Synthesis and unexpected reactivity of [Ru(η 6-cymene)Cl2(PPh2Cl)], leading to [Ru(η 6-cymene)Cl2(PPh2H)] and [Ru(η 6-cymene)Cl 2 (PPh2OH)] complexes

Article abstract of DOI:10.1007/s12039-015-0905-z

The reaction of [Ru(η ⁶-cymene)Cl₂]₂ and PPh₂Cl in the ratio 1:2 gives a stable [Ru(η ⁶-cymene) Cl₂(PPh₂Cl)] complex. Attempts to make the cationic [Ru(η ⁶-cymene)Cl(PPh₂Cl)₂]Cl with excess PPh₂Cl and higher temperatures led to adventitious hydrolysis and formation of [Ru(η ⁶-cymene)Cl₂(PPh₂OH)]. Attempts to make a phosphinite complex by reacting [Ru(η ⁶-cymene)Cl₂]₂ with PPh₂Cl in the presence of an alcohol results in the reduction of PPh₂Cl to give [Ru(η ⁶-cymene)Cl₂(PPh₂H)] and the expected phosphinite. The yield of the hydride complex is highest when the alcohol is 1-phenyl-ethane-1,2-diol. All three half-sandwich complexes are characterized by X-ray crystallography. Surprisingly, the conversion of chlorodiphenylphosphine to diphenylphosphine is mediated by 1-phenyl-ethane-1,2-diol even in the absence of the ruthenium half-sandwich precursor. [Figure not available: see fulltext.]

Full text of DOI:10.1007/s12039-015-0905-z

c
J. Chem. Sci. Vol. 127, No. 8, August 2015, pp. 1329–1338. ꢀ Indian Academy of Sciences.
DOI 10.1007/s12039-015-0905-z
Synthesis and unexpected reactivity of [Ru(η6-cymene)Cl2(PPh2Cl)],
leading to [Ru(η6-cymene)Cl2(PPh2H)] and
[Ru(η6-cymene)Cl2(PPh2OH)] complexes
ARUN KUMAR PANDIAKUMAR and ASHOKA G SAMUELSON∗
Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012, India
e-mail: ashoka@ipc.iisc.ernet.in
MS received 4 April 2015; revised 22 May 2015; accepted 30 May 2015
Abstract. The reaction of [Ru(η6-cymene)Cl2]2 and PPh2Cl in the ratio 1:2 gives a stable [Ru(η6-cymene)
Cl2(PPh2Cl)] complex. Attempts to make the cationic [Ru(η6-cymene)Cl(PPh2Cl)2]Cl with excess PPh2Cl and
higher temperatures led to adventitious hydrolysis and formation of [Ru(η6-cymene)Cl2(PPh2OH)]. Attempts
to make a phosphinite complex by reacting [Ru(η6-cymene)Cl2]2 with PPh2Cl in the presence of an alcohol
results in the reduction of PPh2Cl to give [Ru(η6-cymene)Cl2(PPh2H)] and the expected phosphinite. The yield
of the hydride complex is highest when the alcohol is 1-phenyl-ethane-1,2-diol. All three half-sandwich com-
plexes are characterized by X-ray crystallography. Surprisingly, the conversion of chlorodiphenylphosphine to
diphenylphosphine is mediated by 1-phenyl-ethane-1,2-diol even in the absence of the ruthenium half-sandwich
precursor.
Keywords. 1-Phenylethane-1,2-diol; chlorodiphenylphosphine; diphenylphosphine; diphenylphosphinous
acid; half sandwich ruthenium complexes.
1. Introduction
for ring opening metathesis polymerization (ROMP)
reactions [Ir(OCH3)(COD)(PPh2Cl)], where COD is the
labile cyclo-octadiene, is obtained from a reaction of
the dimer [Ir(COD)(OCH3)]2 with PPh2Cl.16 However,
these complexes are not very stable and undergo hydro-
lysis of the P-Cl bond or decomposition due to weak
M-P bonds. Thus, the iron-PPh2Cl complex mentioned
above underwent hydrolysis in acetone to give a binuclear
hydrogen bridged species [{Fe(C5H5)(CO)2PPh2PO}2H]
which behaves as an acid of moderate strength.15 Simi-
larly, the anticancer activity of [Pd(dipropyldithiocarba-
mate)(PPh2Cl)Cl]islowerthanexpectedduetothe weak
Pd-P bond. Badshah and co-workers argue that it is
likely to undergo decomposition before carrying out
their expected function inside the cell.17 Interestingly,
PPh2H complexes exhibit a number of reactions.18 Coor-
dinated P-H can react with an M-Cl bond and form a
PPh2Cl complex.19 Such facile substitution reactions
observed in the chemistry of PPh2X ligands, where X is
H or a group more electronegative than C, has deterred
studies with PPh2X ligands.
