Highly Active Dinuclear Titanium(IV) Complexes for the Catalytic Formation of a Carbon-Heteroatom Bond

Article abstract of DOI:10.1021/acs.inorgchem.8b01766

A series of mononuclear titanium(IV) complexes with the general composition κ³-[R{NHPh₂P(X)}₂Ti(NMe₂)₂] [R = C₆H₄, X = Se (3b); R = trans-C₆H₁₀, X = S (4a), Se (4b)] and [{κ²-N(PPh₂Se)₂}₂Ti(NMe₂)₂] (6b) and two dinuclear titanium(IV) complexes, [C₆H₄{(NPh₂PS)(N)}Ti(NMe₂)]₂ (3c) and [{κ²-N(PPh₂Se)}Ti(NMe₂)₂]₂ (6c), are reported. Dinuclear titanium(IV) complex 6c acts as an efficient catalyst for the chemoselective addition of an E-H bond (E = N, O, S, P, C) to heterocumulenes under mild conditions. The catalytic addition of aliphatic and aromatic amines, alcohol, thiol, phosphine oxide, and acetylene to the carbodiimides afforded the corresponding hydroelemented products in high yield at mild conditions with a broader substrate scope. The catalytic efficiency of the dinuclear complex depends on the cooperative effect of the Ti^IV ions, the systematic variation of the intermetallic distance, and the ligand's steric properties of the complex, which enhances the reaction rate. Most interestingly, this is the first example of catalytic insertion of various E-H bonds into the carbodiimides using a single-site catalyst because only the titanium-mediated insertion of E-H into a C-N unsaturated bond is reported to date. The amine and alcohol insertion reaction with the carbodiimides showed first-order kinetics with respect to the titanium(IV) catalyst as well as substrates. A most plausible mechanism for hydroelementation reaction is also proposed, based on the spectroscopic data of the controlled reaction, a time-course study, and the Hammett plot.

Full text of DOI:10.1021/acs.inorgchem.8b01766

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Highly Active Dinuclear Titanium(IV) Complexes for the Catalytic
Formation of a Carbon−Heteroatom Bond
Jayeeta Bhattacharjee,† Adimulam Harinath,† Indrani Banerjee,† Hari Pada Nayek,‡
and Tarun K. Panda*,†
†Department of Chemistry, Indian Institute of Technology Hyderabad Kandi, Sangareddy, Telangana 502 285, India
‡Department of Applied Chemistry, Indian Institute of Technology Dhanbad, Dhanbad, Jharkhand 826004, India
S
* Supporting Information
ABSTRACT: A series of mononuclear titanium(IV) complexes
with the general composition κ3-[R{NHPh2P(X)}2Ti(NMe2)2]
[R = C6H4, X = Se (3b); R = trans-C6H10, X = S (4a), Se (4b)]
and [{κ2-N(PPh2Se)2}2Ti(NMe2)2] (6b) and two dinuclear
titanium(IV) complexes, [C6H4{(NPh2PS)(N)}Ti(NMe2)]2
(3c) and [{κ2-N(PPh2Se)}Ti(NMe2)2]2 (6c), are reported.
Dinuclear titanium(IV) complex 6c acts as an efficient catalyst
for the chemoselective addition of an E−H bond (E = N, O, S, P,
C) to heterocumulenes under mild conditions. The catalytic
addition of aliphatic and aromatic amines, alcohol, thiol,
phosphine oxide, and acetylene to the carbodiimides afforded
the corresponding hydroelemented products in high yield at mild conditions with a broader substrate scope. The catalytic
efficiency of the dinuclear complex depends on the cooperative effect of the TiIV ions, the systematic variation of the
intermetallic distance, and the ligand’s steric properties of the complex, which enhances the reaction rate. Most interestingly,
this is the first example of catalytic insertion of various E−H bonds into the carbodiimides using a single-site catalyst because
only the titanium-mediated insertion of E−H into a CN unsaturated bond is reported to date. The amine and alcohol
insertion reaction with the carbodiimides showed first-order kinetics with respect to the titanium(IV) catalyst as well as
substrates. A most plausible mechanism for hydroelementation reaction is also proposed, based on the spectroscopic data of the
controlled reaction, a time-course study, and the Hammett plot.
intramolecular addition reaction and hydrophosphorylation of
alkenes have been reported.7 Hydroelementation reactions of
alkenes and alkynes are very well reported and have been
studied using a wide range of transition-metal, lanthanide,
actinide, and alkali-metal catalysts.8−11 However, until now,
hydroelementation of heterocumulenes has scarcely been
investigated using a suitable catalyst or metal precursors.
