Trans → Cis isomerization of trans-[(dppm)2Ru(H)(L)][BF4] (L = P(OR)3) complexes: Preparation of cis-[(dppm)2Ru(η2-H2)(L)] [BF4]2

Article abstract of DOI:10.1021/ic020082n

A series of new dicationic dihydrogen complexes of ruthenium of the type cis-[(dppm)₂Ru(η²-H₂)(L)] [BF₄]₂ (dppm = Ph₂PCH₂PPh₂; L = P(OMe)₃, P(OEt)₃, PF(OⁱPr)₂) have been prepared by protonating the precursor hydride complexes cis-[(dppm)₂Ru(H)(L)][BF₄] (L = P(OMe)₃, P(OEt)₃, P(OⁱPr)₃) using HBF₄·Et₂O. The cis-[(dppm)₂Ru(H)(L)][BF₄] complexes were obtained from the trans hydrides via an isomerization reaction that is acid-accelerated. This isomerization reaction gives mixtures of cis and trans hydride complexes, the ratios of which depend on the cone angles of the phosphite ligands: the greater the cone angle, the greater is the amount of the cis isomer. The η²-H₂ ligand in the dihydrogen complexes is labile, and the loss of H₂ was found to be reversible. The protonation reactions of the starting hydrides with trans PMe₃ or PMe₂Ph yield mixtures of the cis and the trans hydride complexes; further addition of the acid, however, give trans-[(dppm)₂Ru(BF₄)Cl]. The roles of the bite angles of the dppm ligand as well as the steric and the electronic properties of the monodentate phosphorus ligands in this series of complexes are discussed. X-ray crystal structures of trans-[(dppm)₂Ru(H)(P(OMe)₃)][BF₄], cis-[(dppm)₂Ru(H)(P(OMe)₃)][BF₄], and cis-[(dppm)₂Ru(H)(P(OⁱPr)₃)][BF₄] complexes have been determined.

Full text of DOI:10.1021/ic020082n

Inorg. Chem. 2003, 42, 187−197
Trans f Cis Isomerization of trans-[(dppm)2Ru(H)(L)][BF4] (L ) P(OR)3)
Complexes: Preparation of cis-[(dppm)2Ru(η2-H )(L)][BF4]2
†
2
,‡
Nisha Mathew,‡ Balaji R. Jagirdar,* and Anupama Ranganathan§
Department of Inorganic & Physical Chemistry, Indian Institute of Science,
Bangalore 560 012, India, and Chemistry and Physics of Materials Unit, Jawaharlal Nehru
Centre for AdVanced Scientific Research, Jakkur, Bangalore 560 064, India
Received January 28, 2002
A series of new dicationic dihydrogen complexes of ruthenium of the type cis-[(dppm)2Ru(η2-H )(L)][BF ] (dppm )
2
4 2
i
Ph PCH PPh ; L) P(OMe)3, P(OEt)3, PF(OPr)2) have been prepared by protonating the precursor hydride complexes
2
2
2
i
cis-[(dppm)2Ru(H)(L)][BF ] (L ) P(OMe)3, P(OEt)3, P(OPr)3) using HBF ‚Et2O. The cis-[(dppm)2Ru(H)(L)][BF ]
4
4
4
complexes were obtained from the trans hydrides via an isomerization reaction that is acid-accelerated. This
isomerization reaction gives mixtures of cis and trans hydride complexes, the ratios of which depend on the cone
angles of the phosphite ligands: the greater the cone angle, the greater is the amount of the cis isomer. The η2-H
2
ligand in the dihydrogen complexes is labile, and the loss of H was found to be reversible. The protonation
2
reactions of the starting hydrides with trans PMe3 or PMe2Ph yield mixtures of the cis and the trans hydride
complexes; further addition of the acid, however, give trans-[(dppm)2Ru(BF )Cl]. The roles of the bite angles of the
4
dppm ligand as well as the steric and the electronic properties of the monodentate phosphorus ligands in this
series of complexes are discussed. X-ray crystal structures of trans-[(dppm)2Ru(H)(P(OMe)3)][BF ], cis-[(dppm)2Ru-
4
i
(H)(P(OMe)3)][BF ], and cis-[(dppm)2Ru(H)(P(OPr)3)][BF ] complexes have been determined.
4
4
Introduction
in chelating phosphine ligands of trans-[(R2PCH2CH2PR2)2M-
(η2-H2)(L)]+ complexes.3,4 They also used different phos-
phines (dppm, dppe, dppp [Ph2P(CH2)3PPh2], and depe
[Et2P(CH2)2PEt2]) in a series of dihydrogen complexes of
the type trans-[(P-P)2Ru(η2-H2)(CN)]+ and trans-[(P-
P)2Ru(η2-H2)(CNH)]2+ and found that these coligands influ-
ence their stability and reactivity.5 Several others have carried
out variations in the cis ligands of [(L)4Ru(η2-H2)(H)]+
complexes to study their influence on the properties of these
complexes.6
In 1994, Morokuma et al.7 reported theoretical studies on
the nature of the [(P-P)2Ru“H3”]+ fragment ([(P-P)2Ru“H3”]+
) [(P-P)2Ru(H)(η2-H2)]+; P-P ) dppb, diop, dpmb, dppe)
and concluded that with an increasing bite angle of the
The nature of the ancillary ligand environment in a
dihydrogen complex can have a profound effect on the
structure and reactivity of the dihydrogen ligand. A thorough
understanding of the structure and reactivity of the dihydro-
gen complexes is required for the rational design of new
homogeneous metal catalysts. Transition metal complexes
containing phosphorus coligands allow for a very systematic
study because both electronic and steric properties of the
phosphorus ligands could be varied systematically.1 We have
previously shown how the cone angles and the π-acceptor
properties of certain phosphorus ligands influence the
structure and reactivity of trans-[(dppe)2Ru(η2-H2)(L)][BF4]2
complexes (dppe ) Ph2PCH2CH2PPh2; L ) phosphite).2
Morris et al. studied the effect of changing the R substituents
(3) Cappellani, E. P.; Drouin, S. D.; Jia, G.; Maltby, P. A.; Morris, R.
H.; Schweitzer, C. T. J. Am. Chem. Soc. 1994, 116, 3375.
(4) Chin, B.; Lough, A. J.; Morris, R. H.; Schweitzer, C. T.; D’Agostino,
C. Inorg. Chem. 1994, 33, 6278.
* To whom correspondence should be addressed. E-mail: jagirdar@
ipc.iisc.ernet.in.
(5) 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) (a) Kubas, G. J. Acc. Chem. Res. 1988, 21, 120. (b) Crabtree, R. H.
Acc. Chem. Res. 1990, 23, 95. (c) Jessop, P. G.; Morris, R. H. Coord.
Chem. ReV. 1992, 121, 155. (d) Heinekey, D. M.; Oldham, W. J., Jr.
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.
(7) Maseras, F.; Koga, N.; Morokuma, K. Organometallics 1994, 13, 4008.
† Dedicated to Prof. Kenneth Klabunde on the occasion of his 60th
birthday.
‡ Indian Institute of Science.
§ Jawaharlal Nehru Centre for Advanced Scientific Research.
(1) Tolman, C. A. Chem. ReV. 1977, 77, 313.
(2) Mathew, N.; Jagirdar, B. R.; Gopalan, R. S.; Kulkarni, G. U.
Organometallics 2000, 19, 4506.
10.1021/ic020082n CCC: $25.00 © 2003 American Chemical Society
Published on Web 12/10/2002
Inorganic Chemistry, Vol. 42, No. 1, 2003 187

Mathew et al.
Table 1. Numbering Scheme for the Complexesa
diphosphine the complexes change from trans hydrido
dihydrogen to trihydride and to cis hydrido dihydrogen
complexes. Chaudret et al.8 recently reported the preparation
of [(diphos)2Ru(H)(η2-H2)]+ (diphos ) thixantphos, sixant-
phos; both have xanthene-like backbones; bite angles, ân )
103.1 and 102.5°, respectively) in which the hydride and
the dihydrogen ligands were found to be in cis conformation,
in agreement with Morokuma’s prediction. These results
show that the tuning of one steric parameter (in this case,
the bite angles of the diphosphine ligands) bears a remarkable
influence on the electronic properties of these complexes.
To date, such studies dealing with the effect of geometrical
changes on the nature and reactivity of the hydrogen
complexes are very few.
The chemical shifts of the 31P nuclei of the chelating
phosphine rings experience large upfield shifts upon com-
plexation with metal with increase in n.9 A steric effect was
observed in the square planar-tetrahedral equilibrium of
[Ph2P(CH2)nPPh2]NiX2 complexes.10 Ruthenium complexes
bearing the fragment [(dppm)2Ru] have been the subject of
current interest due to the ability of the dppm ligands to serve
either as chelates or as monodentate ligands via binding
through only one P atom to a metal or as bidentate ligands
bridging two metal atoms.5,11,12
The objective of this work is the synthesis of dihydrogen
complexes of ruthenium bearing only phosphorus coligands
of the type [(dppm)2Ru(η2-H2)(L)][BF4]2 (L ) phosphite or
phosphine); in addition, we wish to compare the present
results with those of analogous dppe-containing derivatives
that we reported earlier2 to understand the effect of the
smaller bite angle of the chelating phosphine ligands on the
structure-reactivity behavior of these complexes. We also
intend to prepare dihydrogen complexes that are capable of
activating H2 in a heterolytic manner; one could achieve this
by having strong π-acceptor ligands trans to the η2-H2
moiety.
a [M] ) (dppm)2M fragment. b L ) PF(OiPr)2. c Neutral. d +1.
