A Family of Ruthenium Aryls Incorporating an η-Bonded Nitrite or Nitrate and a Pendant Imine - Phenol Function

Article abstract of DOI:10.1021/ic960358p

The reaction of carbonylchloro[4-methyl-6-(NR-iminio)phenolato-C ²O]bis(triphenylphosphine)ruthenium(II), Ru¹¹(η-RL)(PPh₃)₂(CO)CI (R = Ph, p-MeC₆H₄), 1, with NaY (Y = NO₂, NO₃) has afforded new organometallics of the type carbonyl(nitrito or nitrato)[4-methyl-6-(NR-imino)phenol-C ²]bis(triphenylphosphine)ruthenium(II). Ru¹¹(η¹-RL)(PPh₃) ₂(CO)(η²-Y) (2, Y = NO₂; 3, Y = NO₃). The transformation probably occurs via associative cis attack on chloride by Y^-. The reconversion 2(3) → 1 is achievable by treating 2 (3) with excess halide. The X-ray structures of Ru(η¹-PnL)(PPh₃)₂(CO)(η ²-NO₂) and Ru(η¹-PhL)(PPh₃)₂(CO)(η ²-NO₃) have revealed the presence of (i) O,O'-chelated Y^-, (ii) monodentate PhL binding via an aromatic carbon atom lying cis to the CO molecule, and (iii) O(phenolic)?N(imine) hydrogen bonding. The interconversion between 1 and 2 (3) is attended with iminium - phenolate to imine - phenol tautomerization and a change in the rotational conformation of the RL ligand. Crystal data for the complexes are as follows. Ru(η¹-PhL)(PPh₃)₂(CO)(η ²-NO₂): crystal system, monoclinic; space group, P2₁/c; a = 18.597(9) A?, b = 11.947(7) A?, c = 20.362(5) A?, β= 101.15(3)°; V = 4439(4) A?3; Z = 4; R = 0.0427; A_w = 0.0458. Ru(η¹-PhL)(PPh₃)₂(CO)(n²-NO ₃: crystal system, monoclinic; space group, P2₁/c; a = 18.726(11) A?, b = 11.857(4) A?, c = 20.443(8) A?, β = 102.77(4)°; V = 4426(3) A?³; Z = 4; R = 0.0654; R_w = 0.0659.

Full text of DOI:10.1021/ic960358p

64
Inorg. Chem. 1997, 36, 64-69
A Family of Ruthenium Aryls Incorporating an η2-Bonded Nitrite or Nitrate and a Pendant
Imine-Phenol Function
Prasanta Ghosh and Animesh Chakravorty*
Department of Inorganic Chemistry, Indian Association for the Cultivation of Science,
Calcutta 700 032, India
ReceiVed April 3, 1996X
The reaction of carbonylchloro[4-methyl-6-(NR-iminio)phenolato-C2,O]bis(triphenylphosphine)ruthenium(II),
RuII(η2-RL)(PPh3)2(CO)Cl (R ) Ph, p-MeC6H4), 1, with NaY (Y ) NO2, NO3) has afforded new organometallics
of the type carbonyl(nitrito or nitrato)[4-methyl-6-(NR-imino)phenol-C2]bis(triphenylphosphine)ruthenium(II),
RuII(η1-RL)(PPh3)2(CO)(η2-Y) (2, Y ) NO2; 3, Y ) NO3). The transformation probably occurs via associative
cis attack on chloride by Y-. The reconversion 2 (3) f 1 is achievable by treating 2 (3) with excess halide. The
X-ray structures of Ru(η1-PhL)(PPh3)2(CO)(η2-NO2) and Ru(η1-PhL)(PPh3)2(CO)(η2-NO3) have revealed the
presence of (i) O,O′-chelated Y-, (ii) monodentate PhL binding via an aromatic carbon atom lying cis to the CO
molecule, and (iii) O(phenolic)‚‚‚N(imine) hydrogen bonding. The interconversion between 1 and 2 (3) is attended
with iminium-phenolate to imine-phenol tautomerization and a change in the rotational conformation of the RL
ligand. Crystal data for the complexes are as follows. Ru(η1-PhL)(PPh3)2(CO)(η2-NO2): crystal system,
monoclinic; space group, P21/c; a ) 18.597(9) Å, b ) 11.947(7) Å, c ) 20.362(5) Å, â ) 101.15(3)°; V )
4439(4) Å3; Z ) 4; R ) 0.0427; Rw ) 0.0458. Ru(η1-PhL)(PPh3)2(CO)(η2-NO3): crystal system, monoclinic;
space group, P21/c; a ) 18.726(11) Å, b ) 11.857(4) Å, c ) 20.443(8) Å, â ) 102.77(4)°; V ) 4426(3) Å3; Z
) 4; R ) 0.0654; Rw ) 0.0659.
Introduction
plexes as Ru(η1-RL)(PPh3)2(CO)(η2-NO2), 2, and Ru(η1-RL)-
A few years ago a family of ruthenium organometallics of
type 1 incorporating the zwitterionic iminium-phenolato motif
(PPh3)2(CO)(η2-NO3), 3. The treatment of the solution of 1 in
a dichloromethane-acetone mixture with excess aqueous so-
dium nitrite results in a color change from violet to yellow.
