Catalytic Addition of Alcohols into Carbodiimides Promoted by Organoactinide Complexes

Article abstract of DOI:10.1021/acs.inorgchem.7b00357

The insertion of alcohols into carbodiimides mediated by benzimidazolin-2-iminato actinide complexes [(Bim^R₁/R₂N)AnN₃] [N = N(SiMe₃)₂] is presented herein. Analysis of single-crystal data revealed that steric hindrance, rather than electronic properties, plays an important role in determining the accessibility for this insertion process. All actinide complexes showed excellent activities under very mild conditions. Stoichiometric reactions in combination with kinetic and thermodynamic studies allow us to propose a plausible active species and a mechanism for the catalytic cycle.

Full text of DOI:10.1021/acs.inorgchem.7b00357

Communication
pubs.acs.org/IC
Catalytic Addition of Alcohols into Carbodiimides Promoted by
Organoactinide Complexes
Heng Liu,† Maxim Khononov,† Natalia Fridman,† Matthias Tamm,*,‡ and Moris S. Eisen*,†
†Schulich Faculty of Chemistry, TechnionIsrael Institute of Technology. Haifa City 32000, Israel
‡Institut fur Anorganische und Analytische Chemie, Technische Universitat Braunschweig, Hagenring 30, 38106 Braunschweig,
̈
̈
Germany
S
* Supporting Information
active species, mono(imidazolin-2-iminato)thorium(IV) trialk-
oxides, from attacking the carbodiimides, thus leading to no
activity. These considerations raised our curiosity toward
developing a new family of complexes that contain, on the one
hand, a less sterically demanding ligand (i.e., a smaller cone angle
vide infra), which might allow the insertion of alcohols into
carbodiimides to occur, and that exhibit, on the other hand, good
solubility upon protonolysis with alcohols to clearly characterize
the structure of potential intermediates. The monoanionic
imidazolin-2-iminato ligand is of great interest owing to its ability
to act as a 2σ,4π-electron donor, which renders this system
isolobal with the widely used cyclopentadienides.19,43−45 Herein,
we borrowed the concept of η5-indenyl, when compared with the
cyclopentadienyl group, by incorporating a phenyl ring into the
backbone of the imidazolin-2-iminato moiety to change its
electronic properties and synthesized a series of benzimidazolin-
2-iminato ligands. Moreover, to create more accessible, sterically
less encumbered metal atoms, smaller N-substituents (Me, iPr)
were introduced into the ligands. Treating these new ligand
precursors with 1 equiv of the corresponding actinide metalla-
cycle in toluene afforded the corresponding benzimidazolin-2-
iminato actinide complexes 1−4 in high yields (Scheme 1).
The solid-state structures of all of the complexes were
confirmed by X-ray crystallography (Figure 1). Resembling
previous lanthanide and actinide counterparts,19,20,46,47 all four
complexes displayed shorter An−NCN bonds compared to the
corresponding An−Namido bonds, as well as approximate linearity
for An−N−C angles, corroborating a higher bond order of An−
ABSTRACT: The insertion of alcohols into carbodii-
mides mediated by benzimidazolin-2-iminato actinide
complexes [(BimR /R N)AnN″3] [N″ = N(SiMe3)2] is
presented herein. Analysis of single-crystal data revealed
that steric hindrance, rather than electronic properties,
plays an important role in determining the accessibility for
this insertion process. All actinide complexes showed
excellent activities under very mild conditions. Stoichio-
metric reactions in combination with kinetic and
thermodynamic studies allow us to propose a plausible
active species and a mechanism for the catalytic cycle.
