Cationic α-Diimine Nickel and Palladium Complexes Incorporating Phenanthrene Substituents: Highly Active Ethylene Polymerization Catalysts and Mechanistic Studies of syn/ anti Isomerization

Article

Cationic α‑Diimine Nickel and Palladium Complexes Incorporating

Phenanthrene Substituents: Highly Active Ethylene Polymerization

Catalysts and Mechanistic Studies of syn /anti Isomerization

Quan H. Tran, Xiqu Wang, Maurice Brookhart,* and Olafs Daugulis*

Cite This: https://dx.doi.org/10.1021/acs.organomet.0c00696

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sı Supporting Information

ABSTRACT: α-Diimine palladium complexes incorporating phenanthryl-

and 6,7-dimethylphenanthrylimino groups have been synthesized and

characterized. The (diimine)PdMeCl complexes prepared from 2,3-

butanedione and acenaphthenequinone bearing the unsubstituted phenan-

thrylimino groups, 12a and 14a, respectively, exist as a mixtures of syn and

anti isomers in a ca. 1:1 ratio. Separation and X-ray diﬀraction analysis of

4a-syn and 14a-anti isomers conﬁrms the syn/anti assignments. The

⧧

barrier to interconversion of 14a-syn and 14a-anti via ligand rotation, ΔG ,

was found to be 25.5 kcal/mol. The corresponding (diimine)PdMeCl

complex prepared from acenaphthenequinone and incorporating the 6,7-

dimethylphenanthrylimino group exists solely as the anti isomer, 14b, due

to steric crowding which destabilizes the syn isomer. Analogous

(

diimine)NiBr complexes were prepared from 2,3-butanedione incorporat-

ing the phenanthrylimino group, 16a, and the 6,7-dimethylphenanthrylimino group, 16b. Nickel-catalyzed polymerizations of

ethylene were carried out by activation of the dibromide complexes 16a,b using various aluminum alkyl activators. Complex 16a

yields a bimodal distribution polymer, the low-molecular-weight fraction originating from the syn isomer and the high-molecular-

weight fraction arising from the anti isomer. Polymerizations carried out by 16b yield only high-molecular-weight polymers with

monomodal distributions due to the existence of a single isomer (anti) as the active catalyst. All polymers are linear or nearly so. All

catalysts are highly active, but catalysts derived from 16b are somewhat more active than 16a and exhibit turnover frequencies

generally over 10 and up to 5 × 10 per hour (40 °C, 27.2 atm ethylene, 15 min). Active palladium ethylene oligomerization

catalysts were generated by conversion of the neutral methyl chloride complexes 14a,b to the cationic nitrile complexes 15a,b via

halide abstraction.

INTRODUCTION

metal complexes have been developed for oleﬁn polymer-

■

(

−21

ization over the last two decades.

Altering ligand

Cationic α-diimine nickel(II) and palladium(II) complexes

Figure 1, 1a,b) showing high activity for ethylene and α-oleﬁn

polymerization were introduced in 1995. These system₁s

produce high-molecular-weight, branched polyethylenes.

Such complexes are also eﬀective catalysts for the copoly-

frameworks is used in tuning the properties of catalysts,

leading to signiﬁcant variations in polymerization activity as

well as the microstructure of the polymer products.

In 2013, our group introduced an approach for exceptionally

eﬃcient blocking of the axial sites in nickel complexes by

utilizing 8-arylnaphthyl amines which produce “sandwich”-type

merization of ethylene with certain polar vinyl monomers.

The critical structural feature of classical α-diimine systems is

the presence of ortho aryl substituents that signiﬁcantly retard

the rate of chain transfer relative to the rate of chain

propagation, enabling the production of high-molecular-weight

polymers. Due to the approximately perpendicular arrange-

ment of the aryl rings relative to the coordination plane of the

metal, the ortho aryl substituents are positioned near axial sites

above and below the ﬁve-membered chelate ring. The ortho

substituents thus eﬃciently increase steric hindrance at metal

axial positions and greatly retard the rate of polymer chain

structures (Figure 1, 2b). While the substituents of

traditional α-diimine catalysts point away from the coordina-

tion plane at an angle, the 8-aryl substituents are perpendicular

to the naphthyl rings and are positioned over the axial sites of

the complexed metal in a “sandwich-like” arrangement of the

Received: October 30, 2020

displacement by the incoming monomer. Because of the easily

executed structural permutations and highly modular synthesis

of the α-diimine ligands, a plethora of similar late-transition-

XXXX American Chemical Society

Organometallics XXXX, XXX, XXX−XXX

Organometallics

about 3 min runs (Figure 2 , 4 and 5 ). The highest

Article

−

h ) remain rare. The classical α-diimine nickel complex

Figure 1, 1b; R, R = acenaphthyl) exhibits an average

(

−1

polymerization activity of 3.7 × 10 h in a 10 min run at 35

C. Similar activities were obtained for the nickel(II)

26 27

triadamantylphosphine and α-iminoketone catalysts in

Figure 1. Group 10 metal α-diimine catalysts.

capping groups. Due to the extreme hindrance provided by the

incorporation of the bulky 8-arylnaphthylimino groups, these

sandwich complexes eﬀectively inhibit displacement of the

growing polymer chain. Consequently, much lower rates of

chain transfer relative to rates of chain propagation are

observed. The sandwich palladium catalysts (Figure 1, 2a)

exhibit living polymerization behavior, generating hyper-

branched polyethylene with narrow molecular weight distri-

butions. The corresponding nickel sandwich catalysts convert

ethylene to an ultrahigh-molecular-weight polymer with

dispersities narrower than those observed for the classical

diimine systems.

Figure 2. Highly active nickel-based ethylene polymerization catalysts.

polymerization activity provided by a nickel system was

observed using a cationic nickel α-diimine catalyst modiﬁed

with (4-diphenylamino)phenyl substituents (Figure 2, 6). An

−1

ultrahigh activity of 37 × 10 h was achieved in a 1 min

reaction. These notably high catalytic activities were obtained

over very short reaction times, eliminating any deleterious

eﬀects of short catalyst lifetimes.

Recently, we reported a series of complexes derived from 8-

halonapthalen-1-amine imines that are related to sandwich

catalysts by virtue of substituting the capping aryl substituents

We report here the preparation, characterization, and

ethylene polymerization activities of new nickel and palladium

complexes derived from phenanthryl- and 6,7-dimethylphe-

nanthryl-α-diimines. A nickel complex prepared from 6,7-

dimethylphenanthrylamine shows a very high activity level of

with halogen atoms. These complexes exist in solution as

mixtures of syn and anti isomers with syn/anti ratios of 2/1 (X

F), 2/1 (Cl), 1/1.5 (Br), and 1/22 (I) (Figure 1, 3). The

−1

.4 × 10 h for ethylene polymerization in a 30 min run.

halo-substituted nickel complexes exhibit performance in

ethylene polymerization dependent on the syn/anti ratios

and their rates of interconversion. Polyethylenes produced

from nickel complexes display either bimodal or broadened

monomodal (X = Br) molecular weight distributions. This

feature is attributed to the slower rate of interconversion of the

anti and syn isomers of the active catalysts relative to the rate of

polymer chain growth for all cases except when X = Br. The

low-molecular-weight fraction is assigned as polyethylene

formed from the syn isomer, whereas the anti isomer leads to

the formation of the high-molecular-weight fraction. Never-

theless, only crystals of syn complexes were isolated and

characterized by X-ray diﬀraction analysis. Interconversion of

syn/anti isomers in tetrahedral Zn complexes derived from 8-

RESULTS AND DISCUSSION

Synthesis of Diimine Ligands. The preparation of α-

diimine ligands 10a,b is presented in Scheme 1. Friedel−Crafts

acylation of naphthalene and 2,3-dimethylnaphthalene gave the

■

Scheme 1. Synthesis of 2,3-Butanedione Diimines

⧧

halonapthalen-1-amine imines exhibits barriers (ΔG values)

in the range 16.9−19.1 kcal/mol, which is about 1−4 kcal/mol

higher than barriers to migratory insertion in the nickel

catalysts.

While a large number of nickel ethylene polymerization

catalysts have now been developed, systems that can reach an

−1

activity level of ca. 3.6 × 10 turnovers/h (or ca. 10 g mol

Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

corresponding keto acids that subsequently underwent a

Wolﬀ−Kishner reduction followed by cyclization to provide

dihydrophenanthren-4(1H)-ones 7a,b. Conversion of 7a,b to

oximes followed by pivaloylation gave 8a,b. Subsequent Pd-

catalyzed Semmler−Wolﬀ-type reactions aﬀorded amino-

phenanthrenes 9a,b. The α-diimine ligands 10a,b were readily

prepared by the reaction of 2,3-butanedione with the

aminophenanthrenes in MeOH in the presence of a catalytic

amount of formic acid. While ligand 10a shows good solubility

in methylene chloride, ligand 10b is nearly insoluble in most

common solvents, including toluene, methanol, diethyl ether,

and methylene chloride.

Considering the analogy with 3 (Figure 1), the most likely

explanation is that complex 12a exists as a 1.5/1 syn/anti

mixture. The reaction of ligand 10b with Pd(COD)MeCl in

methylene chloride did not lead to a pure diimine-palladium

complex, presumably due to the poor solubility of 10b.

Ligands 11a,b react with Pd(COD)MeCl to aﬀord

respectively palladium complexes 14a,b in good yields

(Scheme 3). Similar to 12a, a nearly 1/1 equilibrium mixture

of syn/anti conformers of complex 14a was observed by H

NMR spectroscopy, as was evident by the presence of two

signals for the palladium-bound methyl groups centered at 0.78

and 0.74 ppm. The structure of each isomer of 14a was

conﬁrmed by a single-crystal X-ray diﬀraction analysis, and

their structures are shown in Figures 3 and 4 . The syn and anti

The corresponding α-diimine ligands 11a,b derived from

acenaphthenequinone were prepared by using the ZnCl -

template method (Scheme 2). The reactions of amino-

Scheme 2. Synthesis of Acenaphthenequinone Diimines

phenanthrenes with acenaphthenequinone in the presence of

ZnCl gave the diimine zinc complexes as dark red solids.

Decomplexation of zinc chloride with sodium oxalate provided

free ligands 11a,b as red powders. These ligands display good

solubility in methylene chloride. All of the ligands were

characterized by H and C NMR spectroscopy as well as

high-resolution mass spectroscopy (HRMS).

Synthesis and Structure of Palladium Complexes.

The preparation of the palladium complex 12a is shown in

Scheme 3. Displacement of COD from Pd(COD)MeCl by

Figure 3. Molecular structure of palladium complex 14a-syn.

Hydrogen atoms are omitted for clarity. Thermal ellipsoids are

shown at the 50% probability level. Selected bond lengths (Å) and

angles (deg): C20−Pd1 2.053(2); Pd1−N1 2.1874(19); Pd1−N2

.058(2); Pd1−Cl1 2.289(7); C20−Pd1−N1 174.42(11); C20−

Pd1−N2 94.96(11); N1−Pd1−N2 79.45(8); C20−Pd1−Cl1

87.52(9).

Scheme 3. Synthesis of Palladium Complexes

Figure 4. Molecular structure of palladium complex 14a-anti.

