Cationic, neutral, and anionic allyl magnesium compounds: Unprecedented ligand conformations and reactivity toward unsaturated hydrocarbons

Article abstract of DOI:10.1021/ja310112e

Starting from bis(allyl)magnesium [Mg(C₃H₅) ₂], a set of cationic, neutral, anionic, and dianionic allyl magnesium compounds has been isolated and characterized, including [Mg(C ₃H₅)(THF)₅][B(C₆F₅) ₄] (3), [Mg(C₃H₅)₂(1,4-dioxane)(THF) ] (2), [KMg(C₃H₅)₃(THF)] (6), and [MMg(C ₃H₅)₄] (8: M = K₂; 9: M = Ca). In solution, the allyl ligands of the compounds display fluxional behavior, even at low temperatures. Single crystal X-ray analysis reveals unusual μ₂-η¹:η³- and unprecedented μ₃-η¹:η³:η³- coordination modes in the heterobimetallic compounds 6 and [8·(THF) ₂]. Density functional theory calculations confirm that these metal-allyl conformations are energetically stable. The magnesium compounds have been investigated as initiators for butadiene polymerization and ethylene oligomerization. The heterobimetallic compounds display initiation properties, including higher reaction rates, that are distinctively different from those of the monometallic species. Reactivity trends depend on the formal charge of the magnesium compounds (dianionic, higher-order magnesiate > monoanionic, lower-order magnesiate) and on the nature of the counterion (K⁺ > Ca²⁺).

Full text of DOI:10.1021/ja310112e

Subscriber access provided by UNIV OF ALABAMA BIRMINGHAM
Article
Cationic, Neutral, and Anionic Allyl Magnesium Compounds: Unprecedented
Ligand Conformations and Reactivity Towards Unsaturated Hydrocarbons
Crispin Lichtenberg, Thomas Paul Spaniol, Ilja Peckermann, Timothy P. Hanusa, and Jun Okuda
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/ja310112e • Publication Date (Web): 14 Dec 2012
Downloaded from http://pubs.acs.org on December 18, 2012
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a free service to the research community to expedite the
dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts
appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been
fully peer reviewed, but should not be considered the official version of record. They are accessible to all
readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered
to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published
in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just
Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor
changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers
and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors
or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Journal of the American Chemical Society is published by the American Chemical
Society. 1155 Sixteenth Street N.W., Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 37
Journal of the American Chemical Society
1
2
3
Revised
4
5
6
7
Cationic, Neutral, and Anionic Allyl Magnesium
8
9
Compounds: Unprecedented Ligand Conformations and
Reactivity Towards Unsaturated Hydrocarbons
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Crispin Lichtenberg,a Thomas P. Spaniol,a Ilja Peckermann,a Timothy P. Hanusa,b,* and Jun
Okudaa,*
a: Institute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1,
Dꢀ52056 Aachen, Germany
b: Department of Chemistry, Vanderbilt University, Nashville, Tennessee 37235, USA
RECEIVED DATE :
CORRESPONDING AUTHOR FOOTNOTE Institute of Inorganic Chemistry, RWTH
Aachen University, Landoltweg 1, Dꢀ52056 Aachen, Germany. Fax: +49 241 80 92644.
Eꢀmail: jun.okuda@ac.rwthꢀaachen.de.
Department of Chemistry, Vanderbilt University, Nashville, Tennessee 37235, United States.
Eꢀmail: t.hanusa@vanderbilt.edu
Abstract
Starting from bis(allyl)magnesium [Mg(C3H5)2], a set of cationic, neutral, anionic, and
dianionic allyl magnesium compounds has been isolated and characterized, including
[Mg(C3H5)(THF)5][B(C6F5)4] (3), [Mg(C3H5)2(1,4ꢀdioxane)(THF)] (2), [KMg(C3H5)3(THF)]
1
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 2 of 37
1
2
3
4
5
6
7
8
9
(6), and [MMg(C3H5)4] (8: M = K2; 9: M = Ca). In solution, the allyl ligands of the
compounds display fluxional behavior, even at low temperatures. Single crystal Xꢀray
analysis reveals unusual ꢁ2ꢀη1:η3ꢀ and unprecedented ꢁ3ꢀη1:η3:η3 coordination modes in the
heterobimetallic compounds 6 and [8ꢂ(THF)2]. Density functional theory calculations confirm
that these metal–allyl conformations are energetically stable. The magnesium compounds
have been investigated as initiators for butadiene polymerization and ethylene
oligomerization. The heterobimetallic compounds display initiation properties, including
higher reaction rates, that are distinctively different from those of the monometallic species.
Reactivity trends depend on the formal charge of the magnesium compounds (dianionic,
higher order magnesiate > monoanionic, lower order magnesiate) and on the nature of the
counterion (K+ > Ca2+).
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Introduction
As the simplest delocalized carbanion, the allyl anion (C3H5)– is renowned for the flexibility it
displays in its bonding and reactivity in metal complexes. Allyl magnesium complexes, for
example, are commonly used as allyl transfer reagents in organic and organometallic
chemistry.1 Their characteristics in solution and in the solid state have been investigated in
detail.2 Further developments have led to heterobimetallic reagents that show reactivities
distinct from their monometallic components. In particular, different selectivities and
improved functional group tolerance in organic transformations as well as modified activities
and selectivities in polymerization reactions have been reported.3,4
Such heterobimetallic magnesium species can be divided into two classes; firstly, “ate”
compounds with magnesium counterions showing no Mg–allyl interactions; and secondly,
magnesiates with the Mg–allyl bonds remaining intact. Significant differences in terms of
structure and reactivity can be expected for these two types of compounds. Most
heterobimetallic allyl magnesium species that have been investigated belong to the first
2
ACS Paragon Plus Environment

Page 3 of 37
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
category, and heterobimetallic compounds containing [Mg(C3H5)]+, [Mg(C3H5)R2]– or
[Mg(C3H5)R3]2– fragments (R = allyl, alkyl) are rare. A few examples of in situ generated, illꢀ
defined lithium allyl/alkyl magnesiates have been reported as allylation reagents in organic
reactions.3aꢀe However, there are no detailed investigations dealing with the isolation, structure
and reactivity of well defined heterobimetallic compounds containing Mg–allyl bonds. The
development of reagents and catalysts based on earthꢀabundant, nonꢀtoxic metals is obviously
an attractive goal, and toward this end we report the synthesis and characterization of a series
of monocationic, neutral, monoanionic, and dianionic allyl magnesium compounds. These
have been investigated both experimentally and computationally, and their reactivity towards
butadiene and ethylene has been examined.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Results and Discussion
Neutral Allyl Magnesium Compound. Single crystals of a THF/dioxane adduct of
[Mg(C3H5)2] (1) were analyzed for comparison with charged allyl magnesium species.
[Mg(η1ꢀC3H5)2(THF)(ꢃ2ꢀ1,4ꢀdioxane)] (2) crystallizes in the monoclinic space group C2/c
with Z = 4 (Figure 1). The magnesium center is found in a trigonal bipyramidal coordination
geometry with the η1ꢀbound allyl ligands and the THF ligand in the equatorial positions. The
dioxane molecules occupy axial positions and their bridging coordination mode leads to a
oneꢀdimensional coordination polymer of 2 in the solid state. The coordination geometry
around the magnesium center in 2 is closely related to those in the heterobimetallic complexes
[Ln(η3ꢀC3H5)3(ꢃ2ꢀ1,4ꢀdioxane)Mg(η1ꢀC3H5)2(ꢃ2ꢀ1,4ꢀdioxane)1.5] (Ln = Y, La).4e However, in
the latter compounds each magnesium center interacts with three bridging dioxane units,
resulting in a twoꢀdimensional network of dioxaneꢀlinked Mg6Ln4 macrocycles in the solid
state. The Mg–C bond lengths in 2 are similar to those in the above mentioned
heterobimetallic compounds. Mg–O(dioxane) bond lengths in 2 are ca. 0.18 Å longer than the
3
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 4 of 37
1
2
3
Mg–O(THF) bond length, which is due to the weaker donor character of the dioxane ligands
4
5
6
and the fact that they occupy axial positions due to the trans influence.
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 1. Molecular structure of [Mg(η1ꢀC3H5)2(THF)(ꢃ2ꢀ1,4ꢀdioxane)] (2) in the solid state.
Displacement ellipsoids are shown at the 50% probability level. Hydrogen atoms are omitted
for clarity. Selected bond lengths [Å] and angles [°]: Mg1–C1, 2.2021(15); Mg1–O1,
2.0656(17); Mg1–O2, 2.2411(15); C1–C2, 1.4554(15); C2–C3, 1.3429(17); C1–Mg1–C1´,
126.66(7); C1–Mg1–O1, 116.67(4); C1–Mg1–O2, 92.33(4); O2–Mg1–O2´´, 163.59(5).
Cationic Allyl Magnesium Compound. Reaction of bis(allyl)magnesium (1) with one
equivalent of the Brønsted acid [NPhMe2H][B(C6F5)4] in THF allowed the isolation of the
allylmagnesium monocation as a THF adduct, [Mg(C3H5)(THF)5][B(C6F5)4] (3) (Scheme 1).
It is noteworthy that perfluorination of the counterion was necessary, as the analogous
reaction with the [BPh4] counterion led to THFꢀinsoluble products. Colorless 3 is soluble in
THF or dichloromethane, but insoluble in hydrocarbons and reacts with pyridine under
carbometalation.5,6 The allyl ligand in 3 shows fluxional behavior in dichloromethane at
1
temperatures as low as –90 °C as revealed by H NMR spectroscopy. Fluxional behavior of
4
ACS Paragon Plus Environment

