Synthesis of the acidic dihydrogen complexes trans-[M(H2)(CN)L2]+ and trans-[M(H2)(CNH)L2]2+ where M = Fe, Ru, Os and L = dppm, dppe, dppp, depe, and dihydrogen substitution by the trifluoromethanesulfonate anion to give trans-[Ru(OTf)(CN)L2] or trans-[Ru(OTf)(CNH)L2]OTf

Article abstract of DOI:10.1039/a906717e

Very acidic complexes trans-[M(η²-H₂)(CN)L₂]⁺ and trans-[M(η²-H₂)(CNH)L₂]²⁺, with the dihydrogen ligand trans to the cyanide or to the hydrogen isocyanide ligand, are generated by reaction of trifluoromethanesulfonic acid (HOTf) with hydrido(cyano) complexes of Fe(II), Ru(II) and Os(II). The use of the different metals and phosphines (dppm = [bis(diphenylphosphino)methane], dppe = [1,2-bis(diphenylphosphino)ethane], dppp = [1,3-bis(diphenylphosphino)propane], and depe = [1,2-bis(diethylphosphino)ethane]) as ancillary ligands influences the stability and the reactivity of these complexes. The iron and osmium complexes are more stable than the ruthenium complexes that lose the dihydrogen ligand and coordinate the trifluoromethanesulfonate anion. The crystal structure of trans-[Ru(OTf)(CN)(dppe)₂] is reported. The Ru-OTf bond is weak and so the triflate ligand can be displaced by H₂(g) to give trans-[Ru(η²-H₂)(CN)L₂]OTf. There is a delicate balance of stability between the complexes trans-[M(η²-H₂)(CN)L₂]⁺ and trans-[M(H)(CNH)L₂]⁺, M = Fe, Ru, determined by electronics and hydrogen bonding, both classical (CNH ... OTf^-, TfOH ... OTf^-) and non-classical (MH₂ ... OTf^-). Therefore isomerisation reactions between these forms are observed for the first time. In order to determine where the protonation occurs it is useful to use a cyanide group labeled as C¹⁵N or ¹³CN. It is significant that the very acidic dihydrogen complex trans-[Ru(η²-H₂)(CNH)L₂]OTf is observed to form from the reaction of the weak Bronsted acids H₂ and trans-[Ru(OTf)(CNH)L₂]OTf in CH₂Cl₂; the dihydrogen complex releases HOTf. The chemistry is of possible relevance to the action of iron-containing hydrogenases. The Royal Society of Chemistry 1999.

Full text of DOI:10.1039/a906717e

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Synthesis of the acidic dihydrogen complexes trans-[M(H2)-
(CN)L2]؉ and trans-[M(H2)(CNH)L2]2؉ where M ؍ Fe, Ru, Os
and L ؍ dppm, dppe, dppp, depe, and dihydrogen substitution by
the trifluoromethanesulfonate anion to give trans-[Ru(OTf)(CN)L2]
or trans-[Ru(OTf)(CNH)L2]OTf†
Tina P. Fong,a Cameron E. Forde,a Alan J. Lough,a Robert H. Morris,*a Pierluigi Rigo,*b
Eliana Rocchinib and Tim Stephana
a Department of Chemistry, University of Toronto, 80 St. George St., Toronto, Ontario,
Canada M5S 3H6. E-mail: rmorris@chem.utoronto.ca
b Dip. di Scienze e Tecnol. Chimiche, Università di Udine, Via del Cotonificio 108, I-33100
Udine, Italy. E-mail: Pierluigi.Rigo@Dstc.uniud.it
Received 18th August 1999, Accepted 25th October 1999
Very acidic complexes trans-[M(η2-H2)(CN)L2]ϩ and trans-[M(η2-H2)(CNH)L2]2ϩ, with the dihydrogen ligand trans to
the cyanide or to the hydrogen isocyanide ligand, are generated by reaction of trifluoromethanesulfonic acid (HOTf)
with hydrido(cyano) complexes of Fe(), Ru() and Os(). The use of the different metals and phosphines (dppm =
[bis(diphenylphosphino)methane], dppe = [1,2-bis(diphenylphosphino)ethane], dppp = [1,3-bis(diphenylphosphino)-
propane], and depe = [1,2-bis(diethylphosphino)ethane]) as ancillary ligands influences the stability and the reactivity
of these complexes. The iron and osmium complexes are more stable than the ruthenium complexes that lose the
dihydrogen ligand and coordinate the trifluoromethanesulfonate anion. The crystal structure of trans-[Ru(OTf)(CN)-
(dppe)2] is reported. The Ru–OTf bond is weak and so the triflate ligand can be displaced by H2(g) to give trans-
[Ru(η2-H2)(CN)L2]OTf. There is a delicate balance of stability between the complexes trans-[M(η2-H2)(CN)L2]ϩ
and trans-[M(H)(CNH)L2]ϩ, M = Fe, Ru, determined by electronics and hydrogen bonding, both classical
(CNH ؒ ؒ ؒ OTfϪ, TfOH ؒ ؒ ؒ OTfϪ) and non-classical (MH2 ؒ ؒ ؒ OTfϪ). Therefore isomerisation reactions between
these forms are observed for the first time. In order to determine where the protonation occurs it is useful to use a
cyanide group labeled as C15N or 13CN. It is significant that the very acidic dihydrogen complex trans-[Ru(η2-H2)-
(CNH)L2]OTf is observed to form from the reaction of the weak Brønsted acids H2 and trans-[Ru(OTf)(CNH)L2]-
OTf in CH2Cl2; the dihydrogen complex releases HOTf. The chemistry is of possible relevance to the action of iron-
containing hydrogenases.
(η2-H2)]OTf 9 and [(triphos)Ir(η2-H2)(H)2]BPh4 (triphos =
Introduction
MeC(CH2PPh2)3).10
There is an interest in determining how acidic dihydrogen can
In this paper we give the complete details of our studies of
become when coordinated as an η2-H2 ligand. Cationic and
dihydrogen complexes 3Mj or 4Mj derived from protonating
complexes trans-[MH(CN)L2], 1Mj, where the numbering
scheme is explained in Table 1. Protonation can take place at
three different sites in these complexes (Scheme 1): (i) at the
especially dicationic η2-dihydrogen complexes can be more
acidic than strong acids like protonated diethyl ether or triflic
acid (CF3SO3H, HOTf) in CH2Cl2, particularly when π-acid
ligands like CO or CNH are present in the complex. Examples
cyanide to give a hydrogen isocyanide ligand; () at the metal–
from our groups that are as acidic or more acidic than
hydride bond to produce a dihydrogen complex; (iii) at the
triflic acid in CH2Cl2 include trans-[Fe(η2-H2)(CO)(dppe)2]2ϩ 1
,
metal to give a dihydride complex. An interesting complication
is the fact that the pKa of coordinated hydrogen isocyanide
might be in a similar range to that of monocationic dihydrogen
complexes. At least one pKa determination of a CNH ligand
has been reported: the pKa of [Fe(CNH)(CN)5]3Ϫ in water is
4.2.11 Several dihydrogen complexes in CH2Cl2 or THF have
similar acidities to acids that have pKa in the range 0–10 in
water.12 Therefore there is the possibility of tautomers forming
and indeed this is observed in the current work for the first time
for cyanide ligands. There are only a few examples of tauto-
meric equilibria between dihydrogen complexes and hydride
complexes with a protonated ligand. These include [Os(H2)-
(quinS)(CO)(PPh3)2]ϩ (quinS = quinoline-8-thiolate)13,14 and
[{η5-C5H4(CH2)3NMe2Hϩ}RuH(dppm)]BF4.15 Some of us have
already reported the important effect of the ancillary ligand
on the protonation of hydridocyano complexes.16 With the
basic depe ligand, protonation at the Fe–H bond in trans-
[FeH(CN)(depe)2] 1Fe4 is thermodynamically favored to give
trans-[M(CO)(η2-H2)(dppp)2]2ϩ (M = Ru, Os)2 and trans-
[Ru(η2-H2)(CNH)(dppe)2]2ϩ.3 These complexes are surprisingly
stable with respect to the loss of H2(g).1 This was rationalised
in terms of an increase in importance of the metal–H2
σ bond to compensate for the lack of π-backdonating ability
of these electrophilic metal centres. Other highly acidic di-
hydrogen complexes included [Os(η2-H2)(PPh3)2(bpy)(CO)]2ϩ 4
,
cis-[Re(CO)4(η2-H2)(PR3)]ϩ,5
[Ru(η2-H2)(PPh3)(CO)(tacn)]2ϩ
[Ru(C5Me5)(η2-H2)(CO)2]BF4,6
(tacn = 1,4,7-triazacyclo-
nonane),7 trans-[Os(η2-H2)(CH3CN)(dppe)2]2ϩ,8 [Cp*Os(CO)2-
† Supplementary data available: rotatable 3-D crystal structure diagram
in CHIME format. See http://www.rsc.org/suppdata/dt/1999/4475/
Also available: additional experimental and spectroscopic data. For
direct electronic access see http://www.rsc.org/suppdata/dt/1999/4475/,
otherwise available from BLDSC (No. SUP 57672, 6 pp.) or the RSC
library. See Instructions for Authors, 1999, Issue 1 (http://www.rsc.org/
dalton).
J. Chem. Soc., Dalton Trans., 1999, 4475–4486
This journal is © The Royal Society of Chemistry 1999
4475

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triflate. For example there is a related Os(HH) ؒ ؒ ؒ FBF3Ϫ inter-
Table 1 The numbering scheme for the complexes iMJ as triflate salts
and other saltsa
8
action in trans-[Os(η2-H2)(CH3CN)(dppe)2](BF4)2 and IrCl-
ؒ ؒ ؒ (HH)Ir hydrogen bonds in Ir(η2-H2)(Cl)2(H)(PiPr3)2.23
Finally this chemistry is relevant to the chemistry of iron–
nickel and iron-only hydrogenases which also appear to be low-
spin Fe() cyanide complexes that activate dihydrogen.24–27 The
Abbrevi-
ation
iMj
i
M
j
L
[MH(CN)L2]
1
2
3
4
Fe
Ru
Os
1
2
3
4
PPh2CH2PPh2
dppm
[MH(CNH)L2]OTf
[M(η2-H2)(CN)L2]OTf
[M(η2-H2)(CNH)L2]-
(OTf)2
PPh2(CH2)2PPh2 dppe
PPh2(CH2)3PPh2 dppp
PEt2(CH2)2PEt2 depe
iron–nickel active site might have dihydrogen coordinated as
nϪ
(cysteine)2Ni(µ-cysteine)2Fe(η2-H2)(CO)(CN)2
before it is
released as H2(g) while the iron-only active sites might have
(cysteine)3Fe4S4(µ-cysteine)Fe2(CO)x(CN)y(η2-H2) composition
before dihydrogen is separated into protons and electrons. The
possible formation of a hydrogen isocyanide ligand at these
sites has not been discussed.
