Ruthenium piano-stool complexes bearing imidazole-based PN ligands

Article abstract of DOI:10.1016/j.jorganchem.2011.10.006

A variety of piano-stool complexes of cyclopentadienyl ruthenium(II) with imidazole-based PN ligands have been synthesized starting from the precursor complexes [CpRu(C₁₀H₈)]PF₆, [CpRu(NCMe) ₃]PF₆ and [CpRu(PPh₃)₂Cl]. PN ligands used are imidazol-2-yl, -4-yl and -5-yl phosphines. Depending on the ligand and precursor different types of coordination modes were observed; in the case of polyimidazolyl PN ligands these were κ¹P-monodentate, κ²P,N-, κ²N,N- and κ³N,N,N- chelating and μ-κP:κ²N,N-brigding. The solid-state structures of [CpRu(1a)₂Cl ]·H₂O (5 ^.H₂O) and [{CpRu(μ-κ²-N,N- κ'¹-P-2b)}₂](C₆H₅PO ₃H)₂(C₆H₅PO₃H ₂)_2, a hydrolysis product of the as well determined [{CpRu(2b)}₂](PF₆)₂^.2CH ₃CN (7b^.2CH₃CN) were determined (1a = imidazol-2-yldiphenyl phosphine, 2b = bis(1-methylimidazol-2-yl)phenyl phosphine, 3a = tris(imidazol-2-yl)phosphine). Furthermore, the complexes [CpRu(L)₂]PF₆ (L = imidazol-2-yl or imidazol-4-yl phosphine) have been screened for their catalytic activity in the hydration of 1-octyne.

Full text of DOI:10.1016/j.jorganchem.2011.10.006

Journal of Organometallic Chemistry 697 (2012) 33e40
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Ruthenium piano-stool complexes bearing imidazole-based PN ligands
,
a
,
,
,
,3
Peter C. Kunz a , Indre Thiel 1, Anna Louisa Noffke a 2, Guido J. Reiß a 3, Fabian Mohr b
,
*
Bernhard Spingler c
,
3
a Institut für Anorganische Chemie und Strukturchemie, Heinrich-Heine-Universität, Universitätsstr. 1, D-40225 Düsseldorf, Germany
b Bergische Universität Wuppertal, Fachbereich C - Anorganische Chemie, Gaußstr. 20, D-42119 Wuppertal, Germany
c Anorganisch-Chemisches Institut, Universität Zürich-Irchel, Winterthurerstr. 190, CH-8057 Zürich, Switzerland
a r t i c l e i n f o
a b s t r a c t
Article history:
A variety of piano-stool complexes of cyclopentadienyl ruthenium(II) with imidazole-based PN ligands
have been synthesized starting from the precursor complexes [CpRu(C10H8)]PF6, [CpRu(NCMe)3]PF6 and
[CpRu(PPh3)2Cl]. PN ligands used are imidazol-2-yl, -4-yl and -5-yl phosphines.
Received 14 June 2011
Received in revised form
28 September 2011
Accepted 5 October 2011
Depending on the ligand and precursor different types of coordination modes were observed; in
the case of polyimidazolyl PN ligands these were
chelating and P:
2N,N-brigding. The solid-state structures of [CpRu(1a)2Cl ]$H2O (5.H2O) and
[{CpRu(
2-N,N-k’1-P-2b)}2](C6H5PO3H)2(C6H5PO3H2)2, a hydrolysis product of the as well deter-
mined [{CpRu(2b)}2](PF6)2. 2CH3CN (7b.2CH3CN) were determined (1a
imidazol-2-yldiphenyl
k k k k
1P-monodentate, 2P,N-, 2N,N- and 3N,N,N-
m-k k
Keywords:
Ruthenium
PN ligands
Imidazole
Phosphine
m-k
¼
phosphine, 2b ¼ bis(1-methylimidazol-2-yl)phenyl phosphine, 3a ¼ tris(imidazol-2-yl)phosphine).
Furthermore, the complexes [CpRu(L)2]PF6 (L ¼ imidazol-2-yl or imidazol-4-yl phosphine) have been
screened for their catalytic activity in the hydration of 1-octyne.
Imidazolylphosphine
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
the selectivity of ruthenium(II) depends on the nature of the
phosphine ligands [19]. Using PPh2(C6F5) and P(3-C6H4SO3Na)3 as
The addition of water to alkynes is an important step in the
synthesis of carbonyl compounds and has a long history going back
as far as 1860, when Berthelot discovered the hydration of acety-
lene in sulfuric acid [1]. One of the longest known reactions to
catalyze the hydration of alkynes is the reaction with mercury(II)
salts [2e4]. Even though mercury is extremely hazardous, this
reaction is still the favoured process for industrial application
because it is reliable and produces good yields [5]. Other metal-
based catalysts which catalyze the Markovnikov as well as anti-
Markovnikov hydration include NaAuCl4, RuCl3 and [Ru(III)(EDTA-
H)Cl], RhCl3, PtCl4 and the Zeise dimer [{PtCl3(CH2 ¼ CH2)}2], just
to name a few [6e13]. Besides these homogenous catalysts also
heterogenous catalyst systems are used [14e16]
ligands leads to selective anti-Markovnikov addition of water and
satisfactory yields of the aldehyde. However, these catalytic
systems involve a high catalyst/metal loading and yield only
moderate turnovers and selectivity. Using cyclopentadienyl ruth-
enium(II) complexes with monodentate or bidentate phosphine
ligands provides an increased catalytic activity as well as selectivity
towards the anti-Markovnikov product, e.g. [CpRu(dppm)Cl]
(dppm
¼
bis(diphenylphosphino)methane) gives the anti-
Markovnikov product in excellent yield while tolerating a wide
spectrum of substrates [20].
Nature uses proteins as polyfunctional ligands, which show
multiple interactions between the enzyme and either substrate,
intermediate(s), or transition state(s) during the catalytic cycle [3].
For example, the tungsteno enzyme acetylene hydratase of Pelo-
bacter acetylenicus uses acetylene as the sole carbon source, which
is converted to acetaldehyde and then used by the enzyme to build
acetic acid and ethanol, important building blocks for the bacteria’s
metabolism [21e24]. While enzymes are impressive, their struc-
tures are complex, and due to their high level of specificity for
particular conversions, they are only of minor use for the devel-
opment of generally efficient catalysts.
The first ruthenium(II) complex to be known to catalyze the
anti-Markovnikov hydration was a phosphine complex described
by Tokunaga and Wakatsuki [17,18]. The catalytic activity as well as
* Corresponding author. Tel.: þ49 211 8112873; fax: þ49 211 8112287.
E-mail address: peter.kunz@uni-duesseldorf.de (P.C. Kunz).
1
Present address: Leibniz-Institut für Katalyse e.V. an der Universität Rostock,
Albert-Einstein-Str. 29a, D-18059 Rostock, Germany.
More recently, phosphine ligands containing heterocyclic
substituents such as pyridinyl or imidazolyl groups were investi-
gated in bifunctional catalysis [25e29]. By modification of the
2
Present address: Department of Chemistry, University of Warwick, Gibbet Hill
Road, Coventry CV4 7AL, UK.
3
X-ray structure analysis.
