Ruthenium mediated C-H activation of 2-(arylazo)phenols: Characterization of an intermediate and the final organoruthenium complex

Article abstract of DOI:10.1021/ic051874v

Reaction of 2-(arylazo)phenols with [Ru(PPh₃) ₂(CO)₂Cl₂] affords a family of organometallic complexes of ruthenium-(II) of type [Ru(PPh₃)₂(CO)(CNO-R)] , where the 2-(arylazo)phenolate ligand (CNO-R; R = OCH₃, CH ₃, H, Gl, and NO₂) is coordinated to the metal center as tridentate C,N,O-donor. Another group of intermediate complexes of type [Ru(PPh₃)₂(CO)(NO-R)(H)] has also been isolated, where the 2-(arylazo)phenolate ligand (NO-R) is coordinated to the metal center as bidentate N,O-donor. Structures of the [Ru(PPh₃)₂(CO)(NO- OCH₃)(H)] and [Ru(PPh₃)₂(CO)-(CNO-OCH ₃)] complexes have been determined by X-ray crystallography. All the complexes are diamagnetic and show characteristic ¹H NMR signals and intense MLCT transitions in the visible region. Both the [Ru(PPh ₃)₂(CO)-(NO-R)(H)] and [Ru(PPh₃) ₂(CO)(CNO-R)] complexes show two oxidative responses on the positive side of SCE.

Full text of DOI:10.1021/ic051874v

Inorg. Chem. 2006, 45, 460−467
Ruthenium Mediated C−H Activation of 2-(Arylazo)phenols:
Characterization of an Intermediate and the Final Organoruthenium
Complex†
Parna Gupta,‡ Swati Dutta,‡ Falguni Basuli,‡ Shie-Ming Peng,§ Gene-Hsiang Lee,§ and
Samaresh Bhattacharya*,‡
Department of Chemistry, Inorganic Chemistry Section, JadaVpur UniVersity,
Kolkata 700 032, India, and Department of Chemistry, National Taiwan UniVersity,
Taipei, Taiwan, ROC
Received October 28, 2005
Reaction of 2-(arylazo)phenols with [Ru(PPh3)2(CO)2Cl2] affords a family of organometallic complexes of ruthenium-
(II) of type [Ru(PPh3)2(CO)(CNO R)], where the 2-(arylazo)phenolate ligand (CNO R; R OCH3, CH3, H, Cl, and
NO2) is coordinated to the metal center as tridentate C,N,O-donor. Another group of intermediate complexes of
type [Ru(PPh3)2(CO)(NO R)(H)] has also been isolated, where the 2-(arylazo)phenolate ligand (NO R) is coordinated
to the metal center as bidentate N,O-donor. Structures of the [Ru(PPh3)2(CO)(NO OCH3)(H)] and [Ru(PPh3)2(CO)-
(CNO OCH3)] complexes have been determined by X-ray crystallography. All the complexes are diamagnetic and
show characteristic 1H NMR signals and intense MLCT transitions in the visible region. Both the [Ru(PPh3)2(CO)-
−
−
)
−
−
−
−
(NO
−R)(H)] and [Ru(PPh3)2(CO)(CNO
−R)] complexes show two oxidative responses on the positive side of SCE.
Introduction
proceed via a C-H activation of the organic substrate,2
leading to the formation of a reactive organometallic inter-
There has been considerable current interest in the utiliza-
tion of transition metals in promoting interesting chemical
transformations of organic substrates.1 Such reactions often
mediate, which then undergoes further reactions to yield the
final product. Thus, transition metal mediated C-H activa-
tion of organic molecules is of significant importance, and
the present work has originated from our interest in this area.3
For the present study, a group of five 2-(arylazo)phenols (1)
have been chosen as the target organic molecules, and
* To whom correspondence should be addressed. E-mail:
samaresh_b@hotmail.com.
† Dedicated to Professor Animesh Chakravorty, Department of Inorganic
Chemistry, Indian Association for the Cultivation of Science, Kolkata, India,
on the occasion of his 70th birthday.
(2) (a) Jaeger-Fiedle, U.; Arndt, P.; Baumann, W.; Spannenberg, A.;
Burlakov, V. V.; Rosenthal, U. Eur. J. Inorg. Chem. 2005, 14, 2842.
(b) Keuseman, K. J.; Smolinkova, I. P.; Dunina, V. V. Organometallics
2005, 24, 4159. (c) Shi, L.; Tu, Y. Q.; Wang, M.; Zhao, F. M.; Fan,
C. A.; Zhao, Y. M.; Xia, W. J. J. Am. Chem. Soc. 2005, 127, 10836.
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‡ Jadavpur University.
§ National Taiwan University.
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C., Eds.; Wiley-VCH: Weinheim, 1998. (d) Applied Homogeneous
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460 Inorganic Chemistry, Vol. 45, No. 1, 2006
10.1021/ic051874v CCC: $33.50
© 2006 American Chemical Society
Published on Web 12/01/2005

Ru-Mediated C-H ActiWation
ruthenium has been selected as the transition metal for
promoting the C-H activation. The 2-(arylazo)phenols are
(PPh3)2(CO)2Cl2] has indeed afforded a family of organoru-
thenium complexes, where the 2-(arylazo)phenols are coor-
dinated as in 5. In addition, a group of complexes of another
type could also be isolated from the same reaction. The
present report deals with the chemistry of all these com-
plexes, with special reference to their formation, structure,
and spectral and electrochemical properties.
Experimental Section
Materials. Commercial ruthenium trichloride was purchased
from Arora Matthey, Kolkata, India. The para-substituted anilines
and p-cresol were obtained from S.D, India. All other chemicals
and solvents were reagent grade commercial materials and were
used as received. [Ru(PPh3)2(CO)2Cl2] was synthesized by following
a reported procedure.6 The 2-(arylazo)phenol ligands were prepared
by coupling diazotized para-substituted anilines with para-cresol.
Purification of dichloromethane and acetonitrile and preparation
of tetrabutylammonium perchlorate (TBAP) for electrochemical
work were performed as reported in the literature.7
Preparations of Complexes. [Ru(PPh3)2(CO)(NO-R)(H)] and
[Ru(PPh3)2(CO)(CNO-R)]. The [Ru(PPh3)2(CO)(NO-R)(H)] and
[Ru(PPh3)2(CO)(CNO-R)] complexes were obtained by following
a general procedure. Specific details are given below for a particular
complex.
[Ru(PPh3)2(CO)(NO-H)(H)] and [Ru(PPh3)2(CO)(CNO-H)].
