Towards understanding monomer coordination in atom transfer radical polymerization: Synthesis of [CuI(PMDETA)(π-M)][BPh4] (M = methyl acrylate, styrene, 1-octene, and methyl methacrylate) and structural studies by FT-IR and 1H NMR spectroscopy and X-ray crystallography

Article abstract of DOI:10.1016/j.jorganchem.2004.10.035

Cu^I complexes of the form [Cu^I(PMDETA)(π-M)] [BPh₄] (where PMDETA = N,N,N′,N″,N″- pentamethyldiethylenetriamine, and M = vinyl monomer) were synthesized and isolated from solution as crystals with methyl acrylate (MA), styrene (Sty), and 1-octene (Oct). The interaction of the C=C double bond of the vinyl monomer with Cu^I was characterized via FT-IR and ¹H NMR spectroscopy and single crystal X-ray crystallography. A fourth complex with methyl methacrylate (MMA) was synthesized and characterized spectroscopically, but no crystals suitable for X-ray structure analysis could be obtained. In all complexes, PMDETA acts as a tridentate ligand, while the pseudotetrahedral coordination geometry around Cu^I is completed by a π-interaction with the C=C double bond of M in the presence of a non-coordinating counter-ion. A decrease in C=C IR stretching frequencies of Δν(C=C) = -110, -80, -109, and -127 cm^-1 for complexes with MA, Sty, Oct, and MMA, respectively, was observed upon coordination. No significant change in C=C bond length was seen in the crystal structure for complexes with MA and Oct while a slight lengthening was observed for the Sty complex. The upfield shift of the vinyl proton resonances indicated the presence of significant π-back-bonding.

Full text of DOI:10.1016/j.jorganchem.2004.10.035

Journal of Organometallic Chemistry 690 (2005) 916–924
www.elsevier.com/locate/jorganchem
Towards understanding monomer coordination in atom
transfer radical polymerization: synthesis of
[CuI(PMDETA)(p-M)][BPh4] (M = methyl acrylate, styrene,
1-octene, and methyl methacrylate) and structural studies by
1
FT-IR and H NMR spectroscopy and X-ray crystallography
a
a
a
b
Wade A. Braunecker , Tomislav Pintauer , Nicolay V. Tsarevsky , Guido Kickelbick ,
a,
*
Krzysztof Matyjaszewski
a
Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, PA 15213, USA
b
Institute of Materials Chemistry, Vienna University of Technology, Getreidemarkt 9, 1060 Wien, Austria
Received 21 September 2004; accepted 19 October 2004
Available online 21 November 2004
Abstract
CuI complexes of the form [CuI(PMDETA)(p-M)][BPh4] (where PMDETA = N,N,N0,N00,N00-pentamethyldiethylenetriamine,
and M = vinyl monomer) were synthesized and isolated from solution as crystals with methyl acrylate (MA), styrene (Sty), and
1
1-octene (Oct). The interaction of the C@C double bond of the vinyl monomer with CuI was characterized via FT-IR and H
NMR spectroscopy and single crystal X-ray crystallography. A fourth complex with methyl methacrylate (MMA) was synthesized
and characterized spectroscopically, but no crystals suitable for X-ray structure analysis could be obtained. In all complexes, PMD-
ETA acts as a tridentate ligand, while the pseudotetrahedral coordination geometry around CuI is completed by a p-interaction with
the C@C double bond of M in the presence of a non-coordinating counter-ion. A decrease in C@C IR stretching frequencies of
Dm(C@C) = ꢀ110, ꢀ80, ꢀ109, and ꢀ127 cmꢀ1 for complexes with MA, Sty, Oct, and MMA, respectively, was observed upon coor-
dination. No significant change in C@C bond length was seen in the crystal structure for complexes with MA and Oct while a slight
lengthening was observed for the Sty complex. The upfield shift of the vinyl proton resonances indicated the presence of significant
p-back-bonding.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Copper(I) complexes; p-Coordination; X-ray structure; 1H NMR; FT-IR; ATRP
1. Introduction
cent advances toward the copolymerization of polar
monomers and alkenes were made in the field of coordi-
nation polymerization with the introduction of ration-
ally designed Pd- and Ni-based diimine polymerization
catalysts [3]. However, while these compounds were em-
ployed to successfully copolymerize as much as 25 mol%
of methyl acrylate with ethylene and higher a-olefins,
increasing the incorporation of functional groups into
the copolymer required increasing the fraction of polar
monomer in the monomer feed, which in turn resulted
The potential to dramatically improve or modify the
physical properties of polyolefins through the incorpora-
tion of functional groups has fueled the search for new
polymerization catalysts capable of copolymerizing po-
lar functional monomers with simple a-olefins [1,2]. Re-
*
Corresponding author. Tel.: +412 268 3209; fax: +412 268 6897.
