Organoiron compounds derived from the indium 'carbene analogues', [In{N(Ar)C(Me)}2CH] (Ar = dipp = 2,6-iPr2C 6H3; = Mes = 2,4,6-Me3C6H 2)

Article abstract of DOI:10.1039/b801160e

Oxidative insertion of the In(i) 'carbene analogues', [In{N(Dipp)C(Me)} ₂CH] (Ar = Dipp = 2,6-ⁱPr₂C₆H ₃; Ar = Mes = 2,4,6-Me₃C₆H₂) into the Fe-I bond of [CpFe(CO)₂I] occurred cleanly and under mild conditions to yield the In(iii) compounds [CH{(CH₃) ₂CN-2,6-ⁱPr₂C₆H₃} ₂In(I)FeCp(CO)₂] and [CH{(CH₃) ₂CN-2,4,6-Me₃C₆H₃} ₂In(I)FeCp(CO)₂], which have been fully characterised in solution and the solid state. Attempts to abstract the iodide anion from [CH{(CH₃)₂CN-2,6-ⁱPr₂C ₆H₃}₂In(I)FeCp(CO)₂] to form cationic species containing a coordinated indium diyl were unsuccessful and resulted in a complex mixture of products from which two ionic species were isolated. Neither cation was found to contain indium by X-ray crystallographic analysis. These observations were indicative of ill-defined decomposition pathways as have been noted by previous workers. A further attempt to form a cationic iron species containing a coordinated [In{N(Dipp)C(Me)}₂CH] fragment resulted in oxidation of the iron centre from Fe(ii) to Fe(iii), with deposition of indium metal, and the isolation of a cationic Fe(iii) β-diketiminate complex. The Royal Society of Chemistry.

Full text of DOI:10.1039/b801160e

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Organoiron compounds derived from the indium ‘carbene analogues’,
[In{N(Ar)C(Me)}2CH] (Ar = dipp = 2,6-iPr2C6H3; = Mes =
2,4,6-Me3C6H2)†
Michael S. Hill,*a Peter B. Hitchcockb and Ruti Pongtavornpinyoc
Received 22nd January 2008, Accepted 29th February 2008
First published as an Advance Article on the web 8th April 2008
DOI: 10.1039/b801160e
Oxidative insertion of the In(I) ‘carbene analogues’, [In{N(Dipp)C(Me)}2CH] (Ar = Dipp =
2,6-iPr2C6H3; Ar = Mes = 2,4,6-Me3C6H2) into the Fe–I bond of [CpFe(CO)2I] occurred cleanly and
under mild conditions to yield the In(III) compounds [CH{(CH3)2CN-2,6-iPr2C6H3}2In(I)FeCp(CO)2]
and [CH{(CH3)2CN-2,4,6-Me3C6H3}2In(I)FeCp(CO)2], which have been fully characterised in solution
and the solid state. Attempts to abstract the iodide anion from
[CH{(CH3)2CN-2,6-iPr2C6H3}2In(I)FeCp(CO)2] to form cationic species containing a coordinated
indium diyl were unsuccessful and resulted in a complex mixture of products from which two ionic
species were isolated. Neither cation was found to contain indium by X-ray crystallographic analysis.
These observations were indicative of ill-defined decomposition pathways as have been noted by
previous workers. A further attempt to form a cationic iron species containing a coordinated
[In{N(Dipp)C(Me)}2CH] fragment resulted in oxidation of the iron centre from Fe(II) to Fe(III), with
deposition of indium metal, and the isolation of a cationic Fe(III) b-diketiminate complex.
