Halfsandwich complexes of ruthenium(II), rhodium(III) and iridium(III) with N-substituted 3-hydroxy-2-methyl-4-pyridone ligands

Article abstract of DOI:10.1016/S0020-1693(99)00280-7

The synthesis and characterization of (p-cymene)Ru^II, Cp*Rh^III and Cp*Ir^III complexes with N-alkyl and N-aryl substituted 3-hydroxy-2-methyl-4-pyridone ligands is reported. All compounds display an unusually high solubilit

Full text of DOI:10.1016/S0020-1693(99)00280-7

www.elsevier.nl/locate/ica
Inorganica Chimica Acta 294 (1999) 62–67
Halfsandwich complexes of ruthenium(II), rhodium(III) and
iridium(III) with N-substituted 3-hydroxy-2-methyl-4-pyridone
ligands
Roland Lang a, Kurt Polborn b, Theodor Severin a, Kay Severin c,*
a Institut fu¨r Pharmazie der Ludwig-Maximilians-Uni6ersita¨t, Butenandtstr. 5–13, D-81377 Munich, Germany
b Institut fu¨r Organische Chemie der Ludwig-Maximilians-Uni6ersita¨t, Butenandtstr. 5–13, D-81377 Munich, Germany
c Institut fu¨r Anorganische Chemie der Ludwig-Maximilians-Uni6ersita¨t, Butenandtstr. 5–13, D-81377 Munich, Germany
Received 11 March 1999; accepted 14 June 1999
Abstract
The synthesis and characterization of (p-cymene)RuII, Cp*RhIII and Cp*IrIII complexes with N-alkyl and N-aryl substituted
3-hydroxy-2-methyl-4-pyridone ligands is reported. All compounds display an unusually high solubility in water. With the chiral
ligand N-(o-C6H4CO2Me)-3-hydroxy-2-methyl-4-pyridone two isomers were obtained but no diastereoselectivity was observed.
The structure of [(p-cymene)Ru(C9H12NO2)Cl] (2) was determined by single crystal X-ray diffraction. Reactions of [(p-
cymene)Ru(C7H8NO2)Cl] (1) with n-butylamine and triphenylphosphine were shown to result in substitution of the chloride
ligand. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Crystal structures; Ruthenium complexes; Rhodium complexes; Iridium complexes; Hydroxypyridone complexes
1. Introduction
pyridones have emerged as promising candidates for
the treatment of iron-overload [5]. To the best of our
knowledge, no organometallic complexes with these
ligands have been reported. Given the extensive coordi-
nation chemistry of g-pyridones this is somewhat sur-
prising, especially since the reactivities and the catalytic
properties of organometallic complexes should differ
notably from comparable complexes with other O,O-
chelate ligands such as acetyl acetonate. Due to the
unique electronic structure of the pyridone ligand the
metal center in O,O-chelate complexes is predicted to
be very electron rich (Scheme 2). Amongst other effects
this may facilitate (catalytic) reactions which require
the formation of cationic complexes or intermediates.
When maltose or lactose is heated with primary
aliphatic amines in neutral aqueous solutions 3-hy-
droxy-2-methyl-4-pyridones are formed among other
products in low yields [1]. This was reported as early as
1954 [1c] but access to this class of compounds based
on this convenient synthetic method is often inefficient.
Hydroxypyridones are readily prepared in moderate
yields by heating maltol with primary aliphatic amines
in aqueous solution. Later it was shown that N-alkyl
and N-aryl substituted pyridones can be prepared in
good yields by reaction of benzylated maltol with pri-
mary amines and subsequent hydrogenolysis (Scheme
1) [2].