From the reaction mixture 2 is isolated in high yields as a bright
yellow crystalline solid. The reaction of 1 with sodium nitrate
proceeds similarly, affording 3. The syntheses are summerized
in eq 1.
was discovered in this laboratory as the product of decarbonyl-
ative metalation of 4-methyl-2,6-diformylphenol by Ru(PPh3)3-
Cl2 in the presence of a primary amine (RNH2).1 It has now
been found that the chloride atom in 1 is subject to facile
replacement by certain other anions, the process being attended
with interesting secondary structural changes.
Herein we disclose the findings on the reaction of 1 with
sodium nitrite and nitrate. Chloride is displaced, and in each
case the entering anion binds the metal in the chelating O,O-
mode, which is very rare in ruthenium(II)-nitrite/nitrate
coordination chemistry. The displacement of chloride is as-
sociated with concomitant changes in the binding mode,
tautomeric state, and rotameric conformation of the Schiff base
ligand. These transformations are scrutinized and rationalized
in the light of spectral and bond parametric data. The X-ray
structures of two representative examples are reported.
The organometallics synthesized in the present work (R )
Ph and p-MeC6H4L) are listed in Table 1. All of these are
diamagnetic, consistent with the ruthenium(II) description.
(B) Characterization. The complexes display two charac-
teristic allowed electronic transitions at 390 and 320 nm, the
latter being more intense (Table 1). The yellow color of 2 and
3 is to be contrasted with the violet color of 1 associated with
an allowed band near 530 nm.1 The RuII(η1-RL) (2 and 3) and
RuII(η2-RL) (1) chromophores are thus easily distinguishable
from their spectra in the UV-vis region. The infrared spectra
Results and Discussion
(A) Synthetic Reactions. Complex 1 will be abbreviated
as Ru(η2-RL)(PPh3)2(CO)Cl and the nitrite and nitrate com-
X Abstract published in AdVance ACS Abstracts, November 1, 1996.
(1) (a) Bag, N.; Choudhury, S. B.; Pramanik, A.; Lahiri, G. K.;
Chakravorty, A. Inorg. Chem. 1990, 29, 5013. (b) Bag, N.; Choudhury,
S. B.; Lahiri, G. K.; Chakravorty, A. J. Chem. Soc., Chem. Commun.
1990, 1626. (c) Ghosh, P.; Bag, N.; Chakravorty, A. Organometallics
1996, 15, 3042. (d) Ghosh, P.; Pramanik, A.; Chakravorty, A.
Organometallics, in press.
-
(Table 1) of 2 and 3 are consistent with the chelation of NO2
and NO3- and with the imine-phenol hydrogen-bonding mode
within RL; Vide infra.
S0020-1669(96)00358-8 CCC: $14.00 © 1997 American Chemical Society

Ru(II) Aryls with Imine-Phenol Functions
Inorganic Chemistry, Vol. 36, No. 1, 1997 65
Table 1. Electronic, IR Spectral Data, and Reduction Potentials
UV-vis dataa
IR data,c cm-1
reducn potentialsd
-
compound
λ
max (ꢀ,b M-1 cm-1), nm
NO2-/NO3
CtO
CdN
E1/2 (∆Ep, mV), V
2, R ) Ph
390 (4810), 320 (16230)
390 (4730), 320 (16100)
390 (4090), 320 (16140)
390 (3840), 320 (15920)
1270 (m)
1270 (m)
1520 (vs)
1520 (vs)
1195 (s)
1200 (s)
1255 (s)
1255 (s)
860 (m)
855 (m)
1010 (m)
1010 (m)
1920 (vs)
1920 (vs)
1925 (vs)
1925 (vs)
1580 (s)
1590 (s)
1580 (s)
1590 (s)
0.77 (170)
0.69 (180)
0.74 (160)
0.66 (140)
2, R ) p-MeC6H4
3, R ) Ph
3, R ) p-MeC6H4
a Solvent is dichloromethane. b Extinction coefficient. c In KBr disk, vs ) very strong, s ) strong, m ) medium. d Conditions: Solvent,
dichloromethane; supporting electrolyte, TEAP (0.1 M); working electrode, platinum; reference electrode, SCE; solute concentration, 10-3 M;
E1/2 ) 0.5(Epa + Epc) at scan rate 50 mV s-1, where Epa and Epc are anodic and cathodic peak potentials, respectively; ∆Ep ) Epa - Epc.
a-c
Table 2. 1H NMR Data in CDCl3
Table 3. Selected Bond Distances (Å) and Angles (deg) and Their
Estimated Standard Deviations for Ru(η1-PhL)(PPh3)2(CO)(η2-NO2)
δ, ppm
42-Hs 40-Hs 44-Hs 0-Hs 41-Mes 48-Mes
Distances
compound
Ru-P1
2.391(2)
2.239(4)
2.062(5)
1.155(6)
1.268(7)
2.610(12)
Ru-P2
2.397(2)
2.196(4)
1.811(6)
1.274(7)
1.270(7)
2, R ) p-MeC6H4 6.29
3, R ) p-MeC6H4 6.26
7.04
6.84
8.10 12.62
8.09 12.86
1.97
1.92
2.39
2.39
Ru-O3
Ru-C37
O2-C51
O3-N2
O1‚‚‚N1
Ru-O4
Ru-C51
N1-C44
O4-N2
a Atom numbering is as in Figures 1 and 2. b TMS is used as internal
standard. c Aryl protons, 7.10-7.40m. s singlet. m multiplet.
