the solvent,
CH2Cl2.
La bilities of th e P h osp h or u s Liga n d s in tr a n s-
[(dppe)2Ru (H)(L)][BF4](L )P Me3,P Me2P h ,P (OiP r )3).
The trans phosphorus ligands in trans-[(dppe)2Ru(H)-
(L)][BF4] (L ) PMe3, PMe2Ph, P(OiPr)3) were found to
be quite labile with respect to substitution. When these
hydride complexes were dissolved in solvents that were
presaturated with H2, the phosphorus ligand underwent
substitution with H2 in a facile manner at room tem-
perature to yield trans-[(dppe)2Ru(H)(η2-H2)][BF4], re-
ported by Morris and co-workers.18 This reaction was
found to be reversible, as shown in eq 2. Currently we
are studying the kinetics of this reaction and its scope
in catalysis.
F igu r e 5. (a) 1H NMR spectrum (hydride region) of trans-
[(dppe)2Ru(η2-HD)(PF(OiPr)2)][BF4]2 (400 MHz, 298 K) in
CD2Cl2. (b) Spectrum where the resonance due to the η2-
H2 ligand has been nullified.
occurs due to a combination of the lability and the
acidity of the H2 ligand. The η2-HD isotopomers of trans-
[(dppe)2Ru(η2-H2)(L′)][BF4]2 (L′ ) PF(OMe)2, PF(OEt)2,
PF(OiPr)2) have been obtained by purging CD2Cl2 solu-
tions containing the dihydrogen complex with D2 gas
for ca. 5-10 min at a steady rate. The η2-HD ligand has
1H NMR T1 Mea su r em en ts. The variable-temper-
ature spin-lattice relaxation times (T1) for the η2-H2
and the hydride hydrogen signals were determined.
Table 7 lists the measured and calculated T1 values for
the dihydrogen ligand as a function of temperature.32
The T1 minima (400 MHz) for trans-[(dppe)2Ru(η2-H2)-
(L′)][BF4]2 (L′ ) PF(OMe)2, PF(OEt)2, PF(OiPr)2) are
respectively 16.6 ms at 268 K, 16.74 ms at 268 K, and
17.03 ms at 283 K. These values have been obtained
directly from the experiments and also by fitting the
equations that describe the dominant dipolar relaxation
mechanism to the variable-temperature T1 data as
described earlier.33 The H-H distances can be calcu-
lated from the T1 minima values after appropriate
corrections34 have been made for the relaxation contri-
butions from other nuclei in the vicinity. Thus, the H-H
distances are 1.08 and 0.86 Å, 1.08 and 0.86 Å, and 1.09
and 0.87 Å, respectively, for slow and fast rotation
regimes for trans-[(dppe)2Ru(η2-H2)(L′)][BF4]2 complexes
(L′ ) PF(OMe)2, PF(OEt)2, PF(OiPr)2).
1
been observed in the H NMR spectrum without nul-
lifying the η2-H2 signal in the cases of PF(OMe)2 and
PF(OEt)2 complexes and in the case of PF(OiPr)2 deriva-
tive by nullifying the residual signal of the η2-H2 species
by an inversion recovery pulse sequence using the
relationship T1 ) τnull/ln 2 and the known T1 value of
the dihydrogen complex at room temperature.33,36,37 The
η2-HD isotopomer shows a doublet of triplets pattern:
the doublet is due to the coupling of H with trans
phosphorus, and triplets (1:1:1) arise from the coupling
of the proton with deuterium. Figure 5 displays this
pattern in the case of trans-[(dppe)2Ru(η2-HD)(PF-
(OiPr)2)][BF4]2. There is an overlap of signals, as a result
of which all of the six lines are not well-resolved. The
H-H distances have been calculated from these cou-
pling constants using an empirical equation derived
from a database of J (H,D) and H-H distances for
dihydrogen complexes as reported earlier.2d,38,39 The
J (H,D) values for trans-[(dppe)2Ru(η2-HD)(L′)][BF4]2 (L′
) PF(OMe)2, PF(OEt)2, PF(OiPr)2) are respectively 29,
28, and 27 Hz, and the corresponding H-H distances
calculated from these coupling constants are 0.94, 0.95,
and 0.97 Å.
H-D Isotop om er s. The partial incorporation of
deuterium into an H2 ligand of dihydrogen complexes
has been achieved by exposing the complex to deuterium
gas. Albeniz et al.35 proposed that isotopic scrambling
Com m en ts on H,D Cou p lin g Con sta n ts a n d H-H
Dista n ces. Craw et al.40 carried out a quantum chemi-
(32) Temperature-dependent correlation time τ ) τ0eE /RT. Param-
a
eters used for the calculated T1 values: (a) trans-[(dppe)2Ru(η2-H2)-
(PF(OMe)2)][BF4]2 (9), τ0 ) 1.78 × 10-11 s; Ea ) 2.41 kcal mol-1; (b)
trans-[(dppe)2Ru(η2-H2)(PF(OEt)2)][BF4]2 (10), τ0 ) 1.88 × 10-11 s; Ea
) 2.38 kcal mol-1; (c) trans-[(dppe)2Ru(η2-H2)(PF(OiPr)2)][BF4]2 (11),
(36) Chin, B.; Lough, A. J .; Morris, R. H.; Schweitzer, C. T.;
D’Agostino, C. Inorg. Chem. 1994, 33, 6278.