Hydrogen atoms are omitted for clarity. Thermal ellipsoids are

shown at the 50% probability level. Selected bond lengths (Å) and

angles (deg): C20−Pd1 2.039(4); Pd1−N1 2.054(3); Pd1−N2

2.177(3); Pd1−Cl1 2.2920(11); C20−Pd1−N1 93.21(15); C20−

Pd1−N2 171.46(14); N1−Pd1−N2 79.20(12); C20−Pd1−Cl1

89.63(13).

ligand 10a generated deep red 12a in high yield. Complex 12a

is slightly soluble in methylene chloride and nearly insoluble in

toluene and pentane. The H NMR spectrum of 12a in

methylene chloride-d shows two singlet resonances centered

at 0.48 (major) and 0.45 ppm (minor) in a 1.5/1 ratio that are

assigned as the signals of Pd-bound methyl groups.

Organometallics XXXX, XXX, XXX−XXX

Organometallics

in Figure 5 . Complex 14b crystallizes in triclinic space group

Article

conformers crystallize separately, and crystal picking was used

to collect each isomer. As expected, a square-planar geometry

is exhibited at the palladium center. In the single crystal of

complex 14a-syn, two phenanthrene rings face each other,

shielding only one axial position of the coordination site

complex 14a is 25.5 kcal/mol. The contribution of activation

entropies to the free energies of activation is very small, as

expected. For comparison, interconversion between syn and

anti isomers in zinc 8-halonaphthyl-α-diimine complexes

proceeds with much lower barriers of 16.9−19.1 kcal/mol.

In contrast to the palladium complexes derived from

(

Figure 3). In contrast, complex 14a-anti contains two

phenanthrene rings that shield the axial sites above and

below the palladium center (Figure 4). Remarkably, 14a-syn

could be isolated in pure form (>30/1 syn/anti) using a

modiﬁed synthetic procedure. After overnight stirring of 11a

with Pd(COD)MeCl in methylene chloride, toluene was

added to the reaction mixture and the resulting mixture was

carefully evaporated at 60 °C until a precipitate formed. 14a-

syn was collected by ﬁltration as a red solid. The identity of the

product was veriﬁed by NMR spectroscopy, showing a nearly

pure syn isomer.

phenanthrene, complex 14b containing 6,7-dimethyl substitu-

ents exists as a single conformer. The H NMR spectrum of

14b in methylene chloride-d₂contains only one set of

resonances. The structure of complex 14b was veriﬁed by a

single-crystal X-ray diﬀraction analysis after recrystallization by

layering pentane over a solution of 14b in methylene chloride

at room temperature. The molecular structure of 14b is shown

As was established earlier, activation with organoaluminum

cocatalysts in the presence of ethylene yields square-planar

cationic nickel catalysts that structurally resemble the

30−33

corresponding palladium complexes.

The existence of

palladium complexes 12a and 14a as a syn/anti mixture of

isomers suggests that the behavior of the nickel complexes in

polymerization could be complicated. Since the investigation

of the paramagnetic nickel dibromide complexes is problem-

atic, and square-planar Ni(II) catalytic intermediates are

expected to be unstable, an analysis of the model palladium

complex 14a was conducted. In solution, 14a-syn converts to

4a-anti, forming an equilibrium mixture of isomers. The rate

of isomerization of 14a-syn was investigated using NMR

spectroscopic analysis in tetrachloroethane-d . The data are

presented in Table 1. At 313 K, 14a-syn very slowly isomerizes

Table 1. Rates and Activation Parameters for syn−anti

Interconversion of 12b

Figure 5. Molecular structure of palladium complex 14b. Hydrogen

atoms are omitted for clarity. Thermal ellipsoids are shown at the 50%

probability level. Selected bond lengths (Å) and angles (deg): Pd1−

C22 2.0545(11); Pd1−N2 2.0604(12); Pd1−N1 2.1829(12); Pd1−

Cl1 2.2768(4); C22−Pd1−N2 94.67(6); C22−Pd1−N1 172.63(5);

N2−Pd1−N1 79.12(5); C22−Pd1−Cl1 89.03(5).

^kobs = k + k (10⁻s⁻¹

)

^k1 ⁽¹⁰ s⁻¹

−5

)

^k−1 (10⁻⁵s⁻¹

)

temp (K)

−1

P1 and shows a square-planar geometry around the palladium

center in the solid state. As anticipated, the sterically bulky

methyl groups force the palladium complex 14b to adopt an

anti conformation. The two dimethyl-substituted phenan-

threne rings eﬀectively cap the axial sites of the square-planar

coordination plane of palladium.

2.07 ± 0.01

8.10 ± 0.25

29.6 ± 0.82

77.2 ± 3.99

0.92 ± 0.02

3.60 ± 0.11

13.2 ± 0.36

34.8 ± 1.77

1.15 ± 0.03

4.50 ± 0.14

16.4 ± 0.46

43.4 ± 2.21

Activation Parameters

ΔG^⧧₂

= 25.5 ± 0.1 kcal/mol

ΔG

⧧

= 25.4 ± 0.1 kcal/mol

The acetonitrile-ligated palladium complexes 13a, 15a, and

15b were obtained in high yield via halide abstraction from the

corresponding complexes 12a, 14a, and 14b, respectively,

using NaBArF in the presence of acetonitrile (Scheme 3).

98K,1

298K,−1

⧧

ΔH = 25.4 ± 0.9 kcal/mol

ΔS₁= −0.43 ± 2.8 cal/mol

ΔH = 25.4 ± 0.9 kcal/mol

−1

⧧

ΔS = −0.03 ± 2.8 cal/mol

−1

These nitrile complexes were characterized by H and

to 14a-anti, resulting in a nonequilibrium ratio of 2.5/1 syn/

anti after 12 h. An increase in temperature facilitates the

isomerization. The equilibrium ratio of 1.25/1 syn/anti was

achieved after 2 h at 343 K. Using a reversible ﬁrst-order

NMR spectroscopy and HRMS. Similar to those observed with

palladium methyl chloride complexes, the nitrile complexes

decorated with unsubstituted phenanthryl groups gave a syn/

anti mixture of isomers and the nitrile complex bearing

dimethyl-substituted phenanthryl groups was obtained as a

single isomer. The palladium complex 15a-syn was prepared

from 14a-syn at 0 °C.

kinetic analysis, the rate constants, k and k , were obtained

−1

from the k_o_b_s(k + k ) value and the equilibrium constant, k /

−1

k₋₁= 0.8. An Eyring analysis of the rate data between 313 and

43 K gave the activation parameters. The barrier to

isomerization between syn and anti isomers in palladium

Synthesis of Nickel Dibromide Complexes. The

reaction of ligands 10a,b with (DME)NiBr in methylene

Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

chloride at room temperature led to the formation of brick red

nickel(II) dibromide complexes 16a,b in excellent yields

molecular weights that is strongly dependent on the cocatalyst.

When modiﬁed methylaluminoxane MMAO-3A is used (Table

2, entries 1−3), two elution peaks are observed in gel

permeation chromatography (GPC). A minor fraction of high-

(Scheme 4). These paramagnetic nickel complexes exhibit

poor solubility in common organic solvents such as toluene,

diethyl ether, and methylene chloride.

molecular-weight polyethylene is detected with M

mol along with a major fraction of low-molecular-weight

= 76 kg/

polyethylene with M = 7.7 kg/mol (entry 1). When both

fractions are considered, a broad molecular weight distribution

Scheme 4. Synthesis of Nickel Complexes

(

MWD) of 5.2 is calculated (see Figure S6 in the Supporting

Information). When the ethylene pressure is increased from

3.6 to 27.2 atm, the TOF increases only by a factor of 1.24,

−1

from 0.66 × 10 to 0.82 × 10 h and a bimodal molecular

weight distribution is again observed (entry 2; Figure S7). An

increase of temperature from 25 to 40 °C leads to a signiﬁcant

increase in TOF (from 0.82 × 10 to 1.89 × 10 h , entry 3)

and again a bimodal distribution is observed with a MWD of

−1

.6 (Figure S8 ). The branching density increases and the

melting temperature decreases with increasing polymerization

Ethylene Polymerization by Nickel Complexes. Ethyl-

ene polymerizations were carried out by the activation of

nickel(II) dibromide precatalysts 16a,b in toluene using

organoaluminum compounds in a 2500/1 Al/Ni ratio. The

reaction is very exothermic, and low catalyst loadings were

used to eﬃciently maintain the reaction temperature and to

minimize the eﬀect of mass-transport issues due to

precipitation of the polymer. Under 13.6−40.8 atm of ethylene

the reactions proceed to yield linear to lightly branched

polyethylenes. Turnover frequencies (TOFs) were calculated

as (mol of ethylene converted to polymer)/((mol of Ni) time).

As a consequence, they represent an average TOF over the

polymerization time. Polymer branching densities were

temperature, as is commonly observed using other nickel

22,24

catalysts.

Speciﬁcally, complex 16a produces nearly linear

polyethylene (1 branch per 1000 C) at 25 °C, and lightly

branched polyethylene (9 branches per 1000 C) at 40 °C. The

increase in branching with an increase in temperature is

commonly ascribed to an increase in the rate of chain walking

relative to the rate of chain growth. Similar to the case for

MMAO-3A, the use of PMAO-IP activator also produces

polyethylene with a relatively high M /M of 5.9 when the

reaction is run at 25 °C and 13.6 atm of ethylene, showing a

bimodal polymer distribution (entry 4; Figure S9 ). Since the

related palladium complexes 12a and 14a exist as isomeric

mixtures, it is likely that the nickel(II) dibromide precatalyst

obtained by a H NMR spectroscopic analysis. Polymerization

results are presented in Tables 2 and 3.

6a is activated by aluminum-based cocatalysts to generate the

active nickel species as a mixture of the syn and anti isomers

17-syn/17-anti), as shown in Scheme 5. The anti complex will

Table 2 summarizes the behavior of phenanthrene-derived

nickel complex 16a in polymerizations. Cocatalysts greatly

inﬂuence the activity of complex 16a and the microstructure of

the resulting polyethylene. All of the organoaluminum

compounds are eﬀective cocatalysts. Upon activation by

aluminum-based cocatalysts, complex 16a displays high activity

at 13.6 atm of ethylene pressure and 25 °C with TOFs over 30

(

generate the minor high-molecular-weight polymer fraction,

and the syn isomer will form the major low-molecular-weight

fraction. As was established in previous studies, the key aspect

to obtain a high-molecular-weight polymer is eﬀective axial

shielding that considerably retards the rate of chain transfer

over the rate of chain propagation. In the case of the syn

conformer, only one axial position is capped, resulting in an

increased rate of chain transfer. Consequently, low-molecular-

weight polyethylene is produced. In contrast, the anti isomer

possesses two phenanthrene groups that are capable of

eﬃciently shielding axial sites above and below the

coordination plane; thus, high-molecular-weight polyethylene

−1

min ranging from 0.14 × 10 to 1.00 × 10 h . The catalyst

activities increase in the order i-Bu Al < PMAO-IP < MMAO

Et AlCl < EtAlCl . In all cases, nearly linear polyethylenes

2 2

with 1−3 branches per 1000 C are produced, with melting

temperatures of ca. 130 °C.