Transition metal complexes containing organophospho-
rus ligands are ubiquitous.1,2 The primary attraction
in using phosphorus donors is the wide range of electro-
nic and steric effects they exert.3–5 Alkyl, aryl, alkoxy or
aryloxy groups have been extensively used to tune the
property of metal complexes formed by P(III) ligands.6–8
However, P(III) ligands with hydrogen, halogen or the
hydroxy group are less exploited for making metal com-
plexes. In the case of hydroxy groups, the situation is
quite complicated as the free ligand, PR2(OH), is quite
unstable and rearranges to (O)PR2H and the ligand has
to be generated in the coordination sphere of the metal.9,10
Metal complexes of chlorodiphenylphosphine PPh2Cl
and diphenylphosphine PPh2H, on the other hand, are
readily synthesized by reacting the free ligand with an
appropriate metal precursor.11–14 However, these com-
plexes are quite unstable due to the reactivity of P-Cl
and P-H bonds as explained in the following paragraph
with some representative examples.
The reaction of [Fe(C5H5)(CO)2THF]BF4 and PPh2Cl
gives the iron-phosphine complex [Fe(C5H5)(CO)2
(PPh2Cl)]BF4.15 Similarly an iridium catalyst suitable
Several studies have exploited the reactivity of the
coordinated PPh2X to generate a desired complex. A
series of palladium and platinum bisphosphinite com-
plexes were generated in situ using [M(PPh2Cl)2Cl2]
M = Pd or Pt. On reaction with chiral diols, they form
very useful chiral catalysts.20,21 In 2005, Bergamini and
∗For correspondence
1329

1330
Arun Kumar Pandiakumar and Ashoka G Samuelson
co-workers described the synthesis of a thiophosphinite- ploying a Bruker SMART APEX CCD diffractometer
aminophosphane complex from a reaction of the com- equipped with a MoKα X-ray source (50 KV, 40 mA).
plex [M(PPh2Cl)2Cl2] with the hydrochloride salt of the Data acquisition was carried out using SMART soft-
cysteine methyl ester in the presence of triethyl amine.22 ware and data reduction was carried out using SAINT
Another interesting example is the reaction of (μ-S)2 software.32 The empirical absorption corrections were
Fe2(CO)6, where the sulfido ligand in the coordination carried out using the SADABS program.33 The structure
sphere of the metal reacts with the incoming PPh2Cl was solved and refined using the SHELXL-97 pro-
to give an iron complex with the molecular formula gram.34 Hydrogen atoms were fixed in idealized posi-
(η1PPh2PSη1)2Fe2(CO)6 capableofcatalyzingthereduc- tions and refined in a riding model.
tion of a proton to dihydrogen.23 Thus, the study of com-
plexes formed by PPh2X can be a rewarding exercise.
Amongcomplexescontainingphosphorus(III)ligands,
half-sandwich ruthenium complexes are of special
interest due to their versatility.24 They are valuable in
catalysis,25–28 have marked anticancer activity29 and
their non-linear optical properties are tunable.30,31 In
this paper we report the synthesis, structure and reac-
tivity of [Ru(η6-cymene)Cl2(PPh2Cl)], [Ru(η6-cymene)
Cl2(PPh2H)] and [Ru(η6-cymene)Cl2(PPh2OH)]. Inter-
estingly it is observed that the 1-phenylethane-1,2-diol
mediates the transformation of PPh2Cl to PPh2H even
in the absence of the half-sandwich precursor although
in poorer yields. The source of hydrogen is not unam-
biguously identified due to the exchangeable nature of
the P-H bond.
2.3 Preparation of 1-phenylethane-1,2-diol
To a suspension of lithium aluminium hydride (0.745 g,
19.71 mmol) in diethyl ether (20 mL) kept in an ice bath
was added a solution of mandelic acid (0.5 g, 3.284
mmol) in dry diethyl ether (20 mL) over a period of 10
minutes. Once the addition was complete, the reaction
mixture was refluxed for 3 h and cooled in an ice bath.
