Synthesis, characterization and chemistry of bis-(pentafluorophenyl)boryl ferrocene

Article abstract of DOI:10.1139/v00-185

Bis-(pentafluorophenyl)boryl ferrocene, 1, was prepared via borylation of ferrocene with HB(C₆F₅)₂ or via a transmetallation reaction involving FcHgCl and ClB(C₆F₅)₂ in 87-91% yield. The compound is characterized by a deep maroon colour. A significant intramolecular iron-boron interaction is manifested in the solution spectroscopic (Fe → B charge transfer band at ～230 nm, ε = 1.33 × 10⁴) and solid-state crystallographic data (Fe-B = 2.924 A) This interaction has an impact on the Lewis acidity of the boron center which, unlike the related compound B(C₆F₅)₃, does not strongly bind Lewis bases such as acetone, THF, or acetonitrile. However, an adduct between the stronger base PMe₃ and 1 forms readily and this complex (2) was fully characterized. The electron withdrawing -B(C₆F₅)₂ group causes 1 to be oxidized at +450 mV relative to ferrocene. Oxidation of 1 with [NO][BF₄], AgOSO₂CF₃, or AgC₆F₅ leads to the zwitterionic ferrocenium borates 3-F, 3-OTf, and 3-C₆F₅, respectively. Each of these compounds was characterized spectroscopically and via X-ray crystallography. The properties of these compounds relative to 1 suggest that oxidation of the iron center significantly enhances the Lewis acidity of the boron center. Due to the σ-donating ability of the borate substituents, zwitterions 3 are weaker oxidizing agents than unsubstituted ferrocenium salts.

Full text of DOI:10.1139/v00-185

857
Synthesis, characterization and chemistry of bis-
(pentafluorophenyl)boryl ferrocene
Bryon E. Carpenter, Warren E. Piers, Masood Parvez, Glenn P.A. Yap, and Steven
J. Rettig
Abstract: Bis-(pentafluorophenyl)boryl ferrocene, 1, was prepared via borylation of ferrocene with HB(C6F5)2 or via a
transmetallation reaction involving FcHgCl and ClB(C6F5)2 in 87–91% yield. The compound is characterized by a deep
maroon colour. A significant intramolecular iron–boron interaction is manifested in the solution spectroscopic (Fe → B
charge transfer band at -230 nm, ε = 1.33 × 104) and solid-state crystallographic data (Fe-B = 2.924 Å) This interac-
tion has an impact on the Lewis acidity of the boron center which, unlike the related compound B(C6F5)3, does not
strongly bind Lewis bases such as acetone, THF, or acetonitrile. However, an adduct between the stronger base PMe3
and 1 forms readily and this complex (2) was fully characterized. The electron withdrawing -B(C6F5)2 group causes 1
to be oxidized at +450 mV relative to ferrocene. Oxidation of 1 with [NO][BF4], AgOSO2CF3, or AgC6F5 leads to the
zwitterionic ferrocenium borates 3-F, 3-OTf, and 3-C6F5, respectively. Each of these compounds was characterized
spectroscopically and via X-ray crystallography. The properties of these compounds relative to 1 suggest that oxidation
of the iron center significantly enhances the Lewis acidity of the boron center. Due to the σ-donating ability of the bo-
rate substituents, zwitterions 3 are weaker oxidizing agents than unsubstituted ferrocenium salts.
Key words: organoboranes, ferrocene derivatives, Lewis acids.
Résumé : On a préparé le bis-(pentafluorophénylboryl)ferrocène, 1, par le biais d’une borylation du ferrocène à l’aide
de HB(C6F5)2 ou par une réaction de transmétallation impliquant le FcHgCl et le ClB(C6F5)2; les rendements varient de
87 à 91%. Le composé est caractérisé par une couleur marron foncé. Il se manifeste une interaction intermoléculaire
fer–bore significative tant en spectroscopie en solution (un transfert de bande Fe → B à environ 230 nm, ε = 1,33 ×
104) que dans les données cristallographiques à l’état solide (Fe-B = 2,924 Å). Cette interaction a une influence sur
l’acidité de Lewis du bore qui, contrairement au composé B(C6F5)3 apparenté, ne se lie pas fortement aux bases de Le-
wis telles que l’acétone, le THF ou l’acétonitrile. Toutefois, il se forme facilement un adduit entre le composé 1 et
PMe3, une base plus forte, et on a fait une caractérisation complète de ce complexe, 2. La présence du groupe élec-
troaffinitaire B(C6F5)3 fait que le composé 1 peut s’oxyder à +450 mV par rapport au ferrocène. L’oxydation du com-
posé 1 par [NO][BF4], AgOSO2CF3 ou AgC6F5 conduit suivant le cas à la formation des borates de ferrocénium
zwitterioniques 3-F, 3-Otf et 3-C6F5. Chacun de ces composés a été caractérisé par spectroscopie et par diffraction des
rayons X. Les propriétés de ces composés, comparées à celles du composé 1, suggèrent que l’oxydation du fer aug-
mente de beaucoup l’acidité de Lewis du bore. En raison de la possibilité des substituants borates de donner des élec-
trons σ, les zwitterions 3 sont des agents d’oxydation plus faibles que les sels de ferrocénium non substitués.
Mots clés : organoboranes, dérivés ferrocènes, acides de Lewis.
[Traduit par la Rédaction] Carpenter et al. 867
Nonetheless, borylated ferrocenes have been studied in some
Introduction
detail, initially due to the fact that they are isoelectronic to
stable ferrocenyl carbocations (2), and are synthons for other
substituted ferrocenes. Early examples involve mainly
dihaloboryl derivatives, prepared by direct borylation of the
metallocene with BX3 (3). In these reactions, the ferrocene
Cp rings can be borylated up to four times. These haloboryl
derivatives can be further derivatized and used as precursors
Substituted ferrocenyl derivatives play an important role
in many different areas of chemistry (1). While much activ-
ity has focussed on ferrocenes substituted with Lewis base
donors as ligands for various transition metal catalysts,
ferrocene derivatives with Lewis acid centers bonded to the
cyclopentadienyl (Cp) ring have seen fewer applications.
Received August 8, 2000. Published on the NRC Research Press Web site at http://canjchem.nrc.ca on July 5, 2001.
Dedicated with warmth and deep respect to Professor Brian James on the occasion of his 65th birthday.
B.E. Carpenter, W.E. Piers,1 and M. Parvez. Department of Chemistry, University of Calgary, 2500 University Drive N.W.,
Calgary, AB T2N 1N4, Canada.
G.P.A. Yap. Department of Chemistry, University of Ottawa, 10 Marie Curie, Ottawa, ON K1N 6N5, Canada.
S.J. Rettig.2 Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, BC V6T 1Y6, Canada.
1Corresponding author (telephone: (403) 220-5746; fax: (403) 289-9488; e-mail: wpiers@ucalgary.ca).