The most remarkable feature of complex 16a is the

production of polyethylenes with a bimodal distribution of

Table 2. Ethylene Polymerizations Using Activated Nickel Complex 16a

temp ( C) pressure (atm) TOF (10⁻⁶h⁻¹

M_n(kg/mol) M /M_nM (kg/mol) branches (/1000 C) T_m(^oC)

entry

activator

)

MMAO-3A

PMAO-IP

13.6

27.2

13.6

27.2

13.6

0.66

0.82

1.89

0.56

0.14

0.76

1.00

0.95

1.76

7.8

4.5

2.9

9.2

12.5

8.8

9.5

7.2

10.6

5.2

7.2

6.6

5.9

4.0

3.4

3.0

2.0

2.8

76.0/7.7

60.3/5.7

30.7/3.6

73.0/10.1

52.5/19.7

130.0

130.4

122.7

130.0

130.9

130.5

130.4

130.8

120.9

iBu Al

Et AlCl

13.0

EtAlCl₂

15.1

8.9

15.7

Conditions: Ni (0.2 μmol), activator (0.5 mmol), toluene (150 mL), 0.5 h. Absolute molecular weight determined by GPC in 1,2,4-

trichlorobenzene. Branching numbers per 1000 carbons determined by H NMR spectroscopy. T determined by DSC. Low-molecular-weight

peak with a high-molecular-weight shoulder.

Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

Table 3. Ethylene Polymerizations Using Activated Nickel Complex 16b

TOF (10⁻⁶h⁻¹

T_m(^oC)

entry

activator

temp ( C)

pressure (atm)

)

M_n(kg/mol)

M /M_n

branches (/1000 C)

MMAO-3A

PMAO-IP

EtAlCl₂

13.6

27.2

40.8

27.2

1.09

1.05

0.48

1.58

1.63

4.43

5.16

5.14

2.74

122

121

134

2.2

2.0

1.9

1.7

2.0

1.8

132.1

131.8

130.3

131.0

131.9

121.7

125.2

125.5

116.8

Et AlCl

1.8

Conditions unless speciﬁed otherwise: Ni (0.2 μmol), activator (0.5 mmol), toluene (150 mL), 0.5 h. Absolute molecular weight determined by

GPC in 1,2,4-trichlorobenzene. Branching numbers per 1000 carbons determined by H NMR spectroscopy. T determined by DSC. 15 min.

Scheme 5. Interconversion of syn/anti Isomers in a Ni Alkyl

Ethylene Intermediate

isomer exclusively, thus aﬀording high-molecular-weight,

monomodal polyethylenes (Scheme 5).

In most of the cases, the activity of activated 16b is

noticeably higher than that of 16a. For example, upon

activation by MMAO-3A, 16b displays a TOF at a 13.6 atm

−1

ethylene pressure of 1.09 × 10 h in comparison to the TOF

−1

of 0.66 × 10 h observed for 16a under similar conditions

Table 2, entry 1 vs Table 3, entry 1). A similar TOF is

(

obtained using PMAO-IP as an activator (entry 2). Polymers

formed with either MMAO-3A or PMAO-IP activators possess

high molecular weights in the range of 72−96 kg/mol and

branching densities of less than 5 branches per 1000 C.

EtAlCl is also a competent activator, albeit the activities

observed are lower. Linear high-molecular-weight polyethylene

with an M value of 122 kg/mol and 3 branches per 1000 C

(

entry 3) was obtained.

The best results were obtained by employing Et AlCl as an

activator. Under these conditions, activated complex 16b not

only exhibits higher productivity than complex 16a (TOF =

−1

is formed. The observation of a bimodal distribution of

molecular weight indicates that the rate of interconversion of

syn/anti isomers is slower than the rate of formation of a single

chain. If a rapid interconversion were taking place, a

monomodal GPC trace would be observed. The behavior of

complex 16a is consistent with that seen for nickel α-diimine

1.58 × 10 h vs 0.76 × 10 h ; entry 4, Table 3, vs entry 6,

Table 2) but also produces high-molecular-weight poly-

ethylene with M = 121 kg/mol. Consequently, Et AlCl was

used as an activator in all other runs. At 25 °C, increasing the

ethylene pressure from 13.6 to 27.2 atm had little eﬀect on the

TOFs observed in 30 min runs (Table 3, entries 4 and 5). The

same situation was observed at 40 °C when the pressure was

increased from 27.2 atm (entry 7) to 40.8 atm (entry 8).

catalysts generated from 8-halo-1-naphthylamines and from

34,35

unsymmetrical ligands.

The use of other cocatalysts including iBu Al, Et AlCl, and

Turnover frequencies stayed about the same at ca. 5.2 × 10

−

EtAlCl (Table 2, entries 5−7; Figures S10 −12) decreases the

h . These results suggest that the catalyst resting state is likely

the alkyl ethylene species 18, which would show no

dependence of TOF on ethylene pressure.

molecular weight distributions to 4.0, 3.4, and 3.0, respectively.

Low-molecular-weight polyethylenes were found to be the

major fraction, consistent with the data observed for MMAO-

Average TOFs are appreciably dependent on polymerization

temperature. An increase in temperature from 25 to 40 °C

leads to approximately 3-fold increase in TOF in 30 min runs,

A and PMAO-IP. Notably, at 25 °C and 27.2 atm of ethylene,

complex 16a activated by EtAlCl produces polyethylene with

−1

a M /M value of 2.0 (entry 8, Figure S13). A low-MW

from 1.63 × 10 to 4.43 × 10 h (Table 3, entries 5 and 6). A

−1

polymer with an M value of 7.2 kg/mol was obtained. An

high TOF of 2.74 × 10 h could be achieved even at 60 °C

(entry 9). The experimental results show that the activity

remains at high levels over 30 min, revealing a relatively good

stability of the catalyst derived from complex 16b. For

comparison, the TOF determined for the tri-1-adamantylphos-

increase in temperature from 25 to 40 °C leads to a ca. 2-fold

−1

increase in TOF from 1.00 × 10 to 1.76 × 10 h , and

polyethylene with 12 branches per 1000 C and a T value of

20.9 was obtained (entry 9, Figure S14 ).

Table 3 shows polymerization results upon activation of

−1

phine-nickel complex 4 is 3.7 × 10 h at 10 °C and 27.2 atm

nickel(II) dibromide 16b containing dimethylphenanthryl

substituents. Complex 16b forms highly active catalysts upon

activation by various aluminum-based cocatalysts and exhibits

single-site catalytic behavior, allowing for the formation of

polyethylenes with molecular weight distributions in the range

of 1.7−2. In contrast to the active Ni species 17, it is likely that

the active dimethyl-substituted complex 18 exists as the anti

of ethylene, measured over 3.5 min. The TOFs substantially

dropped with even a minor lengthening of the reaction time.

Similarly, Zhang and Jian described that by using (4-

diphenylamino)phenyl-modiﬁed α-diimine nickel catalyst 6,

−1

an ultrahigh activity of 37 × 10 h could be achieved when

the reaction was carried out for 1 min. The classical α-

diimine and α-iminoketone nickel catalysts (Figure 1, 1b,

Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

−1

and Figure 2, 5) gave activities of 3.7 × 10 h over 10 and 3

min, respectively. Previously reported high catalytic activities

were stated for relatively short reactions, while the current

catalyst remains highly active in substantially longer runs. This

feature may be important for practical applications.

active syn/anti isomers. Two phenanthryl rings of the syn

isomer are situated at the same side of the coordination plane

and block one axial site of the metal center. Consequently,

polyethylene produced by the syn isomer has relatively low

molecular weight. The anti isomer in which both axial sites are

blocked generates polyethylene with high molecular weight.

At 15 min, complex 16b exhibits a slightly higher TOF of

.16 × 10 h and gives polyethylene with an M value of 48

−1

Surprisingly, the use of EtAlCl activator results in the

kg/mol (entry 7). At increased temperatures, the polymer

microstructure is altered from linear to lightly branched and

the molecular weight decreases. For example, complex 16b at

generation of largely low-molecular-weight polyethylene. It is

not clear how the nature of the cocatalysts inﬂuences the

molecular weight distributions of the polymers.

7.2 atm produces polyethylene with an M value of 134 kg/

Nickel and palladium complexes bearing more hindered 6,7-

dimethylphenanthryl substituents exist as single isomers. An X-

ray diﬀraction study of palladium complex 14b conﬁrms the

anti orientation of the 6,7-dimethylphenanthryl groups and

indicates axial shielding more extensive than that observed in

complex 14a. Nickel complex 16b is anticipated to adopt a

similar conformation and produces linear to lightly branched

polyethylenes with molecular weight distributions of ca. 2 and

mol and 2 branches per 1000 carbons, while at 60 °C the

polymer exhibits an M value of 28 kg/mol and 15 branches

per 1000 C.

Ethylene Oligomerization with Palladium Com-

plexes. The catalytic behavior of palladium complexes was

explored at room temperature in methylene chloride solution

under 13.6 atm of ethylene. Somewhat unexpectedly,

palladium catalysts showed behavior remarkably distinct from

that of nickel complexes. The results are summarized in Table

M values of ca. 72−134 kg/mol at 25 °C. At 40 °C and 27.2

atm of ethylene, complex 16b exhibits an average TOF of 5.16

−1

10 h over 15 min. Notably, the catalytic activity is capable

−1

of remaining at a very high level of 4.43 × 10 h when the

reaction is carried out for 30 min. Previous examples of similar

catalytic activities by nickel diimine complexes were observed

at short reaction times, typically 10 min or less.

Table 4. Oligomerization by Palladium Complexes

time (h) pressure (atm) TOF (h⁻¹

)

entry

catalyst

M (g/mol)

13a

15a

15a-syn

15b

13.6

190

150

170

130

530

250

260

630

EXPERIMENTAL SECTION

■

General Materials and Methods. All procedures were carried

out under a nitrogen atmosphere using standard glovebox and

Schlenk techniques unless otherwise noted. Diethyl ether, pentane,

methylene chloride, and toluene were puriﬁed by an JC Meyer solvent

puriﬁcation system. Column chromatography was performed on 60 Å

silica gel (SiliCycle Inc.) using EtOAc/hexanes mixtures as eluents.

Conditions: Pd catalyst (10 μmol), ethylene (13.6 atm), CH Cl (50

mL), 25 °C. M_nwas determined by H NMR spectroscopy.

Oligomers contain 90−110 branches/1000 C.

