Decarbonylative metalation of diformylphenol Schiff bases: New osmium and ruthenium organometallics incorporating the iminium-phenolato zwitterionic motif

Article abstract of DOI:10.1021/om960018b

The reaction of Schiff bases of 2,6-diformyl-4-methylphenol with M(PPh₃)₃X₂ in ethanol has afforded carbonylhalo[4-methyl-6-(N-R-iminiomethyl)phenolato-C ²,O]bis(triphenylphosphine)metal(II) compounds, MII(RL)(PPh₃)₂(CO)X (M = Os, X = Br; M = Ru, X = Cl; R = alkyl, aryl). The process is believed to proceed via oxidative addition of the aldehydic C(O)-H bond to the metal followed by CO extrusion and reductive proton elimination. The X-ray structure of Os(EtL)(PPh₃)₂(CO)Br·CH₂Cl₂ has revealed the presence of the distorted octahedral OsC₂P₂BrO coordination sphere. In the four-membered, Os(C,O) chelate ring, the metal atom is bonded to the carbon site to which an aldehyde group was attached in the parent ligand. The presence of the iminium-phenolato zwitterionic motif is consistent with the N?O length as well as with IR and ¹H NMR spectra. Bond parameters of the osmium and ruthenium systems are compared. Significant dπ-pπ back-bonding with the metalated aromatic ring occurs in the case of osmium. The complexes display a quasi-reversible one-electron cyclic voltammetric couple (E1/2 = 0.50-0.70 V), but the oxidized congeners are too unstable to be isolated. Upon reaction of M(RL)(PPh₃)₂(CO)X with carboxylates, the latter gets chelated, the M-O(phenolato) linkage is cleaved, and the iminium-phenolato function tautomerizes to the imine-phenol function.

Full text of DOI:10.1021/om960018b

3042
Organometallics 1996, 15, 3042-3047
Deca r bon yla tive Meta la tion of Difor m ylp h en ol Sch iff
Ba ses: New Osm iu m a n d Ru th en iu m Or ga n om eta llics
In cor p or a tin g th e Im in iu m -P h en ola to Zw itter ion ic
Motif
Prasanta Ghosh, Nilkamal Bag, and Animesh Chakravorty*,†
Department of Inorganic Chemistry, Indian Association for the Cultivation of Science,
Calcutta 700 032, India
Received J anuary 12, 1996X
The reaction of Schiff bases of 2,6-diformyl-4-methylphenol with M(PPh3)3X2 in ethanol
has afforded carbonylhalo[4-methyl-6-(N-R-iminiomethyl)phenolato-C2,O]bis(triphenylphos-
phine)metal(II) compounds, MII(RL)(PPh3)2(CO)X (M ) Os, X ) Br; M ) Ru, X ) Cl; R )
alkyl, aryl). The process is believed to proceed via oxidative addition of the aldehydic C(O)-H
bond to the metal followed by CO extrusion and reductive proton elimination. The X-ray
structure of Os(EtL)(PPh3)2(CO)Br‚CH2Cl2 has revealed the presence of the distorted
octahedral OsC2P2BrO coordination sphere. In the four-membered, Os(C,O) chelate ring,
the metal atom is bonded to the carbon site to which an aldehyde group was attached in the
parent ligand. The presence of the iminium-phenolato zwitterionic motif is consistent with
1
the N‚‚‚O length as well as with IR and H NMR spectra. Bond parameters of the osmium
and ruthenium systems are compared. Significant dπ-pπ back-bonding with the metalated
aromatic ring occurs in the case of osmium. The complexes display a quasi-reversible one-
electron cyclic voltammetric couple (E1/2 ) 0.50-0.70 V), but the oxidized congeners are too
unstable to be isolated. Upon reaction of M(RL)(PPh3)2(CO)X with carboxylates, the latter
gets chelated, the M-O(phenolato) linkage is cleaved, and the iminium-phenolato function
tautomerizes to the imine-phenol function.
In tr od u ction
of type 3 and 4, incorporating the unprecedented four-
membered C,O-chelate and an iminium function, -CHd
N+HR, ortho to the phenolato group. Iminium chem-
istry is of general interest in the context of visual and
bacterial rhodopsins.5
The salicyl chelate motif 1 has been documented for
ruthenium1,2 and osmium.3 This prompted us to explore
In the present work we disclose the chemistry of the
osmium family 4. The results are compared and con-
trasted with those of ruthenium congeners, 3, on which
preliminary reports are available.6
Resu lts a n d Discu ssion
A. Syn th esis. a . Meth od s. The complexes 3 and
4 will be generally abbreviated as M(RL)(PPh3)2(CO)X.
The osmium chelates were obtained in excellent yields
by the stoichiometric reaction of Os(PPh3)3Br2 with the
dialdehyde 2a and the amine RNH2 in ethanol, eq 1.
the possible binucleation4 of ligands of type 2 by these
metals. This objective has remained unrealized, but the
endeavor has led to the discovery of new organometallics
† Telefax: +91-33-473-2805. E-mail: icac@iacs.ernet.in.
X Abstract published in Advance ACS Abstracts, May 15, 1996.