Page 5 of 37
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
allyl ligands at low temperature has also been reported for bis(allyl)magnesium,7 whereas the
η1ꢀbonding mode can be frozen out in the case of allyl Grignard reagents.2c Thus, the allyl
exchange rate in allyl magnesium compounds is decreased by substitution of one allyl ligand
for halides rather than by formation of a cation.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Scheme 1. Synthesis of charged allyl magnesium compounds: cationic 3, lower order
(monoanionic) magnesiate 6 as well as higher order (dianionic) magnesiates 8 and 9; [A] =
[B(C6F5)4]; 6: n = 0.5 or 1 (see main text and experimental).
1
The THF ligands in 3 give rise to one set of signals in the H NMR spectrum in CD2Cl2 at
ambient temperature. Upon cooling this sample to –90 °C, the THF resonances first broaden
and finally split into two sets of signals of relative intensity 1:4. This is ascribed to an
octahedral coordination geometry of the magnesium center in solution with the THF ligand
trans to the allyl ligand being distinguishable from the four cisꢀTHF ligands at low
temperature (Scheme 2). For the exchange of THF ligands in cisꢀ and trans positions, a rate
constant of k = 33 s–1 was estimated at the coalescence temperature of TC = –20 °C.
5
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 6 of 37
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Scheme 2. Exchange of THF ligands in cisꢀ and trans positions in compound 3.
The THF ligands of 3 are labile in THFꢀd8 solution and can be substituted for stronger donors
as demonstrated by the formation of [Mg(C3H5)(PMDTA)(THF)][B(C6F5)4] (4) (PMDTA =
N,N,N’,N’,N’’ꢀpentamethyldiethylenetriamine). 4 was analyzed by single crystal Xꢀray
diffraction and crystallizes in the monoclinic space group P21/c with Z = 4. The magnesium
atom shows a coordination number of five and no interactions with the counterion are
observed (Figure 2). The magnesium center is found in a distorted square pyramidal
coordination geometry with the allyl ligand occupying the apical position.8 The
Figure 2. Cationic part of molecular structure of 4 in the solid state. Displacement ellipsoids
are shown at the 50% probability level. Hydrogen atoms are omitted for clarity. Selected bond
lengths [Å] and angles [°]: Mg1–C1, 2.181(3); Mg1–N1ꢀ3, 2.198(3)ꢀ2.295(3); Mg1–O1,
2.127(2); C1–C2, 1.447(5); C2–C3, 1.323(5); C1–Mg1–N1, 108.52(12); C1–Mg1–N2,
103.66(12); C1–Mg1–N3, 120.12(12); C1–Mg1–O1, 98.94(12); N1–Mg1–N2, 80.30(9); N1–
Mg1–N3, 130.32(10); N1–Mg1–O1, 93.19(9); N2–Mg1–N3, 79.26(9); N2–Mg1–O1,
157.39(10); N3–Mg1–O1, 88.96(9); C1–C2–C3, 129.4(3).
6
ACS Paragon Plus Environment

Page 7 of 37
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
allyl ligand adopts an η1ꢀbonding mode with the Mg–C(allyl) bond being slightly shortened
compared to the corresponding value in neutral [Mg(η1ꢀC3H5)2(THF)(ꢃ2ꢀ1,4ꢀdioxane)] (2)
(2.181(3) Å vs. 2.2021(15) Å; vide supra). The preference of the allyl ligand for η1ꢀbonding at
magnesium centers in the presence of donor ligands is well established for neutral
compounds.2f,g Our results indicate that these findings can be extended to monocationic
magnesium species. In comparison, polyhapto bonding has been reported for the related
cyclopentadienyl compound [Mg(η5ꢀC5H5)(PMDTA)][C5H5].9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Monoanionic Allyl Magnesium Compound. The potassium tris(allyl)magnesiate
[KMg(C3H5)3(THF)n] (6) was obtained by reaction of stoichiometric amounts of allyl
potassium (5) with bis(allyl)magnesium (1) in THF (Scheme 1). 6 contains stoichiometric
amounts of THF (n = 1) when crystallized and dried at ambient pressure, and
substoichiometric amounts of THF (n = 0.5) when dried in vacuo. The magnesiate is soluble
in THF, insoluble in diethyl ether or hydrocarbons and reacts under carbometalation with
pyridine.5,10 The allyl ligands in 6 show fluxional behavior in THF solution as revealed by an
1
AX4 pattern in the H NMR spectrum, which only shows slight broadening of the signals at
temperatures as low as –95 °C. Thus, no experimental indications could be obtained that 6
undergoes equilibrium reactions to reform the starting materials 1 and 4.
Single crystals of 6 (n = 1) were obtained by gas phase diffusion of toluene into a solution
of 6 in THF at ambient temperature. 6 crystallizes in the monoclinic space group P21/m with
Z = 2 (Figure 3). The atoms Mg1, K1, O1, and C1 are located within a crystallographic mirror
plane. Mg1 is tetrahedrally coordinated by the THF ligand and by three η1ꢀbonded allyl
ligands.11 The potassium center K1 is coordinated by allyl ligands of four different
[Mg(C3H5)3(THF)]– units. The allyl ligands show η3ꢀ, η2ꢀ, and weak η1ꢀinteractions12 with K1
resulting in a distorted octahedral coordination geometry. This is the first example of one
metal center interacting with six allyl ligands.
7
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 8 of 37
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 3. Molecular structure of 6 in the solid state. a) Coordination geometry around Mg and
K. Displacement ellipsoids are shown at the 30% probability level. Hydrogen atoms are
omitted for clarity; disordered carbon atoms are shown with one split position. Atoms that
exceed one formula unit of 6 are drawn as empty ellipsoids. b) Two dimensional arrangement
of 6 in the solid state. Carbon atoms are shown in wire frame model. Allyl I, II(‘) refers to C1ꢀ
3, and C4(‘)ꢀ6(‘), respectively. Selected bond lengths [Å] and angles [°]: Mg1–C1, 2.238(5);
Mg1–C4, 2.212(4); Mg1–O1, 2.068(4); K1–C2, 3.575(6); K1–C3, 3.129(6); K1–C1’,
3.103(5); K1–C2’, 3.111(6); K1–C3’, 3.466(6); K1–C4’, 3.791(4); K1–C4’’, 3.179(4); C4–
Mg1–C4’, 122.6(2); C4–Mg1–O1, 106.49(11).
Compound 6 displays two different kinds of allyl ligands in the solid state.13 Firstly, two
allyl ligands (Allyl II,II’) interact with two different metal centers (with Mg (η1) and with K
(η3)) resulting in a ꢃ2ꢀη1:η3ꢀcoordination mode (Figure 3). Only few examples of complexes
containing functionalized allyl ligands have been reported to adopt this coordination
mode.2e,f,14 6 is the first example of the parent allyl ligand to show this structural feature.15
Secondly, one allyl ligand in 6 (Allyl I) interacts with three metal centers (with Mg (η1) and
with K (η2,η3)) resulting in a ꢃ3ꢀη1:η2:η3ꢀcoordination mode (Figure 3). Such a coordination
mode of the allyl ligand is unprecedented and adds a new facet to the coordination chemistry
8
ACS Paragon Plus Environment

