Tethered bis(amidate) and bis(ureate) supported zirconium precatalysts for the intramolecular hydroamination of aminoalkenes

Article abstract of DOI:10.1002/zaac.201400201

Tethered bis(amide) and bis(urea) proligands featuring a neutral chalcogen donor (O or S) in the backbone were synthesized and installed on zirconium via protonolysis. The bis(amidate) zirconium complexes adopt a κ⁴(N,N,O,O) binding motif and were characterized in the solid state with a pyridine donor. Likewise, the bis(ureate)-supported complexes are also found to have a κ⁴(N,N,O,O) binding motif in the solid state however no additional donor ligand is required for discrete complex formation. No evidence for interaction between the neutral chalcogen donor and the zirconium atom is found for any of the transition metal species. All complexes were screened as precatalysts for the intramolecular hydroamination reaction with both primary and secondary aminoalkene substrates. Interestingly, the bis(ureate) species show similar reactivity to the bis(amidate) species, in contrast to a recently reported alkyl-bridged bis(ureate) complex, which readily cyclizes secondary aminoalkenes.

Full text of DOI:10.1002/zaac.201400201

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DOI: 10.1002/zaac.201400201
Tethered Bis(amidate) and Bis(ureate) Supported Zirconium Precatalysts for
the Intramolecular Hydroamination of Aminoalkenes
Jean Michel P. Lauzon[a] and Laurel L. Schafer*[a]
Keywords: Homogeneous catalysis; Zirconium; Amidate; Ureate; Hydroamination
Abstract. Tethered bis(amide) and bis(urea) proligands featuring a neutral chalcogen donor and the zirconium atom is found for any of
neutral chalcogen donor (O or S) in the backbone were synthesized and
installed on zirconium via protonolysis. The bis(amidate) zirconium
complexes adopt a κ4(N,N,O,O) binding motif and were characterized
in the solid state with a pyridine donor. Likewise, the bis(ureate)-sup-
the transition metal species. All complexes were screened as precata-
lysts for the intramolecular hydroamination reaction with both primary
and secondary aminoalkene substrates. Interestingly, the bis(ureate)
species show similar reactivity to the bis(amidate) species, in contrast
ported complexes are also found to have a κ4(N,N,O,O) binding motif to a recently reported alkyl-bridged bis(ureate) complex, which readily
in the solid state however no additional donor ligand is required for cyclizes secondary aminoalkenes.
discrete complex formation. No evidence for interaction between the
Introduction
The development of atom-economic methods to form car-
bon-element bonds is a fundamental challenge faced by syn-
thetic chemists.[1] One such reaction, hydroamination, gener-
ates new C–N bonds, while avoiding the use of protecting
groups and stoichiometric co-reagents.[2] Catalysts based on
zirconium have shown promising reactivity[3] and are particu-
larly attractive due to their reduced cost and low toxicity.[4]
Recent advances in Zr hydroamination catalyst development
have focused on ligand design, including tethered bidentate
amidate[5] and ureate ligands.[6] To date, none of these N,O-
chelating bidentate ligands have included a neutral donor atom
in the tether. However, the analogous diamido ligands have
been developed by Schrock and co-workers to support early
transition metal catalysts for the polymerization of terminal
olefins (Figure 1).[7]
Figure 1. Diamido ligands with an aryl tether featuring a neutral oxy-
gen donor.
Titanium and zirconium complexes supported by this class
of ligand with R = tBu-d6 were found to be highly active as
polymerization catalysts as well as more robust than the estab-
lished metallocene-based systems.[7d] Notably, the steric bulk
of the R group has been found to affect the binding geometry
of group 4 systems. Whereas the R substituents of the diamido
ligand are pointing towards the reactive ligands in the meridio-
nal isomer (mer, Scheme 1), thereby maximizing steric interac-
tions between the ancillary ligands and the reactive site, the
facial isomer (fac, Scheme 1) has the bulky R groups pulled
* Dr. L. L. Schafer
Scheme 1. Two possible isomers for group 4 metal complexes sup-
ported by diamido ligands with an aryl tether featuring a neutral oxy-
gen donor.
E-Mail: schafer@chem.ubc.ca
[a] Department of Chemistry
University of British Columbia
2036 Main Mall
Vancouver, BC, Canada, V6T 1Z1
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/zaac.201400201 or from the au-
thor.
away from the metal atom and the reactive ligands, alleviating
unfavorable steric pressure on the system. As a result, the
tBu-d6 substituted ligand adopts a facial binding mode while
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the less bulky iPr group crystallizes in a meridional fashion.[7e] nium amidate and ureate compexes, and the investigation of
However, by altering the design, Danopoulos and co-workers these complexes in catalytic amine synthesis. This series of
found that a secondary aryl tether could force sterically bulky precatalysts features a neutral donor, either O or S, in the tether
diamido ligands to adopt the planar mer isomer when installed that modifies coordination arrangements, electron density at
on titanium (Figure 1).[8]
the central metal atoms and catalytic reactivity.
