Synthesis, crystal structure and spectroscopic characterisation of mono- and dimuclear 5,5-diethylbarbiturato complexes of Chromiuin(0) and Rhenium(I)

Article abstract of DOI:10.1002/zaac.200801342

Addition of 5,5-diethylbarbituric acid (H₂debarb, 1) to [CpCr(NO)₂Cl], [Re(CO)₅Br] or 1(PPh₃)Re(CO) ₄Br] in the presence of triethylamine and AgO₃SCF ₃ (= AgOTf) resulted in the

Full text of DOI:10.1002/zaac.200801342

ARTICLE
DOI: 10.1002/zaac.200801342
Synthesis, Crystal Structure and Spectroscopic Characterisation of Mono- and
Dinuclear 5,5-Diethylbarbiturato Complexes of Chromium(0) and Rhenium(I)
Nadera Haque,[a] J. Nicolas Roedel,[a] and Ingo-Peter Lorenz*[a]
Keywords: Barbiturates; Chromium; N ligands; Rhenium; Solid-state structures
Abstract. Addition of 5,5-diethylbarbituric acid (H2debarb, 1) to
complexes, AgO3SCF3 must be used additionally to cleave off bro-
[CpCr(NO)2Cl], [Re(CO)5Br] or [(PPh3)Re(CO)4Br] in the presence mide. All of the complexes were fully characterised by means of
of triethylamine and AgO3SCF3 (ϭ AgOTf) resulted in the mono-
barbiturato complexes [CpCr(NO)2(Hdebarb)] (2), [PPh3Re(CO)4-
IR, mass and 1H, 13C and 31P NMR spectra and elemental analysis.
In addition, their solid-state structures were determined by single-
(Hdebarb)] (3) and [Re(CO)5(Hdebarb)] (4), respectively. Bis-barbi- crystal X-ray diffraction studies. The complexes exhibit distorted
turato complex [{(CO)5Re}2(debarb)] (5) with a doubly depro-
tonated barbiturate dianion formed when a molar ratio of metal
complex to ligand of 2:1 was used. In the case of the rhenium
pseudo-tetrahedral (2) or pseudo-octahedral (3Ϫ5) configuration
around the metal atom. In all complexes the ring system of the
Hdebarb ligand is essentially planar.
organometallic fragments into biomolecules to produce
organometallically labelled drugs [12]. Different barbituric
acid derivatives were labelled with transition metal com-
pounds of chromium and manganese [13] as well as iron,
rhenium and ruthenium [14]. Rudolf et al. introduced the
CpFe(CO)2 moiety (Cp ϭ η5-C5H5) into barbiturates, as
such iron derivatives can be used as IR-detectable markers
in carbonyl metallo immunoassay (CMIA), but they did not
reveal the crystal structure of the complexes [15]. Organo
transition metal nitrosyl complexes such as [CpCr(NO)2Cl]
have been shown to cause endotheliumin-independent
relaxation of aortic rings in vitro [16]. Here we report the
synthesis and structural and spectroscopic characterisation
of four new chromium(0) and rhenium(I) complexes of 5,5-
diethylbarbituric acid (1): the three mononuclear com-
plexes, [Cp(NO)2Cr(Hdebarb)] (2), [PPh3Re(CO)4(Hdeb-
arb)] (3) and [Re(CO)5(Hdebarb)] (4) with the monodepro-
tonated HdebarbϪ anion and the dinuclear complex
[{Re(CO)5}2(debarb)] (5) with the double deprotonated
debarb2Ϫ dianion as ligands. Their molecular structures
have been elucidated by X-ray structure analysis.
Introduction
The coordination chemistry of organo transition metal
complexes with biologically active ligands has attracted
enormous interest over the years. Studying such complexes
may lead to a greater understanding of the role of the li-
gand in biological systems, and may also contribute to the
development of new metal-based chemotherapeutic agents
[1]. Barbiturates are a class of drugs that have diverse appli-
cations such as sedatives, hypnotics and anticonvulsants [2].