The H, C, and F NMR spectra were recorded on a JEOL EC-400,

JEOL EC-500, or JEOL EC-600 spectrometer using the residual

solvent peak as a reference. Analytical thin-layer chromatography was

performed on silica gel TLC Al foils with a ﬂuorescent indicator (254

nm) from SiliCycle Inc. Compounds for HRMS were analyzed by

positive mode electrospray ionization (CI or ESI) using an Agilent

QTOF mass spectrometer in the Mass Spectrometry Facility (MSF)

of the Department of Chemistry and Biochemistry of the University

of Texas Austin. Elemental analyses were performed by Atlantic

Microlabs Inc. (Norcross, GA, USA). Reagents and starting materials

were obtained from commercial sources and used without further

puriﬁcation unless otherwise noted. MMAO-3A (7 wt % solution in

heptane) and PMAO-IP (7 wt % solution in toluene) were purchased

While the substantially lower activity of complexes 13a and

5a,b was anticipated, only low-molecular-weight oligomers

were produced. Turnover frequencies are comparable to those

observed using “sandwich” palladium catalysts. The more

hindered catalyst 15b bearing dimethyl-substituted phenanthr-

−

yl groups exhibits a TOF of 130 h . The decreased steric

hindrance in phenanthrene-derived catalysts 13a and 15a

resulted in slightly higher TOFs and a concurrent reduction in

oligomer molecular weight. No signiﬁcant diﬀerence between

an oligomerization behavior of 15a-syn and a 15a-syn/-anti

mixture was observed (entries 2 and 3).

from AkzoNobel. EtAlCl (1.8 M solution in toluene) was purchased

CONCLUSIONS

from Acros. Et AlCl (25 wt % solution in toluene) was purchased

■

from Sigma-Aldrich. Polymerization reactions were carried out in a

Parr 450 mL mini reactor with Matheson purity ethylene from

Matheson Gas. X-ray measurements were made with a Bruker DUO

platform diﬀractometer equipped with a 4K CCD APEX II detector

and an Incoatec 30 W Cu microsource with compact multilayer

optics. Data were collected using a narrow-frame algorithm with scan

widths of 0.5° in ω and an exposure time of 25 s/frame at 123 K. The

data were integrated using the Bruker-Nonius SAINT program, with

the intensities corrected for Lorentz factor, polarization, air

absorption, and absorption due to variation in the path length

through the detector faceplate. The data were scaled, and an

absorption correction was applied using SADABS. Redundant

reﬂections were averaged. The structure was solved by using the

program SHELXT and reﬁned using SHELXL. DSC measurements

were collected on a TA Instruments DSC2500 system using a heat−

cool−heat method with a nitrogen ﬂow of 80 mL/min. The sample

was heated at 10 °C/min from 25 to 200 °C then cooled from 200 °C

to −90 °C at 5 °C/min. The sample was then heated from −90 to

200 °C at 10 °C/min. All reported melting temperatures come from

The synthesis and use as polymerization catalysts of nickel and

palladium complexes incorporating phenanthrene substituents

on ligands is described. The cationic α-diimine nickel and

palladium complexes incorporating unsubstituted phenanthry-

limino groups exist as mixtures of syn and anti isomers. Crystals

of both syn and anti isomers of acenaphthenequinone-derived

palladium complex 14a were analyzed by an X-ray diﬀraction

analysis. Pure 14a-syn was obtained and used to investigate the

syn/anti isomerization. The energy barrier to syn/anti isomer-

ization in 14a is 25.5 kcal/mol, as established by kinetic

analysis using NMR spectroscopy at various temperatures. The

ethylene polymerization behavior of nickel complex 16a

depends on the organoaluminum cocatalyst. Upon activation

by MMAO-3A or PMAO-IP, the nickel complex 16a

polymerizes ethylene to yield a polymer with a bimodal

distribution of molecular weight. The bimodal molecular

weight distribution is ascribed to the presence of catalytically

Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

10 min. The precipitate was collected by ﬁltration and was thoroughly

washed with H O. The solid was recrystallized from acetic acid to

aﬀord purple crystals of 4-(naphthalen-2-yl)-4-oxobutanoic acid (8.1

g, 55%). To a solution of the keto acid (7.3 g, 32 mmol) in diethylene

glycol (200 mL) was added hydrazine monohydrate (5.7 g, 113

mmol), and the reaction mixture was stirred at 100 °C for 1 h. KOH

(6.2 g, 110 mmol) was added, and the reaction mixture was stirred at

260 °C for 2 h. After the mixture was cooled to room temperature,

H O (100 mL) was added, and the mixture was poured into a mixture

of ice and concentrated HCl. The precipitate was removed by

ﬁltration and was thoroughly washed with H O. The crude product

was dissolved in CH Cl (400 mL) and washed with H O (2 × 100

mL). The organic phase was dried over anhydrous MgSO₄and

ﬁltered. The solvent was evaporated, aﬀording the product as greenish

yellow solid of 4-(naphthalen-2-yl)butanoic acid (5.8 g, 85%). A 250

mL round-bottom ﬂask equipped with a magnetic stir bar was charged

with the acid (5.6 g, 26 mmol) and methanesulfonic acid (40 mL).

The solution was stirred for 1 h at 95 °C. After it was cooled to room

temperature, the reaction mixture was poured into ice and extracted

with Et O (3 × 100 mL). The combined organic phases were washed

with saturated aqueous NaHCO (2 × 100 mL) and were dried over

anhydrous MgSO . The solvent was evaporated, aﬀording the product

as yellow solid (4.7 g, 92%). This compound is known. H NMR

(600 MHz, CDCl , ppm): δ 9.43 (d, J = 8.4 Hz, 1H), 7.90 (d, J = 8.4

Hz, 1H), 7.80 (d, J = 8.4 Hz, 1H), 7.67−7.58 (m, 1H), 7.49 (dd, J =

7.3, 7.3 Hz, 1H), 7.29 (d, J = 8.4 Hz, 1H), 3.09 (t, J = 6.1 Hz, 2H),

2.78 (dd, J = 7.3, 6.0 Hz, 2H), 2.23−2.12 (m, 3H). C NMR (151

MHz, CDCl , ppm): δ 200.6, 146.9, 134.3, 132.8, 131.4, 128.9, 128.4,

127.3, 127.1, 126.7, 125.9, 41.2, 31.6, 23.1.

6,7-Dimethyl-2,3-dihydrophenanthren-4(1H)-one (7b). This

compound was synthesized using a modiﬁed literature proce-

36−38

dure.

A 500 mL three-necked round-bottom ﬂask equipped

with a magnetic stir bar was charged with CH Cl₂(30 mL),

nitromethane (25 mL), succinic anhydride (2.9 g, 29 mmol), and

AlCl (12.8 g, 96 mmol). The ﬂask was immersed in an ice bath, and a

solution of 2,3-dimethylnaphthalene (5.0 g, 32 mmol) in CH C1 (40

mL) was added dropwise to the stirred mixture over a 1 h period.

After 30 min, the ice bath was removed and the dark solution was

stirred overnight. The reaction mixture was carefully poured into a

mixture of ice and concentrated HCl. Hexanes (200 mL) was added,

and the mixture was stirred for 10 min. The precipitate was collected

by ﬁltration and was thoroughly washed with H O. The solid was

recrystallized from acetic acid to aﬀord purple crystals of 4-(6,7-

dimethylnaphthalen-2-yl)-4-oxobutanoic acid (5.9 g, 72%). To a

solution of the keto acid (5.1 g, 20 mmol) in diethylene glycol (150

mL) was added hydrazine monohydrate (3.5 g, 70 mmol), and the

reaction mixture was stirred at 100 °C for 1 h. Potassium hydroxide

(3.9 g, 70 mmol) was added, and the reaction mixture was stirred at

260 °C for 2 h. After the mixture was cooled to room temperature,

H O (50 mL) was added, and the mixture was poured into a mixture

of ice and concentrated HCl. The precipitate was removed by

NMR tube. The tube was capped, wrapped with Paraﬁlm, and

removed from the glovebox. The tube was then transferred to a NMR

probe for data acquisition. The sample was allowed to equilibrate for

at least 5 min at the indicated probe temperature prior to each

measurement. The isomerization of 14a exhibits reversible ﬁrst-order

kinetics and was monitored by following the integration of signals at

ﬁltration and was thoroughly washed with H O. The crude product

was dissolved in CH Cl (400 mL), and the solution was washed with

H O (2 × 100 mL). The organic phase was dried over anhydrous

MgSO₄and ﬁltered. The solvent was evaporated, aﬀording the

product as greenish yellow solid of 4-(6,7-dimethylnaphthalen-2-

yl)butanoic acid (4.0 g, 83%). A 250 mL round-bottom ﬂask

equipped with a magnetic stir bar was charged with the acid (4.0 g,

16.5 mmol) and methanesulfonic acid (60 mL). The solution was

stirred for 2 h at 50 °C. After it was cooled to room temperature, the

0.00−9.89 ppm (14a-syn) and at 9.77−9.74 ppm (14a-anti). At

equilibrium, the syn/anti isomer ratio is ca. 1.2/1.

,3-Dihydrophenanthren-4(1H)-one (7a). This compound was

36−38

synthesized using a modiﬁed literature procedure.

A 500 mL

reaction mixture was poured into ice and extracted with Et O (3 ×

three-necked round-bottom ﬂask equipped with a magnetic stir bar

100 mL). The combined organic phases were washed with saturated

was charged with CH Cl (100 mL), nitromethane (500 mL),

aqueous NaHCO (2 × 100 mL) and were dried over anhydrous

succinic anhydride (8.2 g, 64 mmol), and AlCl (25.6 g, 192 mmol).

MgSO . The solvent was evaporated, aﬀording the product as a yellow

The ﬂask was immersed in an ice bath, and a solution of naphthalene

solid (2.9 g, 77%). This compound is known. H NMR (400 MHz,

(

5.8 g, 58 mmol) in CH C1 (40 mL) was added dropwise to the

CDCl , ppm): δ 9.20 (s, 1H), 7.81 (d, J = 8.4 Hz, 1H), 7.54 (s, 1H),

stirred mixture over a 1 h period. After 30 min, the ice bath was

removed and the dark solution was stirred overnight. The reaction

mixture was carefully poured into a mixture of ice and concentrated

HCl. Hexanes (200 mL) was added, and the mixture was stirred for

7.22 (d, J = 8.4 Hz, 1H), 3.09 (t, J = 6.1 Hz, 2H), 2.77 (t, J = 6.6 Hz,

2H), 2.47 (s, 3H), 2.41 (s, 3H), 2.24−2.10 (m, 2H). C NMR (151

MHz, CDCl , ppm): δ 200.7, 146.0, 139.0, 135.4, 133.5, 131.9, 130.2,

128.0, 126.7, 126.3, 126.1, 41.2, 31.7, 23.2, 20.9, 20.0.

Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

,3-Dihydrophenanthren-4(1H)-one O-Pivaloyl Oxime (8a).

7.72−7.55 (m, 4H), 7.47−7.36 (m, 2H), 7.01 (dd, J = 6.6, 2.2 Hz,

A 100 mL round-bottom ﬂask equipped with a magnetic stir bar and a

1H), 4.42 (s, 2H). C NMR (151 MHz, CDCl , ppm): δ 145.2,

condenser was charged with 7a (4.7 g, 24 mmol), NH OH·HCl (2.7

134.5, 132.9, 131.0, 128.8, 127.9, 127.3, 126.8, 126.1, 125.8, 125.6,

g, 39 mmol), NaOH (5.1 g, 128 mmol), EtOH (60 mL), and H O (6

120.3, 119.7, 115.6. HRMS (+ESI): calculated for C H N [M + H]

14 11

mL). The reaction mixture was stirred at reﬂux for 30 min. After it

was cooled to room temperature, the reaction mixture was poured

194.0964, found 194.0962.

