5,6-Dihydrodibenzo[ c, e][1,2]azaphosphinine-Based PNP Ligands, Cr(0) Coordination, and Cr(III) Precatalysts for Ethylene Oligomerization

Article abstract of DOI:10.1021/acs.organomet.8b00427

We elaborated a synthetic approach to a new family of PNP ligands that involves assembling sequential molecules based on the rigid 5,6-dihydrodibenzo[c,e][1,2]azaphosphinine backbone (-Z-). This approach allowed us to obtain PNP-type ligands of the genera

Full text of DOI:10.1021/acs.organomet.8b00427

Communication
pubs.acs.org/Organometallics
Cite This: Organometallics XXXX, XXX, XXX−XXX
5,6-Dihydrodibenzo[c,e][1,2]azaphosphinine-Based PNP Ligands,
Cr(0) Coordination, and Cr(III) Precatalysts for Ethylene
Oligomerization
Ilya E. Nifant’ev,*,†,‡ Alexander A. Vinogradov,† Alexey A. Vinogradov,† Vitaly A. Roznyatovsky,‡
Yuri K. Grishin,‡ Alexey V. Ivanyuk,† Igor V. Sedov,§ Andrei V. Churakov,∥ and Pavel V. Ivchenko†,‡
†A.V. Topchiev Institute of Petrochemical Synthesis, Leninsky pr. 29, Moscow 119991, Russian Federation
‡Department of Chemistry, M. V. Lomonosov Moscow University, Leninskie Gory, Moscow 119991, Russian Federation
§Institute of Problems of Chemical Physics, Academician Semenov pr. 1, Chernogolovka, Moscow 142432, Russian Federation
∥N.S. Kurnakov Institute of General and Inorganic Chemistry, Leninsky pr. 31, Moscow 119991, Russian Federation
S
* Supporting Information
ABSTRACT: We elaborated a synthetic approach to a new
family of PNP ligands that involves assembling sequential
molecules based on the rigid 5,6-dihydrodibenzo[c,e][1,2]-
azaphosphinine backbone (−Z−). This approach allowed us to
obtain PNP-type ligands of the general formula Ar2P−Z−Ar′
(Ar, Ar′ = Ph, o-MeOC6H4) with high yields and without the
formation of PPN byproducts. Ar2P−Z−Ar′/Cr(acac)3 (acac =
acetylacetonate) adducts activated by modified methylalumox-
ane (MMAO-12) effectively catalyzed ethylene oligomeriza-
tion; the number of ortho-methoxyphenyl fragments n controls
the direction of the process, from slow polymerization (n = 0)
to rapid oligomerization (n = 3), thereby producing a mixture
of 1-hexene and 1-octene in ∼2:1 ratio with very low formation
of polyethylene (∼0.6%).
ligands, the chromium complexes of tetrakis(2-methoxyphen-
yl)-diphosphinoamine 1 (discovered in 2002 as a selective
trimerization catalyst),13,14 and tetraphenyl diphosphinoamine
2 (discovered in 2004 as moderately selective tetramerization
catalyst)9,21,22 are still the leading compounds (Chart 1b).
The PNP ligands obtained so far are conformationally
flexible molecules. In our research, we fixed one of the aryl
substituents at the phosphorus atom by introducing it into a
rigid 5,6-dihydrodibenzo[c,e][1,2]azaphosphinine fragment
(Scheme 1).
iphosphine ligands of various types are widely used in
1−5
Dcoordination catalysis.
Cr(III) complexes with
diphosphine ligands effectively initiate selective trimerization
and tetramerization of ethylene, and bis(diarylphosphino)-
amine derivatives (PNP ligands) demonstrate high catalytic
activity.3,6−12 Currently, the variation of R substituents at the
nitrogen atom, as well as the introduction of various R′ groups
to phenyl substituents at the phosphorus atom, are used in the
design of diphosphine PNP ligands (Chart 1a).13−42 Despite
the efforts undertaken to optimize the structure of the PNP
PNP ligands are usually obtained by reacting amines RNH2
or the corresponding alkali metal amides with disubstituted
chlorophosphines R′2PCl. This reaction is sensitive to the
nature of the substituents R and R′, as well as to the solvent
used. This process is complicated by the ambident
nucleophilicity of the intermediate product RNH−PR′2.43
Both the amines RNH−PR′2 and the amides M[RN−PR′2]
(M = Li, Na) interact with R′2PCl to form target PNP ligands
a
Chart 1. Design Pathways
45
and NPP byproducts.44 We found that PhNH−PPh2 reacts
with Ph2PCl/Et3N in MeCN to form PNP ligand 3 and ∼20%
NPP adduct (Scheme 1, top). In contrast to PhNH−PPh2,
a
(a) Traditional design pathways for PNP ligands and (b) ligands 1
and 2 forming effective ethylene trimerization and tetramerization
catalysts, respectively.