Hydroelementation of heterocumulenes, which affords the
guanidine, phosphaguanidine, propargylamine, and thiourea
products in a straightforward manner, has found considerable
utility as ligands in coordination compounds,12 medicinal
applications,13 and synthons for challenging organic trans-
formations.14 Recently, Eisen et al. reported the actinide-
mediated insertion of E−H bonds (E = N, P, O, S) into
various heterocumulenes including carbodiimides, isocyanates,
and isothiocyanates (Figure 1).15−18 Similarly, Hill et al. have
reported that the magnesium alkyl complex [CH{C(Me)-
NDipp}2}MgnBu] (Dipp = 2,6-iPr2C6H3) is an effective
precatalyst for the catalytic hydroboration of alkyl- and aryl-
substituted carbodiimides with pinacolborane as well as the
catalytic C−C bond formation reaction between alkynes and
INTRODUCTION
■
The catalytic hydroelementation reaction, usually achieved by
the addition of E−H moieties (E = N, O, S, P, C, Si, B) to
unsaturated bonds, represents an atom-economical reaction in
the functionalization of unsaturated compounds. This process
has experienced a phenomenal acceleration in research activity
over the past 2 decades.1 Some representative results of
hydroelementation for the construction of C−heteroatom
bonds consist of hydroamination,2 hydrothiolation,3 hydro-
silylation,4 alkyne oligomerizations,5 hydroboration6 reactions,
and so on. These types of catalytic processes are at the
receiving end of intense interest because they involve atom-
economical routes for the synthesis of various families of
organic molecules, and this renders them attractive to both
green chemistry and low-cost industrial processes. However,
this reaction cannot proceed without the presence of a suitable
catalyst to overcome the electrostatic repulsion between
electron-rich π systems such as alkynes, alkenes, carbodiimides,
and Lewis bases such as amines (hydroamination), phosphins
(hydrophosphination) or phosphine oxides (hydrophosphor-
ylation), alcohol (hydroalkoxylation), thiols (hydrothiolation),
and so on. Moreover, this reaction is entropically not favored.
Further, in the absence of a catalyst, limited substrate scopes
such as hydroamination of activated alkenes via a catalytic
Received: June 26, 2018
© XXXX American Chemical Society
A
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Figure 1. Selective examples of catalysts known for hydroelementation of heterocumulenes.
isocyanates to form bis(imidazolidine-2,4-diones) (Figure
1).6,19 In addition, Westerhausen et al. have also recently
described the use of potassium-mediated tetramers [(thp)K-
(OPMes2)]4 and [(thf)3{K(OPMes2)}4] for the hydrophos-
phorylation of heterocumulenes with diarylphosphine oxide
and sulfide (Figure 1).20 In all cases, the catalytic hydro-
elementation of heterocumulenes usually involves only two or
four kinds of E−H nucleophiles (E = N, P, O, S) or
heterocumulene substrates, which provide only a limited
substrate scope.21−23 Therefore, developing a single catalytic
system that can perform versatile reactions such as the addition
of E−H (E = N, O, S, P, C) moieties to heterocumulenes with
a broader substrate scope is highly challenging. Nevertheless, it
is interesting to develop catalysts that exhibit high tolerance
toward heteroatoms and various functional groups that are able
to catalyze diversified substrates.
