A family of organoruthenium nitrites: Alkyne insertion, linkage isomerization and ring nitration

Article abstract of DOI:10.1039/b009719p

The reaction of [Ru(C₆H₂OH-2-CHNR-3-Me-5) (PPh₃)₂(CO)(NO₂)] 1 (R = Et, p-MeC₆H₄ or p-ClC₆H₄) with an excess of alkyne HC≡CX (X = H, Ph or CH₂OH) in CH₂Cl₂-MeOH medium was accompanied by linkage isomerization of nitrite (O,O′-bonded → N-bonded) and formation of a six-membered vinyl-phenolato chelate ring to give [Ru(η²-C₆H₂CXCH-1-O-2-CHNHR-3-Me-5) (PPh₃)₂(CO)(NO₂)] 4. The active substrate is the solvate 1·MeOH, and the 2 + 2 addition of the bulky ≡CX (X = Ph or CH₂OH) group proceeds regiospecifically to the carbon end of the Ru-C bond. Compound 4 has also been obtained metathetically by treating 3 (the chloro analogue of 4) with NaNO₂ in neutral media. However in acid media ring nitration of 3 (R = Et, X = Ph) occurs furnishing [Ruη²-C₆HCPhCH-1-O-2-CHNHEt-3-NO₂-4- Me-5)(PPh₃)₂(CO)Cl] 7 which can metathetically be converted into the corresponding N-bonded NO₂ analogue, 8. The iminium proton is hydrogen bonded to the phenolato oxygen in 4, 7 and 8 and also weakly to a nitro oxygen in 4 and 8 (IR and ¹H NMR data). All the species display a quasireversible cyclic voltammetric Ru^III-Ru^II couple, the E_1/2 of which shifts to higher potential by ≈200 mV upon replacing chloride by nitrite (3 → 4; 7 → 8) as well as upon aromatic nitration (3 → 7). The crystal structures of the solvate 4b·C₆H₆ in which R = p-MeC₆H₄ and X = H, 4h in which R = p-ClC₆H₄ and X = CH₂OH and 7 have been determined. The σ-vinyl-phenolato chelate ring is approximately planar. The Ru-N bond in the planar RuNO₂ fragment of 4b·C₆H₆ and 4h is lengthened by ≈0.1 A due to the trans influence of the vinyl group. The Ru-C(vinyl) bond in 7 is significantly shortened due to electron withdrawal by the nitro group, thus promoting Ru-ligand back bonding. The distances of the iminium nitrogen from phenolic oxygen and a nitrito oxygen (in 4b·C₆H₆ and 4h) lie in the ranges 2.55-2.67 and 2.90-2.98 A respectively.

Full text of DOI:10.1039/b009719p

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A family of organoruthenium nitrites: alkyne insertion, linkage
isomerization and ring nitration
Swarup Chattopadhyay, Kaushik Ghosh, Sujay Pattanayak and Animesh Chakravorty*
Department of Inorganic Chemistry, Indian Association for the Cultivation of Science,
Calcutta 700 032, India
Received 5th December 2000, Accepted 30th January 2001
First published as an Advance Article on the web 23rd March 2001
The reaction of [Ru(C6H2OH-2-CHNR-3-Me-5)(PPh3)2(CO)(NO2)] 1 (R = Et, p-MeC6H4 or p-ClC6H4)
᎐
with an excess of alkyne HC᎐CX (X = H, Ph or CH OH) in CH Cl –MeOH medium was accompanied
᎐
2
2
2
by linkage isomerization of nitrite (O,OЈ-bonded → N-bonded) and formation of a six-membered vinyl–
phenolato chelate ring to give [Ru(η2-C6H2CXCH-1-O-2-CHNHR-3-Me-5)(PPh3)2(CO)(NO2)] 4. The active
᎐
substrate is the solvate 1ؒMeOH, and the 2 ϩ 2 addition of the bulky ᎐CX (X = Ph or CH OH) group proceeds
᎐
2
regiospecifically to the carbon end of the Ru–C bond. Compound 4 has also been obtained metathetically by
treating 3 (the chloro analogue of 4) with NaNO2 in neutral media. However in acid media ring nitration of 3
(R = Et, X = Ph) occurs furnishing [Ru(η2-C6HCPhCH-1-O-2-CHNHEt-3-NO2-4-Me-5)(PPh3)2(CO)Cl] 7
which can metathetically be converted into the corresponding N-bonded NO2 analogue, 8. The iminium proton
is hydrogen bonded to the phenolato oxygen in 4, 7 and 8 and also weakly to a nitro oxygen in 4 and 8 (IR and
1H NMR data). All the species display a quasireversible cyclic voltammetric RuIII–RuII couple, the E1/2 of which
shifts to higher potential by ≈200 mV upon replacing chloride by nitrite (3 → 4; 7 → 8) as well as upon
aromatic nitration (3 → 7). The crystal structures of the solvate 4bؒC6H6 in which R = p-MeC6H4 and X = H,
4h in which R = p-ClC6H4 and X = CH2OH and 7 have been determined. The σ-vinyl–phenolato chelate ring is
approximately planar. The Ru–N bond in the planar RuNO2 fragment of 4bؒC6H6 and 4h is lengthened by ≈0.1 Å
due to the trans influence of the vinyl group. The Ru–C(vinyl) bond in 7 is significantly shortened due to electron
withdrawal by the nitro group, thus promoting Ru–ligand back bonding. The distances of the iminium nitrogen
from phenolic oxygen and a nitrito oxygen (in 4bؒC6H6 and 4h) lie in the ranges 2.55–2.67 and 2.90–2.98 Å
respectively.
Introduction
Linkage isomerization1 of ambidentate ligands is of inherent
interest in inorganic chemistry, the first reported example
being the nitrite ligand.2 In the present work we describe
an unusual instance of such isomerization promoted by
insertion of an alkyne into the organoruthenium nitrite
1 incorporating the rare O,OЈ-bonded-NO2 chelation mode.
