Chemistry of the PCNHCP ligand: Silver and ruthenium complexes, facial/meridional coordination, and catalytic transfer hydrogenation

Article abstract of DOI:10.1021/om049070v

The silver complex of PC^NHCP was identified as [Ag ₃(μ-Cl)(PC^NHCP)₂]Cl₂ (1). Anion exchange of 1 with AgNO₃ affords a white compound, which crystallizes into two forms, [Ag₃(μ-Cl)-(PC^NHCP)] ₂(NO₃)₂ (2a) and [Ag₃(Cl)(NO ₃)(0.5DMF)(PC^NHCP)₂]NO₃ (2b), from different solvent combinations. Their structural determination reveals interesting structural features, including a short Ag...Ag interaction in both of them. Unlike the common preparation of ruthenium(II) NHC complexes in the literature, a novel silver carbene transfer reaction between 1 and RuCl ₂(PPh)₃ produces fac-[Ru₂(μ-Cl) ₃(PC^NHCP)₂]Cl (3) in good yield. The nonredox nature of the carbene transfer reaction is different from that of an earlier report and shows that the preparation of divalent ruthenium NHC complexes via silver carbene transfer is a feasible synthetic route. Significantly, complex 3 can also be prepared directly from PC^NHCP·HC1 and RuCl ₂(PPh₃)₃ in the absence of base. Reactions of 3 with CO, phenylacetylene, and pyridine afford mer complexes mer,cis-RuCl ₂(CO)(PC^NHCP) (4), mer,trans-RuCl₂(=C=CHPh) (PC^NHCP) (6), and mer,trans-[RuCl(py)₂(PC ^NHCP)]Cl (7), respectively. The fac complex, fac,cis-[RuCl(bipy) (PC^NHCP)]Cl (8), was produced in reaction of either 3 or 7 with 2,2′-bipyridine. Treatment of 4 with excess NaBH₄ produced the hydride complex mer-RuHCl(CO)(PC^NHCP) (5). Complex 7 is slowly oxidized to mer-[Ru^IIICl₃(PC^NHCP)] (9) in the air. The structures of 2a, 2b, 3, 4, 7, 8, and 9 have been confirmed by X-ray crystallography. The reactivity study shows that PC^NHCP is capable of accommodating extra steric requirement by readily switching from facial to meridional coordination mode, and the preliminary catalytic study indicates that 3 is effective in transfer hydrogenation of ketones.

Full text of DOI:10.1021/om049070v

1692
Organometallics 2005, 24, 1692-1702
Chemistry of the PCNHCP Ligand: Silver and Ruthenium
Complexes, Facial/Meridional Coordination, and
Catalytic Transfer Hydrogenation
Pei Ling Chiu and Hon Man Lee*
Department of Chemistry, National Changhua University of Education,
Changhua, Taiwan 50058
Received November 28, 2004
The silver complex of PCNHCP was identified as [Ag3(µ-Cl)(PCNHCP)2]Cl2 (1). Anion exchange
of 1 with AgNO3 affords a white compound, which crystallizes into two forms, [Ag3(µ-Cl)-
(PCNHCP)]2(NO3)2 (2a) and [Ag3(Cl)(NO3)(0.5DMF)(PCNHCP)2]NO3 (2b), from different solvent
combinations. Their structural determination reveals interesting structural features,
including a short Ag‚‚‚Ag interaction in both of them. Unlike the common preparation of
ruthenium(II) NHC complexes in the literature, a novel silver carbene transfer reaction
between 1 and RuCl2(PPh)3 produces fac-[Ru2(µ-Cl)3(PCNHCP)2]Cl (3) in good yield. The
nonredox nature of the carbene transfer reaction is different from that of an earlier report
and shows that the preparation of divalent ruthenium NHC complexes via silver carbene
transfer is a feasible synthetic route. Significantly, complex 3 can also be prepared directly
from PCNHCP‚HCl and RuCl2(PPh3)3 in the absence of base. Reactions of 3 with CO,
phenylacetylene, and pyridine afford mer complexes mer,cis-RuCl2(CO)(PCNHCP) (4), mer-
,trans-RuCl2(dCdCHPh)(PCNHCP) (6), and mer,trans-[RuCl(py)2(PCNHCP)]Cl (7), respectively.
The fac complex, fac,cis-[RuCl(bipy)(PCNHCP)]Cl (8), was produced in reaction of either 3 or
7 with 2,2′-bipyridine. Treatment of 4 with excess NaBH4 produced the hydride complex
mer-RuHCl(CO)(PCNHCP) (5). Complex 7 is slowly oxidized to mer-[RuIIICl3(PCNHCP)] (9) in
the air. The structures of 2a, 2b, 3, 4, 7, 8, and 9 have been confirmed by X-ray
crystallography. The reactivity study shows that PCNHCP is capable of accommodating extra
steric requirement by readily switching from facial to meridional coordination mode, and
the preliminary catalytic study indicates that 3 is effective in transfer hydrogenation of
ketones.
Introduction
its corresponding palladium(II) complexes are robust
Heck catalysts, capable of producing high TONs. There
is much current interest in the preparation of ruthe-
nium NHC complexes because of their catalytic proper-
ties in olefin metathesis.1c,3 Other catalytic applications
such as hydrogenation,4 transfer hydrogenation,5,6 and
oxidation of olefins have also been investigated.6 To
further explore the utility of the PCNHCP ligand, we
report new ruthenium complexes with PCNHCP and a
preliminary catalytic application in hydrogen transfer
reactions.
Transition metal complexes with N-heterocyclic car-
bene (NHC) ligands are attracting a considerable amount
of research interest because of their successful applica-
tions in diverse catalytic reactions.1 We were interested
in the preparation of transition metal complexes with
functionalized N-heterocyclic carbene ligands and the
study of their catalytic applicability.2 The incorporation
of the carbene functionality into ligand systems contain-
ing other “classical” donor groups offers vast opportuni-
ties for ligand design which promises the discovery of
new efficient catalysts. Along this direction, we have
recently reported a new tridentate phosphine/NHC
pincer ligand, PCNHCP.2a Catalytic studies showed that
Similar to the preparation of [PdII(PCNHCP)Cl]Cl,2a we
also employed the silver carbene transfer reaction for
the synthesis of the Ru(II) PCNHCP complex. In the
course of investigation, we found that the silver com-
pound of PCNHCP is indeed a trisilver complex contain-
* Corresponding author. Tel: +886 4 7232105, ext. 3523. Fax: +886
4 7211190. E-mail: leehm@cc.ncue.edu.tw.
(1) For reviews, see: (a) Arduengo, A. J., III. Acc. Chem. Res. 1999,
32, 913. (b) Bourissou, D.; Guerret, O.; Gabba¨ı, F. P.; Bertrand, G.
Chem. Rev. 2000, 100, 39. (c) Trnka, T. M.; Grubbs, R. H. Acc. Chem.
Res. 2001, 34, 18. (d) Herrmann, W. A. Angew. Chem., Int. Ed. 2002,
41, 1290. (e) Hillier, A. C.; Grasa, G. A.; Viciu, M. S.; Lee, H. M.; Yang,
C.; Nolan, S. P. J. Organomet. Chem. 2002, 653, 69. (f) Perry, M. C.;
Burgess, K. Tetrahedron: Asymmetry 2003, 14, 951.
(2) (a) Lee, H. M.; Zeng, J. Y.; Hu, C.-H.; Lee, M.-T. Inorg. Chem.
2004, 43, 6822. (b) Lee, H. M.; Lu, C. Y.; Chen, C. Y.; Chen, W. L.;
Lin, H. C.; Chiu, P. L.; Cheng, P. Y. Tetrahedron 2004, 60, 5807. (c)
Lee. H. M.; Chiu, P. L.; Zeng, J. Y. Inorg. Chim. Acta 2004, 357, 4313.
(d) Lee, H. M.; Chiu, P. L.; Hu, C.-H.; Lai, C.-L.; Chou, Y.-C. J.
Organomet. Chem. 2005, 690, 403.
(3) (a) Furstner, A.; Ackermann, L.; Gabor, B.; Goddard, R.; Leh-
mann, C. W.; Mynott, R.; Stelzer, F.; Thiel, O. R. Chem. Eur. J. 2001,
7, 3236. (b) Jafarpour, L.; Hillier, A. C.; Nolan, S. P. Organometallics
2002, 21, 442. (C) Bielawski, C. W.; Benitez, D.; Grubbs, R. H. Science
2002, 297, 2041. (d) Denk, K.; Fridgen, J.; Herrmann, W. A. Adv. Synth.
Catal. 2002, 344, 666.
(4) (a) Lee, H. M.; Smith, D. C., Jr.; He, Z.; Stevens, E. D.; Yi, C. S.;
Nolan, S. P. Organometallics 2001, 20, 794. (b) Csabai, P.; Joo´, F.
Organometallics 2004, 23, 5640.
(5) Danopoulos, A. A.; Winston, S.; Motherwell, W. B. Chem.
Commun. 2002, 1376.
(6) Poyatos, M.; Mata, J. A.; Falomir, E.; Crabtree, R. H.; Peris, E.
Organometallics 2003, 22, 1110.
10.1021/om049070v CCC: $30.25 © 2005 American Chemical Society
Publication on Web 03/01/2005

Chemistry of the PCNHCP Ligand
Organometallics, Vol. 24, No. 7, 2005 1693
Scheme 1
Scheme 2
ing 2 equiv of PCNHCP, [Ag3(µ-Cl)(PCNHCP)2]Cl2 (1).
Reaction of 1 with RuCl2(PPh3)3 cleanly produced a
novel bimetallic ruthenium(II) NHC complex, fac-[Ru2-
(µ-Cl)3(PCNHCP)2]Cl, after simple workup procedure.
This fac complex can also be produced from a direct
reaction between PCNHCP‚HCl and RuCl2(PPh3)3 with-
out the need of base. Interestingly, the reactivity study
of PCNHCP complexes shows that the PCNHCP ligand can
coordinate either in facial or meridional mode depending
on the steric environment around the ruthenium center.