Experimental Section
General Procedures. All reactions were carried out under N2
or Ar atmosphere at room temperature using standard Schlenk13a,b
and inert-atmosphere techniques unless otherwise noted. Solvents
used for the preparation of dihydrogen complexes were thoroughly
saturated with either H2 or Ar just before use. CHCl3 was purified
using standard procedures.13c Although sufficient measures were
taken to ensure that the CHCl3 solvent was free of acid and other
impurities, it was found to have small amounts of acid impurities.13d
The NMR spectra were obtained using an AMX Bruker 400 MHz
spectrometer. The shift of the residual protons of the deuterated
solvent was used as an internal reference. Variable-temperature
proton T1 measurements were carried out at 400 MHz using the
inversion recovery method.14 The 31P{1H} NMR spectra were
measured in CD2Cl2 relative to 85% H3PO4 (aqueous solution) as
an external standard and 19F NMR spectra with respect to CFCl3.
Elemental analyses were carried out using a Heraues CHNO Rapid
elemental analyzer. Bis(diphenylphosphino)methane (dppm),15 cis-
[(dppm)2RuCl2],16 and cis/trans-[(dppm)2Ru(H)2]17 were prepared
by literature methods. The numbering scheme for the compounds
reported in this work is summarized in Table 1.
Preparation of trans-[(dppm)2Ru(H)(L)][BF4] (L ) P(OMe)3
(trans-2H), P(OEt)3 (trans-3H), P(OiPr)3 (trans-4H), PMe3
(trans-5H), PMe2Ph (trans-6H), CH3CN (trans-7H)). All of these
compounds were prepared using similar procedures. The preparation
of trans-2H only is described here: To a CH2Cl2 (10 mL) solution
of cis/trans-[(dppm)2RuH2] (0.200 g, 0.2 mmol) was added 1 equiv
(32 µL) of 54% HBF4‚Et2O. To this solution containing the trans-
[(dppm)2Ru(η2-H2)(H)][BF4] (trans-1H) complex was added P(OMe)3
(0.04 mL, 0.3 mmol) dropwise. The reaction mixture was stirred
for only 1 min after which time N2 was introduced and the volume
increased to ca. 30 mL by adding CH2Cl2. Addition of excess
petroleum ether caused the precipitation of a cream colored product
In the current work, we have attempted to carry out
protonation reactions of a series of hydride complexes trans-
[(dppm)2Ru(H)(L)][BF4] (L ) P(OMe)3 (cone angle θ )
107°), P(OEt)3 (θ ) 109°), P(OiPr)3 (θ ) 130°), PMe3 (θ )
118°), and PMe2Ph (θ ) 122°)) with HBF4‚Et2O. We found
that these hydrides, in the presence of e1 equiv of HBF4‚
Et2O, isomerize to give new hydride complexes cis-[(dppm)2-
Ru(H)(L)][BF4]. Further addition of acid to the cis-[(dppm)2-
Ru(H)(L)][BF4] complexes afforded the cis-[(dppm)2Ru(η2-
H2)(L)][BF4]2 complexes. These are the first examples in this
class of complexes wherein the H2 ligand and a monodentate
phosphorus ligand are in cis conformation.
(13) (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;
Johnassen, H. B., Ed.; Interscience: New York, 1969; Vol. VII. (c)
Furniss, B. S.; Hannaford, A. J.; Smith, P. W. G.; Tatchell, A. R.
Vogel’s Textbook of Practical Organic Chemistry, 5th ed.; Longman:
Singapore, 1996; p 399. (d) The concentration of the acid impurity
(HCl) was found to be approximately 4 × 10-7 M.
(8) Kranenburg, M.; Kamer, P. C. J.; van Leeuwen, W. N. M.; Chaudret,
B. Chem. Commun. 1997, 373.
(9) (a) Grim, S. O.; Briggs, W. L.; Barth, R. C.; Tolman, C. A.; Jesson,
J. P. Inorg. Chem. 1974, 13, 1095. (b) Garrou, P. E. Inorg. Chem.
1975, 14, 1435.
(10) McGarvey, J. J.; Wilson, J. J. Am. Chem. Soc. 1975, 97, 2531.
(11) (a) Puddephatt, R. J. Chem. Soc. ReV. 1983, 12, 99. (b) Chaudret, B.;
Delavaux, B.; Poilblanc, R. Coord. Chem. ReV. 1988, 86, 191.
(12) (a) Szczepura, L. F.; Giambra, J.; See, R. F.; Lawson, H.; Janik, T.
S.; Jircitano, A. J.; Churchill, M. R.; Takeuchi, K. J. Inorg. Chim.
Acta 1995, 239, 77. (b) Ruiz, J.; Mosquera, M. E. G.; Riera, V. J.
Organomet. Chem. 1997, 527, 35. (c) Winter, R. F.; Scheiring, T. Z.
Anorg. Allg. Chem. 2000, 626, 1196.
(14) Hamilton, D. G.; Crabtree, R. H. J. Am. Chem. Soc. 1988, 110, 4126.
(15) Hewertson, W.; Watson, H. R. J. Chem. Soc. 1962, 1490.
(16) Chaudret, B.; Commenges, G.; Poilblanc, R. J. Chem. Soc., Dalton
Trans. 1984, 1635.
(17) Hill, G. S.; Holah, D. G.; Hughes, A. N.; Prokopchuk, E. M. Inorg.
Chim. Acta 1998, 278, 226.
188 Inorganic Chemistry, Vol. 42, No. 1, 2003

trans-[(dppm)2Ru(H)(L)][BF4] Complexes
Table 2. 1H NMR Spectral Data (δ) for trans-[(dppm)2Ru(H)(L)][BF4] Complexes in CD2Cl2
compd no.
δ(Ru-H)
J(H,Ptr ans), Hz
J(H,Pcis), Hz
δ(CH2)
δ(L)
J(H,E), Hz
δ(Ph)
trans-2H
-5.31 (d qnt, 1H)
106.8
21.0
4.90 (m, 2H)
4.46 (m, 2H)
4.81 (m, 2H)
4.53 (m, 2H)
4.69 (m, 2H)
4.12 (m, 2H)
4.80 (m, 2H)
4.58 (m, 2H)
4.73 (m, 2H)
4.50 (m, 2H)
4.40 (m, 2H)
4.91 (m, 2H)
2.60 (d, 9H)
12.0a
6.96-7.69 (m, 40H)
trans-3H
trans-4H
trans-5H
trans-6H
trans-7H
-5.51 (d qnt, 1H)
-6.53 (d qnt, 1H)
-6.20 (d qnt, 1H)
-6.39 (d qnt, 1H)
-11.93 (qnt, 1H)
104.1
105.0
50.0
21.0
21.5
21.0
21.0
19.0
3.00 (q, 6H)
0.40 (t, 9H)
4.26 (m, 3H)
0.54 (d, 18H)
0.43 (d, 9H)
8.0b
8.0b
8.0b
8.0b
6.84-7.40 (m, 40H)
6.81-7.51 (m, 40H)
6.94-7.48 (m, 40H)
6.55-7.39 (m, 45H)
7.04-7.35 (m, 40H)
52.0
0.62 (d, 6H)
1.13 (s, 3H)
a E ) P. b E ) H.
Table 3. 31P{1H} NMR Spectral Data (δ) for
manually separated from the trans isomer (colorless crystals). The
trans-[(dppm)2Ru(H)(L)][BF4] Complexes in CD2Cl2
isomerizations of trans-3H, trans-4H, trans-5H, and trans-6H were
1
also carried out using this method. H NMR of the products in
compd no.
P(L)
P(dppm)
J(P,P), Hz
CD2Cl2: (a) L ) P(OEt)3, mixture of trans- and cis-[(dppm)2Ru-
(H)(P(OEt)3)][BF4] (trans- and cis-3H) complexes in a ratio of 3
and 97%; (b) L ) P(OiPr)3, the cis isomer, 100%; cis-4H complex
crystallized from a CH2Cl2 solution via diffusion of petroleum ether;
(c) L ) PMe3, ratio of trans to cis, 42 to 58%; (d) L ) PMe2Ph,
41% trans to 59% cis. The NMR data for these compounds are
summarized in Tables 4 and 5.
trans-2H
trans-3H
trans-4H
trans-5H
trans-6H
trans-7H
136.6 (qnt, 1P)
135.9 (qnt, 1P)
133.3 (qnt, 1P)
-30.8 (qnt, 1P)
-15.8 (qnt, 1P)
-1.2 (d, 4P)
-1.3 (d, 4P)
-3.5 (d, 4P)
-2.9 (d, 4P)
-3.5 (d, 4P)
-1.4 (s, 4P)
33.2
33.3
32.7
23.8
23.8
that was washed several times with more petroleum ether and then
dried in vacuo. Yield: 0.200 g, 81%. Anal. Calcd for C53H54-
BF4O3P5Ru‚CH2Cl2: C, 55.59; H, 4.83. Found: C, 56.09; H, 5.13.