1
2
arly-actinide (An) uranium- and thorium-complex-medi-
Eated carbon-heteroatom bond formations are at the
scientific forefront because of their unique catalyst structure−
reactivity relationships, as well as their high atom efficiency.1−12
However, because of the formation of strong oxygen−actinide
bonds due to their oxophilicities,8,13,14 catalytic organic trans-
formations with oxygen-containing substrates have been
extremely challenging. In contrast to some recent progress in
lanthanide-mediated reactions of oxygen-containing sub-
strates,8,15,16 only a very limited number of catalytic examples
are available so far for organoactinides.17−26
Catalytic insertions of E−H (NH, PH, SH, CH, etc.) bonds
into carbodiimides has attracted considerable attention in recent
years.27−39 On the basis of the observation in Tishchenko and
hydroalkoxylation reactions that An−O can be an active moiety
in catalytic processes,21−26 uranium and thorium-based com-
plexes were used for the intermolecular addition of alcohols to
heterocumulenes. Exploratory investigations with mono-
(imidazolin-2-iminato)thorium(IV) and -uranium(IV) com-
plexes [(ImRN)AnN″3] [An = Th, U; R = Dipp; N″ =
−N(SiMe3)2] indicated, in spite of their high activities in the
hydroelementation of nonoxygenated substrates, that the
insertion of alcohols into carbodiimides was unfeasible.40,41
Recent attempts using sterically less demanding amido actinide
metallacycles allowed us to achieve the unprecedented actinide-
catalyzed addition of alcohols to carbodiimides; however,
attempts to elucidate the structure of the active species were
challenging because of the formation of a mixture of actinide
alkoxides upon protonolysis of the amido moieties by the
alcohols.42 The difference of the two aforementioned systems is
the presence of a sterically highly encumbered imidazolin-2-
iminato ligand in the former one, which might keep the expected
Scheme 1. Synthesis of Benzimidazolin-2-iminato Actinide
Complexes [(BimR /R N)AnN″3]
1
2
Received: February 11, 2017
© XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.7b00357
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Communication
Table 1. Catalytic Insertion of Alcohols into Carbodiimides
a
b
c
run Cat. RNCNR
R′OH
MeOH
time (h) conv (%) product
1
1
2
3
4
1
2
3
4
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
DIC
24
24
24
24
1
28
12
5ac
2
DIC
3
DIC
56
4
DIC
26
5
DTC
DTC
DTC
DTC
DTC
>99
>99
>99
>99
20
5bc
6
1
7
1
8
1
9
EtOH
24
24
1
5ad
5bd
5be
5bf
5bg
5bh
5bi
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
20
DTC
DTC
DTC
DTC
DTC
DTC
DTC
DTC
96
1
>99
98
iPrOH
tBuOH
PhOH
3
5
>99
>99
94
5
5
2
>99
94
2
Figure 1. Solid-state structures of complexes 1−4 (thermal ellipsoids are
drawn at 50% probability). Hydrogen atoms are omitted for clarity.
2,6-Me2C6H3OH
2,4-tBu2C6H3OH
PDO
2
93
2
95
12
12
2
94
NCN bonds. The geometric parameters of complexes 1−4 are
very much alike as to the corresponding imidazolin-2-iminato
complexes.19,20,43 These similarities among the complexes lead
to the conclusion that the presence of the phenyl ring on the
backbone has little influence on the electronic structure of the
ligand attached to the metal. Despite the smal changes in the
electronic structures, when it comes to the cone angle, which is
an important parameter to evaluate the proximity of the ligand
substituents to the metal center,48,49 compared to the ca. 204° in
[(ImDippN)ThN″3], much smaller cone-angle values were
displayed for the benzimidazolin-2-iminato actinide complexes
(138°, 140°, 122°, and 119° for 1−4, respectively), indicating
that these new actinide complexes exhibited much more open
spaces available to the metal toward the incoming substrates.
On the basis of these observations, we attempted to investigate
the intermolecular insertion of methanol (MeOH) into
diisopropylcarbodiimide (DIC) and 1,3-di-p-tolylcarbodiimide
(DTC) (Table 1). To our pleasure, all new complexes are active
in the intermolecular addition reaction, affording the corre-
sponding isourea products with moderate-to-high yields, where-
as no reaction was observed in the absence of actinide complexes.
