www.elsevier.com/locate/ica

Inorganica Chimica Acta 358 (2005) 1225–1230

[Hg(9-methyl-1-deazapurine)2](NO3)2 Æ H2O: a complex witha distorted hexagonal bipyramidal metal ion coordination sphere

Jens Muller *, Fabian-Alexander Polonius, Michael Roitzsch

Department of Chemistry, University of Dortmund, Otto-Hahn-Str. 6, 44227 Dortmund, Germany

Received 4 November 2004; accepted 24 November 2004

Available online 11 February 2005

Abstract

Reaction of 9-methyl-1-deazapurine (9-MeDP) with Hg(CF3COO)2 in the presence of NaNO3 yields the title compound [Hg(9-

MeDP)2](NO3)2 Æ H2O with the two 9-MeDP ligands bound to the metal ion via their N7 positions. The X-ray structure is reported:

monoclinic, P21/c (no. 14), a = 5.4015(11), b = 20.467(4), c = 17.775(4) A, b = 97.00(3)�, V = 1950.4(7) A3, Z = 4. Hg is eight-coor-

dinate with two trans-oriented Hg–N bonds (2.073(3) and 2.075(3) A) and three nearly coplanar, bidentate nitrate moieties (Hg–O:

2.716(3)–2.985(4) A), leading to a distorted hexagonal bipyramidal environment of the metal ion. Within this structure, the nitrate

ions form a honeycomb-like chain structure with HgII being positioned inside the combs. This work represents the first report of

such geometry for a transition metal ion surrounded by symmetrically bidentate nitrate ions. The corresponding nucleoside, 1-dea-

zapurine 2 0-deoxyribonucleoside, also forms a stable 2:1 complex with HgII, as was shown by 1H NMR spectroscopy, making it a

potential candidate for incorporation into nucleic acids based on metal-mediated base pairs.

� 2004 Elsevier B.V. All rights reserved.

Keywords: Bioinorganic chemistry; Deazapurine; Metal-mediated base pair; Mercury

1. Introduction

The coordination behaviour of HgII towards nucleic

acids and their components has been extensively studied[1–3]. Many examples are known of methylmercury com-

plexes [1,4] as well as of HgCl2 adducts [5] to nucleo-

bases. Although there is increasing experimental

evidence that HgII inserts into base pairs by substitution

of an imino proton [2,6,7], only three X-ray crystal struc-

tures have been reported as yet in which HgII is (more or

less) linearly coordinated to two nucleobases or deriva-

tives thereof: A bis(methylthyminato-N3) complex [8],a bis(9-methyladeninium-N7) complex [9], and a bis(8-

azahypoxanthinato-N9) complex [10] represent the

only structurally characterized examples of a possible

0020-1693/$ - see front matter � 2004 Elsevier B.V. All rights reserved.

doi:10.1016/j.ica.2004.11.038

* Corresponding author. Tel.: +49 231 755 5034; fax: +49 231 755

3797.

E-mail address: jens.mueller@uni-dortmund.de (J. Muller).

interstrand cross-link imposed by HgII, although strictly

seen the HgII coordination mode found in the latter com-

pound cannot be present in DNA because here the pur-

ine N9 position is not available for metal binding.1-Deazapurine represents a model for the purine nucleo-

bases in which due to the lack of coordination sites on

the Watson–Crick edge metal coordination is feasible

only via the Hoogsteen edge, corresponding to the for-

mation of a metal-mediated base pair within a triple helix

[11]. Although 1-deazapurine has not been observed in

nucleic acids as yet, a recent report suggests that it might

be formed in vivo by reaction of the purine precursoraminoimidazole ribonucleotide with malondialdehyde,

the endogenous product of lipid peroxidation, and hence

might inadvertently be incorporated into DNA at very

low levels [12]. Furthermore, 1-deazapurine has lately

been used in a study on the possibility of expanding the

genetic alphabet by using unnatural nucleoside ana-

logues [13]. In this context, 1-deazapurine appears to

Chart 1.