Page 9 of 37
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
of this small πꢀelectron system. The average Mg1–C bond length of 2.23 Å (ranging from
2.212(4) to 2.238(5) Å) is much larger than the corresponding value of 1.996(8) Å in the only
other fully characterized charged allyl magnesium species, [Mg(C3H5)4]2–.16 This is ascribed
to the simultaneous interaction of the allyl ligands in 6 with two or three metal centers,
whereas the allyl ligands in the previously reported [Mg(C3H5)4]2– dianion bind exclusively to
one magnesium center. The effect of elongated metal carbon bonds due to interaction of one
allyl ligand with multiple metal centers is also observed for the K–C distances in 6, which
range from 3.103(5) Å to 3.575(6) Å. The highest values exceed K–C distances found for η3ꢀ
allyl potassium compounds (2.87 Å ꢀ 3.15 Å),17 but fall into the range of K–Colefin bonding
(cut off value: K–C, 3.57 Å).18 The C–C distances in the allyl ligands hint at predominant
charge localization at the terminal carbon atom bound to Mg, which agrees with the
literature.2f,14,19 The bridging bonding modes of the allyl ligands lead to a two dimensional
network of 6 in the solid state (Figure 3b). Potassium centers are connected via allyl ligands
(Allyl I) to form an infinite chain along the aꢀaxis. In perpendicular direction, the potassium
and magnesium centers are linked by allyl ligands (Allyl II,II’) to form infinite
K/Allyl II/Mg/Allyl II’ chains along the bꢀaxis.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Dianionic Allyl Magnesium Compounds. Reaction of bis(allyl)magnesium with two
equivalents of allyl potassium (5) or one equivalent of bis(allyl)calcium (7) in THF gave the
dipotassium
tetrakis(allyl)magnesiate
[K2Mg(C3H5)4]
(8)
and
calcium
tetrakis(allyl)magnesiate [CaMg(C3H5)4] (9), respectively (Scheme 1).20 The allyl ligands in 8
and 9 show fluxional behavior at ambient temperature in THF as indicated by an AX4 signal
pattern in the 1H NMR spectrum. The signals only broaden at temperatures as low as –95 °C.
Thus, no experimental indication could be obtained that 8 or 9 undergo equilibrium reactions
to reform monometallic starting materials 1, 5 and 7, respectively. In case of 9 a composition
Ca[Mg(C3H5)4] is assumed, rather than the presence of an ion pair such as
9
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 10 of 37
1
2
3
1
Ca(C3H5)][Mg(C3H5)3], as the H NMR resonances of the allylcalcium monocation clearly
4
5
6
shows a different coupling pattern in THFꢀd8.21
7
8
9
Single crystals of [8ꢂ(THF)2] were obtained by cooling a saturated solution in
THF/pentane to –30 °C. [8ꢂ(THF)2] crystallizes in the monoclinic space group P21/c with Z =
4 (Figure 4). The magnesium center interacts with four allyl ligands in an η1ꢀfashion resulting
in a distorted tetrahedral coordination geometry (Figure 4a). No Mg–THF interactions are
observed in the solid state, which is in contrast to the bonding situation found in monoanionic
tris(allyl)magnesiate 6. One of the crystallographically independent potassium atoms in
[8ꢂ(THF)2], K1, is coordinated by one THF ligand and by four allyl groups (1 × η2; 3 × η3)
resulting in a distorted trigonal bipyramidal coordination geometry with the η2ꢀallyl and the
THF ligand in the axial positions. Three of the allyl ligands bind to K1 as donors of a
chelating [Mg(C3H5)4]2– group (Allyl IꢀIII; Figure 4a). The fourth allyl group, Allyl IV, acts
as a bridging ligand between K1 and a neighboring Mg1’. The second potassium center, K2,
interacts with three allyl ligands (3 × η3) of three different neighboring [Mg(C3H5)4]2– units
and with one THF molecule, resulting in a distorted tetrahedral coordination geometry (Figure
4b). The allyl ligands in [8ꢂ(THF)2] show two different types of coordination modes in the
solid state, resembling the bonding situation found for 6 (vide supra). (i) Allyl IV interacts
with two different metal centers resulting in a ꢃ2ꢀη1:η3ꢀcoordination. (ii) Allyl IꢀIII interact
with three metal centers in a ꢃ3ꢀη1:η2:η3ꢀ or ꢃ3ꢀη1:η3:η3ꢀfashion. The Mg–C distances in
[8ꢂ(THF)2] range from 2.175(18) to 2.41(4) Å and average 2.27 Å, which is clearly elongated
compared those in the previously reported [Mg(C3H5)4]2– ion.16 K–C distances range from
2.932(13) Å to 3.481(7) Å. The highest values are larger than K–C distances found for η3ꢀ
allyl potassium compounds (2.87 Å ꢀ 3.15 Å),17 but fall into the range of K–Colefin bonding
(cut off value: K–C, 3.57 Å).18 As in case of compound 6, the effect of elongated M–C
distances was ascribed to each allyl ligand interacting with two or three metal centers. In
agreement with the literature, the allyl ligands in [8ꢂ(THF)2] show strongly localized C–C
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
10
ACS Paragon Plus Environment

Page 11 of 37
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 4. Cutouts of solid state structure of [K2Mg(C3H5)4(THF)2] ([8ꢂ(THF)2]).
Displacement ellipsoids are shown at the 50% probability level. Hydrogen atoms are omitted
for clarity, disordered carbon atoms are shown with one split position Coordination
geometries around Mg1 and K1 (a) and K2 (b). Atoms that exceed one formula unit of
[8ꢂ(THF)2] are drawn as empty ellipsoids. c) Arrangement of ([8ꢂ(THF)2] as a three
dimensional coordination polymer with carbon atoms shown as wire frame (Callyl) or omitted
for clarity (CTHF). Allyl IꢀIV refers to C1ꢀ3, C4ꢀ6, C7ꢀ10, and C10ꢀ12, respectively. Selected
bond lengths [Å] and angles [°]: Mg1–C1, 2.253(6); Mg1–C4, 2.254(6); Mg1–C7A, 2.29(2);
Mg1–C7B, 2.26(3); Mg1–C10A, 2.175(18); Mg1–C10B, 2.41(4); K1–C1, 3.301(6); K1–C2,
3.144(6); K1–C3, 3.082(6); K1–C4, 3.481(7); K1–C5, 3.135(7); K1–C6, 3.044(7); K1–C7A,
3.87(3); K1–C8A, 3.155(8); K1–C9A, 3.22(7); K1–C10A, 3.242(18); K1–C11A, 3.056(9);
K1–C12A, 3.18(2); K1–O1, 2.671(4); K2–C1, 3.165(6); K2–C2, 3.039(6); K2–C3, 3.243(6);
K2–C4, 3.334(6); K2–C5, 3.049(8); K2–C6, 3.082(7); K2–C7A, 3.06(2); K2–C8A, 2.991(8);
K2–C9A, 3.14(7); K2–O2, 2.709(4); C1–C2, 1.447(8); C2–C3, 1.311(9); C4–C5, 1.454(10);
C5–C6, 1.306(11); C7A–C8A, 1.52(3); C8A–C9A, 1.37(6); C10A–C11A, 1.441(19); C11A–
C12A, 1.37(2).
11
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 12 of 37
1
2
3
4
5
6
7
8
9
bonds (ꢄC–C = 0.07 Å to 0.15 Å).2f,14 The bridging bonding modes of the allyl ligand result in
a three dimensional network of [8ꢂ(THF)2] in the solid state (Figure 4c).22 Specifically,
infinite chains of Allyl II/K1,Mg1/Allyl I/K2 along the aꢀaxis, K1,Mg1/Allyl III/K2 along the
bꢀaxis, and K1/Allyl IꢀIII/Mg1/Allyl IV along the cꢀaxis are observed. Neighboring chains
along the aꢀaxis are related by a glide reflection along the bꢀaxis. Only a few organometallic
ate compounds of group 2 metals have been shown to form one23 or two dimensional24
carbanionꢀbridged coordination polymers in the solid state. While 6 adds to the examples of
the latter category, the solid state structure of [8ꢂ(THF)2] demonstrates that well defined threeꢀ
dimensional networks can also be formed by this class of compounds. This is possible due to
the unprecedented ꢃ3ꢀη1:η2(3):η3ꢀcoordination mode of the allyl ligand found for [8ꢂ(THF)2]
(and for 6), in which the (C3H5)– fragment acts as a Tꢀshaped linker between three different
metal centers.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Computational Results. The unusual metal–ligand bonding arrangements displayed by the
allyls in the polymeric structures of 6 and 8 were investigated with a series of DFT
calculations on various discrete model compounds. As the goal was to reproduce specific
metal–allyl arrangements, rather than to duplicate exactly the coordination environments
around the metals, in some cases methyl groups and additional THF ligands were used to
complete the metal coordination spheres.
A. The Mg/K ꢀ2ꢁη1:η3ꢁallyl interaction. Attempts to model the ꢁ2ꢀη1:η3 interaction
(found in both 6 and 8) with a MgR2 (R = CH3, C3H5, or H) fragment and K+ placed on
opposite sides of a (C3H5)– anion were unsuccessful. Regardless of the asymmetry of the
starting conformation, geometry optimization consistently led to ꢁ2ꢀη3:η3 structures with the
Mg and K atoms centered or nearly centered over the allyl plane (see Supporting Information
for an example). The results reflect the preference for Mg to engage in symmetrical η3
bonding to allyls in the absence of sufficient perturbation (e.g., coordinated ethers).2f This
12
ACS Paragon Plus Environment