by its absence, six membered b-diketiminate-stabilised, IV–VIII,8
and four-membered guanidinato Group 13 ‘carbene analogues’,
IX and X,9,10 have recently been reported. For Group 14-centred
compounds, divalent tin species in particular, have long been
known to display a useful Lewis base character and a viable
Introduction
In the decade and a half since the discovery of the formally
univalent Group 13 compounds Cp*E and TsiE (E = Al, Ga, In;
Tsi = {(Me3Si)3C}),1 and the realisation that these species could be
coordination chemistry.11 Our own studies of the indium and
thallium species, IV and VIII,8c,d therefore, have focussed upon the
possible relationships to their isoelectonic analogues from Group
14, the stannylenes and plumbylenes. The reactivities of the model
compounds [:E{[N(R)C(Rꢀ)]2CH}] (E = B, Al, Ga, In or Tl; R =
H, Me or 2,6-iPr2C6H3; Rꢀ = H or Me) with a typical Lewis acid
have already been assessed by DFT methods.12 Although these
model compounds were all found to complex to BF3, the Lewis
base character of the metal lone pair was dramatically reduced
on descending the group to the extent that for E = In there was
no donor–acceptor bond formed. Further theoretical studies have
suggested that for the six-membered heterocyclic species IV–VIII
the large HOMO–LUMO gaps (ca. 100 kcal mol−1) will mitigate
against any advantageous level of p-back-bonding.8d Despite such
apparently unpromising foundations, the groups of Power and
Fischer have reported several main group and low valent (d8 and
d10) transition metal derivatives of the aluminium and gallium
complexes IV and V, in which the Group 13 centre behaves as a
‘carbenoid’ two electron donor ligand.13a,14 Other derivatives of V
containing direct gallium to metal bonds have been obtained by
redox insertion reactions into M–X bonds of various transition
metal to halide and, in one instance, metal to carbon (Zn–Me)
bonds.15 In this paper we outline our initial synthetic assessment
of the Lewis base character of the indium analogue of IV and
V, compound VI, along with attempts to elaborate a halide
abstraction chemistry of some organoiron derivatives formed by
oxidative insertion of indium into an iron–iodine bond.
viewed as isolobal to CO and PR3 ligands, the landscape apparent
to the coordination chemist has altered considerably. While yet
to demonstrate any indication of real practicality, the synthesis of
derivatives of these species ligated to transition metal fragments
has provided a striking diversity of structure and reactivity.2 The
reaction and coordination chemistry of Group 13-centred species
that are valence isoelectronic and isolobal to the other ligand ‘du
jour’, the N-heterocyclic carbene (NHC) I,3 is, however, rather
more limited and more recent in origin. The studies of Jones
and co-workers of the anionic gallium species II have yielded a
variety of s, p, d and f-block derivatives in which the primary
gallium to element interaction is provided by electron density
which may be naively viewed as originating from a lone pair
contained within a gallium orbital of essentially sp-hybridised
character.2b,4,5 Although a nascent coordination chemistry of the
corresponding boryl species, III,6 has also been demonstrated,7 it
is clear that these studies cannot yet be described as approaching
even the early stages of maturity. Among charge neutral species,
although an example of a neutral boron-centred diyl is notable
aDepartment of Chemistry, University of Bath, Claverton Down, Bath, UK
BA2 7AY. E-mail: m.s.hill@bath.ac.uk
bThe Chemistry Laboratory, University of Sussex, Falmer, Brighton, East
Sussex, UK BN1 9QJ
cDepartment of Chemistry, Imperial College London, Exhibition Road,
South Kensington, London, UK SW7 2AZ
† CCDC reference numbers 675700–675705. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b801160e
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Scheme 1
cationic indium diyl systems (Scheme 1). As has been observed in
compounds containing ‘naked’ cationic Group 13 centres bearing
electron rich transition metal fragments,18 it was reasoned that
localisation of the positive charge at indium could then lead
to appreciable Fe→In back-bonding and stabilisation of the
coordinated cationic diyl.18b
Addition of [CpFe(CO)2I] to a THF solution of either the
N-2,6-diisopropyl-substituted derivative, VI,8c or its mesityl-
substituted analogue, VII,19 produced red-brown solutions with
no visible sign of decomposition of the indium starting ma-
terial to indium metal. Work-up and crystallisation from hex-
ane of the red-brown solid material produced, upon removal
of volatiles from the reactions, the desired oxidative addi-
tion products [{CpFe(CO)2}(I)In{N(2,6-iPr2C6H3)C(Me)}2CH],
1, and [{CpFe(CO)2}(I)In{N(2,4,6-Me3C6H2)C(Me)}2CH], 2, in
good (ca. 70%) yields as red-orange crystalline materials. The
similar outcome of both reactions is in line with our previous
solution studies which indicated that compound VII is strictly
mononuclear in solution despite its dimerisation via a weak
In · · · In interaction in the solid-state.20 Both compounds gave 1H
and 13C NMR spectra and CHN microanalytical data consistent
with the proposed formulations. The 1H NMR spectra were
particularly diagnostic for 1 and featured two well resolved
