Synthesis and molecular structures of nitrosoarene metalloporphyrin complexes of ruthenium

Article abstract of DOI:10.1039/b315051h

Several new ruthenium porphyrins containing nitrosoarene ligands have been synthesized and characterized by IR and ¹H NMR spectroscopy, and by single-crystal X-ray crystallography. Bis-nitrosoarene complexes of the form (por)Ru(ArNO)₂ (Ar = aryl group; por = TPP, TTP; TPP = tetraphenylporphyrinato dianion, TTP = tetratolylporphyrinato dianion) were prepared in good yields from the reaction of the nitrosoarenes with (por)Ru(CO). The IR spectra of the complexes (as KBr pellets) display new bands in the 1346-1350 cm^-1 region due to v_NO. Reactions of the (por)Ru(ArNO)₂ complexes with excess pyridine and 1-methylimidazole produce the mono-nitrosoarene complexes (por)Ru(ArNO)(py) and (por)Ru(ArNO)(1-MeIm), respectively. The IR spectra of these mono-nitrosoarene complexes reveal a lowering of v_NO by 14-44 cm^-1, a feature consistent with the replacement of one of the π-acid ArNO ligands with the more basic pyridine and 1-MeIm ligands. The solid-state molecular structures of two members of each of the three classes of compounds, namely (por)Ru(ArNO)₂, (por)Ru(ArNO)(py) and (por)Ru(ArNO)(1-MeIm) were determined by single-crystal X-ray diffraction, and reveal the N-binding mode of the ArNO ligands.

Full text of DOI:10.1039/b315051h

View Article Online / Journal Homepage / Table of Contents for this issue
Synthesis and molecular structures of nitrosoarene
metalloporphyrin complexes of ruthenium
Jonghyuk Lee,a Brendan Twamleyb and George B. Richter-Addo*a
a Department of Chemistry and Biochemistry, University of Oklahoma, 620 Parrington Oval,
Norman, Oklahoma, USA 73019. E-mail: grichteraddo@ou.edu
b X-ray Structural Laboratory, University Research Office, 109 Morrill Hall,
University of Idaho, Moscow, Idaho, USA 83844-3010.
Received 1st August 2003, Accepted 20th November 2003
First published as an Advance Article on the web 9th December 2003
Several new ruthenium porphyrins containing nitrosoarene ligands have been synthesized and characterized
by IR and 1H NMR spectroscopy, and by single-crystal X-ray crystallography. Bis-nitrosoarene complexes
of the form (por)Ru(ArNO)2 (Ar = aryl group; por = TPP, TTP; TPP = tetraphenylporphyrinato dianion,
TTP = tetratolylporphyrinato dianion) were prepared in good yields from the reaction of the nitrosoarenes with
(por)Ru(CO). The IR spectra of the complexes (as KBr pellets) display new bands in the 1346–1350 cmϪ1 region
due to νNO. Reactions of the (por)Ru(ArNO)2 complexes with excess pyridine and 1-methylimidazole produce the
mono-nitrosoarene complexes (por)Ru(ArNO)(py) and (por)Ru(ArNO)(1-MeIm), respectively. The IR spectra of
these mono-nitrosoarene complexes reveal a lowering of νNO by 14–44 cmϪ1, a feature consistent with the replacement
of one of the π-acid ArNO ligands with the more basic pyridine and 1-MeIm ligands. The solid-state molecular
structures of two members of each of the three classes of compounds, namely (por)Ru(ArNO)2, (por)Ru(ArNO)(py)
and (por)Ru(ArNO)(1-MeIm) were determined by single-crystal X-ray diffraction, and reveal the N-binding mode of
the ArNO ligands.
(TPP)Ru(PhNO)(1-MeIm) compounds.13 We were particularly
Introduction
interested in the possible variation in nitrosoarene coordination
Nitrosoalkanes and nitrosoarenes belong to the general class of
modes as a function of the substitution in the phenyl ring of the
C-nitroso compounds, and they have extensive coordination
nitrosoarene ligands. For example, it is known that the struc-
tures of some para-substituted nitrosoarenes have significant
dipolar character which places a significant negative charge on
the nitroso O-atom; two examples of these nitrosoarenes are
chemistry.1 The ability of nitrosoarenes (ArNO; Ar = aryl
group) to bind to metal centers has consequences in biological
chemistry. Nitrosoarenes are known to bind to the heme bio-
molecules such as hemoglobin (Hb) and myoglobin (Mb) which
shown in Fig. 1. Indeed, we showed that para-amino substituted
contain histidine-liganded hemes.1 The binding of C-nitroso
nitrosoarene ligands are capable of O-binding to iron4 and
compounds to cytochrome P450 is also thought to inhibit
manganese14 centers in metalloporphyrins.
enzyme activity (reviewed in reference 1). Although no crystal
structure of a nitrosoarene adduct of Hb or Mb has been
reported, the crystal structure of the nitrosobenzene adduct of
the related monomeric leghemoglobin from Lupinus luteus is
known and reveals an N-binding of the PhNO ligand to the
iron center of the heme prosthetic group.2 We recently reported
the crystal structure of a nitrosoalkane adduct of ferrous horse
heart myoglobin, namely that of Mb(EtNO).3 The nitroso-
ethane ligand was found to bind to the iron center also
through the nitroso N-atom. Only a small number of crystal
structures of nitrosoarene4,5 and nitrosoalkane6,7 complexes of
iron porphyrins are known. The study of nitrosoarene ligation
to heme centers in biomolecules is particularly important,
since such heme–nitrosoarene adducts are products in various
Fig. 1 Two examples of the C-nitroso compounds for which dipolar
resonance forms are possible: (a) p-aminosubstituted nitrosobenzenes
and (b) nitrosoanisoles.
metabolic processes involving organonitrogen molecules. For
example, the Hb(PhNO) complex is a known metabolic product
that results from nitrobenzene poisoning.8,9
James and co-workers10 reported the first synthesis of
ruthenium porphyrins containing C-nitroso ligands. They
prepared the (OEP)Ru(PhNO)2 complex and showed that it
converted to the (OEP)Ru(PhNO)(L) (OEP = octaethyl-
porphyrinato dianion; L = CO, PPh3, py) derivatives in solution
in the presence of the exogenous ligands. We extended this
work to the preparation of (OEP)Ru(N(O)C6H4NMe2-p)2 and
determined its structure by X-ray crystallography.11 Elegant
work by Che and co-workers12 resulted in the preparation of
the (por)Ru(PhNO)-containing products (por)Ru(PhNO)2,
(por)Ru(PhNO)(PhNH2) and (por)Ru(PhNO)(PhNHOH) (por
= porphyrinato dianion) from the reactions of dioxoruthenium
porphyrins with phenylhydroxylamine. We recently reported a
In this article, we report the synthesis and spectroscopic
characterization of a new series of ruthenium porphyrins of
the form (por)Ru(ArNO)2, (por)Ru(PhNO)(py) and (por)-
Ru(ArNO)(1-MeIm).15 The spectroscopic data and X-ray
crystallographic data provide valuable information on the
π-donor and -acceptor properties of the axial ligands, and we
demonstrate that significant differences exist in these three
classes of compounds.