2-(Phenylazo)-4-methylphenol (30 mg, 0.14 mmol) was dissolved
in ethanol (40 mL), and [Ru(PPh3)2(CO)2Cl2] (100 mg, 0.14 mmol)
was added to it. The mixture was then refluxed for 6 h to yield a
red solution. The solvent was evaporated, and the solid mass, thus
obtained, was subjected to purification by thin-layer chromatography
on a silica plate. With 1:1 hexane-benzene as the eluant, a red
band and a green band separated, and the corresponding materials
were extracted separately with acetonitrile. Evaporation of these
acetonitrile extracts gave [Ru(PPh3)2(CO)(NO-H)(H)] and [Ru-
(PPh3)2(CO)(CNO-H)] as red and green crystalline solids, respec-
tively. Yields: 45% and 50%, respectively.
[Ru(PPh3)2(CO)(CNO-R)]. The [Ru(PPh3)2(CO)(CNO-R)]
complexes were also prepared by following two different proce-
dures, which are described below for a specific complex.
[Ru(PPh3)2(CO)(CNO-H)]. Method A. 2-(Phenylazo)-4-me-
thylphenol (30 mg, 0.14 mmol) was dissolved in 2-methoxyethanol
(40 mL), and [Ru(PPh3)2(CO)2Cl2] (100 mg, 0.14 mmol) was added
to it. The mixture was then refluxed for 6 h to yield a greenish
brown solution. The solvent was evaporated, and the solid residue,
thus obtained, was purified by thin-layer chromatography on a silica
plate. With 1:1 hexane-benzene as the eluant, a green band
separated, and the corresponding material was extracted with
acetonitrile. Evaporation of the acetonitrile extract gave [Ru(PPh3)2-
(CO)(CNO-H)] as a green crystalline solid. Yield: 70%.
Method B. The red [Ru(PPh3)2(CO)(NO-H)(H)] complex (100
mg, 0.12 mmol) was taken in 2-methoxyethanol (50 mL). The
solution was heated at reflux for 10 min, whereby it turned green.
Evaporation of the solvent afforded [Ru(PPh3)2(CO)(CNO-H)] as
a green crystalline solid. Yield: quantitative.
known to bind to metal ions usually as bidentate N,O-donors,
via dissociation of the phenolic proton, forming a six-
membered chelate ring (2).4 However, in a recent study the
2-(arylazo)phenols have been observed to coordinate the
metal center as bidentate N,O-donors forming a stable five-
membered chelate ring (3).5 In the solid state the pendent
phenyl ring in the arylazo fragment in 3 is observed to remain
almost orthogonal to the plane of the chelate ring. However,
in view of the possible rotation of this phenyl ring around
the C-N bond in the solution phase, and particularly in view
of the resulting closeness of the phenyl ring to the metal
center when it becomes coplanar with the chelate ring, C-H
activation at the ortho position of the phenyl ring appears to
be a possibility. A necessary prerequisite for such speculated
C-H activation to occur is the existence of a potentially
labile ligand (X) trans to the phenolate oxygen (4), which
would facilitate the targeted C-H activation leading to the
formation of the corresponding orthometalated species (5)
via elimination of HX. With this strategy in mind, [Ru-
(PPh3)2(CO)2Cl2] has been selected as the ruthenium starting
material. This particular complex has been picked up because
of its demonstrated ability to accommodate monoanionic
bidentate (L-L) ligands via displacement of one CO and
one chloride,3d and hence, it is expected to provide a labile
Ru-Cl bond in the equatorial plane containing the Ru(L-
L)(CO)Cl fragment, as required for the targeted C-H
activation. Reaction of the 2-(arylazo)phenols (1) with [Ru-
(3) (a) Nag, S.; Gupta, P.; Butcher, R. J.; Bhattacharya S. Inorg. Chem.
2004, 43, 4814. (b) Acharyya, R.; Basuli, F.; Wang, R. Z.; Mak, T.
C. W.; Bhattacharya, S. Inorg. Chem. 2004, 43, 704. (c) Pal, I.; Dutta,
S.; Basuli, F. Goverdhan, S.; Peng, S. M.; Bhattacharya, S. Inorg.
Chem. 2003, 42, 4338. (d) Basuli, F.; Peng, S. M.; Bhattacharya, S.
Inorg. Chem. 2001, 40, 1126. (e) Majumder, K.; Peng, S. M.;
Bhattacharya, S. J. Chem. Soc., Dalton Trans. 2001, 284. (f) Basuli,
F.; Peng, S. M.; Bhattacharya, S. Inorg. Chem. 2000, 39, 1120. (g)
Dutta, S.; Peng, S. M.; Bhattacharya, S. J. Chem. Soc., Dalton Trans.
2000, 4623.
Anal. Calcd for [Ru(PPh3)2(CO)(NO-OCH3)(H)]: C, 68.10; H,
4.77; N, 3.17. Found: C, 68.83; H, 4.72; N, 3.10. 1H NMR:8 -10.5
(t, hydride, J ) 22.0); 2.11 (CH3); 3.57 (OCH3); 6.31 (d, 1H, J )
(4) (a) Rath, R. K.; Nethaji, M.; Chakravarty, A. R. J. Organomet. Chem.
2001, 633, 79. (b) Sui, K.; Peng, S. M.; Bhattacharya, S. Polyhedron
1999, 19, 631. (c) Bhawmik, R.; Biswas, H.; Bandyopadhyay, P. J.
Organomet. Chem. 1995, 498, 81. (d) Sinha, C. R.; Bandyopadhyay,
D.; Chakravorty, A. J. Chem. Soc., Chem. Commun. 1988, 468. (e)
Dyachenko, O. A.; Atovmyan, L. O.; Aldosin, S. M. J. Chem. Soc.,
Chem. Commun. 1975, 105. (f) Kalia, K. C. Indian J. Chem. 1970, 8,
1035. (g) Price, R. J. J. Chem. Soc. A 1969, 1296. (h) Jarvis, J. A. J.
Acta Crystallogr. 1961, 14, 961.
(6) Ahmad, N.; Robinson, S. D.; Uttley, M. F. J. Chem. Soc., Dalton
Trans. 1972, 843.
(7) (a) Sawyer, D. T.; Roberts, J. L., Jr. Experimental Electrochemistry
for Chemists; Wiley: New York, 1974; pp 167-215. (b) Walter, M.;
Ramaley, L. Anal. Chem. 1973, 45, 165.
(5) Basuli, F.; Peng, S. M.; Bhattacharya, S. Polyhedron 1998, 18, 391.