these precatalysts is very limited. In this context, we wanted to
design a new class of ligands that can preferably stabilize two
Ti ions simultaneously to realize a dinuclear titanium(IV)
complex, where the structure-bonding relationship of such
complexes can provide a better understanding of the efficiency
of the catalytic process. Here, we report the synthesis and
structural details of a series of mononuclear titanium(IV)
complexes with the general composition κ3-[R{NHPh2P-
(X)}2Ti(NMe2)2] [R = C6H4, X = Se (3b); R = trans-
C6H10, X = S (4a), Se (4b)] and [{κ2-N(PPh2Se)2}2Ti-
(NMe2)2] (6b) along with dinuclear titanium(IV) complexes
κ3-[C6H4{(NPh2PS)(N)}Ti(NMe2)]2 (3c) and [{κ2-N-
(PPh2Se)}Ti(NMe2)2]2 (6c). We also describe a general and
efficient protocol for the catalytic insertion of E−H bonds (E =
N, O, S, P, C) into heterocumulenes with a broader substrate
scope using the dinuclear titanium(IV) catalyst 6c to yield a
chemoselective product.
In recent years, several researchers have developed a rich
catalytic chemistry from the relatively inexpensive and earth-
abundant group 4 metals in a variety of heterofunctionalisa-
tion, dehydrocoupling, and polymerization reactions.24−31
Among the group 4 metals, titanium is the most abundant.
Moreover, it is also an inexpensive and relatively less toxic
metal, and its bioaffinity makes it suitable for innumerable
applications in chemical synthesis compared to the more
expensive and hazardous actinide and Ae metals.24−31
Therefore, various research groups worldwide are working to
develop a suitable titanium-metal-mediated catalyst that can
efficiently catalyze hydroelementation for the construction of
C−heteroatom bonds. Recently, Bergman and Mindiola et al.
reported titanium-mediated hydroamination and C−H bond
activation reactions of unsaturated bonds.32 Similarly, Tonks,
Odom, and Doya et al. also developed a titanium-mediated
catalyst for carboamination, multicomponent, and hydro-
phosphination reactions.33,34 In a continuation to this, our
group also successfully synthesized a titanium-mediated
catalyst of the bis(phosphinoselenoic amide) ligand [{Ph2P-
(Se)NCH2CH2NPPh2(Se)}Ti(NMe2)2] and the imidazolin-2-
iminato ligand [(ImDippN)Ti(NMe2)3] (ImN = imidazolin-2-
iminato; Dipp = 2,6-iPr2C6H3) for the catalytic hydro-
amination of various heterocumulenes,35,36 but the scope of
RESULTS AND DISCUSSION
■
Preparation of Titanium(IV) Complexes. Tetrakis-
(dimethylamido)titanium(IV) [Ti(NMe2)4] was made to
react with 1 equiv of the protic ligand [R{NHPh2P(X)}2] [R
= C6H4, X = S (1a), Se (1b); R = C6H10, X = S (2a), Se
(2b)]37−39 in toluene at ambient temperature for 3 h to afford
the corresponding titanium complexes κ3-[R{NP(X)Ph2}2Ti-
(NMe2)2] [R = C6H4, X = Se (3b); R = C6H10, X = S (4a), Se
(4b)] in good yield (Scheme 1) as yellow solids. The solid-
state structure of the titanium complex 4a is already reported
by Zhang et al.,39 whereas the molecular structures of the other
titanium(IV) complexes (3b and 4b) in their solid state were
confirmed by single-crystal X-ray diffraction analysis. In a
similar fashion, the reaction between the diselenoimidodiphos-
phine ligand [HN(PPh2Se)2}2] (5b) and [Ti(NMe2)4] in a 2:1
molar ratio at ambient temperature gave the corresponding
titanium complex [{κ2-N(PPh2Se)2}2Ti(NMe2)2] (6b; Scheme
2). All of the titanium complexes (3b, 4a, 4b, and 6b)
exhibited good solubility in common organic solvents such as
1
tetrahydrofuran and toluene and were characterized by H,
13C{1H}, and 31P{1H} NMR spectroscopy and combustion
B
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Scheme 1. Synthesis of Titanium(IV) Complexes 3a,3b, 4a,
and 4b
Figure 2. Molecular solid-state structure of 3b. H atoms are omitted
for clarity. Selected bond lengths (Å) and angles (deg): N1−Ti2
2.112(5), N2−P2 1.613(4), N2−Ti2 2.058(4), N3−Ti2 1.886(5),
N4−Ti2 1.853(5), N5−P4 1.659(5), N5−Ti1 2.126(4), P1−Se1
2.1267(16), P2−Se2 2.1466(16), Ti2−Se2 2.6785(12); C1−N1−Ti2
116.8(3), P1−N1−Ti2 124.8(3), C6−N2−P2 132.7(4), C6−N2−
Ti2 118.8(3), P2−N2−Ti2 106.4(2), N4−Ti2−N3 117.0(2), N4−
Ti2−N2 130.7(2), N3−Ti2−N2 110.9(2), N4−Ti2−N1 102.6(2),
N3−Ti2−N1 103.48(19), N2−Ti2−N1 75.80(17), N4−Ti2−Se2
90.06(15), N3−Ti2−Se2 95.82(15), N2−Ti2−Se2 74.19(13), N1−
Ti2−Se2 148.55(12).