Dilute HCl was added carefully to the stirred solution till
the pH was between4 and 5. Theresulting suspension was
passedthroughacelitepadandwashedwithdiethylether
(50 mL). The diethyl ether solution was dried over anhy-
drous sodium sulphate and concentrated to give the
solid product. Recrystallization from toluene-hexane
(1:2) gave colorless crystals. Yield: 72%. 1H NMR (400
MHz, CDCl3): δ 7.28-7.38 (m, 5H, Harom), 4.81 (t, 1H,
J = 4 Hz, CHOH), 3.63-3.75 (m, 2H, CH2OH), 2.94
(s, 1H, CHOH), 2.52(s, 1H, CH2OH). 13C NMR (100
MHz, CDCl3): δ 140.9, 129.0, 128.5, 126.6, 75.2, 68.5.
2. Experimental
2.1 Materials and methods
2.4 Preparation of [Ru(η6-cymene)Cl2(PPh2Cl)] (2)
All reactions and manipulations were routinely perform-
ed under nitrogen atmosphere using standard Schlenk
techniquesinoven-driedglassware.Tetrahydrofuranand
diethyl ether were distilled over sodium/benzophenone.
Triethylamine was distilled over KOH followed by
LiAlH4. Diphenylphosphine chloride was purified by
distillation under nitrogen atmosphere. Nuclear magnetic
resonance spectra were recorded on a Bruker AMX 400
To a solution of [Ru(η6-cymene)Cl2]2 1 (0.1 g, 0.163
mmol) in THF (5 mL) was added a solution of PPh2Cl
(0.12 mL, 0.652 mmol) in THF(1 mL) resulting in a
blood red colored solution which was allowed to stir for
7 h at room temperature. The reaction mixture was then
concentrated to 1/3 of the original volume and dry ether
(10 mL) was added. It was stirred for two hours to give
a dark red precipitate was obtained which upon recrys-
tallization from chloroform-hexane mixture gave dark
red crystals. Yield: 82%. 1H NMR (400 MHz, CDCl3):
δ 7.92 (m, 4H), 7.39 (m, 6H), 5.36 (d, J = 6.4 Hz, 2H,
Hcym), 5.32 (d, J = 6.4 Hz, 2H, Hcym), 2.88 (sept,
1H, CHMe2), 1.99 (s, 3H, CH3), 1.18 (d, 3H, J = 6.8
Hz, CH(CH3)2). 31P{1H}NMR (162.02 MHz, CDCl3):
δ 95.9 (s). Anal.Calcd for C22H24Cl3PRu: C 50.1927; H
4.5987. Found: C 50.6434; H 4.6817.
1
spectrometer operating at 400 MHz for H, 100 MHz
for 13C, 162.02 MHz for 31P (CDCl3 as solvent). Chem-
ical shifts for 1H NMR spectra are reported in parts per
million (ppm) downfield from SiMe4(δ 0.0) and relative
to the signal of chloroform-d (δ 7.26, singlet). Phos-
phorus nuclear magnetic resonance spectra (31P NMR)
are reported in δ units, parts per million (ppm) relative
to external H3PO4(δ 0.0).
2.2 X-ray Structure Determination of 2, 4 and 5
2.5 Preparation of [Ru(η6-cymene)Cl2(PPh2OH)] (4)
Crystals of complexes 2, 4 and 5 suitable for X-ray dif-
fraction study were carefully chosen and mounted on
the Goniometer head. The unit cell parameters and [Ru(η6-cymene)Cl2]2 (0.1 g, 0.163 mmol) was dis-
intensity data were collected at room temperature em- solved in THF (5 mL) followed by addition of PPh2Cl

Unusual reactivity of the [Ru(η6-cymene)Cl2(PPh2Cl)] half-sandwich complex
1331
(0.12 mL, 0.652 mmol) solution in THF (1 mL) that a 1.99 (s, 3H, CH3), 0.97 (d, 6H, J = 8.0 Hz, CH(CH3)2).
gave a blood red colored solution which was refluxed 31P{1H}NMR (162.02 MHz, CDCl3): δ 21.1 (s) and
for 10 h. The reaction mixture was then concentrated to [Ru(η6-cymene)Cl2(PPh2OCH(CH3)2)] (72%) 1H NMR
1/3 of the original volume and dry ether (10 mL) was (400 MHz, CDCl3): δ 7.91 (m, 4H), 7.46 ( m, 6H ), 5.22
added and stirred for two hours. A dark red precipitate (d, J = 6.12 Hz, 2H), 5.11 (d, J = 5.3 Hz, 2H), 4.58
obtained was filtered and dried in air. It was recrystal- (sept, 1H, OCH(CH3)2), 2.69 (sept, 1H, CHMe2), 1.84
lized from chloroform-hexane mixture to give dark red (s, 3H), 1.10 (dd, J = 7.0, 6.2 Hz, 12H, OCH(CH3)2,
1
crystals. Yield: 85%. H NMR (400 MHz, CDCl3): δ -CH(CH3)2 ). 31P{1H}NMR (162.02 MHz, CDCl3): δ
7.69-7.72(m, 4H), 7.44-7.49(m, 6H), 5.38(d, J = 5.2 Hz, 107.9 (s).