Experimental
All reactions were performed under an atmosphere of pre-
purified nitrogen using standard Schlenk glassware and/or in an
12
comparative structural analysis of the (TPP)Ru(PhNO)2 and
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4
D a l t o n T r a n s . , 2 0 0 4 , 1 8 9 – 1 9 6
189

View Article Online
Innovative Technology Labmaster 100 Dry Box. Solutions for
spectral studies were also prepared under a nitrogen atmos-
phere. Solvents were distilled from appropriate drying agents
under nitrogen just prior to use: CH2Cl2 (CaH2), hexane
(CaH2), toluene (Na).
CH2Cl2), 1.53 (br, 2H, o-H of o-tolNO), Ϫ1.23 (br, 6H, CH3 of
o-tolNO). Low-resolution mass spectrum (FAB): m/z 835
[(TPP)Ru(o-tolNO)]ϩ (45%), 714 [(TPP)Ru]ϩ (100%).
The other (por)Ru(ArNO)2 compounds were generated
similarly, except for the two nitrosoanisole complexes (TTP)-
Ru(N(O)C6H4OMe-p)2 and (TTP)Ru(N(O)C6H2Me2OMe-p)2
which were synthesized in refluxing toluene (30 min reaction
time).
Chemicals
(TPP)Ru(CO) and (TTP)Ru(CO) were prepared by published
procedures (TPP = meso-tetraphenylporphyrinato dianion,
TTP = meso-tetratolylporphyrinato dianion).16 PhNO (97%),
o-tolNO (97%), anhydrous pyridine (99.8%) and 1-methylimid-
azole (1-MeIm, 99ϩ%) were purchased from Aldrich Chemical
Company and used as received. 4-Nitrosoanisole (p-ONC6-
H4OMe) and 2,6-dimethyl-4-nitrosoanisole (p-ONC6H2Me2-
OMe) were prepared by literature methods.17 15NOBF4 was syn-
thesized by a published procedure18 using Na15NO2 (99% iso-
topic purity, Isotec). Chloroform-d (99.8%) was obtained from
Cambridge Isotope Laboratories.
(TTP)Ru(o-tolNO)2
71% Isolated yield. IR (KBr, cmϪ1): νNO 1350 s (overlapping
with a porphyrin band); also 3022 vw, 2956 vw, 2921 vw, 1529
w, 1512 vw, 1480 vw, 1455 vw, 1306 m, 1278 vw, 1263 vw, 1212
w, 1181 m, 1115 w, 1107 w, 1071 m, 1011 vs, 880 m, 859 m, 798 s,
752 m, 719 m, 661 vw, 642 w, 525 m. 1H NMR (CDCl3): δ 8.57
(s, 8H, pyrrole-H of TTP), 7.93 (d, J = 8, 8H, o-H of TTP), 7.49
(d, J = 8, 8H, m-H of TTP), 6.25 (br, 2H, p-H of o-tolNO), 5.73
(br, 4H, m-H of o-tolNO), 2.68 (s, 12H, CH3 of TTP), 1.53 (br,
2H, o-H of o-tolNO), Ϫ1.26 (br, 6H, CH3 of o-tolNO). Low-
resolution mass spectrum (FAB): m/z 891 [(TTP)Ru(o-tolNO)]ϩ
(24%), 770 [(TTP)Ru]ϩ (100%).
Instrumentation
Infrared spectra were recorded on a Bio-Rad FT-155 FTIR
spectrometer. Proton NMR spectra were obtained on Varian
400 MHz or Varian Mercury VX 300 MHz spectrometers
and the signals referenced to the residual signal of CHCl3 at
δ 7.24 ppm. All coupling constants are in Hz. FAB mass spectra
were obtained on a VG-ZAB-E mass spectrometer. UV-vis
spectra were recorded on a Hewlett-Packard model 8453 diode
array instrument. Wavelengths are reported with ε values or as
percentage intensities for the samples whose yields were too
small for accurate concentration measurements. Elemental
analyses were performed by Atlantic Microlab, Norcross,
Georgia.
(TTP)Ru(N(O)C6H4OMe-p)2
49% Isolated yield. IR (KBr, cmϪ1): νNO 1348 s (overlapping
with a porphyrin band); also 3020 vw, 2922 vw, 2836 vw, 1595 s,
1584 s, 1528 w, 1497 m, 1461 w, 1439 w, 1425 w, 1329 m, 1304 m,
1257 vs, 1212 w, 1180 m, 1134 s, 1109 m, 1070 m, 1031 m, 1009
vs, 866 m, 833 m, 797 s, 777 w, 716 m, 671 vw, 645 vw, 613 m,
1
525 m. H NMR (CDCl3): δ 8.52 (s, 8H, pyrrole-H of TTP),
8.01 (d, J = 8, 8H, o-H of TTP), 7.50 (d, J = 8, 8H, m-H of
TTP), 5.43 (br, 4H, m-H of N(O)C6H4OMe-p), 3.35 (br s,
6H, N(O)C6H4OMe-p), 2.67 (s, 12H, CH3 of TTP), 2.56 (br,
4H, o-H of N(O)C6H4OMe-p). Low-resolution mass spectrum
(FAB): m/z 907 [(TTP)Ru(N(O)C6H4OMe-p)]ϩ (61%), 770
[(TTP)Ru]ϩ (100%).
Synthesis of p-O15NC6H4OMe
This 15N-labeled 4-nitrosoanisole was synthesized by the direct
nitrosation of anisole with 15NOBF4 in acetonitrile using the
same procedure employed for the preparation of unlabeled
(TTP)Ru(15N(O)C6H4OMe-p)2
IR (KBr, cmϪ1): νNO 1318 s.
1
p-O14NC6H4OMe.17 The H NMR spectrum of p-O15NC6H4-
OMe was identical to that of p-O14NC6H4OMe. Three bands
in the IR spectrum at 1450, 1414 and 762 cmϪ1 of solid
p-O14NC6H4OMe17 showed isotope shifts upon 15N substi-
tution, by Ϫ6, Ϫ8 and Ϫ7 cmϪ1, respectively.
(TTP)Ru(N(O)C6H2Me2OMe-p)2
52% Isolated yield. IR (KBr, cmϪ1): νNO 1346 s (overlapping
with a porphyrin band); also 3022 vw, 2962 w, 2922 w, 2863 vw,
1587 m, 1549 vw, 1528 w, 1474 m, 1447 w, 1413 w, 1304 m, 1263
m, 1222 m, 1180 m, 1105 s, 1070 m, 1009 vs, 967 w, 873 vw, 798
Preparation of (por)Ru(ArNO)2 compounds (por ؍ TPP, TTP;
ArNO ؍ o-tolNO, N(O)C6H4OMe-p, N(O)C6H2Me2OMe-p)
1
vs, 753 vw, 715 m, 694 w, 526 m. H NMR (CDCl3): δ 8.56 (s,
These compounds were prepared from the reaction of
(por)Ru(CO) with an excess of the corresponding nitrosoarene
compounds. The following reaction is representative:
8H, pyrrole-H of TTP), 7.99 (d, J = 8, 8H, o-H of TTP), 7.50 (d,
J = 8, 8H, m-H of TTP), 3.21 (br s, 6H, N(O)C6H2Me2OMe-p),
2.67 (s, 12H, CH3 of TTP), 2.09 (br s, 4H, o-H of N(O)C6H2-
Me2OMe-p), 1.45 (br s, 12H, N(O)C6H2Me2OMe-p). Low-
resolution mass spectrum (FAB): m/z 935 [(TTP)Ru(N(O)-
C6H2Me2OMe-p)]ϩ (31%), 770 [(TTP)Ru]ϩ (100%).