5,5-Diethylbarbituric acid (H2debarb, 1), also known as
barbital, veronal or diemal, is chemically the simplest hyp-
notic barbiturate and was first synthesised by Fischer in
1903 [3]. Because of the wide range of medicinal appli-
cations of barbiturates and their ability to coordinate to
transition metals through one or both deprotonated nitro-
gen atoms and the carbonyl oxygen atoms, synthesis of their
metal complexes has attracted considerable attention. Most
metal barbital complexes are of general formula [MII(Hdeb-
arb)2L2], where M is cobalt, zinc, cadmium, palladium,
platinum or copper; Hdebarb is the mono anion of
barbital and L is an organic base such as ammonia,
pyridine or a picoline [4Ϫ9]. Some platinum [1] and gold
[10] complexes of barbituric acid derivatives have been syn-
thesised. Cotton et al. published the crystal structure of the
salt Li2[Cr(Hdebarb)4]·EtOH [11]. Moreover, one of the
most investigated fields of research is to incorporate
Results and Discussion
Synthesis and Properties
Complexes containing H2debarb are not known, and
therefore proton loss from at least one of the amine nitro-
gen atoms is necessary for complexation of Hdebarb or
debarb [17]. In the present work, the anion (HdebarbϪ) and
dianion (debarb2Ϫ) of 5,5-diethylbarbituric acid (1) were
used in the preparation of metal complexes. Addition of an
excess of triethylamine to a solution of 1 in chloroform to
which one molar equivalent of [CpCr(NO)2Cl] had been ad-
* Prof. Dr. I.-P. Lorenz
Fax: ϩ49-89-2180-77867
E-Mail: ipl@cup.uni-muenchen.de
[a] Department Chemie und Biochemie
Ludwig-Maximilians-Universität München
Butenandtstraße 5Ϫ13 (Haus D)
81377 München, Germany
496
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2009, 635, 496Ϫ502

5,5-Diethylbarbiturato Complexes of Cr0 and ReI
Scheme 1. Synthesis of HdebarbϪ complexes of chromium (2) and rhenium (3).
Scheme 2. Synthesis of mono- and dinuclear rhenium complexes 4 and 5.
ded resulted in the formation of 2 (Scheme 1). Only after 3Ϫ5 are air stable, but 2 decomposes in solution when ex-
the treatment with AgO3SCF3 (ϭ AgOTf) and separation posed to moist air. All products 2Ϫ5 are soluble in polar
of the precipitated AgBr react rhenium(I) complexes organic solvents such as acetone or dichloromethane, but
[(PPh3)Re(CO)4Br] and [Re(CO)5Br] with the stoichio- insoluble in non-polar pentane and hexane.
metric amount (1:1) of the HdebarbϪ anion to give mono-
nuclear barbiturato complexes 3 (Scheme 1) and 4 (Scheme
2) in 42Ϫ50 % yield. Without the addition of AgOTf no
Spectroscopy
reaction was observed. An excess of triethylamine was
The IR spectrum of 2 (in CHCl3) shows two strong
always used in these reactions to remove one hydrogen ν(NO) bands at 1825 and 1720 cmϪ1, and for the three car-
atom from barbituric acid (H2debarb). When a twofold bonyl groups of the ligand only two ν(CO) bands at 1621
excess of [Re(CO)5Br] was used, the dinuclear complex and 1682 cmϪ1 are observed. The band at 1682 cmϪ1 is very
[{Re(CO)5}2(debarb)] (5) with the dianionic debarb2Ϫ li- weak and resembles a shoulder on the 1720 cmϪ1 band.
gand was formed in 53 % yield. Despite several attempts However, in KBr besides four strong absorptions at 1814,
the synthesis of the analogous dinuclear chromium complex 1727 cmϪ1 (NO) and 1671, 1620 cmϪ1 (CO) a shoulder of
[{CpCr(NO)}2(debarb)] was not successful. Compounds medium intensity at 1714 cmϪ1 is additionally observed.
Z. Anorg. Allg. Chem. 2009, 496Ϫ502
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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497

N. Haque, J. N. Roedel, I.-P. Lorenz
ARTICLE
This may be assigned to the third ν(CO) absorption band, at 55.69 ppm. The phenyl carbon atoms of the PPh3 ligand
which was concealed by one of the ν(NO) bands in the solu- of 3 show multiplets in the range 133.35Ϫ128.79 ppm with
tion spectrum. In the IR spectra of 3Ϫ5 (in CHCl3) the doublet character because of PϪC coupling. In the 31P
stretching vibrations of the carbonyl groups of Hdebarb NMR spectrum of 3 the PPh3 signal is found at 11.64 ppm.
and debarb appear as three bands in the range of
1723Ϫ1586 cmϪ1, similar to those observed for disubsti- Crystal Structure Analysis
tuted barbiturate complexes [10, 14]. The carbonyl ligands
Crystals of the complexes suitable for X-ray diffraction
on rhenium show three bands (in CHCl3) in all the com-
were obtained by isothermal diffusion of pentane into their
plexes which are typical for σ-donor/π-acceptor ligands. As
solutions in dichloromethane at room temperature over 2 d.