Catalytic study shows that fac-[Ru2(µ-Cl)3(PCNHCP)2]Cl
is an effective catalyst in transfer hydrogenation of
olefins.
vide an ideal to the structure of 1. Our strategy was
proven to be successful. Reactions of 1 with 2 equiv of
AgNO3 in methanol produced a white solid (2). In
contrast to the parent complex 1, which exhibits only a
single, broad 31P{1H} NMR signal at δ -10.0,2a the 31P-
{1H} NMR spectrum of 2 shows two broad signals
centered at δ -3.1 and 0.6, indicating the presence of
two types of chemically nonequivalent phosphorus
atoms. The coupling of the 31P nuclei with both 107Ag
and 109Ag (I ) 1/2) was unresolved. The two phosphorus
signals coalesce into a single resonance on heating a
CDCl3 solution of the compound at 54 °C, indicating the
fluxionality of the compound at elevated temperature.
Colorless crystals can be obtained from the solid
sample employing the solvent combinations of either
acetonitrile/ether or DMF/ether. The X-ray structural
determinations on the two batches of crystals afford two
different structures (Scheme 2). The thermal ellipsoid
plot of the cationic portion of 2a obtained from the
former solvent combination is shown in Figure 1. The
crystallographic data are listed in Table 1. The struc-
ture, [Ag3(µ-Cl)(PCNHCP)2]2NO3, consists of an unsym-
metrical molecular dication in which three Ag+ ions are
spanned by two PCNHCP ligands. Two of the Ag+ ions
are linked by a bridging Cl- anion, and the net +2
charge is balanced by two noninteracting nitrate ions.
The central Ag+ is bound to the two ligands via the NHC
functionality, whereas the other two Ag+ ions are bound
via the phosphine groups. The Ag+ ions are situated on
a noncrystallographic mirror plane, which renders the
two ligands chemically equivalent. As seen in Figure 1,
the gauche conformation of the ethylene spacers (dihe-
dral angles ) 54.35° and 51.13°) on the right-hand side
results in one short d10-d10 Ag1-Ag2 distance of
2.9281(14) Å, whereas the anti conformation of the
ethylene groups (dihedral angles ) 159.22° and 159.29°)
on the left-hand side precludes the formation of such
short contact between Ag1 and Ag3 (nonbonding dis-
tance ) 4.480 Å). The Ag2 and Ag3 are linked by the
Results and Discussion
Silver Compounds of PCNHCP. The NHC/phos-
phine ligand precursor, PCNHCP‚HCl, has been reported
by us recently.2a The reaction between a 1:1 molar
mixture of Ag2O and PCNHCP‚HCl in dichloromethane
has been shown to produce a silver carbene complex (1),
which is able to transfer its carbene moiety on to PdCl2
very readily, producing the [PdII(PCNHCP)Cl]Cl complex.2a
However, the formulation of this solid compound was
ambiguous, as it has been shown that formation of
either Ag(NHC)X (A), which contains both NHC and
chloride ligands coordinated to the silver, or [Ag-
(NHC)2]X (B), which contains two trans coordinating
NHC ligands, was possible in reactions of Ag2O with
imidazolium salt.2d,7 In addition, structures A and B are
indistinguishable by their NMR spectra. The initial
formulation of 1 was Ag(PCNHCP)Cl, containing dangling
phosphine groups.2a However, in further utilization of
this white solid as carbene transfer reagent, we noticed
that the molecular weight of 1 should be much heavier.
A reinvestigation on 1 dissolved in dichloromethane by
electrospray mass spectrometry revealed unambigu-
ously that 1 is a trinuclear silver compound containing
three silver and three chloride atoms with two PCNHC
P
ligands present. The peak at m/z 1114 corresponds to
the molecular ion [Ag3(PCNHCP)2Cl3]+. Peaks observed
at m/z 1379, 1272, 1093, 743, and 599 correspond to
molecular fragments [Ag3(PCNHCP)2Cl2]+, [Ag2(PCNHCP)2-
Cl2]+, [Ag2(PCNHCP)2Cl]+, [Ag(PCNHCP)2]+, [Ag2(PCNHCP)-
Cl]+, and [Ag(PCNHCP)]+, respectively. On the basis of
the molecular structure of its derivatives (vide infra),
the proposed structure of 1 is illustrated in Scheme 1.
It is conceivable that the extra chloride present in the
compound should come from the dichloromethane sol-
vent during the reaction.
Despite our attempts, we were not able to obtain
crystals of 1 with sufficient quality. We thought that
by preparation of derivatives of 1, X-ray structural
determination may become possible, which would pro-
(8) (a) Wang, H. M. J.; Lin, I. J. B. Organometallics 1998, 17, 972.
(b) Bildstein, B.; Malaun, M.; Kopacka, H.; Wurst, K.; Mitterbo¨ck, M.;
Ongania, K.-H.; Opromolla, G.; Zanello, P. Organometallics 1999, 18,
4325.
(9) (a) Scholl, M.; Ding, S.; Lee, C. W.; Grubbs, R. H. Org. Lett. 1999,
1, 953. (b) Jafarpour, L.; Hillier, A. C.; Nolan, S. P. Organometallics
2002, 21, 442.
(7) Tulloch, A. A. D.; Danopoulos, A. A.; Winston, S.; Kleinhenz, S.;
Eastham, G. J. Chem. Soc., Dalton Trans. 2000, 4499.
(10) Arnold, P. L.; Scarisbrick, A. C. Organometallics 2004, 23, 2519.

1694 Organometallics, Vol. 24, No. 7, 2005
Chiu and Lee
Figure 1. Thermal ellipsoid plot (30%) of cationic portion
of 2a with hydrogen atoms omitted for clarity. Selected
bond distances (Å) and angles (deg): Ag1-C1, 2.117(14);
Ag1-C33, 2.095(14); Ag1-Ag2, 2.9281(14); Ag2-P2, 2.472-
(4); Ag2-P3, 2.466(4), Ag2-Cl1, 2.664(3); Ag3-P1, 2.421-
(4); Ag3-P4, 2.418(4); Ag3-Cl1, 2.798(4); C1-Ag1-C33,
173.7(5), C1-Ag1-Ag2, 76.29(9); C33-Ag1-Ag2, 91.2(3);
P2-Ag2-Ag1, 106.10(9); P2-Ag2-Cl1, 114.27 (12), P2-
Ag2-P3, 124.08(12); P3-Ag2-Cl1, 119.37(12); P3-Ag2-
Ag1, 100.72(9); Ag2-Cl1-Ag3, 145.53(15); Ag1-Ag2-Cl1,
76.27(9); P1-Ag3-P4, 154.18(13); P1-Ag3-Cl1, 111.23-
(13); P4-Ag3-Cl1, 94.31(12).
Figure 2. Thermal ellipsoid plot (30%) of 2b with hydro-
gen atoms omitted for clarity. Selected bond distances (Å)
and angles (deg): Ag1-C1, 2.110(5); Ag1-C33, 2.110(5);
Ag1-Ag2, 3.0585 (15), Ag2-P2, 2.4571(18); Ag2-P3, 2.4432-
(16); Ag2-Cl1, 2.528(2); Ag3-P1, 2.428(2); Ag3-P4, 2.4194-
(19), C1-Ag1-C33, 173.07(19); C1-Ag1-Ag2, 90.98(13);
C33-Ag1-Ag2, 88.81(14); P2-Ag2-Ag1, 102.32(5); P2-
Ag2-Cl1, 117.44(6); P2-Ag2-P3, 122.16(6); P3-Ag2-Cl1,
119.74(6); P3-Ag2-Ag1, 104.67(5); Ag1-Ag2-Cl1, 69.47-
(6); P1-Ag3-P4, 139.62(6).
Table 1. Crystallographic Data for 2a and 2b
The structure obtained from the DMF/ether solvent
system is depicted in Figure 2. The crystallographic data
are listed in Table 1. The striking difference between
structures 2a and 2b is the incorporation of DMF sol-
vent molecules in the crystal lattice and one Ag+ ion
with coordinated phosphine groups is projected outward
such that, unlike 2a, the coordinating chloride is only
ligated to one Ag+ ion in 2b with a Ag2-Cl1 distance
of 2.528 (2) Å. The protruded Ag(3) is weakly coordi-
2a
2b
empirical formula
[C62H60Ag3ClN4P4]- [C62H60Ag3ClN4P4‚
2NO3
NO3‚0.5DMF]NO3‚
DMF
fw
1468.10
monoclinic
P21/n
1577.45
cryst syst
space group
a, Å
triclinic
P1h
18.543(8)
14.980(5)
23.226(8)
90
106.215(17)
90
6195(4)
273(2)
4
15.023(7)
15.734(8)
17.460(8)
65.55(3)
66.36(2)
87.31(3)
3406(3)
273(2)
2
b, Å
-
nated to a chelating NO3 ligand (Ag3-O2 ) 2.658 Å;
c, Å
R, deg
â, deg
γ, deg
V, Å3
Ag3-O3 ) 2.701 Å) and a DMF molecule (Ag3-O7 )
2.624 Å) refined to have 50% occupancy factor. There-
fore, the structure of the compound is described as a
trinuclear silver monocation with a noncoordinating nit-
rate anion, [Ag3(Cl)(NO3)(PCNHCP)(0.5DMF)]NO3‚DMF.
The nonbonding Ag1‚‚‚Ag3 distance of 4.863 Å becomes
much longer than that of 4.480 Å in 2a. Similar to the
structure 2a, the gauche conformation of the ethylene
spacers on the depicted right side of the cation (dihedral
angles ) 57.07° and 50.11°) affords a short Ag1-Ag2
distance of 3.0585(15) Å, which is, however, significantly
longer than that in 2a. In contrast, the dihedral angles
of the ethylene linkage on the depicted left side are
173.54° and 172.38°, which are significantly greater
than the corresponding angles of 159.22° and 159.29°
in 2a, as a consequence of the conformational flexibility
of the ethylene spacer in projecting the Ag3 atom out
and hence the absence of a µ-chloride bridge in 2b.