E-mail address: kmb3@andrew.cmu.edu (K. Matyjaszewski).
0022-328X/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.10.035

W.A. Braunecker et al. / Journal of Organometallic Chemistry 690 (2005) 916–924
917
in a loss of activity of the catalyst [4]. Controlling the
reaction still remains a challenge, and detailed mecha-
nistic studies concerning olefin coordination to transi-
tion metals will be necessary for any further advances
made in this field. Olefin-transition metal complexes
have been the subject of numerous reviews [5–10].
According to the widely accepted model proposed by
Dewar [11] and by Chatt and Duncanson [12], the me-
tal–olefin bond has both r and p components; which
component dominates depends on the direction of trans-
fer of electron density (from the metal to the olefin
p*-orbital, or from the olefin p-orbital to the vacant
r-type metal orbital).
Radical polymerization represents a different ap-
proach to the goal of copolymerizing polar monomers
with a-olefins. The tolerance that radical polymerization
shows toward polar functional groups, as opposed to
traditional coordination and ionic polymerization,
makes this technique attractive for polymerizing polar
monomers. Nevertheless, a number of well-known
drawbacks, including the inability to control molecular
weight distribution or chain end functionality and devel-
op well-defined complex structures, make conventional
radical polymerization less than ideal. Atom transfer
radical polymerization (ATRP) has emerged in the last
decade as a powerful technique for the synthesis of mac-
romolecules with well defined compositions, architec-
tures and functionalities [13–18]. This controlled living
radical polymerization technique has produced a pleth-
ora of polymeric materials with predictable molecular
weights and narrow molecular weight distributions
[19–23].
However, while radical polymerization techniques are
well suited for polar monomers, a-olefins typically do
not polymerize via a radical mechanism as they are sub-
ject to degradative chain transfer in the presence of a
reactive propagating radical [24]. Recent publications
have reported that while degradative chain transfer does
occur, the copolymerization of methyl acrylate with var-
ious 1-alkenes under ATRP conditions is possible under
mild conditions [25–27]. Well-controlled polymers of
methyl acrylate constituting approximately 25 mol% of
1-octene have since been reportedly attained using
ATRP [28]. However, increasing the level of incorpora-
tion of the olefin into the copolymer by increasing its
fraction in the monomer feed resulted in low overall
conversion, plausibly due to the irreversible deactivation
of growing chains by formation of un-reactive alkyl ha-
lide chain ends derived from a-olefins. The unfavorable
reactivity ratios of these monomers in radical polymeri-
zations have made statistical copolymers with a high de-
gree of olefin incorporation difficult to attain and a high
conversion difficult to reach.
the nature of the CuI-olefin bonding. Several p-coordi-
nated complexes of methyl acrylate and methyl metha-
crylate have been extensively studied with other
transition metals, including Ru [29], Rh [30], Pt [31],
and Ni [32]. However, little is known about the coordi-
nation of methyl acrylate with CuI [33,34], and there are
no literature reports to date of p-coordination of methyl
methacrylate to CuI. Information on the nature of this
bonding will be necessary to later study the change in
reactivity of a monomer in a radical polymerization
upon coordination to a transition metal. Potentially,
the altered reactivity could allow for an increased incor-
poration of a-olefin into a copolymer with polar func-
tional monomers. Second, concurrent reactions that
may occur during the ATRP and will affect its efficiency
warrant further examination. Disproportionation of the
CuI catalyst in aqueous media [35], transfer reactions
associated with the complexing ligand [36–38], and sol-
vent coordination [39] to the active catalyst have already
been documented in this polymerization system.
[CuI(PMDETA)X] (X = Cl or Br) is successfully used
as an ATRP catalyst [40], but these complexes could
not be isolatþed with coordinated monomer.
½CuIðPMDETAÞ ꢁ½BPhꢀ4 ꢁ, for which the counter-ion
does not compete with monomer for coordination to
CuI, was thus studied in an effort to address the side
reaction of monomer coordination to the CuI catalyst.
Third, correlating reaction parameters including activa-
tion, deactivation, initiation, overall reaction rate con-
stants, and evolution of molecular weight distribution
[41–48] with catalyst, alkyl halide, and monomer struc-
ture, solvent composition and temperature should ulti-
mately lead to the development of more active
catalysts and are crucial to any future developments of
ATRP [49–54]. This paper will address the nature of
the bonding in these CuI complexes, and subsequent
publications will address the quantification of this coor-
dination process under various conditions and with
CuI(PMDETA)Br, the effect that coordination has on
the reactivity of the monomer, and the performance of
the catalyst in polymerization.
