Transition metal coordination and reactivity of 2-(azidomethyl)-, 2-(chloromethyl)- and 2-(iodomethyl)phenyl isocyanides

Article abstract of DOI:10.1016/S0020-1693(03)00407-9

2-(Azidomethyl)phenyl isocyanide, 2-(CH₂N₃)C ₆H₄N≡C (AziNC), coordinates to {M(CO)₅} (M=W, Cr) fragments to afford the corresponding isocyanide complexes [M(CO) ₅(AziNC)] (M=W (1), Cr (2)). AziNC coordinates also to some Au(I) species such as [AuCl(AziNC)] (3), derived from the reaction of [AuCl(Me ₂S)] with AziNC, and [Au(AziNC)₂][BF₄] (4), obtained from the reaction of 3 with AgBF₄, followed by treatment with AziNC. Complexes 1 and 2 undergo the Staudinger reaction with PPh ₃ affording the phosphinimine-isocyanide derivatives [M(CO) ₅{C≡NC₆H₄-2-(CH₂N=PPh ₃)}] (M=W (5), Cr (6)). Complex 6 reacts with H₂O affording a mixture of the amino-isocyanide [Cr(CO)₅{C≡NC ₆H₄-2-(CH₂NH₂)}] (7) and the carbene [Cr(CO)₅{CN(H)C₆H₄-2-CH ₂N(H)}] (8) species. Complexes 3 and 4 react with 1 or 2 equiv. of PPh₃ displacing the isocyanide with the formation of the complexes [AuCl(PPh₃)] (9) and [Au(PPh₃)₂][BF ₄] (10), respectively. The halogeno-isocyanide complexes [W(CO) ₅(CNC₆H₄-2-CH₂Cl)] (11) and [W(CO)₅(CNC₆H₄-2-CH₂I)] (12) show different reactivity towards amines so that only 12 reacts with MeNH ₂ to afford in low yield the N-heterocyclic carbene species [W(CO)₅{CN(H)C₆H₄-2-CH₂N(Me)}] (13).

Full text of DOI:10.1016/S0020-1693(03)00407-9

Inorganica Chimica Acta 356 (2003) 349Á356
/
www.elsevier.com/locate/ica
Transition metal coordination and reactivity of 2-(azidomethyl)-,
2-(chloromethyl)- and 2-(iodomethyl)phenyl isocyanides
Marino Basato a, Giacomo Facchin b, Rino A. Michelin c,*, Mirto Mozzon c,
Sandra Pugliese c, Paolo Sgarbossa c, Augusto Tassan c
a Dipartimento di Chimica Inorganica, Metallorganica ed Analitica, Universita` di Padova, Via F. Marzolo 1, 35131 Padua, Italy
b Istituto di Scienze e Tecnologie Molecolari, ISTM-C.N.R., c/o Dipartimento di Processi Chimici dell’Ingegneria, Via F. Marzolo 9, 35131 Padua, Italy
c Dipartimento di Processi Chimici dell’Ingegneria, Universita` di Padova, Via F. Marzolo 9, 35131 Padua, Italy
Received 16 May 2003; accepted 3 June 2003
Dedicated to Prof. Joao J.R. Frau´sto da Silva, an outstanding scientist in the field of bioinorganic chemistry, on the occasion of his retirement
˜
Abstract
2-(Azidomethyl)phenyl isocyanide, 2-(CH2N3)C6H4NÅ
/
C (AziNC), coordinates to {M(CO)5} (Mꢀ
/
W, Cr) fragments to afford
W (1), Cr (2)). AziNC coordinates also to some Au(I) species such
the corresponding isocyanide complexes [M(CO)5(AziNC)] (Mꢀ
/
as [AuCl(AziNC)] (3), derived from the reaction of [AuCl(Me2S)] with AziNC, and [Au(AziNC)2][BF4] (4), obtained from the
reaction of 3 with AgBF4, followed by treatment with AziNC. Complexes 1 and 2 undergo the Staudinger reaction with PPh3
affording the phosphinimine-isocyanide derivatives [M(CO)5{CÅ
with H2O affording a mixture of the aminoÁisocyanide [Cr(CO)5{CÅ
(H)}] (8) species. Complexes 3 and 4 react with 1 or 2 equiv. of PPh3 displacing the isocyanide with the
formation of the complexes [AuCl(PPh3)] (9) and [Au(PPh3)2][BF4] (10), respectively. The halogenoÁisocyanide complexes
[W(CO)5(CNC6H4-2-CH2Cl)] (11) and [W(CO)5(CNC6H4-2-CH2I)] (12) show different reactivity towards amines so that only 12
/
NC6H4-2-(CH2NÄ
/
PPh3)}] (Mꢀ
/
W (5), Cr (6)). Complex 6 reacts
/
/
NC6H4-2-(CH2NH2)}] (7) and the carbene [Cr(CO)5{
/
ꢀ
ꢁ
/
CN(H)C6H4-2-CH2N
/
ꢀ
ꢁ
reacts with MeNH2 to afford in low yield the N-heterocyclic carbene species [W(CO)5{/CN(H)C6H4-2-CH2N/(Me)}] (13).
# 2003 Elsevier Science B.V. All rights reserved.
Keywords: Functionalized isocyanides; Transition metal complexes; N-Heterocyclic carbene complexes
1. Introduction
metal complexes such as metathesis (ADMET, RCM,
etc.), the Heck and Suzuki reactions, is well-established
[15].
