Synthesis, Structure, and Properties of Biimidazole-Chelated Arylruthenium Complexes

Article abstract of DOI:10.1002/ejic.200300293

By reacting Ru(η²-RL)(PPh₃)₂(CO)Cl (1) with excess 4,5-dimethyl-2,2′-biimidazole (dmbi), organometallics of the type [Ru(η¹-RL)(PPh₃)₂(CO)(dmbi)](PF ₆) (2) have been isolated in excellent yield (η²-RL is C₆H₂O-2-CHNHC₆H₄R(p)-3-Me-5, η¹-RL is C₆H₂OH-2-CHNC₆H ₄R(p)-3-Me-5 and R is Me, OMe and Cl). In this process the dmbi ligand undergoes five-membered chelation, the iminium-phenolato function tautomerizes to the imine-phenol function and the Schiff base performs a large rotation around the Ru-C bond. The crystal and molecular structure of [Ru(η¹-MeL)(PPh₃)₂(CO)(dmbi)]-(PF ₆)·CH₂Cl₂ is reported. For steric reasons the carbon monoxide ligand is located syn to the phenolic oxygen atom as opposed to anti in the precursor 1. In the hydrogen bonded imine-phenol function the O-H, H...N, and N...O distances are 0.83(8), 1.77(8), and 2.552(6) A, respectively, the O-H...N angle being 156(2)°. The Ru(dmbi) chelate along with the metallated carbon atom and the CO ligand define an equatorial plane from which the metallated aldimine fragment is rotated by 34.5° due to interligand repulsion. This results in two unequal [2.348(2) and 2.411(2)A] Ru-P bonds and an apparent suppression of the trans influence of the metallated carbanionic site. The cation and anion in the complex are engaged in N-H...F and C-H...F hydrogen bonding, generating a centrosymmetric dimer in the lattice. One of the hydrogen bonds, characterized by H...F, 2.03(8) A and N-H...F, 166(2)°, is particularly strong. Solutions of 2 absorb near 400 nm and emit near 460 nm with quantum yields and lifetimes of ca. 10^-3 and ≤ 20 ns, respectively. The emission, which probably involves the ³MLCT state incorporating a π* (dmbi) contribution, is peculiar to the coligation of η¹-RL and dmbi to bivalent ruthenium. In dichloromethane solution 2 displays a quasireversible 2⁺/2 couple near 0.70 V vs. SCE [2⁺ is the ruthenium(m) analogue of 2]. Coulometrically generated solutions of 2⁺ display a strong absorption near 400 nm and rhombic EPR spectra with g values near 2.55, 2.15, and 1.83. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.

Full text of DOI:10.1002/ejic.200300293

FULL PAPER
Synthesis, Structure, and Properties of Biimidazole-Chelated Arylruthenium
Complexes
Bikash Kumar Panda,[a] Suman Sengupta,[a] and Animesh Chakravorty*[a,b]
Keywords: Ruthenium / Fluorescence / Marcocyclic ligands / Hydrogen bonding
By reacting Ru(η2-RL)(PPh3)2(CO)Cl (1) with excess 4,5-di-
methyl-2,2Ј-biimidazole (dmbi), organometallics of the type
[Ru(η1-RL)(PPh3)2(CO)(dmbi)](PF6) (2) have been isolated in
excellent yield (η2-RL is C6H2O-2-CHNHC6H4R(p)-3-Me-5,
two unequal [2.348(2) and 2.411(2) A] Ru−P bonds and an
apparent suppression of the trans influence of the metallated
carbanionic site. The cation and anion in the complex are
engaged in N−H···F and C−H···F hydrogen bonding, generat-
˚
η1-RL is C6H2OH-2-CHNC6H4R(p)-3-Me-5 and R is Me, ing a centrosymmetric dimer in the lattice. One of the hydro-
˚
OMe and Cl). In this process the dmbi ligand undergoes five-
membered chelation, the iminium-phenolato function tauto-
gen bonds, characterized by H···F, 2.03(8) A and N−H···F,
166(2)°, is particularly strong. Solutions of 2 absorb near
merizes to the imine-phenol function and the Schiff base per- 400 nm and emit near 460 nm with quantum yields and life-
forms a large rotation around the Ru−C bond. The crystal and
times of ca. 10−3 and Յ 20 ns, respectively. The emission,
3
molecular structure of [Ru(η1-MeL)(PPh3)2(CO)(dmbi)]- which probably involves the MLCT state incorporating a π*
(PF6)·CH2Cl2 is reported. For steric reasons the carbon mon-
oxide ligand is located syn to the phenolic oxygen atom as
opposed to anti in the precursor 1. In the hydrogen bonded
imine-phenol function the O−H, H···N, and N···O distances
(dmbi) contribution, is peculiar to the coligation of η1-RL and
dmbi to bivalent ruthenium. In dichloromethane solution 2
displays a quasireversible 2+/2 couple near 0.70 V vs. SCE
[2+ is the ruthenium(III) analogue of 2]. Coulometrically gen-
erated solutions of 2+ display a strong absorption near
400 nm and rhombic EPR spectra with g values near 2.55,
2.15, and 1.83.