Scheme 2. Synthesis of the Titanium(IV) Complex 6b from
5b
analysis (Figures FS5 and FS16). In the 31P NMR spectra of
complexes 3b and 4b, only one signal at 59.7 and 73.4 ppm
was observed in each case along with two satellite peaks
(Figures FS9 and FS12), indicating that both the P atoms are
chemically equivalent. This is due to the rapid exchange
between two Se atoms, one of which is bonded with Ti and the
rate of exchange is faster than the NMR spectroscopy time
scales. This kind of dynamic process is quite common in
phosphorus chemistry and well reported in the literature.36
The molecular structures of 3b and 4b confirm the
attachment of ligands 1b and 2b to a Ti ion in each case.
Complex 3b crystallizes in the monoclinic space group P21/c,
with eight molecules in the unit cell. However, the analogous
complex 4b crystallizes in the centrosymmetric triclinic space
̅
group P1, with two molecules in the unit cell. Complex 6b
crystallizes in the monoclinic space group C2/c, with four
molecules of 6b and one toluene molecule in the unit cell. The
details of the structural parameters are given in Table TS1. The
solid-state structures of complexes 3b and 4b are given in
Figures 2 and 3, respectively, and that of complex 6b is given in
Figure FS1. In both complexes 3b and 4b, the coordination
polyhedron is formed by the dianionic ligand −[R{NPh2P-
(Se)}2]2− [R = C6H4 (3b), trans-C6H10 (4b)] and two −NMe2
groups to provide the metal-ion 5-fold coordination. Ligands
1b and 2b are bonded to the Ti metal ion through the
chelation of two amido N atoms and one Se atoms attached to
the P atoms. However, in complex 6b, the TiIV ion adopts 6-
fold coordination through the attachment of four Se atoms
from two monoanionic P,P-diphenylphosphinoselenoic amido
ligands [N(PPh2Se)2]− and two −NMe2 groups, which are
attached to the Ti atom cis to each other (Figure FS1).
When the time for the reaction between [Ti(NMe2)4] and
1a in a 1:1 molar ratio in toluene was extended to 12 h at
ambient temperature, dinuclear titanium(IV) complex 3c was
obtained. A similar dinuclear complex of the molecular
Figure 3. Molecular solid-state structure of 4b. H atoms are omitted
for clarity. Selected bond lengths (Å) and angles (deg): Ti1−N4
1.872(4), Ti1−N3 1.877(4), Ti1−N1 2.043(4), Ti1−N2 2.096(4),
Ti1−Se1 2.7202(10), Se1−P1 2.1527(13), Se2−P2 2.1316(15), P1−
N1 1.612(4); N4−Ti1−N3 114.97(18), N4−Ti1−N1 128.82(17),
N3−Ti1−N1 114.75(17), N4−Ti1−N2 101.13(17), N3−Ti1−N2
104.00(16), N1−Ti1−N2 77.95(14), N4−Ti1−Se1 88.98(13), N3−
Ti1−Se1 96.89(12), N1−Ti1−Se1 73.81(10), N2−Ti1−Se1
150.00(10).
composition [{κ2-N(PPh2Se)}Ti(NMe2)2]2 (6c) resulted in
an analogous reaction of [Ti(NMe2)4] and 5b in a 1:1 molar
ratio after 12 h of stirring (Scheme 3). Both complexes 3c and
1
6c were characterized by H, 13C{1H}, and 31P{1H} NMR
spectroscopy and combustion analysis (Figures FS17−FS22),
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Scheme 3. Synthesis of the Titanium(IV) Complexes 3c and 6c
and their solid-state structures were confirmed by single-crystal
X-ray diffraction analysis (see the Supporting Information).
