Reactions of InMe3 with isocyanides in the presence of amines: Chemical and mass spectrometric evidence of unprecedented insertion into In-N bonds

Article abstract of DOI:10.1016/S0022-328X(01)00649-0

InMe₃ reacts with CNR (R=C₆H₄-p-OMe, C₆H₄-p-Me) affording the corresponding adducts Me₃InCNR, which are formed even in the presence of an excess of CNR. Me₃InCNR reacts with pyrr

Full text of DOI:10.1016/S0022-328X(01)00649-0

Journal of Organometallic Chemistry 626 (2001) 11–15
www.elsevier.nl/locate/jorganchem
Reactions of InMe3 with isocyanides in the presence of amines:
chemical and mass spectrometric evidence of unprecedented
insertion into InꢀN bonds
R. Bertani a,*, L. Crociani a, G. D’Arcangelo b, G. Rossetto c, P. Traldi d, P. Zanella c
a Dipartimento di Processi Chimici dell’Ingegneria, Uni6ersita´ di Pado6a,
e Centro di Chimica e Tecnologia dei Composti Metallorganici degli Elementi di Transizione del C.N.R., 6ia Marzolo 9, I-35131 Pado6a, Italy
b Dipartimento di Scienze e Tecnologie Chimiche, Uni6ersita´ di Roma ‘‘Tor Vergata’’, V.le della Ricerca Scientifica, I-00133 Rome, Italy
c Istituto di Chimica e Tecnologie Inorganiche e dei Materiali A6anzati, Consiglio Nazionale delle Ricerche, C.so Stati Uniti 4,
Area della Ricerca di Pado6a, I-35020 Pado6a, Italy
d Ser6izio di Spettrometria di Massa, Area di Ricerca di Pado6a, Consiglio Nazionale delle Ricerche, C.so Stati Uniti 4, Area della Ricerca,
I-35020 Pado6a, Italy
Received 10 August 2000; received in revised form 28 November 2000; accepted 4 December 2000
Abstract
InMe3 reacts with CNR (RꢁC6H4-p-OMe, C6H4-p-Me) affording the corresponding adducts Me3InCNR, which are formed
even in the presence of an excess of CNR. Me3InCNR reacts with pyrrolidine to give the [Me2InC(ꢁNR)(Pyrr)] products
[Pyrr=conjugated base of pyrrolidine], which form through the insertion of CNR into the InꢀNPyrr bond. These insertion
products decompose easily to give the corresponding formamidines. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Isocyanides; Pyrrolidine; Formamidines
(ꢁNPh)C(ꢁNPh)Al[CH(SiMe3)2]2 [11] and [(Me3Si)2-
HC]2GaC(ꢁNR)C(ꢁNR)Ga[CH(SiMe3)2]2 (R=aryl, t-
Bu) [12], respectively, while tert-butyl isocyanide forms
the adduct AlCp3(CNCMe3), Cp=cyclopentadienyl
[13] with Al.
1. Introduction
The synthesis of indium complexes containing nitro-
gen ligands which, in principle, can behave as precur-
sors to InN in various deposition processes [1–3], have
been extensively studied. In particular, the preparation
and thermal behavior of indium/alkyl/amino [4], in-
dium/azide and nitride [5] have been described. The
studies reported in the literature mostly concern the
reactivity of InCl3 [6], InMe3 [7] or InMe2Cl [8] with
amines or Li-amides to form monomers or dimers
depending on the reaction conditions [9].
While the chemistry of the transition elements with
isocyanides has been extensively developed [10], few
data have been collected on their complexes with
Group 13 elements: aryl isocyanides are known to
insert in AlꢀAl or GaꢀGa bonds of some organometal-
lic Al or Ga compounds, to give [(Me3Si)2HC]2AlC-
As for indium, to the best of our knowledge, only
one reaction has been described between an indium
substrate,
CH(SiMe3)2), with tert-butyl and phenyl-isocyanides to
afford the corresponding addition products
(ArNꢂC)R2InꢀInR2(CꢂNAr) [14].
tetraalkyldiindane,
R2InꢀInR2
(R=
In this area we thought it would be of interest to
investigate the reactivity of InMe3 and InMe2Pyrr
(Pyrr=coniugated base of pyrrolidine) with aryl
isocyanides.
2. Results and discussion
InMe3 reacted slowly with CNR (RꢁC6H4-p-OCH3,
C6H4-p-CH3) at room temperature in n-hexane to form
the 1:1 adducts, according to Eq. (1). The products
* Corresponding author. Tel.: +39-49-8275731; fax: +39-49-
8275525.