This disparity in binding mode corresponds to a general
change in reactivity: while the fac-bound zirconium system
(R = tBu-d6) is found to catalyze the living polymerization of
1-hexene, the mer isomer (R = iPr) produces only oligomers
under the same conditions.[7e] However, even at temperatures
as low as –80 °C, the auxiliary ligands appear equivalent in
the NMR spectra, suggesting rapid interconversion between
the two isomers in solution.[7d] When the group 4 metal atoms
are exchanged for a larger yttrium atom, the tBu-d6 substituted
diamido ligand crystallizes in a mer fashion, suggesting this
isomer is preferred when sterically accessible.[7f]
Results and Discussion
Tethered Bis(amidate) Complexes
The general synthesis of the tethered diamide proligands is
shown in Scheme 2. The oxy-bridged dianiline is prepared by
reducing the corresponding dinitro compound, which itself is
synthesized via nucleophilic aromatic substitution.[12] In both
cases, the amide functionality is installed by reacting the dian-
iline with two equivalents of the appropriate acid chloride.[13]
Schrock and co-workers have also synthesized diamido li-
gands using sulfur as the neutral donor in the aryl tether.[9]
When installed on zirconium, these ligands adopt the fac bind-
ing mode in the solid state and do not rapidly isomerize to the
mer binding mode in solution. Substituting the hard oxygen
atom in the diamido tether for a softer sulfur donor makes the
ligand more attractive for coordination to late transition metals,
exemplified by the ruthenium complexes synthesized by Hidai
and co-workers as precatalysts for the hydrogenation of benzo-
nitrile.[10] Additionally, Deng and co-workers have shown that
the bulky mesityl-substituted diamido ligand supports high
spin iron(II) complexes.[11] In line with the aforementioned zir-
conium systems, the sulfur bridged diamido ligands adopt the
fac binding mode in the solid state for both Ru and Fe com-
plexes.
Our group has recently reported an alkyl-tethered bis(ureate)
zirconium complex as a broadly applicable hydroamination
catalyst (Figure 2), while untethered bis(ureate) complexes
show reduced reactivity.[6]
Scheme 2. Synthesis of diamide proligands.
After synthetic investigations focused on the oxy-bridged
proligand, the tBu substituted diamide was found to be the
most promising based on the solubility of both the proligand
and the corresponding complex (vide infra). As a result, only
the tBu version of the thio-bridged diamide was synthesized.
In solution, all ligands display C2 symmetry as evidenced by
1
the single set of H NMR signals observed for both the tert-
butyl groups and the aromatic protons. Despite the possibility
of a delocalized π network between the bridged aryl groups,
both ligands experience an out of plane twisting in the solid
state (Figure 3), possibly due to crystal packing interactions.
The metrical parameters for the bridged ligands are compar-
able except for the C–E bond length, with the C–O bond
lengths [1.386(3) Å average] being significantly shorter than
the C–S contacts [1.786(1) Å average] as anticipated. This in-
Figure 2. Alkyl-tethered bis(ureate) zirconium hydroamination precat-
alyst.
In an effort to build upon the success of the bis(ureate) zir- crease in bond length is accompanied by a more acute C–E–C
conium precatalyst and to further explore the effects of the bong angle for the thio-bridged diamide [102.26(6)°] com-
tether on hydroamination catalysts, the monoanionic amido do- pared to the oxygen congener [117.23(16)°]. It was anticipated
nors of the aryl-bridged framework of Scheme 1 were replaced that the longer C–S bond could offer more flexibility in the
with N,O-chelating functional groups, namely amides and ligand and therefore different binding modes for amidate coor-
ureas. Herein we report the synthesis of new tethered zirco- dination.
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Scheme 3. Synthesis of bis(amidate) zirconium complexes 1 and 2 via
protonolysis.
Figure 3. ORTEP representations of the solid-state molecular struc-
tures for oxy- (left) and thio-bridged (right) diamide proligands drawn
at 50% probability for thermal ellipsoids. Only one part of a disordered
tBu group for the oxy-bridged species is shown for clarity. Hydrogen
atoms omitted for clarity.
Table 1. Selected bond lengths /Å and angles /° for complexes 1 and
2.