(1) Bag, N.; Lahiri, G. K.; Bhattacharya, S.; Falvello, L. R.; Chakra-
vorty, A. Inorg. Chem. 1988, 27, 4396 and references therein.
(2) (a) Lahiri, G. K.; Bhattacharya, S.; Ghosh, B. K.; Chakravorty,
A. Inorg. Chem. 1987, 26, 4324 and references therein. (b) Doine, H.;
Stephens, F. F.; Cannon, R. D. Bull. Chem. Soc. J pn. 1985, 58, 1327.
(c) Gopinathan, S.; Deshpande, S. S.; Gopinathan, C. Synth. React.
Inorg. Met.-Org. Chem. 1989, 19, 321. (d) Taqui Khan, M. M.; Srinivas,
D.; Kureshy, R. I.; Khan, N. H. Inorg. Chem. 1990, 29, 2320. (e)
Mondal, S. K.; Chakravarty, A. R. J . Chem. Soc., Dalton Trans. 1992,
1627.
The same result is achievable by using the preformed
Schiff monobase 2b in place of 2a + RNH2, eq 2. The
Schiff dibase 2c also affords 4 via hydrolysis by the
water present in the solvent, eq 3. The reactions of eqs
(3) (a) Che, C.-M.; Cheng, W.-K.; Mak, T. C. W. Inorg. Chem. 1988,
27, 250. (b) Che, C.-M.; Cheng, W.-K.; Mak, T. C. W. Inorg. Chem.
1986, 25, 703.
(4) (a) Robson, R. Aust. J . Chem. 1970, 23, 2217. (b) Okawa, H.;
Kida, S. Bull. Chem. Soc. J pn. 1972, 45, 1759. (c) Casellato, U.; Vigato,
P. A.; Fenton, D. E.; Vidali, M. Chem. Soc. Rev. 1979, 8, 199. (d)
Zanello, P.; Tamburini, S.; Vigato, P. A.; Mazzocchin, G. A. Coord.
Chem. Rev. 1987, 77, 165. (e) Nag, K. Proc. Indian Acad. Sci. (Chem.
Sci.) 1990, 102, 269.
(5) Sandorfy, C.; Vocelle, D. Mol. Phys. Chem., Biol. 1989, IV, 195.
(6) Preliminary communications on Ru(RL)(PPh3)2(CO)Cl: (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.
S0276-7333(96)00018-0 CCC: $12.00 © 1996 American Chemical Society
+
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New Os and Ru Organometallics
Organometallics, Vol. 15, No. 13, 1996 3043
Ta ble 1. IR a n d UV-Vis Sp ectr a l Da ta
IR data: νmax, cm-1
compd
CdNa
NsHb
CtOa
UV-vis data:c max, nm (ꢀ,d M-1 cm-1
λ )
Os(MeL)(PPh3)2(CO)Br
Os(EtL)(PPh3)2(CO)Br
Os(PhL)(PPh3)2(CO)Br
Os(MeC6H4L)(PPh3)2(CO)Br
1630
1630
1630
1640
3380
3380
3400
3400
1860
1865
1870
1870
500 (3234), 360 (5074)
500 (3172), 360 (4991)
560 (3211), 410 (9037), 325 (7478)
560 (3634), 415 (10 572), 335 (9140)
Ru(MeL)(PPh3)2(CO)Cl
Ru(EtL)(PPh3)2(CO)Cl
Ru(PhL)(PPh3)2(CO)Cl
Ru(MeC6H4L)(PPh3)2(CO)Cl
1630
1630
1630
1630
3400
3400
3440
3440
1885
1885
1920
1900
480 (3950), 360 (5280)
480 (3900), 360 (6270)
535 (5650), 405 (13 900), 325s (10 000)e
530 (4560), 405 (11 430), 320s (7700)e
In KBr disk. In hexachlorobutadiene. c Solvent is dichloromethane. Extinction coefficient. e s ) shoulder.
a
b
d
1-3 afford 3 when Ru(PPh3)3Cl2 is used in place of
Os(PPh3)3Br2.
The complexes synthesized in this work are listed in
Table 1. These are red (R ) alkyl) or violet (R ) aryl)
diamagnetic (t26) solids which afford nonelectrolytic
solutions in polar solvents.
b. Rea ction P a th . The synthesis of 4 constitutes a
rare example of aldehyde decarbonylation by osmium.
Decarbonylation promoted by ruthenium7 and rhodium8
usually proceeds via oxidative addition of the QC(O)-H
bond to the metal site followed by CO extrusion and Q
migration (Q ) alkyl, aryl).9 In the present system
oxidative addition with concomitant phenolato chelation
and azomethine protonation would afford the motif 5
(PPh3 and Br not shown), which then undergoes Q
migration: 5 f 6.
F igu r e 1. Perspective view and atom-labeling scheme for
Os(EtL)(PPh3)2(CO)Br‚CH2Cl2 (excluding CH2Cl2).