Angles
P1-Ru-P2
P1-Ru-O4
P1-Ru-C51
P2-Ru-O4
P2-Ru-C51
O3-Ru-O4
O4-Ru-C37
C37-Ru-C51
Ru-O3-N2
O3-N2-O4
178.5(1)
85.4(1)
93.9(2)
93.2(1)
87.6(2)
56.3(1)
99.1(2)
96.3(2)
95.3(3)
111.1(5)
P1-Ru-O3
P1-Ru-C37
P2-Ru-C37
P2-Ru-O3
O3-Ru-C37
O3-Ru-C51
O4-Ru-C51
Ru-C51-O2
Ru-O4-N2
92.7(1)
89.8(2)
90.2(2)
86.6(1)
154.9(2)
108.4(2)
164.5(2)
174.1(5)
97.3(3)
available isoshielding F-z plots3 in the case of 2 (R ) Ph): 42-
H, 0.97; 40-H, 0.75; 41-Me, 0.61 ppm. The nature and shift of
1H signals of protons within the hydrogen-bonded RL ligand
will be considered in a later section.
In dichloromethane solution, 2 displays a quasireversible one-
electron response assigned to the RuIII/RuII couple. The
behavior of 3 is similar. The oxidized complexes are however
unstable and could not be isolated. For a given R and E1/2 (Table
1) values do not differ significantly between the nitrite and
nitrate complexes.
Figure 1. ORTEP plot (40% probability ellipsoids) and atom-labeling
scheme for Ru(η1-PhL)(PPh3)2(CO)(η2-NO2).
(C) Structure of Nitrites. (1) Geometry and Bond Pa-
rameters. The X-ray structure of Ru(η1-PhL)(PPh3)2(CO)(η2-
NO2) has authenticated the binding mode 2. A view of the
molecule is displayed in Figure 1, and selected bond parameters
are listed in Table 3. The nitrite ligand is chelated and the two
PPh3 donors lie in trans positions, the P1-Ru-P2 angle being
178.5(1)°. The RuII-P lengths, 2.391(2) and 2.397(2) Å, are
normal.4 The PhL ligand is coordinated to the metal only at
the C37 site, the phenolic oxygen being too far away for
significant coordination, Ru‚‚‚O1, 3.441(10) Å. The coordinated
carbon monoxide is located cis to C37.
Figure 2. Perspective view and atom-labeling scheme for Ru(η1-PhL)-
(PPh3)2(CO)(η2-NO3).
On the basis of covalent radii, the RuII-C(sp2) length has
been estimated to be 2.06 Å.5 Depending on ligands, the
1
The high-resolution H NMR spectra of two representative
complexes (CDCl3, 270 MHz) have been assigned (Table 2).
Using the atom numbering schemes of Figures 1 and 2 (see
below), we note that the singlets due to 40-H ( 7 ppm), 41-
Me ( 2 ppm), and 42-H ( 6 ppm) occur at relatively high
fields. The X-ray structures described in the next section reveal
that these protons indeed lie well within the shielding cones at
phosphine phenyl rings.1c,2 The extent of upfield shift due to
this effect has been estimated from crystallographic data and
(3) Johnson, C. E., Jr.; Bovey, F. A. J. Chem. Phys. 1958, 29, 1012.
(4) (a) Kolomnikov, I. S.; Gusev, A. I.; Aleksandrov, G. G.; Lobeeva, T.
S.; Struchkov, Yu, T.; Vol’pin, M. E. J. Organomet. Chem. 1973, 59,
349. (b) Skapski, A. C.; Stephens, F. A. J. Chem. Soc., Dalton Trans.
1974, 390. (c) Hitchcock, P. B.; Nixon, J. F.; Sinclair, J. J. Organomet.
Chem. 1975, 86, C34. (d) Moody, D. C.; Ryan, R. R. Cryst. Struct.
Commun. 1976, 5, 145. (e) Clark, G. R.; Waters, J. M.; Whittle, K.
R. J. Chem. Soc., Dalton Trans. 1975, 2556. (f) Brown, L. D.; Ibers,
J. A. J. Am. Chem. Soc. 1976, 98, 1597; Inorg. Chem. 1976, 15, 2788.
(g) Clark, G. R.; James, S. M. J. Organomet. Chem. 1977, 134, 229.
(h) McGuiggan, M. F.; Pignolet, L. H. Inorg. Chem. 1982, 21, 2523.
(i) Sahajpal, A.; Robinson, S. D.; Mazid, M. A.; Motevalli, M.;
Hursthouse, M. B. J. Chem. Soc., Dalton Trans. 1990, 2119. (j)
Pramanik, A.; Bag, N.; Chakravorty, A. J. Chem. Soc., Dalton Trans.
1992, 97. (k) Menon, M.; Pramanik, A.; Chattopadhyay, S.; Bag, N.;
chakravorty, A. Inorg. Chem. 1995, 34, 1361.
(2) (a) Jia, G.; Rheingold, A. L.; Haggerty, B. S.; Meek, D. W. Inorg.
Chem. 1992, 31, 900. (b) Jia, G.; Meek, D. W.; Gallucci, J. C.
Organometallics 1990, 9, 2549. (c) Mahapatra, A. K.; Bandyo-
padhyay, D. Bandyopadhyay, P.; Chakravorty, A. Inorg. Chem. 1986,
25, 2214.