We have been involved since several years in the
synthesis of g-functionalized isocyanides of the type I
(Scheme 1), whose reactivity, when coordinated to a
suitable transition metal center II, has been shown to
The chemistry of several functionalized isocyanides
has been recently reviewed [1,2]. The reactivity of these
ligands towards transition metal complexes has been
often addressed to the formation of N-heterocyclic
carbene (NHC) derivatives through an intramolecular
nucleophilic attack of the proper function on the
depend on the type of the function [16Á21]. Thus, for
/
instance, the phosphonium-substituted isocyanides react
in the presence of a base to give indolin-2-ylidene
derivatives III, while the OH-functionalized isocyanides
afford benzoxazin-2-ylidene complexes IV.
isocyanide carbon [1Á
in homogeneous catalytic processes promoted by NHCÁ
/
14]. The relevance of NHC ligands
/
The reaction chemistry described in Scheme 1 led us
to further explore the reactivity of other transition-metal
coordinated g-functionalized isocyanides of the type I
* Corresponding author. Tel.: ꢁ
8275 525.
E-mail address: rino.michelin@unipd.it (R.A. Michelin).
/
39-049-8275 522; fax: ꢁ39-049-
/
0020-1693/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0020-1693(03)00407-9

350
M. Basato et al. / Inorganica Chimica Acta 356 (2003) 349Á356
/
1H, 31P {1H} and 13C {1H} NMR spectra were run at
298 K, unless otherwise stated, on a Bruker 200 AC
spectrometer operating at 200.13, 81.015 and 50.32
MHz, respectively. Peak positions are relative to
Me4Si and were calibrated against the residual solvent
resonance (1H) or the deuterated solvent multiplet (13C);
the 31P NMR spectra were referenced against external
H3PO4 85%. Electrospray ionization mass spectrometry
(ESI MS) experiments [23] were performed on a LCQ
(Thermoquest, San Jose´, CA) ion trap instrument
equipped with an electrospray ion source. The experi-
ments were performed using the positive ion mode, with
spray voltage of 4.3 kV, capillary temperature 150 8C,
N2 sheath gas flow 40 (a.u.). Samples were dissolved in
CH3CN at a concentration of 10ꢂ6 M and supplied to
the ESI source by a rate of infusion of 5 ml minꢂ1
.
The elemental analyses were performed by the De-
partment of Analytical, Inorganic and Organometallic
Chemistry of the University of Padova. The compounds
2-(azidomethyl)phenyl isocyanide, 2-(CH2N3)C6H4NC
(AziNC) [22], and 2-(chloromethyl)phenyl isocyanide, 2-
(CH2Cl)C6H4NC [18], were synthesized according to
reported procedures. The complexes [W(CO)5(AziNC)]
(1) [22], [Cr(CO)5I][NEt4] [24] and [W(CO)5(CNC6H4-2-
Scheme 1.
such as 2-(azidomethyl)phenyl- and 2-(halogen-
omethyl)phenyl isocyanides, 2-(CH2Y)C6H4NC (Yꢀ
N3 [22]; Cl, I [18]), with the aim of synthesizing cyclic
/
CH2X)] (XꢀCl (11), I (12)) [16] were prepared as
/
described in the literature, while the complex
[AuCl(SMe2)] was purchased from Aldrich.
aminocarbenes of the type shown in Eq. (1).
2.2. Synthesis of the AziNC complexes
ð1Þ
2.2.1. Synthesis of [Cr(CO)5(AziNC)] (2)
To a suspension of [Cr(CO)5I][NEt4] (1.46 g, 3.25
mmol) in acetone (25 ml) at 0 8C was added dropwise
with stirring a 0.45 M acetone solution of AgBF4 (7.7
ml, 3.08 mmol, diluted to 15 ml) over a period of 20 min.
After the addition was complete, the mixture was
quickly filtered off and the dark orange solution was
treated dropwise with a solution of AziNC (0.47 g, 2.98
mmol) in acetone (15 ml). After being stirred for an
additional 20 min, the green solution was allowed to
reach room temperature (r.t.) and then evaporated to
dryness to give a green oil, which was chromatographed
The synthesis of these new NHC ligands will take
advantage of the reactivity of the azido and the
halogeno groups of the functional isocyanides to
produce through different synthetic routes
ÁNHR
/
(RꢀH, Me) amino groups, which eventually undergo
/
intramolecular cyclization to quinazolin-2-ylidenes. The
results of this study are reported herein.
2. Experimental
on a column (36ꢃ
/
3 cm) of silica gel (70Á
/
230 mesh)
n-hexane (1:2 v/v) as eluant.
using a mixture of Et2Oꢁ
/
2.1. General procedures and materials
The green band that formed was collected and then
taken to dryness under reduced pressure to afford a
green oil that rapidly solidifies. The green solid 2 was
then dried under vacuum. Yield 0.68 g, 59.7%. Anal.
Calc. for C13H6CrN4O5: C, 44.59; H, 1.73; N, 16.00.
All work was carried out under a nitrogen atmosphere
using standard Schlenck techniques. Solvents were
distilled under dinitrogen prior to use; CH2Cl2 was
distilled from CaH2, diethyl ether and THF were
distilled from sodium benzophenone. IR spectra were
Found: C, 45.23; H, 1.36; N, 15.93%. IR (
2134 (s, NÅC); k(NÅ
C) 1735 N mꢂ1; 2103 (s, N3); 1961,
2051 (s, CÅO). H NMR (d, CDCl3): 4.51 (CH2, s);
7.39Á
7.45 (C6H4, m). 13C {1H} NMR (d, CDCl3): 51.56
(CH2, s); 126.71Á132.56 (C6H4, m); 176.94 (NÅC, s);
216.62 (trans CO, s); 214.62 (cis CO, s).