Species of type 1 are formed3 upon treating the chloride4–6
2 with sodium nitrite. It has also been shown that 2 under-
goes facile alkyne insertion, the four-membered metallacycle
expanding to the six-membered system 3.7,8 Instances of
alkyne insertion into the Ru–C bond are otherwise relatively
sparse.9–13
This has prompted us to explore the possible insertion of
alkynes into compound 1 where the Ru–C(aryl) bond is unsup-
ported by chelation and to examine the consequence thereof on
binding and geometry. Such insertion has indeed been realized,
the process being accompanied by linkage isomerization of the
coordinated nitrite as in eqn. (1). The nature of the reaction as
(1)
Results and discussion
Reaction of compound 1 with alkynes: synthesis of Ru(ꢀ2-L)-
(PPh3)2(CO)(NO2) 4
well as the structures and properties of the new family of
N-bonded NO2 organometallics so isolated are scrutinized. We
also report an unusual case of nitration of a metallated ring
revealed in the course of a search for an alternative route to the
N-bonded species.
Three type 1 substrates have been employed: R = Et, p-MeC6H4
or p-ClC6H4. Upon treating 1 with an excess of alkyne in
boiling 2 : 1 CH2Cl2–MeOH organometallics of type 4 are
afforded in excellent yield, eqn. (2). Eight products (4a–4h)
DOI: 10.1039/b009719p
J. Chem. Soc., Dalton Trans., 2001, 1259–1265
This journal is © The Royal Society of Chemistry 2001
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᎐
1 ϩ HC᎐CX → 4
(2)
᎐
[X = H, Ph or CH2OH]
differing in the R and X substituents of the L ligand (L1–L8)
have been isolated and characterized. To our knowledge
reaction (2) represents the first example of the insertion of
propargyl alcohol (X = CH2OH) into a Ru–C bond.
Fig. 1 Spectra of compound 1 (R = p-MeC6H4, 3.27 × 10Ϫ5 M) in
CH2Cl2–MeOH mixtures corresponding to MeOH concentrations of
3.702, 4.936, 7.404, 12.340 and 17.276 M. The absorbance at 510 nm
increases with increasing MeOH concentration.
of solutions of 1 containing MeOH invariably afforded pure 1
as the only solid product. It is likely that in 1ؒMeOH the solvent
binds to the metal making nitrite monodentate (presumably
N-bonded14) as stylized in 5.
Reaction (2) is accompanied by several bonding reorganiz-
ations as shown by crystallographic and spectroscopic data
reported later. Prominent among these are the O,OЈ-bonded
NO2 → N-bonded NO2 isomerization and establishment of
six-membered vinyl–phenolato chelation. More subtle changes
concern the Schiff base ligand. In 1 the pendant phenolic
function is hydrogen bonded with the imine function. In 4 it is
the anionic phenolato function that is coordinated and the
hydrogen bonding is now of the iminium–phenolato type which
also characterizes species of type 2.4–6 Owing to steric reasons,
the transformation 2 → 1 is accompanied by rotation of the
Schiff base ligand by 180Њ around the Ru–C bond such that
the CO ligand is placed cis to the uncoordinated phenolic
function.3 In the reaction 1 → 4 the phenolic function is
utilized for coordination generating the stable six-membered
vinyl–phenolato chelate ring. This requires that the original
(as in 2) rotameric conformation (CO trans to phenol) be
reestablished.
Regiospecificity and anion metathesis
The alkyne is believed to π-anchor to the metal as in 6 via
displacement of MeOH from 5. The subsequent 2 ϩ 2 alkyne
addition to the Ru–C bond is subject to steric control by NO2
7
᎐
and PPh ligands. The bulky ᎐CX (X = Ph or CH OH) end of
᎐
3
2
the alkyne is thus expected to add regiospecifically to the
carbon end of the Ru–C bond. This indeed happens as has been
proven directly in the case of propargyl alcohol by structure
determination of compound 4h and indirectly for phenylacetyl-
ene via metathetical interconversion between 4 (X = Ph) and
structurally characterized 3 (X = Ph).7,8 Such interconversions
are readily achieved in dichloromethane–acetone–water media
in the presence of an excess of the entering anion. The inter-
relationship of the species 1–4 in terms of insertion and
metathesis is set out in Scheme 1.
Methanol adduct in solution
Reaction (2) fails to occur in pure dichloromethane and the
presence of methanol is essential. Indeed spectrophotometric
examination (Fig. 1) in CH2Cl2–MeOH mixtures with variable
MeOH concentration has revealed the presence of the equi-
librium (3). The case of 1 (R = p-MeC6H4) has been studied in
K
(3)
1 ϩ MeOH
1ؒMeOH
detail. The band at 510 nm is characteristic of the solvate and
the spectra are characterized by an isosbestic point at 361 nm
(Fig. 1). The equilibrium constant K at 298 K was found to be
3.81 × 10Ϫ2 MϪ1
.
The lack of insertion in pure dichloromethane strongly
suggests that it is 1ؒMeOH rather than 1 that is the active sub-
strate. We have not succeeded in isolating 1ؒMeOH; evaporation
Scheme 1
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J. Chem. Soc., Dalton Trans., 2001, 1259–1265

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Table 1 Electronic absorption and cyclic voltammetric reduction
potential data
Compound
(R = Et, X = Ph) λmax/nm (ε/dm3 molϪ1 cmϪ1
UV-vis dataa
Reduction potentialb
E1/2/V (∆Ep/mV)
)
3
520 (3760)
510 (3290)
555 (3810)
534 (3816)
0.31 (170)
0.47 (100)
0.52 (110)
0.73 (100)
4d
7
8
a Solvent is dicholoromethane. b Conditions: solvent, dichloromethane;
supporting electrolyte, NEt4ClO4 (0.1 M); working electrode, platinum;
Ϫ1
1
2
–
reference electrode, SCE; scan rate 50 mV s
E
= (Epa ϩ Epc), where
1/2
Epa and Epc are the anodic and cathodic peak potentials respectively;
∆Ep = Epa Ϫ Epc.
Ring nitration
The metathetical 3 → 4 conversion occurs in neutral media.
In acidic media an entirely different reaction viz. aromatic
nitration takes place. Thus compound 3 (R = Et; X = Ph) reacts
smoothly at room temperature with NaNO2 in dichloro-
methane solution acidified with acetic acid affording 7 with
retention of chloride ligand in nearly quantitative yield. It
could be readily converted into 8 by the usual metathetical
procedure of Scheme 1 in neutral media. Type 3 compounds
other than those noted above also appeared to undergo nuclear
nitration by acidified nitrite but we have not succeeded in isolat-
ing pure products. Ring nitration of type 2 species could not be
achieved at all due to decomposition.
