The reaction of [Fe2(η-C5H5) 2(CO)(CNMe)(μ-CO)(μ-CNMe2)]+ and related salts with trifluoromethanesulphonic acid, HOSO2CF3: Structure of cis-[Fe2(η-C5H5)2(CO) 2(μ-CNMe) (μ-CNMe2)] [BPh4]

Article abstract of DOI:10.1016/S0022-328X(99)00008-X

[Fe₂(η-C₅H₅) ₂(L)(CNMe)(μ-CO)(ν-CNMe₂)][SO₃CF ₃] where L = CO reacts with HOSO₂CF₃ in chloroform solution at room temperature (r.t.) to give [Fe₂(η-C₅H₅)₂(CO) ₂{μ-CN(H)Me}(μ-CNMe₂)][SO₃CF ₃]₂ (reaction (i)). This salt readily and reversibly loses a proton to form [Fe₂(η-C₅H₅)₂(CO) ₂(μ-CNMe)(μ-CNMe₂)][SO₃CF₃] (reaction (ii)) which, in solution, slowly reverts to [Fe₂(η-C₅H₅) ₂(CO)(CNMe)(μ-CO)(μ-CNMe₂)][SO₃CF ₃] under the influence of UV radiation (reaction (iii)) although it can be trapped by reaction with RX (R = H or alkyl; X^- = I^- or [SO₃CF₃]^-) to give [Fe₂(η-C₅H₅)₂(CO) ₂{μ-CN(R)Me}(μ-CNMe₂)][SO₃CF ₃]₂ (reaction (iv)). In reactions closely related to (i) and (iii), [Fe₂(η-C₅H₅) ₂(L)(CN)(μ-CO)(μ-CNMe₂)] (L = CO or CNMe) is converted by HOSO₂CF₃ to [Fe₂(η-C₅H₅) ₂(L)(CO)(μ-CNH₂)(μ-CNMe₂)][SO ₃CF₃]₂ (reaction (v)); this is reversed by deprotonation and no intermediates are observed (reaction (vi)). The scope and limitations of these reactions have been investigated. Replacement of L by isocyanides shows that the ease with which t-CNR is converted to μ-CN(H)R (reactions (i) and (v)) decreases along the series CNR = CN^-/CNH ? CNXy′(Xy′ = C₆H₃Et₂-2,6) > CNMe > CNEt which reflects the μ-seeking ability of the CNR ligands and not their basicity. Reaction (i) does not take place with cis constrained complexes where the two cyclopentadienyl ligands are linked by a -CH₂C(O)-group, in donor solvents such as acetonitrile, or with weaker acids such as CF₃CO₂H or CH₃CO₂H. Reaction (iii) does not take place when L = CNMe or CNEt, or when μ-CNMe is replaced by μ-CNXy′ even when L = CO. Reaction (vi) always takes place; however, if L = CNMe either it or the t-CO may end-up in the μ-site but the latter is preferred. During reactions (i), (iii), (v) and (vi), cis?trans isomerism may accompany ligand migration, but the cis is always the predominant product. Spectroscopic data is presented, assigned and used to distinguish between these isomers. Most is straight-forward, but the IR spectrum of [Fe₂(η-C₅H₅)₂(CO) ₂(μ-CNXy′)(μ-CNMe₂)][SO₃CF ₃] is very unusual as in solution its ν(μ-C-NXy′) absorption band has a very high frequency, > 1900 cm^-1, and is very broad, ca. 200 cm^-1. The structure of cis-[Fe₂(η-C₅H₅)₂(CO) ₂(μ-CNMe)(μ-CNMe₂)][BPh₄] has been determined by X-ray crystallography.

Full text of DOI:10.1016/S0022-328X(99)00008-X

Journal of Organometallic Chemistry 579 (1999) 252–268
The reaction of [Fe2(h-C5H5)2(CO)(CNMe)(m-CO)(m-CNMe2)]+ and
related salts with trifluoromethanesulphonic acid, HOSO2CF3: structure
of cis-[Fe2(h-C5H5)2(CO)2(m-CNMe) (m-CNMe2)] [BPh4]
Kevin Boss a, Conor Dowling a, Anthony R. Manning a,*, Desmond Cunningham b,
Patrick McArdle b
a Department of Chemistry, Uni6ersity College, Belfield, Dublin 4, Ireland
b Department of Chemistry, Uni6ersity College, Galway, Ireland
Received 7 December 1998
Abstract
[Fe2(h-C5H5)2(L)(CNMe)(m-CO)(m-CNMe2)][SO3CF3] where L=CO reacts with HOSO2CF3 in chloroform solution at room
temperature (r.t.) to give [Fe2(h-C5H5)2(CO)2{m-CN(H)Me}(m-CNMe2)][SO3CF3]2 (reaction (i)). This salt readily and reversibly
loses a proton to form [Fe2(h-C5H5)2(CO)2(m-CNMe)(m-CNMe2)][SO3CF3] (reaction (ii)) which, in solution, slowly reverts to
[Fe2(h-C5H5)2(CO)(CNMe)(m-CO)(m-CNMe2)][SO3CF3] under the influence of UV radiation (reaction (iii)) although it can be
trapped by reaction with RX (R=H or alkyl; X− =I− or [SO3CF3]−) to give [Fe2(h-C5H5)2(CO)2{m-CN(R)Me}(m-
CNMe2)][SO3CF3]2 (reaction (iv)). In reactions closely related to (i) and (iii), [Fe2(h-C5H5)2(L)(CN)(m-CO)(m-CNMe2)] (L=CO or
CNMe) is converted by HOSO2CF3 to [Fe2(h-C5H5)2(L)(CO)(m-CNH2)(m-CNMe2)][SO3CF3]2 (reaction (v)); this is reversed by
deprotonation and no intermediates are observed (reaction (vi)). The scope and limitations of these reactions have been
investigated. Replacement of L by isocyanides shows that the ease with which t-CNR is converted to m-CN(H)R (reactions (i) and
(v)) decreases along the series CNR=CN−/CNHꢀCNXy%(Xy%=C6H3Et2-2,6)\CNMe\CNEt which reflects the m-seeking
ability of the CNR ligands and not their basicity. Reaction (i) does not take place with cis constrained complexes where the two
cyclopentadienyl ligands are linked by a –CH2C(O)-group, in donor solvents such as acetonitrile, or with weaker acids such as
CF3CO2H or CH3CO2H. Reaction (iii) does not take place when L=CNMe or CNEt, or when m-CNMe is replaced by m-CNXy%
even when L=CO. Reaction (vi) always takes place; however, if L=CNMe either it or the t-CO may end-up in the m-site but
the latter is preferred. During reactions (i), (iii), (v) and (vi), cisltrans isomerism may accompany ligand migration, but the cis
is always the predominant product. Spectroscopic data is presented, assigned and used to distinguish between these isomers. Most
is straight-forward, but the IR spectrum of [Fe2(h-C5H5)2(CO)2(m-CNXy%)(m-CNMe2)][SO3CF3] is very unusual as in solution its
w(m-C-NXy%) absorption band has a very high frequency,\1900 cm−1, and is very broad, ca. 200 cm−1. The structure of
cis-[Fe2(h-C5H5)2(CO)2(m-CNMe)(m-CNMe2)][BPh4] has been determined by X-ray crystallography. © 1999 Elsevier Science S.A.
All rights reserved.
Keywords: Isocyanide; Cyclopentadienyl; Iron; Carbonyl
(CO)(CNMe)(m-CO)(m-CNMe2)][SO3CF3], [7][SO3CF3]
and [Fe2(h-C5H5)2(CO)2(m-CNMe2)2][SO3-CF3]2, [14]-
[SO3CF3]2 [1]. However, [7][SO3CF3] cannot be con-
verted to [14][SO3CF3]2 even by dissolution in neat
MeOSO2CF3. Consequently, it was very surprising
when, during a workup of one of these reaction mix-
tures, we obtained the previously unknown [Fe2(h-
1. Introduction
The reaction of [Fe2(h-C5H5)2(CO)2(CNMe)2] with
MeOSO2CF3 gives
a
mixture of [Fe2(h-C5H5)2-
* Corresponding author. Fax: +353-1-706-21-27.
E-mail address: armanwin@ollamh.ucd.ie (A.R. Manning)
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00008-X

