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Cateholates as - and -Donationg Ligands The Synthesis and Structure of (Et4N)2[W(CO)4(O2C6H4)] and the УSixteen ElectronФ Analogue Resulting from CO Dissociation.

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(&, = 0.032); equivalent reflections were merged. The structure was solved by a combination of Patterson and difference Fourier techniques. The
final cycle of full-matrix least-squares refinement was based on 5784 observed reflections ( I > 3.00a(I)) and 326 variable parameters and converged
(largest parameter shift was less than 0.009 times its esd) with R = 0.060
and R , = 0.063. A final difference Fourier map showed no chemically
significant features. Crystal data are a = 13.084(2), b = 13.089(2),
c =13.194(2) ,&,a = 60.08(1),8 = 64,78(1),y =72.88(1)”, V =1762(1)A3,
space group Pi,Z = 2. Further details of the crystal structure investigation may be obtained from the Facbinformationszentrum Karlsruhe, Gesellschaft fur wissenschaftlich-technische Information mbH, D-W-7514
Eggenstein-Leopoldshafen 2 (FRG), on quoting the depository number
CSD-56535, the names of the authors, and the journal citation.
Catecholates as c- and n-Donating Ligands:
The Synthesis and Structure of
( E ~ ~ N ) z [ W ( C ~ ) ~ ( ~ Z and
C , Hthe
,)~
“Sixteen Electron” Analogue Resulting from
CO Dissociation**
gen-bond lengths ( 0 .. ’ 0 2.535(10)
and tungsten to
oxygen-bond lengths of 2.175(11) A. One notable feature in
the structure is the deviation from linearity of the axial carbony1 groups (C-W-C angle of 167.3(8)”).
0131
n
Fig. 1. Ball-and-stick representation of the non-hydrogen atoms of the anion
of 1.
The complex 2 containing only coordinated catechol was
obtained by reacting 1.6 mmol of 1 with three equivalents of
By Donald J. Darensbourg,* Kevin K . Kluusmeyer,
Brian L. Mueller, and Joseph H . Reibenspies
Carbon dioxide insertion into the metal-oxygen bond of
metal hydroxides, alkoxides, and aryloxides is a fundamental step in several chemical and biochemical catalytic processes. Notable among these processes are the coupling of
CO, and epoxides to provide cyclic carbonates[’] or polymeric materials,”] and the hydration of CO, to afford carbonic acid.[31Attendant with reactions involving low-valent
anionic Group 6 metal alkoxy- or aryloxycarbonyl complexes is the lability of the carbonyl ligands which can subsequently lead to P-hydrogen elimination or metal aggregation
reaction^.'^' In this communication, we report the synthesis
and structural characterization of carbonyl catecholatotungsten complexes and the effect of the n-donating property of
these dihydroxo ligands on the reactivity patterns of the
metal complexes.
A solution of [W(CO),thf] (prepared photochemically
from 1.9 mmol of [W(CO),] in tetrahydrofuran) was transferred to a Schlenk flask containing 3.8 mmol of
(Et,N)(OC,H,OH) and stirred. An orange powder precipitated within one hour and orange crystals of 1 were isolated
by filtration (1.3 g or 90 % yield) and recrystallization from
CH,CN/ether. The infrared spectrum of 1 in CH,CN exhibited vco vibrations at 1975(w), 1829(vs), 1807(m, sh) and
1773(m) cm-’. Two sharp doublets of equal intensity were
observed for the CO ligands in the 13C NMR spectrum at
=131 Hz).
6 = 217.6 (Jw,c=I65 Hz) and 207.5
NaOMe in acetonitrile. Na,0,C,H4 and excess NaOMe
were removed by filtration through Celite, and dark orange
crystals (yield 0.91 g, 82 %) were obtained upon addition of
THF/Et,O to the filtrate. As anticipated, the vco vibrations
of 2 in CH,CN (1965(w), 1817(vs), 1800(m,sh) and 1763(m)
cm-’) are shifted to lower frequencies than those of 1, indicative of‘ some hydrogen bonding of 1 in solution as well.
