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Oxidation Reactions with УNakedФ Permanganate Ions under Aprotic Conditions.

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The unexpected reactivity of 1 presumably results from
an electron transfer from the Pt atom to [AuPPh3]@with
subsequent elimination of H @ . The resulting bimetallic
PtAu intermediate could then add a further [AuPPh3]@unit
to give 3. Alternatively, a w2-H intermediate might also be
involved. This would be relevant to reactivity studies on bimetallic platinum hydride complexes[71.
Received: December 19, 1983;
revised: February 15, 1984 [Z 658 IE]
German version: Angew. Chem. 96 (1984) 307
CAS Registry numbers:
1, 16842-17-4; 2, 89346-95-2; 3, 89346-97-4; AuCI(PPhx), 14243-64-2; Pt,
7440-06-4; Au, 7440-57-5.
[l] L. Abis, R. Santis, J. Halpern, J. Organomet. Chem. 215 (1981) 263.
[21 0. Bars, P. Braunstein, Angew. Chem. 94 (1982) 319; Angew. Chem. Int.
Ed. Engl. 21 (1982) 308.
[31 R. Ros, R. A. Michelin, R. Bataillard, R. Roulet, J . Organomet. Chem. 161
(1978) 75.
(41 Triclinic space group P i , 2 = 2 , a = 14.209(14), b=21.938(14),
C = 10.614(5)
a=81.65(6), b= 106.89(7), y=76.57(7)", V=2998(4) A3,
4204 observed reflections (I>3u(Q), MoKo irradiation, R =0.062,
R,, = 0.068. Further details on the crystal structure investigation can be
obtained from the Fachinformationszentrum Energie Physik Mathematik,
D-7514 Eggenstein-Leopoldshafen 2 by quoting the depository number
CSD 50764, the names of the authors, and the journal citation.
[ 5 ] P. Braunstein, J. Dehand, J . Organomet. Chem. 88 (1975) C24; P. Braunstein, U. Schubert, M. Burgard, Inorg. Chem., in press, and literature
cited therein.
161 P. G. Jones, Gold Bull. 14 (1981) 102; C. E. Briant, K. P. Hall, D. M. P.
Mingos, J. Chem. SOC.Chem. Commun. 1983, 843; E. Roland, K. Fischer,
H. Vahrenkamp, Angew. Chem. 95 (1983) 524; Angew. Chem. Int. Ed.
Engl. 22 (1983) 326.
171 See e.g.: G. Bracher, D. M. Grove, P. S. Pregosin, L. M. Venanzi, Angew.
Chem. 91 (1979) 169; Angew. Chem. Int. Ed. Engl. 18 (1979) 155; R. S.
Paonessa, W. C. Trogler, Inorg. Chem. 22 (1983) 1038.
[8] R. Bender, P. Braunstein, A. Tiripicchio, M. Tiripicchio-Camellini, J.
Chem. SOC.Chem. Commun. 1984, 42.
[9] Experimental: All reactions and operations, including the distillation of
the solvents, were carried out under N2. AgCF3SOI (0.260 g, 1.01 mmol)
was allowed to react with AuCI(PPh3) (0.500 g, 1.01 mmol) in 20 mL
THF. AgCl was filtered off and the solution was added to 1 (0.235 g,
0.50 mmol) in 10 mL THF. The reaction mixture became yellow and
acidic (pH monitoring) and after stirring for 1 min was filtered and concentrated. Addition of hexane and cooling to -15°C produced 3 as
white crystals. Suitable crystals for X-ray diffraction were obtained from
CH2C12/pentaneat - 15°C. Yield: 0.709 g (92%); m.p. 148°C (decomp.).
Correct elemental analysis (C, H).
A,
Oxidation Reactions with "Naked"
Permanganate Ions under Aprotic Conditions* *
By Hans Bock* and Dieter Jaculi
Dedicated to Professor Heinz Gerischer on the occasion
of his 65th birthday
In teaching basic chemistry, water-enveloped MnO: anions are introduced as the prototype of pH-dependent oxidation reagents"aJ and are used, inter alia, in "manganometric" analyses. "Naked", i.e. considerably less solvated
MnOF anions, which occur in aprotic solutions such as
"purple benzene", can readily be prepared by lipophilic
complexation of the counterions with crown ethers or
cryptands and be used for the selective oxidation of organic cornpounds1lb1;for example, for the synthesis of
[*I Prof. Dr. H. Bock, DipLChem. D. Jaculi
Institut fur Anorganische Chemie der Universitat
Niederurseler Hang, D-6000 Frankfurt am Main 50 (FRG)
[**I Radical Ions, Part 63. This work was supported by the Land Hessen, by
the Deutsche Forschungsgemeinschaft, and the A. Messer-Stiftung. Part
62: H. Bock, B. Roth, J. Daub, Z. Naturforsch. B, in press.
