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Effects of Environment on Intramolecular Electron Transfer in Mixed-valence 1 1-Dinaphthylmethyl(biferrocenium) Triiodide Structural and 57Fe Mssbauer Characteristics.

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Effects of Environment on Intramolecular
Electron Transfer in Mixed-Valence
l',l'"-Dinaphthy lmethyl(biferrocenium)
Triiodide: Structural and 57Fe Mossbauer
Teng-Yuan Dong,* Xiao-Qian Lai, Zhi-Wei Lin, and
Kuan-Jiuh Lin
Electron transfer in chemical''] and biological[2]systems has
received considerable attention in the last few years. Recent
studies of electron transfer in mixed-valence biferrocenium
complexes 1-6 revealed that the environment surrounding a
cation is perhaps the most important factor in determining the
rate of intramolecular electron transfer.['" 31 Complexes 1-6
give unusual temperature-dependent Mossbauer spectra.[4] At
temperatures below 77 K they each show two doublets,
one for the Fe" and one for the Fe"' site (electron-transfer
rate < lo7 s-I). In each case the two doublets move together
upon increasing temperature and eventually become a single
"average-valence'' doublet. Hendrickson et al. suggested that
the temperature dependence of the Mossbauer spectrum is due
to the onset of lattice dynamics associated with the triiodide
counterions and alkyl s~bstituents.[~l
At low temperatures
(< 100 K) all parts of the crystal lattice of the complex are static.
As the temperature is increased, the thermal energy formed
could be sufficient to trigger a cooperative phase transition in
the crystal
A crystallographic phase change was not
observed in 1-6; we believe that the transition may be described
in terms of a gradual (second-order) change with temperature.
l x =
Dark crystals in the triclinic space group Pi were formed
when a solution of 7 in CH,CI, was slowly concentrated.rS1An
ORTEP plot of the molecular structure is given in Figure la.
The refinement of the structure imposed inversion centers on
both the cation and the triiodide anion. Thus, the two ferrocenyl
moieties are crystallographically equivalent. The average Fe-C
distance of 2.059(5) 8, is intermediate to values for ferrocene
and the ferrocenium ion (2.075(1) A).[71The distances from the iron atom to the planes of the Cp ligands
(1.668(2) and 1.676(2) A) are also between the corresponding
values for ferrocene (1.65 A)[61 and the ferrocenium ion
(1.70 A) .I7] The plane of the Cp ring forms a dihedral angle of
4.4" with the fulvalenide plane, and the two Cp rings in each
ferrocenyl moiety are not perfectly eclipsed but rotated relative
to one another by 7.0".
Dark crystals in the monoclinic space group P2Jn were obtained when a layer of hexane was allowed to diffuse slowly into
a solution of 7 in CH,CI, .I5]
The molecular structure is shown
in Figure 1b. The two metallocene moieties in the cation are not
equivalent. The average Fel-C distance (2.052(4) A) and the
Fel-Cp distance (1.660(4) A) indicate that the iron in this
metallocene is in the oxidation state 11. In contrast, the average
Fe2-C (2.086(5) A) and Fe2-Cp distances (1.693(4) A) india)
2 x = CH3
3 x = CZH5
4 x =
5 x = n -C4H9
6 X = benzyl
7 x = 1-naphthylmethyl
The mixed-valence complex 6 has two distinct crystallographic phases that show that the electron-transfer rates are extremely
sensitive to changes in the crystal
Two different crystalline morphologies (needle and platelike crystals) of 6 were
found. The needle crystal in the triclinic space group Pi shows
a Mossbauer spectrum characteristic of a valence-detrapped
electronic structure down to 25 K. The platelike crystal in the
space group P2,ln shows a valence-trapped Mossbauer spectrum up to 300 K. However, because of the poor quality of the
diffraction data and disorder in the triiodide anion, a satisfactory refinement of the structure was not obtained. Here we report
on 7, the first mixed-valence complex in two crystallographic
phases with satisfactory structural refinements. Compound 7
was formed from 8 via 9 and 10 (see Experimental Section).