˚
are 0.83(8), 1.77(8), and 2.552(6) A, respectively, the O−H···N
angle being 156(2)°. The Ru(dmbi) chelate along with the
metallated carbon atom and the CO ligand define an equat-
orial plane from which the metallated aldimine fragment is
rotated by 34.5° due to interligand repulsion. This results in
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2004)
Introduction
New orthometallated ruthenium compounds are of cur-
rent interest in terms of synthesis[1Ϫ3] reactivity[1,4Ϫ9] and
photophysical properties.[10,11]
The decarbonylative metallation of 4-methyl-2,6-difor-
mylphenol by Ru(PPh3)3Cl2 in the presence of primary aro-
matic amines (RC6H4NH2) furnishes organoruthenium
species of the type Ru(η2-RL)(PPh3)2(CO)Cl, (1), incorpor-
ating a four-membered chelate ring adjacent to a hydrogen-
bonded iminium-phenolato ring.[12Ϫ14] The reactivity of 1
is under our scrutiny. Alkynes and isocyanides promote me-
tallacycle expansion[5,6,8,15,16] but bidentate monoanionic σ-
donor reagents such as carboxylates, nitrate, nitrite, xan-
thate, and pyridine-2-thiolate invariably form a four-mem-
bered chelate ring.[17Ϫ20]
The richness of this reaction chemistry prompted us to
explore the treatment of 1 with an electroneutral hetero-
cyclic ligand suited for five-membered N,N-chelation Ϫ
with the result that 4,5-dimethyl-2,2Ј-biimidazole (dmbi)
has been used to afford a crystalline organoruthenium sys-
tem, characterized by hydrogen bonding interactions within
itself and with anions in the lattice. This is accompanied by
changes in the rotameric and tautomeric states of the Schiff
base ligand. The structure and properties of the new or-
ganometallics, which are also luminescent in the visible re-
gion, are scrutinized here.
[a]
Department of Inorganic Chemistry, Indian Association for the
Cultivation of Science,
Results and Discussion
Kolkata 700032, India
Fax: (internat.) ϩ91-(0)33-2473-2805
E-mail: icac@mahendra.iacs.res.in
Reaction of 1 with dmbi: Chelation and Tautomerization
Addition of excess dmbi to a violet solution of Ru(η2-
RL)(PPh3)2(CO)Cl (1) in boiling MeOH/CH2Cl2 solution
[b]
Jawaharlal Nehru Centre for Advanced Scientific Research,
Bangalore 560 064, India
178
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/ejic.200300293
Eur. J. Inorg. Chem. 2004, 178Ϫ184

Biimidazole-Chelated Ruthenium Aryls
FULL PAPER
in the presence of NH4PF6 afforded the yellow salt [Ru(η1-
RL)(PPh3)2(CO)(dmbi)](PF6) (2) according to Equa-
tion (1).
1 ϩ dmbi ϩ PF6Ϫ Ǟ 2 ϩ ClϪ
(1)
In this work R ϭ Me, OMe, and Cl, and specific com-
pounds are identified with R in parenthesis, e.g. for 2 (Me)
R ϭ Me. Ruthenium complexes of biimidazoles have re-
ceived some attention[21Ϫ25] but organoruthenium species
incorporating chelation by such ligands as in 2 appear to
be unprecedented. The salt 2 has been uniformly isolated
in pure form in Ͼ80% yield. An isomer (the coordinating
nitrogen atoms interchanged) of 2 is possible in principle
Characterization
Type 2 organometallics are diamagnetic (RuII, idealized
t2g6) and behave as 1:1 electrolytes in acetone solution (Λ,
133Ϫ138 ΩϪ1 cm2 molϪ1). The CϵO stretching frequency
(ca. 1940 cmϪ1) in 2 is indicative of dπ(Ru)Ϫpπ(dmbi)
back-bonding. In 1 as well as in the acetate and other de-
rivatives this stretch lies systematically at lower frequencies,
1
but it has never been observed. Careful examination of H
NMR spectra of crude samples (before recrystallization)
did not reveal any extra methyl or other signals apart from
those characterizing 2 (see Exp. Sect.).
near 1920 cmϪ1 [12,17Ϫ20]
.
1
In the H NMR spectra the 3-H and 5-H proton signals
of the metallated ring are sharp singlets near 6.5 ppm. The
C(4)-Me signals near δ ϭ 1.8 ppm are subject to shielding
by phosphane phenyl rings.[12,17,29] The same applies to the
C(22)-Me signal near 1.7 ppm; the C(21)-Me resonance is
near 2.0 ppm. The PPh3, Schiff base (C6H4R), and the bi-
imidazole aromatic proton signals form a complex multiplet
in the region 6.8Ϫ7.4 ppm. The dmbi NϪH protons res-
onate near 10.2 ppm. The chemical shifts of the imine-phe-
nol protons are considered above. The photophysical and
redox properties of the complexes are examined below.
In Equation (1) the RuϪCl and RuϪO (phenolato)
bonds are displaced by the chelating dmbi ligand. With the
liberation of the phenolato oxygen, the Schiff base fragment
assumes the imine-phenol tautomeric form 3, as opposed
to the zwitterionic iminium-phenolato form 4 present in
1.[12] This has been proven by structure determination (vide
infra) and is fully consistent with spectroscopic data.