3 has Cs or pseudo-C2v symmetry one would expect four
Molecular views of 2Ϫ5 are shown in Figures 1Ϫ4, together
bands for the carbonyl ligands of rhenium. However, we
with selected bond lengths and angles. The molecular struc-
ture of 2 shows a distorted three-legged piano-stool ar-
rangement around the metal atom, and the three NϪCrϪN
bond angles between 96.0 and 99.9° are typical for pseudo-
see only three main absorptions (2105, 2011, 1946 cmϪ1),
in CHCl3 but in KBr the three bands appear now at 2106,
2020 and 1926 cmϪ1 with one additional shoulder at
1999 cmϪ1
.
tetrahedral configuration and therefore of the same size as
found in the starting compound [CpCr(NO)2Cl] [18]. The
N1ϪCr1ϪN2 96.0(9)° angle between the two NO ligands
is the smallest. The average CrϪNϪO angle of 169.5°
corresponds to an almost linear NOϩ mode of coordi-
nation. Both of the CrϪN bonds to the π-acidic NO ligands
are very short (Cr1ϪN1 and Cr1ϪN2 1.709(18) and
The mass spectra of 3Ϫ5 show no unexpected behaviour
and are easily interpreted because of the metal isotope dis-
tribution. The FABϩ mass spectrum exhibited the parent
signals for the intact molecules at m/z ϭ 743 (3), 509 (4)
and 834 (5). In the spectra of all rhenium complexes the
fragmentation pattern is characterised by successive loss of
the CO ligands. In the case of 2 the mass spectrum showed
a peak at m/z ϭ 300 which corresponds to the cation
formed by the loss of both NO ligands [MϪ2NO]ϩ.
˚
1.722(18) A, respectively) in comparison to the
˚
CrϪNHdebarb bond (2.055(18) A), which has a typical
CrϪN single-bond length [19]. All CrϪN bond lengths in
After coordination of the ligand to the metal complexes
the ethyl groups of 2Ϫ4 are no longer equivalent. So, in the
1H NMR spectra of 3 the CH2 resonances show dia-
stereotopism and appear as multiplets, rather than the ex-
pected quartet. The two different CH2 groups appear as one
set of multiplets. This may arise because the differences in
chemical shifts are very small and they coincide with one
another. Although the ethyl groups are not equivalent, 2
and 4 show simple quartets and triplets for the different
CH2 and CH3 groups, respectively. These values are in good
agreement with those found in [Cp(CO)2Fe(Hdebarb)] [15].
As 5 is almost symmetrical, it does not show multiplets for
the two ethyl groups. The signals of 3 are shifted further
downfield than those of the other complexes, indicative of
an electron-enriched system, because of the more strongly
electron donating triphenylphosphine ligands. The signals
for the CH2 and CH3 hydrogen atoms of 2Ϫ5 are shifted
slightly upfield in comparison with 1 (1H: CH2 1.93 and
CH3 0.84 ppm in CD3OD).
2
are very similar to the analogous ones in
[Cp(NO)2Cr{N(BF3)SNSiMe3}] [20]. The environment of
N3 is trigonal-planar [sum of angles at N3 ϭ 359.9°;
C1ϪN3ϪCr1
119.0(13)°; C4ϪN3ϪCr1
119.7(13)°;
C4ϪN3ϪC1 121.2(16)°].
The 13C NMR spectra of 2Ϫ4 display three signals for
the three different carbonyl groups within the coordinated
barbiturate moiety, and 3Ϫ4 show three signals for the car-
bonyl ligands attached to rhenium. However, some weak
unresolved signals (181.31Ϫ156.22 ppm) were observed for
the thirteen carbonyl carbons of complex 5. In all com-
plexes the remaining the barbiturate carbon atoms show
only one signal for each of CEt2 [58.23 (2), 56.17 (3), 57.18
(4) ppm), CH2 (32.99 (2), 32.05 (3), 33.17 (4), 32.83 ppm
(5)] and CH3 [9.93 (2), 9.46 (3), 9.86 (4), 9.51 ppm (5)]. In
the case of 5 it was not possible to identify the signal for
the CEt2 carbon atom, as it was in the same region as the
signal of CD2Cl2. When the NMR spectrum of this com-
Figure 1. Molecular structure of 2. Thermal ellipsoids are drawn at
˚
30 % probability. Selected bond lengths /A and angles /°: Cr1ϪN1
1.709(18), Cr1ϪN2 1.722(18), Cr1ϪN3 2.055(18), O2ϪN1
1.167(2), O1ϪN2 1.163(2), N3ϪC1 1.374(2), N3ϪC4 1.366(2),
N4ϪC4 1.390(3), C2ϪC5 1.539(3), C5ϪC6 1.519(3), C7ϪC8
1.526(3), Cr1ϪC11 2.201(2), Cr1ϪC13 2.184(3), N1ϪCr1ϪN2
96.0(9),
N1ϪCr1ϪN3
99.9(8),
N2ϪCr1ϪN3,
99.3(7),
C4ϪN3ϪCr1 119.7(13), C1ϪN3ϪCr1 119.0(13), O2ϪN1ϪCr1
169.4(18), O1ϪN2ϪCr1 169.6(16), N1ϪCr1ϪC10 134.0(11),
N2ϪCr1ϪC10 128.3(11), C3ϪC2ϪC1 114.5(16), C3ϪN4ϪC4
plex was measured in CDCl3, the CEt2 signal was detected 126.4(17), C4ϪN3ϪC1 121.2(16), O3ϪC1ϪN3 120.6 (18).