Inorganic Chemistry, Vol. 45, No. 1, 2006 461

Gupta et al.
6.0); 6.36 (s, 1H); 7.10-7.90 (2PPh3); 7.55-7.57 (d, 2H).* 13C
NMR: 19.72 (s, CH3); 44.54 (s, OCH3); 127.47 (t, PPh3, J ) 17.85);
129.11(s, PPh3); 131.86 (t, PPh3, J ) 27.30); 133.83 (t, PPh3, J )
23.68); 100.15, 101.91, 115.38, 121.34, 123.98, 125.50, 127.44,
131.45, 133.33, 144.40, 153.12, and 161.44 (phenyl carbons of
NO-OCH3 ligand); 202.20 (s, CO). 31P NMR: 41.13 (s, 2PPh3).
IR: 1928 cm-1 (νCO).
1H, J ) 9.0); 6.67 (s, 1H); 7.16-7.36 (2PPh3). 13C NMR: 29.69
(s, CH3); 30.83 (s, CH3); 127.71 (t, PPh3, J ) 16.80); 129.52 (s,
PPh3); 131.96 (t, PPh3 J ) 27.80); 134.02 (t, PPh3, J ) 22.20);
110.29, 118.20, 123.27, 127.50, 129.46, 130.22, 132.25, 137.14,
138.57, 162.06, and 166.00 (phenyl carbons of CNO-CH3 ligand);
180.50 (metalated carbon); 208.27 (s, CO). 31P NMR: 30.99 (s,
2PPh3). IR: 1920 cm-1 (νCO).
Anal. Calcd for [Ru(PPh3)2(CO)(NO-CH3)(H)]: C, 68.60; H,
5.01; N, 3.18. Found: C, 68.77; H, 5.04; N, 3.24. 1H NMR:8 -10.50
(t, hydride, J ) 22.0); 2.10 (CH3); 2.30 (CH3); 6.91 (d, 1H, J )
9.0); 7.07 (s, 1H); 7.30-7.87 (2PPh3); 7.11 (d, 1H, J ) 6.0); 7.54
(d, 1H, J ) 6.0). 13C NMR: 19.71 (s, CH3); 20.01 (s, CH3); 127.47
(t, PPh3, J ) 18.20); 129.11(s, PPh3); 131.86 (t. PPh3, J ) 27.45);
133.83 (t, PPh3, J ) 23.59); 106.54, 108.71, 117.88, 122.34, 125.88,
127.55, 129.44, 134.44, 137.43, 148.41, 155.12, and 169.50 (phenyl
carbons of NO-CH3 ligand); 202.33 (s, CO). 31P NMR: 41.22 (s,
2PPh3). IR: 1930 cm-1 (νCO).
Anal. Calcd for [Ru(PPh3)2(CO)(NO-H)(H)]: C, 69.36; H, 4.85;
N, 3.23. Found: C, 69.45; H, 5.02; N, 3.60. 1H NMR:8 -10.67 (t,
hydride, J ) 22.0); 2.10 (CH3); 6.02 (d, 1H, J ) 9.0); 6.43 (d, 1H,
J ) 9.0); 6.58 (d, 1H, J ) 9.0); 6.93 (t, 1H, J ) 9); 7.05 (t, 1H, J
) 7.5); 7.15 (s, 1H); 7.10-7.90 (2PPh3). 13C NMR: 19.74 (CH3);
127.53 (t, PPh3, J ) 18.00); 129.11(s, PPh3); 131.86 (t, PPh3, J )
27.30); 133.83 (t, PPh3, J ) 23.70); 116.54, 119.91, 121.38, 122.34,
125.98, 127.47, 128.24, 133.45, 134.23, 146.46, 157.02, and 171.50
(phenyl carbons of NO-H ligand); 202.40 (s, CO). 31P NMR: 41.19
(s, 2PPh3). IR: 1928 cm-1 (νCO).
Anal. Calcd for [Ru(PPh3)2(CO)(NO-Cl)(H)]: C, 66.70; H, 4.56;
N, 3.11. Found: C, 66.97; H, 4.64; N, 3.42.1H NMR:8 -10.61 (t,
hydride, J ) 22.0); 2.11 (CH3); 6.00 (d, 1H, J ) 6.0); 6.28 (d, 1H,
J ) 6.0); 7.10 (s, 1H); 7.20-7.52 (2PPh3). 13C NMR: 19.67 (CH3);
127.47 (t, PPh3, J ) 18.30); 129.11(s, PPh3); 131.86 (t, PPh3, J )
27.57); 133.83 (t, PPh3, J ) 23.72); 122.54, 124.81, 127.38, 130.44,
132.78, 136.50, 138.34, 140.15, 153.23, 161.40, 178.12, and 185.45
(phenyl carbons NO-Cl ligand); 202.38 (s, CO). 31P NMR: 41.20
(s, 2PPh3). IR: 1931 cm-1 (νCO).
Anal. Calcd for [Ru(PPh3)2(CO)(NO-NO2)(H)]: C, 65.93; H,
4.50; N, 4.62. Found: C, 66.00; H, 4.45; N, 4.33. 1H NMR:8 -10.36
(t, hydride, J ) 22.0); 2.12 (CH3); 5.96 (d, 1H, J ) 9.0); 6.30 (d,
1H, J ) 9.0); 6.60 (d, 1H, J ) 9.0); 7.19 (s, 1H); 7.18-7.40
(2PPh3). 13C NMR: 19.70 (CH3); 127.47 (t, PPh3, J ) 18.15);
129.11(s, PPh3); 131.86 (t, PPh3, J ) 27.45); 133.83 (t, PPh3, J )
23.74); 125.54, 128.71, 133.18, 139.64, 142.28, 148.50, 156.14,
162.15, 163.23, 167.50, 180.42, and 189.50 (phenyl carbons of
NO-NO2 ligand); 202.29 (s, CO). 31P NMR: 40.99 (s, 2PPh3).
IR: 1930 cm-1 (νCO).
Anal. Calcd for [Ru(PPh3)2(CO)(CNO-H)]: C, 69.52; H, 4.63;
N, 3.24. Found: C, 69.47; H, 4.77; N, 3.22. 1H NMR:8 2.10 (CH3);
5.50 (d, 1H, J ) 9.0); 5.95 (s, 1H); 6.25-6.35 (2H);* 7.07-7.25
(2PPh3). 13C NMR: 29.68 (s, CH3); 127.71 (t, PPh3, J ) 16.85);
129.52 (s, PPh3); 132.06 (t, PPh3, J ) 27.76); 134.02 (t, PPh3, J )
22.30); 116.66, 124.10, 129.97, 132.20, 134.46, 135.52, 137.20,
143.84, 144.87, 162.16, and 168.20 (phenyl carbons of CNO-H
ligand); 181.09 (metalated carbon); 208.30 (s, CO). 31P NMR:
31.10 (s, 2PPh3). IR: 1922 cm-1 (νCO).