pairs of doublet signals and two muliplets which were assigned
to the diastereotopic disposition of the b-diketiminate N-Dipp
isopropyl methyl and methine groups respectively. The N-mesityl
o-methyl groups of 2 were similarly split into two separate singlet
resonances. These data were interpreted as a clear indication that
the crystallographically-confirmed structures (vide infra) of 1 and
2 were retained in solution on the NMR timescale. The two
carbonyl stretching frequencies of both compounds (1: 2001 and
1954 cm−1; 2: 2004, 1960 cm−1) are also comparable to previously
reported derivatives in which the same iron fragment is bonded
to indium, for example the dimeric species [CpFe(CO)2In(I)Br]
which has been reported to display two m(CO) bands at 2012 and
1969 cm−1.17b The solid state structures of both 1 and 2 were
confirmed through single crystal X-ray diffraction analyses the
results of which are displayed in Fig. 1. A subsequent attempted
synthesis of 1 also yielded a small number of single crystals
which had a less intense orange colouration. These latter crystals
were identified in a further X-ray determination as an additional
modification of compound 1, which had co-crystallised as a 2 : 1
mixture with the dimeric Fe/In trimethylsiloxide, 3, (Fig. 2). This
latter species, which lies about an inversion centre, was formed
presumably by reaction of 1 (or intermediates en route to 1) with
a siloxane grease contaminant from the experimental glassware.
Details of the analyses for all three structures are provided in
Table 1, while selected bond length and angle data are provided in
Tables 2 and 3 respectively. Although compound 1 crystallised with
two independent molecules within the unit cell, the conformational
variations between the individual units, as well as in the identical
Results and discussion
Our initial attempts to utilise the lone pair electron density of
VI to coordinate to zerovalent transition metal carbonyls and
olefin derivatives were completely unsuccessful. Reactions with
Fe(CO)5, W(CO)6 (under thermal or photochemical initiation)
and Ni(COD)2 in our hands produced either no reaction and
recovery of the starting materials or, under more forcing condi-
tions, decomposition of either the In(I) species, with the deposition
of indium metal, or the transition metal reagent. Furthermore,
although an NMR scale reaction of IV with the potent Lewis
acid B(C6F5)3 produced minor shifts in both the 1H and 13C
resonances of the starting materials indicative of a coordinative
interaction similar to that crystallographically confirmed for both
the analogous reactions with IV and V,13a,14a any attempt to repeat
this reaction on a preparative scale resulted in recovery of the
unreacted starting materials upon crystallisation from hexane
or toluene irrespective of the conditions of crystallisation (i.e.
ambient or low temperature). These observations are in line with
the expectations provided by the aforementioned computational
investigations and we conclude that any Lewis base character
attributed to VI will be very weak at best.8d,12 Although we do
not completely discount the possibility that a viable NHC-type
coordination chemistry for VI will be eventually forthcoming, at
this point we turned our attention to alternative strategies for the
utilisation of VI for the construction of a direct transition metal
to indium bond.
We have recently reported that oxidative addition of alkyl
iodides and bromides to VI results in the facile formation of
the expected heteroleptic b-diketiminato supported indium alkyl
halides.16 A similar strategy involving insertion of an indium(I)
halide into a metal halogen bond has previously been applied
to the synthesis of compounds in which a transition metal
is r-bonded to an InX2 fragment.17 Following the precedent
provided by Aldridge et al., therefore, reaction of compound
VI, with the iron iodide precursor [CpFe(CO)2I] was identified
as a likely candidate for the straightforward synthesis of iron-
bound haloindyl species (Scheme 1).17b Compounds of this latter
type were particularly attractive as they offered the potential
for subsequent iodide abstraction and the formation of base-free
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Fig. 1 Thermal ellipsoid (50%) plot of compounds 1 (In(1B)-containing molecule not illustrated) and 2. Hydrogen atoms omitted for clarity.
reports of successful halide abstraction from indium to yield the
‘naked’ (i.e. unstabilised by an additional Lewis base) indium–
transition metal cations are much more limited. Indeed, as far
as we are aware, such species are restricted to the striking delo-
calised trimetallic cation [{Cp*Fe(CO)2}2(l-In)]+ which features
a linear bridging indium atom.18c Other attempts to carry out
halide abstraction from supported indium complexes in non-
coordinating solvents, notably the amidinate-substituted species
[{CpFe(CO)2In(Br){(CyN)2CtBu}], have been reported to result
in no reaction, while similar procedures in the presence of ether
solvents gave complex and intractable mixtures of products.18d
Despite this unencouraging precedent, reaction of compound 1
with [Na{BArf4}] (Arf = C6H3(CF3)2-3,5) in dichloromethane
produced a dark solution along with the formation of a precipitate.