498 www.zaac.wiley-vch.de
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5,5-Diethylbarbiturato Complexes of Cr0 and ReI
Figure 4. Molecular structure of 5. Thermal ellipsoids are drawn at
30 % probability. The disordered protons of two ethyl groups and
one molecule of the complex are omitted for clarity. Selected bond
˚
lengths /A and angles /°: Re1ϪN1 2.208(8), Re2ϪN2 2.181(8),
Re1ϪC1 2.049(11), Re1ϪC2 2.058(11), Re1ϪC3 2.029(12),
Re1ϪC4 2.020(11), Re1ϪC5 1.936(11), Re2ϪC14 2.007(11),
Re2ϪC15 2.031(12), Re2ϪC16 2.019(11), Re2ϪC17 2.009(13),
Re2ϪC18 1.937(12), C5ϪO5 1.142(14), C18ϪO13 1.169(14),
N1ϪC6 1.378(13), N1ϪC9 1.360(13), N2ϪC6 1.407(14) N2ϪC7
1.345(13), C5ϪRe1ϪN1 175.7(4), C18ϪRe2ϪN2 178.0(4),
C9ϪN1ϪRe1 118.7(6), C6ϪN1ϪRe1 118.6(7), N1ϪC6ϪN2
121.3(9), C7ϪN2ϪC6 121.4(8), C9ϪN1ϪC6 122.5(9).
Figure 2. Molecular structure of 3. Thermal ellipsoids are drawn at
30 % probability. Hydrogen atoms of ethyl and phenyl groups are
˚
omitted for clarity. Selected bond lengths /A and angles /°:
Re1ϪN1 2.220(2), Re1ϪP1 2.494(10), Re1ϪC1 2.010(3), Re1ϪC2
1.977(3), Re1ϪC3 2.002(3), Re1ϪC4 1.926(3), O1ϪC1 1.130(4),
O2ϪC2 1.129(4), O3ϪC3 1.134(3), O4ϪC4 1.149(4), N1ϪC5
1.374(3), N2ϪC8 1.388(3), C5ϪC6 1.527(4), N2···H2···O7 2.908,
N1ϪRe1ϪP1 96.2(6), C1ϪRe1ϪN1 89.3(11), C2ϪRe1ϪN1
87.2(10), C3ϪRe1ϪN1 89.5(10), C4ϪRe1ϪN1 176.8(10),
C5ϪN1ϪRe1 117.2(17), C8ϪN1ϪRe1 121.8(17), C5ϪN1ϪC8
In all three rhenium complexes 3Ϫ5 pseudo-octahedral
coordination is observed around the rhenium atom. In 3
the barbiturate and PPh3 ligands are cis to one another, as
illustrated in Figure 2. In this structure the two ethyl groups
are inequivalent, one being directed towards the carbonyl
ligands and the other towards the phenyl ring. The ReϪN
120.4(2),
C8ϪN2ϪC7
126.9(2),
C7ϪC6ϪC5
113.8(2),
C4ϪRe1ϪN1ϪC5 77.2(18), C4ϪRe1ϪN1ϪC8 Ϫ94.6(18),
N2···H2···O(7) 176.0(6).