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) a n d Th eir Estim a ted Sta n d a r d Devia tion s
for Os(EtL)(P P h 3)2(CO)Br ‚CH2Cl2
Distances
Os-Br
2.636(2)
Os-P1
Os-O1
Os-C29
N1-C8
2.379(2)
Os-C2
O2-C29
O1-C1
1.980(19)
1.194(15)
1.353(23)
2.151(10)
1.846(12)
1.253(34)
Angles
The intermediacy of 5 is supported by the isolation
and structural characterization of a rhodium(III) analog
of 5.10 Since carbonyls of osmium(IV) are inherently
unstable,11 6 could spontaneously transform to 4 via
reductive proton elimination (OsIV(CO)(H) f OsII(CO)
+ H+).12
Br-Os-P1
Br-Os-C2
P1-Os-C29
Br-Os-O1
P1-Os-C2
P1-Os-P1A
88.9(2)
154.8(3)
90.1(1)
88.2(4)
91.0(2)
177.8(3)
Br-Os-C29
C2-Os-C29
P1-Os-O1
O1-Os-C2
O1-Os-C29
Os-C29-O2
101.3(7)
103.9(7)
90.1(1)
66.6(5)
170.6(8)
178.1(19)
B. Str u ctu r e. a . Geom etr y. The X-ray structure
of the dichloromethane adduct Os(EtL)(PPh3)2(CO)Br‚
CH2Cl2 has authenticated the bonding mode 4. A view
of the structure (CH2Cl2 excluded) is shown in Figure
1, and selected bond parameters are listed in Table 2.
We have here a structural situation that is unprecen-
dented in osmium chemistry. Structurally character-
ized OsII-O(phenolato) systems are virtually unknown.
Orthometalated OsII-C species are rare,13 and the four-
membered organometallic ring incorporating OsII(C,O)
chelation is a novelty. The metal atom is bonded to C2
where the aldehyde group was originally attached in the
parent ligand. The extruded carbon monoxide and the
Br atom are coordinated in positions respectively cis and
trans to C2. The non-hydrogen atoms of the EtL ligand
as well as Br and CO lie on a crystallographic plane of
symmetry along with the metal atom (0,0,0). The
methyl group in Et displays 2-fold disorder with respect
to the plane.
The OsC2P2BrO coordination sphere is severely dis-
torted from octahedral geometry as can be seen from
the angles at the metal center (Table 2). The angles
due to atoms lying trans to each other span the range
177.8(3)-154.7(4)°. The cis angles have an even wider
range, 66.6(5)-103.9(7)°. The minimum cis angle cor-
(7) (a) Prince, R. H.; Raspin, K. A. J . Chem. Soc. A. 1969, 612. (b)
Chaudret, B. N.; Cole-Hamilton, D. J .; Nohr, R. S.; Wilkinson, G. J .
Chem. Soc., Dalton Trans. 1977, 1546. (c) Domazetis, G.; Tarpey, B.;
Dolphin, D.; J ames, B. R. J . Chem. Soc., Chem. Commun. 1980, 939.
(8) (a) Suggo, J . W. J . Am. Chem. Soc. 1978, 100, 640. (b) Milstein,
D. Acc. Chem. Res. 1984, 17, 221. (c) J ames, B. R.; Young, C. G. J .
Organomet. Chem. 1985, 285, 321. (d) Bianchini, C.; Meli, A.;
Peruzzini, M.; Ramirez, J . A.; Vacca, A.; Vizza, F.; Zanobini, F.
Organometallics 1989, 8, 337. (e) Song, L.; Arif, A. M.; Stang, P. J .
Organometallics 1990, 9, 2792.
(9) (a) Sahajpal, A.; Robinson, S. D.; Mazid, M. A.; Motevalli, M.;
Hursthouse, M. B. J . Chem. Soc., Dalton Trans. 1990, 2119. (b)
Doughty, D. H.; Pignolet, L. H. Homogeneous Catalysis with Metal
Phosphine Complexes; Pignolet, L. H., Ed.; Plenum Press: New York,
1983; p 343.
(10) Pattanayak, S.; Ghosh, P.; Chakravorty, A. Unpublished results.
(11) (a) Knox, G. R. Organometallic Compounds of Ruthenium and
Osmium; Chapman and Hall: London, 1985. (b) Adams, R. D.;
Selegne, J . P. Comprehensive Organometallic Chemistry; Wilkinson,
G., Ed.; Pergamon Press: Oxford, U.K., 1982; p 967.
(13) Dawodi, Z.; Mays, M. J .; Raithby, P. R. Acta Crystallogr., Sect.
B 1981, 37, 252.
(12) Pearson, R. G. Chem. Rev. 1985, 85, 41.
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3044 Organometallics, Vol. 15, No. 13, 1996
Ta ble 3. 1H NMR Da ta in CDCl3
δ, ppm
4-Mes
Ghosh et al.
a ,b
compd
3-Hs
5-Hs
dN+Hs
-CHdN+ s
Os(MeL)(PPh3)2(CO)Br
Os(EtL)(PPh3)2(CO)Br
Os(MeC6H4L)(PPh3)2(CO)Br
Ru(MeL)(PPh3)2(CO)Cl
Ru(PhL)(PPh3)2(CO)Cl
Ru(MeC6H4L)(PPh3)2(CO)Cl
5.78
5.78
5.88
5.80
5.89
5.88
6.34
6.21
6.42
6.00
6.03
6.02
1.76
1.74
1.80
1.70
1.69
1.69
10.90
10.90
12.55
11.65
13.17
13.19
7.06
7.11
7.54
7.10
c
7.58
a
b
Atom numbering is as in Figure 1. Other signals: aryl protons, 6.80-7.70m; aryl-Me, 2.40s; N-Me, 2.90s; N-Et, 3.11q and 1.17t ppm.