Received: June 21, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.8b00427
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Communication
Scheme 1. Preparation of PNP Ligands
Figure 2. Molecular structure of PNP ligand 6. Ellipsoids are shown
at the 50% probability level. Selected bond distances (Å) and angles
(deg): N1−P1, 1.7192(15); N1−P2, 1.7296(15); N1−C31,
1.436(2); P1−N1−P2, 124.82(9).
An exploratory study of the coordination chemistry of PNP
ligands 5−8 with chromium has been undertaken to examine
the ability to attain a bidentate binding mode analogous to that
of established PNP ligands. The chromium tetracarbonyl
complexes 9−11 were prepared starting from ligands 5, 6, and
8, respectively, by thermally induced displacement of CO in
Cr(CO)6 (Scheme 2). The product of the reaction of 7 with
Cr(CO)6 was not isolated in pure form.
compound 4a obtained from 6-chloro-5,6-dihydrodibenzo-
[c,e][1,2]azaphosphinine46,47 selectively formed the target
ligand 5 (Scheme 1, middle) and only 3% NPP adduct (see
the Figure S17).
The observed difference in the reactivity of PhNH−PPh2
and 4a can be explained by the results of DFT modeling (see
the Supporting Information for details). In the PhNH−PPh2
molecule (Figure 1, left) free rotation around the P−N bond is
Scheme 2. Preparation of Cr(CO)4 Derivatives of PNP
Ligands
The NMR spectra reveal dynamic behavior of complexes 9−
11 due to the hindered internal rotation of aromatic rings.
Figure 1. Optimized molecular structures of PhNH−PPh2 (left) and
4a (right), and the values of dihedral angles n−P−N−n.
1
Dynamic H and 31P NMR studies for the most strained
complex 11 were implemented at the temperature range from
−55 to 55 °C (see the Supporting Information for details). We
found that exchange process occurs between two conformers
(rotamers) of 11 with the relative difference in free energies of
0.7 kcal/mol. The activation barriers of internal rotation
possible, and in the most stable conformer of PhNH−PPh2,
the lone electron pairs of the N and P atoms are divergent (the
n−P−N−n dihedral angle is 103.1°), whereas this angle is
much smaller (68.2°) in conformationally rigid molecule 4a
(Figure 1, right). As a result, the PN fragment of 4a molecule is
a common reaction center with only a single possible direction
of nucleophilic attack.
The reaction of (2-methoxyphenyl)magnesium bromide
with 6-chloro-5,6-dihydrodibenzo[c,e][1,2]azaphosphinine
provided compound 4b. Starting from 4a and 4b, PNP ligands
6−8 (Scheme 1, bottom) were obtained via interacting with
Ph2PCl or (2-MeOC6H4)2PCl. Structures of 5−8 were
identified by high-resolution NMR spectroscopy (see the
Supporting Information for details), and the molecular
structure of ligand 6 was confirmed by X-ray diffraction
analysis (Figure 2).
ΔG⧧ are 12.6 and 11.8 kcal/mol, respectively.
273
Single-crystal X-ray structures of 9−11 (crystallized at −20
°C from toluene-hexane) confirm the distorted octahedral
geometries with cis-bidentate P,P coordination of the PNP
ligands (Figure 3). The geometrical features of 9−11 are very
similar. As expected, P−Cr−P angles (∼69°) are the smallest
due to the steric requirements of the four-membered
metallocycle. In contrast, cis-interligand angles OC−Cr−CO
are close to 90°. The Cr−C(1) and Cr−C(2) bond lengths
(trans to P atoms) are slightly shorter than the two other bond
lengths (∼0.03 Å). In the coordinated ligands, nitrogen atoms
adopt a distorted trigonal planar geometry. However, the P−
N−P angles are much smaller than that in free diphosphino-
B
DOI: 10.1021/acs.organomet.8b00427
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Communication
Figure 3. Molecular structures of complexes 9−11 with thermal ellipsoids at the 50% probability level; hydrogen atoms are omitted for clarity.