Anal. Calcd for [Ru(PPh3)2(CO)(CNO-Cl)]: C, 66.85; H, 4.34;
N, 3.11. Found: C, 66.65; H, 4.27; N, 3.45. 1H NMR:8 2.05 (CH3);
5.01 (d, 1H, J ) 9.0); 5.85 (s, 1H); 6.25 (d, 1H, J ) 9.0); 6.50 (s,
1H); 7.30-7.60 (2PPh3). 13C NMR: 29.67 (s, CH3); 127.71 (t, PPh3,
J ) 16.78); 129.52 (s, PPh3); 132.06 (t, PPh3, J ) 27.83); 134.02
(t, PPh3, J ) 22.20); 120.96, 128.00, 133.87, 137.10, 139.56, 140.82,
142.30, 148.64, 149.97, 168.16, and 170.00 (phenyl carbons of
CNO-Cl ligand); 183.59 (metalated carbon); 208.28 (s, CO). 31P
NMR: 30.99 (s, 2PPh3). IR: 1921 cm-1 (νCO).
Anal. Calcd for [Ru(PPh3)2(CO)(CNO-NO2)]: C, 66.07; H,
4.29; N, 4.26. Found: C, 66.15; H, 4.80; N, 3.97. 1H NMR:8 2.10
(CH3); 4.95 (d, 1H, J ) 9.0); 5.72 (s, 1H); 6.15 (d, J ) 9.0); 6.01-
(s, 1H); 7.20-7.70 (2PPh3). 13C NMR: 29.71 (s, CH3); 127.71 (t,
PPh3, J ) 16.70); 129.52 (s, PPh3); 132.06 (t, PPh3, J ) 27.80);
134.02 (t, PPh3, J ) 22.30); 121.76, 129.10, 134.77, 139.56, 143.66,
143.88, 144.90, 149.19, 149.97, 169.26, and 171.20 (phenyl carbons
of CNO-NO2 ligand); 185.59 (metalated carbon); 208.31 (s, CO).
31P NMR: 30.89 (s, 2PPh3). IR: 1920 cm-1 (νCO).
Physical Measurements. Microanalyses (C, H, N) were per-
formed using a Heraeus Carlo Erba 1108 elemental analyzer. IR
spectra were obtained on a Perkin-Elmer 783 spectrometer with
samples prepared as KBr pellets. Electronic spectra were recorded
on a JASCO V-570 spectrophotometer. Magnetic susceptibilities
were measured using a PAR 155 vibrating sample magnetometer
fitted with a Walker Scientific L75FBAL magnet. NMR spectra
were recorded in CDCl3 solution with a Bruker AV 300 NMR
spectrometer. ESR spectra were recorded with a Varian E-109C
X-band spectrometer fitted with a quartz Dewar for measurements
at 77 K (liquid dinitrogen). All ESR spectra were calibrated with
an aid of DPPH (g ) 2.0037). Electrochemical measurements were
made using a CH Instruments model 600A electrochemical analyzer.
A platinum disk working electrode, a platinum wire auxiliary
electrode, and an aqueous saturated calomel reference electrode
(SCE) were used in the cyclic voltammetry experiments. A
platinum-wire gauge working electrode was used in the coulometric
experiments. All electrochemical experiments were performed under
a dinitrogen atmosphere. All electrochemical data were collected
at 298 K and are uncorrected for junction potentials.
Anal. Calcd for [Ru(PPh3)2(CO)(CNO-OCH3)]: C, 68.53; H,
4.70; N, 3.14. Found: C, 68.78; H, 4.44; N, 2.92. 1H NMR:8 2.07
(CH3); 3.67 (OCH3); 6.03 (d, 1H, J ) 9.0); 6.39 (d, 1H, J ) 9.0);
6.53-6.61 (3H);* 7.07 (s, 1H), 7.22-7.49 (2PPh3). 13C NMR:
29.71 (s, CH3); 54.83 (s, OCH3); 127.71 (t, PPh3, J ) 16.83); 129.52
(s, PPh3); 132.06 (t, PPh3, J ) 27.88); 134.02 (t, PPh3, J ) 22.30);
108.96, 115.80, 120.97, 124.10, 126.16, 127.52, 128.25, 133.84,
134.37, 158.16, and 161.20 (phenyl carbons of CNO-OCH3
ligand); 179.59 (metalated carbon); 208.31 (s, CO). 31P NMR:
31.00 (s, 2PPh3). IR: 1922 cm-1 (νCO).
Crystallography. Single crystals of [Ru(PPh3)2(CO)(NO-
OCH3)(H)] and [Ru(PPh3)2(CO)(CNO-OCH3)] were obtained by
slow diffusion of hexane into dichloromethane solutions of the
respective complexes. Selected crystal data and data collection
parameters are given in Table 1. Data were collected, respectively,
on a Nonius Kappa CCD diffractometer and a Bruker Smart Apex
CCD diffractometer using graphite monochromated Mo KR radia-
tion (λ ) 0.71073 Å) by ω scans. X-ray data reduction, structure
Anal. Calcd for [Ru(PPh3)2(CO)(CNO-CH3)]: C, 69.78; H,
4.79; N, 3.19. Found: C, 69.92; H, 4.32; N, 2.94. 1H NMR:8 1.88
(CH3); 1.80 (CH3); 5.93 (d, 1H, J ) 9.0); 6.04 (s, 1H); 6.35 (d,
(8) Chemical shifts are given in ppm and multiplicity of the signals along
with the associated coupling constants (J in Hz) are given in
parentheses. Overlapping signals are marked with an asterisk.