Structure: Nonbonded Interactions, Rotameric Change, and
Hydrogen Bonding
The dichloromethane solvate [Ru(η1-MeL)(PPh3)2(CO)-
(dmbi)](PF6)·CH2Cl2, afforded crystals suitable for struc-
ture determination. A view of the cation (Figure 1) and
Thus the CϭN stretching frequency in 2 is significantly
lower at ca. 1600 cmϪ1 than that in 1 (ca. 1620 cmϪ1), as
1
expected.[26,27] Also, the aldimine CH signal in H NMR in
2 is at a lower field, ca. 8.0 ppm as compared to ca. 7.5 ppm
in 1. The OϪH resonance in 2 is a relatively sharp signal
near 13 ppm, having a half-height width of ca. 30 Hz. In
contrast the iminium NϪH resonance in 1 is broad (width,
ca. 150 Hz) due to the quadrupole moment of the nitrogen
atom.[12] The prototropic transformation between 1 and 2
has certain similarities with the imineϪiminium tautomeriz-
ation in rhodopsins.[26]
Equation (1) is believed to proceed[17,28] via cis attack of
chloride/O(phenolato) by dmbi as stylized in 5. The anch-
ored ligand can then displace both chloride and phenolato
oxygen atom to achieve chelation as in 6 with concomitant
prototropic and rotameric (vide infra) changes.
Figure 1. Perspective view and atom labeling scheme for the cation
of 2(Me)·CH2Cl2. All non-hydrogen atoms are represented by 30%
thermal probability ellipsoids.
Eur. J. Inorg. Chem. 2004, 178Ϫ184
www.eurjic.org
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
179

B. K. Panda, S. Sengupta, A. Chakravorty
FULL PAPER
˚
angle between them is 34.5°. As a result the environment is
Table 1. Selected bond lengths (A) and angles (°) for complex
2(Me)·CH2Cl2
˚
more crowded around P(2), and RuϪP(2) [2.411(2) A] is
˚
significantly longer than RuϪP(1) [2.348(2) A]. In the pre-
Bond lengths
cursor complex 1 the Schiff base lies on the equatorial plane
[12]
˚
and the two RuϪP lengths are both 2.387(2) A.
RuϪP(1)
RuϪP(2)
RuϪC(2)
RuϪC(9)
RuϪN(2)
2.348(2)
2.411(2)
2.068(5)
1.791(5)
2.166(4)
RuϪN(3)
2.157(4)
1.152(6)
1.259(7)
1.347(6)
2.552(6)
The noncoplanarity of A and B planes arise from the
repulsive nonbonded interactions between the dmbi and
C(9)ϪO(2)
C(7)ϪN(1)
C(1)ϪO(1)
N(1)···O(1)
˚
Schiff base ligands. Thus C(17)···C(3) [3.298(7) A] is less
˚
than the sum (3.40 A) of the van der Waals (vdW) radii of
the two carbon atoms.[31] The distance would have been
even lower, further augmenting the repulsion, if the A and
B planes were coplanar. The repulsive interaction is also
expressed in an effective lengthening of the RuϪN(2) bond.
The trans influence of the carbanionic C(2) site should nor-
mally make the RuϪN(3) bond longer than the RuϪN(2)
bond although the electron-donating methyl group adjacent
to N(3) may marginally counter this effect. In practice the
Angles
P(1)ϪRuϪP(2)
P(1)ϪRuϪN(2)
P(1)ϪRuϪN(3)
P(1)ϪRuϪC(9)
P(1)ϪRuϪC(2)
P(2)ϪRuϪN(2)
P(2)ϪRuϪN(3)
P(2)ϪRuϪC(9)
175.7(1)
91.0(1)
90.8(1)
87.0(2)
90.5(1)
85.2(1)
90.3(1)
97.1(2)
P(2)ϪRuϪC(2)
RuϪC(9)ϪO(2)
C(2)ϪRuϪN(2)
C(9)ϪRuϪN(3)
C(9)ϪRuϪN(2)
N(2)ϪRuϪN(3)
C(9)ϪRuϪC(2)
87.9(1)
174.8(5)
95.4(2)
96.5(2)
172.4(2)
76.3(2)
91.9(2)
˚
two bond lengths Ϫ 2.157(4) and 2.166(4) A, respectively
Ϫ are equal within experimental error, primarily due to the
nonbonded repulsion noted above.
The conversion of 1 into 2 is attended by a large rotation
of the Schiff base fragment around the RuϪC(2) bond. The
carbon monoxide ligand lies syn to the metallated carbon
atom in both 1 and 2 but it is respectively syn and anti to
selected bond parameters (Table 1) are given here. All the
hydrogen atoms in the structure, except those of CH2Cl2,
were directly observable in difference Fourier maps, which
helped in characterizing the hydrogen bonds, vide infra. In
Figure 1 only the phenolic hydrogen is explicitly shown.
The solvent of crystallization CH2Cl2 displays a nonbonded
Cl···Cl interaction [3.576(4) A] with another symmetry re-
lated CH2Cl2 molecule, the two forming a centrosymmetric
pair in the lattice.
the phenolic CϪO function in
2
and 1.[12] The
O(1)ϪC(1)···C(9)ϪO(2) torsion angle in 2(Me)·CH2Cl2 is
46.7°. The computer-generated hypothetical anti configura-
tion of dmbi fragment is shown in 8 where the estimated
˚
˚
˚
C(17)···O(1) and N(2)···O(1) are 2.416(5) A and 2.621(6) A,
respectively, are far below the respective sums of the vdW
[31]
˚
The RuC2P2N2 coordination sphere has a severely dis-
torted octahedral geometry. The angles subtended by cis
and trans pairs of ligands span the ranges 76Ϫ98° and
171Ϫ176°, respectively. On the basis of covalent radii, the
radii (3.20 and 3.05 A).
