New iridium(I) complexes with labile ligands: Reactivity and structural characterization by atmospheric pressure mass and tandem mass spectrometry

Article abstract of DOI:10.1016/j.ica.2003.12.025

Reaction of diphosphine complexes [IrCl{(C₆F₅) ₂P(CH₂)₂P(C₆F₅) ₂}]₂ (I) and [IrCl(dppe)]₂ (II) with coordinating solvents (acetonitrile, acetone, DMSO) leads to several square-planar complexes of the type [IrCl(diphosphine)(solvent)] which are stable only in solution ([IrCl{(C₆F₅)₂P(CH ₂)₂P(C₆F₅)₂}(NCCH ₃)] (III) and [IrCl{(C₆F₅)₂P(CH ₂)₂P(C₆F₅)₂}(acetone)], IV) and/or can be detected only under APCI-MS/MS conditions ([IrCl(dppe) (solvent)]). When III is allowed to react with CO for at least 30 min, the unusual five coordinated trans-dicarbonyl complex [IrCl{(C₆F ₅)₂P(CH₂)₂P(C₆F ₅)₂}(CO)₂] (Vb) is formed, as characterized by ¹H and ³¹P NMR, FT-IR, TGA and APCI-MS/MS. A new and stable square-planar complex [Ir(OCH₃)(cod)(PClPh₂)] (IX) was also synthesized. Its APCI-MS/MS spectrum is simple and unique as it shows exclusively the loss of a neutral C₃H₂ species. Along with the APCI-MS and APCI-MS/MS analyses, whenever it was possible all complexes were also characterized by ¹H and ³¹P NMR spectroscopy.

Full text of DOI:10.1016/j.ica.2003.12.025

Inorganica Chimica Acta 357 (2004) 2100–2106
www.elsevier.com/locate/ica
New iridium(I) complexes with labile ligands: reactivity and structural
characterization by atmospheric pressure mass and tandem mass
spectrometry
a,
b
b,
*
Regina M.S. Pereira *, Vanderlei I. Paula , Regina Buffon
,
b
Daniela M. Tomazela , Marcos N. Eberlin
b
a
Universidade Bandeirante de S~ao Paulo, Rua Maria C^andida 1813, S~ao Paulo, SP, Brazil
Instituto de Quꢀımica, Universidade Estadual de Campinas, P.O. Box 6154, 13084-971 Campinas, SP, Brazil
b
Received 30 September 2003; accepted 20 December 2003
Abstract
Reaction of diphosphine complexes [IrCl{(C6F5)2P(CH2)2P(C6F5)2}]2 (I) and [IrCl(dppe)]2 (II) with coordinating solvents
(acetonitrile, acetone, DMSO) leads to several square-planar complexes of the type [IrCl(diphosphine)(solvent)] which are stable
only in solution ([IrCl{(C6F5)2P(CH2)2P(C6F5)2}(NCCH3)] (III) and [IrCl{(C6F5)2P(CH2)2P(C6F5)2}(acetone)], IV) and/or can be
detected only under APCI-MS/MS conditions ([IrCl(dppe)(solvent)]). When III is allowed to react with CO for at least 30 min, the
1
unusual five coordinated trans-dicarbonyl complex [IrCl{(C6F5)2P(CH2)2P(C6F5)2}(CO)2] (Vb) is formed, as characterized by H
and 31P NMR, FT-IR, TGA and APCI-MS/MS.
A new and stable square-planar complex [Ir(OCH3)(cod)(PClPh2)] (IX) was also synthesized. Its APCI-MS/MS spectrum is
simple and unique as it shows exclusively the loss of a neutral C3H2 species. Along with the APCI-MS and APCI-MS/MS analyses,
1
whenever it was possible all complexes were also characterized by H and 31P NMR spectroscopy.
Ó 2003 Elsevier B.V. All rights reserved.
Keywords: Iridium(I) complexes; APCI; APCI-MS/MS
1. Introduction
Ir(I) complexes are, however, important synthetic tar-
gets as they can participate in several catalytic reactions
such as hydrosilylation [7] and hydrogen-transfer [8].