Abbreviations: s ) singlet; t ) triplet; q ) quartet; m ) multiplet. c Nonresolvable peak.
responds to the four-membered chelate ring, and the
maximum, to C2-Os-C29.
2.654(20) Å. Here none of the hydrogen atoms of the
structure could be resolved in difference Fourier maps.
However in Ru(MeC6H4L)(PPh3)2(CO)Cl the motif 8 is
b. Bon d Len gth Tr en d s. The Os-P and Os-C29
lengths are unexceptional14,15 while the Os-C2 length,
1.98(1) Å, is shorter than that (2.08 Å) in the ortho-
metalated azobenzene complex.13 Between the two
Os-C bonds, Os-C29 is shorter (1.85(1) Å) in agree-
ment with the expected size trend C2(sp2) > C29(sp)
and with OsII-CO back-bonding. The trans effect of the
carbanionic C2 atom lengthens the Os-Br bond to
2.636(2) Å (usual range, 2.50-2.60 Å).15a,16 The Os-
O1 length is 2.151(10) Åsno other OsII-O(phenolato)
complex appeared to have been structurally character-
ized. In a catechol complex the average OsIII-O length
is 2.02 Å.17
The covalent radii of bivalent osmium and ruthenium
are virtually the same, 1.33 Å.18 The Os-O1 and Os-
C2 lengths are however found to be shorter than the
corresponding Ru-O and Ru-C lengths in Ru(MeC6-
H4L)(PPh3)2(CO)Cl6 by 0.09 and 0.06 Å respectivelysas
though the metalated ring is pulled closer to the metal
in the case of osmium. The Os‚‚‚i and Ru‚‚‚i lengths in
the complexes are 3.30 and 3.49 Å, respectively (i )
center of gravity of the metalated benzene ring). The
osmium atom is believed to be engaged in dπ-pπ back-
bonding,19 7, with an aromatic π* orbital such as the
directly observable: N-H, 0.99(6) Å; O‚‚‚H, 1.75(5) Å;
N‚‚‚O, 2.665(12) Å; N-H‚‚‚O, 144(1)°.6 The N-H‚‚‚O
bridge is highly unsymmetrical, and the weakness of
the O‚‚‚H hydrogen bond is consistent with the IR data
(see below). The structure of the iminium function is
of considerable interest in the context of rhodopsins, but
in very few cases has the N+-H hydrogen been directly
located.5,21
We note that the N‚‚‚O length in Os(EtL)(PPh3)2(CO)-
Br‚CH2Cl2 is same as that in the ruthenium complex
within experimental error. This result taken collec-
1
tively with IR and H NMR results (vide infra) demon-
strates that 3 and 4 generally contain the iminium-
phenolato motif, 8.
C. Sp ectr a . Relevant UV-vis and IR spectral
features are listed in Table 1, and 1H chemical shifts
are set out in Table 3.
Two (R ) alkyl) and three (R ) aryl) allowed bands
observed in the range 300-700 nm are diagnostic of the
chelate chromophore in 3 and 4. The MLCT (t2 f π*)
band near 500 nm is red-shifted in going from ruthe-
nium to osmium as well as from R ) alkyl to R ) aryl.
The significant effect of the R substituent is indicative
of sizable iminium character of the acceptor π* orbital.
idealized e2 of benzene.20 Back-bonding of this type is
expected to be much weaker in the case of ruthenium.
c. Th e Im in iu m -P h en ola to Zw itter ion ic Motif.
The N‚‚‚O length in Os(EtL)(PPh3)2(CO)Br‚CH2Cl2 is
1
In H NMR the aromatic 3-H and 5-H singlets occur
at relatively high fields (5.8-6.4 ppm) and so does the
4-Me resonance of the metalated ring (1.7-1.8 ppm).
The X-ray structure of Os(EtL)(PPh3)2(CO)Br‚CH2Cl2
indeed reveals that these protons lie well within the
shielding cones of phosphine phenyl rings.22 The extent
of upfield shifts due to this factor estimated from
crystallographic data and isoshielding F-z plots23 is as
(14) (a) Pramanik, A.; Bag, N.; Ray, D.; Lahiri, G. K.; Chakravorty,
A. Inorg. Chem. 1991, 30, 410. (b) Pramanik, A.; Bag, N.; Ray, D.;
Lahiri, G. K.; Chakravorty, A. J . Chem. Soc., Chem. Commun. 1991,
139. (c) Pramanik, A.; Bag, N.; Chakravorty, A. J . Chem. Soc., Dalton
Trans. 1993, 237.
(15) (a) Bottomley, F.; Ivan, J . B.; Peter, L.; White, S. J . Chem. Soc.,
Dalton Trans. 1978, 1726. (b) Bucher, J . W.; Lay, K. L.; Smith, P. D.;
Scheidt, R. W.; Kenney, J . E.; Rupercht, G. A. J . Organomet. Chem.