It is important to point out that the ligand itself does not induce
the addition reaction, and freshly recrystallized complexes are
used in the catalytic reactions. Table 1 shows a clear trend in the
activity of the complexes for alcohol insertion when different
carbodiimides were employed. Higher conversions, even in a
short amount of time, were obtained for the more electrophilic
substrate DTC, suggesting that the addition of the alkoxo moiety
to the carbodiimide sp carbon is easier because of the presence of
92
>99
>99
>99
94
6bj
2
TEOA
3
7bk
6
a
Reaction conditions: 7 μmol of catalysts, [Cat.]/[RNCNR]/[OH] =
b
1/50/50, 500 μL of C6D6, room temperature. PDO = propane-1,3-
diol [HO(CH2)3OH]; TEOA = triethanolamine (N[(CH2)2OH]3).
c
1
The yield was determined by H NMR spectroscopy of the crude
reaction mixture.
impact on this intermolecular addition reaction. Hence, using the
sterically hindered 2,4-tBu2C6H3OH resulted in lower activities
compared to using 2,6-Me2C6H3OH. Moreover, the diol (1,3-
propanediol) and triol (triethanolamine) were employed in this
catalytic reaction to show the scope capabilities for these
organoactinides (Scheme 2).
Combining these catalytic results with the bond properties
shown in the single-crystal X-ray structures, as well as the
different catalytic behaviors revealed for [(BimR /R N)AnN″3]
1
2
compared to the [(ImDippN)ThN″3] systems, we can conclude
Scheme 2. Catalytic Insertion of Alcohols into Carbodiimides
i
the p-tolyl group compared to the electron-releasing Pr group.
The scope of the reaction with regard to the alcohol substrate was
studied by varying the steric bulkiness and acidity of the alcohols.
The catalytic addition of the less sterically encumbered alcohols,
i.e., MeOH and ethanol (EtOH), to DIC by precatalysts 1 and 2
led to moderate yields; however, no turnovers were observed
when using larger alcohols [isopropyl alcohol (iPrOH) and tert-
butyl alcohol (tBuOH)]. Similar trends were revealed when DTC
was used, which required longer reaction times to fully consume
i
t
the bulkier PrOH and BuOH. Like the aliphatic alcohols,
changing the size of the phenol substrates has an important
B
DOI: 10.1021/acs.inorgchem.7b00357
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Communication
that the steric hindrances play a more important role in catalyzing
the intermolecular addition of alcohols to carbodiimides.
Scheme 3. Proposed Mechanism for the Intermolecular
Addition of Alcohols to Carbodiimides Promoted by Actinide
Complexes
To shed some light on the mechanism, stoichiometric
reactions of the precatalyst 2 with 3 and 10 equiv of DTC
were first carried out in situ in benzene-d6, showing no reactivity.
This result indicates that the amido moieties do not insert into
DTC, forming a guanidinate ligand. In contrast, reactions
between the catalyst 2 and 3 equiv of 2,4-tBu2C6H3OH took
place rapidly to afford 3 equiv of hexamethyldisilazane and the
corresponding mono(benzimidazolin-2-iminato)thorium(IV)
trialkoxide [(BimMe/DippN)Th(O-2,4-tBu2Ph)3] complex, whose
structure was determined by 1H NMR spectroscopy. It is
important to note that the resulting [(BimMe/DippN)Th(O-
2,4-tBu2Ph)3] complex was completely dissolved in the nonpolar
solvent benzene at room temperature and led to a clearly
transparent solution. Further, reacting the precatalyst 2 with 10
equiv of 2,4-tBu2C6H3OH generated a mixture of
[(BimMe/DippN)Th(O-2,4-tBu2C6H3)3] and 7 equiv of unreacted
phenol, to which 10 equiv of DTC was added, and a rapid
consumption of ca. 70% of DTC was observed, implying that
[(BimMe/DippN)Th(O-2,4-tBu2C6H3)3] is an active species for
the addition of an alcohol to a carbodiimide. During these
stoichiometric studies, the freshly formed intermediate
[(BimMe/DippN)Th(O-2,4-tBu2Ph)3] was stable at room temper-
ature for at least 24 h. However, exposing it to higher
temperatures (50 °C) in the presence of excessive
2,4-tBu2C6H3OH resulted in protonation of the ligand, forming
the intermediate C [(BimMe/DippNH)2Th(O-2,4-tBu2C6H3)4],
whose structure had been confirmed by single-crystal spectros-
copy (Figure 2). It is interesting to note that this intermediate
species B. Protonation of B by another alcohol molecule releases
the product with concomitant regeneration of the active species
Cat-A. Deuterium-labeling studies using 2,4-tBu2C6H3OD,
DTC, and the catalyst 2 afforded a KIE value of kH/kD = 1.02
0.04, indicating that the protonolysis of B is not the turnover
limiting step of the catalytic cycle.
