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CyanideЦIsocyanide Isomerism in CN-Bridged Organometallic Complexes.

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Cyanide- lsocy anide Isomerism in CN-Bridged
Organometallic Complexes**
N i a n y o n g Zhu and Heinrich Vahrenkainp*
Fig. 1. Molecular structure of 2. Selected bond length, [pni] and angles [ I: Zn-CI
219.8(1). Zn-O 202.0(4): 0 - Z n - 0 100.2(2). C1-Zn-Cl 130.0(1). CI-Zn-0 105.0(1)
and 106.5(1). Zn-0-C 127.3(4).
standard range, except for a slight increase of the CI-Zn-CI
angle. Thus, there are no bonding features supporting the argument that such complexes should be difficult to obtain. This in
turn means that unusual steric hindrance or the presence of
special chalcogenolate hgands"*] are not prerequisites for their
isolability. However. care must be taken in handling the compounds, since they are extremely hygroscopic. The structure
(also obtained crystallographically) of 3, which initially resulted
from accidental access of water, underlines this.
The comparison of 1.2, and 3 points to the subtleties governing the coordination behavior of the three aldehydes. In solid 1
the aldehyde donor seems to be unable to compete with a Zn-CI
unit for a coordination position on zinc despite the large excess
of the aldehyde in solution. In 2 the p-methoxy substituent on
the phenyl ring has sufficiently increased the donor capacity of
the aldehyde to enable this. Complex 3 shows yet another way
of balancing the donor abilities of the aldehyde and chloro
ligands: one zinc ion binds both chelating aldehydes. the second
one is only coordinated by chloro ligands.
These findings underline the ambiguity about the inode of
coordination of the aldehydes. which is due to their low donor
capacity. This in turn means that mechanistic implications
about metal salt mediated organic reactions of aldehydes[" 1 3 ]
may have an equally high degree of ambiguity.
Received: May 9, 1994 [Z 6911 IE]
Geriixin version: Ati~zcii.Chrtii. 1994. 106. 2164
[ I ] a) C h n t ~ " h r r , . s i l r Organic C h e n i u r r j , V d . I (Eds.: D. Barton. W D. Ollis. J. F.
Stoddart). Pergamon, Oxford. 1979; b) R. Brettle in ref [ l a ] , pp. 943- 1016;
c)T. Laird in ref. [ l a ] . pp. 1105 -1160
121 Y. H. Huanp. J. A. Cladysr. J Climi. €dirt. 1988. 6i. 298 303.
[3] Papers [hat conlain srructural data: D. Hall. A. J. McKinnon. T. N . Waters. J.
C h i . Snc. 1965.425 -430; M. R. Truter. R . C. Watling, J C'hrm. So<..4 1967.
1955-1963, R. J. Hill. C. E. F. Rickard. J. Inorg. Nircl. Chcni. 1977. 3Y. 1593
1596; J. B. Hodgson. C C. Percy. S p ~ r r o c h i n iActa
.
Purr A 1978.34.777 780.
[4] F. Filippini. B. P. Suw. Hrlr. Chrnr. A ~ r u1971. 54. 1175 1178. and references
therri n
[5] P. L. Verheijdt. P. H. van der Voort. W. L. Groeneveld. W. L. Driessen. R d .
TYIIK
C'iiini. P l i ~ - B a . !1972. 91. 1201 - 1204. and references therein.
[6] S. E. Denmark. B. R. Henke. E. Weber. J. A i n Clinii. So(. 1987. I O Y . 2512
2514.
17) Further structural studie3 involve ii Bi-, adduct of' anisaldehyde [ X a ] and a
MeAI(OR), adduct of rBuCHO [8 b]
[XI a ) T. M. Reetr, M . Hullmann, W. Massa. S. Berger. P. Radeinacher. P. Heyrnanns. J A m . C/iem. Soc. 1986. IOH. 2405-2408; b) M. €3. Power. S. G. Bott.
U. L. Clark. J. L. Atwood, A. R. Barron. Orxunonierullics 1990.9,3086-3097.
\
I. Bertini. C. Luchi[Y] H. Eklund, A. Jones. C . Schneider in Zinc,€ n ; y n i ~ ~(Eda.:
nat. W. Maret. M. Zepperauer). BirkhBuser, Basel. 1986. p p 377-392.
[lo] M. Bochmann, K. J. Webb, M. B. Hursthouae, M. Mazid. J C I i ~ n iSO<.
.
Cheni.
Coi?iniitii. 1991, 1735- 1737.