Page 13 of 37
Journal of the American Chemical Society
1
2
3
4
5
contrasts with the behavior of allyl zinc compounds which favor σꢀtype M–allyl interactions
regardless of the presence of donor ligands.25
6
7
8
9
Addition of a single THF to the MgR2 fragment causes a shift to a stable ꢁ2ꢀη1:η3
interaction (10a, Figure 5a). The asymmetric position of the Mg relative to the allyl is evident
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
…
in the Mg–C1 distance of 2.416 Å and the Mg C2 separation of 2.900 Å; the corresponding
(a)
(b)
(c)
(d)
Figure 5. Calculated structures of Mg/K allyl complexes: (a) 10a [(CH3)2Mg(THF)(C3H5)K];
(b) 10b [(C3H5)Mg(C3H5)2K(C3H5)K(THF)3] (hydrogen atoms have been omitted from the THF
ligands for clarity); (c) 10c and (d) 10d [(C3H5)Mg(C3H5)2K(C3H5)][K(THF)6] (only the oxygen
atoms of the THF ligands are shown; dotted lines represent closest approaches of the potassium
to the allyl ligands).
13
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 14 of 37
1
2
3
4
5
6
7
8
9
Mg–C1–C2 angle is 94.9°. The small difference between the C–C bonds in the allyl (C1–C2 =
1.412 Å; C2–C3 = 1.390 Å) suggests that the π electrons in the ligand are largely delocalized.
The potassium is still nearly centered over the allyl plane (K–C1 = 2.810 Å; K–C3 = 2.788
Å).
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Additional analysis supports the bonding picture suggested by the geometric parameters.
The NalewajskiꢀMrozek (NꢀM) bond index, which takes into account both covalent and ionic
contributions to bonding,26 is useful in this regard. The NꢀM indices between the Mg–
C(methyl) bonds average 0.51; in contrast, the Mg–C1 and K–C1 bond indices are 0.10 and
0.17, respectively, indicating weak but not negligible interaction between the atoms (that
between Mg and the oxygen in the THF, for example, is 0.12).
B. The Mg/K2 ꢀ3ꢁη1:η3:η3ꢁallyl interaction. As with the ꢁ2ꢀη1:η3 interaction, attempts to
model a trimetallic ꢁ3ꢀη1:η3:η3 arrangement using only the metals and allyl anions (i.e., with
[K(η3ꢀC3H5)K]+ and [Mg(C3H5)3]– fragments) were not successful. With THF ligands added
to one of the potassium centers, however, stable arrangements displaying allyl ꢁ3ꢀη1:η3:η3
interactions could be generated. With three THFs, structure 10b (Figure 5b) is obtained. K2 is
η3–bonded to C1/C3 at distances in the narrow range from 3.085 Å to 3.090 Å. K1 is also η3–
bonded to C1/C3, but over a larger range (2.955 Å–3.197 Å); the bond distances in the allyl
are consistent with substantial localization of the πꢀelectrons (C1–C2 = 1.521 Å; C2–C3 =
1.388 Å). In addition, K1 is η3–bonded to C7/C9 (2.986 Å–3.066 Å), and the πꢀelectrons in
C7/C9 are also localized (C7–C8 = 1.450 Å; C8–C9 = 1.364 Å). K1 displays a contact to C6
at 3.201 Å; contact distances to C4 and C5 are >3.5 Å, and can be considered to be
nonbonding. The Mg–C1 contact is 2.626 Å, which is substantially longer than the bonds
from Mg to C4, C7, and C10 (2.191–2.414). In total, the allyls in contact with Mg display
four different bonding modes: ꢁ3ꢀη1:η3:η3, ꢁ2ꢀη1:η3, ꢁ2ꢀη1:η1, and simple η1. In addition, the
14
ACS Paragon Plus Environment

Page 15 of 37
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
experimentally observed trend that M–allyl bond lengths increase with the number of metal
centers interacting with the allyl ligand was reproduced in the calculated model compounds.
The NꢀM bond indices generally support the bonding picture suggested by the geometric
parameters. The Mg–C1 index is 0.16, roughly half the average of the Mg–C(4,7,10) values
(0.31), but about the same as the average K2–O(THF) indices (0.13). There is no evidence,
either in 10b or in the structures below, for any substantial interaction between Mg and K1.
The addition of more THF molecules to K2 provides some simulation of the effect of
solvation, and a measure of the robustness of the metal–allyl interactions. With three more
THF ligands on K2, the resulting structure minimizes to that of 10c (Figure 5c). Although
complete separation of charged fragments will not occur under the (gasꢀphase) conditions of
the calculations, analysis of the interactions suggests that appreciable fractionation into
[KMg(C3H5)4]– and [K(THF)6]+ units has occurred. One metric for this is the distance from
K1 to K2, which is 5.21 Å in 10b, but 5.68 Å in 10c. In addition, the average K2–C distance
has increased from 3.088 Å in 10b to 3.159 Å in 10c. Based on distance criteria, the
interaction of K1 with the C1/C3 allyl is now η2; i.e., K1–C3 = 3.082 Å, K1–C2 = 3.091 Å,
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
27
3
…
but K1 C1 = 3.554 Å. The bonding of K1 to the C7/C9 allyl is η (distances range from
3.009ꢀ3.115 Å); the same is true for the C4/C6 allyl (distances range from 3.023ꢀ3.056 Å).
The Mg–C1 distance is 2.376 Å, a shrinkage of 0.25 Å from the value in 10b. The NꢀM bond
index for Mg–C1 has slightly increased to 0.19, and is now appreciably larger than the
average K2–O(THF) indices (0.08), which have collectively weakened compared to the value
in 10b (this mirrors the longer average K–O bond length in 10c (3.04 Å) compared to 10b
(2.72 Å).
Owing to the highly polarized bonding associated with the K+ and Mg2+ cations, ligand
rearrangements need not require much energy in these systems. For example, with a slightly
different arrangement of the THF ligands (obtained by successively adding THFs to 10b, and
reminimizing the energy after each addition), structure 10d (Figure 5d) is obtained. The
15
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 16 of 37
1
2
3
4
5
6
7
8
9
immediately obvious difference from 10c is that K2 is η1ꢀbonded to C1/C3; the distance to C1
is 3.211 Å, but that to C2 and C3 is >4.3 Å. K1 remains η3ꢀbonded to C1/C3, although in a
slightly distorted fashion (2.959ꢀ3.180 Å); it is also η3–bonded to C7/C9 over a narrower
range (2.954ꢀ3.055 Å). The Mg–C1 distance is now 2.405 Å. The NꢀM bond indices support
these structural assignments; the K2–C1 index is 0.03, consistent with very weak η1ꢀbonding
between the metal and allyl, and the interaction of Mg–C1 has a bond index of 0.21,
compared to an average of 0.29 for the bonds from Mg to C4, C7, and C10.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The sensitivity of the allyl alignments to the number of THFs on the potassium reflects the
relatively flat potential energy surface associated with the Mg2+ and K+ centers. Despite what
appears to be substantial differences in the bonding arrangements of 10c and 10d, particularly
as regards the relationship of K2 to the C1/C3 allyl, both represent local minima on their
potential energy surfaces (Nimag = 0), and the two structures differ by only 2.5 kcal mol–1 in
∆H° (1.1 kcal–1 mole in ∆G°; 10d is the lower). The small energy difference between the two
structures underscores the weak association of the [KMg(C3H5)4]– and (highly distorted)
[K(THF)6]+ fragments.
Butadiene Polymerization. Heterobimetallic allyl ate compounds of rare earth elements
containing magnesium as the counterion have been investigated in detail as initiators for
isoprene (co)polymerization.4a,c,f,g In contrast, similar investigations of magnesium based
initiators containing Mg–C bonds are rare. Hsieh and coworkers reported on lithium
(alkyl)magnesiate species as initiators for butadiene polymerization, which exhibit properties
in these reactions that differ from those of their monometallic components.28 However, the
focus of that work was dedicated to the polymerization studies. The ate compounds were
generated in situ by reaction of [Mg(nBu)2] with [Li(nBu)], have not been characterized, and
remain illꢀdefined. The K–allyl interactions found in the solid state structures of 6 and
[8ꢂ(THF)2] encouraged us to compare the reactivity of cationic 3 and 4, lower order
(monoanionic) magnesiate 6, and higher order (dianionic) magnesiates 8 and 9 towards the
16
ACS Paragon Plus Environment