/
n˜; CH2Cl2):
/
/
1
taken on a FT-IR AVATAR 320 (4000Á
FT-IR Nexus (range 600Á
50 cmꢂ1) of the Nicolet
Instrument Corporation (polyethylene (PE) films) spec-
trophotometers; the wavenumbers (
n˜) are given in cmꢂ1
/
400 cmꢂ1) or
/
/
/
/
/
/
.

M. Basato et al. / Inorganica Chimica Acta 356 (2003) 349Á
/356
351
2.2.2. Synthesis of [AuCl(AziNC)] (3)
final complex 5 having similar solubilities in common
organic solvents such as diethyl ether and n-hexane. The
overall yield was 0.56 g, 87.7%. Anal. Calc. for
C31H21N2O5PW: C, 51.98; H, 2.95; N, 3.91. Found: C,
To a pale yellow solution of [AuCl(SMe2)] (0.50 g,
1.70 mmol) in dry CH2Cl2 (50 ml) was added under
stirring at r.t. AziNC (0.28 g, 1.77 mmol) to give a dark
green solution. After a few minutes, a grey solid started
to precipitate. The reaction mixture was stirred at r.t. for
an additional 20 min. An IR spectrum of the green
51.95; H, 2.65; N 3.73%. IR (
k(NÅC) 1750 N/m; 1949, 2059 (s, CÅ
CDCl3): 4.49 (CH2, d, 3JHÁP 15.6); 7.20Á
31P{1H} NMR (d, CDCl3): ꢂ
5.17 (PPh3 ca. 9%); 14.93
(NÄPPh3, 79%); 29.61 (OÄPPh3, 12%). ESI MS: m/z
633 [Mꢂ3CO; base peak]; 717 [MꢁH]. Peaks at m/z
/
n˜; CH2Cl2): 2143 (s, NÅ
/
C);
O). H NMR (d,
8.15 (C6H4, m).
1
/
/
/
solution showed the disappearance of the CÅ
/
N absorp-
/
tion of the free isocyanide at 2121 cmꢂ1, while a strong
absorption at 2217 cmꢂ1 was present. The volume of
the solution was reduced to 10 ml under reduced
pressure and then Et2O (30 ml) was added. The greyish
/
/
/
/
689, 661, 633, 577 corresponding to the loss of one, two,
three and five CO ligands, respectively, were also
detected.
solid was filtered off, washed with Et2O (2ꢃ15 ml) and
/
then dried under vacuum. Yield 0.62 g, 93.5%. Anal.
Calc. for C8H6AuClN4: C, 24.60; H, 1.55; N, 14.34.
2.3.2. Reaction of [Cr(CO)5(AziNC)] (2) with PPh3.
Found: C, 24.75; H, 1.24; N, 13.88%. IR (
2217 (s, NÅC); k(NÅ
C) 1873 N mꢂ1; 2105 (s, N3). IR (
PE film): 356 (m,w, AuÁ
Cl). 1H NMR (d, CDCl3): 4.55
(CH2, s); 7.47Á7.68 (C6H4, m).
/
n˜; CH2Cl2):
Synthesis of [Cr(CO)5(CNC6H4-2-CH2NÄ
/
PPh3)] (6)
/
/
/
n˜;
This complex was prepared as described for 5 starting
from 2 (0.24 g, 0.68 mmol) and PPh3 (0.18 g, 0.68 mmol)
in CH2Cl2 (25 ml). Also in this case, complex 6 could not
/
/
be purified from the presence of Ph3Pꢀ
based on the integration ratios with the phosphinimine
PPh3 signal in the 31P {1H} NMR spectrum). Yield
(calculated taking into account the integration ratios of
the signals in the 31P {1H} NMR spectrum) 0.33 g,
/
O (ca. 29%
2.2.3. Synthesis of [Au(AziNC)2][BF4] (4)
To a pale green solution of 3 (0.20 g, 0.51 mmol) in
CH2Cl2 (30 ml) was added under stirring at r.t. a 0.86 M
acetone solution of AgBF4 (0.6 ml, 0.52 mmol). The
reaction mixture was stirred for 10 min and the solid
AgCl formed was filtered off. It was then treated with
AziNC (0.09 g, 0.57 mmol) to give a dark green solution.
An IR spectrum of the green solution run after 10 min
Á
/
NÄ
/
82.3%. IR (
/
n˜; CH2Cl2): 2142 (s, NÅ
/
C); k(NÅ
O). H NMR (d, CDCl3): 4.50
(CH2, d, JHÁP 15.4); 7.16Á
8.10 (C6H4, m). 31P {1H}
NMR (d, CDCl3): 14.66 (NÄPPh3, s, 71%); 29.51 (OÄ
PPh3, s, 29%).
/
C) 1748 N
mꢂ1; 1954, 2058 (s, CÅ
/
1
3
/
/
/
showed the disappearance of the CÅ
/
N absorption of the
free isocyanide at 2121 cmꢂ1, while a strong absorption
at 2231 cmꢂ1 was present. The volume of the solution
was reduced to 10 ml under reduced pressure and then
Et2O (30 ml) was added. The grey solid that formed, was
2.3.3. Reaction of [Cr(CO)5(CNC6H4-2-CH2NÄ
/
PPh3)] (6) with H2O. Synthesis of [Cr(CO)5(CNC6H4-
ꢀ
ꢁ
/
2-CH2NH2)] (7) and [Cr(CO)5{
/
CN(H)C6H4-2-CH2N
filtered off, washed with Et2O (3ꢃ10 ml) and then dried
/
under vacuum. Yield 0.30 g, 97.7%. Anal. Calc. for
C16H12AuBF4N8: C, 32.02; H, 2.02; N, 18.67. Found: C,
H}] (8)
Complex 6 (0.12 g, 0.205 mmol) was dissolved in wet
acetone (25 ml) and stirred for 30 h at 40 8C using a
thermostatted water bath. After this time, an IR
32.88; H, 1.79; N, 18.51%. IR (
C); k(NÅ
C) 1896 N mꢂ1; 2106 cmꢂ1 (s, N3). H NMR
(d, CDCl3): 4.65 (CH2, s); 7.48Á7.79 (C6H4, m).