6,7-Dimethylphenanthren-4-amine (9b). This compound was

into H O (200 mL). The precipitate was collected by ﬁltration and

synthesized using the procedure described for 9a with oxime 8b (1.62

thoroughly washed with H O, aﬀording the 2,3-dihydrophenanthren-

g, 5 mmol), Pd(OAc) (0.12 g, 0.5 mmol), tricyclopentylphosphine

(1H)-one oxime as a white solid (5.0 g, 99%). A 100 mL round-

(0.25 mL, 1.0 mmol), pivalic acid (0.16 g, 1.5 mmol), K CO (2.8 g,

20 mmol), and toluene (35 mL). Yield: 0.93 g, 84%. H NMR (400

bottom ﬂask equipped with a magnetic stir bar was charged with the

oxime (2.1 g, 10 mmol) and CH Cl (150 mL). The ﬂask was

immersed in an ice bath, and Et N (4.2 mL, 30 mL) was added,

followed by pivaloyl chloride (2.6 mL, 20 mmol). The ice bath was

removed, and the reaction mixture was stirred at room temperature

overnight. The reaction mixture was transferred to a separatory

MHz, CDCl , ppm): δ 8.99 (s, 1H), 7.65 (s, 1H), 7.57 (s, 2H), 7.37−

7.32 (m, 2H), 7.01−6.94 (m, 1H), 4.42 (s, 2H), 2.51 (s, 3H), 2.46 (s,

3H). C NMR (101 MHz, CDCl , ppm): δ 145.0, 135.2, 134.8,

134.3, 131.5, 129.3, 129.0, 126.9, 126.8, 126.3, 126.1, 120.3, 119.6,

115.2, 20.9, 19.9. HRMS (+ESI): calculated for C H N [M + H]

funnel. The organic phase was washed with H O (3 × 100 mL). The

222.1277, found 222.1275.

Ligand 10a. This compound was synthesized using a modiﬁed

literature procedure. A 2 dram vial was charged with 9a (235 mg,

1.2 mmol), 2,3-butadione (52 mg, 0.6 mmol), formic acid (2 drops),

and methanol (2 mL). The reaction mixture was stirred at 80 °C

overnight. A yellow precipitate formed. After the mixture was cooled

to room temperature, the solid was collected by ﬁltration, washed

combined organic phases were dried over anhydrous MgSO , ﬁltered,

concentrated on silica gel, and puriﬁed by column chromatography on

silica gel (eluent hexanes/EtOAc 6/1), aﬀording the product as a light

yellow solid (2.9 g, 94%). H NMR (600 MHz, CDCl , ppm): δ 9.27

(

d, J = 8.3 Hz, 1H), 7.80 (d, J = 8.3 Hz, 2H), 7.67−7.57 (m, 1H),

.46 (dd, J = 7.2, 7.1 Hz, 1H), 7.28 (d, J = 8.3 Hz, 1H), 3.04 (t, J =

.8 Hz, 2H), 2.92−2.85 (m, 2H), 1.94−1.83 (m, 2H), 1.39 (s, 9H).

with cold methanol, and dried under vacuum, aﬀording the product as

C NMR (151 MHz, CDCl , ppm): δ 175.3, 163.2, 142.3, 133.4,

a yellow solid (233 mg, 89%). H NMR (600 MHz, CDCl , ppm): δ

31.2, 130.9, 128.4, 128.2, 127.6, 126.7, 125.6, 125.3, 39.0, 31.3, 27.5,

9.07 (d, J = 8.5 Hz, 2H), 7.93 (d, J = 7.5 Hz, 2H), 7.84−7.71 (m,

6H), 7.64 (dd, J = 7.6, 7.6 Hz, 2H), 7.58 (dd, J = 7.0, 7.3 Hz, 2H),

7.48 (dd, J = 7.3, 7.2 Hz, 2H), 6.96 (d, J = 7.3 Hz, 2H), 2.43 (s, 6H).

7.0, 20.9. HRMS (+ESI): calculated for C H NO [M + Na]

18.1465, found 318.1466.

,7-Dimethyl-2,3-dihydrophenanthren-4(1H)-one O-Pivalo-

C NMR (151 MHz, CDCl , ppm): δ 167.9, 149.2, 134.4, 133.3,

yl Oxime (8b). A 100 mL round-bottom ﬂask equipped with a

magnetic stir bar and a condenser was charged with 7b (2.85 g, 12.7

mmol), NH OH·HCl (1.41 g, 20.3 mmol), NaOH (2.54 g, 63.5

mmol), EtOH (15 mL), and H O (3 mL). The reaction mixture was

stirred at reﬂux for 30 min. After it was cooled to room temperature,

the reaction mixture was poured into H O (100 mL). The precipitate

was collected by ﬁltration and thoroughly washed with H O, aﬀording

130.8, 128.7, 128.1, 127.9, 127.7, 126.5, 126.4, 126.1, 125.5, 121.7,

116.7, 16.8. HRMS (+ESI): calculated for C H N [M + H]⁺

437.2012, found 437.2012..

Ligand 10b. This compound was synthesized using the procedure

described for ligand 10a with amine 9b (332 mg, 1.5 mmol), 2,3-

butadione (60 mg, 0.7 mmol), HCOOH (2 drops), and methanol (5

mL). Yield: 0.29 g, 83%. H NMR (400 MHz, CD Cl , ppm): δ 8.82

the 6,7-dimethyl-2,3-dihydrophenanthren-4(1H)-one oxime as a

white solid (3.0 g, 99%). A 100 mL round-bottom ﬂask equipped

with a magnetic stir bar was charged with the oxime (1.2 g, 5 mmol)

and CH Cl (80 mL). The ﬂask was immersed in an ice bath, and

(s, 2H), 7.91−7.36 (m, 10H), 6.92 (d, J = 7.5 Hz, 2H), 2.41 (s, 12H),

2.09 (s, 6H). C NMR (101 MHz, CD Cl , ppm): δ 168.1, 149.6,

136.0, 135.8, 134.6, 132.2, 129.0, 128.9, 127.7, 127.0, 126.4, 125.6,

121.6, 116.6, 31.2, 20.8, 20.0, 16.6. HRMS (+ESI): calculated for

Et N (2.1 mL, 15 mL) was added, followed by pivaloyl chloride (1.3

C H N [M + H] 493.2638, found 493.2639.

36 32

mL, 10 mmol). The ice bath was removed, and the reaction mixture

was stirred at room temperature overnight. The reaction mixture was

transferred to a separatory funnel. The organic phase was washed with

Ligand 11a. This compound was synthesized using a modiﬁed

22,29

literature procedure.

A 2 dram vial was charged with 9a (440 mg,

2.3 mmol), acenaphthenequinone (200 mg, 1.1 mmol), ZnCl (180

H O (3 × 50 mL). The combined organic phases were dried over

mg, 1.3 mmol), and acetic acid (4 mL). The reaction mixture was

stirred at 120 °C for 30 min. After the mixture was cooled to room

temperature, the solid was separated by ﬁltration, washed with acetic

acid, and dried under vacuum, aﬀording the zinc complex as a dark

red solid. A 100 mL round-bottom ﬂask equipped with a magnetic stir

bar was charged with the zinc complex, sodium oxalate (1.34 g, 10

anhydrous MgSO , ﬁltered, concentrated on silica gel and puriﬁed by

column chromatography on silica gel (eluent hexanes/EtOAc 6/1),

aﬀording the product as a white solid (1.5 g, 90%). H NMR (400

MHz, CDCl , ppm): δ 9.10 (s, 1H), 7.69 (d, J = 8.3 Hz, 1H), 7.54 (s,

H), 7.18 (d, J = 8.3 Hz, 1H), 3.02 (t, J = 6.8 Hz, 2H), 2.86 (t, J = 6.0

Hz, 2H), 2.50 (s, 3H), 2.41 (s, 3H), 1.93−1.81 (m, 2H), 1.40 (s, 9H).

mmol), methylene chloride (10 mL), and H O (2 mL). The reaction

C NMR (101 MHz, CDCl , ppm): δ 175.3, 163.3, 141.4, 138.0,

mixture was stirred at room temperature for 1 h. The two phases were

separated, the organic layer was dried over anhydrous Na SO and

35.1, 132.3, 130.3, 129.7, 127.9, 127.4, 125.8, 124.3, 39.0, 31.3, 27.6,

7.0, 21.2, 21.0, 20.0. HRMS (+ESI): calculated for C H NO [M +

ﬁltered, and the solvents were evaporated, aﬀording the product as a

Na] 346.1778, found 346.1779.

Phenanthren-4-amine (9a). This compound was synthesized

using a modiﬁed literature procedure. A 150 mL pressure vessel

equipped with a magnetic stir bar was charged with 8a (1.48 g, 5

red solid (0.58 g, 98%). The H NMR spectrum shows two isomers in

a ca. 7:1 ratio in CD Cl at room temperature. H NMR (600 MHz,

CD Cl , ppm): major isomer, δ 9.81−9.49 (m, 2H), 7.96−7.88 (m,

6H), 7.84 (d, J = 8.8 Hz, 2H), 7.77 (d, J = 8.2 Hz, 2H), 7.71 (dd, J =

7.6, 7.8 Hz, 2H), 7.67−7.61 (m, 2H), 7.59−7.53 (m, 2H), 7.40 (d, J =

7.3, 2H), 7.19 (dd, J = 7.8, 7.8 Hz, 2H), 6.53 (d, J = 7.5 Hz, 2H);

minor isomer, δ 9.33 (d, J = 8.5 Hz, 2H), 8.44 (d, J = 7.0 Hz, 2H),

8.07 (d, J = 8.3 Hz, 2H), 7.46 (t, J = 7.7, 7.7 Hz, 2H), 7.12 (dd, J =

7.7, 7.9 Hz, 2H), 7.06 (dd, J = 6.9, 7.4 Hz, 2H), 6.88 (d, J = 6.5 Hz,

2H), 6.20 (d, J = 7.2 Hz, 2H). Signals of 10 protons of the minor

mmol), Pd(OAc) (0.12 g, 0.5 mmol), and pivalic acid (0.16 g, 1.5

mmol). The vessel was ﬂushed with nitrogen, capped, and placed

inside a glovebox. To this mixture were added K CO (2.8 g, 20

mmol), toluene (35 mL), and tricyclopentylphosphine (0.25 mL, 1

mmol). The vessel was capped, taken out of the glovebox, stirred at

room temperature for 5 min, and placed in a preheated oil bath (110

C) for 3 days. After it was cooled to room temperature, the reaction

isomer could not be located due to overlap with the major isomer.

mixture was ﬁltered through a pad of neutral alumina. The solids were

washed with EtOAc (200 mL). The combined ﬁltrate and washings

were concentrated on silica gel and puriﬁed by column chromatog-

raphy on silica gel (eluent hexanes/EtOAc 10/1), aﬀording 9a as a tan

NMR (151 MHz, CD Cl , ppm): major isomer, δ 151.0, 142.1, 135.1,

133.7, 131.7, 131.2, 129.6, 129.5, 129.4, 128.9, 128.5, 128.1, 128.0,

127.4, 126.6, 126.4, 126.1, 124.0, 122.2, 116.8, 116.6. Signals of

carbons of the minor isomer are not listed due to their low intensity.

solid (0.49 g, 51%). This compound is known. H NMR (600 MHz,

HRMS (+ESI): calculated for C H N [M + H] 533.2012, found

CDCl , ppm): δ 9.26 (d, J = 8.4 Hz, 1H), 7.91 (d, J = 7.7 Hz, 1H),

533.2010.

Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

Ligand 11b. This compound was synthesized using the procedure

described for ligand 11a with amine 9b (0.48 g, 2.2 mmol),

syn), 8.10−8.05 (m, syn and anti signals overlap), 8.03−7.57 (m, syn

and anti signals overlap), 7.21−7.08 (m, syn and anti signals overlap),

6.30 (d, J = 7.5 Hz, 1H, syn), 8.28 (d, J = 7.4 Hz, 1H, anti), 6.07 (d, J

= 7.5 Hz, 1H, syn), 6.03 (d, J = 7.6 Hz, 1H, anti), 0.79 (s, 3H, anti),

acenaphthenequinone (0.18 g, 1 mmol), ZnCl (0.16 g, 1.2 mmol),

acetic acid (5 mL), sodium oxalate (1.34 g, 10 mmol), CH Cl (20

mL), and H O (10 mL). Yield: 0.53 g, 90%. H NMR (600 MHz,

0.75 (s, 3H, syn). C NMR (151 MHz, CD Cl , ppm): δ 173.4,

CD Cl , ppm): δ 9.35 (s, 2H), 7.90 (dd, J = 7.8, 1.3 Hz, 2H), 7.81 (d,

J = 8.8 Hz, 2H), 7.76 (dd, J = 8.2, 8.8 Hz, 4H), 7.68 (dd, J = 7.6, 7.6

Hz, 2H), 7.65 (s, 2H), 7.32 (dd, J = 7.4, 1.3 Hz, 2H), 7.19 (dd, J =

173.1, 168.5, 168.3, 145.8, 145.7, 145.4, 145.2, 144.73, 144.68, 135.0,

134.9, 134.7, 134.6, 134.2, 134.1, 134.0, 133.9, 131.84, 131.81, 131.52,

131.50, 131.40, 131.36, 130.0, 129.8, 129.7, 129.63, 129.60, 129.5,

129.38, 129.35, 129.3, 129.21, 129.18, 129.16, 129.11, 129.08, 129.02,

128.98, 128.87, 128.85, 128.8, 128.7, 128.5, 128.00, 127.96, 127.9,

127.77, 127.75, 127.7, 127.62, 127.55, 127.4, 127.29, 127.26, 127.22,

127.21, 127.16, 127.0, 126.6, 126.5, 125.4, 125.3, 125.19, 125.15,

123.8, 123.7, 123.6, 123.5, 122.6, 122.2, 121.1, 120.6, 3.2, 3.1. The

.6, 8.2 Hz, 2H), 6.49 (d, J = 7.4 Hz, 2H), 2.46 (s, 6H), 2.40 (s, 6H).

C NMR (151 MHz, CD Cl , ppm): δ 160.9, 151.3, 142.6, 136.8,

(

36.4, 135.3, 132.7, 132.0, 130.9, 129.7, 129.64, 129.62, 129.3, 128.5,

28.4, 127.2, 127.1, 126.4, 124.3, 122.3, 115.8, 21.8, 20.4. HRMS

+ESI): calculated for C H N [M + H]⁺589.2638, found

44 32 2

89.2639.

Palladium Complex 12a. Ligand 10a (120 mg, 0.275 mmol) and

signals of six carbons could not be located. HRMS (+ESI): calculated

for C41H

Pd [M] 653.1218, found 653.1199.

Pd(COD)MeCl (67 mg, 0.25 mmol) were placed in a 50 mL Schlenk

ﬂask equipped with a magnetic stir bar. Methylene chloride (10 mL)

was added, and the reaction mixture was stirred at room temperature

overnight. Pentane (20 mL) was added, and the solid was collected by

ﬁltration, washed with pentane (2 × 10 mL), and dried under

vacuum, aﬀording the product as an orange solid (110 mg, 74%). The

Palladium Complex 14a-syn. Ligand 11a (150 mg, 0.275 mmol)

and Pd(COD)MeCl (67 mg, 0.25 mmol) were placed in a 500 mL

Schlenk ﬂask equipped with a magnetic stir bar. Methylene chloride

(50 mL) was added, and the reaction mixture was stirred at room

temperature overnight. A small sample was taken and characterized by

H NMR, showing a ca. 1/1 mixture of syn/anti isomers. Toluene

H NMR spectrum shows two isomers in a ca. 1.5/1 ratio in CD Cl

(250 mL) was added, and the resulting mixture was carefully

concentrated at 60 °C until ca. 100 mL. The solid was collected by

ﬁltration, washed with toluene (10 mL), and dried under vacuum,

at room temperature. H NMR (600 MHz, CD Cl , ppm): δ 9.54 (d,

J = 8.4 Hz, 1H, minor), 9.41 (d, J = 8.5 Hz, 1H, minor), 9.22 (d, J =

.5 Hz, 1H, major), 9.16 (d, J = 8.5 Hz, 1H, major), 8.07−7.64 (m,

aﬀording the product as red solid (93 mg, 54%). The H NMR

major and minor signals overlap), 7.38 (dd, J = 7.5, 1.4 Hz, 1H,

major), 7.36 (dd, J = 7.4, 1.3 Hz, 1H, major), 7.32 (dd, J = 4.2, 1.4

Hz, 1H, minor), 7.31 (dd, J = 4.2, 1.4 Hz, 1H, minor), 1.86 (s, 3H,

minor), 1.84 (s, 3H, major), 1.83 (s, 3H, minor), 1.78 (s, 3H, major),

spectrum shows nearly pure 14a-syn with a syn/anti isomer ratio of ca.

30/1. The ﬁltrate was brought to dryness at 60 °C. The residue was

dissolved in CD

and characterized by H NMR, showing a ca. 3/1

mixture of syn/anti isomers. X-ray-quality crystals were grown by

.49 (s, 3H, major), 0.47 (s, 3H, minor). C NMR measurements

layering pentane over a solution of 12b-syn in CH

2 2

Cl at −20 °C. H

were not taken due to the poor solubility of the compound. HRMS

NMR (600 MHz, CD Cl , ppm): δ 9.95 (dd, J = 8.5, 8.5 Hz, 2H),

(

+ESI): calculated for C H N Pd [M] 557.1216, found 557.1214.

8.14 (d, J = 7.6 Hz, 1H), 8.06 (d, J = 7.7 Hz, 1H), 8.03−7.82 (m,

11H), 7.80 (dd, J = 7.6, 7.6 Hz, 1H), 7.75−7.55 (m, 4H), 7.18 (dd, J

= 7.9, 7.9 Hz, 1H), 7.14 (dd, J = 7.9, 7.9 Hz, 1H), 6.30 (d, J = 7.5 Hz,

Palladium Complex 13a. Complex 12a (89 mg, 0.15 mmol),

NaBArF (140 mg, 0.15 mmol), and acetonitrile (0.1 mL) were placed

in a 50 mL Schlenk ﬂask equipped with a magnetic stir bar. Methylene

chloride (30 mL) was added, and the reaction mixture was stirred at

room temperature for 4 h. The mixture was ﬁltered through a pad of

Celite, and the volatiles were removed. The residue was washed with

pentane (2 × 10 mL) and dried under vacuum, aﬀording the product

1H), 6.07 (d, J = 7.5 Hz, 1H), 0.75 (s, 3H). C NMR (151 MHz,

CD Cl , ppm): δ 173.2, 168.3, 145.6, 145.0, 144.5, 134.5, 134.3,

133.8, 133.6, 131.7, 131.2, 131.1, 129.7, 129.48, 129.46, 129.2, 128.1,

129.01, 128.95, 128.9, 128.7, 128.6, 128.2, 127.83, 127.77, 127.61,

127.56, 127.4, 127.12, 127.07, 127.0, 126.2, 125.2, 125.1, 123.3, 122.3,

as a red solid (190 mg, 87%). The H NMR spectrum shows two

120.8, 3.0. The signals of three carbons could not be located. HRMS

isomers in a ca. 1/1 ratio in CD Cl at room temperature. 1H NMR

(+ESI): calculated for C41

Pd [M] 653.1218, found 653.1214.

(

600 MHz, CD Cl , ppm): δ 9.19 (d, J = 8.5 Hz, 1H), 9.09 (d, J = 8.4

Palladium Complex 14b. This complex was synthesized using

the procedure described for complex 12a with ligand 11b (130 mg,

Hz, 1H), 8.87 (d, J = 8.3 Hz, 1H), 8.83 (d, J = 8.4 Hz, 1H), 8.13−

.99 (m, syn and anti signals overlap), 7.97−7.88 (m, syn and anti

0.22 mmol), Pd(COD)MeCl (54 mg, 0.20 mmol), and CH

mL). Yield: 120 mg, 80%. X-ray-quality crystals were grown by

layering pentane over a solution of 14b in CH Cl at room

temperature. H NMR (600 MHz, CD Cl , ppm): δ 9.81 (s, 1H),

2 2

Cl (10

signals overlap), 7.87−7.70 (m, syn and anti signals overlap), 7.55 (s,

H), 7.32−7.169 (m, syn and anti signals overlap), 2.492 (s, 3H),

.490 (s, 3H), 2.13 (s, 3H), 2.09 (s, 3H), 1.28 (s, 3H), 1.25 (s, 3H),

.402 (s, 3H), 0.400 (s, 3H). C NMR (151 MHz, CD Cl , ppm): δ

9.80 (s, 1H), 8.11 (dd, J = 7.9, 1.4 Hz, 1H), 8.03 (dd, J = 7.9, 1.3 Hz,

1H), 7.91−7.77 (m, 7H), 7.74 (d, J = 8.8 Hz, 1H), 7.67 (s, 1H), 7.63

(s, 1H), 7.56 (dd, J = 7.4, 1.4 Hz, 1H), 7.53 (dd, J = 7.4, 1.3 Hz, 1H),

7.14 (dd, J = 7.9, 7.9 Hz, 1H), 7.11 (dd, J = 7.9, 7.9 Hz, 1H), 6.15 (d,

J = 7.4 Hz, 1H), 5.96 (d, J = 7.4 Hz, 1H), 2.69 (s, 3H), 2.67 (s, 3H),

81.4, 181.2, 172.3, 171.8, 162.3 (q, J_C₋_B= 50 Hz), 144.1, 144.0,

43.8, 143.6, 135.3 (bs), 135.0, 134.9, 134.8, 134.5, 134.4, 134.0,

33.9, 130.5, 130.4, 130.15, 130.13, 130.09, 130.06, 130.0, 129.7,

29.6, 129.5, 129.44, 129.38 (q, J_C₋_F= 32 Hz), 129.3, 129.1, 128.9,

28.7, 128.29, 128.27, 128.2, 128.04, 127.99, 127.96, 127.9, 127.80,

27.78, 127.6, 127.5, 127.4, 127.22, 127.20, 127.1, 126.9, 126.6, 125.1

2.41 (s, 3H), 2.40 (s, 3H), 0.82 (s, 3H). C NMR (151 MHz,

CD Cl , ppm): δ 172.9, 168.1, 145.6, 145.0, 144.8, 137.3, 136.9,

(

q, J_C₋_F= 273 Hz), 123.5, 123.4, 123.0, 122.9, 121.7, 121.29, 121.26,

21.1, 121.0, 120.5, 118.1−117.9 (m), 22.4, 22.0, 21.6, 21.1, 7.1, 7.0,

.3, 2.2. The signals of ﬁve carbons could not be located. F NMR

(

565 MHz, CD Cl , ppm): δ −62.7. HRMS (+ESI): calculated for

C H N Pd [M] 598.1482, found 598.1475.