1226 J. Muller et al. / Inorganica Chimica Acta 358 (2005) 1225–1230

be a good candidate for an artificial nucleobase inoligonucleotides that incorporate metal-mediated base

pairs [14–20]. These systems are of great scientific interest

because of their potential application as self-assembling

electronic circuits [21,22]. Towards this end, we describe

studies of the metal coordination behaviour of 9-methyl-

1-deazapurine (9-MeDP, Chart 1) and 1-deazapurine

b-2 0-deoxyribonucleoside using mercuric ions. Although

HgII is known to adopt a variety of coordinationgeometries, it prefers the linear coordination mode neces-

sary for the formation of a metal-mediated base pair

[2,23].

2. Experimental

2.1. Preparations

2.1.1. 9-Methyl-1-deazapurine (1a) and 7-methyl-1-

deazapurine (1b)1-Deazapurine [24] (1035 mg, 8.69 mmol) and sodium

hydride (emulsion in mineral oil, washed with dry

diethyl ether) (207 mg, 8.63 mmol) were dissolved in

dry DMF (30 ml), the clear solution was cooled to

0 �C and stirred for 90 min. After addition of methyl io-dide (639 ll, 1.44 g, 10.1 mmol), the reaction was al-

lowed to proceed until the ice bath had reached

ambient temperature (2 1/2 h). DMF was then removed

by vacuum distillation at 35 �C and the crude product

was purified by flash chromatography (SiO2, EtOH).

Collected fractions contained 1a (Rf = 0.52) and 1b

(Rf = 0.40). Re-crystallization from CHCl3 gave hygro-

scopic white foams (1a: 345 mg, 2.59 mmol, 30%; 1b:212 mg, 1.59 mmol, 18%). 1a: Calc. for C7N3H7 Æ 0.83-H2O: C, 56.7; H, 5.9; N, 28.4. Found: C, 56.7; H, 5.8;

N, 28.3%. 1H NMR (D2O, pD 6.6, d, ppm): 8.14 (d,

J = 4.4 Hz, H2), 8.10 (s, H8), 7.88 (d, J = 8.0 Hz, H6),

7.20 (dd, J = 4.4 Hz, 8.0 Hz, H1), 3.71 (s, CH3). 1b:

Calc. for C7N3H7 Æ 4.1H2O: C, 40.6; H, 7.4; N, 20.3.

Found: C, 40.6; H, 6.4; N, 20.0%. 1H NMR (D2O, pD

5.6, d, ppm): 8.32 (d, J = 4.4 Hz, H2), 8.19 (s, H8),7.83 (d, J = 8.0 Hz, H6), 7.27 (dd, J = 4.4 Hz, 8.0 Hz,

H1), 3.79 (s, CH3).

2.1.2. [Hg(9-MeDP)2](NO3)2 Æ H2O (2)To a solution of 1a (45 mg, 0.37 mmol) in H2O (1 ml)

were added 250 ll of a 0.74 mM solution of

Hg(CF3COO)2 in H2O (0.185 mmol) and 200 ll of a

2.2 mM solution of NaNO3 in H2O (0.44 mmol). After

one day, colourless crystals of 2 were collected, which

were suitable for X-ray crystallography. Upon drying

at 40 �C overnight, 2 lost its water of crystallization

(54 mg, 91 lmol, 50%). 2: Calc. for C14H14HgN8O6:C, 28.5; H, 2.4; N, 19.0. Found: C, 28.3; H, 2.6; N,

19.0%. 1H NMR (D2O, pD 4.0, d, ppm): 9.16 (s, H8),

8.72 (d, J = 4.8 Hz, H2), 8.59 (d, J = 8.0 Hz, H6), 7.73

(dd, J = 4.8 Hz, 8.0 Hz, H1), 4.18 (s, CH3).199Hg

NMR (D2O, pD 4.0, d, ppm): �1948.