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.10.006

34
P.C. Kunz et al. / Journal of Organometallic Chemistry 697 (2012) 33e40
pyridine ring the reactivity and catalytic activity of the corre-
sponding complexes can be tuned [30]. Grotjahn suggested that the
nitrogen heterocycle acts as a bifunctional acid/base catalyst,
initiating the protonation of the alkyne and leading to the ruth-
enium(IV) vinylidene species [31].
In this report we investigated the hydration of terminal alkynes
catalyzed by CpRu(II) compounds containing different imidazolyl
phosphines as potentially bifunctional PN ligands. The imidazol-2-
yl and imidazol-4-yl phosphine ligands employed bear substituents
of varying steric demand. Also included were selected bis and tri-
s(imidazolyl)phosphine ligands.
solution, which turns yellow and is then stirred over night at room
temperature. The solvent is removed and the residue is dissolved in
with ammonia-saturated dichloromethane. This solution is stirred
over night and the white solid is filtered off. The solvent is removed
from the filtrate and the residue dissolved in acetone/water (10:1)
and 2 mL of conc. hydrochloric acid added. The mixture is refluxed
for 4 h, all volatiles removed in vacuo and the residue dissolved in
a minimum amount of ethanol and sodium hydroxide solution
added. The precipitate is filtered off, washed with diethyl ether and
dried in vacuo. Yield: 1.06 g (43%). 1H NMR (200 MHz, CDCl3):
d
¼ 1.34 (s, 9H, CH3), 6.91 Hz (s, Him), 7.25e7.35 (m, 10H, Ph), 10.80
(very broad, 1H, NH). 31P{1H} NMR (81 MHz, CDCl3):
d
¼ ꢀ31.0. ESIþ
2. Experimental section
(methanol): m/z (%) ¼ 309 [M þ H]þ (100), 249 [M-tBu]þ (95).
C19H21N2P$5/3H2O (308.36): calc. C 67.44, H, 7.23, N 8.27; found C
67.49, H 6.90, N 8.14.
2.1. Synthesis
Compounds 1a,b,d e 3a,b,d [32,33] and 1h [34] as well as
[CpRu(PPh3)2Cl] [35] and [CpRu(C10H8)]PF6 [36] were prepared
according to literature procedures. All reactions were carried out in
Schlenk tubes under an atmosphere of dry nitrogen using anhy-
drous solvents purified according to standard procedures. All
chemicals were purchased from commercial sources and used as
received. 1H and 31P NMR spectra were recorded on a Bruker DRX
200 spectrometer. The [1]H spectra were calibrated against the
residual proton signal of the solvent as an internal reference (CDCl3:
2.1.3. Synthesis of 2-phenylimidazole-4(5)-yldiphenylphosphine (4-
MIPPh, 1f)
1-Methoxymethyl-2-phenylimidazole (1.5 g, 8.0 mmol) is
placed in a Schlenk tube equipped with a magnetic stirring bar and
dissolved in dry thf (100 mL). At ꢀ78 ꢁC tert.-butyllithium (5.3 mL,
1.6 M in hexane) is added slowly to the solution, which turns deep
red. The reaction mixture is stirred at ꢀ78 ꢁC for 1 h until the
diphenylchlorophosphine (1.6 mL, 8.0 mmol) is slowly added to the
solution, which turns yellow and is then stirred over night at room
temperature. The solvent is removed and the residue is dissolved in
with ammonia-saturated dichloromethane. This solution is stirred
over night and the white solid is filtered off. The solvent is removed
from the filtrate and the residue (which is the protected phosphine,
dH
¼
7.30 ppm; methanol-d4: dH
¼
3.31 ppm; acetone-d6:
dH ¼ 2.05 ppm, acetonitrile-d3: dH ¼ 1.94 ppm) while the 31P{1H}
NMR spectra were referenced to external 85% H3PO4. The ESI mass
spectra were recorded on a Finnigan LCQ Deca ion trap API mass
spectrometer. The MALDI mass spectra were recorded on a Bruker
Ultraflex MALDI-TOF mass spectrometer. The FAB mass spectra
were recorded on a Finnigan MAT 8200 mass spectrometer using
a nitrobenzylic alcohol (NBA) matrix. Infrared spectra were recor-
ded with a Bruker IFS 66 FT-IR spectrometer. The elemental
composition of the compounds was determined with a Perkin
Elmer Analysator 2400 at the Institut für Pharmazeutische und
Medizinische Chemie, Heinrich-Heine Universität Düsseldorf.
1H NMR (200 MHz, CDCl3):
CH2), 6.86 Hz (s, Him), 7.33e7.85 (m, 15H, Ph). 31P{1H} NMR
(81 MHz, CDCl3):
d
¼ 3.23 (s, 3H, OCH3), 5.40 (d, J ¼ 1.5 Hz,
d
¼ ꢀ34.0) dissolved in acetone/water (10:1) and
2 mL of conc. Hydrochloric acid added. The mixture is refluxed for
4 h, all volatiles removed in vacuo and the residue dissolved in
a minimum amount of ethanol and sodium hydroxide solution
added. The precipitate is filtered off, washed with diethyl ether and
dried in vacuo. Yield: 1.39 g (53%). 1H NMR (200 MHz, CDCl3):
d
¼ 6.71 Hz (s, 1H, Him), 7.15e8.00 (m, 15H, Ph) 8.44 (s, 1H, Him),
2.1.1. Synthesis of 1-methyl-4,5-diphenylimidazole-2-yl-
15.17 (s, broad, 1H, NH). 31P{1H} NMR (81 MHz, CDCl3):
d
¼ ꢀ29.8.
diphenylphosphine (2-MIPdiPh-NMe, 1c)
ESI MS (methanol): m/z (rel. int.) ¼ 386 (100) [M þ NaCl]þ, 329 (15)
[M þ H]þ. C21H17N2P$C2H5OH (374.42): calc. C 73.78, H, 6.19, N 7.48;
found C 73.85, H 5.50, N 7.02.
1-Methyl-4,5-diphenylimidazole (2 g, 8 mmol) is placed in
a Schlenk tube equipped with a magnetic stirring bar and dissolved
in dry thf (100 mL). At ꢀ78 ꢁC n-butyllithium (5.3 mL, 1.6 M in
hexane) is added slowly to the solution, which turns deep red. The
reaction mixture is stirred at ꢀ78 ꢁC for 1 h until the diphenyl-
chlorophosphine (1.6 mL, 8.0 mmol) is slowly added to the solution,
which turns yellow and is then stirred over night at room
temperature. The solvent is removed and the residue is dissolved in
with ammonia-saturated dichloromethane. This solution is stirred
over night and the white solid is filtered off. The solvent is removed
from the filtrate yielding the product as a white-yellow solid, which
is dried under vacuum. Yield 2.00 g (60%). 1H NMR (200 MHz,
2.1.4. Synthesis of 1-methyl-2-isopropylimidazole-4-
yldiphenylphosphine (4-MIPiPr,NMe, 1i)
1-Methyl-4-iodo-2-isopropylimidazole (1 g, 4 mmol) is dis-
solved in dichloromethane. One equivalent of ethyl magnesium
bromide (3 M in ether) is slowly added to the solution at 0 ꢁC. The
clear solution is stirred for 30 min at room temperature before the
diphenylchlorophosphine (0.75 mL, 4.0 mmol) is added. The solu-
tion is stirred at room temperature over night. The solvent is
removed and the soft solid is redissolved in ammonia-saturated
dichloromethane and stirred over night. A white solid precipi-
tates which is filtered off. The solvent of the filtrate is removed,
yielding a white-yellow solid, which is then stirred in ethanol
under addition of 1 mL of hydrochloric acid. The solvent is removed
and the solid stirred in ammonia-saturated dichloromethane. The
precipitated white solid is removed by filtration and the solvent of
the filtrate is removed, resulting in a white powder, which is dried
under vacuum. Yield 0.71 g (58%). 1H NMR (200 MHz, methanol-
CDCl3):
d
¼ 3.57 (s, 3H, CH3), 7.15e7.74 (m, 20H, Ph). 31P{1H} NMR
(200 MHz, CDCl3):
d
¼ ꢀ28.74 (s); ESI (methanol): m/z ¼ 419
[MþþH], 341 [Mþ-Ph]; C28H23N2P$2/3CH2Cl2 (475.49): calc. C 72.5,
H 5.2, N 5.9; found C 72.6, H 5.3, N 5.5.