Prof. TY
Dong, X.-Q. La], 2.-W Lin
Department of Chemistry
National Sun Yat-Sen University
Kaohsuing (Taiwan)
Fax: Int. code f(7)525-3908
Dr. K. 1. Lin
The Institute of Chemistry, Academia Sinica
Nankang, Taipei (Taiwan)
This work was supported by the National Science Council (NSC86-2113-M110.003) and National Sun Yat-Sen University.
0 WILEY-VCH Verlag GmbH, D-69451 Wemhelm, 1997
Figure 1. a) ORTEP plot of the crystal structure of 7, space group Pi. Selected
distances [A] and angles["] (standard deviations are given in parentheses): Fe-Cl
2.090(5), Fe-C2 2.055(6), Fe-C3 2.039(6), Fe-C4 2.046(6), Fe-CS 2.050(6),
Fe-C6 2.074(5), Fe-C7 2.043(5), Fe-C8 2.053(6), Fe-C9 2.064(6), Fe-C10
2.073(6), 11-12 2.8936(8); 12-11-12 180. b) ORTEP plot of the crystal structure of
7, space group P2,/n. Selected distances [A] and angles I"]: Fel-Cl 2 053(6),
Fel-C2 2.054(7), Fel-C3 2.067(7), Fel-C42.056(7). Fel-C5 2.028(7), Fel-C6
2.065(6), Fel-C7 2.046(6), Fel-C8 2.043(6), Fel-C9 2.055(6), Fel-'210
2.043(6), Fe2-Cl1 2.129(6), Fe2-Cl2 2.095(7), Fe2-Ct3 2.047(7), Fe2-Cl4
2.050(7), Fe2-Cl5 2.079(7), Fe2-Cl6 2.126(7), Fe2-Cl7 2.091(7), Fe2-Cl8
2.067(7), Fe2-Cl9 2.069(7), Fe2-C20 2.1107. 11-12 2.89(1), 11-13 2 932(1); 1211-13 176.31
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Angew. Chem Inl. Ed. Engf. 1997.36, No. 18
cate that the iron in this metallocene is in the oxidation state III.
The two Cp rings associated with Fel and Fe2 are not quite
parallel; the dihedral angles are 2.1 and 5.5". Furthermore, the
two Cp rings associated with Fel and Fe2 are nearly eclipsed
with average staggering angles of 3.0 and 2.3".
A comparison of the structural features of the two different
crystallographic phases of 7 is interesting. The naphthylmethyl
substituents on the Cp rings are situated differently. The two
nonequivalent naphthylmethyl groups in the cation of the P2,/n
phase show a cisoid conformation relative to the fulvalenide
ligand ; this is similar to other dialkyl mixed-valence biferrocenium triiodide salts.'4. 91 In the case of the cation of the P i phase
the two equivaIent naphthylrnethyl groups show a transoid conformation relative to the fulvalenide ligand. Consequently, the
packing arrangement of the cations and anions of 7 in the P 2 J n
phase is different from that in the Pi phase. In the case of the
latter the packing arrangement can be described as columns of
cations and anions developing approximately along the a axis.
In P2,/n phase the packing arrangement has a layer structure.
Furthermore. it appears that the naphthylmethyl substituents
lead to further slippage of the cations from the steplike stacks
seen in dialkyl biferrocenium cations.
In the P7 phase the I; anion is at the inversion center
and shows a symmetric structure. The 1-1 bond length is
2.8936(8) A. In the case of the P2Jn phase the 1; anion is
asymmetric (I1 -12 2.895(1), I1 -13 2.932(1) A). In other words,
the I3 atom carries more negative charge and shows
12-11 . 13- character. Furthermore, the 1; anion is not quite
linear. In the Pi phase an intermolecular phenyl-phenyl (z-z)
interaction is observed between adjacent cations.