2. Results and discussion
2.1. X-ray crystallography
The [CuI(PMDETA)(p-M)]+ cations and [BPh4]ꢀ
anions (where M = MA (1), Sty (2), Oct (3), and
MMA (4)) build up the crystal structures of 1–3; no
interactions are observed between these respective coun-
terions. PMDETA acts as a tridentate ligand, while the
pseudotetrahedral coordination geometry around CuI is
completed by a p-interaction with the C@C double bond
of the coordinated monomer. Figs. 1–3 show the molec-
ular structures of the respective cations of complexes
This project has a threefold purpose. First, the study
of the coordination of various polar and non-polar ole-
fins to CuI complexes will provide valuable insight into

918
W.A. Braunecker et al. / Journal of Organometallic Chemistry 690 (2005) 916–924
and the terminal nitrogen atoms (N, N00) range from
84.07(6)ꢁ to 87.35(13)ꢁ while the N–CuI–N bond angles
range from 113.13(12)ꢁ to 114.93(6)ꢁ in complexes 1–3.
This deviation from tetrahedral geometry has been doc-
umented in the structurally related [CuI(dien)(1-hex)]-
[BPh4] (dien = diethylenetriamine), where the equivalent
bond angles in the coordinated dien ligand are 83.2(7)ꢁ,
83.5(6)ꢁ, and 127.4(9)ꢁ [55]. The CuI-N and CuI–N00
bond lengths in the coordinated PMDETA ligand in
1–3 are significantly longer than the length of the CuI–
N0 bond (Table 1). While an elongation has been
observed in the copper-nitrogen bonds of [CuI(dien)-
(1-hex)][BPh4] and [CuI(dien)(norbornene)][BPh4] [56],
the elongation occurred at the central nitrogen rather
than the terminal nitrogen atoms.
Fig. 1. Molecular structure of complex 1 cation. Hydrogen atoms have
been removed for clarity.
The two CuI–C distances for the coordinated mono-
mers are not equal; the CuI atom is always closer to
the unsubstituted carbon atom (Cb) than the substituted
carbon atom (Ca) in 1–3. This result is typical of metal–
carbon bonds for a variety of metals and alkenes; the
Ca–metal bond is invariably longer than the Cb–metal
bond [57]. In complex 1, the Cb-CuI distance is
I
2.021(4) A and the Ca–Cu distance is 2.067(4) A. In
˚
˚
˚
2, those respective distances are 2.052(4) A and
˚
˚
˚
2.108(4) A, and in 3 2.028(4) A) and 2.094(4) A. This
difference between the two CuI–C distances is fully con-
sistent with the chemical shifts in the 1H NMR spectrum
of the complexes as will be discussed. The vinyl double
bond length of coordinated MA in 1 was determined
˚
˚
to be 1.360(6) A, compared to 1.355 A estimated for free
MA [58]. The C@C distance of coordinated Sty in 2 was
˚
determined to be 1.367(3) A, which is longer than
Fig. 2. Molecular structure of complex 2 cation. Hydrogen atoms have
been removed for clarity.
˚
1.325(2) A observed for the vinyl double bond in a
crystal structure of free Sty at 83ꢁ K [59], and also
˚
longer than 1.358(10)
A
observed for the vinyl
double bond length in the structurally similar
½CuIðbipyÞðp-StyÞꢁClO4 [60] compound where Sty was
p-coordinated to CuI. The C@C distance of coordinated
˚
Oct in 3 was determined to be 1.354(3) A; no significant
lengthening was observed in comparison with the value
˚
commonly reported for free olefins of 1.34 A [61] and
˚
that known for other 1-alkenes of 1.35 A [58]. Addition-
ally, complex 3 exists as two optical isomers which co-
crystallize in equal amounts. The coordinated double
bond in 3 occupied positions of C14 and C14A. The
CuI–(14A) and C(13)–(C14A) bond lengths for this opti-
Fig. 3. Molecular structure of complex 3 cation. Hydrogen atoms have
been removed for clarity.
˚
cal isomer are 2.077(9) and 1.346(15) A, respectively.
The carbons found in positions C(14) and C(14A) would
˚
be approximately 1.017(14) A from each other and make
1–3 with their atomic numbering schemes. Selected bond
lengths and angles are given in Table 1. While crystals of
4 suitable for X-ray analysis could not be obtained, the
complex was studied by FT-IR and H NMR spectros-
copy (vide infra).
an angle C(14)–C(13)–C(14A) of 44.3ꢁ.