Bond/Angle
1
2
When one equivalent of the oxy-bridged proligand is reacted
with homoleptic Zr(NMe2)4 in [D6]benzene, clean conversion
to one symmetric product is observed in the H NMR spec-
Zr–O1
Zr–O2
Zr–N1
2.2531(15)
2.2415(14)
2.3194(17)
2.3242(17)
2.1006(18)
2.0822(18)
2.4780(18)
56.71(6)
2.2512(13)
2.2320(13)
2.3179(15)
2.3354(15)
2.0911(16)
2.0894(16)
2.4789(16)
57.03(5)
1
trum. Only one set of signals is observed for both the tBu (δH Zr–N2
Zr–N3
= 1.00) and aryl protons (δH = 6.77, 6.86, 6.99). In addition to
Zr–N4
the signal assigned to the dimethylamido protons at δH = 3.18,
Zr–N5
a broad signal attributed to a coordinated neutral dimeth-
ylamine molecule at δH = 2.21 is observed.[5]
O1–Zr–N1
O2–Zr–N2
57.32(6)
57.32(5)
The X-ray crystallographic data reveals seven coordinate
complexes (1 and 2, Figure 4) for related complexes synthe-
sized in the presence of pyridine. These isostructural com-
plexes are more easily crystallized (Scheme 3) than the di-
methylamine analogues. The κ4(N,N,O,O) bis(amidate) com-
plexes adopt a pseudo-trigonal bipyramidal arrangement with
the amidate chelates occupying one equatorial and one axial
coordination site. This is in contrast to a previously reported
κ4(N,N,O,O) axially chiral bis(amidate) Zr complex, where
both amidate contacts are found in the equatorial plane.[5]
Interestingly, the Zr–Oamidate bond lengths for 1 and 2
[2.2444(15) Å average] are significantly shorter than the re-
ported tethered bis(amidate) zirconium species [2.2846(37) Å
average] while the Zr–Namidate contacts [2.3242(17) Å average
for 1 and 2] are not statistically different.[5] These solid state
molecular structures show that there is no interaction between
the zirconium atom and the chalcogen donor in the ligand
(Zr–O ≈ 3.813; Zr–S ≈ 3.962 Å) (Table 1).
proligands were also synthesized.[14] Reaction of the oxy- or
thio-dianiline starting material with phenyl chloroformate
gives the intermediate dicarbamate which, upon exposure to
diisopropylamine, is converted into the desired diurea product
in good yields (Scheme 4).
Scheme 4. Synthesis of diurea proligands.
In line with observations made for the diamide proligands,
the diurea compounds are twisted about the chalcogen bridges
in the solid state (Figure 5). As expected, the C–S bond lengths
[1.7798(15) Å average] are considerably longer than the corre-
sponding C–O distances [1.4018(16) Å average] and the C–E–
C bond angles are comparable to the diamide values. Akin to
the diamide proligands, the diurea species adopt a C2v symmet-
Figure 4. ORTEP representations of the solid state molecular structure
of 1 (left) and 2 (right) drawn at 50% probability for thermal ellip-
soids. Hydrogen atoms omitted for clarity.
Tethered Bis(ureate) Complexes
Encouraged by the success of the aforementioned tethered ric arrangement in solution as evidenced by the presence of a
1
bis(ureate) zirconium hydroamination precatalyst, two diurea single methine signal in the H NMR spectrum.
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In an attempt to encourage a dative interaction between the
oxygen atom of the tether and the zirconium atom of
3·HNMe2, the dimethylamine donor was removed in vacuo.
Removal of the amine donor herein yields the monometallic
complex 3 supported by a κ4(N,N,O,O) bound bis(ureate) li-
gand (Figure 7), in contrast to a dimeric species that has been
previously observed with the alkyl-tethered complex in Fig-
ure 2.[15] This complex is structurally similar to the thio-
bridged variant 4 (Scheme 6).
Figure 5. ORTEP representations of the solid-state molecular struc-
tures for oxy- and thio-bridged diurea proligands drawn at 50% prob-
ability for thermal ellipsoids. Only one part of a disordered N(iPr)2
group for the thio-bridged species is shown for clarity. Hydrogen atoms
omitted for clarity.
Following literature procedure,[6] the oxy-bridged diurea
proligand was reacted with Zr(NMe2)4 in pentane at reflux to
yield the κ3(N,O,O) bis(amidate) complex 3·HNMe2 in 80%
yield (Scheme 5). In this case the pseudo-trigonal bipyramidal
arrangement of 3·HNMe2 features both κ1(O) and κ2(N,O) ure-
ate contacts in the equatorial plane with the neutral dimeth-
ylamine donor occupying an axial position (Figure 6). The
presence of dimethylamine in the axial position is in good
agreement with the solid-state molecular structure of the re-
Figure 7. ORTEP representation of the solid-state molecular structure
of 3 (left) and 4 (right) drawn at 50% probability for thermal ellip-
soids. Only one part of a disordered N(iPr)2 group for 3 is shown for
clarity. Hydrogen atoms omitted for clarity.
lated bis(ureate) zirconium hydroamination precatalyst.[6]
A
1
broad signal in the H NMR spectrum at δH = 2.21 suggests
the amine remains coordinated in solution as well.[5] Once
again, the presence of the neutral amine donor negates the need
for electron density from the oxy-bridge resulting in a Zr–O
distance of approximately 3.724 Å.