The observation of only two broad singlets in the 31P-
{1H} NMR spectrum of 2 indicates that 2a and 2b are
in rapid equilibrium at room temperature. At high
temperature, these two signals coalesce, which can be
explained by the fluxional interchange between 2a and
2a′ (2b and 2b′) due to the gauche/anti conformational
interchange of the two ethylene spacers, which renders
the two phosphorus atoms in PCNHCP equivalent (Scheme
T, K
Z
Dcalcd, Mg/m3
1.574
1.140
1.538
µ, mm-1
1.045
no. of data collected 34 462
21 227
15 042
901
0.0505
0.01420
no. of unique data
12 176
no. of params refined 715
R1 [I > 2σI]
wR2 (all data)
0.0709
0.2482
bridging Cl1 anion asymmetrically with a Ag2-Cl1
distance of 2.664(3) Å, Ag3-Cl1 distance of 2.798(4) Å,
and Ag-Cl-Ag angle of 145.53(15)°. The chemically
nonequivalent phosphorus atoms in PCNHCP are con-
sistent with the solution NMR data, which exhibit two
31P{1H} NMR signals. Interestingly, in 2a, each Ag+ ion
is in different coordination geometries. The Ag1 center
is in a T-shaped coordination geometry with the three
relevant angles 173.7(5)°, 86.3(3)°, and 91.2(3)°, whereas
the Ag2 center is in a distorted tetrahedral geometry
with the average of bond angles equal to 106.80°. The
Ag3 center is in a distorted trigonal planar geometry
with the sum of bond angles (154.18(13)°, 94.31(12)°,
111.23(13)°) of 359.72°.

Chemistry of the PCNHCP Ligand
Organometallics, Vol. 24, No. 7, 2005 1695
Scheme 3
Scheme 4
nonequivalence of the two phosphorus nuclei in PCNHCP.
The magnitude of the coupling constant (2JPP ) 31.3 Hz)
clearly suggests a cis disposition of phosphorus atoms
and therefore facial coordination geometry in 3. Only
two phosphorus signals instead of four are observed,
indicating the presence of a symmetry element in the
diruthenium complex (vide infra). In the 31C{1H} NMR
spectrum, the carbene resonance is observed at δ 174.5
3). The two signals do not resolve at -35 °C, however.
A similar trinuclear structure can be expected for 1, and
it is reasonable to suggest that the absence of the
chelating anion in 1 renders the exchange much faster
2
as a virtual triplet with JCP ) 21.6 Hz. Interestingly,
1
in the H NMR spectrum, seven different signals were
than in 2 and hence the observation of only a broad 31
P
observed for the ethylene protons, which span over a
wide range of chemical shifts from δ 1.0 to 5.7. Also, a
triplet corresponding to two phenyl protons is observed
at δ 5.42, which resonates at a remarkably higher field
than one of the CH signals at δ 5.72. The spectroscopic
data strongly imply that, in solution, the PCNHCP is
coordinated in a sterically demanding facial fashion with
some of the ethylene or phenyl protons localizing in the
anisotropic shielding and deshielding regions of the
phenyl rings.
An X-ray structural determination on single crystals
of 3, obtained by slow evaporation of an acetone/
dichloromethane solution of 3, was performed. A ther-
mal ellipsoid plot of the molecular cation is shown in
Figure 3 with crystallographic data and selected struc-
tural parameters in Tables 2 and 3, respectively.
Complex 3 exists as a cationic triply µ-Cl-bridged
diruthenium complex with an anionic chloride. The
triply halide-bridged bioctahedral architecture is a
recurring structure of remarkable stability and concep-
tual interest in ruthenium chemistry. Monodentate
phosphines and tripodal and linear tridentate phos-
phines are common supporting ligands in these diru-
thenium complexes.12 As predicted from the spectro-
scopic data, the two PCNHCP ligands coordinate to the
ruthenium centers in a facial mode. The two Ru-
(PCNHCP) fragments are positioned across the µ-Cl
bridges in a staggered conformation. A noncrystallo-
NMR signal at ambient temperature.2a
Synthesis and Characterization of fac-[Ru2(µ-
Cl)3(PCNHCP)2]Cl (3). While silver carbene transfer
reaction is a frequently used route for the preparation
of NHC complexes of late transition metals, such as
palladium,8 the majority of ruthenium NHC complexes
are typically prepared by trapping the NHC, preformed
or generated in situ from an appropriate imidazolium
salt in the presence of base, with a suitable Ru(II)
precursor.9 A recent article by Arnold et al. showed that
the carbene transfer reaction between AgL [L ) O-CPh-
(CH2{1-C[NCHCHNBut]}2) and RuCl2(PPh3)3 afforded
a Ru(III) complex, [RuIIILCl2(PPh3)]. The coproducts of
the reaction were PPh3 and metallic silver.10 We also
conducted a similar reaction by stirring a 1:1 molar
mixture of the silver carbene 1 and RuCl2(PPh3)3 in
dichloromethane at room temperature overnight (Scheme
4). In sharp contrast to the report by Arnold, a Ru(II)
compound, subsequently identified by the X-ray struc-
tural analysis as a triply halide-bridged diruthenium
complex, [Ru2(µ-Cl)3(PCNHCP)2]Cl (3), is produced. Also
the coproduct is, instead of Ag0, AgCl(PPh3)2.11 This
known compound is indentified by NMR spectra, which
were the same as those of an authentic sample. Because
of the ionic nature, complex 3 can easily be isolated from
the reaction mixture by complete removal of DMF and
then precipitation with THF, in which 3 is completely
insoluble, whereas AgCl(PPh3)2 dissolves readily. Simple
filtration affords the orange compound in good yields
(72%). Complex 3 appears to be quite robust in both
solution and solid state. In the 31P{1H} NMR spectrum,
an AX spin splitting pattern having two sets of doublet
at δ 43.4 and 48.5 is observed, reflecting the chemical
(12) See, for example: (a) Cotton, F. A.; Torralba, R. C. Inorg. Chem.
1991, 30, 2196. (b) Albinati, A.; Jiang, Q.; Ru¨egger, H.; Venanzi, L. M.
Inorg. Chem. 1993, 32, 4940. (c) Ohta, T.; Tonomura, Y.; Nozaki, K.;
Takaya, H.; Mashima, K. Organometallics 1996, 15, 1521. (d) Rhodes,
L. F.; Sorato, C.; Venanzi, L. M.; Bachechi, F. Inorg. Chem. 1998, 27,
604. (e) Mashima, K.; Nakamura, T.; Matsuo, Y.; Tani, K. J. Orga-
nomet. Chem. 2000, 607, 51. (f) Redwine, K. D.; Nelson, J. H.
Organometallics 2000, 19, 3054. (g) Doherty, S.; Newman, C. R.;
Hardacre, C.; Nieuwenhuyzen, M.; Knight, J. G. Organometallics 2003,
22, 1452.
(11) Uso´n, R.; Laguna, A. Organomet. Synth. 1986, 3, 322.

1696 Organometallics, Vol. 24, No. 7, 2005
Table 2. Crystallographic Data for 3, 4, 7, 8, and 9
Chiu and Lee
3
4
7
8
9
empirical formula
[C62H60Cl3N4P4-
Ru2]Cl
1328.96
monoclinic
P21/n
14.096(3)
18.891(4)
25.927(6)
90
92.846(4)
90
6896(3)
298(2)
4
1.280
0.723
37 974
13 512
716
0.0903
0.3160
C
32H30Cl2N2O-
[C41H40ClN4P2Ru]Cl‚
DMF
[C41H38ClN4P2Ru]Cl‚
DMF‚0.5(H2O)
902.77
monoclinic
P21/c
18.8238(7)
20.9699(8)
29.5630(10)
90
126.477(2)
90
C
31H30Cl3N2P2Ru‚
P2Ru‚ DMF
DMF
fw
765.59
monoclinic
P21/n
13.332(7)
12.287(6)
20.891(10)
90
95.538(8)
90
3406(3)
150(2)
4
1.493
0.748
18 584
7615
449
0.0390
0.1049
895.78
765.59
monoclinic
P21/n
13.332(7)
12.287(6)
20.891(10)
90
95.535(8)
90
3406(3)
298(2)
4
1.493
0.748
18 584
7615
449
0.0390
0.1049
cryst syst
space group
a, Å
monoclinic
C2/c
40.7001(14)
11.7146(4)
20.3929(7)
90
b, Å
c, Å
R, deg
â, deg
105.996(2)
90
γ, deg
V, Å3
9346.6(6)
150(2)
9383.4(6)
150(2)
T, K
Z
8
8
Dcalcd, Mg/m3
1.273
1.278
µ, mm-1
0.555
0.554
no. of data collected
no. of unique data
no. of params refined
R1 [I > 2σI]
wR2 (all data)
77 235
13 2276
19 455
10 180
487
1072
0.0856
0.0842
0.2992
0.2760
Table 3. Selected Bond Lengths (Å) and Angles
(deg) of 3
graphic C2 axis orthogonal to the Ru-Ru axis renders
the two halves chemically equivalent. The presence of
only a C2 rotation axis in the molecule means that 3 is
chiral and it crystallizes in the centrosymmetric space
group P21/n so that the two enantiomers are situated
across a center of inversion in the crystal lattice.