Palladium Complex 14a. This complex was synthesized using

the procedure described for complex 12a with ligand 11a (150 mg,

.275 mmol), Pd(COD)MeCl (70 mg, 0.25 mmol), and CH Cl (50

mL). Yield: 120 mg, 70%. The H NMR spectrum shows two isomers

in a ca. 1/1 ratio in CD Cl at room temperature. X-ray-quality

crystals were grown by layering pentane over a solution of 14a in

CH Cl at room temperature. The syn and anti isomers crystallize

concurrently, and crystal picking allowed us to obtain each isomer for

9.50 (d, J = 9.2 Hz, 1H, syn), 9.40 (d, J = 8.6 Hz, 1H, anti), 9.27 (d, J

= 8.5 Hz, 1H, anti), 8.27−8.15 (m, syn and anti signals overlap),

8.14−8.04 (m, syn and anti signals overlap), 8.03−7.71 (m, syn and

anti signals overlap), 7.67−7.46 (m, syn and anti signals overlap),

X-ray analysis. H NMR (600 MHz, CD Cl , ppm): δ 9.94 (dd, J =

.2, 8.2 Hz, 2H, syn), 9.76 (d, J = 8.6 Hz, 1H, anti), 9.73 (d, J = 8.5

Hz, 1H, anti), 8.16 (d, J = 7.9 Hz, 1H, anti), 8.14 (d, J = 7.9 Hz, 1H,

Organometallics XXXX, XXX, XXX−XXX

Organometallics

The Supporting Information is available free of charge at

Article

.36−7.26 (m, syn and anti signals overlap), 6.28 (d, J = 7.5 Hz, 1H,

red solid. Yield: 130 mg, 91%. Anal. Calcd for C H Br N Ni: C,

36 32 2 2

60.80; H, 4.54; N, 3.94. Found: C, 60.64; H, 4.57; N, 3.99.

syn), 6.17 (d, J = 7.5 Hz, 1H, anti), 1.29 (s, 3H, anti), 1.28 (s, 3H,

syn), 0.67 (s, 3H, anti), 0.60 (s, 3H, syn). C NMR (151 MHz,

CD Cl , ppm): δ 177.4, 177.2, 168.7, 168.4, 162.3 (q, J = 50 Hz),

C−B

ASSOCIATED CONTENT

sı Supporting Information

■

46.3, 144.1, 144.1, 144.0, 143.9, 135.1 (bs), 135.2, 135.1, 134.5,

34.4, 134.0, 133.9, 133.6, 133.03, 132.97, 131.9, 131.8, 130.9, 130.7,

30.7, 130.3, 130.2, 130.0, 129.9, 129.8, 129.70, 129.67, 129.6, 129.53,

29.52, 129.41 (q, J_C₋_F= 32 Hz), 129.40, 129.3, 129.2, 128.9, 128.8,

28.6, 128.4, 128.3, 128.2, 128.10, 128.06, 128.03, 128.01, 127.96,

27.93, 127.89, 127.85, 127.82, 127.80, 127.7, 127.63, 127.57, 126.9,

26.8, 126.5, 126.3, 125.8, 125.7, 125.1 (q, J_C₋_F= 273 Hz), 123.9,

23.9, 123.5, 123.3, 122.40, 121.8, 121.4, 121.2, 121.2, 120.9, 118.3−

https://pubs.acs.org/doi/10.1021/acs.organomet.0c00696.

NMR spectra of the compounds, supporting ﬁgures,

characterization of polymers, and X-ray crystallographic

data (PDF )

17.8 (m), 7.7, 7.6, 2.2 (two Pd-CH signals overlap). Signals of nine

Accession Codes

carbons could not be located. F NMR (565 MHz, CD Cl , ppm): δ

CCDC 2042450−2042452 contain the supplementary crys-

tallographic data for this paper. These data can be obtained

free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by

emailing data_request@ccdc.cam.ac.uk, or by contacting The

Cambridge Crystallographic Data Centre, 12 Union Road,

Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

−

62.7. HRMS (+ESI): calculated for C H N Pd [M] 694.1484,

43 30 3

found 694.1478.

Palladium Complex 15a-syn. Complex 14a-syn (74 mg, 0.11

mmol), NaBArF (100 mg, 0.11 mmol), and acetonitrile (0.05 mL)

were placed in a 50 mL Schlenk ﬂask equipped with a magnetic stir

bar. Methylene chloride (15 mL) was added, and the reaction mixture

was stirred at 0 °C for 4 h. The mixture was ﬁltered through a pad of

Celite, and the volatiles were removed under vacuum at 0 °C. The

residue was washed with pentane (2 × 10 mL) and dried under

vacuum, aﬀording the product as a red solid (140 mg, 86%). The H

NMR spectrum shows syn/anti isomers in ca. 10/1 ratio in CD Cl at

room temperature. H NMR (500 MHz, CD Cl , ppm): δ 9.60 (d, J =

AUTHOR INFORMATION

Corresponding Authors

■

Maurice Brookhart − Department of Chemistry, University of

Houston, Houston, Texas 77204-5003, United States;

Email: mbrookha@central.uh.edu

.6 Hz, 1H), 9.51 (d, J = 8.4 Hz, 1H), 8.20 (d, J = 7.9 Hz, 1H), 8.16

(

dd, J = 7.5, 1.3 Hz, 1H), 8.14−8.04 (m, 4H), 8.03−7.95 (m, 4H),

Olafs Daugulis − Department of Chemistry, University of

Houston, Houston, Texas 77204-5003, United States;

orcid.org/0000-0003-2642-2992; Email: olafs@uh.edu

.89−7.72 (m, 14H), 7.62−7.47 (m, 8H), 7.31 (dd, J = 7.9, 8.0 Hz,

H), 6.29 (d, J = 7.4 Hz, 1H), 1.28 (s, 3H), 0.61 (s, 3H). C NMR

= 50 Hz),

(

151 MHz, CD Cl , ppm): δ 177.2, 168.2, 162.1 (q, J

C−B

46.0, 143.74, 143.72, 135.1 (bs), 134.8, 134.7, 134.1, 133.6, 133.4,

32.8, 131.5, 130.7, 130.5, 130.0, 129.8, 129.5, 129.40, 129.36, 129.2,

29.1 (q, J_C₋_F= 32 Hz), 129.03, 128.98, 128.9, 128.8, 128.5, 128.2,

28.0, 127.8, 127.7, 127.6, 127.5, 126.7, 126.2, 126.1, 125.6, 124.8 (q,

Authors

Quan H. Tran − Department of Chemistry, University of

Houston, Houston, Texas 77204-5003, United States;

orcid.org/0000-0002-7269-3163

Xiqu Wang − Department of Chemistry, University of

Houston, Houston, Texas 77204-5003, United States

J_C₋_F= 273 Hz), 123.7, 122.9, 122.2, 121.2, 120.9, 118.1−117.6 (m),

.2, 2.1. The signal of one carbon could not be located. F NMR

(

565 MHz, CD Cl , ppm): δ −62.6. HRMS (+ESI): calculated for

C H N Pd [M] 694.1484, found 694.1480.

Complete contact information is available at:

https://pubs.acs.org/10.1021/acs.organomet.0c00696

Palladium Complex 15b. This complex was synthesized using

the procedure described for complex 13a with complex 14b (120 mg,

.16 mmol), NaBArF (150 mg, 0.16 mmol), acetonitrile (0.15 mL),

and CH Cl (10 mL). Yield: 250 mg, 96%. H NMR (600 MHz,

Notes

CD Cl , ppm): δ 9.39 (s, 1H), 9.26 (s, 1H), 8.18 (dd, J = 8.0, 1.3 Hz,

The authors declare no competing ﬁnancial interest.

H), 8.15 (dd, J = 7.9, 1.3 Hz, 1H), 8.07 (d, J = 8.0 Hz, 1H), 8.05 (d,

J = 8.3 Hz, 1H), 7.92−7.80 (m, 7H), 7.79−7.69 (m, 10H), 7.56 (s,

ACKNOWLEDGMENTS

■

H), 7.54−7.43 (m, 3H), 7.29 (dd, J = 7.9, 7.9 Hz, 1H), 6.11 (d, J =

This research was supported by the U.S. Department of

Energy, Oﬃce of Science, Oﬃce of Basic Energy Sciences,

under Award DE-SC0021403, and by the Welch Foundation

(Chair No. E-0044 to O.D. and Grant No. E-1893 to M.B.).

The DSC systems used in polymer analysis were funded by the

Welch Foundation (Grant No. H-E-0041) through the UH

Center of Excellence in Polymer Chemistry.

.5 Hz, 1H), 2.75 (s, 3H), 2.58 (s, 3H), 2.54 (s, 3H), 2.43 (s, 3H),

.27 (s, 3H), 0.74 (s, 3H). C NMR (151 MHz, CD Cl , ppm): δ

77.0, 168.1, 162.4 (q, J_C₋_B= 50 Hz), 146.4, 143.8, 143.7, 138.2,

37.7, 137.3, 136.9, 135.4 (bs), 135.3, 135.1, 133.6, 133.0, 132.9,

32.6, 131.8, 130.7, 130.5, 130.1, 129.8, 129.6, 129.5 (q, J_C₋_F= 32

Hz), 129.39, 129.35, 129.3, 129.2, 129.0, 128.1, 127.3, 127.1, 127.04,

27.00, 126.9, 126.8, 126.4, 126.3, 125.7, 125.2 (q, J_C₋_F= 273 Hz),

23.6, 123.2, 121.3, 121.1, 120.1, 118.3−117.9 (m), 21.80, 21.78,

0.3, 20.0, 7.8, 2.2. F NMR (565 MHz, CD Cl , ppm): δ −62.5.

REFERENCES

HRMS (+ESI): calculated for C H N Pd [M] 750.2112, found

■

50.2105.

Nickel Complex 16a. Ligand 10a (120 mg, 0.275 mmol) and

DME)NiBr (74 mg, 0.24 mmol) were placed in a 50 mL Schlenk

(1) Johnson, L. K.; Killian, C. M.; Brookhart, M. New Pd(II)- and

Ni(II)-Based Catalysts for Polymerization of Ethylene and α -Olefins.

J. Am. Chem. Soc. 1995, 117, 6414−6415.

(

ﬂask equipped with a magnetic stir bar. Methylene chloride (10 mL)

was added, and reaction mixture was stirred at room temperature

overnight. Diethyl ether (10 mL) was added, and the solid was

collected by ﬁltration, washed with ether (2 × 10 mL), and dried

under vacuum, aﬀording the product as a brick red solid (140 mg,

(2) Johnson, L. K.; Mecking, S.; Brookhart, M. Copolymerization of

Ethylene and Propylene with Functionalized Vinyl Monomers by

Palladium(II) Catalysts. J. Am. Chem. Soc. 1996, 118, 267−268.

(3) Mecking, S.; Johnson, L. K.; Wang, L.; Brookhart, M.

Mechanistic Studies on the Palladium-Catalyzed Copolymerization

of Ethylene and α -Olefins with Methyl Acrylate. J. Am. Chem. Soc.

1998, 120, 888−899.

(4) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Late Metal Catalysts

for Ethylene Homo- and Copolymerization. Chem. Rev. 2000, 100,

1169−1203.

9%). Anal. Calcd for C H Br N Ni: C, 58.67; H, 3.69; N, 4.28.

32 24 2 2

Found: C, 58.88; H, 3.60; N, 4.26.