Herein, we report the synthesis of new four-coordinate
square-planar iridium(I) complexes by reacting
R2P(CH2)2PR2 (R ¼ C6H5 or C6F5) with [IrCl(coe)2]2,
as well as [Ir(OCH3)(cod)(PClPh2)] by reacting PClPh2
with [Ir(OCH3)(cod)]2. These new Ir(I) complexes bear
labile ligands and are therefore candidates for novel
carbene precursors upon reaction with diazocom-
pounds. Structural characterization of the Ir(I) com-
Four coordinate, 16-electron, square-planar Ir(I)
complexes are important intermediates in organome-
tallic chemistry. Depending on the nature of ligands,
these complexes easily undergo oxidative addition, li-
gand substitution and even migratory insertion reactions
[1–3]. Although convenient synthesis of Vaska-type
complexes from [IrCl(cod)]2 and monophosphines has
been reported by Crabtree et al. [2], square-planar Ir(I)
complexes with diphosphines are relatively rare [4],
whereas alkoxide square-planar Ir(I) complexes are hard
to isolate owing to easy decomposition by b-hydride
elimination [5] or hydrolysis [6]. These relatively rare
1
plexes has been performed by H, 13C and 31P NMR,
and IR, but most particularly by atmospheric pressure
chemical ionization mass and tandem mass spectrome-
try (APCI-MS and APCI-MS/MS), whereas some in-
termediates could only be identified by APCI-MS and
APCI-MS/MS. APCI together with two other novel,
soft and wide-ranging atmospheric pressure ionization
(API) techniques: electrospray (ESI) [9], and APPI
* Corresponding authors. Tel.: +55-19-3788-3090; fax: +55-19-3788-
3023.
E-mail addresses: rpereira02@hotmail.com (R.M.S. Pereira), rbuf-
fon@iqm.unicamp.br (R. Buffon).
0020-1693/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2003.12.025

R.M.S. Pereira et al. / Inorganica Chimica Acta 357 (2004) 2100–2106
2101
[10,11], as well as ‘‘in-vacuum’’ and atmospheric pres-
2.2. Synthesis of [IrCl(dppe)]2 (II)
sure matrix-assisted laser desorption ionization (MAL-
DI) have recently revolutionized the way molecules are
ionized and transferred to mass spectrometers for mass
and property measurements, and structural character-
ization. API techniques have greatly expanded the ap-
plicability of mass spectrometry to a variety of new
classes of molecules with thermal instability, high po-
larity and mass. Although APCI mass (and tandem
mass) spectrometry has been mainly (and most suc-
cessfully) applied to the analysis of bio-molecules [12–
19], these techniques have also been proven as highly
suitable for the structural characterization of inorganic
and organometallic compounds [20–29]. Herein, we de-
scribe the synthesis of novel iridium(I) complexes and
their detailed structural characterization, most particu-
larly by APCI-MS and APCI-MS/MS.
A solution of [IrCl(coe)2]2 (60 mg, 6:6 ꢀ 10ꢁ2 mmol)
in toluene (4 mL) was treated with dppe (106 mg,
2:7 ꢀ 10ꢁ1 mmol) under continuous stirring at room
temperature, leading to the formation of an orange
precipitate. The solution was stirred for 30 min. The
precipitate was filtered, washed with toluene and dried
under reduced pressure. Yield: 75 mg (90%); mp. 181 °C;
1H NMR (CDCl3, 300.06 MHz) d 2.32 (br m, 1H, CH2
of dppe), 2.54 (br m, 1H, CH2 of dppe), d 7.55 (m, 20H,
Ph); 31P{1H} NMR (CDCl3, 121.46 MHz): d 51.00 (s).
Mass analysis: m/z 1252.35.
2.3. Synthesis of [IrCl{(C6F5)2P(CH2)2P(C6F5)2}
(NCCH3)] (III)
A solution of I (60 mg, 3:0 ꢀ 10ꢁ2 mmol) in NCCH3
(4 mL) was stirred for 50 min at 40 °C. The 31P{1H}
NMR of the solution was obtained using a capillary
tube of D2O. 31P{1H} NMR (D2O, 121.46 MHz): d 1.8
(br s) and d 14.0 (br s). Mass analysis: m=z 1026.55.