2Deceased.
Can. J. Chem. 79: 857–867 (2001)
DOI: 10.1139/cjc-79-5/6-857
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Can. J. Chem. Vol. 79, 2001
Fig. 1. UV–vis spectra of compounds 1 and 2 in 1,2-
to coordination polymer type materials (4). More recently, a
class of ansa-ferrocenophanes utilizing a boron atom in the
linking bridge have been prepared (5) and subjected to ring-
opening polymerization reactions (5c).
dichloroethane (concentration -2 × 10–4 M).
Our interest in perfluoroaryl substituted boranes (6) led us
to develop routes to bis-(pentafluorophenyl)boryl substituted
boranes and to explore their properties as Lewis acids. In
this paper, we detail the synthesis, properties, and reaction
chemistry of the monoborylated ferrocene complex bis-
(pentafluorophenyl)boryl ferrocene (1).
Results and discussion
Previously, boryl-substituted ferrocenes have been pre-
pared via direct borylation or transmetallation reactions (3).
Accordingly, bis-(pentafluorophenyl)borylferrocene (1) can
be synthesized either via borylation with bis-
(pentafluorophenyl)borane, HB(C6F5)2, (7) or through reac-
tion of the well-known (chloromercuric)ferrocene, FcHgCl,
(8) with bis-(pentafluorophenyl)chloroborane, ClB(C6F5)2
(9) (eq. [1]). The former route requires heating for several
hours and involves loss of H2 during the course of the reac-
tion, while the latter reaction occurs at room temperature
and produces HgCl2 as the by-product. Both routes are effi-
cient, giving 1 in 87–91% isolated yield.
80 ppm range, neutral, four coordinate centers typically fall
into the 5–25 ppm range, while anionic borates appear up-
field at –10 to –35 ppm. Similarly, the chemical shift differ-
ence between the meta and para fluorines of the C6F5 rings
is influenced by the amount of electron density at the boron
center (11): as the boron proceeds from neutral, three-
coordinate through four-coordinate adducts with Lewis
bases, to anionic borates, the para fluorines become more
shielded as the charge on boron increases, and shift upfield
closer to the resonance for the meta fluorines. 11B chemical
shifts and ∆m,p values for all the new compounds reported
here as well as some comparable compounds are collected in
Table 1. Inspection of this data shows that, for 1, the 11B
chemical shift (53 ppm) and the ∆m,p value (9.2 ppm) is in-
termediate to the numbers observed for purely neutral, three-
coordinate examples and neutral, four-coordinate Lewis base
adducts. These observations are consistent with the presence
of a weak Fe → B interaction in 1, which is maintained in
nondonating solvents.
This interaction is also manifested in the solid-state struc-
ture of 1, determined by X-ray crystallography. Compound 1
crystallizes in the P212121 space group with two crystallo-
graphically independent molecules in the asymmetric unit.
Figure 2 shows the molecular structure of one of these mole-
cules, along with selected metrical parameters; further de-
tails on this structure (and the others reported herein) can be
found in the Supplementary information.3 Immediately evi-
dent from the view shown is that the B(C6F5)2 moiety is
Boryl ferrocene 1 is a deeply maroon coloured solid
which is highly soluble in common aliphatic and aromatic
solvents. The UV–vis spectrum of 1 (Fig. 1) exhibits an in-
tense absorption at -230 nm (ε = 1.33 × 104) likely assign-
able to an Fedz2/dx2 – y2 → Bp charge transfer process. Wagner
and co-workers (3j) have detailed this Fe → B interaction in
related dibromoboryl ferrocenes both experimentally and
computationally and conclude that the occupied dz2 and dx2 – y2
orbitals on the iron center have appropriate symmetry to in-
teract with the empty p-orbital on the boron center, effec-
tively forming a loose intramolecular Lewis acid–Lewis base
adduct. A similar phenomenon accounts for the observed
stability of ferrocenyl carbocations (2).
The NMR data for 1 also supports the notion that an Fe → B
interaction is present in the compound. In perfluoroaryl sub-
stituted boranes, the chemical shift of the 11B nucleus in the
11B NMR spectrum is reflective of the coordination number
and charge associated with the boron center (10). Neutral,
three-coordinate boranes generally resonate in the 65–
3 Copies of material on deposit may be purchased from the Depository of Unpublished Data, Document Delivery, CISTI, National Research
Council Canada, Ottawa, ON K1A 0S2, Canada (http://www.nrc.ca/cisti/irm/unpub_e.shtml for information on ordering electronically). Some
of this material has also been deposited with the Cambridge Crystallographic Data Centre. Copies of the data can be obtained, free of charge,
on application to the Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, U.K. (Fax: 44-1223-336033 or e-mail: deposit@ccdc.cam.ac.uk).
© 2001 NRC Canada

Carpenter et al.
859
Table 1. 11B and 19F ∆m,p values for various pentafluorophenyl-
Fig. 2. ORTEP diagram of molecule one of 1. Selected bond dis-
tances (Å): Fe(1)—C(13) 2.043(3), Fe(1)—C(14) 2.027(3),
Fe(1)—C(17) 2.036(3), Fe(1)—C(15) 2.060(2), Fe(1)—C(16)
2.062(2), C(13)—C(14) 1.444(3), C(13)—C(17) 1.448(3),
C(14)—C(15) 1.414(3), C(16)—C(17) 1.407(4), C(15)—C(16)
1.418(3), B(1)—C(13) 1.501(4), B(1)—C(6) 1.604(4),
B(1)—C(12) 1.584(4). Selected nonbonded distance (Å):
Fe(1)···B(1), 2.924. Selected bond angles (°): C(6)-B(1)-C(12)
118.4(2), C(6)-B(1)-C(13) 118.0(2), C(12)-B(1)-C(13) 122.5(2).
substituted boranes.
Compound
19F ∆m,p
δ
11B
Reference
HB(C6F5)2
B(C6F5)3
C6H5B(C6F5)2
FcBBr2
1
18.3
16.3
12.6
—
9.2
5.6
6.2
6.8
3.7
3.7
60.1
80
72.6
46.7
53.0
–13.5
–4.8
–23.7
–13.2
–17.3
7
a
b
3d
2
3-OTf
3-C6F5
4
b
LiB(C6F5)4
aA.G. Massey and A.J. Park. J. Organomet. Chem. 5, 218 (1966).
bP.A. Deck, C.L. Beswick, and T.J. Marks. J. Am. Chem. Soc. 120,
1771 (1998).
Table 2. Oxidation potentials for ferrocenyl boranes
and borates vs. ferrocene+1/0
.