Filtration and removal of solvent provided an oily material,
which was deduced by 1H NMR analysis to contain at least
five separate b-diketiminato ligand N-aryl environments. Slow
diffusion of hexane into a toluene solution of this mixture
produced a mixture of two crystalline materials, a colourless
complex, 4, and a very much smaller quantity of a dark brown
compound, compound 5, over the course of one month. Careful
mechanical separation of the individual crystalline complexes
from other amorphous materials within the crystallisation vessel
allowed the unambiguous identification of two cationic species
by single crystal X-ray diffraction analysis (Scheme 1), neither of
which was found to contain indium. The results of both analyses
are illustrated in Fig. 3 and 4, while details of the analyses and
selected bond length and angle data are provided in Tables 2 and 3.
The colourless compound 4 proved to be a protonated form of the
iminoenamine ligand precursor with charge balance maintained
through crystallisation with the {BArf4} anion. Although the
b-iminoenamine hydrochloride is a common intermediate in
the synthesis of the of the b-diketiminate ligand precursor, no
characterising data has ever been presented. In the structure of
4 both the cation and anion lie on two-fold rotation axes. In the
former case this indicates that the positive charge is effectively
delocalised throughout the framework of the cationic moiety.
This observation is reinforced by comparison of the C(1)–N
Fig. 2 Thermal ellipsoid (50%) plot of the indium siloxide, compound 3.
Hydrogen atoms omitted for clarity. The (’) character in the atom labels
indicates atoms at equivalent position (−x, −y, 1 − z).
molecules of 1 identified in the cocrystal with compound 3, are only
minor and we restrict ourselves to a broad discussion of the four
variations. The structures of 1 and 2 also display several common
˚
features. The In–N distances (av. 2.179 A) and N–In–N bond
angles (av. 88.76◦) in all five b-diketiminate-containing molecules
lie within narrow ranges, and are typical of previously reported
b-diketiminate derivatives of trivalent indium.21 The geometry at
indium in all four cases is dominated by the minimisation of steric
interactions between the N-aryl substituent of the b-diketiminate
ligands and the relatively bulky {CpFe(CO)2} substiuent. This
is most clearly demonstrated by a widening of the N–In–Fe
(av. 125.4◦) and narrowing of the N–In–I (av. 98.9◦) bond
angles away from the idealised tetrahedral values. We have noted
similar, but less pronounced, deviations away from ideality in our
previous studies of b-diketiminato indium alkyl halides.16 The In–
Fe distances are similar irrespective of the identity of the N-aryl
substituents within all four b-diketiminate-containing molecules
˚
(av. 2.52 A) as well as within the dimeric, and thus four coordinate,
˚
˚ ˚
indium siloxide 3 (2.4889(12) A).
[1.334(5) A] and C(1)–C(2) [1.383(5) A] bond lengths to the
˚ ˚
localised and alternating C–N [1.358(4) A], C C [1.362(4) A],
=
The use of halide abstraction as a means to access cationic
Group 13 diyl complexes with the potential to display some
level of multiple bonding to a transition metal fragment has
been demonstrated for a variety of compound types during the
past 5 years.18 While several interesting and unusual cationic
gallium species have been isolated and studied by this method
˚
˚
=
C–C [1.434(4) A] and C N [1.313(4) A] bonds observed in the
structure of the parent b-iminoenamine ligand precursor.22 The
red-brown decomposition product, compound 5, was identified by
a further X-ray determination as an unusual ionic species in which
the organic chelate ligand had been transferred from indium to
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Fig. 3 Thermal ellipsoid (20%) plot of the cationic component of
compound 4. Hydrogen atoms omitted for clarity except for those attached
to N.