[M(OTf)(CN)L2]
[M(OTf)(CNH)L2]OTf
5
6
Other salts
i
M
j
[Ru(η2-H2)(CN)(dppe)2](TfO ؒ ؒ ؒ HOTf)
[Ru(η2-H2)(CNH)(dppe)2]-
(TfO ؒ ؒ ؒ HOTf)2
3Ј
4Ј
Ru
Ru
2
2
Results and discussion
Observation of the species formed by protonation of trans-
[MH(CN)L2]
[Os(η2-H2)(CN)(dppe)2]BF4
3*
3*
3*
4*
Os
Fe
Ru
Fe
2
4
4
4
[M(η2-H2)(CN)(depe)2]BF4
[Fe(η2-H2)(CNH)(depe)2](BF4)2
Ά
Scheme 2 outlines the formation of the important hydride and
a In addition further symbols are used for 13C labelled complexes (c), 2H
labelled complexes (d) and 15N labelled complexes (n) e.g. iMj-c.
Scheme 1 Protonation can take place at (i) the cyanide, () the metal–
hydride bond, or (iii) the metal.
trans-[Fe(η2-H2)(CN)(depe)2]OTf 3Fe4 while with the analo-
gous dppe complex 1Fe2, the proton ends up on the nitrogen to
give trans-[Fe(H)(CNH)(dppe)2]OTf 2Fe2. Further chemistry
of 2Fe2 has recently been reported.17
Scheme 2 The preparative routes. [M] refers to the M(diphosphine)2
fragment. The solvent is CH2Cl2 or CD2Cl2 although parts of the
Scheme are valid for other solvents as indicated in the text.
In certain cases, as described in our recent communication,3
very acidic dihydrogen complexes such as trans-[Ru(η2-H2)-
(CNH)(L)2]2ϩXϪ L = dppe, X = (TfO ؒ ؒ ؒ HOTf) 4ЈRu2, L =
dihydrogen complexes characterised in this work. Only certain
of the pathways are followed for each combination of ligands,
metal, solvent and acid. The protonation reactions of the dppp
complexes 1M3, M = Ru, Os, are the most straightforward and
will be described first. Then the other systems will be described
and finally the detailed characterization of the complexes. In
general these highly acidic, reactive complexes are difficult to
crystallise and characterise by elemental analysis. Most of the
characterization is spectroscopic in nature. In particular,
important NMR properties of the dihydrogen complexes are
listed in Table 2. The properties of complexes 1Mj and 2Mj can
be found elsewhere.28
2
dppp, X = OTf 4Ru3 can be generated by displacing coordin-
ated triflate in trans-[Ru(OTf)(CNH)(L)2]OTf (6Ru2 or 6Ru3)
with dihydrogen gas. Only a few other highly acidic complexes
have been generated by use of dihydrogen gas. These are
[(triphos)Ir(η2-H2)(H)2]BPh4 by hydrogenation of the ethene
complex [(triphos)Ir(η2-C2H4)(H)2]BPh4,10 and cis-[Re(η2-H2)-
(PR3)(CO)4] by displacement of CH2Cl2 from cis-[Re(η1-
ClCH2Cl)(PR3)(CO)4]ϩ.5
Hydrogen-bonding interactions are expected to be very
important for this chemistry in low dielectric solvents. The
CNH ligand is an excellent hydrogen bond donor. It is known
Ϫ
to donate hydrogen bonds to the fluoride of a PF6 anion and
Addition of HOTf to trans-[RuH(CN)(dppp)2] 1Ru3 and related
reactions
to the oxygen of ethers.18 Recently, Sapunov et al. reported the
crystalline structures of [Ru2Cp2(PPh3)4(µ-CNHNC)]CF3SO3,
a bridged complex with a short (2.573 Å) N(H) ؒ ؒ ؒ N bond
length, and of [RuCp(PPh3)2(CNH)]CF3SO3, where the CNH
group forms a strong hydrogen bond to the triflate group,
N ؒ ؒ ؒ O = 2.75 Å.19 We have also previously published the solid-
state structure of trans-[Ru(OTf)(CNH)(dppe)2]OTf, 6Ru2,
where the N ؒ ؒ ؒ O distance is found to be 2.62 Å.3 This complex
has a long Ru–OTf bond of 2.299 Å, longer than that of other
ruthenium()-triflate complexes.20–22
The stepwise protonation of 1Ru3 in CD2Cl2 with HOTf can be
conveniently followed by NMR spectroscopy. 31P and 1H NMR
measurements confirm that the addition of HOTf to a solution
of 1Ru3 results mainly in protonation of the CN ligand to give
trans-[RuH(CNH)(dppp)2]OTf, 2Ru3 (step i, Scheme 2). When
less than one equivalent is added, the hydride resonances and
the 31P resonances of 1Ru3 and 2Ru3 are averaged by fast pro-
ton transfer. However there is also the immediate formation of
a small amount of the dihydrogen complex trans-[Ru(η2-H2)-
(CN)(dppp)2]OTf 3Ru3 (step ii, Scheme 2) as indicated by
In addition there is the possibility that the dihydrogen ligand
might act as an unconventional hydrogen bond donor to
4476
J. Chem. Soc., Dalton Trans., 1999, 4475–4486

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Table 2 Characteristics of dihydrogen complexes observed (in CD2Cl2)
J(HD)/
Hz
d(H–H) from
J(HD)/Å
d(H–H) from
Complex
1H NMR/δ
31P{1H}NMR/δ
T1(min)/ms
T1(min)/Åa
3Ru1
Ϫ4.7 (br)
Ϫ3.7 (br)b
Ϫ8.7 (br)
Ϫ9.1 (br)
Ϫ7.3 (br)c
Ϫ5.5 (br)
Ϫ5.9 (br)
Ϫ6.4 (br)
Ϫ6.1 (br)
Ϫ5.4 (br)
Ϫ4.2 (br)
Ϫ4.6 (br)
Ϫ14.0 (br)
Ϫ12.1 (br)
Ϫ9.1 (br)
Ϫ9.5 (br)
Ϫ8.1 (br)
Ϫ6.1 (br s)
Ϫ12.2 (br s)b
72.2 (s)
32.0
32.2b
32.7
32.5
32.5
32.0
32.4
28.7
29.1
31.6
31.8
28.8
31.6
0.89
0.88b
0.87
0.88
0.88
0.89
0.88
0.94
0.93
0.89
0.89
0.94
0.89
5.8d (213 K)
6.4d (233 K)
11.7e (234 K)
21.5f (262 K)
0.81, 1.02
0.82, 1.04
0.85, 1.07
0.87, 1.09
4Ru1
3Fe2
4Fe2
70.4 (s)
3Ru2
53.7 (s)c
54.2 (s)
3ЈRu2g
4ЈRu2
3*Os2h
4Os2-c
3Ru3
12.4e (240 K)
13.6e (247 K)
14.7e (233 K)
14e (253 K)
5.4d (223 K)
5.9d (233 K)
7.6d (233 K)
15.2i (262 K)
19.0i (229 K)
12.8e (191 K)
16e (213 K)
12e (223 K)
0.86, 1.08
0.87, 1.10
0.88, 1.11
0.88, 1.11
0.80, 1.01
0.81, 1.02
0.85, 1.07
0.85, 1.07
0.88, 1.11
0.86, 1.09
0.90, 1.13
0.86, 1.08
52.2 (s)
21.7 (s)
22.0 (d)
9.7 (br s)
8.9 (br s)
Ϫ29.4 (br s)
77.7 (s)
72.5 (s)
54.4 (s)
4Ru3
4Os3
3*Fe4 h
4Fe4
3*Ru4h
3Os4-c
4Os4
21.7 (d)
17.9 (s)
25.4
1.00
a The first value is calculated for the fast spinning while the second is referred to the slow spinning. b Values measured at 193 K. c NMR spectra
recorded at 263 K. d T1 measured at 200 MHz. e T1 measured at 300 MHz. f T1 measured at 500 MHz; see ref. 1. g (TfO ؒ ؒ ؒ HOTf)Ϫ counter anion.
h BF4Ϫ counter anion. i T1 measured at 400 MHz.
1
the appearance in the H NMR spectrum of a broad signal at
δ Ϫ5.4 due to a dihydrogen ligand. This new complex is also
visible in the 31P NMR spectrum as a broad singlet centered at
δ 9.7. The integration of the 31P NMR signals indicates that
in a 32 mM solution of 1Ru3 the amount of the dihydrogen
complex 3Ru3 formed is ca. 6% and 10% for the molar ratios
HOTf–1Ru3 of 0.5 and 1, respectively. We do not know why
3Ru3 forms quickly in this reaction when it is only produced
slowly when pure 2Ru3 is dissolved in CH2Cl2 (see below).
For HOTf–1Ru3 > 1 both complexes 2Ru3 and 3Ru3 react
with HOTf to give the dihydrogen complex trans-[Ru(η2-H2)-
(CNH)(dppp)2](OTf)2, 4Ru3 (steps vii, viii, Scheme 2). Thus for
a molar ratio = 2 the solution contains a mixture of the com-
plexes 2Ru3, 3Ru3 and 4Ru3; if the solution is under Ar, the H2
is slowly lost and an increasing amount of the derivative trans-
[Ru(OTf)(CNH)(dppp)2]OTf 6Ru3 is formed (step xiii, Scheme
2). If the protonation is carried out under H2 the formation of
6Ru3 is inhibited. When a molar ratio greater than 3 is used the
complex 4Ru3 is quantitatively formed.
NMR spectrum shows 90% of 2Ru3 and 10% of 3Ru3; in
Cl2CDCDCl2 (after 12 hours) the percentage is 53% for 2Ru3
and 47% for 3Ru3. The same equilibrium mixtures are slowly
obtained starting from the complex 3Ru3. This complex can be
generated by reacting a red solution of [Ru(OTf)(CN)(dppp)2]
5Ru3 (see below) with H2 (step v, Scheme 2).
The addition of an excess of HOTf to a solution of 1Ru3
in C6H6 or CH2Cl2 under 1 atm H2 gives trans-[Ru(η2-H2)-
(CNH)(dppp)2](OTf)2 4Ru3 as a yellow oil. The dicationic
dihydrogen complex is very acidic because, when it is treated
with diethyl ether, it produces a mixture of complexes trans-
[RuH(CNH)(dppp)2]OTf 2Ru3 and trans-[Ru(η2-H2)(CN)-
(dppp)2]OTf 3Ru3 and presumably the strong acid [HOEt2]OTf.
Addition of HOTf to trans-[OsH(CN)(dppp)2] 1Os3. When
HOTf is added to a CD2Cl2 solution of 1Os3 at room temper-
ature, the CNH derivative 2Os3 is the first species observed by
1
use of 31P and H NMR. In contrast to 1Ru3, there is no evi-
dence for the formation of the cyanide dihydrogen complex
trans-[Os(η2-H2)(CN)(dppp)2]ϩ. Further protonation at the
hydride (step vii, Scheme 2) produces the dicationic dihydrogen
complex trans-[Os(η2-H2)(CNH)(dppp)2] (OTf)2 4Os3 as indi-
cated by the appearance of the broad signal at δ Ϫ4.6 in the
high-field range of the 1H NMR spectrum. The protonation of
trans-[OsH(CN)(dppp)2] 1Os3 in C6H6 or CH2Cl2 solution
under 1 atm. of H2 with an excess of HOTf gives 4Os3 as white
solid. This dihydrogen complex is stable with respect to the loss
of H2 both in the solid state and in solution.