462 Inorganic Chemistry, Vol. 45, No. 1, 2006

Ru-Mediated C-H ActiWation
Table 1. Crystallographic Data for [Ru(PPh3)2(CO)(NO-OCH3)(H)]
and [Ru(PPh3)2(CO)(CNO-OCH3)]
[Ru(PPh3)2(CO)(NO-
OCH3)(H)]‚H2O
[Ru(PPh3)2(CO)-
(CNO-OCH3)]
empirical formula
fw
C51H46N2O4P2Ru
913.91
C51H42N2O3P2Ru
893.88
space group
a, Å
b, Å
monoclinic, C2/c
36.6120(5)
10.8869(2)
22.6351(3)
90
95.5736(5)
90
8979.5(2)
8
triclinic, P1h
11.1402(5)
11.9230(5)
17.4378(7)
72.366(1)
74.471(1)
80.368(1)
2117.36(16)
2
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
λ, Å
0.71073
0.15 × 0.05 × 0.05
295(2)
0.467
0.0575
0.71073
cryst size, mm3
T, K
0.15 × 0.15 × 0.10
295(2)
µ, mm-1
R1a
0.492
0.0579
0.1222
1.060
wR2b
0.129
1.051
GOFc
2
2
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) [∑[w(Fo2 - Fc )2]/∑[w(Fo )2]]1/2
.
c GOF ) [∑[w(Fo2 - Fc2)2]/(M - N)]1/2, where M is the number of reflections
and N is the number of parameters refined.
solution, and refinement were done using SHELXS-97 and SHELXL-
97 programs.9 The structure was solved by the direct methods.
Results and Discussion
Reactionofeach2-(arylazo)phenol(1)with[Ru(PPh3)2(CO)2-
Cl2] has afforded two complexes with distinctly different
colors, viz. red10 and green, in comparable yields. Preliminary
characterizations (microanalysis, IR, NMR, etc.), although
gave some idea about the compositions of these two types
of complexes, could not point to any definite formulation or
stereochemistry of these complexes. For an unambiguous
identification of these complexes, structure of a selected
member from each family, viz. the red and green complexes
obtained from the reaction with 2-(4′-methoxy-
phenylazo)-4-methylphenol (1, R ) OCH3), has been
determined by X-ray crystallography. The structures are
shown in Figures 1 and 2, and some selected bond parameters
are given in Table 2.
Structure of the red complex (Figure 1) shows that the
2-(arylazo)phenol is coordinated to ruthenium, via dissocia-
tion of the phenolic proton, as a bidentate N,O-donor forming
a five-membered chelate ring (3). Two triphenylphosphines,
a carbon monoxide, and a hydride are also coordinated to
the metal center. The red10 complexes are therefore formu-
lated in general as [Ru(PPh3)2(CO)(NO-R)(H)], where
NO-R refers to the N,O-coordinated 2-(arylazo)phenolate
ligand (3). Microanalytical data of these [Ru(PPh3)2(CO)-
(NO-R)(H)] complexes agree well with their compositions.
The coordinated 2-(arylazo)phenolate ligand, CO, and hy-
dride constitute one equatorial plane with the metal at the
center (Figure 1b), where the CO is trans to the phenolate
oxygen and the hydride is trans to the coordinated azo-
nitrogen. The two PPh3 ligands have taken up the remaining
Figure 1. View of (a) the [Ru(PPh3)2(CO)(NO-OCH3)(H)] complex and
(b) the equatorial plane.
two axial positions, and hence, they are mutually trans. The
Ru-H, Ru-C, Ru-O, and Ru-P distances are all quite
normal.11 However, the Ru-N distance is found to be
significantly longer than usual, and this elongation may be
attributed to the strong trans effect of the coordinated
hydride.12 Structure of the green complex (Figure 2) shows
that in this complex the 2-(arylazo)phenol is coordinated to
the metal, via loss of the phenolic proton as well as another
proton from one ortho position of the phenyl ring in the
arylazo fragment, as a tridentate C,N,O-donor (5). The
remaining three coordination sites are occupied by two
triphenylphosphines and a carbon monoxide. The green
complexes are therefore represented in general as [Ru(PPh3)2-
(CO)(CNO-R)], where CNO-R stands for the C,N,O-
coordinated 2-(arylazo)phenolate ligand (5). The observed
microanalytical data of these [Ru(PPh3)2(CO)(CNO-R)]
(11) (a) Basuli, F.; Das, A. K.; Golam, M.; Peng, S. M.; Bhattacharya, S.
Polyhedron 2000, 19, 1663. (b) Menon, M.; Pramanik, A.; Chatto-
padhyay, S.; Bag, N. Chakravorty, A. Inorg. Chem. 1995, 34, 1361.
(c) Barral, M. C.; Aparicio, R. J.; Royer, E. C.; Saucedo, M. J.;
Urbanos, F. A.; Puebla, E. G.; Valero, C. R. J. Chem. Soc., Dalton
Trans. 1991, 1609.
(9) Sheldrick, G. M. SHELXS-97 and SHELXL-97, Fortran programs for
crystal structure solution and refinement; University of Gottingen:
Gottingen, Germany, 1997.
(10) Color of the [Ru(PPh3)2(CO)(NO-NO2)(H)] complex is purple.
(12) Douglas, P. G.; Shaw, B. L. J. Chem. Soc. A 1970, 1556.
Inorganic Chemistry, Vol. 45, No. 1, 2006 463

Gupta et al.
Scheme 1. Probable Steps for the Formation of
[Ru(PPh3)2(CO)(NO-R)(H)] and [Ru(PPh3)2(CO)(CNO-R)] Complexes
where the CO is trans to the coordinated azo-nitrogen. The
PPh3 ligands have occupied the axial positions as before.
The bond parameters around the metal center are found to
be quite normal.11,3a As all five complexes belonging to each
group, viz. [Ru(PPh3)2(CO)(NO-R)(H)] and [Ru(PPh3)2-
(CO)(CNO-R)], have been synthesized similarly and they
show similar spectroscopic and electrochemical properties
(vide infra), the other four members of each group (with R
* OCH3) are assumed to have structures similar to those of
their respective structurally characterized (R ) OCH3)
analogues.
Figure 2. View of (a) the [Ru(PPh3)2(CO)(CNO-OCH3)] complex and
(b) the equatorial plane.
Table 2. Selected Bond Distances and Bond Angles for
[Ru(PPh3)2(CO)(CNO-OCH3)] and [Ru(PPh3)2(CO)(NO-OCH3)]
[Ru(PPh3)2(CO)(CNO-OCH3)]
Bond Distances (Å)
Ru-C(1)
Ru-C(2)
Ru-N(1)
Ru-O(2)
Ru-P(1)
Ru-P(2)
1.865(4)
2.028(4)
2.034(3)
2.198(3)
2.3650(9)
2.3697(10)
C(1)-O(1)
N(1)-N(2)
C(8)-N(1)
C(7)-N(2)
1.117(4)
1.286(4)
1.398(5)
1.401(5)
Formation of the two types of complexes, viz. [Ru(PPh3)2-
(CO)(NO-R)(H)] and [Ru(PPh3)2(CO)(CNO-R)], from the
reaction of the 2-(arylazo)phenols (1) with [Ru(PPh3)2(CO)2-
Cl2] in refluxing ethanol has been quite interesting. A careful
examination of the equatorial plane of these two species,
viz. [Ru(PPh3)2(CO)(NO-R)(H)] and [Ru(PPh3)2(CO)(CNO-
R)], reveals that the relative disposition of the coordinated
CO is different in the two types of complexes, which has
also been interesting. The exact mechanism of formation of
these two types of complexes is not completely clear to us.