2.1.2. Synthesis of 2-tert-butylimidazole-4(5)-yl-
diphenylphosphine (4-MIPtBu, 1e)
1-Methoxymethyl-2-tert-butylimidazole (1.3 g, 8.0 mmol) is
placed in a Schlenk tube equipped with a magnetic stirring bar and
dissolved in dry thf (100 mL). At ꢀ78 ꢁC tert-butyllithium (5.3 mL,
1.6 M in hexane) is added slowly to the solution, which turns deep
red. The reaction mixture is stirred at ꢀ78 ꢁC for 1 h until the
diphenylchlorophosphine (1.6 mL, 8.0 mmol) is slowly added to the
d4):
1H, CH), 7.36e7.84 (m, 10H, Ph); 31P{1H} NMR (81 MHz, methanol-
d4):
308 [Mþ].
d
¼ 1.34 (d, 6H, CH3), 3.19 (m, 1H, CH), 3.63 (s, 3H, CH3), 6.56 (s,
d
¼ ꢀ24.44 (s); EI MS (methanol): m/z ¼
C19H21N2P$H2O (326.15): calc. C 66.50, H 6.70, N 9.83; found C
66.88, H 6.68, N 10.04.

P.C. Kunz et al. / Journal of Organometallic Chemistry 697 (2012) 33e40
35
2.1.5. Synthesis of 1-methyl-2-tert-butylimidazole-4-
NMR (81 MHz, CDCl3):
d
¼ 31.7 (s). MALDI-TOF-MS: m/z (rel.
yldiphenylphosphine (4-MIPtBu,NMe, 1j)
Int.) ¼ 671 [M ꢀ Cl]þ (100), 460 [M-1a-Cl]þ (25).
C35H31N4P2ClRu (706.13): calc. C 59.5, H 4.4, N 7.9; found C 60.0,
H 4.6, N 8.1.
1-Methyl-4-iodo-2-tert-butylimidazole (1.2 g, 45 mmol) is dis-
solved in dichloromethane. One equivalent of ethyl magnesium
bromide (3 M in ether) is slowly added to the solution at 0 ꢁC. The
clear solution is stirred for 30 min at 0 ꢁC and another 30 min at
room temperature before the diphenylchloro phosphine (0.82 mL,
4.5 mmol) is added. The solution is stirred at room temperature
over night. The solvent is removed and the solid is redissolved in
ammonia-saturated dichloromethane and stirred over night. A
white solid precipitates which is filtered off. The solvent of the
filtrate is removed, yielding a white-yellow solid, which is then
stirred in ethanol under addition of 1 mL of hydrochloric acid. The
solvent is removed and the solid stirred in ammonia-saturated
dichloromethane. The precipitated white solid is removed by
filtration and the solvent of the filtrate is removed, resulting in
a white powder, which is dried under vacuum. The solid is
recrystallized from acetone and dried under vacuum. The product
was yielded as MgBr2 adduct. Yield 0.88 g (42%). 1H NMR (200 MHz,
2.1.9. Synthesis of [CpRu(kP-1d)2Cl] (6)
[CpRu(PPh3)2Cl] (0.51 g, 0.70 mmol) and 1d (0.38 g, 1.5 mmol)
were heated for 20 h in toluene to reflux. The volatiles were
removed in vacuo and the residue treated with n-hexane to give
a yellow solid. After filtration the product was chromatographed on
silica (ethyl acetate). Crystallization from methanol/n-hexane
yielded 18 mg (30%) of 6. 1H NMR (200 MHz, CDCl3):
d
¼ 1.28 (dd,
3JHH ¼ 6.9 Hz, 14.1 Hz, 12H, CH(CH3)2), 2.85 (sept, 2H, 3JHH ¼ 6.9 Hz,
CH(CH3)2), 4.27 (s, 5H, C5H5), 6.75 (s, 2H, ImC5H), 7.06e7.28 (m,
10H, Ph), 7.35e7.80 (m, 10H, Ph), 11.0 (s, 2H, ImNH). 31P{1H} NMR
(81 MHz, CDCl3):
d
¼ 26.4 (s). MALDI-TOF-MS: m/z (rel. Int.) ¼ 755
[M ꢀ Cl]þ (100), 461 [M-1d-Cl]þ (25). C41H43N4P2ClRu (790.29):
calc. C 62.3, H 5.5, N 7.1; found C 62.6, H 5.1, N 7.4.
CDCl3):
7.42e8.09 (m, 10H, Ph). 31P{1H} NMR (81 MHz, CDCl3):
(s). MS ESI (methanol): m/z 527 [LMgBr2
d
¼ 1.67 (s, 9H, CH3), 3.91 (s, 3H, CH3), 6.34 (s, 1H, CH),
¼ ꢀ30.48
Na]þ (15).
2.1.10. Synthesis of [{CpRu(m-k
2N,N:k’1P-2a)}2](PF6)2 (7a)
d
50 mg (0.12 mmol) of [CpRu(NCCH3)3]PF6 and 2a (0.12 mmol,
36 mg) were dissolved in acetonitrile and heated to gentle reflux
for 24 h. The volatiles were removed in vacuo, the residue washed
with n-hexane and diethyl ether and dried in vacuo. Yield: 69 mg
¼
þ
C20H23N2PMgBr2NH3 (523.53): calc. C 45.88, H 5.01, N 8.03; found C
45.15, H 5.75, N 7.65.
(90%). 1H NMR (500 MHz, acetonitrile-d3):
d
¼ 3.09 (s, 12H NCH3),
2.1.6. Synthesis of imidazole-2-yl-phenylphosphine (2-BIPH, 2a)
A solution of n-butyl lithium in n-hexane (1.6 M, 12 mL,
19 mmol) was added drop-wise to a solution of 3.0 g (18 mmol) of
1-diethoxymethylimidazole in diethyl ether (150 mL) at ꢀ78 ꢁC.