[ l l ] Previously described as a yellow powder: F. Filippini. B. P. Susz. H e h . Chnn.
4crn 1971. 54. 835-845.
(121 Crystal data for 2: space group P2,2,2, u = 896.4(1). h = 1991.8(6),
I' = 417 6( 1) pm, 1689 reflections. 105 parameters. R = 0.053. The inoleculc of
2 is bisected by ii twofold symmetriy axis. Further details of the crystal structure inve5tigation may be obtained from the Fachinformationszentrum Karl?.
ruhe. D-76344 Eggenstein-Leopoldshafen (FRG). on quoting the depository
number CSD-380052.
[I 31 ('~~nrpri,li(,/i.si,.e
O,-goiik S1.nrhrsr.s. I,ii/. 3 (Eds.: B. M. Trost. I. Fleming), Pergainon. Oxford. 1991
Bridged dinuclear complexes are a prime object of studies for
mixed valence and electron transfer."] Among these complexes
those with cyanide bridges have often been mentioned because
of their obvious relation with Prussian Blue.[21The actual number of studies of their redox and mixed-valence behavior. however, is still rather small.13]
We have started a systematic preparative, structural, and electrochemical investigation of cyanide-bridged complexes, in
search of "organometallic Prussian Blue".[41 Such complexes
are amazingly easy to prepare, since almost any organoinetallic
complex with cyanide ligands (neutral o r anionic) can be used as
a ligand itself for another organometallic unit. thereby establishing the CN links. Furthermore the oligonuclear species obtained this way seem to be highly inert towards M-CN-M' +
M -NC-M' isomerizations, which are a common fate of classical complexes with C N links. leading to the thermodynamically
preferred isomers.[', 5 1 This behavior has allowed us to prepare
and characterize for the first time stable pairs of organometallic
species with cyanideiisocyanide isomerism, that is species which
exist in the M(p-CN)M' as well as in the M(pNC)M' forms.[61
Here we report on two such pairs which relate to complexes
that we have described before. The first pair, 1 a and 1 b, can be
[CP(CO),F~(~J-CN)M~(CO),CPI [ C P ( C O ) ~ F ~ ( ~ ~ - N C ) M I ~ ( C O ) ~ C ~ I
la
Ib
derived from the pseudosymmetrical anion [Cp(CO),Mn(V-CN)M~(CO)~C
~ ]Replacing one neutral Cp(CO),Mn
.I4]
fragment on the left- or right-hand side of this complex by
an isoelectronic cationic Cp(CO),Fe fragment results in the pair
of isomers 1. Chemically this is achieved by either reacting
[Cp(CO),FeCN] in T H F with [(thf)Mn(CO),Cp] to give 1 a or
[Cp(CO),Fe(thf)]BF, in CH,Cl, with Na[Cp(CO),Mn-CN] to
give 1 b. Recrystallization from CH,CI,/petroleum ether provides 1 a and 1 b in 25 and 4 5 % yield, respectively.
Complexes 1 a (orange-red) and 1b (red) can be distinguished
by their colors, as evidenced by their absorptions in the visible
range showing a broad featureless band extending from the U V
for 1 a and one exhibiting a weak maximum at 495 nm for 1 b.
The differences in their vco bands and 'H N M R spectra are very
small.[91 However, the CN stretching frequency for l b
(2100 c m - ' ) is 50 cm-' lower than that for 1 a, which means
that for this pair of isomers the different electronic situations are
not accommodated by the M-CO units but by the bridging CN
ligand. The redox behavior of 1 a and 1 bI9' reflects the orientation of the bridging CN by a difference of 0.24 V in the E,:,(ox)
values.
The second pair of isomers completes a series of compounds
starting with 2 a and [2a]i.['01 While 2 a was obtained from
Na[Cr(CO),CN] and [BrFe(dppe)Cp] (dppe = 1,2-bis(diphenylphosphano)ethane),['O1 2 b was prepared from [(CO),Cr(thf)]
-
[*I
Prof. Dr. H Vahrenkamp. N . Zhu
Institut fur Anorganische und Analytische Chemie der Unikcrsitlt
Albertstrasse 21. D-79104 Freiburg (FRG)
Telefax: Int code + (761)203-6001
[**I This work was supported by the Ciraduiertenkolleg "Systeme mit ungepaarten
Elektronen" 'ind by the Landes-Sciiwerpunktprogwmm ..Elektroaktive Systeme fur die Sensorik".