(TPP)Ru(CO) (0.100 g, 0.135 mmol) and excess o-tolNO
(0.050 g, 0.400 mmol) were dissolved in CH2Cl2 (30 mL). The
reaction mixture was stirred at room temperature for 30 min,
during which time it turned from red to brown. The solvent
was removed in vacuo. The residue was redissolved in CH2Cl2
(15 mL), and filtered through a neutral alumina column
(2 × 20 cm) in air with CH2Cl2 as eluent. The brown band was
collected and dried in vacuo. The residue was dissolved in a
CH2Cl2 (15 mL) solution. Slow evaporation of the solvent in air
gave crystalline (TPP)Ru(o-tolNO)2ؒ0.3CH2Cl2 (0.083 g, 0.084
mmol, 63% isolated yield). Anal. Calc. for C58H42N6O2Ru1ؒ
0.3CH2Cl2: C, 71.34; H, 4.37; N, 8.56; Cl, 2.17. Found: C, 71.24;
H, 4.46; N, 8.60; Cl, 2.06%. IR (KBr, cmϪ1): νNO 1348 s (over-
lapping with a porphyrin band); also 3054 vw, 3022 vw, 2925
vw, 1596 m, 1574 vw, 1528 w, 1480 w, 1440 w, 1305 m, 1278 w,
1206 w, 1175 w, 1156 w, 1108 vw, 1071 m, 1010 vs, 879 m, 860 m,
834 vw, 794 m, 754 s, 738 w, 714 m, 702 s, 664 w, 620 vw, 527 w.
1H NMR (CDCl3): δ 8.56 (s, 8H, pyrrole-H of TPP), 8.05 (m,
8H, o-H of TPP), 7.70 (m, 12H, m,p-H of TPP), 6.29 (br, 2H,
p-H of o-tolNO), 5.77 (br, 4H, m-H of o-tolNO), 5.28 (s,
Preparation of (por)Ru(PhNO)(py) compounds
(por ؍ TPP, TTP)
These compounds were prepared from the reaction of
the corresponding (por)Ru(PhNO)2 with excess pyridine. The
following reaction is representative:
13
To a CH2Cl2 solution (10 mL) of (TPP)Ru(PhNO)2 (0.020
g, 0.022 mmol) was added ∼2 equiv. of pyridine. This mixture
was stirred at room temperature for 30 min, during which time
it turned from brown to red–purple. The solvent was removed
in vacuo. A 1H NMR spectrum of the residue in CDCl3 showed
the quantitative formation of (TPP)Ru(PhNO)(py), together
with the presence of some unreacted pyridine. Spectro-
scopically pure (TPP)Ru(PhNO)(py) was obtained in 71% yield
by recrystallization of the residue from a CH2Cl2–hexane solu-
tion (1 : 3) at Ϫ20 ЊC. IR (KBr, cmϪ1): νNO 1328 s; also 3075 vw,
D a l t o n T r a n s . , 2 0 0 4 , 1 8 9 – 1 9 6
190

View Article Online
3052 w, 3023 w, 1598 m, 1529 w, 1485 w, 1442 m, 1346 m sh,
1308 m sh, 1217 w, 1177 w, 1155 w, 1071 m, 1008 vs, 888 vw, 833
vw, 793 m, 753 s, 714 m, 700 s, 664 w, 527 w. 1H NMR (CDCl3):
δ 8.42 (s, 8H, pyrrole-H of TPP), 8.05 (m, 8H, o-H of TPP),
7.65 (m, 12H, m,p-H of TPP), 6.40 (tt, J = 7.2/0.8, 1H, p-H of
PhNO), 6.09 (tt, J = 7.6/1.6, 1H, p-H of pyridine), 5.96 (m, 2H,
m-H of PhNO), 5.24 (m, 2H, m-H of pyridine), 2.55 (m, 2H,
o-H of PhNO), 1.76 (m, 2H, o-H of pyridine). Low-resolution
mass spectrum (FAB): m/z 900 [(TPP)Ru(PhNO)(py)]ϩ (7%),
851 [(TPP)Ru(NO)(PhNO)]ϩ (24%), 821 [(TPP)Ru(PhNO)]ϩ
(40%), 793 [(TPP)Ru(py)]ϩ (9%), 714 [(TPP)Ru]ϩ (100%). UV-
vis spectrum (λ/nm (ε/mMϪ1 cmϪ1), 3.30 × 10Ϫ6 M in CH2Cl2):
308 (34), 411 (230), 533 (18).
(TTP)Ru(o-tolNO)(1-MeIm)
58% Isolated yield. IR (KBr, cmϪ1): νNO 1311 s; also 3127 vw,
3021 w, 2954 vw, 2921 w, 2867 vw, 1529 m, 1514 w, 1479 w, 1442
w, 1347 m, 1284 w sh, 1237 w, 1211 w, 1181 w, 1108 m, 1090 w,
1072 m, 1008 vs, 947 vw, 906 w, 797 s, 755 w, 718 m, 672 vw, 658
1
w, 616 vw, 524 m. H NMR (CDCl3): δ 8.38 (s, 8H, pyrrole-H
of TTP), 7.90 (dd (overlapping with oЈ-H of TTP), 4H, o-H of
TTP), 7.87 (dd (overlapping with o-H of TTP), 4H, oЈ-H of
TTP), 7.45 (br d, J = 7.6, 4H, m-H of TTP), 7.41 (br d, J = 7.6,
4H, mЈ-H of TTP), 6.23 (br ddd (apparent br td), J = 7.6/7.6/
1.2, 1H, p-H of o-tolNO), 5.78 (br d, J = 7.6, 1H, m-H of
o-tolNO), 5.71 (br dd (apparent br t), J = 7.6/7.6, 1H, mЈ-H of
o-tolNO), 4.68 (dd (apparent t), J = 1.6/1.6, 1H of 1-MeIm),
2.64 (s, 12H, CH3 of TTP), 2.14 (s, 3H, CH3 of 1-MeIm), 2.05
(br dd, J = 7.6/1.2, 1H, o-H of o-tolNO), 1.47 (br, 1H of
1-MeIm), 1.11 (dd (apparent t), J = 1.6/1.6, 1H of 1-MeIm),
Ϫ1.01 (s, 3H, CH3 of o-tolNO). Low-resolution mass spectrum
(FAB): m/z 973 [(TTP)Ru(o-tolNO)(1-MeIm)]ϩ (10%), 891
[(TTP)Ru(o-tolNO)]ϩ (26%), 852 [(TTP)Ru(1-MeIm)]ϩ (45%),
770 [(TTP)Ru]ϩ (100%).