Selected bond distances (Å) and angles (deg) are as follows. 9: N1−P1, 1.707(3); N1−P2, 1.708(3); Cr1−P1, 2.3194(12); Cr1−P2, 2.3492(12);
Cr1−C1, 1.867(4); Cr1−C2, 1.848(4); Cr1−C3, 1.901(4); Cr1−C4, 1.881(4); P1−N1−P2, 101.41(17); P1−Cr1−P2, 68.94(4). 10: N1−P1,
1.721(3); N1−P2, 1.708(3); Cr1−P1, 2.3171(9); Cr1−P2, 2.3316(10); Cr1−C1, 1.847(3); Cr1−C2, 1.863(4); Cr1−C3, 1.879(4); Cr1−C4,
1.894(4); P1−N1−P2, 100.61(13); P1−Cr1−P2, 69.15(3). 11: N1−P1, 1.7013(18); N1−P2, 1.7322(19); Cr1−P1, 2.3184(7); Cr1−P2,
2.4006(7); Cr1−C1, 1.862(2); Cr1−C2, 1.842(2); Cr1−C3, 1.898(3); Cr1−C4, 1.875(3); P1−N1−P2, 101.54(9); P1−Cr1−P2, 68.58(2).
amine 6 (∼101 vs 124.82(9)°). Generally, the geometric
parameters of 9−11 are close to those reported earlier for
analogous compounds (η2-Ar2P−NR−PAr2)Cr(CO)4.28
Complexes 9−11 were inactive in ethylene oligomerization.
However, when combined with Cr(acac)3 (acac = acetylacet-
onate) and modified methylalumoxane (MMAO-12), ligands
5−8 proved to be effective catalysts. The efficiency of the
catalysts based on 5−8 was compared with the catalysts
obtained from benchmark ligands 1 and 2. We carried out a
series of experiments using trimethylaluminum as a reaction
scavenger in n-heptane and in chlorobenzene (Figure 4). The
complex formed by ligand 5 was poorly active and
predominantly catalyzed the polymerization.
We analyzed the composition of the reaction mixtures after
the completion of the reaction in heptane by gas chromatog-
raphy and the weighing of the polymer products (Table 1) and
a
Table 1. Ethylene Oligomerization Results
b
c
c
d
run ligand
solvent
TOF (h−1
)
1-hexene 1-octene
PE
1
2
3
4
5
6
7
8
9
1
2
6
7
8
1
2
6
7
8
n-heptane
n-heptane
n-heptane
n-heptane
n-heptane
PhCl
PhCl
PhCl
PhCl
PhCl
124800
29900
41600
85.1
21.6
41.9
15.4
61.0
86.7
29.7
48.3
23.4
74.9
7.9
73.5
49.4
84.1
30.0
7.2
67.9
40.9
69.1
19.5
0.9
4.6
17.9
49.6
0.6
1.3
1.2
5.2
29.3
0.7
48700
126900
220900
145400
128000
46800
10
312500
a
General conditions: Cr(acac)3 (30 μmol), PNP ligands 1−3 or 5−8
(40 μmol), MMAO-12 (260 equiv), TMA (1 mL of 1 M solution)
and solvent (100 mL), p(C2H4) = 20 bar; T = 50 °C. Details of
catalysis procedures are available in the Supporting Information.
b
Moles of ethylene consumed per 1 mol of Cr; extrapolation for 1 h
c
d
reaction period. Weight percentage of liquid fraction. Weight
percentage of total product.
found that the most active complex based on 8 catalyzes
ethylene oligomerization to form 1-hexene and 1-octene in the
molar ratio of 2:1, with an extremely low polyethylene (PE)
formation (Table 1, run 5). Cyclic trimerization products in
appreciable (<0.1%) amounts was not detected in the reaction
mixture.
An interesting result was demonstrated by the adduct with
ligand 7: Unlike the structurally similar complex based on
Ph2P−N(iPr)−P(2-MeOC6H4)2, which is a nonselective
trimerization catalyst,16 7/Cr(acac)3 catalyzed ethylene
tetramerization with extremely high selectivity (the content
of 1-octene in the volatile fraction was as high as 84%).