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and [Cp(dppe)FeCN] in THF and recrystallized from CH,Cl,/'
petroleum ether in 62 "/o yield. Both isomers of 2. just like those
of I , cannot be interconverted thermally up to their decomposition points around 150 "C. 2 a (red) and 2 b (yellow) differ clearly
in their colors and in their optical absorption maxima (472 nm
for 2 a and 401 nm for 2 b ) . This time the fi(Cp) and v(CN)
v ~ ~ u K sare
~ "quite
'
similar, and the electronic difference is mostly
reflected in the CO vibrations.['I Specifically the A t band of the
Cr(CO), group which corresponds to the CO vibration /runs to
C N is about 30 cm-' higher for 2 a (1898 cm-') than for 2b.
This might be expected because N-bonded C N is a weaker
acceptor than C-bonded CN. A comparison of 2 b with
[(CO),CrNCMe] ( A : bands at 1869 and 1930 cm-', respectively) reveals clearly that the "ligand" [Cp(dppe)FeCN] in 2 b is
extremely electron-rich. Irrespective of this, the HOMOS of 2 a
and 2 b seem to be lower in energy than those of 1 a and 1 b. since
both complexes 2 are about 0.2 V more difficult to oxidize than
their counterparts
reveal that
The structure determinations of 2 a and 2b'".
it is almost impossible to distinguish the compounds in the solid
state. The crystals are isomorphous (but clearly distinguished by
their colors), and both structures can be presented by one drawing (Fig. l ) . The bonding parameters are all normal. The differ-
($
@=-a-
Fig. 1. Molecular geometry of 2 a and 2b. Pertinenl distances [pm] and angles [ ]
(values for 2 b in ?quare brackets) Cr-CCr-N 206.4(5) [208.6(3)].C-N 115.8(7)
[ I IS.l(S)]. Fe-N'Fe-C 193.5(4) [18Y.7(4)], Cr-C(CO t r ( i m ) 183.8(6) [184.4(5)], CrC ( C 0 ( I \ . iiverage) 188.6(6)[189.5(5)].Fe-P (average) ?20.2(1) [218.5(1)]: Cr-C(N)N(C) 1 70.7(4) [I 65. 1( 3 )I. Fe-N( C)-C(N) 169 .8(4) [I 74.3(4)]
ences between 2 a and 2 b are almost insignificant, but the trends
in the Cr-CN-Fe backbones are as expected. Thus, the M - N
distances are longer than the corresponding M -C distances
because ofweaker M-N vs. M-C backbonding, and the Fe-C
bond in 2 b is the shortest of the M-(CN) bonds because the
electron-rich iron unit has the most backbonding to offer, while
the C-N bond length shows very little variation. The largest
difference between 2 a and 2 b lies in the deviations from h e a r ity at the bridging C and N atoms. We consider this bending of
the moiecules to result from packing forces. Isomorphism, a
similar bending. and the near-to-identity of all bonding parameters were also observed for the pair of complexes [(NH3)sCo(p-L)Co(CN),] ( L = CN, NC).'*]
The spectroscopic and structural similarity within the pair of
isomers 2 a and 2 b, which may be explained by their delocalized
nature. extends itself to their cationic species. The molecular
structure of the cation in [2b] [BF,]["] is again most similar to
that of 2 a and 2b. and a detailed investigation has revealed that
the radical ion 2 b + possesses a high degree of charge delocalization.""
The physical properties of the isomers and their tolerance of
a change in the electron count underline the ability of the
cyanide ligand to act as a mediator and transducer of electronic
effects. The position of the v(CN) vibration in the IR spectrumLY1
and preliminary extended-Huckel MO calculations['31
indicate that the bridging cyanide ligand can respond to the
donor/acceptor properties of both organometallic units by variation of its electronic situation without altering its bond length.
just as has been observed for many solid-state metal-cyanide
compounds."41 Thus. it does not seem to be utterly unrealistic
to search for "organometallic Prussian Blue".
Received: May 9. lY94 [Z 6912 IE]
German version: Anpc,ii.. Chc,ni. 1994. 106. 2166
[I] C. Creutz. Prop. lnorg. C%rm. 1983. 30. 1-73.
[2] W. P. Fehlhammer, M . Friti. Chrm. Krv. 1993. Y3. 1243--1280.
[3] F. L. Atkinson, A. Christofides. N.G. Connelly. H. J. Lawson. A . C. Loyns.
D u l t o ~ il k u n \ . 1993.