Similarly the two 13C NMR resonances in CH,CN shift
downfield to 6 = 219.6 (Jw.c= 159 Hz) and 208.8
( J . , = 133 Hz). More importantly, in contrast to species 1, the carbonyl ligands in the non-hydrogen-bonded
form of the complex are fluxional. Coalescence of the two
carbonyl carbon signals into one symmetrical peak at
6 = 214.2 occurred at temperatures greater than
23°C.[71The activation parameters for the CO exchange
were determined to be AHq = 12.0 0.7 kcalmol-’ and
AS* = - 4.5 f 2.5 calK-’mol-’.[81 The facile nature of
this process is attributed to the n-donor property of the
catecholato ligand. This conclusion is supported by the fact
that upon addition of excess catechol, which forms hydrogen
bonds to the ligated catechol and hence diminishes its ndonor character, the fluxional process is slowed down.[”
Furthermore, in the instance where the catecholate ligand
contains electron-releasing tert-butyl substituents in the 3,5positions (+ 4), the coalescence temperature is much lower
than ambient temperature.
0
Definitive assignment of the structure of 1 was obtained
by X-ray crystallography; the result is shown in Figure 1.151
The solid-state structure of 1 is characterized by continuous
hydrogen bonding between the bridging catechol moiety and
two adjacent dianions. The structure shows typical hydro[*] Prof. Dr. D. J. Darensbourg, DipLChem. K. K. Klausmeyer,
Dr. B. L. Mueller, Dr. J. H. Reibenspies
Department of Chemistry, Texas A & M University
College Station, TX 77843 (USA)
I**]
This work was supported by the National Science Foundation (Grant
91-19737) and the Robert A. Welch Foundation.
Angew. Chrm. Inr. Ed. Engl. 1992, 31, No. 11
0 VCH
2,R=H
4, R = tBu
1
3,R=H
5, R = tBu
In a slower process, 2 readily expels CO to provide the
tricarbonyl derivative 3 [Eq. (a)].[1o1Formation of 3 was indicated by the two bands for the vco vibrations in CH,CN
Verlagsgesellschaft mbH. W-6940 Weinheim,1992
0570-0833~92/11ll-1503
$3.50+.25/0
1503
(1863(s) and 1726(vs) cm- '), and a single broad 3C NMR
signal at 6 = 234.2 at - 35 "C. Upon exposing an acetonitrile
solution of 3 to a carbon monoxide atmosphere, 2 is regenerated rapidly and quantitatively. Hence, an equilibrium between the 18-electron complex 2 and its formally "16-electron" unsaturated species 3 exists in solution. Because the
reaction is carried out in a strongly coordinating solvent,
CH,CN, it is possible that CH,CN is in the coordination
sphere of 3.
Synthesis of the 3,5-di-tert-butyl derivative of 2 was accomplished in a completely analogous manner. The vco region of the solution infrared spectrum indicated the presence
of both the tetra- and tricarbonyl species (4 and 5)even in the
absence of a CO atmosphere, that is, a four band pattern
(1962(w), 1815(s), 1796(m,sh), and 1755(m)cm-') and a two
band pattern (1859(s) and 1721(vs) cm-I), respectively.
Consistent with the presence of the electron-donating t-butyl
groups, this equilibrium lies farther to the right than that
formulated in Equation (a). The 3C NMR spectrum of the
tetracarbonyl derivative, stabilized by a CO atmosphere, exhibited three resonances at 6 = 220.2,219.8, (Jw,c= 161 Hz)
and 209.0 (Jw,c= 136 Hz) of intensity ratio I : 1 :2 at -40 "C.
That is, the two equatorial CO ligands are not equivalent
because of the unsymmetrically substituted catecholate ligand. The coalescence of the three carbon signals occurred at
temperatures above 5 "C.