(37) Chinn, M. S.; Heinekey, D. M.; Payne, N. G.; Sofield, C. D.
Organometallics 1989, 8, 1824.
(38) Maltby, P. A.; Schlaf, M.; Steinbeck, M.; Lough, A. J .; Morris,
R. H.; Klooster, W. T.; Koetzle, T. F.; Srivastava, R. C. J . Am. Chem.
Soc. 1996, 118, 5396.
(39) dHH ) -0.0167[J (H,D)] + 1.42.
(40) Craw, J . S.; Bacskay, G. B.; Hush, N. S. J . Am. Chem. Soc. 1994,
116, 5937.
τ0 ) 7.40 × 10-12 s; Ea ) 2.94 kcal mol-1
.
(33) Bautista, M. T.; Earl, K. A.; Maltby, P. A.; Morris, R. H.;
Schweitzer, C. T.; Sella, A. J . Am. Chem. Soc. 1988, 110, 7031.
(34) Desrosiers, P. J .; Cai, L.; Lin, Z.; Richards, R.; Halpern, J . J .
Am. Chem. Soc. 1991, 113, 4173.
(35) Albeniz, A. C.; Heinekey, D. M.; Crabtree, R. H. Inorg. Chem.
1991, 30, 3632.

4516 Organometallics, Vol. 19, No. 22, 2000
Mathew et al.
cal study on a series of osmium dihydrogen complexes
and brought out a qualitative model in which a linear
correlation between the observed J (H,D) coupling con-
stants and the effective spectrochemical parameter
f*(Lz)41,42 was established. One perhaps could extend
this model qualitatively to ruthenium derivatives as
well to find the correlation. They found that in an
idealized octahedral environment, a large ligand field
parameter f *(Lz) brings about a large splitting ∆(Lz) of
the osmium t2g(π) and eg*(σ) levels. The stabilization of
the t2g orbitals reduces the π-donor ability of the metal.
As a consequence, back-bonding into the σ* orbital of
the η2-H2 ligand gets reduced, resulting in a shorter
H-H bond or a larger J (H,D) coupling constant. There-
fore, the J (H,D) coupling constant can be expected to
be large for stronger field ligands such as halophos-
phites (f *(Lz) > 2) compared to the phosphites (f *(Lz)
= 2) or phosphines (f *(Lz) = 1.25).43 Although we do
not have the data for a direct comparison of the J (H,D)
coupling constants in these three kinds of derivatives,
we can expect the trend to be in the order PF(OR)2 >
P(OR)3 > PR3, corresponding to a decrease in the
π-acidity44 and to increasing steric bulk45 of the trans
phosphorus ligand in that order. The suggested correla-
tion by Craw et al.40 that a dihydrogen complex with a
ligand that has a large spectrochemical constant would
be quite unstable does not seem to be in accord with
our observation in the case of the complexes reported
here. Our dihydrogen complexes are quite stable at room
temperature.
using the slow- and the fast-spinning approximations
of H2. In the case of a family of complexes of the type
[(PP)2Ru(H)(H2)]+ reported by Morris and co-work-
ers18,33 the H-H distances obtained from the H-D
coupling constants are consistent with the fast-spinning
result calculated from the T1(min) data. Our complexes
differ from those of Morris’ in this aspect. Morris and
Wittebort48 suggested that the H-H distances calcu-
lated from J (H,D) that fall between those derived from
the T1(min) data indicates that librational motion
significantly influences the relaxation process. There are
many examples reported in the literature where such a
situation has been observed.48
One exciting challenge would be to attempt the
synthesis of a complex having PF3 trans to the dihy-
drogen ligand and study its properties. In addition, it
would be interesting to compare the properties of such
a complex with those of trans-[(dppp)2Ru(η2-H2)(CO)]2+ 4a
.
Efforts toward this goal are in progress in our labora-
tories.
Con clu sion s
The protonation reactions of the hydride complexes
of the type trans-[(dppe)2Ru(H)(L)][BF4] (L ) P(OR)3)
with HBF4‚Et2O result in new hydride derivatives,
trans-[(dppe)2Ru(H)(L′)][BF4] (L′ ) PF(OR)2). The driv-
ing force for such reactivity seems to be the cone angle
reduction induced by the reaction of HBF4‚Et2O, thereby
minimizing the steric crowding around the ruthenium
center. Protonation of these hydride derivatives gives
the corresponding dihydrogen complexes. Substantial
coupling of the dihydrogen with the trans phosphorus
moiety on the order of 49-51 Hz has been observed.