1
2.2. H NMR spectroscopy
1
1
The H NMR solution spectra of complexes 1–4 are
In the coordinated PMDETA ligand, the angles be-
tween the central nitrogen atom (N00), the CuI atom,
fully consistent with the X-ray structures of the crystal-
line complexes discussed above. The proton resonances

W.A. Braunecker et al. / Journal of Organometallic Chemistry 690 (2005) 916–924
919
Table 1
˚
Selected bond distances (A) and angles (ꢁ) for 1–3
1
2
3
Distances
Cu(1)–N(2)
Cu(1)–N(5)
Cu(1)–N(8)
2.220(3)
2.043(3)
2.110(3)
Cu(1)–N(1)
Cu(1)–N(4)
Cu(1)–N(7)
2.2255(16)
2.1275(16)
2.1282(17)
Cu(1)–N(1)
Cu(1)–N(4)
Cu(1)–N(7)
2.251(3)
2.061(3)
2.177(3)
Cu(1)–C(14)
Cu(1)–C(15)
C(14)–C(15)
2.021(4)
2.067(4)
1.360(6)
Cu(1)–C(13)
Cu(1)–C(14)
C(13)–C(14)
2.052(2)
2.108(2)
1.367(3)
Cu(1)–C(13)
Cu(1)–C(14)
C(13)–C(14)
2.028(4)
2.094(8)
1.354(11)
Angles
N(2)–Cu(1)–N(5)
N(5)–Cu(1)–N(8)
N(8)–Cu(1)–N(2)
85.58(12)
87.35(13)
113.65(12)
N(1)–Cu(1)–N(4)
N(4)–Cu(1)–N(7)
N(7)–Cu(1)–N(1)
84.07(6)
85.80(6)
114.93(6)
N(1)–Cu(1)–N(4)
N(4)–Cu(1)–N(7)
N(7)–Cu(1)–N(1)
84.98(11)
85.48(13)
113.13(12)
C(14)–Cu(1)–N(2)
C(14)–Cu(1)–N(5)
C(14)–Cu(1)–N(8)
C(15)–Cu(1)–N(2)
C(15)–Cu(1)–N(5)
C(15)–Cu(1)–N(8)
111.64(13)
156.15(17)
108.26(16)
103.52(15)
117.33(15)
129.55(14)
C(13)–Cu(1)–N(1)
C(13)–Cu(1)–N(4)
C(13)–Cu(1)–N(7)
C(14)–Cu(1)–N(1)
C(14)–Cu(1)–N(4)
C(14)–Cu(1)–N(7)
109.86(8)
153.29(8)
107.14(8)
102.84(8)
117.43(9)
137.76(9)
C(13)–Cu(1)–N(1)
C(13)–Cu(1)–N(4)
C(13)–Cu(1)–N(7)
C(14)–Cu(1)–N(1)
C(14)–Cu(1)–N(4)
C(14)–Cu(1)–N(7)
110.1(2)
156.23(18)
104.1(2)
131.6(3)
118.0(3)
110.8(3)
C(14)–Cu(1)–C(15)
Cu(1)–C(14)–C(15)
Cu(1)–C(15)–C(14)
C(14)–C(15)–C(16)
38.84(16)
72.4(2)
68.8(2)
C(13)–Cu(1)–C(14)
Cu(1)–C(13)–C(14)
Cu(1)–C(14)–C(13)
C(13)–C(14)–C(15)
38.65(9)
68.46(14)
72.89(14)
127.2(2)
C(13)–Cu-C(14)
38.3(3)
73.5(4)
68.2(4)
127.0(9)
Cu(1)–C(13)–C(14)
Cu(1)–C(14)–C(13)
C(13)–C(14)–C(15)
119.94(4)
associated with the [BPh4]ꢀ anion do not change in any
of the four CuI complexes and are the same as in
Na[BPh4], indicating an absence of interaction between
the ions. The downfield shift of approximately 0.5
ppm in the proton resonances of the PMDETA ligand
upon coordination to CuI is typical of nitrogen based
ligands complexing with a CuI center [33,62–64]. Fur-
thermore, when coordination of the C@C double bond
to CuI is relatively strong, p-back-donation from CuI
to the olefin bond can be expected to shift the proton
signals of the complexing PMDETA ligand further
downfield. This effect is most pronounced in the case
of 1 where the complexing monomer has strong electron
withdrawing groups and p-back-donation from CuI is
the strongest of complexes 1–4 (as evident by the extent
of the upfield shift in C@C proton signals which will be
further discussed). Relative to [CuI(PMDETA)][BPh4],
the PMDETA proton resonances of 1 are further shifted
downfield approximately 0.1 ppm (Fig. 4).
The upfield shift of the C@C proton resonances of
the monomer upon coordination indicates p-back-dona-
tion where the olefin occupies one coordination site
around the CuI center [11,12,65]. Because the complexes
undergo fast monomer exchange on the NMR time scale
at room temperature at the given concentration of dis-
solved complex (0.02 M), the average signal of the free
and coordinated C@C protons is observed. The proton
spectra were thus taken at sufficiently low temperatures
where distinct signals for the free and coordinated
monomers could be seen. Table 2 shows the change in
chemical shift of the C@C protons for complexes 1–4.