However, about half of the absorbed ethylene formed the
polymer.
With the exception of the 7-based complex, all catalysts
showed higher performance when heptane was replaced with
Figure 4. Ethylene consumption in catalytic experiments with ligands
1, 2, and 6−8 in heptane (top) and in chlorobenzene (bottom).
C
DOI: 10.1021/acs.organomet.8b00427
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Communication
chlorobenzene. However, in chlorobenzene, even for the most
active catalysts based on 1 and 8, a noticeable formation of PE
and an increase in the content of the C10 fraction were
detected.
within the M. V. Lomonosov Moscow State University
Program of Development.
REFERENCES
■
In summary, we have reported an original approach in the
design of chelating diphosphines that uses direct binding of a
substituent at the phosphorus atom with a bridging fragment
to form a conformationally rigid backbone. We synthesized
novel PNP ligands 5−8 containing 5,6-dihydrodibenzo-[c,e]-
[1,2]azaphosphinine fragment and demonstrated their coordi-
nation chemistry by the formation of Cr(CO)4 complexes,
with their structures studied by X-ray diffraction analysis. We
also demonstrated the potential of Cr(acac)3 adducts of PNP
ligands in the trimerization/tetramerization of ethylene. We
have observed that depending on the number of ortho-
methoxyphenyl fragments n at the phosphorus atoms (n = 0−
3), the selectivity may be tuned from slow polymerization (5, n
= 0), through nonselective oligomerization with low PE
content (6, n = 1) and selective tetramerization with high PE
content (7, n = 2) to facile 1-hexene/1-octene formation (8, n
= 3). In these preliminary experiments, ligand 8 chromium
complex was superior to reference ligand 1 and 2 complexes in
terms of the total catalytic productivity. Further studies to
explore the potential of the sterically rigid PNP ligands for
selective ethylene oligomerization are underway.
(1) Tolman, C. A. Steric Effects of Phosphorus Ligands in
Organometallic Chemistry and Homogeneous Catalysis. Chem. Rev.
1977, 77, 313−348.
(2) Tang, W.; Zhang, X. New Chiral Phosphorus Ligands for
Enantioselective Hydrogenation. Chem. Rev. 2003, 103, 3029−3069.
(3) Fliedel, C.; Ghisolfi, A.; Braunstein, P. Functional Short-Bite
Ligands: Synthesis, Coordination Chemistry, and Applications of N-
Functionalized Bis(diaryl/dialkylphosphino)amine-type Ligands.
Chem. Rev. 2016, 116, 9237−9304.
(4) Allen, D. W. Chapter 1: Phosphines and related P−C−bonded
compounds. In Organophosphorus Chemistry; Royal Society of
Chemistry, 2014; Vol. 43.
(5) Wong, S. M.; So, C. M.; Kwong, F. Y. The Recent Development
of Phosphine Ligands Derived from 2-Phosphino-Substituted Hetero-
cycles and Their Applications in Palladium-Catalyzed Cross-Coupling
Reactions. Synlett 2012, 23, 1132−1153.
(6) Dixon, J. T.; Green, M. J.; Hess, F. M.; Morgan, D. H. Advances
in selective ethylene trimerisation - a critical overview. J. Organomet.
Chem. 2004, 689, 3641−3668.
(7) Alferov, K. A.; Belov, G. P.; Meng, Y. Chromium catalysts for
selective ethylene oligomerization to 1-hexene and 1-octene: Recent
results. Appl. Catal., A 2017, 542, 71−124.
(8) Wass, D. F. Chromium-catalysed ethene trimerisation and
tetramerisation - breaking the rules in olefin oligomerisation. Dalton.
Trans. 2007, 816−819.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.8b00427.
■
S
́
(9) van Leeuwen, P. W. N. M.; Clement, N. D.; Tschan, M. J.-L.
New processes for the selective production of 1-octene. Coord. Chem.
Rev. 2011, 255, 1499−1517.
(10) McGuinness, D. S. Olefin Oligomerization via Metallacycles:
Dimerization, Trimerization, Tetramerization, and Beyond. Chem.
Rev. 2011, 111, 2321−2341.