2H, Hcym), 5.24 (d, J = 6.0 Hz, 2H, Hcym), 2.50 (sept,
1H, CHMe2), 2.0 (s, 3H, CH3), 0.98 (d, J = 6.8 Hz,
3H, CH(CH3)2). 31P {1H}NMR (162.02 MHz, CDCl3):
δ 107 (s) Anal.Calcd for C22H25Cl2OPRu: C 51.9679;
H 4.9597. Found: C 51.5800; H 5.0516.
3. Results and Discussion
3.1 Synthesis and characterization of
[Ru(η6-cymene)Cl2(PPh2Cl)]
2.6 Preparation of [Ru(η6-cymene)Cl2(PPh2H)] (5)
Reacting the dinuclear [Ru(η6-cymene)Cl2]2 1 with
PPh2Cl in THF at room temperature led to the for-
mation of complex 2 in nearly quantitative yields as
shown in scheme 1. Formation of the half sandwich
complex [Ru(η6-cymene)Cl2(PPh2Cl)] 2 was inferred
To a solution of [Ru(η6-cymene)Cl2]2 1 (0.1 g, 0.163
mmol) in THF (5 mL) was added a solution of PPh2Cl
(0.12mL, 0.652mmol)inTHF(1mL)resultinginablood
red coloration, a THF solution of 1-Phenylethane-1,2-
diol (0.045g, 0.326mmol) was added to this solution and
stirred for 7 h. The reaction mixture was concentrated
to 1/3 of the original volume and dry ether (10 mL) was
added and stirred for two hours. A red precipitate was
obtained that gave deep red crystals upon recrystalliza-
1
from the H and 31P NMR spectra. The proton decou-
pled 31P NMR spectrum exhibited a singlet at 95.9 ppm
consistent with a coordinated PPh2Cl. After work up
and crystallization from a mixture of chloroform and
hexane, the product was obtained as dark red crystals
and was characterized further by single crystal X-ray
crystallography.
1
tion from chloroform/hexane. Yield: 93%. H NMR
(400 MHz, CDCl3): δ 7.40-7.75 (m, 10H, Ph), 6.44 (d,
1H, JP−H = 416 Hz, PPh2H), 5.40 (q, 4H, J = 4.0 Hz,
Hcym), 2.56 (sept, 1H, CHMe2), 1.99 (s, 3H, CH3),
0.97 (d, 6H, J = 8.0 Hz, CH(CH3)2)31P{1H}NMR
(162.02 MHz, CDCl3): δ 21.1 (s). 31P NMR (162.02
MHz, CDCl3): δ 21.2 (doublet of quintet, JP−H = 414
Hz, 3JP−Harom = 10.4 Hz) Anal.Calcd for C22H25Cl2PRu:
C 53.6573, H 5.1209. Found C 53.1555, H 5.0060.
3.2 Attempted synthesis of of [Ru(η6-cymene)Cl
(PPh2Cl)2]Cl and formation of
[Ru(η6-cymene)Cl2(PPh2OH)]
An attempt was made to generate the complex [Ru(η6-
cymene)Cl(PPh2Cl)2]Cl a proposed intermediate as
shown in scheme 2, en-route to the ruthenium bispho-
sphinite complex 3. Since a room temperature reaction
of [Ru(η6-cymene)Cl2]2 1 and PPh2Cl in the appropri-
ate ratio only resulted in the formation of 2, the reaction
mixture was refluxed for 10 h to force the formation of
2.7 Reaction of [Ru(η6-cymene)Cl2]2 with PPh2 Cl
and isopropyl alcohol
To a solution of [Ru(η6-cymene)Cl2]2 (0.1 g, 0.163
mmol) in THF (5 mL) was added a solution of PPh2Cl
(0.06 mL, 0.326 mmol) in THF (1 mL) resulting in the
characteristic red color, a THF solution of isopropyl
alcohol (0.024 mL, 0.326 mmol) was added to this solu-
tion and stirred for 7 h. The reaction mixture was concen-
trated to 1/3 of the original volume and dry ether (10
mL) was added and stirred for a further period of two
hours. The red precipitate obtained was filtered and
1
[Ru(η6-cymene)Cl(PPh2Cl)2]Cl. In the H NMR spec-
trum of the product isolated from this reaction mixture,
the ratio of the cymene isopropyl -CH(CH3)2 proton
at 2.50 ppm, to the aromatic protons from the phenyl
1
dried in air. H NMR spectrum recorded in CDCl3
showed the presence of two complexes. [Ru(η6-cymene)
Cl2(PPh2H)] (28%) 1H NMR (400 MHz, CDCl3): 7.40-
7.75 (m, 10H, Ph), 6.44 (d, 1H, JP−H = 416 Hz, PPh2H),
5.40 (q, 4H, J = 4.0 Hz, Hcym), 2.56 (sept, 1H, CHMe2),
Scheme 1. [Ru(η6-cymene)Cl2(PPh2Cl)] 2 using [Ru(η6-
cymene)Cl2]2 and chlorodiphenylphosphine.