2. Experimental
All reactions were carried out under an atmosphere
of argon using Schlenk techniques. Solvents were dried
by known procedures and distilled before use. The start
materials [IrCl(coe)2]2, [IrCl(cod)]2 and [Ir(OCH3)(cod)]
were prepared as described in the literature [30]. NMR
spectra were recorded at room temperature on Gemini
2.4. Attempted synthesis of [IrCl{(C6F5)2P(CH2)2P
(C6F5)2}(acetone)] (IV)
A solution of I (30 mg, 1:5 ꢀ 10ꢁ2 mmol) in NCCH3
(4 mL) was stirred for 50 min at 40 °C. The solution was
concentrated and the addition of 2 mL of acetone re-
sulted in a color change from orange to yellow after 2
days in a freezer. The solvent was removed under vac-
uum and the yellow powder washed with hexane. The
31P{1H} NMR shows several peaks, suggesting the
formation of many unidentified products.
1
300 MHz or Inova 500 MHz instruments. The H and
13C spectra were referenced to the solvent resonance and
are reported relative to TMS. 31P chemical shifts were
referenced to external 85% H3PO4. FT-IR spectra were
measured on a Nicolet–Nexus spectrometer. Elemental
analyses (C, H) were carried out on a Perkin Elmer
Series 11 2400 Analyzer. Mass and tandem mass spec-
trometric data were acquired using a Q-Tof (micro-
massâ, UK) high-resolution hybrid Qq(orthogonal)Tof
mass spectrometer operating at near 7000 resolution
using atmospheric pressure chemical ionization. Thermo
Gravimetric Analysis was performed using a TGA 2050,
TA 5100 instrument, under an atmosphere of argon.
2.5. Synthesis of [IrCl(CO){(C6F5)2PCH2CH2P
(C6F5)2}] (Va) and [IrCl(CO)2{(C6F5)2PCH2CH2P
(C6F5)2}] (Vb)
A solution of III (30 mg, 2:9 ꢀ 10ꢁ2 mmol) in
NCCH3 (4 mL) was treated with CO for 6 min at at-
mospheric pressure. The solvent was removed under
1
2.1. Synthesis of [IrCl{(C6F5)2P(CH2)2P(C6F5)2}]2
(I)
vacuum. Yield: 14.7 mg (97%). H NMR (CDCl3, 300
MHz): d 2.85 (m, 4H, CH2P); 31P{1H} NMR (CDCl3,
121.46 MHz): d 0.62 (s); 30.00 (s). IR (nujol, cmꢁ1):
2028.2 (mCO). Mass analysis (Vaþ): m/z 1014.20. When
the solution of III was allowed to react with CO for at
least 30 min, after removal of the solvent under vacuum,
Vb was isolated as a yellow powder. Yield: 15 mg (97%).
mp. 118oC; 1H NMR (CDCl3, 300 MHz): d 2.10 (m 1H,
CH2P), 2.74 (m, 1H, CH2P), 2.94 (m, 1H, CH2P) and
3.34 (m, 1H, CH2P); 31P{1H} NMR (CDCl3, 121.46
MHz): d )17.0 (s). IR (nujol, cmꢁ1): m 1999.2 (mCO).
Mass analysis (Vbþ): m/z 1043.14. All attempts to re-
crystallize Vb from benzene, toluene, hexane or aceto-
nitrile solutions have failed owing to its decomposition
A solution of [IrCl(coe)2]2 (30 mg, 3:3 ꢀ 10ꢁ2 mmol)
in
toluene
(4
mL)
was
treated
with
(C6F5)2PCH2CH2P(C6F5)2 (68 mg, 88 lmol) under
continuous stirring for 50 min at room temperature.
Upon addition of the phosphine, the color changed
from orange to yellow. After removal of the solvent
under reduced pressure, the residue was washed with
hexane and dried under vacuum: yield 58.5 mg (90%).
1
mp: 143 °C; H NMR (CDCl3, 300 MHz): d 1.88 (m,
CH2); 31P{1H} NMR (CDCl3, 121.46 MHz): d 6.70 (s).
Mass analysis: m/z 1972.05.

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R.M.S. Pereira et al. / Inorganica Chimica Acta 357 (2004) 2100–2106
when allowed to stand in such solutions for long periods
of time.
PPh2Cl); d 5.30 (s, 2H, CH of cod), d 3.16 (s, 3H,
OCH3), d 2.26–1.76 (m, 2H (CH) and 8H (CH2) of cod);
31P{1H} NMR (CDCl3, 121.46 MHz): d 103.09 (s).
Anal. Calc. for C23H22ClOPIr: C 45.67; H 4.50. Found:
C, 46.08; H 4.33%. Mass analysis (IX + Hþ): m/z 552.09.