The reaction mixture was stirred at ꢀ40 ꢁC for 1 h and then was
cooled to ꢀ78 ꢁC and PCl3 (1.56 g, 8.72 mmol) was added. The
reaction mixture was stirred at ꢀ78 ꢁC for 1 h and at ambient
temperature over night. Concentrated ammonia solution (5 mL)
was added, the phases separated, the organic phase was collected
and all volatiles were removed in vacuo. The oily residue was
dissolved in 100 mL acetone/water (10:1) and stirred at ambient
temperature for 72 h. The resulting precipitate was collected
by filtration and dried in vacuo. Yield: 1.1 g (52%). 1H NMR
5.23 (s, 5H Cp), 6.79 (s, 2H arom. Im), 6.95 (t, 3JH,H ¼ 8.2 Hz, 1H Ph),
3
7.13 (s, 2H arom. Im.), 7.40 (t, JH,H ¼ 7.6 Hz, 1H Ph), 7.65 (t,
3JH,H ¼ 7.4 Hz, 1H Ph), 7.75 (t, JH,H ¼ 7.0 Hz, 1H Ph), 8.23 (t,
3
3JH,H ¼ 9.6 Hz, 1H Ph) 31P{1H} NMR (81 MHz, acetonitrile-d3):
d
¼ 45.4 (s), ꢀ142.7 (sept., 1JPF ¼ 707 Hz). ESI MS (methanol): m/z
(rel. int.) ¼ 437 (100) ½ [M þ H]þ, 355 (15) ½ [M-ImNMe]þ. MALDI-
TOF-MS (methanol): m/z (rel. int.)
¼
437 (100) [M]þ.
C38H40N8F12P4Ru2 (1162.81) calc. C 39.3, H 3.5, N 9.6; found C 39.6,
H 3.9, N 10.0.
2.1.11. Synthesis of [{CpRu(m-k
2N,N:k’1P-2b)}2](PF6)2 (7b)
50 mg (0.12 mmol) of [CpRu(NCCH3)3]PF6 and 2a (36 mg) were
dissolved in acetonitrile and heated to gentle reflux for 24 h. The
volatiles were removed in vacuo, the residue washed with n-
hexane and diethyl ether and dried in vacuo. Yield 46 mg (67%). 1H
(methanol-d4):
d
¼ 7.27e7.35 (m, 9H). 31P{1H} NMR (methanol-
d4):
d
¼
ꢀ46 (s). ESIþ (methanol): m/z (%)
¼
243 [L]þ.
C12H11N4P$CH3OH (274.26): calc. C 56.93, H 5.51, N 20.43; found C
NMR (acetonitrile-d3):
d
¼ 4.91 (s, 5H Cp), 6.95 (s, 2H ImCH), 6.99 (s,
56.4, H 5.6, N 20.7.
2H ImCH), 7.58e7.80 (m, 5H PPh). 31P{1H} NMR (acetonitrile-d3):
d
¼ 44.4 (s), ꢀ143.4 (hept.). MALDI-TOF-MS (CH3CN): m/z (rel.
2.1.7. Synthesis of [CpRu(kP-1d)(PPh3)Cl] (4)
int.) ¼ 816 [M]þ (100), 574 (5), 468 (45), 453 [½ M þ NCCD3]þ (30),
409 [½ M]þ (80). C36H35N9P4Ru2F12 (1147.75): calc. C 37.7,H 3.1, N
11.0; found C 37.5, H 3.2, N 10.7.
[CpRu(PPh3)2Cl] (0.5 g, 0.69 mmol) and 1d (0.17 g, 0.67 mmol)
were heated for 4 h in toluene to reflux. The volatiles were removed
in vacuo and the residue treated with n-hexane to give a yellow
solid. After filtration the product was chromatographed on silica
(CH2Cl2:n-hexane 3:1, followed by CH2Cl2). Yield 52 mg (10%). 1H
2.1.12. Synthesis of [CpRu(k
3N,N,N-3b)]Cl (8)
100 mg (0.138 mmol) of [CpRu(PPh3)2Cl] were dissolved in
warm toluene. To the clear orange solution 3a (38 mg, 0.14 mmol)
was added. The solution was warmed to 100 ꢁC and after 30 min
a yellow solid precipitated. The reaction mixture was stirred at
100 ꢁC for additional 3 h. After cooling to ambient temperature and
filtration the solid was washed with small amounts of toluene and
diethyl ether and dried in vacuo. Yield: 51 mg (78%). 1H NMR
NMR (200 MHz, CDCl3):
d
¼ 1.20 (dd, 3JHH ¼ 6.9 Hz, 3JHH ¼ 12.9 Hz,
3
6H, CH(CH3)2), 2.77 (m, 1H, CH(CH3)2), 4.22 (d, JHH ¼ 9.3 Hz, 5H,
Cp), 6.72 (s, 1H, Im), 6.98e7.24 (m, 15 H, PPh3), 7.26e7.83 (m, 11H,
Ph). 31P{1H} NMR (81 MHz, CDCl3):
d
¼ 45.0 (dd, JPP ¼ 28.3 Hz,
2
2
43.0 Hz), 30.4 (t, JPP
¼
21.3 Hz). MALDI-TOF-MS: m/z (rel.
Int.) ¼ 755 [M ꢀ 2H]þ (25), 723 [M ꢀ Cl]þ (100), 461 [M-PPh3Cl]þ
(25). C41H39ClN2P2Ru (758.29): calc. C 65.0, H 5.2, N 3.7; found C
65.1, H 4.9, N 3.7.
(200 MHz, methanol-d4):
d
¼ 4.06 (s, 9H, NCH3), 4.50 (s, 5H, Cp),
3
4
7.38 (dd, JH,H ¼ 4.0 Hz, JH,H ¼ 1.6 Hz, 3H, ImH5), 7.99 (s) (d,
3JH,H ¼ 4.0 Hz, 3H, ImH4). 31P{1H} NMR (81 MHz, methanol-d4):
2.1.8. Synthesis of [CpRu((
kP-1a)2Cl] (5)
d
¼ ꢀ116.5 (s). MALDI-TOF MS: m/z (rel. Int.) ¼ 441 [M ꢀ Cl]þ (100).
[CpRu(PPh3)2Cl] (100 mg, 0.138 mmol) and 1a (70 mg,
0.28 mmol) were heated to 90 ꢁC for 8 h in toluene (15 mL). The
volatiles were removed in vacuo and the residue treated with n-
hexane (15 mL). The resulting solid was filtered and dried in vacuo.
C17H22N6ClPRu$H2O (493.90): calc. C 41.4, H 4.5, N 17.0; found C
41.7, H 4.7, N 16.7.
2.1.13. Synthesis of [CpRu(kP-3a)(PPh3)Cl] (9)
100 mg (0.132 mmol) [CpRu(PPh3)2Cl] were dissolved in 20 mL
toluene upon gentle heating. 32 mg (0.13 mmol) of 3a were added
Yield 61 mg (63%). 1H NMR (200 MHz, CDCl3):
d
¼ 4.38 (s, %H, Cp),
3.44 (br, NH), 6.93 (s, 2H, im), 9.09e7.60 (m, 22H, Ph,im). 31P{1H}

36
P.C. Kunz et al. / Journal of Organometallic Chemistry 697 (2012) 33e40
and the solution was stirred at 70 ꢁC for 6 h. A greenish white solid
was separated and the orange solution was subsequently reduced
in vacuo. The orange residue was taken up in 2 mL dichloro-
methane. Column-chromatography on silica gel with dichloro-
methane and ethyl acetate respectively, gave the product as an
orange solid. Yield: 55 mg (57%) 1H NMR (200 MHz, methanol-d4):
Table 2
31P{1H} NMR shifts of the ligands (dL) and the respective ruthenium complexes (dC
)
as well as the coordination shift Dd
¼
d
CedL (in methanol-d4).
dL
(
31P)/ppm
dC
(
31P)/ppm
Dd (
31P)/ppm
CpRu(PPh3)(L)Cl
2-MIPH (1a)
ꢀ23.8
ꢀ29.6
ꢀ24.4
45.0; 29.3
42.5; 27.6
45.0; 30.4
68.8
64.3
73.0
2-MIPNMe (1b)
4-MIPiPr (1d)
CpRu(L)2PF6
d
¼ 4.54 (s, 5H, Cp), 7.08e7.34 (m, 21H, arom.). 31P{1H} NMR
(81 MHz, methanol-d4):
d
¼ 46 (d, 2JP,P ¼ 45 Hz), 4 (d, 2JP,P ¼ 45 Hz).