1332
Arun Kumar Pandiakumar and Ashoka G Samuelson
Scheme 2. Proposed pathway for the synthesis of ruthenium bisphosphinite complex 3 using
PPh2Cl and 1-phenylethane1,2-diol.
Scheme 4. Formation of [Ru(η6-cymene)Cl2(PPh2H)] 5
employing 1-phenylethane1,2-diol and PPh2Cl.
Scheme 3. Formation of [Ru(η6-cymene)Cl2(PPh2OH)] 4
in the reaction of 1 and PPh2Cl.
group at 7.46-7.74 ppm remained 1:10 suggesting that
the expected complex was not formed. The H decou-
was inferred from spectroscopic studies and later con-
firmed by X-ray crystallography.
1
pled 31P NMR spectrum with a singlet at 107.2 ppm
suggested that the phosphorus atom was now attached
to an oxygen atom. A tentative assignment of structure
4, (scheme 3) to the complex due to hydrolysis of the
P-Cl bond in the starting material by the adventitious
moisture present to form [Ru(η6-cymene)Cl2PPh2OH],
was confirmed by the X-ray crystal structure analysis
(vide infra). This also suggested that the formation of
[Ru(η6-cymene)Cl(PPh2Cl)2]Cl was unfavourable com-
pared to hydrolysis.
In the 1H NMR spectrum of [Ru(η6-cymene)Cl2(PPh2
H)] 5, the proton attached to the phosphorus atom
appeared as a doublet at 6.44 ppm due to coupling with
the phosphorus atom. The 1JP−H value was found to be
412 Hz. The proton coupled 31P NMR spectrum showed
the phosphorus atom attached to the proton appeared
as a doublet of a quintet at 21.2 ppm with a coupling
constant of 413 Hz. This suggested that the phospho-
rus atom and the proton are directly connected to each
other. Toconfirmthe1JP−H coupling between 31P and 1H,
2D heteronuclear single quantum coherence experiment
was carried out. It showed a correlation peak between
31P NMR at 21.2 ppm and the doublet at 6.44 ppm
3.3 Synthesis and characterization of [Ru(η6-cymene)
Cl2(PPh2H)]
1
in H NMR and confirmed the formation of [Ru(η6-
cymene)Cl2(PPh2H)] 4. Reactions in the absence of an
alcohol only led to hydrolysis clearly demonstrating
that 1-phenylethane-1,2-diol promotes the formation
of [Ru(η6-cymene)Cl2(PPh2H)] 4 by acting as a good
hydrogen donor.
Previous reports on the facile formation of palladium
and platinum bisphosphinite complexes employing
[M(COD)Cl2] M=Pd and Pt, chlorodiphenylphosphine
and chiral diols encouraged us to attempt an in situ
reaction.20,21 Attempts to prepare ruthenium bisphos-
phinite complex using chlorodiphenylphosphine and 1-
phenylethane-1,2-diol were made employing the dimer
[Ru(η6-cymene)Cl2]2 1 as a metal precursor as depicted
in scheme 2.
3.4 X-ray structural studies of 2, 4 and 5
Molecular structures of 2, 4 and 5 have been confirmed
The reaction was carried out at room temperature by X-ray crystallographic studies and their molecular
for 7 h in THF. After workup and crystallization from structures are depicted in figures 1, 2 and 3 respectively.
chloroform-hexane solutions, the formation of red crys- The crystallographic details, selected bond distances
tals was observed. It was analyzed in a similar way as and angles have been summarized in tables 1 and 2.
mentioned earlier for the isolation of complex 2. Instead The three complexes adopt the three-legged piano stool
of the expected product, the unusual formation of structure and are quite similar to one another. The ruthe-
[Ru(η6-cymene)Cl2(PPh2H)] 5 in 93% yield (scheme 4) nium center thus has a pseudo-octahedral geometry.