Recently, there has been a significant interest in these
compounds as sequestering agents for various metal
ions [2a, 3–5]. The focus of attention has been particu-
larly on FeIII since very stable 3:1 complexes are
formed. Being orally available 3-hydroxy-2-methyl-4-
Scheme 1. Synthesis of N-substituted 3-hydroxy-2-methyl-4-pyridones
from 3-O-benzylmaltol: (a) R-NH2, (EtOH, H2O), 8–10 h; (b) Pd/C,
H2, MeOH/EtOH, 12 h.
* Corresponding author. Fax: +49-89-2180 7866.
E-mail address: kse@cup.uni-muenchen.de (K. Severin)
0020-1693/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(99)00280-7

R. Lang et al. / Inorganica Chimica Acta 294 (1999) 62–67
63
tence of such species in CD3OD was previously postu-
lated for a (h6-benzene)Ru complex with a pyrrol-
carbaldiminato ligand [15].
The N-aryl substituted complex 4 is obtained as a
mixture of two diastereoisomers. In solution the relative
1
ratio is 1:1 as determined by integration of selected H
NMR signals (CDCl3). The formation of isomers is
caused by hindered rotation of the C(arene)–N(pyri-
done) bond. For ortho substituted aryl groups this
barrier is known to be sufficiently high to allow the
separation of rotational isomers [16].
Scheme 2. Mesomeric forms which contribute to the electronic struc-
ture of coordinated 3-hydroxy-2-methyl-4-pyridone ligands.
In this paper (p-cymene)RuII, Cp*RhIII and Cp*IrIII
complexes with N-substituted 3-hydroxy-2-methyl-4-
pyridone ligands are described. These organometallic
fragments were chosen because they are known to form
monomeric complexes with bidentate, monoanionic lig-
ands such as acetyl acetonate [6] and a-amino acid
anions [7]. Furthermore, highly reactive catalysts for a
variety of different transformations were found among
complexes of this kind. For example (p-cymene)RuII
complexes were used as catalysts for hydrogen transfer
reactions [8], for the oligomerization of a-amino acid
esters [9], for olefin cyclopropanations [10] and for
isomerization reactions [11]; Cp*Rh and Cp*Ir com-
plexes were utilized as catalysts for Diels–Alder [12]
and hydrogenation reactions [13].
Similarly to 1–4, the rhodium and iridium complexes
5 and 6 were obtained in good yields using the chloro-
1
bridged dimers [Cp*RhCl2]2 or [Cp*IrCl2]2. The H and
13C NMR spectroscopic data are in agreement with the
structures depicted. Both complexes show good solubil-
ity in polar organic solvents and water. Epimerization
processes could not be studied because the enantiomeric
forms are indistinguishable by NMR. Contrary to 1, at
−60°C (and above) only one isomer was observed for
5 and 6 in CD3OD.
2. Results and discussion
2.1. Synthesis
Racemic mixtures of the ruthenium complexes 1–4
were prepared by reaction of [(p-cymene)RuCl2]2 with
the sodium salts of the corresponding N-alkyl and
N-aryl substituted 3-hydroxy-2-methyl-4-pyridones in
dichloromethane. The orange products are soluble in
chloroform, methanol and water (see Section 2.3) but
insoluble in diethyl ether and hexanes. All complexes
are chiral with the ruthenium atom being the stereo-
genic center and the pyridone ligands acting as biden-
2.2. Structural analysis
1
tate O,O%-chelates. Consequently the H NMR spectra
Single crystals of 2 suitable for X-ray structural
analysis were obtained by slow diffusion of hexane into
a solution of 2 in chloroform. The geometry around the
ruthenium atom can be described as a distorted tetrahe-
dron with the h6-arene ring and the other donor atoms
adopting a ‘piano stool’ configuration (Fig. 1). The
Ru–Cl bond length, 242.8(1) pm, is similar to that
found in related molecules [14,17]. As a result of the
constrained geometry of the chelate ligand the O1–
Ru–O2 angle (79.41°) is smaller than the O2–Ru–Cl
angle (85.50°) and the O1–Ru–Cl angle (86.74°).
