Amine involvement in the self-association of planar complexes of the type, cis-Ir(CO)2Cl(primary amine)

Article abstract of DOI:10.1016/j.jorganchem.2019.01.002

Examination of crystals of cis-Ir(CO)₂X(p-toluidine) (X = Cl, Br, I), by single crystal X-ray diffraction shows that the individual monomers self-associate to form extended columns with Ir?Ir separations ranging from 3.33 ? for the chloro compl

Full text of DOI:10.1016/j.jorganchem.2019.01.002

Accepted Manuscript
Amine involvement in the self-association of planar complexes of the type, cis-
Ir(CO) Cl(primary amine)
2
Emily M. Gussenhoven, Marilyn M. Olmstead, Alan L. Balch
PII:
S0022-328X(18)30922-7
DOI:
https://doi.org/10.1016/j.jorganchem.2019.01.002
JOM 20680
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 15 October 2018
Revised Date: 30 December 2018
Accepted Date: 3 January 2019
Please cite this article as: E.M. Gussenhoven, M.M. Olmstead, A.L. Balch, Amine involvement
in the self-association of planar complexes of the type, cis-Ir(CO) Cl(primary amine), Journal of
2
Organometallic Chemistry (2019), doi: https://doi.org/10.1016/j.jorganchem.2019.01.002.
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Graphical Abstract
Text
Hydrogen bonding between chlorine (green) and nitrogen (light blue) reinforced the
iridium···iridium (deep blue) interactions to from nearly eclipsed dimers of cis-Ir(CO)2Cl(o-
toluidine). The methyl groups of the amine ligands block opposite faces of the dimer and
prevent additional iridium···iridium interactions
Illustration

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Amine Involvement in the Self-Association of Planar Complexes of the Type, cis-
Ir(CO)2Cl(primary amine)
Contribution from:
Emily M. Gussenhoven, Marilyn M. Olmstead*, Alan L. Balch*
Department of Chemistry
University of California
Davis, California 95616
1

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Abstract
Examination of crystals of cis-Ir(CO)2X(p-toluidine) (X= Cl ,Br, I), by single crystal X-
ray diffraction shows that the individual monomers self-associate to form extended columns with
Ir···Ir separations ranging from 3.33 Å for the chloro complex to 3.68 Å in the iodo complex.
The columnar structure is reinforced by hydrogen bonding between the halide ligand in one
molecule with an N-H group in an adjacent molecule. This hydrogen bonding causes adjacent
molecules to adopt nearly eclipsed orientations. In contrast, the positions of the methyl groups in
cis-Ir(CO)2Cl(o-toluidine) and cis-Ir(CO)2Cl(2,6-dimethylaniline) limit intermolecular
interactions to the formation of dimers connected by Ir···Ir interactions, and hydrogen bonding
again occurs between the halide ligand in one molecule and the N-H group in an adjacent
molecule. The UV/vis spectrum of cis-Ir(CO)2Cl(p-toluidine) provides evidence that the self-
association also occurs in solution. The positive ion mass spectrum of laser ablated crystals of
cis-Ir(CO)2Br(p-toluidine) reveals the presence of monomeric, dimeric, and trimeric cations.
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Introduction
Coordination complexes of metal ions with d8 or d10 electronic configuration frequently
undergo self-assocation in the solid phase to form dimers, trimers and extended linear
chains.1,2,3,4 Such self-assocation is particularly common for four-coordinate Pt(II)5,6,7,8,9 and
Rh(I)10-,11,12,13,14,15 as well as for two-coordinate Au(I)16,17 complexes. This self-association
occurs because of interactions between the filled dz orbital and the empty pz orbitals that are
2
directed colinearly and perpendicular to the molecular plane.18,19 These orbitals can overlap with
similarly directed orbitals on the adjacent molecules to form metallophillic interactions These
metallophillic interactions direct the supramolecular assembly of these compounds, particularly
in the solid state. However, because such pseudo-closed shell interactions tend to be rather
weak, the structures that result can be altered and/or augmented by other weak interactions such
as hydrogen-bonding and ligand size.
The self-association of Ir(I) complexes has received less attention than their isoelectronic
Pt(II) and Rh(I) counterparts.
Crystals of cis-Ir(CO)2Cl(pyridine)20 and cis-
Ir(CO)2Cl(pyrazine)21 contain extended columns of the metal complexes with Ir···Ir separations
of 3.602(12) Å and 3.579(3) Å, respectively. Light yellow needles of Ir(CO)2(acetylacetonate)
crystallize in columns with alternating Ir···Ir distances of 3.242 Å and 3.260 Å.22,23 Four
polymorphs of the planar chelate IrI(CO)2(OC(CH3)CHC(CH3)N(p-tol) have been identified
(amber, pale yellow, orange, and low temperature orange).24 The amber and pale yellow forms
contain dimers connected by Ir···Ir interactions (3.5540(2) Å for the amber polymorph,
3.5934(8) and 4.0397(8) Å for the pale yellow polymorph at 90 K). The orange and low
temperature orange forms contain extended columns of molecules with Ir···Ir separations of
3.4126(5) and 3.6237(5) Å at 90 K. Finally, the dimer (F3P)2Ir(µ-Cl)2Ir(PF3)2 (with an
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intramolecular Ir···Ir separation of 2.941(1) Å) self-associates into chains with an intermolecular
Ir···Ir separation of 3.271(1) Å.25
Unlike the previous examples, copper-colored needles of Ir(CO)3Cl contain stacks of the
planar complex with a remarkably short Ir···Ir distance of 2.844 Å.26,27 Within the stacks, the
planar complexes are staggered.