Unusual reactivity of the [Ru(η6-cymene)Cl2(PPh2Cl)] half-sandwich complex
1333
Figure 3. ORTEP view of [Ru(η6-cymene)Cl2(PPh2H)] 5
Figure 1. ORTEP view of [Ru(η6-cymene)Cl2(PPh2Cl)] 2 at the 50% probability level showing selected atom labeling.
at the 50% probability level showing selected atom labeling. Hydrogen atoms are omitted for clarity.
Hydrogen atoms are omitted for clarity.
multinuclear NMR spectroscopic techniques. In the 1H
NMR spectrum, apart from the presence of cymene iso-
propyl group protons, resonances for additional isopro-
pyl groups were observed from the isopropoxy moiety
attached to the phosphorus atom. In the 31P{1H}NMR
spectrum two peaks were observed. A peak at 21.8
ppm was assigned for the ruthenium-PPh2H complex
5, and a peak at 107.9 ppm was assigned to the com-
plex [Ru(η6-cymene)Cl2(PPh2OCH(CH3)2)] 6. So even
in the case of isopropanol, a good hydrogen donor,
a mixture of ruthenium-PPh2H 5, and a ruthenium
monophosphite complex 6 were observed in the ratio
28:72. The ratio of products was calculated from the
1H NMR spectrum as the separation and purification
of these products could not be carried out. Studies
with a variety of other alcohols showed that 1-phenyl-
Figure 2. ORTEP view of [Ru(η6-cymene)Cl2(PPh2OH)],
4 at the 50% probability level showing selected atom label-
ing. Hydrogen atoms are omitted for clarity.
ethane1,2-diol was indeed unique as it led to exclusive
formation of complex 5.
3.6 Reaction of 1-phenylethane-1,2-diol with PPh2 Cl
3.5 Reaction of [Ru(η6-cymene)Cl2]2 with PPh2 Cl and
It was evident that the diol promotes the reduction of
PPh2Cl to PPh2H. However it was not clear if the reac-
isopropanol
The formation of the ruthenium phosphine complex 5 tion was happening in the coordination sphere of the
was then attempted with isopropanol a well established Ru or if the free ligand could be reduced by the diol
hydrogen donor in transfer hydrogenation reactions35,36 resulting in PPh2H independant of ruthenium. To verify
to see if it can mediate the reduction of PPh2Cl to gen- this possibility, a stoichiometric reaction was carried
erate PPh2H more effectively than 1-phenylethane-1,2- out using 1-phenylethane-1,2-diol and PPh2Cl in THF
diol. The reaction was carried out with the ruthenium for 7 h at room temperature (scheme 6). After removal
cymene dimer 1, chlorodiphenylphosphine and isopro- of the solvent, THF, dry CDCl3 was added and 1H and
panol in THF at room temperature for 7 h (scheme 5).
31P NMR spectra recorded.
The reaction mixture was concentrated to one-third
In the proton decoupled 31P NMR spectrum, a peak
of its volume and dry diethyl ether was added to get a at –39.8 ppm was observed close to the reported value
red precipitate. It was filtered, dried and analyzed by of free diphenylphosphine (–37.12 ppm)42 in addition

1334
Arun Kumar Pandiakumar and Ashoka G Samuelson
Table 1. Crystal data and refinement details for 2, 4 and 5.
2
4
5
Formula
Formula weight
C22H24Cl3PRu
527.81
C22H25Cl2OPRu
507.35
C22H25Cl2PRu
492.36
Crystal system
Space group
Monoclinic
P21/C
Monoclinic
P21/C
Monoclinic
P21/C
T (K)
a, Å
b, Å
c, Å
α, deg
B
293(2)
293(2)
293(2)
12.581(12)
10.599(10)
17.415(17)
90.00
106.073(16)
90.00
10.3643(10)
12.2350(12)
17.5312(17)
90.00
99.185(2)
90.00
10.4231(2)
11.7729(3)
17.5265(4)
90.00
97.0820(10)
90.00
ꢀ
V, Å
Z
2231(4)
4
1.571
2194.6(4)
4
1.536
2134.27(8)
4
d
calc, g cm−3
1.529
1.063
μ (mm−1
)
1.139
1.040
λ(Å)
0.71073
0.0957
0.1913
ꢀ
0.71073
0.0438
0.0861
ꢀ
0.71073
0.0274
0.0567
Ra
Rw
ꢀ
ꢀ
aR = (|Fo|-|Fc|)/ |Fo|, Rw = [ w(|Fo|-|Fc|)2/ w|Fo|2]1/2 (based on reflections
with I >2σ (I)).