However, the sequences shown in Scheme 1 seem probable.
In the initial step, the 2-(arylazo)phenol binds to the metal
center, via displacement of a CO and elimination of HCl, as
a bidentate N,O-donor. The remaining Ru-Cl bond is also
converted to a Ru-H bond under the prevailing reaction
conditions,13 and thus, two isomers (6 and 7) of the [Ru-
Bond Angles (deg)
P(1)-Ru-P(2)
C(1)-Ru-N(1)
C(2)-Ru-O(2)
176.86(4)
175.98(15)
156.05(13)
C(2)-Ru-N(1)
N(1)-Ru-O(2)
Ru-C(1)-O(1)
78.00(15)
78.17(12)
177.4(4)
[Ru(PPh3)2(CO)(NO-OCH3)(H)]
Bond Distances (Å)
Ru-H(1)
Ru-C(1)
Ru-N(1)
Ru-O(2)
Ru-P(1)
Ru-P(2)
1.56(5)
C(1)-O(1)
N(1)-N(2)
C(7)-N(1)
C(9)-N(2)
1.163(6)
1.281(6)
1.432(7)
1.421(7)
1.816(6)
2.211(4)
2.113(4)
2.3590(15)
2.3570(15)
Bond Angles (deg)
P(1)-Ru-P(2)
C(1)-Ru-N(1)
H(1)-Ru-C(1)
168.24(5)
107.9(2)
85.2(17)
H(1)-Ru-O(2)
N(1)-Ru-O(2)
Ru-C(1)-O(1)
89.4(17)
77.47(16)
174.8(5)
complexes are consistent with their compositions. The
coordinated 2-(arylazo)phenolate ligand and CO share an
equatorial plane with the metal at the center (Figure 2b),
(13) (a) Winter, R. F.; Hornung, F. M. Inorg. Chem. 1997, 36, 6197. (b)
Young, R.; Wilkinson, G. Inorg. Synth. 1977, 17, 79. (c) Levison, J.
J.; Robinson, S. D. J. Chem. Soc. A 1970, 2947.
464 Inorganic Chemistry, Vol. 45, No. 1, 2006

Ru-Mediated C-H ActiWation
(PPh3)2(CO)(NO-R)(H)] complexes are formed. In one of
these two isomers (isomer 6), the hydride is trans to the
nitrogen and the CO is trans to the phenolate oxygen, while
in other isomer (isomer 7) relative disposition of the hydride
and CO is the reverse. It appears that isomer 6 does not
undergo any further reaction in refluxing ethanol, and hence,
it is obtained as the red10 [Ru(PPh3)2(CO)(NO-R)(H)]
complexes. In isomer 7, the coordinated hydride is in the
appropriate location to allow orthometalation of the pendent
phenyl ring via elimination of molecular hydrogen, and this
seems to have happened irreversibly to afford the green [Ru-
(PPh3)2(CO)(CNO-R)] complexes. Rapid transformation of
isomer 7 into the corresponding orthometalated species
appears to have vitiated its isolation. This speculated scheme
indicates that the isomer 6, that is the red10 [Ru(PPh3)2(CO)-
(NO-R)(H)] complexes, cannot as such undergo any cy-
clometalation because of the inappropriate disposition of the
hydride as well as CO. This scheme further indicates that
isomerization of 6 to 7 could not take place in refluxing
ethanol, presumably because of its relatively lower boiling
point. To verify whether transformation of 6 to 7, followed
by the desired orthometalation, can take place at a higher
(with respect to boiling ethanol) temperature, the red10 [Ru-
(PPh3)2(CO)(NO-R)(H)] complexes (isomer 6) were simply
treated in refluxing in 2-methoxyethanol (boiling point 125
°C), which indeed afforded the cyclometalated [Ru(PPh3)2-
(CO)(CNO-R)] complexes in a quantitative yield. Further-
more, when direct reactions between [Ru(PPh3)2(CO)2Cl2]
and the 2-(arylazo)phenols (1) were carried out in refluxing
2-methoxyethanol, the cyclometalated green [Ru(PPh3)2(CO)-
(CNO-R)] complexes were obtained as the sole product.
All these results suggest that from the ethanol reaction the
red10 [Ru(PPh3)2(CO)(NO-R)(H)] complex (6) as well as
its geometrical isomer (7) are generated, probably via
different kinetic routes. While the red complex (6) remains
stable in refluxing ethanol, its isomer (7) undergoes rapid
cyclometalation via elimination of H2.14 Isomerization of the
red10 complex 6 into complex 7, followed by its rapid
transformation into the cyclometalated product, takes place
at a higher temperature.
in the expected region. Besides the absence of the hydride
signal, the H NMR spectrum of each [Ru(PPh3)2(CO)-
1
(CNO-R)] complex is qualitatively similar to that of the
corresponding [Ru(PPh3)2(CO)(NO-R)(H)] complex. 13C
NMR spectra of the [Ru(PPh3)2(CO)(NO-R)(H)] complexes
show all the expected signals within 19.7-202.4 ppm, of
which the signal near 19.74 ppm is assigned to the methyl
carbon in the para-cresol fragment and the most deshielded
signal near 202.4 ppm to the carbonyl carbon. 13C NMR
spectra of the [Ru(PPh3)2(CO)(CNO-R)] complexes show
all the expected signals within 29.7-208.4 ppm. The signal
for the methyl carbon in the para-cresol fragment is observed
near 29.7 ppm, and that for the carbonyl carbon is observed
near 208.4 ppm. A distinct signal around 180 ppm is assigned
to the metalated carbon of the CNO-R ligand. 31P NMR
spectra of all the complexes show a single resonance within
30-41 ppm, as expected. The NMR spectral data of the [Ru-
(PPh3)2(CO)(NO-R)(H)] and [Ru(PPh3)2(CO)(CNO-R)]
complexes are therefore in well accordance with their
respective composition and stereochemistry.
Infrared spectra of the [Ru(PPh3)2(CO)(NO-R)(H)] com-
plexes show many bands of different intensities below 2400
cm-1. Assignment of each individual band to a specific
vibration has not been attempted. However, in each of these
complexes a sharp band is observed near 2360 cm-1, which
is assigned to the Ru-H stretching. Another strong band,
observed around 1930 cm-1, is assigned to the CO stretching.