Crystals of this compound are electrically conductive.
Consequently, Ir(CO)3Cl has been considered to be a partially oxidized material such as
28
Ir(CO)2.93Cl1.07
.
Computations can explain the short Ir···Ir separation without invoking partial
oxidation, but they cannot account for the conductivity of this material.29 Several other partially
oxidized and electrically conductive iridium complexes such as A0.60[Ir(CO)2X2] (with A = K,
Cs, TTF (TTF = tetrathiafulvalene) and X = Cl, Br) and K[Ir(CO)2X2]2 have been made through
chemical or electrochemical oxidation of the planar anion cis-[Ir(CO)2X2]- or reduction of
iridium(III) salts.30,31,32,33
The metallic red color of solid cis-Ir(CO)2Cl(p-toluidine)34 contrasts with the usual
35
yellow color seen for monomeric iridium(I) complexes such as Ir(CO)Cl(PPh3)2 and
(Ph4As)[Ir(CO)2Cl2]36 and suggests that this compound undergoes some sort of self-association
in the solid state. Cis-Ir(CO)2Cl(p-toluidine), has been used on several occasions as a starting
material for the synthesis of more complex molecules and ions.37,38,39 Here, we examine the
structures of some compounds of the type cis-Ir(CO)2X(primary amine) (X =Cl, Br, I) with
attention to the role of the amine group in the assisting interactions between individual
molecules.
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Results and Discussion.
The complexes , cis-Ir(CO)2X(p-toluidine) (X= Cl ,Br, I), cis-Ir(CO)2Cl(o-toluidine), and
cis-Ir(CO)2Cl(2,6-dimethylaniline) have been prepared by minor variations of the route
previously reported for the synthesis of cis-Ir(CO)2Cl(p-toluidine).34
The Structures of cis-Ir(CO)2Cl(p-toluidine), cis-Ir(CO)2Br(p-toluidine), cis-Ir(CO)2I(p-
toluidine) with Exended Columnar Aggregates. The solid-state structures of the solvate-free
iridium(I) complexes cis-Ir(CO)2Cl(p-toluidine), cis-Ir(CO)2Br(p-toluidine), cis-Ir(CO)2I(p-
toluidine) have been determined by X-ray crystallography at 90(2) K. The complexes differ only
by the nature of the halide ligand, which results in subtle, yet interesting differences in their
solid-state properties. The three crystal structures are isostructural, and each contains two
molecules in the asymmetric unit in the monoclinic space group P21/n. Crystallographic data are
presented in Table 1, while Table 2 contains selected bond lengths and angles, together with
metallophilic geometry and hydrogen bonding. Scheme 1 defines the interplanar separations (IS)
and lateral shifts (LS) used to characterize the self-association of these planar molecules.
Scheme 1. A diagram of (a) interplanar separations (IS), (b) lateral shifts (LS), and (c) the
metal-metal distances between adjacent planar Ir(I) molecules.
RH2N
X
M
OC
CO
c.
a.
RH2N
X
M
b.
OC
CO
5

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Table 1. Crystallographic Data for Iridium Complexes
cis-Ir(CO)2Cl(p-
cis-Ir(CO)2Br(p-
cis-Ir(CO)2I(p-
toluidine)
toluidine)
toluidine)
Compound
Emp. Formula
Formula weight
Color
C9H9ClIrNO2
390.82
C9H9BrIrNO2
435.28
red-green
needle
Monoclinic
P21/n
C9H9IIrNO2
428.27
metallic green
needle
Monoclinic
P21/n
metallic red
block
Habit
Crystal system
Space group
a (Å)
Monoclinic
P21/n
6.6695(2)
15.4857(6)
20.4408(8)
90
6.7639(7)
15.5272(15)
20.466(2)
90
7.1440(13)
15.545(3)
20.651(4)
90
b (Å)
c (Å)
α
β
γ
(º)
(º)
(º)
99.7980(10)
90
99.326(2)
90
99.781(4)
90
V (Å3)
2080.37(13)
8
2121.0(4)
8
2260.1(7)
8
Z (units/cell)
T (K)
90(2)
90(2)
90(2)
ρcalc (g cm−3)
2.496
2.725
2.835
MoK
µ (mm−1)
α
,
λ
(Å)
0.71073
13.064
0.71073
16.320
6279
0.71073
14.521
4204
Unique data
Obs. data (I>2
Restraints
6083
σ
(I)) 4730
5140
3836
4
6
0
Params. refined
R1 a (obs. data)
wR2 b (all data, F2
refinement)
271
0.0192
256
241
0.0451
0.0246
0.034
0.1277
0.0653
1 / 2
2
2
a R1 =
.
b wR2 = [ [
(
)
]
[
(
)
]]
.