K. Boss et al. / Journal of Organometallic Chemistry 579 (1999) 252–268
253
CNMe2+ by CN(Me)Et+ and CNEt2+. Some cases a
mixture of cis and trans isomers were formed but could
not always be separated even though they could be
C5H5)2(CO)2{m-CN(H)Me}(m-CNMe2)][SO3CF3]2, [34]-
[SO3CF3]2. It was ascertained that this was the product
of the reaction of [7][SO3CF3] with HOSO2CF3, the
presence of which was fortuitous. It arose because the
reaction had been carried out in chloroform using an old
sample of MeOSO2CF3 which had partially hydrolysed
to HOSO2CF3. This did not hinder the methylation of
[Fe2(h-C5H5)2(CO)2-(CNMe)2], but promoted the subse-
quent migration/protonation reaction.
1
identified by H-NMR spectroscopy. In other instances
the cis isomer was the sole product, e.g. cis-[Fe2(h-
C5H5)2(CO)2{m-CN(H)But}(m-CNMe2)][SO3CF3]2 only
was obtained from the reaction of [Fe2(h-
C5H5)2(CNBut)(CO)(m-CO)(m-CNMe2)][SO3CF3].
The same procedure was also used in the reaction of
HOSO2CF3 with [Fe2(h-C5H5)2(CNBut)2(m-CO)(m-
CNMe2)][SO3CF3]. However, the product was recrys-
tallised from acetonitrile solution to give the green
acetonitrile derivative [Fe2(h-C5H5)2(NCMe)(CNBut)-
{m-CN(H)But}(m-CNMe2)][SO3CF3]2 in 58% yield.
A detailed study of this and related reactions has been
carried out and is described herein. A preliminary report
has appeared [2].
2. Experimental
The following compounds were prepared by methods
described elsewhere: [4][SO3CF3] [1], [5], [6][SO3CF3],
[7][SO3CF3], [8][SO3CF3], [9]I, [10], [11][SO3CF3] and
[12]I [3]. Other chemicals were purchased.
Table 1
Analyses of the various compounds described in the text
Reactions were carried out under an atmosphere of
nitrogen at r.t. in dried and deoxygenated solvents unless
it is stated otherwise. They were monitored by IR
spectroscopy. Chromatography was carried out using
Merck 1097 alumina, activity II/III.
Elemental analyses (Table 1) were carried out by the
Analytical Laboratory of University College, Dublin. IR
spectra (Table 2) were run on Perkin–Elmer 1710 and
1720 FTIR spectrometers, and NMR spectra (Tables 3
and 4) on a JEOL JNM-GX270 spectrometer. These
tables are restricted to complexes containing the m-
CNMe2+ ligand. Others were prepared and characterised
fully, but are not directly relevant to the main arguments
and are not included so as to keep the tables to a
manageable size.
CNR/La
[X]−
Analysesb
%C
%H
%N
[Fe2(h-C5H5)2(CO)2(m-CNR)(m-CNMe2)]X
CNMe/–
CNMe/–
CNMe/–
CNMe/–
CNMe/–
[SO3CF3]−
[BPh4]−
[Cl]− · 0.5H2O
Br−
39.6 (39.7) 3.3 (3.5) 5.3 (5.2)
68.7 (68.9) 5.5 (5.5) 3.7 (3.9)
46.6 (46.4) 4.6 (4 6) 6.4 (6 4)
43.1 (43.0) 4.1 (4.0) 5.8 (5.9)
39.2 (39.1) 3.7 (3.6) 5.2 (5.4)
39.9 (39.8) 3.4 (3.5) 4.8 (5.1)
39.9 (39.6) 3.4 (3.5) 5.1 (5.3)
40.7 (40.9) 3.8 (3.8) 4.8 (5.0)
49.1 (48.9) 4.5 (4.4) 4.2 (4.2)
71.8 (72.1) 5.8 (5.9) 3.3 (3.4)
I−
13CNMe/– [SO3CF3]−
C15NMe/– [SO3CF3]−
CNEt/–
CNXy%/–
CNXy%/–
[SO3CF3]−
[SO3CF3]−
[BPh4]−
[Fe2(h-C5H5)2(L)(CNMe)(m-CNR)(m-CNMe2)]X
CNMe/CO [SO3CF3]−
CNXy%/CO [BPh4]−
CNMe/I−
40.6 (40.9) 4.0 (4.0) 7.3 (7.5)
72.4 (72.4) 6.0 (6.2) 4.7 (5.0)
37.8 (37.5) 4.0 (4.1) 7.3 (7.5)
2.1. The reaction of HOSO2CF3 with [7][SO3CF3] and
related compounds (reaction (i))
[Fe2(h-C5H5)2(CO)2{m-CN(H)R}(m-CNMe2)]X2
CNH/–
[SO3CF3]− · 0.5H2O
[SO3CF3]−
31.1 (31.0) 2.7 (2.9) 4.0 (4.0)
32.2 (31.9) 2.6 (2.6) 3.9 (4.1)
31.6 (31.7) 2.7 (2.6) 3.9 (4.3)
33.2 (32.9) 3.0 (2.9) 3.9 (4.0)
32.9 (33.0) 2.9 (2.9) 3.9 (4.0)
34.3 (33.9) 3.2 (3.1) 3.7 (4.0)
32.8 (32.9) 3.0 (2.9) 3.9 (4.0)
32.9 (33.0) 3.3 (2.9) 3.9 (4.0)
31.6 (31.6) 3.0 (3.2) 3.5 (4.0)
34.2 (33.9) 3.5 (3.1) 3.8 (4.0)
13CNH/–
C15NH/–
CNHc/–
[SO3CF3]−
A solution of [7][SO3CF3] (2 mmol) and HOSO2CF3
(10 mmol) in dry chloroform (50 cm3) was stirred at r.t.
for 1 h. The solvent was removed at reduced pressure,
and the residue dissolved in a minimum of an ethanol–
ether mixture. Cooling this overnight gave a 2.5:1 mix-
ture of orange cis and purple trans-[34][SO3CF3]2 in a
total yield of 85%. The two isomers could be separated
by fractional crystallization to give each in \95% purity
in this particular instance, but this was not always
possible.
The same procedure was used for the reactions of
HOSO3CF3 with analogues of [7][SO3CF3] in which
CNMe had been replaced by 13CNMe, C15NMe, CNEt
([8][SO3CF3]), CNBut, CNXy%([9]I) (Xy%=2,6-Et2C6H3
throughout this paper) and CNH ([6][SO3CF3]), and
[SO3CF3]−
13CNHc/– [SO3CF3]−
CNHd/–
CNMe/–
[SO3CF3]−
[SO3CF3]−
13CNMe/– [SO3CF3]−
C15NMe/– [SO3CF3]− · 0.75H2O
CNEt/–
CNBut/–
CNXy%/–
[SO3CF3]−
[SO3CF3]− · 0.25CHCl3 33.2 (33.9) 3.3 (3.3) 3.4 (3.5)
[SO3CF3]−
41.5 (41.4) 3.9 (3.7) 3.2 (3.5)
[Fe2(h-C5H5)2(CO)2{m-CN(Me)R}(m-CNMe2)]X2
CNEt/–
[SO3CF3]− · 0.5CHCl3 31.7 (31.4) 3.0 (3.0) 3.4 (3.3)
a Xy%=2,6-(Et)2C6H3.
b Found (calculated).
c m-CNMe2 replaced by m-CN(Et)Me.
d m-CNMe2 replaced by m-CNEt2.

254
K. Boss et al. / Journal of Organometallic Chemistry 579 (1999) 252–268
Table 2
IR spectra of the complexes described in the text in the 1580–2200 cm−1 and w(N–H) regions
Compounda
Absorption bandsb
CNR/L
[Fe2(h-C5H5)2(CO)2(m-CNR)(m-CNMe2)][SO3CF3]
CNMe/– (cis)
2013(10)
1981(3.0)
1985(10)
1980(2.3)
1981(2.4)
1985(10)
1980(2.3)
1984(1.6)
1961(4.6)
1786(1.8)
1806(1.5)
1752(1.6)
1760(1.8)
1790(2.0)
1795(1.7)
1864(1.4, br)
1777(4.1)
1600(2.2)
1588(1.8)
1598(1.8)
1599(2.0)
1587(1.9)
1598(2.2)
1582(2.9)
1584(4.7)
CNMe/– (trans)
13CNMe/– (cis)
C15NMe/– (cis)
C15NMe/– (trans)
CNEt/– (cis)
2012(10)
2013(10)
2012(10)
2017(10)
1996(10)
CNXy%/– (cis)c
CNXy%/– (cis)c,d
[Fe2(h-C5H5)2(L)(CNMe)(m-CNR)(m-CNMe2)][SO3CF3]
CNMe/CO
CNXy%/COc,d
CNMe/I−e
2176(9.0)
2178(6.4)
2151(8.3)
1979(10)
1962(10)
1763(5.9)
1789(6.7)
1765(10)
1584(5.2)
1578(7.2)
1564(4.2)
1539(4.2)
1570(5.7)
1534(3.8)
1574(4.6)
1547(5.0)
CNMe/Br−e
CNMe/Cl−e
2153(5.6)
2156(9.6)
1767(10)
1769(10)
[Fe2(h-C5H5)2(CO)(L){m-CN(H)R}(m-CNMe2)][SO3CF3]2
CNH/CO (cis)d
CNH/CO (trans)d
13CNH/CO (cis)d
2058(10)
2030(5.0)
2023(10)
2030(5.3)
1614(3.4)
1611(5.9)
1616(3.2)
1597(2.6)
1611(5.1)
1615(3.4)
1601(4.9)
1625(3.0)
1598(5.4)
1599(4.4)
1627(2.7)
1588(5.4)
1631(2.3)
1588(4.7)
1600(5.3)
1620(6.5)
1616(3.1)
1599(2.1)
1615(6.8)
1625(2.5)
1603(5.0)
1625(2.6)
1604(5.9)
1625(2.6)
1602(3.9)
1610(5.1)
1614(3.6)
1625(2.9)
1594(1 5)
1616(3.1)
1597(2.3)
3110(2.2) 3021(1.8)
3117(2.4) 2951(2.8)
3110(2.3) 3009(1.9)
2057(10)
13CNH/CO (trans)d
C15NH/CO (cis)d
CNH/CO (cis)d,f
CNH/CO (trans)d,f
2022(10)
2030(5.1)
2027(6.9)
2022(10)
3117(2.7) 2916(2.9)
3115(3.3) 3007(2.7)
3111(3.0) 3008(2.4)
3115(2.9) 2916(3.1)
2056(10)
2055(10)
13CNH/CO (cis)d,f
CNH/CO (cis)d,g
2054(10)
2059(10)
2027(6.9)
2029(6.8)
3115(2.7) 3015(2.2)
CNH/CO (trans)d,g
2027(10)
3114(3.1) 2995(2.5)
3122(5.9)
CNH/CNMed
2215(5.5)
2048(10)
2051(8.2)
2010(10)
2023(6.6)
2014(10)
1981(2.4)
2028(10)
2023(6.1)
CNMe/CO (cis)d
CNMe/CO (cis)h
1796(1.6)
CNMe/CO (trans)d
13CNMe/CO (cis)d
2048(10)
2048(10)
C15Nme/CO (cis)d
2023(6.9)
2027(10)
C15Nme/CO (trans)d
CNEt/CO (cis)d
CNBut/(cis)d
2054(10)
2046(10)
2040(10)
2027(5.2)
2023(6.4)
2022(7.1)
CNXy%/CO (cis)d
CNXy%/CO (cis)i
2049(5.3)
2014(10)
1981(2.4)
1794(2.1)
[Fe2(h-C5H5)2(CO)2{m-CN(Me)R}(m-CNMe2)][SO3CF3]2
CNEt/CO (cis)d
2054(10) 2029(6.1)
1601(6.9)
a Isomer in parentheses where known. Xy%, 2,6-(Et)2C6H3.
b Peak positions with relative peak heights in parentheses. Absorption bands due to w(CNR) (2150–2180 cm−1), w(CO) (1960–2060 cm−1),
w(m-CNR) (1750–1870 cm−1), w(m-CꢀNR2)(1530–1635 cm−1), and w(N–H) (2910–3120 cm−1) vibrations. Spectra run in dichloromethane solution
unless it is stated otherwise.
c [BPh4]− salt.
d Spectra run on solid samples (KBr disc).
e Not a salt. It does not contain [SO3CF3]− anion.
f m-CNMe2 ligand replaced by m-CN(Et)Me.
g m-CNMe2 ligand replaced by m-CNEt2.
h Spectra run in methanol solution.
i Spectra run in ethanol solution.