Table 2. Selected bond distances (Å) and bond angles (◦) for complexes 2, 4 and 5.
2
4
5
Ru1-P1
Ru1-Cl1
Ru1-Cl2
P1-Cl3
2.311(3)
2.399(3)
2.406(3)
2.053(4)
Ru1-P1
Ru1-Cl1
Ru1-Cl2
P1-O1
2.3115(10) Ru1-P1
2.4144(10) Ru1-Cl1
2.4152(10) Ru1-Cl2
2.3226(5)
2.4124(6)
2.4214(6)
1.35(2)
1.601(3)
P1-H1
Cl2-Ru1-Cl1 87.56(2)
Cl2-Ru1-Cl1 89.62(12)
Cl2-Ru1-Cl1 87.32(4)
P1-Ru1-Cl1
P1-Ru1-Cl2
Cl3-P1-Ru1
87.33(11)
84.38(9)
110.36(16) O1-P1-Ru1
P1-Ru1-Cl1
P1-Ru1-Cl2
84.37(4)
82.94(4)
112.62(10) H1-P1-Ru1
P1-Ru1-Cl1
P1-Ru1-Cl2
82.800(19)
81.43(2)
110.6(8)
Scheme 5. Ruthenium-PPh2H 5 and monophosphite complex 6 with ruthenium cymene dimer 1, PPh2Cl and isopropanol.
to a number of other peaks (figure 4). A proton coupled 3.7 Arresting PPh2H exchange
31P NMR spectrum was recorded to verify P-H cou-
pling. Unexpectedly, no coupling of the phosphorus To verify if the exhange of H on the phosphorus atom
with the hydrogen atom could be detected. As the reac- with HCl could be slowed down, variable temperature
tion involves formation of HCl, it was suspected that the NMR studies were carried out. The proton coupled 31
P
metal free reaction results in the formation of PPh2H as NMR spectrum of the reaction mixture obtained by the
an adduct coordinated to HCl. As the H in PPh2H would stoichiometric reaction of PPh2Cl and 1-phenylethnae-
exchange rapidly with an external proton it would not 1,2-diol was recorded at different temperatures. At
exhibit 31P-1H coupling. Two experiments described –30◦C a peak at –39.8 ppm which was assigned for the
below suggested that this was indeed the case.
free diphenylphosphine started splitting and at –50◦C

Unusual reactivity of the [Ru(η6-cymene)Cl2(PPh2Cl)] half-sandwich complex
1335
and in the case of proton decoupled NMR spectrum a
singlet was observed (figure 6). This study clearly sug-
gests that the formation of free diphenylphopshine is
possible even in the absence of the ruthenium com-
plex. A subsequent reaction with 1 would result in the
formation of the ruthenium-PPh2H complex 5.
a clear doublet was observed at –40.8 ppm due to cou-
pling with the hydrogen atom. The observed coupling
constant is 222 Hz, close to the reported coupling
constant 218 Hz42 (figure 5).
To further ascertain the coupling with the hydrogen
atom, both proton coupled and proton decoupled 31P
NMR spectra were recorded at –50◦C. In the proton
coupled 31P NMR spectrum, a doublet was observed
1
If the loss in coupling between 31P and H was due
to exchange between the two hydrogen atoms (P-H and
H-Cl), addition of a base to remove HCl would also
regenerate the coupling. The 1H coupled 31P NMR spec-
trum of the reaction mixture obtained by the reaction
of PPh2Cl and 1-phenylethane-1,2-diol was recorded at
room temperature after adding a stoichiometric amount
of triethylamine (figure 7). The coupling between 31P
1
and H was observed at room temperature under these
Scheme 6. Stoichiometric reaction of PPh2Cl with 1-
phenylethane-1,2-diol.
conditions. This suggests that in the absence of Et3N,
Figure 4. Proton coupled 31PNMR spectrum obtained by the reaction 1-phenylethane-1,2-diol with PPh2Cl.
Figure 5. The proton coupled 31P NMR spectra of the reaction mixture
obtained by the reaction of 1-phenylethane-1,2-diol with PPh2Cl at different
temperatures.