Angew. Chem. lnt. Ed. Engl. 23 (1984) No. 4
3,5-di-tert-butyl-o-benzoquinonein almost quantitative
yield [eq. (l)]['"I.
We have reinve~tigatedl~l
this model reaction of catechols, a class of compounds which is also of biochemical
interestc2'.Formation of water as a reaction product can be
prevented using the dialkali-metal catecholates, obtained
either from the catechol by treatment with butyllithium or
from the quinone by treatment with sodium- or potassiumamalgam. Under aprotic conditions and with repurified argon as inert gas, reaction (1) proceeds stoichiometrically as
a one-electron transfer (2) to yield the semiquinone radical
anion, which can be detected in the reaction solution by
ESR spectroscopy.
v
(M8 = Lie, Na8, KO)
Manganese dioxide is not precipitated since the MnOZe
dianion does not disproportionate under aprotic conditions['"]. Subsequent reaction of the semiquinone radical
anion with excess MnOF is not observed.
Numerous measurements corroborate this unexpected
result:
-
The half-wave potentials of the dialkali-metal catecholates determined by cyclic voltammetry both in the presence and absence of cryptands (Table 1) and especially
the ENDOR spectra of the ion pairs which contain the
semiquinone radical anion (Fig. 1) illustrate the influence of the alkali-metal cations[''.
Table 1. Half-wave potentials
[Vl and AE values [rnw for dialkali-metal
3,5-di-tert-butylcatecholates in the absence and presence of cryptands in
DMF/&N"CIOF, determined at room temperature relative to SCE (scan
rate 100 mV/sec).
A2'[a]
2 M" [Cryptand]
Li
"
+ [2. 1.11
Na"
+ [2.2.1]
K"
+[2.2.2]
nBu4N" [b]
E#
AE
E\?2
AE
-0.29
-0.44
-0.38
-0.44
-0.43
-0.4.5
-0.4X
100
80
90
90
80
90
100
-0.74
-1.1
-0.75
-1.1
-0.86
-1.1
-1.29
100
irrev.
90
irrev.
90
irrev.
200
Both sets of data, the potentials Ey)2 (Table 1) and the
radical anion coupling constants aH,M(Fig. 1), can be linearly correlated with the characteristic cation quantity
charge/ionic r a d i ~ s l ~ After
, ~ ] . cryptand complexation or
with the large cation tetra-n-butylammonium as counterion, the half-wave potentials for the catechol dianion
0 Verlag Chemie GmbH, 0-6940 Weinheim, 1984
0570-0833/84/0404-0305 $02.50/0
305
and for the semiquinone radical anion in dimethylformamide (DMF), for example, approach - 1.29 V (irreversible ; presumably due to subsequent reaction) and
- 0.48 V (quasi-reversible, cf. Table 1; theoretical value
for a reversible potential AE = 60 mv), respectively. The
ion-pair interactions detected by cyclic voltammetry or
by ENDOR spectroscopy in the redox reaction ( 2 ) under
the conditions chosen here are therefore reduced to an
approximately negligible amount by addition of cryptand.
For the "naked" MnO," anion with K@([18]crown-6)as
counterion, the cyclic voltammogram in DMF affords a
quasi-reversible (AE=80 mv) half-wave potential at
- 0.73 V versus SCE; this is shifted by more than 1 V relative to the value of 0.32 v[']measured in aqueous solution versus the calomel electrode (SCE)! Compared to
the Mn0," reduction in aqueous solution, in which the
presumably initially (kinetically controlled) formed
HMnO: monoanion cannot be observed because of
rapid subsequent reactions, the (thermodynamically determined) uptake of an electron to afford the nonprotonated MnO:'
dianion is therefore considerably handicapped in weakly solvating, organic solvents.
+
Under similar, aprotic conditions (Table l), the halfwave potentials of other redox equilibria, e.g. the hyperoxide ion or the radical anions of cyano-substituted nsystems, were, in part, re-determinedf3]in dimethylformamide and arranged in an electrochemical potential series (Fig. 2).
-
-1.58
-
-1.30
9
-1.5
&;
=
-1.0
->
I
!
VH
-0.5
-
10
I
,
12 MHz
SCE
'Rf
___)
,
+
0.4
Fig.
'Na
VH
I
I
2. Electrochemical potential series of redox systems in DMF/
%N"CIOF (0.1 M) at 298 K versus SCE.