Venanzi et al. has shown that the binuclear complex
[Ru2(µ-Cl)2(ETP)2]Cl (ETP ) Ph2PCH2CH2P(Ph)CH2-
CH2PPh2) is a mixture in solution in which the central
phosphorus atoms of the linear triphosphine ligand can
be either eclipsed or staggered, producing the symmetric
isomer having Cs symmetry (ec-form) and the chiral
isomer having C2 symmetry (st-form), respectively.12b
Crystal structures of the ec-form were obtained, whereas
the st-form was only inferred by NMR spectroscopy. In
Ru1-C1
Ru1-P1
Ru1-P2
Ru1-Cl1
Ru1-Cl2
Ru1-Cl3
1.993(11)
2.269(3)
2.272(3)
2.528(3)
2.515(3)
2.497(3)
Ru2-C32
Ru2-P4
Ru2-P3
Ru2-Cl1
Ru2-Cl2
Ru2-Cl3
1.992(12)
2.272(3)
2.273(3)
2.509(3)
2.532(3)
2.494(3)
C1-Ru1-P1
C1-Ru1-P2
P1-Ru1-P2
C1-Ru1-Cl3
P1-Ru1-Cl3
P2-Ru1-Cl3
C1-Ru1-Cl2
P1-Ru1-Cl2
P2-Ru1-Cl2
Cl3-Ru1-Cl2
C1-Ru1-Cl1
P1-Ru1-Cl1
P2-Ru1-Cl1
Cl3-Ru1-Cl1
Cl2-Ru1-Cl1
C32-Ru2-P4
91.6(3)
83.2(4)
97.07(11)
87.3(4)
C32-Ru2-P3
P4-Ru2-P3
82.5(3)
97.77(11)
88.1(3)
94.15(10)
164.98(11)
169.8(3)
93.25(10)
105.79(11)
82.53(9)
97.9(3)
169.25(10)
88.65(11)
81.04(10)
76.65(9)
83.74(8)
83.53(8)
84.68(9)
C32-Ru2-Cl3
P4-Ru2-Cl3
P3-Ru2-Cl3
C32-Ru2-Cl1
P4-Ru2-Cl1
P3-Ru2-Cl1
Cl3-Ru2-Cl1
C32-Ru2-Cl2
P4-Ru2-Cl2
P3-Ru2-Cl2
Cl3-Ru2-Cl2
Cl1-Ru2-Cl2
Ru2-Cl1-Ru1
Ru1-Cl2-Ru2
Ru2-Cl3-Ru1
93.97(11)
165.64(10)
168.0(4)
92.90(11)
107.17(11)
81.33(10)
98.2(3)
169.22(11)
88.57(10)
82.10(9)
76.62(9)
91.5(4)
contrast, NMR spectroscopy and structural determina-
tion show that 3 exists only in the chiral st-form in both
solution and solid state. It is conceivable from the
structure that steric repulsion between the phenyl rings
prevents the formation of the sterically demanding ec-
form. Each ruthenium is in a distorted octahedral
geometry. All of the six Cl-Ru-P and Cl-Ru-C angles
(average 167.8°) are deviated significantly from the ideal
180°. The nonbonding RuII‚‚‚RuII distance of 3.362 Å is
in the usual range of RuII(µ-Cl)3RuII complexes.12,13 The
Ru-carbene distance is 1.99 Å, which is comparable to
that of a reported ruthenium complex with the same
donor set (2.02 Å).14 Notably, short intramolecular CH/π
hydrogen bonds are present in the structure, which are
consistent with the NMR data. The CH/π hydrogen
bond, a kind of hydrogen bond operating between a soft
acid CH and a soft base π-system, plays a significant
role in intramolecular interaction and supramolecular
(13) Yeomans, B. D.; Humphrey, D. G.; Heath, G. A. J. Chem. Soc.,
Dalton Trans. 1997, 4153, and references therein.
(14) Gischig, S.; Togni, A. Organometallics 2004, 23, 2479.
Figure 3. Thermal ellipsoid plot (30%) of cationic portion
of 3 with hydrogen atoms omitted for clarity.

Chemistry of the PCNHCP Ligand
Organometallics, Vol. 24, No. 7, 2005 1697
Scheme 5
Scheme 6
chemistry.15 The phenyl proton on C52 points toward
the face of the central imidazole ring, making short
CH/π hydrogen contacts (N3, 2.546 Å; C32, 2.686 Å; N4,
2.880 Å; C33, 2.957 Å; C34, 2.716 Å). Similarly, the
hydrogen on C21 makes short CH/π hydrogen contacts
with the other imidazole ring (N1, 3.002 Å; C1, 2.747
Å; N2, 2.553 Å; C3, 2.764 Å; C2, 3.054 Å). Indeed these
two hydrogen atoms are located only 2.49 and 2.46 Å
above the best plane of the neighboring imidazole rings,
respectively. The localization of the two chemically
equivalent hydrogen atoms over the π-cloud results in
an upfield shift of its NMR resonance. Hence, the signal
at δ 5.42 can be safely assigned to these hydrogen
atoms. For comparison, in the crystal structures of cis-
1,4-dihydro-4-tritylbiphenyl and its bromo derivative,
the short contacts between an aromatic CH and the best
plane of a phenyl ring were 2.55 and 2.48 Å, respec-
tively.16 The two corresponding CH protons were ob-
served at δ 6.3 and 6.15. It should be noted that the
NMR data and structural determination clearly indicate
that the crystal conformation of 3 is kept in solution.
We have shown that for the preparation of [Pd-
(PCNHCP)Cl]Cl the ligand precursor, PCNHCP‚HCl, can
react with PdCl2 without the need of base.2a Consistent
with this previous finding, PCNHCP‚HCl can similarly
react with RuCl2(PPh3)3 without base at 90 °C in DMF,
affording 3 (Scheme 5). However, this synthetic route
is not as clean as the silver carbene transfer reaction
because in situ NMR study shows that minor unidenti-
fied coproducts with phosphorus signals δ 10-22 were
produced. Nevertheless, recrystallization of the crude
product with dichloromethane/THF gives pure 3 in 62%
of yield.
three broad signals corresponding to the eight CH2
protons are observed at δ 2.67, 4.11, and 4.81 with a
2:1:1 integration ratio. The broadening of these signals
can be similarly attributed to the involvement of a
dynamic interconversion between left- and right-twisted
forms in solution observed in Pd(PCNHCP) complexes.2a
Similar to what we have observed for the Pd(PCNHCP)
complexes, the fluxionality is not resolved down to -60
°C. In its 13C{1H} NMR spectrum, the coordinating Ct
O ligand gives a triplet at δ 199.6 with a 2JCP coupling
constant of 13.2 Hz, which indicates that the carbonyl
ligand is cis to the two phosphorus atoms. The carbene
signals also appear as a triplet at δ 169.1 with the 2JCP
coupling constant of 11.0 Hz, the magnitude of which
is significantly smaller than the corresponding value of
21.6 Hz in 3 (vide supra). The question whether the
carbonyl ligand is trans or cis to the carbene donor was
answered by structural determination. Crystals of 4
were readily obtained by vapor diffusion of diethyl ether
into a DMF solution. The crystallographic data are
summarized in Table 2. The molecular structure of 4 is
shown in Figure 4. The ruthenium center is in an
Reactivity of fac-[Ru2(µ-Cl)3(PCNHCP)2]Cl (3). On
refluxing a 1,2-dichloroethane solution of 3 under CO
atmosphere, RuCl2(CO)(PCNHCP) (4) was obtained
(Scheme 6). In sharp contrast to 3, the 31P{1H} NMR
spectrum of 4 consists of only a singlet at δ 10.9,
indicating the equivalence of the two phosphorus atoms
in the PCNHCP ligand by the presence of symmetry. It
has been shown that the chemical shifts of the phos-
phorus atoms are diagnostic for the coordination modes
of linear tridentate phosphine ligands.17,18 Because of
the remarkable trans influence of the phosphine ligands,
the phosphorus nuclei of the mer complex typically
resonate at higher field than those of the facial isomers.
The high-field resonance of the 31P signal compared with
those in 3 strongly indicates a meridional chelation
Figure 4. Thermal ellipsoid plot (30%) of 4 with hydrogen
atoms omitted for clarity. Only the major orientation (0.60
site occupancy) is shown. Selected bond distances (Å) and
angles (deg) of the major orientation: Ru1-C1, 2.038(3);
Ru1-C32, 1.792(9); Ru1-Cl1, 2.4846(12); Ru1-Cl2, 2.432-
(3); Ru1-P1, 2.3737(13); Ru1-P2, 2.3780(13); C32-Ru1-
Cl2, 175.3(4); C1-Ru1-Cl1, 177.35(9); P1-Ru1-P2, 178.20-
(3); C1-Ru1-P1, 91.02(9); C1-Ru1-P2, 90.55(9); C1-
Ru1-C32, 89.4(4); C1-Ru1-Cl2, 94.77(9); Cl1-Ru1-P1,
86.34(3); Cl1-Ru1-P2, 92.10(3); Cl1-Ru1-C32, 89.4(4);
Cl1-Ru1-Cl2, 94.77(9).
1
mode of PCNHCP in 4. Also, in its H NMR spectrum,
(15) Nishio, M. CrystEngComm 2004, 6, 130.
(16) Grossel, M. C.; Cheetham, A. K.; Hope, D. A. O.; Weston, S. C.
J. Org. Chem. 1993, 58, 6654.
(17) Meek, D. W.; Mazanec, T. J. Acc. Chem. Res. 1981, 14, 266.
(18) Bianchini, C.; Innocenti, P.; Peruzzini, M.; Romerosa, A.;
Zanobini, F. Organometallics 1996, 15, 272.

1698 Organometallics, Vol. 24, No. 7, 2005
Chiu and Lee
octahedral geometry with the PCNHCP ligand chelating
in a meridional fashion. One of the chloride ligands is
trans to the carbene moiety, whereas the other chloride
(CtO) is disordered between the two apical sites in a
60:40 ratio. Hence, the two chlorides are cis to each
other with the carbonyl ligand also cis to the carbene
moiety. Similar to the reported palladium complexes of
PCNHCP,2a the ligand is twisted to one side, forming an
overall chiral environment of the complex. The twist
angle between the best planes defined by the imidazole
ring and the equatorial plane is 28.9°. Notably, the
disorder model implies that there are two overlapping
diastereomers present in the asymmetric unit of the
centrosymmetric P21/n unit cell. Their corresponding
enantiomers are present about centers of inversion in
the crystal lattice. In solution, it is the rapid intercon-
version between the left- and right-twisted forms that
leads to the broadening of ethylene signals and single
phosphorus resonance observed. In the major orienta-
tion, the Ru-carbene distance is 2.038(3) Å, which is
longer than that of 1.99 Å in 3, whereas the Ru-CO
distance is significantly shorter (1.792(9) Å). The Ru-
Cl distance trans to the carbene (2.4846(12) Å) is slightly
longer than that trans to Cl (2.432(3) Å), which can be
attributed to the bigger trans influence exerted by the
NHC moiety.