K. Boss et al. / Journal of Organometallic Chemistry 579 (1999) 252–268
255
Table 3
1H-NMR spectra of the compounds described in the text
CNR; L; isomer; solventa
Resonancesb
C5H5
m-CNMe2
m-CNR
t-CNR or NH
[Fe2(h-C5H5)2(CO)2(m-CNR)(m-CNMe2)][SO3CF3]
CNMe; –; cis; A
CNMe; –; trans; A
13CNMe; –; cis; B
13CNMe; –; trans; B
C15NMe; –; cis; B
C15NMe; –; trans; B
CNEt;–;cis;A
5.25(10)
5.09(10)
5.48(10)
5.32(10)
5.48(10)
5.31(10)
5.26(10)
5.20(10)
5.03(10)
4.22(6)
4.36(6)
4.28(6)
4.40(6)
4.29(6)
4.41(6)
4.21(6)
4.12(6)
4.38(6)
3.22(3)
3.88(3)
3.78(3,d, J=7.0)
3.97(3,d, J=7.0)
3.78(3,d, J=1.4)
3.96(3,d, J=1.40)
3.95(2,q), 1.42(3,t, J=7.3)
2.77(4,q), 1.27(6,t, J=7.5)
2.90(4,q), 1.39(6,t, J=7.5)
CNXy%;–; cis; Cc
CNXy%;–; trans; Cc
[Fe2(h-C5H5)2(L)(CNMe)(m-CNR)(m-CNMe2)][SO3CF3]
CNMe; CO; –; C
13CNMe; CO; –;C
CNXy%; CO; –; Cc
4.92(5)
5.07(5)
4.92(5)
5.07(5)
4.92(5)
4.99(5)
4.03(3)
4.08(3)
4.03(3)
4.08(3)
4.07(3)
4.12(3)
3.67(3)
2.99(3)
2.99(3)
3.04(3)
3.67(3,d, J=7.15)
2.77(4,q)
1.27(6, t, J=7.5)
7.21(m)
CNMe; CNMe; –; C
13CNMe; CNMe/ –; C
CNMe; I−; –; Cd
4.78(10)
4.78(10)
4.62(5)
4.70(5)
4.06(6)
4.06(6)
4.23(3)
4.53(3)
3.67(3)
3.67(3,d, J=7.15)
2.94(3)
[Fe2(h-C5H5)2(CO)(L){m-CN(H)R}(m-CNMe2)][SO3CF3]2
CNH; CO; cis; C
5.61(10)
5.54(10)
5.98(10)
5.89(10)
5.62(5)
4.11(6)
12.05(2,br)
12.05(2,br)
CNH; CO; trans; C
CNH; CO; cis; B e
CNH; CO; trans; B e
CNH; CO; cis; Ce,f
4.23(6)
4.42(6)
4.54(6)
4.08(3)
12.07(2,br)
12.07(2,br)
5.65(5)
4.44(2, m)
1.59(3,t, J=7.3)
4.22(3)
4.62(2,m)
1.64(3,t, J=7.3)
4.47(4,m)
1.56(6,t, J=7.3)
4.64(4,m)
1.59(6,t, J=7.3)
4.20(3)
CNH; CO; trans; Ce,f
5.53(5)
5.55(5)
CNH; CO; cis; Cg
5.62(10)
5.52(10)
12.1(2,br)
12.1(2,br)
CNH; CO; trans; Cg
CNH; CNMe; cis; C
CNH; CNMe; trans; C
5.27(5)
5.38(5)
5.32(5)
5.43(5)
5.65(10)
5.59(5)
5.64(5)
5.57(10)
5.49(10)
5.21(10)
6.01(10)
5.88(10)
5.64(10)
5.64(5)
5.59(5)
5.57(10)
5.66(10)
5.64(5)
5.59(5)
5.88(10)
5.64(10)
3.10(3)
3.08(3)
11.6(1,br)
11.9(1,br)
11.6(1,br)
11.9(1,br)
12.3(1,br)
11.7(1,br)
4.24(3)
4.07(3)
4.11(3)
4.12(6)
CNMe; CO; cis; C
CNMe; CO; cis; Ch
3.89(3)
3.88(3,d, J=5.1)
4.11(6)
CNMe; CO; trans; C
CNMe; CO; cis; D
CNMe; CO; trans; D
CNMe; CO; cis; B
CNMe; CO; trans; B
13CNMe; CO; cis; C
13CNMe; CO; cis; Ch
4.24(6)
4.19(6)
4.27(6)
4.41(6)
4.54(6)
4.12(6)
4.11(6)
4.06(3)
3.83(3)
3.93(3)
4.11(3)
12.3(1,br)
4.26(3)
3.89(3,d, JCH=5.3)
3.88(3,t, JCH=5.1, JHH=5.1)
12.3(1,br)
11.68(1,br)
13CNMe; CO; trans; C
C15NMe; CO; cis; C
C15NMe; CO; cis; Ch
4.24(6)
4.12(6)
4.11(6)
4.05(3,d, J=5.3)
3.89(3,d, J=1.5)
3.88(3,dd, JNH=1.84, JHH=4.9)
12.3(1,br)
12.3(1,br)
11.68(1,br,d, JNH=91.7)
C15NMe; CO; trans; B
CNEt; CO; cis; C
4.54(6)
4.11(6)
4.26(3,d, J=1.5)
4.39(2,m,br)
12.3(1,br)
1.53(3,t, J=7.3)

256
K. Boss et al. / Journal of Organometallic Chemistry 579 (1999) 252–268
Table 3 (Continued)
CNR; L; isomer; solventa
Resonancesb
C5H5
m-CNMe2
4.11(6)
m-CNR
t-CNR or NH
11.65(1,br)
12.3(1,br)
CNEt; CO; cis; Ch
CNEt; CO; trans; C
5.60(5)
5.63(5)
5.69(10)
4.39(1,m,br)
1.53(3,t, J=7.3)
4.07(2,m,br)
1.59(3,t, J=7.3)
1.70(9)
4.07(6)
CNBut; CO; cis; A
CNBut; CO; cis; Ah
5.66(10)
5.62(5)
5.66(5)
5.23(5)
5.74(5)
4.11(6)
4.10(3)
4.11(3)
4.13(3)
4.15(3)
1.70(9)
CNXy%; CO; cis; Cc,h
2.28(2,m) 2.95(2,m)
1.10(3,t, J=7.51)
7.5(3,m)
11.70(1,br)
[Fe2(h-C5H5)2(CO)2{m-CN(Me)R}(m-CNMe2)][SO3CF3]2
CNEt; CO; cis; C
5.69(5)
5.70(5)
4.10(3) 4.11(3)
4.07(3) 4.45(2,m)
1.56(3,t, J=7.3)
a Isomer when known; solvent, A, CDCl3; B. (CD3)2CO; C, CD3CN; and D, CD3OD.·Xy%, 2,6-(Et)2C6H3.
b Chemical shifts l measured as ppm downfield from Me4Si as an internal standard with relative integrations in parentheses. Resonances are
singlets unless it is stated otherwise (d=doublet, dd=double doublet, t=triplet, m=multiplet, br=broad) with coupling constants J in Hz. NH
resonances are those at ca. 12 ppm.
c Anion is [BPh4].
d This does not contain an anion. I− is coordinated.
e m-13CNH2 and m-C15NH2 complexes have identical spectra.
f m-CNMe2 replaced by m-CN(Me)Et.
g m-CNMe2 replaced by m-CNEt2.
h HOSO2CF3 added to NMR tube.
[Fe2(h-C5H5)2(CNMe)(CNEt)(m-CO)(m-CNMe2)]-
[SO3CF3], [11][SO3CF3], gave two products which were
identified by spectroscopy as [Fe2(h-C5H5)2(CO)
(CNMe){m-CN(H)Et}(m-CNMe2)][SO3CF3]2, [36][SO3-
CF3]2, and [Fe2(h-C5H5)2(CO)(CNEt){m-CN(H)Me}(m-
CNMe2)][SO3CF3]2, [37][SO3CF3]2, in the ratio of
40:60, These could not be separated by fractional crys-
tallization and when they were eluted down an
alumina column with acetone they gave a 40:60 mix-
ture of [Fe2(h-C5H5)2(CO)(CNMe)(m-CNEt)(m-CNMe2)]
[SO3CF3], [27][SO3CF3], and [Fe2(h-C5H5)2(CO)-
(CNEt)(m-CNMe)(m-CNMe2)][SO3CF3], [28][SO3CF3],
which could be identified by spectroscopy but not sepa-
rated. A similar work-up of the product from the
reaction of [Fe2(h-C5H5)2(CNxy%)(CNMe)(m-CO)(m-
CNMe2)][SO3CF3], [12][SO3CF3], with HOSO2CF3 fol-
lowed by anion exchange with Na[BPh4] in
dichloromethane solution and recrystallization from
all attempts to identify this failed as it reverted instan-
taneously to [4][SO3CF3] on work-up.
The reaction does not take place if (a) chloroform is
replaced by a more donating solvent such as acetoni-
trile, (b) if neat HOSO2CF3 is replaced by weaker acids
such as neat CF3CO2H or CH3CO2H, 48% aqueous
HBF4 or 60% aqueous HPF6 (strong mineral acids such
as H2SO4, HNO3 or HClO4 were not investigated), or
(c) if the two cyclopentadienyl rings in [7][SO3CF3] are
linked by a –CH2C(O)– bridge which constrains the
molecule to a cis configuration.
2.2. Deprotonation of [34][SO3CF3]2 and related salts
(reaction (ii))
A solution of [Fe2(h-C5H5)2(CO)2{m-CN(H)Me}(m-
CNMe2)][SO3CF3]2, [34][SO3CF3]2, in acetone was
passed down a chromatography column packed with
basic alumina (Merck 1097 activity II-III). Removal of
the solvent at reduced pressure and recrystallization of
the residue from ethanol–ether mixtures gave [Fe2(h-
C5H5)2(CO)2(h-CNMe)(m-CNMe2)][SO3CF3], [23][SO3-
CF3] in \90% yields.
ethanol–ether
(CO)(CNMe)(m-CNXy%)(m-CNMe2)][BPh4], [29][BPh4],
in 90% yield. The H-NMR spectrum of this showed
mixtures
gave
[Fe2(h-C5H5)2-
1
that it contained traces (B5%) of [Fe2(h-
C5H5)2(CO)(CNXy%)(m-CNMe)(m-CNMe2)][BPh4].
In a related reaction, the addition of HOSO2CF3 to a
solution of [Fe2(h-C5H5)2(CO)2(m-CO)(m-CNMe2)]-
[SO3CF3] [4][SO3CF3], precipitated a deep red oil, but
This general procedure was extended to the prepara-
tion of [Fe2(h-C5H5)2(CO)2(m-CNXy%)(m-CNMe2)]-
[SO3CF3], [25][SO3CF3], [Fe2(h-C5H5)2(CO)2(m-CNEt)-