(a)
(b)
(c)
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
Fig. 4. Comparison of 500 MHz 1H NMR spectra at 30 ꢁC of 0.02 M
1 (a), 0.02 M [CuI(PMDETA)][BPh4] (b), and MA (c).
The shielding effect is most pronounced in the case of
coordinated unsaturated esters, which indicates that
the contribution from p-back-bonding in 1 and 4 is
stronger than in 2, which in turn is more pronounced
than in 3. This result is expected since the COOCH3
group is more electron withdrawing than the Ph group
in styrene and the alkyl chain in 1-octene. Thus, the con-
tribution from p-back bonding increases in 1 and 4 be-
cause the electron density around the double bond is
lower. Basicity of the nitrogen based ligands is another
factor that can effect the relative contribution from p-
back-bonding [5,6]. The vinyl protons of 2 (designated
in Table 2 as HA, HB, and HC) shift upfield approxi-
mately 1.11, 0.68, and 0.96 ppm relative to free styrene.

920
W.A. Braunecker et al. / Journal of Organometallic Chemistry 690 (2005) 916–924
Table 2
Chemical shifts (300 MHz, (CD3)2CO) of vinyl protons in coordinated
monomers
The complexation of MA in 1 results in a decrease in
C@C IR stretching frequencies from 1634 cmꢀ1 to 1524
cmꢀ1 (Dm(C@C) = ꢀ110 cmꢀ1), and the coordination of
MMA in 4 similarly results in a decrease from 1638
cmꢀ1 to 1511 cmꢀ1 (Dm(C@C) = ꢀ127 cmꢀ1). Addition-
ally, the frequencies of vibration of the carbonyl group
in both MA and MMA decrease from 1730 cmꢀ1 to
1710 cmꢀ1 (Dm(C@O) = ꢀ20 cmꢀ1) and from 1726
cmꢀ1 to 1720 cmꢀ1 (Dm(C@O) = ꢀ6 cmꢀ1), respectively,
upon coordination to CuI (Fig. 5). This negative shift
can be attributed to the increased electron density at
the C@C double bond, due to the back-donation from
the metal center. (The NMR analyses of the complexes
(vide supra) demonstrate that this back donation indeed
predominates over the monomer-to-metal electron den-
sity donation.) Similar changes in the carbonyl group
frequency upon altering the electron density at a p-elec-
tron substituent in conjugated carbonyl compounds
have been observed in many instances. The Dm value in
m- or p-substituted benzoic acids [70] or methyl benzo-
HC
HB
HA
R
Complex
dHA (DdHA)a
dHB (DdHB)
dHC (DdHC)
1b
2b
3b
4c
a
4.59 (1.76)
4.78 (1.11)
4.10 (0.87)
4.52 (1.52)
5.09 (1.09)
6.07 (0.68)
5.10 (0.67)
4.32 (1.61)
4.28 (0.96)
4.15 (0.74)
4.40 (1.30)
DdHA = dHA (free MA) ꢀ dHA (observed), ppm.
b
c
ꢀ60 ꢁC.
ꢀ80 ꢁC.
Comparatively, the vinyl protons of the [CuI(2,20-bipyri-
dine)(p-CH2CH(C6H5)][ClO4] complex [66] are less
shielded and the upfield shift of 0.16, 0.03, and 0.19
ppm is less pronounced. Explained in terms of ligand
basicity, the PMDETA ligand, being more basic than
2,2Õ-bipyridine, increases the electron density around
CuI which results in a higher contribution from p-back
bonding and thus stronger shielding.
(a)
The presence of p-back bonding in complexes 1–4 is
further demonstrated by unequal shielding of the vinyl
protons in the coordinated monomers. In the single crys-
tal X-ray structures of 1–3, the Ca was 0.046, 0.056, and
I
˚
0.066 A, respectively, further away from the Cu coordi-
(b)
1634
nation sphere than was the Cb. Because p-back-donation
will have a stronger influence on the chemical shifts of
the protons closer to CuI, the shielding effect is expected
and observed to be the weakest in all the complexes (Ta-
ble 2) at the Ca (DdHB(MA) = 1.09, DdHB(Sty) = 0.68,
DdHB(Oct) = 0.67). This unequal shielding of vinyl pro-
tons was also observed in the aforementioned [CuI(2,20-
bipyridine)(p-CH2CH(C6H5)][ClO4] [66] complex.