These structural characteristics are consistent with the results
of the Mossbauer studies. The variable-temperature 'Fe
Mossbauer spectra of the two different crystallographic phases
are shown in Figures 2 and 3. The 57FeMossbauer spectrum of
the Pi phase at 80 K shows two doublets (Fe", AEQ.=
1.610 mms-'; Fe"', AEQ = 0.818 mms-'), which is characteristic of a valence-trapped cation in which the rate of intramolecuThe two doublets
lar electron transfer is less than 10' s - ' . ~ ' ' ~
move together as the temperature is increased, and finally become a single average doublet (valence-detrapped) at about
130 K. On the o t b x hand, the sample of the P2,/n phase ex-
T I % o.5
- 4 - 3 - 2 - 1
4 3 - 2 - 1
0 1 2 3 4 ' 1-3-2-1
0 1 2 3 4
v h m s-'
Figure 2. Variable-temperature 57Fe Mossbauer spectra of 7 in the Pi phase:
T = transmission. c = velocity
AngeW Chew. h r . E d Engi. 1997, 36, No. 18
t .
Figure 3 *'Fe Mossbauer spectra of 7 in the P2Jn phase at 300 K
hibits a Mossbauer spectrum that is characteristic of a valencetrapped cation which remains trapped even at 300 K (Fe",
AEQ = 2.085 mms-'; Fe"' , AEQ = 0.407 mms-'; Figure 3).
The differences in the 57FeMossbauer spectral properties of the
two phases of 7 are attributable to differences in the molecular
conformation around the mixed-valence cation. The crystal
structure analysis of the Pi phase shows that the environment of
the cation is symmetric with respect to the two iron ions; rapid
electron transfer is therefore possible. The asymmetric environment of the cations in the P2,/n phase energetically favors one
valence state over the other, and, as a consequence, slow electron transfer results." '1
The observations for the mixed-valence cation 7 definitively
show that the crystallographic properties of the lattice play an
important role in controlling the rate of electron transfer. There
are several cases known in chemical and biological systems in
which sluggish solvent-molecule motion and lattice dynamics
can dramatically affect the rate of electron transfer.[1a. 21 In
biological systems conformational changes of protein and the
motion of amino acid groups have been suggested as providing
control and specificity in electron transfer between proteins.[''
Our observation is an interesting result, which shows that the
crystallographic properties can turn the electron transfer on or
Experimen f a1 Sect ion
1'-Naphthoyl-1-bromoferrocene(8): Dibromoferrocene [131 (1.72 g, 5 mmol) was
placed in a freshly dried flask (250 mL), and dried under vacuum at 2 Torr and 30 "C
for 4 h. Dry THF (20 mL) and then butyllithium (3.15 mL, 1.611 in hexane) were
added under N,. The solution was stirred at -2S"C for 30min, during which
1-lithio-1'-bromoferrocenegradually precipitated. 1-Naphthylnitrile (5 mmol) was
then added, and the solution stirred at -25°C for another 25 mln. Water (20 mL)
was added, and the mixture extracted with CH,CI, (50 mL x 2). The combined
extracts were dried over sodium sulfate and concentrated under reduced pressure.
The residue was purified by chromatography on a column of neutral alumina (activity grade 11). Elution with hexane gave fractions containing dibromoferrocene and
bromoferrocene. Further elution with ethylacetate/hexane (1 125) provided the desired8In20'Ayield. 'HNMR(300 MHz,CDCI,,TMS):J = 8.25(t, 1H),794(m,
2H), 7.77 (d, 1 Hj, 7.53 (m, 3H), 4.87 (s, 2H), 4.60 (s. 2 H ) . 4.45 (s. 2Hj, 4.19 (s,
2H); MS (40 eV): m/z (%) = 418,420 (100) [ M ' ] .
Reduction o f 8 to 1'-naphthylmethyl-1-bromoferrocene
(9):Small portions of AICI,
were carefully added with stirring to a mixture of 8 and LiAIH, In dry ether. After
1 h the solution became yellow. An excess of H,O was added, and the ether layer
isolated, washed with H,O, and dried over MgSO,. After removal ofthe solvent the
crude product was purified by chromatography on neutral Al,O, with hexane as
eluant. The first fraction contained the desired 9 in 71 % yield. ' H NMR (300 MHz.