/
n˜; CH2Cl2): 2231 (s, NÅ
/
1
/
/
spectrum still showed the presence of the NÅ
/C band.
The solvent was then evaporated under reduced pressure
to give a sand-coloured solid residue, which was treated
with n-hexane and filterd off, washed with n-hexane
2.3. Reactivity of the AziNC complexes
2.3.1. Reaction of [W(CO)5(AziNC)] (1) with PPh3.
(2ꢃ
IR (
n˜; CH2Cl2): 2139 (w, NÅ
CÅO); 3438 (w, NH). H NMR (d, CDCl3): 4.50 (CH2,
s); 6.76Á
7.71 (C6H4, m). 31P {1H} NMR (d, CDCl3):
29.77 (OÄPPh3).
The product was then chromatographed on a silica
plate (0.5 mm thick) using a mixture of Et2Oꢁn-hexane
(1:1 v/v) as eluant. Two bands having Rf 0.50 and 0.12,
respectively, were formed, which were collected, ex-
tracted with CH2Cl2 and then taken to dryness under
reduced pressure. The band with Rf 0.12 affords 0.036 g
of a white solid, which was assigned to compound 7 on
/
10 ml) and dried under vacuum. Total yield 0.060 g.
Synthesis of [W(CO)5(CNC6H4-2-CH2NÄ
/
PPh3)] (5)
/
/C); 1927, 1956, 2057 (m,s,
1
To an orange solution of 1 (0.43 g, 0.89 mmol) in
CH2Cl2 (20 ml) was added PPh3 (0.25 g, 0.95 mmol).
The reaction course was followed via IR spectroscopy
/
/
/
by monitoring the decrease of the n˜
2102 cmꢂ1. After one night stirring at r.t., no n˜
band of the starting material was present. The reaction
mixture was taken to dryness to give an orangeÁbrown
solid, which was dried under vacuum. A 31P {1H} NMR
showed the presence of Ph3PÄO and unreacted PPh3 (ca.
12 and 9%, respectively, based on integration ratios with
the phosphinimine ÁNÄ
PPh3 signal in the 31P {1H}
NMR spectrum), which could not be separated from the
/(N3) absorption at
/(N3)
/
/
/
/
/
the basis of spectroscopic data. IR (/
n˜; CDCl3): 2136 (w,
1
NÅC); 1959, 2055 (m,s, CÅO); 3451 (w, NH). H NMR
/
/

352
M. Basato et al. / Inorganica Chimica Acta 356 (2003) 349Á356
/
(d, CDCl3): 4.52 (CH2, s); 7.33Á
band with Rf 0.50 gives 0.020 g (yield 30%) of a white
solid, which was now assigned to compound 8 on the
/
7.71 (C6H4, m). The
spectroscopy for 18 h at r.t. Since no changes were
observed in the IR spectra, the solution was taken to
dryness to give a yellow solid, which was dried under
vacuum. It was then analyzed by 1H NMR which
confirmed the presence of only unreacted 11.
basis of spectroscopic data. IR (
/
n˜; CDCl3): 1926, 2057
O); 3444 (w, NH). H NMR (d, CDCl3): 4.51
(s, CH2); 6.72Á7.24 (m, C6H4); 6.48, 7.61 (s,br, NH).
1
(m,s, CÅ
/
/
2.4.2. Reaction of [W(CO)5(CNC6H4-2-CH2I)] (12)
2.3.4. Reaction of [AuCl(AziNC)] (3) with PPh3.
Synthesis of [AuCl(PPh3)] (9)
with MeNH2. Synthesis of [W(CO)5{/
ꢀ
ꢁ
CN(H)C6H4-2-CH2N/(Me)}] (13)
This reaction was carried out in a NMR tube and
followed by multinuclear NMR spectroscopy. Complex
3 (0.0188 g, 0.05 mmol) was placed in a NMR tube and
dissolved in CDCl3. It was then treated with PPh3 (0.013
g, 0.05 mmol). A 31P {1H} NMR spectrum of the
reaction mixture immediately showed the presence of a
singlet resonance at 33.5 ppm, while the 1H NMR
spectrum showed a singlet at 4.55 ppm. The IR
spectrum in CDCl3 shows two bands at 2124 and 2105
A solution of 12 (0.58 g, 1.02 mmol) in 1,2-dichlor-
oethane (30 ml) was treated with a 2.0 M solution of
MeNH2 in THF (1.3 ml, 2.6 mmol). The reaction was
followed by IR spectroscopy for 3 days at r.t. until the
the NÅ/C absorption was not observed. A TLC on silica
gel using n-hexane/chloroform (4:1 v/v) as eluant did not
show the band corresponding to the starting complex
12. The solvent was then evaporated to dryness to give a
yellow solid residue, which was treated with Et2O (50
cmꢂ1 corresponding to n˜
/
(NÅ/C) and n˜/(N3), respectively,
ml), filtered off, washed with Et2O (3ꢃ10 ml) and dried
/
of the free isocyanide. All the above spectroscopic data
indicate the formation of complex 9 by displacement of
coordinated AziNC by PPh3.