E-mail address: bertani@ux1.unipd.it (R. Bertani).
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)00649-0

12
R. Bertani et al. / Journal of Organometallic Chemistry 626 (2001) 11–15
were brown solids, which must be handled under an
inert atmosphere and decompose easily even in the solid
state
an easy dissociation of CNR ligands comparable to the
dissociation that occurs in adducts containing amine
ligands even if data for heats of formation of CNR
adducts are not available. In the case of Me3InNMe3
gas phase studies give DHf value of −83.3 kJ mol−1
[4a].
InMe3+CNRnꢀ−ꢀhꢀeꢀxꢀanꢃe Me3In(CNR)
1a R=C H -p-OCH
3
(1)
r.t., 24 h
6
4
1b R=C H -p-CH
3
6
4
The compounds 1a and 1b have been characterized
via elemental analyses, IR and NMR spectroscopy.
The IR spectra clearly indicate the coordination of
the CNR ligands, showing strong adsorptions at 2174
and 2173 cm−1 for 1a and 1b, respectively, ca. 50 cm−1
at higher frequencies with respect to the corresponding
free ligands (2126 and 2124 cm−1, respectively), as
reported for CNR coordination to metal centers in high
oxidation state [10c]. These values are in agreement
with those reported for the adduct (ArNꢂC)R2Inꢀ
InR2(CꢂNAr) [14] where the CꢂN stretchings of the
coordinated Me3NꢂC and PhNꢂC are observed at 2187
and 2168 cm−1, respectively.
The reactions of Eq. (1), which were followed by IR
spectroscopy, are complete in 24 h. It is noteworthy
that reactions performed in the presence of an excess
(1:2) of CNR at room temperature do not provide
evidence for the insertion process. This observation is in
agreement with the behavior previously described for
R2InꢀInR2, which did not give insertion into the InꢀC
or InꢀIn bonds, even when mixtures containing an
excess of CNR were heated in n-hexane under reflux
[14]. On the contrary, twofold insertion of isocyanide
has been observed for [(Me3SiCH)2M]2 (M=Ga, Al)
with aryl and alkyl isocyanides to form the correspond-
ing bridged 1,4-diazabutadiene derivatives (Me3SiCH)2-
M[C(ꢁNR)C(ꢁNR)]M(CHSiMe3)2 [11,12].
1
The H-NMR spectra show singlets at 0.03 and 0.10
ppm for 1a and 1b, respectively, due to the methyl
groups bonded to the In center. As expected, the signals
are shifted downfield with respect to InMe3 (−0.23
ppm), as a consequence of coordination of a donor
ligand [4,15].
However, the reactions of Eq. (1) performed in
refluxing n-hexane or acetonitrile gave rise to a small
quantity of the products 1a and 1b, with significant
amounts of free isocyanides also being produced, indi-
cating that the isocyanide dissociation is a favored
process at higher temperatures.
Compounds 1a and 1b react slowly at room tempera-
ture with one equivalent of pyrrolidine according to
Scheme 1 forming the imino derivatives 2a and 2b
(route a).
FAB mass spectrometric measurements confirmed
the coordination of CNR and formation of 1a and 1b,
showing the corresponding molecular ions at m/z 293
(18%) and m/z 277 (7%), respectively, together with
fragmentation processes involving the subsequent
methyl and isocyanide losses. In both spectra the ions
at m/z 145 corresponding to [InMe2]+, which represent
the base peak in EI spectra previously reported for
Me3InL adducts [3c,6,16,17], are well evident (ca. 15%).
Ions at m/z 381, corresponding to [In(CNC6H4-p-
OMe)2]+ are also evident in the FAB mass spectrum of
1a. These ions presumably originate by a gas phase
reaction occurring in the mass spectrometer due to the
presence of free isocyanide. All of these results are
consistent with the reported mass spectral data for
other Me3InL adducts [4,15,16]. This behavior indicates
The reactions have been followed by IR spec-
troscopy: a preliminary step involves the substitution of
coordinated CNR with pyrrolidine, as indicated by the
appearance of the wCꢂN of free CNR and by the shift of
wNꢀH from 3284 cm−1 in free pyrrolidine to 3261 cm−1
.
Then, a slow increase of new CꢁN absorptions at 1634
and 1631 cm−1 for 2a and 2b, respectively, is observed,
suggesting the occurrence of insertion processes. The IR
1
and H-NMR spectra of 2a and 2b do not contain a
signal attributable to NꢀH, indicating that the reactions
proceed with elimination of CH4, to yield the corre-
Scheme 1.