Page 17 of 37
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
simple delocalized πꢀelectron system butadiene (BD). Cationic 3 and 4 showed no reaction
with BD in coordinating or weakly coordinating solvents (Table 1, entry 1).29 Monoanionic 6
polymerized BD in THF solution at 0 °C in a rapid, exothermic reaction to give polybutadiene
(PBD) with a low polydispersity index (PDI) of 1.04 and a high 1,2ꢀPBD content of 69%
(entry 2). When dianionic potassium magnesiate 8 was used as an initiator, PBD with similar
properties was obtained at a higher rate (entry 3).30 BD polymerization initiated by the
dianionic calcium magnesiate 9 gave PBD of higher 1,2ꢀPBD content, lower molecular
weight, and a slightly increased PDI at higher temperature and prolonged reaction times
(entry 4). The living polymerization reactions initiated by 6, 8, and 9 show first order kinetics
revealing reaction rates of k(8, –25 °C)31 = 1.6 s–1, k(6, 0 °C) = 6.9×10–1 s–1, k(9, 45 °C) =
8.7×10–5 s–1 (for details see Supporting Information). Differences in the reactivity of higher
order magnesiates 8 and 9 might be due to differences in the strength and polarity of the M–C
interactions (M = K, Ca). Furthermore, equilibria between the higher order magnesiates and
their corresponding lower order magnesiates and neutral compounds might play a role.32
Altogether these results reveal that (i) in contrast to cationic allyl magnesium compounds,
anionic allyl magnesium species initiate BD polymerization, (ii) the rate of reaction is higher
for dianionic than for monoanionic potassium magnesiates,33 and (iii) the counter ion (K+ vs.
Ca2+) is crucial for determining reaction rates and to a lesser extent the selectivities of BD
polymerization initiated by dianionic magnesiates. The BD polymerization initiators 6, 8, and
9 may be compared to literature known catalyst systems for this reaction. The production of
PBD with high contents of transꢀ1,4ꢀPBD (94%),34 cisꢀ1,4ꢀPBD (>99.9%),35,36 atactic 1,2ꢀ
PBD (100%),37 syndiotactic 1,2ꢀPBD (99.7% 1,2ꢀPBD; 99.6% syndiotacticity),38 and isotactic
1,2ꢀPBD (97ꢀ99% 1,2ꢀPBD; 99% isotacticity)39 has been reported. The microstructure of the
PBD obtained from reactions initiated by 6, 8, and 9 (69ꢀ77% 1,2ꢀPBD) is similar to that of
PBD produced with alkyllithium initiators in polar media such as THF.40,41,42 For further
comparison, the monometallic components of heterobimetallic compounds 6, 8, and 9 were
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
17
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 18 of 37
1
2
3
4
5
6
7
8
9
also tested as initiators for BD polymerization. As expected, [Mg(C3H5)2] (1) did not react
with butadiene under given conditions (entry 5). [K(C3H5)] (5) did not initiate BD
polymerization under standard conditions (entry 6),43 but PBD with a slightly increased PDI
was obtained upon increasing the catalyst loading (entry 7), revealing the high sensitivity of 5
towards trace impurities in the monomer solution. In turn, this demonstrates the increased
robustness of compounds 6 and 8. [Ca(C3H5)2] (7) has been reported to act as an initiator for
BD polymerization (entry 8).44 In comparison, heterobimetallic 9 gave PBD with a lower PDI
value and a higher 1,2ꢀPBD content at a significantly higher rate. In summary, properties
distinct from their monometallic components have been revealed for heterobimetallic
compounds 6 and 8 (higher robustness, lower PDI) as well as 9 (higher reaction rate, higher
1,2ꢀPBD content, lower PDI) when applied as initiators for BD polymerization.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Table 1. Butadiene polymerization with initiators 1 and 3ꢀ9.
Initiator
[BD] /
[Initiator]
T
t
Yield
[%]
Microstructure of PBD [%]
Mn
[g/mol]
Mw/Mn
[°C] [min]
1,2ꢀ
ꢀ
cisꢀ1,4ꢀ
transꢀ1,4ꢀ
1a
2
[Mg(C3H5)(THF)5][A] (3)
200
200
200
200
45
0
1200
4
0
ꢀ
ꢀ
ꢀ
ꢀ
>99
97
69
71
77
17
18
14
14
11
9
17300
24600
7800
1.04
1.04
1.10
[KMg(C3H5)3(THF)0.5] (6)
3
[K2Mg(C3H5)4] (8)
[CaMg(C3H5)4] (9)
0
1
4
45
540
>99
5
6
[Mg(C3H5)2] (1)
[K(C3H5)] (5)
[K(C3H5)] (5)
[Ca(C3H5)2] (7)
200
200
50
45
0
1200
4
0
0
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
7
0
4
>99
75
67
47
12
17
21
36
9200
39700
1.17
1.21
844
200
45
1200
BD = butadiene; PBD = polybutadiene; [A] = [B(C6F5)4]; reactions carried out in THF;
a: no reaction of 3 or 4 with BD was observed in reaction times of t > 1 d at temperatures of
up to 50 °C (sealed tube), when CD2Cl2 was used as a solvent.
Reactivity Towards Ethylene. Reactivity studies of potassium, magnesium, and calcium
compounds towards ethylene are rare. Cumylpotassium has been investigated as an initiator
for the copolymerization of αꢀmethylstyrene and ethylene at ambient temperature giving an
18
ACS Paragon Plus Environment