Of special interest are the bond lengths of the pyri-
done ligand. The relatively long C–O2 bond distance,
129.5(4) pm, as well as the bond lengths within the
six-membered ring (Fig. 2) indicate that the zwitterionic
form ‘B’ (Scheme 2) contributes significantly to the
electronic structure of 2. Based on X-ray structural
(CDCl3) show two doublets for the methyl groups (i-Pr)
and four doublets for the aromatic protons of the
cymene ligand. To elucidate the configurational stabil-
1
ity of the metal center H NMR spectra of 1 in the
more polar solvent CD3OD were recorded in the tem-
perature range of −60 to +23°C. The results indicate
that epimerization is fast on the NMR time scale: even
at −20°C only one doublet for the methyl group (i-Pr)
and two doublets for the aromatic protons were ob-
served. This contrasts to other [(p-cymene)Ru(A–B)Cl]
complexes for which epimerization in methanol was
detected only at elevated temperatures [14]. Interest-
ingly, at −60°C, signals of two isomers were recorded
the relative ratio of which was determined to be 2.8:1.
Most likely, a cationic solvate complex and the neutral
chloro complex coexist at this temperature. The coexis-

64
R. Lang et al. / Inorganica Chimica Acta 294 (1999) 62–67
Scheme 3. Reaction of 1 with n-butylamine and triphenylphosphine.
It should be noted that the reaction of n-BuNH2 with
1 does not afford a N,O-chelating pyridonimine [2a]
despite the fact that metal assisted condensation reac-
tions of primary amines with anionic ligands containing
a-keto groups in the coordination sphere of (p-
cymene)Ru(II) complexes are well known [19]. This result
is in agreement with the phenolate character of the
carbonyl group deduced from the X-ray structural anal-
ysis.
Fig. 1. Molecular structure of complex 2.
analyses similar conclusions were drawn for some ho-
moleptic pyridone complexes of Al3+ and Ga3+ [4].
2.3. Reacti6ity
The electron donating character of the pyridone ligand
is expected to facilitate substitution reactions at the
remaining coordination site. And indeed, the chloro
ligand in 1 is easily replaced by the neutral N- and
P-donor ligands n-BuNH2 and PPh3 (Scheme 3).
Analogous reactions with PPh3 occur with the rhodium
and iridium compounds 5 and 6 as shown by in situ NMR
experiments (1H and 31P, CDCl3). The high lability of the
chloro ligand contrasts to the behavior of other halfsand-
wich complexes with monoanionic chelate ligands for
which silver salts such as AgBF4 were used as chloride
abstracting agents [6,18]. A substitution reaction of the
chloro ligand with a neutral solvent molecule may also
account for the good solubility of all complexes in water
which is unusual for this type of compound.
3. Experimental
3.1. General
All solvents were of analytical grade quality, obtained
commercially and used without further purification. The
complexes [(p-cymene)RuCl2]2 [20], [Cp*RhCl2]2 [21],
and [Cp*IrCl2]2 [21] were prepared as described in the
literature. The pyridone ligands were synthesized accord-
ing to published procedures. Infrared spectra were mea-
sured with Perkin–Elmer 841 or Nicolet 520 instruments.
The NMR spectra were obtained on a JEOL EX 400 or
GSX 270 with the solvent as internal standard.
3.2. 3-Hydroxy-2-methyl-1-propyl-4-pyridone
A total of 2.52 g maltol (20 mmol) and 2.36 g
n-propylamine (40 mmol) in 50 ml water are heated
under reflux for 4 h. After evaporation under reduced
pressure the residue is crystallized from methanol. Ac-
cording to spectral data the product is identical to a
substance prepared from O-benzylmaltol as described in
Ref. [2a].