2H), 4.19 (s, 2H). 4 16 (s, 2H), 4.08 (t, 2H); MS (40 eV): mi; (%) = 404,406(100)
[ M ' ] ; m.p. 113.5-114.5'C.
I',l"'-Dinaphthylmethylbiferrocene (10):A mixture of 9 (1 g) and activated copper
( 5 g) was heated under N,at 120 "C for 24 h. After the mixture was cooled to room
temperature, it was repeatedly exrracted with CH,CI, until the extracts were colorless. The extracts were concentrated and purified by chromatography. The first
fraction eluted with hexane yielded startlng material. Further elution with CH,CI,
afforded the desired 10 ~n 78% yield, which was recrystallized from hexanei
8 WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1997
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benzene. 'H NMR (300 MHz, CDCI,, TMS): 6 = 7.94 (d, 2H), 7.81 ( t , 2H), 7 66
(d, ZH), 7.48 (m, 4H), 7.31 (m, 2H), 7.08 (d, ZH), 4.42 (s, 4H), 4.30 (s, 4H), 4.01
(s, 8 H ) , 3.79 (s, 4H); MS (40eV): m/z (%) = 650 (100) [ M + ] ;m.p. 170.0"C
7: A stoichiometric amount of I, in benzene/hexane (l/l) was added to a solution
of 10 in benzene at 0 "C. The resulting dark green crystals were isolated by filtration
and washed with cold hexane. A better crystalline sample was prepared by slowly
concentrating a solution of 7 in CH,CI, (method 1) or by slowly diffusing hexane
into a solution of 7 in CH2CI, (method 2). Microanalyses of the two different
preparations were identical withm experimental error. Elemental analysis calcd for
7 (C42H34Fez13):
C 50.91, H 3.14; found: C 51.02, H 3.53 (method 1); found: C
50.99, H 3.55 (method 2).
Received: December 30, 1996
Revised version: May 23, 1997 [29941 IE]
German version: Angew. Chem. 1997,109,2093-2096
Keywords: electron transfer * iron * mixed-valent compounds
Moessbauer spectroscopy
[I] a) R. D. Cannon, Ekctron Transfer Reactions, Butterworths, London, 1980;
b) A. Haim, Comments Inorg. Chem. 1985, 4, 113; c) D. N. Hendrickson,
S. M. Oh, T.-Y Dong, M. F. Moore, ibid. 1985,4,329; d) J. Jortner, M. Bixon,
J. Chem. Phys. 1988,88, 167.
121 a) G. McLendon, Acc. Chem. Res. 1988, 21, 160; b) G. Williams, G. R
Moore, R. J. P. Williams, Comments Inorg. Chem. 1985, 4, 55.
I31 a) R. J. Webb, T.-Y. Dong, C. G. Pierpont, S. R. Boone, R. K. Chadha, D. N.
Hendrickson, J. Am. Chem. Sac. 1991, 113, 4806; b) T.-Y. Dong, C. C. Shei,
M. Y Hwang, T. Y. Lee, S. K. Yeh. Y. S. Wen, Organometa//ics1992, 11, 574;
c) R. J. Webb, A. 2.Rheingold, S. I. Geib, D. L. Staley, D. N. Hendrickson,
Angew. Chem. 1989, 101, 1422; Angew. Chem. Int. Ed. Eng. 1989.28, 1388.
I41 a) T.-Y. Dong, M. I. Cohn, D. N. Hendrickson, C. G. Pierpont, J. Am. Chem.
SOC.1985,107,4777; b) T.-Y Dong, D. N. Hendrickson, K. Iwai, M. J. Cohn,
A. L. Rheingold, H. Sano, I. Motoyama, S. Nakashima, ibid. 1985,107,7996;
c) M. J. Cohn, T.-Y Dong, D. N. Hendrickson, S. J. Geib, A. L. Rheingold, J.