66 Inorganic Chemistry, Vol. 36, No. 1, 1997
Ghosh and Chakravorty
experimental values span the range 1.96-2.16 Å.4h,6 In the
nitrite complex, however, the Ru-C37 length has a near-ideal
value, 2.062(5) Å. Because of the radius trend C(sp2) > C(sp)
and Ru-CO back-bonding, the RuII-CO(Ru-C51) length is
expected to be much shorter than the Ru-C37 length, and so it
is at 1.811(6) Å which is normal for ruthenium(II) carbonyls.4h,i,7
In Ru(η2-MeC6H4L)(PPh3)2(CO)Cl, the two Ru-C lengths are
2.043(6) and 1.800(7) Å.1a
Table 4. Selected Bond Distances (Å) and Angles (deg) and Their
Estimated Standard Deviations for Ru(η1-PhL)(PPh3)2(CO)(η2-NO3)
Distances
Ru-P1
2.384(6)
Ru-P2
2.386(7)
Ru-O3
Ru-C37
O2-C51
O3-N2
O1‚‚‚N1
2.262(14)
2.057(15)
1.145(19)
1.268(23)
2.609(23)
Ru-O4
Ru-C51
N1-C44
O4-N2
O5-N2
2.179(12)
1.790(16)
1.246(21)
1.276(20)
1.217(27)
(2) Nitrite Chelation and Related Parameters. The nitrite
chelation bite angle is 56.3(1)° and because of this extreme
acuteness some other cis angles become obtuse, e.g., O3-Ru-
C51, 108.4(2)°. Similarly trans angles involving nitrite O3 or
O4 deviate considerably from the ideal 180°, such as O3-Ru-
C37, 154.9(2)°. In effect, the RuC2P2O2 coordination sphere
in the complex is severely distorted from the model octahedral
geometry.
Angles
P1-Ru-P2
P1-Ru-O4
P1-Ru-C51
P2-Ru-O4
P2-Ru-C51
O3-Ru-O4
O4-Ru-C37
C37-Ru-C51
Ru-O3-N2
O3-N2-O4
O3-N2-O5
177.2(2)
85.1(4)
94.7(6)
92.1(4)
88.1(6)
57.9(4)
98.5(5)
96.4(7)
P1-Ru-O3
P1-Ru-C37
P2-Ru-C37
P2-Ru-O3
O3-Ru-C37
O3-Ru-C51
O4-Ru-C51
Ru-C51-O2
Ru-O4-N2
O4-N2-O5
92.7(4)
89.6(5)
90.6(5)
86.0(4)
155.9(6)
107.3(6)
165.2(6)
175.7(14)
95.1(11)
122.3(17)
The four-membered Ru(η2-NO2) chelate ring is nearly
perfectly planar (plane A, mean deviation 0.001 Å). The Ru-
(η1-PhL) fragment minus the pendant Ph group also makes a
good plane (plane B, mean deviation 0.06 Å) to which the Ph
group makes a dihedral angle of 52°. The inclination between
planes A and B is 9.9°. The metal center along with the
coordinated carbon and oxygen atoms (C37, C51, O3, O4)
defines a good plane (mean deviation 0.05 Å). Interestinghly
the P1-Ru-P2 axis is nearly perpendicular to plane B.
Otherwise, at least one phenyl ring of each PPh3 ligand would
approach the plane too closely. The observed distances of the
centroids of the PPh3 phenyl rings from the centroid of the
metallated benzene ring are 4.11, 5.94, and 7.31 Å for P(1)Ph3
and 4.10, 5.94, and 7.12 Å for P(2)Ph3.
91.5(11)
115.5(18)
122.2(15)
(D) Structure of Nitrates. Crystals of Ru(η1-PhL)(PPh3)2-
(CO)(η2-NO3) were weakly diffracting, and the final estimated
standard deviations of bond parameters are relatively large
(Table 4). The structure (Figure 2) is very similar to that of
the nitrite complex. The PhL ligand is coordinated at C37 only.
The Ru-P, Ru-C37, and Ru-C51 distances are comparable
to those in the nitrite complex. The various planarity relation-
ships and the distortions of the RuC2P2O2 coordination sphere
are also analogous for the two compounds.
The Ru(η2-NO3) fragment is highly planar (mean deviation
0.002 Å), and the bite angle is 57.9(4) Å. The Ru-O lengths
are 2.262(14) and 2.179(12) Åsthe longer distance being
expectedly trans to C37. The N2-O3, 1.268(23) Å, and N2-
O4, 1.276(20) Å, lengths are equal within experimental error,
but the N2-O5 length, 1.217(27) Å, is significantly shorter.
The resonance form of type 7a is thus more important than that
of type 7b. This is not unusual in chelated nitrates.11 However,
In the Ru(η2-NO2) fragment the Ru-O3 distance, 2.239(4)
Å, is significantly longer than the Ru-O4 distance, 2.196(4)
Å, due to the trans influence of the carbanionic C37 site. The
two N-O distances, 1.268(7) and 1.270(7) Å, are, however,
equal within experimental error corresponding to virtually equal
weightage of the resonance forms 4a and 4b. Ruthenium(II)
is known to afford numerous η1-NO2 complexes, incorporating
the N-bonded motif 5.8 The monodentate O-bonded motif 6
has been shown to be present in Ru(salen)(NO)(NO2).9
no ruthenium(II) motif of type 7 appears to have been structur-
ally characterized, although a ruthenium(IV) analogue has
been.11b The present nitrate complexes display two strong bands
at 1520 and 1255 cm-1 and one moderately strong band at 1010
cm-1. These are assigned to N-O stretching modes, the band
at 1520 cm-1 representing the uncoordinated NdO moiety.10c,11
(E) Tautomeric Shift between 2 (or 3) and 1. The distances
between phenolic oxygen and Schiff base nitrogen, O1‚‚‚N1
are 2.610(12) and 2.609(23) Å in the nitrite and nitrate
The η2-motif 4 characterized in this work does not appear to
have been encountered before among ruthenium(II) complexes.