3.3. General procedure for the synthesis of 1–6
A solution of 0.4 mmol NaOMe in methanol (2 M)
was added to a suspension of 0.4 mmol N-substituted
3-hydroxy-2-methyl-4-pyridone in 10 ml of dichlo-
Fig. 2. Selected bond lengths (pm) of complex 2. Only the parts of the
pyridone ligand and the ruthenium atom are shown.

R. Lang et al. / Inorganica Chimica Acta 294 (1999) 62–67
65
3
romethane. The resulting clear solution was subse-
quently added to 0.2 mmol of [(p-cymene)RuCl2]2,
[(Cp*)RhCl2]2, or [(Cp*)IrCl2]2 dissolved in 10 ml of
dichloromethane. After 2 h the solvent was removed in
vacuo. The products were extracted with 30 ml of
diethyl ether/dichloromethane (1:2). Yellow or orange
powders were obtained after evaporation of the solvent
under reduced pressure and drying in vacuo at 50°C.
CDCl3): l=1.26 [d, J=6.9 Hz, 3H, CH(CH3)2], 1.31
3
[d, J=6.6 Hz, 3H, CH(CH3)2], 2.09 (s, 3H, CH3), 2.29
(s, 3H, CH3), 2.90 (sept., J=6.9 Hz, 1H, CH(CH3)2],
5.23 (d, J=6.0 Hz, 1H, CH, cymene), 5.29 (d, J=5.9
Hz, 1H, CH, cymene), 5.43 (d, J=5.5 Hz, 1H, CH,
3
3
3
3
3
cymene), 5.48 (d, J=5.5 Hz, 1H, CH, cymene), 6.47
3
3
(d, J=6.9 Hz, 1H, C5H2N), 6.94 (d, J=6.8 Hz, 1H,
C5H2N), 7.16–7.19 (m, 2H, C6H5), 7.43–7.45 (m, 3H,
C6H5). 13C NMR (68 MHz, CDCl3): l=13.87 (N–
C(CH3)ꢀC), 18.67 (CH3, cymene), 22.47, 22.56
[CH(CH3)2], 31.11 [CH(CH3)2], 78.66, 79.26, 79.70,
95.46, 99.26 (cymene), 109.40, 126.37, 129.45, 129.75,
132.20, 132.50, 142.18 (NꢁCHꢀCH, N–C(CH3)ꢀC,
C6H5), 160.67, 176.19 (CO). Anal. Calc. for
C22H24ClNO2Ru (470.96): C, 56.11; H, 5.14; N, 2.97.
Found: C, 55.37; H, 5.14; N, 2.77%.
3.4. [(p-Cymene)Ru(C7H8NO2)Cl] (1)
Yield: 85%, m.p. 247–249°C (dec.). IR (KBr): w=
1
1599 cm−1 (s), 1543 (s), 1506 (s). H NMR (400 MHz,
3
CDCl3): l=1.22 [d, J=6.8 Hz, 3H, CH(CH3)2], 1.27
3
[d, J=7.0 Hz, 3H, CH(CH3)2], 2.26 (s, 3H, CH3), 2.34
3
(s, 3H, CH3), 2.84 (sept., J=7.2 Hz, 1H, CH(CH3)2],
3.52 (s, 3H, NCH3), 5.18 (d, 3J=5.1 Hz, 1H, CH,
3
3.7. [(p-Cymene)Ru(C14H12NO4)Cl] (4)
cymene), 5.24 (d, J=5.6 Hz, 1H, CH, cymene), 5.37
3
3
(d, J=5.5 Hz, 1H, CH, cymene), 5.44 (d, J=5.8 Hz,
Yield: 82%, m.p. 185–187°C (dec.). IR (KBr): w=
3
1H, CH, cymene), 6.30 (d, J=6.6 Hz, 1H, C5H2N),
1716 cm−1 (s, CO2Me), 1591 (s), 1536 (s), 1506 (s). H
1
6.86 (d, 3J=7.2 Hz, 1H, C5H2N). 13C NMR (101 MHz,
CDCl3): l=12.20 (N–C(CH3)ꢀC), 18.68 (CH3,
cymene), 22.36, 23.50 [CH(CH3)2], 31.07 [CH(CH3)2],
42.47 (NCH3), 77.60, 78.56, 79.22, 79.58, 95.50, 99.05
(cymene), 109.19, 132.22, 132.38 (N–CHꢀCH, N–
C(CH3)ꢀC), 160.99, 175.30 (CO). Anal. Calc. for
C17H22ClNO2Ru (408.89): C, 49.94; H, 5.42; N, 3.43.