1976, 110, 109. (c) Clark, G. R.; Collins, T. J .; Marsden, K.; Roper, W.
R. J . Organomet. Chem. 1978, 157, C23.
(16) Fergusson, J . E.; Robinson, W. T.; Coll, R. K. Inorg. Chim. Acta
1991, 181, 37. (b) Robinson, P. D.; Ali, I. A.; Hinckley, C. C. Acta
Crystallogr., Sect. C 1991, 47, 1397. (c) Robinson, P. D.; Hinckley, C.
C.; Ikuo, A. Acta Crystallogr., Sect. C 1989, 45, 1079.
(17) Haga, M.; Isobe, K.; Boone, S. R.; Pierpont, C. G. Inorg. Chem.
1990, 29, 3795.
(18) Pauling, L. The Nature of the Chemical Bond and the Structure
of Molecules and Crystals, 3rd ed.; Cornell University Press: Ithaca,
NY, 1960.
(19) (a) Hasegawa, T.; Sekine, M.; Schaefer, W. P.; Taube, H. Inorg.
Chem. 1991, 30, 449. (b) Taube, H. Pure Appl. Chem. 1991, 63, 651.
(c) Herman, W. D.; Taube, H. J . Am. Chem. Soc. 1987, 109, 1883. (d)
Cordone, R.; Taube, H. J . Am. Chem. Soc. 1987, 109, 8101. (e) Taube,
H. Pure Appl. Chem. 1979, 51, 901.
(20) Cotton, F. A. Chemical Applications of Group Theory; Wiley
Eastern Limited: New Delhi, 1971.
(21) Bohme, H.; Haake, M. Advances in organic chemistry; Ed.
Bohme, H., Viehe, H. G., Eds.; Interscience Publication: New York,
1976; Part 1, Vol. 9, p 1.
(22) There are instances where high-field shifts have been qualita-
tively assigned to PPh3 ring currents: (a) J ia, G.; Rheingold, A. L.;
Haggerty, B. S.; Meek, D. W. Inorg. Chem. 1992, 31, 900. (b) J ia, G.;
Meek, D. W.; Gallucci, J . C. Organometallics 1990, 9, 2549. (c)
Mahapatra, A. K.; Bandyopadhyay, D.; Bandyopadhyay, P.; Chakra-
vorty, A. Inorg. Chem. 1986, 25, 2214. (d) Bandyopadhyay, P.;
Mascharak, P. K.; Chakravorty, A. J . Chem. Soc., Dalton Trans. 1982,
675.
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New Os and Ru Organometallics
Organometallics, Vol. 15, No. 13, 1996 3045
Ta ble 4. Cyclic Volta m m etr ic Red u ction
P oten tia lsa a t 298 K
E1/2[M(III)-M(II)],b
compd
V(∆Ep, mV)
Os(MeL)(PPh3)2(CO)Br
Os(EtL)(PPh3)2(CO)Br
Os(PhL)(PPh3)2(CO)Br
Os(MeC6H4L)(PPh3)2(CO)Br
0.52 (160)
0.50 (120)
0.59 (180)
0.57 (190)
Ru(MeL)(PPh3)2(CO)Cl
Ru(EtL)(PPh3)2(CO)Cl
Ru(PhL)(PPh3)2(CO)Cl
Ru(MeC6H4L)(PPh3)2(CO)Cl
0.56 (100)
0.54 (200)
0.68 (150)
0.65 (150)
yellow colored solid in excellent yield. This however did
not contain any copper but was found to have the
composition Ru(MeC6H4L)(PPh3)2(CO)(MeCO2). Fur-
ther scrutiny has revealed that here the acetate ion is
chelated while the RL ligand is η1-bonded via the
aromatic carbon center, the phenolic oxygen being
engaged in imine-phenol hydrogen bonding as shown
in 10, a tautomer of 8. Families of ruthenium and
a
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
b
rate 50 mV s-1, where Epa and Epc are anodic and cathodic peak
potentials respectively; ∆Ep ) Epa - Epc
.
follows (ppm): 3-H, +0.4; 5-H, +0.5; 4-Me, +0.6. Ortho-
metalation is expected to further augment the upfield
shifts of the ring protons.24
The presence of the iminium function 8 is revealed
in both IR and 1H NMR spectra. A broad band of
medium intensity near 3400 cm-1 is assigned to the
N+-H stretch. The observed frequency is indicative of
the presence of weak hydrogen bonding.5,25,26 The
relatively high (∼1620 cm-1) CdN stretching frequency
is also consistent with nitrogen protonation.5,21 The
osmium complexes of type 10 have been synthesized by
reacting 3 and 4 with metal carboxylates, and their
detailed chemistry will be described elsewhere.