The anti configuration is thus
unstable and the above-noted conformational change oc-
curs to relieve the strain. The observed C(17)···O(1) and
N(2)···O(1) distances in the syn-configured complex are
idealized RuIIϪC(sp2) bond length is estimated to be 2.06
˚
5.660(5) and 4.930(6) A, respectively.
[17,30]
˚
˚
A.
The observed RuϪC(2) is 2.068(5) A. The
RuϪN(3) bond is not lengthened by the trans influence of
the carbanionic C(2) site due to certain repulsive interac-
tions in the structure, see below.
The Ru(dmbi) chelate fragment (excluding the methyl
groups) along with the metallated carbon atom C(2) and
the carbon monoxide ligand constitute a satisfactory plane
˚
of mean deviation 0.03 A (plane A). Another relevant plane
(plane B) is the metallated aldimine ring defined by Ru,
˚
C(1) to C(8), N(1), O(1) (mean deviation 0.03 A). The two
planes are noncoplanar as highlighted in 7, the dihedral
Within the imine-phenol fragment of 8, OϪH, H···N, and
˚
N···O are 0.83(8), 1.77(8), and 2.552(6) A respectively, the
OϪH···N is 156(2)°. The hydrogen bonding is thus very un-
symmetrical. In the iminium-phenolato fragment 4 of the
precursor 1 the relevant bond lengths and angle are: NϪH,
˚
˚
˚
0.99(6) A, H···O, 1.75(5) A, N···O, 2.665(12) A, and
NϪH···O, 144(1)°.[12] In effect, the hydrogen bonding is
stronger (shorter N···O distance) in the imine-phenol spec-
ies.
The dmbi ligand in the cation and the PF6Ϫanion are
engaged in NϪH···F and CϪH···F hydrogen bonding. The
180
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2004, 178Ϫ184

Biimidazole-Chelated Ruthenium Aryls
FULL PAPER
centrosymmetric dimer thus generated is shown in Figure 2 sity and is believed to have significant dπ(Ru)Ϫπ*(dmbi)
along with approximate bond parameters. In organometal- MLCT character. Dichloromethane solutions of 2 are fluor-
˚
lic hexafluorophosphate salts, H···F distances Ͻ2.6 A, escent at room temperature, the emission peak lying near
along with XϪH···F (X ϭ C, N, O) angles Ͼ90°, generally 460 nm. The quantum yields (ϕr) are nearly one order of
indicate significant hydrogen bonding.[32] Of the three hy- magnitude lower than that of the [Ru(bpy)3]2ϩ standard[33]
drogen bond types in Figure 3 the, N(5)ϪH···F(1) bond is (Table 2).
˚
particularly strong [H···F, 2.03(8) A; NϪH···F, 166(2)°].
Excitation spectral studies have revealed that the emis-
sion is associated with the absorption band near 400 nm. A
representative case is shown in Figure 3. Assuming that the
band has MLCT character, as suggested above, the possible
3
involvement of the MLCT state incorporating a π*(dmbi)
contribution is implicated in the emission process. However,
tris-biimidazole complexes of bivalent ruthenium are non-
emitters at room temperature.[21,34] Further the parent type
1 organometallics also do not emit in the visible region.
Thus the observed emission in 2 is a property peculiar to
the coligation of η1-RL and dmbi to bivalent ruthenium.
Lifetime studies revealed single-exponential decay with τ0
Յ 20 ns, which is shorter than the usual (102Ϫ103 ns) life-
times of fluorescent ruthenium() complexes of conjugated
nitrogenous ligands.[21,23]
Figure 2. Hydrogen bonding in crystals of 2(Me)·CH2Cl2. Relevant
˚
bond lengths (A) and angles (°) are N(5)···F(1), 2.775(5);
H(5)···F(1), 2.03(8); N(4)···F(4), 2.945(5); H(4)···F(4), 2.31(9);
C(18)···F(3), 3.144(6); H(18)···F(3), 2.54(7). N(5)ϪH(5)···F(1),
166(2); N(4)ϪH(4)···F(4), 131(3); C(18)ϪH(18)···F(3), 123(1)
Electrochemistry: Metal Oxidation
In dichloromethane solution 2 displays a quasireversible
(peak-to-peak separation, ca. 100 mV) cyclic voltammetric
response assigned to the couple of Equation (2) where 2ϩ
represents the ruthenium() analogue of 2.
2
ϩ ϩ e Ǟ 2
(2)
The reduction potentials (E1/2) lie near 0.70 V vs. SCE
and become more positive as the electron-withdrawing
power of the R group increases (OMe Ͻ Me Ͻ Cl), see
Table 2. The one-electron nature of the couple is consistent
with current height data, as compared to those of the one-
electron standard [Ru(bpy)3]2ϩ. More importantly exhaus-
tive coulometric oxidation at 0.9 V afforded a coulomb
count corresponding to a one-electron transfer (Table 2).