Found: C, 49.31; H, 5.33; N, 3.24%.
NMR (270 MHz, CDCl3): l=1.19–1.39 [m, 12H,
CH(CH3)2], 2.00 (s, 3H, CH3), 2.01 (s, 3H, CH3), 2.30
(s, 3H, CH3), 2.33 (s, 3H, CH3), 2.85–2.96 (m, 2H,
CH(CH3)2], 3.58 (s, 3H, CO2CH3), 3.65 (s, 3H,
CO2CH3), 5.21–5.51 (m, 8H, CH, cymene), 6.47 (d,
3J=6.4 Hz, 1H, C5H2N), 6.50 (d, 3J=6.3 Hz, 1H,
C5H2N), 6.86 (d, 3J=6.8 Hz, 1H, C5H2N), 6.87 (d,
3J=6.8 Hz, 1H, C5H2N), 7.26–7.28 (m, 2H,
C6H4CO2Me), 7.55–7.68 (m, 4H, C6H4CO2Me), 8.04–
8.07 (m, 2H, C6H4CO2Me). 13C NMR (68 MHz,
CDCl3): l=13.45 (N–C(CH3)ꢀC), 18.57, 18.82 (CH3,
cymene), 22.08, 22.58, 22.72 [CH(CH3)2], 31.08, 31.65
[CH(CH3)2], 52.65, 53.69 (CO2CH3), 77.78, 78.50,
78.73, 79.18, 79.27, 79.42, 80.26, 95.38, 95.79, 99.13,
99.26 (cymene), 109.26, 109.41, 127.87, 127.96, 128.57,
128.77, 129.98, 131.87, 132.48, 133.10, 133.36, 133.73,
3.5. [(p-Cymene)Ru(C9H12NO2)Cl] (2)
Yield: 82%, m.p. 215–217°C (dec.). IR (KBr): w=
1
1600 cm−1 (s), 1538 (s), 1507 (s). H NMR (270 MHz,
CDCl3): l=0.94 (t, 3J=7.4 Hz, 3H, CH2CH2CH3],
3
3
1.27 [d, J=6.9 Hz, 3H, CH(CH3)2], 1.32 [d, J=7.0
Hz, 3H, CH(CH3)2], 1.65–1.79 (m, 2H, CH2CH2CH3),
2.31 (s, 3H, CH3), 2.42 (s, 3H, CH3), 2.93 (sept.,
3J=6.9 Hz, 1H, CH(CH3)2], 3.74–3.80 (m, 2H,
140.97,
141.23
(N–CHꢀCH,
N–C(CH3)ꢀC,
C6H4CO2Me), 160.35, 160.50, 164.89, 165.34, 176.38,
176.77 (CO, CO2). Anal. Calc. for C24H26ClNO4Ru
(528.99): C, 54.49; H, 4.95; N, 2.65. Found: C, 54.27;
H, 4.89; N, 2.55%.