1
N+H proton gives rise to a broad H resonance of correct
intensity in the range 10.9-12.6 ppm (Table 3). The
signal disappears upon shaking with D2O. In free
phenols of type 2b,c the OH resonance occurs as a
relatively sharp feature near 13 ppm. The aldimine CH
proton in these phenols resonates near 8.7 ppm. The
corresponding resonances in 3 and 4 lie in the region
7.0-7.6 ppm. A significant high-field shift of the
aldimine CH is indeed expected upon protonation at
nitrogen.27
D. Rea ctivity. a . Meta l Red ox. In dichloro-
methane solution the M(RL)(PPh3)2(CO)X species dis-
play a characteristic quasi-reversible one-electron cyclic
voltammetric response corresponding to the M(III)-
M(II) couple, eq 4. The E1/2 values (Table 4) follow the
Con clu d in g Rem a r k s
New families of organometallics, 3 and 4, have been
synthesized via decarbonylative metalation. The os-
mium complexes, 4, constitute rare examples of OsII-
O(phenolato) and ortho-metalated OsII-C binding. The
four-membered Os(C,O) chelate ring is unprecedented.
Other points of special interest include (i) osmium-
aromatic dπ-pπ bonding as depicted in 7 and (ii) the
conversion of 3 and 4 to 10 via reaction with carboxy-
lates resulting in iminium-phenolato to imine-phenol
tautomerization. Item ii as well as reactions of 3 and 4
with oxo anions like NO2- and NO3- are under scrutiny.
MIII(RL)(PPh3)2(CO)X+ + e h
Exp er im en ta l Section
Ma ter ia ls. Thestartingmaterials Ru(PPh3)3Cl2,29 Os(PPh3)3-
Br230 (from (NH4)2OsBr631), and 2,6-diformyl-4-methylphenol32
were synthesized by literature methods. The purification of
dichloromethane and the preparation of tetraethylammonium
perchlorate (TEAP) for electrochemical work were done as
before.33 All other chemicals and solvents were of analytical
grade and used as received. The Schiff bases 2b,c were
prepared by reacting 2,6-diformyl-4-methylphenol with the
amine RNH2 in 1:1 (in ethanol at 60 °C) and 1:2 (in boiling
ethanol) ratios, respectively.
P h ysica l Mea su r em en ts. Spectra were recorded on the
following equipments: UV-vis, Hitachi 330 spectrophotom-
eter; IR, Perkin-Elmer 783 IR spectrophotometer; 1H NMR,
Bruker 270-MHz FT NMR spectrometer (tetramethylsilane is
used as an internal standard). A Perkin-Elmer 240 C elemen-
MII(RL)(PPh3)2(CO)X (4)
expected trend: Os < Ru (for fixed R) and alkyl < aryl
(for fixed M). The oxidized complexes are unstable, and
attempted synthesis in bulk concentration by constant-
potential coulometry did not suceed.
b. M-O Clea va ge a n d Ca r boxyla te Ch ela tion .
In view of the presence of the motif 8, it seemed possible
that 3 and 4 might act as ligands for binding a second
metal (M′) at the N,O sites via proton displacement as
in 9. The high affinity of copper(II) for salicylaldi-
mines28 led us to try copper(II) as M′. The reaction of
Ru(MeC6H4L)(PPh3)2(CO)Cl with copper(II) acetate
monohydrate in aqueous organic solvent yielded a
(29) Stephenson, T. A.; Wilkinson, G. J . Inorg. Nucl. Chem. 1966,
28, 945.
(30) Hoffman, P. R.; Caulton, K. G. J . Am. Chem. Soc. 1975, 99,
4221.
(31) Dwyer, F. P.; Hogarth, J . W. Inorg. Synth. 1957, 5, 204.
(32) (a) Ullmann, F.; Brittner, K. Chem. Ber. 1909, 42, 2539. (b)
Gagne, R. R.; Spiro, C. L.; Smith, T. J .; Hamann, C. A.; Thies, T. J .;
Shiemke, A. K. J . Am. Chem. Soc. 1981, 103, 4073.
(33) Ghosh, P.; Pramanik, A.; Bag, N.; Lahiri, G. K.; Chakravorty,
A. J . Organomet. Chem. 1993, 454, 237.
(23) J ohnson, C. E., J r.; Bovey, F. A. J . Chem. Phys. 1958, 29, 1012.
(24) Mahapatra, A. K.; Datta, S.; Goswami, S.; Mukherjee, M.;
Mukherjee, A. K.; Chakravorty, A. Inorg. Chem. 1986, 25, 1715.
(25) Chevalier, P.; Sandorfy, C. Can. J . Chem. 1960, 38, 2524.
(26) Favrot, J .; Vocelle, D.; Sandorfy, C. Photochem. Photobiol. 1979,
30, 417.
(27) Sharma, G. M.; Roels, O. A. J . Org. Chem. 1973, 38, 3648.
(28) Holm, R. H.; Everett, G. W., J r.; Chakravorty, A. Prog. Inorg.
Chem. 1966, 84, 7.
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3046 Organometallics, Vol. 15, No. 13, 1996
Ghosh et al.
Ta ble 5. Cr ysta l, Da ta Collection , a n d Refin em en t
tal analyzer was used to collect microanalytical data (CHN).
Magnetic susceptibilities of solids were measured with a Model
155 PAR vibrating-sample magnetometer fitted with a Walker
Scientific L75FBAL magnet. Electrochemical measurements
were performed under nitrogen atmosphere on a PAR 370-4
electrochemistry system as reported earlier.33 All potentials
reported 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.