The IR bands near 1270, 1200, and 860 cm-1 (Table 1) in the
nitrite complexes are assigned to asymmetric N-O stretching,
symmetric N-O stretching, and O-N-O bending, respec-
tively.10
(8) (a) Leising, R. A.; Kubow, S. A.; Churchill, M. R.; Buttrey, L. A.;
Ziller, J. W.; Takeuchi, K. J. Inorg. Chem. 1990, 29, 1306. (b)
Szczepura, L. F.; Takeuchi, K. J. Inorg. Chem. 1990, 29, 1772. (c)
Adeymi, S. A.; Miller, F. J.; Meyer, T. J. Inorg. Chem. 1972, 11,
994. (d) Godwin, J. B.; Meyer, T. J. Inorg. Chem. 1971, 10, 471.
(e) Blake, A. J.; Gould, R. O.; Johnson, B. F. G.; Parisini, E. Acta
Crystallogr. 1992, C48, 982.
(9) Carrondo, M. A. A. F. de C. T.; Rudolf, P. R.; Skapski, A. C.;
Thornback, J. R.; Wilkinson, G. Inorg. Chim. Acta 1977, 24, L95.
(10) (a) Finney, A. J.; Hitchman, M. A.; Kepart, D. L.; Raston, C. L.;
Rowbottom, G. L.; White, A. H. Aust. J. Chem. 1981, 34, 2177, and
references cited therein. (b) Hitchman, M. A.; Rowbottom, G. L.
Coord. Chem. ReV. 1982, 42, 55. (c) Nakamoto, K. Infrared and
Raman Spectra of Inorganic and Coordination Compounds, 4th ed.;
Wiley: New York, 1986.
(5) Pauling, L. The Nature of the Chemical Bond and the Structure of
Molecules and Crystals, 3rd ed.; Cornell University Press: New York,
1960.
(6) Fryzuk, M. D.; Montgomery, C. D.; Rettig, S. J. Organometallics 1991,
10, 467. (b) Jameson, G. B.; Muster, A.; Robinson, S. D.; Wingfield,
J. N.; Ibers, J. A. Inorg. Chem. 1981, 20, 2448. (c) Reveco, P.;
Schmehl, R. H.; Cherry, W. R.; Fronczek, F. R.; Selbin, J. Inorg. Chem.
1985, 24, 4078. (d) Partrick, J. M.; White, A. H.; Bruce, M. I.;
Beatson, M. J.; Black, D. St. C.; Deacon, G. B.; Thomas, N. C. J.
Chem. Soc., Dalton Trans. 1983, 2121.
(11) (a) Critchlow, P. B.; Robinson, S. D. Inorg. Chem. 1978, 17, 1896;
Inorg. Chem. 1978, 17, 1902. (b) Steed, J. W.; Tocher, D. A.
Polyhedron 1994, 13, 167.
(7) Brown, L. D.; Barnard, C. F. J.; Daniels, J. A.; Mawby, R. J.; Ibers,
J. A. Inorg. Chem. 1978, 17, 2932.

Ru(II) Aryls with Imine-Phenol Functions
Inorganic Chemistry, Vol. 36, No. 1, 1997 67
complexes, respectively. Hydrogen atoms could not be directly
located in the present X-ray structural works, but charge balance
consideration Vis-a-Vis spectral evidences leaves no doubt that
hydrogen bonding of the imine-phenol type 8 is present in 2
the O1‚‚‚O4 length is estimated to be 2.13 Å which represents
a strongly repulsive interaction because the van der Waals radius
of oxygen is 1.4 Å.5 The situation for the nitrate complex is
analogous; the O1‚‚‚O4 distance in a conformation like 10, being
2.10 Å.
The conversion of 1 to 2 (or 3), eq 1, can be rationalized14 in
terms of cis attack on chloride by nitrite (or nitrate). The
anchored anion can then displace the phenolic oxygen, achieving
chelation with concomitant conformational and tautomeric
changes. These plausible events are depicted in 11-13 in the
and 3. In contrast the parent chloro complexes, 1, have the
iminium-phenolate bonding in which the O‚‚‚N length is
significantly longer: 2.665(12) Å as in Ru(η2-p-MeC6H4L)-
(PPh3)2(CO)Cl.1a Between motifs 8 and 9 there is thus a
prototropic shift from phenolic oxygen to azomethine nitrogen.
This is very logical since metal binding to the phenolic function
(as in 1) is expected to promote proton dissociation from the
function.
The two motifs 8 and 9 can be distinguished with the help
of IR and 1H NMR. The Schiff base CdN stretching frequency
in the nitrite and nitrate complexes (motif 8) occurs at 1580-
1590 cm-1 (Table 1) which is significantly lower than that in
motif 9 in 1 ( 1620 cm-1) as expected.12 The νOH stretches in
2 and 3, however, are too broad to be clearly observable in IR.