2.1.3. 1-Deazapurine 2 0-deoxyribonucleoside (a: 3a, b:3b)

To a suspension of 1-deazapurine [24] (1.191 g, 10.0

mmol) in acetonitrile (50 ml) was added sodium hydride

(0.520 g, 13.0 mmol, 60% in mineral oil). The mixture

was cooled to 0 �C and 2-deoxy-3,5-di-O-p-toluoyl-a-DD-erythro-pentofuranosyl chloride [25] (5.20 g, 13.4

mmol) was added in four portions. After stirring at 0

�C for 3 h, the solvent was removed in vacuo. The crude

product was purified by flash chromatography (SiO2,ethyl acetate:methanol:chloroform 20:1:3) to give 1.52

g (3.22 mmol, 32%) of an anomeric mixture of 2 0-

deoxy-3 0,5 0-di-O-p-toluoyl-a-DD-erythro-pentofuranosyl-3H-imidazo[4,5-b]pyridine. This product was dissolved

in methanol (20 ml) and saturated methanolic ammonia

(20 ml) was added. After 4 d at ambient temperature, the

solvent was removed in vacuo and the product was puri-

fied by flash chromatography (SiO2, methanol:dichlo-romethane 1:9) to give 188 mg (0.799 mmol, 25% for

the deprotection and anomeric resolution steps) of 1-

deazapurine b-2 0-deoxyribonucleoside 3b as a white so-

lid. The total amount of the side product 1-deazapurine

a-2 0-deoxyribonucleoside 3a was not quantified. 3a: 1H

NMR (D2O, pD 6.5, d, ppm): 8.63 (s, H8), 8.40 (dd,

J = 1.4 Hz, 4.8 Hz, H2), 8.18 (dd, J = 1.4 Hz, 8.2 Hz,

H6), 7.44 (dd, J = 4.8 Hz, 8.2 Hz, H1), 6.60 (dd,J = 2.8 Hz, 7.8 Hz, H1 0), 4.56 (m, H3 0), 4.39 (m, H4 0),

3.73 (m, H5 0, H500), 2.98 (m, H2 0), 2.62 (m, H200). 3b:1H NMR (D2O, pD 6.9, d, ppm): 8.55 (s, H8), 8.39

(dd, J = 1.4 Hz, 5.0 Hz, H2), 8.17 (dd, J = 1.4 Hz, 8.2

Hz, H6), 7.44 (dd, J = 5.0 Hz, 8.2 Hz, H1), 6.61 (dd,

J = 6.4 Hz, 7.6 Hz, H1 0), 4.67 (m, H3 0), 4.21 (m, H4 0),

3.82 (m, H5 0, H500), 2.90 (m, H2 0), 2.57 (m, H200).

2.2. Instrumentation

1H NMR spectra were recorded on Varian Mercury

200 and Bruker DRX 400 spectrometers. 199Hg NMR

spectra were recorded at 53.51 MHz on a Bruker DPX

300 instrument. Chemical shifts were referenced to inter-

nal sodium 3-(trimethylsilyl)propanesulfonate (1H) and

external dimethylmercury (199Hg). pD values were ob-tained by adding 0.4 to the pH meter reading [26]. The

pKa values in H2O were calculated from the pK�a values

Table 1

Crystallographic data for [Hg(9-MeDP)2](NO3)2 Æ H2O (2)

Formula C14 H16 HgN8O7

Formula weight 608.94

Crystal system monoclinic

Space group P21/c (no. 14)

Unit cell dimensions

a (A) 5.4015(11)

b (A) 20.467(4)

c (A) 17.775(4)

b (�) 97.00(3)

V (A3) 1950.4(7)

Z 4

Dcalc (g/cm�3) 2.074

l (Mo Ka) (mm�1) 7.948

F(000) 1168

Crystal size (mm) 0.10 · 0.12 · 0.26

Temperature (K) 293

Radiation (A) Mo Ka (0.71073)

hmin, hmax (�) 3.2, 27.5

Dataset �6: 7; �26: 23; �15: 22

Total, unique data, Rint 14611, 4429, 0.046

Observed data [I > 4r(I)] 2890

Nref, Npar 4429, 335

R, wR2, S 0.0320, 0.0420, 0.98

Maximum and average shift/error 0.00, 0.00

Minimum and maximum

residual density (e A�3)

�0.60, 0.62

J. Muller et al. / Inorganica Chimica Acta 358 (2005) 1225–1230 1227

in D2O according to pK�a ¼ 1:015pKa þ 0:45 [27].

Microanalyses were measured on a Leco CHNS 932

instrument.

2.3. X-ray crystallography

Crystal data were collected at 293 K on an Enraf–

Nonius–KappaCCD diffractometer using graphite-

monochromated Mo Ka radiation (k = 0.71073 A).