The trivalent organometallics 2ϩ, generated coulometr-
ically, have been examined in solution. Their cyclic voltam-
mograms (initial scan cathodic) are virtually superimpos-
able on those of 2 (initial scan anodic), showing that 2ϩ
Figure 3. Absorption (···) fluorescence (——) and excitation
(Ϫ Ϫ Ϫ) spectra of 2(Cl) in dichloromethane solution.
Photophysical Properties
Type 2 complexes display two allowed transitions near retains the gross structure of 2. Orange-red solutions of 2ϩ
320 and 400 nm (Table 2). The later band is weaker in inten- are characterized by an intense band near 400 nm, associ-
Table 2. Spectral and electrochemical data of 2
Complexes
UV/Vis data[a]
Emission data
Electrochemical data
λmax, nm (ε,[b]

Ϫ1cmϪ1
)
λmax, nm (ϕr)[a] [c]
E1/2,V (∆Ep, mV)[d]
n[e]
2(Me)
2(OMe)
2(Cl)
320 (20970), 390 (4680)
322 (23700), 394 (5210)
321 (22760), 397 (4470)
464 (5.6 ϫ 10Ϫ3
461 (3.0 ϫ 10Ϫ3
467 (5.3 ϫ 10Ϫ3
)
)
)
0.69 (130)
0.65 (85)
0.71 (95)
1.07
1.03
0.98
[a]
[b]
[c]
[d]
Solvent is dichloromethane.
Molar absorption coefficient.
Excitation at the higher wavelength absorption peak.
Solvent is
dichloromethane; ∆Ep is peak-to-peak separation. [e] n ϭ Q/QЈ where Q is the observed coulomb count and QЈ is the calculated coulomb
count for one-electron transfer.
Eur. J. Inorg. Chem. 2004, 178Ϫ184
www.eurjic.org
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
181

B. K. Panda, S. Sengupta, A. Chakravorty
FULL PAPER
Table 3. Electronic and EPR spectroscopic data of 2ϩ
was obtained from Aldrich. Dichloromethane was purified for elec-
trochemical work as described before.[35,38] All other chemicals and
solvents were of analytical grade and were used as received.
Complexes UV/Vis data[a]
EPR g values[c]
g1 g2 g3
λmax, nm (ε,[b] Ϫ1cmϪ1
 )
Physical Measurements: Electronic and IR spectra were recorded
with a Shimadzu UV-1601 PC spectrophotometer and a Nicolet
Magna IR series II spectrometer respectively. 1H NMR spectra
were obtained using a Bruker 300 MHz FT NMR spectrometer.
The numbering scheme used for 1H NMR is the same as in the
crystallography. SpinϪspin structures are abbreviated as: s, singlet;
d, doublet; t, triplet; m, multiplet. EPR spectra were recorded on
a Varian E-109C X-band spectrometer fitted with a quartz dewar.
Microanalyses (C, H, N) were performed using a PerkinϪElmer
240C elemental analyzer. Solution electrical conductivity was meas-
ured in acetone with a Phillips PR 9500 bridge by using a platinized
electrode (cell constant of 1.05). The electrochemical measurements
were performed at a platinum electrode under a nitrogen atmos-
phere in dichloromethane solution by using a model 620A electro-
chemical analyzer of CH Instruments. The supporting electrolyte
was tetraethylammonium perchlorate and potentials are referenced
to the saturated calomel electrode (SCE). For EPR studies 2؉ was
generated coulometrically in dichloromethane solution to which
dry toluene was added before freezing into the glassy state.
2(Me)ϩ
324 (356560), 397(26710), 518 (4830) 2.528 2.141 1.818
2(OMe)ϩ 319 (34960), 401 (24410), 512 (2530) 2.553 2.158 1.818
2(Cl)ϩ
321 (37950), 403 (27710), 515 (3500) 2.578 2.159 1.856
[a]
[b]
[c]
Solvent is dichloromethane.
Molar absorption coefficient.
In 1:1 dichloromethane/toluene frozen glass (77 K).
ated with a shoulder near 520 nm (Table 3). The solutions
are EPR-active when frozen into the glassy state (dichloro-
methane/toluene, 77 K), giving rise to well-resolved rhom-
bic spectra that are consistent with a low-spin 4d5 configu-
ration in a nonaxial geometry.[35,36] A representative spec-
trum (Figure 4) and the g values (Table 3) are given here.
Fluorescence and quantum yields (using [Ru(bpy)3]2ϩ as stand-
ard,[33] ϕ ϭ 0.042) were recorded with a PerkinϪElmer model LS
55 luminescence spectrometer. Luminescence lifetimes were meas-
ured in an Applied Photophysics SP-70 nanosecond fluorescence
spectrometer based on a time-correlated single-photon counting
technique. The decay curves were deconvoluted using the Global
Fluorescence Analysis version 1.2 software of Photon Technology
International.
Synthesis of Complexes: The [Ru(η1-RL)(PPh3)2(CO)(dmbi)](PF6)
(2) complexes were synthesized in excellent yield (ca. 85%) by re-
acting Ru(η2-RL)(PPh3)2(CO)Cl (1) with excess 4,5-dimethyl-2,2Ј-
biimidazole. Details of a representative case are given below. The
other compounds were prepared analogously.