Fig. 2 ORTEP plot (30% probability ellipsoids, as in all Figures) and
atom-labeling scheme for compound 4bؒC6H6 (excluding C6H6).
Fig. 3 ORTEP plot for compound 4h.
Instances of nitration of metallated aryl compounds with
retention of the metal–carbon bond are relatively sparse
because of reagent promoted decomposition. In a few cases
copper() nitrate in acetic anhydride has successfully been
used.15,16 The utilization of NaNO2 in acidic dichloromethane
for nuclear nitration of organometallics appears to be
unprecedented. It has, however, been documented that NaNO2
can nitrate aromatic compounds in acidic media, the reaction
proceeding by a free radical pathway in the case of phenols17,18
and by an electrophilic pathway in the case of simple aromat-
ics.19 The active reagents are NO2 and NO2ϩ respectively. Since
radical formation is unlikely in our system, the reaction
3 → 7 probably proceeds by the electrophilic route. Metall-
ation is expected to activate the aromatic ring towards electro-
philic substitution. Nitration of 3 occurs selectively in the
position para to the metallated carbon, the ortho position (C3)
being hindered by Me and Ph substituents.
replacement of chloride by N-bonded NO2. EHMO comput-
ations have revealed8 that this band corresponds approximately
to a t2(Ru) → π* (metallated ring and aldimine) transition.
The observed shifts of the band energy are consistent with this
assignment. Nuclear nitration depresses the π* orbital and the
N-bonded NO2 ligand (as compared to the chloride ligand)
stabilizes14 the t2 shell.
In dichloromethane solution the compounds exhibit a
quasireversible cyclic voltammetric RuIII–RuII couple (Table 1).
The E1/2 of 4 is higher than that of 37 by ≈200 mV consistent
with the above-noted stabilization of the redox-active t2 shell by
N-bonded NO2 coordination. Similarly between 7 and 8 there is
a shift of ≈200 mV. In going from 3 to 7 nuclear nitration causes
a shift of ≈200 mV towards higher potential due to electron
withdrawal by the nitro substituent.
Structure
Characterization: spectra and reduction potential
The crystal structures of compounds 4bؒC6H6, 4h and 7 have
been determined, authenticating regiospecific alkyne insertion,
nitrite isomerization and ring nitration. Molecular views are
shown in Figs. 2–4 and selected bond parameters are listed in
Tables 2 and 3.
Characterization data are collected in the Experimental section.
Compounds of type 4, 7 and 8 display a moderately intense
absorption band in the region 500–600 nm. Selected data for
a group of compounds with R = Et and X = Ph are listed in
Table 1. Two significant energy trends are: a red-shift of the
band maximum upon nuclear nitration and a blue-shift upon
A few general geometrical features will be noted first. In the
distorted octahedral coordination sphere the Ru, O1, C10
J. Chem. Soc., Dalton Trans., 2001, 1259–1265
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mately planar (md: 4bؒC6H6, 0.06; 4h, 0.04; 7, 0.08 Å) due to the
presence of a fold (4bؒC6H6, 9.2; 4h, 4.9 7, 8.3Њ) along the
C10 ؒ ؒ ؒ O1 line. The plane of the NO2 group in 7 makes a
dihedral angle of 61.0Њ with the aromatic ring.
The RuNO2 fragment is highly planar (md < 0.01 Å) in both
compounds 4bؒC6H6 and 4h. The Ru–N2 length is ≈0.1 Å
longer than those normally observed (2.06–2.09 Å)20–23 in
complexes incorporating the Ru–NO2 moiety due to the trans
influence of the σ-vinyl group which also lengthens the Ru–Cl
bond in 7 as it also does in type 3 species.7 The Ru–C10 length
in 7, 2.008(5) Å, is significantly shorter than those (2.03–2.05 Å)
in 4bؒC6H6, 4h and type 3 species7 consistent with electron
withdrawal by the nitro group and consequent augmented
Ru–L1 backbonding.
Hydrogen bonding
The O1, C1, C6, C8 and N1 atoms define planes with md of
0.04, 0.02 and 0.01 Å respectively in compounds 4bؒC6H6, 4h
and 7. The observed N1 ؒ ؒ ؒ O1 lengths (2.55–2.67 Å) are
consistent7,4–6,14 with zwitterionic iminium–phenolato hydrogen
bonding of type ᎐Nϩ–H ؒ ؒ ؒ OϪ. Significantly the N-bonded
᎐
Fig. 4 ORTEP plot for compound 7.
NO2 group in 4bؒC6H6 and 4h makes relatively small dihedral
angles (19.8 and 10.3Њ respectively) with the plane of the O1,
C1, C6, C8 and N1 atoms. The N1 ؒ ؒ ؒ O3 lengths are 2.981(6)
and 2.897(11) Å respectively in 4bؒC6H6 and 4h. The iminium
function is thus involved in weak bifurcated hydrogen bonding
with the O3 atom of the N-bonded NO2 group as highlighted
in 9.
Table 2 Selected bond distances (Å) and angles (Њ) for complexes
4bؒC6H6 and 4h
4bؒC6H6
4h
Ru–P1
Ru–P2
2.410(2)
2.383(2)
2.050(3)
2.106(3)
1.808(5)
2.217(4)
1.302(5)
1.157(5)
1.304(6)
1.334(1)
2.668(10)
2.981(6)
2.387(3)
2.395(3)
2.041(9)
2.077(6)
1.825(9)
2.176(8)
1.324(10)
1.120(11)
1.345(12)
1.351(14)
2.673(10)
2.897(11)
Ru–C10
Ru–O1
Ru–C11
Ru–N2
O1–C1
O2–C11
N1–C8
C9–C10
O1 ؒ ؒ ؒ N1
N1 ؒ ؒ ؒ O3
The iminium proton has been observed directly in 1H NMR
and IR. In 1H NMR the Nϩ–H proton of compound
4 (R = aryl) occurs as a doublet (δ 13.3–14.0, J ≈ 12 Hz) which
disappears upon shaking with D2O. The doublet structure is
due to trans coupling with the azomethine proton at δ 7.0–7.5.