Compound
Solvent
E1/2 (mV)
1
2
TFTa
TFT
TFT
+450
–100
–472
+270b
3-C6F5
FcC(O)CH3
CH2Cl2
a
α,α,α-Trifluorotoluene.
bTaken from ref. 22.
tilted towards the iron center such that the dip angle of the
B(1)-C(13) vector out of the plane defined by the five Cp
carbons is -16°. This compares to the values of 17.7° and
18.9° found for the same parameter in crystallographically
independent molecules of the related compound Fc(BBr2)
(3j). As a consequence of this interaction in 1, the B(1) cen-
ter is slightly pyramidalized (the sum of the angles about
B(1) is 358.2°) and the Fe(1)—B(1) distance is 2.924 Å. The
metrical parameters for the borylated Cp ring suggest a par-
tial contribution from a boratafulvene-like structure (12)
akin to I is operative for this ligand. Furthermore, the
B(1)—C(13) distance of 1.501(4) Å is intermediate between
values found for a B(sp2)-C(sp2) double bond (e.g., 1.44 Å
in LiCH2=B(mes)2 (13)) and that of a B(sp2)-C(sp2) single
bond (e.g., 1.58 Å in BPh3 (14)). Thus it appears that, in ad-
dition to accepting electron density directly from the iron
center, the B(C6F5)2 group withdraws π-electron density
from the Cp ring as well.
as the supporting electrolyte (15). Use of the standard
[NBu4][BF4] electrolyte led to irreversible oxidations, a re-
sult of chemical reactions subsequent to oxidation (vide in-
fra). An internal standard of ferrocene was employed; all
E1/2 values reported (Table 2) are relative to the Fc/Fc+ cou-
ple under these conditions. As can be seen in Fig. 3, 1 ex-
hibits a reversible oxidation wave at +450 mV relative to
ferrocene, indicating that it is more difficult to oxidize ow-
ing to the electron-withdrawing -B(C6F5)2 substituent.
The flow of electron density into the empty boron p-or-
bital dampens the Lewis acidity of 1 in comparison to other
perfluoroaryl substituted boranes. For example, while car-
bonyl functions, (16) ethers and water, (17) isonitriles and
nitriles (18) form strong adducts with B(C6F5)3, when 1 is
treated with oxygen nucleophiles such as acetophenone,
acetylferrocene, N,N-di-iso-propylbenzamide or THF, the
equilibrium for adduct formation lies far towards the reac-
tants at room temperature. Treatment of 1 with 1 equiv of
water leads to rapid formation of FcH and HOB(C6F5)2 (9),
indicating that coordination occurs to some extent. Toluene-
d8 solutions of 1 containing a few equiv of acetonitrile,
when cooled, change in colour from the deep maroon of 1 to
light yellow, indicative of disruption of the Fe → B interac-
tion upon adduct formation. However, the acetonitrile ligand
remains labile even at 193 K, as judged by the single reso-
nance for free vs. bound acetonitrile in the sample’s 1H
NMR spectrum at this temperature. Use of the Childs’
method for assessing Lewis acid strength (19) shows that 1
has a Lewis acid strength of 0.37 ± 0.03 relative to BBr3 at
1.00. Comparative values for other Lewis acids, for example,
The electron-withdrawing capacity of the -B(C6F5)2 group
is manifested in the electrochemical behaviour of 1. Cyclic
voltammetric measurements were performed against a silver
wire quasireference electrode in ≈100 mM solutions of sub-
strate in α,α,α-trifluorotoluene (TFT) with [NBu4][B(C6F5)4]
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Can. J. Chem. Vol. 79, 2001
Fig. 3. Representative CV of 1 (1 mM) in α,α,α-trifluorotoluene with [Bu4N][B(C6F5)4] (100 mM) as supporting electrolyte. Scan
rate = 100 mV s–1.
AlCl3 (0.88 ± 0.03), B(C6F5)3 (0.77) (20), and SnCl4 (0.56 ±
0.03), show that 1 is a relatively weak Lewis acid by virtue
of this Fe → B interaction.
The solid-state structure of 2 was determined by X-ray
crystallography, and an ORTEP diagram along with selected
metrical data is given in Fig. 4. The B(1)—P(1) distance of
1.992(9) Å is comparable to the 2.046(8) Å and 2.015(3) Å
values found for the PH3 and t-BuPH2 adducts, respectively,
of B(C6F5)3 (21). The now four-coordinate boron atom is
tilted out of the Cp plane away from the iron center by 6.4°.
As expected, the boratafulvene character of 1 is lost and the
B(1)—C(1) distance of 1.61(1) Å is characteristic of a
B(sp3)—C(sp2) bond.
Only strong Lewis bases, such as PMe3, form adducts ir-
reversibly with 1 (eq. [2]). When maroon solutions of 1 are
exposed to PMe3, an instantaneous colour change to a yel-
low hue signals formation of adduct 2. This material was
isolated and fully characterized. Notably, the UV–vis spec-
trum of 2 (Fig. 1) no longer contains a prominent charge
transfer band, supporting the assignment of this band for 1
given above. The chemical shift of the 11B nucleus in the
NMR spectrum of 2 (–13.5 ppm) is somewhat upfield of the
region expected for such four-coordinate adducts but is split
into a doublet due to coupling to the 31P nucleus (JB-P = 46 ±
10 Hz). The ∆m,p value of 5.6 ppm (Table 1) is consistent
with strong coordination of the phosphine to the boron cen-
ter, although the relatively small value of JB-P suggests that
the phosphine may be labile. The PMe3 ligated boryl group
is now a net electron donator to the Cp ring as judged by the
E1/2 value of –100 mV (relative to Fc/Fc+, Table 2) in the cy-
clic voltammagram of 2. Since the p-orbital on boron is
plugged with the phosphine lone pair of electrons, the σ-do-
nating ability of the boryl group now dominates the elec-
tronic effect of this group on the Fe(II)–Fe(III) redox couple
of the iron center.
Given the nature of the Fe → B interaction in 1 and re-
lated compounds and its dampening effect on the Lewis
acidity of the boron center, it seemed logical to presume that
oxidation of the iron center should weaken the Fe → B inter-
action and concommitantly impart stronger Lewis acidity on
the borane. Experiments involving chemical oxidation of 1
appear to bear this out. For example, treatment of 1 with
[NO][BF4], a common oxidizing agent for ferrocene deriva-
tives (22), led to oxidation to a ferrocenium complex as indi-
cated by a change in the solution’s colour from maroon to
dark green, with visible evolution of NO gas. 19F NMR
spectroscopy on the crude product showed that the BF4 an-
ion was no longer present and that one major B(C6F5)2 con-
taining product was present as ≈80% of the mixture. Due to
the paramagnetism of this compound, 1H and 11B NMR
spectroscopy provided little useful information; however, the
C6F5 rings are far enough removed to be relatively unaf-
fected by the paramagnetic iron center. While isolable quan-
tities of pure product were not obtained, analysis of crystals
isolated from this product mixture by X-ray crystallography,
revealed the fluoroborate zwitterion 3-F to be this major
product (Fig. 5). Evidently, the boron center in the putative
ferrocenium intermediate 3 (Scheme 1) is Lewis acidic
enough to abstract a fluoride ion from the BF4 counteranion.