P r ep a r a tion of Com p lexes. The complexes having R )
aryl were synthesized by reacting M(PPh3)3X2 with the pre-
formed Schiff monobases (2b), and those with R ) alkyl were
prepared from the dialdehyde (2a ) in the presence of the
corresponding primary amines. Yields were generally 90-95%
on the basis of M(PPh3)3X2. Details are given for representa-
tive cases.
Ca r b on ylb r om o[4-m et h yl-6-(N-p-t olylim in om et h yl)-
p h en ola to-C2,O]bis(tr ip h en ylp h osp h in e)osm iu m (II), Os-
(MeC6H4L)(P P h 3)2(CO)Br . To a solution of 2-formyl-4-
methyl-6-(N-p-tolyliminomethyl)phenol (40 mg, 0.15 mmol) in
hot ethanol (25 mL) was added Os(PPh3)3Br2 (115 mg, 0.10
mmol). The mixture was heated to reflux for 2 h. A violet
solution was formed, from which a dark violet solid progres-
sively deposited. The solution was cooled to complete the
deposition. The solid was filtered out, washed thoroughly with
ethanol, and dried in vacuo. Anal. Calcd for OsC52H44NO2P2-
Br: C, 59.62; H, 4.24; N, 1.34. Found: C, 59.60; H, 4.28; N,
1.33.
P a r a m eter s for Os(EtL)(P P h 3)2(CO)Br ‚CH2Cl2
mol formula
mol wt
cryst syst
space group
a, Å
C48H44NO2P2Cl2BrOs
1069.8
monoclinic
Cm
18.389(8)
b, Å
14.880(5)
c, Å
10.134(3)
â, deg
123.13(3)
2322(1.5)
V, Å3
Z
D
2
calcd, g cm-3
1.530
temp, °C
radiation
λ, Å
22
Mo KR (graphite monochromated)
0.710 73
ω
38.28
0.1953-0.2332
3.42
3.81
1.19
scan technique
µ, cm-1
transm coeff
R,a
%
Rw,b %
GOFc
a
b
2
R ) ∑||Fo| - |Fc||/∑|Fo|. Rw ) [∑w(|Fo| - |Fc|)2/∑w|Fo| ]1/2; w-1
) σ2|Fo| + g|Fo| ; g ) 0.0005. 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.
2
solution of Ru(MeC6H4L)(PPh3)2(CO)Cl (50 mg, 0.05 mmol) in
dichloromethane (20 mL) and acetone (20 mL) was added
dropwise an aqueous solution of Cu(MeCO2)2‚H2O (50 mg, 0.25
mmol). The mixture was stirred until the violet solution
turned yellow. The organic solvents were then removed in
vacuo leaving an aqueous suspension of a yellow residue which
was isolated by filtration, washed repeatedly with water, and
dried in vacuo. Anal. Calcd for RuC54H47NO4P2: C, 69.19;
H, 5.06; N, 1.49. Found: C, 69.23; H, 5.00; N, 1.55.
X-r a y Str u ctu r e Deter m in a tion . A single crystal (0.16
× 0.20 × 0.54 mm3) of Os(EtL)(PPh3)2(CO)Br‚CH2Cl2 grown
(at 298 K) by slow diffusion of hexane into dichloromethane
solution was used. Cell parameters were determined by a
least-squares fit of 30 machine-centered reflections (2θ ) 15-
30°). Data were collected by the ω-scan technique in the range
3° E 2θ E 55° 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 significant intensity reduction. All data were
corrected for Lorentz-polarization effects, and an empirical
absorption correction was done on the basis of azimuthal scan
of six reflections.34 Of the 3036 reflections collected, 2950 were
unique of which 2787 were taken as observed (I > 3σ(I)) for
structure solution and refinement. On the basis of systematic
absences, possible space groups were Cm, C2, and C2/m.
Successful structure solution was achieved in the Cm space
group only.
The metal atom was located from Patterson maps, and the
rest of the non-hydrogen atoms emerged from successive
Fourier synthesis. The structure was refined by full-matrix
least-squares procedures. The Me group of the Et substituent
is disordered with respect to the mirror plane. All non-
hydrogen atoms were refined anisotropically, and the hydrogen
atoms were added at calculated positions with fixed U ) 0.08
Å2 in the final cycle of refinement. The highest residual was
1.20 e Å-3 close to the metal atom. All calculations were done
on a MicroVax II computer using the SHELXTL-PLUS pro-
gram package.35 Significant crystal data are listed in Table
5.
The complex Os(PhL)(PPh3)2(CO)Br was similarly prepared.
Anal. Calcd for OsC51H42NO2P2Br: C, 59.27; H, 4.10; N, 1.35.
Found: C, 59.32; H, 4.04; N, 1.38.
Ca r bon ylbr om o[4-m eth yl-6-(N-m eth ylim in iom eth yl)-
p h en ola to-C2,O]bis(tr ip h en ylp h osp h in e)osm iu m (II), Os-
(MeL)(P P h 3)2(CO)Br . To a solution of 2,6-diformyl-4-
methylphenol (50 mg, 0.30 mmol) in warm ethanol was added
a 40% aqueous solution of methylamine (25 mg). The resulting
solution was heated to reflux for 0.5 h. Thereafter Os(PPh3)3-
Br2 (250 mg, 0.22 mmol) was added to the hot solution and
heating was continued for an additional 2 h. A red solid
separated, and the mixture was then cooled and finally filtered.