(TTP)Ru(PhNO)(py)
67% Isolated yield. IR (KBr, cmϪ1): νNO 1332 s; also 3077 vw,
3023 vw, 2955 vw, 2920 vw, 1602 w, 1528 m, 1510 w, 1487 w,
1445 m, 1400 vw, 1347 m, 1306 m, 1262 w, 1212 w, 1181 m, 1153
w, 1108 m, 1069 m, 1037 vw, 1007 vs, 886 w, 847 vw, 800 s, 794 s,
1
764 w, 754 w, 715 m, 691 m, 665 vw, 644 vw, 523 m. H NMR
(CDCl3): δ 8.42 (s, 8H, pyrrole-H of TTP), 7.94 (dd, J = 7.6/1.6,
4H, o-H of TTP), 7.90 (dd, J = 7.6/1.6, 4H, oЈ-H of TTP), 7.48
(br d, J = 7.6, 4H, m-H of TTP), 7.43 (br d, J = 7.6, 4H, mЈ-H
of TTP), 6.36 (tt, J = 7.2/0.8, 1H, p-H of PhNO), 6.07 (tt,
J = 7.6/1.6, 1H, p-H of pyridine), 5.93 (m, 2H, m-H of PhNO),
5.22 (m, 2H, m-H of pyridine), 2.65 (s, 12H, CH3 of TTP), 2.52
(m, 2H, o-H of PhNO), 1.74 (m, 2H, o-H of pyridine). Low-
resolution mass spectrum (FAB): m/z 907 [(TTP)Ru(NO)-
(PhNO)]ϩ (46%), 770 [(TTP)Ru]ϩ (100%). UV-vis spectrum
(λ/nm, CH2Cl2): 310 (10), 413 (100), 533 (5%).
(TTP)Ru(N(O)C6H4OMe-p)(1-MeIm)
70% Isolated yield. IR (KBr, cmϪ1): νNO 1323 s, 1306 s; also 3127
vw, 3021 w, 2921 w, 1599 w, 1563 w, 1528 m, 1510 w, 1497 m,
1460 w, 1441 w, 1348 m, 1246 s, 1212 w, 1182 m, 1156 w, 1108 m,
1093 w, 1072 m, 1034 w, 1008 vs, 947 vw, 903 w, 831 w, 797 s, 717
1
m, 671 w, 616 w, 524 w. H NMR (CDCl3): δ 8.37 (s, 8H, pyr-
role-H of TTP), 7.96 (dd, J = 7.6/2.0, 4H, o-H of TTP), 7.90
(dd, J = 7.6/2.0, 4H, oЈ-H of TTP), 7.47 (br d, J = 7.6, 4H, m-H
of TTP), 7.42 (br d, J = 7.6, 4H, mЈ-H of TTP), 5.44 (m, 2H,
m-H of N(O)C6H4OMe-p), 4.70 (dd (apparent t), J = 1.2/1.2,
1H of 1-MeIm), 3.40 (s, 3H, N(O)C6H4OMe-p), 2.67 (d (over-
lapping with CH3 of TTP), 2H, o-H of N(O)C6H4OMe-p), 2.64
(s, 12H, CH3 of TTP), 2.15 (s, 3H, CH3 of 1-MeIm), 1.56 (br,
1H of 1-MeIm), 1.20 (dd (apparent t), J = 1.2/1.2, 1H of
1-MeIm). Low-resolution mass spectrum (FAB): m/z 989
[(TTP)Ru(N(O)C6H4OMe-p)(1-MeIm)]ϩ (11%), 907 [(TTP)-
Ru(N(O)C6H4OMe-p)]ϩ (19%), 852 [(TTP)Ru(1-MeIm)]ϩ
(35%), 770 [(TTP)Ru ]ϩ (100%).
Preparation of (por)Ru(ArNO)(1-MeIm) compounds
(por ؍ TPP, TTP; ArNO ؍ o-tolNO, N(O)C6H4OMe-p,
N(O)C6H2Me2OMe-p).
These compounds were prepared from the reaction of
the corresponding (por)Ru(ArNO)2 with excess 1-MeIm. The
following reaction is representative:
To a CH2Cl2 solution (20 mL) of (TPP)Ru(o-tolNO)2ؒ
0.3CH2Cl2 (0.050 g, 0.051 mmol) was added ∼2 equiv. of
1-MeIm. This mixture was stirred at room temperature for
30 min, during which time it turned from brown to red–purple.
The solvent was removed in vacuo. A 1H NMR spectrum
of the residue in CDCl3 showed the quantitative formation of
(TPP)Ru(o-tolNO)(1-MeIm), together with the presence of
some unreacted 1-MeIm. Spectroscopically pure (TPP)-
Ru(o-tolNO)(1-MeIm)ؒ0.7CH2Cl2 was obtained in 72% yield
by recrystallization of the residue from a CH2Cl2–hexane
solution (1 : 3) at Ϫ20 ЊC. Anal. Calc. for C55H41N7O1Ru1ؒ
0.7CH2Cl2: C, 68.51; H, 4.38; N, 10.04; Cl, 5.08. Found: C,
68.75; H, 4.71; N, 9.76; Cl, 5.00%. IR (KBr, cmϪ1): νNO 1321 s,
1310 s; also 3125 vw, 3054 vw, 3022 vw, 2952 vw, 2922 vw, 1596
m, 1576 vw, 1530 m, 1486 w, 1439 m, 1347 m, 1334 m, 1277 vw,
1236 w, 1206 w, 1175 w, 1156 vw, 1107 w, 1089 w, 1069 m, 1006
vs, 947 w, 905 w, 834 vw, 818 vw, 793 m, 754 s, 738 m, 713 m,
(TTP)Ru(15N(O)C6H4OMe-p)(1-MeIm)
IR (KBr, cmϪ1): νNO 1296 s, 1275 s.
(TTP)Ru(N(O)C6H2Me2OMe-p)(1-MeIm)
78% Isolated yield. IR (KBr, cmϪ1): νNO 1321 s, 1309 s; also 3124
vw, 3019 vw, 2951 vw, 2920 w, 1530 m, 1469 w, 1453 w, 1347 m,
1286 w, 1214 m, 1181 m, 1127 w, 1109 m, 1091 w, 1072 m, 1007
1
vs, 947 vw, 885 vw, 848 vw, 799 s, 717 m, 615 vw, 524 m. H
NMR (CDCl3): δ 8.38 (s, 8H, pyrrole-H of TTP), 7.95 (dd,
J = 7.6/2.0, 4H, o-H of TTP), 7.90 (dd, J = 7.6/2.0, 4H, oЈ-H of
TTP), 7.47 (br d, J = 7.6, 4H, m-H of TTP), 7.42 (br d, J = 7.6,
4H, mЈ-H of TTP), 4.71 (dd (apparent t), J = 1.2/1.2, 1H of
1-MeIm), 3.27 (s, 3H, N(O)C6H2Me2OMe-p), 2.65 (s, 12H, CH3
of TTP), 2.22 (s, 2H, o-H of N(O)C6H2Me2OMe-p), 2.16
(s, 3H, CH3 of 1-MeIm), 1.59 (br, 1H of 1-MeIm), 1.45 (s,
6H, N(O)C6H2Me2OMe-p), 1.23 (dd (apparent t), J = 1.2/1.2,
1H of 1-MeIm). Low-resolution mass spectrum (FAB):
m/z 1017 [(TTP)Ru(N(O)C6H2Me2OMe-p)(1-MeIm)]ϩ (14%),
935 [(TTP)Ru(N(O)C6H2Me2OMe-p)]ϩ (17%), 852 [(TTP)-
Ru(1-MeIm)]ϩ (37%), 770 [(TTP)Ru]ϩ (100%).