Fluoride abstraction by other perfluoroaryl boranes, specifi-
© 2001 NRC Canada

Carpenter et al.
861
Fig. 5. ORTEP diagram of one molecule of 3-F. Selected bond
distances (Å): C(1)—B(1) 1.626(15), B(1)—F(1) 1.452(12),
B(1)—C(11) 1.697(15), B(1)—C(17) 1.651(14). Selected bond
angles (°): F(1)-B(1)-C(1) 108.1(11), F(1)-B(1)-C(11) 105.8(9),
F(1)-B(1)-C(17) 109.2(8), C(1)-B(1)-C(11) 112.3(8), C(1)-B(1)-
C(17) 111.5(10), C(11)-B(1)-C(17) 109.9(10).
Fig. 4. ORTEP diagram of 2. Selected bond distances (Å):
Fe(1)—C(1) 2.098(7), Fe(1)—C(2) 2.044(8), Fe(1)—C(3)
2.012(9), Fe(1)—C(4) 2.037(8), Fe(1)—C(5) 2.022(8),
C(1)—C(2) 1.447(9), C(1)—C(5) 1.424(10), C(2)—C(3)
1.400(12), C(4)—C(5) 1.425(10), C(3)—C(4) 1.401(12),
B(1)—C(1) 1.609(11), B(1)—C(11) 1.665(10), B(1)—C(17)
1.637(10), B(1)—P(1) 1.992(9). Selected bond angles (°): P(1)-
B(1)-C(1) 109.3(5), P(1)-B(1)-C(11) 102.1(5), P(1)-B(1)-C(17)
116.0(6), C(1)-B(1)-C(11) 110.6(6), C(1)-B(1)-C(17) 109.0(6),
C(11)-B(1)-C(17) 109.8(6).
in dichloromethane, whereas the reaction leading to 3-C6F5
required several hours in toluene solvent. Complex 3-OTf
exhibits a resonance at –89.6 ppm in the 19F NMR spectrum,
attributable to the triflate CF3 group, in addition to those of
the C6F5 fluorines. The solid-state structure of this com-
pound was determined by X-ray crystallography and an
ORTEP diagram and selected metrical data is given in
Fig. 6. Again, the quaternized boron center is now directed
away (6.0°) from the iron center. The metrical parameters
associated with the OTf moiety are similar to other η1-coor-
dinated trifluoromethanesulfonates (26).
cally B(C6F5)3 (23) and the chelating diboryl species 1,2-
C6F4[B(C6F5)2]2 (24) has also been documented. Signifi-
cantly, boryl ferrocene 1 does not react with [NBu4][BF4],
even upon heating. Recall, however, that electrochemical
oxidation of 1 in the presence of this electrolyte was irre-
versible. Taken together, these observations suggest that oxi-
dation of the iron center significantly increases the Lewis
acidity of the boron center attached to the Cp ring.
Zwitterion 3-F crystallizes as two independent molecules
with essentially identical metrical parameters, differing only
in the orientation of the fluoroborate moiety with respect to
the Cp ligand plane. One of the molecules is shown in
Fig. 5, along with selected metrical parameters; a picture of
the other is given in the deposited material. The borate boron
is tetrahedral in geometry and the B(1)—F(1) distance of
1.452(12) Å is typical of these bonding partners.
Zwitterion 3-C6F5 was also structurally characterized
(Fig. 7). Consistent with boron quaternization, the boron
atom is 3.59 Å away from the iron center (5.8° tilt). In addi-
1
tion, H, 11B, and 19F NMR spectroscopy were fully consis-
tent with the structure found in the solid state. Furthermore,
one-electron reduction using cobaltocene gave a diamagnetic
ion pair, [FcB(C6F5)3][Cp2Co] (4, eq. [4]), which was also
characterized spectroscopically and via elemental analysis.
We were interested in 3-C6F5 as a potential activator for
metallocene and related olefin polymerization catalyst pre-
cursors, since it is known that ferrocenium salts are capable
of oxidizing neutral dialkyl metallocenes to the active
cationic alkyl catalysts (27). Unfortunately, 3-C6F5 is not a
strong enough oxidizing agent to remove an electron from
Cp2ZrMe2. In fact, electrochemical measurements on this
Two other zwitterionic ferrocenium compounds were pre-
pared in high yield and purity by oxidation of 1 with AgOTf
and AgC6F5 (25) as shown in eq. [3]. Formation of 3-OTf
was essentially immediate upon dissolution of the reactants
© 2001 NRC Canada

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Can. J. Chem. Vol. 79, 2001
Scheme 1.
Fig. 7. ORTEP diagram of 3-C6F5. Selected bond distances (Å):
Fe(1)—C(1) 2.152(2), Fe(1)—C(2) 2.100(2), Fe(1)—C(3)
2.065(2), Fe(1)—C(4) 2.069(2), Fe(1)—C(5) 2.098(2),
C(1)—C(2) 1.433(3), C(1)—C(5) 1.434(3), C(2)—C(3) 1.428(3),
C(4)—C(5) 1.414(3), C(3)—C(4) 1.409(3), B(1)—C(1) 1.666(3),
B(1)—C(11) 1.648(3), B(1)—C(17) 1.657(3), B(1)—C(23)
1.666(3). Selected bond angles (°): C(1)-B(1)-C(11) 106.0(2),
C(1)-B(1)-C(17) 105.7(2), C(1)-B(1)-C(23) 112.0(2), C(11)-B(1)-
C(17) 113.2(2), C(11)-B(1)-C(23) 110.9(2), C(17)-B(1)-C(23)
108.9(2).
Fig. 6. ORTEP diagram of 3-OTf. Selected bond distances (Å):
B—C(5) 1.601(5), B—C(16) 1.624(5), B—C(22) 1.658(4),
B—O(1) 1.575(4), S—O(1) 1.486(2), S—O(2) 1.416(7), S—O(3)
1.392(8), S—C(23) 1.824(6). Selected bond angles (°): O(1)-B-
C(5) 107.7(3), O(1)-B-C(16) 109.0(3), O(1)-B-C(22) 104.8(2),
C(5)-B-C(16) 112.7(3), C(5)-B-(C(22) 111.7(3), C(16)-B-C(22)
110.5(3).
The observations above infer that the boron center of the
putative species 3 is more Lewis acidic than that of neutral
borane 1. Unfortunately, attempts to prepare 3 with a weakly
coordinating anion, namely [B(C6F5)4]– met with failure, al-
though some of the experiments aimed at preparing 3 with
this counteranion support the notion that 3 is a stronger
Lewis acid than 1. For example, 1 may be oxidized using the
acetylferrocenium
reagent
[FcAc]+[B(C6F5)4]–.