The stepwise protonation of the 13CN enriched compound
trans-[RuH(13CN)(dppp)2] 1Ru3-c to give the corresponding
complexes 2Ru3-c, 3Ru3-c and 4Ru3-c was also studied in
CD2Cl2 by 13C{1H} NMR. The protonation of the 13CN group
to produce 13CNH results in a broadening of the 13C resonance
which shifts to low field (from δ 156.7 for 1Ru3-c to δ 165.5
for 2Ru3-c). For HOTf–1Ru3-c in a molar ratio less than one,
a binomial quintet attributable to 3Ru3-c is also observed at
δ 142.4. When the molar ratio HOTf–1Ru3-c increases, the
protonation occurs both at the Ru–H of 2Ru3-c and at the
nitrogen of the 13CN of 3Ru3-c with the final formation of
4Ru3-c, which shows the 13CNH resonance as a broad quintet
at δ 149.9. In solution the complex 4Ru3-c slowly loses H2
to give trans-[Ru(OTf)(13CNH)(dppp)2]OTf 6Ru3-c which
exhibits a 13C signal at δ 159.7.
Addition of HOTf to trans-[MH(CN)(dppm)2] 1Ru1, 1Os1 and
related reactions
When 1 equivalent of HOTf is added to a solution of 1Ru1 in
CD2Cl2 under H2, the complexes [Ru(H)(CNH)(dppm)2]OTf
2Ru1 and [Ru(η2-H2)(CN)(dppm)2]OTf 3Ru1 appear in the
ratio 91:9. The NMR properties of 3Ru1 are listed in Table 2.
This ratio is modified to 58:42 if the reaction occurs in Cl2-
CDCDCl2. An excess of triflic acid added to a CD2Cl2 solution
of 1Ru1 produces a dihydrogen complex, probably 4Ru1, that is
highly unstable at room temperature. It loses the dihydrogen
ligand rapidly to give [Ru(OTf)(CNH)(dppm)2]OTf 6Ru1,
which is identified by a singlet at δ Ϫ11.0 in the 31P NMR
spectrum. A solution of this dihydrogen complex 4Ru1 at
Ϫ80 ЊC has been characterised by NMR (Table 2). Formation
of the dihydrogen complex 3Ru1 can also be observed start-
ing from a 2Ru1 solution in CD2Cl2 or in Cl2CDCDCl2. The
When the protonation of 1Ru3 with HOTf under H2 is
carried out in Cl2CDCDCl2, a larger ratio of 3Ru3 to 2Ru3 is
observed (47:53) compared to the reaction in CD2Cl2 solution.
Furthermore, when argon is bubbled into the Cl2CDCDCl2
solution, the hydrogen is easily displaced with the quantitative
formation of a red solution containing 5Ru3 via steps iii, vi,
Scheme 2.
The complex 2Ru3, which can be obtained as a pure solid,28
appears to be stable in solution under H2 in oxygenated solvents
such as acetone or THF, but converts slowly in chlorinated
solvents to an equilibrium mixture with the dihydrogen com-
plex 3Ru3 (step iii, Scheme 2). In CD2Cl2 (after 12 hours) the
J. Chem. Soc., Dalton Trans., 1999, 4475–4486
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Between 1.0 and 4.0 equivalents of acid added, a species,
suspected to be the aqua complex trans-[Ru(H2O)(CNH)-
(dppe)2](OTf)2 (7Ru2, see below), is produced from impurities
of H2O/H3Oϩ. The relative amount of complex 7Ru2 increases
as acid is added, to a maximum of 16% at 2.0 equivalents of
acid added. It then decreases as more acid is added until only
complex 4ЈRu2 is present at 4.5 equivalents of acid added.
Therefore this aqua complex can be converted to 4ЈRu2 accord-
ing to eqn. (1).
[Ru(H2O)(CNH)(dppe)2](OTf)2 ϩ 3HOTf ϩ H2 →
[Ru(H2)(CNH)(dppe)2](TfOH ؒ ؒ ؒ OTf)2 ϩ H3Oϩ (1)
Complex 3ЈRu2 appears to be the most unstable of the com-
plexes since the maximum amount of side-reaction complexes
6Ru2 and 7Ru2, coincides at 2.0 equivalents of acid added,
when complex 3ЈRu2 is the predominant species. This is con-
sistent with the observation that complex 7Ru2 is only observed
in the synthesis of complex 6Ru2 or complex 3ЈRu2. Anytime
that complex 3ЈRu2 forms, complex 7Ru2 also forms. Therefore,
complex 7Ru2 must form by the reaction of trace amounts of
water with complex 3ЈRu2. When these reactions are performed
under Ar, more than 7 equivalents of acid are required to form
complex 4ЈRu2 from complex 1Ru2. Under Ar, when 2 equiv-
alents of acid are added, the amount of complex 6Ru2 present
is 46.4% while under H2, the amount of complex 6Ru2
present is only 10.0%.
Fig. 1 Relative amounts of species observed during the titration of
trans-RuH(CN)L2, L = dppe, in CH2Cl2 under H2 with HOTf. Small
amounts of [Ru(OTf)(CNH)L2]ϩ (10%) are present at 2.0 equiv. of
HOTf. Small amounts of [Ru(H2O)(CNH)L2]2ϩ are present at 1.0
equiv. (9%), 2.0 equiv. (16%) and 3.0 equiv. of HOTf (4%).
relative percentages measured are the same as found after the
protonation of 1Ru1 with 1 equivalent of triflic acid.
The addition of one equivalent of HOTf to 1Os1 in CD2Cl2
at room temperature leads to the formation of exclusively trans-
[OsH(CNH)(dppm)2]OTf28 while excess acid produces a violet
1
The unstable dihydrogen complex trans-[Ru(η2-H2)(CN)-
(dppe)2]OTf, 3Ru2, has been observed at low temperatures
solution that does not have a dihydrogen resonance in the H
NMR spectrum.
when H2(g) is introduced into
a solution of trans-
Addition of HOTf to trans-[RuH(CN)(dppe)2] 1Ru2 and related
[Ru(OTf)(CN)(dppe)2], 5Ru2 (see below) in CD2Cl2 (step v,
Scheme 2). The 1H NMR spectrum of 3Ru2 recorded at Ϫ10 ЊC
shows a broad singlet at δ Ϫ7.3 and the 31P{1H} NMR spec-
trum, a singlet at δ 53.7. As the sample was warmed to 10 ЊC,
the appearance of a quintet at δ Ϫ9.1 (RuH) and a broad singlet
at 10.2 (NH) in the 1H NMR spectrum signalled the formation
of 2Ru2 as did the appearance of a singlet at δ 66.6 in the
31P{1H} NMR spectrum. Complex 2Ru2 was the major species
after 1 h on warming the sample to room temperature. Thus
at room temperature, complex 3Ru2 rearranges to the more
thermodynamically stable product, complex 2Ru2 (step iv,
Scheme 2). The triflate anion is probably weakly hydrogen-
bonded to the dihydrogen ligand in 3Ru2 (see below) and could
serve as a shuttle to carry the proton from the η2-H2 ligand to
the CN ligand, producing 2Ru2.
reactions
The quantitative titration of complex 1Ru2 in CD2Cl2 with
HOTf was monitored by 31P{1H} NMR spectroscopy to deter-
mine the approximate relative amounts of the complexes pro-
duced (Fig. 1). The acid addition was done under H2 gas to
minimise the formation of the triflate coordinated species trans-
[Ru(OTf)(CNH)(dppe)2]OTf, 6Ru2. The addition of 0.5 mol of
acid to complex 1Ru2 produces a mixture of 1Ru2 and trans-
[Ru(H)(CNH)(dppe)2]OTf 2Ru2. Complex 2Ru2 is the pre-
dominant species after one equivalent of acid is added. At
1.5 equivalents of acid added, a mixture of the dihydrogen
complex trans-[Ru(η2-H2)(CN)(dppe)2](TfO ؒ ؒ ؒ HOTf), 3ЈRu2,
and complex 2Ru2 forms (steps iii, ix, Scheme 2). The 3Ј
nomenclature indicates that there is an anion effect; this
stable complex, which is thought to have the hydrogen-
bonded (TfO ؒ ؒ ؒ HOTf)Ϫ anion, has different solution
properties to the unstable dihydrogen complex trans-[Ru(η2-
H2)(CN)(dppe)2]OTf, 3Ru2, with the OTfϪ anion (see below).
When two equivalents of acid have been added, complex 3ЈRu2
is the predominant species. The proton of one HOTf is used to
protonate the hydride giving the dihydrogen complex while the
proton of the other is used to form (TfO ؒ ؒ ؒ HOTf)Ϫ. This
chemical behaviour is different from that of the dppp com-
plexes. Apparently the triflate anion is more basic than the Ru–
H bond in 2Ru2 while the metal–hydride bond in 2Ru3 and
2Os3 is more basic than a triflate anion so that protonation
produces the dications 4Ru3 and 4Os3. Between 2.5 and 4.0
equivalents of acid added, the ratio of complex trans-[Ru(η2-
H2)(CNH)(dppe)2](TfO ؒ ؒ ؒ HOTf)2, 4ЈRu2, over complex
3ЈRu2 increases until it is the only complex present at 4.5
equivalents of acid added (step xi, Scheme 2). In theory, only
four equivalents of acid would be required to go from 1Ru2 to
4ЈRu2 since two protons from HOTf form complex 4ЈRu2 while
the rest form the two (TfO ؒ ؒ ؒ HOTf)Ϫ counter-ions. The
requirement of a slight excess reflects the high acidity of com-
plex 4ЈRu2. Under H2, only a small amount of complex trans-
[Ru(OTf)(CNH)(dppe)2]OTf, 6Ru2, forms between 1.5 and 2.5
equivalents of added acid, the maximum relative amount being
10.0% at 2.0 equivalents of acid added.
There are two routes to the white complex trans-[Ru(η2-H2)-
(CN)(dppe)2](TfO ؒ ؒ ؒ HOTf) 3ЈRu2. When the yellow oil of
complex 4ЈRu2 is stirred in Et2O for 30 min, then decanted and
quickly dried, complex 3ЈRu2 forms (step xii, Scheme 2). In this
reaction the very acidic complex 4ЈRu2 is deprotonated, pre-
sumably to form the strong acid [Et2OH](TfO ؒ ؒ ؒ HOTf) which
is detected in the 1H NMR spectrum as a broad singlet at
δ 13. The dihydrogen complex 3ЈRu2 is soluble in methylene
chloride but insoluble in diethyl ether. Under Ar, it is unstable
with respect to the loss of H2 over time to give complex 6Ru2
(step xv, Scheme 2). The addition of H2 gas to complex 6Ru2 is
another route to complex 3ЈRu2 (step xvi, Scheme 2).