2
2
2
Fo − F
F
w F − F
w F
∑
o
∑
∑
∑
c
o
o
c
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Table 1. Continued
cis-Ir(CO)2Cl (o-
cis-Ir(CO)2Cl (2,6-
toluidine)
dimethylaniline)
Compound
Emp. Formula
Formula weight
Color
C9H9ClIrNO2
390.82
C10H11ClIrNO2
424.30
Red
Orange-red
Plate
Habit
Prism
Crystal system
Space group
a (Å)
Monoclinic
P21/n
Monoclinic
P21/n
14.8018(13)
7.9031(7)
19.4446(17)
90
17.012(15)
13.415(12)
21.747(19)
90
b (Å)
c (Å)
α
β
γ
(º)
(º)
(º)
104.2845(12)
90
102.05(2)
90
V (Å3)
2204.3(3)
8
4854(7)
16
Z (units/cell)
T (K)
90(2)
90(2)
ρcalc (g cm−3)
2.355
2.322
MoK
µ (mm−1)
α
,
λ
(Å)
0.71073
12.329
0.71073
11.415
11120
8536
Unique data
Obs. data (I>2
Restraints
5064
σ
(I)) 4461
0
0
Params. refined
R1 a (obs. data)
wR2 b (all data, F2
refinement)
255
0.0265
581
0.0361
0.0650
0.0754
1 / 2
2
2
a R1 =
.
b wR2 = [ [
(
)
]
[
(
)
]]
.
2
2
2
Fo − F
F
w F − F
w F
∑
o
∑
∑
∑
c
o
o
c
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Table 2. Dimensions within Linear Chain Complexes (see Scheme 1)
cis-Ir(CO)2Cl(p-toluidine)
Molecule 1 Molecule 2
cis-Ir(CO)2Br(p-toluidine)
cis-Ir(CO)2I(p-toluidine)
Molecule 1 Molecule 2
Compound
Molecule 1
Molecule 2
Distances (Å)
M1···M2, 2A c
M1–X1
3.3341(2)
2.3752(9)
3.3576(2)
2.3699(9)
3.3801(6)
2.4750(13)
3.4201(6)
2.4670(13)
3.5409(7)
2.6623(6)
3.6767(8)
2.6573(6)
N1–H1A···Cl2A 3.488(3)
3.552(9)
3.530(9)
3.782(7)
3.753(7)
N1–H1B···Cl2
N2–H2A···Cl1A
N2–H2B···Cl1
Interplanar
3.453(3)
3.464(3)
3.472(2)
3.33
3.542(9)
3.532(9)
3.39
3.771(7)
3.760(7)
3.63
3.33
3.37
3.51
Sepn. a
Lateral Shift b
M Displacement
M/Ring Plane
0.40
0.0063(16)
87.6
0.24
0.003(4)
89.6
0.45
0.002(5)
87.3
0.19
0.0072(16)
89.2
0.43
0.002(4)
89.8
0.61
0.006(4)
86.5
Angles (°)
M2···M1···M2A 170.675(6)
168.39(2)
163.62(1)
In cis-Ir(CO)2Cl(p-toluidine), and also in the analogous bromo and iodo complexes, the
four-coordinate molecular units pack to form crystals with the planar moieties aligned in
columnar arrays with non-covalent, face-to-face interactions through d8-d8 contacts as seen in
Figure 1. This column is composed of alternating Ir···Ir interactions with distances of 3.3341(2)
and 3.3575(2) Å. There is a minimal kinking of the columnar chains, with an Ir2···Ir1···Ir2A
angle of 170.682(6)°. Individual columns are separated by 6.669(4) Å.
In crystals of cis-Ir(CO)2Cl(p-toluidine) the carbonyl ligands are oriented cis to each
other in the columns and adopt nearly eclipsed conformations. In addition, the cis-Ir(CO)2Cl(p-
toluidine) molecules are oriented with alternating locations of the p-toluidine and chloride
groups. This arrangement not only prevents potential repulsive interactions between aryl carbon
atoms, but also maximizes potential hydrogen bonding contacts between the primary amine
protons and adjacent chloro ligands. The extensive hydrogen bonds are integral to the columnar
structure within the crystalline structure; they help to direct the self-association of these units and
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to supplement the weak metallophilic networks between iridium(I) centers. A similar hydrogen
bonding pattern along
a
columnar structure is also present in crystalline cis-
Rh(CO)2Cl(methylamine), although this hydrogen bonding interaction was over looked by the
original authors.40
Figure 1.
Linear chains of four square planar cis-Ir(CO)2Cl(p-toluidine) molecules.
Metallophilic interactions between the Ir(I) centers alternate with short and long contacts,
which are supported by parallel hydrogen bonding interactions between N–H···Cl. The
structures of cis-IrX(CO)2X(p-toluidine) (X = Br, I) are similar.
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Although the molecular structures for the chloro, bromo and iodo iridium(I) complexes of
cis-Ir(CO) X(p-toluidine) are similar, the isostructural complexes are differentiated mainly in
2
the dimensions of the solid-state structural packing. In the case of the bromo and iodo
complexess, again the two unique molecules in each asymmetric unit pack to form metal-metal
contacts that increase as the size of the halogen increases: 3.3801(6) and 3.4201(6) Å for cis-
Ir(CO)2Br(p-toluidine); 3.5409(7) and 3.6767(8) Å for cis-Ir(CO)2I(p-toluidine). Additionally,
the hydrogen bonding interactions for both the bromo and iodo forms are slightly longer than for
the chloro analog: ca. 3.54 Å for cis-Ir(CO) Br(p-toluidine) and 3.76 Å for cis-Ir(CO)2I(p-
2
toluidine);. The chain linearity decreases with increasing size of the halide ligand, and the chains
become more kinked: Ir2A···Ir1···Ir2 = 168.39(2) ° for cis-Ir(CO)2Br(p-toluidine), 163.62(1) °
for cis-Ir(CO)2I(p-toluidine).