ESI MS (methanol): m/z (rel. int.) ¼ 399 (100) [M-PPh3Cl]þ. MALDI-
TOF MS (methanol): m/z (rel. int.) ¼ 399 (60) [M-PPh3Cl]þ, 415 (15)
[CpRu(2-TIPOH)]þ. C32H31N6ClP2Ru$2H2O (732.12): calc. C 52.5, H
4.5, N 11.5; found C 52.3, H 4.6, N 11.4.
2-MIPH (1a)
ꢀ24.8
ꢀ30.6
ꢀ24.4
31.7
29.3
31.3
56.5
60.0
55.7
2-MIPNMe (1b)
4-MIPiPr (1d)
an EOS CCD area detector and a four-circle kappa goniometer using
Mo-K radiation (
¼ 0.71073 Å). Data integration, scaling and
2.2. General procedure for the catalytic hydration reaction
a
l
empirical absorption correction was carried out using the CrysAlis
Pro program package [37]. The structure of was solved using Direct
Methods and refined by Full-Matrix-Least-Squares against F2. All
non-hydrogen atoms positions were refined freely and simulta-
neously using anisotropic displacement parameters. The positional
parameters of the hydrogen atoms of the CH groups were refined
freely. The positional parameters of the hydrogen atoms of the NH
groups were refined with soft NeH distance restraints and indi-
vidual Uiso values. The hydrogen atoms of the water molecule were
refine with soft O-H and H-H distance restraints giving these
hydrogen atoms a fixed isotropic displacement parameters. All
calculations were carried out using the program SHELX97 [39].
[RuCp(C10H8)]PF6 (22 mg, 0.05 mmol) and the respective ligand
(2.2 eq., 0.11 mmol) were dissolved in acetonitrile or dichloro-
methane, respectively. The solution was stirred at 60 ꢁC over night.
Removal of most of the solvent under vacuum and addition of
diethyl ether or hexane resulted in the respective ruthenium
complex as a fine yellow powder, which is dried under vacuum
after filtration. This preformed, but not further purified ruthenium
catalyst (0.05 mmol, 5 mol% catalyst loading) was dissolved in
acetone (2 mL) and degassed 1-octyne (150 mL) and water (90 mL)
were added to the solution. The reaction mixture was stirred at
60 ꢁC in an oil bath. The progress of the reaction was monitored by
GC.
Orange crystals of [CpRu(k
1P-3a)(PPh3)]Cl$CH2Cl2 (9.CH2Cl2) were
mounted on a MiTeGen cryoloop with a small amount of inert oil.
Data collection was carried out at 150 K using an Oxford Diffraction
Gemini E Ultra diffractometer, equipped with an EOS CCD area
2.3. X-ray crystallography
Crystallographic data of [{CpRu(m-k
2-N,N-k’1-P-2b)}2](C6H5-
detector and a four-circle kappa goniometer using Mo-K
a radiation
PO3H)2(C6H5PO3H2)2, [{CpRu(2b)}2](PF6).22CH3CN (7b.2CH3CN),
[CpRu(1a)2Cl ].H2O (5.H2O) and [CpRu(PPh3)2Cl]$CHCl3 were
collected at 183(2) K on an Oxford Diffraction Xcalibur system with
(l
¼ 0.71073 Å). Data integration, scaling and empirical absorption
correction was carried out using the CrysAlis Pro program package
[37]. The structure was solved using Direct Methods and refined by
Full-Matrix-Least-Squares against F2. All non-hydrogen atoms were
refined anisotropically and hydrogen atoms were placed at ideal-
ised positions and refined using the riding model. All calculations
were carried out using the program Olex2 [41]. Important crystal-
lographic data and refinement details are summarised in Table 4.
The crystallographic data has been deposited at the CCDC with the
ref codes CCDC 820763, 828860, 828861, 837344 and 845941.
a Ruby detector using Mo Ka radiation (
l
¼ 0.7107 Å) that was
graphite-monochromated. Suitable crystals were covered with oil
(Infineum V8512, formerly known as Paratone N), mounted on top
of a glass fibre and immediately transferred to the diffractometer.
The program suite CrysAlisPro was used for data collection, multi-
scan absorption correction and data reduction [37]. Structures
were solved with direct methods using SIR97 [38] and were refined
by full-matrix least-squares methods on F2 with SHELXL-97 [39].
The structures were checked for higher symmetry with help of the
program Platon [40]. The crystal of [{CpRu(2b)}2](PF6).22CH3CN
(7b.2CH3CN) is non-merohedrally twinned. The two twin domains
are related by a 180ꢁ rotation along uvw (0 0 1). Both domains (ratio
52:48) were integrated with the CrysalisPro software and refined as
hklf5. Yellow crystals of 5.H2O were mounted on a glass fibre with
a small amount of inert oil. Data collection was carried out at 100 K
using an Oxford Diffraction Xcalibur diffractometer, equipped with
3. Results and discussion
3.1. Synthesis of PN ligands
Pyridin-2-ylphosphines are privileged hemilabile PN ligands
in transition metal catalysis. Also, imidazole-2-ylphosphines are
well-established ligands for transition metal complexes, e.g. Grot-
jahn et al. recently described the ability of imidazole-2-
yldiphenylphosphine to act as a hemilabile PN ligand in Cp*Ir
complexes [42] and Caballero et al. observed rearrangement of
1-methylimidazole-2-yldiphenylphosphine (1b) in complexes
[(arene)Ru(1b)Cl2] including PeC bond cleavage in this process
Table 1
Spectroscopic data of the synthesized ligands.
Ligand
d
(1H)/ppm
d (
31P)/ppm
4-MIPNMe
(1h)a 3.73 (s, 3H, CH3), 6.93 (t, 1H, CH),
7.31e7.42 (m, 10H, Ph), 7.80 (t, 1H, CH)
(1i)a 1.34 (d, 6H, CH3), 3.19 (m, 1H, CH),
3.63 (s, 3H, CH3), 6.56 (s, 1H, CH),
ꢀ22.8 (s)
ꢀ24.4 (s)
4-MIPiPr,NMe
Table 3
31P{1H} NMR data of [CpRu(PPh3)(1d)Cl] (4) in different solvents.