2(Me): dmbi (89 mg, 0.549 mmol) was added to a hot solution of
1(Me) (100 mg, 0.109 mmol) in a mixture of methanol (20 mL) and
dichloromethane (10 mL). On subsequent heating to reflux for 3 h,
the mixture changed from violet to yellow. NH4PF6 (30 mg,
0.184 mmol) was then added and the resultant solution was further
boiled under reflux for 20 min. The solvent was then evaporated
under reduced pressure and the yellow solid thus obtained was
washed thoroughly with water (for removal of excess NH4PF6),
dried, and then dissolved in dichloromethane (excess dmbi remains
insoluble). The filtered solution was then stripped of solvent under
reduced pressure and the residue was recrystallized from a di-
chloromethane/hexane (1:3) mixture followed by drying in vacuo
to furnish the complex in nonsolvated form. Yield: 110 mg (85%).
C60H54F6N5O2P3Ru (1185.10): calcd. C 60.81, H 4.59, N 5.91;
found C 60.75, H 4.63, N 5.85. IR (KBr): ν˜ ϭ 1939 cmϪ1(νCO),
1591 (νCϭN), 847 (νPF6). 1H NMR (300 MHz, CDCl3, 298 K): δ ϭ
12.96 (s, 1 H, OϪH), 10.30 (s, 1 H, NϪH), 10.20 (s, 1 H, NϪH),
7.96 (s, 1 H, H7), 6.59 (s, 1 H, H5), 6.52 (s, 1 H, H3), 2.37 (s, 3 H,
13-Me), 2.02 (s, 3 H, 21-Me), 1.84 (s, 3 H, 4-Me), 1.72 (s, 3 H, 22-
Me), 6.90Ϫ7.25 (m, 36 H, 2PPh3, H11, H12, H14, H15, H17, H18).
Figure 4. X-band EPR spectrum of electrogenerated 2(OMe)ϩ in
dichloromethane/toluene glass at 77 K. Instrument settings: power,
30 dB; modulation, 100 kHz; sweep centre, 3200 G.
Conclusions
Organometallics of type 1 are transformed into salts of
type 2 upon reacting with dmbi. The conversion is attended
by five-membered dmbi chelation, iminium-phenolato Ǟ
imine-phenol prototropic shift and rotameric isomerization
(antiǞ syn) of the phenolic function with respect to the
carbon monoxide ligand. The metallated aromatic ring is
turned away from the dmbi chelate plane due to steric re-
pulsion, resulting in significant inequality of the two RuϪP
bonds. Also, the carbanionic trans influence is apparently
suppressed. In solution 2 is emissive in the visible region
and is electrooxidizable to its ruthenium() analogue 2ϩ,
which is characterized by rhombic EPR spectra.
ΛM ϭ 133 ΩϪ1cm2molϪ1
.
2(OMe): 1(OMe) (100 mg, 0.107 mmol) and dmbi (87 mg,
0.536 mmol) were employed. Yield: 106 mg (82%). C60H54F6N5O3-
P3Ru (1201.10): calcd. C 60.00, H 4.53, N 5.83; found C 60.05, H
Experimental Section
[37]
Materials: Ru(PPh3)3Cl2
and Ru(η2-RL)(PPh3)2(CO)Cl[12] were 4.58, N 5.77. IR (KBr): ν˜ ϭ 1938 cmϪ1 (νCO), 1611 (νCϭN), 846
prepared by reported methods, and 4,5-dimethyl-2,2Ј-biimidazole
(νPF6). 1H NMR (300 MHz, CDCl3, 298 K): δ ϭ 12.99 (s, 1 H,
182
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2004, 178Ϫ184

Biimidazole-Chelated Ruthenium Aryls
FULL PAPER
Computer Generation of Motif 5: The relative positions of CO and
the dmbi chelate were retained as in the structure of [Ru(η1-
MeL)(PPh3)2(CO)(dmbi)](PF6)·CH2Cl2 but the phenolic oxygen
O(1) was shifted so as to correspond to the relative position in 1
Table 4. Crystallographic data for 2 (Me)·CH2Cl2
Empirical formula
Molecular mass
T/K
C61H56Cl2F6N5O2P3Ru
1269.99
293(2)
˚
(Me), the CϪO length being set at 1.347(6) A. The same software
Crystal system
Space group
triclinic
P1
as noted above was used.
¯
˚
a (A)
13.437(7)
13.662(8)
16.150(9)
77.67(5)
86.76(4)
89.46(4)
2892(3)
2
1.459
0.514
8598
8460
Acknowledgments
˚
b (A)
We are thankful to the Department of Science and Technology, the
Council of Scientific and Industrial Research, New Delhi, India,
for financial support. The help received from Professor M. Choud-
hury, Dr. S. Goswami, and Dr. D. Nath is acknowledged.
˚
c (A)
α (°)
β (°)
γ (°)
3
˚
V (A )
Z
[1]
M. Poyatos, J. A. Mata, E. Falomir, R. H. Crabtree, E. Peris,
Calcd. density/gmϪ3
Organometallics 2003, 22, 1110Ϫ1114.
J. Perez, V. Riera, A. Rodriguez, D. Miguel, Organometallics
µ (mmϪ1
)
[2]
Total reflections
2002, 21, 5437Ϫ5438.