In 4 (R = alkyl), 7 and 8 the doublet structure of Nϩ–H is
obscured by broadening presumably due to coupling with alkyl
protons on the α-carbon. The Nϩ–H resonance of 4 is system-
atically shifted downfield by ≈1 ppm compared to that7 (δ ≈ 12)
of 3 presumably due to the weak hydrogen bonded interaction
between N-bonded NO2 and Nϩ–H as revealed in the structural
work (see 9). Another notable downfield shift is that of the
azomethine proton (δ ≈ 8) in 7 and 8 compared to 3 (δ ≈ 7). In 7
and 8 the azomethine proton lies close to the electron with-
drawing aromatic nitro group.
N2–Ru–P1
N2–Ru–C10
P1–Ru–C11
N2–Ru–O1
P1–Ru–C10
P1–Ru–P2
N2–Ru–C11
C10–Ru–C11
P1–Ru–O1
O1–Ru–C10
O1–Ru–C11
Ru–C11–O2
92.01(11)
170.43(14)
89.5(2)
83.21(14)
88.81(11)
175.11(4)
97.3(2)
92.3(2)
170.8(3)
91.6(3)
84.4(3)
85.0(3)
172.88(9)
95.7(4)
93.2(4)
89.3(2)
86.8(3)
179.1(3)
177.3(10)
92.2(2)
90.67(10)
87.25(13)
179.4(2)
177.1(4)
Table 3 Selected bond distances (Å) and angles (Њ) for complex 7
Ru–P1
Ru–P2
2.392(2)
2.382(2)
2.008(5)
2.066(4)
1.794(6)
2.512(2)
1.293(7)
1.161(6)
1.283(7)
1.371(7)
2.547(10)
Cl–Ru–P1
90.16(6)
165.2(2)
90.0(2)
79.68(11)
90.0(2)
179.54(5)
101.1(2)
93.7(2)
89.58(11)
85.5(2)
In the IR the Nϩ–H stretch in compounds 4, 7 and 8
is observed as a broad feature of medium intensity near
Cl–Ru–C10
P1–Ru–C11
Cl–Ru–O1
P1–Ru–C10
P1–Ru–P2
C1–Ru–C11
C10–Ru–C11
P1–Ru–O1
O1–Ru–C10
O1–Ru–C11
Ru–C11–O2
Ru–C10
Ru–O1
Ru–C11
Ru–C1
O1–C1
O2–C11
N1–C8
C9–C10
O1 ؒ ؒ ؒ N1
3440 cmϪ1 consistent with weak hydrogen bonding. The C᎐N
᎐
stretching frequency is relatively high (≈1630 cmϪ1) due to the
protonation of nitrogen.7,4–6,24–26
Conclusion
179.1(2)
177.5(5)
The facile reaction of compound 1 with alkynes in CH2Cl2–
MeOH media affording 4 is accompanied by linkage isomeriz-
ation (1) as well as vinyl–phenolato chelation and bifurcated
nitrite–iminium–phenolato hydrogen bonding. The methanol
adduct 5 is believed to be the active intermediate in the
regiospecific reaction.
atoms together with the carbonyl (C11, O2) and nitrite (N2, O3,
O4) ligands define an excellent equatorial plane with mean
deviation (md) of 0.01 Å in 4bؒC6H6, and 0.03 Å in 4h. In 7
where Cl replaces NO2 the planarity is nearly perfect. The six-
membered (σ-vinyl) phenolato chelate ring is only approxi-
In neutral media sodium nitrite causes metathesis as in the
reactions 3 → 4 and 7 → 8. However in weakly acidic
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J. Chem. Soc., Dalton Trans., 2001, 1259–1265

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media it promotes nuclear nitration of type 3 → 7 which
constitutes the first example of organometallic aromatic
nitration by this reagent. The RuIII–RuII reduction potentials
and t2 → π* MLCT transition energies undergo character-
istic shifts associated with nitrite ligation and nuclear nitration.
7.43 (d, 1H, CH᎐Nϩ, JHH 15.0 Hz). E1/2 (vs. SCE, CH2Cl2, scan
᎐
rate, 50 mV sϪ1): 0.57 V (∆Ep = 140 mV).
[Ru(ꢀ2-L3)(PPh3)2(CO)(NO2)] 4c. This violet solid was
obtained in 82% yield from compound 1 (R = p-ClC6H4) using
the same procedure as for 4a, mp 176 ЊC (Found: C, 65.62; H,
4.39; N, 2.93. Calc. for C53H43ClN2O4P2Ru: C, 65.60; H, 4.47;
N, 2.89%). UV-vis [λmax/nm (ε/dm3 molϪ1 cmϪ1)]: 560 (3730)
and 410 (7610). IR (KBr, cmϪ1): 1615 (νCN), 1910 (νCO), 1270
(νasym(NO2)), 1260 (νsym(NO2)), 820 (δ(NO2)) and 3435
Experimental
Materials
The starting materials Ru(PPh3)3Cl2,27 1,3 24–6 and 37 were
prepared by reported methods. Phenylacetylene and propargyl
alcohol were obtained from Aldrich and locally available
acetylene (in cylinder) was used. Sodium nitrite and other
chemicals and solvents were of analytical grade used as
received. The purification28 of dichloromethane and methanol
were done as before.
1
(νNH, hexachlorobutadiene). H NMR (CDCl3, δ): 6.23 (s, 1H,
H3), 6.45 (s, 1H, H5), 7.12–7.59 (m, 34H, 2PPh3, H13, H14, H16,
H17 and 1H, CH᎐C(Ru)), 2.02 (s, 3H, CH ), 6.14 (d, 1H,
᎐
3
C᎐CH(Ru), J 11.4), 13.98 (d, 1H, ᎐Nϩ–H, JHH 15.0) and 7.41
᎐
᎐
HH
(d, 1H, CH᎐Nϩ, JHH 15.1 Hz). E1/2 (vs. SCE, CH2Cl2, scan rate,
᎐
50 mV sϪ1): 0.58 V (∆Ep = 160 mV).