Synthetic procedures, characterizing data, DFT calcu-
lations results, NMR spectra of PNP ligands and
Cr(CO)4 complexes, details of the catalytic experiments
(PDF)
(11) Do, L. H.; Labinger, J. A.; Bercaw, J. E. Spectral studies of a
Cr(PNP)-MAO system for selective ethylene trimerization catalysis:
searching for the active species. ACS Catal. 2013, 3, 2582−2585.
(12) Liu, R.; Xiao, S.; Zhong, X.; Cao, Y.; Liang, S.; Liu, Z.; Ye, X.;
Shen, A.; Zhu, H. Advances in Selective Ethylene Oligomerization
Based on [PNP]-Ligand Chromium Catalysts. Youji Huaxue 2015, 35,
1861−1888.
Cartesian coordinates (XYZ)
Accession Codes
CCDC 1555929−1555932 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.
(13) Carter, A.; Cohen, S. A.; Cooley, N. A.; Murphy, A.; Scutt, J.;
Wass, D. F. High activity ethylene trimerisation catalysts based on
diphosphine ligands. Chem. Commun. 2002, 858−859.
(14) Wass, D. F. Olefin trimerization using a catalyst comprising a
source of chromium, molybdenium or tungsten and a ligand
containing at least one phosphorus, arsenic or antimony atom
bound to at least one hetero(hydrocarbyl) group. WO0204119 (A1),
2002.
AUTHOR INFORMATION
Corresponding Author
*E-mail: ilnif@yahoo.com.
■
(15) de Boer, E. J. M.; Van Der Heijen, H.; On, Q. A.; Smit, J. P.;
Van Zon, A. Catalytic oligomerization of olefinic monomers.
US2007129583 (A1), 2007.
ORCID
(16) Overett, M. J.; Blann, K.; Bollmann, A.; Dixon, J. T.; Hess, F.;
Killian, E.; Maumela, H.; Morgan, D. H.; Neveling, A.; Otto, S.
Ethylene trimerisation and tetramerisation catalysts with polar-
substituted diphosphinoamine ligands. Chem. Commun. 2005, 622−
624.
Ilya E. Nifant’ev: 0000-0001-9151-1890
Igor V. Sedov: 0000-0001-9648-4895
Andrei V. Churakov: 0000-0003-3336-4022
Notes
(17) Gao, X.; Carter, C. A. G.; Henderson, L. D. Trimerization.
US8252955 (B2), 2012.
The authors declare no competing financial interest.
(18) Gao, X.; Carter, C. A. G.; Henderson, L. D. Tetramerization.
US7906681 (B2), 2011.
ACKNOWLEDGMENTS
■
This work was supported by the Russian Science Foundation
(Grant No. 18-13-00351, in part of ligand and catalyst design,
synthetic, structural, and NMR study) and partially supported
by the TIPS RAS plan (experimental study of oligomerization
product distribution carried out by A.V.I.). The authors wish
to acknowledge the use of the NMR equipment purchased
(19) Bollmann, A.; Blann, K.; Dixon, J. T.; Hess, F. M.; Killian, E.;
Maumela, H.; McGuinness, D. S.; Morgan, D. H.; Neveling, A.; Otto,
S.; Overett, M.; Slawin, A. M. Z.; Wasserscheid, P.; Kuhlmann, S.
Ethylene Tetramerization: A New Route to Produce 1-Octene in
Exceptionally High Selectivities. J. Am. Chem. Soc. 2004, 126, 14712−
14713.
D
DOI: 10.1021/acs.organomet.8b00427
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Communication
(20) Dixon, J. T.; Morgan, D. H.; Killian, E.; Bollmann, A.; Walsh, R.
N.; Overett, M. J.; Blann, K. Oligomerization of olefinic compounds
in an aliphatic medium. WO2005123633 (A1), 2005.
(21) Blann, K.; Bollmann, A.; Dixon, J.; Navaling, A.; Morgan, D.;
Maumela, H.; Killian, E.; Hess, F. M.; Otto, S.; Pepler, L.; Mahomed,
H. A.; Overett, M. J. Tetramerization of olefins. WO2004056479
(A1), 2004.
Highly selective chromium-based ethylene trimerisation catalysts with
bulky diphosphinoamine ligands. Chem. Commun. 2005, 620−621.
