Preparation and reactivity of dihydrogen complexes [MX(ii2-H2)P4]BF4 (M = Ru or Os; X = halogenide or SEt~; P = phosphite)

Article abstract of DOI:10.1039/b004833j

Monohydride complexes MHXP₄ [M = Ru or Os; X = CP, Br, T, SEr or N3~; P = P(OEt)3, PPh(OEt)2 or PPh₂OEt] were prepared by treating dihydride species MH2P₄ first with CF3SO3Me and then with an excess of the anionic ligand X. In an argon atmosphere, protonation of MHXP₄ with HBF4-Et2O gives dihydrogen cations [MX(n²-H₂)P₄⁺, with X = Cl, Br, I or SEt; the classical dihydride [MH2(N3)P₄]+ was obtained with the azide ligand. Instead, in a hydrogen atmosphere, protonation of MHXP₄ with HBF4-Et2O gives hydride-dihydrogen [MH(r)2-H2)P₄]+ species, according to a proposed mechanism involving interaction of Bronsted acid with ligand X. Some [MX(Η²-H2)P₄]⁺ cations were thermally unstable and fully characterised in solution ('H and P NMR, variable temperature Tl measurements), whereas the [OsX(η²-H²){PPh(OEt)2}4]BF4 complexes were stable and isolated as solids. Treatment of [MX(n2-H2)P₄]⁺ cations with alkyne PhOCH gave evolution of H2 and formation of the vinylidene intermediate [MX{=C=C(H)Ph}P₄]⁺ which, by reaction with base, afforded the final acetylide M(OCPh)XP₄ derivatives. Treatment with propargyl alcohols HOCC(OH)RR' of the [MX(n2-H2)P₄r cations, instead, gave propadienylidene derivatives [MX(=C=C=CRR')P₄]BPh4 (M = Ru or Os; R = R' = Ph or R = Ph, R' = Me). Hydrazine complexes [MX(NH2NH2)P₄]BPh4 were also prepared by substitution of the dihydrogen ligand in the new n2-H2 derivatives. The Royal Society of Chemistry 2000.

Full text of DOI:10.1039/b004833j

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Preparation and reactivity of dihydrogen complexes
[MX(ꢀ2-H2)P4]BF4 (M ؍ Ru or Os; X ؍ halogenide
or SEt؊; P ؍ phosphite)
Gabriele Albertin,* Stefano Antoniutti, Emilio Bordignon and Michela Pegoraro
Dipartimento di Chimica, Università Ca’ Foscari di Venezia, Dorsoduro 2137, I-30123 Venezia,
Italy
Received 16th June 2000, Accepted 23rd August 2000
First published as an Advance Article on the web 26th September 2000
Monohydride complexes MHXP4 [M = Ru or Os; X = ClϪ, BrϪ, IϪ, SEtϪ or N3Ϫ; P = P(OEt)3, PPh(OEt)2 or
PPh2OEt] were prepared by treating dihydride species MH2P4 first with CF3SO3Me and then with an excess of
the anionic ligand X. In an argon atmosphere, protonation of MHXP4 with HBF4ؒEt2O gives dihydrogen cations
[MX(η2-H2)P4]ϩ, with X = Cl, Br, I or SEt; the classical dihydride [MH2(N3)P4]ϩ was obtained with the azide
ligand. Instead, in a hydrogen atmosphere, protonation of MHXP4 with HBF4ؒEt2O gives hydride–dihydrogen
[MH(η2-H2)P4]ϩ species, according to a proposed mechanism involving interaction of Brønsted acid with ligand
X. Some [MX(η2-H2)P4]ϩ cations were thermally unstable and fully characterised in solution (1H and 31P NMR,
variable temperature T1 measurements), whereas the [OsX(η2-H2){PPh(OEt)2}4]BF4 complexes were stable and
2
ϩ
᎐
isolated as solids. Treatment of [MX(η -H )P ] cations with alkyne PhC᎐CH gave evolution of H and formation
᎐
2
4
2
of the vinylidene intermediate [MX{᎐C᎐C(H)Ph}P ]ϩ which, by reaction with base, afforded the final acetylide
᎐ ᎐
4
2
ϩ
᎐
᎐
᎐
M(C᎐CPh)XP derivatives. Treatment with propargyl alcohols HC᎐CC(OH)RRЈ of the [MX(η -H )P ] cations,
᎐
4
2
4
instead, gave propadienylidene derivatives [MX(᎐C᎐C᎐CRRЈ)P ]BPh (M = Ru or Os; R = RЈ = Ph or R = Ph,
᎐ ᎐ ᎐
4
4
RЈ = Me). Hydrazine complexes [MX(NH2NH2)P4]BPh4 were also prepared by substitution of the dihydrogen
ligand in the new η2-H2 derivatives.
The chemistry of transition metal dihydrogen complexes has
extensively been developed in the past fifteen years, and numer-
ous studies on their synthesis, structure bonding and reactivity
have been reported.1–4 They have also shown how the nature of
the ancillary ligands in a η2-H2 complex may have a dramatic
influence on the structure and reactivity of the dihydrogen lig-
and. However, while a large amount of information has been
reported on the influence of phosphine, carbonyl, amine or
other neutral ligands, relatively little is known about that
anionic ligands X (HϪ, ClϪ, BrϪ, IϪ, N3Ϫ, SEtϪ, CNϪ, etc.) may
have on the properties of [MX(η2-H2)L4]nϩ complexes.1–4 Some
studies on the effects of hydride HϪ and halogenide ClϪ, BrϪ, IϪ
on the H–H distance and JHD values have recently been
reported5,6 for [RuX(η2-H2)L2]ϩ (X = ClϪ or HϪ; L2 = bidentate
phosphine) and [OsX(η2-H2)L4]ϩ (X = ClϪ, BrϪ or IϪ; L = NH3)
derivatives.
stable in air, but were stored in an inert atmosphere (H2, argon)
at Ϫ25 ЊC. All solvents were dried over appropriate drying
agents, degassed on a vacuum line, and distilled into vacuum-
tight storage flasks. Triethyl phosphite was an Aldrich product,
purified by distillation under nitrogen; phosphites PPh(OEt)2
and PPh2OEt were prepared by the method of Rabinowitz
and Pellon.9 Salts RuCl3ؒxH2O (ChemPur) and (NH4)2OsCl6
(Johnson Matthey) were used as received. Methyl triflate
(CF3SO3Me), triflic acid (CF3SO3H), HBF4ؒEt2O (54% solution
᎐
᎐
in Et O), NaN , Na(SEt) and alkynes PhC᎐CH, HC᎐CC-
᎐
᎐
2
3
᎐
(Ph )OH and HC᎐CC(Me)(Ph)OH were Aldrich products
᎐
2
used without further purification. Hydrazine NH2NH2 was
prepared by decomposition of hydrazine cyanurate (Fluka) fol-
lowing the reported method.10 Other reagents were purchased
from commercial sources in the highest available purity and
used as received. Infrared spectra were recorded on Digilab
Bio-Rad FTS-40 or Nicolet Magna 750 FT-IR spectrophoto-
meters, NMR spectra (1H, 13C, 31P) on a Bruker AC200 spec-
trometer at temperatures varying between Ϫ90 and ϩ30 ЊC,
unless otherwise noted. 1H and 13C spectra are referred to
internal tetramethylsilane. 31P-{1H} chemical shifts are reported
with respect to 85% H3PO4, with downfield shifts considered
positive. The SWAN-MR software package11 was used to treat
NMR data. Proton T1 values were measured by the inversion–
recovery method between ϩ30 and Ϫ90 ЊC with a standard
180Њ–τ–90Њ pulse sequence: the error in T1 measurements is
typically 10%. The conductivities of 10Ϫ3 mol dmϪ3 solutions
of the complexes in MeNO2 at 25 ЊC were measured with a
Radiometer CDM 83 instrument.