Yield of trans-3H): 80%. Anal. Calcd for C56H60BF4O3P5Ru‚
0.5CH2Cl2: C, 58.19; H, 5.27. Found: C, 58.25; H, 5.43. Yield of
trans-4H: 85%. This product contained certain impurities, and
purification procedures resulted in its partial decomposition. Anal.
Calcd for C59H66BF4O3P5Ru‚0.5CH2Cl2: C, 59.14; H, 5.59.
Found: C, 59.91; H, 5.57. Yield of trans-5H: 84%. Anal. Calcd
for C53H54BF4P5Ru: C, 61.58; H, 5.27. Found: C, 61.24; H, 5.12.
Yield of trans-6H: 78%. Anal. Calcd for C58H56BF4P5Ru‚CH2Cl2:
C, 60.02; H, 4.95. Found: C, 60.49; H, 4.89. Yield of trans-7H:
84%. Anal. Calcd for C52H48BF4NP4Ru: C, 62.54; H, 4.84.
Found: C, 62.18; H, 4.99. The presence or absence of solvent
Method B. To a CHCl3 solution (7 mL) of trans-2H (0.100 g,
0.09 mmol) under H2 atmosphere was added 1 equiv (13 µL) of
HBF4‚Et2O. This solution was stirred for 1 min, and Et2O (2 mL)
and excess petroleum ether were added. The precipitated product
was washed with Et2O and petroleum ether and dried in vacuo. 1H
NMR spectrum indicated the presence of trans-2H (minor) and cis-
2H (major) complexes.
Protonation Reaction of trans-[(dppm)2Ru(H)(L)][BF4] (L )
P(OMe)3 (trans-2H), P(OEt)3 (trans-3H)). A 12 mg portion of
trans-[(dppm)2Ru(H)(L)][BF4] was dissolved in 0.9 mL of CD2-
Cl2 in an NMR tube. This solution was freeze-pump-thaw
degassed and then purged with H2 gas for 5 min. Upon addition of
1 equiv of HBF4‚Et2O (1.8 µL for L ) P(OMe)3; 1.4 µL for L )
P(OEt)3) the 1H NMR spectrum evidenced the formation of the cis
isomer, cis-[(dppm)2Ru(H)(L)[BF4] (L ) P(OMe)3 (cis-2H), P(O-
Et)3 (cis-3H)). Thereafter, the acid was added in small increments.
Addition of excess acid gave a mixture of trans- and cis-dihydrogen
complexes [(dppm)2Ru(η2-H2)(L)][BF4]2 (L ) P(OMe)3 (trans-2H2
and cis-2H2); P(OEt)3 (trans-3H2 and cis-3H2)), respectively.
Characterization data for trans-2H2 are as follows. 1H NMR (CD2-
Cl2): δ -3.07 (d, 2H, Ru-η2-H2, J(H2,Ptrans) ) 50 Hz). Signals
due to other moieties could not be assigned with confidence. 31P-
{1H} NMR (CD2Cl2): δ 116.25 (qnt, 1P, P(OMe)3, J(P,P) ) 41.8
Hz), -10.01 (d, 4P, dppm). Characterization data for trans-3H2
1
molecules in the samples was ascertained by recording their H
NMR spectra in CDCl3 and measuring the integrals for the CH2-
Cl2 (δ 5.3) of solvation (if present) with respect to the dppm -CH2
signal. The integrals reproduced fairly well for multiple samples
of the same compound. The NMR data are summarized in Tables
2 and 3. Characterization data for trans-[(dppm)2Ru(η2-H2)(H)]-
[BF4] (trans-1H) are as follows. 1H NMR (CD2Cl2): δ -6.63 (qnt,
1H, Ru-H, J(H,Pcis) ) 18.7 Hz); -2.34 (br s, 2H, η2-H2), 4.10
(m, 2H, PCH2P), 4.54 (m, 2H, PCH2P), 6.28-7.79 (m, 40H, PPh2).
31P NMR (CD2Cl2): δ -0.03 (s, 4P, Ph2PCH2PPh2). T1 (400 MHz,
CD2Cl2, 298 K): η2-H2 ligand, 17.3 ms; J(H,D) ) 29 Hz, dHH
0.94 Å; hydride ligand, 216 ms.
)
1
are as follows. H NMR (CD2Cl2): δ -3.11 (br d, 2H, η2-H2,
Isomerization of trans-[(dppm)2Ru(H)(L)][BF4] (L ) P(OMe)3
(trans-2H), P(OEt)3 (trans-3H), P(OiPr)3 (trans-4H), PMe3
(trans-5H), PMe2Ph (trans-6H)). Method A. A CHCl3 solution
(30 mL) of trans-2H (0.150 g, 0.13 mmol) was refluxed for 20 h
and then cooled to room temperature, filtered, and concentrated.
Addition of Et2O (2 mL) and excess petroleum ether caused the
precipitation of a mixture of trans-2H and cis-[(dppm)2Ru(H)-
(P(OMe)3)][BF4] (cis-2H) complexes. 1H NMR spectroscopy
evidenced the presence of the trans and the cis isomers in a ratio
of 19:81. The product was washed with Et2O and petroleum ether
and then dried in vacuo. Yield: 0.090 g. It was crystallized from
a CH2Cl2 solution containing a few drops of toluene and P(OMe)3
via diffusion of petroleum ether over a period of several days at
room temperature. The cis isomer (pale orange crystals) could be
J(H2,Ptrans) ) 43 Hz). Signals due to other moieties could not be
assigned definitively. 31P NMR (CD2Cl2): δ 114.5 (qnt, 1P,
P(OEt)3), J(P,P) ) 40.2 Hz), -10.8 (d, 4P, Ph2PCH2PPh2).
Protonation Reaction of trans-[(dppm)2Ru(H)(L)][BF4] (L )
P(OiPr)3 (trans-4H)). The protonation of trans-4H was carried out
in a manner similar to that of trans-2H. Upon addition of 1 equiv
of 54% HBF4‚Et2O new hydride complexes were formed, cis-
[(dppm)2Ru(H)(P(OiPr)3)][BF4] (cis-4H) and trans-[(dppm)2Ru(H)-
(PF(OiPr)2)][BF4]. When excess acid was added, trans-[(dppm)2-
Ru(η2-H2)(PF(OiPr)2)][BF4]2 (trans-4H2) and cis-[(dppm)2Ru(η2-
H2)(PF(OiPr)2)][BF4]2 (cis-4H2), respectively, were obtained.
Characterization data for trans-4H2 are as follows. 1H NMR
(CD2Cl2, rt (room temperature)): δ -2.94 (br d, 2H, η2-H2,
Inorganic Chemistry, Vol. 42, No. 1, 2003 189

Mathew et al.
Table 4. 1H NMR Spectral Data (δ) for cis-[(dppm)2Ru(H)(L)][BF4] Complexes in CD2Cl2
compd no.
δ(Ru-H)a
J(H,Ptrans), Hz
J(H,Pcis-av), Hz
δ(L)
J(H,E), Hz
δ(CH2)
δ(Ph)
cis-2H
cis-3H
-8.51 (1H)
-8.49 (1H)
68.0
68.0
8.5
10.2
3.07 (d, 9H)
3.43 (m, 6H)
0.68 (t, 9H)
4.27 (m, 3H)
0.8 (dd, 18H)
0.76 (d, 9H)
1.00 (d, 6H)
20b
8c
5.95 (m, 4H)
5.90 (m, 4H)
6.57-7.81 (m, 40H)
6.63-7.70 (m, 40H)
cis-4H
-8.52 (1H)
80.4
9.0
32b
8c
5.62 (m, 4H)
6.40-7.90 (m, 40H)
cis-5H
cis-6H
-8.73 (1H)
-8.35 (1H)
82.0
92.4
9.5
15.0
4c
5.95 (m, 4H)
5.74 (m, 4H)
6.73-7.79 (m, 40H)
6.42-7.80 (m, 45H)
4c
a XABCDM spin system. b E ) P. c E ) H.
Table 5. 31P NMR Spectral Dataa (δ) for cis-[(dppm)2Ru(H)(L)][BF4] Complexes in CD2Cl2
δ(PM) (J(PM,PB);
J(PM,Pav(A,C,D), Hz))
δ(PD) (J(PD,PC);
J(PD,Pav(A,B,M), Hz))
δ(PC)
(J(PC,Pav(A,B,M), Hz))
δ(PB)
(J(PB,Pav(A,C,D), Hz))
compd no.
δ(PA)
cis-2H
cis-3H
cis-4H
cis-5H
cis-6H
144.1 (353.5; 36.4)
139.4 (350.7; 21.9)
134.7 (353.3; 25.5)
6.1 (240.0; 21.1)
3.0 (230.0; 19.9)
3.6 (233.3; 17.4)
4.7 (230.0; 17.2)
2.3 (235.0; 17.4)
-6.1 (205.0; 20.0)
0.9 (221.0; 23.5)
-3.7 (22.6)
-4.7 (22.7)
-3.4 (22.6)
-12.6 (22.0)
-4.9 (24.9)
-10.5 (15.7)
-11.7 (16.1)
-11.0 (15.6)
-3.2 (20.0)
-4.8 (22.0)
-16.3
-16.2
-19.3
-17.3
-19.4
a ABCDM spin system.