3
CH2CH2CH3), 5.23 (d, J=5.8 Hz, 1H, CH, cymene),
3
3
5.28 (d, J=5.4 Hz, 1H, CH, cymene), 5.42 (d, J=5.7
3
Hz, 1H, CH, cymene), 5.48 (d, J=5.4 Hz, 1H, CH,
cymene), 6.41 (d, 3J=6.5 Hz, 1H, C5H2N), 6.90 (d,
3J=6.8 Hz, 1H, C5H2N). 13C NMR (101 MHz,
CDCl3): l=10.99, 11.80 (N–C(CH3)ꢀC, CH2CH2-
CH3), 18.61 (CH3, cymene), 22.40, 23.51 [CH(CH3)2],
24.07 (CH2CH2CH3), 31.06 [CH(CH3)2], 56.25
(CH2CH2CH3), 77.66, 78.58, 79.28, 79.68, 95.33, 99.06
(cymene), 109.69, 131.47, 131.69 (N–CHꢀCH, N–
C(CH3)ꢀC), 161.07, 175.07 (CO). Anal. Calc. for
C19H26ClNO2Ru (436.94): C, 52.23; H, 6.00; N, 3.21.
Found: C, 52.32; H, 6.10; N, 3.09%.
3.8. [Cp*Rh(C7H8NO2)Cl] (5)
Yield: 85%, m.p. 217–220°C (dec.). IR (KBr): w=
1596 cm−1 (s), 1541 (s), 1504 (s). H NMR (270 MHz,
1
CDCl3): l=1.70 (s, 15H, Cp*), 2.37 (s, 3H, N–
3
C(CH3)ꢀC), 3.56 (s, 3H, NCH3), 6.29 (d, J=7.0 Hz,
1H, C5H2N), 6.87 (d, 3J=6.8 Hz, 1H, C5H2N). 13C
NMR (68 MHz, CDCl3): l=8.92 [C5(CH3)5], 12.31
(N–C(CH3)ꢀC), 42.40 (NCH3), 90.59 [d, 1JRhC=9.3
3
Hz, C5(CH3)5], 109.60 (d, JRhC=1.6 Hz, N–CHꢀCH),
131.52 (N–CHꢀCH), 132.08 (d, 3JRhC=2.0 Hz, N–
C(CH3)ꢀC), 161.55, 175.73 (CO). Anal. Calc. for
C17H23ClNO2Rh·0.5H2O (420.74): C, 48.53; H, 5.75; N,
3.33. Found: C, 48.80; H, 5.51; N, 3.22%.
3.6. [(p-Cymene)Ru(C12H10NO2)Cl] (3)
Yield: 75%, m.p. 226–228°C (dec.). IR (KBr): w=
1
1584 cm−1 (s), 1534 (s), 1496 (s). H NMR (270 MHz,

66
R. Lang et al. / Inorganica Chimica Acta 294 (1999) 62–67
Table 1
3.9. [Cp*Ir(C9H12NO2)Cl] (6)
Crystallographic data of complex 2
Yield: 78%, m.p. 235–237°C (dec.). IR (KBr): w=
Empirical formula
C19H26ClNO2Ru
436.93
0.10×0.37×0.53
1
1600 cm−1 (s), 1540 (s), 1505 (s). H NMR (270 MHz,
Molecular weight (g mol−1
)
CDCl3): l=0.94 (t, 3J=7.4 Hz, 3H, CH2CH2CH3],
1.65–1.76 (m, 2H, CH2CH2CH3), 1.69 (s, 15H, Cp*),
2.43 (s, 3H, N–C(CH3)ꢀC), 3.77–3.83 (m, 2H,
Crystal size (mm−1
Crystal system
Space group
)
triclinic
(
P1
,
a (A)
7.654(2)
3
CH2CH2CH3), 6.40 (d, J=6.8 Hz, 1H, C5H2N), 6.94
,
b (A)
9.8818(13)
13.920(2)
104.149(10)
103.910(14)
98.976(13)
964.8(3)
(d, 3J=6.5 Hz, 1H, C5H2N). 13C NMR (68 MHz,
CDCl3): l=9.22 [C5(CH3)5], 11.07, 11.95 (N–
C(CH3)ꢀC, CH2CH2CH3), 24.16 (CH2CH2CH3), 56.26
(CH2CH2CH3), 81.60 [C5(CH3)5], 109.66, 131.21,
132.11 (N–CHꢀCH, N–C(CH3)ꢀC), 163.28, 176.45
(CO). Anal. Calc. for C19H26ClIrNO2 (529.10): C,
43.13; H, 5.14; N, 2.65. Found: C, 42.87; H, 5.22; N,
2.56%.