K. Boss et al. / Journal of Organometallic Chemistry 579 (1999) 252–268
257
(m-CNMe2)][SO3CF3], [24][SO3CF3], [Fe2(h-C5H5)2-
(CO)(CNMe)(m-CNXy%)(m-CNMe2)][SO3CF3], [29][SO3-
CF3] (see above), and an inseparable mixture of
[Fe2(h-C5H5)2(CO)(CNMe)(m-CNEt)(m-CNMe2)][SO3-
CF3] [27][SO3CF3], and [Fe2(h-C5H5)2(CO)(CNEt)(m-
CNMe)(m-CNMe2)][SO3CF3], [28][SO3CF3] (see above).
In some instances anion exchange was effected by the
addition of KX(X− =Cl−, Br− or I−; 5 mmol) to a
solution of, for example, cis-[Fe2(h-C5H5)2(CO)2(m-
CNMe)(m-CNMe2)][SO3CF3] [23][SO3CF3] (1 mmol) in
methanol (50 cm3). After 10 min the solvent was re-
moved from the mixture at reduced pressure, and the
residue extracted into dichloromethane. This solution
was dried over magnesium sulphate, and then evapo-
rated to dryness. Recrystallization of the residue from
ethanol–ether mixtures gave the various cis-[Fe2(h-
C5H5)2(CO)2(m-CNMe)(m-CNMe2)]X salts in 90%
yields.
daylight (ca. 1 day), and a very slow reaction (weeks) in
the solid state in daylight.
After 20 min irradiation cis-[Fe2(h-C5H5)2(CO)2(m-
CNMe*)(m-CNMe2)]X, [23]X, (X− =[SO3CF3]− or
[BPh4]−; CNMe*=12CNMe or 13CNMe) gave cis-
[Fe2(h-C5H5)2(CO)(CNMe)(m-CO)(m-CNMe2)]X, [7]X,
in 90% yields. In contrast, trans-[Fe2(h-C5H5)2(CO)2(m-
CNMe)(m-CNMe2)]X gave a 60:40 mixture of cis and
trans-[Fe2(h-C5H5)2(CO)(CNMe*)(m-CO)(m-CNMe2)]X
in 85% total yield.
If the irradiation of cis-[Fe2(h-C5H5)2(CO)2(m-
CNMe)(m-CNMe2)][SO3CF3] (CNMe*=12CNMe or
13CNMe) is carried out in the presence of CNMe (18.0
mmol),
a
mixture of [Fe2(h-C5H5)2(CO)(CNMe)-
(m-CNMe)(m-CNMe2)][SO3CF3], [13][SO3CF3], and
[Fe2(h-C5H5)2(CNMe)2(m-CNMe)(m-CNMe2)][SO3CF3],
[30][SO3CF3], were obtained. They were separated by
chromatography (total yield=90%). Irradiation for 45
min gave [Fe2(h-C5H5)2(CNMe)2(m-CNMe*)(m-CN-
Me2)][SO3CF3] as the major product (yield 90%) but it
contained traces (B5%) of [Fe2(h-C5H5)2(CNMe)-
(CNMe*)(m-CNMe)(m-CNMe2)][SO3CF3]. When CN-
Me*=13CNMe the reactions were carried out on 1/10
scale and the products identified by spectroscopy only.
There was no reaction on the photolysis of [Fe2-
(h-C5H5)2(CO)(CNMe)(m-CNMe)(m-CNMe2)][SO3CF3],
[13][SO3CF3], in the absence of CNMe even after 2 h.
Continued photolysis in the presence of CNMe (18
2.3. Bridging to terminal migration of CNMe ligand of
[23][SO3CF3] and related compounds (reaction (iii))
A
stirred solution of [Fe2(h-C5H5)2(CO)2(m-
CNMe*)(m-CNMe2)]X, [23]X, (0.37 mmol) in
dichloromethane (50 cm3) was irradiated with a Philips
HPR 125 W lamp, and the reaction monitored using IR
spectroscopy. When it was complete, the solvent was
removed from the mixture at reduced pressure and the
product recrystallized from ethanol–ether mixtures.
There was no reaction in the dark, a slow reaction in
mmol)
gave
[Fe2(h-C5H5)2(CNMe)2(m-CNMe)(m-
CNMe2)][SO3CF3], [30][SO3CF3].
Table 4
13C-NMR spectra of the compounds described in the text
CNR; L; isomer; solventa
Resonancesb
C5H5 m-CNMe2
[Fe2(h-C5H5)2(CO)2(m-CNR)(m-CNMe2)][SO3CF3]
m-CNR/m-CN(H)R
t-CNR
t-CO
m-CNR/m-CN(H)R
m-CNMe2
CNMe; –; cis; A
13CNMe; –; cis; B
C15NMe; –; cis; C
88.9
89.9
89.9
53.9
54.4
54.4
44.3
44.7 (d, J=5.1)
44.8(br)
208.9
210.6
210.6
226.7
226.1
225.7 (d, J=10.2)
318.8
320.1
319.9
[Fe2(h-C5H5)2(L)(CNMe)(m-CNR)(m-CNMe2)][SO3CF3]
CNMe; CO; –; C 87.9 88.453.2 53.6 45.1
31.1
31.1
212.6
238.0
325.6
[Fe2(h-C5H5)2(CO)(L){m-CN(H)R}(m-CNMe2)][SO3CF3]2
CNH; CO; cis; C
13CNH; CO; cis; C
CNH; CNMe; cis; C
93.6
93.5
93.2
93.8
93.4
98.5
93.1
93.2
55.8
55.8
54.5
54.6
55.5
55.5
55.7
55.7
205.1
205.4 (d, J=6.9)
206.9
318.8
319.0
327.6
309.0
309.3
319.8
CNMe; CO; cis; B
CNMe; CO; trans; B
13CNMe; CO; cis; C
C15NMe; CO; cis; C
45.4
46.1
45.8(br)
45.8 (d, J=7.2)
206.1
205.1
205.6 (d, J=6.8)
205.4
309.5
315.0
309.5
309.1
309.3 (d, J=6.8)
a Isomer when known; solvent A, CDCl3; B, (CD3)2CO; C, CD3CN; and D, CD3OD.
b Chemical shifts l measured as ppm downfield from Me4Si as an internal standard. Resonances are singlets unless it is stated otherwise
(d=doublet, br=broad) with coupling constants J in Hz.

258
K. Boss et al. / Journal of Organometallic Chemistry 579 (1999) 252–268
Irradiation
of
[Fe2(h-C5H5)2(CO)2(m-CNMe)(m-
Me2)][SO3CF3]2 in 90% yield. By a judicious choice of
substrate and reagents it is possible to prepare a wide
range of
CNMe2)]X (X− =I−) gave an unisolable product
which on further photolysis was largely converted to
[Fe2(h-C5H5)2(CO)2{m-CN(R)R%}{m-CN-
isolable
[Fe2(h-C5H5)2(CNMe)(I)(m-CO)(m-CNMe2)],
(R%%)-R%%%}][SO3CF3]2 salts but not all would crystallize.
[31], after 3 h (brown crystals; yield 60%). Similar
behaviour was observed when X− =Cl− or Br−, but
the reaction times were longer, 4.5 and 6 h. respectively,
and the final products too unstable to be isolated. If the
irradiation of [Fe2(h-C5H5)2(CO)2(m-CNMe)(m-CN-
Me2)]I is carried out in the presence of CNMe (18
mmol), the sole detectable product contained the
[Fe2(h-C5H5)2(CNMe)2(m-CNMe)(m-CNMe2)]+ cation,
but it was not isolated.
Neither [Fe2(h-C5H5)2(CO)2(m-CNXy%)(m-CNMe2)]I,
[25]I, nor [Fe2(h-C5H5)2(CO)(CNMe)(m-CNXy)(m-CN-
Me2)][SO3CF3], [29][SO3CF3], were affected even after
extended irradiation (\6 h), and these salts could be
isolated in yields of \90% from their reaction
mixtures.
2.5. The reaction of HOSO2CF3 with [5] and related
compounds (reaction (6))
A
solution of [Fe2(h-C5H5)2(CO)(CN*)m-CO)-
(m-CNMe2)], [5], (2 mmol; CN*=12C14N, 13C14N or
12C15N) and HOSO2CF3 (3 mmol) in chloroform (50
cm3) was stirred at r.t. for 1 h. The solvent was
removed at reduced pressure, and the residue
recrystallized from an ethanol–ether mixture to give
solid
[Fe2(h-C5H5)2(CO)2(m-CNH2)(m-CNMe2)][SO3-
CF3]2, [32][SO3CF3]2, in 85% yield. This could be
separated by fractional crystallization into orange
crystals of the cis isomer as the major product, and the
dark purple crystals of the less abundant trans isomer.
The same procedure may be used to prepare other
[Fe2(h - C5H5)2(CO)2(m - CNH2){m - CN(R%)R)][SO3CF3]2
salts where (R%)R=(Me)Et or Et2.
2.4. The reaction of [23][SO3CF3] and related compounds
with protic and alkyl electrophiles (reaction (i6))
Under the same conditions, [Fe2(h-C5H5)2(CN-
Me)(CN)(m-CO)(m-CNMe2)], [10], gives green crystals
A solution of [Fe2(h-C5H5)2(CO)2(m-CNMe)(m-CN-
Me2)][SO3CF3], [23][SO3CF3], (1 mmol) and MeI (50
mmol) in dry chloroform was stirred overnight. Orange
crystals of [Fe2(h-C5H5)2(CO)2(m-CNMe2)2][I][SO3CF3]
[14][I][SO3CF3], precipitated. They were filtered off,
washed with cold chloroform–ether mixtures and dried
(yield 40%).
If MeI is replaced by ROSO2CF3(R=H, Me or Et)
the reaction is complete within 3 h. giving orange
crystals of [Fe2(h-C5H5)2(CO)2{m-CN(R)Me}(m-CN-
of
[Fe2(h-C5H5)2(CO)(CNMe)(m-CNH2)(m-CNMe2)]
[SO3CF3]2, [33][SO3CF3]2, in 50% yield. Spec-
troscopy showed that this was a 10:1 mixture of two
isomers which could not be separated.
2.6. Deprotonation of [32][SO3CF3]2 and [33][SO3CF3]2
(reaction (6i))
When a solution of [Fe2(h-C5H5)2(CO)2(m-CNH*2 )(m-
CNMe2)][SO3CF3]2, [32][SO3CF3]2, in acetone is chro-
Fig. 1. Structure and atom labelling for the [Fe2(h-C5H5)2(CO)2(m-CNMe)(m-CNMe2)]+ cation, [23]+
.