Fig. 4 Thermal ellipsoid (50%) plot of the cationic component of
compound 5.
a {CpFe(CO)} fragment. Furthermore, the b-diketiminate ligand
of 1 had undergone a remarkable degradation reaction requiring
C–N bond cleavage of one of the Dipp substituents as well as
2
=
protonation of the anion. The {j - CH2(C N)2} chelate binds to
the iron centre, therefore, as a neutral diimine ligand, reflected in
the individual C–N and C–C bonds around the six membered
ring (Table 2). Although the process of ligand oxidation and
coordination also required the loss of a single carbonyl ligand
from iron to maintain an 18 electron count at the transition
metal centre, the most striking feature of 5 is the loss of one
of the N-Dipp substituents. The widespread application of the
b-diketiminate class of ligand, particularly examples bearing N-
aryl substitution, over the past decade has resulted from the
remarkable resilience of these species to a variety of highly reactive
media.23 Although several examples of C–N bond cleavage have
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˚
Table 2 Selected bond lengths (A) for compounds 1–6
1
2
3d,e
4h
5
6
M–N(1)
M–N(2)
In–Fe
2.190(3)a
2.165(3)a
2.5118(7)
2.8100(4)
1.711(5)
1.319(5)
1.442(5)
1.341(5)
1.446(5)
1.400(6)
1.388(6)
2.170(2)a
2.169(2)
2.5094(4)
2.7882(3)
1.716(4)
1.328(4)
1.448(4)
1.341(4)
1.439(4)c
1.411(4)
1.391(5)
2.531(5)f
2.152(5)g
2.4889(12)
2.7585(8)
1.709(11)
—
—
—
—
—
—
—
—
—
2.006(3)l
1.938(3)l
—
2.029(3)l
2.019(3)l
—
In–I
—
—
Fe–M(1)b
N(1)–C(1)
N(1)–C(6)
N(2)–C(3)
N(2)–C(18)
C(1)–C(2)
C(2)–C(3)
—
1.734(5)
1.283(4)
1.466(4)
1.269(5)
1.466(4)m
1.517(5)
1.486(6)
1.739(4)
1.286(5)
1.464(5)
1.279(5)
1.464(5)
1.503(5)
1.502(5)
1.334(5)l
1.457(6)j
—
—
1.383(5)
—
1.504(6)k
a M = In. b M(1) = Cp centroid. c N(2)–C(15). d Siloxide-containing component only. e Symmetry transformations used to generate equivalent atoms:
−x, −y, −z + 1. f In(1B)–O(3B). g In(1B)–O(3B)’. h Symmetry transformations used to generate equivalent atoms: −x, y, −z + 1/2; −x + 1, y, −z + 1/2.
i N–C(1). j N–C(4). k C(1)–C(3). l M = Fe. m N(1)–C(6).
Table 3 Selected bond angles (◦) for compounds 1, 2, 3, 5 and 6
1
2
3c,d
5
6
N(1)–M–N(2)
N(1)–In–Fe
N(2)–In–Fe
N(1)–In–I
89.90(13)a
88.89(9)a
78.8(2)e
87.42(13)j
—
—
—
89.54(12)j
—
—
—
122.93(9)
129.34(9)
99.38(9)
99.49(9)
120.3(3)a
117.0(3)a
120.2(3)a
119.4(3)a
123.49(6)
125.44(7)
101.29(6)
101.29(6)
121.0(2)
120.64(14)f
122.04(14)g
103.39(14)h
99.96(14)i
—
N(2)–In–I
—
—
C(1)–N(1)–M
C(6)–N(1)–M
C(3)–N(2)–M
C(18)–N(2)–M
124.8(2)j
117.0(2)j
128.3(3)j
—
123.1(3)j
119.1(2)j
123.2(3)j
119.9(2)j
118.70(17)
119.3(2)
—
—
—
121.96(17)b
a M = In. b C(15)–N(2)–In. c Siloxide-containing component only. d Symmetry transformations used to generate equivalent atoms: −x, −y, −z + 1.
e O(3B)-In(1B)-O(3B)’. f O(3B)–In(1B)–Fe(1B). g O(3B)’–In(1B)–Fe(1B). h O(3B)–In(1B)–I(1B). i O(3B)’–In(1B)–I(1B). j M = Fe.