(36) Muller, B. H.; Peulecke, N.; Peitz, S.; Aluri, B. R.; Rosenthal,
̈
̈
̈
U.; Al-Hazmi, M. H.; Mosa, F. M.; Wohl, A.; Muller, W. Activity
Enhancement of a Catalyst System for the Selective Trimerization of
Ethene to 1-Hexene by Modification of the Chromium to Chloride to
Aluminium Ratio. Chem. - Eur. J. 2011, 17, 6935−6938.
(37) Cloete, N.; Visser, H. G.; Engelbrecht, I.; Overett, M. J.;
Gabrielli, W. F.; Roodt, A. Ethylene Tri- and Tetramerization: a Steric
Parameter Selectivity Switch from X-ray Crystallography and
Computational Analysis. Inorg. Chem. 2013, 52, 2268−2270.
(38) Do, L. H.; Labinger, J. A.; Bercaw, J. E. Mechanistic Studies of
Ethylene and α-Olefin Co-Oligomerization Catalyzed by Chromium−
PNP Complexes. Organometallics 2012, 31, 5143−5149.
(22) Blann, K.; Bollmann, A.; Dixon, J.; Navaling, A.; Morgan, D.;
Maumela, H.; Killian, E.; Hess, F. M.; Otto, S.; Pepler, L.; Mahomed,
H. A.; Overett, M. J.; Green, M. J. Tetramerization of olefins.
WO2004056478 (A1), 2004.
(23) Blann, K.; Bollmann, A.; de Bod, H.; Dixon, J. T.; Killian, E.;
Nongodlwana, P.; Maumela, M. C.; Maumela, H.; McConnell, A. E.;
́
Morgan, D. H.; Overett, M. J.; Pretorius, M.; Kuhlmann, S.;
(39) Stennett, T. E.; Hey, T. W.; Ball, L. T.; Flynn, S. R.; Radcliffe, J.
E.; McMullin, C. L.; Wingad, R. L.; Wass, D. F. N,N-Diphospholyl-
amines - A New Family of Ligands for Highly Active, Chromium-
Based, Selective Ethene Oligomerisation Catalysts. ChemCatChem
2013, 5, 2946−2954.
Wasserscheid, P. Ethylene tetramerisation: Subtle effects exhibited
by N-substituted diphosphinoamine ligands. J. Catal. 2007, 249, 244−
249.
(24) Spitzmesser, S. K.; Elowe, S. K.; Elowe, P. R.; Bercaw, J. E.
Transition metal catalysts. WO2007088329 (A1), 2007.
(25) Kwon, H.-Y.; Cho, K.-J.; Kim, S.-Y.; Lee, S.-M.; Lee, K.-S.; Lim,
K.-C. Ligand compound, organochromium compound, catalyst
system for ethylene oligomerization, method for preparing same
and ethylene oligomerization method using same. EP2899196 (A1),
2013.
(26) Sa, S.; Lee, S. M.; Kim, S. Y. Chromium-based ethylene
tetramerization with diphosphinoamines bearing pendent amine
donors. J. Mol. Catal. A: Chem. 2013, 378, 17−21.
(27) Killian, E.; Blann, K.; Bollmann, A.; Dixon, J. T.; Kuhlmann, S.;
Maumela, M. C.; Maumela, H.; Morgan, D. H.; Nongodlwana, P.;
̈
̈
(40) Hohne, M.; Peulecke, N.; Konieczny, K.; Muller, B. H.;
Rosenthal, U. ChemCatChem 2017, 9, 2467−2472.
(41) Weng, Z.; Teo, S.; Andy Hor, T. S. Chromium(III) catalysed
ethylene tetramerization promoted by bis(phosphino)amines with an
N-functionalized pendant. Dalton Trans. 2007, 3493−3498.
(42) Shaikh, Y.; Gurnham, J.; Albahily, K.; Gambarotta, S.;
Korobkov, I. Aminophosphine-Based Chromium Catalysts for
Selective Ethylene Tetramerization. Organometallics 2012, 31,
7427−7433.
(43) Fei, Z.; Scopelliti, R.; Dyson, P. J. Influence of the functional
group on the synthesis of aminophosphines, diphosphinoamines and
iminobiphosphines. Dalton Trans. 2003, 2772−2779.