,
c (A)
h (°)
i (°)
k (°)
3
,
Volume (A )
Z
2
Density (g cm−3
)
1.504
0.961
Absorption coefficient (mm−1
q range (°)
)
2.80–23.96
−8“8, −11“0, −15“15
3227
Index ranges
Reflections collected
Independent reflections
Absorption correction
Max. and min. transmission
Weights
3.10. [(p-Cymene)Ru(C7H8NO2)(C4H9NH2)]Cl (7)
3024
semi-empirical
0.9998 and 0.8381
A total of 82 mg (0.2 mmol) 1 and 30 ml (0.3 mmol)
n-butylamine in 5 ml of methanol were stirred for 3 h.
After removal of the solvent under reduced pressure the
product was washed with 30 ml of diethyl ether and
dried in vacuo. Yield: 92%. IR (KBr): w=1601 cm−1
w=1/(|2(Fo2)+(0.0344
P)2+0.7624P]; P=(Fo
2Fc2)/3
+
2
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I\2|(I)]
R indices (all data)
2764/0/222
1.117
R1=0.0277, wR2=0.0674
R1=0.0325, wR2=0.0708
0.643/−0.720
1
(s), 1547 (s), 1503 (s). H NMR (270 MHz, CDCl3):
3
3
l=0.66 (t, J=7.0 Hz, CH3, Bu), 1.00 (sext., J=7.2
−3
,
Largest difference peak/hole (e A
)
Hz, CH2, Bu), 1.23 [d, 3J=6.7 Hz, 3H, CH(CH3)2],
1.25 [d, J=6.8 Hz, 3H, CH(CH3)2], 1.29–1.50 (m, 2H,
3
CH2, Bu), 2.14–2.43 (m, 2H, NCH2, Bu), 2.20 (s, 3H,
3
CH3), 2.31 (s, 3H, CH3), 2.84 (sept., J=7.0 Hz, 1H,
3J=6.2 Hz, 1H, CH, cymene), 5.31 (d, 3J=5.9 Hz, 1H,
CH(CH3)2], 3.08 (br, NH), 3.70 (s, 3H, NCH3), 4.84 (s,
3H, NCH3), 5.42 (d, J=5.8 Hz, 1H, CH, cymene),
5.59–5.61 (m, 3H, CH, cymene), 6.30 (d, J=6.6 Hz,
3
CH, cymene), 5.43 (d, J=5.9 Hz, 1H, CH, cymene),
3
3
3
5.97 (d, J=7.0 Hz, 1H, C5H2N), 7.14 (d, J=6.8 Hz,
1H, C5H2N), 7.24–7.43 (m, 15H, PPh3). 13C NMR (68
MHz, CDCl3): l=11.50 (N–C(CH3)ꢀC), 18.00 (CH3,
cymene), 22.04, 22.35 [CH(CH3)2], 30.96 [CH(CH3)2],
3
1H, C5H2N), 7.18 (d, 3J=6.8 Hz, 1H, C5H2N). 13C
NMR (68 MHz, CDCl3): l=11.81, 13.63 (N–
C(CH3)ꢀC, CH3, Bu), 18.01, 19.89 (CH3, cymene, CH2,
Bu), 22.53, 22.66 [CH(CH3)2], 31.19 [CH(CH3)2], 33.69
(CH2, Bu), 42.78 (NCH3), 44.20 (NCH2, Bu), 79.65,
80.25, 80.59, 80.92 (cymene), 109.39, 133.97, 133.83
(N–CHꢀCH, N–C(CH3)ꢀC), 160.27, 174.84 (CO).