2.6. Attempted synthesis of [IrCl(dppe)(NCCH3)]
A solution of [IrCl(dppe)]2 (60 mg, 4:8 ꢀ 10ꢁ1 mmol)
in NCCH3 (3 mL) was stirred for 5 h at 55 °C. The
31P{1H} NMR of the solution was obtained using a
capillary tube of D2O. 31P{1H} NMR (D2O, 121.46
MHz): d 13.27(s) and d 17.82 (s). Mass analysis: m=z
667.62.
3. Results
[IrCl(coe)2]2 reacts with diphosphines via replacement
of coe (cyclooctene) without breaking the bridge. Thus,
reaction of [IrCl(coe)2]2 with (C6F5)2P(CH2)2P(C6F5)2
or 1,2-bis(diphenylphosphino)ethane (dppe) in toluene
affords [IrCl{(C6F5)2P(CH2)2P(C6F5)2}]2 (I) (Scheme 1)
and [IrCl(dppe)]2 (II) (Scheme 2), respectively, in high
yields (near 90% in both cases).
2.7. Attempted synthesis of VI
A solution of [IrCl(dppe)]2 (60 mg, 4:8 ꢀ 10ꢁ1 mmol)
in NCCH3 (3 mL) was stirred for 5 h at 55 °C. The
solution was concentrated and the addition of 2 mL of
acetone resulted in a color change from orange to yellow
after 2 days in a freezer. The solvent was removed under
vacuum and the yellow powder washed with hexane.
Yield: 64.5 mg (98%). mp. 170 °C (dec.); 1H NMR
(CDCl3, 300 MHz): d 1.58 (br m, 1H, CH2 of dppe),
1.95 (br m, 1H, CH2 of dppe), 2.31 (br m, 1H, CH2 of
dppe), 2.36 (br m, 1H, CH2 of dppe), d 7.55 (m, 20H,
Ph); 31P{1H} NMR (CDCl3, 121.46 MHz): d 13.73 (t,
J ¼ 4:5 Hz) and d 18.25 (s). Mass analysis: m/z 684.74.
The 31P{1H} NMR spectrum of I shows a single
signal in d 6.70; for II, the signal appears in d 51.00. The
APCI-MS spectra of I (Fig. 1(a)) and II taken from
acetone solutions show mainly the ionized complexes
which form clusters of isotopomeric ions with the most
intense ones of m/z 1972.05 (Iþ) and m/z 1252.35 (IIþ),
respectively, and with isotopic patterns that clearly
reveal the presence of the multiple isotopic elements
iridium and chlorine. The observed isotopic patterns
match perfectly the theoretical isotopic patterns calcu-
lated for their elemental compositions. The APCI-MS/
MS tandem mass spectra of I and II taken from acetone
solutions also support their bridged spiro square-planar
5-4-5-membered tricyclic structure, since Iþ (Fig. 1(b))
and IIþ are found to dissociate under low energy colli-
sions with argon nearly exclusively by the pathway de-
picted in Scheme 3, with the symmetrical breaking of the
most labile four-membered square-planar Ir–Cl ring.
When dissolved in more coordinating solvents, these
complexes react as discussed below.
2.8. Synthesis of [Ir(cod)(Cl)P(Cy)3] (VIII)
To a solution of [Ir(Cl)(cod)]2 (60 mg, 9:0 ꢀ 10ꢁ2
mol) in methanol (4 mL), a solution of PCy3 (25 mg,
9:0 ꢀ 10ꢁ2 mmol) in hexane was added dropwise under
continuous stirring. A color change from pale yellow to
gold yellow was observed. The solvent was removed
under vacuum and the solid washed with hexane. Yield:
1
49.85 mg (90%). mp. 185.1 °C; H NMR (CDCl3, 300
MHz): d 4.72 (br s, 2H, CH of cod), d 3.10 (br s, 2H, CH
of cod), d 2.00–2.15 (m, 8H, CH2 of cod), 1.55–1.82 (m
33H of Cy); 13C{1H} NMR (CDCl3, 75.45 MHz): d
88.48 (CH, cod), d 88.41 (CH, cod), d 50.39 (2, CH,
cod), d 32.67 (CH2 of cod), d 32.63 (CH2 of cod), d 31.40
(CH2 of cod), d 31.10 (CH2 of cod), d 29–25(CH2 of cy);
31P{ 1H} NMR (CDCl3, 121.46 MHz): d 15.07 (s). Mass
analysis (VIII + Hþ): m/z 615.85.