The solid residue was washed thoroughly with cold ethanol
and dried in vacuo. Anal. Calcd for OsC46H40NO2P2Br: C,
56.88; H, 4.15; N, 1.44. Found: C, 56.91; H, 4.10; N, 1.43.
The complex Os(EtL)(PPh3)2(CO)Br was similarly synthe-
sized. Anal. Calcd for OsC47H42NO2P2Br: C, 57.28; H, 4.30;
N, 1.42. Found: C, 57.22; H, 4.29; N, 1.43.
Ca r b on ylch lor o[4-m et h yl-6-(N-p-t olylim in om et h yl)-
p h e n ola t o-C2,O]b is(t r ip h e n ylp h osp h in e )r u t h e n iu m -
(II), Ru (MeC6H4L)(P P h 3)2(CO)Cl. To a solution of 2-formyl-
4-methyl-6-(N-p-tolyliminomethyl)phenol (40 mg, 0.15 mmol)
in hot ethanol (25 mL) was added Ru(PPh3)3Cl2 (100 mg, 0.10
mmol). The mixture was heated to reflux for 0.5 h. Upon
cooling, a dark violet solid separated, which was collected by
filtration, washed thoroughly with cold ethanol, and dried in
vacuo. Anal. Calcd for RuC52H44NO2P2Cl: C, 68.35; H, 4.85;
N, 1.53. Found: C, 68.49; H, 4.79; N, 1.49.
The complex Ru(PhL)(PPh3)2(CO)Cl was similarly prepared.
Anal. Calcd for RuC51H42O2P2Cl: C, 68.08; H, 4.70; N, 1.55.
Found: C, 67.98; H, 4.67; N, 1.58.
Ca r b on ylch lor o[4-m et h yl-6-(N-m et h ylim in om et h yl)-
p h e n ola t o-C2,O]b is(t r ip h e n ylp h osp h in e )r u t h e n iu m -
(II), Ru (MeL)(P P h 3)2(CO)Cl. This complex was prepared by
the same procedure as used in the case of Os(MeL)-
(PPh3)2(CO)Br. Only Ru(PPh3)3Cl2 (200 mg) was used in place
of Os(PPh3)3Br2. Anal. Calcd for RuC46H40NO2P2Cl: C, 65.96;
H, 4.81; N, 1.67. Found: C, 65.88; H, 4.71; N, 1.63.
The complex Ru(EtL)(PPh3)2(CO)Cl was similarly prepared.
Anal. Calcd for RuC47H42NO2P2Cl: C, 66.28; H, 4.97; N, 1.64.
Found: C, 66.23; H, 4.87; N, 1.58.
Com p u t a t ion of Ch em ica l Sh ift Du e t o P P h 3 R in g
Cu r r en ts. The required parameters computed from crystal-
lographic data of Os(EtL)(PPh3)2(CO)Br‚CH2Cl2 are (i) distance
(34) North, A. C. T.; Phillips, D. C.; Mathews, F. A. Acta Crystallogr.,
Sect. A 1968, A24, 351.
(35) Sheldrick, G. M. SHELXTL-Plus Structure Determination
Software Programs; Siemens Analytical X-ray Instruments Inc.: Madi-
son, WI, 1990.
Ca r bon yl(a ceta to)[4-m eth yl-6-(N-p-tolylim in om eth yl)-
ph en olato-C2]bis(tr iph en ylph osph in e)r u th en iu m (II), Ru -
(MeC6H4L)(P P h 3)2(CO)(MeCO2). To a vigorously stirring
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New Os and Ru Organometallics
Organometallics, Vol. 15, No. 13, 1996 3047
of the concerned proton from the centroid (G) of each PPh3
phenyl ring and (ii) the angle between each distance vector
and the normal to the plane of the phenyl ring at G. From
these distances and angles the cylindrical coordinates36 F and
z of the concerned proton were calculated in units of the radius
of the benzene hexagon.23 The F and z values were then used
to compute the shift with the help of available isoshielding
plots.23 The net shift was calculated by summing up individual
contributions. Further details are given in a dissertation.37
cial support. Affiliation with the J awaharlal Nehru
Centre for Advanced Scientific Research, Bangalore,
India, is acknowledged.
Su p p or tin g In for m a tion Ava ila ble: For Os(EtL)(PPh3)2-
(CO)Br‚CH2Cl2, tables of complete bond distances (Table S1)
and angles (Table S2), anisotropic thermal parameters (Table
S3), hydrogen atom positional and U parameters (Table S4),
and non-hydrogen atomic coordinates and U values (Table S5)
(5 pages). Ordering information is given on any current
masthead page.
Ack n ow led gm en t. We are thankful to the Depart-
ment of Science and Technology, New Delhi, for finan-
OM960018B
(37) Ghosh, P. Chemistry of Heavier Transition Elements Particu-
larly Ruthenium and Osmium. Ph.D. Thesis, J adavpur University,
Calcutta, India, 1995.
(36) Margenan, H.; Murphy, G. M. The Mathematics of Physics and
Chemistry; D. Van Nostrand Co., Inc.: Princeton, NJ , 1956.
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