When one half an equivalent of PPh3 is added to complex
3ЈRu2, complex 2Ru2 forms (steps x, iv, eqn. (2)). The quintet
1
of complex 2Ru2 is observed in the hydride region of the H
NMR spectrum while in the 31P{1H} NMR spectrum, a singlet
at δ 66.6 corresponding to complex 2Ru2 is observed. Reson-
ances for [HPPh3](TfO ؒ ؒ ؒ HOTf) at δ 3.4 and complex 7Ru2 at
δ 48.4 are also observed in the 31P{1H} NMR spectrum. This
reaction probably proceeds via the formation of complex 3Ru2
as an intermediate.
trans-[Ru(η2-H2)(CN)(dppe)2](TfO ؒ ؒ ؒ HOTf) ϩ 0.5 PPh3 →
trans-[Ru(H)(CNH)(dppe)2]OTf ϩ
0.5 [HPPh3](TfO ؒ ؒ ؒ HOTf) (2)
4478
J. Chem. Soc., Dalton Trans., 1999, 4475–4486

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The addition of excess HOTf (>5 equiv.) to complex trans-
[RuH(CN)(dppe)2] 1Ru2 or complex trans-[RuH(CNH)-
(dppe)2]OTf 2Ru2 in CH2Cl2 under Ar produces the complex
trans-[Ru(η2-H2)(CNH)(dppe)2](TfO ؒ ؒ ؒ HOTf)2 4ЈRu2 which
was isolated as a yellow oil. Complex 4ЈRu2 is a very air sensi-
tive, acidic dihydrogen complex, which is quite stable in the
presence of excess acid. It is soluble in methylene chloride and
can be deprotonated by diethyl ether. Its spectroscopic proper-
ties are discussed below.
(CN)(depe)2]BF4 (3*Ru4, 3*Fe4) as analyzed by NMR spec-
troscopy (see Table 2). One equivalent of the weaker acid
[Ph3PH]BF4 can also be used to prepare 3*Fe4. Similarly one
equivalent of [Ph3PH]OTf is used to prepare [Os(η2-H2)-
(13CN)(depe)2]OTf, 3Os4-c.
The formation of trans-[M(η2-H2)(CNBF3)(depe)2]BF4 by
the known reaction of BF4Ϫ with CNH ligands can be ruled out
because only one equivalent of acid is added. At least two
equivalents of acid would be required to supply both the BF3
and BF4Ϫ of such a complex.
The addition of excess HBF4ؒEt2O to complex 1Ru4 at room
temperature causes immediate gas evolution. Thus a dicationic
dihydrogen complex such as 4Ru4 is not stable under these con-
ditions. The addition of two equivalents of 85% [Et2OH]BF4
to 1Fe4 produces trans-[Fe(η2-H2)(CNH)(depe)2](BF4)2, 4*Fe4.
Protonation of trans-[FeH(CN)(dppe)2] 1Fe2 and related
reactions
The addition of 1 equiv. of HOTf to 1Fe2 in CH2Cl2 produces
the hydrogen isocyanide complex 2Fe2 (step i, Scheme 2). The
complex trans-[Fe(H2)(CNH)(dppe)2]OTf2, 4Fe2, is prepared by
the addition of at least two equivalents of HOTf to 1Fe2 in
CH2Cl2 solution (steps i, vii, Scheme 2). The orange colour of
1Fe2 fades to yellow on addition of acid. Some H2 is liberated
from 4Fe2 in solution as revealed by the presence of a signal
1
The H NMR spectrum of 4*Fe4 contains a broad singlet at
high field attributed to the dihydrogen ligand. The infrared
spectrum of 4*Fe4 shows a strong absorption due to the hydro-
gen isocyanide ligand at 2100 cmϪ1 (Nujol mull) or 2103 cmϪ1
(CH2Cl2 solution). Preliminary results indicate that 4Os4 can be
prepared and is stable under vacuum in solution.
1
at δ 4.5 in the H NMR spectrum. Complex 4Fe2 can also be
prepared by the addition of HOTf to a yellow CD2Cl2 solution
of 2Fe2 (step vii, Scheme 2). Complex 4Fe2 is stable to the loss
of dihydrogen in the solid state under vacuum for short periods.
This dihydrogen complex is very acidic as indicated by the
deprotonation of 4Fe2 on addition of excess Et2O to produce
an orange solution of trans-[Fe(η2-H2)(CN)(dppe)2]OTf, 3Fe2.
Complex 3Fe2 can be isolated as an impure solid by washing
the oil, produced by removal of the solvent from a CH2Cl2
solution of 4Fe2, with Et2O. The yellow oil turns to an orange
powder on contact with the ether. Compound 3Fe2 is stable in
the solid state as determined by recording the 1H and 31P NMR
spectra after a period of weeks. It is unstable with respect to
tautomeric rearrangement to 2Fe2 in CD2Cl2 solution (step iv,
Scheme 2). A solution of 3Fe2 in CD2Cl2 shows resonances in
the 31P spectrum due to both 3Fe2 and 2Fe2 after standing
overnight. This process can be promoted by the addition of a
small amount of triphenylphosphine as in the case of 3ЈRu2.
Characterisation of the dihydrogen complexes trans-[M(ꢀ2-H2)-
(CN)L2]OTf 3Mj, 3ЈRu2, 3*Mj
The properties of these complexes depend on the anion present.
Solutions of complexes 3Ru1, 3Fe2, 3Ru2, 3Ru3, 3Os4 with the
triflate anion can be prepared by one of the methods discussed
above. These compounds tend to be unstable, readily losing H2
to give 5Mj or rearranging to the CNH form 2Mj. The most
stable complex is the osmium one. Similarly the BF4Ϫ complex
3*Os2 is stable with respect to the loss of H2. In the case of the
Ϫ
depe complexes, the BF4 complexes 3*Fe4 and 3*Ru4 are
much more stable than the OTfϪ complexes. This can be
explained by a M–OTf bond strength that is greater than that
of M–FBF3. Attempts to grow crystals of complex 3ЈRu2 by
slow diffusion of Et2O into a saturated solution of complex
3ЈRu2 in CH2Cl2 under H2 produced complex 2Ru2 as identified
by NMR spectroscopy.
Protonation of trans-[OsH(CN)(dppe)2] 1Os2 and trans-
[OsH(13CNH)(dppe)2]OTf 2Os2-c. The addition of acid to
1Os2 usually results in the formation of 2Os2. However if one
equivalent of HBF4ؒEt2O is added to a solution of 1Os2 in
benzene, white trans-[Os(η2-H2)(CN)(dppe)2]BF4, 3*Os2 pre-
cipitates (where * denotes the BF4Ϫ salt). This dihydrogen com-
pound in CD2Cl2 is stable to H2 evolution under Ar but it slowly
converts to 2*Os2 and another complex tentatively identified as
trans-[OsH(CNBF3)(dppe)2].28 The addition of water or ether
causes the rearrangement to 2*Os2. For example when D2O–
HBF4 was used as the acid to prepare 3*Os2-d under the same
conditions as the preparation of 3Os2, a significant amount of
2*Os2-d also formed.
When 2 equiv. of HOTf or 1 equiv. of DOTf are added to
2Os2-c, colourless solutions of the complexes trans-[Os-
(η2-H2)(13CNH)(dppe)2](OTf)2, 4Os2-c, or trans-[Os(η2-HD)-
(13CNH)(dppe)2](OTf)2, 4Os2-c,d form (step vii, Scheme 2). The
NH resonance is averaged with the free acid peak at room tem-
perature in the 1H NMR spectrum, but at Ϫ40 ЊC it appears as
a doublet at δ 10.8 (2J(13CH) = 31 Hz). Other NMR proper-
ties are listed in Table 2.
These complexes are in the trans configuration according to
the 31P NMR spectra. The spectra are singlets at room temper-
ature while that of 3Ru3, at Ϫ90 ЊC, resolves to an A2X2 pattern
with triplets at δ 2.7 and 16.8 (J(P,PЈ) = 28.9 Hz). This is
typical of trans-M(dppp)2XY complexes. The usual periodic
trend of δ(PFe) > δ(PRu) > δ(POs) is observed. Compound
3ЈRu2 with the (TfO ؒ ؒ ؒ HOTf)Ϫ anion has a slightly different
chemical shift (δ 54.2) than 3Ru2 (53.7) with the OTfϪ anion,
although the sample temperatures were different (Table 2). This
may reflect the difference in ion-pairing and hydrogen-bonding
that is more marked in the 1H spectra (see below).
The dihydrogen ligand is identified by a broad resonance
located at between δ Ϫ8 and Ϫ14 for iron and between Ϫ4 and
–10 for ruthenium and osmium (Table 2). The T1(min) values of
the η2-H2 ligand in all of the complexes 3Mj are quite similar
when converted to a common frequency: about 11 ms for Fe, 8
to 13 ms for Ru and 15 and 16 ms for the two Os complexes.
Typically osmium dihydrogen complexes have longer T1(min)
values than corresponding Fe and Ru analogues, indicative of a
longer H–H distance in the Os case. This is supported by the
correlation between J(HD) and d(HH)29 where the 3Fej-d and
3Ruj-d complexes have J(HD) of 31.6 to 32.7 Hz corresponding
to d(H–H) of 0.89–0.87 Å while 3*Os2-d and 3Os4-d have
J(HD) of 28.7 and 25.4 corresponding to d(H–H) of 0.94 and
1.06 Å, respectively. The 1H NMR resonances of the HD ligand
in the complexes 3Ru2-d and 3Ru3-d appear as 1:1:1 triplets of
quintets with rarely observed 2J(H,P) couplings of 5 and 3 Hz,
respectively while those of the Fe and Os complexes are broad
1:1:1 triplets. The complexes with dppe and depe ligands
appear to have “fast-spinning” dihydrogen ligands on the basis
of the agreement of the H–H distances calculated from J(HD)
Protonation of trans-[MH(CN)(depe)2] 1M4, M ؍ Fe, Ru,
Os. When one equivalent or an excess of triflic acid is added to
a solution of complex 1Ru4 in CH2Cl2, the yellow solution
changes to a light green colour and effervesces vigorously.
Apparently a triflate complex is formed but the characterization
of the product was not pursued. Complex 1Fe4 reacts in a
similar fashion to give a red solution.
One equivalent of HBF4ؒEt2O reacts with complexes 1M4
in CH2Cl2 to give the dihydrogen complexes trans-[M(η2-H2)-
J. Chem. Soc., Dalton Trans., 1999, 4475–4486
4479

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and T1(min) (Table 2) while those with the dppm and dppp
ligands have H2 moving in a way that does not influence dipolar
relaxation as much as free spinning, possibly undergoing a tor-
sional libration in a potential well that restricts rotation.30 The
T1 data examined fit the conventional lnT1 versus 1/T curve (see
the Supplementary information for fitting parameters, SUP
57672). The complex trans-[Ru(H2)(CCPh)(PiPr2CH2CH2-
PiPr2)2]ϩ which has a structure related to that of 3Ru4 has been
reported to have a similar T1(min).31,32
resonance at betweens δ ca. Ϫ3 and δ Ϫ12 (Table 2). The
chemical shift in each case is downfield of the monocationic
dihydrogen complex 3Mj. The short minimum T1 values
indicate H–H distances in the range 0.8 to 1.0 Å depending
on interpretation of the relative motions of the H2 ligand
and the molecule as a whole. The values are not significantly
different from those of corresponding complexes 3Mj. The
HD analogues were produced by reacting complexes 1Mj in
CD2Cl2 solution with excess CF3SO3D. The ruthenium
complexes all have coupling constants J(HD) of about 32 Hz,
not significantly different than those of 3Ruj. The correlation
between J(HD) and distance yields a value of about 0.88–0.89
Å. For the dppe complex 4ЈRu2 this distance agrees well with
the H–H distance calculated from the T1(min) value for a
fast spinning dihydrogen ligand. For the dppm and dppp
complexes, the distance from J(HD) is intermediate in the
range from the T1 calculation. This suggests that there may
be a barrier to rotation, so that torsional–librational motion
becomes important.30
Carbon-13 labelling provides evidence for the 13CN ligand in
3Ru3-c and 3Os4-c. The 31P NMR spectrum in each case is a
doublet with 2J(PC) = 14.3 and 11.8 Hz, respectively, while
the 13C resonances at δ 142.4 and 120.9, respectively, are quin-
tets. A Nujol mull of 3Os4-c has a 13C–N mode at 2064 cmϪ1
while a film of 3Fe2 has a 12C–N band at 2006 cmϪ1
.