For data reduction and cell refinement, the Bruker–

Nonius HKL 2000 Suite was used. The structures were

solved by direct methods and subsequent Fourier syn-theses and refined by full-matrix least squares on F2

using the SHELXTL PLUSSHELXTL PLUS and SHELXLSHELXL-97 programs

[28]. All non-hydrogen atoms were refined anisotropi-

cally, hydrogen atoms were refined isotropically. Rele-

vant crystallographic data are listed in Table 1.

3. Results and discussion

3.1. Syntheses and characterization of compounds

9-Methyl-1-deazapurine (1a) was synthesized by

methylation of 1-deazapurine using methyl iodide. The

isomeric 7-methyl-1-deazapurine (1b) was obtained as

a side product. 7-MeDP and 9-MeDP could be distin-

guished with the help of 1H,1H NOESY experiments,which gave rise to two cross-peaks involving the methyl

group in the first case (close contacts to H6 and H8) and

one cross-peak only in the second case (close contact to

H8). In order to rule out any possible competition be-

tween protonation and metalation of the ligand, the

pKa values of 1a and 1b need to be known. pD-depen-

dent 1H chemical shifts of the aromatic protons have

been measured in order to verify pKa values determinedspectrophotometrically more than 40 years ago [29]. In

the case of 9-MeDP, fitting of these data leads to a

pKa value (corrected for H2O) of 3.67(5). The isomeric

7-MeDP is slightly less acidic; its pKa amounts to

3.83(5). Both values correlate well with the photometri-

cally determined ones (3.93 and 4.10, respectively).

Based on these results, no competing effect of proton-

ation should be expected when performing the metala-tion reactions at pH P 5. Addition of NaNO3 to a

solution of 1a and 0.5 equivalents of HgII gave colour-

less crystals of [Hg(9-MeDP)2](NO3)2 Æ H2O (2) that

were suitable for X-ray crystallography.

During the synthesis of 1-deazapurine 2 0-deoxyribo-

nucleoside at 0 �C, both a- and b-anomers 3a and 3b

were obtained. This finding is different from studies de-

scribed earlier, where formation of the b-product onlyhad been observed [30]. The anomers could easily be

distinguished by the characteristic coupling constants

of the H1 0 sugar proton in N-glycosides. Whereas the

coupling constants H1 0/H2 0 and H1 0/H200 are almost

identical in b-deoxyriboses (3b: 6.4 and 7.4 Hz), often

leading to the appearance of a pseudo-triplet in the1H NMR spectrum, they are fairly distinct in a-deoxy-riboses (3a: 2.8 and 7.8 Hz). The assignment was furthercorroborated by 1H,1H NOESY experiments. In the

spectra of 3b, H1 0 displays a strong cross-peak to H200

but only a very moderate one to H2 0, with the opposite

trend being observed in the spectra of 3a. The stereospe-

cific assignment of H2 0 and H200 was facilitated by com-

paring the intensities of their respective cross-peaks to

H3 0 (strong and weak, respectively). It turned out to

be of importance to perform the glycosylation reactionat 0 �C, because with increasing temperature the forma-

tion of undesired regioisomers with an N7-glycosidic

bond was observed as was discernible from an intense

cross-peak between H1 0 and H6 in a 1H,1H NOESY

experiment of the respective side product. A similar

observation had already been made during the synthesis

of 1-deaza-6-nitropurine 2 0-deoxyribonucleosides [30].

3.2. Structure of [Hg(9-MeDP)2](NO3)2 Æ H2O (2)

Fig. 1 provides a view of the cation of the title com-

pound [Hg(9-MeDP)2](NO3)2 Æ H2O (2). Selected inter-

atomic distances and angles are listed in Table 2. HgII

is bound to the N7 positions of two 9-MeDP ligands

that are arranged approximately trans to each other

(173.1(1)�) and are oriented at an angle of 82.98(7)�.The Hg–N distances of 2.073(3) and 2.075(3) A are in

the range of those typically found in complexes between

Fig. 1. View of [Hg(9-MeDP)2]2+ cation in 2 with atom numbering

scheme. Coordinated nitrate ions have been omitted for clarity.