In summary, this present work showed our approach to
preparing isourea products through the intermolecular addition
of alcohols to carbodiimides promoted by the precatalysts
[(BimR /R N)AnN″3].
1
2
ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.7b00357.
Figure 2. Single crystal and structure of the reaction intermediate
[(BimMe/DippNH)2Th(O-2,4-tBu2Ph)4].
NMR spectra, kinetic and stoichiometric experiments, and
deuterium-labeling studies (PDF)
Crystallographic data for complexes 1−4, intermediate C
(CIF)
was also found to be active for the intermolecular addition of
2,4-tBu2C6H3OH to DTC (with slightly lower reactivity
compared to complex 2), corroborating again the reactivity of
the An−O moieties.
Kinetic studies of the catalytic addition of 2,4-tBu2C6H3OH to
DTC using complex 2 gives rise to the rate equation (1).
AUTHOR INFORMATION
■
Corresponding Authors
*E-mail: m.tamm@tu-bs.de (M.T.).
*E-mail: chmoris@tx.technion.ac.il (M.S.E.).
∂p
= Kobs[2]1[DTC]1[2,4‐t Bu2PhOH]−1
(1)
∂t
Thermodynamic parameters for the same system were
calculated from the Erying and Arrhenius plot, displaying an
activation barrier (Ea) of 16.2(9) kcal mol−1 and the enthalpy
(ΔH⧧) and entropy (ΔS⧧) of activation of 15.6(7) kcal mol−1
and −27.0(3) eu, respectively, indicating an organized transition
state at the rate-determining step. A plausible mechanism for the
intermolecular addition of alcohols is presented in Scheme 3.
ORCID
Matthias Tamm: 0000-0002-5364-0357
Moris S. Eisen: 0000-0001-8915-0256
Notes
The authors declare no competing financial interest.
The reaction of the precatalyst [(BimR /R N)AnN″3] with the
ACKNOWLEDGMENTS
1
2
■
alcohol gave the active intermediate [(BimR /R N)AnOR3] (Cat-
A) through an acid−base protonolysis reaction. The insertion of
the alkoxide into a carbodiimide produces the actinide isourea
This work was supported by the German Israel Foundation
under Contract I-1264-302.5/2014 and, in part, by a Technion−
Guangdong Fellowship.
1
2
C
DOI: 10.1021/acs.inorgchem.7b00357
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Communication
(22) Barnea, E.; Moradove, D.; Berthet, J. C.; Ephritikhine, M.; Eisen,
M. S. Surprising activity of organoactinide complexes in the polymer-
ization of cyclic mono- and diesters. Organometallics 2006, 25, 320−322.
(23) Karmel, I. S. R.; Fridman, N.; Eisen, M. S. Actinide amidinate
complexes with a dimethylamine side arm: synthesis, structural
characterization, and reactivity. Organometallics 2015, 34, 636−643.
(24) Karmel, I. S. R.; Khononov, M.; Tamm, M.; Eisen, M. S. Uranium-
mediated ring-opening polymerization of ε-caprolactone: a comparative
study. Catal. Sci. Technol. 2015, 5, 5110−5119.