[Ru(ꢀ2-L4)(PPh3)2(CO)(NO2)] 4d. To a yellow solution of
compound 1 (R = Et) (50 mg, 0.058 mmol) in 2 : 1 (50 mL)
dichloromethane–methanol was added phenylacetylene (45 mg,
0.44 mmol). The reaction mixture was heated to reflux for 9 h
turning orange. Upon concentrating and cooling an orange
crystalline solid separated, which was collected by filtration and
washed thoroughly with methanol and dried in vacuo. Yield 47
mg (84%), mp 178 ЊC (Found: C, 68.51; H, 4.93; N, 2.86. Calc.
for C55H48N2O4P2Ru: C, 68.53; H, 5.02; N, 2.91%). UV-vis
[λmax/nm (ε/dm3 molϪ1 cmϪ1)]: 510 (3290) and 360 (5170). IR
(KBr, cmϪ1): 1640 (νCN), 1900 (νCO), 1260 (νasym(NO2)), 1240
(νsym(NO2)), 830 (δ(NO2)) and 3400 (νNH, hexachlorobutadiene).
1H NMR (CDCl3, δ): 6.34 (s, 1H, H3), 6.97 (s, 1H, H5), 7.08–
7.64 (m, 33H, 2PPh3, H20, H21 and H22), 1.89 (s, 3H, CH3),
6.25 (s, 1H, C᎐CH(Ru)), 13.28 (s, 1H, ᎐Nϩ–H), 7.02 (d, 1H,
Physical measurements
IR (KBr disc), UV-vis (CH2Cl2 solution) and 1H NMR (CDCl3
solvent, standard SiMe4) spectra were recorded on Perkin-
Elmer 783, Shimadzu UVPC 1601 (thermostatted cell com-
partments) and Bruker 300 MHz FT NMR spectrometers
1
respectively. The numbering scheme used for H NMR is the
same as in crystallography. Spin–spin structures are abbreviated
as: s, singlet; d, doublet; t, triplet; q, quartet; m, multiplet.
Microanalyses (C,H,N) were done by using a Perkin-Elmer
240C elemental analyzer. All electrochemical measurements
were performed under a nitrogen atmosphere using a PAR
370-4 electrochemistry system.29 The supporting electrolyte was
tetraethylammonium perchlorate and potentials are referenced
to the saturated calomel electrode (SCE) without junction
correction.
᎐
᎐
CH᎐Nϩ, JHH 11.1 Hz), 5.94 (m, 2H, H19 and H23), 3.17 (q, 2H,
᎐
NEt) and 1.11 (t, 3H, NEt). E1/2 (vs. SCE, CH2Cl2, scan rate,
50 mV sϪ1): 0.47 V (∆Ep = 100 mV).
Syntheses
[Ru(ꢀ2-L5)(PPh3)2(CO)(NO2)] 4e. This was prepared using
compound 1 (R = p-MeC6H4) by the same procedure as a violet
solid in 86% yield, mp 175 ЊC (Found: C, 70.26; H, 4.83;
N, 2.71. Calc. for C60H50N2O4P2Ru: C, 70.23; H, 4.91; N,
2.73%). UV-vis [λmax/nm (ε/dm3 molϪ1 cmϪ1)]: 560 (3090)
and 405 (6910). IR (KBr, cmϪ1): 1625 (νCN), 1915 (νCO), 1300
(νasym(NO2)), 1280 (νsym(NO2)), 840 (δ(NO2)) and 3450
The type 4 complexes were synthesized in ≈85% yields by
treating 1 with an excess of alkyne in 2 : 1 CH2Cl2–MeOH
mixture. Details of representative cases are given below.
[Ru(ꢀ2-L1)(PPh3)2(CO)(NO2)] 4a. A warm solution of com-
pound 1 (R = Et) (50 mg, 0.058 mmol) in 2 : 1 dichloromethane–
methanol (50 mL) was purged with acetylene gas and then
heated to reflux for 14 h in an acetylene atmosphere with the
help of a balloon filled with acetylene. The solution turned
from yellow to orange. The solvent was then removed under
reduced pressure and the desired compound isolated as an
orange solid. Yield 42 mg (82%), mp 168 ЊC (Found: C, 66.21;
H, 4.99; N, 3.14. Calc. for C49H44N2O4P2Ru: C, 66.28; H, 4.99;
N, 3.16%). UV-vis [λmax/nm (ε/dm3 molϪ1 cmϪ1)]: 504 (2290)
and 361 (3930). IR (KBr, cmϪ1): 1645(νCN), 1915 (νCO),
1270 (νasym(NO2)), 1250 (νsym(NO2)), 830 (δ(NO2)) and 3425
1
(νNH, hexachlorobutadiene). H NMR (CDCl3, δ): 6.39 (s, 1H,
H3), 7.02 (s, 1H, H5), 7.07–7.58 (m, 37H, 2PPh3, H13, H14, H16,
H17, H20, H21 and H22), 2.33 and 1.89 (2s, 6H, 2CH3), 6.29 (s,
1H, C᎐CH(Ru)), 13.82 (d, 1H, ᎐Nϩ–H, JHH 15.0), 7.42 (d, 1H,
᎐
᎐
CH᎐Nϩ, J 15.0 Hz) and 6.03 (m, 2H, H19 and H23). E1/2 (vs.
᎐
HH
SCE, CH2Cl2, scan rate, 50 mV sϪ1): 0.53 V (∆Ep = 110 mV).
[Ru(ꢀ2-L6)(PPh3)2(CO)(NO2)] 4f. The procedure was the
same as for compound 4d: violet crystalline solid, yield 87%,
mp 180 ЊC (Found: C, 67.68; H, 4.45; N, 2.72. Calc.
for C59H47ClN2O4P2Ru: C, 67.72; H, 4.53; N, 2.68%). UV-vis
[λmax/nm (ε/dm3 molϪ1 cmϪ1)]: 568 (3280) and 410 (7120).
IR(KBr, cmϪ1); 1630 (νCN), 1920 (νCO), 1310 (νasym(NO2)), 1270
(νsym(NO2)), 840 (δ(NO2)) and 3440 (νNH, hexachlorobutadiene).