Table 6. 1H NMR Spectral Data (δ) for cis-[(dppm)2Ru(η2-H2)(L)][BF4]2 Complexes in CD2Cl2
compd no.
δ(Ru-(η2-H2))
δ(L)
J, Hz
δ(CH2)
δ(Ph)
cis-2H2
cis-3H2
-4.88 (br s, 2H)
-4.81 (br s, 2H)
3.17 (d, 9H)
3.61 (q, 6H)
0.85 (t, 9H)
4.50 (m,2H)
0.87 (d,12H)
12 (J(P,H))
8 (J(H,H))
5.65 (m, 4H)
5.62 (m, 4H)
6.60-7.93 (m, 40H)
6.69-7.98 (m, 40H)
cis-4H2
-4.57 (br s, 2H)
6 (J(H,H))
5.88 (m, 4H)
6.80-7.95 (m, 40H)
Table 7. 31P NMR Spectral Data (δ) for cis-[(dppm)2Ru(η2-H2)(L)][BF4]2 Complexes in CD2Cl2
compd no.
δ(PM)
δ(PD)
δ(PC)
δ(PB)
δ(PA)
a
cis-2H2
124.3
-16.7
-21.0
-23.6
J(PM,PC) ) 35 0.8 Hz
J(PM,Pav(A,B)) ) 35.2 Hz
120.2
J(PM,PA) ) 34 6.0 Hz
J(PM,Pav(B,C,D)) ) 34.9 Hz
124.6
J(PC,Pav(A,B,M)) ) 28.0 Hz
J(PB,Pav(A,C,M)) ) 24.1 Hz
J(PA,Pav(B,C,M)) ) 24.8 Hz
b
cis-3H2
-9.6
-17.8
-19.4
-22.9
-26.9
J(PD,PC) ) 204.0 Hz
b
cis-4H2
5.9
-14.6
J(PC,PA) ) 258.0 Hz
-22.6
J(PM,PB) ) 40 0.0 Hz
J(PM,F) ) 1160.0 Hz
a ABB′CM spin system. b ABCDM spin system.
J(H2,Ptrans) ) 46.8 Hz), 0.74 (d, 12H, CH(CH3)2, J(H,H) ) 6 Hz),
4.59 (m, 2H, CH(CH3)2), 6.23 (m, 4H, CH2). 31P NMR (CD2Cl2,
rt): δ -1.27 (d, 4P, Ph2PCH2PPh2, J(P,P) ) 34.3 Hz), 121.5 (d
qnt, 1P, PF(OiPr)2, J(P,F) ) 1120.0 Hz).
(cis-5H), PMe2Ph (cis-6H)), trans-[(dppm)2Ru(η2-H2)(H)][BF4]
(trans-1H), trans-[(dppm)2Ru(η2-H2)(Cl)][BF4] (trans-8H2), and cis-
[(dppm)2Ru(η2-H2)(L)][BF4]2 (L ) PMe3 (cis-5H2), PMe2Ph (cis-
6H2)) complexes. When ca. 10 equiv of acid was added, no signals
were found in the hydride region of the spectrum except that of
the trans-8H2 complex. The 31P NMR spectrum, in addition to
indcating trans-8H2, showed trans-[(dppm)2Ru(BF4)Cl] (trans-9)
(37%) and free ligand. The presence of the bound BF4 moiety was
confirmed using 19F NMR spectroscopy in the presence of a large
excess of acid. Characterization data for trans-9 are as follows.
31P NMR (CD2Cl2, rt): δ 12.5 (br s, 2P), -17.8 (t, 2P). The signal
at 12.5 ppm sharpens to a triplet at 223 K. 19F NMR (CD2Cl2, rt):
δ -132.3 (s, 4F, Ru-BF4), -150.5 (br s, free BF4-). Attempts to
measure the T1 and J(H,D) for [(dppm)2Ru(η2-H2)(L)][BF4]2 (L )
PMe3, PMe2Ph) complexes failed due to the high lability of the
dihydrogen ligand in these complexes.
Protonation Reaction of cis/trans-[(dppm)2Ru(H)2]. To an
NMR tube charged with 15 mg of cis/trans-[(dppm)2Ru(H)2] was
transferred CD2Cl2 (0.9 mL) saturated with Ar or H2 just before
inserting the tube into the NMR probe; this was done due to the
instability of the dihydride complex in CD2Cl2 for long periods of
time. The 1H NMR spectrum showed the presence of a small
amount of trans-[(dppm)2Ru(H)(Cl)][BF4] (trans-8H). Addition of
Preparation of the Dihydrogen Complexes trans-[(dppm)2Ru-
(η2-H2)(L)][BF4]2 (L ) P(OMe)3 (trans-2H2), P(OEt)3 (trans-
3H2), PF(OiPr)2 (trans-4H2)) and cis-[(dppm)2Ru(η2-H2)(L)]-
[BF4]2 (L ) P(OMe)3 (cis-2H2), P(OEt)3 (cis-3H2), PF(OiPr)2 (cis-
4H2)). Similar procedures were employed for the preparation of
these derivatives. A 12 mg portion of trans-[(dppm)2Ru(H)(L)][BF4]
was dissolved in 0.9 mL of CD2Cl2 in an NMR tube, and the
solution was degassed. Then it was purged with H2 gas for 5 min.
Addition of ca. 8 equiv of HBF4‚Et2O (15 µL for L ) P(OMe)3;
14 µL for L ) P(OEt)3; 16 µL for L ) P(OiPr)3) gave the
dihydrogen complexes which were characterized using NMR
spectroscopy. The NMR data for these complexes are summarized
in Tables 6 and 7.
Protonation Reactions of trans-[(dppm)2Ru(H)(L)][BF4] (L
) PMe3 (trans-5H), PMe2Ph (trans-6H)). The protonation reac-
tions of these complexes were carried out in a manner similar to
that of trans-2H. Upon addition of 1 equiv of HBF4‚Et2O (1.6 µL
1
for L ) PMe3; 1.8 µL for L ) PMe2Ph) the H NMR spectrum
evidenced the formation of cis-[(dppm)2Ru(H)(L)][BF4] (L ) PMe3
190 Inorganic Chemistry, Vol. 42, No. 1, 2003

trans-[(dppm)2Ru(H)(L)][BF4] Complexes
Table 8. Crystallographic Data for
ca. 1 equiv of 54% HBF4‚Et2O (2.6 µL) gave trans-[(dppm)2Ru-
(η2-H2)(H)][BF4] (trans-1H) along with some trans-8H2. Addition
of further acid resulted in the disappearance of trans-1H; however,
the trans-8H2 remained intact. The 31P NMR spectrum of this
mixture was identical to that of trans-9 observed in the protonation
of the PMe3 and PMe2Ph hydrides. In the presence of excess acid,
the signals due to trans-9 broaden as well as shift slightly downfield.
Preparation of trans-[(dppm)2Ru(η2-H2)(Cl)][BF4] (trans-
8H2). A 15 mg portion of trans-[(dppm)2Ru(H)(Cl)] (trans-8H)
dissolved in 0.7 mL of CD2Cl2 in an NMR tube was degassed and
then saturated with Ar or H2. Then ca. 1 equiv of HBF4‚Et2O (2.2
µL) was added. The dihydrogen complex was characterized using
NMR spectroscopy. Characterization data for trans-8H2 are as fol-
trans-[(dppm)2Ru(H)(P(OMe)3)][BF4] (trans-2H),
cis-(dppm)2Ru(H)(P(OMe)3)][BF4] (cis-2H), and
cis-[(dppm)2Ru(H)(P(OiPr)3)][BF4] (cis-4H)
trans-2H
cis-2H
cis-4H
formula
C54H56BCl2F4-
O3P5Ru
C53H53BF4-
O3P5Ru
1080.68
triclinic
P1h
9.77640(10)
15.0833(2)
20.72300(10)
75.75
76.1020(10)
77.1270(10)
2831.23(5)
2
C59H62BF4-
O3P5Ru
1161.82
monoclinic
P21/n
12.5092(3)
33.9863(7)
12.9395(2)
89.95
92.4970(10)
89.9820(10)
5495.89(19)
4
fw
1165.61
cryst syst
space group
a, Å
b, Å
c, Å
monoclinic
P21/c
10.21610(10)
24.6584(3)
22.0474(2)
89.9970(10)
91.3580(10)
90.0780(10)
5552.45(10)
4
R, deg
â, deg
γ, deg
V, Å3
Z
1
lows. H NMR (CD2Cl2): δ -9.07 (br s, 2H, η2-H2, J(H2,Pcis) )
6 Hz (HD isotopomer)), 4.54 (m, 2H, PCH2P), 5.04 (m, 2H,
PCH2P), 6.31-7.89 (m, 40H, PPh2). 31P NMR (CD2Cl2): δ -6.57
(s, 4P, Ph2PCH2PPh2). T1 (400 MHz, CD2Cl2, 298 K): η2-H2 ligand,
15.87 ms; J(H,D) ) 26 Hz, dHH ) 0.99 Å.