We have previously reported7,8 the synthesis and reactivity of
dihydrogen complexes stabilised by monodentate phosphite lig-
ands and have shown how the steric and electronic properties of
the ligand influence7a,8b H–H distance and JHD values. As an
extension of these studies, we report here the preparation and
protonation reactions of a series of MHXP4 complexes (M =
Ru or Os), with the aim of synthesizing new “classical” or
“non-classical” [MX(H2)P4]ϩ hydride complexes stabilised by
monodentate phosphite ligands. Furthermore, study of their
chemical and spectroscopic properties should give information
on the influence of the anionic ligand on the η2-H2 group and
allow comparisons with related hydride8 [MH(η2-H2)P4]ϩ or
halogenide5,6 [MCl(η2-H2)(P–P)2]ϩ derivatives.
Synthesis of complexes
Experimental
All synthetic work was carried out in an inert atmosphere using
standard Schlenk techniques or a Vacuum Atmosphere dry-
box. Once isolated, the complexes were found to be relatively
Hydrides RuH2P4 and OsH2P4 [P = PPh(OEt)2, P(OEt)3 or
PPh2(OEt)] and [RuH(η2-H2){PPh(OEt)2}4]BF4 were prepared
following the methods previously reported.8a,b,12,13
DOI: 10.1039/b004833j
J. Chem. Soc., Dalton Trans., 2000, 3575–3584
This journal is © The Royal Society of Chemistry 2000
3575

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OsHXP4 1–3 [P ؍ PPh(OEt)2 1, P(OEt)3 2 or PPh2OEt 3;
X ؍ Cl؊ a, Br؊ b, I؊ c, SEt؊ d or N3؊ e]. To a solution of OsH2P4
(0.25 mmol) in 10 cm3 of toluene cooled to Ϫ80 ЊC was added
an equimolar amount of CF3SO3Me (0.25 mmol, 28 µL) and
the reaction mixture, brought to room temperature, was stirred
for 1 h. An excess of the appropriate lithium or sodium salt
of anionic ligand XϪ (0.75 mmol of NaX or LiX) in 5 cm3 of
ethanol was added, and the resulting solution stirred for 3 h.
The solvent was removed under reduced pressure, giving an oil
which was triturated with ethanol (2–3 cm3). A white or yellow
solid slowly separated from the resulting solution, which was
filtered off and crystallised from ethanol; yield between 40
and 70% (Found: C, 47.2; H, 5.8; Cl, 3.65. C40H61ClO8OsP4 1a
requires C, 47.1; H, 6.0; Cl, 3.5. Found: C, 45.0; H, 5.7. C40H61-
BrO8OsP4 1b requires C, 45.2; H, 5.8. Found: C, 43.4; H, 5.7.
C40H61IO8OsP4 1c requires C, 43.25; H, 5.5. Found: C, 48.15; H,
6.5. C42H66O8OsP4S 1d requires C, 48.3; H, 6.4. Found: C, 47.0;
H, 5.9; N, 4.05. C40H61N3O8OsP4 1e requires C, 46.8; H, 6.0; N,
4.10. Found: C, 29.1; H, 6.2. C24H61IO12OsP4 2c requires C,
29.3; H, 6.3. Found: C, 56.7; H, 5.1. C56H61BrO4OsP4 3b
requires C, 56.4; H, 5.2. Found: C, 54.2; H, 4.9. C56H61IO4OsP4
3c requires C, 54.3; H, 5.0%).
requires C, 41.7; H, 5.4. Found: C, 40.0; H, 5.3. C40H62BF4-
IO8OsP4 6c requires C, 40.1; H, 5.2%).
؊
[Os(SEt)(ꢀ2-H2){PPh(OEt)2}4]؉BF4 6d. This compound is
thermally unstable and was prepared only in solution by adding
3.9 µL (0.027 mmol) of HBF4ؒEt2O to a solution of OsH-
(SEt)[PPh(OEt)2]4 (0.025 mmol, 0.026 g) in 0.5 cm3 of CD2Cl2
placed in a 5 mm NMR tube cooled to Ϫ80 ЊC. The tube was
shaken and brought to Ϫ10 ЊC to complete the reaction, and
then 1H and 31P NMR spectra were recorded: δH(CD2Cl2,
273 K) 3.80–3.21 (18 H, m, CH2), 1.23 (3 H, t, CH3 sulfide),
1.13 (24 H, t, CH3 phosphite) and Ϫ10.38 (2 H, br, η2-H2);
δP(CD2Cl2, 273 K) 105.0 (s); (183 K) A2BC spin system,
δA 113.1, δB 102.1, δC 101.5, JAB = 29.5, JAC = 31.9, JBC = 36.8
Hz.
؊
[OsH2(N3){PPh(OEt)2}4]؉BF4 6e. This compound too is
thermally unstable and decomposes above Ϫ5 to Ϫ10 ЊC, both
as a solid and in solution. It was therefore prepared only in
solution by adding 3.9 µL (0.027 mmol) of HBF4ؒEt2O to a
solution of OsH(N3)[PPh(OEt)2]4 (0.025 mmol, 0.026 g) in 0.5
cm3 of CD2Cl2 placed in a 5 mm NMR tube cooled to Ϫ80 ЊC.
The tube was shaken and brought to Ϫ10 ЊC to complete the
1
OsHBr[P(OEt)3]4 2b. This complex was prepared like related
species 1–3 resulting, in this case, in an oily product with low
yield (about 30%).
reaction, and then H and 31P NMR spectra were recorded:
δH(CD2Cl2, 203 K) 3.35 (16 H, m, CH2), 1.06 (24 H, t, CH3) and
Ϫ15.62 (2 H, br, hydride); δP(CD2Cl2, 203 K) 123.0 (s, br).
؊
RuHXP4 4, 5 [P ؍ PPh(OEt)2 4 or P(OEt)3 5; X ؍ Br؊ b, I؊ c
or N3؊ e]. These complexes can be obtained by two methods.
(i) An equimolar amount of CF3SO3Me (0.25 mmol, 28 µL)
was added to a solution of RuH2P4 (0.25 mmol) in 10 cm3
of toluene cooled to Ϫ80 ЊC and the reaction mixture, brought
to 0 ЊC, was stirred for 30 min. An excess of the appropri-
ate lithium or sodium salt of anionic ligand X (0.40 mmol of
NaX or LiX) in 5 cm3 of ethanol was added, and the solution
stirred for 1 h. The solvent was removed under reduced pres-
sure, giving an oil which was treated with 3 cm3 of ethanol.
Cooling of the resulting solution to Ϫ25 ЊC gave a white or pale
yellow microcrystalline solid, which was slowly separated,
filtered off, and dried under vacuum; yield was between 35 and
70%.
(ii) An excess of the appropriate lithium or sodium salt of
anionic ligand X (0.4 mmol) and compound [RuH(η2-H2)-
{PPh(OEt)2}4]BF4 (0.2 mmol, 0.20 g) were placed in a 25 cm3
three-necked round-bottomed flask and, after cooling to
Ϫ80 ЊC, treated with 10 cm3 of ethanol. The reaction mixture,
brought to room temperature, was stirred for 1 h, and the
volume of the solution then reduced to about 3 cm3 by evapor-
ation under reduced pressure. Cooling to Ϫ25 ЊC of the result-
ing solution gave white or pale yellow microcrystals, which were
separated, filtered off, and dried under vacuum; yield was
between 40 and 70% (Found: C, 49.1; H, 6.4. C40H61BrO8P4Ru
4b requires C, 49.3; H, 6.3. Found: C, 46.95; H, 6.05. C40H61-
IO8P4Ru 4c requires C, 47.0; H, 6.0. Found: C, 51.4; H, 6.7; N,
4.4. C40H61N3O8P4Ru 4e requires C, 51.3; H, 6.6; N, 4.5. Found:
C, 33.8; H, 7.4. C24H61BrO12P4Ru 5b requires C, 34.05; H,
7.3%).