1
702 m, 664 w, 648 vw, 616 w, 529 w. H NMR (CDCl3): δ 8.37
(s, 8H, pyrrole-H of TPP), 8.01 (m, 8H, o-H of TPP), 7.63
(m, 12H, m,p-H of TPP), 6.26 (ddd (apparent td), J = 7.6/7.6/
1.2, 1H, p-H of o-tolNO), 5.81 (br d, J = 7.6, 1H, m-H of
o-tolNO), 5.74 (br dd (apparent br t), J = 7.6/7.6, 1H, mЈ-H of
o-tolNO), 5.28 (s, CH2Cl2), 4.71 (dd (apparent t), J = 1.2/1.2,
1H of 1-MeIm), 2.16 (s, 3H, CH3 of 1-MeIm), 2.07 (dd,
J = 7.6/1.2, 1H, o-H of o-tolNO), 1.50 (br, 1H of 1-MeIm),
1.14 (dd (apparent t), J = 1.2/1.2, 1H of 1-MeIm), Ϫ0.99 (s, 3H,
CH3 of o-tolNO). Low-resolution mass spectrum (FAB):
m/z 917 [(TPP)Ru(o-tolNO)(1-MeIm)]ϩ (17%), 835 [(TPP)-
Ru(o-tolNO)]ϩ (20%), 796 [(TPP)Ru(1-MeIm)]ϩ (39%), 714
[(TPP)Ru]ϩ (100%).
Solid-state structural determinations
Crystals of representative compounds were grown as follows:
(TTP)Ru(o-tolNO)2ؒCH2Cl2 (1; CH2Cl2–hexane (1 : 2), Ϫ20 ЊC,
3 weeks), (TTP)Ru(N(O)C6H2Me2OMe-p)2 (2; CH2Cl2–hexane
(1 : 10), Ϫ20 ЊC, 3 days), (TPP)Ru(PhNO)(py)ؒCH2Cl2 (3;
CH2Cl2–hexane (1 : 3), Ϫ20 ЊC, 1 week), (TTP)Ru(PhNO)(py)
The other (por)Ru(ArNO)(1-MeIm) compounds were gener-
ated similarly.
D a l t o n T r a n s . , 2 0 0 4 , 1 8 9 – 1 9 6
191

View Article Online
(4; CH2Cl2–hexane (1 : 5), Ϫ20 ЊC, 2 weeks), (TPP)Ru(o-tolNO)-
(1-MeIm)ؒ2.5PhMe (5; toluene–hexane (5 : 1), Ϫ20 ЊC, 1 week)
and (TTP)Ru(N(O)C6H2Me2OMe-p)(1-MeIm)ؒ0.5C6H14 (6;
CH2Cl2–hexane (1 : 1), slow evaporation at room temperature).
Structure solution. Data for 1,2,4,5 and 6 were collected at
203(2) K. Data for 3 was collected at 208(2) K. Data were
collected using a Bruker/Siemens SMART 1K instrument
(Mo-Kα radiation, λ = 0.71073 Å) equipped with a LT2A low-
temperature device. Data were measured using omega scans of
0.3Њ per frame for 30 s (1, 2, 3, 5 and 6) and 50 s (4); a half
sphere of data totaling 1471 frames was collected for 1, 3, 4 and
5; a full sphere of data with 2132 frames was collected for 2 and
6. The first 50 frames were recollected at the end of each data
collection to monitor for decay. Cell parameters were retrieved
using SMART19 software and refined using SAINTPlus20 on all
observed reflections. Data reduction and correction for Lorentz
polarization and decay were performed using the SAINTPlus
software. Absorption corrections were applied using SAD-
ABS.21 The structures were solved by direct methods and
refined by least squares method on F 2 using the SHELXTL
program package.22 All non-hydrogen porphyrin atoms were
refined anisotropically. Solvent molecules presented problems
in 1, 5 and 6. The CH2Cl2 solvent in 1 is disordered with a
shared Cl atom. The disorder was refined at 60% for the major
fraction. Soft restraints were applied in 5 to keep the toluene
solvent molecule geometries similar. The half-occupied toluene
was held isotropic. In compound 6, the hexane solvent molecule
was held isotropic and C–C distances were restrained. No
decomposition was observed during data collection. Details
of the data collection and refinement are given in Table 1.
Displacement ellipsoids in Figs. 2–4 are drawn at the 35%
probability level.
Fig.
2
Molecular structure of (TTP)Ru(N(O)C6H2Me2OMe-p)2.
Hydrogen atoms have been omitted for clarity.
CCDC reference numbers 216560–216565.
See http://www.rsc.org/suppdata/dt/b3/b315051h/ for crystal-
lographic data in CIF or other electronic format.
Results and discussion
Bis-nitrosoarene complexes
The formation of the bis-nitrosoarene complexes from the
reaction of (por)Ru(CO) compounds with nitrosoarenes has
been reported previously.10,11,13 Using similar methodology,
we have prepared a new series of (por)Ru(ArNO)2 compounds
D a l t o n T r a n s . , 2 0 0 4 , 1 8 9 – 1 9 6
192

View Article Online
porphyrins,13 we were not able to observe the formation of the
putative (por)Ru(CO)(PhNO) intermediates by IR spectro-
scopy, suggestive of the fast conversion of (por)Ru(CO) to
(por)Ru(PhNO)2. We were also not able to observe, by IR
spectroscopy, any intermediates during the reaction of o-tolNO
with (por)Ru(CO) to generate (por)Ru(o-tolNO)2. We deter-
mined that the reaction of (TTP)Ru(CO) with 4-nitrosoanisole
required high temperatures to generate the (TTP)Ru(ArNO)2
product. Indeed, when the reaction was performed in CH2Cl2 at
room temperature, the intermediate complex (TTP)Ru(CO)-
(N(O)C6H4OMe-p) was observed by IR spectroscopy (νCO 1967
cmϪ1), indicative of the slow substitution of CO by the second
4-nitrosoanisole. The νCO of this intermediate is 31 cmϪ1 higher
in energy than that of the starting (TTP)Ru(CO) at 1936 cmϪ1
in CH2Cl2. This feature of an increased νCO suggests that the
4-nitrosoanisole ligand acts as a π-acid ligand toward the
(TTP)Ru(CO) fragment, resulting in decreased backbonding of
electron density into the π* orbitals of CO, thus raising νCO. We
previously observed a similar IR spectral result from the reac-
tion of (OEP)Ru(CO) with N,N-dimethyl-4-nitrosoaniline.11
Indeed, the less efficient substitution of CO in (por)Ru(CO)
by 4-nitrosoanisole, and by N,N-dimethyl-4-nitrosoaniline, is
likely due to the contribution of the dipolar resonance form
shown in Fig. 1.
Fig. 3 Molecular structure of (TPP)Ru(PhNO)(py). Hydrogen atoms
have been omitted for clarity.