Infrared Spectra of cis-Ir(CO)2Cl(p-toluidine), cis-Ir(CO)2Br(p-toluidine), and cis-
Ir(CO)2I(p-toluidine)
Information regarding the infrared spectra of cis-Ir(CO)2Cl(p-toluidine), cis-Ir(CO)2Br(p-
toluidine), and cis-Ir(CO)2I(p-toluidine) are collected in Table 3. In solution, cis-Ir(CO)2Cl(p-
toluidine) displays two carbonyl stretching bands due to the carbon monoxide ligands trans to the
chloride and amine ligands.41 However, four bands are seen in the solid state as revealed in
Table 3. These bands arise from the presence of two different iridium sites that are coupled
through metallophillic interactions in the crystals. Similarly, both cis-Ir(CO)2Br(p-toluidine) and
cis-Ir(CO)2I(p-toluidine) display four carbonyl stretching frequencies in the solid state. Notice
that changing the halide anion in these complexes has a rather small effect on the energies of the
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carbonyl stretching bands. A similar situatuion is seen for the anions cis-[Ir(CO)2X2]- with X =
Cl, Br, I.36
Table 3. Selected Infrared Spectroscopic Properties of cis-IrCl(CO)2(amine) Complexes.
Complex
v(C≡O)
v(C≡O)
v(N–H)
(cm-1)
(cm-1)
(cm-1)
cis-[IrCl(CO)2(p-
tol)]
2080vs
2049w
2020vs
1975w
3240
3204
solid state
cis-[IrCl(CO)2(p-
tol)]
2075
1997
dichloromethane
solutiona
cis-[IrBr(CO)2(p-
tol)]
2077vs
2051w
2019vs
1975w
3240
3200
solid state
cis-[IrI(CO)2(p-tol)] 2072vs
solid state 2051w
2014vs
1979w
3233
a A. L. Balch, R. D. Cooper, J. Organomet. Chem. 169 (1979) 97-105
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The Formation of Discrete Dimers in the Structures of cis-Ir(CO)2Cl(o-toluidine) and cis-
Ir(CO)2Cl(2,6-dimethyl aniline).
The effect of the changing the bulk of the amine substituent on the molecular packing,
orientation, and degree of ordering in crystalline structures of cis-Ir(CO)2Cl(primary amine) was
studied. Utilizing the ligands o-toluidine and 2,6-dimethylaniline, crystals were obtained for
complexes cis-Ir(CO)2Cl(o-toluidine)
and cis-Ir(CO)2Cl(2,6-dimethylaniline) and their
structures determined by X-ray crystallography. Crystallographic data and structure refinement
parameters for each complex are listed in Table 1, while selected geometrical parameters are
listed in Table 4.
Table 4. Dimensions within Dimeric Complexes (see Scheme 1)
cis-IrCl(CO)2(o-toluidine)
cis-Ir(CO)2Cl(2,6-dimethylaniline)
Compound
Molecule 1
Molecule 2
Molecule 1
Molecule 2
Molecule 3
Molecule 4
Distances (Å)
M1···M2, c
M1–Cl1
3.4036(3)
2.3552(12)
3.443(3)
2.376(2)
3.453(3)
2.380(2)
2.3477(12)
2.377(2)
3.319(6)
2.390(2)
N1–H1A···Cl2
N2–H2A···Cl1
N2–H2A···Cl2A
N3–H3A···Cl4
N4–H4A···Cl3
3.323(4)
3.383(4)
3.365(6)
3.383(4)
3.437(4)
3.412(6)
3.391(6)
Interplanar Sepn. a 3.37
3.36
3.39
Lat. Shift b
0.47
0.76
0.65
M Displacement
M/Ring Plane
0.014(2)
86.7
0.004(2)
85.7
0.014(3)
85.7
0.037(3)
82.7
0.009(3)
83.4
0.041(3)
80.7
Orange-red plates of cis-Ir(CO)2Cl(o-toluidine) crystallize with two molecules in the
asymmetric unit in monoclinic space group P21/n. Despite the similarity in space group and
number of molecules in the asymmetric unit, the structures of cis-Ir(CO)2Cl(o-toluidine) and cis-
Ir(CO)2Cl(p-toluidine) are quite different. The molecular structure of cis-Ir(CO)2Cl(o-toluidine)
and some aspects of its packing are shown in Figure 2. The two molecules in the asymmetric
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unit form a dimer, with an Ir1···Ir2 distance of 3.4012(7) Å. Within the dimer the ligands are
nearly eclipsed and the amine group positioned so that a hydrogen bond is formed between N2
on one molecule and Cl1 on the adjoining molecule. The o-toluidine ring is nearly perpendicular
to the metal coordination plane. The angles between the two planes are 86.7° for the molecule
involving Ir1 and 85.7° for the molecule containing Ir2. This orientation of the aromatic rings
blocks the outer faces of the dimer and precludes the formation of the extended chains seen for
Ir(CO)2Cl(p-toluidine). The dimers also interact with one another through additional hydrogen
bonding that connects Cl2 of one dimer with N2A of another and also N2 with Cl1A as shown
in Figure 2.