7.36e7.84 (m, 10H, Ph)
4-MIPtBu,NMe
(1j)b 1.67 (s, 9H, CH3), 3.91 (s, 3H, CH3),
6.34 (s, 1H, CH), 7.42e8.09 (m, 10H, Ph)
ꢀ30.4 (bs)c
Solvent
dPPh3
(
31P)/ppm
2JPP/Hz
d1d
(
31P)/ppm
2JPP/Hz
2-MIPdiPh,NMe (1c)b 3.57 (s, 3H, CH3), 7.15e7.74 (m, 20H, Ph) ꢀ28.7 (s)
C6D6
CDCl3
(CD3)2CO
CD3OD
45.8
44.1
44.4
52.8
43
43
43
39
25.3
26.1
23.8
ꢀ5.1
43
43
43
39
a
in methanol-d4.
in CDCl3.
b
c
Mg-salt.

P.C. Kunz et al. / Journal of Organometallic Chemistry 697 (2012) 33e40
37
Table 4
Crystallographic data for [CpRu(1a)2Cl]$H2O (5.H2O), [{CpRu(
[CpRu(
1P-3a)(PPh3)]Cl$CH2Cl2 (9$CH2Cl2) and [CpRu(PPh3)2]Cl$CHCl3.
m
-
k
2-N,N- k’1-P-2b)}2](PF6)2. CH3CN (7b.CH3CN), [{CpRu(
m
-
k
2-N,N- k’1-P-2b)}2](C6H5PO3H)2(C6H5PO3H2)2,
k
Compound
5.H2O
7b.CH3CN
[{CpRu(2b)}2]
9$CH2Cl2
[CpRu(PPh3)2]Cl $CHCl3
(C6H5PO3H)2(C6H5PO3H2)2
Empirical formula
Formula weight
Crystal system
Space group
a [Å]
C35H33ClN4OP2Ru
724.11
Monoclinic
P21/n
9.35991(13)
19.4751(3)
17.2255(3)
90.00
93.3452(13)
90.00
C42H46F12N10P4Ru2
1244.91
Monoclinic
P21/c
12.1695(4)
13.8697(6)
13.9362(5)
90.00
96.327(3)
90.00
C62H66N8O12P6Ru2
1503.19
Triclinic
C33H31Cl3N6P2Ru
781.00
Monoclinic
P21/c
14.6359(6)
8.3887(3)
27.1301(12)
90.00
96.813(4)
90.00
C42H36Cl4P2Ru
845.52
Triclinic
P-1
P-1
11.35775(17)
12.3482(2)
13.2800(3)
117.0250(19)
104.5021(15)
91.1715(13)
1586.69(5)
1
10.0331(3)
13.8107(5)
14.4657(5)
100.141(3)
106.935(3)
99.411(3)
1837.79(11)
2
b [Å]
c [Å]
a
b
g
[ꢁ]
[ꢁ]
[ꢁ]
Volume [Å3]
Z
3134.61(8)
4
2337.93(15)
2
3307.4(2)
4
Density (calculated)
1.534
1.768
1.573
1.568
1.528
[Mg/m3]
Absorption
0.724
0.876
0.696
0.848
0.836
coefficient [mmꢀ1
F(000)
]
1480
1248
768
1584
860
Crystal size [mm3]
Crystal description
Theta range for data
collection [ꢁ]
Index ranges
0.47 ꢂ 0.11 ꢂ 0.10
Yellow needle
5.15 to 25.00
0.19 ꢂ 0.14 ꢂ 0.04
Orange plate
2.57 to 30.51
0.37 ꢂ 0.23 ꢂ 0.16
Yellow block
2.95 to 36.32
0.14 ꢂ 0.07 ꢂ 0.05
Orange needle
2.95 to 29.5
0.20 ꢂ 0.12 ꢂ 0.05
Orange plate
2.61 to 30.51
ꢀ11 ꢃ h ꢃ 7,
ꢀ23 ꢃ k ꢃ 23,
ꢀ20 ꢃ l ꢃ 20
19160
ꢀ17 ꢃ h ꢃ 17,
ꢀ19 ꢃ k ꢃ 19,
ꢀ19 ꢃ l ꢃ 19
24410a
ꢀ18 ꢃ h ꢃ 18,
ꢀ20 ꢃ k ꢃ 20,
ꢀ22 ꢃ l ꢃ 22
59543
ꢀ18 ꢃ h ꢃ 19,
ꢀ11 ꢃ k ꢃ 11,
ꢀ36 ꢃ l ꢃ 34
21611
ꢀ14 ꢃ h ꢃ 14,
ꢀ19 ꢃ k ꢃ 17,
ꢀ20 ꢃ l ꢃ 18
20943
Reflections collected
Independent reflections
Reflections observed
Criterion for observation
Completeness to theta
Absorption correction
5465 [R(int) ¼ 0.0407]
24410a
18628
>2sigma(I)
15362 [R(int) ¼ 0.0247]
7893 [R(int) ¼ 0.0406]
11219 [R(int) ¼ 0.0328]
4671
13058
6313
7958
>2sigma(I)
>2sigma(I)
>2sigma(I)
>2sigma(I)
99,1% to 25.00ꢁ
Semi-empirical
from equivalents
0.9554 and 1.0
5465/5/499
99.9% to 30.51ꢁ
Semi-empirical
from equivalents
0.9658 and 0.8980
24410/0/320
1.032
99.8% to 36.32ꢁ
Semi-empirical
from equivalents
0.8968 and 0.8362
15362/0/412
1.116
99.74% to 26.32ꢁ
Semi-empirical
from equivalents
1.0000 and 0.8779
7893/0/406
99.9% to 30.51ꢁ
Semi-empirical
from equivalents
0.9594 and 0.8045
11219/0/442
0.899
Max. and min. transmission
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices
[I > 2sigma(I)]
R indices (all data)
1.097
1.021
R1 ¼ 0.0307,
wR2 ¼ 0.0631
R1 ¼ 0.0397,
wR2 ¼ 0.0658
0.457/ꢀ0.484
R1 ¼ 0.0454,
wR2 ¼ 0.1232
R1 ¼ 0.0624,
wR2 ¼ 0.1303
1.109 and ꢀ0.844
R1 ¼ 0.0271,
wR2 ¼ 0.0772
R1 ¼ 0.0336,
wR2 ¼ 0.0786
0.797 and ꢀ0.595
R1 ¼ 0.0376,
wR2 ¼ 0.0805
R1 ¼ 0.0528,
wR2 ¼ 0.0838
0.714 and ꢀ0.649
R1 ¼ 0.0360,
wR2 ¼ 0.0627
R1 ¼ 0.0601,
wR2 ¼ 0.0657
0.715 and ꢀ0.853
Largest diff. peak
and hole [e.Åꢀ3
CCDC number
]
845941
837344
828860
820763
828861
a
Due to the twin integration, there are no independent reflections.
[43]. We synthesised several series of imidazole-based phosphine
ligands in the last few years for biomimetic model complexes and
metallo-drugs [33,34,44e47]. Here, these ligands as well as some
new PN ligands, as depicted in Fig. 1, were used in CpRu-complexes,
which should catalyse the hydration of alkynes.
such as 1-methylimidazole-4-yldiphenyl phosphine (1h) were
synthesized.
The reaction scheme for the synthesis of the new imidazol-4-yl
phosphine ligands 1hej is shown in Scheme 1. The respective
imidazole is converted to the 4,5-diiodoimidazole derivative by KI/
I2 in basic solution. Reaction of the 4,5-diiodoimidazole derivative
with methyl iodide leads to the N-methylated imidazole derivative,
which is then converted in two consecutive Grignard reactions to
the respective 1-methylimidazol-4-yldiphenyl phosphine.