Acetylferrocenium reagents have been used to oxidize other
ferrocene derivatives, since its oxidation potential of +270 mV
is higher than most substituted ferrocene derivatives (23). In-
terestingly, it should not be a strong enough oxidizing agent
to oxidize 1, whose potential is at +450 mV relative to
ferrocene, and yet when 1 and [FcAc]+[B(C6F5)4]– are mixed
together, a rapid redox reaction is observed. Presumably the
carbonyl group of the acetyl substituent is able to weakly co-
ordinate the boron center in 1, converting the electron-
withdrawing -B(C6F5)2 substituent into an electron-donating
(relative to H) -B(L)(C6F5)2 group (Scheme 2). Thus, when
the acetylferrocenium species coordinates to the boron cen-
ter in 1, oxidation is rapid, producing the complex 3-FcAc.
1H NMR spectroscopy suggests that the neutral
zwitterion show that its oxidation potential is at –472 mV
relative to Fc/Fc+, indicating that the -B(C6F5)3 borate moi-
ety is a very good σ-donor to the Cp ring, stabilizing the
Fe(III) center substantially relative to unsubstituted
ferrocene. Structurally, there is nothing unusual about this
compound; the borate boron is tetrahedral and the B—C
bond lengths are normal. Compound 3-C6F5 is related to the
zwitterion Fc+B(Fc)3, reported several years ago (28).
© 2001 NRC Canada

Carpenter et al.
863
Scheme 2.
Law. Elemental analyses were performed by Mrs. Dorothy
Fox (University of Calgary) on a Control Equipment Corpo-
ration 440 elemental analyzer.
Toluene, tetrahydrofuran (THF), and hexanes were puri-
fied using the Grubbs purification system (30) and stored in
solvent pots over a drying agent. α,α,α-Trifluorotoluene
(TFT) was predried over phosphorus pentoxide (P2O5) and
stored over CaH2 in a glass bomb. Deuterated solvents were
purchased from Cambridge Isotopes Laboratories and dried
analogously.
All chemicals were purchased from Aldrich–Sigma unless
otherwise stated except tris-(pentafluorophenyl)borane and
ferrocene, which were purchased from Boulder Scientific
Company. The B(C6F5)3 dried as previously described, while
ferrocene was purified by sublimation under dynamic vac-
uum at 55°C. Literature procedures were used to prepare the
following reagents: [n-Bu4N]+[B(C6F5)4] (15), (ClB(C6F5)2)
(9), (HB(C6F5)2) (7), (LiB(C6F5)4·Et2O) (31), (AgC6F5) (25),
(FcHgCl) (8), and [FcAc]+[BF4]– (8).
acetylferrocene product of the electron transfer reaction re-
mains coordinated to the boron center. All attempts to re-
move the acetylferrocene failed; clearly, FcAc is bound
much more tightly to the Lewis acid center in 3 compared to
that in 1.
Preparation of 1
Method A
In
conclusion,
we
have
prepared
bis-
Ferrocene (1.90 g, 10.2 mmol) and HB(C6F5)2 (3.45 g,
9.98 mmol) were dissolved in toluene (60 mL), warmed
slowly to 80°C, and stirred for 22.5 h under argon opened to
a mercury bubbler. The reaction mixture was cooled and the
toluene was removed under vacuum to afford a dark maroon
solid. Boryl ferrocene product was extracted from unreacted
HB(C6F5)2 with hexanes. The hexanes were removed under
vacuum to afford a crimson red crystalline solid. Residual
ferrocene was removed from the product by sublimation
(55°C under full vacuum). Yield of 1: 4.39 g (8.28 mmol,
91%). X-ray quality crystals were grown from a saturated
solution of 1 in dry hexamethyldisiloxane cooled to –35°C.
(pentafluorophenyl)ferrocenylborane and examined its
chemical and electrochemical behaviour. The Lewis acidity
of the boron center is attenuated due to a significant Fe → B
interaction in the Fe(II) species, but oxidation of the iron
center to Fe(III) disrupts this interaction, resulting in a more
strongly Lewis acidic boron center.
Experimental section
General
All reactions were carried out under an argon atmosphere
either on a double manifold high vacuum line or in an Inno-
vative Technology System One dry box. Standard inert at-
mosphere, Schlenk, vacuum line, and glove box techniques
were used throughout, under purified argon. Nuclear mag-
netic resonance (NMR) spectra were obtained in d2-methy-
lene chloride (CD2Cl2), d6-benzene, or d8-toluene on either
Bruker AMX400 (1H NMR, 400.132 MHz, 13C NMR,
100.623 MHz), Bruker AMX300 (1H NMR, 300.138 MHz,
11B NMR, 96.293 MHz, 19F NMR, 282.371 MHz), Varian
XL200 (13C NMR, 50.310 MHz, 11B NMR, 64.184 MHz,
31P NMR, 80.988 MHz) or Bruker ACE-200 (1H NMR,
200.134 MHz) spectrometers. 1H and 13C NMR spectra were
referenced to tetramethylsilane (SiMe4) via solvent reso-
nances. 11B NMR spectra were externally referenced to bor-
ane trifluoride diethyl etherate (δ 0.0 ppm) and 19F NMR
spectra were externally referenced to CFCl3 (δ 0.00 ppm) us-
ing an external standard of hexafluorobenzene (δ –163.0 ppm)
(29). 31P NMR spectra were reference to the external stan-
dard H3PO4 in deuterium oxide (δ 0.00 ppm). UV–vis spec-
tra were obtained in dry ClCH2CH2Cl using a Cary 5E UV–
vis and IR spectrometer. The samples were prepared in volu-
metric flasks (-2.0 × 10–4 M) and transferred to a 1 mm
pathlength air-tight cell fused to a Kontes Teflon tap. A
background spectrum of the solvent was collected and auto-
matically subtracted from the spectrum collected of the sub-
strate. The molar absorptivity was calculated using Beer’s
1
UV (TFT) λmax (nm) (ε): 231 (1.33 × 104). H NMR (C6D6):
4.51 (t, 2H, J = 1.8 Hz, Hβ), 4.03 (s, 5H, C5H5), 3.95 (bs,
1
2H, Ha). 13C NMR (C6D6): 145.9 (d, JCF = 242 Hz), 141.9
1
1
(d, JCF = 242 Hz), 137.7 (d, JCF = 251 Hz), 115.0 (bs,
WHM = 87 Hz, Cipso(C6F5)), 79.5 (s, WHM = 7.4 Hz, Cβ),
77.7 (s, WHM = 8 Hz, Cα), 70.5 (s, WHM = 7.4 Hz, C5H5).
11B NMR (C6D6): 53.7 (bs, WHM = 650 Hz). 19F NMR
(C6D6): –129.3 (dd, 4F, Fo), –152.5 (t, 2F, Fp), –161.7 (dt,
4F, Fm). Anal. calcd. for C22H9BF10Fe: C 49.86, H 1.71;
found: C 49.69, H 1.90.