J. A. Cabeza, I. D. Rio, S. G. Granda, V. Riera, M. Suarez,
Independent reflections
R, ωR2[I Ͼ 2σ(I)][a][b]
Goodness-of-fit on F2 [a][b]
[3]
0.0574, 0.1477
1.057
Organometallics 2002, 21, 2540Ϫ2543.
W. Ferstl, I. K. Sakodinskaya, N. B. Sutter, G. L. Borgne, M.
[4]
Pfeffer, A. D. Ryabov, Organometallics 1997, 16, 411Ϫ418.
K. Ghosh, S. Pattanayak, A. Chakravorty, Organometallics
[a]
[b]
2 2
2 2
R1 ϭ Σ||Fo| Ϫ |Fc||/Σ|Fo|. wR2 ϭ [Σw(Fo2 Ϫ Fc ) /Σ(Fo ) .
[5]
1998, 17, 1956Ϫ1960.
K. Ghosh, S. Chattopadhyay, S. Pattanayak, A. Chakravorty,
[6]
OϪH), 10.32 (s, 1 H, 2NϪH), 10.23 (s,1 H, NϪH) 7.96 (s, 1 H,
H7), 6.57 (s, 1 H, H5), 6.52 (s, 1 H, H3), 2.02 (s, 3 H, 21-Me), 1.84
(s, 3 H, 4-Me), 1.75 (s, 3 H, 22-Me), 3.83 (s, 3 H, OMe), 6.98Ϫ7.25
(m, 36 H, 2 PPh3, H11, H12, H14, H15, H17, H18). ΛM ϭ 137
Organometallics 2001, 20, 1419Ϫ1423.
[7]
P. Steenwinkel, S. L. James, R. A. Gossage, D. M. Grove, H.
Kooijman, W. J. J. Smeets, A. L. Spek, G. V. Koten, Organomet-
allics 1998, 17, 4680Ϫ4693.
B. K. Panda, S. Chattopadhyay, K. Ghosh, A. Chakravorty,
[8]
ΩϪ1 cm2molϪ1
.
Organometallics 2002, 21, 2773Ϫ2780.
[9]
V. Ritleng, M. Pfeffer, C. Sirlin, Organometallics 2003, 22,
2(Cl): 1(Cl) (100 mg, 0.107 mmol) and dmbi (87 mg, 0.536 mmol)
were used. Yield: 107 mg (83%). C59H51ClF6N5O2P3Ru (1205.52):
calcd. C 58.78, H 4.26, N 5.81; found C 58.82, H 4.29, N 5.76. IR
(KBr): ν˜ ϭ 1940 cmϪ1 (νCO), 1605 (νCϭN), 848 (νPF6). 1H NMR
(300 MHz, CDCl3, 298 K): δ ϭ 12.69 (s, 1 H, O-H), 10.19 (s, 1 H,
NϪH), 10.09 (s, 1 H, NϪH), 7.95 (s, 1 H, H7), 6.62 (s, 1 H, H5),
6.54 (s, 1 H, H3), 2.02 (s, 3 H, 21-Me), 1.83 (s, 3 H, 4-Me), 1.75 (s,
3 H, 22-Me), 6.90Ϫ7.34 (m, 36 H, 2 PPh3, H11, H12, H14, H15,
347Ϫ354.
[10]
V. W. W. Yam, B. W. K. Chu, K. K. Cheung, Chem. Commun.
1998, 2261Ϫ2262.
V. W. W. Yam, B. W. K. Chu, C. C. Ko, K. K. Cheung, J.
[11]
Chem. Soc., Dalton Trans. 2001, 1911Ϫ1919.
[12]
P. Ghosh, N. Bag, A. Chakravorty, Organometallics 1996, 15,
3042Ϫ3047.
[13]
N. Bag, S. B. Choudhury, A. Pramanik, G. K. Lahiri, A. Chak-
ravorty, Inorg. Chem. 1990, 29, 5013Ϫ5014.
N. Bag, S. B. Choudhury, G. K. Lahiri, A. Chakravorty, J.
H17, H18). ΛM ϭ 138 ΩϪ1 cm2 molϪ1
.
[14]
X-ray Crystallography: Bright yellow single crystals of [Ru(η1-
MeL)(PPh3)2(CO)(dmbi)](PF6)·CH2Cl2 (2(Me)·CH2Cl2) (0.40 ϫ
0.30 ϫ 0.25 mm3) were grown by slow diffusion of hexane into
dichloromethane solutions at room temperature. Cell parameters
were determined by a least-squares fit of 30 machine-centered re-
flections (2θ range 14Ϫ28°) on a Siemens R3m/V four-circle dif-
fractometer with graphite-monochromated Mo-Kα radiation (λ ϭ
0.71073). Two check reflections measured after every 198 reflec-
tions showed no significant intensity reduction. All data were cor-
rected for Lorentz polarization effects and an empirical absorption
correction[39] was performed on the basis of an azimuthal scan of
six reflections for the crystals. The metal atom was located from
Patterson maps and the rest of the non-hydrogen atoms and all the
hydrogen atoms except those of CH2Cl2 emerged from successive
Fourier syntheses. The structure was refined by a full-matrix least-
squares procedure. All non-hydrogen atoms were refined aniso-
tropically. The hydrogen atoms were refined isotropically with a
fixed U ϭ 0.08 A . Calculations were performed using the
SHELXTL, version 5.03[40] package. Crystal data are listed in
Table 4. CCDC-210733 contains the supplementary crystallo-
graphic data for 2 (Me)·CH2Cl2. These data can be obtained free
of charge at www.ccdc.cam.ac.uk/conts/retrieving.html [or from the
Cambridge Crystallographic Data Centre, 12, Union Road, Cam-
bridge CB2 1EZ, UK; Fax: (internat.) ϩ44-1223-336-033; E-mail:
deposit@ccdc.cam.ac.uk].