The proton of the anion (TfO ؒ ؒ ؒ HOTf)Ϫ of 3ЈRu2 is
observed at δ 13.1. As the temperature is decreased, this peak
shifts downfield. At Ϫ50 ЊC, a new peak at δ 16.8 is observed.
At Ϫ60 ЊC, three peaks are observed in the acid region of the
1H NMR spectrum at δ 12.5 and 12.9 and 16.8. Bullock et al.9
The lack of variation in J(HD) with a variation in ancillary
ligands is typical of complexes that have η2-HD coordinated
trans to a strong field, π-acid ligand like CO, CNH or
CNϪ.34
1
have studied low temperature H NMR spectra of HOTf in
CD2Cl2. They attributed the resonance near δ 17 to (TfO ؒ ؒ ؒ
HOTf)Ϫ while those near δ 12 to excess HOTf present as
(HOTf)n aggregates or possibly partially dissolved (HOTf)n
aggregates in solution at low temperatures. Since excess acid
was not present in the sample of 3ЈRu2, aggregates of HOTf
should not be present. Bullock also noted that the solubility
of HOTf increases in the presence of TfOϪ anions. Therefore
the peaks observed at δ 12.5 and δ 12.9 are probably due to
the formation of some other triflic acid–triflate aggregate
species.
There is 1H, 13C and 15N evidence for the CNH ligands. The
NH resonance for 4Fe2 is a 1:1:1 triplet at δ 8.79 with
1JNH = 80 Hz while that for 4ЈRu2 is a broad singlet at δ 10.3
due to rapid proton exchange with the excess free acid present.
1
The acid peak appears in the H NMR spectra at δ ca. 12.7.
The excess acid is most likely to be present as HOTf hydrogen
bonded to itself or as dynamic clusters involving the TfOϪ
anion such as (TfO ؒ ؒ ؒ HOTf)Ϫ.9 Complex 4Os2-c has a broad
Surprisingly, the dihydrogen complexes trans-[Ru(η2-H2)-
(CN)(dppe)2](TfO ؒ ؒ ؒ HOTf) 3ЈRu2 and trans-[Ru(η2-H2)(CN)-
(dppe)2]OTf 3Ru2 in CD2Cl2 have quite different 1H NMR
properties in the hydride region. The former complex exhibits a
broad singlet at δ Ϫ5.5 while the latter, a broad singlet at δ Ϫ7.3.
The anion of 3ЈRu2 is proposed to have conventional CF3O2-
SO ؒ ؒ ؒ HOSO2CF3 hydrogen bonding while the OTfϪ anion of
3Ru2 may be involved in a non-classical CF3O2SO ؒ ؒ ؒ (HH)Ru
hydrogen bond to the dihydrogen ligand as shown in Scheme 2.
This would explain the differences in the NMR spectra of the
two complexes and why 3Ru2 rearranges readily at room tem-
perature (see below). Such non-classical hydrogen bonds have
been characterised crystallographically for IrCl ؒ ؒ ؒ (HH)Ir in
doublet at δ 10.8 with J(HC) = 30.8 Hz. For 4Ru3 and 4Os3
2
the 1H resonance of the CNH ligand is not observed at
room temperature probably owing to the proton exchange
between the coordinated CNH and the HOTf. It appears as
a broad singlet at δ 13.7 and 14.1, respectively, at Ϫ90 ЊC.
This resonance shows a doublet with 1J(H,15N) = 108.1 and
101.4 Hz, respectively, in the 1H spectrum at the same
temperature of the 15N enriched compounds trans-[M(η2-
H2)(C15NH)(dppp)2](OTf)2 4M3-n. The 15N NMR spectrum of
4Os3-n shows a doublet at δ Ϫ205 with 1J(NH) 102 Hz. There-
fore the ligand is coordinated as MCNH and not MNCH. Simi-
larly the CNH and acid peaks for the species at Ϫ80 ЊC thought
to be 4Ru1 occur at δ 12.8 (broad) and 11.3, respectively.
Ir(η2-H2)(Cl)2(H)(PiPr3)2,23 FeH ؒ ؒ ؒ (HH)Fe in Fe(η2-H2)(H)2-
Further evidence for the CNH ligand in 4M3 derives from
monitoring the protonation of the 13CN enriched compounds
trans-[M(H)(13CN)(dppp)2] 1M3-c to produce trans-[M(η2-H2)-
(13CNH)(dppp)2](OTf)2 4M3-c. In the 13C{1H} NMR spectrum
the 13CN quintet of 1M3-c at δ 156.7 and 137.9 for M =
Ru and M = Os, respectively, broadens and shifts to δ 149.9
(2J(C,P) = 13.6 Hz) and 133.2 (2J(C,P) = 10.2 Hz), respectively,
with the protonation. The 31P signal is a doublet at δ 8.9
(2J(P,C) = 13.5 Hz) and Ϫ29.4 (2J(P,C) = 7.9 Hz), respectively.
The C–N mode at 2056 cmϪ1 of the CNH ligand was detected
by IR spectroscopy of 4Fe2 as a film on NaCl. A CH2Cl2
33
(PEtPh2)3
and BF ؒ ؒ ؒ (HH)Os in [Os(η2-H2)(CH3CN)-
(dppe)2](BF4)2.8 In the last example the acidic η2-H2 ligand
forms a 2.4 Å H ؒ ؒ ؒ F contact with one of the BF4Ϫ anions. The
H–H distance of complex 3Ru2 might be expected to be longer
than that of 3ЈRu2 due to the hydrogen bonding but this
difference is not detectable by J(HD) or T1(min) (Table 2).
The dihydrogen ligand in all of the complexes 3Mj might
act as hydrogen bond donors to triflate but this is difficult to
prove.
Ϫ1
᎐
solution of 4Ru3 has a C᎐N mode at 2125 cm while a Nujol
᎐
Characterisation of the dihydrogen complexes trans-[M(ꢀ2-H2)-
(CNH)L2](OTf)2 4Mj
mull of 4Os3 gives a C᎐N stretch at 2129 cmϪ1. On this basis,
᎐
᎐
the Fe2 centre seems to be more π-basic than the Ru3 and Os3
These complexes are characterised in CD2Cl2 solution, under
centres.
1
H2 in the presence of an excess of HOTf, by H, 13C and 31P
NMR and IR spectroscopy in certain cases. The complexes are
in the trans configuration according to the 31P spectra. The
dppm and dppe complexes show singlets while the dppp com-
plexes at low temperature show a characteristic set of two trip-
lets probably due to the conformation of the backbones of the
dppp ligands. For each pair of complexes 3Mj and 4Mj, the
resonance for 4Mj is between 1 and 6 ppm upfield of that of
3Mj (Table 2). Again the 31P chemical shifts follow the usual
periodic trend Fe > Ru > Os for analogous complexes.
Acidity of the dihydrogen complexes
The determination of pKa values for these complexes is compli-
cated by their reactivity and the myriad of equilibria possible.
The complex 4ЈRu2 is the most acidic complex since it is only
completely formed in an excess of HOTf in CH2Cl2. Therefore
its pKa is near to that of HOTf in CH2Cl2 (the aqueous pKa of
HOTf has been estimated to be Ϫ5).2 Complexes 4Fe2 and
4Os2 are less acidic because they are completely formed by the
addition of two equivalents of HOTf to 1Fe2 or 1Os2. Com-
The dihydrogen ligand in the complexes produce a broad
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J. Chem. Soc., Dalton Trans., 1999, 4475–4486

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Table
3
Selected bond distances (Å) and angles (Њ) for trans-
plex 4Ru3 requires three equivalents of HOTf from 1Ru3 for
complete formation and so it is also very acidic but less
acidic than 4ЈRu2. This is in keeping with the dppp ligand
being more donating than the dppe ligand. Complexes 4ЈRu2
and 4Fe2 are deprotonated by treatment with diethyl ether (the
aqueous pKa of [Et2OH]ϩ is reported to be Ϫ2.4)35 and so
they are very acidic. Complex 3Ru2 at 163 K in CH2Cl2 must
be less acidic than HOTf because it forms the hydrogen-
bonded structure Ru(HH) ؒ ؒ ؒ OTf. The monocationic com-
plex 3Fe2 is less acidic than the dication 4Fe2 because 3Fe2 is
not deprotonated in diethyl ether while 4Fe2 is. The dihydro-
gen site of 3M2, M = Fe, Ru, is more acidic than the CNH
site of 2M2 because these complexes rearrange from 3M2 to
2M2. The depe complexes 3*Fe4 and 3Os4 are less acidic
[Ru(OTf)(CNH)(dppe)2]OTf 6Ru23 and trans-[Ru(OTf)(CN)(dppe)2]
5Ru2
6Ru2
5Ru2
Ru(1)–O(1)
Ru(1)–O(3)
Ru(1)–C(5)
Ru(1)–P(1)
Ru(1)–P(2)
Ru(1)–P(3)
Ru(1)–P(4)
N(1)–C(5)
2.299(2)
2.410(5)
1.94(1)
2.376(2)
2.400(2)
2.361(2)
2.381(2)
1.18(1)
1.882(3)
2.3938(7)
2.3848(8)
2.4364(8)
2.4144(8)
1.150(4)
0.76(4)
N(1)–H(1N)
N(1) ؒ ؒ ؒ O(3S)
H(1N) ؒ ؒ ؒ O(3S)
2.616(4)
1.86
ϩ
than HPPh3 in CH2Cl2 which has an estimated pKa of 2.7 in
water.36
S(1)–O(1)–Ru(1)
S(1)–O(3)–Ru(1)
C(5)–Ru(1)–O(1)
N(1)–C(5)–Ru(1)
H(1N)–N(1)–C(5)
148.4(1)
The pKa of 3*Fe4 was determined in THF by monitoring the
equilibrium between trans-Fe(H)(CN)(depe)2 with [Cy3PH]-
BF4 by 31P{1H} NMR. The gated decoupled spectrum was
collected with a 10 s delay time to allow adequate time for
relaxation of the 31P nuclei. The resonance observed at 22.2
ppm is at an average position between those of free PCy3 (10.9
ppm) and [Cy3PH]ϩ (29.9 ppm). The ratio of [Cy3PH]ϩ to PCy3
is 0.69. The integrations of the resonances due to trans-
Fe(H)(CN)(depe)2, 1Fe4, and 3*Fe4 are used to determine their
molar ratio of 3.74. Therefore the pKa of 3*Fe4 is calculated to
be 9.0 with respect to the pKa of [Cy3PH]ϩ, which is estimated
to be 9.7 in water36 and is used as an arbitrary anchor for the
THF scale.37
160.5(3)
170.7(3)
176.4(7)
171.3(1)
177.1(3)
173(4)
under Ar while 2Ru3 slowly changes to 3Ru3 and then to 5Ru3.
The addition of HOTf causes the rapid conversion of 2Ru2 to
3ЈRu2.