[OsX(ꢀ2-H2){P(OEt)3}4]؉BF4
7
and [OsX(ꢀ2-H2)(PPh2-
؊
OEt)4]؉BF4 8 (X ؍ Br؊ b or I؊ c). These complexes were pre-
pared in CD2Cl2 solution at low temperature by protonation
with HBF4ؒEt2O of the corresponding hydrides, but not
isolated as solids owing to easy loss of H2 above 0 ЊC. A typical
preparation involved the addition by microsyringe of HBF4ؒ
Et2O (0.022 mmol, 3.2 µL) to a solution of the appropriate
hydride (0.020 mmol) in 0.5 cm3 of CD2Cl2 placed in a 5 mm
NMR tube cooled to Ϫ80 ЊC. The tube was shaken to complete
the reaction and then NMR spectra were recorded. [OsBr(η2-
H2){P(OEt)3}4]ϩ 7b: δH(CD2Cl2, 203 K) 4.06, 3.96 (24 H, m,
CH2), 1.27, 1.15 (36 H, t, CH3); δP(CD2Cl2, 203 K) A2B2 spin
system, δA 87.2, δB 74.4, JAB = 42 Hz. [OsI(η2-H2){P(OEt)3}4]-
BF4 7c: δH(CD2Cl2, 273 K) 4.19, 4.05 (24 H, m, CH2), 1.33, 1.28
(36 H, t, CH3); δP(CD2Cl2, 193 K) A2B2 spin system, δA 87.6,
δB 71.8, JAB = 42 Hz. [OsBr(η2-H2)(PPh2OEt)4]ϩ 8b: δH(CD2Cl2,
203 K) 3.40 (8 H, m, CH2), 1.11 (12 H, t, CH3) and Ϫ9.35 (2 H,
br, η2-H2); δP(CD2Cl2, 203 K) 87.0 (s). [OsI(η2-H2)(PPh2OEt)4]ϩ
8c: δH(CD2Cl2, 273 K) 3.98 (8 H, qnt, CH2), 1.35 (12 H, t, CH3)
and Ϫ9.07 (2 H, qnt, η2-H2, JPH = 12 Hz); δP(CD2Cl2, 298 K)
108.3 (s).
[RuX(ꢀ2-H2)P4]؉BF4؊ 9, 10 (P ؍ PPh(OEt)2 9 or P(OEt)3 10;
X ؍ Br؊ b or I؊ c). Owing to easy loss of H2 above Ϫ10 ЊC,
these complexes too were prepared only at low temperature by
protonation with HBF4ؒEt2O (0.022 mmol, 3.2 µL) of the
appropriate hydride RuHXP4 (0.020 mmol) dissolved in 0.5 cm3
of CD2Cl2 placed in a 5 mm NMR tube cooled to Ϫ80 ЊC. After
shaking the tube to complete the reaction, the NMR spectra
were as follows. [RuBr(η2-H2){PPh(OEt)2}4]ϩ 9b: δH(CD2Cl2,
183 K) 3.36 (16 H, m, CH2), 1.09 (24 H, t, CH3) and Ϫ10.83
(2 H, br, η2-H2), (260 K) 3.70, 3.43 (16 H, m, CH2), 1.18 (24 H,
t, CH3) and Ϫ10.75 (2 H, qnt, br, η2-H2); δP(CD2Cl2, 183 K) 145
(m), (246 K) 145.0 (s, br). [RuI(η2-H2){PPh(OEt)2}4]ϩ 9c:
δH(CD2Cl2, 203 K) 3.37 (16 H, m, CH2), 1.10 (24 H, t, CH3) and
Ϫ9.66 (2 H, br, η2-H2); δP(CD2Cl2, 203 K) 146.0 (s, br).
[RuBr(η2-H2){P(OEt)3}4]ϩ 10b: δH(CD2Cl2, 223 K) 4.03 (24 H,
m, CH2), 1.19 (36 H, t, CH3) and Ϫ11.96 (2 H, br, η2-H2);
δP(CD2Cl2, 203 K) 135.5 (s).
[OsX(ꢀ2-H2){PPh(OEt)2}4]BF4 6 (X ؍ Cl؊ a, Br؊ b or I؊ c). A
slight excess of HBF4ؒEt2O (0.137 mmol, 20 µL of 54% solution
in Et2O) was added to a solution of OsHX[PPh(OEt)2]4 (0.12
mmol) in 5 cm3 of diethyl ether cooled to Ϫ80 ЊC and allowed
to stand under argon. The reaction mixture was brought to
room temperature and stirred for about 1 h. A white solid
began to separate from the solution at 0 ЊC, and precipitation
was complete after 1 h of stirring at room temperature. The
solid was filtered off and dried under vacuum; yield ≥90%;
ΛM = 90.4 for 6a, 93.1 for 6b, 88.9 S cm2 molϪ1 for 6c (Found: C,
43.5; H, 5.8; Cl, 3.1. C40H62BClF4O8OsP4 6a requires C, 43.4; H,
5.6; Cl, 3.20. Found: C, 41.55; H, 5.5. C40H62BBrF4O8OsP4 6b
؊
[RuH2(N3){PPh(OEt)2}4]؉BF4 9e. This compound was
prepared exactly like related species 9 and 10 by protonation
with HBF4ؒEt2O of RuH(N3)[PPh(OEt)2]4 in an NMR tube at
3576
J. Chem. Soc., Dalton Trans., 2000, 3575–3584

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Ϫ80 ЊC. δH(CD2Cl2, 203 K) 3.90–3.30 (16 H, m, CH2), 1.10
(24 H, t, CH3) and Ϫ14.81 (2 H, qnt, br, hydride); δP(CD2Cl2,
203 K) 167–158 (m).
[RuBr(NH2NH2){P(OEt)3}4]BPh4 17b. To a solution of Ru-
HBr[P(OEt)3]4 (0.15 mmol, 0.13 g) in 10 cm3 of CH2Cl2 cooled
to Ϫ80 ЊC was added HBF4ؒEt2O (0.165 mmol, 24 µL) and the
reaction mixture, brought to Ϫ40 ЊC, stirred for 2 h. An excess
of NH2NH2 (0.30 mmol, 10 µL) was slowly added, then the
solution was brought to room temperature and stirred for 30
min. The solvent was removed under reduced pressure, giving
an oil which was treated with ethanol containing an excess of
NaBPh4 (0.30 mmol, 0.10 g). A white solid separated from the
resulting solution, and was filtered off and crystallised from
CH2Cl2 (2 cm3) and ethanol (5 cm3); yield ≥70%; ΛM = 52.6 S
cm2 molϪ1 (Found: C, 48.35; H, 7.3; N, 2.2. C48H84BBrN2O12-
P4Ru requires C, 48.2; H, 7.1; N, 2.3%).
᎐
᎐
᎐
OsBr(C᎐CPh)[PPh(OEt) ] 11b. An excess of PhC᎐CH (0.45
᎐
2
4
mmol, 50 µL) was added to a solution of [OsBr(η2-H2)-
{PPh(OEt)2}4]BF4 (0.15 mmol, 0.170 g) in 10 cm3 of CH2Cl2
under an argon atmosphere, and the reaction mixture stirred
for about 1 h. Triethylamine (1.5 mmol, 208 µL) was added
and, after 2 h of stirring, the solvent removed under reduced
pressure giving an oil which was treated with ethanol (2 cm3).