Three strong bands are displayed near 520, 695, and 745
cm-1, which are attributable to the coordinated PPh3 ligands.
Comparison with the spectrum of [Ru(PPh3)2(CO)2Cl2] shows
the presence of some additional bands (near 1094, 1255,
1367, 1435, and 1479 cm-1) in the spectra of the [Ru(PPh3)2-
(CO)(NO-R)(H)] complexes, and these new bands are
attributed to the coordinated 2-(arylazo)phenolate ligand.
Besides the absence of the Ru-H stretch, the infrared
spectrum of any [Ru(PPh3)2(CO)(CNO-R)] complex is
mostly very similar to that of the corresponding [Ru(PPh3)2-
(CO)(NO-R)(H)] complex.
Both the [Ru(PPh3)2(CO)(NO-R)(H)] and [Ru(PPh3)2-
(CO)(CNO-R)] complexes are found to be poorly soluble
in acetone and acetonitrile, but readily soluble in ethanol,
2-methoxyethanol, dichloromethane, and chloroform, pro-
ducing intense red10 and green solutions, respectively.
Electronic spectra of complexes of both the types have been
recorded in dichloromethane solution. All the complexes
show intense absorptions in the visible and ultraviolet region
(Table 3). The absorptions in the ultraviolet region are
attributable to transitions within the ligand orbitals, and those
in the visible region are probably due to allowed charge-
transfer transitions. To have a better understanding of the
nature of the transitions in the visible region, semiempirical
EHMO calculations have been performed15 on computer
generated models of all the complexes, where phenyl rings
of the triphenylphosphines are replaced by hydrogens. The
Both the [Ru(PPh3)2(CO)(NO-R)(H)] and [Ru(PPh3)2-
(CO)(CNO-R)] complexes are found to be diamagnetic,
which corresponds to the +2 state of ruthenium (low-spin
d6, S ) 0) in these complexes. 1H NMR spectra of the [Ru-
(PPh3)2(CO)(NO-R)(H)] complexes show broad signals
within 7.1-7.5 ppm for the coordinated PPh3 ligands. The
hydride signal is observed as a distinct triplet, due to coupling
with the two magnetically equivalent phosphorus nuclei, near
-10.5 ppm. The methyl signal from the phenolate fragment
of the 2-(arylazo)phenolate ligand is observed near 2.0 ppm.
Most of the expected signals from the aromatic protons of
the coordinated 2-(arylazo)phenolate ligand have been clearly
observed in all the complexes, while few could not be
identified because of their overlap with the PPh3 signals.
Signals for the hydrogen containing substituents (R ) OCH3
and CH3) in the arylazo fragment have also been observed
(15) (a) Mealli, C.; Proserpio, D. M. CACAO, version 4.0; Italy, 1994. (b)
Mealli, C.; Proserpio, D. M. J. Chem. Educ. 1990, 67, 399.
(14) The evolved hydrogen could not be detected experimentally.
Inorganic Chemistry, Vol. 45, No. 1, 2006 465

Gupta et al.
Table 3. Electronic Spectral and Cyclic Voltammetric Data
electronic spectral dataa
max/nm (ꢀ, M-1 cm-1
cyclic voltammetric dataa,b
E, V vs SCE
compd
λ
)
[Ru(PPh3)2(CO)(NO-OCH3)(H)]
[Ru(PPh3)2(CO)(NO-CH3)(H)]
[Ru(PPh3)2(CO)(NO-H)(H)]
[Ru(PPh3)2(CO)(NO-Cl)(H)]
[Ru(PPh3)2(CO)(NO-NO2)(H)]
[Ru(PPh3)2(CO)(CNO-OCH3)]
[Ru(PPh3)2(CO)(CNO-CH3)]
[Ru(PPh3)2(CO)(CNO-H)]
514 (8500), 328 (14700)
508(7400), 322(15000)
504(7000), 322(14500)
518 (6000), 322(12900)
512 (9000), 326(17000)
0.73,d 1.18d
0.76,d 1.24d
0.79,d 1.29d
0.82,d 1.35d
0.92,d 1.36d
670 (7300), 390 (10500),c 356 (13000)
680 (2700), 422 (2500),c 356 (6000),
682 (5000), 428 (4800),c 354 (13000)
690 (1850), 424 (1450),c 360 (4000)
668 (6500), 428 (10000), 334 (8000)c
0.45e (70),f 1.13e(80)f
0.48e (90),f 1.00d
0.54e (70),f 1.40d
0.61e (70),f 1.39d
0.73e (60)f
[Ru(PPh3)2(CO)(CNO-Cl)]
[Ru(PPh3)2(CO)(CNO-NO2]
a In dichloromethane. b Supporting electrolyte, TBAP; scan rate 50 mV s-1
Epa and Epc are anodic and cathodic peak potentials, respectively.
.
c Shoulder. Epa value. E1/2 ) 0.5(Epa + Epc). f ∆Ep ) (Epa - Ep), where
d
e
510 nm by these [Ru(PPh3)2(CO)(NO-R)(H)] complexes is
assignable to the transition occurring from the filled ruthe-
nium (t2) orbital (HOMO) to the vacant π*-(azo) orbital of
the 2-(arylazo)phenolate ligand (LUMO). EHMO calcula-
tions of the [Ru(PPh3)2(CO)(CNO-R)] complexes show a
slightly different picture. The HOMOs of these complexes
have comparable contributions from both the metal and the
2-(arylazo)phenolate ligand, but the LUMOs primarily
consist of the azo fragment16 as before. The lower energy
(668-690 nm) absorption in the [Ru(PPh3)2(CO)(CNO-R)]
complexes is therefore attributed to the transition occurring
from the filled HOMO (having both metal as well as ligand
(CNO-R) character) to the vacant π*-(azo) orbital of the
2-(arylazo)phenolate ligand (LUMO).
Electrochemical properties of both the [Ru(PPh3)2(CO)-
(NO-R)(H)] and [Ru(PPh3)2(CO)(CNO-R)] complexes
have been studied by cyclic voltammetry in 1:9 dichlo-
romethane-acetonitrile solution (0.1 M TBAP).17 The vol-
tammetric data are given in Table 3, and a selected
voltammogram is deposited as Supporting Information
(Figure S2). Complexes of both types show two oxidative
responses on the positive side of SCE. In the [Ru(PPh3)2-
(CO)(NO-R)(H)] complexes, the first oxidative response,
observed within 0.73-0.90 V,18 is irreversible in nature, and
in view of the composition of the HOMO (vide infra) this
oxidation is assigned to the Ru(II)-Ru(III) oxidation.