Fig. l. ENDOR spectra of the Li (upper) and N a salts (lower) of 3,5-di-terfbutyl-o-benzosemiquinone radical anion at 190 K in tetrahydrofuran.
306
0 Verlag Chemie GmbH, 0-6940 Weinheim, 1984
Figure 2 indicates that MnO: can indeed oxidize the
dianion of 3,5-di-tert-butylcatechol, but not the semiquinone radical anion thus formed. Furthermore, electronrich n systems like tetrakis(dirnethy1amino)ethene
(ZE;= 5.95 eV['*]) or tetramethyl-p-phenylenediamine
(I&= 6.75 eV[5b1),which form isolable, stable radical cations such as Wursters' blue, are also unable to transfer an
electron to Mn0: in aprotic solutions; traces of e.g. water
are required to initiate the MnO: reduction [cf. (l)], leading to precipitation of manganese dioxidec3].In contrast,
dicyano-substituted benzene radical anions-characterized
by the disappearance of their ESR signals-are immediately discharged to the neutral compound. Deep green solutions Of the Mno:e dianion in DMF remain in the redox reaction with the hyperoxide radical aniod3].
0570-0833/84/0404-0306 $02.50/0
Angew. Chem. Inl. Ed. Engl. 23 (1984) No. 4
w
Many feasible electron transfers between thermodynamically controlled redox systems can be deduced from the
electrochemical potential series (Fig. 2), such as the titration of Wursters' blue [R2NC6H4NRF@]IQ
with the electron-rich (R2N)2C=C(NR2)2to the neutral compound
R2NC6H4NR2and the radical cation (R2N)2C=C(NR2k@Q,
which can be followed by ESR s p e c t r o s ~ o p y ~ ~ ~ .
Orange colored, monoclinic crystals of 1 contain tetrameric molecules (C2 symmetry). The sides of a planar, almost square arrangement of Cu atoms are bridged by
Co(CO), tetrahedra whose edges pointing towards the Cu
atoms are greatly lengthened by the formation of Cu-Co
bonds. In the Cu4C04 ring thus formed, Co atoms project
out oppositely from one another from the Cud-plane
(48.5(1) and -68.3(1) pm). Two arrays of seven carbonyl
groups, one above and one below the metallacycle, form
two layers representing fragments of layers in a close
packed structure; the two remaining CO groups of a molecule (CO' groups) are located between these (C0)Jayers
(Figs. 1 and 2).
Received: December 22, 1983;
supplemented: February 3, 1984 [Z 669 IE]
German version: Angew. Chem. 96 (1984) 298
t
CAS Registry numbers:
MnO; . K + , 7722-64-7; MnO,, 14333-13-2; n-Bu4N+ . CIO:, 1923-70-2;
3,5-di-rert-butylpyrocatechol dianion dilithium salt, 61373-03-3; 3,5-di-tertbutylpyrocatechol dianion disodium salt, 61373-02-2; 3,5-di-ferf-butylpyrocatechol dianion dipotassium salt, 89398-62-9; 3,5-di-terf-butyl-o-benzosemiquinone lithium salt, 4942-48-7; 3,5-di-ferf-butyl-o-benzosemiquinone
sodium salt, 54858-88-7; 3,5-di-fert-butyl-o-benzosemiquinone
potassium salt,
4942-49-8; 3,5-di-tert-butylpyrocatecholdianion, 65767-24-0; 3,5-di-rert-butyl-0-benzosemiquinone, 34515-66-7; [2.2.2lcryptand, 23978-09-8; 3,5-di-tertbutyl-o-benzoquinone, 3383-21-9.
[I] a) Cf. e.g. Hollemann-Wiberg: Lehrbuch der Anorgunischen Chemie, 90th
edit., de Gruyter, Berlin 1976, p. 204f., 908f.; b) cf. e.g. F. Vogtle, E. Weber, U. Elben, Konfukte (Merck) 1980 (2), 36 and literature cited therein;
c) G. W. Gokel, H. D. Durst, Synthesis 1976, 168.
[2] Cf. M. D. Stallings, M. M. Morrison, D. T. Sawyer, Inorg. Chem. 20
(1981) 2655,4257 and literature cited therein.
[3] D. Jaculi, Diplomarbeit, Universitat Frankfurt 1983 and literature cited
therein. For reactions of the hyperoxide radical anion cf. E. J. Nanni, M.
D. Stallings, D. T. Sawyer, J. Am. Chem. SOC. 102 (1980) 4481; or for
reactions of cyano-substituted benzenes: P. H. Rieger, I. Bernal, W. H.