Cooling to Ϫ25 ЊC gave a solution from which a yellow solid
separated, this was filtered off and crystallised from toluene
(1 cm3) and ethanol (5 cm3); yield ≥60% (Found: C, 49.7; H, 5.7.
C48H65BrO8OsP4 requires C, 49.5; H, 5.6%).
Oxidation reactions. The oxidation of hydrazine complexes
was carried out at low temperature (Ϫ30 ЊC) using Pb(OAc)4 as
oxidant. In a typical experiment, a sample of the appropriate
complex (0.1 mmol) was placed in a 25 cm3 three-necked flask
fitted with a solid-addition sidearm containing an equimolar
amount or an excess of Pb(OAc)4. Dichloromethane was
added, the solution cooled to Ϫ40 ЊC, and the oxidant added
portionwise, in about 20–30 min, to the cold stirred solution.
The reaction mixture was brought to 0 ЊC, stirred for 10 min,
and the solvent then removed under reduced pressure, giving an
oil which was treated with ethanol (3 cm3) containing an excess
of NaBPh4 (0.2 mmol, 0.070 g). A white solid slowly separated
out, which was filtered off and dried under vacuum.
᎐
RuBr(C᎐CPh)[PPh(OEt) ] 12b. To a solution of RuHBr-
᎐
2
4
[PPh(OEt)2]4 (0.15 mmol, 0.15 g) in 10 cm3 of CH2Cl2, cooled to
Ϫ80 ЊC, was added a slight excess of HBF4ؒEt2O (0.165 mmol,
24 µL) and the resulting solution, brought to Ϫ40 ЊC, stirred
᎐
for 30 min. An excess of PhC᎐CH (0.45 mmol, 50 µL) was
᎐
added and, after 30 min of stirring, triethylamine (0.45 mmol,
62 µL). The reaction mixture was brought to room temper-
ature and, after 1 h, the solvent removed under reduced pres-
sure giving an oil which was treated with 5 cm3 of ethanol.
Stirring the resulting solution gave a yellow solid which was
separated, filtered off, and crystallised from ethanol; yield ≥40%
(Found: C, 53.75; H, 6.0. C48H65BrO8P4Ru requires C, 53.6; H,
6.1%).
Results and discussion
Monohydride complexes
[OsBr(᎐C᎐C᎐CPh ){PPh(OEt) } ]BF 13b and [OsBr{᎐C᎐
᎐ ᎐ ᎐ ᎐ ᎐
2
2
4
4
C᎐C(Me)Ph}{PPh(OEt) } ]BF 14b. An excess of the appropri-
᎐
2
4
4
The new monohydride complexes MHXP4 1–5 were prepared
by allowing the MH2P4 species to react first with CF3SO3Me
and then with the appropriate anionic ligand X, as shown in
Scheme 1. The reaction of dihydride MH2P4 with methyl triflate
᎐
᎐
ate alkyne [HC᎐CC(Ph )OH or HC᎐CC(Me)(Ph)OH] (0.15
᎐
᎐
2
mmol) was added to a solution of [OsBr(η2-H2){PPh(OEt)2}4]-
BF4 (0.15 mmol, 0.17 g) in 10 cm3 of CH2Cl2, and the reaction
mixture stirred for about 3 h. The solvent was removed under
reduced pressure, giving an oil which was treated with 5 cm3 of
ethanol. Vigorous stirring of the resulting solution caused the
separation of a reddish brown solid which was filtered off and
dried under vacuum; yield ≥70%; ΛM = 93.6 for 13b, 90.9 S cm2
molϪ1 for 14b (Found: C, 49.5; H, 5.4. C55H70BBrF4O8OsP4
13b requires C, 49.30; H, 5.3. Found: C, 46.9; H, 5.5. C50H68-
BBrF4O8OsP4 14b requires C, 47.00; H, 5.4%).
Scheme 1 M = Os 1, 2, 3 or Ru 4, 5; P = PPh(OEt)2 1, 4, P(OEt)3 2, 5
or PPh2OEt 3; X = ClϪ a, BrϪ b, IϪ c, SEtϪ d or N3Ϫ e.
1
proceeds with the evolution of CH4 (by H NMR) and form-
[RuBr(᎐C᎐C᎐CPh ){PPh(OEt) } ]BPh 15b. A slight excess
ation of the triflate complex14 MH(η1-OSO2CF3)P4 which, by
substitution with anionic ligand X, gives the final complexes
MHXP4 1–5. Alternatively, ruthenium complexes RuHXP4 can
be prepared by substituting the η2-H2 ligand in [RuH(η2-H2)-
P4]ϩ cations8a with the appropriate ligand X, as shown in
Scheme 2.
᎐ ᎐ ᎐
2
2
4
4
of HBF4ؒEt2O (0.165 mmol, 24 µL) was added to a solution of
RuHBr[PPh(OEt)2]4 (0.15 mmol, 0.15 g) in 10 cm3 of CH2Cl2
cooled to Ϫ80 ЊC, and the reaction mixture, brought to Ϫ40 ЊC,
᎐
wasstirredfor30min. 1,1-Diphenyl-2-propyn-1-ol(HC᎐CCPh -
᎐
2
OH, 0.15 mmol, 0.031 g) was then added and the solution,
brought to room temperature, stirred for about 3 h. The solvent
was removed under reduced pressure, giving an oil which was
treated with ethanol containing an excess of NaBPh4 (0.3
mmol, 0.10 g). A reddish orange solid slowly separated from the
resulting solution, which was filtered off and crystallised from
CH2Cl2 (3 cm3) and ethanol (5 cm3); yield ≥60%; ΛM = 53.4 S
cm2 molϪ1 (Found: C, 64.1; H, 6.3. C79H90BBrO8P4Ru requires
C, 64.0; H, 6.1%).
Scheme 2
All the new hydride complexes 1–5 were isolated as white or
pale yellow solids, stable in air (except 3), diamagnetic and non-
electrolytic. Analytical and spectroscopic data (Table 1) support
the proposed formulations. Furthermore, IR and NMR data
allowed trans geometry I to be established in solution for
hydride complexes 1, 3, 4 and 5; cis geometry II was shown by
[OsBr(NH2NH2){PPh(OEt)2}4]BPh4 16b. To a solution of
[OsBr(η2-H2){PPh(OEt)2}4]BF4 (0.15 mmol, 0.17 g) in 10 cm3
of CH2Cl2 was added a slight excess of NH2NH2 (0.30 mmol,
10 µL) and the reaction mixture stirred for about 3 h. The sol-
vent was removed under reduced pressure, giving an oil which
was treated with ethanol containing an excess of NaBPh4 (0.30
mmol, 0.10 g). A white solid separated from the resulting
solution, which was filtered off and crystallised from CH2Cl2
(2 cm3) and ethanol (5 cm3); yield ≥70%; ΛM = 51.7 S cm2 molϪ1
(Found: C, 54.2; H, 6.1; N, 2.0. C64H84BBrN2O8OsP4 requires
C, 54.4; H, 6.0; N, 2.0%).