1
The H NMR spectra of the bis-nitrosoarene complexes in
CDCl3 show peaks for the coordinated ArNO ligands in addi-
tion to the peaks typical of the porphyrin macrocycles associ-
ated with the diamagnetic RuII center. The 1H NMR spectra of
the p-substituted tetraphenylporphyrin complexes, namely the
(TTP)Ru(ArNO)2 compounds, show only one set of o-H peaks
and one set of m-H peaks for the meso-aryl substituents on the
porphyrin rings, suggestive of axial symmetry in these com-
plexes or fast rotation of the porphyrin aryl substituents on the
NMR time scale. The pyrrole-H resonances of the porphyrin
macrocycles occur in the narrow 8.52–8.57 ppm range.
Mono-nitrosoarene complexes
We were interested in preparing ruthenium nitrosoarene com-
plexes of the form (por)Ru(ArNO)(L) (L = pyridine or imid-
azole derivative) as models of C-nitroso adducts of histidine–
liganded heme. Reactions of the (por)Ru(ArNO)2 complexes
with pyridine or 1-MeIm produce the mono-nitrosoarene
derivatives as shown in Scheme 2. The (por)Ru(ArNO)(py)
(por = TPP, TTP) and (por)Ru(ArNO)(1-MeIm) compounds
(por = TPP, TTP; ArNO = o-tolNO, N(O)C6H4OMe-p,
N(O)C6H2Me2OMe-p) are readily prepared via these substi-
tution reactions. The pyridine complexes were obtained in 67–
71% isolated yields, and the 1-methylimidazole complexes were
obtained in 58–78% isolated yields. These red–purple mono-
nitrosoarene complexes are moderately air-stable, showing no
signs of decomposition in air after 1 month in the solid state
Fig.
4
Molecular structure of (TPP)Ru(o-tolNO)(1-MeIm).
Hydrogen atoms have been omitted for clarity.
that differ in the nature of porphyrin substitution and the Ar
group.
Nitrosoarenes (ArNO
N(O)C6H2Me2OMe-p) react with the (por)Ru(CO) compounds
(por = TPP, TTP) in CH2Cl2 or refluxing toluene to generate
the bis-nitrosoarene complexes (por)Ru(ArNO)2 in 49–71%
isolated yields (Scheme 1).
=
o-tolNO, N(O)C6H4OMe-p,
Scheme 1
These brown bis-nitrosoarene complexes are moderately air-
stable in solution and can be stored in air in the solid state for
several months without noticeable decomposition. They are
soluble in CH2Cl2 and toluene, but are insoluble in hexane. The
IR spectra of the (por)Ru(ArNO)2 complexes (as KBr pellets)
show new bands in the 1346–1350 cmϪ1 range assigned to the
νNO of the coordinated ArNO groups. Employing the 15N-
labeled ligand results in a shift of the band at 1348 cmϪ1 (over-
lapping with a porphyrin band) in the IR spectrum of the
unlabeled analog (TTP)Ru(N(O)C6H4OMe-p)2 to 1318 cmϪ1
,
consistent with the assignment of this band as νNO (∆νNO Ϫ30
cmϪ1; expected shift of Ϫ24 cmϪ1 based on a simple two-body
model). In our previous work with nitrosobenzene ruthenium
Scheme 2
D a l t o n T r a n s . , 2 0 0 4 , 1 8 9 – 1 9 6
193

View Article Online
Fig. 5 Structural data for the (por)Ru(ArNO)2 and (por)Ru(PhNO)(py) complexes. Selected bond lengths and angles are shown at the top.
Perpendicular atom displacements from the 24-atom porphyrin plane (in 0.01 Å units) are shown at the bottom. Also shown are the axial ligand
orientations: α is the torsion angle involving O–N–Ru–N(por), and β is the torsion angle involving O–N–Ru–N(por) (for (por)Ru(ArNO)2) or C–N–
Ru–N(por) (for (por)Ru(PhNO)(py)). The solid dot represents the nitroso oxygen atom, and the solid line represents the O–N–C unit of the ArNO
ligand situated above the porphyrin plane. The dashed line represents the O–N–C unit of the second ArNO ligand situated below the porphyrin plane
(for (por)Ru(ArNO)2), or the C–N–C unit of the pyridine ligand (for (por)Ru(PhNO)(py)) situated below the porphyrin plane.
and at least 8 h in solution. They are readily soluble in CH2Cl2
and toluene, but are insoluble in hexane.
and Ϫ31 cmϪ1; expected shifts of Ϫ24 and Ϫ23 cmϪ1, respect-
ively, based on a simple two-body model). A likely explanation
is that the presence of the π-interacting and unsymmetrical
1-MeIm ligand results in two axial ligand conformations in
these complexes.
The 1H NMR spectra of the crude product mixtures in
CDCl3 (after 30 min reaction in CH2Cl2 at room temperature)
revealed the quantitative conversion of (por)Ru(ArNO)2 to
(por)Ru(ArNO)L (L = py or 1-MeIm), together with the pres-
ence of the unreacted excess pyridine or 1-MeIm. This suggests
that only one ArNO ligand in the (por)Ru(ArNO)2 complexes is
susceptible to substitution by pyridine or 1-MeIm under our
reaction conditions. Furthermore, unlike the case of the bis-
nitrosoarene complex preparations, where we observed a tem-
perature dependence of the CO substitution depending on the
type of ArNO ligand used, the substitution reactions of (por)-
Ru(ArNO)2 by pyridine or 1-MeIm proceed at room temper-
ature for all the nitrosoarene ligands employed in this study.
The IR spectra of the (por)Ru(PhNO)(py) complexes (as
KBr pellets) show bands in the 1328–1332 cmϪ1 range assigned
to νNO. These bands are 20 cmϪ1 (for TPP) and 14 cmϪ1 (for
TTP) lower than those of their (por)Ru(PhNO)2 precursors,13
and the lower wavenumbers are consistent with the replace-
ment of one PhNO ligand in (por)Ru(PhNO)2 with the more
basic pyridine ligand and subsequent increased Ru PhNO
backdonation of electron density.
As expected, the 1H NMR spectra of the mono-nitrosoarene
complexes (in CDCl3) also reveal the peaks due to both the
coordinated ArNO and pyridine or 1-MeIm ligands. The chem-
ical shifts of the pyrrole protons of the nitrosoarene complexes
prepared in this study decrease slightly in the order (por)-
Ru(ArNO)2 (8.52–8.57 ppm) > (por)Ru(ArNO)(py) (8.42 ppm)
> (por)Ru(ArNO)(1-MeIm) (8.37–8.38 ppm), indicative of a
slightly increased electron density on the porphyrin macrocycles
in the mono-nitrosoarene complexes relative to the bis-nitroso-
arene complexes, and in the imidazole complexes relative to the
1
pyridine complexes.23 This H NMR feature is also consistent
with the IR spectroscopic results discussed earlier. Further-
more, the similar chemical shift values observed for the pyrrole
protons in each class of compounds indicate the similar
π-accepting abilities of the ArNO ligands used in this work.
1
The H NMR spectra of the p-substituted tetraphenyl com-
plexes (TTP)Ru(ArNO)(py) and (TTP)Ru(ArNO)(1-MeIm)
reveal the inequivalence of the o-H protons and the m-H
protons of the meso-aryl substituents on the porphyrin rings.