1H NMR (CDCl3, δ): 6.39 (s, 1H, H3), 7.01 (s, 1H, H5), 7.09–
7.58 (m, 37H, 2PPh3, H13, H14, H16, H17, H20, H21 and H22), 1.89
(s, 3H, CH ), 6.29 (s, 1H, C᎐CH(Ru)), 13.84 (d, 1H, ᎐Nϩ–H,
1
(νNH, hexachlorobutadiene). H NMR (CDCl3, δ): 6.17 (s, 1H,
H3), 6.39 (s, 1H, H5), 7.08–7.70 (m, 30H, 2PPh3 and 1H,
CH᎐C(Ru)), 2.00 (s, 3H, CH ), 6.09 (d, 1H, C᎐CH(Ru), J
᎐
᎐
3
HH
12.0), 13.53 (s, 1H, ᎐Nϩ–H), 7.45 (d, 1H, CH᎐Nϩ, JHH 11.1 Hz),
᎐
᎐
3.33 (q, 2H, NEt) and 0.87 (t, 3H, NEt). E1/2 (vs. SCE, CH2Cl2,
scan rate, 50 mV sϪ1): 0.51 V (∆Ep = 160 mV).
[Ru(ꢀ2-L2)(PPh3)2(CO)(NO2)] 4b. Using the same procedure
as above, violet, compound 4b was obtained in 80% yield from
1 (R = p-MeC6H4), mp 173 ЊC (Found: C, 68.25; H, 4.87; N,
2.91. Calc. for C54H46N2O4P2Ru: C, 68.27; H, 4.88; N, 2.95%).
UV-vis [λmax/nm (ε/dm3 molϪ1 cmϪ1)]: 550 (2560) and 380
(5330). IR (KBr, cmϪ1): 1620 (νCN), 1900 (νCO), 1280
(νasym(NO2)), 1260 (νsym(NO2)), 830 (δ(NO2)) and 3440
᎐
᎐
3
JHH 12.0), 7.34 (d, 1H, CH᎐Nϩ, JHH 12.0 Hz) and 6.02 (m, 2H,
᎐
H19 and H23). E1/2 (vs. SCE, CH2Cl2, scan rate, 50 mV sϪ1):
0.55 V (∆Ep = 140 mV).
[Ru(ꢀ2-L7)(PPh3)2(CO)(NO2)] 4g. To a yellow solution of
compound 1 (R = p-MeC6H4) (50 mg, 0.054 mmol) in 2 : 1
(50 mL) dichloromethane–methanol was added propargyl
alcohol (30 mg, 0.53 mmol). The reaction mixture was heated
to reflux for 6 h, turning violet. Upon concentrating and cool-
ing a violet crystalline solid separated which was collected by
1
(νNH, hexachlorobutadiene). H NMR (CDCl3, δ): 6.22 (s, 1H,
H3), 6.42 (s, 1H, H5), 7.10–7.58 (m 34H, 2PPh3, H13, H14, H16,
H17 and 1H, CH᎐C(Ru)), 2.01 and 2.34 (2s, 6H, 2CH ), 6.12 (d,
᎐
3
1H, C᎐CH(Ru), J 11.4), 13.99 (d, 1H, ᎐Nϩ–H, JHH 15.0) and
᎐
᎐
HH
J. Chem. Soc., Dalton Trans., 2001, 1259–1265
1263

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Table 4 Crystal data for complexes 4bؒC6H6, 4h and 7
4bؒC6H6
4h
7
Formula
M
C60H52N2O4P2Ru
1028.05
C54H45ClN2O5P2Ru
1000.38
C55H47ClN2O4P2Ru
998.41
T/K
Crystal system
Space group
293
Monoclinic
C2/c
293
Monoclinic
P21/c
293
Monoclinic
C2/c
a/Å
b/Å
c/Å
20.97(2)
15.677(8)
30.95(3)
95.70(7)
10123(13)
8
14.784(4)
15.106(4)
21.971(7)
90.06(3)
4907(3)
4
32.572(7)
12.269(3)
26.013(5)
99.09(3)
10265(4)
8
β/Њ
U/Å3
Z
µ(Mo-Kα) cmϪ1
Total reflections
4.23
6986
4.88
7617
4.65
5396
Independent reflections (Rint
R1, wR2 [I > 2σ(I)]
(all data)
)
6655 (0.0277)
0.0393, 0.0904
0.0672, 0.1381
7232 (0.0268)
0.0724, 0.1889
0.1188, 0.2655
5210 (0.0244)
0.0436, 0.1194
0.0619, 0.1408
filtration and washed thoroughly with methanol and dried in
vacuo. Yield: 44 mg (83%), mp 171 ЊC (Found: C, 67.37; H,
4.87; N, 2.84. Calc. for C55H48N2O5P2Ru: C, 67.41; H, 4.94;
N, 2.86%). UV-vis [λmax/nm (ε/dm3 molϪ1 cmϪ1)]: 558 (3205)
and 408 (6650). IR (KBr, cmϪ1): 1625 (νCN), 1920 (νCO), 1310
pink. The solvent was removed under reduced pressure leaving
an aqueous suspension of the pink complex. This was filtered
off, washed repeatedly with water and dried in vacuo. Yield
39 mg (96%), mp 204 ЊC (Found: C, 65.32; H, 4.52; N, 4.29.
Calc. for C55H47N3O6P2Ru: C, 65.47; H, 4.69; N, 4.16%).
UV-vis [λmax/nm (ε/dm3 molϪ1 cmϪ1)]: 534 (3816). IR (KBr,
cmϪ1): 1650 (νCN), 1920 (νCO), 1480 (νasym(NO2)), 1340, 1250
(νsym(NO2)), 850, 825 (δ(NO2)) and 3445 (νNH, hexachlorobuta-
diene). 1H NMR (CDCl3, δ); 6.98 (s, 1H, H3), 6.27 (s, 1H,
C᎐CH(Ru)), 7.16–7.55 (m, 33H, 2PPh , H16, H17 and H18) 13.65
(νasym(NO2)), 1280 (νsym(NO2)), 830 (δ(NO2)) and 3440 (νNH
,
1
hexachlorobutadiene). H NMR (CDCl3, δ): 7.04 (s, 1H, H3),
6.34 (s, 1H, C᎐CH(Ru)), 7.07–7.92 (m, 36H, 2PPh , H5, H14,
᎐
3
H15, H17, H18 and HC᎐Nϩ), 2.07 and 2.31 (2s, 6H, 2CH ), 3.65–
᎐
3
3.71 (m, 2H, CH ), 2.41 (s, 1H, OH) and 13.79 (d, 1H, ᎐Nϩ–H,
᎐
᎐
2
3
JHH 15.0 Hz). E1/2 (vs. SCE, CH2Cl2, scan rate, 50 mV sϪ1):