Scheme 5. Synthesis of bis(ureate) zirconium complex 3·HNMe2 via
protonolysis.
Scheme 6. Synthesis of bis(ureate) zirconium complexes 3 and 4 via
protonolysis.
With an average angle of 109.3° between the atoms bound
to the metal atom, and no obviously defined planes, 3 and 4
are best described as tetrahedral complexes with each κ2(N,O)
ureate unit occupying one formal coordination site. The oxy-
bridged species 3 has slightly longer Zr–Oureate bonds
[2.190(2) Å average] compared to complex 4 [2.181(1) Å
average], corresponding to shorter Zr–Nureate contacts
[2.283(2) and 2.319(1) Å average, respectively]. Bis(ureate)
complexes
3 and 4 have shorter average Zr–Oureate
[2.1854(2) Å] and Zr–Nureate [2.3011(2) Å] contacts than the
comparable bis(amidate) species 1 and 2 [2.2444(2) and
2.3242(2) Å], putting the κ2(N,O) ureate chelate closer to the
Figure 6. ORTEP representation of the solid-state molecular structures
for 3·HNMe2 drawn at 50% probability for thermal ellipsoids.
Hydrogen atoms omitted for clarity.
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metal atom (Table 2). These metrical parameters are in line Table 3. Catalytic screening of complexes 1–4 for the intramolecular
hydroamination of primary (1° HA, top) and secondary amines (2° HA,
bottom).
with other examples comparing and contrasting the bonding in
amidate and ureate complexes.[16] However, one key structural
difference between the chalcogen- and alkyl-tethered com-
plexes is the fact that the alkyl-tethered system displays in-
plane binding of the bis(ureate) ligand. Even with the ad-
ditional flexibility offered by the sulfur linker than its oxygen
congener, neither species allows both κ2(N,O) ureate units to
bind to the zirconium in the equatorial plane as found with the
alkyl bridge. This attribute may significantly impact the cata-
lytic activity of the complex (vide infra).
Table 2. Selected bond lengths /Å and angles /° for complexes 3 and
4.
Bond/Angle
3
4
Zr–O1
Zr–O2
Zr–N1
Zr–N2
Zr–N5
Zr–N6
O1–Zr–N1
O2–Zr–N2
2.1948(15)
2.1856(16)
2.3128(16)
2.2529(18)
2.0312(18)
2.0464(17)
57.68(5)
2.1749(12)
2.1863(12)
2.3156(14)
2.3229(13)
2.0525(14)
2.0532(14)
58.81(4)
a)
Catalyst
Conversion /%
1° HA
2° HA
1
2
3
4
Ͼ 98
Ͼ 98
Ͼ 98
Ͼ 98
Ͻ 2
Ͻ 2
10
6
59.20(6)
58.20(4)
1
a) Conversions determined by H NMR spectroscopy using 1,3,5-tri-
methoxybenzene as an internal standard.
The solution phase data for 3 and 4 is characterized by broad
signals for the isopropyl methyl protons in the H NMR spec-
1
plexes may be attributable to the non-planar arrangement of
the κ4(N,N,O,O) bis(ureate) ligand, as the secondary amine
substrate is completely converted under these conditions with
the in-plane alkyl-bridged complex.[6] The results observed
herein are consistent with most other reported neutral zirco-
nium precatalysts invoking an imido intermediate and dis-
playing a substrate scope limited to primary amines. In fact,
most reported precatalysts for secondary amine hydroamin-
ation are sensitive cationic species.[19] Our previously reported
alkyl-tethered neutral zirconium complex is a rare exception.[6]
tra (0.5–1.5 ppm for 3; 0.0–2.0 ppm for 4). Due to the ob-
served broadening and high multiplicity, the methine C–H sig-
nals cannot be distinguished from the baseline in either spec-
trum. However, well-resolved signals are observed for both the
aryl protons of the bis(ureate) ligand and the methyl protons
of the dimethylamido ligands.
Catalytic Activity of Tethered Bis(amidate) and Bis(ureate)
Complexes
In light of the excellent reactivity observed for the alkyl-
bridged bis(ureate) zirconium species, complexes 1–4 were in-
vestigated as precatalysts for the intramolecular hydroamin-
ation of aminoalkenes.[6] All the zirconium precatalysts were
prepared in situ to avoid the competitive binding from the pyr-
Conclusions
A series of zirconium complexes supported by bis(amidate)
idine donor found in the crystalline complexes 1 and 2. The and bis(ureate) ligands with a neutral chalcogen donor in the
catalytic results are summarized in Table 3 along with the spe- tether were synthesized and characterized in the solution phase
cific reaction conditions.