˚
and ReϪP bond lengths of 2.220(2) and 2.494(10) A,
respectively, are similar to those of aziridine complexes of
˚
Re [e.g., 2.220(4) and 2.496(1) A] [19]. Due to the steric hin-
drance of the bulkier phenyl group, the N1ϪRe1ϪP1 bond
angle of 96.2(6)° is larger than the CnϪRe1ϪN1 (n ϭ 1Ϫ3)
bond angles, which lie between 87.2 and 89.5°. The fact that
˚
the ReϪC4 distance of 1.926(3) A is considerably shorter
than the MϪC bonds of all other carbonyl ligands in the
˚
complex (1.977(3), 2.002(3) and 2.010(3) A) indicates
greater π back-donation to this CO ligand because of the
good σ-donor barbiturate ligand in trans position. For the
˚
same reason the O4ϪC4 bond length [1.149(4) A] is longer
than the other OϪC bond lengths [1.129(4), 1.130(4),
˚
1.134(3) A]. The same characteristic is observed in com-
plexes 4 and 5. The ReϪCO bond lengths in these com-
˚
plexes trans to the barbiturate N ligand (1.936Ϫ1.943 A)
Figure 3. Molecular structure of 4. Thermal ellipsoids are drawn at
are shorter than the other ReϪCO distances
30 % probability. The disordered protons of the ethyl group are
˚
(2.007Ϫ2.058 A). The NϪReϪC bond angle deviates only
˚
omitted for clarity. Selected bond lengths /A and angles /°:
slightly from 180° [3: C4ϪRe1ϪN1 176.87(10)°, 4:
C3ϪRe1ϪN1 176.8(2)°; 5: C5ϪRe1ϪN1 175.7(4)° and
C18ϪRe2ϪN2 178.0(4)°], which may be attributed to the
lower steric hindrance in comparison to the complex in
which the deviation is the largest because the bulky PPh3
ligand is in the cis position. The plane of the ligand in 3 is
approximately perpendicular to the equatorial co-ordi-
Re1ϪN1 2.197(4), Re1ϪC3 1.943(6), Re1ϪC5 2.019(6), Re1ϪC4
2.020(6), Re1ϪC1 2.021(6), Re1ϪC2 2.023(5), C3ϪO3 1.129(7),
C4ϪO4 1.121(6), C1ϪO1 1.108(6), C2ϪO2 1.116(6), C3ϪRe1ϪN1
176.8(2), C5ϪRe1ϪN1 87.88(19), C1ϪRe1ϪN1 89.55(18),
C6ϪN1ϪRe1 119.5(3), C9ϪN1ϪRe1 119.6(3), C4ϪRe1ϪC2
91.6(2),
C3ϪRe1ϪC4
88.7(2),
C4ϪRe1ϪC1
178.0(2),
O3ϪC3ϪRe1 177.5(5), C6ϪN1ϪC9 120.8(4), N1ϪC9ϪN2
119.4(4), C5ϪRe1ϪC2 176.9(2).
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499

N. Haque, J. N. Roedel, I.-P. Lorenz
ARTICLE
δ ϭ 8.14 (br., 1 H, NH), 5.66 (s, 5 H, Cp), 1.88 (q, 3J ϭ 7.4 Hz,
nation plane containing the PPh3 ligand [torsion angles
C4ϪRe1ϪN1ϪC5 and C4ϪRe1ϪN1ϪC8 are 77.2(18)°
and Ϫ94.6(18)°, respectively]. This is in good agreement
with the corresponding torsion angles of cis-[PtCl-
(Hdebarb)(PPh3)2] [1]. Furthermore, the X-ray structure
analysis of 5 shows that, although equivalent Re(CO)5 moi-
eties are bonded with the nitrogen atoms of the same li-
gand, their bond lengths and angles in the two complex
fragments are not exactly same. This indicates that the two
rhenium atoms interact with the ligand in slightly different
manner, and therefore the Re1ϪN1 and Re2ϪN2 bond
3
4 H, CH2), 0.75 (t, J ϭ 7.4 Hz, 6 H, CH3). 13C NMR (CD2Cl2):
δ ϭ 181.19 (s, CO), 174.79 (s, CO), 156.43 (s, CO), 102.80 (s, Cp),
58.23 (s, CEt2), 32.99 (s, CH2), 9.93 (s, CH3).
General Procedure for the Synthesis of 3؊5
AgOTf was added to a stirred solution of metal complex in 20 mL
of chloroform, and the solution was stirred for 1 h until AgBr had
precipitated. After centrifugation and separation of the solution by
decantation, 1 was added to the solution followed by triethylamine
to give a clear, pale brown solution which was stirred at room tem-
perature for 2 d, after which the solvent was removed in vacuo.
After crystallisation, the crystals of 3 were washed with 10 mL and
4 and 5 with 5 mL of methanol and then dried in vacuo.