Preparation and properties of the complexes trans-[Ru(OTf)-
(CNH)L2]OTf 6Ruj
When the excess acid is removed from complexes 4ЈRu2 and
4ЈRu2-d4 by washing with Et2O, complexes 3ЈRu2 or 3ЈRu2-d2
form but the η2-H2 or η2-HD ligands in these complexes
are labile. A slow substitution by triflate produces the com-
plexes trans-[Ru(OTf)(CNH)(dppe)2]OTf (6Ru2) and trans-
[Ru(OTf)(CND)(dppe)2]OTf (6Ru2-d) (step xv, Scheme 2).
Complexes 6Ru2 and 6Ru2-d are white solids that are soluble
in CH2Cl2 but insoluble in diethyl ether. Complex 6Ru2 has a
1:1:1 triplet corresponding to the NH group at δ 10.2
(1J(HN) = 79.2 Hz) in the 1H NMR spectrum. A singlet at
δ 48.8 is observed in the 31P{1H} NMR spectrum for this trans
complex. An X-ray diffraction study3 as well as microanalysis
confirm the identity of complex 6Ru2. The bond distances and
angles for this complex are listed in Table 3 for comparison with
the structure of 5Ru2.
The pKa of trans-[Fe(H2)(CNH)(depe)2](BF4)2, 4*Fe4, was
determined in THF by monitoring the equilibrium between
[Ph3PH](BF4) and trans-[Fe(H2)(CN)(depe)2]BF4, 3*Fe4, by
1H and 31P NMR. The resonance at δ Ϫ2.47 in the 31P
NMR spectrum is intermediate between the chemical shifts of
PPh3 (δ Ϫ6) and [Ph3PH](BF4) (δ 4). The integrations of the
1
dihydrogen resonances in the H NMR spectrum were used to
calculate the ratio of 3*Fe4 to 4*Fe4 of 1.29. Therefore the pKa
of 4*Fe4 in CH2Cl2 must be similar to that of [Ph3PH]ϩ (pKa
approx. 2.7 in water).
It is significant that the very acidic dihydrogen complexes
4ЈRu2 and 4Ru3 can be formed by reaction of complexes 6Ruj
in HOTf–CH2Cl2 with dihydrogen gas. In the absence of an
excess of acid, complex 4ЈRu2 eliminates HOTf as TfO ؒ ؒ ؒ
HOTfϪ (step xvi, Scheme 2). There are only a few other
examples of very acidic dihydrogen complexes being gener-
ated by reaction with hydrogen gas as mentioned in the
introduction.
The IR spectrum of complex 6Ru2 was recorded in Nujol. A
weak broad band is observed at 2533 cmϪ1 as a combination
of the NH ؒ ؒ ؒ O and C–N modes. The deuterated analogue
6Ru2-d gave a more intense, broad peak at 2275 cmϪ1, similar to
that shown for complex 2Ru2-d.28
Interconversion of [M(H)(CNH)L2]؉ and [M(H2)(CN)L2]؉
[Ru(OTf)(CNH)(dppp)2]OTf 6Ru3 was prepared by bub-
bling argon through a stirred solution of excess triflic acid and
complex 1Ru3 or 2Ru3 and then by precipitating with diethyl
ether. The 31P NMR spectrum is a singlet at room temperature
and an A2X2 pattern at Ϫ80 ЊC comprised of two triplets at
δ 0.9 and Ϫ7.3 with 2J(P,PЈ) = 32.7 Hz. The NH resonance
Some qualitative statements can be made about the relative
rates of these reactions and implications for the mechanism.
The rate of rearrangement of 3Ru2 to 2Ru2 in CH2Cl2 (step iv,
Scheme 2) is much faster than that of 3Ru3 to 2Ru3. The triflate
anion might serve to shuttle the proton from the dihydrogen on
one side to the cyanide on the other side of the molecule. There
is evidence that the addition of a base or the use of a basic
solvent destabilises 3Ruj, 3Fe2, and 3*Os2 with respect to com-
plexes 2Mj and speeds the rearrangement. For example acetone
and THF favour 2Ru3 over 3Ru3. In the presence of Et2O,
complexes 3ЈRu2 and 3*Os2 rearrange to the thermodynamic-
ally stable complexes 2Ru2 and 2*Os2 over time. This reaction
of 3ЈRu2 is similar to the addition of PPh3 to complex 3ЈRu2
to form complex 2Ru2 (eqn. (2)). Basic solvents might de-
stabilise the putative Ru(HH) ؒ ؒ ؒ OTfϪ interaction over the
CNH ؒ ؒ ؒ OTfϪ hydrogen bond.
1
is observed in the H NMR spectrum as a broad singlet at
δ 11.0 at Ϫ80 ЊC but is not observed at room temperature
because of exchange processes. The 13C enriched complex
6Ru3-c shows a doublet at δ 1.9 in the 31P NMR spectrum
with 2J(P,C) = 13.5 Hz and a broad signal at δ 159.7 in
the 13C NMR spectrum. A weak C–N vibrational band of
the complex in Nujol was detected at 2074 cmϪ1 by IR
spectroscopy.
When H2 gas is bubbled into a CD2Cl2 solution of complex
6Ru2 or 6Ru3 in the presence of HOTf, complexes 4ЈRu2 or
4Ru3 form, respectively (step xiv, Scheme 2).
The reverse reaction, step iii (Scheme 2), is not observed for
2Ru2 in the absence of acid while it is slow for 2Ru3 on
approaching an equilibrium with 3Ru3 under H2 in chlorinated
solvents. This is also illustrated by the fact that 2Ru2 is stable
Preparation and properties of the complexes trans-[Ru(OTf)-
(CN)L2] 5Ruj
The yellow complexes 5Ru2 and 5Ru3 can be prepared by
J. Chem. Soc., Dalton Trans., 1999, 4475–4486
4481

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an NH resonance. A singlet at δ 52.1 is observed in the 31P{1H}
Table 4 Crystallographic data for 5Ru2
5Ru2
NMR spectrum. The IR spectrum of 5Ru2 in Nujol has two
sharp bands at 2078 cmϪ1 (strong) and at 2068 cmϪ1 (medium
intensity). Complexes 5Ru1 and 5Ru3 are characterised by
broad singlets at δ Ϫ9.1 and 4.8, respectively, in their 31P NMR
spectra. The latter changes to a doublet with 13CN labeling
(J(13CP) = 13.5 Hz).
Empirical formula
Formula weight
C54H48F3NO3P4RuS
1072.94
T/K
λ/Å
150.0(1)
0.71073
It is interesting that when complex 5Ru2 is dissolved in THF,
the solution remains yellow but when complex 5Ru2 is dis-
solved in CH2Cl2, a red solution forms but becomes yellow
after approximately 1 h. Yellow crystals of complex 5Ru2 were
formed by dissolving it in CH2Cl2 and diffusing in Et2O. When
the yellow crystals are redissolved in CH2Cl2, a red solution
reforms. Perhaps the red species is [Ru(CN)(dppe)2]OTf while
the yellow species in a THF or CH2Cl2 solution is [Ru(CN)-
(solv)(dppe)2]OTf with a coordinated solvent molecule. For
example Huhmann-Vincent et al. have recently synthesised and
structurally characterised the complexes cis-[Re(CO)4(PR3)-
(CH2Cl2)]ϩ (R = Ph or Cy) containing a monodentate CH2Cl2
ligand.5
Crystal system
Space group
a/Å
b/Å
Monoclinic
P21/n
16.6236(5)
17.0227(6)
18.0640(8)
91.978(5)
5108.7(3)
4
1.395
0.527
c/Å
β/Њ
V/Å3
Z
Dcalc/Mg mϪ3
µ/mmϪ1
Final R indices [I > 2σ(I)]
R indices (all data)
R1 = 0.0668, wR2 = 0.1617
R1 = 0.1241, wR2 = 0.1831
trans-[Ru(H2O)(CNH)(dppe)2](OTf)2 7Ru2
This complex was detected as an impurity in the crude complex
6Ru2 when prepared from complex 3ЈRu2 or if pure 6Ru2 is left
in a moist Ar atmosphere. Complex 7Ru2 is associated with a
singlet at δ 48.4 in the 31P{1H} NMR spectrum (in CD2Cl2) and
a triplet at δ 11.7 (1J(HN) = 79.2 Hz) and a sharp singlet at
1
δ 3.2 (OH2) in the H NMR spectrum. A drop of degassed
water added to the NMR tube containing impure complex
1
6Ru2 in CD2Cl2 causes the peak at δ 3.2 in the H spectrum
and at δ 48.4 in the 31P{1H} NMR spectrum to intensify.
For comparison, the aqua ligand in trans-[Os(η2-H2)(H2O)-
(dppe)2](OTf)2 and [Ru(tpb)(PCy3)(OH2)(η2-H2)]BF4 (tbp =
40
trispyrazolylborate, Cy = cyclohexyl)41 produce singlets in the
1H NMR spectra at δ 3.2 and δ 3.43, respectively. Crystals of
7Ru2 were grown and X-ray diffraction studies were carried
out. Unfortunately, the results were inconclusive due to dis-
order across a centre of symmetry located at Ru.
Fig. 2 The structure and labelling of trans-[Ru(OTf)(CN)(dppe)2]
5Ru2. Thermal ellipsoids represent the 30% probability surfaces.
Conclusions
removing one equivalent of HOTf from the corresponding
A range of dihydrogen complexes of the type trans-[M(η2-H2)-
(CN)L2]ϩ and trans-[M(η2-H2)(CNH)L2]2ϩ where M = Fe,
Ru, Os have been characterized. The stability of these com-
plexes 3Mj and 4Mj with respect to dihydrogen displacement
increases qualitatively as Ru < Fe < Os. This order is paralleled
in the other known series of complexes with the triad of iron
group metals: trans-[M(H2)(H)L2]ϩ L = dppe, dtfpe or depe42,43
and trans-[M(H2)(H)(PPh2OEt)4]ϩ 44 and trans-[M(H2)(H)-
complexes 6Ruj by use of triethylamine (eqn. (3)).
[Ru(OTf)(CNH)L2]OTf ϩ NEt3 →
[Ru(OTf)(CN)L2] ϩ HNEt3OTf (3)
In addition, complexes 5Ru1, 5Ru2 and 5Ru3 have been
observed to form from corresponding complexes 3Ruj by loss
of H2 (step vi of Scheme 2). In a similar fashion the unstable
dihydrogen complex [Cp*Re(H2)(NO)(CO)](OTf) loses H2 at
253 K to give Cp*Re(OTf)(NO)(CO).6
(meso-tetraphos)]ϩ
(meso-tetraphos = (R,S/S,R)-PPh2(CH2-
1
CH2PPh)2CH2CH2PPh2).45 The J(HD) and T1(min) values of
3Mj and 4Mj are very similar to those of similar complexes
trans-[M(H2)(H)L2]ϩ.2,42 This indicates that hydride and
cyanide and hydrogen isocyanide all have a high trans-influence
on the dihydrogen ligand.