J. Chem. Soc., Dalton Trans., 2000, 3575–3584
3577

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Table 1 Selected infrared and NMR data for osmium and ruthenium complexes
IRa
1H NMRb,c
31P-{1H}
NMRb,d
δ (J/Hz)
Spin
system
Compound
ν˜
/cmϪ1
Assignment
δ (J/Hz)
Assignment
CH2
1a
trans-OsHCl[PPh(OEt)2]4
2089w
ν(OsH)
3.72 (qnt)
3.35 (m)
1.01 (t)
A4
121.1 (s)
120.5 (s)
119.2 (s, br)
117.6 (s)
121.1 (s)
CH3
OsH
Ϫ19.20 (qnt)
JPH = 18
3.97 (qnt)e
3.57 (m)
CH2
A4
e
1.08 (t)
CH3
OsH
Ϫ18.47 (qnt)
JPH = 18
e
1b
1c
1d
trans-OsHBr[PPh(OEt)2]4
trans-OsHI[PPh(OEt)2]4
trans-OsH(SEt)[PPh(OEt)2]4
2098w
2122w
2006w
ν(OsH)
ν(OsH)
ν(OsH)
3.98 (qnt)e
3.60 (qnt)
1.08 (t)
CH2
A4
CH3
OsH
Ϫ18.10 (qnt)
JPH = 18
3.96 (qnt)e
3.62 (qnt)
1.09 (t)
CH2
A4
e
CH3
OsH
Ϫ16.53 (qnt)
JPH = 18
3.70 (m)
3.34 (m)
1.26 (t)
1.00 (t)
CH2
A4
SCH2CH3
POCH2CH3
OsH
Ϫ19.21 (qnt)
JPH = 18
1e
2b
trans-OsH(N3)[PPh(OEt)2]4
cis-OsHBr[P(OEt)3]4
2099w
2070m
ν(OsH)
ν(N3)
3.59 (s)
CH2
A4
123.8 (s)
3.23 (m)
f
1.01 (t)
CH3
OsH
A2B2
δA 129.7
δB 123.5
Ϫ18.47 (qnt)
JPH = 18
JAB = 38
δA 120.3
δB 116.6
1960m
1966m
ν(OsH)
ν(OsH)
4.15–3.80 (m)
1.22 (t)
CH2
CH3
AB2C
1.17 (t)
1.01 (t)
δC 103.9
JAB = 31.3
JAC = 23.6
JBC = 39.1
δA 105.7
δB 102.2
Ϫ8.71 to Ϫ9.57
(m)
OsH
2c
cis-OsHI[P(OEt)3]4
4.21 (m)e
1.31 (m)
CH2
CH3
OsH
AB2Ce
Ϫ9.57 to
Ϫ10.42 (m)
δC 93.5
JAB = 33.8
JAC = 21.6
JBC = 38.3
101.5 (s, br)
f
3b
3c
4b
trans-OsHBr(PPh2OEt)4
trans-OsHI(PPh2OEt)4
trans-RuHBr[PPh(OEt)2]4
3.02 (m)
0.52 (t)
Ϫ18.34 (qnt)
JPH = 18
3.06 (m)
0.62 (t)
Ϫ16.60 (qnt)
JPH = 18
3.75 (m)
3.42 (m)
1.03 (t)
Ϫ16.45 (qnt)
JPH = 22
3.99 (m)e
3.66 (m)
1.09 (t)
Ϫ15.77 (qnt)
JPH = 22
3.77 (m)
3.47 (m)
1.07 (t)
Ϫ14.65 (qnt)
JPH = 20
3.60 (m)
3.25 (m)
1.00 (t)
Ϫ16.94 (qnt)
JPH = 22
4.11 (m)
1.27 (t)
CH2
CH3
OsH
A4
2118w
1992m
ν(OsH)
ν(RuH)
CH2
CH3
OsH
A4
A4
96.2 (s, br)
161.2 (s)
CH2
CH3
RuH
e
CH2
A4
160.8 (s)
161.5 (s)
162.8 (s)
134.8 (s)
CH3
RuH
4c
4e
5b
trans-RuHI[PPh(OEt)2]4
trans-RuH(N3)[PPh(OEt)2]4
trans-RuHBr[P(OEt)3]4
2027m
ν(RuH)
CH2
A4
A4
A4
CH3
RuH
2087s
1983w
ν(N3)
ν(RuH)
CH2
CH3
RuH
2027m
ν(RuH)
CH2
CH3
1.22 (t)
Ϫ17.46 (qnt)
JPH = 22
RuH
3578
J. Chem. Soc., Dalton Trans., 2000, 3575–3584

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Table 1 (Contd.)
IRa
/cmϪ1
1H NMRb,c
31P-{1H}
NMRb,d
δ (J/Hz)
Spin
system
Compound
ν˜
Assignment
δ (J/Hz)
Assignment
CH2
6a
trans-[OsCl(η2-H2){PPh(OEt)2}4]BF4
3.72 (m)
3.54 (m)
1.16 (t)
Ϫ10.31 (qnt)
JPH = 12
3.67 (m)
1.17 (t)
Ϫ10.34 (qnt,
br)
JPH = 12
3.60 (m)
1.19 (t)
A4
A4
A4
105.0 (s)
102.8 (s)
100.3 (s)
CH3
η2-H2
6b trans-[OsBr(η2-H2){PPh(OEt)2}4]BF4
CH2
CH3
η2-H2
6c
trans-[OsI(η2-H2){PPh(OEt)2}4]BF4
CH2
CH3
η2-H2
f
Ϫ10.13 (qnt,
br)
A2B2
δA 112.5
δB 100.0
JAB = 30
δA 118.5
δB 109.8
δC 107.3
JAB = 31.0
JAC = 17.3
JBC = 33.9
163.8 (s)
JPH = 12
4.10–3.60 (m)
1.40 (t)
᎐
᎐
11b cis-OsBr(C᎐CPh)[PPh(OEt)2]4
2083m
ν(C᎐C)
CH2
CH3
AB2C
᎐
᎐
1.27 (t)
1.23 (t)
1.11 (t)
᎐
᎐
12b trans-RuBr(C᎐CPh)[PPh(OEt)2]4
2091s
1969s
ν(C᎐C)
3.89 (m)
3.76 (m)
1.30 (t)
3.86 (m)
3.67 (m)
1.32 (t)
1.29 (t)
1.25 (t)
CH2
A4
᎐
᎐
CH3
CH2
13b cis-[OsBr(᎐C᎐C᎐CPh2){PPh(OEt)2}4]-
ν(C᎐C᎐C)
᎐ ᎐
AB2C
δA 117.6
δB 96.8
δC 94.3
᎐
᎐
᎐
BF4
CH3
JAB = 47.2
JAC = 24.1
JBC = 26.6
δA 117.0
δB 97.6
14b cis-[OsBr{᎐C᎐C᎐C(Me)Ph}-
1973s
1952s
ν(C᎐C᎐C)
᎐ ᎐
3.81 (m)
3.61 (m)
1.35–1.20 (m)
CH2
CH3
AB2C
᎐
᎐
᎐
{PPh(OEt)2}4]BF4
δC 94.7
JAB = 45.8
JAC = 25.6
JBC = 26.8
163.9 (s)
15b trans-[RuBr(᎐C᎐C᎐CPh2){PPh(OEt)2}4]-
ν(C᎐C᎐C)
᎐ ᎐
3.86 (m)
3.75 (m)
1.30 (t)
4.48 (br)
4.00–3.50 (m)
3.25 (br)
1.34 (t)
1.28 (t)
1.25 (t)
4.41 (br)
4.20–3.90 (m)
2.93 (br)
1.30 (m)
CH2
A4
᎐
᎐
᎐
BPh4
CH3
OsNH2
CH2
NH2
CH3
16b cis-[OsBr(NH2NH2){PPh(OEt)2}4]BPh4
3332m
3317w
3263w
1595sh
ν(NH)
δ(NH2)
ν(NH)
A2BC
δA 112.8
δB 106.1
δC 100.0
JAB = 32.2
JAC = 33.6
JBC = 31.5
δA 134.8
17b cis-[RuBr(NH2NH2){P(OEt)3}4]BPh4
3344sh
3335m
3263m
RuNH2
CH2
NH2
CH3
ABC2
δB 126.6
δC 121.6
JAB = 63.3
JAC = 59.2
JBC = 59.8
a In KBr pellets. b In CD2Cl2 at 25 ЊC. c Phenyl proton resonances are omitted. d Positive shift downfield from 85% H3PO4. e In C6D6. f At Ϫ70 ЊC.