(25) Walshe, A.; Fang, J.; Maron, L.; Baker, R. J. New mechanism for
the Ring-Opening Polymerization of lactones uranyl aryloxide-induced
intermolecular catalysis. Inorg. Chem. 2013, 52, 9077−9086.
(26) Jantunen, K. C.; Batchelor, R. J.; Leznoff, D. B. Synthesis,
characterization, and organometallic derivatives of diamidosilyl ether
thorium(IV) and uranium(IV) halide complexes. Organometallics 2004,
23, 2186−2193.
(27) Zhang, W.; Xu, L.; Xi, Z. Recent development of synthetic
preparation methods for guanidines via transition metal catalysis. Chem.
Commun. 2015, 51, 254−265.
(28) Ishikawa, T.; Kumamoto, T. Guanidines in organic synthesis.
Synthesis 2006, 2006, 737−752.
(29) Zhang, W.; Nishiura, M.; Hou, Z. Alkali-metal-catalyzed addition
of primary and secondary phosphines to carbodiimides. A general and
efficient route to substituted phosphaguanidines. Chem. Commun. 2006,
3812−3814.
(30) Alonso-Moreno, C.; Antinolo, A.; Carrillo-Hermosilla, F.; Otero,
A. Guanidines: from classical approaches to efficient catalytic syntheses.
Chem. Soc. Rev. 2014, 43 (10), 3406−3425.
(31) Ong, T.-G.; O’Brien, J. S.; Korobkov, I.; Richeson, D. S.
Organometallics 2006, 25, 4728−4730.
(32) Coles, M. P.; Swenson, D. C.; Jordan, R. F.; Young, V. G.
Synthesis and structures of mono- and bis(amidinate) complexes of
aluminum. Organometallics 1997, 16, 5183−5194.
(33) Rowley, C. N.; DiLabio, G. A.; Barry, S. T. Theoretical and
synthetic investigations of carbodiimide insertions into Al−CH3 and
Al−N(CH3)2 bonds. Inorg. Chem. 2005, 44, 1983−1991.
(34) Ong, T.-G.; Yap, G. P. A.; Richeson, D. S. Catalytic construction
and reconstruction of guanidines: Ti-mediated guanylation of amines
and transamination of guanidines. J. Am. Chem. Soc. 2003, 125, 8100−
8101.
(35) Naktode, K.; Das, S.; Bhattacharjee, J.; Nayek, H. P.; Panda, T. K.
Imidazolin-2-iminato ligand-supported titanium complexes as catalysts
for the synthesis of urea derivatives. Inorg. Chem. 2016, 55, 1142−1153.
(36) Mukherjee, A.; Sen, T. K.; Mandal, S. K.; Maity, B.; Koley, D.
Construction of oxygen-bridged multimetallic assembly: dual catalysts
for hydroamination reactions. RSC Adv. 2013, 3, 1255−1264.
(37) Schweizer, P. D.; Wadepohl, H.; Gade, L. H. Titanium-catalyzed
hydrohydrazination of carbodiimides. Organometallics 2013, 32, 3697−
3709.
REFERENCES
■
(1) Stubbert, B. D.; Marks, T. J. Mechanistic investigation of
intramolecular aminoalkene and aminoalkyne hydroamination/cycliza-
tion catalyzed by highly electrophilic, tetravalent constrained geometry
4d and 5f complexes. evidence for an M−N σ-bonded insertive pathway.
J. Am. Chem. Soc. 2007, 129, 6149−6167.
(2) Haskel, A.; Straub, T.; Eisen, M. S. Organoactinide-catalyzed
intermolecular hydroamination of terminal alkynes. Organometallics
1996, 15, 3773−3775.
(3) Straub, T.; Haskel, A.; Neyroud, T. G.; Kapon, M.; Botoshansky,
M.; Eisen, M. S. Intermolecular hydroamination of terminal alkynes
catalyzed by organoactinide complexes. scope and mechanistic studies.
Organometallics 2001, 20, 5017−5035.