The molecular structures of complexes 3c and 6c in the solid
state are given in Figures 4 and 5, respectively. Both complexes
Figure 5. Molecular solid-state structure of 6c. H atoms are omitted
for clarity. Selected bond lengths (Å) and angles (deg): Ti1−N3
1.889(4), Ti1−N2 1.904(3), Ti1−N1i 1.970(3), Ti1−N1 2.044(3),
Ti1−Se1 2.7654(9); N3−Ti1−N2 107.85(17) N3−Ti1−N1i
100.63(15), N2−Ti1−N1i 104.61(15), N3−Ti1−N1 116.62(15),
N2−Ti1−N1 134.26(15), N1i−Ti1−N1 77.97(15), N3−Ti1−Se1
99.35(12), N2−Ti1−Se1 88.03(11), N1i−Ti1−Se1 151.65(10), N1−
Ti1−Se1 75.17(9).
Catalytic Hydroelementation. All of the mono- and
dinuclear titanium complexes 3a−3c, 4a, 4b, 6b, and 6c were
investigated as catalysts for the hydroelementation reaction. As
a control experiment, a blank reaction was carried out at 65 °C
for 24 h in the presence of only diisopropylcarbodiimide
(DIC) and ethanol, which showed that ethyl N,N′-
diisopropylcarbamimidate was not formed as a product. In
order to determine the highest possible efficiency of the
catalyst, the insertion of ethanol and aniline into DIC was
monitored using 1H NMR spectroscopy, showing the progress
of the reaction as a function of DIC consumption, followed by
the formation of ethyl N,N′-diisopropylcarbamimidate and
guanidine, respectively (Table 1). After preliminary evaluation
of the catalysts for hydroalkoxylation and hydroamination of
DIC, we concluded that the dinuclear titanium(IV) catalysts
(3c and 6c) are substantially more efficient than their
mononuclear analogues (3a, 3b, 4a,4b, and 6b). A dinuclear
catalytic system is significantly effective compared to the
mononuclear catalyst of a similar structure because of
cooperative interactions between the two metals and the
substrate of the reaction.40 Alternatively, a bimetallic catalyst
design can be achieved by linking two discrete metal centers of
proven catalytic efficiency through a covalently bound tether
Figure 4. Molecular solid-state structure of 3c. H atoms are omitted
for clarity. Selected bond lengths (Å) and angles (deg): Ti1−N1i
1.8765(14), Ti1−N3 1.8913(15), Ti1−N1 2.0410(14), Ti1−N2
2.0714(13), Ti1−S1 2.5867(6); N1i−Ti1−N3 110.04(6), N1i−Ti1−
N1 82.90(6), N3−Ti1−N1 108.42(6), N1i−Ti1−N2 129.30(6),
N3−Ti1−N2 120.18(6), N1−Ti1−N2, 75.61(5), N1i−Ti1−S1
107.21(5), N3−Ti1−S1 98.81(5), N1−Ti1−S1 145.75(4), N2−
Ti1−S1 72.85(4), P1−S1−Ti1 79.66(2).
̅
3c and 6c crystallize in the triclinic space group P1; however,
the unit cell of complex 3c contains two toluene molecules as
solvates. The details of the structural parameters are given in
Table TS1. To the best of our knowledge, complexes 3c and 6c
are the first examples of dinuclear titanium(IV) complexes with
the N-(2-aminophenyl)-P,P-diphenylphosphinothioic amido
and P,P-diphenylphosphinoselenoic amido ligands, respec-
tively, where, in each case, [Me2NP(E)Ph2] (E = S or Se) is
eliminated from the parent ligands 1a and 5b under the
reaction conditions. The formation of titanium complexes 3c
and 6c can be explained as shown in Scheme 1 in the
Supporting Information.