Recently, a number of ruthenium hydride complexes
with NHC as supporting ligand have been reported.4,19
But it is rather surprising that they are generally
prepared by reactions between preformed ruthenium
hydride precursors and NHC ligands. So far, none of
them are prepared from reactions of ruthenium halide
complexes with hydride transfer reagent, such as NaBH4,
which is a common synthetic route for other ruthenium
hydride complexes.20 We carried out a reaction by
stirring a mixture of 4 with excess NaBH4 in ethanol,
which results in the isolation of the ruthenium hydride
RuHCl(CO)(PCNHCP) (5). The 31P{1H} NMR spectrum
reveals a single resonance at δ 9.56, indicating the
meridional chelation of PCNHCP. The presence of the
hydride ligand is clearly indicated by the high-field
triplet at δ -14.8 (2JHP ) 19.3 Hz). The integral ratio
indicates 5 is a monohydride compound. Although the
poor solubility of 5 precludes the acquisition of its 13C
NMR spectrum, the presence of the CtO ligand is
confirmed by the presence of an intense IR absorption
at 1928.6 cm-1. This lower frequency number compared
with that in 4 is in accord with the more electron-
donating nature of hydride than chloride. On the basis
of the NMR data, three possible structures of complex
5 can be proposed. The possibility of the hydride trans
to the CtO is precluded first because such a hydride
would be significantly upfield shifted and appear in the
range δ -3 to -8. For example, the hydride signal is at
δ -3.75 for Ru(IMes)2(CO)2(OH)H,19a δ -5.15 for RuHCl-
(CO)2(P(i-Pr)3)2,21 and δ -3.68 to -7.25 for [RuH(CO)-
Scheme 7
(PP)2]+ (PP ) dppm, dppe, dppp).22 The hydride in 5
should be trans to the chloride, rather than trans to the
carbene, as its chemical shift (δ -14.8) is close to those
of related hydride structures; δ ) -13.65 for RuHCl-
(CO)(PMP) (PMP ) 2,6-(Ph2PCH2)2C5H3N)20b and δ )
-13.5 to -15.4 for RuHCl(CO)(PPh3)(PP) (PP ) dppm,
dppp).22
On refluxing a 1,2-dichlorethane solution of 3 with
excess phenylacetylene, a vinylidene complex, RuCl2(d
CdCHPh)(PCNHCP) (6), is produced. There is only a
single 31P resonance observed at δ 7.00, indicating the
meridional chelation of PCNHCP. The presence of a
vinylidene ligand is characterized by the presence of the
vinylidene proton observed as a triplet at δ 3.52 (4JHP
) 3.8 Hz), the low-field metal bonded vinylidene carbon
signal at δ 348.1 (2JCP ) 16.1 Hz), and its â-carbon
signal at δ 108.3. The Ru-carbene signal is observed
as a triplet with a smaller coupling constant of JCP
2
)
10.6 Hz. Similar to 4, three broad signals for the
ethylene protons at δ 2.64, 4.18, and 4.70 (integration
ratio ) 2:1:1) are observed, indicating the fluxionality
of the complex. Unfortunately, we were not able to
obtain crystals for the structural determination. But
based on related vinylidene structures of linear triden-
tate phosphine complexes,18,23 presumably the vi-
nylidene ligand in 6 is trans to the carbene moiety with
two mutually trans chloride ligands. Similar to other
reported vinylidene complexes,24 complex 6 is air-stable
in the solid state but slowly undergoes oxidative cleav-
age (4-5 days) to give the carbonyl complex 4 and
benzaldehyde. The transformation can be speeded up
by refluxing a solution of 6 in the air overnight.
Complex 3 reacts with excess pyridine in DMF to
produce a cationic ruthenium bis(pyridine) compound,
[RuCl(py)2(PCNHCP)] (7) (Scheme 7). The 31P{1H} NMR
spectrum of the yellow solid in CDCl3 shows a major
single resonance at δ 9.56, suggesting a meridional
chelation of the PCNHCP ligand around the metal center.
However, even with a prolonged reaction time, the set
(19) (a) Jazzar, R. F. R.; Bhatia, P. H.; Mahon, M. F.; Whittlesey,
M. K. Organometallics 2003, 22, 670. (b) Ho, V. M.; Watson, L. A.;
Huffman, J. C.; Caulton, K. G. New J. Chem. 2003, 27, 1446. (c) Abdur-
Rashid, K.; Fedorkiw, T.; Lough, A. J.; Morris, R. H. Organometallics
2004, 23, 86.
(20) See, for example: (a) Jia, G.; Meek, D. W.; Gallucci, J. C. Inorg.
Chem. 1991, 30, 403. (b) Jia, G.; Lee, H. M.; Williams, I. D. Organo-
metallics 1997, 16, 3941. (c) Albertin, G.; Antoniutti, S.; Bacchi, A.;
D’Este, C.; Pelizzi, G. Inorg. Chem. 2004, 43, 1336.
(21) Esteruelas, M. A.; Werner, H. J. Organomet. Chem. 1986, 303,
221.
(22) Santo, A.; Lo´pez, J.; Motoya, J.; Noheda, P.; Romero, A.;
Echavareen, A. M. Organometallics 1994, 13, 3605.
(23) Katayama, H.; Wada, C.; Taniguchi, K.; Ozawa, F. Organome-
tallics 2002, 21, 3285.
(24) (a) Bruce, M. I.; Swincer, A. G.; Wallis, R. C. J. Organomet.
Chem. 1979, 171, C5. (b) Oro, L. A.; Ciriano, M. A.; Campo, M.; Foces-
Foces, C.; Cano, F. H. J. Organomet. Chem. 1985, 289, 117 (c) Mezzetti,
A.; Consiglio, G.; Morandini, F. J. Organomet. Chem. 1992, 430, C15.
(d) Yang, S.-M.; Chan, M. C.-W.; Cheung, K.-K.; Che, C.-M.; Peng, S.-
M. Organometallics 1997, 16, 2819.

Chemistry of the PCNHCP Ligand
Organometallics, Vol. 24, No. 7, 2005 1699
Figure 6. Thermal ellipsoid plot (30%) of cationic portion
of 8 (one of the two independent molecules in the asym-
metry unit) with hydrogen atoms omitted for clarity.
Selected bond distances (Å) and angles (deg): Ru1-C1,
2.040(6); Ru1-Cl1, 2.4791(14); Ru1-P1, 2.2785(15); Ru1-
P2, 2.3155(15); Ru1-N3, 2.127(5); Ru1-Cl1, 2.4791(14);
C1-Ru1-N4, 173.4(2); N3-Ru1-P2, 167.97(13); P1-Ru1-
Cl1, 171.00(5); C1-Ru1-N3, 97.5(2); C1-Ru1-P2, 81.53-
(16); C1-Ru1-P1, 89.75(17); C1-Ru1-Cl1, 94.84(17); N4-
Ru1-N3, 75.96(18); N4-Ru1-P2, 104.72(13); N4-Ru1-
Cl1, 83.53(13); N4-Ru1-P1, 91.03(13).
Figure 5. Thermal ellipsoid plot (30%) of cationic portion
of 7 with hydrogen atoms omitted for clarity. Selected bond
distances (Å) and angles (deg): Ru1-C1, 2.027(7); Ru1-
Cl1, 2.4996(18); Ru1-N3, 2.136(6); Ru1-N4, 2.131(6);
Ru1-P1, 2.3458(18); Ru1-P2, 2.3948(19); C1-Ru1-Cl1,
175.9(2); N3-Ru1-N4, 177.8(2); P1-Ru1-P2, 175.43(7);
C1-Ru1-P1, 91.0(2); C1-Ru1-P2, 90.5(2); C1-Ru1-N3,
86.6(3); C1-Ru1-N4, 91.2(3); Cl1-Ru1-P1, 88.93(6); Cl1-
Ru1-P2, 89.90(6); Cl1-Ru1-N3, 89.26(17); Cl1-Ru1-N4,
92.89(17).
of two doublets due to the starting complex 3 always
remains about 8% according to the integral ratio. Proton
signals due to the free pyridine are also observed.
Interestingly, with addition of a few drops of pyridine
inside the NMR tube, the phosphorus signals due to 3
disappear completely, resulting in a clean spectrum of
7. The observation is consistent with an equilibrium
existing between 3 and 7. When dissolved in solution,
a small fraction of 7 undergoes pyridine dissociation to
re-form 3. Complex 7 is quite air-sensitive in chlorinated
solvent. When exposed to air, a dichloromethane solu-
tion of 7 will be oxidized to a RuIIICl3 complex (vide
infra). Crystals of 7 were successfully obtained by vapor
diffusion of diethyl ether into a DMF solution. The
crystallographic data are reported in Table 2. The
ruthenium center is in an octahedral geometry with the
PCNHCP ligand coordinating in meridional mode (Figure
5). The two pyridine ligands are in trans positions to
each other. The complex is symmetry-related by the
presence of a noncrystallographic C2 along the C‚‚‚Ru‚
‚‚Cl axis. The twist angle between the imidazole ring
and the equatorial plane is 27.9°, which is similar to
that in 4. The two pyridine rings are staggered, making
an interplanar angle of 53.6°. Interestingly, while
examples of trans-Ru(py)2 complexes with tridentate/
tetradentate nitrogen donors are known,25 complex 7
appears to be the first trans-Ru(py)2 containing triden-
tate phosphorus donors.