The IR spectra of the (por)Ru(ArNO)(1-MeIm) complexes
(as KBr pellets) also show one or two new band(s) in the 1306–
1323 cmϪ1 range assigned to νNO. These νNO bands are slightly
lower than those of the (por)Ru(PhNO)(py) analogues, reflect-
ing the better electron-donating ability of the 1-MeIm ligand
X-Ray crystallographic characterization
We were able to crystallize and obtain X-ray crystal structures
for two members of each of the (por)Ru(ArNO)2, (por)-
Ru(PhNO)(py) and (por)Ru(ArNO)(1-MeIm) classes of com-
pounds, and one example from each class is shown in Figs. 2–4.
Selected metrical data for the complexes are summarized in
Figs. 5 and 6. Perpendicular atom displacements of the atoms in
the porphyrin skeleton from the 24-atom mean porphyrin plane
and the axial ligand orientations are also shown in Figs. 5 and
6.
As can be seen in Figs. 2 and 5, the nitrosoarene ligands in
the bis-nitrosoarene complexes are bound to the RuII centers via
the η1-N bonding mode, similar to that observed for the four
other (por)Ru(ArNO)2 compounds that have been structurally
1
to the (por)Ru moiety relative to the pyridine ligand. The H
NMR spectroscopic results are also consistent with this view
(see later). Interestingly, two νNO bands of comparable intensity
are observed in the IR spectra of bulk samples of three of the
(por)Ru(ArNO)(1-MeIm) complexes (as KBr pellets), namely
(TPP)Ru(o-tolNO)(1-MeIm),
(TTP)Ru(N(O)C6H4OMe-p)-
(1-MeIm) and (TTP)Ru(N(O)C6H2Me2OMe-p)(1-MeIm). For
example, the IR spectrum of (TTP)Ru(N(O)C6H4OMe-p)-
(1-MeIm) shows two strong bands at 1323 and 1306 cmϪ1. Both
these bands are assigned as νNO by the comparative analysis of
the IR spectrum of the 15N-labeled nitroso analogue (i.e., νNO
1323 and 1306 cmϪ1, ν
= 1296 and 1275 cmϪ1, ∆νNO Ϫ27
15NO
D a l t o n T r a n s . , 2 0 0 4 , 1 8 9 – 1 9 6
194

View Article Online
lengths in the bis-nitrosoarene complexes) and reflect the basic
character of the 1-MeIm and pyridine ligands and the
predominant π-acid character of the ArNO ligands. Unlike
the (por)Ru(ArNO)2 and (por)Ru(PhNO)(py) complexes, the
ArNO and 1-MeIm ligands in crystals of the ordered (por)-
Ru(ArNO)(1-MeIm) complexes are oriented essentially parallel
to each other, and their C–N–O (for ArNO) and C–N–C (for
1-MeIm) groups essentially bisect porphyrin nitrogens (Fig. 6).
This suggests a moderate π-donor character of the 1-MeIm
ligand in these mono-nitrosoarene complexes. Although the IR
spectral results reveal two νNO bands suggestive of two orien-
tations of the 1-MeIm ligands in the bulk samples, the observ-
ation of only one 1-MeIm orientation in the crystal structures
may simply be due to crystal preparation or selection. Thus, it is
possible that other (por)Ru(ArNO)(1-MeIm) complexes may
possess non-parallel axial ligand orientations. Indeed, a pre-
liminary X-ray crystallographic analysis of (TTP)Ru(o-tolNO)-
(1-MeIm) (data not included) reveals a non-parallel arrange-
ment of the axial disordered ArNO and 1-MeIm ligands.
Furthermore, we have very recently observed
a nearly-
perpendicular arrangement of nitosoalkane and 1-MeIm
ligands in (TPP)Fe(i-PrNO)(1-MeIm).7 This is consistent with
the observation of nearly perpendicular arrangements of the
C-nitroso ligands and the trans-axial histidine imidazole planes
in the protein complexes legHb(PhNO)2 and Mb(EtNO).3
The largest deviations from the strict linearity for the
axial N–Ru–N bonds are observed for the very bulky (2,6-di-
methyl-4-nitrosoanisole)-containing complexes (i.e., (TTP)-
Ru(N(O)C6H2Me2OMe-p)2 (167.34(8)Њ) and (TTP)Ru(N(O)-
C6H2Me2OMe-p)(1-MeIm) (170.32(18)Њ)). This implies that the
deviations from strict linearity could be (at least partly) deter-
mined by sterics, although deviations from strict linearity in
group 8 metalloporphyrins may also result from intrinsic
electronic factors.25,26
Fig. 6 Structural data for the (por)Ru(ArNO)(1-MeIm) complexes.
Selected bond lengths and angles are shown at the top. Perpendicular
atom displacements from the 24-atom porphyrin plane (in 0.01 Å units)
are shown at the middle. Also shown are the axial ligand orientations at
the middle and the bottom: α is the torsion angle involving O–N–Ru–
N(por), and β is the torsion angle involving C–N–Ru–N(por). The solid
dot represents the nitroso oxygen atom, and the solid line represents the
O–N–C unit of the ArNO ligand situated above the porphyrin plane.
The dashed line represents the C–N–C unit of the 1-MeIm ligand
situated below the porphyrin plane.
Summary
We have prepared a new series of six-coordinate ruthenium
porphyrins containing nitrosoarene ligands. The symmetrical
(por)Ru(ArNO)2 and unsymmetrical (por)Ru(ArNO)(L) (L =
py or 1-MeIm) complexes were studied by spectroscopy and by
X-ray crystallography. In all the complexes studied, the ArNO
ligands are bound to the ruthenium centers through the nitroso
N-atoms. IR and NMR spectroscopic results suggest a pre-
dominant π-acid character of the ArNO ligands in these com-
plexes. The ArNO ligands in (por)Ru(ArNO)2 are oriented
perpendicular to each other and essentially bisect porphyrin
nitrogens, consistent with the ArNO ligands behaving as
π-acids in these complexes. Thus, the perpendicular orientation
of the two axial π-acid ligands maximizes the π-backbonding
from two filled dπ orbitals (i.e., dxz and dyz orbitals) of the low-
spin (por)RuII fragment into the empty π* orbitals of the axial
ArNO ligands. The axial Ru–N(ArNO) bond lengths (1.967(3)–
2.029(3) Å) in the bis-nitrosoarene complexes are slightly longer
than the related axial Ru–N(ArNO) distances of 1.892(3)–
1.904(5) Å (for the pyridine complexes) and 1.915(4)–1.920(5)
Å (for the 1-MeIm complexes) seen in the mono-nitrosoarene
complexes, suggestive of decreased Ru–N(O)Ar backbonding
in (por)Ru(ArNO)2 relative to those in (por)Ru(PhNO)(py)
and (por)Ru(ArNO)(1-MeIm). Although the IR and 1H
NMR spectral results suggest that the 1-MeIm ligands in the
mono-nitrosoarene complexes show a slightly stronger overall
electron-donating ability than the pyridine ligands, there are no
significant differences in the axial Ru–N(ArNO) distances
within the mono-nitrosoarene complexes containing pyridine
or 1-MeIm ligands in the solid state. The O–N(Ar) bond
lengths are also not significantly different within these bis- and
mono-nitrosoarene complexes.
characterized to date.11–13 The ArNO ligands in (por)-
Ru(ArNO)2 are oriented perpendicular to each other, and their
C–NO groups essentially bisect porphyrin nitrogens (Fig. 5(a)
and (b)). Similar axial ligand orientations have been observed in
other bis-nitrosoarene complexes of Fe,4 Ru,11–13 and Os,24 and
have been attributed to favorable overlap between the filled
HOMO orbitals of the MII centers (namely the dxz and dyz
orbitals) with the π* orbitals of the ArNO ligands.