̈
Overett, M. J.; Pretorius, M.; Hofener, K.; Wasserscheid, P. The use of
bis(diphenylphosphino)amines with N-aryl functionalities in selective
ethylene tri- and tetramerisation. J. Mol. Catal. A: Chem. 2007, 270,
214−218.
(44) Maumela, M. C.; Blann, K.; de Bod, H.; Dixon, J. T.; Gabrielli,
W. F.; Williams, D. B. G. Efficient synthesis of novel N-substituted
bulky diphosphinoamines. Synthesis 2007, 2007, 3863−3867.
(45) Cross, R. J.; Green, T. H.; Keat, R. Conformational Effects on
P-N-P Coupling Constants in Diphosphinoamines and Related
Compounds. J. Chem. Soc., Dalton Trans. 1976, 1424−1428.
(46) Campbell, I. G. M.; Way, J. K. Synthesis and Stereochemistry of
Heterocyclic Phosphorus Compounds. Part I. Preparation of (+)- and
(−)-10-p-Dimethylaminophenyl-9,10-dihydro-9-aza-10-phospha-phe-
nanthrene. J. Chem. Soc. 1960, 0, 5034−5041.
(28) Agapie, T.; Day, M. W.; Henling, L. M.; Labinger, J. A.; Bercaw,
J. E. A Chromium-Diphosphine System for Catalytic Ethylene
Trimerization: Synthetic and Structural Studies of Chromium
Complexes with a Nitrogen-Bridged Diphosphine Ligand with
ortho-Methoxyaryl Substituents. Organometallics 2006, 25, 2733−
2742.
(29) Schofer, S. J.; Day, M. W.; Henling, L. M.; Labinger, J. A.;
Bercaw, J. E. Ethylene Trimerization Catalysts Based on Chromium
Complexes with a Nitrogen-Bridged Diphosphine Ligand Having
ortho-Methoxyaryl or ortho-Thiomethoxy Substituents: Well-Defined
Catalyst Precursors and Investigations of the Mechanism. Organo-
metallics 2006, 25, 2743−2749.
(47) Dewar, M. J. S.; Kubba, W. P. New Heteroaromatic
Compounds. Part VI. Novel Heterocyclic Compounds of Phosphorus.
J. Am. Chem. Soc. 1960, 82, 5685−5688.
(30) Elowe, P. R.; McCann, C.; Pringle, P. G.; Spitzmesser, S. K.;
Bercaw, J. E. Nitrogen-Linked Diphosphine Ligands with Ethers
Attached to Nitrogen for Chromium-Catalyzed Ethylene Tri- and
Tetramerizations. Organometallics 2006, 25, 5255−5260.
(31) Jiang, T.; Chen, H.; Ning, Y.; Chen, W. Preparation of 1-octene
by ethylene tetramerization with high selectivity. Chin. Sci. Bull. 2006,
51, 521−523.
(32) Mao, G.; Ning, Y.; Hu, W.; Li, S.; Song, X.; Niu, B.; Jiang, T.
Synthesis of a novel triple-site diphosphinoamine (PNP) ligand and
its applications in ethylene tetramerization. Chin. Sci. Bull. 2008, 53,
3511−3515.
(33) Peitz, S.; Peulecke, N.; Aluri, B. R.; Hansen, S.; Mu
Spannenberg, A.; Rosenthal, U.; Al-Hazmi, M. H.; Mosa, F. M.; Wohl,
A.; Muller, W. A Selective Chromium Catalyst System for the
̈
ller, B. H.;
̈
̈
Trimerization of Ethene and Its Coordination Chemistry. Eur. J. Inorg.
Chem. 2010, 2010, 1167−1171.
(34) Kuhlmann, S.; Blann, K.; Bollmann, A.; Dixon, J. T.; Killian, E.;
́
Maumela, M. C.; Maumela, H.; Morgan, D. H.; Pretorius, M.;
Taccardi, N. N-substituted diphosphinoamines: Toward rational
ligand design for the efficient tetramerization of ethylene. J. Catal.
2007, 245, 279−284.
(35) Blann, K.; Bollmann, A.; Dixon, J. T.; Hess, F. M.; Killian, E.;
Maumela, H.; Morgan, D. H.; Neveling, A.; Otto, S.; Overett, M.
E
DOI: 10.1021/acs.organomet.8b00427
Organometallics XXXX, XXX, XXX−XXX