R. Bertani et al. / Journal of Organometallic Chemistry 626 (2001) 11–15
13
sponding dialkylamido derivatives, as previously re-
ported for reactions of InMe3 with secondary amines
[4c,8,17].
166.8 ppm for 3b. The mass spectra of 3a and 3b show
the molecular ions at m/z 204 and 188 for 3a and 3b,
respectively, together with the fragments originated by
the loss of the pyrrolidine moiety.
Both reactions a and c of Scheme 1 affording the
imino derivatives 2, can be interpreted assuming that
slow insertion processes of the isocyanides CNR occurs
in the InꢀNPyrr bond of Me2InPyrr previously prepared
according to route c or generated ‘‘in situ’’ according to
route a.
Even if complexes 2a and 2b easily decompose, the
process is confirmed by the isolation and characteriza-
tion of the corresponding formamidine derivatives 3a
and 3b, suitably formed by the unprecedented insertion
of CNR into the InꢀN bond.
It is noteworthy that reactions described by route a
do not occur with formation of carbene species by
nucleophilic attack of the amine on the carbon atom of
the coordinated isocyanide, even if the increasing of the
intensity of wCꢂN may indicate an activation of the
isocyanide towards this process [18a]. This observation
may be related to the fact that the only method re-
ported in the literature for the preparation of indium
carbene complexes involves the reaction of stable carbe-
nes with suitable indium substrates [18b,c].
NMR data are in agreement with the proposed struc-
1
tures of 2a and 2b and a H/13C heteronuclear correla-
tion 2D experiment allowed the peak assignments. The
1H-NMR spectrum exhibits singlets at 0.072 and 0.019
ppm corresponding to the methyl groups bonded to
indium for 2a and 2b, respectively. These signals are
shifted downfield with respect to InMe3, complexes 1
and InMe2Pyrr [19]. Methyl groups in complexes 2a
and 2b give rise in 13C-NMR spectra singlets at ca.
−10 ppm. The signals corresponding to the CH2 pyrro-
lidine ring appear as multiplets at ca. 1.4 ppm (CH2)
and 2.9 (NCH2) in the 1H-NMR spectra. The CꢁN
carbon is evident only in the 13C-NMR spectrum of 2a
at 163.8 ppm.
The FAB mass spectra of compounds 2a and 2b
show the presence of the molecular ions at m/z 348
(15%) and 332 (15%), respectively. The base peak in
both spectra is represented by In+ at m/z 115 and ions
at m/z 145 corresponding to Me2In+. The ions corre-
sponding to the losses of pyrrolidine are also present at
m/z 278 (29%) for 2a and 262 (25%) for 2b.
3. Experimental
Pyrrolidine (PyrrH) was purchased from Aldrich.
The solvents and amine have been purified and dried
according to the procedures reported in the literature
[20].
InMe3, p-tolyl isocyanide and p-methoxyphenyl iso-
cyanide were prepared according to procedures re-
ported in the literature [21,22]. InMe2Pyrr was prepared
according to the method of Ref. [19]. The synthesis of
InMe2X was achieved by following a similar procedure
to that reported in Ref. [23] which involves the reaction
of InMe2Cl with LiPyrr (PyrrꢁNCH2ꢀ(CH2)2ꢀCH2)
[24]. LiPyrr was prepared by reacting n-BuLi (Fluka)
and pyrrolidine.
Elemental analyses (C, H, N) were performed on a
Fisons EA 1108 elemental analyzer. IR spectra were
recorded on a Mattson 3030 Fourier-transform spec-
trometer (4000–400 cm−1) using KBr disks. NMR
spectra were collected on a Bruker AC-200 instrument.
The mass spectrometric measurements were performed
on a triple quadrupole (VG Quattro, VG Fisons, Al-
trinchan, UK) instrument and on ZAB 2F (VG, Altrin-
chan, UK) instrument equipped with a FAB source (8
keV Xe atoms), bombarding the sample deposited on
the probe by evaporation of its Et2O solution.
The FAB cesium gun in the VG Quattro Mass
Spectrometer operated from 2 to 10 kV. Positive ion
mass spectra were obtained with MS-1 scanning over
m/z 50–1500 at 9.6 s decade−1. GC/MS determinations
were carried out on a QMD 1000 instrument (column
PS 264, 30 m, 1 ml/min He flow, from 80 to 280°C,
10°/min).
Compounds 2a and 2b are brown powders, which
decompose giving rise to the corresponding formamidi-
nes 3a and 3b (Scheme 1, route b).