the P(OEt)3 derivatives OsHX[P(OEt)3]4 2b and 2c. In the
hydride region, the H NMR spectra showed a quintet for the
observed 31P spectra. Examples of inequivalent phosphorus
1
15
nuclei in octahedral complexes containing four PPhMe2 or
trans complexes and a multiplet for the cis. The 31P-{1H} NMR
spectra are consistent with the proposed geometries, showing
only one sharp singlet for trans complexes 1, 3, 4 and 5, while an
AB2C multiplet appears in the spectra of cis derivatives 2. It
may be observed, however, that the spectra of some trans com-
plexes do not remain unchanged between ϩ30 and Ϫ90 ЊC, and
the sharp singlet observed to Ϫ60 ЊC resolves, in the case of 1e,
into an A2B2 multiplet at Ϫ90 ЊC. This result implies the pres-
ence of inequivalent phosphorus nuclei, and seems to be in
contrast with both the proposed trans and cis geometry, for
which an AB2C multiplet should be expected. However, the
spectra may be interpreted on the basis of trans geometry, in
which the four PPh(OEt)2 ligands are made inequivalent by
restricted rotation around M–P as the temperature is lowered.
The probable different arrangement of the phenyl and ethoxy
groups of one phosphite with respect to the other may give the
PPh(OEt)2 ligand7c,16 in a plane have recently been reported and
these precedents further support the trans geometry proposed
for complexes 1, 3, 4 and 5.
Protonation reactions
Protonation reactions of monohydrides MHXP4 with HBF4ؒ
Et2O were studied at low temperature in both argon and hydro-
gen atmospheres. The results are summarised in Schemes 3
and 4.
In an argon atmosphere, hydrides MHXP4 1–5 react with
HBF4ؒEt2O to give dihydrogen complexes [MX(η2-H2)P4]ϩ 6–10
which are stable at room temperature only in the case of
osmium with PPh(OEt)2 (6), and were isolated as BF4Ϫ salts and
characterised. Instead, the related [OsX(η2-H2)P4]ϩ 7, 8 and
[RuX(η2-H2)P4]ϩ 9, 10 cations are thermally unstable and lose
J. Chem. Soc., Dalton Trans., 2000, 3575–3584
3579

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addition of even a small amount of HBF4ؒEt2O gave rise to the
transformation of all the starting complexes into the [MH-
(η2-H2)P4]ϩ cations (Scheme 6). The presence of acid seems to
Scheme 3 M = Os 6, 7, 8 or Ru 9, 10; P = PPh(OEt)2 6, 9, P(OEt)3 7, 10
or PPh2OEt 8; X = ClϪ a, BrϪ b, IϪ c or SEtϪ d.
Scheme 6
be crucial for the formation of hydride–dihydrogen complexes
and, also in this case, interaction of the Brønsted acid with
ligand X of [MX(η2-H2)P4]ϩ may be invoked to explain its
formation, according to the path shown in Scheme 7. The
Scheme 4 X = ClϪ, BrϪ, IϪ or SEtϪ.
H2 even at temperatures below Ϫ10 ЊC, preventing their separ-
ation as solids. In solution, however, they are stable to Ϫ5 to
Ϫ10 ЊC and were characterised spectroscopically.
Azido complexes MH(N3)P4 also react with HBF4ؒEt2O
but, in this case, they afford the classical dihydride species
[MH2(N3)P4]ϩ 6e, 9e, which are thermally unstable and were
characterised in solution at low temperature.
Surprisingly, operating in a hydrogen atmosphere, proton-
ation of OsHXP4 gives hydride–dihydrogen cations [OsH(η2-
Ϫ
H2)P4]ϩ, which were isolated as BF4 salts in very high yields
(Scheme 4). Protonation of the related RuHXP4 also afforded
[RuH(η2-H2)P4]ϩ, but in low yield and with some decom-
position products. The formation of hydride-dihydrogen species
under H2 may be due to substitution of ligand X with H2 in
the starting complex MHXP4. In order to test this hypothesis,
we treated all MHXP4 species with H2, but no reaction was
observed after 24 h at room temperature, and only further addi-
tion of HBF4ؒEt2O caused the formation of [MH(η2-H2)P4]ϩ
derivatives. It may also be noted that the addition of even
a small amount (less than the 1:1 ratio) of HBF4ؒEt2O or
another Brønsted acid to a solution of MHXP4 under H2 led to
[MH(η2-H2)P4]ϩ cationic species. These results may be inter-
preted on the basis of labilisation of ligand X in MHXP4,
caused by interaction with the Brønsted acid (or with Hϩ)
and subsequent substitution of X with H2, affording the final
complex shown in Scheme 5.
Scheme 7 [M] = RuP4 or OsP4.
substitution of ligand X labilised by interaction with acid (Hϩ)
gives the bis(dihydrogen) dicationic complex [M(η2-H2)2P4]2ϩ
,
which must be very acidic and can easily lose Hϩ to give
the final [MH(η2-H2)P4]ϩ derivative. Therefore, both the mech-
anisms of Schemes 5 and 7 may operate to give the final
hydride–dihydrogen complexes, by protonation of MHXP4
under H2. However, the experimental data do not distinguish
the two paths, which may also be concurrent.
In order to obtain further information on these reactions and
to support the mechanism proposed in Schemes 5 and 7, we
1
studied the reactions by H and 31P NMR spectra, but no new
species, apart from the starting MHXP4 or [MX(η2-H2)P4]ϩ,
were observed in the spectra of the reaction mixture, and even
the use of deuteriated species such as D2 and CF3SO3D did not
give any further information on the possible mechanism. How-
ever, the formation of [MH(η2-H2)P4]ϩ by protonation of both
MHXP4 and [MX(η2-H2)P4]ϩ under H2 may reasonably be
explained on the basis of Schemes 5 and 7: although other
mechanisms may be operating, the proposed labilisation of
ligand X by interaction with Brønsted acid is plausible and fits
experimental data.
Scheme 5
Although this mechanism, involving the interaction of Hϩ
with one or two M–X fragments, is plausible, it is probably not
the only possible or only operating one in this transformation,
because treatment of MHXP4 with an acid, even in H2, and
at least in small amounts, should give [MX(η2-H2)P4]ϩ species.
In fact, the potential protonation sites present in the MHXP4
complexes are the X ligand, the metal, the oxygen atoms of the
phosphites and the hydride ligand, whose protonation gives
the [MX(η2-H2)P4]ϩ cation. Instead, no trace of any halide–
dihydrogen complex was detected when the protonation
reaction was carried out under H2.