Especially imidazole derivatives with bulky groups such as iso-
propyl, phenyl or tert-butyl in ortho-position to the imine N atom
were chosen since they are known to prevent k
2PN-coordination
[30]. Furthermore, ligands without sterically demanding groups
H
N
H
N
I
I
I
I
i)
ii)
N
N
R
R
R
N
N
iii)
iv)
N
N
N
R
R
N
Ph2P
I
Scheme 1. General route for the synthesis of 1-methylimidazol-4-yldiphenyl-
phosphines 1hej (4-MIPNMe’s), i) I2/KI in aq. NaOH, ii) KOtBu, MeI, thf, iii) EtMgBr,
H2O, thf, iv) EtMgBr, Ph2PCl, thf.
Fig. 1. Imidazol-2-yl- and imidazol-4-yl-phosphine ligands used.

38
P.C. Kunz et al. / Journal of Organometallic Chemistry 697 (2012) 33e40
H
N
Ph
Ph
Ph
Ph
Ph
Ph
i)
ii)
N
N
N
N
Ru
PPh2
PPh3
Ru
+ Tl+, – TlCl
acetone
PPh3
Ph2P
N
Ph2P
Cl
N
iPr
N
Scheme 2. Route for the synthesis of 1-Methyl-4,5-diphenylimidazol-2-yl-diphenyl-
phosphine (2-MIPdiPhNMe, 1c): i) KOtBu, MeI, thf, ii) n-BuLi, Ph2PCl, thf.
HN
N
H
iPr
Scheme 4. Reaction of [CpRu(PPh3)(1d)Cl] (4) with TlNO3 in acetone gives a PN
chelate.
All steps, including the first Grignard reaction, proceed in good
yields, whereas the second Grignard reaction raised some prob-
lems. The product was obtained as the magnesium complex, since
magnesium coordinates strongly to the imidazole N atom(s). This
problem of magnesium adduct formation has already been
addressed by Kluwer in the preparation of pyridinylphosphines
[48]. Repeated alternating stirring in ethanol, spiked with hydro-
chloric acid, or ammonia-saturated dichloromethane led to isola-
tion of the ligands 1-methylimidazol-4-yldiphenylphosphine (1h)
and 1-methy-2-isopropylimidazole-4-yldiphenylphosphine (1i). In
the case of 1-methyl-2-tert-butylimidazole-4-yldiphenylphosphine
(1j), even after repeated crystallisation from ethanol, the MgBr2
adduct was obtained.
In addition to the three 1-methylimidazol-4-yl phosphine
ligands 1hej, 1-methyl-4,5-diphenylimidazol-2-yl-diphenylphos-
phine (1c) was synthesized as a new imidazole-2-yl ligand bearing
bulky phenyl substituents (Scheme 2). The methylation of 4,5-
diphenylimidazol is carried out using methyl iodide. Subsequent
lithiation with n-butyllithium and addition of diphenyl-
chlorophosphine leads to the 1-methyl-4,5-diphenylimidazol-2-yl-
diphenylphosphine ligand in very good yields. Since lithium does
not coordinate as strongly to the imidazole nitrogen atoms as
magnesium, the separation of the lithium salts from the ligand is
easily accomplished by stirring the crude product with ammonia-
saturated dichloromethane followed by filtration.
spectra are also in accordance with the proposed formula. The
reaction of two equivalents of 1a with [CpRu(PPh3)2Cl] below 70 ꢁC
in toluene gives [CpRu(1a)2Cl] (5) by substitution of both PPh3
ligands (singlet,
mono-substituted complex (doublet,
d
(
31P) ¼ 31.7 ppm). Minor contamination of the
d
(
31P) ¼ 45.0, 29.3 ppm,
J ¼ 44 Hz) ligands were transformed into [CpRu(1a)2Cl] (5) by
addition of a slight excess of 1a. When the reaction mixtures of
[CpRu(PPh3)2Cl] and the NH-ligand 1a were heated above 90 ꢁC,
doublets at 120 and 50 ppm in the 31P{1H} NMR spectra were
observed. The reaction with one or two equivalents of 1d gives
[CpRu(PPh3)(1d)Cl] (4) and [CpRu(1d)2Cl] (6), respectively. For the
latter we were not able to obtain a sufficient CHN analysis, although
1H and 31P{1H} NMR and MALDI-TOF mass spectrometry clearly
demonstrate the existence of [CpRu(1d)2Cl] (6). The compound
[CpRu(PPh3)(1d)Cl] (4) shows, as expected, two signals in the 31P
NMR spectrum. In non-coordinating or weakly coordination
2
solvents the resonances are found at 45 and 25 ppm with a JPP
coupling constant of 43 Hz. In the more strongly coordination
solvent methanol, which is a good solvent for the solvation of
chloride, the resonances are shifted to 53 and e5 ppm with
a coupling constant of 39 Hz (Table 3). Especially the high-field shift
of the resonance of the P-atom of the ligand 1d from about 25
to ꢀ5 ppm is typical for the change in the coordination mode of the
Spectroscopic data of the four new ligands 1c,hej is summa-
rized in Table 1. The chemical shifts observed in the 31P NMR
spectra are in the typical regime for monoimidazolyldiphenyl
phosphines (MIPs) [45,49].
ligand from kP to k
2PN [50]. This can also be forced in acetone by
abstraction of the chloride ligand upon addition of TlNO3 (Scheme 4
and ESI).
The reaction of 2a with [CpRu(PPh3)2Cl] or [CpRu(NCCH3)3]PF6
gave a single product with a singlet at 45 ppm in the 31P{1H} NMR
spectrum and one set of the protons of the methyl groups (singlet at
3.09 ppm), the Cp protons (singlet at 5.23 ppm) and the imidazolyl
protons (two doublets at 6.79 and 7.13 ppm) in the 1H NMR,
respectively. The most intense signal in the MALDI spectrum is
found at m/z ¼ 437 and shows an isotopic pattern characteristic for
a compound with two ruthenium atoms and thus a charge of þ2.
Additionally, a peak with small intensity is found at 874. This is in
accordance with a dimeric structure (Scheme 5), which was
confirmed by single crystal analysis (see below).
3.2. Synthesis of CpRu-complexes with PN ligands
We exemplarily investigated the basic coordination chemistry of
some of the presented imidazole-based PN ligands towards
CpRu(II). As ruthenium(II) precursor compounds we used
[CpRu(C10H8)]PF6,
[CpRu(NCMe)3]PF6
and
[CpRu(PPh3)2Cl]
(Scheme 3).When [CpRu(PPh3)2Cl] was reacted with 1b at room
temperature for three weeks, only one PPh3 ligand was replaced by
1b yielding [CpRu(PPh3)(1b)Cl], as is indicated by two doublets in
the31P NMR spectrum (Table 2). These appeared only in small
quantities in addition to signals of the starting materials and free
triphenylphosphine. However, reaction of 1b with the more labile
complex [CpRu(NCCH3)3]PF6 in dichloromethane yielded the
complex [CpRu(1b)2(solvent)]PF6 which exhibits a single singlet in
the 31P NMR spectrum at 38 ppm. Both 1H NMR and MALDI mass
The tripodal tetradentate ligands 3a and 3b react with
[CpRu(PPh3)2Cl] at elevated temperatures and prolonged reaction
times to complexes in which the CpRu-moiety is facially bound
by the tripodal ligands in a k
3N,N,N coordination mode (Scheme 6).