(4) Hayes, C. E.; Platel, R. H.; Schafer, L. L.; Leznoff, D. B. Diamido-
ether actinide complexes as catalysts for the intramolecular hydro-
amination of aminoalkenes. Organometallics 2012, 31, 6732−6740.
(5) Wang, J.; Zheng, C.; Maguire, J. A.; Hosmane, N. S. A new class of
constrained-geometry metallocenes: Synthesis and crystal structure of a
carboranyl-thiol-appended half-sandwich titanocene and its conversion
to halotitanocene. Organometallics 2003, 22, 4839−4841.
(6) Weiss, C. J.; Wobser, S. D.; Marks, T. J. Organoactinide-mediated
hydrothiolation of terminal alkynes with aliphatic, aromatic, and
benzylic thiols. J. Am. Chem. Soc. 2009, 131 (6), 2062−2063.
(7) Weiss, C. J.; Wobser, S. D.; Marks, T. J. Organometallics 2010, 29,
6308−6320.
(8) Weiss, C. J.; Marks, T. J. Organo-f-element catalysts for efficient
and highly selective hydroalkoxylation and hydrothiolation. Dalton
Trans. 2010, 39, 6576−6588.
(9) Fox, A. R.; Bart, S. C.; Meyer, K.; Cummins, C. C. Towards
uranium catalysts. Nature 2008, 455, 341−349.
(10) Arnold, P. L. Uranium-mediated activation of small molecules.
Chem. Commun. 2011, 47, 9005−9010.
(11) Gardner, B. M.; Stewart, J. C.; Davis, A. L.; McMaster, J.; Lewis,
W.; Blake, A. J.; Liddle, S. T. Homologation and functionalization of
carbon monoxide by a recyclable uranium. Proc. Natl. Acad. Sci. U. S. A.
2012, 109, 9265−9270.
(12) Evans, W. J.; Mueller, T. J.; Ziller, J. W. Reactivity of
( C 5 M e 5 ) 3 L a L x c o m p l e x e s : s y n t h e s i s o f
a t r i s -
(pentamethylcyclopentadienyl) complex with two additional ligands,
(C5Me5)3La(NCCMe3)2. J. Am. Chem. Soc. 2009, 131, 2678−2686.
(13) Lin, Z.; Marks, T. J. Metal, bond energy, and ancillary ligand
effects on actinide-carbon.sigma.-bond hydrogenolysis. A kinetic and
mechanistic study. J. Am. Chem. Soc. 1987, 109, 7979−7985.
(14) Haynes, W. M. CRC Handbook of Chemistry and Physics, 96th ed.;
CRC Press: Boca Raton, FL, 2015−2016; pp 9−69.
(15) LeBlanc, F. A.; Piers, W. E.; Parvez, M. Selective hydrosilation of
CO2 to a bis(silylacetal) using an anilido bipyridyl-ligated organo-
scandium catalyst. Angew. Chem., Int. Ed. 2014, 53, 789−792.
(16) Yu, X.; Seo, S.; Marks, T. J. Effective, selective hydroalkoxylation/
cyclization of alkynyl and allenyl alcohols mediated by lanthanide
catalysts. J. Am. Chem. Soc. 2007, 129, 7244−7245.
(17) Andrea, T.; Barnea, E.; Eisen, M. S. Organoactinides promote the
tishchenko reaction: The myth of inactive actinide-alkoxo complexes. J.
Am. Chem. Soc. 2008, 130, 2454−2455.
(18) Sharma, M.; Andrea, T.; Brookes, N. J.; Yates, B. F.; Eisen, M. S.
Organoactinides promote the dimerization of aldehydes: scope, kinetics,
thermodynamics, and Ccalculation studies. J. Am. Chem. Soc. 2011, 133,
1341−1356.
(19) Karmel, I. S. R.; Fridman, N.; Tamm, M.; Eisen, M. S.