and the solid state. The bis(amidate) zirconium complexes 1
The zirconium species perform well as hydroamination pre- and 2 coordinate an amine donor within the coordination
catalysts with both bis(amidate) and bis(ureate) complexes sphere (HNMe2 or pyridine) and display a κ4(N,N,O,O)
achieving full conversion of the primary aminoalkene substrate bis(amidate) binding mode. Bis(ureate) species 3 and 4 are
after 2 h. However, bis(amidate) complexes 1 and 2 show no found to have a κ3(N,O,O) binding mode in the solid state with
reactivity for the secondary amine substrate under the de- the ureate moieties cis to one another when in the presence of
scribed reaction conditions. This reactivity profile is similar to neutral donor. This is in contrast to the in-plane binding of an
other reported Zr catalysts and is consistent with an imido- alkyl-bridge bis(ureate) zirconium complex found to be a
based mechanism for 1 and 2.[17]
broadly applicable hydroamination catalyst. None of the data
Furthermore, the bis(ureate) zirconium precatalysts 3 and 4 collected for the bis(amidate) or bis(ureate) species suggests
show very limited conversions with the secondary amino- there is electron donation from the neutral donor to the metal
alkene substrate (10 and 6%, respectively). Once again these atom in solution or the solid state.
results are more consistent with imido species as being key
Complexes 1–4 were screened as catalysts for the intramo-
catalytic intermediates and is in contrast to a proton-assisted lecular hydroamination of primary and secondary aminoalk-
C–N bond formation that has been proposed for the alkyl- enes, with complete conversion of the primary amine substrate
bridged species.[15,18] The change in reactivity of these com- observed for each Zr complex. While the bis(amidate) com-
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thiodianiline (2.00 g, 9.24 mmol) was dissolved in DCM (25 mL). Tri-
plexes 1 and 2 were unable to catalyze the cyclization of the
ethylamine (3.9 mL, 27.7 mmol) was added in one portion and the
solution was cooled to –78 °C before pivoyl chloride (2.8 mL,
23.1 mmol) was introduced. Yield: 3.03 g (85%). 1H NMR (300 MHz,
secondary aminoalkene substrates, and bis(ureate) complexes
3 and 4 were found to affect a small amount of reactivity.
These results point toward the importance of a controlled bind-
ing mode with the N,O-chelates in the equatorial plane to pro-
mote improved good reactivity with both primary and second-
ary amines. Thus, on-going efforts in catalyst development
aimed at realizing more challenging alkene hydroamination re-
actions, such as intermolecular hydroamination, need to take
3
chloroform-d, 25 °C): δ = 1.24 [s, 18 H, C(CH3)3], 7.02 (td, JH,H
=
=
3
3
3
7.42, JH,H = 1.10 Hz, 2 H, CHarom.), 7.12 (dd, JH,H = 7.97, JH,H
3
3
1.65 Hz, 2 H, CHarom.), 7.32, (td, JH,H = 7.15, JH,H = 1.37 Hz, 2 H,
CHarom.), 8.07 (br. s, 2 H, NH), 8.26 (dd, 3JH,H = 7.15, 3JH,H = 1.10 Hz,
2 H, CHarom.). 13C{1H} NMR (75 MHz, chloroform-d, 25 °C): δ =
27.4 [C(CH3)3], 39.9 [C(CH3)3], 122.2, 122.2, 124.9, 129.2 (CHarom.),
advantage of ligand tethers that promote such equatorial bind- 131.7 (CN), 137.5 (Carom.OC), 176.6 (C=O). MS (ESI) m/z 385 (M+
+ H), 407 (M+ + Na). C22H28N2O2S: calcd. C 68.72; H 7.34; N 7.29%;
ing.
found: C 68.72; H 7.38; N 7.29%. Single crystals suitable for X-ray
analysis (CCDC-991476) were obtained by recrystallization from hex-
Experimental Section
anes and ethyl acetate.
General: Reagents and solvents for proligand synthesis were used as
received without further purification. All preparative scale reactions
for complexes 1–4 were conducted in oven dried (160 °C) glassware
with magnetic stirring in a glove box in an atmosphere of dry dinitro-
gen. Toluene and pentane were purified by passage over an activated
aluminum oxide column and degassed prior to use. Catalytic experi-
ments were carried out in Teflon cap sealed NMR tubes (5 mm).
[D8]Toluene and [D6]benzene were dried with 4 Å molecular sieves
and degassed by 3 freeze-pump-thaw cycles. NMR spectra were re-
corded with Bruker Avance 300 (1H: 300, 13C: 75), Bruker Avance
400 (1H: 400, 13C: 100), or Bruker Avance 600 (1H: 600 13C: 150)
instruments operating at the denoted spectrometer frequency given in
mega Hertz (MHz) for the specified nucleus. Shifts (δ) are reported in
parts per million (ppm) and coupling constants J are given in Hertz
(Hz). Mass spectra were measured with a Kratos MS-50 and elemental
analyses were performed with a Carlo Erba Elemental Analyzer EA
1108. Single crystal X-ray structure determinations were performed
with either a Bruker APEX X8 or APEX DUO.