the In(I) complex VI. This procedure provided an instantaneous
precipitation of a grey metallic powder upon addition of VI and
the isolation after work-up of a low yield (< ca. 10%) of a further
cationic b-diketiminate complex, 6, containing the {CpFe(CO)}
fragment. The ion-paired component of this complex is illustrated
in Fig. 5, while selected bond length and angle data are collected
in Tables 2 and 3 respectively. While the mechanism of formation
is again open to speculation it is clear in this case that the initially
formed iron(II) cation most likely undergoes oxidation to Fe3+
by the monovalent indium centre with concurrent reduction to
In(0). Examination of the relevant standard reduction potentials
(E◦Fe3+/Fe2+, +0.771 V, E◦In+/In0, −0.126 V) indicate that this reaction
outcome is entirely feasible.25 Transfer of the intact b-diketiminate
ligand and loss of one molecule of CO, therefore, yield the
Fig. 5 Thermal ellipsoid (50%) plot of the ion paired compound 6.
17 electron paramagnetic Fe(III) cation observed in compound
6. Although sufficient material was mechanically separated to
enable the acquisition of acceptable microanalytical data, at-
tempted NMR analysis was uninformative due to paramagnetic
broadening and the likely presence of unidentifiable impurities
in the bulk material employed. The impure nature of the bulk
sample also prevented a confident estimation of a magnetic
moment by attempted Evans’ method determination. Somewhat
surprisingly, the Fe–N bond lengths within the cationic component
Hydrogen atoms omitted for clarity.
been reported, all required the presence of a highly reducing metal
centre and occurred with cleavage of one of the iminato C–N
bonds of the NCCCN chelate.24 The observation of cleavage of an
exocylic N-aryl substituent, although by a completely unknown
mechanism, is apparently, therefore, unique.
Although this outcome led to the abandonment of this halide
abstraction-based strategy, an additional experiment further
emphasised the unpredictable nature of this chemistry. In an
additional attempt to form a cationic {CpFe(CO)2} species
with a coordinated indium diyl, we carried out the reaction of
[CpFe(CO)2I] with [Na{BArf4}] in THF prior to addition of
˚
of 6 [2.019(3), 2.029(3) A] do not show the expected decrease
in comparison to the similar bonds observed within the Fe(II)-
˚
containing cation of 5 [1.938(3), 2.006(3) A]. These distances are
also significantly longer than those observed by Holland et al.
2858 | Dalton Trans., 2008, 2854–2860
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for several neutral Fe(III) derivatives bearing the same ligand (av.
C), 141.7 (Ar-C–N), 165.7 (CN), 214.0 (CO). IR m/cm−1 2004,
1960 (CO).
˚
1.97 A) and possibly reflect an effect of relative steric demands and
5
denticity of the g -coordinated cyclopentadienyl substituent of 6
Reaction of [CH{(CH3)2CN-2,6-iPr2C6H3}2In(I)FeCp(CO)2], 1
and [Na(BArf4}]
in comparison to the exclusively monodentate ligands employed
in the previous reports.26
In conclusion, we have demonstrated that an oxidative
addition-based strategy can successfully enable the elabora-
tion of transition metal derivatives of the indium fragment
[In{N(Dipp)C(Me)}2CH]. We are continuing to study this chem-
istry and related redox chemistry and will report the outcome of
these investigations in subsequent publications.
Addition of CH2Cl2 (10 mL) to a mixture of compound 1 (0.30 g,
0.36 mmol) and [Na{BArf4}] (0.29 g, 0.36 mmol) produced a
dark solution and the formation of a precipitate. Filtration and
removal of solvent provided an oily material which was re-
dissolved in toluene (10 mL). Slow diffusion of hexane into this
toluene solution produced a mixture of two crystalline materials,
a colourless complex, 4, and a very much smaller quantity
of a dark brown compound, compound 5, over the course of
one month. Careful mechanical separation of the individual
crystalline complexes from other amorphous materials within the
crystallisation vessel allowed the unambiguous identification of
two cationic species by single crystal X-ray diffraction analysis.