˚
lengths differ by 0.03 A. Intermolecular hydrogen bonding
is observed only in 3. Here, the molecules of Hdebarb are
connected to each other by an NϪH···O bond involving the
amino hydrogen atom of one Hdebarb and the carbonyl
oxygen atom of another Hdebarb ligand.
[PPh3Re(CO)4(C8H11N2O3)] (3): Reagents: 27.6 mg (0.15 mmol) 1;
31 μL
(0.221 mmol)
NEt3;
96.1 mg
[(PPh3)Re(CO)4Br]
(0.15 mmol); 38.5 mg (0.15 mmol) AgOTf. Yield 50 %; colourless
crystals; decomp. 180Ϫ186 °C. C30H26N2O7PRe (743.71); C 47.82
(calcd. 48.45); H 3.70 (3.53); N 3.94 (3.77). IR (KBr): ν(ReCϵO)
2106 s, 2020 vs, 1999 sh, 1926 vs, ν(COHdebarb) 1716 s, 1675 s,
1615 vs. cmϪ1. IR (CHCl3): ν(NH) 3390 w, ν(ReCϵO) 2105 s,
2011 vs, 1946 s, ν(COHdebarb) 1718 m, 1697 sh, 1681 m, 1619 s
cmϪ1. MS (FABϩ): m/z ϭ 745 (MH22ϩ, 8.5 %), 743 (Mϩ, 5 %), 686
(MϩϪ2COϪHϩ, 1.8 %), 630 (MϩϪ4COϪHϩ, 2.3 %), 262 (PPh3,
53 %). 1H NMR (CD2Cl2): δ ϭ 7.76 (br., 1 H, NH), 7.47Ϫ7.37 (m,
15 H, ArϪH), 1.77 (m, 4 H, CH2), 0.65 (t, 3J ϭ 7.4 Hz, 6 H, CH3).
13C NMR (CD2Cl2): δ ϭ 188.39 (d, 2J(P,C) ϭ 6.7 Hz, ReCO),
Experimental Section
General
All reactions were carried out under argon by using standard
Schlenk and vacuum-line techniques. Solvents were purified by
standard procedures; dichloromethane was distilled from calcium
hydride. Triethylamine was distilled prior to use. [CpCr(NO)2Cl]
[21], [Re(CO)5Br] [22] and cis-[PPh3Re(CO)4Br] [23] were prepared
and purified according to literature procedures. Other reagents
were commercially available and used without further purification.
2
2
187.16 (d, J(P,C) ϭ 9.1 Hz, ReCO), 184.26 (d, J(P,C) ϭ 56.0 Hz,
ReCO), 181.08 (s, COHdebarb), 173.33 (s, COHdebarb), 156.59 (s,
COHdebarb), 133.30 (d, 2J(P,C) ϭ 10.54 Hz, o-ArC), 131.97 (d,
NMR spectra were measured with a Jeol Eclipse 270, Jeol Eclipse
400 or Jeol EX 400 spectrometer; the chemical shifts are given rela-
tive to external standards (TMS and 85 % H3PO4). Mass spectra
were recorded with a Jeol MStation JMS 700, NBA matrix (FABϩ).
IR spectra were recorded from KBr pellets or in solution by using
a Perkin-Elmer Spectrum One FTIR spectrometer. The melting
points, obtained with a Büchi Melting Point B-540 device, are un-
corrected. Elemental analysis was performed by the Microana-
lytical Laboratory of the Department of Chemistry and Biochemis-
try, LMU, using a Hereaus Elementar Vario El apparatus.
4
1J(P,C) ϭ 47.92 Hz, ArCq), 130.87 (d, J(P,C) ϭ 1.92 Hz, p-ArC),
128.79 (d, 3J(P,C) ϭ 9.58 Hz, m-ArC), 56.17 (s, CEt2), 32.05 (s,
CH2), 9.46 (s, CH3). 31P NMR (CD2Cl2): δ ϭ 11.64 (s, PPh3).
[Re(CO)5(C8H11N2O3)] (4): Reagents: 36.8 mg (0.2 mmol) 1; 40 μL
(0.286 mmol) NEt3; 81.3 mg [Re(CO)5Br] (0.2 mmol); 51.4 mg
(0.2 mmol) AgOTf. Yield 49 %; colourless crystals; decomp.
160Ϫ164 °C. C13H11N2O8Re (509.45); C 30.86 (calcd. 30.65); H
2.29 (2.18); N 5.67 (5.50). IR (CHCl3): ν(NH) 3386 w, ν(ReCϵO)
2151 w, 2043 vs, 1992 s, ν(COHdebarb) 1723 m, 1683 m, 1620 s cmϪ1
.