-
BPh4
1524
1730
1710
1800
1700
1600
1500
(c)
Wavenumber/ cm -1
2.3. FT-IR spectroscopy
The coordinated C@C bonds in complexes 1–4 were
further examined by IR spectroscopy. The C@C stretch-
ing frequency of Sty decreases from 1630 cmꢀ1 to 1550
cmꢀ1 (Dm(C@C) = ꢀ80 cmꢀ1) upon coordination, and
that of Oct decreases from 1642 cmꢀ1 to 1533 cmꢀ1
(Dm(C@C) = ꢀ109 cmꢀ1). As indicated in the literature,
both r-donation from the monomer and p-back bond-
ing from the metal (the latter which results in the occu-
pation of the p* orbitals of the coordinated monomer)
weaken the C@C bond and decrease its stretching fre-
quency [33,65,67]. This decrease in frequency is a result
of the p-bond formation between vinyl monomer and
the CuI center leading to a decrease in the double bond
character of the coordinated C@C [68] and has been ob-
served previously in CuI olefin complexes [69].
(d)
1638
1511
BPh4-
1726
1720
1700
1800
1600
1500
Wavenumber / cm-1
Fig. 5. Comparison of FT-IR spectra of MA (a), 1 (nujol) (b), MMA
(c), and 4 (KBr pellet) (d).

W.A. Braunecker et al. / Journal of Organometallic Chemistry 690 (2005) 916–924
921
ates [71] has been correlated to the electron-donating
4.2. Preparation of CuI complexes
ability of the substituent attached to the benzene ring
(HammetÕs r-parameter). The carbonyl group frequen-
cies in b-substituted ethyl acrylates similarly decrease
as the electron-releasing ability (either via inductive or
resonance effect) of the substituent increases, i.e., in
the order CF3 (1737 cmꢀ1) > H (1727 cmꢀ1)>Me (1722
cmꢀ1) > EtO (1711 cmꢀ1) [72].
The thermal and photo-stability of these complexes is
currently being investigated. Detailed studies concerning
the equilibrium between free and coordinated mono-
mers and the effect of coordination on the reactivity of
these monomers in free radical polymerizations and
ATRP are currently being carried out.
4.2.1. Synthesis
CuIBr (0.0800 g, 5.58 · 10ꢀ4 mol) was added to a
deoxygenated methanol (10.0 mL)/acetone (2.0 mL)
solution containing (PMDETA) (0.0968 g, 5.58 · 10ꢀ4
mol) at room temperature. The addition of CuIBr re-
sulted in the formation of a light blue homogeneous
solution. One equivalent of monomer was added before
the introduction of one equivalent of NaBPh4 (0.1910 g,
5.58 · 10ꢀ4 mol). Storage in a ꢀ18 ꢁC freezer resulted in
the formation of a precipitate which was filtered and
washed with 15.0 mL of cold methanol and dried under
vacuum for 12 h. Similar procedures were used for the
synthesis of all four complexes.
3. Conclusions
4.2.2. CuI(PMDETA)(p-MA)][BPh4] (1)
The CuI(PMDETA)Br solution changed color to a
light yellow upon the addition of one equivalent of
MA (0.0502 g, 5.58 · 10ꢀ4 mol). The introduction of
NaBPh4 at RT resulted in the formation of a yellow
precipitate, which was dissolved by warming the solu-
tion to 40 ꢁC. When cooled in an H2O/ice bath, yellow
crystalline needles were obtained in one hour to yield
0.272 g (76.1%) of complex 1. 1H NMR (300 MHz,
Investigating the nature of the CuI-olefin bonding of
the four novel CuI complexes 1–4 was the primary objec-
tive in this paper. PMDETA acts as a tridentate ligand,
while the pseudotetrahedral coordination geometry
around CuI is completed by a p-interaction with the
C@C double bond of the coordinated olefin. No interac-
tions are observed between the respective counterions.
No significant lengthening of the C@C vinyl double
bond in MA or Oct upon coordination is observed,
while the C@C bond length in Sty increases from
(CD3)2CO, RT, 0.02 M): d 7.35 (m, 8 o-H, BPhꢀ),
4
6.93 (broad td, Jortho = 7.3 Hz, 8 m-H, BPhꢀ4 ), 6.78
(tt, Jortho = 7.3 Hz, Jmeta = 1.4 Hz, 4 p-H, BPhꢀ4 ), 5.38
(dd, Jtrans = 15.4 Hz, Jcis = 9.2 Hz, 1H, CHCOOMe),
5.07 (broad dd, overlapping, 1H, CHHtrans@CHCO-
˚
1.325(2) to 1.367(3) A. Coordination of the monomers
to CuI results in a decrease in C@C IR stretching fre-
quencies of Dm(C@C) = ꢀ110, ꢀ80, ꢀ109, and ꢀ127
cmꢀ1for complexes 1–4, respectively. The extent to
which the coordinated C@C proton resonances for all
four complexes are shifted upfield, as compared to the
shift in resonances of similar literature compounds, is
indicative of significant p-back-bonding.