Table 2

Selected interatomic distances (A) and angles (�) for [Hg(9-MeDP)2]-

(NO3)2 Æ H2O (2)

Hg–N7a 2.075(3) N7a–Hg–N7b 173.1(1)

Hg–N7b 2.073(3) N10–O11–Hg 92.5(3)

Hg–O11 2.985(4) N10–O13–Hg 104.1(3)

Hg–O13 2.747(3) N20–O21–Hg 98.2(2)

Hg–O21 2.716(3) N20–O22–Hg 96.1(3)

Hg–O22 2.774(3) N20a–O21a–Hg 99.0(2)

Hg–O21a 2.758(2) N20a–O23a–Hg 94.8(3)

Hg–O23a 2.856(3)

Hg� � �O1w 6.065(5)

Hg� � �Hga 5.402(1)

Fig. 2. Distorted hexagonal bipyramidal coordination of HgII in 2,

viewed along the N–Hg–N axis.

Fig. 3. Honeycomb-like chain structure of mercuric and nitrate ions in

2. The N–Hg–N axis is oriented perpendicular to the plane shown,

only the N7 positions of the 9-MeDP ligands are shown for clarity.

1228 J. Muller et al. / Inorganica Chimica Acta 358 (2005) 1225–1230

ligands coordinated via trans-oriented endocyclic nitro-

gen atoms and HgII, such as 1-methylthymine (2.04 A),

9-methylguanine (2.06(1), 2.08(1) A) or 1-methylcyto-

sine (2.07(1), 2.08(1) A) [5,8,9,31,32].Mercuric complexes are known to simultaneously

contain both close and distant bonded atoms [23]. Using

a van der Waals radius of 1.70 A for mercury, which is

the lower limit of the values suggested in the literature

[33], and 1.40 A for oxygen, the Hg–O contacts between

the metal ion and nitrate oxygen atoms observed in the

title compound (Hg–O: 2.716(3)–2.985(4) A) can defi-

nitely be considered bonding interactions. Additionalbonds exist to two symmetry-generated nitrate oxygen

atoms from a neighbouring unit cell (Hg–O: 2.758(2),

2.856(3) A). Hence, the HgII coordination sphere is com-

pleted by six longer contacts to three nitrate ions ori-

ented more or less perpendicular to the N–Hg–N

plane (65.2(2)�, 72.8(3)� and 72.8(3)�). Applying the cri-

teria proposed by Driessen and coworkers [34], all ni-

trate moieties in the title compound can be consideredsymmetrically bidentate, leading to a distorted hexago-

nal bipyramidal geometry around the metal ion (Fig.

2). The sum of inner angles within the distorted hexago-

nal plane amounts to 696� and deviates only slightly

from that of an ideal hexagon (720�). This kind of

arrangement of nitrate ions has previously been ob-

served for cadmium and tin complexes only [35–37],

although strictly seen the nitrate ions in the cadmiumcompound are asymmetrically bidentate. As the nitrate

ion comprising N20, O21, O22 and O23 is bridgingtwo neighbouring mercuric ions, an unprecedented

honeycomb-like chain structure of nitrate moieties is

generated that is held together by HgII ions positioned

inside the combs (Fig. 3). No unusual bond lengths

are observed for nitrate N–O bonds (1.229(4)–1.258(4)

A). The water of crystallization present in the structure

does not show any contacts with the mercuric ion

(Hg� � �O1w: 6.065(5) A). It does, however, display theonly hydrogen bonds feasible in 2, i.e., it bridges neigh-

bouring nitrate ions within a nitrate chain via O1w–

H� � �O12 hydrogen bonds (O1w� � �O12: 2.964(6) A,

O1w� � �O12a: 2.928(6) A). The intermetallic distance be-

tween two neighbouring mercuric ions of 5.402(1) A is

too long to account for a metal–metal interaction.

3.3. Solution studies of 1-deazapurine b-2 0-

deoxyribonucleoside

As supported by the crystal structure reported in this

work, 1-deazapurine b-2 0-deoxyribonucleoside (3b)

Fig. 4. 1H NMR chemical shifts of the aromatic protons of 1-

deazaadenine b-2 0-deoxyribonucleoside (3b) upon titration with

Hg(CF3COO)2 in a buffered solution (100 mM sodium acetate, pD

5.0, 30 mM 3b). The formation of a 2:1 complex can clearly be seen.