under vacuum. Yield 0.14 g, 29.1%. Anal. Calc. for
C14H10N2O5W: C, 35.77; H, 2.14; N, 5.96. Found: C,
35.22; H, 2.07; N, 5.54%. IR (
/
n˜; CH2Cl2): 1922, 2064
O); 3439 (w, NH). H NMR (d, CDCl3): 3.53
(s, Me); 4.48 (s, CH2); 6.76Á7.28 (m, C6H4); 7.60 (s,br,
1
(m,s, CÅ
/
2.3.5. Reaction of [Au(AziNC)2][BF4] (4) with PPh3.
Synthesis of [Au(PPh3)2][BF4] (10)
/
NH).
This reaction was carried out by stepwise addition of
1 equiv. of PPh3 to complex 4. To a pale green solution
of 4 (0.16 g, 0.267 mmol) in CH2Cl2 (20 ml), solid PPh3
(0.08 g, 0.305 mmol) was added in one portion. The
reaction was monitored by IR spectroscopy. After 10
min, a band at 2123 cmꢂ1 due to free AziNC formed,
while an absorption at 2229 cmꢂ1 clearly indicated that
the second molecule of AziNC was still coordinated to
the metal center. This experimental evidence suggested
the initial formation of the complex [Au(PPh3)(A-
ziNC)][BF4]. Since the IR spectrum did not change after
30 min, a second equiv. of PPh3 was added to the
reaction mixture. An IR spectrum run immediately after
the addition showed only the presence of the band at
2123 cmꢂ1 due to free AziNC. The solution was
concentrated to a small volume and then treated with
Et2O (30 ml). A white solid precipitated, which was
3. Results and discussion
3.1. Synthesis of the AziNC complexes
In order to explore the chemical behavior of the
isocyanide AziNC also in comparison with that shown
by the other N3-functionalized isocyanide 2-azidophenyl
isocyanide, 2-N3C6H4NC, reported by Hahn and cow-
orkers [2], we have initially prepared the carbonyl
complexes [M(CO)5(AziNC)] (Mꢀ
(Eq. (2)).
/W (1) [22], Cr (2))
filtered off, washed with Et2O (3ꢃ10 ml) and dried
/
under vacuum. Yield 0.19 g, 88.2%. Anal. Calc. for
C36H30AuBF4P2: C, 53.49; H, 3.74. Found: C, 53.46; H,
ð2Þ
1
3.78%. H NMR (d, CDCl3): 7.37Á
/
7.68 (C6H4, m). 31P
{1H} NMR (d, CDCl3): 33.49 (AuÁ
/PPh3, s).
2.4. Reactions of [W(CO)5(CNC6H4-2-CH2Y)] (Yꢀ
/
Cl (11); I (12)) complexes
2.4.1. Reaction of [W(CO)5(CNC6H4-2-CH2Cl)] (11)
with MeNH2
A solution of 11 (0.42 g, 0.88 mmol) in THF (35 ml)
was treated with a 2.0 M solution of MeNH2 in THF
(1.1 ml, 2.2 mmol). The reaction was followed by IR
The chromium complex 2 was obtained in good yield by
the same procedure described previously for 1 by
reacting [M(CO)5I][NEt4] with an equivalent of AgBF4
in acetone at 08 C followed by treatment with a
stoichiometric amount of AziNC. The two complexes

M. Basato et al. / Inorganica Chimica Acta 356 (2003) 349Á
/356
353
have been characterized by comparison of their IR
spectral features in the NC and CO stretching regions
(see Experimental) with those reported for analogous
carbonylÁ
and 2 display the NÅ
cmꢂ1 (k(NÅ 1740 and 1735 N mꢂ1 [25]), respec-
C)ꢀ
tively, and for both complexes the N3 band appears at n˜
2103 cmꢂ1. The D
n˜ n˜(NÅC)coord n˜(NÅC)free values
of approximately 15Á
10 cmꢂ1 shown by 1 and 2 reflect
/isocyanide complexes [18,21]. In particular, 1
/
C absorption at n˜ 2137 and 2134
/
ꢀ
/
/
/
/
ꢀ
/
/
/
ꢀ
/
/
/
Á
/
/
/
/
a low electrophilicity of the isocyanide carbon toward
nucleophilic attack [1,26].
In the 1H NMR spectra, the methylene resonance
appears as a singlet at 4.51 ppm. The 13C {1H} NMR
spectra show the signal of the isocyanide carbon as a
broad singlet at 157.2 and 176.9 ppm for 1 and 2,
respectively. Again, these data are consistent with those
previously reported for structurally similar complexes
[18,21].
Scheme 2.
3.2. Reactivity of the AziNC complexes
3.2.1. Reactions of complexes 1 and 2 with PPh3
The azidoÁisocyanide complexes 1 and 2 undergo the
so-called Staudinger reaction [27] with 1 equiv. of PPh3
in CH2Cl2 at room temperature to afford the phosphi-
/
AziNC reacts with the Au(I) complex, [AuCl(SMe2)]
by displacement of the sulfide to give in high yield the
nimine derivatives 5 (Mꢀ
tively, and liberation of N2 (Scheme 3).