However, in the [Ru(PPh3)2(CO)(CNO-R)] complexes the
first oxidation, observed within 0.46-0.73 V, is reversible
in nature, characterized by a peak-to-peak separation (∆Ep)
of 70 mV, which remains unchanged upon changing the scan
rate, and the anodic peak current (ipa) is almost equal to the
cathodic peak current (ipc) as expected for a reversible
electron-transfer process. In view of the composition of the
HOMO in these complexes (vide supra), assignment of the
oxidation to the metal center alone seemed unjustified. For
a satisfactory assignment of this oxidation, each [Ru(PPh3)2-
(CO)(CNO-R)] complex was coulometrically oxidized at
an appropriate (Epa + 0.2 V) potential. The oxidations have
been smooth and quantitative, associated with a color change
of green to brownish-green (brown for R ) NO2). ESR
spectra recorded on the oxidized solutions show sharp and
Figure 3. Partial molecular orbital diagram of the [Ru(PPh3)2(CO)(NO-
H)(H)] complex.
results of these calculations are found to be similar16 for the
five complexes in each group. Compositions of some selected
molecular orbitals are given in Table S1, and a partial MO
diagram of a representative [Ru(PPh3)2(CO)(NO-R)(H)]
complex is shown in Figure 3. A partial MO diagram of a
selected [Ru(PPh3)2(CO)(CNO-R)] complex is shown in
Figure S1. In the [Ru(PPh3)2(CO)(NO-R)(H)] complexes,
the highest occupied molecular orbital (HOMO) has a major
(>60%) contribution from the ruthenium d-orbitals, and the
lowest unoccupied molecular orbital (LUMO) is delocalized
almost entirely on the 2-(arylazo)phenolate ligand and is
concentrated heavily (>50%)16 on the azo (-NdN-)
fragment. Hence, the intense absorption displayed around
(17) A little dichloromethane was necessary to take the complex into
solution. Addition of large excess of acetonitrile was necessary to
record the redox responses in proper shape.
(16) In the case of R ) NO2, the LUMOs of both the types of complexes
have a considerable contribution (>45%) from the nitro group.
(18) Potentials are recorded with reference to SCE.
466 Inorganic Chemistry, Vol. 45, No. 1, 2006

Ru-Mediated C-H ActiWation
nearly isotropic signals with g ∼ 2.0. The signals are
representative of free radicals with very little anisotropic
effect arising from the metal center. This result corresponds
well with the composition of the HOMO in such species.
The site of the first oxidation in the [Ru(PPh3)2(CO)(NO-
R)(H)] complexes could not be verified because of the
irreversible nature of this oxidation.
or CNO-R) centered oxidation. The potential of this
irreversible oxidation does not show any systematic variation
with the nature of the substituent R.
Conclusion
The present study shows that [Ru(PPh3)2(CO)2Cl2] can
successfully mediate C-H activation of the 2-(arylazo)-
phenols (1). This study also indicates that similar bond
activation of organic molecules that have structural similarity
with the 2-(arylazo)phenols (1) should also be possible upon
their reaction with [Ru(PPh3)2(CO)2Cl2], and such possibili-
ties are currently under exploration.
The potential of the irreversible Ru(II)-Ru(III) oxidation
in the [Ru(PPh3)2(CO)(NO-R)(H)] complexes has been
found to be sensitive to the nature of the substituent R in
the arylazo fragment. The potential increases with increasing
electron-withdrawing character of the substituent R. The plot
of oxidation potential versus σ [σ ) Hammett para sub-
stituent constant of R;19 OCH3 ) -0.27, CH3 ) -0.17, H
) 0.00, Cl ) 0.23, and NO2 ) 0.78] is found to be linear
(Figure S3) with a slope (F) of 0.17 V (F ) reaction constant
of this couple20), which shows that the nature of para-
substituent R on the 2-(arylazo)phenolate ligand, which is
seven bonds away from the metal center, can still influence
the metal-centered oxidation potential in a predictable
manner. The potential of the reversible oxidation in the [Ru-
(PPh3)2(CO)(CNO-R)] complexes also shows a linear
dependence on the electronic nature of the substituent R
(Figure S4) with a considerably higher slope (F ) 0.27 V).
The observed higher value of F may be attributed to the
combined effect of closeness of R to the metal center (four
bonds away) and larger contribution of ligand (CNO-R) in
the redox active HOMO. The second oxidative response,
displayed by the [Ru(PPh3)2(CO)(NO-R)(H)] and [Ru-
(PPh3)2(CO)(CNO-R)] complexes, above 1.1 V, is irrevers-
ible in nature and is tentatively assigned to a ligand (NO-R
Acknowledgment. The authors thank the reviewers for
their comments and suggestions, which have been helpful
in preparing the revised version of the manuscript. Financial
assistance received from the Department of Science and
Technology [Grant SR/S1/IC-15/ 2004] is gratefully ac-
knowledged. The authors thank the RSIC at Central Drug
Research Institute, Lucknow, India, for the C,H,N analysis
data. S.D thanks the CSIR, New Delhi, for her fellowship
[Grant No. 9/96(410)/2003-EMR-I].
Supporting Information Available: Partial molecular orbital
diagram of [Ru(PPh3)2(CO)(CNO-H)] (Figure S1), cyclic volta-
mmogram of [Ru(PPh3)2(CO)(CNO-OCH3)] (Figure S2), least-
squares plots of Epa values of Ru(II)-Ru(III) couple versus σ for
the [Ru(PPh3)2(CO)(NO-R)(H)] complexes (Figure S3), least-
squares plots of E1/2 values of Ru(II)-Ru(III) couple versus σ for
the [Ru(PPh3)2(CO)(CNO-R)] complexes (Figure S4),1H NMR
spectrum of [Ru(PPh3)2(CO)(NO-H)(H)] (Figure S5), molecular
orbital interaction diagram of [Ru(PPh3)2(CO)(NO-CH3)(H)] (Fig-
ure S6), composition of selected molecular orbitals for all the
complexes (Table S1), and X-ray crystallographic data in CIF
format.This material is available free of charge via the Internet at
http://pubs.acs.org.
(19) Hammett, L. P. Physical Organic Chemistry, 2nd ed.; McGraw-Hill:
New York, 1970.
(20) Mukherjee, R. N.; Rajan, O. A.; Chakravorty, A. Inorg. Chem. 1982,
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