The aldimine CH proton of the present complexes resonates at
8.1 ppm (Table 2) compared to 7.5 ppm in 1.1c This high-field
shift between 8 and 9 is as predicted.12a,13 The phenolic O-H
resonance of 2 and 3 occurs as a relatively sharp peak (width
at half-height 0.1 ppm) near 12.7 ppm (Table 2) compared
to the N-H resonance of 1 near 13 ppm. The latter resonance
is very broad (width at half-height 0.5 ppm) presumably due
to the nitrogen-quadrupole moment.
case of nitrite. Interestingly the prototropic and conformational
reorganizations can be looked upon as distant analogues of the
photochemical imine-iminium tautomerization in visual and
bacterial rhodopsins, eq 2.12a This process is associated with
an olefinic geometrical isomerization.
(G) Interconversion. Treatment of 2 with excess tetraeth-
ylammonium chloride regenerates 1. The two species are thus
interconvertible, eq 3. The forward process is particularly
Finally we wish to note that the reaction of 1 with sodium
acetate affords yellow colored complexes of the type Ru(η1-
RL)(PPh3)2(CO)(η2-MeCO2) which are structural analogues of
favorable in acidic media, possibly due to initial proton attack
on coordinated nitrite. The best method of converting 2 (or 3)
to 1 is to treat it with hydrochloric acid. The interconversion
process, eq 3, is consistent with the proposed steps 11-13.
For example the replacement of nitrite (the forward reaction
in eq 3) could begin by cis halide attack on the chelated nitrite
in 13.
1
2 and 3 with acetate replacing nitrite/nitrate. The IR and H
NMR characteristics of the RL ligand in the acetates are very
alike those in 2 and 3. More importantly X-ray structural
characterization in one case (R ) p-MeC6H4) has directly
revealed the presence of motif 8, including the crucial bridged
H-atom.1d Here the N‚‚‚O distance, 2.592(10) Å, compares very
well with those in the nitrite and nitrate species. The acetate
and other carboxylate complexes will be reported elsewhere.
(F) Conformational Reorganization. In 2 and 3 the carbon
monoxide molecule lies cis to both the metallated carbon and
phenolic oxygen as depicted in 8. In 1 the corresponding
locations are cis and trans, respectively; see 9. The RL fragment
is effectively rotated by 180° around the Ru-C37 axis
between the two structures. If a conformation of type 9 is
imposed on the nitrite complex, we get a motif like 10. Here
Concluding Remarks
The new organometallic family, Ru(η1-RL)(PPh3)2(CO)-
(η2-Y) (2, Y ) NO2; 3, Y ) NO3) incorporating the unprec-
edented O,O′-chelated RuII(η2-NO2 or η2-NO3) motif, has been
synthesized by reacting Ru(η2-RL)(PPh3)2(CO)Cl, 1, with NaY.
Apart from a change in the hapticity of the RL, the synthesis is
associated with iminium-phenolate to imine-phenol tautomer-
ization and sterically driven conformational reorganization of
the RL fragment with reference to the rest of the molecule. An
associative pathway is proposed, and expectedly the reverse
reaction (nitrite or nitrate to chloride) is achievable in the
presence of excess chloride. We are currently engaged in
exploring the nature of the osmium and rhodium chemistry of
the RL ligand system occurring in conjunction with carbon
monoxide, triphenylphosphine, and an anion.
(12) (a) Sandorfy, C.; Vocelle, D. Molecules in Physics, Chemistry and
Biology 1989, IV, 195. (b) Bohme, H.; Haake, M. In AdVances in
Organic Chemistry, Part 1; Bohme, H., Viehe, H. G., Eds.; Inter-
science: New York, 1976; Vol. 9, p 1.
(13) Sharma, G. M.; Roels, O. A. J. Org. Chem. 1973, 38, 3648.
(14) Serpone, N.; Bickley, D. G. Inorg. Chem. 1972, 17, 391.

68 Inorganic Chemistry, Vol. 36, No. 1, 1997
Ghosh and Chakravorty
Table 5. Crystallographic Data for Ru(η1-PhL)(PPh3)2(CO)(η2-NO2) and Ru(η1-PhL)(PPh3)2(CO)(η2-NO3)
Ru(η1-PhL)(PPh3)2(CO)(η2-NO2)
Ru(η1-PhL)(PPh3)2(CO)(η2-NO3)
chem formula
fw
space group
a, Å
b, Å
c, Å
â, deg
V, Å3
Z
C51H42N2O4P2Ru
909.9
P21/c
18.597(9)
11.947(7)
20.362(5)
101.15(3)
4439(4)
4
C51H42N2O5P2Ru
925.9
P21/c
18.726(11)
11.857(4)
20.443(8)
102.77(4)
4426(3)
4
T, °C
λ, Å
23
0.710 73
1.362
4.72
0.7732-0.8212
4.27
23
0.710 73
1.393
F
calcd, g cm-3
µ, cm-1
transm coeff
R,a %
4.78
6.54
6.59
1.33
Rw,b %
4.58
1.30
GOFc
2
a R ) ∑ Fo
-
Fc /∑ Fo . b Rw ) [∑w( Fo - Fc )2/∑ Fo
]
1/2; w-1 ) σ2( Fo ) + g Fo 2; g ) 0.0003 for Ru(η1-PhL)(PPh3)2(CO)(η2-NO2) and
0.0005 for Ru(η1-PhL)(PPh3)2(CO)(η2-NO3). c The goodness of fit is defined as [w( Fo - Fc )2/(no - nv)]1/2, where no and nv denote the numbers
of data and variables, respectively.
using NaNO3 in place of NaNO2. Anal. Calcd for RuC51H42N2O5P2:
C, 66.14; H, 4.57; N, 3.03. Found: C, 66.20; H, 4.50; N, 3.10.