The reaction was followed by IR spectroscopy by
monitoring the decrease of the n˜(N3) absorption at 2102
cmꢂ1. After 12 h stirring at room temperature, no n˜
(N3)
/
W) and 6 (Mꢀ
/
Cr), respec-
isocyanideÁ/gold(I) complex 3 as a white solid:
/
/
band of the starting material was present. Work-up of
the reaction mixtures (see Experimental) afforded the
phosphinimino compounds, which were characterized
by IR and multinuclear NMR spectroscopies. The
31P{1H} NMR spectra show the phosphinimine signal
at 14.9 and 14.6 ppm for 5 and 6, respectively. These
chemical shifts well agree with those reported for other
phosphinimine species [28]. The phosphorous NMR
spectra show also the presence of a small amount (ca.
ð3Þ
1
Complex 3 was characterized by IR, H NMR and
microanalysis (Section 2). The IR spectrum (CH2Cl2) of
C) at 2217 cmꢂ1 (k(NÅ
3 shows n˜
/
(NÅ
/
/
C) ca. 1873 N
m
ꢂ1) with a stretching value shifted of approximately 90
10%) of the phosphine oxide, Ph3PÄ
/
O, which is likely
cmꢂ1 to higher wavenumbers with respect to the free
isocyanide. This behaviour is expected for isocyanides
coordinated to transition metal ions in medium to high
oxidation states [1] and now the high positive shift
indicates the susceptibility of the isocyanide carbon to
nucleophilic attack. The IR spectrum (CH2Cl2) of 3
formed by hydrolysis of the phosphinimine group as
1
known in the literature [28]. The H NMR spectra of 5
and 6 show the methylene resonance of the Á
/
CH2NÄ
/
PPh3 group at 4.50 ppm as a doublet due to the coupling
with the P-atom (3JHÁP ca. 15.5 Hz). The IR spectra
confirm the absence of the N3 absorption.
shows also n˜
spectrum (PE film) in the 600Á
AuÁ
Cl stretching at 356 cmꢂ1 as a medium intensity
absorption.
The subsequent reaction of 3 in CH2Cl2Á
/
(N3) at 2105 cmꢂ1, while the far IR
50 cmꢂ1 shows the
There is no spectroscopic evidence that complexes 5
and 6 undergo intramolecular nucleophilic attack by the
phosphinimino nitrogen to the isocyanide carbon as
/
/
indicated by the presence of the NÅ/C absorption at ca.
2140 cmꢂ1 due to the isonitrile ligand. On the other
hand, the phosphinimine moiety easily undergoes hy-
drolysis reaction converting into an amino group. This
type of reactivity was exploited in the case of complex 6
which, in a non anhydrous acetone solution (equation
4), shows, in the 31P{1H} NMR, the disappearance of
the phosphinimino signal at 14.7 ppm and the simulta-
neous formation of a signal at 29.8 ppm characteristic of
the triphenylphosphine oxide. The isocyanide function is
not involved in this reaction displaying, in the IR
/
acetone at
room temperature with an 1 equiv. of AgBF4 likely
affords initially the cationic solvento complex [Au(A-
ziNC)(solv)][BF4], which, on treatment with a stoichio-
metric amount of AziNC, produces the di-isocyanide
complex 4 in almost quantitative yield (Scheme 2).
Complex 4 is a pale green solid, air-stable, soluble in
chlorinated solvents, which was characterized by IR, 1H
NMR and microanalysis (Section 2). In particular, the
IR spectrum (CH2Cl2) shows n˜
/
(NÅ
/
C) at 2231 cmꢂ1
(k(NÅ
/
C) ca. 1896 N mꢂ1) and n˜(N3) at 2106 cmꢂ1
/
.
spectrum, a CÅ
/
N stretching band at 2139 cmꢂ1
.

354
M. Basato et al. / Inorganica Chimica Acta 356 (2003) 349Á356
/
Scheme 3.
31P{1H} NMR spectroscopy. Immediately, the forma-
tion of a signal at 33.5 ppm was observed which is
characteristic of a PPh3 ligand coordinated to a gold(I)
center.
ð5Þ
ð4Þ
An IR spectrum of the solution showed two bands at
2105 and 2124 cmꢂ1 corresponding to those of the free
azido-isonitrile ligand. This experimental evidence in-
dicates that the reaction between complex 3 and PPh3
proceeds in a selective manner with complete displace-
ment of the coordinated isocyanide from the metal
center rather than with attack of triphenylphosphine to
the N3 functionality to afford a phosphinimine group, as
The residue, which was recovered from the hydrolysis
mixture, was cromatographed on a silica gel plate
affording two bands, which were extracted with
CH2Cl2 giving two spectroscopically different products.
Thus, one of them shows in the IR spectrum the original
stretching band of the metal coordinated isocyanide
group at 2136 cmꢂ1 and a new weak band at 3451 cmꢂ1
1
previously observed for the CrÁ
/
and WÁcarbonyl
/
which can be attributed to a NH moiety. The H NMR
isocyanide complexes 5 and 6. Such reactivity is
completely different from that reported by Hahn et al.
[2] for the Au(I) coordinated 2-azidophenyl isocyanide
which was found to react with PPh3 giving the corre-
sponding phosphinimino derivative via the Staudinger
reaction. In order to verify whether the observed
different reactivity could be due to different steric effects
around the metal center, the reaction with PPh3 was
spectrum exhibits the methylene signal at 4.52 ppm.
These data suggest for this derivative the structure 7
(Eq. (4)). The IR spectrum of the second compound
shows the characteristic carbonyl bands in the 1926 Á
/
2057 cmꢂ1 range of the {M(CO)5} moiety and a NH
band at 3444 cmꢂ1 but not the isocyanide stretching
absorption. In the corresponding 1H NMR spectrum
two signals at 6.48 and 7.61 ppm were observed
indicating two different NH groups. These results could
be in agreement with a compound containing the 3,4-
dihydro-quinazolin-2-ylidene carbene structure 8, which
can be formed by intramolecular cyclization of the
amino group, generated from the hydrolysis of the
phosphinimine moiety, with the metal coordinated
isonitrile group.