(C6F5)2
P
(C6F5)2
P
Ir
(C6F5)2
P
Ir
(C6F5)2
P
Ir
O
Cl
Cl
NCCH3
Cl
NCCH3
O
Ir
P
P
P
Cl
P
(C6F5)2
(C6F5)2
(C6F5)2
(C6F5)2
I
III
IV
CO
(C6F5)2
P
Cl
2.9. Synthesis of [Ir(OCH3)(cod)(PClPh2)] (IX)
Ir
Va
CO
P
(C6F5)2
To a solution of [Ir(OCH3)(cod)]2 (60 mg, 9 ꢀ 10ꢁ2
lmol) in hexane (4 mL), a solution of PPh2Cl (50 mg,
2; 3 ꢀ 10ꢁ1 lmol) in hexane (1 mL) was added dropwise.
A color change from yellow to orange and a white
precipitate were observed. The solution was filtered and
cooled to )20 °C until an orange complex precipitated.
The orange solid was washed thrice with hexane (2 mL)
and dried under vacuum. Yield: 10 mg (20%). mp. 97 °C;
1H NMR (CDCl3, 300 MHz): d 7.79–7.27 (m, Ph of
CO
(C6F5)2
P
(C6F5)2
CO
P
CHCl2
Cl
+
Ir
CHCl3
APCI
Cl
Ir
P
P
(C6F5)2
CO
(C6F5)2
A
Vb
Scheme 1.

R.M.S. Pereira et al. / Inorganica Chimica Acta 357 (2004) 2100–2106
2103
Ph2
R
R
R
R
R
R
R
R
P
NCCH3
Cl
+
NCCH3
APCI
P
P
P
P
P
P
Ir
Cl
Cl
CID
P
Cl
Ir
Ir
Ir
Ph2
Ph2
P
Ir
P
Ph2
Ph2
P
Cl
Cl
II
B
R
R
R
R
Ir
P
R = C6F5, m/z 986
R = C6H5, m/z 626
R = C6F5, m/z 1972
R = C6H5, m/z 1252
Ph2
O
Ph2
P
O
Scheme 3.
+
Ir
APCI
P
Cl
Ph2
C
2.41 and 2.44, corresponding to the CH2 groups of the
phosphine. The APCI-MS spectrum of III in acetonitrile
shows a major cluster of ions centered at m/z 1026.55
(IIIþ) with an isotopic pattern that fully supports its
composition assignment. The APCI-MS/MS spectrum
of IIIþ also supports its structural assignment, since IIIþ
is found to dissociate mainly by acetonitrile (41 u) loss.
This dissociation indicates therefore that Ir–acetonitrile
is the weakest bond for complex III, which is stable only
in acetonitrile; fast decomposition of III occurs when
acetonitrile is removed under vacuum.
When acetone is added to a concentrated solution of
III in acetonitrile, and the corresponding system is al-
lowed to stand at )20 °C for 48 h, the color of the so-
lution changes from orange to yellow, suggesting that a
new complex is formed, IV (Scheme 1). Now, when the
APCI-MS spectrum is taken from this acetone solution,
a major cluster of ions centered at m/z 1044.60 (IVþ) is
Scheme 2.
3.1. Reactivity of I
When (I) [IrCl{(C6F5)2P(CH2)2P(C6F5)2}]2, is dis-
solved in acetonitrile, acetonitrile breaks the Ir–Cl
bonds of the four-membered ring and the corresponding
square-planar complex [IrCl{(C6F5)2P(CH2)2P(C6F5)2}
(NCCH3)] (III) is formed (Scheme 1). Formation of III
is suggested by 31P{1H} NMR spectrum (CDCl3), which
shows broad signals centered at d 1.8 and 14.0, ham-
pering the determination of the coupling constants be-
tween the P atoms.
When recorded using deuterated acetonitrile
(NCCD3), the 1H NMR of III shows two multiplets at d
1972.21
100
1972.21
100
%
%
0
1971.76
100
%
0
m/z
1960
1970
1980
0
m/z
2200
(a)
1200
1300 1400 1500 1600
1700 1800
1900
2000 2100
1973.34
100
1972
Ar
%
986.85
0
m/z
(b)
800
1000
1200
1400
1600
1800
2000
Fig. 1. (a) APCI-MS spectrum of the Ir(I) complex I and (b) APCI-MS/MS spectrum of Iþ. The insets in (a) show the observed and theoretical
isotopic patterns for Iþ.