The Ru(η1-p-MeC6H4L)(PPh3)2(CO)(η2-NO3) complex was similarly
prepared. Anal. Calcd for RuC52H44N2O5P2: C, 66.42; H, 4.72; N,
2.98. Found: C, 66.49; H, 4.80; N, 2.95.
Experimental Section
Materials. The starting materials Ru(PPh3)3Cl2,15 Os(PPh3)3Br2,16
and Ru(η2-RL)(PPh3)2(CO)Cl 1 complexes were prepared by reported
methods. For electrochemical work the purification of dichloromethane
and the preparation of tetraethylammonium perchlorate (TEAP) were
done as described in the previous work.17 Sodium nitrite, sodium
nitrate, and other chemicals and solvents were of analytical grade and
were used as received.
Conversion of Ru(η1-p-MeC6H4L)(PPh3)2(CO)(η2-NO2) to Ru-
(η2-p-MeC6H4L)(PPh3)2(CO)Cl. To a stirred solution of Ru(η1-p-
MeC6H4L)(PPh3)2(CO)(η2-NO2) (25 mg) in acetone (20 mL) and
dichloromethane (5 mL) was added 3 drops of 0.3 N HCl in acetone.
The yellow solution immediately turned violet, and the mixture was
stirred for 0.5 h. The solvent was removed under reduced pressure,
and the violet residue was washed thoroughly with water and finally
filtered. The residue was dried in vacuo. Yield was 85% on the basis
of the nitrite complex. Anal. Calcd for RuC52H44NO2P2Cl: C, 68.35;
H, 4.85; N, 1.53. Found: C, 68.27; H, 4.80; N, 1.50. The complex
was characterized with the help of spectra and other features.
X-ray Structure Determination. Single crystals (0.16 0.22
0.58 mm3 for Ru(η1-PhL)(PPh3)2(CO)(η2-NO2) and 0.22 0.12 0.16
mm3 for Ru(η1-PhL)(PPh3)2(CO)(η2-NO3)) grown by slow diffusion
of hexane into benzene solution in both cases were used. In each case
cell parameters were determined by least-squares fit of 30 machine
centered reflections (rotation photograph). Data were collected using
the ω-scan technique in the range 3° e 2θ e 50° for Ru(η1-PhL)-
(PPh3)2(CO)(η2-NO2) and 2° e 2θ e 47° for Ru(η1-PhL)(PPh3)2(CO)-
(η2-NO3) on a Siemens R3m/V four-circle diffractometer with graphite-
monochromated Mo KR radiation (λ ) 0.710 73 Å). Two check
reflections measured after every 98 reflections showed no intensity
reduction in any case. Data were corrected for Lorentz-polarization
effects, and an empirical absorption correction18 was done on the basis
of an azimuthal scan of six reflections for the nitrite crystal. Total
reflections collected, unique reflections, and used reflections for
structure solution satisfying I > 3σ(I) were as follows: (i) Ru(η1-PhL)-
(PPh3)2(CO)(η2-NO2), 8572, 7878, and 4395; (ii) Ru(η1-PhL)(PPh3)2-
(CO)(η2-NO3), 6168, 5600, and 1738. Systematic absences led to the
space group P21/c for both complexes.
Physical Measurement. Infrared spectra were recorded on a Perkin-
Elmer 783 spectrometer from 4000 to 200 cm-1
. An Hitachi 330
spectrometer was used to obtain electronic spectra. A Bruker 270 MHz
FT NMR spectrometer was used to record H NMR data (tetrameth-
1
ylsilane is the internal standard). Magnetic behavior was examined
on a PAR 155 vibrating-sample magnetometer fitted with a Walker
Scientific magnet. Microanalyses (C,H,N) data were obtained from a
Perkin-Elmer 240 C elemental analyzer. All electrochemical measure-
ments were performed under nitrogen atmosphere using a PAR 370-4
electrochemistry system as reported before.17 All of the reported
potentials in this work are uncorrected for junction contribution.
Solution ( 10-3 M) electrical conductivities were measured with the
help of a Philips PR 9500 bridge.
Preparation of Complexes. The nitrito, Ru(η1-RL)(PPh3)2(CO)-
(η2-NO2), and the nitrato, Ru(η1-RL)(PPh3)2(CO)(η2-NO3), complexes
were synthesized by reacting Ru(η2-RL)(PPh3)2(CO)Cl with NaNO2
and NaNO3, respectively. Yields were 80-85% on the basis of Ru-
(η2-RL)(PPh3)2(CO)Cl. Details are described for representative cases.