3.2.2. Reactions of complexes 3 and 4 with PPh3
Complex 3 was reacted with 1 eq. of PPh3 and the
progress of the reaction (Eq. (5)) was monitored by
Scheme 4.

M. Basato et al. / Inorganica Chimica Acta 356 (2003) 349Á
/356
355
investigated also with the cationic bis-isocyanide Au(I)
complex 4 (Scheme 4).
We found, however, that the reaction of complex 11
with 2 equiv. of MeNH2 in THF at room temperature
for 18 h did not afford the expected amino-alkylated
product, but only unreacted starting material was
spectroscopically detected. On the other hand, the
corresponding reaction of 12 with 5 equiv. of MeNH2
in 1,2-dichloroethane for 3 days at room temperature
gave, after work-up of the reaction mixture, a pale
The reaction was carried out adding initially 1 equiv.
of PPh3 to a CH2Cl2 solution of 4 and following the
reaction progress by IR spectroscopy in solution. After
a few minutes the IR spectrum showed both free and
coordinated isonitrile ligand bands at 2123 and 2229
cmꢂ1, respectively, together with the N3 signal at 2105
cmꢂ1. These results suggest that also in this case the
reaction proceeds by substitution of one gold-coordi-
nated isocyanide by PPh3 likely giving the complex
[Au(PPh3)(AziNC)][BF4] as intermediate. This com-
pound was not isolated but was reacted in situ with
another equivalent of PPh3. The reaction affords only
the bis-phosphino complex [Au(PPh3)2][BF4] (10) as the
final product, indicating that also the second PPh3
molecule prefers the metal site as the electrophilic center,
while there is no evidence that suggests an attack, even
partial, on the other potentially electrophilic site given
by the N3 moiety.
yellow product whose IR spectrum did not show the CÅ
/
N band of the starting isocyanide compound but
exhibited a new band at 3439 cmꢂ1 attributable to a
1
NH stretching. In addition, the H NMR showed two
signals at 3.53 and 4.48 ppm corresponding to the NCH3
and CH2 groups, respectively, and a broad resonance at
7.60 ppm which can be attributed to a NH moiety.
These spectroscopic data are in agreement with the
carbene structure of complex 13 derived by an intramo-
lecular attack of the intermediate methylamino group,
formed by the reaction of the iodomethyl moiety of 12
with MeNH2, on the tungsten-coordinated isocyanide.
3.3. Alkylation reactions of complexes 11 and 12 with
MeNH2
4. Concluding remarks
In this study we have explored the reactivity of some
coordinated g-functionalized isocyanide ligands as pos-
sible sources of N-heterocyclic carbenes. The synthetic
routes that have been investigated are completely
different each other, although they both lead to the
formation of amino-functionalized isocyanide ligands of
the type V (Scheme 6).
The first route (Scheme 3 and Eq. (4)) takes advan-
tage of the reactivity of the azido group of the metal-
coordinated 2-(azidomethyl)phenyl isocyanide toward
PPh3 (i.e. the so-called Staudinger reaction) to give,
upon N2 liberation, the corresponding phosphinimine
derivative, which, in turn, can be hydrolyzed to afford
the amino-functionalized isocyanide V. Such reactivity
is observed to occur only when the isocyanide is ligated
to coordinatively saturated metal complexes such as
The reactions of alkyl halides R-X with primary
(R’NH2) or secondary (R’2NH) amines is a well known
synthetic method in organic synthesis [29] to afford
secondary (RR’NH) or tertiary (RR’2N) amines, respec-
tively. These reactions are influenced by several factors
such as the nature of the R group and the halogen atom;
as a general feature, it is observed that benzyl and iodo
groups are the most reactive [29]. Accordingly, we
thought that the [W(CO)5]-coordinated 2-(chloro-
methyl)- and 2-(iodomethyl)phenyl isocyanides 11 and
12 (Scheme 5), respectively, could be potentially con-
venient substrates for the alkylation reaction with a
primary amine to yield amino-functionalized isocyanide
derivatives.
those represented by the {M(CO)5} (MꢀCr, W) frag-
/
ments or is bound to sterically hindered metal groups.
This latter finding is supported by other studies [30]
involving Pt(II) and Pd(II) complexes of AziNC which
demonstrate that the Staudinger reaction occurs only
when AziNC is coordinated to sterically encumbered
metal species such as those given, for instance, by
Scheme 5.
Scheme 6.

356
M. Basato et al. / Inorganica Chimica Acta 356 (2003) 349Á356
/
{trans-[MCl(PPh3)2]ꢁ} fragments. On the other hand,
with the sterically unhindered coordinatively unsatu-
rated Au(I) complexes [AuCl(AziNC)] (3) and
[Au(AziNC)2]ꢁ (4), PPh3 selectively attacks the metal
center instead of the azido group and the final result is
the displacement of coordinatd AziNC rather than the
Staudinger reaction.
A further observation is related to the relative
stability of the coordinated 2-(aminomethyl)phenyl
isocyanide of the type V compared to the 2-aminophenyl
isocyanide reported by Hahn et al. [2], which rapidly
cyclizes to the corresponding benzimidazol-2-ylidene. In
that case, the greater tendency to ring closure was
suggested to be the formation of a planar aromatic
heterocycle, which is not the case of the quinazolin-2-
ylidene derivative VI (Scheme 6). We observe that the
[3] K. Bartel, W.P. Fehlhammer, Angew. Chem., Int. Ed. Engl. 13
(1974) 599.