Compounds 2a and 2b can also be prepared by
reacting InMe2Pyrr 4 [19] with the corresponding isocy-
anide (Scheme 1, route c). InMe2Pyrr has been previ-
ously prepared by reacting InMe3 and PyrrH
(pyrrolidine) with CH4 elimination [18] and has been
completely characterized. The reactions (c) have been
studied by IR spectroscopy by following the appear-
ance of the wCꢂN stretching bands of compounds 2.
Free formamidines 3a and 3b have been quantita-
tively obtained by reaction of compounds 2a and 2b,
respectively, with HClexc (route b, Scheme 1). The for-
mation of InMe2Cl was checked by comparison with
1
previously reported H-NMR data (a singlet at 0.418
ppm for methyl groups in C6D6).
3.1. InMe3·CNC6H4-p-OMe (1a)
1
3a and 3b have been also characterized by IR, H-
and 13C-NMR. The 1H/13C heteronuclear correlation
2D spectra show the imine protons at 7.87 ppm with
the corresponding carbon atom at 167.7 ppm for 3a
and at 7.90 ppm with the corresponding carbon atom at
The isocyanide CNC6H4-p-OMe (0.089 g, 0.68 mmol)
was added to a solution of InMe3 (0.109 g, 0.68 mmol)
in freshly distilled n-hexane (15 ml). After stirring for a
day at room temperature, the solution was evaporated

14
R. Bertani et al. / Journal of Organometallic Chemistry 626 (2001) 11–15
in vacuo yielding a brown powder. The product was
recrystallized by dissolution in n-hexane and filtration
from a cold (−10°C) suspension of ca. 2 ml of n-hex-
ane. Yield 175 mg (87%).
3.4. InMe2{C(ꢁNC6H4-p-CH3)[N(CH2)3CH2]} (2b)
Route (a): pyrrolidine (45 ml, d=0.83 g l−1, 1 mmol)
was added to a solution of 1b (0.147 g, 0.53 mmol) in
n-hexane (3 ml). After stirring for three weeks at room
temperature, the solution was dried to yield a dark
brown powder.
1
IR (n-hexane): w(CN) 2174 cm−1. H-NMR (C6H6-d6,
r.t., l ppm): 3.21 (s, 3H, Ar-OCH3), 0.03 (s, 9H,
InCH3). 13C-NMR (C6H6-d6, r.t., l ppm): −7.66
(In(CH3)3), 55.03 (OCH3), and 117.15 (InCN). FAB
mass spectrum (ZAB 2F); m/z: 293 (18%) [M]+, 278
(2%) [M−CH3]+, 263 (5%) [M−2CH3]+, 248 (2%)
[M−3CH3]+, 133 (100%) [CNC6H4-p-OMe]+, 145
(15%) [Me2In]+, 381 (5%) [In(CNC6H4-p-OMe)2]+.
Anal. Found: C, 45.56; H, 5.02; N, 4.75. Calc. for
C11H16NOIn: C, 45.07; H, 5.55; N, 4.78%.
Route (b): the isocyanide CNC6H4-p-CH3 (0.124 g,
0.93 mmol) was added to a solution of InMe2Pyrr
(0.200 g, 0.93 mmol) in n-hexane (3 ml). After stirring
for two months at room temperature, the solution was
dried to yield a dark brown powder.
1
IR (n-hexane): w(CN) 1631 cm−1. H-NMR (C6H6-d6,
r.t., l ppm): 0.019 (s, 6H, InCH3), 1.40 (m, 4H, CH2),
2.07 (s, 3H, CH3), 2.95 (m, 4H, NCH2). 13C-NMR
(C6H6-d6, r.t., l ppm): −10.3 (InCH3), 20.7 (ArCH3),
25.3 (CH2), 53.3 (NCH2). FAB mass spectrum (VG
Quattro); m/z: 332 (30%) [M]+, 318 (15%) [M−CH3]+
, 303 (45%) [M−2CH3]+, 262 (30%) [M−Pyrr]+, 247
(20%) [M−Pyrr−CH3]+, 145 (25%) [Me2In]+, 115
(100%) [In]+.
3.2. InMe3·CNC6H4-p-Me (1b)
The isocyanide CNC6H4-p-Me (0.171 g, 1.46 mmol)
was added to a solution of InMe3 (0.233 g, 1.46 mmol)
in n-hexane (30 ml). After stirring for a day at room
temperature, the solution was evaporated in vacuo
yielding a brown powder. The product was recrystal-
lized by dissolution in n-hexane and filtration from a
cold (−10°C) suspension of ca. 2 ml of n-hexane. Yield
3.4.1. Reaction of 2a with HCl
339 mg (84%). IR (n-hexane): w(CN) 2173 cm−1 1H-
.