Method B
1-(Chloromercuric)ferrocene (2.403 g, 5.32 mmol) and
ClB(C6F5)2 (1.987 g, 5.23 mmol) were placed into a 100 mL
bomb and hexanes (80 mL) added under vacuum transfer
conditions. The mixture was warmed to room temperature
and stirred for 22 h. The orange chalky suspension changed
to a dark maroon solution with a green–grey precipitate. The
suspension was cannula-transferred under argon flow into a
100 mL RBF and filtered to extract 1 from the mercuric
chloride by-product. The HgCl2 was washed with hexanes
until the washings were colourless. The solvent was re-
moved in vacuo to afford the maroon solid 1. Yield: 2.461 g
(4.64 mmol, 87%). The crude product was subjected to sub-
limation to remove any residual ClB(C6F5)2.
© 2001 NRC Canada

864
Can. J. Chem. Vol. 79, 2001
100 mL bomb to which was added 50 mL of toluene. The
vessel was sealed and warmed to 100°C in an oil bath for
23.5 h. The flask was cooled to room temperature and the
green solution was cannula-transferred to a two-neck round-
bottom flask with a frit assembly under an argon flow. The
toluene was removed under vacuum and CH2Cl2 was con-
densed in at –78°C. The green solution was extracted from
the silver powder by filtration and washed until the extracts
were colourless. The solvent was removed in vacuo to afford
a dark green solid. Yield: 1.397 g (2.00 mmol, 90%). Crys-
tals of 3-C6F5 were grown at 25°C when dissolved into a
minimum amount of dry CH2Cl2 layered with hexane. UV
(TFT) λmax (nm) (ε): 258 (1.33 × 104). 1H NMR (d8-toluene):
Preparation of 2
Compound 1 (394 mg, 0.743 mmol) was dissolved in to-
luene and the solution degassed by a freeze–pump–thaw rou-
tine. At –196°C, an excess of PMe3 (>15 cmHg in a 115 cm3
bulb) was condensed into the flask. The reaction was
warmed to –78°C during which time the maroon solution
changed colour to light yellow. The solvent was removed in
vacuo to afford
(0.731 mmol, 98%). A single crystal was grown from a satu-
rated toluene solution. H NMR (d8-toluene): 4.15 (t, 2H,
a yellow powder. Yield: 443 mg
1
J = 1.80 Hz, Hβ), 3.99 (s, 5H, Fe(C5H5)), 3.62 (bs, 2H, Ha),
2
0.47 (d, 9H, JPH = 10.7 Hz, P(CH3)3). 13C NMR (d8-tolu-
ene): 148.1 (d, 1JCF = 234 Hz), 139.7 (d, 1JCF = 263 Hz, Cp),
1
43.8 (bs, WHM = 1150 Hz), 30.2 (bs, WHM = 1400 Hz),
137.7 (d, JCF = 246 Hz), 120.3 (bs, Cipso(C6F5)), 80.2 (bs,
1
24.2 (bs, WHM = 780 Hz). 13C NMR: 142.7 (d, 4C, JCF
=
Cipso(C5H4)), 73.7 (s, Cα), 69.9 (s, Cβ), 68.8 (s, Fe(C5H5)),
1
9.5 (d, 1JCP = 37 Hz, P(CH3)3). 11B NMR (d8-toluene): –13.5
225 Hz), 139.3 (d, 2C, JCF = 246 Hz, Cp), 133.6 (d, 4C,
1JCF = 246 Hz). 11B NMR: –23.7 (bs, 55 Hz). 19F NMR: –139.6
(bs, 6F, Fo), –161.0 (s, 3F, Fp), –167.8 (d, 6F, Fm). Anal.
calcd. for C28H9BF15Fe: C 48.24, H 1.30; found: C 48.25, H
1.30.
1
(br d, JBP = 46 ± 10 Hz). 19F NMR (d8-toluene): –127.6 (d,
4F, Fo), –157.6 (t,2F, Fp), –163.2 (dt, 4F, Fm). 31P NMR (d8-
1
toluene): –12.1 (br m, JPB = 46 ± 10 Hz).
Preparation of 3-F
Preparation of [FcB(C6F5)3][Cp2Co] (4)
Borane 1 (306 mg, 0.577 mmol) and nitrosonium
tetrafluoroborate (NOBF4) (65 mg, 0.557 mmol) were dis-
solved in CH2Cl2 (20 mL). The reaction vessel was placed
into a 60°C oil bath and stirred for 30 min. The solution was
cooled, degassed, and taken into the dry box where it was
transferred to a flask fitted with a frit assembly. The solution
was concentrated and the slurry sonicated; filtration afforded
a dark blue solid. Yield: 250 mg (0.405 mmol, 72%). Crys-
tals were grown by layering hexane on a concentrated solu-
tion in CH2Cl2 at 25°C. 1H NMR: 33.1 (bs, WHM =
1360 Hz, 2H), 28.0 (bs, WHM = 700 Hz, 5H, Fe(C5H5)),
30.1 (bs, WHM = 2150 Hz, 2H). 19F NMR: –157.1 (bs, 4F,
Fo), –162.4 (t, 2F, Fp), –166.8 (bs, 4F, Fm); the B-F fluorine
was not located.
3-C6F5 (420 mg, 0.619 mmol) and cobaltocene (117 mg,
0.619 mmol) were dissolved in dry CH2Cl2 (12 mL). The so-
lution was stirred at room temperature for 2 h. The solution
was run through a frit and the solvent removed to afford a
brown crystalline solid. Yield: 490 mg (0.564 mmol, 91%).
1H NMR: 5.60 (s, 10H, Co(C5H5)), 4.00 (t, 2H, J = 1.68 Hz,
Hβ), 3.94 (bs, 2H, Hα), 3.67 (s, 5H, Fe(C5H5)). 13C NMR:
1
1
149.3 (d, JCF = 246 Hz), 138.4 (d, JCF = 245 Hz, Cp),
1
137.0 (d, JCF = 258 Hz), 85.2 (s, Co(C5H5)), 75.9 (s, Cα),
68.3 (s, Fe(C5H5)), 67.0 (s, Cβ). 11B NMR: –13.2 (bs, WHM
= 39 Hz). 19F NMR: –128.3 (d, 6F, Fo), –164.5 (dt, 3F, Fp),
–168.0 (t, 6F, Fm). Anal. calcd. for C38H19BCoF15Fe: C
51.51, H 2.16; found: C 51.30, H 2.34.
Preparation [FcAc]+[B(C6F5)4]–
Preparation of 3-Otf
Acetylferrocenium
tetrafluoroborate
(298
mg,
Silver trifluoromethanesulfonate (245 mg, 0.953 mmol)
and 1 (505 mg, 0.953 mmol) were placed into a flask fitted
with a frit assembly. CH2Cl2 (25 mL) was condensed into
the vessel under vacuum transfer conditions. The reaction
was warmed to room temperature and stirred for 2 h during
which time the solution changed from maroon to navy blue.