K. Boss et al. / Journal of Organometallic Chemistry 579 (1999) 252–268
259
Table 5
Table 6
Atomic coordinates (×104) and equivalent isotropic displacement
parameters for cis-[Fe2(h-C5H5)2(CO)2(m-CNMe)(m-CNMe2)][BPh4]
Crystal data and structure refinement for cis-[Fe2(h-C5H5)2(CO)2(m-
CNMe)(m-CNMe2)][BPh4]
a
Empirical formula
Formula weight
Temperature (K)
Wavelength (A)
Crystal system
Space group
C41H39BFe2N2O2
714.25
293(2)
0.70930
Monoclinic
P21/n
Atom
x
y
z
Ueq
Fe(1)
Fe(2)
N(1)
N(2)
O(1)
O(2)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
C(9)
3202(1)
1303(1)
185(1)
360(2)
753(2)
477(2)
8491(1)
7383(1)
8494(3)
7969(3)
34(1)
37(1)
57(1)
41(1)
80(1)
85(1)
40(1)
34(1)
76(2)
58(1)
61(1)
43(1)
47(1)
45(2)
47(2)
47(2)
42(2)
42(2)
63(2)
59(2)
70(2)
61(2)
57(2)
32(3)
48(4)
47(4)
57(5)
45(4)
33(3)
33(3)
46(3)
28(3)
52(4)
31(1)
32(1)
42(1)
51(1)
51(1)
47(1)
40(1)
32(1)
43(1)
57(1)
58(1)
49(1)
40(1)
32(1)
41(1)
46(1)
50(1)
47(1)
40(1)
33(1)
44(1)
57(1)
59(1)
56(1)
47(1)
˚
3129(1)
1421(3)
5097(2)
3796(3)
3576(3)
2200(3)
4164(3)
810(4)
Unit cell dimensions
10195(2)
8726(3)
8248(3)
7926(3)
9185(4)
8580(4)
7446(4)
9537(3)
8205(3)
8111(5)
9066(4)
9060(3)
8101(4)
7515(2)
5969(4)
6181(4)
6407(4)
6335(4)
6065(4)
8581(11)
9255(5)
8755(12)
7771(9)
7663(7)
6069(8)
6295(8)
6341(8)
6144(8)
5976(9)
2868(3)
2793(3)
3577(3)
3495(3)
2616(3)
1820(3)
1919(3)
2057(3)
1669(3)
1016(3)
731(4)
˚
a (A)
13.8960(10)
17.853(4)
14.116(3)
94.06(2)
3493.2(11)
4
1.358
0.869
1488
0.40×0.35×0.25
2.13–27.91
−85h515, 05k519,
−165l516
7988
−1011(2)
540(2)
˚
b (A)
˚
c (A)
758(2)
682(3)
1269(3)
217(3)
819(2)
−533(2)
2101(3)
2208(3)
2378(3)
2377(3)
2206(3)
316(4)
−452(3)
−546(3)
164(4)
i (°)
3
˚
V (A )
5682(3)
5662(3)
3546(3)
3413(3)
2111(2)
2479(5)
3477(4)
3726(3)
2882(5)
3509(3)
3369(5)
2396(6)
1936(3)
2624(5)
2133(6)
2917(12)
3760(6)
3497(10)
2492(11)
3683(5)
2912(10)
2073(6)
2326(8)
3322(9)
1668(3)
2776(3)
3448(3)
4401(3)
4741(3)
4111(3)
3156(3)
909(3)
Z
Dcalc. (g cm−3
)
Absorption coefficient (mm−1
F(000)
)
Crystal size (mm)
Theta range for data collection (°)
Index ranges
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
C(108)
C(109)
C(110)
C(111)
C(112)
C(113)
C(114)
C(115)
C(116)
C(117)
B(1)
C(18)
C(19)
C(20)
C(21)
C(22)
C(23)
C(24)
C(25)
C(26)
C(27)
C(28)
C(29)
C(30)
C(31)
C(32)
C(33)
C(34).
C(35)
C(36)
C(37)
C(38)
C(39)
C(40)
C(41)
Reflections collected
Independent reflections
Reflections observed (\2|)
Refinement method
7611 [Rint=0.0126]
4442
Full-matrix least-squares on
F2
697(2)
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I\2|(I)]
R indices (all data)
7611/0/263
1.112
2170(6)
2318(7)
2411(7)
2321(8)
2172(7)
−166(7)
−640(4)
−191(7)
561(6)
R1=0.0593 awR2=0.1703
R1=0.1082 awR2=0.1866
0.785 and −0.498
Largest difference peak and hole
−3
˚
(e A
)
a R indices; R1=[ꢀꢁꢁFoꢁ−ꢁFcꢁꢁ]/ꢀꢁFoꢁ (based on F), wR2=
[[ꢀw(ꢁFo2−Fc2ꢁ)2]/[ꢀw(Fo2)2]]1/2 (based on F2). W=1/[(|Fo)2+
(0.1*P)2]. Goodness-of-fit=[ꢀw(Fo2−Fc2)2/(Nobs–Nparameters)]1/2
.
576(5)
1161(2)
1457(2)
1527(2)
1722(3)
1851(3)
1766(3)
1578(2)
1545(2)
2255(2)
2578(3)
2202(3)
1508(3)
1193(2)
1376(2)
2018(2)
2196(3)
1738(3)
1113(3)
936(2)
matographed on alumina it is deprotonated and reverts
immediately to [Fe2(h-C5H5)2(CO)(CN*)(m-CO)(m-CN-
Me2)], [5], in quantitative yield.
Under the same conditions [Fe2(h-C5H5)2-(CO)-
(CNMe)(m-CNH2)(m-CNMe2)][SO3CF3]2,
[33][SO3-
CF3]2, gives
a
70:30 mixture of [Fe2(h-C5H5)2-
1044(3)
363(4)
−472(4)
−628(3)
40(3)
1218(3)
1468(3)
1042(3)
341(3)
(CNMe)(CN)(m-CO)(m-CNMe2)], [10], and [Fe2(h-
C5H5)2(CO)(CN)(m-CNMe)(m-CNMe2)], [26].
1112(3)
1772(3)
3883(3)
4417(3)
5254(3)
5585(3)
5067(3)
4240(3)
2716(3)
3475(3)
3329(4)
2436(4)
1682(4)
1815(3)
2.7. The structure of cis-[Fe2(p-C5H5)2(CO)2(v-
CNMe)(v-CNMe2)][BPh4]
A crystal grown from acetonitrile solution was sub-
ject to a X-ray diffraction study. Crystal data is given in
Table 5. The structure was solved by direct methods,
SHELX-86 [4], and refined by full matrix least squares
using SHELXL-93 [5]. SHELX operations were rendered
paperless using ORTEX [6] which was also used to
obtain the drawings. Data were corrected for Lorentz
and polarisation effects but not for absorption. Hydro-
gen atoms were included in calculated positions with
thermal parameters 30% larger than the atom to which
55(3)
486(3)
1736(3)
1944(3)
2001(4)
1883(4)
1733(3)
1652(3)
247(2)
−244(2)
−1019(3)
−1308(3)
−845(3)
−81(3)
a Ueq is defined as one third of the trace of the orthogonalised Uij
tensor.

260
K. Boss et al. / Journal of Organometallic Chemistry 579 (1999) 252–268
they were attached. The cyclopentadienyl rings were
disordered over two positions. The remaining
non-hydrogen atoms in the metal coordination sphere
were refined anisotropically. All calculations were
performed on a Silicon Graphics R4000 computer. The
structure of the cation together with the atom labelling
is illustrated in Fig. 1. Atom coordinates are given in
Table 6 and selected bond lengths and bond angles are
listed in Table 7.
3. Results and discussion
The six general reactions studied in the course of this
course of this work are (i) those of [Fe2(h-
C5H5)2(L)(CNR)(m-CO)(m-CNMe2)]+
salts
with
HOSO2CF3 to give [Fe2(h-C5H5)2(CO)(L){m-CN(H)-
Me}(m-CNMe2)]2+, (ii) their subsequent deprotonation
to give [Fe2(h-C5H5)2(CO)(L)(m-CNR)(m-CNMe2)]+
which may revert (iii) to [Fe2(h-C5H5)2(L)(CNR)(m-
CO)(m-CNMe2)2]+ or are trapped (iv) by protonation
or alkylation with R%X to give (h-C5H5)2(CO)(L){m-
CN(R%)Me}(m-CNMe2)]2+. In these reaction CNMe
can be replaced by other organoisocyanides, and the
Me groups in the m-CNMe2+ by ethyl groups. A special
case of this overall scheme is (v) the reaction of [Fe2(h-
C5H5)2(L)(CN)(m-CO)(m-CNMe2)] and [Fe2(h-C5H5)2-
(L)(CNH)(m-CO)(m-CNMe2)]+ salts with HOSO2CF3
to give [Fe2(h-C5H5)2(CO)(L)(m-CNH2)(m-CNMe2)]2+
salts, and (vi) their instantaneous reversion to [Fe2(h-
C5H5)2(L)(CN)(m-CO)(m-CNMe2)]+ on deprotonation.
These are shown in Scheme 1 where cis isomers only
are illustrated, but the scheme also applies to trans
isomers (see Section 3.6). L is a two-electron donor
ligand, usually CO but it may be anorgano-isocyanide.
The individual reactions carried out in the course of
this work are summarised in Schemes 2 and 3 which are
based on compounds containing the m-CNMe2+ ligand,
but many of the reactions have also been carried out
using compounds containing m-CN(Me)Et+ or
m-CNEt2+ instead. These are listed in Tables 1–4 where
appropriate. The numbering of the various compounds
continues on from that given in Ref. [3], but some are
common to both papers. Compounds [5]+ –[12]+ and
[31] are of the type [Fe2(h-C5H5)2(L)(L%)(m-CO)(m-
CNMe2)]+, [23]+ –[30]+ are of the type [Fe2(h-
C5H5)2(L)(L%)(m-CNR)(m-CNMe2)]+ and [32]2+ –[41]2+
are of the type [Fe2(h-C5H5)2(L)(L%){m-CN(R%)R}(m-
CNMe2)]2+ (R=H, alkyl or aryl; L, L%=CO or
CNR).
Scheme 1.
Table 7
Selected bond lengths and angles for cis-[Fe2(h-C5H5)2(CO)2(m-
CNMe)(m-CNMe2)][BPh4]
˚
Bond length (A)
Fe(l)–Fe(2)
Fe(1)–C(6)
Fe(1)–C(1)
Fe(1)–C(2)
C(6)–O(1)
C(1)–N(1)
N(1)–C(3)
2.532(1)
1.748(4)
1.960(4)
1.876(4)
1.145(5)
1.204(5)
1.457(7)
Fe(2)–C(7)
Fe(2)–C(1)
Fe(2)–C(2)
C(7)–O(2)
C(2)–N(2)
N(2)–C(4)
N(2)–C(5)
1.754(5)
1.945(4)
1.884(4)
1.139(5)
1.293(5)
1.468(6)
1.470(6)
Bond angles (°)
Fe(2)–Fe(1)–C(6)
C(1)–Fe(1)–C(2)
Fe(1)–C(1)–Fe(2)
Fe(1)–C(1)–N(1)
Fe(1)–C(2)–N(2)
C(1)–N(1)–C(3)
97.4(2)
94.9(2)
80.9(2)
141.0(4)
136.6(3)
131.8(5)
Fe(1)–Fe(2)–C(7)
C(1)–Fe(2)–C(2)
Fe(1)–C(2)–Fe(2)
Fe(2)–C(1)–N(1)
Fe(2)–C(2)–N(2)
C(2)–N(2)–C(4)
C(2)–N(2)–C(5)
99.9(2)
95.1(2)
84.7(2)
138.1(5)
138.5(3)
122.4(4)
123.4(4)
3.1. Acid-promoted RNC- and CN-migration (reactions
(i) and (6))
The various complexes are air-stable crystalline
solids, but some are deliquescent especially those
containing the m-CNH2+ ligand. All are soluble in polar
organic solvents.
The addition of neat trifluoromethanesulphonic acid
to a solution of [Fe2(h-C5H5)2(CO)(CNMe)(m-CO)(m-
CNMe2)][SO3CF3], [7][SO3CF3], in chloroform results
in the formation of [Fe2(h-C5H5)2(CO)2{m-CN(H)Me}-