Synthesis of Chromium Complex 2
MS (FABϩ): m/z ϭ 511 (MH22ϩ, 32 %), 509 (Mϩ, 20 %), 453
(MϩϪ2CO, 16 %), 424 (MϩϪ3COϪ Hϩ, 2.8 %). 1H NMR
(CD2Cl2): δ ϭ 8.33 (br., 1 H, NH), 1.92 (q, 3J ϭ 7.4 Hz, 4 H, CH2),
0.74 (t, 3J ϭ 7.4 Hz, 6 H, CH3). 13C NMR (CD2Cl2): δ ϭ 181.97 (s,
ReCO), 180.67 (s, ReCO), 180.15 (s, COHdebarb), 174.02 (s, ReCO),
172.49 (s, COHdebarb), 157.23 (s, COHdebarb), 57.18 (s, CEt2), 33.17
(s, CH2), 9.86 (s, CH3).
A method for the preparation of cis-[PtCl(Hdebarb)(PPh3)2] re-
ported by Fawcett et al. [1] was modified for the preparation of
2. Triethylamine (43 μL, 0.307 mmol) was mixed with 1 (38.7 mg,
0.21 mmol) in chloroform (10 mL) whilst stirring. To this clear
colourless solution [CpCr(NO)2Cl] (44.6 mg, 0.21 mmol) was ad-
ded. The green-brown solution was stirred for 2 d at room tempera-
ture and the solvent evaporated to dryness under reduced pressure.
The residue was extracted with chloroform (30 mL), washed with
water (20 mL) and the chloroform layer separated, dried (CaCl2)
and filtered and the solvent evaporated. The green solid was dried
in vacuo.
[Re2(CO)10(C8H11N2O3)] (5): Reagents: 27.6 mg (0.15 mmol) 1;
72 μL (0.514 mmol) NEt3; 121.8 mg [Re(CO)5Br] (0.3 mmol);
79.6 mg (0.31 mmol) AgOTf. Yield 53 %; colourless crystals; de-
comp. 169 °C. C18H10N2O13Re2 (834.70); C 25.34 (calcd. 25.89); H
1.55 (1.21); N 3.25 (3.36). IR (CHCl3): ν(ReCϵO) 2145 m, 2044 vs,
1987 s, ν(COHdebarb) 1682 w, 1618 m, 1586 m cmϪ1. MS (FABϩ):
m/z ϭ 835 (MHϩ, 40 %), 834 (Mϩ, 5 %), 806 (MϩϪCO, 15 %), 778
(MϩϪ2CO, 34 %), 750 (MϩϪ3CO, 12 %), 722 (MϩϪ4CO, 26 %),
[Cp(NO)2Cr(C8H11N2O3)] (2): Yield 42 %; green crystals; de-
composition 166 °C. C13H16CrN4O5 (360.30); C 43.25 (calcd.
43.33); H 4.53 (4.49); N 15.52 (15.55). IR (KBr): ν(NO) 1814 vs,
1727 vs, ν(COHdebarb) 1714 sh, 1671 m, 1620 s cmϪ1. IR (CHCl3): 694 (MϩϪ5CO, 11 %), 453 (MϩϪ5COϪRe(CO)2Hϩ, 27 %). 1H
3
3
ν(NH) 3389 w, ν(NO) 1825 s, 1720 vs, ν(COHdebarb
1621 m cmϪ1 MS (FABϩ): m/z 361 (MHϩ, 38 %), 331 7.4 Hz, 6 H, CH3). 13C NMR (CD2Cl2): δ ϭ 181.31Ϫ156.22 (m,
(MHϩϪNO, 18 %), 300 (MϩϪ2NO, 31 %). 1H NMR (CD2Cl2):
COHdebarb and ReCO), 32.83 (s, CH2), 9.51 (s, CH3).
) 1682 sh, NMR (CD2Cl2): δ ϭ 1.93 (q, J ϭ 7.4 Hz, 4 H, CH2), 0.75 (t, J ϭ
.
ϭ
500
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2009, 496Ϫ502

5,5-Diethylbarbiturato Complexes of Cr0 and ReI
Table 1. Crystal data and details of structural refinement for compounds 2Ϫ5.