Chem. SOC.Chem. Commun. 1985,1095; d) S. Iijima, R. Saida. I. Motoyama,
H. Sano, BKN. Chem. Sor. Jpn. 1981,54, 1375.
151 The X-ray structures of 7 (C,,H,,Fe,I,,
M =1031.14) were determined at
298 K. a) Crystals were obtained by slowly concentrating a solution of 7 in
CH,CI,: triclinic, space group Pi, a = 9.836(2), b = 10.418(2), c =
10.638(3)A, a = 62.83(1), B = 86.06(1), y = 69.74(1)", Y = 904.S(4)A3,
F(000) = 497, ?.(MoKJ = 0.71073 A, p = 3.391 mm-', 2 =1, P . . ~ , =
1.893 gcm-j. Data were collected on an Enraf Nonius CAD4 diffractometer
in the range 2.16<6<22.42" (of 2356 reflections collected 1973 were jndependent). The structure was solved by heavy-atom methods, and refined, based on
F2, by full-matrix leasf-squares techniques. A11 non-hydrogen atoms were refined anisotropically, and hydrogen atoms were included in calculated positions and allowed to ride on the relevant carbon atom. Final residuals were
R1 = 0.0354and wRU2) = 0.0875for2356 uniquedata with 1>2u((r).Absorption corrections were made with empirical @ rotation. b) Crystals were obtained by slowly diffusing hexane into a solution of 7 in CH,CI,: monoclinic,
space group P2,/n, Q = 17.286(5), b = 9.188(7), c = 23.069(4) A,
93.44(2)", V = 3658(3) A3, F(OO0) = 1988, L(Mo,.) = 0.71073 A, p =
3.355 mm-', 2 = 4, pCaad=1.873 gcm-'. Data were collected in the range
1.43 <0<22.43" (of 4764 reflections collected 4764 were independent). The
structure was refined as described above. Final residuals were Rl = 0.0348
and wR(f') = 0.0980 for 3289 unique data with i z 2 u ( i ) . Crystallographic
data (excluding structure factors) for the structures reported in this paper
have been deposited with the Cambridge Crystallographic Data Centre as
supplementary publication no. CCDC-100423. Copies of the data can be obtained free of charge on application to The Director, CCDC, 12 Union Road,
Cambridge CBZIEZ, UK (fax: int. code +(1223)336-033; e-mail:
[6] P. Seiler, J. D. Dunitz, Acla CrptaNogr. Seer. B 1979, 35, 1068.
171 N.J. Mammano, A. Zalkin, A. L. Rheingold, Inorg. Chem. 1 9 7 , 16, 297.
[8] K. Michiko, H. Sano, Bull. Chem. Soc. Jpn. 1988, 61, 1455.
[9] K. Michiko, H. Sano, BKN.Chem. SOC.Jpn. 1982,55, 2327.
I101 W. H. Momson Jr., D. N. Hendrickson, Inorg. Chem. 1975,14, 2331.
[ll] K. Y Wong, P. N. Schatz, Prog. Inorg. Chem. 1981,28, 369.
1121 a) H. G. Jang, S. J. Geih, Y. Kaneko, M. Nakano, M. Sorai, A. L. Rheingold,
B. Montez, D. N Hendrickson, J. Am. Chem. SOC.1989, 111, 173; b) S. M.
Oh, S. R. Wilson, D. N. Hendrickson, S. E. Woehler, R. J. Wittebort, D. Inniss, C. E. Strouse, ibid. 1987, 109, 1073; c) s. E. Woehler, R. J. Wittebort,
S. M. Oh, T. Kambara, D. N. Hendrickson, D. Inniss, C. E. Strouse, ibid. 1987,
109,1063; d) Y. Kaneko, M. Nakano, M. Sorai, H. G. Jang, D. N. Hendrickson, Inorg. Chem. 1989,28, 1067; e) R. D. Cannon, R. P. White, Prog. Inorg.
Chem. 1988,36,195.