A. G Orpen. G . M. Rosair. G . H. Worth. J. Cheni..%I(
1441-1450, and references therein: F. Scandola. R. Argazri, C. A. Bignozri. C .
Chiorboli. M. T. Indelli, N. A. Rdmpi. c'oorif. c'him. R e v 1993. 125. 283-292.
and references therein.
[4] First communication: B. Oawald. A. K. Powell. F. Rashwan. J. Heinie. 11.
Vdhrenkamp. Cheni. B w . 1990. 123. 243- 250.
[S] For a case of terminal M -NC + M -CN isomerization cl: S. Alviarez. C'.
Lopez. /iior~q. Chim. A c f o 1982, 64. LYV-LIOO
[6] Among the inert classical complexes two such pairs have been reported:
[(H,O),Cr(/i-CN)Co(CN),1 (spectroscopic characterrzition) [7] and
[ (NH,),Co(/i-CN)Co(CN),1 (structure determinations) [8].
[7] D. Gaswick, A. H a m . J. h i o , ~ N. u d . C'hetit. 1978. 40, 437- 439.
[8] F. R. Fronczek. W. P. Schaefer. /tior,q Client 1974. 13, 727 732.
[9] I R (CH,CI,): r(CO): l a : F[cm-l] = 2062s. 2017s. 1920s, 1843s: I b 2063\.
2018s. 1922s. 1854s; 2 a 2 0 5 6 ~ .1 9 3 0 ~ s 1898m:
.
2b: 2064%. 192Xvs. 1869ni.
i>(CN):la:2147vw: l b : 2 0 9 9 r n : 2 a : 2 1 1 5 ~ ~ : 2 b : 2 1 0 3 w' H
. NMR(h(Cp)TMS
mt., CDCI,): l a ' 5.07. 4.41; Ib: 5.08. 4 40: 2 a . 4.15: 2 b - 4.22. Cyclovoltammetric data (first oxidation. Evs. Ag;AgCl. CH,CN): I a : 0.1 1 V (quasi-rev.).
1 b: 0.35 V (rev.): 2 a : 0.31 V (rev.): 2 b : 0.53 V ( m e \ . ) .
[lo] N. Zhu. H. Vdhrcnkamp, J. Orjiimonicr. Chcm.1994. 472. CS C7.
[ I l l Crystal data: 2 a : space group P 2 , : c . 0=1501.4(1). /J =1299.5(1).
c =1718.2(l)pm. /l
= 95.49(1) . 5034rcflcctions. 424 parametcrs. R = 0.068.
2 b . space group P2,,c. u =1500.7(1). h =1297.6(1). ( =1716.4(2) pm. =
Y5.60(1) , 5314 reflectionc. 424parameters, K = 0.045 [I21
[I21 Further details of the crystal structure investigation muy be obtained upon
request from the Fachinforinalionsrentrum Karlsruhe. D-76344 EggensteinLeopoldshafen (FRO). on qnotinz the depository numbers CSD-380055 (for
2 a ) and CSD-380056 (for 2b).
1131 C Marchand. H Grutrmacher. private communication
1141 A . M . Golub, H. Kohler, V. V. Skopenko. C ~ I z m i i i s t r i(.I / P\e~uddiulirL.s( 7 i p . . \
in Iiiwquiiic fiiiil Gcnwiil Chiwti.vtrj, I id. 21 (Ed : R J. H. C l x k ) ) . Elsevier.
Amsterdam. 1986. pp. 77 185.
Calixarene-Based Macrocyclic Nonet (S = 4)
Octaradical and its Acyclic Sextet (S = 5/2)
Pentaradical Analogue**
A n d r z e j Rajca,* Suchada Rajca, a n d Raghavakaimal
Padmakumar
Very high-spin organic molecules are of current interest in
relation to fundamental aspects of bonding and novel approaches to materials.['] Synthesis of mesoscopic-size and well-defined
high-spin organic molecules is one of the ultimate goals in the
area of organic magnetism.12.31 The organic molecule with the
[*I
[**I
Prof A. Rajca. Dr. S. Rajca. Dr. R. Padinakumar
Department of Chemistry. University of Nebraska
Lincoln. N E 68588-0304 (USA)
Telekx: Int. code +(402) 472-9402
This research was supported by the National Science Foundation (CHE920391 8). Mass spectral determinations were performed by the Midwest Center for Mass Spectrometry with partial support by the National Science Foundation (DIR-9017262). Wc thank Professor S. H. Liou for access to a SQUID
ma_metometer.
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