The reaction mixture was filtered with a grey residue re-
maining on the frit and the solvent was removed under vac-
uum to afford 585 mg (0.858 mmol, 90%) of a paramagnetic
dark blue solid of high purity by 19F NMR. Crystals were
grown at 25°C from a minimum amount of CH2Cl2 layered
0.946 mmol) and lithium tetrakis(pentafluorophenyl)borate
etherate (843 mg, 0.947 mmol) were dissolved in CH2Cl2
and stirred for 12 h. The mixture was filtered and the solid
washed with CH2Cl2 three times. The solvent was removed
from the filtrate to afford a fluffy blue solid. Yield: 794 mg
1
(0.875 mmol, 92%). H NMR: 35.8 (bs, WHM = 750 Hz),
30.4 (bs, WHM = 1800 Hz), 0.90 (s, 3H, COOCH3), –12.1
(bs, WHM = 120 Hz). 13C NMR: 147.5 (d, JCF = 242 Hz),
1
1
1
138.2 (d, JCF = 232 Hz), 135.9 (d, JCF = 232 Hz), 126.3
(bs, Cipso(C6F5)). 11B NMR: –16.9 (s, WHM = 28 Hz). 19F
NMR: –135.6 (s, 8F, Fo), –164.4 (s, 4F, Fp), –169.4 (s, 8H,
Fm). Anal. calcd. for C36H12BF20FeO: C 47.66, H 1.33;
found: C 46.88, H 1.53.
1
with hexane. UV (TFT) λmax (nm) (ε): 256 (1.42 × 104). H
NMR: 42.0 (bs, WHM = 2780 Hz), 33.1 (bs, WHM =
2500 Hz), 30.1 (bs, WHM = 1050 Hz). 13C NMR: 142.9 (d,
1
1
1JCF = 245 Hz), 137.7 (d, JCF = 257 Hz), 133.0 (d, JCF
=
241 Hz), 92.1 (bs, Cipso). 11B NMR: –4.75 (bs, WHM =
394 Hz). 19F NMR: –89.6 (s, 3F, CF3), –155.8 (bs, 4F, Fo),
–159.6 (s, 2F, Fp), –165.8 (s, 4F, Fm). Anal. calcd. for
C23H9BF13FeO3S: C 40.68, H 1.34; found: C 40.51, H 1.13.
Preparation of 3-FcAc
Borane 1 (262 mg, 0.494 mmol) and [FcAc]+[B(C6F5)4]–
(440 mg, 0.485 mmol) were loaded into flask fitted with a
frit assembly. CH2Cl2 (15 mL) was condensed onto the sol-
ids under vacuum transfer conditions. The solution was
warmed to room temperature and stirred for 80 min. The
solvent was removed in vacuo to afford a violet solid which
was triturated with dry hexanes and filtered to collect the
Preparation of 3-C6F5
Pentafluorophenyl silver(I) (AgC6F5) (614 mg,
2.23 mmol) and 1 (1.183 g, 2.23 mmol) were placed into a
© 2001 NRC Canada

Carpenter et al.
865
solid, which was washed with hexanes three times. Yield:
683 mg (0.475 mmol, 98%). IR (cm–1): 3123, 1644 (C=O),
1516, 1464, 1277, 1089, 979. H NMR: 45.2 (bs, 2H, WHM
= 1630 Hz, Hα/β); 31.9 (bs, 5H, WHM = 900 Hz,
BCpFe(C5H5)), 22.3 (bs, 2H, WHM = 1900 Hz, Hα/β), 7.21
(s, 2H), 6.85 (s, 5H, AcCpFe(C5H5)), 2.15 (s, 3H, CH3). 11B
NMR: –17.0 (s, WHM = 17.4 Hz, B(C6F5)4). 19F NMR: –149.8
(s, 1F), –151.2 (s, 2F), –153.4 (s, 1F), –158.9 (s, 1F), 164.8
(s, 1F), –133.2 (s, Fo, 8F), –162.4 (s, Fp, 4F), –167.2 (s, Fm,
8F).
Unit-cell parameters were determined from 60 data frames
collected at different sections of the Ewald sphere.
Semiempirical absorption corrections based on equivalent
reflections were applied (32) to 1. Attempts to correct the
data set of 3-OTf for absorption yielded Tmin/Tmax of unity
and no correction was applied. Systematic absences in the
diffraction data and unit-cell parameters were uniquely con-
sistent with the reported space groups. The structures were
solved by direct methods, completed with difference Fourier
syntheses, and refined with full-matrix least-squares proce-
dures based on F2. Refinement of the Flack parameter for 1
yielded 0.39(1) indicating that the true hand of the data set
could not be determined. All non-hydrogen atoms were re-
fined with anisotropic displacement parameters. The triflate
ion in 3-OTf was located disordered in two positions with
refined site occupancy of roughly 50/50. All hydrogen atoms
were treated as idealized contributions. All scattering factors
and anomalous dispersion factors are contained in the
SHEXTL 5.1 program library (Sheldrick, 1997, WI.).
1
Relative Lewis acidity
In the dry box a known amount of Lewis acid was placed
into an NMR tube, dissolved in a measured volume of
CD2Cl2 and capped with a rubber septum. The sample was
cooled to –78°C to which dry crotonaldehyde was added via
microsyringe to the NMR tube. The tube was quickly shaken
1
to ensure mixing. The H NMR spectrum was collected at
–20°C.
Structural determination of 2 and 3-F
Cyclic voltammetry
Measurements were made on
a
Rigaku AFC6S
Cyclic volammetric measurements were made on α,α,α-
trifluorotolune (TFT) solutions under argon at 25°C, using a
three-electrode cell attached to a Hitek Instruments of Eng-
land Potentiostat (Type DT2101) and a Waveform Generator
PPRI system. The electrolyte employed was [n-
Bu4N]+[B(C6F5)4]– with electrolyte:substrate concentrations
of approximately 100:1. The air tight electrochemical cell
consisted of a thick-walled glass bulb, Kontes Teflon tap, a
set of platinum wire electrodes (working and secondary),
and a silver wire quasireference electrode. Each experiment
involved collecting the data for the substrate alone, which
was then referenced to the Fc/Fc+ couple in this medium.