D
calcd, g/cm3
1.394
1.268
130(2)
0.710 73
0.469
0.0635
1.404
130(2)
0.710 73
0.489
0.0386
T, K
293(2)
λ, Å
0.710 73
0.577
0.0536
µ, mm-1
Ra
1H NMR Spin-Lattice Relaxation Time Measurements. The
dihydrogen ligand in the complexes cis-[(dppm)2Ru(η2-H2)(L)]-
[BF4]2 (L ) phosphite or phosphine) and trans-[(dppm)2Ru(η2-
H2)(L)][BF4]2 were found to be quite labile. Although variable-
temperature T1 measurements were carried out, precise values of
T1 could not be obtained because the data were rendered unreliable
by the high lability of the H2 ligand. Therefore, we report here
(Table 10) only the room-temperature T1 data for all the complexes.
These measurements were carried out within few minutes of the
generation of the dihydrogen complexes. The short T1 values for
our complexes evidence the intact nature of the H-H bond in these
derivatives.
Observation of the H-D Isotopomers. The HD isotopomers
were obtained as follows: (a) D2 gas was purged through a CD2-
Cl2 solution of trans/cis-[(dppm)2Ru(η2-H2)(L)][BF4]2 (L ) P(OMe)3
(trans-2HD and cis-2HD), P(OEt)3 (trans-3HD and cis-3HD)) for
ca. 10 min. (b) Excess DBF4‚Et2O (prepared from HBF4‚Et2O and
D2O in a 3:1 ratio) was added to a CD2Cl2 solution of trans-
[(dppm)2Ru(H)(L)][BF4] (L ) P(OiPr)3 (trans-4H)) (12 mg)/cis/
trans-[(dppm)2Ru(H)2] (12 mg)/trans-[(dppm)2Ru(H)Cl] (trans-8H)
(12 mg). The H-D isotopomers formed were observed by 1H NMR
spectroscopy.
X-ray Structure Determination of trans-[(dppm)2Ru(H)-
(P(OMe)3)][BF4] (trans-2H) and cis-[(dppm)2Ru(H)(L)][BF4] (L
) P(OMe)3 (cis-2H), P(OiPr)3 (cis-4H)). Suitable crystals of trans-
2H, cis-2H, and cis-4H were chosen after examination under a
microscope. X-ray diffraction intensities were measured by ω scans
using a Siemens three-circle diffractometer attached with a CCD
area detector and a graphite monochromator for the Mo KR
radiation (50 kV, 40 mA). The crystals of cis-2H and cis-4H were
cooled to 130 K on the diffractometer using a stream of cold N2
gas from a vertical nozzle; this temperature was maintained during
the data collection. In the case of trans-2H, the data collection was
carried out at 298 K. The unit cell parameters and the orientation
matrix were initially determined using 80 reflections from 25 frames
collected over a small ω scan of 7.5° sliced at 0.3° intervals. A
hemisphere of reciprocal space was then collected using the
SMART software18 and 2θ settings of the detector at 28°. Data
reduction was done using the SAINT program,18 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 are summarized in Table 8. An empirical absorption correction
based on symmetry-equivalent reflections was applied using the
a
Rw
0.1192
0.2032
0.0780
a R ) Σ(|Fo| - |Fc|)/Σ|Fo|; Rw ) [Σw(|Fo| - |Fc|)2/Σw|Fo| ]1/2 (based
on reflections with I > 2σ(I)).
2
SADABS program,19 taking the merged reflection 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 respectively 0.1 and 0.0688,
0.0433 and 0.0338, and 0.56 and 0.0481 for trans-2H, cis-2H, and
cis-4H. 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.20 H atoms other than those on ruthenium were fixed and
refined isotropically.
Results and Discussion
Synthesis of New Hydride Complexes. The new ruthe-
nium hydride complexes trans-[(dppm)2Ru(H)(L)][BF4] (L
) P(OMe)3 (trans-2H), P(OEt)3 (trans-3H), P(OiPr)3 (trans-
4H), PMe3 (trans-5H), PMe2Ph (trans-6H), CH3CN (trans-
7H)) were prepared from trans-[(dppm)2Ru(η2-H2)(H)][BF4]
(trans-1H) (generated in situ) similar to the preparation of
the analogous dppe hydride derivatives reported by us2 and
the trans-[(dppe)2Os(H)(CH3CN)][BF4] by Schlaf et al.21 (eq
1). The reaction mixtures have to be worked up rapidly,
typically 1 min after the addition of the phosphorus ligands,
otherwise the trans hydrides isomerize to give mixtures of
trans and cis hydride phosphite/phosphine derivatives (see
text later).
trans-1H was prepared by reacting cis/trans-[(dppm)2Ru-
(H)2] with exactly 1 equiv of HBF4‚Et2O in Et2O under H2
atmosphere. It was characterized using NMR spectroscopy
(see Experimental Section).22 For the preparation of trans-
(19) Sheldrick, G. M. SADABS User Guide; University of Go¨ttingen:
Go¨ttingen, Germany, 1993.
(20) SHELXTL (SGI Version); Siemens Analytical X-ray Instruments,
Inc.: Madison, WI, 1995.
(21) Schlaf, M.; Lough, A. J.; Maltby, P. A.; Morris, R. H. Organometallics
1996, 15, 2270.
(22) The following two references report partial NMR data: (a) Jessop, P.
G.; Rastar, G.; James, B. R. Inorg. Chim. Acta 1996, 250, 351. (b)
Ayllo´n, J. A.; Gervaux, C.; Sabo-Etienne, S.; Chaudret, B. Organo-
metallics 1997, 16, 2000.
(18) Siemens Analytical Instruments, Inc., Madison, WI, 1995.
Inorganic Chemistry, Vol. 42, No. 1, 2003 191

Mathew et al.
[(dppm)2Ru(H)(L)][BF4] complexes (L ) P(OR)3, PR3, CH3-
CN) the amount of phosphorus/CH3CN ligand that was
reacted with trans-1H was based on the concentration of the
starting dihydride complex. All the new hydrides were
obtained in good yields as off-white to dull cream-colored
solids. They were purified by crystallization from CH2Cl2-pe-
troleum ether solutions in the presence of a slight excess of
the appropriate phosphite or phosphine or acetonitrile in the
crystallization mixture in the absence of which the trans
hydrides isomerize with time to give a mixture of the trans
and cis isomers. This means that the trans P ligand is very
labile in these complexes.
Figure 1. ORTEP view of the trans-[(dppm)2Ru(H)(P(OMe)3)]+ (trans-
2H) cation at the 50% probability level. The phenyl groups on the dppm
phosphorus atoms have been omitted for clarity; only one carbon atom of
each of the phenyl groups is shown.
Table 9. Selected Bond Lengths (Å) and Angles (deg) for
trans-(dppm)2Ru(H)(P(OMe)3)][BF4] (trans-2H),
cis-[(dppm)2Ru(H)(P(OMe)3)][BF4] (cis-2H), and
cis-[(dppm)2Ru(H)(P(OiPr)3)][BF4] (cis-4H)
The 1H NMR spectra of the trans-[(dppm)2Ru(H)(L)][BF4]
(L ) P(OR)3 or PR3) complexes show a doublet of quintets
for the hydride ligand due to coupling with the trans P
(P(OR)3 or PR3) and the four cis P (dppm) nuclei. The
J(H,Ptrans) is on the order of 100 Hz for the P(OR)3 and 50
Hz for the trans PR3 complexes. We2 and others23 observed
this trend earlier. The 31P{1H} NMR spectra show a doublet
(J(P,P) ) 23-33 Hz) for the dppm P nuclei due to coupling
with the phosphite/phosphine ligand and a quintet for the
phosphite/phosphine coupled to the four dppm phosphorus
nuclei.
Our attempts to prepare the PBu3, PPh3, and PCy3 hydride
complexes failed, and the starting trans-1H complex was
recovered. To understand the steric effects of the dppm
ligand, we carried out an X-ray crystallographic study of
trans-2H.
trans-2H
cis-2H
cis-4H
Ru(1)-P(5)
2.3153(17)
2.3375(16)
2.3347(15)
2.3554(16)
2.3680(16)
1.579(5)
1.600(5)
1.596(5)
92.45(6)
94.53(6)
71.95(5)
95.50(6)
169.95(6)
95.53(6)
171.84(6)
2.249(2)
2.417(2)
2.349(2)
2.316(2)
2.379(2)
1.612(5)
1.585(5)
1.605(5)
92.15(7)
93.22(7)
70.89(7)
90.20(7)
176.23(7)
152.14(8)
113.58(7)
2.2924(9)
2.4252(9)
2.3380(9)
2.3466(9)
2.4048(9)
1.602(2)
1.605(3)
1.600(2)
92.97(3)
92.51(3)
69.64(3)
94.95(3)
172.38(3)
159.03(3)
107.04(3)
Ru(1)-P(4)
Ru(1)-P(3)
Ru(1)-P(2)
Ru(1)-P(1)
P(5)-O(1)
P(5)-O(2)
P(5)-O(3)
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(3)-Ru(1)-P(2)
P(5)-Ru(1)-P(1)
P(4)-Ru(1)-P(1)
bite angles P(1)-Ru(1)-P(2) and P(3)-Ru(1)-P(4) are
69.59(5) and 71.95(5)°, respectively. The Ru-P(dppm) bond
lengths vary from 2.3347(15) to 2.3680(16) Å while the
Ru-P distance (P(OMe)3) is 2.3153(17) Å. The Ru-
P(P(OMe)3) bond of the trans-2H complex is elongated by
ca. 0.07 Å compared to its cis isomer (see later). The plane
of the four dppm phosphorus atoms in trans-2H is nearly
perfect whereas the analogous dppe derivative2 is slightly
puckered. The P(1)-C(13)-P(2) and P(3)-C(38)-P(4)
bond angles are 92.7 and 95.6(3)°, respectively, falling in
the lower end of the range of P-C-P bond angles (92-
133°) that dppm ligand exhibits in its complexes. The
selected bond lengths and angles have been summarized in
Table 9.