Page 19 of 37
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
oligormer (Mn = 605 g/mol) with a low ethylene content of 15% corresponding to ca. one
ethylene unit per oligomer in a slow reaction (t = 12 d).45 Under more forcing conditions (60
°C, 40 bar C2H4), organoalkali compounds catalyze the oligoethylation of aromatic
hydrocarbons.46 While organomagnesium species alone have been reported to react with
ethylene under high pressures at elevated temperature,47 aryl Grignard reagents carbometalate
ethylene in the presence of transition metal salts under less forcing conditions.5,48 In this
context, the allyl compounds that initiated the polymerization of BD were also tested in their
reactivity towards ethylene. The calcium compound [Ca(C3H5)2] (7) was reported not to react
with ethylene.49 [CaMg(C3H5)4] (9) did not react with ethylene either (THF, r.t., 2 bar
ethylene).50 Under identical conditions, the more reactive potassium compounds [K(C3H5)]
(5), [KMg(C3H5)3(THF)0.5] (6), and [K2Mg(C3H5)4] (8) reacted with ethylene under
carbometalation (Figure 6, for extended time conversion plots see Supporting Information).5
This reaction was extremely slow, but selective for lower order magnesiate 6 (insertion of 2
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1
equiv. of ethylene after t = 25 d, no side products detected by H NMR spectroscopy, for
details see Supporting Information). Organopotassium compound 5 expectedly showed an
increased reactivity, but formation of side products was observed at early stages of the
reaction (after consumption of 0.2 equiv. of ethylene). GC/MS analysis of the reaction
19
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 20 of 37
1
2
3
Figure 6. Course of reaction of compounds 5, 6, and 8 with ethylene.5
4
5
6
7
8
mixture after aqueous workup revealed a mixture of C5ꢀ11ꢀhydrocarbons resulting from
multiple insertion of ethylene as the main components (for details see Supporting
Information). For higher order magnesiate 8, the rate of ethylene consumption is similar to
that of 5. However, selective monoinsertion is observed up to consumption of ca. 2 equiv. of
ethylene, which was ascribed to the stabilizing effect of the magnesiate component. After
prolonged reaction times, the reaction mixture was quenched with water and analyzed by
GC/MS revealing a mixture of C5ꢀ11 hydrocarbons similar to that observed in case of 5 (for
details see Supporting Information). Thus, allyl potassium (5) and higher order magnesiate 8
insert ethylene more readily than cumyl potassium45 and under milder conditions than neutral
magnesium compounds such as [Mg(nBu)2] or [Mg(nBu)Br],47 but are significantly less
active than any transition metal based catalysts.51
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Conclusion
In order to clarify the structure and reactivity of heterometallic allyl complexes containing
magnesium, a series of cationic, neutral, anionic and dianionic compounds has been isolated
and characterized. Potassium or calcium centers balance the charge in case of the magnesiate
complexes. In solution, the allyl ligands of all magnesium compounds show fluxional
behavior, even at temperatures ≤ –90 °C.7 In the solid state, the allyl magnesium compounds
evidence the structural diversity of the allyl ligand as typical molecular structures (η1ꢀ
coordination; cationic and neutral compounds) and coordination polymers (ꢁ2ꢀη1:η3ꢀ and ꢁ3ꢀ
η1:η3:η3ꢀcoordination; lower order (monoanionic) and higher order (dianionic) magnesiates)
are observed. A description of the bonding situation in the unusual ꢁ2ꢀη1:η3ꢀ and the
unprecedented ꢁ3ꢀη1:η3:η3 coordination mode has been derived from structural parameters
obtained by single crystal Xꢀray crystallography in combination with DFT calculations on
20
ACS Paragon Plus Environment

Page 21 of 37
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
model compounds. The latter confirm that the metal–allyl interactions can be replicated in
discrete molecules, and are not simply artifacts of the extended structures observed in the
solid state. All magnesium compounds have been investigated as initiators for butadiene
polymerization. Cationic [Mg(C3H5)(THF)5][B(C6F5)4] and neutral [Mg(C3H5)2] do not
initiate the polymerization of butadiene under the chosen conditions, but the heterobimetallic
compounds [KMg(C3H5)3(THF)n] (6, n = 0.5, 1), [K2Mg(C3H5)4] (8), and [CaMg(C3H5)4] (9)
give polybutadiene (PBD) with low polydispersity indices below 1.10 and high 1,2ꢀPDB
contents up to 77%. These compounds show initiation properties that are distinct from their
monometallic components, such as increased robustness and higher reaction rates. The
counterions, K+ vs. Ca2+, and the formal charge of the magnesiate have a strong effect on the
reaction rates (K+ > Ca2+; higher order > lower order magnesiate). Whereas the calcium
magnesiate 9 does not react with ethylene, [K(C3H5)] (5) and the potassium magnesiates 6 and
8 react under insertion of 1 ethylene unit in case of 6 and 1ꢀ4 ethylene units per allyl ligand in
case of 5 and 8. Taken together, these results should broaden our understanding of the metalꢀ
ligand relationships that emerge from the interaction of multiple dissimilar metals and the
allyl anion. This knowledge should help the design of new active catalyst incorporating the
earthꢀabundant sꢀblock metals.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Experimental
General Remarks. All operations were carried out under argon using standard Schlenkꢀline
and glovebox techniques. Starting materials were purchased from Sigma Aldrich or Boulder
Scientific and purified following standard laboratory procedures. [Mg(C3H5)2] (1),
[Ca(C3H5)2] (7), and [K2Mg(C3H5)4] (8) were prepared according to the literature.2c,20,44a Nonꢀ
deuterated solvents were purified using an MB SPSꢀ800 solvent purification system. THFꢀd8
was distilled from sodium benzophenone ketyl. CD2Cl2 and pyridineꢀd5 were distilled from
21
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 22 of 37
1
2
3
CaH2. All NMR spectra were recorded at ambient temperature (if not stated otherwise) using
4
5
6
7
1
13
a Bruker Avance II 400 MHz spectrometer. The chemical shifts of H and C NMR spectra
were referenced internally using the residual solvent resonances and are reported relative to
8
9
1
the chemical shift of tetramethylsilane. The resonances in H and 13C NMR spectra were
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
assigned on the basis of two dimensional NMR experiments (COSY, HMQC, HMBC). The
11B NMR resonances are reported relative to an external standard (an ethereal solution of
[BF3ꢂEt2O]). Metal titrations were performed according to the literature. Molecular weights
and polydispersities were determined by size exclusion chromatography in THF at ambient
temperature, at a flow rate of 1 mL/min utilizing an Agilent 1100 Series HPLC, G1310A
isocratic pump, an Agilent 1100 Series refractive index detector (at 35 °C) and 8 × 600 mm, 8
× 300 mm, 8 × 50 mm PSS SDV linear M columns. Calibration standards were commercially
available narrowly distributed linear polystyrene samples that cover a broad range of molar
masses (103 < Mn < 2×106 g/mol). Microstructure determinations were performed according
to the literature.52
[Mg(η1ꢁC3H5)2(THF)(ꢂ2ꢁ1,4ꢁdioxane)] (2). Single crystals of 2 were obtained from a
concentrated solution of [Mg(C3H5)2] (1) in THF/dioxane at –30 °C. Anal. calcd. for
C14H26MgO3 (266.66 g/mol): C, 63.06; H, 9.83; found: C, 62.31; H, 9.78.
[Mg(η1ꢁC3H5)(THF)5][B(C6F5)4] (3). A solution of [NPhMe2H][B(C6F5)4] (350 mg, 0.44
mmol) in THF (1.0 mL) was added to a solution of [Mg(C3H5)2] (47 mg, 0.44 mmol) in THF
(0.5 mL). The reaction mixture was filtered. The filtrate was concentrated under reduced
pressure to a volume of 1.0 mL. Upon addition of pentane (10 mL), a colorless solid
precipitated, which was filtered off, washed with pentane (3 × 2.0 mL) and dried in vacuo.
Yield: 449 mg, 0.41 mmol, 93%.
1H NMR (400.1 MHz, THFꢀd8): δ = 1.75ꢀ1.80 (m, 20H, βꢀTHF), 2.43 (d, 3JHH = 11.4 Hz, 4H,
CH2CHCH2), 3.60ꢀ3.64 (m, 20H, αꢀTHF), 6.28 (quint, 3JHH = 11.4 Hz, 1H, CH2CHCH2) ppm.
3
1H NMR (400.1 MHz, CD2Cl2, 23 °C): δ = 2.02ꢀ2.05 (m, 20H, βꢀTHF), 2.56 (d, JHH = 11.3
22
ACS Paragon Plus Environment