Proof of the structure of the tricarbonyl derivative 5 was
obtained by X-ray crystallography (Fig. 2).["] The structure
is quite similar to that previously reported for its manganese
analogue,['21in which the coordination geometry is interme-
h
kL
C1161 .
Fig. 2. Ball-and-stick representation of the non-hydrogen atoms of the anion
of 5.
diate between trigonal bipyramidal and square pyramidal,
and there is no CH,CN in the metal's coordination sphere.
The tungsten atom lies out of the plane defined by the two
carbonyl carbon atoms, C1 and C2, and one of the catecholate's oxygen atoms 0 5 by 0.048 (towards the axial 0 4
atom). The 04-W-C3 angle is 166.7'. The W-05 bond,
which is ortho to the electron-releasing t-butyl substituent, is
significantly shorter than the W-04 bond (2.059 vs.
2.1 54 A). Indeed, both W-0 bond lengths are shorter than
those in the tetracarbonyl species 1. Concomitantly, the WC1 bond, which is closest to trans to 0 5 (cO5-W-Cl =
143.3 is the shortest W-C bond. The bond lengths within
O),
1504
0 VCH
Verlagsgesellschaft mbH, W-6940 Weinheim, 1992
the catecholato ligands in complexes 1 and 5 are extremely
similar.
These results emphasize the emerging opinion that strongly n-donating hydroxo ligands stabilize unsaturated
organometallic derivatives.[' 31 The reactivity of the coordinatively unsaturated derivatives 3 and 5 with dihydrogen or
carbon dioxide are currently under investigation. Preliminary observations indicate that these catecholato complexes
readily react with one equivalent of CO, at low temperature
to afford cyclic carbonato metal complexes.
Received: June 19, 1992 [Z 5418 IE]
German version. Angen. Chem. 1992. f04, 1501
CAS Registry numbers:
1, 143958-31-0; 2, 143958-30-9; 3, 143958-33-2; 3 . CH,CN, 143958-35-4;
4, 143958-37-6; 5, 143958-39-8.
[I] a) R. J. De Pasquale, J. Chem. SOC.Chem. Commun. 1973, 157; b) J. E.
Blckvall, 0. Karlsson, S . 0. Ljunggren, Tetrahedron Lett. 1980, 4985;
c) M. Ratzenhofer. H. Kisch, Angew. Chem. 1980,92,303; Angew. Chem.
Int. Ed. Engl. 1980, 19,317; d) D. P. Klein, J. C. Hayes, R. G. Bergman, J.
Am. Chem. Sor. 1988, 110, 3704; e) K.-T. Aye, L. Gelmini, N. C. Payne,
J. J. Vittal, R. J. Puddephatt, ibid. 1990, ff2, 2464.
[2] a) S. Inoue, CHEMTECH 1976, 588; b) A. Rokicki, W. J. Kuran, Macromol. Sci-Rev. Macromol. Chem. 1981, CZf(l), 135; c)T. Aidd, M.
Ishakawa, S. Inoue, Macromolecules 1986, 19, 8.
131 a) R. S. Brown in Enzymatic and Model Carboxylation and Reduction Reactions f o r Carbon Dioxide Utilization (NATO ASI Ser. C 1990, 314,
145-180): b) R. Alsfasser, S . Trofimenko, A. Looney, G. Parkin, H.
Vahrenkamp, Inorg. Chem. 1991,30, 4098; c) R. Han, G. Parkin, J. Am.
Chem. SOC.1991, 113, 9707.
[4] a) P. A. Tooley, C. Ovalles, S . C. Kao, D. J. Darenshourg, M. Y Darensbourg, 1 Am. Chem. Sor. 1986,108,5465; b) T. J. McNeese, T. E. Mueller.