K. Boss et al. / Journal of Organometallic Chemistry 579 (1999) 252–268
261
(m-CNMe2)][CF3SO3]2, [34][CF3SO3]2, salts in near
quantitative yields as determined by NMR
spectroscopy. The product is a 2.5:1 mixture of the
orange cis isomer and the purple trans isomer which
can be separated by fractional crystallization.
the t-CO ligand was very labile and readily replaced
by solvent molecule when the product was
recrystallized. Eventually the green acetonitrile
a
derivative
[Fe2(h-C5H5)2(NCMe)(CNBut){m-CN(H)-
But}(m-CNMe2)][SO3CF3]2 was precipitated from
acetonitrile solution.
The reaction also takes place with analogues of [7]+
in which the m-CNMe2 ligand is replaced by
m-CN(Et)Me or m-CNEt2, and t-CNMe is replaced by
t-13CNMe, t-C15NMe, t-CNEt, CNBut or t-CNXy%
(Xy%=2,6-Et2C6H3). However, it is not completely
general. It does not take place if the two
When the precursors contain two different t-CNR
ligands, they do not show an equal propensity to
migrate. Thus protonation of [11]+ gives a mixture of
[36]+, as a consequence of EtNC migration, and [37]+,
resulting from MeNC migration, in the ratio of 40:60.
On the other hand, with [12]+ MeNC migration gives
[38]+ as the minor product of protonation (B5%
detected by 1H-NMR spectroscopy) and the major
(\95%) product, [40]+, arises from Xy%NC migration.
The addition of HOSO2CF3 to a chloroform solution
of the cyano complex [5] results in the formation of
[32]2+, presumably via the HNC salt [6]+ which also
reacts with the acid to give [32]+. Under the same
conditions [10], which contains t-CNMe and t-CN−,
gives [33]2+ as the sole product i.e. there is only CN−
(or CNH) migration and no CNMe migration.
In a relevant experiment, a solution of [4][SO3CF3] in
chloroform was treated with an excess of neat
HOSO2CF3. The colour of the solution changed and a
deep red oil precipitated. It was clear that something
had happened, but all attempts to isolate the product
gave only [4][SO3CF3].
cyclopentadienyl rings of [7]+ are linked by
a
–CH2C(O)– bridge. It takes place in polar, non-donor
solvents such as chloroform or dichloromethane but
not in donor solvents such as acetonitrile. It is brought
about only by the very strong acid HOSO2CF3, and
weaker acids such as neat CF3CO2H, neat CH3CO2H,
40% aqueous HBF4 or 60% aqueous HPF6 are not
effective.
A similar reaction takes place with the complex-
es [Fe2(h-C5H5)2(CNR)(CNR%)(m-CO)(m-CNMe2)][SO3-
CF3] which have two terminal isonitrile ligands.
Unfortunately, in no case could the anticipated initial
products be isolated although they were formed and
could be identified by spectroscopy. Where R=R% a
single product would be expected, [Fe2(h-C5H5)2-
(CO)(CNR){m-CN(H)R}(m-CNMe2)][SO3CF3]2 but in
the only reaction of this type attempted, where R=But,
Scheme 2.

262
K. Boss et al. / Journal of Organometallic Chemistry 579 (1999) 252–268
Scheme 3.
3.2. Deprotonation of complexes containing the
CN(H)R+ and CNH+2 ligands (reactions ii and 6i)
Me2)][SO3CF3]2, [40][SO3CF3]2, are completely deproto-
nated by alumina to give the m-CNR complexes
[23][SO3CF3] and its analogues, [24][SO3CF3], [27][SO3-
CF3], [28][SO3CF3], [25][SO3CF3], and [29][SO3CF3] re-
spectively. These reactions can be reversed by the addi-
tion of acids (see below).
[Fe2 (h-C5H5)2(CO)2{m-CN(H)Me}(m-CNMe2)][CF3-
SO3]2, [34][SO3CF3]2, dissolves unchanged in acetone or
acetonitrile, but there is spectroscopic evidence for fast
protonation–deprotonation processes (see below). In
contrast in methanol its colour changes from green to
red. Even though only [34][SO3CF3]2 may be recovered
If [Fe2(h-C5H5)2(CO)(CNMe)(m-CNH2)(m-CNMe2)]-
[SO3CF3]2, [33][SO3CF3]2, is dissolved in dichloro-
methane, IR spectroscopy shows that a mixture of
compound are present and that they contain t-CN,
t-CNH, t-CNMe, t-CO, m-CO, m-CNMe, and m-
CNMe2+ ligands. They could not be separated as, when
solutions of this compound in acetone are passed down
an alumina column, a double deprotonation of the
m-CNH2+ ligand takes place and two products are
obtained, [26] and [10] in the ratio 30:70. In the first of
these it is the CNMe ligand which exchanges with
m-CN− or m-CNH ligand formed on deprotonation,
and in the second it is CO. Similarly [32][SO3CF3]2 is
deprotonated to [5]. In neither instance could we
achieve a stepwise deprotonation of the CNH2+ ligand
with the formation of complexes containing CNH or
m-CN ligands.
1
from this solution, IR and H-NMR spectroscopy (see
below) show that the solution contains an equilibrium
mixture of [34]2+ and [23]+ salts which are intercon-
verting rapidly at r.t. The addition of a single drop of
HOSO2CF3 to the solution shifts the equilibrium so
that only [34]2+ could be detected.
The m-CNXy% ligand is much less basic than m-CNMe
so it is not surprising that [39]2+ is dissociated to [25]+
in acetonitrile and acetone as well as methanol. How-
ever, [39][SO3CF3]2 can be isolated from these solutions
whereas all attempts to isolate [40]2+ salts failed. The
green colour showed that they were formed but would
not crystallize, and only the unprotonated [29]+ could
be isolated as its [BPh4]− salt.
The m-CN(H)R+ ligands in [34][SO3CF3]2 and
analogous salts [Fe2(h-C5H5)2(CO)2{m-CN(H)Et}(m-
CNMe2)][SO3CF3]2, [35][SO3CF3]2, [Fe2(h-C5H5)2-(CO)-
(CNMe){m-CN(H)Et)(m-CNMe2)][CF3SO3]2, [36][SO3-
CF3]2, [Fe2(h-C5H5)2(CO)(CNEt){m-CN(H)Me}(m-CN-
Me2)][SO3CF3]2, [37][SO3CF3]2, [Fe2(h-C5H5)2(CO)2-
{m-CN(H)Xy%}(m-CNMe2)] [SO3CF3]2, [39][SO3CF3]2,
and [Fe2(h-C5H5)2(CO)(CNMe){m-CN(H)Xy%}(m-CN-
3.3. The protonation and alkylation of [23]+ and related
complexes (reaction (i6))
The reaction used to prepare the [Fe2(h-
C5H5)2(L)(CO)(m-CNMe)(m-CNMe2)]+ complexes, the
deprotonation of [Fe2(h-C5H5)2(L)(CO){m-CN(H)Me}-
(m-CNMe2)]2+, may be reversed by their treatment with
a strong acid. However, these m-CNR ligands are rela-