J. Muller et al. / Inorganica Chimica Acta 358 (2005) 1225–1230 1229

might find application as an artificial nucleobase in oligo-

nucleotides containing metal-mediated base pairs. For

this purpose, we have synthesized 3b. Its pKa value

was determined to be 2.84(2) using 1H NMR spectros-

copy as described above for 9-MeDP. As is customary

for nucleosides, it is slightly more acidic than the corre-sponding methyl nucleobase 1a [38]. A 1H NMR study

was performed in which Hg(CF3COO)2 was titrated to

a buffered solution of 3b at pD 5.0. Fig. 4 shows that

binding of HgII to the ligand takes place in the fast ex-

change limit so that no individual signals of starting

material and product but only average chemical shifts

are observed. The data can be fitted best by defining

two almost linear segments which intersect at 0.5 equiv-alents of HgII, showing the formation of a 2:1 complex

between 3b and the metal ion. Hence, the nucleoside

3b reacts with mercuric ions to adopt presumably the

same kind of 2:1 adduct in solution that its methyl ana-

logue 1a forms in the solid state. The minor downfield

shifts observed especially for the H8 proton between

0.5 and 1.0 equivalents of added metal ion might be ex-

plained with the presence of an equilibrium between 2:1and 1:1 complexes at elevated HgII concentrations. In

this case, the 2:1 and 1:1 complexes should have very

similar 1H chemical shifts.

3.4. Summary

Mercuric complexes of 9-methyl-1-deazapurine (9-

MeDP, 1a) and 1-deazapurine b-2 0-deoxyribonucleoside(3b) have been prepared. In [Hg(9-MeDP)2](NO3)2 ÆH2O (2), the metal ion is coordinated in a distorted hex-

agonal bipyramidal fashion by two axial 9-MeDP li-

gands and three equatorial nitrate ions that each bind

symmetrically bidentate. Nitrate ions are arranged in

layers of honeycomb-like chains, with HgII being lo-

cated in the centre of the combs. The corresponding

nucleoside 3b was shown to form a stable 2:1 complex

with HgII in solution. It can therefore be anticipated that

incorporation of 3b into oligonucleotides might lead to

the formation of double helices based on metal-medi-

ated base pairs. Work on studying this aspect further

is currently being pursued in our laboratory.

4. Supplementary material

CCDC No. 254736 contains the supplementary crys-

tallographic data for this paper. These data can be ob-

tained free of charge via www.ccdc.cam.ac.uk/

data_request/cif, by emailing data_request@ccdc.cam.ac.

uk, or by contacting The Cambridge Crystallographic

Data Centre, 12, Union Road, Cambridge CB2 1EZ,

UK; fax: +44 1223 336033.

Acknowledgements

This work was supported by the Deutsche For-

schungsgemeinschaft (Emmy Noether-Programme), the

Department of Chemistry of the University of Dort-

mund and the Fonds der Chemischen Industrie. We

thank Oliver Gerbersmann for help with the syntheses.J.M. thanks Prof. Dr. Bernhard Lippert for his continu-

ous support.

References

[1] I. Onyido, A.R. Norris, E. Buncel, Chem. Rev., ASAP Article

(DOI: 10.1021/cr030443w).

[2] E. Sletten, W. Nerdal, in: A. Sigel, H. Sigel (Eds.), Metal Ions in

Biological Systems, vol. 34, Marcel Dekker Inc., New York, 1997,

pp. 479–501.

[3] R.B. Simpson, J. Am. Chem. Soc. 86 (1964) 2059.

[4] A.R. Norris, R. Kumar, Inorg. Chim. Acta 93 (1984) L63.

[5] S. Menzer, E.C. Hillgeris, B. Lippert, Inorg. Chim. Acta 211

(1993) 221.

[6] Z. Kuklenyik, L.G. Marzilli, Inorg. Chem. 35 (1996) 5654.

[7] N.A. Frøystein, E. Sletten, J. Am. Chem. Soc. 116 (1994) 3240.

[8] L.D. Kosturko, C. Folzer, R.F. Stewart, Biochemistry 13 (1974)

3949.

[9] F. Zamora, M. Sabat, B. Lippert, Inorg. Chim. Acta 267 (1998)

87.

[10] B.J. Graves, D.J. Hodgson, Inorg. Chem. 20 (1981) 2223.