It appears that PCNHCP can adopt both fac and mer
chelation modes. The trans disposition of pyridines in
7 prompts us to react 3 with 2,2′-bipyridine because it
will enforce a cis chelation of the two pyridine rings,
which may lead to a structural change from meridional
to facial geometry. Reaction of 3 with 2,2′-bipyridine
produces cleanly the red complex [RuCl(bipy)(PCNHCP)]-
Cl (8). Similar to 3, the 31P{1H} NMR display an AX
splitting pattern of two doublets at δ 38.5 and 42.3 with
2
a Jpp coupling constant of 29.4 Hz. The CH protons of
the ethylene spacers are also spread out into six signals
spanning a range from δ 2.58 to 5.72. Obviously, similar
to 3, the PCNHCP also adopts a facial chelation. In situ
NMR experiments shows that 8 can also be formed by
reacting the mer complex 7 with excess 2,2′-bipyridine
at elevated temperature.
The stereochemistry of 8 was confirmed by structural
determination. Crystals were obtained by vapor diffu-
sion of diethyl ether into a DMF solution of 8. The
crystallographic data are reported in Table 2. The
structure is solved in the space group P21/c with the
presence of two independent molecules in the asym-
metric unit. The geometric parameters of the two
molecules are almost identical, and so only one set will
be discussed in the following text. As depicted in the
Figure 6, which shows the thermal ellipsoid plot of the
cationic portion, the ruthenium center is coordinated to
a PCNHCP, a 2,2′-bipyridine, and a chloride ligand. The
PCNHCP ligand is chelated in facial mode, consistent
with the NMR data, and the coordinated chloride is
trans to a PPh2 group. The resultant coordination
environment around the ruthenium center is, similar
to that in 3, a distorted octahedral geometry with the
(25) (a) Hua, X.; Shang, M.; Lappin, A. G. Inorg. Chem. 1997, 36,
3735. (b) Collman, J. P.; Brauman, J. I.; Fitzgerald, J. P.; Sparapany,
J. W.; Ibers, J. A. J. Am. Chem. Soc. 1998, 110, 3486. (c) Stern, C.;
Franceschi, F.; Solari, E. Floriani, C.; Re, N.; Scopelliti, R. J. Orga-
nomet. Chem. 2000, 593, 86. (d) Miller, J. A.; Hennessy, E. J.; Marshall,
W. J.; Scialdone, M. A.; Nguyen, S. T. J. Org. Chem. 2003, 68, 7884.

1700 Organometallics, Vol. 24, No. 7, 2005
Chiu and Lee
Table 4. Catalytic Transfer Hydrogenation of
Ketones with 2-Propanol Catalyzed by 3a
entry cat. mol %
base
substrate
time, h yield, %
1
2
0.1
KOBut cyclohexanone
KOBut cyclohexanone
KOBut cyclohexanone
0.5
1
91
0.1
90
3
0.1
0.1
2
98
96
trace
77
85
4
KOH
cyclohexanone
2
2
24
3
4.5
3
24
12
24
24
5
0.01
0.01
0.1
KOBut cyclohexanone
KOBut cyclohexanone
KOBut acetophenone
KOBut acetophenone
KOBut acetophenone
KOBut acetophenone
KOBut benzophenone
KOBut benzophenone
KOBut benzophenone
6
7
8
0.1
100
5
9
0.01
0.01
0.1
11
12
13
14
51
58
0.1
0.01
94
trace
a Conditions: ketone, 1 mmol; base, 10 mol %; catalyst, 0.1 or
0.01 mol %; 2-propanol, 10 mL; temp, 80 °C. Yield determined by
1H NMR spectroscopy.
Figure 7. Thermal ellipsoid plot (30%) of 9 with hydrogen
atoms omitted for clarity. Selected bond distances (Å) and
angles (deg): Selected bond distances (Å) and angles
(deg): Ru1-C1, 2.050(4); Ru1-Cl1, 2.3604(14); Ru1-Cl2,
2.3751(15); Ru1-Cl3, 2.4387(14); Ru1-P1, 2.3964(14);
Ru1-P2, 2.3893(14); C1-Ru1-Cl3, 177.62(12); Cl1-Ru1-
Cl2, 171.36(5); P1-Ru1-P2, 178.50(4); C1-Ru1-P1, 90.39-
(12); C1-Ru1-P2, 91.03(12); C1-Ru1-Cl1, 86.38(13); C1-
Ru1-Cl2, 85.26(12); Cl3-Ru1-P1, 91.94(4); Cl3-Ru1-P2,
96.64(4); Cl3-Ru1-Cl1, 93.10(5); Cl3-Ru1-Cl2, 95.33(5).
Catalytic Transfer Hydrogenation of Ketones.
Ruthenium complexes of both NCN and PCP pincer
ligands have been shown to be efficient catalysts in the
transfer hydrogenation of ketones.26 Recently, new
catalysts of ruthenium CNC-pincer bis(NHC) complexes
are reported.5,6 On the other hand, bimetallic ruthenium
compounds, such as [{RuX(µ-X)(CO)(PP)}2] (PP ) dppf,
dippf; X ) Cl, Br)27 and [Ru2(µ-Cl)3(η4-1,2,3,4-Me4-
NUPHOS)2]X (X ) Cl, SbF6),28 are also shown to be
highly active in the catalytic reaction. Inspired by these
reports, we were interested in investigating whether the
bimetallic ruthenium NHC/phosphine complex 3 is also
an efficient catalyst. A preliminary investigation (un-
optimized conditions) was carried out, which shows that
3 catalyzes the hydrogenation of ketones via hydrogen
transfer from 2-propanol in the presence of base (Table
4). Entry 1 shows that a 0.1 mol % of 3 can catalyze the
conversion of cyclohexanone to cyclohexanol with KOBut
as base in 30 min, affording a 91% yield. Replacement
with KOH as base gives identical results (entries 3 and
4). Prolongation of reaction time is needed if the catalyst
loading is reduced to 0.01 mol % (entries 5 and 6). With
acetophenone as substrate, a 0.1 mol % catalyst loading
gives quantitative conversion in 4.5 h (entry 8); a much
longer reaction time (24 h) is needed for benzophenone
to produce a 94% yield (entry 13).
average Cl1-Ru1-P1, N3-Ru1-P2, and N4-Ru1-C1
angle equal to 170.79°. The Ru-N bond trans to the
carbene (2.178(5) Å) is slightly longer than that trans
to a phosphorus (2.127(5) Å). The Ru-P bond trans to
a nitrogen (2.3155(15) Å) is longer compared with that
trans to a chloride (2.2785(15) Å). A noticeable feature
of the structure is that one of the phenyl rings of the
PPh2 group is parallel to the 2,2′-bipyridine. The inter-
planar distance of 3.22 Å suggests an intramolecular
π-π stacking. A comparison of 7 and 8 clearly indicates
that the cis chelation of the rigid 2,2′-bipyridine causes
a larger steric effect than two free pyridines and PCNHC
P
is able to accommodate the additional steric require-
ment by switching from the sterically demanding me-
ridional to the less demanding facial chelation mode.
Crystal Structure of mer-[RuIIICl3(PCNHCP)] (9).
As mentioned above, mer,trans-[RuCl(py)2(PCNHCP)] in
solution is sensitive to air. In fact, an attempted
crystallization of 7 from DMF in air resulted in sole
production of green crystals, mer-[RuIIICl3(PCNHCP)] (9),
which was successfully determined by X-ray diffraction.
The crystal data are listed in Table 2. The ruthenium
is in an octahedral geometry with PCNHCP chelating in
meridional mode (Figure 7). The twist angle between
the imidazole ring and the equatorial plane is 28.6°,
essentially the same as those in 4 and 7. The longer
Ru-Cl distance trans to the carbene (2.4387(14) Å)
compared with those of the two mutually trans chlorides
(2.3751(15) and 2.3604(14) Å) is due to the bigger trans
influence of carbene donor. Ru(II) NHC complexes,
because of their importance in catalysis,1c,3-6 are receiv-
ing much attention, and numerous crystal structures
of Ru(II) NHC complexes have been reported. In con-
trast, only until recently has the first example of a Ru-
(III) NHC complex been prepared.10 To the best of our
knowledge, complex 9 appears to be the first structur-
ally characterized Ru(III) complex bearing a NHC
moiety. Despite the smaller ionic radius of Ru(III), the
Ru-carbene bond distance in 9, 2.050(4) Å, is similar
to those found in 4, 7, and 8.
Conclusions
The silver PCNHCP complex 1 is identified by electro-
spray mass spectroscopy as a trinuclear compound, [Ag3-
(µ-Cl)(PCNHCP)2]Cl2. Anion exchange of 1 with AgNO3
affords 2, which crystallizes into two forms, [Ag3(µ-Cl)-
(PCNHCP)]2NO3 (2a) and [Ag3(Cl)(NO3)(0.5DMF)-
(PCNHCP)]NO3‚DMF (2b), from different solvent com-
binations. In both forms, short Ag‚‚‚Ag interactions are
present. In 2a, a µ-Cl bridging two silver centers exists,
whereas in 2b, such µ-Cl bridge is absent because of a
weak coordination of NO3- ion to one of the silver ions.
In solution, fast interconversion between 2a and 2b
(26) (a) Dani, P.; Karlen, T.; Gossage, R. A.; Gladiali, S.; van Koten,
G. Angew. Chem., Int. Ed. 2000, 39, 743. (b) Albrecht, M.; Kocks, B.
M.; Spek, A. L.; van Koten, G. J. Organomet. Chem. 2001, 624, 271.
(c) van der Boom, M. E.; Milstein, D. Chem. Rev. 2003, 103, 1759.
(27) Cadierno, V.; Crochet, P.; D´ıez, J.; Garc´ıa-Garrido, S. E.;
Gimeno, J.; Garc´ıa-Granda, S. Organometallics 2003, 22, 5226.