0.56 V (∆Ep = 120 mV).
(s, 1H, ᎐NϩH), 1.86 (s, 3H, CH ), 7.93 (s, 1H, CH᎐Nϩ), 5.94 (m,
᎐
᎐
3
2H, H15 and H19), 3.21 (q, 2H, NEt) and 1.15 (t, 3H, NEt). E1/2
-
(vs. SCE, CH2Cl2, scan rate, 50 mV sϪ1): 0.73 V (∆Ep = 100
[Ru(ꢀ2-L8)(PPh3)2(CO)(NO2)] 4h. This was prepared using
compound 1 (R = p-ClC6H4) by the same procedure as a violet
solid in 85% yield, mp 182 ЊC (Found: C, 64.79; H, 4.52; N, 2.77.
Calc. for C54H45ClN2O5P2Ru: C, 64.83; H, 4.53; N, 2.80%).
UV-vis [λmax/nm (ε/dm3 molϪ1 cmϪ1)]: 564 (3820) and 408
(6720). IR (KBr, cmϪ1): 1620 (νCN), 1925 (νCO), 1310
mV).
Interconversion of compounds 4 and 3 by metathesis
Upon treating the type 3 species with an excess of NaNO2 in
dichloromethane–acetone–water (2 : 2 : 1) followed by vigorous
stirring for several hours the type 4 nitro complexes were
formed in virtually quantitative yield. The reverse reaction was
achieved by similarly treating 4 with an excess of Et4NCl.
Representative details are as follows.
To a vigorously stirring pink solution of compound 3
(R = Et, X = H) (40 mg, 0.045 mmol) in dichloromethane
(20 mL) and acetone (20 mL) was added dropwise an aqueous
solution (10 mL) of NaNO2 (20 mg, 0.289 mmol). Stirring was
continued for 4 h until the pink colour turned orange. The
solvent was removed under reduced pressure leaving an
aqueous suspension of the orange complex. This was filtered
off, washed repeatedly with water and the crystalline solid of 4a
was dried in vacuo. Yield: 40 mg (99%).
To a vigorously stirring orange solution of compound 4
(R = Et, X = H) (40 mg, 0.045 mmol) in dichloromethane (20
mL) and acetone (20 mL) was added dropwise an aqueous solu-
tion (10 mL) of tetraethylammonium chloride (60 mg, 0.362
mmol). Stirring was continued for 4 h until the orange solution
turned pink. The solvent was removed under reduced pressure
leaving an aqueous suspension of the pink complex. This was
filtered off, washed repeatedly with water and the crystalline
solid 3 (R = Et, X = H) dried in vacuo. Yield: 36 mg (91%).
(νasym(NO2)), 1270 (νsym(NO2)), 830 (δ(NO2)) and 3430 (νNH
,
1
hexachlorobutadiene). H NMR (CDCl3, δ): 7.06 (s, 1H, H3),
6.34 (s, 1H, C᎐CH(Ru)), 7.14–7.78 (m, 36H, 2PPh , H5, H14,
᎐
3
H15, H17, H18 and HC᎐Nϩ), 2.08 (s, 3H, CH ), 3.65–3.75 (m, 2H,
᎐
3
CH ), 2.41 (s, 1H, OH) and 13.79 (d, 1H, ᎐Nϩ–H, JHH 15.0 Hz).
᎐
2
E1/2 (vs. SCE, CH2Cl2, scan rate, 50 mV sϪ1): 0.57 V (∆Ep = 160
mV).
[Ru(ꢀ2-NO2L4)(PPh3)2(CO)Cl] 7. To a stirring pink solution
of compound 3 [40 mg (0.042 mmol) (R = Et, X = Ph)] in 50
mL of dichloromethane were added 0.05 mL glacial acetic acid
and 25 mg (0.36 mmol) sodium nitrite. The solution turned
violet within a few minutes. Stirring was continued for 15 min-
utes. The solvent was immediately evaporated under reduced
pressure. The solid violet mass was collected by filtration and
repeatedly washed with water and dried in vacuo. Yield 39 mg
(94%), mp 171 ЊC (Found: C, 66.14; H, 4.69; N, 2.78. Calc. for
C55H47ClN2O4P2Ru: C, 66.16; H, 4.74; N, 2.81%). UV-vis
[λmax/nm (ε/dm3 molϪ1 cmϪ1)]: 555 (3810) and 415 (3690). IR
(KBr, cmϪ1): 1640 (νCN), 1900 (νCO), 1480 (νasym(NO2)), 1360
(νsym(NO2)), 840 (δ(NO2)) and 3430 (νNH, hexachlorobutadiene).
1H NMR (CDCl , δ): 6.98 (s, 1H, H3), 6.29 (s, 1H, C᎐CH(Ru)),
᎐
3
7.00–7.70 (m, 33H, 2PPh3, H16, H17 and H18), 12.24 (s, 1H,
᎐Nϩ–H), 1.93 (s, 3H, CH ), 8.13 (s, 1H, CH᎐Nϩ), 5.81 (m, 2H,
Determination of equilibrium constant
᎐
᎐
3
H15 and H19), 3.72 (q, 2H, NEt) and 0.90 (t, 3H, NEt). E1/2 (vs.
SCE, CH2Cl2, scan rate, 50 mV sϪ1): 0.52 V (∆Ep = 110 mV).
The reaction was studied spectrophotometrically at 298 K in
CH2Cl2–MeOH mixture, the MeOH concentration being in
the range 3.7–17.3 M. The concentration of compound 1
(R = p-MeC6H4) was kept constant at 3.27 × 10Ϫ5 M. The
variation of absorbance (A) at 510 nm with the concentration
(M) of methanol is as follows: 0.034, 3.702; 0.041, 4.936; 0.057,
7.404; 0.087, 12.340; 0.110, 17.276. The A values are corrected
for the small absorption by 1 (R = p-MeC6H4) at 510 nm as
[Ru(ꢀ2-NO2L4)(PPh3)2(CO)(NO2)] 8. To a vigorously stirred
violet solution of compound 7 (40 mg, 0.040 mmol) in dichloro-
methane (20 mL) and acetone (20 mL) was added dropwise an
aqueous solution (10 mL) of NaNO2 (20 mg, 0.289 mmol).