Figure 2. Interactions between four molecules of cis-Ir(CO)2Cl(o-toluidine) molecules.
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Red prisms of cis-Ir(CO) Cl(2,6-dimethylaniline) crystallize with four molecules in the
2
asymmetric unit in monoclinic space group P21/n. These the four unique molecules form two
dimeric units with similar Ir•••Ir distances: 3.394(3) Å for Ir1•••Ir2 and 3.402(3) Å for Ir3•••Ir4.
Again as the data in Table 4 indicate, the two coordination planes in each dimer are nearly
parallel to each other. As in cis-Ir(CO)2Cl(o-toluidine), there are hydrogen bonds between amine
and chloro groups in each dimer. These hydrogen bonding interactions insure that the dimers
have nearly eclipsed arrangements and augment the Ir•••Ir interactions in holding the dimers
together. The angle of the plane of the aniline group with the metal coordination plane varies
from an 80.7° in in the dimer formed by Ir3 and Ir4 to 85.7° in the dimer involving Ir1 and Ir2.
Again these groups protrude outward and protect opposite faces of the dimer so that extended
chains do not form. For this complex, there are no hydrogen bonds that connect the two dimers.
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Figure 3. Interactions between the four independent molecules of cis-Ir(CO)2Cl(2,6-
dimethylaniline).
Self-Association in Solution
The dicarbonylhalide(amine) complexes of rhodium(I) and iridium(I) are readily soluble
in halogenated solvents such as dichloromethane and chloroform. For the electronic spectra of
these complexes dichloromethane was used to obtain absorption data in solution. When
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dissolved in dichloromethane, cis-Ir(CO)2Cl(p-toluidine) forms dark amber solutions at 298 K.
UV/vis spectra in the solid-state were obtained in Nujol mulls.
Figure 4 shows some representative data for cis-Ir(CO)2Cl(p-toluidine). The absorbance
features vary with concentration. In dilute solutions, the maxima for are 310 nm and 356 nm; in
addition, a low-energy shoulder occurs at ca. 395 nm. However, at the higher concentration new
absorption bands are observed at 430, 525 and 694 nm. These additional features are associated
with the formation of aggregates similar to the self-association seen in the solid state. Notice
that the spectrum obtained from the solid itself shows features similar to those seen in the more
concentrated solution.
Figure 4.
UV/vis of cis-Ir(CO)2Cl(p-toluidine) in Nujol mulls (red trace) and in
dichloromethane solutions (4.5 mM ---; 45 mM ▬. Solution spectra were normalized to
the peak at 356 nm.
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Self-Association in the Gas Phase, Mass Spectrometry
We have seen aggregation of iridium(I) dicarbonylhalide(amine) complexes in both the
solid and solution phases and wanted to determine if the supramolecular organization of the
square planar moieties could be detected in the gas phase. Thus, the matrix-assisted laser
desorption/ionization (MALDI) mass spectrum of cis-Ir(CO)2Br(p-toluidine)was collected.
Crystals of the iridium(I) complex were affixed (without the presence of a matrix) to a stainless
steel plate using a minimum amount of Super Glue and were subsequently ionized. This
represents a novel dry method for obtaining mass spectral time of flight (TOF) data, without the
assistance of ionizing matrices that are typically acidic in nature and can interfere with the metal
coordination site. Mass spectra, which show peaks for the monomeric, dimeric and trimeric
forms of [cis-Ir(CO)2Br(p-toluidine)]+, are shown in Figure 5 along with the computed spectra.
Both positive and negative ionization conditions were attempted; however, intelligible results
were only obtained in the positive ion mode. Under positive ionization conditions, peaks due to
monomers, dimers, and trimers were observed. The corresponding isotope distributions correlate
well with the theoretical absolute mass assignments and splitting patterns. Interestingly, the
dimer peaks were nearly four times more intense than either the monomer or trimer signals. The
results show that the self-association of these metal complexes can be detected even in the gas
phase. Detection of self-association of d8 metal complexes by mass spectrometry is rare.33
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Figure 5. MALDI TOF/TOF mass spectra (positive ion mode) isotope distributions for the peaks
of the monomeric, dimeric and trimeric units of cis-Ir(CO)2Br(p-toluidine). The upper plots show
the theoretical isotope distributions. The lower plots show the experimental data from a cluster
of crystals of cis-Ir(CO)2Br(p-toluidine), glued to the target plate.
Conclusions.