The coordination mode can be deduced by the typical high-field
L
L
Ru
Ru
Ru
PPh3
PPh3
L
Ph
P Ru
Ph3P
L
L
L
Cl
Cl
Cl
R
N
R
N
[CpRu(PPh3)2Cl] or
[CpRu(NCCH3)3]PF6
N
(X)2
PhP
N
2
2
N
2
N
R
L
Ru P
or
Ru
Ru
PF6
Ru
PF6
PF6
L
NCCH3
CH3CN
H3CCN
Ph
NCCH3
NCCH3
Scheme 3. Reaction of ligands (L) 1a, 1b and 1d with [CpRu(PPh3)2Cl] and
[CpRu(NCCH3)3]PF6 or [CpRu(C10H8)]PF6.
Scheme 5. Reaction of [CpRu(PPh3)2Cl] or [CpRu(NCCH3)3]PF6 with 2-BIPNH (2a) and
2-BIPNMe (2b) to complexes 7a/b (X ¼ PF6).

P.C. Kunz et al. / Journal of Organometallic Chemistry 697 (2012) 33e40
39
R
N
R
Ru
P
N
N
[CpRu(PPh3)2Cl]
toluene
Ru
N
N
Cl
Cl
Ph3P
P
P
toluene, 110 °C
2
3
N
3
N
R
N
R
Scheme 6. Reaction of [CpRu(PPh3)2Cl] with 2-TIPNH (R ¼ H, 3a) and 2-TIPNMe (R ¼ Me, 3b).
shift of the phosphorus resonance of 40e60 ppm to about
3N,N,N complexes of these ligands.
inert conditions from the reaction solution of [CpRu(PPh3)2Cl]
together with 2b, we found yellow crystals of [{CpRu(
2-N,N-
ꢀ110 ppm in
k
m - k
At 70 ꢁC and in the non-protic solvent toluene the reaction of 3a
with [CpRu(PPh3)2Cl] leads to substitution of only one PPh3 ligand,
which can easily be observed in the 31P NMR spectra of the reaction
mixture. Two doublets occur for the new species [CpRu(PPh3)(3a)
k’1-P-2b)}2](C6H5PO3H)2(C6H5PO3H2)2 which crystallized in the
triclinic space group P-1 (see ESI). Additionally, we found red
crystals of a chloroform solvate of [CpRu(PPh3)2Cl] which crystal-
lises in the triclinic space group P-1 (see ESI). Obviously, 2b partially
hydrolysed under P-C bond cleavage and oxidized to give the
phenylhydrogenphosphonate counter ion and the phenyl-
dihydrogenphosphonate respectively. Both structures have essen-
tially an identical cationic part. Only the cyclopentienyl and the
phenyl ring are conformational slightly twisted along the ruthe-
nium - cyclopentadienyl centroid and the ispo - para atoms of the
phenyl ring respectively.
2
Cl] (9) with JP,P values of w50 Hz. This product is also obtained
from a reaction of the starting material with 2 equivalents of ligand
3a. Recrystallisation from chloroform yielded a crystal suitable for
single crystal analysis (see below).
3.3. Solid-state structures
Red crystals of [CpRu(k
1P-3a)(PPh3)]Cl$CH2Cl2 (9$CH2Cl2) were
Crystals of [CpRu(1a)2Cl ].H2O (5.H2O) suitable for single crystal
structure determination were obtained by slow evaporation of
a chloroform solution at air. The CpRu center is coordinated octa-
obtained by crystallisation from chloroform. The compound crys-
tallizes in the monoclinic space group P21/c. Two of the three H
atoms of the NH-functionalities of the ligand 3a form intra-
molecular hydrogen bonds towards Cl1. Another intramolecular
hydrogen bond N-H.A N1AA results in the formation of a nearly
coplanar six-membered ring (Fig. 4). The metric parameters are
within the range found in phosphine complexes of the type
[CpRu(L)2Cl] [52e55].
hedral by the
h kP-coordi-
5-Cp ligand, a chlorido ligand and two
nated ligands 1a. Both ligands 1a form NH.Cl hydrogen bonds
towards the coordinated chlorido ligand and one is also involved in
hydrogen bonding to the co-crystallised water molecule (Fig. 2).
The structural motif in [CpRu(1a)2Cl ].H2O (5.H2O) resembles the
one found in [CpRu(L)2(H2O)]CF3SO3 (L ¼ 1-methyl-3-tert.butyldi-
phenyl phosphine) [28].
3.4. Catalytic trials with CpRu-based complexes of PN ligands
Crystals of [{CpRu(m-k k
2N,N: 1P-2b)}2](PF6)2. CH3CN (7b.CH3CN)
suitable for single crystal structure determination were obtained by
slow diffusion of n-hexane into a solution of 7b in acetonitrile. Here
ligand 2b acts as bridging ligand between two CpRu centers (Fig. 3).
Grotjahn et al. described the catalytic activity of the complex
[CpRu(L)2(NCCH3)]PF6 with the PN ligand 2-diphenylphosphino-6-
tert-butylpyridine (L) in the hydration of several terminal alkynes
to give up to 99.9% yield within 3 h with a catalyst loading of just
2 mol-% [27].
We used a protocol established for the catalytic hydration of
ruthenium(II) pyridinyl phosphine complexes and [CpRu(NCCH3)3]
PF6 as well as [CpRu(C10H8)]PF6 for the preparation of compounds
Such a bridging
m-k k
2N,N: 1P-coordination mode has tentatively
been assigned to the phenylbis(pyridin-2-yl)phosphine ligand
(PhPpy2) in the compound [Mo(CO)3(PhPpy2)], which is thought to
be a coordination polymer and not a cyclic dimer [51]. In the
[{CpRu(
the Ru(II) atoms in the {CpRu(2b)} unit is distorted octahedral with
a facially bound
5-Cp ligand and the P atom of the 2b ligand as
m-k k
2N,N: 1P-2b)}2]2þ cation the coordination geometry of
h
well as two N atoms of the 2b ligand of the other unit of the
{CpRu(2b)}2 dimer. In one crystallisation experiment under non
Fig. 3. Solid-state structure of the cation [{CpRu(
k
2-N,N- k’1-P-2b)}2](PF6)2. CH3CN (7b.CH3CN). Displacement ellipsoids are drawn at
50% level. The counter ions, cocrystallized solvent molecules and hydrogen atoms are
omitted for clarity.
m-k m -
2-N,N-k’1-P-2b)}2]2þ in [{CpRu(
Fig. 2. Solid-state structure of [CpRu(1a)2Cl]$H2O (5.H2O). Displacement ellipsoids are
drawn at 50% level. Hydrogen atoms are drawn at arbitrary radius and non-acidic
hydrogen atoms are omitted for clarity.

40
P.C. Kunz et al. / Journal of Organometallic Chemistry 697 (2012) 33e40
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and non-acidic hydrogen atoms are omitted for clarity.
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4. Conclusions
We prepared CpRu-complexes with imidazole-based PN ligands.
Three types of coordination modes for the PN ligands have been
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k
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have screened 11 imidazole-based PN ligands in the CpRu(II)-
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the formation of aldehyde over ketone. When poly(imidazolyl)
ligands are used, the formation of coordinatively saturated
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Appendix. Supplementary material
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