OMe),
4.75
(broad
dd,
overlapping,
1H,
CHHcis@CHCOOMe), 3.75 (s, 3H, COOCH3), 2.90 –
2.30
m(C@O) = 1712 cmꢀ1
cmꢀ1, m(C@C) = 1524 cmꢀ1
(br, 23H,
PMDETA). FT-IR
,
(nujol):
mðC@Carom:; BPhꢀ4 Þ ¼ 1579
.
4.2.3. CuI(PMDETA)(p-Sty)][BPh4] (2)
The CuI(PMDETA)Br solution remained a light
homogeneous blue upon the addition of one equivalent
of Sty (0.0639 g, 5.58 · 10ꢀ4 mol). The addition of
NaBPh4 did not form a precipitate, but when the solu-
tion was stored in a ꢀ18 ꢁC freezer for one hour,
white crystalline needles were obtained to yield 0.253
g (68.7%) of complex 2. 1H NMR (300 MHz,
(CD3)2CO, RT, 0.02 M): d 7.55 (broad dt, Jortho = 7.2
Hz, 2 o-H, CH2@CHPh), 7.36 (broad td, Jortho = 7.2
Hz, 2 m-H, CH2@CHPh), 7.33 (m, 9 H, 1 p-H
4. Experimental
4.1. General remarks
All reagents used in this study were obtained from
commercial sources and used without further purifica-
tion. Solvents were distilled and deoxygenated by purg-
ing with nitrogen for at least one hour prior to usage. All
compounds were prepared under a nitrogen atmosphere
using standard Schlenk techniques or in a dry box, un-
less otherwise noted. All 1H NMR spectra were ob-
tained in (CD3)2CO using Bruker Avance DMX-500
(operating at 500.13 MHz) and Bruker Avance AV-
300 (operating at 300.13 MHz) variable temperature
spectrometers and chemical shifts are given in ppm rela-
tive to the residual acetone solvent peak. IR spectra
were obtained with KBr pellets or nujol mulls using an
FTIR-NIR Spectrometer (Mattson ATI Affinity 60AR).
CH2@CHPh and
Jortho = 7.3 Hz, 8 m-H, BPhꢀ4 ), 6.78 (tt, Jortho = 7.3
Hz, Jmeta = 1.4 Hz,
p-H, BPhꢀ4 ), 6.32 (dd,
8
o-H BPhꢀ4 ), 6.93 (broad tt,
4
Jtrans = 16.4 Hz, Jcis = 10.0 Hz, 1 H, CHPh), 5.18
(broad dd, overlapping, 1H, CHHtrans@CH), 4.63
(broad dd, overlapping, 1H, CHHcis@CH), 2.90–2.30
(br, 23H, PMDETA). FT-IR (nujol): mðC@
Carom:; BPhꢀ4 Þ ¼ 1579 cmꢀ1
,
m(C@C, CH2@CH–) =
1550 cmꢀ1
.

922
W.A. Braunecker et al. / Journal of Organometallic Chemistry 690 (2005) 916–924
4.2.4. CuI(PMDETA)(p-Oct)][BPh4] (3)
0.180 g (49.1%) of complex 4. Crystals suitable for X-
ray analysis could not be obtained. 1H NMR (300
MHz, (CD3)2CO, RT, 0.02 M): d 7.35 (m, 8 o-H,
BPhꢀ4 ), 6.93 (broad td, Jortho = 7.3 Hz, 8 m-H, BPhꢀ4 ),
6.78 (tt, Jortho = 7.3 Hz, Jmeta = 1.4 Hz, 4 p-H, BPhꢀ4 ),
5.89 (m, 1H, CHHtrans@CMe), 5.57 (m, 1H,
CHHcis@CMe), 3.70 (s, 3H, OCH3), d 2.80–2.20
(br, 23H, PMDETA), d 1.90 (dd, J = 1.5, 1.0 Hz,
3Hꢀ, 1 CH2=CCH3). FT-IR (KBr): m(C@O) = 1720
cm , mðC@Carom:; BPhꢀ4 Þ ¼ 1579 cmꢀ1, m(C@C) = 1511
No color change from light homogeneous blue was
observed in the CuI(PMDETA)Br solution upon the
addition of one equivalent of Oct (0.0639 g,
5.58 · 10ꢀ4 mol). The introduction of NaBPh4 did not
form a precipitate, but when the solution was stored in
a ꢀ18 ꢁC freezer for one hour, off-white crystalline nee-
dles were obtained to yield 0.205 g (55.0%) of complex 3.