The solid state structures of d8 planar complexes of the type cis-Ir(CO)2X(primary amine) (X=
Cl, Br, I) are influenced by the presence of Ir···Ir interactions, hydrogen bonding between an N-
H group on one molecule and a halide ligand on an adjacent molecule, and the steric bulk of the
amine ligand. In cis-Ir(CO)2X(p-toluidine) (X = Cl, Br, I) the four-coordinate, planar molecules
pack so that the molecules form columnar arrays with unsupported, face-to-face interactions
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through d8-d8 contacts with additional hydrogen bonding between N-H groups and chloride
ligands that runs along the columns. In cis-Ir(CO)2Cl(o-toluidine) and cis-Ir(CO)2Cl(2,6-
dimethylaniline) the methyl groups of the amine protrude from one face of the monomer in such
a fashion that the formation of extended chains is precluded. In these two cases, dimers are
formed. These dimers are again connected by Ir···Ir interactions and by N-H…Cl hydrogen
bonding. The Ir···Ir distances in the dimers (3.4036(3) Å for cis-IrCl(CO)2(o-toluidine),
3.443(3), 3.453(3) Å for cis-Ir(CO)2Cl(2,6-dimethylaniline)) are similar but slightly longer than
the Ir···Ir distances 3.3341(2) and 3.3576(2) Å for in the extended chain complex cis-
Ir(CO)2Cl(p-toluidine). In all cases, the adjacent planar molecules have nearly eclipsed
structures.
The extended chains in cis-Ir(CO)2Cl(p-toluidine) with Ir···Ir separations of 3.3341(2)
and 3.3576(2) Å and a nearly eclipsed arrangement of adjacent molecules are quite different
from those in Ir(CO)3Cl, where the Ir···Ir separation is shorter (2.844 Å) and adjacent complexes
are arranged in a eclipsed fashion. However, the stacking of molecules of the type in cis-
Ir(CO)2Cl(primary amine) resembles that seen in cis-Ir(CO)2Cl(pyridine),20 cis-
Ir(CO)2Cl(pyrazine),21 and Ir(CO)2(acetylacetonate)22,23 where with Ir···Ir separations fall in the
range 3.242 to 3.602(12) Å. Thus, Ir(CO)3Cl remains as an outlier in the nature of self-
association of Ir(I) complexes. As expected, the Ir···Ir separations seen in the crystals
considered here are significantly longer than the range of Ir-Ir distances (2.6622(3) Å to
2.8393(12) Å) found in Ir(II) dimers that contain single Ir(II)-Ir(II) bonds.42
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Experimental
Materials.
ꢀ
Samples of IrCl3·3H2O were purchased from Pressure Chemical Company.
Sodium bromide, sodium iodide, 2-methoxyethanol, p-toluidine, o-toluidine, and 2,6-
dimethylaniline were purchased from Aldrich Chemicals and used as received. Carbon monoxide
gas (C.P. grade) was obtained from Airgas Inc. Carbon monoxide is a toxic gas that needs to be
handled in a well ventilated fume hood.
Synthesis of cis-Ir(CO)2Cl(amine) where amine =
p-toluidine, o- toluidine, or 2,6-
dimethylaniline. These complexes were prepared with minor modifications to the literature
procedure developed for cis-Ir(CO)2Cl(p-toluidine).34 A sample of IrCl3·3H2O (0.729 g, 2.07
mmol) was treated with lithium chloride (0.421 g, 9.94 mmol) and excess carbon monoxide in a
solution of 2-methoxyethanol (27 mL), and water (3 mL). After refluxing overnight under a
stream of carbon monoxide, the pale yellow solution containing the non-isolated Li[IrCl2(CO)2]
was charged with p-toluidine (0.224 g, 2.09 mmol) and concentrated to ca. 5 mL under
dinitrogen. The concentrated solution was poured into 100 mL of deionized water.
A
navy/purple fluffy precipitate formed immediately. The solid was collected by filtration on a
Büchner funnel, washed with water, and dried over anhydrous sodium sulfate (yield, 0.540 g,
67%).
For cis-Ir(CO)2Cl(p-toluidine), deep red blocks with a metallic sheen suitable for X-ray
diffraction experiments were grown by the slow evaporation of a concentrated hexane solution of
the complex under dinitrogen.
For cis-Ir(CO)2Cl(o-toluidine) orange-red, metallic plate-like crystals were grown from the slow
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evaporation of a concentrated benzene solution of the complex under dinitrogen. Mp 143-144
°C.
For cis-Ir(CO)2Cl(2,6-dimethylaniline), red prisms, suitable for X-ray diffraction experiments,
were grown by the slow evaporation of a pentane solution of the complex. Mp 155-156 °C.
Synthesis of cis-Ir(CO)2X (p-toluidine) where X = Br or I.
To prepare cis-Ir(CO)2I(p-toluidine), a three-neck, 100 mL round bottom flask was charged with
IrCl ·3H O (0.701 g, 1.99 mmol), sodium iodide (1.529 g, 10.20 mmol), 2- methoxyethanol (27
3
2
mL), and water (3 mL). A reflux condenser topped with an oil bubbler was affixed to the center
neck, while a carbon monoxide inlet tube was placed in a side port; the third neck was stoppered.
The reaction solution was initially degassed with flowing carbon monoxide for 15 min at room
temperature, then refluxed at 393 K overnight, with continuous passage of carbon monoxide.
Overnight, the reaction solution turned from dark red to yellow. After cooling to room
temperature, p-toluidine (0.262 g, 2.44 mmol) was added, and the solution was concentrated to
ca. 5 mL under a stream of dinitrogen. This concentrated solution was poured into 100 mL of
deionized water; a purple fluffy precipitate formed immediately. The solid was collected on a
Büchner funnel by filtration, washed with water, and dried over anhydrous sodium sulfate (yield:
0.724 g, 76%). Green, dichroic needles of cis-Ir(CO)2I(p-toluidine), suitable for X-ray diffraction
experiments, were grown from the slow diffusion of hexane into a dichloromethane solution of
the complex.