The structure of a crystal of 5Ru2 was determined by X-ray
diffraction (Fig. 2, Tables 3, 4). Complexes 6Ru2 and 5Ru2 have
very similar structures with very similar bond lengths and bond
angles. Since both complexes readily lose the triflate ligand to
form dihydrogen complexes under H2, it is not surprising to find
very long Ru–O distances. Complex 6Ru2 contains an Ru(1)–
O(1) distance of 2.299(2) Å with a C(5)–Ru(1)–O(1) angle of
171.3(1)Њ, while complex 5Ru2 contains an exceptionally long
Ru(1)–O(3) distance of 2.410(5) Å and a C(5)–Ru(1)–O(1)
angle of 170.7(3)Њ. The long Ru–O distances may be due to the
steric interactions of the oxygen and fluorine atoms on the tri-
flate ligand with the Ph groups of the dppe ligands. A typical
Ru–O distance is approximately 2.1 Å.38 For example the com-
plex CpRu(P(CF2CF3)2CH2CH2P(CF2CF3)2)(OTf) has a Ru–O
distance of 2.2 Å.39
The thermodynamically favoured site of protonation of
trans-[M(H)(CN)(L)2] can be directed to hydride when L = depe
(producing a dihydrogen ligand tautomer) or to cyanide when
L = dppe (producing a hydrogen isocyanide ligand tautomer).
In no case does protonation occur at the metal to produce a
stable dihydride. In the case of the dppe, dppp and dppm lig-
ands, the tautomers are on a delicate balance that can be tipped
one way ([M(η2-H2)(CN)L2]ϩ) or the other ([MH(CNH)L2]ϩ)
by changes in solvent and the hydrogen bonding characteristics
of the anion. The isocyanide complexes of the type [MH-
(CNH)(depe)2]ϩ are not observed and seem to be thermo-
dynamically much less stable than the dihydrogen tautomers.
This can be rationalised mainly as an electronic effect that
drops off with the number of bonds from the site of change of
1
The H NMR spectrum of complex 5Ru2 in CD2Cl2 is very
similar to that observed for complex 6Ru2 except for the lack of
4482
J. Chem. Soc., Dalton Trans., 1999, 4475–4486

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the substituent R on phosphorus. The dihydrogen ligand is two
bonds from the change at P while the N–H bond is four bonds
removed. Therefore the depe complexes are expected to have
metal-hydride sites that are more basic than the other com-
plexes but have nitrogen sites that are of similar basicity.16 The
greater donor effect of depe has been demonstrated by studying
properties of diphosphine complexes trans-[MX(Y)(PR2(CH2)2-
PR2)2] by use of IR, electrochemical and pKa measure-
ments.43,46–50 Another important factor is the strength of
hydrogen-bonding in the ion pairs in solution. The CNH ligand
forms a strong hydrogen bond to the triflate anion as indicated
by IR and X-ray studies and this will tend to favour complexes
2Mj unless the metal hydride site becomes very basic as in the
case of the depe complexes.
The thermodynamically less stable isomers can be accessed
in some cases by other routes. The reaction of trans-[Ru(OTf)-
(CN)L2] 5Ruj in CD2Cl2 with dihydrogen produces the less
stable complexes trans-[Ru(η2-H2)(CN)L2]OTf 3Ruj. Complexes
3Mj are suspected of having ion pairs with M(HH) ؒ ؒ ؒ OTf
non-classical hydrogen bonding. The deprotonation of trans-
[M(η2-H2)(CNH)(dppe)2](OTf)2 4M2, M = Fe, Ru by Et2O also
leads to the 3ЈM2 tautomers where the triflate is mainly
hydrogen-bonded to HOTf in CH2Cl2. Under dihydrogen,
complexes 3Ruj rearrange partially (dppp) or completely (dppe)
to the hydrogen isocyanide form 2Ruj. The triflate ion could act
as a proton shuttle to facilitate this rearrangement which also
appears to be promoted by other bases (Et2O, PPh3) in the case
of 3*Fe2, 3ЈRu2 and 3*Os2.
the acidic dihydrogen complexes 3Ruj. The reactivity of the
triflate complexes 6Ruj and 5Ruj is attributed to the long Ru–O
bonds identified in the structure determinations of 5Ru2 and
6Ru2.
The iron dihydrogen complexes are of interest because of the
recent infrared and crystallographic work on hydrogenase
enzymes that suggest that cyanide ligands on iron are present in
nature. Our work indicates that iron(), when it is low spin due
to the presence of strong field cyanide, hydrogenisocyanide and
phosphine ligands, is an excellent binding site for dihydrogen
and that the proton from the H2 ligand can move to cyanide and
back again easily. Such a migration has not been discussed in
studies of the mechanism of hydrogenase action.52–54 We have
reported IR data for the CN and CNH ligands that might be
useful in enzymatic studies.
Experimental
General procedures
All manipulations involving solutions of the complexes were
performed under argon with use of Schlenk-line techniques or
in a vacuum atmosphere glovebox under Ar unless otherwise
noted. HD gas was prepared via reaction of NaH with 99.92%
D2O (generously donated by Ontario Hydro). Solvents were
purified by standard methods. All chemicals used were of
reagent grade or comparable purity. NMR solvents were
obtained from Sigma-Aldrich. The ligand dppp, RuCl3ؒH2O
and (NH4)2OsCl6 were purchased from Aldrich. The phosphine
ligand dppe was donated by Digital Specialty Chemicals Ltd.
[HPPh3]OTf was prepared by reaction with HOTf in a similar
fashion to the preparation of [HPPh3]BF4.55 The preparation
of the complexes 1Mj and 2Mj are reported elsewhere.28 The
yields of complexes reported below were calculated on the basis
of the starting metal complex. Crystals were obtained by the
slow evaporation of the solvent into an Ar glovebox atmos-
phere. Infrared spectra were recorded on a Nicolet Magna
550 FT-IR or on a Nicolet 5DX FTIR spectrometer as Nujol
mulls on NaCl plates. Microanalyses were performed by the
Microanalytical Laboratory of the Dipartimento di Scienze e
Tecnologie Chimiche, Università di Udine or by Guelph
Chemical Laboratories Ltd., Guelph, ON. 1H, 31P{1H} and
13C{1H} NMR spectra were obtained with Bruker AC 200 or
with Varian Gemini 300 spectrometers. 15N{1H} NMR spectra
were obtained with a Bruker AC 500 spectrometer. 31P chemical
shifts are relative to 85% H3PO4 and (NH4)H2PO4 for solutions
and solids, respectively, and 15N chemical shifts to external
aqueous solution of KC15N. Inverse-gated decoupling was used
to record the 31P NMR spectra when their integration was
required. All 31P NMR spectra were proton decoupled. 1H
NMR T1 measurements were made using the inversion recovery
The highly acidic and stable dicationic dihydrogen com-
plexes, trans-[Ru(η2-H2)(CNH)L2]2ϩ (L = dppe, dppp) are only
stable with respect to the loss of protons or dihydrogen under
strongly acidic conditions (excess HOTf). The very acidic
complex trans-[Ru(η2-H2)(CNH)(dppm)2]2ϩ is observable at
temperatures below Ϫ40 ЊC but decomposes at room temper-
ature. The less acidic trans-[Os(η2-H2)(CNH)(dppp)2]2ϩ can be
obtained as a white solid, while trans-[Os(η2-H2)(CNH)-
(dppm)2]2ϩ does not form. The pKa of the complexes 4Fe2,
ϩ
4ЈRu2, 4Ru3 are less than that of HOEt2 since they are
deprotonated by Et2O. The dihydrogen complexes trans-[M(η2-
H2)(CNH)L2]2ϩ (L = dppe, dppp) are stable despite the fact that
there is very little π-backbonding because of the strong σ bond
component. The high Lewis acidity of the metal is created by
the 2ϩ charge and the presence of the π-acidic CNH ligand
trans to H2. The H–H bond length was determined by use of
accepted NMR methods to be short (0.9 Å) in these complexes.
The dihydrogen complexes trans-[Ru(η2-H2)(CN)L2]ϩ (L =
dppm, dppe, dppp) are unstable under Ar, liberating H2 and
forming trans-[Ru(OTf)(CN)L2] (L = dppm, dppe, dppp). It is
interesting to note that the monocationic dihydrogen complexes
3Ru2, 3ЈRu2, 3Ru3 are less stable with respect to H2 loss than
the dicationic dihydrogen complexes, 4Ruj. This could reflect
the lower Lewis acidity of the metal centre in 3Ruj and also
possibly the greater trans influence of CN over CNH (the latter
could be influenced by hydrogen bonding to the counter anion).
A greater M–H2 bond weakening in 3Mj, M = Fe, Ru would
explain why the H–H bond lengths are comparable in 3Mj and
4Mj. Otherwise the monocationic complexes would be expected
to be more π-basic, an effect that usually results in H–H bond
lengthening by dπ→σ* backdonation. There is theoretical
support for the idea that the dσ interaction increases as dπ
electrons become unavailable for π-bonding (e.g. on going
from complexes 3Ruj to 4Ruj).51 This difference in stability
might also be explained by the fact that in 4Mj the TfOϪ is
not as nucleophilic because it is hydrogen bonded to HOTf.
When trans-[Ru(OTf)(CNH)(dppe)2]OTf 6Ru2 is placed
under H2, a very strong acid is released (HOTf) in the form
of (TfO ؒ ؒ ؒ HOTf)Ϫ and the complex trans-[Ru(η2-H2)(CN)-
(dppe)2](TfO ؒ ؒ ؒ HOTf) 3ЈRu2 is formed. This is a rare example
of the formation of an acidic dihydrogen complex from H2 gas.
The reaction of complexes 5Ruj with dihydrogen also generates
1
method. Further experimental details and H, 13C, 31P NMR
data for the complexes can be found in the supplementary
information (SUP 57672).
Preparations
trans-[Ru(ꢀ2-H2)(CNH)(dppm)2](OTf)2 4Ru1. trans-[RuH-
(CN)(dppm)2] (21.8 mg, 24 µmol) was dissolved in 0.5 mL of
CD2Cl2 under H2 in an NMR tube and, after cooling at Ϫ80 ЊC,
HOTf (6.4 µL, 72 µmol) was added thereto by means of a
syringe. trans-[Ru(η2-HD)(CND)(dppm)2](OTf)2 4Ru1-d2 was
prepared in a similar fashion by use of DOTf.
trans-[Fe(ꢀ2-H2)(CN)(dppe)2]OTf, 3Fe2. Method A. Excess
triflic acid (70 mg; 0.4 mmol) was added to a CH2Cl2 solution
of trans-Fe(H)(CN)(dppe)2 (57 mg; 0.06 mmol) and the solu-
tion was stirred for 5 min. The solvent was removed in vacuo
and the resultant yellow oil washed twice with Et2O (5 mL)
producing a brown powder. Yield 61 mg (98%). Method B. Et2O
was added to a solution of 4Fe2 generated in situ by Method B
J. Chem. Soc., Dalton Trans., 1999, 4475–4486
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(see below). IR (cmϪ1, solid on NaCl) 2006 (s, νCN). trans-
[Fe(HD)(CN)(dppe)2](OTf), 3Fe2-d was made using DOTf as
in Method A.
CD2Cl2 (see below) in an NMR tube until the red solution
turned colourless. trans-[Ru(η2-HD)(CN)(dppp)2]OTf 3Ru3-d
was made by use of 5Ru3 and HD(g). trans-[Ru(η2-H2)(13CN)-
(dppp)2]OTf 3Ru3-c was prepared starting with 5Ru3-c.
trans-[Fe(H2)(CNH)(dppe)2](OTf)2, 4Fe2. Method A. 1Fe2,
(13 mg; 0.015 mmol) was dissolved in CH2Cl2 (1 mL) and cold
(0 ЊC) triflic acid (15 mg; 0.1 mmol) was added. The initial
orange colour of the solution fades to yellow immediately.