Experimental section
All manipulations were carried out using standard Schlenk
and glovebox techniques under an inert atmosphere of either
dinitrogen or argon. All solvents were distilled under dinitrogen
and dried over conventional drying agents. Compounds VI and
VII were synthesised by literature procedures.8c,19 Dr G. Britovsek
and Dr R. Taylor (Imperial College London) are thanked for
supplying the [Na{BArf4}] used in this study while all other
chemicals and reagents were purchased from Sigma Aldrich and
used as received. Elemental analyses were carried out by Mr
Stephen Boyer at London Metropolitan University.
Isolation of compound 6
Addition of THF (20 mL) to a solid mixture of [FeCp(CO)2I]
(0.10 g, 0.33 mmol) and [Na{BArf4}] (0.28 g, 0.33 mmol) produced
a brown solution. Addition of a THF solution of compound
VI (0.18 g, 0.33 mmol) gave an instantaneous grey precipitate.
Removal of volatiles provided a sticky dark brown material which
was extracted into toluene and the solution filtered. Careful
layering of the resultant brown solution with hexane and storage
for one week yielded compound 6 as a few pale brown crystals, in
ca. 10% overall yield based on Fe, suitable for X-ray diffraction
analysis. Anal. Calc. (Found) for C67H58BF24FeN2O: C 56.23
(56.33); H 4.06 (4.16); N 1.96 (2.01%). Mp 165 ◦C (decomp.).
IR m/cm−1 1978 (CO).
[CH{(CH3)2CN-2,6-iPr2C6H3}2In(I)FeCp(CO)2], 1
THF (50 mL) was added to a mixture of [FeCp(CO)2I] (0.17 g, 0.56
mmol) and compound VI (0.30 g, 0.56 mmol) to produce a red-
brown solution at room temperature. Volatiles were removed and
the brown solid residue extracted with hexane (50 mL). Filtration
to remove a small amount of insoluble material and concentration
of the filtrate followed by storage at 5 ◦C produced compound
1 as red-brown crystals suitable for X-ray diffraction analysis
(0.32 g, 68%). A subsequent and similar preparation also yielded
a small quantity of pale orange crystals which were identified
by a further X-ray analysis as compound 1 co-crystallised with
the indium siloxide, compound 3. Anal. for 1; Calc. (Found) for
C36H46FeIInN2O2: C 51.65 (51.81); H 5.50 (5.41); N 3.35 (3.34%).
Mp 110–112 ◦C (decomp.). 1H NMR (400 MHz, C6D6) d 1.11 (d,
3H, 3JHH = 6.8 Hz, CHMe2), 1.29 (d, 3H, 3JHH = 6.9 Hz, CHMe2),
1.33 (d, 3H, 3JHH = 6.8 Hz, CHMe2), 1.48 (d, 3H, 3JHH = 6.9 Hz,
Crystal structure determinations
Data were collected at 173 K on a Nonius Kappa CCD diffrac-
˚
tometer, k(Mo-Ka) = 0.71073 A; details are given in Table 1.
The structures were solved by direct methods (SHELXS-97)27 and
refined by full matrix least squares (SHELXL-97)28 with non-
H atoms anisotropic and H atoms included in riding mode. In
compound 5 the H atom attached to N(2) was refined and the
six disordered CF3 groups were included with SADI geometry
restraints. For compound 6 two of the CF3 groups were disordered
and were included with isotropic F atoms.
3
CHMe2), 1.68 (s, 6H, C(CH3)), 3.90 (sept, 2H, JHH = 6.9 Hz),
3
3.93 (s, 5H, CpH), 4.15 (sept, 2H, JHH = 6.9 Hz), 5.15 (s, 1H,
1
CH), 7.05–7.19 (m, 6H, ArH). 13C{ H} NMR (125.8 MHz, C6D6)
d 23.9 (CHMe2), 24.5 (CHMe2), 25.0 (CHMe2), 25.1 (CHMe2),
28.2 (CMe), 81.3 (Cp), 98.6 (c-CH), 123.6, 125.4, 126.8 (Ar-C),
142.6 (Ar-C-N), 145.2 (CCHMe2), 169.7 (CN), 213.6 (CO). IR
m/cm−1 2001, 1954 (CO).
Acknowledgements
We thank the Royal Society for the provision of a University
Research Fellowship.
[CH{(CH3)2CN-2,4,6-Me3C6H3}2In(I)FeCp(CO)2], 2
References
Made by the same general method as for 1 but employing VII in
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