Compound
2
3
4
5
formula
C13H16CrN4O5
360.30
200(2)
C30H26N2O7PRe
743.71
200(2)
C13H11N2O8Re
509.45
200(2)
C18H10N2O13Re2
834.70
200(2)
FW /g·molϪ1
T /K
˚
λ/ A
0.71073
0.71073
0.71073
0.71073
crystal system
space group
triclinic
P1
8.0472(16)
10.061(2)
10.825(2)
63.84(3)
85.62(3)
85.11(3)
783.1(3)
2
triclinic
P1
9.5486(19)
10.974(2)
13.998(3)
92.29(3)
91.41(3)
95.91(3)
1457.0(5)
2
1.6953(6)
4.274
monoclinic
P21/c
12.468(3)
6.7750(14)
20.018(4)
90
103.81(3)
90
1642.1(7)
4
triclinic
P1
7.0648(14)
13.593(3)
14.288(3)
109.38(3)
91.36(3)
98.92(3)
1274.5(5)
2
2.1749(7)
9.552
772
¯
¯
˚
a /A
˚
b /A
˚
c /A
Ͱ /°
β /°
γ /°
3
˚
V /A
Z
ρcalcd. /g·cmϪ1
μ /mmϪ1
F(000)
1.5282(6)
0.761
372
2.061(8)
7.444
967
732
crystal size /mm
θ range /°
index range
0.21 ϫ 0.16 ϫ 0.09
3.23 to 27.52
Ϫ10 Յ h Յ 10,
Ϫ13 Յ k Յ 13,
Ϫ14 Յ l Յ 14
6812
0.19 ϫ 0.14 ϫ 0.09
3.26 to 27.48
Ϫ12 Յ h Յ 12,
Ϫ14 Յ k Յ 14,
Ϫ18 Յ l Յ 18
8977
0.30 ϫ 0.25 ϫ 0.22
3.37 to 27.48
Ϫ16 Յ h Յ 16,
Ϫ8 Յ k Յ 8,
Ϫ25 Յ l Յ 25
12028
0.25 ϫ 0.09 ϫ 0.06
3.23 to 27.44
Ϫ9 Յ h Յ 9,
Ϫ17 Յ k Յ 17,
Ϫ18 Յ l Յ 18
10571
reflns collected
independent reflns
Rint
3595
0.0234
4648
0.0204
3743
0.0849
10571
0.0000
completeness to θ
refinement method
99.7 %
99.7 %
99.4 %
99.3 %
full-matrix least-squares full-matrix least-squares full-matrix least-squares full-matrix least-squares
on F2
on F2
on F2
on F2
data/restraints/parameters
S on F2
Final R indices [I>2 σ (I)]
3595/0/208
1.072
R1 ϭ 0.0342,
wR2 ϭ 0.0778
R1 ϭ 0.0450,
wR2 ϭ 0.0872
0.393 and Ϫ0.414
6652/0/370
1.064
R1 ϭ 0.0223,
wR2 ϭ 0.0499
R1 ϭ 0.0265,
wR2 ϭ 0.0515
1.156 and Ϫ1.364
3743/0/217
1.059
R1 ϭ 0.0366,
wR2 ϭ 0.0945
R1 ϭ 0.0445,
wR2 ϭ 0.0995
1.185 and Ϫ1.753
10571/3/632
1.048
R1 ϭ 0.0473,
wR2 ϭ 0.1250
R1 ϭ 0.0491,
wR2 ϭ 0.1274
2.712 and Ϫ2.272
R indices (all data)
largest difference peak and
Ϫ3
˚
hole /e·A
absolute structure parameter
Ϫ
Ϫ
Ϫ
0.121(12)
[2] D. A. Williams, T. L. Lemke in Foye’s Principles of Medicinal
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X-ray Crystal Structure Determinations
Single-crystal X-ray diffraction data were collected on a Nonius
Kappa CCD diffractometer by using graphite-monochromated
MoKα radiation. Structure analyses were performed by direct meth-
ods using the SHELXS software and refined by full-matrix least-
squares techniques with SHELXL-97 [24]. The crystal data and
details of the structural refinement of complexes are given in Table
1. CCDC-704391 (2), -704392 (3), -704393 (4) and -704394 (5) con-
tain the supplementary crystallographic data for this paper. These
data can be obtained free of charge from the Cambridge crystallo-
graphic data centre via www.ccdc.cam.ac.uk/data_request/cif.
[9] L. Nassimbeni, A. Rodgers, Acta Crystallogr., Sect. B 1974,
30, 1953Ϫ1961.
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Acknowledgement
Financial support from the Bayerische Forschungsstiftung,
München is gratefully acknowledged. We thank B. Koehler and
S. Kammerer for their helpful assistance.
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Received: October 30, 2008
Published Online: January 20, 2009
502
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2009, 496Ϫ502