Page 23 of 37
Journal of the American Chemical Society
1
2
3
3
Hz, 4H, CH2CHCH2), 3.89ꢀ3.92 (m, 20H, αꢀTHF), 6.28 (quint, JHH = 11.3 Hz, 1H,
4
5
6
7
CH2CHCH2) ppm. 1H NMR (400.1 MHz, CD2Cl2, –60 °C): δ = 1.95ꢀ1.98 (m, 16H, βꢀTHFeq),
3
1.98ꢀ2.02 (m, 4H, βꢀTHFax), 2.39 (d, JHH = 11.5 Hz, 4H, CH2CHCH2), 3.78ꢀ3.80 (m, 4H, αꢀ
8
9
THFax), 3.80ꢀ3.83 (m, 16H, αꢀTHFax), 6.26 (quint, 3JHH = 11.5 Hz, 1H, CH2CHCH2) ppm. 13C
NMR (100.6 MHz, THFꢀd8): δ = 26.38 (s, βꢀTHF), 58.22 (s, CH2CHCH2), 68.36 (s, αꢀTHF),
125.27 (br s, ipsoꢀC6F5), 137.19 (dm, 1JCF = 247.1 Hz, mꢀC6F5), 139.19 (dm, 1JCF = 244.5 Hz,
pꢀC6F5), 149.22 (dm, 1JCF = 241.0 Hz, oꢀC6F5), 149.50 (s, CH2CHCH2) ppm. 11B NMR (128.4
MHz, THFꢀd8): δ = –18.46 (s) ppm. Anal. calcd. for C39H29BF20MgO3 (1104.94 g/mol): Mg,
2.20; found: Mg, 2.51.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
[Mg(η1ꢁC3H5)(PMDTA)(THF)][B(C6F5)4] (4). A solution of PMDTA (8 mg, 0.046 mmol)
in THF (0.5 mL) was added to a solution of 3 (50 mg, 0.045 mmol) in THF (0.5 mL). All
volatiles were removed from the reaction mixture under reduced pressure. The residue was
washed with pentane (3 × 1.5 mL), to give a colorless solid that was dried in vacuo. Yield: 45
mg, 0.045 mmol, quantitative.
1H NMR (400.1 MHz, THFꢀd8): δ = 1.76ꢀ1.80 (m, 4H, βꢀTHF), 2.45 (s, 12H, NMe2) 2.49 (d,
3JHH = 11.5 Hz, 4H, CH2CHCH2), 2.50ꢀ2.53 (m, 2H, (CHaHbCHcHd)), 2.53 (s, 3H, NMe),
2.65ꢀ2.68 (m, 2H, (CHaHbCHcHd)), 2.81ꢀ2.94 (m, 4H, (CHaHbCHcHd)), 3.60ꢀ3.64 (m, 4H, αꢀ
THF), 6.31 (quint, 3JHH = 11.5 Hz, 1H, CH2CHCH2) ppm. 13C NMR (100.6 MHz, THFꢀd8): δ
= 26.53 (s, βꢀTHF), 45.11 (s, NMe), 45.81 (br s, CH2CHCH2), 46.75 (br s, NMe2), 55.95 (s,
(CHaHbCHcHd)), 58.48 (s, (CHaHbCHcHd)), 68.39 (s, αꢀTHF), 125.33 (br s, ipsoꢀC6F5), 137.28
1
1
1
(dm, JCF = 246.2 Hz, mꢀC6F5), 139.29 (dm, JCF = 244.5 Hz, pꢀC6F5), 149.32 (dm, JCF
=
245.4 Hz, oꢀC6F5), 149.41 (s, CH2CHCH2) ppm. 11B NMR (128.4 MHz, THFꢀd8): δ = –16.60
(s) ppm. Anal. calcd. for C40H36BF20MgN3O (989.82 g/mol): Mg, 2.46; found: Mg, 2.36.
[KMg(C3H5)3(THF)n] (n = 0.5, 1) (6). Method A (n = 0.5): K(C3H5) (75 mg, 0.94 mmol)
was added to a solution of [Mg(C3H5)]2 (1) (100 mg, 0.94 mmol) in THF (2.0 mL). The
23
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 24 of 37
1
2
3
4
5
6
7
8
reaction mixture was filtered. Upon addition of pentane (3.0 mL) to the filtrate, a colorless
solid precipitated, which was isolated by decantation, washed with pentane (3 × 2.0 mL) and
dried in vacuo. Yield: 206 mg, 0.93 mmol, 99%.
9
Method B (n = 1): [K(THF)0.5][Mg(C3H5)3] (50 mg) was dissolved in THF (0.5 mL). Pentane
was added via gas phase diffusion at ambient temperature. After 3 d, colorless single crystals
were obtained, which were isolated by decantation and dried at ambient pressure under inert
gas atmosphere. Yield: 32 mg, 0.12 mmol, 55%. Larger single crystals of
[K(THF)][Mg(C3H5)3] were obtained in lower yield when toluene was used as a precipitant
instead of pentane.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1H NMR (400.1 MHz, THFꢀd8): δ = 1.75ꢀ1.80 (m, 2H, βꢀTHF), 2.26 (d, 3JHH = 11.5 Hz, 12H,
3
CH2CHCH2), 3.60ꢀ3.64 (m, 2H, αꢀTHF), 6.35 (quint, JHH = 11.5 Hz, 3H, CH2CHCH2) ppm.
A spectrum with identical chemical shifts, but integrals with relative intensity of four for the
13
THF signals, was obtained for the compound prepared by method B. C NMR (100.6 MHz,
THFꢀd8): δ = 26.54 (s, βꢀTHF), 56.44 (s, CH2CHCH2), 68.40 (s, αꢀTHF), 151.74 (s,
CH2CHCH2) ppm. Anal. calcd. for C13H23KMgO (258.72 g/mol): Mg, 9.39; found: Mg, 9.34
(a sample prepared by method B was analyzed).
[K2Mg(C3H5)4(THF)2] ([8ꢃ(THF)2]). A concentrated solution of [K2Mg(C3H5)4] in
THF/pentane (1:1; 1 mL) was cooled to –30 °C. After 7 d, a blockꢀlike, colorless single
crystal had formed.
[CaMg(C3H5)4] (9). THF (1.0 mL) was added to a mixture of 1 (20 mg; 0.19 mmol) and 7 (23
mg; 0.19 mmol). All volatiles were removed from the yellow solution under reduced pressure.
The residue was washed with pentane (2 × 3 mL) to give a pale yellow solid, which was dried
in vacuo. The product contained substoichiometric amounts of THF (typically 0.21ꢀ0.25
equiv.). Yield: 37 mg, 0.15 mmol, 79%.
24
ACS Paragon Plus Environment