[11] J. Muller, M. Drumm, M. Boudvillain, M. Leng, E. Sletten, B.

Lippert, J. Biol. Inorg. Chem. 5 (2000) 603.

[12] R. Narukulla, Y.-Z. Xu, D.E. Shuker, In: Abstracts of Papers of

the American Chemical Society, 228th ACS National Meeting,

2004, TOXI-105.

[13] Y. Wu, M. Fa, E.L. Tae, P.G. Schultz, F.E. Romesberg, J. Am.

Chem. Soc. 124 (2002) 14626.

[14] K. Tanaka, A. Tengeiji, T. Kato, N. Toyama, M. Shionoya,

Science 299 (2003) 1212.

[15] K. Tanaka, A. Tengeiji, T. Kato, N. Toyama, M. Shiro, M.

Shionoya, J. Am. Chem. Soc. 124 (2002) 12494.

[16] K. Tanaka, M. Shionoya, J. Org. Chem. 64 (1999) 5002.

[17] N. Zimmermann, E. Meggers, P.G. Schultz, Bioorg. Chem. 32

(2004) 13.

1230 J. Muller et al. / Inorganica Chimica Acta 358 (2005) 1225–1230

[18] E. Meggers, P.L. Holland, W.B. Tolman, F.E. Romesberg, P.G.

Schultz, J. Am. Chem. Soc. 122 (2000) 10714.

[19] D.-L. Popescu, T.J. Parolin, C. Achim, J. Am. Chem. Soc. 125

(2003) 6354.

[20] H. Weizman, Y. Tor, Chem. Commun. (2001) 453.

[21] T. Carell, C. Behrens, J. Gierlich, Org. Biomol. Chem. 1 (2003)

2221.

[22] N. Robertson, C.A. McGowan, Chem. Soc. Rev. 32 (2003) 96.

[23] D. Grdenic, Q. Rev. Chem. Soc. 19 (1965) 303.

[24] I. Antonini, G. Cristalli, P. Franchetti, M. Grifantini, S. Martelli,

F. Petrelli, J. Pharm. Sci. 73 (1984) 366.

[25] V. Rolland, M. Kotera, J. Lhomme, Synth. Comm. 27 (1997)

3505.

[26] R. Lumry, E.L. Smith, R.R. Glantz, J. Am. Chem. Soc. 73 (1951)

4330.

[27] R.B. Martin, Science 139 (1963) 1198.

[28] G.M. Sheldrick, SHELXTL-PLUSSHELXTL-PLUS (VMS), Siemens Analytical X-ray

Instruments, Inc., Madison, WI, 1990;

G.M. Sheldrick, SHELXLSHELXL-97 Program for the Refinement of

Crystal Structures, University of Gottingen, 1997.

[29] Y. Mizuno, M. Ikehara, T. Itoh, K. Saito, J. Org. Chem. 28

(1963) 1837.

[30] T. Wenzel, F. Seela, Helv. Chim. Acta 79 (1996) 169.

[31] J. Muller, E. Zangrando, N. Pahlke, E. Freisinger, L. Randaccio,

B. Lippert, Chem. Eur. J. 4 (1998) 397.

[32] M.S. Luth, E. Freisinger, F. Glahe, B. Lippert, Inorg. Chem. 37

(1998) 5044.

[33] A.J. Canty, G.B. Deacon, Inorg. Chim. Acta 45 (1980)

L225.

[34] G.J. Kleywegt, W.G.R. Wiesmeijer, G.J. Van Driel, W.L.

Driessen, J. Reedijk, J.H. Noordik, J. Chem. Soc., Dalton Trans.

(1985) 2177.

[35] B. Viossat, P. Khodadad, N. Rodier, Acta Crystallogr. C 40

(1984) 24.

[36] C. Pelizzi, G. Pelizzi, P. Tarasconi, J. Organomet. Chem. 277

(1984) 29.

[37] M. Nardelli, C. Pelizzi, G. Pelizzi, P. Tarasconi, J. Chem. Soc.,

Dalton Trans. (1985) 321.

[38] B. Lippert, in: K.D. Karlin (Ed.), Progress in Inorganic Chem-

istry, vol. 54, Wiley-VCH, Weinheim, 2005.