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R.M.S. Pereira et al. / Inorganica Chimica Acta 357 (2004) 2100–2106
observed, which is assigned to [IrCl{(C6F5)2P(CH2)2-
P(C6F5)2}(acetone)]. The APCI-MS/MS spectrum of
IVþ shows major dissociation by acetone loss (58 u).
Complex IV is therefore stable in acetone solution, but
all attempts to isolate IV have failed. Complex III also
reacts quickly, in 6 min, with CO under atmospheric
pressure to produce a yellow complex, Va (Scheme 1), in
good yield (97%). The infrared spectrum of Va shows a
single CO at 2028.2 cmꢁ1. The APCI-MS spectrum of Va
taken from a benzene solution shows two clusters of
ions centered at m/z 986.88 [Va–1CO]þ and 1014.20
[Va]þ, whereas the APCI-MS/MS spectra of the Vaþ
shows a fragment ion at m/z 986.88, corresponding to
the loss of CO as observed under APCI conditions. Its
31P{1H} NMR shows two broad singlets at d 0.62 and
30.00 and not the doublets expected for a square-planar
Ir(I) complex (Scheme 1). The non-observation of dou-
blets could be associated to the broadening of the signals
owing to the presence of meta, ortho and para-fluorine
atoms [35]. The corresponding 1H NMR spectrum
shows a large multiplet (CH2 groups of dppe), charac-
teristic of this kind of complex [31]. Interestingly, when
the reaction of III with CO is carried out for a longer
time (at least 30 min), a new yellow complex is observed,
Vb (Scheme 1). Isolation of Vb is relevant since com-
plexes of the type [Ir(X)(dppe)(CO)2] are normally very
unstable and have been characterized only in solution
[31]. The reported infrared spectra of such complexes
of an Ir(I) complex with two carbonyls in trans positions
characterized in the solid state.
3.2. Reactivity of [IrCl(dppe)]2 (II)
When II is dissolved in CH3CN, formation of a new
species is suggested by the 31P{1H} NMR spectrum
(CDCl3), which shows signals at d 13.00 and 18.00. The
APCI-MS spectrum shows a cluster of ions centered at
m/z 667.72 (B), Scheme 2. When the APCI-MS spectrum
of II is taken from an acetone/acetonitrile solution, a
cluster of ions centered at m/z 684.74 (C) is detected with
masses and isotopic patterns that suggests the
[IrCl(dppe)(acetone)] composition. However, the 1H
NMR (CDCl3) spectrum of the yellow powder resulting
from the addition of acetone to an acetonitrile solution
of II, from now on called VI, does not show the coor-
dination of acetone to the iridium atom: only signals at d
2.05 (m), 2.28 (m) and 2.60 (m), related to the CH2
groups from dppe, and at d 6.28–7.68 (m), correspond-
ing to the phenyl groups of dppe are observed. The later
signals appear in a broad range, suggesting that the
phenyl groups are located in distinct chemical environ-
ments. This kind of spectrum suggests either an ortho-
metallation [32] or the addition of the phenyl group to
the coordination sphere of the metal [33]. Since a hy-
dride is not observed, an orthometallation is ruled out.
According to the P ꢀ H (HETCOR) correlation spec-
trum of VI, only the signal at d 2.28 (m) interacts with
the two phosphorous atoms, showing that these signals
correspond to the equatorial Hs from CH2. The corre-
sponding 31P{1H} NMR spectrum shows a singlet at d
18.25 and a pseudo triplet at 13.73 (t, J ¼ 4:5 Hz). When
the 31P{1H} NMR spectrum of VI is obtained in
DMSO, the two signals appear as pseudo triplets. These
results strongly suggest a fluxional process at room
temperature. If a dynamic rearrangement were taking
place, such a process should be frozen at lower tempe-
ratures. However, at least down to )40 °C, the 31P{1H }
spectrum does not change. (The temperature could not
be lowered further owing to the low solubility of the
complex.) In addition, during experiments to determine
the melting point of VI, color changed from yellow to
orange at 170 °C, but melting takes place at 181 °C, the
same melting temperature determined for the parent
complex II. All these results suggest that complex VI
does not present a square-planar structure. A possibility
to be considered is that a molecule of acetonitrile would
coordinate to each metal center of II without breaking
the bridge. One phenyl group of each dppe would co-
ordinate to an iridium atom via a 3c,2e bonding
(Scheme 4).