(28) Doherty, S.; Newman, C. R.; Hardacre, C.; Nieuwenhuyzen, M.;
Knight, J. G. Organometallics 2003, 22, 1452.

Chemistry of the PCNHCP Ligand
Organometallics, Vol. 24, No. 7, 2005 1701
and 75.48, respectively, on a Bruker AV-300 spectrometer.
occurs. Although the structure of 1 is not available, it
can be anticipated that 1 should adopt a structure
similar to 2a and 2b. The exchange of chloride anions
in 1 with nitrate anions apparently slows the fluxional
exchange, which renders the two halves of PCNHCP in
2a and 2b nonequivalent.
1
Chemical shifts for H and 13C spectra were recorded in ppm
relative to residual protons of CDCl3 (1H: δ 7.24; 13C: δ 77.0)
and DMSO-d6 (1H: δ 2.50; 13C: δ 39.5). Elemental analyses
were performed on a Heraeus CHN-OS-Rapid elemental
analyzer at Instrument Center, National Chung Hsing Uni-
versity, Taiwan.
Unlike the common preparation of ruthenium(II)
NHC complexes, we successfully employ a silver carbene
transfer reaction between 1 and RuCl2(PPh)3, affording
the pure diruthenium(II) complex 3 in good yield. The
nonredox nature of this transfer reaction is remarkably
different from the reported reaction in which the car-
bene transfer is coupled with oxidation of ruthenium-
(II).10 This shows that the preparation of divalent
ruthenium NHC complexes via silver carbene transfer
is also a feasible synthetic route. Consistent with our
previous findings, 3 can be produced by reaction of
PCNHCP with RuCl2(PPh)3 without the necessity of base.
The structural analysis on 3 reveals the formation of a
novel triply µ-Cl-bridged diruthenium complexes in
which the PCNHCP ligands coordinate to the Ru centers
in a facial manner. Obviously, the formation of the µ-Cl
bridge enables each ruthenium center to have a formally
18e configuration. However, because of the steric bulki-
ness, the formation of such diruthenium complexes is
not possible if the PCNHCP ligand is in meridional mode.
Among the two possible facial chelating isomers, ec-form
and st-form, and because of steric reasons, 3 adopts
solely the latter structure both in solution and in the
solid state.
Preparation of [Ag3(µ-Cl)(PCNHCP)2]Cl2 (1). 1 was pre-
pared according to the literature procedure.2a MS (ES+): m/z
1414 [Ag3(PCNHCP)2Cl3]+ (M), 1379 [Ag3(PCNHCP)2Cl2]+, 1272
[Ag2(PCNHCP)2Cl2]+, [Ag2(PCNHCP)2Cl]+, 1093 [Ag(PCNHCP)2]+,
743 [Ag2(PCNHCP)Cl]+, 599 [Ag(PCNHCP)]+.
Preparation of [Ag3Cl(PCNHCP)2](NO3)2 (2). To a mixture
of 1 (140 mg, 0.12 mmol) and AgNO3 (36 mg, 0.21 mmol) was
added 10 mL of methanol. The solution was heated under
reflux for 4 h and was then passed through a small plug of
Celite. The solvent was pumped dry under vacuum. Upon
addition of diethyl ether, a colorless precipitate was formed,
which was filtered on a frit and dried under vacuum. Yield:
52 mg, 33%. Anal. Calcd for C62H60Ag3ClN6O6P4: C, 50.72; H,
4.12; N, 5.72. Found: C, 50.75; H, 4.21; N, 5.70. Mp: 170-
1
172 °C. H NMR (CDCl3): δ 3.06 (br s, 8H, CH2), 4.61 (br s,
8H, CH2), 6.42 (br s, 4H, imi-CH), 7.18-7.45 (m, 40H, Ph-H).
13C{1H} NMR (CDCl3): δ 29.4 (CH2), 49.5 (CH2), 121.6 (imi-
CH); 129.0, 130.6, 130.7, 132.8 (Ph-CH), the carbene carbon
was not observed. 31P{1H} NMR (CDCl3): δ -3.1 (br s), 0.6
(br s). Single crystals of 2a and 2b were obtained by slow
diffusion of diethyl ether into an acetonitrile and DMF solution
of 2, respectively.
Preparation of fac-[Ru2(µ-Cl)3(PCNHCP)2]Cl (3). Method
A. Complex 1 (366 mg, 0.26 mmol) was dissolved in dichlo-
romethane (10 mL), and to this solution was added RuCl2-
(PPh3)3 (552 mg, 0.58 mmol). The solution was allowed to stir
overnight at ambient temperature, which was then passed
through a small plug of Celite. The solvent was pumped dry
under reduced pressure. Upon addition of THF, an orange solid
was formed, which was filtered on a frit and dried under
vacuum. Yield: 249 mg, 72%. Anal. Calcd for C62H60Cl4N4P4-
Ru2: C, 56.03; H, 4.55; N, 4.22. Found: C, 56.00; H, 4.53; N,
The ability of PCNHCP to accommodate the steric
requirement is demonstrated in reactions of fac com-
plexes 3 with CO, phenylacetylene, and pyridine, which
result in the formation of mononuclear mer complexes
4, 6, and 7. The structural determinations show that
the central imidazole rings in the mer complexes are
twisted from the equatorial planes. We have previously
shown that in Pd(PCNHCP) complexes a wide range of
twisting of the imidazole ring from the equatorial plane
(twist angle ) 27-49°) is possible, and theoretical
calculation has shown that the rotation barrier about
the Pd-carbene bond is indeed very small.2a However,
in Ru(PCNHCP) complexes, the twist angles observed are
limited to 28-29°, which can be attributed to the fact
that the presence of axial ligands obscures the twisting
to a limited extent. The relatively sharp NMR signals
for the ethylene protons observed in fac complexes, 3
and 8, indicate that the facial coordination mode is
conformationally more rigid, whereas in mer complexes
4-7, the broad NMR signals indicate that the ethylene
spacers are flexible, which enables fast interconversion
between the left- and right-twist forms. Reactions of 3
1
4.30. Mp: 228-230 °C. H NMR (CDCl3): δ 1.00 (t, J ) 13.0
Hz, 1H, CH), 2.44 (t, J ) 13.0 Hz, 1H, CH), 2.65 (m, 1H, CH),
2.79 (m, 1H, CH), 4.26-4.41 (m, 2H, CH), 4.37 (q, J ) 13.4
Hz, 1H, CH). 5.42 (t, J ) 7.5 Hz, 2H, Ph-H), 5.72 (br, 1H, CH),
6.81-7.30 (m, 16H, Ph-H and imi-H), 7.40 (t, J ) 7.1 Hz, 2H,
Ph-H), 7.67 (t, J ) 8.9 Hz, 2H, Ph-H), 8.19 (t, J ) 9.2 Hz, 2H,
Ph-H). 13C{1H} NMR (CDCl3): δ 23.5 (d, 1JCP ) 31.6 Hz, PCH2),
31.9 (d, 1JCP ) 35.1 Hz, PCH2), 46.6 (d, 2JCP ) 58.8 Hz, NCH2),
122.0-140.7 (aromatic), 174.5 (virtual t, 2JCP ) 21.6 Hz, RuC).
31P{1H} NMR (CDCl3): δ 43.4 (d, 2JPP ) 31.3 Hz), 48.5 (d, 2JPP
) 31.3 Hz). Single crystals were obtained by slow evaporation
of an acetone/dichloromethane solution of 3.
Method B. A mixture of PCNHCP‚HCl (188 mg, 0.35 mmol)
and RuCl2(PPh3)3 (340 mg, 0.35 mmol) in 10 mL of DMF was
heated at 90 °C overnight. After the reaction, the solvent was
removed completely under vacuum. To the residue was added
20 mL of dichloromethane, and the solution was then filtered
through a plug of Celite. The solvent was removed again under
vacuum. Upon addition of THF, a solid was formed, which was
filtered and collected on a frit. Recrystallization of this crude
product with dichloromethane/THF gave pure 3. Yield: 146
mg, 62%.
or 4 with 2,2′-bipyridine further confirm that PCNHC
P
can accommodate the extra steric requirement by
switching readily from facial to meridional coordination
mode.
Preparation of mer,cis-RuCl2(CO)(PCNHCP) (4). A solu-
tion of 3 (250 mg, 0.19 mmol) in 20 mL of 1,2-dichloroethane
was bubbled with CO and heated under reflux overnight. The
solution was then allowed to pass through a small plug of
Celite. The solvent was pumped dry under reduced pressure.
Upon addition of n-hexane, a white solid was formed, which
was filtered on a frit and dried under vacuum. Yield: 200 mg,
77%. Anal. Calcd for C32H30Cl2N2OP2Ru2: C, 55.50; H, 4.37;
N, 4.05. Found: C, 55.48; H, 4.31; N, 4.00. Mp: 205-207 °C.
1H NMR (CDCl3): δ 2.67 ((br s, 4H, CH2), 4.11 (br, 2H, CH2),
Experimental Section
General Procedures. All reactions were performed under
a dry nitrogen atmosphere using standard Schlenk techniques.
All solvents used were purified according to standard proce-
dures.29 1H and 13C{1H} NMR spectra were recorded at 300.13
(29) Armarego, W. L. F.; Chai, C. L. L. Purification of Laboratory
Chemicals, 5th ed.; Elsevier Science: Burlington, 2003.