K. Boss et al. / Journal of Organometallic Chemistry 579 (1999) 252–268
263
tively poor nucleophiles even when R=alkyl and very
3.5. Infrared spectra
poor nucleophiles when it is aryl. This is because the
strong electron-withdrawing effect of the m-CNMe2+
ligand reduces back-bonding to the m-CNR and hence its
nucleophilicity. Consequently reprotonation requires a
strong acid and alkylation requires strong electrophiles
such as MeOSO2CF3; MeI is not effective.
This route to compounds such as [Fe2(h-
C5H5)2(CO)2(m-CNMe2)2][SO3CF3]2 allows the prepara-
tion of both their cis and trans isomers whereas only the
former were obtained by alkylating [Fe2(h-
C5H5)2(CO)2(CNMe)2]. It also allows analogues of such
salts to be prepared which contain various combination
of alkyl groups in their two m-CN(R%)R+ ligands.
The various compounds show strong absorption
bands in the 1550–2200 cm−1 region which can be
assigned to the CN or CO stretching vibrations of
m-CNR2+, m-CNR, m-CO, t-CO, t-CNR and t-CN−
ligands (Table 2). This has been discussed elsewhere
[1,3], except for the those due to the m-CNR ligands (see
below). The spectra also show characteristic absorption
bands which confirm the presence of the [SO3CF3]− ions
when appropriate, and other weaker bands which yield
no important structural information.
Where cis and trans isomers are formed they usually
have different spectra in this region. However, it is only
where the complexes contain the Fe2(t-CO)2 moiety that
the number and relative intensities of the absorption
bands due to the w(t-CO) vibrations can be used to
distinguish the cis and trans isomers unambiguously [7].
Isotopic labelling of the CN, CNR and m-CN(R%)R+
ligands results in changes in the frequencies of their
vibrations. This has been discussed elsewhere for all
complexes except those with labelled m-CNMe, m-
CN(H)Me+ and m-CNH2+ ligands. It is only for the first
of these that 13C or 15N labelling results in decreases in
w(m-CN) stretching frequencies which are close to those
calculated on the basis of the reduced mass of the C–N
simple harmonic oscillator. For example, the w(m-C-
NMe) of cis-[23][CF3SO3] decreases from 1786 to 1752
cm−1 (13C) or 1760 cm−1 (15N) (Table 2) compared with
calculated values of 1749 cm−1 for 13C–14N and 1758
cm−1 for 12C–15N. For the m-CN(H)Me+ and m-CNH2+
ligands, isotopic substitution results in frequency reduc-
tions which are much smaller than would be anticipated
on the basis of this simple model. Similar behavior has
been observed on isotopic substitution of t-CNMe in
[7]+ salts and has been attributed to the effect of the Me
group on the reduced mass of the C–N oscillator [3].
The m-CNMe and m-CNEt ligands in [13]+, [23]+,
[24]+, [26]+, [27]+, [28]+ and [30]+ salts give rise to
absorption bands between ca. 1780 and 1810 cm−1. In
general, these are rather broad and symmetrical in the
solid state, but in solution are broad and unsymmetri-
cal or with two clearly distinguishable components. The
band shapes depend on the solvent. This is attributed to
cation–anion or cation–solvent interactions similar to
those invoked to account for the shape of the w(m-CO)
absorption band of [4]+ salts [8]. Their frequencies
decrease as the t-CO ligands are replaced by t-CNR,
and are not greatly dependent on the medium or the
solvent. However, the same is not true for both cis and
trans-[25][SO3CF3] where the w(CN) band due to its
m-CNXy% ligand is extremely broad in solution and lies
at very high frequencies as compared with the solid
state. This is illustrated in Fig. 2 for the trans isomer.
This is unprecedented behaviour for which there is no
3.4. The migration of CNR from bridging to terminal sites
(reaction (iii))
The [25]+ and [29]+ salts with their m-CNXy% ligands
are indefinitely stable in both the solid state and in
solution. In contrast, under the influence of light [23]+
salts revert to [7]+ salts in solution with t-CO/m-CNMe
exchange. The reaction is accelerated by UV radiation,
but then the product depends on the counteranion, X−.
[23]X gives [7]X when X− =[SO3CF3]− or [BPh4]−, but
when X− =Cl−, Br− or I− the reaction proceeds via
an unknown but detectable intermediate to [Fe2(h-
C5H5)2(X)(CNMe)(m-CO)(m-CNMe2)]. Although these
complexes have similar IR spectra, only [31] where X=I
was sufficiently stable to be isolated and characterised.
The only IR absorption bands of the intermediates
which are not obscured by the bands of their precursors
or successors are at 1973 cm−1 (X=Cl), 1971 (X=Br)
and 1969 cm−1 (X=I). These are probably due to their
w(CO) vibrations and as their frequencies depend on X,
it suggests that the intermediates may be of the type
[Fe2(h-C5H5)2(X)(CO)(m-CNMe)(m-CNMe2)] with coor-
dinated X−.
The photolysis of [23][SO3CF3] and its 13CNMe coun-
terpart were studied in detail. The cis isomers of both
gave cis-[7][SO3CF3] or its labelled counterpart as the
sole products in \90% isolated yields, whereas trans-
[23][SO3CF3] gave a mixture of cis and trans-[7][SO3CF3]
in 60:40 ratio and 85% total yield. If the irradiation of
the cis salts are carried out in the presence of an 18-fold
excess of CNMe, [13][SO3CF3] and [30][SO3CF3] are
formed in turn, again in \90% yield. However, the
labelled m-13CNMe ligand of [23][SO3CF3] is retained
almost exclusively (\98%) in the bridging site in both
of these compounds and m-CNMe/t-CO interchange
does not take place. Pure [13][SO3CF3] is unaffected by
irradiation but in the presence of CNMe it undergoes
CO substitution to give [30][SO3CF3]. Furthermore irra-
diation of [23]I in the presence of excess CNMe results
in complete substitution of CO by CNMe to give [13]I
without ligand migration or coordination of I−.

264
K. Boss et al. / Journal of Organometallic Chemistry 579 (1999) 252–268
Fig. 2. The inhered spectrum of trans-[Fe2(h-C5H5)2(CO)2(m-CNMe)(m-CNMe2)][SO3CF3], [25][SO3CF3], in (a) the solid state (KBr) and (b)
CH2Cl2 solution.
ready explanation especially as the frequencies of the
other vibrations are almost unchanged.
inversion at N which is fast even at low temperatures in
both cis and trans isomers. Consequently in [23]+ and
related species the two Fe(h-C5H5) moieties and the
two Me groups of the m-CNMe2+ ligand are rendered
equivalent on the NMR timescale so that only one
signal due to each is observed in the NMR spectrum
whereas two could have been expected for a static
molecule. This rapid inversion at N also renders equiv-
alent the two methylene protons of the m-CNEt ligand
of [24]+, [Fe2(h-C5H5)2(CO)2(m-CNEt)(m-CNMe2)]+.
Furthermore, for complexes containing the m-
CN(H)R+ ligand, N–H+ dissociation is facile, rapid
and reversible. As the resultant m-CNR ligand under-
goes a fast inversion at N, the overall process deproto-
nation=inversion=protonation is fast on the NMR
timescale at r.t. and results in a fast exchange of H and
R groups of the m-CN(H)R+ ligands so that for [34]+,
for example, the NMR spectra is simpler than would
have been expected and in such complexes it is not
possible to distinguish between the two (h-C5H5)Fe
sites or the Me groups of the m-CNMe2+ ligands. If acid
is added to the solution, the dissociation of H+ is
suppressed, the N–H resonance shifts noticeably, two
(h-C5H5) signals are observed and the m-CN(H)Me
group gives rise to a doublet due to the N(H)CH3
because of their coupling with the N(H) proton even
though there is still a single m-CNMe2 resonance. Simi-
lar behaviour is observed in acetone solution, but the
N–H resonance was not detected, perhaps due to H-
bonding with the solvent.
There is a weak band in the IR spectrum of cis-
[Fe2(h-C5H5)2(CO)2{m-CN(H)Me}2][SO3CF3]2 at 3011
cm−1 (KBr disc) which is absent from the spectrum of
cis-[Fe2(h-C5H5)2(CO)2(m-CNMe2)2][SO3CF3]2. It is at-
tributed to the w(N–H) vibration of the m-CN(H)Me
ligands. Bands of similar frequency are observed in the
spectra of all of the complexes containing this ligand
and anion. The w(N–H) vibrations of the m-CNH2+
ligands of [Fe2(h-C5H5)2(CO)2(m-CNH2)(m-CNMe2)]-
[SO3CF3]2 and related salts give rise to strong and
broad absorption bands at ca. 2910–3120 cm−1 (KBr
disc). The relatively low frequencies of these w(NH)
vibrations may be due to hydrogen bonding of the
m-CN(H)Me+ or m-CNH2+ ligands with the [SO3CF3]−
anion. We were unable to identify absorption bands
due to the l(N–H) bending modes.
3.6. NMR spectra
The 1H-NMR spectra of the complexes (Tables 3 and
4) are readily assigned by comparison with the spectra
of related compounds. Those of cis and trans isomers
are distinguishable as are those of the syn and anti
forms of unsymmetrical complexes (see below). Those
complexes containing m-CN(H)R+ and m-CNH2+ lig-
ands show broad resonances at ca. 12.3 l due to the
N-bound protons.
In general, complexes containing the m-CN(R%)R+
ligands do not undergo cis–trans isomer interchange or
ligand site exchange and the same is true for the
complexes described herein. However, the m-CNR lig-
and in derivatives [23]+ –[30]+ is bent at N (see the
structure of [23][BPh4] below), so they undergo rapid
IR spectroscopy has shown that in methanol-D4 solu-
tion, cis-[34]2+ partially dissociates and coexists in
equilibrium with cis-[23]+ (mole ratio=ca. 8:10).
1
However the H-NMR spectrum shows single signals
due to C5H5, m-CNMe2, and m-CN(H)Me ligands confi-

K. Boss et al. / Journal of Organometallic Chemistry 579 (1999) 252–268
265
where R=alkyl, but when R=Xy% dissociation of H+
is complete in all solvents except in the presence of
excess acid which suppresses not only deprotonation=
inversion=protonation but also the rotation of the Xy%
group about the N–Xy% bond. As this rotation takes
place in [Fe2(h-C5H5)2(CO)2(m-CNXy)(m-CNMe2)]+, it
does imply that rotation of Xy% and inversion at N in
[25]+ are connected.
1
All spectra show the anticipated couplings of H to
13C or 15N nuclei when suitably labelled CNR or
CN(R%)R+ ligands are used.
The 13C-NMR spectra of the complexes in CD3CN
solution are as would be expected (Table 4). Single
C5H5 and m-CN(CH3)2+ resonances show that there is
fast inversion at N of the m-CNR ligand of [23]+ and
its counterparts, and fast deprotonation=inversion=
reprotonation of [34]2+ and its counterparts. Compari-
son of the various spectra show that the chemical shifts
of ligating 13C atoms decreases along the ligand series
CN− Bt-CNMeBt-COBm-CNMeBm-COBm-CN-
(H)Me+ ꢁm-CNMe2+, although the actual values de-
pend on the ligand combination. The spectra of com-
plexes containing 13C-labelled ligands exhibit some
interesting coupling constants. Thus the m-13CNMe lig-
and does not couple to the t-CO or m-CNMe2+ ligands
in cis-[23]+, but the t-13CNMe ligand in cis-[7]+ cou-
ples to both m-CO and m-CNMe2+ ligands. The m-
13CN(H)R+ ligands in [34]2+ (R=Me) or [32]2+
(R=H) couple to t-CO but not m-CNMe2+ ligands.
Fig. 3. (a) and (b) are cis and trans isomers; (c) and (d) are a and b
isomers; and (e) and (f) are syn and anti isomers.
rming that interconversion of these two species is fast at
r.t.
Similar behaviour and NMR spectra have also
been observed for other complexes of the general
type [Fe2(h-C5H5)2(CO)(L){m-CN(H)R}(m-CNMe2)]2+
Scheme 4.