D. A. Wierda, D. J. Darensbourg, T. J. Delord, Inorg. Chem. 1985, 24,
3465; c) T. J. McNeese, M. B. Cohen, B. M. Foxman, OrganometaNirs
1984, 3, 552; d) D. J. Darensbourg, K. M. Sanchez, J. H. Reibenspies,
A . L. Rheingold, J Am. Chem. SOC.1989,f i f , 7094: e) D. J. Darensbourg,
B. L. Mueller, J. H. Reibenspies, C. J. Bischoff, Inorg. Chem. 1990, 29,
1789; f) D. J. Darensbourg, B. L. Mueller, C. J. Bischoff, C. C. Johnson,
K. M. Sanchez, J. H. Reibenspies, Isr. J. Chem. 1990, 30, 369.
[5] 1: Crystallographic data (- 80°C): a =17.742(5), b =19.452(5),
c = 10.345(2) A, 2 = 4, spacegroup Pnu2,; 2306 reflections with I > &(I)
used, R = 0.050, R , = 0.049 [14].
[6] a) K. Osakada, Y Kim, M. Tanaka, S . Ishiguro, A. Yamamoto, Inorg.
Chem. 1991,30,197; h) Y Kim, K. Osakada, A. Takenaka, A. Yamamoto,
J Am. Chem. Sor. 1990, f i2,1096; c) S. E. Kegley, C. J. Schaverien, J. H.
Fruedenberger. R. G. Bergman, S. P. Nolan, C. D. Hoff, J. Am. Chem.
SOC.
1987,109,6563;d) D. Brdga, P. Sabatino, C. Di Bugno, P. Leoni, M.
Pasquali, J Organomet. Chem. 1987, 334, C46.
[7] a) NMR spectra were simulated by a density matrix procedure (software
by Dr. John Horner at Wayne State University) for an exchange between
two sites of equal population to determine rate constants: b) J. I. Kaplan,
J. Chem. Phys. 1958, 28. 278; ibid. 1958, 29, 462.
[XI Activation parameters were calculated by the method of Christian and
Tucker. S. K. Christian, E. E. Tucker, Am. Lab. (Fairfield, C T ) 1982, 14
(X), 36; S. D. Christian; E. E. Tucker Am. Lab. (Fairfield, C T ) 1982,14(9),
31.
[9] A slight excess of catechol was added to the NMR tube containing the
sample used in the variable temperature experiment. After addition of the
alcohol the I3C NMR spectrum showed no broadening of the axial and
equatorial carbonyl resonance signals at ambient temperature.
[lo] Preliminary rate measurements for CO dissociation in these derivatives
indicate rate constants in the range of lo-' sec-' at 5 "C, whereas the rate
constant for intramolecular CO exchange at 0°C was determined to be
153 secc'.
1111 5: Crystallographic data (- 80°C): a =18.089(4), b = 8.618(2), r =
22.194(5) A, f3 = 91.25(2)", V = 3459.0(14) A', Z = 4, space group C2;
3266 reflections with I > 2 4 1 ) used, R = 0.047 and R, = 0.048 [14].
[12] F. Hartl, A. VlEek. Jr., L. A. deleark, C. G. Pierpont, Inorg. Chem. 1990,
29, 1073.
[13] D. M. Lunder, E. B. Lobkovsky, W. E. Streib, K. G. Caulton, J. Am.
Chem. Soc. 1991, 113, 1837.
1141 Further details of the crystal structure investigations are available on request from the Fachinformationszentrum Karlsruhe, Gesellschaft fur wissenschaftlich-technische Information mbH, D-W-7514 Eggenstein-Leopoldshafen 2 (FRG), on quoting the depository number CSD-56480, the
names of the authors, and the journal citation.
0570-0833/92jflff-1504 $3.50+ .25/0
Angew. Chem. In(. Ed. Engl. 1992, 31, No. i f
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structure, synthesis, electrons, donations, o2c6h4, уsixteen, dissociation, resulting, cateholates, ligand, et4n, analogues
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