Mono(imidazolin-2-iminato) actinide complexes: synthesis and appli-
cation in the catalytic dimerization of aldehydes. J. Am. Chem. Soc. 2014,
136, 17180−17192.
(20) Karmel, I. S. R.; Fridman, N.; Tamm, M.; Eisen, M. S. Mixed
imidazolin-2-iminato−Cp* thorium(IV) complexes: synthesis and
reactivity toward oxygen-containing substrates. Organometallics 2015,
34, 2933−2942.
(21) Wobser, S. D.; Marks, T. J. Organothorium-catalyzed hydro-
alkoxylation/cyclization of alkynyl alcohols. scope, mechanism, and
ancillary ligand effects. Organometallics 2013, 32, 2517−2528.
(38) Barker, J.; Kilner, M. The coordination chemistry of the amidine
ligand. Coord. Chem. Rev. 1994, 133, 219−300.
(39) Zhang, W.-X.; Nishiura, M.; Hou, Z. Catalytic addition of terminal
alkynes to carbodiimides by half-sandwich rare earth metal complexes. J.
Am. Chem. Soc. 2005, 127, 16788−16789.
(40) Karmel, I. S. R.; Tamm, M.; Eisen, M. S. Actinide-mediated
catalytic addition of E-H bonds (E = N, P, S) to carbodiimides,
isocyanates, and isothiocyanates. Angew. Chem., Int. Ed. 2015, 54,
12422−12425.
(41) For a copper complex, see: Dabritz, E. Snytheses and reactions of
̈
O, N, N′-trisubstituted isoureas. Angew. Chem., Int. Ed. Engl. 1966, 5,
470−477.
(42) Batrice, R. J.; Kefalidis, C. E.; Maron, L.; Eisen, M. S. Actinide-
catalyzed intermolecular addition of alcohols to carbodiimides. J. Am.
Chem. Soc. 2016, 138, 2114−2117.
(43) Wu, X.; Tamm, M. Transition metal complexes supported by
highly basic imidazolin-2-iminato and imidazolin-2-imine N-donor
ligands. Coord. Chem. Rev. 2014, 260, 116−138.
D
DOI: 10.1021/acs.inorgchem.7b00357
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Communication
(44) Karmel, I. S. R.; Botoshansky, M.; Tamm, M.; Eisen, M. S.
Uranium(IV) imidazolin-2-iminato complexes: a New class of actinide
complexes. Inorg. Chem. 2014, 53, 694−696.
(45) Shoken, D.; Sharma, M.; Botoshansky, M.; Tamm, M.; Eisen, M.
S. Mono(imidazolin-2-iminato) titanium complexes for ethylene
polymerization at low amounts of methylaluminoxane. J. Am. Chem.
Soc. 2013, 135, 12592−12595.
(46) Trambitas, A. G.; Panda, T. K.; Jenter, J.; Roesky, P. W.; Daniliuc,
C.; Hrib, C. G.; Jones, P. G.; Tamm, M. Rare-earth metal alkyl, amido,
and cyclopentadienyl complexes supported by imidazolin-2-iminato
ligands: synthesis, structural characterization, and catalytic application.
Inorg. Chem. 2010, 49, 2435−2446.
(47) Panda, T. K.; Trambitas, A. G.; Bannenberg, T.; Hrib, C. G.;
Randoll, S.; Jones, P. G.; Tamm, M. Imidazolin-2-iminato complexes of
rare earth metals with very short metal−nitrogen bonds: Experimental
and Theoretical Studies. Inorg. Chem. 2009, 48, 5462−5472.
(48) Tolman, C. A. Steric effects of phosphorus ligands in
organometallic chemistry and homogeneous catalysis. Chem. Rev.
1977, 77, 313−348.
(49) Mohring, P. C.; Coville, N. J. Group 4 metallocene polymerisation
̈
catalysts: quantification of ring substituent steric effects. Coord. Chem.
Rev. 2006, 250, 18−35.
E
DOI: 10.1021/acs.inorgchem.7b00357
Inorg. Chem. XXXX, XXX, XXX−XXX