266
K. Boss et al. / Journal of Organometallic Chemistry 579 (1999) 252–268
Scheme 5.
3.7. Isomers
(CO)4−n(CNR)n] complexes [10] and not their basicities
when they occupy such sites. This suggests that the
reactions proceed via protonated intermediates which
are able to undergo ligand site exchange and that
protonation of the CNR ligand takes place subsequently.
Furthermore a reaction appears to take place when
[4][SO3CF3], which does not possess a CNR ligand, is
treated with HOSO2CF3 in chloroform solution. There
is a colour change and an oil is precipitated, but it could
not be identified.
All of the complexes described have structures based
on that of [Fe2(h-C5H5)2(CO)2(m-CO)2] [9] with a ca.
planar Fe2(m-C)2 moiety. Consequently cis and trans
isomers are possible (Fig. 3), but because of the presence
of m-CN(R%)R+ ligands they do not interconvert and
may often be separated by chromatography and frac-
tional crystallization.
Reactions (ii) and (iv) involve only the periphery of
ligands and so do not affect the Fe2(CO)4 part of the
molecule or cis–trans isomer ratios. In contrast the
reactions (i), (iii), (v) or (vi) involve migration of ligands
between terminal and bridging sites so that cis–trans
isomerisation can and does take place. However, the cis
isomer is always the major product and may be the only
product of these reactions no matter what the configura-
tion of the starting complex.
There are two obvious sites of protonation in
[4][SO3CF3], [7][SO3CF3] and related salts. The first is the
m-CN(R%)R+ ligand which would be converted to m-
CN(H)(R%)R2+. There is a precedent for this in the
conversion of [Co3(h-C5H5)3(m3-S)(m3-CNMe2)]+ salts
to [Co3(h-C5H5)3(m3-S){m3-CN(H)Me2}]2+ [11]. How-
ever, as the m-CN(R%)R+ ligand inhibits ligand site
exchange and cis–trans isomerism in [7]+ and related
species because of its m-seeking abilities [1,3], it is
probable that a m-CN(H)(R%)R2+ ligand in [Fe2(h-
The identification of cis and trans isomers has been
discussed in detail elsewhere [1,3].
There are two other forms of isomerism exhibited by
some of these complexes. The first are syn and anti
C5H5)2(CO)(CNMe)(m-CO){m-CN(H)Me2}]2+
have a similar effect.
would
The second potential site of protonation is the Fe–Fe
bond as has been observed in the reversible reaction of
strong acids with [Fe2(h-C5H5)2(CO)4] which give
[{Fe(h-C5H5)2(CO)2}2H]+ salts [12]. This is more plau-
sible, and a possible mechanism for reaction (i) based on
it is illustrated in part in Scheme 4. The initially formed
intermediate A could be in equilibrium with the species
B or B% with two fewer m-ligands. It is possible to envisage
a series of reactions involving bridge closing-and-open-
ing and partial rotation about an Fe–CNMe2 bond in
B which would convert A to one of its isomers with a
m-CNR ligand. The possibility is then open for a se-
quence of reactions which would lead eventually to the
protonation of this ligand and precipitation of the final
product.
isomers arising from the presence of
a Fe2{m-
CN(H)R}{m-CN(R%)R} moiety and the second are the a
and b isomers arising from the presence of both m-
CN(H)R+ ligands and an Fe2(t-L)(t-L%) moiety within
the same molecule (Fig. 3). Instances of both types of
isomerism have been detected by NMR spectroscopy,
but the isomers have never been separated.
3.8. Mechanism of reaction (i)
The facility with which the t-CNR ligand is converted
to m-CN(H)R+ increases along the series CNEtB
CNMeBCNAr. This series reflects the increasing m-
seeking ability of these ligands in [Fe2(h-C5H5)2-

K. Boss et al. / Journal of Organometallic Chemistry 579 (1999) 252–268
267
This proposed mechanism accounts for the observed
characteristics of the reaction. A very strong acid would
be required to protonate a cation, and donor solvents
such as acetonitrile would reduce its efficacy in this
respect. The preferred isomer of A would depend on
the m-seeking abilities of the CY and CZ ligands and
not their basicities provided that the rates of intercon-
version between A and B and their various isomers/ro-
tamers were fast as compared with the deprotonation of
A. The cis–trans isomerism which is observed is easily
rationalized as a single rotation through 60° about the
Fe(1)–CNMe2 bond in B which would interchange CO
with CZ in B and hence in A would also result in
cis–trans isomerism in A. Two such transformations
would be required to bring about CO and CZ inter-
change without cis–trans isomerisation. Furthermore,
this means that if the two cyclopentadienyl ligands are
linked (in our case by a CH2C(O) moiety), the partial
rotation in B/B% cannot take place and no reaction
would be expected.
removal of both protons and the migratory exchange of
CN− with either CO or CNMe in a fast reaction that
takes place even in the dark. Similar behaviour has
been observed in the deprotonation of [Fe2(h-
C5H5)2(CO)2(m-CO)(m-CNH2)]X salts [13], and it is
quite clear that the CN− ion, though isoelectronic with
CO, has a much reduced capacity to act as a two-elec-
tron donor, m2 ligand.
When the ‘bridging’ CN− exchanges with a terminal
ligand, it does so preferentially with CO rather than
CNMe so that [Fe2(h-C5H5)2(CO)(CNMe)(m-CNH2)(m-
CNMe2)][SO3CF3]2
giving
[Fe2(h-C5H5)2(CNMe)-
(CN)(m-CO)(m-CNMe2)] and [Fe2(CO)(CN)(m-CNMe)-
(m-CNMe2)] in a ratio, 70:30. This is consistent with the
relative m-seeking abilities of CO and CNMe ligands in
various [Fe2(h-C5H5)2(CO)4−n(CNMe)n)] complexes
(n=1 or 2) [10].
3.10. Structure of cis-[Fe2(p-C5H5)2(CO)2(v-CNMe)-
(v-CNMe2)][SO3CF3]
The structure and atom labelling of the cation is
illustrated in Fig. 1, and selected bond lengths and
angles are given in Table 7. The cation has a structure
which is based on that of cis-[Fe2(h-C5H5)2(CO)2(m-
CO)2] [9] and similar to that found previously in cis-
[Fe2(h-C5H5)2(CO)2(m-CO){m-CN(H)Me}][BF4] [8] and
cis-[Fe2(h-C5H5)2(CO)2(m-CO)(m-CNMe2)]I [14] but
with the m-CO ligand replaced by a m-CNMe ligand
which is bent at N. Bond lengths and angles are as
would be expected. However, it should be noted that
3.9. Mechanism of reactions (ii) and (6i)
These are difficult to rationalize; (ii) is observed only
when [Fe2(h-C5H5)2(CO)2(m-CNMe)(m-CNMe2)][SO3-
CF3] converts to [Fe2(h-C5H5)2(CO)(CNMe)(m-CO)(m-
CNMe2)][SO3CF3]. It does not take place (a) in the
dark, so it appears to be photolytic rather than thermal,
(b) if m-CNMe is replaced by m-CNAr, and (c) when
one of the terminal CO ligands of [23] is replaced by
CNMe, the use of labelled m-CNMe* shows that there
is no exchange of m and t CNMe ligands. As the CNAr
ligand has an inherently greater preference for m as
opposed to t coordination as compared with CNMe
[10], (b) suggests that the reaction takes place via an
intermediate which allows this isocyanide coordination
preference to be exercised. If this is combined with (a),
a possible intermediate Y is shown in Scheme 5. In step
1 of this scheme CO loss is more probable than CNR
loss because the relatively electron-deficient nature of
the precursor W favours the retention of the better
s-donor ligand in the intermediate Y. Re-attack of Y
by CO would result in the reformation of Z (or its trans
isomer), or of W (step 2) which is the product of
CX–CY site exchange. As the various reactions (exem-
plified by steps 1 and 2 in Scheme 5) are reversible, the
final products would be those in which the most suit-
able ligand would occupy the m-site i.e. CNMeBCOB
CNXy% but the mechanism does not explain why such
an intermediate is not formed from [Fe2(h-
C5H5)2(CO)(CNMe)(m-CNMe)(m-CNMe2)][SO3CF3].
In reaction (vi) it does not appear to be possible to
remove one proton from the m-CNH2+ ligand of [Fe2(h-
˚
the m-CꢀNMe2 separation of 1.296(6) A it is normal for
a double bond but much longer than m-C–NMe of
˚
1.208(7) A, indicating C–N triple bond character in the
latter. This is consistent with the Fe–C bonds to the
very strong acceptor ligand m-CNMe2+ (1.874, 1.884(5)
˚
A) being significantly shorter than those to the poorer
˚
acceptor m-CNMe (1.940, 1.955(6) A). As would be
expected, the dimensions of the m-CNMe ligand in
[23]+ differ from those of t-CNMe in its isomer [7]+
˚
˚
[3] with C–N of 1.208(7) A vs. 1.157(6) A and N–Me
˚
of 1.470(9) vs. 1.429(7) A. The CO ligand undergoes
similar variations in C–O bond length i.e. 1.163(6) A
for m-CO in [7][BPh4] and 1.142(7) A for t-CO.
˚
˚
4. Supplementary material
Crystallographic data for the structural analysis has
been deposited with the Cambridge Crystallographic
Data Centre, CCDC No. 116144 for cis-[Fe2(h-
C5H5)2(CO)2(m-CNMe)(m-CNMe2)][BPh4]. Copies of
this information may be obtained free of charge from
The Director, CCDC, 12 Union Road, Cambridge,
CB2 1EZ, UK (Fax: +44-1223-336-033; e-mail: de-
posit@ccdc.cam.ac.uk or www: http://www.ccdc.cam.
ac.uk).
C5H5)2(CO)(L)(m-CNH2)(m-CNMe2)][SO3CF3]2
CO or CNMe) to give complexes containing the
m-CNH ligand. Every attempt to do so resulted in the
(L=
.

268
K. Boss et al. / Journal of Organometallic Chemistry 579 (1999) 252–268
[9] R.F. Bryan, P.T. Greene, M.J. Newlands, D.S. Field, J. Chem.
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