The nitrosobenzene ligands of the two (por)Ru(PhNO)(py)
(por = TPP, TTP) compounds are also bound to the RuII center
in an η1-N fashion (Figs. 3 and 5). The axial Ru–N(PhNO)
bond lengths fall in the 1.892(3)–1.904(5) Å range, and are
shorter than those of (TPP)Ru(PhNO)2 (1.953(2) and 2.049(2)
Å;13 1.954(3) and 2.052(3) Å12). Such a shortening is consistent
with an increased electron donation to the Ru center by the
pyridine ligands relative to the displaced PhNO ligands and
increased Ru PhNO backdonation of electron density, as
1
suggested by the IR and H NMR spectroscopic results pre-
sented and discussed earlier. The axial ligand orientations
observed for (por)Ru(PhNO)(py) are very similar to those
observed for (por)Ru(ArNO)2. Thus, the PhNO and pyridine
ligands in (por)Ru(PhNO)(py) are oriented perpendicular to
each other (Fig. 5(c) and (d)), an observation that suggests
moderate π-acid character for the pyridine ligand when located
trans to the π-acid ArNO ligand.
The X-ray crystal structures of the two mono-nitrosoarene
compounds containing the axial 1-MeIm ligands (e.g., Fig. 4)
present an interesting comparison with the other structures
described in this work. The axial Ru–N(ArNO) bond lengths
in the two (por)Ru(ArNO)(1-MeIm) complexes fall in the
1.915(4)–1.920(5) Å range, and are similar to those determined
for the pyridine derivatives (i.e., shorter than the related bond
Differences in the axial ligand orientations in the (por)-
Ru(ArNO)2 and (por)Ru(PhNO)(py) vs. the (por)Ru(ArNO)-
D a l t o n T r a n s . , 2 0 0 4 , 1 8 9 – 1 9 6
195

View Article Online
2003, New Orleans, LA, USA, 2003. Abstract INORG 166;
manuscript in preparation.
8 R. F. Loeb, A. V. Bock and R. Fitz, Am. J. Med. Sci., 1921, 161,
539–546 (Chem. Abstr., 1921, 51:1761).
9 W. Filehne, Arch. Exptl. Pathol. Pharmakol., 1878, 9, 329.
10 C. Crotti, C. Sishta, A. Pacheco and B. R. James, Inorg. Chim. Acta,
1988, 141, 13–15.
11 L. Chen, J. B. Fox, Jr., G.-B. Yi, M. A. Khan and G. B. Richter-
Addo, J. Porphyrins Phthalocyanines, 2001, 5, 702–707.
12 J.-L. Liang, J.-S. Huang, Z.-Y. Zhou, K.-K. Cheung and C.-M. Che,
Chem. Eur. J., 2001, 7, 2306–2317.
(1-MeIm) suggest a prominent role of the metal dπ orbitals in
the binding of the nitrosoarene ligands. Menyhárd and
Keserú27 reported recently that proximal histidine orientations
in myoglobin play a role in NO ligand dissociation from
myoglobin. We are currently in the process of designing
experiments to investigate the role that the axial ligand orien-
tations play in the dissociation and reaction chemistry of the
nitrosoarene ligands.
13 J. Lee, B. Twamley and G. B. Richter-Addo, Can. J. Chem., 2002, 80,
1252–1258.
Acknowledgements
14 S. J. Fox, L. Chen, M. A. Khan and G. B. Richter-Addo,
Inorg. Chem., 1997, 36, 6465–6467.
15 Taken in part from: J. Lee, PhD Thesis, University of Oklahoma,
2002.
16 D. P. Rillema, J. K. Nagle, L. F. Barringer, Jr. and T. J. Meyer, J. Am.
Chem. Soc., 1981, 103, 56–62.
17 E. Bosch and J. K. Kochi, J. Org. Chem., 1994, 59, 5573–5586.
18 N. G. Connelly, P. T. Draggett, M. Green and T. A. Kuc, J. Chem.
Soc., Dalton Trans., 1977, 70–73.
19 SMART: v.5.059: Bruker Molecular Analysis Research Tool,
Madison, WI, 1997–1998.
20 SAINTPlus: Data Reduction and Correction Program. Version
6.02, Madison, WI, 1998.
21 G. M. Sheldrick, SADABS (Siemens Area Detector ABSorption
Correction Program), Madison, 1999.
22 G. M. Sheldrick, SHELXTL : Structure Determination Software
Suite, Madison, WI, 1998.
23 J. W. Buchler, W. Kokisch and P. D. Smith, Struct. Bonding (Berlin),
1978, 34, 79–134.
24 L. Chen, M. A. Khan, G. B. Richter-Addo, V. G. Young, Jr. and
D. R. Powell, Inorg. Chem., 1998, 37, 4689–4696.
25 G. B. Richter-Addo, R. A. Wheeler, C. A. Hixon, L. Chen, M. A.
Khan, M. K. Ellison, C. E. Schulz and W. R. Scheidt, J. Am. Chem.
Soc., 2001, 123, 6314–6326.
We thank the National Science Foundation of the USA for
funding for this work (Grant No. CHE-0076640). The Bruker
(Siemens) SMART APEX diffraction facility was established
at the University of Idaho with the assistance of the NSF-
EPSCoR program and the M. J. Murdock Charitable Trust,
Vancouver, WA, USA.
References
1 J. Lee, L. Chen, A. H. West and G. B. Richter-Addo, Chem. Rev.,
2002, 102, 1019–1065.
2 I. P. Kuranova, A. V. Teplyakov, G. V. Obmolova, A. A. Voronova,
A. N. Popov, D. M. Kheiker and E. G. Arutyunyan, Bioorg. Khim.
(in Russian), 1982, 8, 1625–1636 (PDB codes 1LH4 and
2LH4).
3 D. M. Copeland, A. H. West and G. B. Richter-Addo, Proteins:
Struct. Funct. Genet., 2003, 53, 182–192.
4 L.-S. Wang, L. Chen, M. A. Khan and G. B. Richter-Addo, Chem.
Commun., 1996, 323–324.
5 N. Godbout, L. K. Sanders, R. Salzmann, R. H. Havlin,
M. Wojdelski and E. Oldfield, J. Am. Chem. Soc., 1999, 121, 3829–
3844.
6 D. Mansuy, P. Battioni, J.-C. Chottard, C. Riche and A. Chiaroni,
J. Am. Chem. Soc., 1983, 105, 455–463.
7 C. D. Sohl, J. Lee and G. B. Richter-Addo, Presented at the 225th
National Meeting of the American Chemical Society; March 23–27,
26 G. R. A. Wyllie and W. R. Scheidt, Chem. Rev., 2002, 102, 1067–
1089.
27 D. K. Menyhárd and G. M. Keserú, J. Am. Chem. Soc., 1998, 120,
7991–7992.
D a l t o n T r a n s . , 2 0 0 4 , 1 8 9 – 1 9 6
196