For cis-Ir(CO) Br(p-toluidine), an analogous procedure was used with sodium bromide
2
replacing sodium iodide. Red/green dichroic needles of of cis-Ir(CO) Br(p-toluidine), suitable
2
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for X-ray diffraction, were grown by the vapor diffusion of hexane into a dichloromethane
solution of the complex.
Mass Spectrometry.ꢀMass spectra for the metal complexes were acquired in the positive ion
mode, after calibration, on an Applied Biosystems 4700 MALDI TOF/TOF (Foster City, CA)
instrument using direct laser desorption. A crystalline sample was manually fixed to the stainless
steel target plate using Super Glue, before insertion into the instrument. The sample was
subjected to irradiation from a Nd:YAG laser (354 nm), and the accelerating voltage applied was
20 kV. The instrument was operated in a standard reflectron operating mode and spectra were the
average of 2000 shots, and the laser fluence used was the minimum necessary to achieve a signal
from the analyte.
Spectroscopic Methods.ꢀElectronic absorption spectra were recorded on a PharmaSpec UV-
1700 spectrophotometer (Shimadzu). Spectra of solids were acquired from samples dispersed in
Nujol mulls. Infra red spectra of neat powders of these complexes were recorded on a Mattson
Genesis II FT-IR spectrometer, fitted with a Specac Attenuated Total Reflectance (ATR)
accessory.
Single Crystal X-ray Diffraction. The crystals were removed from the vials or tubes in which
they were grown and immediately coated with hydrocarbon oil on microscope slides. Suitable
crystals were mounted on glass fibers with silicone grease and placed in a cold stream of either a
Bruker SMART 1000 or a Bruker SMART ApexII diffractometer. Dinitrogen cooling (90(2) K)
was accomplished by use of CRYO Industries devices. A multiscan method utilizing equivalents
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was employed to correct for the absorption of heavy atoms.43 The crystal structures were solved
by direct methods, and all data were refined (based on F2) using SHELXTL 5.144 or SHELXL-
201845 software. Hydrogen atoms were located in a difference map, added geometrically, and
refined with a riding model with the exception that the N-H protons were restrained to have N-H
distances of 0.91(2) Å and were otherwise freely refined in all chloro complexes.
Crystallographic data are found in Table 1.
ꢀ
Acknowledgements. We thank the Petroleum Research Fund (Grant 37056-AC) for support,
and the Tyco Foundation for a fellowship for E. M. G., and Dr. Jay R. Stork for collecting the
diffraction data for cis-Ir(CO)2Cl(p-toluidine). The Bruker SMART 1000 diffractometer was
funded in part by NSF Instrumentation grant CHE-9808259.
Appendix A. Supplementary data. Supplementary data related to this article can be found at:
CCDC 1887970-1887974 contain the supplementary crystallographic data for this paper. These
data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from
the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax:
(+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Dedication
Dedicated to Professor Richard J. Puddephatt for his many significant contributions to
organometallic chemistry on the occasion of his 75th birthday.
References
[1]
A. L. Balch, Structure and Bonding 123 (2007) 1-40.
23

ACCEPTED MANUSCRIPT
[2]
[3]
[4]
[5]
G. Aullón, S. Alvarez, Chem. Eur. J. 3 (1997) 655- 664.
V. W.-W. Yam, V. K.-M. Au, S. Y.-L. Leung, Chem. Rev. 115 (2015) 7589−7728 .
P. Pyykkö, Chem. Rev. 97 (1997) 597−636.
J. M. Williams, A. J. Schultz, A. E. Underhill, K. Carneiro, In Extended Linear Chain
Compounds; Miller, J. S., Ed.; Plenum Press: New York, 1982; Vol. 1, p 73.
A. E. Underhill, D. M. Watkins, J. M. Williams, K. Carneiro, In Extended Linear Chain
Compounds; Miller, J. S., Ed.; Plenum Press: New York, 1982; Vol. 1, p 119.
K. M.-C. Wong, V. W.-W. Yam, Accounts Chem. Res. 44 (2011) 424-434.
J. Kang, X. Zhang, H. Zhou, X. Gai, T. Jia, L. Xu, J. Zhang, Y. Li, J. Ni, Inorg. Chem. 55
(2016) 10208−10217.
[6]
[7]
[8]
[9]
C. Po, A. Y.-Y. Tam, K. M.-C. Wong, V. W.-W. Yam, J. Am. Chem. Soc. 133 (2011)
12136–12143.
[10] K. R, Mann, J. G. Gordon, II, H. B. Gray, J. Am. Chem. Soc., 97 (1975) 3553–3555.
[11] K. R, Mann, N. J. Lewis, R. M. Williams, H. B. Gray, J. G. Gordon, II, Inorg. Chem., 17
(1978) 828–834.
[12] N. Tran, J. R. Stork, D. Pham, M. M. Olmstead, J. C. Fettinger, A. L. Balch. Chem.
Commun., (2006)1130-1132.
[13] N. T. Tran, J. R. Stork, D. Pham, C. J. Chancellor, M. M. Olmstead, J. C. Fettinger, A. L.
Balch, Inorg. Chem. 46 (2007) 7998−8007.
[14] Y. Chen, K. Li, H. O. Lloyd, W. Lu, S. S.-Y. Chui, C.-M. Che, Angew. Chem. Int. Ed. 49
(2010) 9968 –9971.