Structure of trans-[(dppm)2Ru(H)(P(OMe)3)][BF4] (trans-
2H). The structure of trans-2H cation is shown in Figure 1.
The cation is made up of a nearly perfect square pyramid
defined by four coplanar dppm phosphorus atoms and the
P(OMe)3 moiety perpendicular to this plane. In addition to
a discrete [BF4]- counterion a molecule of CH2Cl2 is also
present. The hydride ligand that occupies the sixth coordina-
1
tion site on the metal was not located; however, H NMR
spectroscopy provides evidence of its presence. The dppm
(23) (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. (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.
Protonation Reaction of the Hydride Complexes trans-
[(dppm)2Ru(H)(L)][BF4] (L ) P(OMe)3 (trans-2H), P(O-
Et)3 (trans-3H), P(OiPr)3 (trans-4H)). The hydride com-
192 Inorganic Chemistry, Vol. 42, No. 1, 2003

trans-[(dppm)2Ru(H)(L)][BF4] Complexes
small amount of cis isomer was already present in solution
before the addition of the acid.
Synthesis of cis-[(dppm)2Ru(H)(L)][BF4] Complexes (L
) P(OMe)3 (cis-2H), P(OEt)3 (cis-3H), P(OiPr)3 (cis-4H),
PMe3 (cis-5H), PMe2Ph (cis-6H)). The protonation of the
trans hydride phosphite/phosphine complexes with 1 equiv
of HBF4‚Et2O in CHCl3 yielded the isomerized derivatives.
Upon workup of the reaction mixture, the products were
obtained as off-white solids containing both the isomers.
Separation of the trans and the cis hydride phosphite
complexes was accomplished via crystallization in the case
of P(OMe)3 derivative. The cis isomer crystallized as pale
orange crystals whereas the trans one was colorless; thus,
manual separation was possible.
When CHCl3 solutions of the trans hydrides were refluxed,
they isomerized, the facilities of which are dependent on the
cone angles of the phosphorus ligands: easier for ligands
that have larger cone angles, that is, P(OiPr)3 > P(OEt)3 >
P(OMe)3.24 1H NMR spectroscopy of the products showed
the presence of the trans and the cis isomers in ratios of
19:81 (P(OMe)3), 3:97 (P(OEt)3), 0:100 (P(OiPr)3), 42:58
(PMe3), and 41:59 (PMe2Ph), respectively. We have deter-
mined the Keq values for the isomerization using NMR
spectroscopy, and the data have been deposited in the
Supporting Information.25
Figure 2. Hydride region of the 1H NMR spectrum for the titration of
trans-[(dppm)2Ru(H)(P(OiPr)3)][BF4] (trans-4H) with HBF4‚Et2O in CD2-
Cl2. The number of equivalents of acid added with respect to the starting
hydride complex is indicated on the left of each spectrum. Key: (a) trans-
[(dppm)2Ru(H)(P(OiPr)3)][BF4] (trans-4H); (b) cis-[(dppm)2Ru(H)(P(O-
iPr)3)][BF4] (cis-4H); (c) trans-[(dppm)2Ru(H)(PF(OiPr)2)][BF4]; (d) trans-
[(dppm)2Ru(η2-H2)(PF(OiPr)2)][BF4]2 (trans-4H2); (e) cis-[(dppm)2Ru(η2-
H2)(PF(OiPr)2)][BF4]2 (cis-4H2).
1
The H NMR spectra of the cis hydride complexes show
Table 10. T1 (400 MHz, 298 K) Data for the Dihydrogen Complexes
multiplet pattern (spin system XABCDM) for the hydride
ligand. The hydride region of the spectrum of cis-4H was
simulated using a simulation program,26 which matched the
observed spectrum. The cis conformation was also ascer-
tained from the 31P NMR coupling constants (Table 5).4,27
In addition, we determined the X-ray crystal structures of
[(dppm)2Ru(H)(L)][BF4] (L ) P(OMe)3 and P(OiPr)3) com-
plexes to prove the cis conformation without any ambiguity.
complex
T1 (ms)
complex
T1 (ms)
trans-2H2
cis-2H2
trans-3H2
15.8
13.7
14.4
cis-3H2
trans-4H2
cis-4H2
12.3
12.9
12.5
plexes were titrated with HBF4‚Et2O in CD2Cl2. Addition
of 1 equiv of the acid to the hydride complexes transformed
the doublet of quintets into a multiplet pattern in the hydride
1
region of the H NMR spectrum. It was apparent from the
The trans phosphorus ligands in the hydride complexes
were found to be labile. We found small amounts of the free
ligand in CH2Cl2 solutions of the trans hydrides as evidenced
by 31P NMR spectroscopy. When these solutions were
refluxed, the trans hydrides isomerized slowly to give small
quantities of the cis isomers over a period of several days.
Addition of free ligand to these solutions suppressed the
isomerization (Scheme 1). However, when the trans hydrides
were refluxed in CHCl3 solvent (with traces of acid impuri-
ties), the isomerization proceeded much faster. We monitored
the trans-2H to cis-2H isomerization in CHCl3 (with traces
of acid impurities; CDCl3 as external lock) in a sealed NMR
coupling constants that the multiplet was due to a cis isomer,
cis-[(dppm)2Ru(H)(L)][BF4]. Further acid addition led to a
broad singlet due to cis-[(dppm)2Ru(η2-H2)(L)][BF4]2 (L )
P(OMe)3, P(OEt)3) complex that increased in intensity with
increasing number of equivalents of the acid. The complete
conversion required 6 equiv of the acid. The isomerization
proceeds slowly in the presence of e1 equiv of the acid. In
addition to the broad singlet, a weak broad doublet due to
trans-[(dppm)2Ru(η2-H2)(L)][BF4]2 was also obtained.
In the case of trans-4H, the addition of 1 equiv of acid
affords the cis isomer. A small amount of another hydride,
trans-[(dppm)2Ru(H)(PF(OiPr)2)][BF4] (observation of J(P,F)
in the 31P NMR), was also seen. We reported the mechanism
of the formation of an analogous dppe-containing species
earlier.2 The cis-[(dppm)2Ru(η2-H2)(PF(OiPr)2)][BF4]2 (cis-
4H2) and trans-[(dppm)2Ru(η2-H2)(PF(OiPr)2)][BF4]2 (trans-
4H2) complexes resulted upon addition of more acid (Figure
2). The cone angle reduction (in PF(OiPr)2) in the otherwise
sterically crowded P(OiPr)3 to give the trans-[(dppm)2Ru-
(H)(PF(OiPr)2)][BF4] that was observed spectroscopically
seems reasonable. In the cases of the P(OMe)3 and P(OEt)3
(smaller cone angles) hydrides, no fluorine substitution was
observed. We, however, found that, in all the three cases, a
+
tube using 31P NMR. A small amount of HP(OMe)3 (25.0
ppm)23a was found initially along with some free ligand
(138.4 ppm).23a As the reaction progressed, the integral of
the signal due to free ligand reduced and did not undergo
(24) We are studying the kinetics of the isomerization reactions currently,
the results of which will be published shortly.
(25) We were unable to determine the Keq values for the acid-accelerated
isomerization reactions because some amounts of dihydrogen com-
plexes were also formed in the protonation reactions with HBF4‚Et2O
and not just the two isomers.
(26) Bruker WIN-DAISY, 4.05 version.
(27) Mezzetti, A.; Del Zotto, A.; Rigo, P.; Farnetti, E. J. Chem. Soc., Dalton
Trans. 1991, 1525.
Inorganic Chemistry, Vol. 42, No. 1, 2003 193

Mathew et al.
Scheme 1
Scheme 2
Figure 3. ORTEP view of the cis-[(dppm)2Ru(H)(P(OMe)3)]+ (cis-2H)
cation at the 50% probability level. The phenyl groups on the dppm
phosphorus atoms have been omitted for clarity; only one carbon atom of
each of the phenyl groups is shown.
further change with time. The mechanism thus involves the
trans phosphorus ligand loss that is trapped by some external
acid thereby accelerating the isomerization; some free ligand
still remains in equilibrium that binds back to the metal cis
to the hydride to give the isomerized derivative (Scheme 2).
On the other hand, the HBF4‚Et2O added in the protonation
of the trans hydrides serves to trap the free phosphorus ligand
thus accelerating the isomerization. It must be noted that acid
is not required for the isomerization; however, the presence
of it accelerates the reaction.