A C6H6-d6 solution of 2a (50 mg, 0.14 mmol) was
reacted with HClexc. An immediate reaction was noted
as the reaction mixture changed color from brown to
yellow. 1H-NMR spectra of the reaction mixture
showed the quantitative formation of Me2InCl (singlet
at 0.418 ppm).
NMR (C6H6-d6, r.t., l ppm): 1.82 (s, 3H, Ar-CH3), 0.10
(In(CH3)3). 13C-NMR (C6H6-d6, r.t., l ppm): −7.55
(InCH3), 21.08 (Ar-CH3), and 121.86 (InCN). FAB
mass spectrum (ZAB 2F); m/z: 277 (7%) [M]+, 262
(2%) [M−CH3]+, 247 (5%) [M−2CH3]+, 232 (2%)
[M−3CH3]+, 117 (100%) [CNC6H4-p-Me]+, 145 (15%)
[Me2In]+, 349 (5%) [In(CNC6H4-p-Me)2]+. Anal.
Found: C, 47.38; H, 5.71; N, 4.90. Calc. for C11H16NIn:
C, 47.68; H, 5.83; N, 5.06%.
3a was identified on the basis of spectroscopic NMR
and mass spectrometric data.
1H-NMR (C6H6-d6, r.t., l ppm): 7.53 (s, 1H, HCꢁN),
1.40 (m, 4H, CH2), 3.00 (m, 4H, NCH2), 3.40 (s, 3H,
OCH3). 13C-NMR (C6H6-d6, r.t., l ppm): 149.6 (HCN),
20.7 (ArCH3), 26.2 (CH2), 53.3 (NCH2), 55.0 (OCH3).
Mass spectrum; m/z: 204 (10%) [M]+, 188 (80%) [M−
CH3]+.
3.3. InMe2{C(ꢁNC6H4-p-OCH3)[N(CH2)3CH2]} (2a)
Route (a): pyrrolidine (45 ml, d=0.83 g l−1, 1 mmol)
was added to a solution of 1a (0.155 g, 0.53 mmol) in
n-hexane (3 ml). After stirring for 33 days at room
temperature, the solution was dried to yield a dark
brown powder.
3.4.2. Reaction of 2b with HCl
Route (b): the isocyanide CNC6H4-p-OCH3 (0.124 g,
0.93 mmol) was added to a solution of InMe2Pyrr
(0.200 g, 0.93 mmol) in n-hexane (3 ml). After stirring
for two months at room temperature, the solution was
dried to yield a brown powder.
A C6H6-d6 solution of 2b (50 mg, 0.15 mmol) was
reacted with HClexc. An immediate reaction was noted
as the reaction mixture changed color from brown to
yellow. 1H-NMR spectrum of the reaction mixture
shows the quantitative formation of Me2InCl (singlet at
0.418 ppm).
1
IR (n-hexane): w(CN) 1634 cm−1. H-NMR (C6H6-d6,
r.t., l ppm): 0.072 (s, 6H, InCH3), 1.38 (m, 4H, CH2),
2.97 (m, 4H, NCH2), 3.26 (s, 3H, O-CH3). 13C-NMR
(C6H6-d6, r.t., l ppm): −10.3 (InCH3), 25.2 (CH2),
53.0 (NCH2), 55.0 (OCH3), 163.8 (C=N). FAB mass
spectrum (VG Quattro); m/z: 348 (22%) [M]+, 333
(10%) [M−CH3]+, 317 (20%) [M−OCH3]+, 278
(29%) [M−Pyrr]+, 145 (25%) [Me2In]+, 115 (100%)
[In]+.
3b was identified on the basis of spectroscopic NMR
and mass spectrometric data.
1H-NMR (C6H6-d6, r.t., l ppm): 7.50 (s, 1H, HCꢁN),
1.65 (m, 4H, CH2), 2.85 (m, 4H, NCH2), 2.12 (s, 3H,
CH3). 13C-NMR (C6H6-d6, r.t., l ppm): 149.8 (HCN),
20.8 (ArCH3), 25.8 (CH2), 51.5 (NCH2). Mass spec-
trum; m/z: 188 (70%) [M]+, 159 (30%) [C10H11N2]+,
118 (30%) [C8H8N2]+.

R. Bertani et al. / Journal of Organometallic Chemistry 626 (2001) 11–15
15
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The authors would like to thank CNR (Cooperation
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