[4] W.P. Fehlhammer, K. Bartel, B. Weinberger, U. Plaia, Chem.
Ber. 118 (1985) 2220.
[5] W.P. Fehlhammer, U. Plaia, Z. Naturforsch., Teil b 41 (1986)
1005.
[6] W.P. Fehlhammer, H. Hoffmeister, H. Stolzenberg, B. Boyadjiev,
Z. Naturforsch., Teil b 44 (1989) 419.
[7] W.P. Fehlhammer, H. Hoffmeister, B. Boyadjiev, T. Kolrep, Z.
Naturforsch., Teil b 44 (1989) 917.
[8] U. Kernbach, W.P. Fehlhammer, Inorg. Chim. Acta 235 (1995)
299.
[9] F.E. Hahn, M. Tamm, J. Chem. Soc., Chem. Commun. (1993)
842.
[10] F.E. Hahn, M. Tamm, J. Organomet. Chem. 456 (1993)
C11.
[11] F.E. Hahn, M. Tamm, T. Lugger, Angew. Chem., Int. Ed. Engl.
¨
33 (1994) 1356.
[12] F.E. Hahn, T. Lugger, J. Organomet. Chem. 481 (1994)
¨
189.
[13] U. Kernbach, T. Lugger, F.E. Hahn, W.P. Fehlhammer, J.
¨
intramolecular cyclization of V to VI ([M]ꢀCr(CO)5) is
/
hampered also because the isocyanide carbon is not
sufficiently activated toward nucleophilic attack as
Organomet. Chem. 541 (1997) 51.
[14] F.E. Hahn, L. Imhof, Organometallics 16 (1997) 763.
[15] W.A. Herrmann, T. Weskamp, V.P.W. Bohm, Adv. Organomet.
Chem. 48 (2002) 1, and references therein.
evidenced by the small D
/
n˜ value (see for instance the
IR data for 7).
[16] R.A. Michelin, G. Facchin, P. Uguagliati, Inorg. Chem. 23 (1984)
961.
The second synthetic route described in this work
involves the amino alkylation reaction of metal-coordi-
nated 2-(iodomethyl)phenyl isocyanide using MeNH2 as
the amination reagent (Scheme 5). Also in this case, the
[17] G. Facchin, R. Campostrini, R.A. Michelin, J. Organomet.
Chem. 294 (1985) C21.
[18] R.A. Michelin, G. Facchin, D. Braga, P. Sabatino, Organome-
tallics 5 (1986) 2265.
formation of the amino-functional isocyanide V (Rꢀ
/
[19] R.A. Michelin, M. Mozzon, G. Facchin, D. Braga, P. Sabatino, J.
Chem. Soc., Dalton Trans. 1803 (1988).
Me) and the subsequent intramolecular cycloaddition to
yield VI are not easy processes, thus supporting the
previous results described above.
In conclusion, experimental evidences indicate that g-
amino-functional isocyanides of the type V (Scheme 6)
[20] G. Facchin, M. Mozzon, R.A. Michelin, M.T.A. Ribeiro, A.J.L.
Pombeiro, J. Chem. Soc., Dalton Trans. 2827 (1992).
[21] G. Facchin, R.A. Michelin, M. Mozzon, A. Tassan, J. Organo-
met. Chem. 662 (2002) 70.
[22] G. Facchin, R.A. Michelin, M. Mozzon, S. Pugliese, P. Sgar-
bossa, A. Tassan, Inorg. Chem. Commun. 5 (2002) 915.
[23] C.M. Whitehouse, R.N. Dreyer, M. Yamashita, J.B. Fenn, Anal.
Chem. 57 (1985) 675.
coordinated to {M(CO)5} (MꢀCr, W) species are much
/
less reactive toward ring closure than the 2-aminophenyl
isocyanide reported by Hahn and co-workers.
[24] E.W. Abel, I.S. Butler, J.G. Reid, J. Chem. Soc. (1963) 2068.
[25] (a) F.A. Cotton, C.S. Kraihanzel, J. Am. Chem. Soc. 84 (1962)
4432;
Acknowledgements
(b) D.A. Skoog, J.J. Leary, Principles of Instrumental Analysis,
4th ed., Saunders, Philadelphia, PA, 1992, pp. 255Á257.
[26] U. Belluco, R.A. Michelin, P. Uguagliati, B. Crociani, J.
Organomet. Chem. 250 (1983) 565.
/
R.A.M. thanks MURST, the University of Padua and
C.N.R. for financial support.
[27] (a) H. Staudinger, J. Meyer, Helv. Chim. Acta 2 (1919) 132;
(b) Y.G. Gololobov, L.F. Kasukhin, Tetrahedron 48 (1992) 1353.
[28] C.-Y. Liu, D.-Y. Chen, G.-H. Lee, S.-M.- Peng, S.-T. Liu,
Organometallics 15 (1996) 1055.
References
[29] M.B. Smith, J. March, Advanced Organic Chemistry, Ch. 10, 5th
ed., Wiley, New York, 2001, p. 499.
[1] R.A. Michelin, M.F.C. Guedes da Silva, A.J.L. Pombeiro, Coord.
Chem. Rev. 218 (2001) 75.
[2] M. Tamm, F.E. Hahn, Coord. Chem. Rev. 182 (1999) 175.
[30] R.A. Michelin, M. Basato, F. Benetollo, J. Organomet. Chem.,
submitted.