Nickel Complex 16b. This complex was synthesized using the

procedure described for complex 16a with ligand 10b (108 mg, 0.22

mmol), (DME)NiBr (62 mg, 0.20 mmol), and CH Cl (7 mL). Brick

Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

5) Rhinehart, J. L.; Mitchell, N. E.; Long, B. K. Enhancing α -

(22) Zhang, D.; Nadres, E. T.; Brookhart, M.; Daugulis, O. Synthesis

of Highly Branched Polyethylene Using “Sandwich ” (8-p-Tolyl

naphthyl α -diimine)nickel(II) Catalysts. Organometallics 2013, 32,

5136−5143.

(23) Allen, K. E.; Campos, J.; Daugulis, O.; Brookhart, M. Living

Polymerization of Ethylene and Copolymerization of Ethylene/

Methyl Acrylate Using “Sandwich ” Diimine Palladium Catalysts. ACS

Catal. 2015, 5, 456−464.

Diimine Catalysts for High-Temperature Ethylene Polymerization.

ACS Catal. 2014, 4, 2501−2504.

6) Dai, S.; Zhou, S.; Zhang, W.; Chen, C. Systematic Investigations

of Ligand Steric Effects on α -Diimine Palladium Catalyzed Olefin

Polymerization and Copolymerization. Macromolecules 2016, 49,

(

855−8862.

7) Liu, F.-S.; Hu, H.-B.; Xu, Y.; Guo, L.-H.; Zai, S.-B.; Song, K.-M.;

Gao, H.-Y.; Zhang, L.; Zhu, F.-M.; Wu, Q. Thermostable α -Diimine

Nickel(II) Catalyst for Ethylene Polymerization: Effects of the

Substituted Backbone Structure on Catalytic Properties and

Branching Structure of Polyethylene. Macromolecules 2009, 42,

(24) Wang, B.; Daugulis, O.; Brookhart, M. Ethylene Polymerization

with Ni(II) Diimine Complexes Generated from 8-Halo-1-naphthyl-

amines: The Role of Equilibrating Syn/Anti Diastereomers in

Determining Polymer Properties. Organometallics 2019, 38, 4658−

4668.

789−7796.

(

25) Gates, D. P.; Svejda, S. A.; Onate, E.; Killian, C. M.; Johnson, L.

8) Rose, J. M.; Cherian, A. E.; Coates, G. W. Living Polymerization

K.; White, P. S.; Brookhart, M. Synthesis of Branched Polyethylene

Using (α -Diimine)nickel(II) Catalysts: Influence of Temperature,

Ethylene Pressure, and Ligand Structure on Polymer Properties.

Macromolecules 2000, 33, 2320−2334.

of α -Olefins with an α -Diimine Ni(II) Catalyst: Formation of Well-

Defined Ethylene −Propylene Copolymers through Controlled Chain-

Walking. J. Am. Chem. Soc. 2006, 128, 4186−4187.

9) Gong, Y.; Li, S.; Gong, Q.; Zhang, S.; Liu, B.; Dai, S. Systematic

(26) Kocen, A. L.; Brookhart, M.; Daugulis, O. A highly active

Investigations of Ligand Steric Effects on α -Diimine Nickel Catalyzed

Olefin Polymerization and Copolymerization. Organometallics 2019,

Ni(II)-triadamantylphosphine catalyst for ultrahigh-molecular-weight

polyethylene synthesis. Nat. Commun. 2019 , 10 , 438.

10) Zhong, L.; Li, G.; Liang, G.; Gao, H.; Wu, Q. Enhancing

8, 2919−2926.

Thermal Stability and Living Fashion in α -Diimine −Nickel-Catalyzed

Co)polymerization of Ethylene and Polar Monomer by Increasing

the Steric Bulk of Ligand Backbone. Macromolecules 2017, 50, 2675−

682.

11) (a) Camacho, D. H.; Salo, E. V.; Ziller, J. W.; Guan, Z.

(27) Liang, T.; Goudari, S. B.; Chen, C. A simple and versatile nickel

platform for the generation of branched high molecular weight

polyolefins. Nat. Commun. 2020, 11, 372.

(28) Xia, J.; Zhang, Y.; Kou, S.; Jian, Z. A concerted double-layer

steric strategy enables an ultra-highly active nickel catalyst to access

(29) Rosa, V.; Aviles, T.; Aullon, G.; Covelo, B.; Lodeiro, C. A New

ultrahigh molecular weight polyethylenes. J. Catal. 2020, 390, 30 −36.

Cyclophane-Based Highly Active Late-Transition-Metal Catalysts for

Bis(1-naphthylimino)acenaphthene Compound and Its Pd(II) and

Zn(II) Complexes: Synthesis, Characterization, Solid-State Structures

and Density Functional Theory Studies on the syn and anti Isomers.

Inorg. Chem. 2008, 47, 7734−7744.

Ethylene Polymerization. Angew. Chem., Int. Ed. 2004 , 43 , 1821 −

825. (b) Camacho, D. H.; Guan, Z. Living Polymerization of α -

Olefins at Elevated Temperatures Catalyzed by a Highly Active and

Robust Cyclophane-Based Nickel Catalyst. Macromolecules 2005, 38,

(30) Svejda, S. A.; Johnson, L. K.; Brookhart, M. Low-temperature

spectroscopic observation of chain growth and migratory insertion

544−2546.

barriers in (α -diimine)Ni(II) olefin polymerization catalysts. J. Am.

Chem. Soc. 1999, 121, 10634−10635.

12) Liu, J.; Chen, D.; Wu, H.; Xiao, Z.; Gao, H.; Zhu, F.; Wu, Q.

Polymerization of α -Olefins Using a Camphyl α -Diimine Nickel

Catalyst at Elevated Temperature. Macromolecules 2014, 47, 3325−

(31) Leatherman, M. D.; Svejda, S. A.; Johnson, L. K.; Brookhart, M.

Mechanistic studies of nickel(II) alkyl agostic cations and alkyl

331.

ethylene complexes: Investigations of chain propagation and isomer-

ization in (α -diimine)Ni(II)-catalyzed ethylene polymerization. J. Am.

Chem. Soc. 2003, 125, 3068−3081.

13) Leung, D. H.; Ziller, J. W.; Guan, Z. Axial Donating Ligands: A

New Strategy for Late Transition Metal Olefin Polymerization

Catalysis. J. Am. Chem. Soc. 2008, 130, 7538−7539.

(

14) Meinhard, D.; Wegner, M.; Kipiani, G.; Hearley, A.; Reuter, P.;

(32) Tempel, D. J.; Johnson, L. K.; Huff, R. L.; White, P. S.;

Fischer, S.; Marti, O.; Rieger, B. New Nickel(II) Diimine Complexes

and the Control of Polyethylene Microstructure by Catalyst Design. J.

Am. Chem. Soc. 2007, 129, 9182−9191.

Brookhart, M. Mechanistic studies of Pd(II)-α -diimine-catalyzed

olefin polymerizations. J. Am. Chem. Soc. 2000, 122, 6686 −6700.

(33) Shultz, L. H.; Tempel, D. J.; Brookhart, M. Palladium(II) β

15) Zhang, Y.; Wang, C.; Mecking, S.; Jian, Z. Ultrahigh Branching

agostic alkyl cations and alkyl ethylene complexes: Investigation of

polymer chain isomerization mechanisms. J. Am. Chem. Soc. 2001,

of Main-Chain-Functionalized Polyethylenes by Inverted Insertion

Selectivity. Angew. Chem., Int. Ed. 2020, 59, 14296 −14302.

23, 11539−11555.

16) Rhinehart, J. L.; Brown, L. A.; Long, B. K. A Robust Ni(II) α -

34) Zou, H.; Hu, S.; Huang, H.; Zhu, F.; Wu, Q. Synthesis of

Diimine Catalyst for High Temperature Ethylene Polymerization. J.

Am. Chem. Soc. 2013, 135, 16316 −16319.

bimodal molecular weight distribution polyethylene with α -diimine

nickel(II) complexes containing unsym-substituted aryl groups in the

presence of methylaluminoxane. Eur. Polym. J. 2007 , 43 , 3882 −3891.

17) Zhai, F.; Jordan, R. F. (α -Diimine)nickel Complexes That

Contain Menthyl Substituents: Synthesis, Conformational Behavior,

(35) Sui, X.; Hong, C.; Pang, W.; Chen, C. Unsymmetrical α -

and Olefin Polymerization Catalysis. Organometallics 2017, 36, 2784−

diimine palladium catalysts and their properties in olefin (co)-

18) Chen, Z.; Brookhart, M. Exploring Ethylene/Polar Vinyl

799.

polymerization. Mater. Chem. Front. 2017 , 1 , 967 −972.

(36) Pirkle, W. H.; Selness, S. R. Chiral Recognition Studies: Intra-

Monomer Copolymerizations Using Ni and Pd α -Diimine Catalysts.

Acc. Chem. Res. 2018, 51, 1831−1839.

and Intermolecular 1H{1H}-Nuclear Overhauser Effects as Effective

Tools in the Study of Bimolecular Complexes. J. Org. Chem. 1995, 60,

(

19) Vaccarello, D. N.; O’Connor, K. S.; Iacono, P.; Rose, J. M.;

252−3256.

Cherian, A. E.; Coates, G. W. Synthesis of Semicrystalline Polyolefin

Materials: Precision Methyl Branching via Stereoretentive Chain

Walking. J. Am. Chem. Soc. 2018, 140, 6208 −6211.

(37) Harada, N.; Saito, A.; Koumura, N.; Uda, H.; de Lange, B.;

Jager, W. F.; Wynberg, H.; Feringa, B. L. Chemistry of Unique Chiral

Olefins. 1. Synthesis, Enantioresolution, Circular Dichroism, and

Theoretical Determination of the Absolute Stereochemistry of trans-

and cis-1,1 ‘,2,2 ‘,3,3 ‘,4,4 ‘-Octahydro-4,4 ‘-biphenanthrylidenes. J. Am.

Chem. Soc. 1997, 119, 7241−7248.

20) Kanai, Y.; Foro, S.; Plenio, H. Bispentiptycenyl −Diimine −

Nickel Complexes for Ethene Polymerization and Copolymerization

with Polar Monomers. Organometallics 2019, 38, 544−551.

21) Jia, D.; Zhang, W.; Liu, W.; Wang, L.; Redshaw, C.; Sun, W.-H.

(38) Premasagar, V.; Palaniswamy, V. A.; Eisenbraun, E. J.

Methanesulfonic acid catalyzed cyclization of 3-arylpropanoic and 4-

arylbutanoic acids to 1-indanones and 1-tetralones. J. Org. Chem.

1981, 46, 2974−2976.

Unsymmetrical α -diiminonickel bromide complexes: synthesis,

characterization and their catalytic behavior toward ethylene. Catal.

Sci. Technol. 2013, 3, 2737−2745.

Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

39) Hong, W. P.; Iosub, A. V.; Stahl, S. S. Pd-Catalyzed Semmler −

Wolff Reactions for the Conversion of Substituted Cyclohexenone

Oximes to Primary Anilines. J. Am. Chem. Soc. 2013, 135, 13664−

40) Beringer, F. M.; Chang, L. L.; Fenster, A. N.; Rossi, R. R.

3667.

Synthesis of 4-halophenanthrenes and 4,5-phenanthryleneiodonium

salts. Tetrahedron 1969, 25, 4339−4345.

41) Klimovica, K.; Kirschbaum, K.; Daugulis, O. Synthesis and

Properties of “Sandwich ” Diimine-Coinage Metal Ethylene Com-

plexes. Organometallics 2016, 35, 2938−2943.