Samples were prepared in the dry box as follows: a known
amount of electrolyte [nBu4N]+[B(C6F5)4]– was dissolved
into a minimum amount of dry TFT and added quantitatively
to a volumetric flask. This solution was diluted to a known
volume with additional TFT. The solution was mixed thor-
oughly and transferred to the electrochemical cell which
contained the substrate and a small stir bar under argon. The
Teflon tap was closed and a small amount of ferrocene was
placed in a side arm. Outside the dry box, the electrochemi-
cal cell was attached to the potentiostat and the data were
collected with a scan rate of 0.1 V s–1 without stirring. After
the data for the substrate were collected the Teflon tap was
opened to allow the ferrocene in the side arm to be added
and dissolved. The stirring was halted and the CV data for
the internal reference were collected along with the sub-
strate. The half-wave potential of the substrate was refer-
enced to that of the Fc/Fc+ redox couple.
diffractometer with graphite monochromated Mo Kα radia-
tion for 2 and on an Enraf–Nonius CAD-4 diffractometer
with graphite monochromated Cu Kα radiation for 3-F. Cell
constants and an orientation matrix for data collection were
obtained from 25 reflections. The data were collected at a
temperature of 170(2) K (2) and 295(2) K (3-F) using the ω-
2θ scan technique. The intensities of three standard reflec-
tions were measured after every 200 reflections and de-
creased by 1.1% (2) and 0.69% (3-F). The data were
corrected for decay, absorption (33), and for Lorentz and po-
larization effects. The structure of 2 was solved by direct
methods (34) and expanded using Fourier techniques (35).
The non-hydrogen atoms were refined anisotropically. The
Cp and phenyl rings were constrained as regular pentagons
and hexagons, respectively. H-atoms were included at geo-
metrically idealized positions. The structure of 3-F was
solved by direct methods and expanded using Fourier tech-
niques. There were two independent molecules in an asym-
metric unit. The non-hydrogen atoms were refined
anisotropically. H-atoms were included at geometrically ide-
alized positions. For both structures, the weighting scheme
was based on counting statistics and the final difference Fou-
rier map was essentially featureless. Neutral atom scattering
factors were taken from Cromer and Waber (36). Anomalous
dispersion effects were included in Fcalc (37); the values for
∆f′ and ∆f′ ′ were those of Creagh and McAuley (38). The
values for the mass attenuation coefficients are those of
Creagh and Hubbel (39). All calculations were performed
using the teXsan (40) crystallographic software package of
Molecular Structure Corporation.
X-Ray crystallography
Suitable crystals were mounted on glass fibers using par-
affin oil and cooled to the data collection temperature; de-
tails of crystal data, data collection, and structure refinement
have been provided in Table 3.
Structural determination of 3-C6F5
Measurements were made on a Rigaku/ADSC CCD area
detector with graphite monochromated Mo Kα radiation.
The data were collected at a temperature of –93(1)°C to a
max 2θ value of 61.1° in 0.50° oscillations with 14.0 s expo-
sures. A sweep of data was done using φ oscillations from
0.0 to 190.0° at χ = –90° and a second sweep was performed
Structural determination of 1 and 3-Otf
Data were collected on a Bruker AX SMART 1k CCD
diffractometer using 0.3° ω-scans at 0, 90, and 180° in φ.
© 2001 NRC Canada

866
Can. J. Chem. Vol. 79, 2001
Table 3. Summary of data collection and structure refinement details for 1, 2, 3-F, 3-OTf, and 3-C6F5.
1
2
3-F
3-OTf
3-C6F5
Formula
Fw
Temperature (K)
λ (Å)
C22H9BF10Fe
529.95
203(2)
C25H18BF10PFe
606.02
170(2)
C22H9BF11Fe
548.95
295(1)
C23H9BF13FeO3S C28H9BF15Fe
679.02
203(2)
0.71073
697.01
180(1)
0.71069
0.71073
0.71069
1.54178
Dimensions (mm3)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
α (°)
β (°)
γ (°)
V (Å3)
0.4 × 0.2 × 0.1 0.42 × 0.38 × 0.4 0.5 × 0.4 × 0.22 0.1 × 0.1 × 0.2
0.45 × 0.40 × 0.40
Monoclinic
P21/n
15.9529(13)
10.0171(7)
16.5882(3)
Orthorhombic
P212121
Monoclinic
P21/n
Triclinic
P
Monoclinic
P21/c
9.758(1)
11.994
33.255(4)
10.899(3)
12.953(2)
17.012(3)
12.226(2)
13.1790(10)
14.123(4)
109.40(2)
108.87(2)
93.150(10)
1997.1(9)
4
10.909(3)
12.896(4)
17.017(5)
92.95(2)
95.177(6)
111.1394(5)
3892.2(7)
8
2398.5(8)
4
2384(1)
4
2472.4(2)
4
1.872
1372
0.743
Z
dcalc (mg m–3)
F(000)
1.809
2096
0.878
1.678
1216
0.786
1.826
1084
0.7113
1.892
1340
0.850
µ (mm–1)
Max/min transmission
Scan type
Scan range (°)
0.9281/0.5980
0.7334/7541
ω-2θ
0.8082–1.000
ω-2θ
0.8629–1.000
1.22–28.65
2.27–27.57
0.80+0.35θ
119.9
1.87–22.50
4.0–66.1
2θ (max) (°)
Reflections
Unique reflections
No. of variables
55.1
5798
5531
283
0
66.1
21 247
6493
406
29 867
9296
614
5953
5645
632
5510
3039
443
38
Restraints
0
0
0
R
0.063
0.033
0.035
0.032
Rw
R1a
0.0373
0.0616
1.008
0.0584
0.1455
1.010
0.0327
0.0621
1.082
wR2a
gof
2.73
1.26
Max ∆/σ (final cycle)
Residual density (e Å–3) –0.588–0.585
0.00
–0.46–0.58
0.0003
–0.61–0.59
–0.656–0.744
–0.292–0.295
aFinal indices I > 2θ(I).
using ω oscillations between –23.0 and 18.0° at χ = –90°.
The crystal-to-detector distance was 38.851(6) mm and the
detector swing angle was –10.0°. The data were corrected
for decay, absorption (33), and for Lorentz and polarization
effects. The structure was solved by direct methods (34) and
expanded using Fourier techniques.(35) The non-hydrogen
atoms were refined anisotropically and hydrogen atoms were
fixed in calculated positions with C-H = 0.98 Å. The final
cycle of full-matrix least-squares refinement was based on
all 6493 unique reflections and 406 variable parameters.
Neutral atom scattering factors were taken from Cromer and
Waber (36). Anomalous dispersion effects were included in
Fcalc (37); the values for ∆f′ and ∆f′′ were those of Creagh
and McAuley (38). The values for the mass attenuation coef-
ficients are those of Creagh and Hubbel (39). All calcula-
tions were performed using the teXsan (40) crystallographic
software package of Molecular Structure Corporation.
Council of Canada (NSERC) are gratefully acknowledged.
BEC and WEP thank Professor Scott Hinman (Calgary) for
use of his electrochemical equipment and helpful discus-
sions. Also, we thank Professor Bill Gieger (Vermont) for
details on the synthesis and use of [Bu4N][B(C6F5)4] prior to
publication.
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© 2001 NRC Canada