Characterisation of complexes
The spectroscopic data of new classical and non-classical com-
plexes 6–10 are listed in Tables 1 and 2. Some complexes were
obtained as pale yellow solids (6), stable in air and in solution
of polar organic solvents, where they behave as 1:1 electro-
lytes;17 the others (7–10) are thermally unstable and were
characterised only in solution. However, the presence of
η2-H2 ligand in [MX(η2-H2)P4]ϩ and of HϪ in [MH2(N3)P4]ϩ
1
derivatives was confirmed by H NMR spectra and variable-
temperature T1 measurements: in the low-frequency region of
the proton spectra of all the η2-H2 complexes a slightly broad
quintet at δ Ϫ9.11 to Ϫ10.75 is present, due to the H2 ligand
coupled with four equivalent phosphorus atoms (Fig. 1). The
These results prompted us to study the stability of [MX(η2-
H2)P4]ϩ under different conditions, and we observed that the
compounds were quite stable in solution, even under H2, but the
3580
J. Chem. Soc., Dalton Trans., 2000, 3575–3584

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Table 2 1H NMR data at 200 MHz in the hydride region for some osmium and ruthenium complexes
Compound
T/K
δ(M–H2)
δ(M–H)
T1/ms
r(H–H)a/Å fast rotation
1b
3b
6b
6c
6d
6e
8b
9b
9c
9e
OsHBr[PPh(OEt)2]4
OsHBr(PPh2OEt)4
210
208
206
209
206
203
203
209
203
203
Ϫ16.75 (qnt)
Ϫ11.9 (br)
191 20
161 16
[OsBr(η2-H2){PPh(OEt)2}4]ϩ
[OsI(η2-H2){PPh(OEt)2}4]ϩ
[Os(SEt)(η2-H2){PPh(OEt)2}4]ϩ
[OsH2(N3){PPh(OEt)2}4]ϩ
[OsBr(η2-H2)(PPh2OEt)4]ϩ
[RuBr(η2-H2){PPh(OEt)2}4]ϩ
[RuI(η2-H2){PPh(OEt)2}4]ϩ
[RuH2(N3){PPh(OEt)2}4]ϩ
Ϫ10.37 (qnt)
Ϫ10.33 (qnt)
Ϫ10.30 (qnt)
22
21
22
2
2
2
1.01 0.02
1.00 0.02
1.01 0.02
Ϫ15.6 (br)
Ϫ14.8 (br)
233 20
Ϫ9.2 (br)
Ϫ10.8 (br)
Ϫ9.7 (br)
28
9
9
3
1
1
1.05 0.02
0.87 0.02
0.87 0.02
449 40
[OsH(η2-H2){PPh(OEt)2}4]ϩ b
[OsH(η2-H2)(PPh2OEt)4]ϩ b
[RuH(η2-H2){PPh2(OEt)2}4]ϩ
209
215
200
Ϫ7.0 (br)
Ϫ4.7 (br)
Ϫ3.8 (br)
32
10
4
3
1
0.5
1.07 0.02
0.89 0.02
0.76 0.02
a For calculations, see ref. 19. b See ref. 8(b).
topomers could not unambiguously determine the JHD values
for these compounds. However, T1(min.) values and compar-
isons with values obtained for the MHXP4 precursors support
the non-classical nature of these [MX(η2-H2)P4]ϩ species. It
1
may be noted that the H NMR spectra of osmium complexes
[OsX(η2-H2){P(OEt)3}4]ϩ 7 containing P(OEt)3 ligands do not
show any signal between ϩ20 and Ϫ80 ЊC, easily attributable to
η2-H2 resonance. This absence may be due to the loss of H2,
with formation of an unsaturated complex [MXP4]ϩ, but treat-
ment of 7 with NEt3 gave the starting MHXP4 complexes,
thus confirming the presence of the η2-H2 ligand (Scheme 8). A
Scheme 8 M = Ru or Os; P = P(OEt)3, PPh(OEt)2 or PPh2OEt.
similar deprotonation reaction was observed for all the new
dihydrogen complexes. Therefore, the absence of the η2-H2 1H
NMR signal of 7 may be attributed to fluxionality of the
molecule, which even at Ϫ80 ЊC does not give a low-exchange
spectrum, or to a very short T1 value of the η2-H2 proton,
giving a very broadened signal difficult to observe.
Fig. 1 Proton NMR spectrum of [OsCl(η2-H2){PPh(OEt)2}4]BF4 6a
(in CD2Cl2 at 295 K).
In the temperature range between ϩ30 and Ϫ70 ЊC, the
31P-{1H} NMR spectra of all η2-H2 complexes 6–10 show sharp
singlets (Table 1), suggesting trans geometry III. In some cases,
however, the 31P-{1H} NMR spectra at temperatures below
Ϫ70 ЊC begin to broaden and resolve (about at Ϫ90 ЊC) into
multiplets which, for some compounds, are of A2B2, or A2BC
type. The magnetic inequivalence of the phosphine ligands
at very low temperatures may be explained, as proposed for
the related MHXP4 1–5 precursors, on the basis of restricted
rotation of the phosphite ligand around the M–P bond. How-
ever, the A2B2 spectra observed for [OsX(η2-H2){P(OEt)3}4]ϩ 7
may also be explained on the basis of a distorted trans octa-
hedral geometry of type IV and previously proposed for the
related hydride–dihydrogen [MH(η2-H2)P4]ϩ derivatives.8 In
every case, the A2B2-type 31P spectra observed for 7 do not seem
to be consistent with cis geometry, for which an AB2C or A2BC
spectrum is expected, but rather with trans which, at very low
temperatures, displays two-by-two equivalent phosphorus
nuclei (geometry IV).
Fig. 2 Plot of ln(T1) vs 1/K for [OsI(η2-H2){PPh(OEt)2}4]BF4 6c.
presence of a quintet for the signal of the η2-H2 ligand, which
also determines the JPH value of 12 Hz, is rather surprising,
because a broad signal is always observed for dihydrogen
complexes1–4 of the iron triad and a well resolved signal is
often associated with the classical hydride. However, variable-
temperature T1 measurements (Fig. 2) gave T1(min.) values
of 9–28 ms (Table 2), consistent with the non-classical nature
of the H2 ligand.18 Hydride precursors MHXP4 1b and 3b
give T1(min.) values of 191 and 161 ms, respectively. We also
attempted to support the attribution further by determining the
JHD values of isotopomers [MX(η2-HD)P4]ϩ, prepared either by
treating MHXP4 with CF3CO2D or [MX(η2-H2)P4]ϩ in solution
with gaseous HD. Unfortunately, the proton spectra of the iso-
Both azido derivatives [MH2(N3)P4]ϩ 6e and 9e are thermally
unstable and could not be obtained in the solid state owing to
J. Chem. Soc., Dalton Trans., 2000, 3575–3584
3581

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their decomposition above 0 ЊC. However, NMR data in solu-
tion support their formulation and suggest, in contrast with
related complexes 6–9, the presence of a classical dihydride with
the central metal in the formal oxidation state of ϩ4 [MIV]. The
1H NMR spectra, in the hydride region, do show a broad signal
at δ Ϫ15.6 for osmium 6e and at δ Ϫ14.8 for ruthenium 9e,
the T1 measurements of which, at variable temperatures, give
T1(min.) of 232 (6e) and 449 ms (9e), consistent18 with the
classical nature of H2 ligands. The protonation reaction of the
azido derivative MH(N3)P4 thus proceeds through oxidative
addition of Hϩ, giving a dihydride species [MH2(N3)P4]ϩ of MIV.
For further structural information in solution of these seven-
co-ordinate complexes [MH2(N3)P4]ϩ 6e and 9e, we recorded
31P-{1H} NMR spectra in the temperature range between ϩ30
and Ϫ90 ЊC. Unfortunately, the spectra appear as broad signals
which do not resolve, even at Ϫ100 ЊC.
The results obtained on the protonation reaction of MHXP4
complexes indicate the influence that ligand X has, not only on
the reaction course, but also on the H–H distance and stability
to the loss of H2 from [MX(η2-H2)P4]ϩ derivatives. First of all,
protonation gives an η2-H2 complex for all the halogenide ClϪ,
BrϪ and IϪ and thiol SEtϪ species, whereas a classical dihydride
[MH2(N3)P4]ϩ was obtained only in the case of the azide
derivative. Instead, stability to the loss of H2 in the dihydrogen
complexes does not depend on the nature of ligand X, but on
the central metal and the nature of the phosphite ligands, as
only osmium complexes 6 containing the PPh(OEt)2 ligand are
stable and capable of being isolated. Furthermore, all the η2-H2
complexes are stable in solution in an H2 atmosphere, but give
hydride–dihydrogen [MH(η2-H2)P4]ϩ derivatives even in the
presence of small amounts of Brønsted acids.