N,NЈ-(2,2Ј-Oxybis(2,1-phenylene))bis(tert-butylamidate)bis(di-
methylamido)(pyridine)zirconium (1): N,NЈ-(2,2Ј-Oxybis(2,1-phen-
ylene))bis(tert-butylamide) (0.276 g, 0.748 mmol), Zr(NMe2)4
(0.200 g, 0.748 mmol), and pyridine (60 μL, 0.748 mmol) were sus-
pended in toluene (3 mL) and the mixture was allowed to stir overnight
(18 h) to give a clear yellow solution. All volatiles were removed in
vacuo and the remaining solid was washed thrice with hexanes and
then recrystallized from the minimal amount of hot hexanes. The col-
orless crystals were collected and identified as the title compound.
Yield: 0.265 g (0.426 mmol, 57%). 1H NMR (600 MHz, [D6]benzene,
25 °C): δ = 0.99 [s, 18 H, C(CH3)3], 3.20 [s, 12 H, N(CH3)2], 6.67 (m,
3
2 H, CHarom.), 6.77 (m, 4 H, py–CHarom.), 6.89 (d, JH,H = 7.2 Hz, 2
3
H, CHarom.), 6.97 (m, 1 H, py–CHarom.), 7.01 (d, JH,H = 7.2 Hz, 2 H,
CHarom.), 8.62 (m, 2 H, CHarom.). 13C{1H} NMR (150 MHz, [D6]ben-
zene, 25 °C): δ = 28.7 (CCH3), 41.2 [C(CH3)2], 43.6 [br. s,
N(CH3)2], 122.5, 123.8, 124.5, 125.0, 127.3, 128.7, 136.0 (CHarom.),
139.8 (Carom.OC), 150.5 (CN), 151.3 (C=O). MS (EI): m/z 500 (M+ –
pyridine, – NMe2). C31H43N5O3Zr: calcd. C 59.58; H 6.94; N 11.21%;
found: C 59.84; H 6.84; N 10.99%. Single crystals suitable for X-ray
analysis (CCDC-991477) were obtained by recrystallization from hot
hexanes.
N,NЈ-(2,2Ј-Oxybis(2,1-phenylene))bis(tert-butylamide): 2,2Ј-Oxydi-
aniline (2.09 g, 10.4 mmol) was dissolved in dichloromethane (DCM)
(35 mL). Triethylamine (4.3 mL, 30.9 mmol) was added in one portion
and the solution was cooled to –78 °C. Trimethylacetyl chloride
(2.6 mL, 21.1 mmol) was added dropwise and the solution was allowed
to warm to room temperature overnight. A precipitate formed and was
dissolved in DCM (25 mL) and 1 m aqueous NaOH solution (50 mL)
and was added to the solution. The organic portion was washed with
50 mL portions of 1 M aqueous HCl solution (3ϫ), water and brine
and dried with MgSO4. The solution containing the remaining product
was run through a short silica gel plug using DCM. The solvent was
removed by rotary evaporation and the resulting solid was washed with
hexanes. The crude compound was recrystallized from hexanes and
ethyl acetate and isolated as a colorless crystalline solid. Yield: 3.29 g
N,NЈ-(2,2Ј-Thiobis(2,1-phenylene))bis(tert-butylamidate)bis(di-
methylamido)(pyridine)zirconium (2): N,NЈ-(2,2Ј-Thiobis(2,1-phen-
ylene))bis(tert-butylamide) (0.288 g, 0.75 mmol), Zr(NMe2)4 (0.200 g,
0.75 mmol), and pyridine (60 μL, 0.75 mmol) were suspended in tolu-
ene (3 mL) and the mixture was allowed to stir overnight (18 h) to
give a clear yellow solution. All volatiles were removed in vacuo and
the remaining solid was washed with hexanes and then recrystallized
from the minimal amount of hexanes at –35 °C. The colorless crystals
were collected and identified as the title compound. Yield: 0.239 g
(0.375 mmol, 50%). 1H NMR (600 MHz, [D6]benzene, 25 °C): δ =
0.92 [s, 18 H, C(CH3)3], 3.21 [s, 12 H, N(CH3)2], 6.71 (m, 4 H,
CHarom.), 6.88 (m, 4 H, CHarom.), 6.99 (br. s, 1 H, CHarom.), 7.55 (d,
3JH,H = 7.7 Hz, 2 H, CHarom.), 8.62 (br. s, 2 H, CHarom.). 13C{1H}
NMR (150 MHz, [D6]benzene, 25 °C): δ = 28.7 (CCH3), 41.1
[C(CH3)2], 44.1 [br. s, N(CH3)2], 123.9, 124.8, 126.5, 128.7, 129.1,
129.2, (CHarom.), 136.0 (Carom.OC), 149.5 (CN), 150.5 (C=O). MS
(EI): m/z 516 (M+ – pyridine, – NMe2). C31H43N5O2SZr: calcd. C
58.09; H 6.76; N 10.93%; found: C 58.28; H 6.48; N 10.74%. Single
crystals suitable for X-ray analysis (CCDC-991478) were obtained by
recrystallization from hexanes at –35 °C.