1131 T.-y.Dong, L. L. Lai, J. Organornet. G e m . 1% 509, 131.
0 WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1991
[Ru(Ph)( CO)(PtBuzMe),1 :
A Unique 14-Electron Ru" Complex with Two
Agostic Interactions**
Dejian Huang, William E. Streib, Odile Eisenstein,*
and Kenneth G. Caulton*
In a number of molecular settings the ligand PtBu,Me (L)
is very bulky, even in comparison to PzR, and PCy,
(Cy = cyclohexyl). Thus, this ligand significantly diminishes the
enthalpy of addition of PhCCPh and even compact MeNC to
[Ru(CO),L,], and this phosphane spontaneously and completely dissociates from [Ru(CO),L,]."~ The two tBu groups have a
similarly large inff uence, for example, on promoting ortho
metalation of [Ir(H),X(PtBu,Ph),] to form [IrHX(PtBu,Ph)(qZ-P(C,H,)tBu,)], and in causing even this 16-electron
complex to eliminate PtBu,Ph.[21Indeed, phenyl metalation is
accompanied by metalation of the tBu carbon atoms. We reloses methane already
ported that [RUH(CH,)(CU)(P~BU,M~)~]
at -40°C with metallation of a tBu group.['' We report here
that PtBu,Me i s the phosphane which leads to a remarkable
example of two agostic aliphatic interactions with a single metal
Essential to this observation is the production of a metai
center with two empty valence orbitals. This is tantamount to
the synthesis of a 14-valence-electroncomplex. Our approach to
this goal is halide removal from a 16-electron complex. For
optimum electrophilicity in a 34-electron complex, it is desirable
to exclude Ir-donor ligands from the coordination sphere. This
also diminishes the possibility of loss ("quenching") of unsaturation by dimerization through halide bridges (e.g., [L,M(p-Cl),ML,]). Unlike in the case of [Ru(CO)(NO)L,][BArk]
(L = PtBu,Me, Ar' = 3,5-(CF,),C,H,),[31 which can be made
by salt metathesis of [RuCI(CO)(NO)L,] with NalBArk],
Na[BArJ does not remove C1- from [Ru(Ph)CI(CO)L,]. Replacement of CIA in [Ru(Ph)Cl(CO)L,] by OTf- with AgOTf
(OTf- = CF,SO;) also fails. However, [Ru(Ph)Cl(CO)LJ can
be transformed into [Ru(Ph)F(CO)L,] quantitatively by salt
metathesis with CsF in acetone. Reaction of [Ru(Ph)F(CO)L,]
with one equivalent of Me,SiOTf affords [Ru(Ph)(OTf)(CO)L,]
in quantitative yield. Subsequent reaction with Na[BArk] in
dichioromethane at 20 "C (5 min) gives [Ru(Ph)(CO)L,][BArk]
in quantitative yield [Eq. (l)].
The 'H NMR spectrum (CD,CI,, 20 "C) of [Ru(Ph)(CO)LJBArh] shows only three broad signals for the phenyl-ring
Prof. 0. Eisenstein
Laboratoire de Structure et Dynamique des Systemes Moleculaire et Solides,
Universitk de Montpellier 2
F-34095 Montpellier Cedex 5 (France)
Fax: lnt. code +(4)6714-4798
e-mail :
Prof. K. G. Caulton, D. Huang, W, E. Streib
Department of Chemistry and Molecular Structure Center
Indiana University
Bloomington, IN 47405-4001 (USA)
Fax: Int. code +(812)855-8300
We thank the National Science.Foundation (NSF) and the Centre National de
la Recherche Scientifique (CNRS) for support of theUS-Francecollaboration
through an internarional NSF/PICS grant. 0. E. thanks E. R. Davidson for a
generous donation of computational time.
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Angew. Chem. Int. Ed. Engl. 1997,36,No. 18
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environment, characteristics, valence, intramolecular, triiodide, dinaphthylmethyl, electro, biferrocenium, mixed, effect, structure, transfer, mssbauer, 57fe
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