This could be due to the bond shrinkage of the Ru-P
(of the trans phosphorus ligand) bond that in turn brings
the trans phosphorus ligand in greater proximity to the
dihydrogen moiety, as evidenced by X-ray crystal-
lographic studies. The Ru-P (of the trans phosphite
ligand) distances successively decrease from the hydride
P(OMe)3 complex (2.337(2) Å) to the hydride PF(OMe)2
derivative (2.264(2) Å) to the PF(OEt)2 dihydrogen
complex (2.167(4) Å).
Morris and co-workers earlier found that their com-
plexes trans-[(dppe)2Fe(η2-H2)(CN)][OTf]2 and trans-
46
[(dppe)2Ru(η2-H2)(CNH)][OTf]25b were quite stable with
respect to loss of H2. This was unexpected on the basis
of the report by Craw et al.40 They explained this
behavior as an increase in Lewis acidity of the metal
centers and a σ-donation from η2-H2 to the metal rather
than π-back-bonding from the metal to the antibonding
orbital of H2. These complexes are most relevant to the
current work because of the similarities in behavior of
our derivatives with those of Morris’ with respect to loss
of H2 and the H-H distances determined by NMR
methods.
An additional point to discuss here is the H-H
distance derived from the T1(min) data. The complexes
described here show distances of 1.08 and 0.86 or 0.87
Å for the slow- and the fast-spinning regimes, respec-
tively, for H-H. Gusev et al.47 reported a correlation of
the H-H distances calculated from J (H,D) and T1(min)
and ∆Gq for the loss of H2 ligand from the metal center.
The H-H distances obtained from J (H,D) in our com-
plexes are on the order of 0.94-0.97 Å. These distances
are intermediate between 1.08 and 0.86 Å, obtained
The lability of the phosphorus ligand in the cases of
trans-[(dppe)2Ru(H)(L)][BF4] (L ) phosphine, P(OiPr)3)
has been exploited to carry out reversible binding of H2
via substitution of the phosphorus ligand under very
mild conditions. In addition, this lability opens the
possibility of catalytic activity for these derivatives,
which is under study in our laboratories. From this
study it can be concluded that the properties of the
dihydrogen complexes bearing only phosphorus co-
ligands can be fine-tuned by an interplay of the cone
angles (steric crowding around the metal center) and
the π-accepting ability of the trans phosphorus ligands.
(41) Gerloch, M.; Slade, R. C. Ligand Field Parameters; Cambridge
University Press: Cambridge, U.K., 1973.
(42) Lever, A. B. P. Inorganic Spectroscopy; Elsevier: Amsterdam,
1984.
(43) J ørgensen, C. K. Modern Aspects of Ligand Field Theory; North-
Holland: Amsterdam, 1971.
(44) (a) Cotton, F. A.; Kraihanzel, C. S. J . Am. Chem. Soc. 1962,
84, 4432. (b) Huheey, J . E. Inorganic Chemistry, 3rd ed.; Harper and
Row: New York, 1983; pp 384, 436. (c) J ones, C. E.; Coskran, K. J .
Inorg. Chem. 1971, 10, 55.
(45) Tolman, C. A. J . Am. Chem. Soc. 1970, 92, 2956.
(46) Forde, C. E.; Landau, S. E.; Morris, R. H. J . Chem. Soc., Dalton
Trans. 1997, 1663.
Ackn owledgm en t. Financial support from the Coun-
cil of Scientific and Industrial Research of India is
gratefully acknowledged. We thank Mr. Chandrashek-
har, Sophisticated Instruments Facility, Indian Insti-
tute of Science, for the NMR spectral data and Dr.
Amitabha Sarkar, NCL, Pune, India, for elemental
(47) Gusev, D. G.; Kuhlman, R. L.; Renkema, K. B.; Eisenstein, O.;
Caulton, K. G. Inorg. Chem. 1996, 35, 6775.
(48) Morris, R. H.; Wittebort, R. J . Magn. Reson. Chem. 1997, 35,
243 and references therein.

Dihydrogen Complexes of Ruthenium
Organometallics, Vol. 19, No. 22, 2000 4517
ature spin-lattice relaxation times of the hydride ligand in
7, a figure showing the observed and simulated 1H NMR
spectra of the hydride region of 8, an ORTEP diagram of 11,
and a figure showing the T1 (400 MHz) plot for a mixture of 8
and 11 at room temperature. This material is available free
of charge via the Internet at http://pubs.acs.org.
analysis data. We also thank Prof. C. N. R. Rao
(J NCASR) for allowing us to use the X-ray diffractom-
eter facility.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data, structure solution and refinement, atomic coordinates,
bond lengths and angles, anisotropic thermal parameters, and
hydrogen atom coordinates for 1, 7, and 11, variable-temper-
OM000371O