Chem. Soc., Chem. Commun. 1990, 1626Ϫ1627.
[15]
S. Chattopadhyay, K. Ghosh, S. Pattanayak, A. Chakravorty,
J. Chem. Soc., Dalton Trans. 2001, 1259Ϫ1265.
S. Chattopadhyay, K. Ghosh, S. Pattanayak, A. Chakravorty,
[16]
Indian J. Chem. 2001, 40A, 1Ϫ3.
[17]
P. Ghosh, A. Pramanik, A. Chakravorty, Organometallics 1996,
15, 4147Ϫ4152.
[18]
P. Ghosh, A. Chakravorty, Inorg. Chem. 1997, 36, 64Ϫ69.
S. Chattopadhyay, B. K. Panda, K. Ghosh, A. Chakravorty,
Israel J. Chem. 2001, 41, 139Ϫ144.
B. K. Panda, S. Chattopadhyay, K. Ghosh, A. Chakravorty,
Polyhedron 2002, 21, 899Ϫ904.
D. P. Rillema, R. Sahai, P. Matthews, A. K. Edwards, R. J.
Shaver, L. Morgan, Inorg. Chem. 1990, 29, 167Ϫ175.
M. Haga, M. M. Ali, H. Maegawa, K. Nozaki, A. Yoshimura,
T. Ohno, Coord. Chem. Rev. 1994, 132, 99Ϫ104.
M. Haga, M. M. Ali, S. Koseki, K. Fujimoto, A. Yoshimura,
K. Nozaki, T. Ohno, K. Nakajima, D. J. Stufkens, Inorg. Chem.
1996, 35, 3335Ϫ3347.
M. Haga, T. Inoue, S. Yamabe, Inorg. Chem. 1987, 26,
4148Ϫ4154.
P. Majumdar, S. M. Peng, S. Goswami, J. Chem. Soc., Dalton
[19]
[20]
[21]
[22]
[23]
2
˚
[24]
[25]
Trans. 1998, 1569Ϫ1574.
[26]
C. Sandorfy, D. Vocelle, Mol. Phys. Chem. Biol. 1989, 4,
195Ϫ211.
[27]
H. Bohme, M. Hakke, in Advances in Organic Chemistry (H.
Bohme, H. G. Viehe, Eds.), Part 1, Vol. 9, Interscience Publi-
cation, New York, 1976, p.1.
Eur. J. Inorg. Chem. 2004, 178Ϫ184
www.eurjic.org
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
183

B. K. Panda, S. Sengupta, A. Chakravorty
FULL PAPER
[28]
[35]
[36]
[37]
[38]
[39]
[40]
N. Serpone, D. G. Bickley, Inorg. Chem. 1972, 17, 391Ϫ397.
G. K. Lahiri, S. Bhattacharya, B. K. Ghosh, A. Chakravorty,
Inorg. Chem. 1987, 26, 4324Ϫ4331.
P. Ghosh, A. Pramanik, N. Bag, G. K. Lahiri, A. Chakravorty,
J. Organomet. Chem. 1993, 454, 237Ϫ241.
T. A. Stephenson, G. Wilkinson, J. Inorg. Nucl. Chem. 1966,
28, 945Ϫ956.
A. Pramanik, N. Bag, D. Ray, G. K. Lahiri, A. Chakravorty,
Inorg. Chem. 1991, 30, 410Ϫ417.
A. C. T. North, D. C. Phillips, F. A. Mathews, Acta Crys-
tallogr., Sect. A 1968, 24, 351Ϫ359.
[29]
P. Ghosh, Polyhedron 1997, 16, 1343Ϫ1349.
[30]
A. K. Rappe, C. J. Caswit, K. Colwell, W. A. Goddard, W. M.
Skiff, J. Am. Chem. Soc. 1992, 114, 10024Ϫ10035.
[31]
J. E. Huheey, E. A. Keiter, R. L. Keiter, Inorganic Chemistry:
Principles of Structure and Reactivity, Hampen Collins College
Publishers, New York, 1993, p. 292.
[32]
F. Grepioni, G. Cojazzi, S. M. Drapen, N. Scully, D. Braga,
Organometallics 1998, 17, 296Ϫ307.
G. M. Sheldrick, SHELXTL, Version 5.03; Siemens Analytical
X-ray system: Madison, WI, 1994.
[33]
D. P. Rillema, D. G. Taghdiri, D. S. Jones, L. A. Worl, T. J.
Meyer, H. A. Levy, C. D. Keller, Inorg. Chem. 1987, 26,
Received May 17, 2003
Early View Article
Published Online October 31, 2003
578Ϫ585.
[34]
M. Haga, Inorg. Chim. Acta 1983, 77, L39ϪL41.
184
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2004, 178Ϫ184