1702 Organometallics, Vol. 24, No. 7, 2005
Chiu and Lee
4.81 (br, 2H, CH2), 6.87 (s, 2H, imi-H), 7.24-7.40 (m, 14H,
Ph-H), 7.97-8.06 (m, 6H, Ph-H). 13C{1H} NMR (CDCl3): δ 25.9
filtered on a frit and dried under a stream of nitrogen. Yield:
47 mg, 76%. Anal. Calcd for C41H38Cl2N4P2Ru: C, 60.00; H,
4.76; N, 6.83. Found: C, 60.05; H, 4.70; N, 6.90. Mp: 150-
1
(t, JCP ) 13.5 Hz, CH2), 46.4 (CH2), 122.3 (imi-CH), 127.4 (t,
1
JCP ) 4.8 Hz, Corth or Cmeta), 128.3 (t, JCP ) 4.5 Hz, Corth or
152 °C. H NMR (CDCl3): δ 2.58 (m, 2H, CH2), 3.28 (m, 1H,
Cmeta), 129.6 (Cpara), 130.0 (Cpara), 131.9 (t, 1JCP ) 23.0 Hz, Cipso),
CH2), 3.52 (m, 1H, CH2), 4.05 (m, 1H, CH2), 4.83 (m, 1H, CH2),
5.72 (m, 2H, CH2), 6.00 (t, J ) 9.0 Hz, 2H, Ph-H), 6.53-8.68.
(m, 28H, imi-CH, 2,2′-bipy-H, Ph-H). 13C{1H} NMR (CDCl3):
δ 26.9 (d, 1JCP ) 33.2 Hz, CH2), 31.6 (d, 1JCP ) 36.2 Hz, CH2),
133.3 (t, JCP ) 5.2 Hz, Corth or Cmeta), 134.2 (t, 1JCP ) 22.0 Hz,
2
Cipso), 134.4 (t, JCP ) 4.8 Hz, Corth or Cmeta), 169.1 (t, JCP
)
11.0 Hz, RuC), 199.6 (t, JCP ) 13.2 Hz, CtO). 31P{1H} NMR
(CDCl3): δ 10.9 (s). IR (KBr): ν(CtO) ) 1948.23 cm-1. Single
crystals were obtained by slow diffusion of diethyl ether into
a DMF solution of 4.
2
2
47.9 (d. JCP ) 81.7 Hz, CH2), 128.7-156.7 (aromatic), 174.4
(virtual t, 2JCP ) 18.0 Hz, RuC). 31P{1H} NMR (CDCl3): δ 38.5
2
2
(d, JPP ) 29.4 Hz), 42.3 (d, JPP ) 29.4 Hz). Single crystals
were obtained by slow diffusion of diethyl ether into a DMF
solution of 8.
Preparation of mer-RuHCl(CO)(PCNHCP) (5). A mixture
of 4 (38 mg, 0.055 mmol) and NaBH4 (20 mg, 0.550 mmol) in
10 mL of ethanol was heated at 70 °C until all solids dissolved
(ca. 30-90 min). The solvent was then removed completely
under vacuum. The residue was extracted with toluene. The
solution was then passed through a plug of Celite. The solvent
was then pumped dry again under vacuum. Upon addition of
diethyl ether, a white solid was formed, which was filtered on
a frit and dried under vacuum. Yield: 18 mg, 50%. Anal. Calcd
for C32H31ClN2OP2Ru: C, 58.40; H, 4.75; N, 4.26. Found: C,
Method B. Solid 7 (ca. 5 mg) and 2,2′-bipyridine (ca. 5 mg)
were dissolved in CDCl3 and transferred into a 5 mm NMR
tube, which was sealed and heated in an oil bath. The reaction
was monitored by 31P{1H} NMR spectroscopy. After overnight,
7 completely disappeared to give 8 without formation of other
phosphorus-containing species.
Preparation of mer-RuCl3(PCNHCP) (9). A 10 mg sample
of 7 in 0.2 mL of DMF was left in the air for about a week.
The green crystalline solid was mer-RuCl3(PCNHCP), as con-
firmed by the X-ray structural analysis. Anal. Calcd for C31H30-
Cl3N2P2Ru2: C, 46.48; H, 3.77; N, 3.50. Found: C, 46.36; H,
3.35; N, 3.51.
1
58.48; H, 4.70; N, 4.26. Mp: 178-180 °C. H NMR (C6D6): δ
2
-14.8 (t, JHP ) 19.3 Hz, Ru-H), 2.03 (m, 2H, CH2), 2.34 (m,
2H, CH2), 3.54 (br, 2H, CH2), 4.38 (br, 2H, CH2), 6.08 (s, 2H,
imi-H), 6.90-7.23 (m, 14H, Ph-H), 7.89-8.14 (m, 6H, Ph-H).
31P{1H} NMR (C6D6): δ 35.5 (s). IR (KBr): ν(CtO) ) 1928.6
General Procedure for Catalytic Transfer Hydroge-
nation of Ketones. Appropriate amounts of 3 (0.01 or 0.1 mol
%), base (10 mol % of KOBut or KOH), and the ketone (1.00
mmol) were dissolved in 10 mL of 2-propanol inside a Schlenk
tube, which was then heated at 80 °C for the required time
(0.5-24 h). After the reaction, the solvent was removed under
reduced pressure. Water and dichloromethane (20 mL each)
were added. The organic layer was then separated and the
solvent was removed under reduced pressure. The residue was
cm-1
.
Preparation of mer,trans-RuCl2(dCdCHPh)(PCNHCP)
(6). A mixture of 3 (100 mg, 0.075 mmol) and phenylacetylene
(1 mL. 9.03 mmol) in 10 mL of 1,2-dichloroethane was heated
under reflux overnight. The solution was pumped dry under
vacuum. Upon addition of diethyl ether, a reddish-brown solid
was formed, which was filtered on a frit and pumped dry under
vacuum. Yield: 93 mg, 80%. Anal. Calcd for C39H36Cl2N2P2-
Ru: C, 61.10; H, 4.73; N, 3.65. Found: C, 61.20; H, 4.80; N,
3.70. Mp: 218-220 °C. 1H NMR (CDCl3): δ 2.64 (br, 4H, CH2),
3.52 (t, 4JHP ) 3.8 Hz, 1H, RudCdCHPh), 4.18 (br, 2H, CH2),
1
then analyzed by H NMR spectroscopy.
X-ray Data Collection. Typically, the crystal was removed
from the vial with a small amount of mother liquor and
immediately coated with silicon grease on a weighting paper.
A suitable crystal was mounted on a glass fiber with silicone
grease and placed in the cold stream of either a Bruker
SMART 1000 CCD or APEX II with graphite-monochromated
Mo KR radiation (λ ) 0.71073 Å) at 273(2) or 150(2) K,
respectively. Calculations for the structures were performed
using SHELXS-97 and SHELXL-97. Tables of neutral atom
scattering factors, f ′ and f′′, and absorption coefficients
are from a standard source.30 All atoms except hydrogen
atoms were refined anisotropically. Hydrogen atoms were
3
4.70 (br, 2H, CH2), 5.88 (d, JHH ) 7.2 Hz, 2H, Ph-H), 6.70-
7.70 (m, 19H, imi-CH, Ph-H), 7.66-8.14 (m, 6H, Ph-H). 13C-
{1H} NMR (CDCl3): δ 25.7 (unresolved t, CH2), 46.3 (CH2),
108.3 (CdCHPh), 122.2-135.1 (Ph-C, imi-C), 166.4 (t, 2JCP
)
2
10.6 Hz, RuC), 348.1 (t, JCP ) 16.1 Hz, RudCdC). 31P{1H}
NMR (CDCl3): δ 7.00.
Oxidative Cleavage of Complex 6. A solution of 6 (45
mg, 0.059 mmol) in 10 mL of 1,2-dichloroethane was heated
under reflux in the air overnight. The solvent was then
pumped dry under vacuum. The residue was washed with
diethyl ether. The white solid formed was pure mer,cis-RuCl2-
(CO)(PCNHCP). Yield: 39 mg, 97%.
calculated using
a riding model. Crystallographic data
(excluding structure factors) for the structures in this
paper have been deposited with the Cambridge Crystallo-
graphic Data Centre as supplementary publication numbers
CCDC 255830-255836. Copies of the data can be obtained,
free of charge, on application to CCDC, 12 Union Road,
Cambridge, CB2 1EZ, UK [fax: +44(0)-1223-336033 or
e-mail: deposit@ccdc.cam.ac.uk].
Preparation of mer,trans-[RuCl(py)2(PCNHCP)]Cl (7).
To a solution of 3 (150 mg, 0.11 mmol) in DMF (10 mL) was
added pyridine (3.0 mL, 36.7 mmol). The solution was heated
at 110 °C overnight. The solution was then pumped dry under
reduced pressure. Upon addition of diethyl ether, a yellow solid
was formed, which was filtered on a frit and dried under a
stream of nitrogen. Yield: 162 mg, 87%. Anal. Calcd for C41H40-
Cl2N4P2Ru: C, 59.86; H, 4.90; N, 6.81. Found: C, 59.90; H,
4.95; N, 6.85. Mp: 136-138 °C. 1H NMR (CDCl3): δ 4.23 (br,
4H, CH2), 6.20 (br, 4H, CH2), 6.97-7.99. (m, 32H, imi-CH, Py-
H, Ph-H). Because of the re-formation of 3 and free pyridine
in solution, its 13C{1H} NMR spectrum was not determined.
31P{1H} NMR (CDCl3): δ 9.56 (s). Single crystals were obtained
by slow diffusion of diethyl ether into a DMF solution of 7.
Preparation of fac,cis-[RuCl(bipy)(PCNHCP)]Cl (8).
Method A. To a solution of 3 (50 mg, 0.038 mmol) in DMF
(10 mL) was added 2,2′-bipyridine (705 mg, 4.51 mmol). The
solution was heated at 100-110 °C overnight. The solution
was then pumped dry under reduced pressure. Upon addition
of diethyl ether, a reddish-brown solid was formed, which was
Acknowledgment. The authors are grateful to the
National Science Council of Taiwan for financial support
of this work.
Supporting Information Available: Full crystallo-
graphic data for compounds 2a, 2b, 3, 4, 7, 8, and 9 are
provided as a CIF file. This material is available free of charge
via the Internet at http://pubs.acs.org.
OM049070V
(30) Sutton, L. E. Tables of Interatomic Distances and Configura-
tions in Molecules and Ions; Chemical Society Publications: UK, 1965.