Stirring was continued for 5 h and the violet solution turned
1264
J. Chem. Soc., Dalton Trans., 2001, 1259–1265

View Article Online
4 N. Bag, S. B. Choudhury, A. Pramanik, G. K. Lahiri and
revealed from its spectrum in CH2Cl2 solution. The intercept of
a linear plot of [MeOH]Ϫ1 vs. AϪ1 (A = absorbance at 510 nm) is
A. Chakravorty, Inorg. Chem., 1990, 29, 5013.
5 N. Bag, S. B. Choudhury, G. K. Lahiri and A. Chakravorty,
J. Chem. Soc., Chem. Commun., 1990, 1626.
the equilibrium constant which equals 3.81 × 10Ϫ2 MϪ1
.
6 P. Ghosh, N. Bag and A. Chakravorty, Organometallics, 1996, 15,
Crystallography
3042.
7 K. Ghosh, S. Pattanayak and A. Chakravorty, Organometallics,
1998, 17, 1956 and references therein.
8 K. Ghosh, Ph.D. Thesis, Jadavpur University, Calcutta, 2000.
9 M. I. Bruce, A. Catlow, M. P. Cifuentes, M. R. Snow and E. R. T.
Tiekink, J. Organomet. Chem., 1990, 397, 187.
10 Z. L. Lutsenko, G. G. Aleksandrov, P. V. Petrovskii, E. S.
Shubina, V. G. Andrianov, Yu. T. Struchkov and A. Z. Rubezhov,
J. Organomet. Chem., 1985, 281, 349.
11 D. Garn, F. Knoch and H. Kish, J. Organomet. Chem., 1993, 444,
155.
12 R. M. Burns and J. L. Hubbard, J. Am. Chem. Soc., 1994, 116, 9514.
13 W. Ferstl, I. K. Sakodinskaya, N. Beydoun-Sutter, G. L. Borgne,
M. Pfeffer and A. D. Ryabov, Organometallics, 1997, 16, 411.
14 K. Pramanik, P. Ghosh and A. Chakravorty, J. Chem. Soc., Dalton
Trans., 1997, 3553.
15 G. R. Clark, C. E. L. Headford, W. R. Roper, L. J. Wright and
V. P. D. Yap, Inorg. Chim. Acta, 1994, 220, 261.
16 A. M. Clark, C. E. F. Rickard, W. R. Roper and L. J. Wright,
Organometallics, 1999, 18, 2813.
17 B. D. Beake, J. Constantine and R. B. Moodie, J. Chem. Soc., Perkin
Trans. 2, 1994, 335.
Single crystals of compound 4bؒC6H6 were grown by slow dif-
fusion of hexane into benzene solution and those of 4h and 7
by slow diffusion of hexane into dichloromethane solutions.
Cell parameters were determined by a least-squares fit of 30
machine-centered reflections. Data were collected by the ω-scan
technique on a R3m/V four-circle diffractometer with graphite-
monochromated Mo-Kα (λ = 0.71073 Å) radiation. Crystals of
4h were relatively poorly diffracting with broad peaks. Two
check reflections measured after every 198 showed no signifi-
cant intensity reduction. All data were corrected for Lorentz-
polarization effects, and an empirical absorption correction30
was done on the basis of azimuthal scan of six reflections for
each crystal.
In each case the metal atom was located from a Patterson
map and the rest of the non-hydrogen atoms emerged from
successive Fourier synthesis. The structures were refined by
full-matrix least-squares procedures. All non-hydrogen atoms
were refined anisotropically and hydrogen atoms added at
calculated positions. Calculations were performed using the
SHELXTL V5.0331 program package. Significant crystal data
are listed in Table 4.
18 B. D. Beake and R. B. Moodie, J. Chem. Soc., Perkin Trans. 2,
1998, 1.
19 S. Uemura, A. Toshimitsu and M. Okano, J. Chem. Soc., Perkin
Trans. 1, 1978, 1076.
20 R. A. Leising, S. A. Kubow, M. R. Churchill, L. A. Buttrey, J. W.
Ziller and K. J. Takeuchi, Inorg. Chem., 1990, 29, 1306.
21 A. J. Blake, R. O. Gould, B. F. G. Johnson and E. Parisini, Acta
Crystallogr., Sect. C, 1992, 48, 982.
CCDC reference numbers 154175–154177.
See http://www.rsc.org/suppdata/dt/b0/b009719p/ for crystal-
lographic data in CIF or other electronic format.
22 C. A. Bessel, R. F. See, D. L. Jameson, M. R. Churchill and K. J.
Takeuchi, J. Chem. Soc., Dalton Trans., 1993, 1563.
23 L. F. Szczepura, S. A. Kubow, R. A. Leising, W. J. Perez, M. H. V.
Huynh, C. H. Lake, D. G. Churchill, M. R. Churchill and K. J.
Takeuchi, J. Chem. Soc., Dalton Trans., 1996, 1463.
24 C. Sandorfy and D. Vocelle, Mol. Phys., Chem., Biol., 1989, 4, 195.
25 J. Favrot, D. Vocelle and C. Sandorfy, Photochem. Photobiol., 1979,
30, 417.
Acknowledgements
We are grateful to the Department of Science and Technology,
New Delhi, India, the Indian National Science Academy, New
Delhi, India and the Council of Scientific and Industrial
Research, New Delhi, India for financial support. Affiliation
with the Jawaharlal Nehru Centre for Advanced Scientific
Research, Bangalore, India is acknowledged.
26 H. Bohme and M. Haake, Advances in Organic Chemistry, eds.
H. Bohme and H. G. Viehe, Interscience, New York, 1976, part 1,
vol. 9, p. 1.
27 T. A. Stephenson and G. Wilkinson, J. Inorg. Nucl. Chem., 1966, 28,
945.
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J. Chem. Soc., Dalton Trans., 2001, 1259–1265
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