1336
Arun Kumar Pandiakumar and Ashoka G Samuelson
PPh2H probably exists in equilibrium with the HCl
Finally, the uniqueness of 1-phenylethane-1,2-diol
adduct in solution leading to rapid exchange of the two in promoting the formation of the ruthenium-PPh2H
hydrogen atoms.
complex 5 was probed by carrying out this reaction
with a variety of alcohols and diols. It was found that
1-phenylethane-1,2-diol gave excellent yields of 5. Sur-
prisingly it was better than benzyl alcohol, hydroben-
zoin and isopropanol in effecting this reaction.
3.8 A Plausible mechanism for the formation of PPh2H
from PPh2Cl and 1-phenylethane-1,2-diol
Till date very few examples are there in the literature
where transfer hydrogenation has been carried out in
the absence of metals.37–41 A plausible path for the
formation of diphenylphosphine using 1-phenylethane-
1,2-diol is given in scheme 7. The mechanism involves
the coordination of 1-phenylethane-1,2-diol through
its oxygen atoms to P of PPh2Cl forming adduct 7.
Transfer of a hydride occurs to the phosphorus atom
to form a cyclic intermediate 9 which then decom-
poses to give free diphenylphosphine and 2-hydroxy-1-
Figure 6. 1H coupled (bottom) and decoupled (top) 31P
NMR spectra at –50◦C.
Figure 7. 1H coupled and 31P NMR spectrum before (bottom) and after (top) adding triethylamine.
Cl
Ph
Ph
H
H
Ph
H
O
OH
P
Ph
Ph
P
+ HCl
Ph
HO
7
HO
8
H
H
P
H
P
Ph
H
O
Ph
H
O
O
Ph
H
Ph
Ph
Ph
Ph
PPh2H +
H
HO
O
H
H
O
H
9
Scheme 7. Plausible pathway for the formation of PPh2H from 1-phenylethane-1,2-diol and PPh2Cl.

Unusual reactivity of the [Ru(η6-cymene)Cl2(PPh2Cl)] half-sandwich complex
1337
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The reaction of ruthenium-cymene dimer 1 with PPh2Cl
resulted in the formation of (2), a ruthenium-PPh2Cl
complex as expected. However, the expected transfor-
mation of this complex to a disubstituted analog was
not observed. Instead, hydrolysis of the P-Cl bond
occurred, leading to the formation of a ruthenium-
PPh2(OH) complex (4). Further, phosphinite complexes
are formed along with a reduced ruthenium-PPh2H (5)
complex when complex 1 was reacted with PPh2Cl and
alcohols. Surprisingly the reduction could be brought
about even in the absence of the metal. Maximum
reduction was observed when 1-phenylethane-1,2-diol
was used as the reducing agent. The ability of this
1,2-diol was significantly greater than the traditional
isopropanol or hydrobenzoin.
19. Jantscher F, Kirchner K and Mereiter K 2009 Acta Cryst.
E65 m941
Supplementary Information
20. Sharma R K, Nethaji M and Samuelson A G 2008
Tetrahedron: Asymmetry 19 655
21. Sharma R K and Samuelson A G 2007 Tetrahedron:
Asymmetry 18 2387
22. Bergamini P, Bertolasi V and Giordani R 2005 Inorg.
Chim. Acta 358 2031
CCDC 884833, 884834 and 880813 contain the supple-
mentary crystallographic data for [Ru(η6-cymene)
Cl2(PPh2Cl)] 2 [Ru(η6-cymene)Cl2(PPh2OH)] 4 and
[Ru(η6-cymene)Cl2(PPh2H)] 5, respectively. These data
can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif. NMR spectra of complexes (figures
S1-S15) are available at www.ias.ac.in/chemsci.
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and Hu Q -M 2008 Organometallics 27 3714
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J M, Miqueu K, Menendez-Rodriguez L, Crochet P,
Cadierno V and Igau A 2014 Organometallics 33 6294
26. Kumar P, Gupta R K and Pandey D S 2014 Chem. Soc.
Rev. 43 707
27. Aydemir M, Meric N, Baysal A, Turgut Y, Kayan C,
Seker S, Togrul M and Gümgüm B 2011 J. Organomet.
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28. Sheeba M M, Tamizh M M, Farrugia L J, Endo A and
Karvembu R 2014 Organometallics 33 540
29. Bugarcic T, Habtemariam A, Deeth R J, Fabbiani F P
A, Parsons S and Sadler P J 2009 Inorg. Chem. 48
9444
Acknowledgements
Financial support from the Department of Science
and Technology, New Delhi vide Project number,
SR/S5/MBD-02/2007, is gratefully acknowledged.
AKP acknowledges CSIR, New Delhi for a SRF
Fellowship.
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