Carbonyl(nitrito-O,O′)[4-methyl-6-(phenylimino)phenol-C2]bis-
(triphenylphosphine)ruthenium(II), Ru(η1-PhL)(PPh3)2(CO)(η2-
NO2). To a vigorously stirring solution of Ru(η2-PhL)(PPh3)2(CO)Cl
(50 mg, 0.05 mmol) in dichloromethane (20 mL) and acetone (20 mL)
was added dropwise an aqueous solution of excess NaNO2 (20 mg,
0.29 mmol). The stirring was continued until the dark violet solution
turned yellow. The solvent was removed under reduced pressure,
leaving an aqueous suspension of the yellow complex. This was
filtered, washed repeatedly with water, and dried in vacuo. Anal. Calcd
for RuC51H42N2O4P2: C, 67.30; H, 4.65; N, 3.08. Found: C, 67.19;
H, 4.69; N, 2.95.
In each case, the ruthenium atom was located from Patterson maps
and the rest of the non-hydrogen atoms emerged from successive Fourier
synthesis. In the case of Ru(η1-PhL)(PPh3)2(CO)(η2-NO3) the six
phenyl rings of two PPh3 displayed disorder and were refined in the
“affixed” condition. The structures were refined by full-matrix least-
squares procedures. All of the non-hydrogen atoms of Ru(η1-PhL)-
(PPh3)2(CO)(η2-NO2) and the ruthenium, phosphorus, oxygen, and
nitrogen atoms of Ru(η1-PhL)(PPh3)2(CO)(η2-NO3) were refined aniso-
tropically. Hydrogen atoms were added at calculated positions with
fixed U ) 0.08 Å2 in both cases. The highest residuals were 0.75 e
Å-3 (Ru(η1-PhL)(PPh3)2(CO)(η2-NO2)) and 0.55 e Å-3 (Ru(η1-PhL)-
The complex Ru(η1-p-MeC6H4L)(PPh3)2(CO)(η2-NO2) was prepared
similarly. Anal. Calcd for RuC52H44N2O4P2: C, 67.58; H, 4.80; N,
3.03. Found: C, 67.65; H, 4.72; N, 3.10.
Carbonyl(nitrato-O,O′)[4-methyl-6-(phenylimino)phenol-C2]bis-
(triphenylphosphine)ruthenium(II), Ru(η1-PhL)(PPh3)2(CO)(η2-
NO3). This was prepared by the same procedure as that described above
(15) Stephenson, T. A.; Wilkinson, G. J. Inorg. Nucl. Chem. 1966, 28,
945.
(16) Hoffman, P. R.; Caulton, K. G. J. Am. Chem. Soc. 1975, 99, 4221.
(17) Ghosh, P.; Pramanik, A.; Bag, N.; Lahiri, G. K.; Chakravorty, A. J.
Organomet. Chem. 1993, 454, 237.
(18) North, A. C. T.; Phillips, D. C.; Mathews, F. A. Acta Crystallogr.
1968, A24, 351.

Ru(II) Aryls with Imine-Phenol Functions
Inorganic Chemistry, Vol. 36, No. 1, 1997 69
(PPh3)2(CO)(η2-NO3)). All calculations were done on a MicroVax II
computer using the SHELXTL-Plus program package.19 Significant
crystal data are listed in Table 5.
Computer Generation of Motif 10. Retaining the relative positions
of CO and the nitrite chelate as in Ru(η1-PhL)(PPh3)2(CO)(η2-NO2)
the phenolic oxygen is shifted to the other ortho position of the
metalated carbon to correspond to the relative position as in 1. The
phenolic C-O length is 1.369 Å. The O1‚‚‚O4 distance is then found
to be 2.13 Å. In the case of Ru(η1-PhL)(PPh3)2(CO)(η2-NO3) the
corresponding distance is 2.10 Å.
Computation of Chemical Shift Due to PPh3 Ring Currents. The
required parameters for this are the cylindrical coordinates (F, z)20 of
the concerned proton with respect to the centroids of PPh3 phenyl rings.
Using the crystallographic data of Ru(η1-PhL)(PPh3)2(CO)(η2-NO2),
these parameters were calculated from (i) the distance of the proton
from the centroid (G) of each PPh3 ring and (ii) the angle between the
distance vector and the normal to the plane of the phenyl ring at G.
Expressing the calculated F and z values in units of the radius of the
benzene hexagon, the shifts were computed with the help of available
isoshielding F-z plots.3 The net shift of a proton was obtained by
summing up individual contributions.
Acknowledgment. We thank the Department of Science and
Technology, New Delhi, for financial support. Affiliation with
the Jawaharlal Nehru Centre for Advanced Scientific Research,
Bangalore, India, is acknowledged. We are thankful to Drs.
N. Bag and A. Pramanik for preliminary experiments.
Supporting Information Available: For Ru(η1-PhL)(PPh3)2(CO)-
(η2-NO2) and Ru(η1-PhL)(PPh3)2(CO)(η2-NO3) tables of complete
atomic coordinates (Tables S1 and S6), bond distances (Tables S2 and
S7) and angles (Tables S3 and S8), anisotropic thermal parameters
(Tables S4 and S9), and hydrogen atoms positional parameters (S5 and
S10) and a figure of electronic spectra of Ru(η1-PhL)(PPh3)2(CO)(η2-
NO2) and Ru(η2-PhL)(PPh3)2(CO)(Cl) (10 pages). Ordering information
is given on any current masthead page.
(19) Sheldrick, G. M. SHELXTL-Plus Structure Determination Software
Programs; Siemens Analytical X-ray Instrument Inc.: Madison, WI,
1990.
(20) Margenau, H.; Murphy, G. M. The Mathematics of Physics and
Chemistry; Van Nostrand: Princeton, NJ, 1956.
IC960358P