Scheme 9 M = Os 11, 13, 14, 16 or Ru 12, 15, 17; X = BrϪ;
P = PPh(OEt)2 or P(OEt)3; R = RЈ = Ph; R = Me, RЈ = Ph.
complexes23 can be isolated. In the case of osmium, we were not
able to separate any vinylidene species, probably owing to the
existence of equilibrium of the type shown in Scheme 10.
T1 measurements allow H–H distances to be calculated,19 and
values are listed in Table 2. Although these values can be con-
sidered as an estimate of the H–H distance, a comparison
among similar compounds such as our [MX(η2-H2)P4]ϩ cations
can reasonably be made. This shows that the H–H distances are
not influenced by the nature of the halogenide ligand and that,
in the case of osmium bound to PPh(OEt)2 ligand, the same
value of 1.01 Å (fast rotation) was found for both halogenide
and thiol derivatives. A longer distance of 1.07 Å was calculated
for the related hydride [OsH(η2-H2){PPh(OEt)2}4]ϩ, indicating
that the effect of trans halogenide or thiol ligands is to shorten
the H–H bonds relative to hydride trans ligands. These results
contrast those of the related ruthenium complexes [RuX(η2-
H2){PPh(OEt)2}4]ϩ 9, which have a longer H–H distance (0.87
Å) than the hydride–hydrogen [RuH(η2-H2){PPh(OEt)2}4]ϩ
derivatives (0.76 Å). In our ruthenium complexes, therefore, the
effect of trans halogenide ligands is to lengthen the H–H bond
relative to trans hydride ligands, in agreement with similar
results5a obtained on other η2-H2 ruthenium complexes
of the type [RuCl(η2-H2)(dppe)]ϩ [dppe = 1,2-bis(diphenyl-
phosphino)ethane]. However, this lengthening does not seem
to be a general trend in η2-H2 complexes, but only concerns
ruthenium complexes. In related osmium derivatives [OsX(η2-
H2)P4]ϩ the opposite trend was observed, which may suggest
that it is the nature of the central metal which determines the
influence of the trans ligand X in η2-H2 complexes, although
only a few complexes have been studied so far.
Scheme 10 M = Ru or Os.
In every case, the addition of an excess of NEt3 to the pink
᎐
solution gives acetylides MX(C᎐CPh)P 11 and 12, which were
᎐
4
isolated in high yield and characterised. This reaction and the
separation of [RuX{᎐C᎐C(H)Ph}P ]BPh strongly suggest, for
᎐ ᎐
4
4
osmium too, the formation of a vinylidene intermediate [A],
which is probably rather unstable towards dissociation of the
᎐ ᎐
᎐C᎐C(H)Ph ligand,24 thus preventing separation of vinylidene
derivatives.
Treatment of [MX(η2-H2)P4]ϩ with propargylic alcohol gives
a dark red solution from which propadienylidene complexes
[MX(᎐C᎐C᎐CRRЈ)P ]BPh 13–15 were isolated in high yield
᎐ ᎐ ᎐
4
4
and characterised. The reaction probably proceeds with evolu-
᎐
tion of H2 and tautomerisation of the alkyne HC᎐CC(R)-
᎐
(RЈ)OH on the metal centre to give a vinylidene intermediate
[MX{᎐C᎐C(H)C(R)(RЈ)OH}P ]ϩ which, by spontaneous loss
᎐ ᎐
4
of H2O, gives the final propadienylidene20 derivative (Scheme
11). Propadienylidene complexes of ruthenium and osmium are
Reactivity
Some reactivity studies of new η2-H2 complexes 6–10 are sum-
marised in Scheme 9. The η2-H2 ligand is rather labile in all
complexes and may easily be substituted by several ligands,
affording new derivatives. However, we focused attention on
particular molecules such as alkynes and hydrazine, which
require the use of appropriate precursors for synthesis of their
related complexes.20–22 Thus, the reaction with an excess of
phenylacetylene gives a pink solution from which, in the case
Scheme 11 M = Os 13, 14 or Ru 15; P = PPh(OEt)2; R = RЈ = Ph 13,
15 or R = Ph, RЈ = Me 14.
of ruthenium, known vinylidene [RuX{᎐C᎐C(H)Ph}P ]BPh
᎐ ᎐
4
4
3582
J. Chem. Soc., Dalton Trans., 2000, 3575–3584

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Table 3 13C-{1H} NMR data of some osmium and ruthenium
complexes
Compound
δ (J/Hz)a
Assignment
11b
122.3 (s, br)
107.9 (dm)
64.7 (m)
Cβ
Cα
CH2
CH3
Cα
Cβ
Cγ
cmϪ1 and δ(NH) at 1595 cmϪ1. However, further support for the
presence of the hydrazine ligand comes from the 1H NMR spec-
tra, which show the NH2 signals as two broad multiplets at
δ 4.48–4.41 and 3.25–2.93, respectively, consistent with the pro-
posed formulation. Furthermore, some structural information
can be detected from the 31P-{1H} NMR spectra of 16 and 17
which show the presence of a complicated multiplet in both
cases. These patterns may be simulated using an A2BC model in
case 16b, and an ABC2 model in 17b, suggesting a mutually cis
position of the NH2NH2 and BrϪ ligands, as in geometry X. We
16.7 (m)
13b
302.6 (dm)
201.4 (dm)
167.2 (s)
66.6 (t)
65.2 (d)
63.4 (t)
63.1 (d)
CH2
16.0 (m)
CH3
Cα
Cβ
14b
15b
301.1 (m)
197.2 (m)
168.7 (s)
66.4–63.1 (m)
16.2 (m)
309.9 (qnt)
JCP = 17
199.9 (qnt, br)
166.5 (s)
Cγ
CH2
CH3
Cα
Cβ
Cγ
63.9 (br)
16.3 (s, br)
CH2
CH3
studied the reactivity of the hydrazine complexes towards oxid-
ation with Pb(OAc)4 at low temperature, and preliminary
a In CD2Cl2 at 25 ЊC. Phenyl carbon resonances are omitted.
results indicate the formation of the 1,2-diazene [MBr(NH᎐
᎐
NH)P4]ϩ derivative. However, the reaction needs further
investigation and will be the subject of a forthcoming paper.
reported to contain mainly cyclopentadienyl or arene rings
as well as bidentate phosphines as ancillary ligands.20 The use
of [MX(η2-H2)P4]ϩ as a precursor allows the preparation of
the first propadienylidene derivatives stabilised by phosphite
coligands. Hydrazine NH2NH2 also substitutes the H2 ligand in
[MX(η2-H2)P4]ϩ, giving the related [MX(NH2NH2)P4]BPh4
derivatives 16, 17.
All the new complexes 11–17 are air-stable solids and sol-
uble in polar organic solvents. Propadienylidene 13–15 and
hydrazine 16, 17 derivatives behave as 1:1 electrolytes.17 Their
analytical and spectroscopic data (Tables 1 and 3) support the
proposed formulation.
Acknowledgements
The financial support of the Ministero della Ricerca Scientifica
e Tecnologica, Rome, Programmi di Ricerca Scientifica di
Rilevante Interesse Nazionale, Cofinanziamento 1998/99, is
gratefully acknowledged. We thank Daniela Baldan for
technical assistance.
References
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J. Chem. Soc., Dalton Trans., 2000, 3575–3584
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