In the case of the trans-4H complex, a competing reaction
takes place in the presence of excess HBF4‚Et2O in CH2Cl2:
protonation of the trans phosphite ligand to generate a new
trans-[(dppm)2Ru(η2-H2)(PF(OiPr)2)][BF4]2 (trans-4H2) de-
rivative through the intermediacy of trans-[(dppm)2Ru(H)-
(PF(OiPr)2)][BF4]. This hydride complex could not be
isolated; however, it was observed in the 1H NMR spectrum.
In the presence of excess acid, the cis-4H complex gives
cis-4H2 presumably via the cis-[(dppm)2Ru(H)(PF(OiPr)2)]-
[BF4] species which could not be observed spectroscopically.
Structure of cis-[(dppm)2Ru(H)(P(OMe)3)][BF4] (cis-
2H). An ORTEP diagram of the cis-2H cation is shown in
Figure 3. The structure consists of a severely distorted
octahedron: three of the four dppm P atoms define a plane
whereas the fourth phosphorus is approximately trans to the
phosphite ligand that is perpendicular to the plane of the
three dppm P atoms. The hydride ligand that occupies the
sixth coordination site on the metal was not located. The
dppm bite angles P(1)-Ru(1)-P(2) and P(3)-Ru(1)-P(4)
are respectively 71.40(7) and 70.89(7)°. The notable feature
Figure 4. ORTEP view of the cis-[(dppm)2Ru(H)(P(OiPr)3)]+ (cis-4H)
cation at the 50% probability level. The phenyl groups on the dppm
phosphorus atoms have been omitted for clarity; only one carbon atom of
each of the phenyl groups is shown.
of the structure is the tightening of the Ru(1)-P(5) bond
(2.249(2) Å) compared to that of the trans isomer (2.3153-
(17) Å). The pertinent bond lengths and angles are listed in
Table 9.
Structure of cis-[(dppm)2Ru(H)(P(OiPr)3)][BF4] (cis-
4H). An ORTEP view of the cis-4H cation is shown in Figure
4. The structure consists of a severely distorted octahedron
around the metal center with three of the four dppm P atoms
forming a plane, phosphite and the fourth dppm phosphorus
being approximately perpendicular to this plane. The hydride
ligand that could not be located completes the sixth
coordination site around ruthenium. The Ru-P bond lengths
(dppm) are in the range 2.3380(9)-2.4252(9) Å whereas the
Ru-P bond distance (P(OiPr)3) is 2.2924(9) Å. The dppm
194 Inorganic Chemistry, Vol. 42, No. 1, 2003

trans-[(dppm)2Ru(H)(L)][BF4] Complexes
Scheme 3
bite angles P(1)-Ru(1)-P(2) and P(3)-Ru(1)-P(4) are
respectively 72.23(3) and 69.64(3)°. We found that one of
the CH3 groups on the P(OiPr)3 ligand was disordered with
occupancies of 44% and 56%, respectively. The figure shows
only one of the orientations. The salient bond distances and
angles are listed in Table 9.
Loss of H2 takes place in our complex with time; we found
that the loss of H2 is reversible. When H2 gas is purged
through the solutions, the dihydrogen complexes were
recovered.
Protonation Reaction of the Hydride Complexes trans-
[(dppm)2Ru(H)(L)[BF4] (L ) PMe3 (trans-5H), PMe2Ph
(trans-6H)). The protonation of these complexes in CD2Cl2
with 1 equiv of HBF4‚Et2O led to the complete disappearance
of the starting hydride accompanied by the appearance of
cis-[(dppm)2Ru(H)(L)][BF4], cis-[(dppm)2Ru(η2-H2)(L)][BF4]2
(L ) PMe3 (cis-5H, cis-5H2), PMe2Ph (cis-6H, cis-6H2)),
trans-[(dppm)2Ru(η2-H2)(H)][BF4] (trans-1H), and trans-
[(dppm)2Ru(η2-H2)Cl][BF4] (trans-8H2) complexes in the 1H
NMR spectrum. Further acid addition resulted in the disap-
pearance of all the species except trans-8H2. When excess
acid was used, two new signals were observed in the 31P
NMR spectrum assignable to trans-[(dppm)2Ru(BF4)Cl]
(trans-9) along with that of the free ligand. The pathway to
these species is unclear. In the presence of a large excess
acid, the 31P NMR signals of trans-9 broaden and at the same
time move slightly downfield. A similar observation was
made by Morris et al.4 for [(dppe)2RuCl]+. The signal
broadening was explained as a monomer to chloride-bridged
dimer equilibrium as observed for [L2Ru(µ-Cl)2RuL2]2+
(L ) Ph2PCH2CH2-2-py)28 and [(PMe3)4Ru(µ-Cl)]2[Cl]2.29
H-D Isotopomers. The H-D isotopomers were obtained
by exposing the η2-H2 complexes to D2 gas or by the use of
DBF4‚Et2O to deuterate the starting hydrides. Albeniz et al.30
proposed that a combination of the lability and the acidity
of the H2 ligand is responsible for the isotopic scrambling
to form the HD isotopomers. The η2-HD ligand was observed
Reactivity of trans-[(dppm)2RuH(Cl)] (trans-8H). The
trans-8H complex was prepared from cis/trans-[(dppm)2RuH2]
using a method adapted from literature: the dihydrides are
unstable in CHCl3; upon dissolving in CHCl3, the hydride
chloride complex was obtained.16 Protonation of trans-8H
with 1 equiv of HBF4‚Et2O gave the corresponding dihy-
drogen complex, trans-[(dppm)2Ru(η2-H2)(Cl)][BF4] (trans-
8H2). In the context of losing HCl instead of H2 in its
reactivity trans-8H2 is similar to trans-[(dppe)2Ru(η2-H2)-
(Cl)][BF4].4 When trans-8H was reacted with 1 equiv of the
acid in the presence of excess P(OEt)3 [(dppm)2RuH-
(P(OEt)3)][BF4] (cis-3H (minor) and trans-3H (major)) were
obtained. The reaction could involve an intermediate η2-H2
complex that loses HCl. We have not detected the HCl
directly. The phosphite attacks the metal on the vacant site
generated by the elimination of HCl resulting in [(dppm)2RuH-
(P(OEt)3)][BF4]. When trans-8H was first protonated with
1 equiv of acid followed by a titration with phosphite (1-5
equiv in increments of 1 equiv), cis-3H was obtained as the
major product with a small amount of the trans isomer. These
reactions are shown in Scheme 3.
Protonation Reactions of cis-[(dppm)2Ru(H)(L)][BF4]
(L ) P(OMe)3 (cis-2H), P(OEt)3 (cis-3H), P(OiPr)3 (cis-
4H)). The protonation reactions of mixtures of trans (minor)
and cis hydride phosphite (major) complexes were carried
out under an H2 atmosphere in CD2Cl2 using excess HBF4‚
Et2O. When the protonation was carried out in an Ar
atmosphere, signals due to the η2-H2 complexes cis-
[(dppm)2Ru(η2-H2)(L)][BF4]2 (L ) P(OMe)3 (cis-2H2), P(O-
Et)3 (cis-3H2), PF(OiPr)2 (cis-4H2)) were not observed. In
fact no resonances were observed in the hydride region which
could mean that although protonation did take place, the H2
ligand due to its lability is eliminated under argon. We found
a singlet at δ 4.6 ppm assignable to free H2 in the 1H NMR
spectrum.
1
in the H NMR spectrum by nullifying the residual η2-H2
signal by an inversion recovery pulse sequence.31,32 The
spectra exhibit triplet signals for the cis-[(dppm)2Ru(η2-HD)-
(L)][BF4]2 complexes the intensity ratios of which are
(28) Costella, L.; Del Zotto, A.; Mezzetti, A.; Zangrando, E.; Rigo, P. J.
Chem. Soc., Dalton Trans. 1993, 3001.
(29) Jones, R. A.; Real, F. M.; Wilkinson, G.; Galas, A. M. R.; Hursthouse,
M. B.; Malik, K. M. A. J. Chem. Soc., Dalton Trans. 1980, 511.
(30) Albeniz, A. C.; Heinekey, D. M.; Crabtree, R. H. Inorg. Chem. 1991,
30, 3632.
(31) Bautista, M. T.; Earl, K. A.; Maltby, P. A.; Morris, R. H.; Schweitzer,
C. T.; Sella, A. J. Am. Chem. Soc. 1988, 110, 7031.
(32) Chinn, M. S.; Heinekey, D. M.; Payne, N. G.; Sofield, C. D.
Organometallics 1989, 8, 1824.
The 1H NMR spectrum of the dihydrogen complex shows
a broad singlet in the hydride region for the η2-H2 ligand.
Inorganic Chemistry, Vol. 42, No. 1, 2003 195

Mathew et al.