Reinmuth, G. K. Fraenkel, J. Am. Chem. Sac. 85 (1963) 683.
[4] Cf. H. Bock, B. Hierholzer, F. Vogtle, G. Hollmann, Angew. Chem. 96
(1984) 74; Angew. Chem. I n f . Ed. Engl. 23 (1984) 54; and literature cited
therein.
[5] a) B. Cetinkaya, G. H. King, S. S. Krishnamurthy, M. F. Lappert, J. B.
Pedley, Chem. Commun. 1971, 1370; b) cf. W. Kaim, H. Bock, Chem. Ber.
111 (1978) 3843 and literature cited therein.
Preparation and Crystal Structure of CUCO(CO)~:
A Carbonylheterometal Complex Containing a
Cu4C04-Ring**
By Peter Klufers*
Structural investigations on compounds of the type
E[CO(CO)~]~
in which n > 2 (E=Zn, Hg, In, Bi) have
shown that in the crystalline state monomeric molecules
with E-Co bonds are present in which E is of normal valence and fully coordinated[']. For n = 1 (E= alkali metal,
Tl'), structural parameters are available for ionic compounds E@[Co(C0),le not having short E-Co contacts[21,
and for AgCo(CO), 2, a compound with Ag-Co bonds in
which coordinative saturation of the Ag atoms is reached
in tetrameric molecules with a planar Ag4C04ring131.
We have now been able to prepare the lighter homologue CuCo(CO), 1 by reaction of NaCo(C0)' in tetrahydrofuran with a hydrochloric acid solution of CuCl (molar
ratio 1 : 1) and to elucidate its str~cture~'~.
[*] Dr. P. Klufers
lnstitut fur Anorganische Chemie der Universitat
Greinstrasse 6, D-5000 Koln 41 (FRG)
[**I This work was supported by the Landesamt fur Forschung, NordrheinWestfalen.
Angew. Chem. Inr. Ed. Engl. 23 (1984) No. 4
Fig. 1. Molecular structure of the bimetal complex 1 in the crystal. Atomic
distances in the heavy-atom skeleton: C:o(I)-Cu(1) 237.2(10), Co(l)-Cu(2)
236.0(3), Co(2)-Cu(1) 236.4(9), Co(2)-Cu(3) 236.5(7), Cu( I)-Cu(2) 273.1(4),
Cu(l)-Cu(3) 270.3(4). Angles ["I in the CulCol ring at: Co(1) 69.65(6), Co(2)
70.55(4), Cu(l) 167.41(4), Cu(2) 158.07(6), Cu(3) 158.42(8). Bold- and thinlined CO groups form densely packed layers above and below the Cu4 plane,
respectively. The two CO' groups not incorporated in the close packing are
shaded.
Related compounds with an eight-membered ring of alternately arranged transition- and d'O-elements are
[CdFe(CO),],. 2 (CH3)2C0and [ ( T ~ ~ - C H ~ C ~ H , ) M ~ ( C O ) ~ H ~ ]
3['l. Molecules containing a central Cu4 unit are known for
a series of organocopper(1) compounds, where the Cu-Cu
distances are about 30 pm shorter than in 1161.Mutual interaction between the metal atoms should have little if any
influence on the molecular structure of organocopper(1)
compoundsI6l,whereas bonding between the Hg atoms has
been discussed in the case of the metallacycle 3.
A comparison of the structure of 1 with that of the silver
compound 2 reveals two outstanding differences : firstly,
in 2 the metal framework is almost planar, while in 1 the
CO atoms are not in the Cud plane; secondly, the Co(CO)'
groups in 2 deviate about 10" more from the tetrahedral
structure than in 1.
The crystal structures must be taken into consideration
for an explanation of these effects, which are probably
caused by the difference in size of the Cu and Ag atoms. In
the structural chemistry of the tetracarbonylcobaltates
ECO(CO)~,
two types of structure can be distinguished: 1)
close packing of E+4CO, with Co atoms in interstices
when E is large; 2) close packing of CO groups alone, with
Co and E in interstices when E is smaller[21.
The former type of structure is present in crystals of 2,
whereas the crystal structure of 1 can be derived from a
strongly distorted, close packing of CO groups. The (CO),fragments of close-packed layers formerly present in the
molecule are part of close-packed CO planes in the crystal.
These planes are distorted by CO' groups which group
pairwise at one position in the close arrangement (Fig. 2).
0 Verlug Chemie GmbH, 0-6940 Weinheim, 1984
0570-0833/84/0404-0307 $02.50/0
307
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