1H NMR (300 MHz, (CD3)2CO, RT, 0.02 M): d 7.35 (m,
8 o-H, BPhꢀ4 ), 6.93 (broad td, Jortho = 7.3 Hz, 8 m-H,
BPhꢀ4 ), 6.78 (tt, Jortho = 7.3 Hz, Jmeta = 1.4 Hz, 4 p-H,
BPhꢀ4 ), 5.39 (m, 1H, @CH–), 4.48 (broad dd,
Jtrans = 17.1 Hz, 1H, CHHtrans@CH), 4.47 (broad dd,
Jcis = 9.9 Hz, 1H, CHHcis@CH), d 3.00–2.40 (br, 23H,
cmꢀ1
.
4.3. X-ray crystal structure analysis
PMDETA),
d
2.07 (dd, J = 14.6, 7.3 Hz, 2H,
The X-ray data were collected at room temperature
for 1 and 3 and at 153 K for 2 on a Bruker-AXS
SMART diffractometer with an APEX CCD area
detector. Graphite-monochromated Mo Ka radiation
(71.073 pm) was used for all measurements. The nom-
inal crystal-to-detector distance was 5.00 cm. A hemi-
sphere of data was collected by a combination of
three sets of exposures at 173 K. Each set had a differ-
ent angle for the crystal, and each exposure took 20 s
and covered 0.3ꢁ in x. The data were corrected for
polarization and Lorentz effects, and an empirical
absorption correction (SADABS) was applied [73]. The
cell dimensions were refined with all unique reflections.
@CHCH2CH2–), 1.43 (m, 2H, @CHCH2CH2), 1.32
(m, 6H, –(CH2)3CH3), 0.90 (t, J = 7.0 Hz, 3H, –CH3).
FT-IR
(KBr):
mðC@Carom:; BPhꢀ4 Þ ¼ 1579 cmꢀ1
,
m(C@C) = 1533 cmꢀ1
.
4.2.5. CuI(PMDETA)(p-MMA)][BPh4] (4)
The CuI(PMDETA)Br solution turned a light green
upon the addition of one equivalent of MMA (0.0597
g, 5.58 · 10ꢀ4 mol). The addition of NaBPh4 did not re-
sult in the formation of a precipitate, but when the solu-
tion was stored in a ꢀ18 ꢁC freezer over night, a light
green-yellow solid precipitate was obtained to yield
Table 3
Crystal data and structure refinement for 1–3
Empirical formula
Formula weight
Crystal system
[C74H96B2Cu2N6O4]
1282.27
[C41H51BCuN3]
660.20
[C41H54BCuN3]
663.22
Triclinic
Monoclinic
P2(1)/c
Orthorhombic
Pbca
ꢀ
Space group
Unit cell dimensions
P1
˚
a (A)
22.593(2)
9.9506(11)
31.989(4)
90
17.479(3)
18.046(3)
22.761(4)
90
11.0904(12)
11.7655(13)
16.7262(19)
80.841(2)
89.442(3)
64.862(2)
1946.5(4)
2
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
100.047(3)
90
90
90
3
˚
Volume (A )
7081.1(13)
4
294(2)
7180(2)
8
153(2)
Z
T/K
Calculated density (g cmꢀ3
Absorption coefficient (mmꢀ1
F(000)
Crystal size (mm)
298(2)
1.132
)
1.203
0.651
2728
1.222
0.641
2816
)
0.591
710
0.80 · 0.70 · 0.06
1.71–24.72
ꢀ21 6 h 6 26
ꢀ11 6 k 6 11
ꢀ37 6 l 6 28
36231
0.36 · 0.28 · 0.10
1.79–28.28
ꢀ23 6 h 6 23
ꢀ14 6 k 6 24
ꢀ30 6 l 6 30
48069
0.33 · 0.27 · 0.22
2.47–23.26
ꢀ12 6 h 6 12
ꢀ13 6 k 6 13
ꢀ14 6 l 6 18
9174
H range for data collection (ꢁ)
Limiting indices
Total reflections
Independent reflections
Goodness-of-fit on F2
R indicies (all data)
12048 [R(int) = 0.0484]
1.012
0.0903
8898 [R(int) = 0.0447]
1.023
0.0653
5558 [R(int) = 0.0207]
1.044
0.0721
Final R indices [I > 2r(I)]
Rw indicies (all data)
0.0539
0.1565
0.0396
0.1097
0.0581
0.1594
Final Rw indices [I>2r(I)]
Largest diff. peak and hole [Aꢀ3
0.1352
0.725 and ꢀ0.537
0.0960
1.246 and ꢀ0.428
0.1490
0.378 and ꢀ0.219
]

W.A. Braunecker et al. / Journal of Organometallic Chemistry 690 (2005) 916–924
923
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(
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rung der wissenschaftlichen Forschung (FWF), Austria
is greatly appreciated. N.V.T. acknowledges support
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