1
show two bands; their H NMR spectra are character-
ized by four large multiplets (CH2 groups of dppe), and
the 31P{1H} spectra show only one signal.
While the IR spectrum of Vb shows only one band at
1
1999.2 cmꢁ1, its H NMR shows four multiplets at d
2.10, 2.74, 2.94 and 3.34 for the CH2 groups of
1
[(C6F5)2P(CH2)2P(C6F5)2].
A
1H ꢀ H correlation
(COSY) shows interactions among the four atoms. The
corresponding 31P{1H} NMR spectrum shows only one
singlet at d )17.00, implying that the phosphorous at-
oms are equivalent. Therefore, Vb should present a tri-
gonal bipyramidal structure, with the two carbonyls in
trans positions (Scheme 1). The APCI-MS spectrum of
Vb taken from a benzene solution shows three major
clusters of ions centered at m/z 987.14 [Vb–2CO]þ,
1015.20 [Vb–CO]þ, and 1043.14 [Vb]þ, whereas the
APCI-MS/MS spectrum of Vbþ shows two major frag-
ment ions of m/z 987 and 1015 corresponding to the
sequential losses of CO as observed under APCI con-
ditions. When the APCI-MS spectrum of Vb is taken
from a chloroform solution, the formation of the
cationic square-planar complex [IrCl{(C6F5)2P(CH2)2P-
(C6F5)2}(CHCl2)]þ (A) is observed as a cluster of iso-
topomeric ions centered at m/z 1068.45 (Scheme 1). A
TGA study of Vb also supports its proposed structure,
since a weight reduction of 78.22% (814.82 g/mol) cor-
responding to the loss of two CO molecules and the
phosphine ligand was observed. This is the first example
When dissolved in acetone or in DMSO, the aceto-
nitrile ligand would be replaced by the solvent. The
square-planar complexes bearing acetonitrile, acetone or
DMSO ligands would be formed only under the condi-

R.M.S. Pereira et al. / Inorganica Chimica Acta 357 (2004) 2100–2106
2105
its reaction with PPh2Cl in hexane yields only
[Ir(OCH3)(cod)(PClPh2)] (IX). This complex was char-
acterized by 31P{1H} NMR (CDCl3), showing a singlet
at d 103.9. Its 1H NMR spectrum shows a signal at 5.30
(2H, CH) of cod, d 3.15 (OCH3) besides the resonances
ascribed to cod at 1.80 (m), 2.00 (m) and 2.36 (m), and
those ascribed to the phenyl groups at d 7.4 (m). The
APCI-MS spectrum of IX shows a cluster of ions at m/z
553.0 [IX + H]þ with an isotopic pattern that fully agrees
with its proposed composition. The so far exclusive
formation of the protonated molecule for IX under
APCI conditions, rather than the ionized molecules, is
favored likely owing to the presence of the more basic
methoxy group. The APCI-MS/MS spectrum of
[IX + H]þ (Fig. 2) is simple and unique as it shows dis-
sociation mainly to m/z 515.
This dissociation is likely to involve the cod ligand, as
confirmed by the Ir plus Cl-containing isotopic pattern
of the ionic cluster centered at m/z 515, and occurs most
likely therefore via the rare loss of a C3H2 neutral spe-
cies (Scheme 5).
In contrast with the diphosphine complexes described
herein, IX is active in the presence of ethyldiazoacetate
for the ring opening metathesis polymerization of cyclic
olefins. A detailed investigation of the catalytic proper-
ties of IX and other complexes prepared in this work is
currently underway.
Ph2
P
Ph2
P
L
Cl
L
Cl
Cl
P
P
P
P
Ir
Ir
Ir
L
Ir
P
Cl
P
Ph2
Ph2
II
VI
L= NCCH3, CH3C(O)CH3, DMSO
Scheme 4.
tions of mass analyses. Whatever its structure, under an
argon atmosphere, VI is relatively stable in solution,
undergoing a slow decomposition in 3–4 days. In the
solid state, at )10 °C, under argon, it is stable for several
weeks. In contrast with the behavior of III, when VI is
allowed to react with CO in the same conditions em-
ployed to synthesize V, many species are formed.