Table 11. Properties of Dihydrogen Complexes of Ruthenium
complex
E1/2, Va
J(H,D), Hz
26
26
24
dHH, Åb
0.99
0.99
1.00
stabilityc
trans-[(dppm)2Ru(H2)Cl]+
trans-[(dppe)2Ru(H2)Cl]+ d
trans-[(dppp)2Ru(H2)Cl]+ e
trans-[(dppm)2Ru(H2)H]+
trans-[(dppm)2Ru(H2)(P(OR)3)]2+
2.0
1.8
1.8
1.9
2.7
s
s
u
s
u
u
u
u
29
0.94
32 (R ) Me)
30 (R ) Et)
29 (R ) Me)
26 (R ) Et)
29 (R ) Me)
28 (R ) Et)
32.2
0.88 (R ) Me)
0.92 (R ) Et)
0.94 (R ) Me)
0.99 (R ) Et)
0.94 (R ) Me)
0.95 (R ) Et)
0.88
cis-[(dppm)2Ru(H2)(P(OR)3)]2+
trans-[(dppe)2Ru(H2)(PF(OR)2)]2+ f
trans-[(dppm)2Ru(H2)(CNH)]2+ i
2.7
nag
nag
1dh
1dh
u
a Calculated E1/2 values of the N2 complexes.41 b Calculated from the J(H,D) values of the HD isotopomers using the equation given in ref 34. c Stability
with respect to loss of H2 at room temperature (s ) stable; u ) unstable); see ref 41 for definition of categories. d Reference 4. e Reference 39. f Reference
2. g Not available. h Loss of H2 starts to occur after ca. 24-36 h. i Reference 5.
approximately 1:1:1 with J(H,D) of 29, 26, and 29 Hz for
cis-2HD, cis-3HD, and cis-4HD, respectively. The trans-
[(dppm)2Ru(η2-HD)(P(OMe)3)][BF4]2 (trans-2HD) and trans-
[(dppm)2Ru(η2-HD)(P(OEt)3)][BF4]2 (trans-3HD) complexes
gave doublets of triplets with J(H,D) of 32 and 30 Hz,
respectively. The H-H distances (dHH) calculated from the
inverse relationship between dHH and J(H,D) of the HD
isotopomers33,34 are 0.88, 0.94, 0.92, 0.99, and 0.94 Å
respectively for trans-2H2, cis-2H2, trans-3H2, cis-3H2, and
cis-4H2.
Comments on H-H Distances and the Stabilities of the
Dihydrogen Complexes. The complexation of H2 to a metal
is considered to result from the σ (η2-H2) donation to the
empty d (M) orbital and π back-donation from the filled d
(M) orbital to the σ* (η2-H2) orbital. Table 11 shows a
comparison of some of the properties of our H2 complexes
and also the ones reported by others. The weak trans
influence of Cl-, a π-donor ligand, favors the σ donation
from H2 to metal d orbitals and an increased back-donation
from the metal to the σ* orbital of H2. These effects,
consequently, weaken the H-H bond and increase the M-H2
hydrides. With respect to exhibiting high reactivity toward
heterolysis combined with tight binding of H2 to the metal,
trans-8H2 behaves similar to certain other derivatives
reported (highly acidic) in the literature.4,38-40
In light of the calculated oxidation potentials of the
corresponding N2 complexes as suggested by Morris,41 our
dihydrogen complexes may be categorized as having labile
H2 ligands. It was suggested that if the E1/2 value of the
corresponding N2 complex is >2.0 V, the dihydrogen
complex can be predicted to be unstable with respect to loss
of H2 at 298 K under Ar. The dihydrogen complexes reported
in this work are fully formed under 1 atm of H2; upon loss
of the H2 ligand, the dihydrogen complex could be recovered
by purging the solution containing the [(dppm)2Ru(P(OR)3)]2+
with H2 gas.42 This is in contrast to our earlier findings2 on
the dppe analogues wherein we noted that the trans-
[(dppe)2Ru(η2-H2)(PF(OR)2)]2+ complexes could be gener-
ated either under Ar or H2 atmosphere.43 Those derivatives
were stable with respect to loss of H2 ligand; however, upon
loss of H2 (typically ca. 24-36 h), the dihydrogen complexes
could not be recovered which could mean that the 5
coordinate species is highly reactive. We44 found that this
species picks up either a water molecule (residual water in
the solvent) or dioxygen and generates species that we have
not able to identify.
interaction. Thus, a relatively long H-H distance (dHH
)
0.99 Å) is consistent with the tight binding of H2 to the metal
as found in trans-8H2. When solutions containing trans-8H2
were exposed to D2 gas for prolonged periods, no observable
deuterium incorporation was found. This is in contrast to
the observations made by Kubas et al.35 on the neutral
tungsten complex, by Heinekey et al.36 on the cationic
rhenium derivatives, and by us2,37 on certain ruthenium dppe
complexes that undergo rapid H2/D2 exchange. It was earlier
suggested that complexes bearing elongated H-H bond are
less acidic compared to those with a short H-H bond.6e
However, we speculate that trans-8H2 might show greater
acidity than expected. This is demonstrated by its reactions
with phosphites. It eliminates HCl to give the phosphite
One another observation is the long H-H bond in the cis
H2 phosphite complexes compared to the trans ones. The
cis complexes have phosphine ligands (not as strong as
phosphites in terms of π acidity) trans to the H2 that results
in this bond elongation.45,46
(38) Luther, T. A.; Heinekey, D. M. Inorg. Chem. 1998, 37, 127.
(39) Rocchini, E.; Mezzetti, A.; Ru¨egger, H.; Burckhardt, U.; Gramlich,
V.; Del Zotto, A.; Martinuzzi, P.; Rigo, P. Inorg. Chem. 1997, 36,
711.
(40) Forde, C. E.; Landau, S. E.; Morris, R. H. J. Chem. Soc., Dalton Trans.
1997, 1663.
(41) Morris, R. H. Inorg. Chem. 1992, 31, 1471.
(33) (a) Heinekey, D. M.; Luther, T. A. Inorg. Chem. 1996, 35, 4396. (b)
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. (c) King, W. A.; Luo, X.-L.; Scott, B. L.; Kubas,
G. J.; Zilm, K. W. J. Am. Chem. Soc. 1996, 118, 6782.
(34) dHH (Å) ) -0.0167[J(H,D) (Hz)] + 1.42.
(42) We have noted the five coordinate species to be quite stable; even
after the complete loss of H2 (typically overnight), the dihydrogen
complex was recovered by purging the solution with H2.
(43) The electrochemical parameter EL for PF(OR)2 ligands is not known.
(44) Mathew, N.; Jagirdar, B. R. Unpublished results.
(45) Jørgensen, C. K. Modern Aspects of Ligand Field Theory; North-
Holland: Amsterdam, 1971.
(46) (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) Jones, C. E.; Coskran, K. J. Inorg. Chem.
1971, 10, 55.
(35) Kubas, G. J.; Burns, C. J.; Khalsa, G. R. K.; Van der Sluys, L. S.;
Kiss, G.; Hoff, C. D. Organometallics 1992, 11, 3390.
(36) Heinekey, D. M.; Schomber, B. M.; Radzewich, C. E. J. Am. Chem.
Soc. 1994, 116, 4515.
(37) Mathew, N.; Jagirdar, B. R. Inorg. Chem. 2000, 39, 5404.
196 Inorganic Chemistry, Vol. 42, No. 1, 2003

trans-[(dppm)2Ru(H)(L)][BF4] Complexes
Conclusions
the cone angles and the π-acidities of the monodentate
phosphorus ligands can have a profound effect on the
properties of the dihydrogen complexes.
The protonation reactions of the hydride complexes trans-
[(dppm)2Ru(H)(L)][BF4] (L ) P(OR)3) with HBF4‚Et2O gave
pure cis hydride phosphite derivative, cis-[(dppm)2Ru(H)-
(L)][BF4] for L ) P(OiPr), whereas, for L ) P(OMe)3 and
P(OEt)3, equilibrium mixtures of both the cis and trans
isomers are produced, the separation of which is somewhat
difficult. The isomerization seems to be accelerated by acid
via the trapping of the labile trans phosphorus ligand by the
added acid. Further addition of acid to the cis hydride
complexes results in the corresponding dihydrogen com-
plexes, the first examples in this class of complexes wherein
the H2 and the monodentate phosphorus ligands are in cis
conformations. The dihydrogen ligand in these systems was
found to be quite labile.
The starting trans hydride complexes bearing the phos-
phine ligands (PR3) also behave in a similar manner with
respect to isomerization. However, further addition of the
acid to mixtures of the cis and the trans hydrides results in
trans-[(dppm)2Ru(BF4)Cl]. From this study it can be con-
cluded that the bite angles of the diphosphine moieties and
Acknowledgment. We are grateful to the Department of
Science and Technology, Government of India, for financial
support; N.M. thanks the Council of Scientific and Industrial
Research for a fellowship. We thank the Sophisticated
Instruments Facility, IISc, for the NMR spectral data and
Prof. C. N. R. Rao and Dr. G. U. Kulkarni (JNCASR) for
allowing us to use the X-ray diffractometer facility. We thank
the reviewers for helpful comments.
Supporting Information Available: Tables of crystal data,
structure solution and refinement, atomic coordinates, bond lengths
and angles, anisotropic thermal parameters, and hydrogen atom
coordinates for trans-2H, cis-2H, and cis-4H, in CIF format, a table
of Keq data for the trans/cis isomerization reaction, and a figure
showing the 1H NMR spectra of the hydride region for the titration
of trans-2H with HBF4‚Et2O. This material is available free of
charge via the Internet at http://pubs.acs.org.
IC020082N
Inorganic Chemistry, Vol. 42, No. 1, 2003 197