1
(86%). H NMR (600 MHz, chloroform-d, 25 °C): δ = 1.22 [s, 18 H,
3
C(CH3)3], 6.83 [dd, 3J(H,H) = 8.19, JH,H = 1.02 Hz, 2 H, CHarom.],
3
3
3
7.03 (td, JH,H = 8.70, JH,H = 1.54 Hz, 2 H, CHarom.), 7.13, (td, JH,H
3
= 7.68, JH,H = 1.02 Hz, 2 H, CHarom.), 7.96 (br. s, 2 H, NH), 8.27 (d,
3JH,H = 8.19 Hz, 2 H, CHarom.). 13C{1H} NMR (150 MHz, chloroform-
d, 25 °C): δ = 27.12 [C(CH3)3], 39.51 [C(CH3)3], 117.2, 122.0, 124.3,
124.3 (CHarom.), 129.0 (CN), 145.2 (Carom.OC), 176.4 (C=O). MS
(ESI) m/z 369 (M+ + H), 391 (M+ + Na). C22H28N2O3: calcd. C 71.71;
H 7.66; N 7.60%; found: C 71.50; H 7.56; N 7.60%. Single crystals
suitable for X-ray analysis (CCDC-991475) were obtained by
recrystallization from ethanol at 4 °C. Disordered tBu group was mod-
eled using two unique parts.
1,1Ј-(Oxybis(2,1-phenylene))bis(3,3-diisopropylurea): This com-
pound was synthesized according to modified literature procedure.[14]
Overall yield: 12.46 g (82%). 1H NMR (400 MHz, chloroform-d,
3
N,NЈ-(2,2Ј-Thiobis(2,1-phenylene))bis(tert-butylamide): The same
method was used as above except for the following changes: 2,2’-
25 °C): δ = 1.22 [d, JH,H = 7.0 Hz, 24 H, CH(CH3)2], 3.97 [m, 4 H,
3
CH(CH3)2], 6.77 (d, JH,H = 7.9 Hz, 2 H, CHarom.), 6.87 (br. s, 2 H,
Z. Anorg. Allg. Chem. 2015, 128–135
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ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
3
NH), 6.90 (m, 2 H, CHarom.), 7.10 (t, 2 H, JH,H = 7.61 Hz, CHarom.), crystals suitable for X-ray analysis (CCDC-991483) were obtained by
3
8.29 (d, 2 H, JH,H = 8.22 Hz, CHarom.). 13C{1H} NMR (100 MHz, recrystallization from pentane at –35 °C.
chloroform-d, 25 °C): δ = 21.1 [CH(CH3)2], 45.0 [CH(CH3)2], 117.2,
General Procedures for Catalytic Reactions: In a nitrogen filled
glove box, the appropriate diamide/diurea proligand (0.015 mmol,
10 mol%) was weighed into a small vial and subsequently dissolved
in [D8]toluene (300.0 μL) before being transferred to an NMR tube
equipped with a Teflon cap. Standard solutions containing 1,3,5-trime-
thoxybenzene (40.0 μL, 1.25 mol·L–1, 0.083 mmol), the aminoalkene
substrate (100.0 μL, 1.5 mol·L–1, 0.15 mmol), and Zr(NMe2)4
(100.0 μL, 0.15 mol·L–1, 0.015 mmol, 10 mol%) in [D8]toluene were
added sequentially by means of a μL-pipette. The corresponding
amount of [D8]toluene required for a total volume of 600 μL (60 μL)
before the NMR tube was closed, shaken, and removed from the glove
box. Following the recording of a 1H NMR spectrum (300 MHz,
25 °C), the NMR tube was placed in a preheated, 100 °C thermostatted
oil bath. The NMR tube was removed from the oil bath after 2 h and
another 1H NMR spectrum was recorded (300 MHz, 25 °C). For the
secondary aminoalkene substrate, the NMR tube was reintroduced to
the oil bath for an additional 16 h before a final 1H NMR spectrum
was recorded (300 MHz, 25 °C). The results presented in Table 3 are
the average of duplicate runs.
120.4, 122.1, 124.6 (CHarom.), 131.1 (CN), 144.3 (Carom.OC), 154.0
(C=O). MS (ESI) m/z 454 (M+), 477 (M+ + Na). C26H38N4O3: calcd.
C 68.69; H 8.43; N 12.32%; found: C 68.36; H 8.29; N 12.34%.
Single crystals suitable for X-ray analysis (CCDC-991479) were ob-
tained by recrystallization from hot hexanes.