Method B. Triflic acid (3 drops) is added to 2Fe2 (20 mg) in
CD2Cl2. IR (film on NaCl) 2056 cmϪ1 (CN); (CH2Cl2 solution)
2059 cmϪ1. trans-[Fe(η2-HD)(CND)(dppe)2](OTf)2, 4Fe2-d2 was
made with DOTf according to Method A.
trans-[Ru(ꢀ2-H2)(CNH)(dppp)2](OTf)2 4Ru3. trans-[RuH-
(CN)(dppp)2] (20 mg, 21 µmol) was dissolved in 0.5 mL of
CD2Cl2 under H2 in an NMR tube and HOTf (6 µL, 68 µmol)
was added thereto by means of a syringe. IR (CH2Cl2), cmϪ1
:
ν(CN) 2125 (s). trans-[Ru(η2-H2)(13CNH)(dppp)2](OTf)2 4Ru3-c
and trans-[Ru(η2-H2)(C15NH)(dppp)2](OTf)2 4Ru3-n were pre-
pared starting with 1Ru3-c and 1Ru3-n, respectively. trans-
[Ru(η2-HD)(CND)(dppp)2](OTf)2 4Ru3-d2 DOTf was used as
in the preparation of 4Ru3.
trans-[Ru(ꢀ2-H2)(CN)(dppe)2]OTf 3Ru2. An NMR tube con-
taining trans-[Ru(OTf)(CN)(dppe)2] (20 mg, 0.02 mmol) in
CD2Cl2 was cooled to Ϫ78 ЊC. H2 gas was bubbled through the
solution until the pale yellow solution turned colourless. The
NMR spectra were recorded at Ϫ10 ЊC. trans-[Ru(η2-HD)(CN)-
(dppe)2]OTf 3Ru2-d was prepared by use of HD(g).
trans-[Os(ꢀ2-H2)(CNH)(dppp)2](OTf)2 4Os3. trans-[OsH-
(CN)(dppp)2] (0.10 g, 0.10 mmol) was dissolved in 2 mL of
CH2Cl2 under H2 and CF3SO3H (30 µL, 0.34 mmol) was added
by means of a syringe. The solution was stirred at room
temperature for 10 minutes and then 15 mL of hexane were
added to precipitate the white product, which was filtered off,
washed with hexane, dried in vacuum and recrystallised
from CH2Cl2–hexane. Yield: 121 mg, 90%. Anal. calc. for
C57H55F6NO6OsP4S2: C, 51.01; H, 4.13; N, 1.04. Found: C,
50.34; H, 4.09; N, 1.03%. IR (Nujol), cmϪ1: ν(CN) 2129 (s).
trans-[Os(η2-HD)(CND)(dppp)2](OTf)2 4Os3-d2 was observed
by reaction of DOTf with 1Os3. trans-[Os(η2-H2)(13CNH)-
(dppp)2](OTf)2 4Os3-c and trans-[Os(η2-H2)(C15NH)(dppp)2]-
(OTf)2 4Os3-n were prepared starting from 1Os3-c and 1Os3-n,
respectively.
trans-[Ru(ꢀ2-H2)(CN)(dppe)2](TfO ؒ ؒ ؒ HOTf)
3ЈRu2.
Method A. A yellow oil containing trans-[Ru(η2-H2)(CNH)-
(dppe)2](TfO ؒ ؒ ؒ HOTf)2 in HOTf was stirred for 30 min in 10
mL Et2O. The solvent was decanted and the product was quick-
ly dried under Ar. The NMR spectra were recorded quickly
since the dihydrogen ligand was found to be very labile. Method
B. H2 gas was bubbled into an NMR tube containing complex
6Ru2 in CD2Cl2.
trans-[Ru(ꢀ2-HD)(CN)(dppe)2](TfO ؒ ؒ ؒ DOTf)
3ЈRu2-d2.
Diethyl ether was added to the yellow oil of 4ЈRu2-d4 (see
below) to produce a light yellow precipitate. The solvent was
decanted and the product was quickly dried under argon.
trans-[Fe(H2)(CN)(depe)2]BF4, 3*Fe4. The addition of 1
equiv. of acid (85% [Et2OH]BF4 in Et2O or [Ph3PH]BF4 in
CD2Cl2) to 1Fe4 produces 3*Fe4 as revealed by NMR. The
compound is isolated by removal of the solvent and washing
the yellow powder with Et2O. Yield >90%.
trans-[Ru(ꢀ2-H2)(CNH)(dppe)2](TfO ؒ ؒ ؒ HOTf)2
4ЈRu2.
Method A. trans-[RuH(CN)(dppe)2] (100 mg, 0.11 mmol) was
dissolved in 10 mL of CH2Cl2 producing a clear colourless solu-
tion. Excess triflic acid (60 mg, 0.40 mmol) was added to the
solution and the resulting light yellow solution was stirred for
1 h. The solvent was removed in vacuo, producing a yellow oil.
Method B. trans-[RuH(CNH)(dppe)2]OTf (15 mg, 0.02 mmol)
was dissolved in 5 mL of CD2Cl2 and triflic acid (7 mg, 0.05
mmol) was added to the solution. The spectra were recorded
immediately. trans-[Ru(η2-HD)(CND)(dppe)2](TfO ؒ ؒ ؒ DOTf)2
4ЈRu2-d4 was prepared by use of Method A and DOTf.
trans-[Ru(ꢀ2-H2)(CN)(depe)2]BF4 3*Ru4. trans-[RuH(CN)-
(depe)2] (63 mg, 0.116 mmol) was dissolved in 5 mL of Et2O.
HBF4ؒEt2O (19 mg, 0.117 mmol) was added to the yellow solu-
tion producing a white precipitate. The solvent was removed
in vacuo and the NMR spectra were recorded.
trans-[Os(ꢀ2-H2)(13CN)(depe)2]OTf 3Os4-c. Complex trans-
[OsH(13CN)(depe)2] 1Os4-c (20 mg, 0.032 mmol) was dissolved
in 3 mL toluene and [HPPh3]OTf (13 mg, 0.032 mmol) was
added with stirring. The white precipitate that formed was
isolated, washed with hexanes three times and then dried
in vacuum. IR (Nujol), cmϪ1: ν(13CN) 2064. [Os(η2-HD)(13CN)-
(depe)2]OTf 3Os4-c,d was generated by use of [DPPh3]OTf.
trans-[Os(ꢀ2-H2)(CN)(dppe)2]BF4 3*Os2.
A solution of
trans-[OsH(CN)(dppe)2] 1Os2 (28 mg, 0.028 mmol) in 1.5 mL
benzene was treated with HBF4ؒEt2O (5 µL of 85% in Et2O,
0.028 mmol) under argon. The white precipitate that formed
after 30 s was isolated after 5 min of stirring. The yield
appeared to be quantitative.
trans-[Os(ꢀ2-H2)(CNH)(depe)2](OTf)2 4Os4. Excess HOTf
(26 mg, 0.17 mmol) were added to trans-[OsH(CN)(depe)2]
1Os4 (20 mg, 0.032 mmol) in 3 mL toluene. The solution was
stirred for 5 min and then the solvent was evaporated under
vacuum to give a beige powder. This was washed with hexanes
and then two times with ether and dried for 1 h in vacuum.
trans-[Os(ꢀ2-HD)(CN)(dppe)2]BF4 3*Os2-d. An acid solu-
tion was prepared containing HBF4ؒEt2O (50 µL, 0.3 mmol)
and D2O (0.1 mL) in benzene. Then 1 mL of this solution was
added to a solution of 1Os2 (30 mg, 0.03 mmol) in 1 mL
benzene. After 2 min. a white precipitate formed. The solvent
was decanted by use of a syringe and the white solid was dried
in vacuum for 5 min. The sample dissolved in CD2Cl2 was
sealed in an NMR tube under Ar.
trans-[Ru(OTf)(CN)(dppe)2] 5Ru2. Under Ar, trans-
[Ru(OTf)(CNH)(dppe)2]OTf (80.0 mg, 0.65 mmol) was sus-
pended in 5 mL of toluene. To this white suspension, NEt3
(7 mg, 0.7 mmol) was added and allowed to stir for 1/2 h form-
ing a yellow suspension. The yellow precipitate was filtered and
washed with 2 mL of toluene. An orange-red solution was
formed when the product was dissolved in a minimal amount of
CH2Cl2. Diethyl ether was diffused in and after 24 h, yellow
needles suitable for X-ray structure determination were
obtained (53% yield). Anal. calc. for C54H48F3NO3P4RuS: C,
60.44; H, 4.51; N, 1.30. Found: C, 59.49; H, 4.78; N, 1.26%.
IR (Nujol), cmϪ1: ν(CN) 2078 (s), 2068 (m).
trans-[Os(ꢀ2-H2)(13CNH)(dppe)2](OTf)2 4Os2-c. Two equiv-
alents of HOTf (9 mg, 0.055 mmol) were added to trans-
[OsH(13CNH)(dppe)2]OTf 2Os2-c in 0.7 mL CD2Cl2. The solu-
tion remained colourless and there was no gas evolution.
trans-[Ru(ꢀ2-H2)(CN)(dppp)2]OTf 3Ru3. H2 gas was bubbled
through a solution of trans-[Ru(OTf)(CN)(dppp)2], 5Ru3, in
4484
J. Chem. Soc., Dalton Trans., 1999, 4475–4486

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trans-[Ru(OTf)(CN)(dppp)2] 5Ru3. Under Ar, trans-
[Ru(OTf)(CNH)(dppp)2]OTf (6Ru3, 22 mg, 18 µmol) was dis-
solved in 0.5 mL of CD2Cl2. To this colourless solution, NEt3
(3 µL, 22 µmol) was added and a red solution of 5Ru3 was
produced. trans-[Ru(OTf)(13CN)(dppp)2] 5Ru3-c was prepared
by use of 6-Ru3-c.
Acknowledgements
We thank NSERC for a grant to R. H. M., DAAD for grants to
T. S. and Patrick Amrhein who did preliminary experiments
and Johnson-Matthey PLC for a loan of ruthenium salts.
Consiglio Nazionale delle Ricerche and Ministero dell’-
Università e della Ricerca Scientifica e Tecnologica are grate-
fully acknowledged. The Regione Autonoma FVG (Italy) is
also acknowledged for a grant to E. R.
trans-[Ru(OTf)(CNH)(dppe)2]OTf 6Ru2. Diethyl ether was
added to the yellow oil of 4ЈRu2 producing a light yellow pre-
cipitate. This suspension was stirred for 30 min. and the solvent
was decanted. The precipitate was washed twice with 5 mL of
diethyl ether and dried in vacuo. Purification of the product
involved slow diffusion of Et2O into a saturated solution of the
complex in CH2Cl2. White crystals suitable for X-ray structure
determination were obtained by slow evaporation of a con-
centrated solution of the product in CH2Cl2 (70.3% yield).
Anal. calc. for C55H49F6NO6P4RuS2: C, 54.01; H, 4.04; N,
References
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Paper 9/06717E
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