All attempts to synthesize carbene complexes via re-
action of III, V or VI with diazomethane or phenyl-
diazomethane failed. Moreover, among all these
complexes, only III presented some activity in the ring
opening metathesis polymerization of norbornene in the
presence of ethyldiazoacetate.
3.3. Synthesis of iridium(I) complexes bearing mono-
phosphines
To study its activity in the ring opening metathesis
polymerization, the iridium(I) complex [IrCl(cod)-
(PCy3)] (VIII) was also synthesized from the reaction of
[IrCl(cod)]2 with PCy3 in hexane. DEPT analysis con-
firms the formation of VIII, whereas its 31P{1H} NMR
(CDCl3) spectrum shows a singlet at d 15.07, and its
13C{1H} spectrum shows three singlets at d 88.58, 88.41
and 50.40, and four singlets d 32.67, 32.63, 31.40 and
31.10, corresponding to the four CH and to the four
CH2 from cod, respectively. The other signals in the
range d 25.40–29.00 can be assigned to the carbons of
the cyclohexyl groups. The 1H NMR shows broad
singlets at d 4.72 and 3.09, corresponding to the CH
groups of cod, according to 1H ꢀ 13C (HETCOR)
analysis, besides a multiplet at d 2.0–2.15, assigned to
515.05
100
553
553.02
Ar
%
0
m/z
350
400
450
500
550
Fig. 2. APCI-MS/MS spectrum of the Ir(I) protonated complex
[IX + H]þ.
1
1
CH2 groups of cod, according to H ꢀ H (COSY), and
a multiplet at d 1.55–1.82 corresponding to CH2 groups
from Cy. The APCI-MS spectrum of VIII shows a
cluster of ions centered at m/z 615.84 VIIIþ with an
isotopic pattern that fully agrees with its expected
composition and proposed structure. Although the
synthesis of VIII has already been published [34], the
synthetic route described here leads to higher yields
(ꢂ90%). In the presence of ethyldiazoacetate, VIII is
active in the ring opening metathesis polymerization of
norbornene and cyclooctene.
Cl
P
Cl
P
Ph
Ph
Ph
Ph
- C3H2
Ir
Ir
CH3O
H
CH3O
H
+
[IX +H]
m/z 553
m/z 515
Whereas the reaction of [Ir(cod)(OCH3)]2 with dppe
or [(C6F5)2P(CH2)2P(C6F5)2] leads to several products,
Scheme 5.

2106
R.M.S. Pereira et al. / Inorganica Chimica Acta 357 (2004) 2100–2106
[6] T. Yoshida, T. Okano, S. Otsuka, J. Chem. Soc., Dalton Trans.
(1976) 993.
4. Conclusions
ꢀ
ꢀ
[7] (a) L.A. Oro, M.J. Fernandez, M.A. Esteruelas, M.S. Jimenez, J.
The diphosphine complexes [IrCl{(C6F5)2P(CH2)2P-
(C6F5)2}]2 (I) and [IrCl(dppe)]2 (II) were successfully
employed as precursors for new iridium(I) complexes
with labile ligands. Although complex [IrCl{(C6F5)2P-
(CH2)2P(C6F5)2}(NCCH3)] (III) is stable only in
solution, it could be fully characterized by NMR and
APCI-MS/MS techniques. Complex IV, [IrCl{(C6F5)2P-
(CH2)2P(C6F5)2}(acetone)], could only be detected by
APCI-MS.
The APCI-MS analysis shows that the intact ionized
species Iþ is stable in the gas phase and observed as so in
the mass spectrum (Fig. 1). However, the gaseous intact
IIþ is unstable and dissociates completely by breaking of
the bridge thus forming, after solvent coordination,
species B and C (Scheme 2), which are observed in
the corresponding mass spectra. Interestingly, when III
is allowed to react with CO for at least 30 min, the
unusual five-coordinated trans-dicarbonyl complex
[IrCl{(C6F5)2P(CH2)2P(C6F5)2}(CO)2] (Vb) is formed,
the first species of this type to be characterized in the
solid state. All these complexes, along with
[IrCl(cod)(PCy3)] (VIII) and [Ir(OCH3)(cod)(PClPh2)]
(IX) failed to produce carbene complexes upon reaction
with diazocompounds. Nevertheless, preliminary ex-
periments showed that III, VIII and IX have some ac-
tivity in the ring opening metathesis polymerization of
cyclic olefins in the presence of ethyldiazoacetate, war-
ranting further investigations of such systems.
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