1,1Ј-(Thiobis(2,1-phenylene))bis(3,3-diisopropylurea): This com-
pound was synthesized according to modified literature procedure.[14]
Overall yield: 4.98 g (79 %). 1H NMR (400 MHz, chloroform-d,
3
25 °C): δ = 1.31 [d, JH,H = 7.0 Hz, 24 H, CH(CH3)2], 3.94 [m, 4 H,
3
3
CH(CH3)2], 6.96 (td, JH,H = 7.9, JH,H = 1.5 Hz, 2 H, CHarom.), 7.01
3
3
(br. s, 2 H, NH), 7.12 (dd, 2 H, JH,H = 7.6, JH,H = 1.2 Hz, CHarom.),
7.31 (td, JH,H = 7.0, JH,H = 1.5 Hz, 2 H, CHarom.), 8.22 (dd, 2 H,
3JH,H = 8.2, JH,H = 0.9 Hz, CHarom.). 13C{1H} NMR (100 MHz, chlo-
3
3
3
roform-d, 25 °C): δ = 21.1 [CH(CH3)2], 45.6 [CH(CH3)2], 120.5,
121.3, 123.1, 129.0 (CHarom.), 131.5 (CN), 139.3 (Carom.OC), 153.9
(C=O). MS (ESI) m/z 471 (M+ + H). C26H38N4O2S: calcd. C 66.35;
H 8.14; N 11.90%; found: C 66.21; H 8.05; N 11.83%. Single crystals
suitable for X-ray analysis (CCDC-991480) were obtained by
recrystallization from hot hexanes. Disordered N(iPr)2 group was mod-
eled using two unique parts.
Crystallographic data (excluding structure factors) for the structures in
this paper have been deposited with the Cambridge Crystallographic
Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK. Copies
of the data can be obtained free of charge on quoting the depository
numbers CCDC-991475, CCDC-991476, CCDC-991477, CCDC-
991478, CCDC-991479, CCDC-991480, CCDC-991482, and CCDC-
991483 (Fax: +44-1223-336-033; E-Mail: deposit@ccdc.cam.ac.uk,
http://www.ccdc.cam.ac.uk)
1,1Ј-(Oxybis(2,1-phenylene))bis(3,3-diisopropylureate)bis(di-
methylamido)zirconium (3): 1,1Ј-(Oxybis(2,1-phenylene))bis(3,3-di-
isopropylurea) (0.297 g, 0.654 mmol) and Zr(NMe2)4 (0.175 g,
0.654 mmol) were suspended in toluene (3 mL) and the mixture was
allowed to stir overnight (18 h) to give a clear solution. All volatiles
were removed in vacuo and the remaining solid was washed thrice
with hexanes and finally recrystallized from the minimal amount of
hot hexanes. The colorless crystals were collected and identified as the
title compound. Yield: 0.145 g (0.229 mmol, 35 %). 1H NMR
(400 MHz, [D6]benzene, 25 °C): δ = 0.97 [br. s, 24 H, CH(CH3)2],
Supporting Information (see footnote on the first page of this article):
More detailed experimental information including characterization
data for other tethered diamide proligands, NMR spectra, and X-ray
data tables.
3
3.27 [s, 12 H, N(CH3)2)], 6.72 (t, JH,H = 7.6 Hz, 2 H, CHarom.), 6.83
(t, 3JH,H = 7.6 Hz, 2 H, CHarom.), 6.97 (d, 3JH,H = 7.6 Hz, 2 H, CHarom.),
3
7.03 (t, 2 H, JH,H = 7.6 Hz, CHarom.). 13C{1H} NMR (100 MHz,
Acknowledgements
[D6]benzene, 25 °C): δ = 21.3 [br., CH(CH3)2], 42.3 [N(CH3)2], 47.1
[br., CH(CH3)2], 121.2, 123.4, 124.5, 126.1 (CHarom.), 141.6 (CN),
152.4 (Carom.OC), 166.4 (C=O). MS (ESI) m/z 586 (M+ – NMe2).
C30H48N6O3Zr: calcd. C 57.02; H 7.66; N 13.30%; found: C 57.24; H
8.06; N 13.57%. Single crystals suitable for X-ray analysis (CCDC-
991482) were obtained by recrystallization from hot hexanes. Disor-
dered N(iPr)2 group was modeled using two unique parts.
We gratefully acknowledge the financial support of the University of
British Columbia and the Natural Sciences and Engineering Research
Council of Canada. We thank Jacky Yim, Scott Ryken, Dr. Neal Yonson,
and Dr. Brian O. Patrick for assistance with X-ray crystallography.
References
1,1Ј-(Thiobis(2,1-phenylene))bis(3,3-diisopropylureate)bis(di-
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3
CHarom.), 6.98 (d, JH,H = 4.0 Hz, 4 H, CHarom.), 7.54 (d, JH,H
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7.6 Hz, 2 H, CHarom.). 13C{1H} NMR (100 MHz, [D8]toluene, 25 °C):
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Published Online: September 12, 2014
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