Page 25 of 37
Journal of the American Chemical Society
1
2
3
4
5
3
1H NMR (400.1 MHz, THFꢀd8): δ = 1.76ꢀ1.79 (m, 0.9H, βꢀTHF), 2.32 (d, JHH = 11.8 Hz,
3
16H, CH2CHCH2), 3.60ꢀ3.64 (m, 0.9H, αꢀTHF), 6.27 (quint, JHH = 11.8 Hz, 4H,
6
7
8
9
CH2CHCH2,) ppm. 13C NMR (100.6 MHz, THFꢀd8, 298.2 K): δ = 26.54 (s, βꢀTHF), 57.68 (s,
CH2CHCH2), 68.40 (s, αꢀTHF), 148.18 (s, CH2CHCH2) ppm. A sample containing 0.25
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1
equiv. of THF according to H NMR spectroscopy was used for microanalysis: Anal. calcd.
for (C12H20CaMg)ꢂ(C4H8O)0.25 (246.70 g/mol): Ca, 16.25; Mg, 9.85; found: Ca, 16.49; Mg,
9.05.
Butadiene Polymerization. Butadiene/THF solutions (BD content: 5.05ꢀ7.81% (m/m)) were
prepared by condensing the desired amount of monomer first over molecular sieve (4 Å) and
then into a defined amount of dry THF. The butadiene content was determined
gravimetrically. Polymerization experiments were typically run on a 50 ꢁmol scale with
respect to the initiator. In a typical experiment carried out at elevated temperature, a solution
of the initiator in THF (0.5 mL) was added to the monomer solution and the reaction mixture
was placed in a preheated oil bath. In a typical experiment carried out at lowered temperature,
a septum sealed Schlenk flask containing the monomer solution was cooled to the desired
temperature while stirring. After few minutes, a solution of the initiator in THF (0.5 mL) was
injected. Reactions were terminated by addition of isopropanol (1.0 mL). After removal of a
1
small aliquot for H NMR spectroscopic determination of conversion, the reaction mixture
was poured into a stirred solution of MeOH/HCl(conc.) (100 mL, 100:1). All volatiles were
removed from the mixture and the resulting colorless polymer was dried in vacuo for 1 h at 70
°C. Gravimetrically and spectroscopically determined yields were in good agreement.
Reactions with Ethylene. In a typical NMR scale experiment, a solution of 5/6/8/9 (45 ꢁmol)
in THFꢀd8 (0.5 mL) was degassed and pressurized with ethylene (2.0 bar). The course of the
reaction was followed by NMR spectroscopy. In a typical lab scale experiment, a solution of
5/8 (0.60 mmol) in THF (1.0 mL) was degassed and pressurized with ethylene (2.0 bar). At
25
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 26 of 37
1
2
3
the end of the desired reaction time, excess ethylene was boiled off and the reaction was
4
5
6
quenched with water (50 ꢁL). The reaction mixture was filtered and analyzed by GC/MS.
7
8
1
3
[K(CH2CH2CH2CH=CH2)] (5ꢁins). H NMR (400.1 MHz, THFꢀd8): δ = 0.89 (t, 2H, JHH
=
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
7.4 Hz, KCH2CH2CH2CH=CH2), 1.35ꢀ1.44 (m, 2H, KCH2CH2CH2CH=CH2), 2.01 (dt, 2H,
3
2
3
3JHH = 6.8 Hz, JHH = 7.5 Hz, KCH2CH2CH2CH=CH2), 4.90 (ddt, 1H, JHH = 2.3 Hz, JHH
=
=
10.3 Hz, JHH = 1.0 Hz, KCH2CH2CH2CH=CHcisHtrans), 4.96 (ddt, 1H, JHH = 2.3 Hz, JHH
4
2
3
17.1 Hz, 4JHH = 1.5 Hz, KCH2CH2CH2CH=CHcisHtrans), 5.78 (ddt, 1H, 3JHH = 6.8 Hz, 10.3 Hz,
17.1 Hz, KCH2CH2CH2CH=CH2) ppm. Resonances due to ethylene, unreacted 5, and trace
amounts of propene53 were also detected.
1
[KMg(CH2CH2CH2CH=CH2)] (6ꢁins). H NMR (400.1 MHz, THFꢀd8): δ = –0.73 (t, 2H,
3
3
3JHH = 8.0 Hz, [Mg]CH2CH2CH2CH=CH2), 1.62 (tt, 2H, JHH = 7.8 Hz, JHH = 8.0 Hz,
3
3
[Mg]CH2CH2CH2CH=CH2), 1.96 (dt, 2H, JHH
=
7.0 Hz, JHH
=
7.8 Hz,
2
3
4
[Mg]CH2CH2CH2CH=CH2), 4.67 (ddt, 1H, JHH = 2.9 Hz, JHH = 10.0 Hz, JHH = 1.3 Hz,
2
3
4
[Mg]CH2CH2CH2CH=CHcisHtrans), 4.80 (ddt, 1H, JHH = 2.9 Hz, JHH = 17.1 Hz, JHH = 1.5
3
Hz, [Mg]CH2CH2CH2CH=CHcisHtrans), 5.85 (ddt, 1H, JHH = 7.0 Hz, 10.0 Hz, 17.1 Hz,
[Mg]CH2CH2CH2CH=CH2) ppm. 13C NMR (100.6 MHz, THFꢀd8): δ = 10.38 (br s,
[Mg]CH2CH2CH2CH=CH2),
32.67
(s,
[Mg]CH2CH2CH2CH=CH2),
45.13
(s,
[Mg]CH2CH2CH2CH=CH2), 111.61 (s, [Mg]CH2CH2CH2CH=CH2), 143.51 (s,
[Mg]CH2CH2CH2CH=CH2) ppm. Resonances due to ethylene, unreacted 6, and trace amounts
of propene53 were also detected.
1
[K2Mg(CH2CH2CH2CH=CH2)] (8ꢁins). H NMR (400.1 MHz, THFꢀd8): δ = –0.76 (t, 2H,
3
3
3JHH = 8.0 Hz, [Mg]CH2CH2CH2CH=CH2), 1.62 (tt, 2H, JHH = 7.8 Hz, JHH = 8.0 Hz,
3
3
[Mg]CH2CH2CH2CH=CH2), 1.96 (dt, 2H, JHH
=
6.8 Hz, JHH
=
7.8 Hz,
2
3
4
[Mg]CH2CH2CH2CH=CH2), 4.66 (ddt, 1H, JHH = 2.9 Hz, JHH = 10.0 Hz, JHH = 1.3 Hz,
[Mg]CH2CH2CH2CH=CHcisHtrans), 4.80 (dd, 1H, 2JHH = 2.9 Hz, 3JHH = 17.2 Hz, 4JHH = 1.5 Hz,
26
ACS Paragon Plus Environment

Page 27 of 37
Journal of the American Chemical Society
1
2
3
3
[Mg]CH2CH2CH2CH=CHcisHtrans), 5.86 (ddt, 1H, JHH = 6.8 Hz; 10.0 Hz; 17.2 Hz,
4
5
6
[Mg]CH2CH2CH2CH=CH2) ppm. 13C NMR (100.6 MHz, THFꢀd8): δ = 11.30 (br s,
7
8
9
[Mg]CH2CH2CH2CH=CH2),
[Mg]CH2CH2CH2CH=CH2),
32.87
(s,
[Mg]CH2CH2CH2CH=CH2),
45.27
(s,
111.43
(s, [Mg]CH2CH2CH2CH=CH2),
143.73
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
([Mg]CH2CH2CH2CH=CH2) ppm. Resonances due to ethylene, unreacted 8, and trace
amounts of propene53 were also detected.
Computational Details. All calculations were performed with the Amsterdam Density
Functional program (ADF2012.1).54 For geometry optimization, the BP86ꢀD3 functional was
used; it is based on the local density approximation (LDA, Slater exchange and VWN
correlation)55 with gradient corrections56 from Becke (exchange) and Perdew (correlation)
added selfꢀconsistently. It also incorporates dispersion corrections according to Grimme’s
DFTꢀD3 method.57 The TZ2P basis set was used for all calculations; it is an uncontracted set
of Slaterꢀtype orbitals of tripleꢀζ quality, augmented by two sets of polarization functions (d
and f on heavy atoms; 2p and 3d sets on H). For geometry optimization, core electrons (e.g.,
1s for second and third periods, 1s2s2p for fourthꢀperiod (K) were treated by the small frozen
core approximation.58 For bond order analysis, the NalewajskiꢀMrozek (NꢀM) bond indices,
which incorporate both covalent and ionic contributions to bonding,26 were used with
equivalent allꢀelectron basis sets. For 10c and 10d, frequency calculations were used with the
same allꢀelectron basis sets to establish the nature of stationary points and for thermodynamic
results.
XꢁRay Crystal Structure Determinations. Data were collected on a Bruker CCD areaꢀ
detector diffractometer with Mo Kα radiation (graphite monochromator, λ = 0.71073 Å) using
φ and ω scans. The SMART program package was used for the data collection and unit cell
determination; processing of the raw frame data was performed using SAINT; absorption
corrections were applied with SADABS.59 The structures were solved by direct methods and
27
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 28 of 37
1
2
3
4
refined against F2 using all reflections with the SHELXLꢀ97 software. The nonꢀhydrogen
5
6
atoms were refined anisotropically, and hydrogen atoms were placed in calculated positions.60
7
8
9
Supplementary Material
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Additional details of the polymerization reaction of 6, 8, and 9 with butadiene; the reaction of
5, 6, and 8 with ethylene; and the reaction of 6, 8, and 9 with pyridine. CIF files giving Xꢀray
crystallographic data for 2, 4, 6, and [8ꢂ(THF)2]. Coordinates of the geometry optimized
structures of 10aꢁd and of the baseꢀfree complex [(CH3)2Mg(THF)(C3H5)K]. These are
available free of charge via the Internet at http://pubs.acs.org.
Acknowledgements
The authors thank Lara Lemmerz for valuable contributions to experimental work, Dr. Elise
Abinet for help in the single crystal Xꢀray structure determination of compound 2, and Dr.
Klaus Beckerle and Dr. Phillip Jochmann for helpful discussions. Financial support by Fonds
der Chemischen Industrie (Kekulé scholarship to C. L.) is gratefully acknowledged. T. P. H.
thanks the National Science Foundation (CHEꢀ1112181) for support.
28
ACS Paragon Plus Environment

Page 29 of 37
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
Graphic Material for Table of Contents
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
29
ACS Paragon Plus Environment