Anal. Calc. for C22H35ClN2O2Ru·0.5H2O (491.04): C,
51.37; H, 6.98; N, 5.70. Found: C, 51.22; H, 6.80; N,
5.58%.
2
42.59 (NCH3), 85.60 (d, JPC=2.8 Hz, CH, cymene),
86.04 (CH, cymene), 86.37 (d, 2JPC=3.9 Hz, CH,
2
cymene), 87.68 (d, JPC=5.2 Hz, CH, cymene), 97.24
(C, cymene), 108.72 (d, 2JPC=5.1 Hz, C, cymene),
109.73, 128.28, 128.422, 129.48, 130.13, 130.88, 130.91,
133.28, 134.09, 134.24, 134.89 (N–CHꢀCH, N–
C(CH3)ꢀC, PPh3), 160.66, 175.39 (CO). 31P NMR (109
MHz, CDCl3): l=30.06 (PPh3). Anal. Calc. for
C35H37ClNO2PRu·1.5H2O (698.2): C, 60.21; H, 5.77; N,
2.01. Found: C, 60.47; H, 5.67; N, 1.95%.
3.11. [(p-Cymene)Ru(C7H8NO2)PPh3]Cl (8)
A total of 82 mg (0.2 mmol) 1 and 52 mg (0.2 mmol)
PPh3 in 7 ml of dichloromethane were stirred for 4 h.
After removal of the solvent under reduced pressure the
product was dried in vacuo. Yield: 98%. IR (KBr):
3.12. X-ray crystallographic in6estigations
An Enraf–Nonius CAD 4 diffractometer was em-
ployed for data collection using Mo Ka radiation (T=
295 K). The structure was solved by direct methods
1
w=1602 cm−1 (s), 1544 (s), 1505 (s). H NMR (270
MHz, CDCl3): l=1.11 [d, 3J=6.7 Hz, 3H,
(SHELXS-86) [22] and was refined by means of the
3
CH(CH3)2], 1.13 [d, J=6.7 Hz, 3H, CH(CH3)2], 1.80
full-matrix least-squares procedures using SHELXL-93
[23] (Table 1). All non-hydrogen atoms were refined
anisotropically. For the hydrogen atoms a riding model
was employed.
(s, 3H, CH3, cymene), 2.05 (s, 3H, N–C(CH3)ꢀC), 2.53
(sept., 3J=6.7 Hz, 1H, CH(CH3)2], 3.59 (s, 3H,
3
NCH3), 4.92 (d, J=5.9 Hz, 1H, CH, cymene), 5.12 (d,

R. Lang et al. / Inorganica Chimica Acta 294 (1999) 62–67
67
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4. Conclusions
We have shown that chiral halfsandwich complexes
of ruthenium, rhodium and iridium with O,O%-coordi-
nating N-substituted 3-hydroxy-2-methyl-4-pyridone
ligands can be obtained in good yields by reaction of
[(p-cymene)RuCl2]2, [Cp*RhCl2]2 or [Cp*IrCl2]2 with
the corresponding chelate anions. The electron donat-
ing character of the pyridone ligands is manifested in
the low configurational stability of the stereogenic
ruthenium center of 1–4, the good solubility of all
complexes in water and the lability of the chloro ligand
towards substitution with neutral donor ligands. Cur-
rently, we are further exploring the organometallic
chemistry of these interesting ligands.
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5. Supplementary material
Further details of the crystal structure determination
may be obtained from the Cambridge Crystallographic
Data Centre. Any request for this material should
quote the full literature citation and the reference num-
ber CCDC-125745.
.
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Acknowledgements
K.S. thanks Professor W. Beck (LMU Mu¨nchen) for
his generous support. Financial funding from the
Bayerischer Habilitations-Fo¨rderpreis (K.S.) is grate-
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