[15] A. K.-W. Chan, K. M.-C. Wong, V. W.-W. Yam, J. Am. Chem. Soc. 137 (2015)
6920−6931.
24

ACCEPTED MANUSCRIPT
[16] R. L. White-Morris, M. M. Olmstead, A. L. Balch, J. Am. Chem. Soc. 125 (2003) 1033-
1040.
[17] M. A. Malwitz, S. H. Lim, R. L. White-Morris, D. M. Pham, M. M. Olmstead, A. L.
Balch, J. Am. Chem. Soc. 134, (2012) 10885-1089.
[18]
M.-H. Whangbo, R. Hoffmann, J. Am. Chem. Soc. 100 (1978) 6093-6098
[19] J. J. Novoa, G. Aullon, P. Alemany, S. Alvarez, J. Am. Chem. Soc, 117 (1995) 7169-
7171.
[20] D. Y. Jeter, E. B. Fleischer, J. Coord. Chem., 4 (1974) 107-111.
[21] C. Dragonetti, M. Pizzotti, D. Roberto, S. Galli, Inorg. Chim. Acta 330 (2002) 128-135.
[22] C. G. Pitt, L. K. Monteith, L. F. Ballard, J. P. Collman, J. C. Morrow, W. R. Roper, and
D. Ulku, J. Amer. Chem. Soc., 88 (1966) 4286-4287.
[23] K. V. Zherikova, N. V. Kuratieva, and N. B. Morozova, J. Struct. Chem. 50 (2009) 574-
576.
[24] E. M. Gussenhoven, M. M. Olmstead, J. C. Fettinger, A. L. Balch, Inorg. Chem., 47
(2008) 4570-4578.
[25] P. B. Hitchcock, S. Morton, J. F. Nixon, J. Chem. Soc., Chem. Commun., (1984) 603-
604.
[26] A. H. Reis Jr., V. S. Hagley, S. W. Peterson, J. Am. Chem. Soc. 99 (1977) 4184-4186.
[27] A. H. Reis, S. W. Peterson, Ann. N.Y. Acad. Sci. 313 (1978) 560-572.
[28] K. W. Krogman, W. Binder, H. D. Hausen, Angew. Chem., Int. Ed. Engl. 7 (1968) 812-
812.
[29] Y. Tsuji, R. Hoffmann, J. S. Miller Polyhedron 103 (2016) 141-149.
25

ACCEPTED MANUSCRIPT
[30] A. P. Ginsberg, J. W. Koepke, J. J. Hauser, K. W. West, F. J. Di Salvo, C. R. Sprinkle, R.
L. Cohen, Inorg. Chem. 15 (1976) 514-519.
[31] M. Wysocka, K. Winkler, J. R. Stork, A. L. Balch, Chem. Mater. 16 (2004) 771-780.
[32] K. Winkler, M. Wysocka-Zołopa, M. M. Oleksicka, K. Recko, L. Dobrzynski, J. R.
Stork, E. M. Gussenhoven, M. M. Olmstead, A. L. Balch, Electrochim. Acta 53 (2008)
7288-7297.
[33] D. E. Bikiel, J. M. Ramallo-López, F. G. Requejo, O. B. Oña, M. B. Ferraro, J. C. Facelli,
F. Doctorovich, Polyhedron 30 (2011) 221–227.
[34]
U. Klabunde, Inorg. Synth. 15 (1974) 82-84.
[35] L. Vaska, J. W. DiLuzio, J. Am. Chem. Soc. 83 (1961) 2784–2785.
[36] D. Forster, Inorg. Nucl. Chem. Letters 5 (1969) 433-436.
[37] M. Rahim, K. J. Ahmed Inorg. Chem. 33 (1994) 3003–3004.
[38] A. L. Balch, L. A. Fossett, M. M. Olmstead, P. E. Reedy, Jr. Organometallics 5 (1986)
1929–1937.
[39] S. W. Carr, B. L. Shaw, Polyhedron 6, (1987) 111-117.
[40] K. Jang, I. G. Jung, H. J. Nam, D.-Y. Jung, S. U. Son, J. Am. Chem. Soc. 131 (2009)
12046–12047.
[41] A. L. Balch, R. D. Cooper, J. Organomet. Chem. 169 (1979) 97-105.
[42] H. Huang, A. L. Rheingold, R. P. Hughes, Organometallics 28 (2009) 1575–1578.
[43] G. M Sheldrick,. SADABS 2007/2; University of Göttingen: Göttingen, Germany, 2007.
26

ACCEPTED MANUSCRIPT
[44] G. M. Sheldrick, SHELXS and SHELXL-97 Acta Crystallographica A64 (2008) 112-
122.ꢀ
[45] G. M. Sheldrick, SHELXL Acta Crystallographica Sect. C71 (2015) 3-8.
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ACCEPTED MANUSCRIPT
Crystals of cis-Ir(CO)2X(p-toluidine) (X= Cl ,Br, I) form columnar structures
Metallophillic d8···d8 interactions and hydrogen bonding reinforce these columns
Methyl groups in amine ortho positions of cis-Ir(CO)2X(amine) produce dimers not
columns
Self-association of cis-Ir(CO)2X(p-toluidine) persists in solution and in the gas phase