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that exhibits a remarkable catalytic cooperative effect, which is
well reported in the literature.41−47 In the case of μ-
imidotitanium complexes that hold two TiIV metal centers at
the proximal position, they are expected to not only assist
electronic interaction between the two Ti metal centers via a μ-
imido ligand but also show the cooperative effects of the two
metal centers in catalytic transformation. Additionally, catalytic
performances can also be fine-tuned by varying the nature of
the ligand attached to the metal ions. Comparing the catalytic
activity between 3c and 6c, we observed that complex 6c is
superior to 3c as a catalyst for hydroalkoxylation and
hydroamination under identical reaction conditions (Table 1,
entries 6 and 7). The higher efficiency of 6c can be attributed
to the lesser crowded atmosphere around both the TiIV centers
and the presence of two labile dimethylamido groups, which
facilitate the addition reaction of incoming nucleophiles
toward active metal centers compared to that of 3c. Thus,
complex 6c was chosen as an effective precatalyst for the
addition of the E−H bond (E = N, O, S, P, C) toward
carbodiimides, and the results are summarized below.
Table 1. Catalytic Addition of Ethanol and Aniline to DIC
Promoted by Titanium(IV) Complexes To Give N,N′-
Diisopropylcarbamimidate (B) and Guanidine (A),
Respectively
yield in hydroalkoxylation
(%)
yield in hydroamination
(%)
entry catalyst
1
2
3
4
5
6
7
3a
3b
4a
4b
6b
3c
6c
50
53
42
45
55
72
95
65
60
52
58
64
89
97
a
1
Yields from H NMR spectroscopy integrals using hexamethylben-
All experiments presented here were performed in the
presence of 1 equiv of heterocumulene and 1 equiv of a E−H
moiety with 5 mol % catalyst loading. It was observed that the
zene as the internal standard. Yield calculated from the consumption
of alcohols as well as amines. All reactions were carried out in toluene
for 6 h.
a
Table 2. Insertion of Various Arylamines to Carbodiimides Using Complex 6c as the Catalyst
a
Reaction conditions: 4 mg of catalyst (0.005 mmol, ∼0.5 mol %); cat./amine = 1/100; cat./carbodiimide = 1/100; 550 μL of CDCl3; 25 °C. The
1
yield was determined by H NMR spectroscopy of the crude reaction mixture.
E
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Table 3. Insertion of Various Alcohols, Thiols, Phosphine Oxides, and Terminal Alkynes into Carbodiimides Using 6c as the
a
Catalyst
a
Reaction conditions: 4 mg of catalyst (0.005 mmol, ∼0.5 mol %); cat./nucleophile = 1/100; cat./carbodiimide = 1/100; 550 μL of CDCl3; at
room temperature (aat 70 °C). The yield was determined by H NMR spectroscopy of the crude reaction mixture.
1
addition of the E−H substrate affects the outcome of the
insertion product. If E is a monoprotic nucleophile such as
alcohol or thiol, the product (B−E) is formed as the sole
insertion product. However, in the case of amine addition,
where E corresponds to a diprotic nucleophile, isomerization
of the initial product occurs, leading to guanidine derivatives
(Aa−An) as the major products.
In the case of the hydroamination reaction, the arylamines
with electron-donating groups such as 2-methylaniline and 4-
methoxyaniline exhibited good conversion, affording the
corresponding guanidines within 2 h at ambient temperature
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Table 4. Insertion of Amines, Alcohols, Thiols, and Phosphine Oxide to Phenyl Isothiocyanate and Isocyanate in the Presence
a
of Catalyst 6c
a
Reaction conditions: 4 mg of catalyst (0.005 mmol, ∼0.5 mol %); cat./nucleophile = 1/100; cat./carbodiimide = 1/100; 550 μL of CDCl3; 25 °C.
1
The yield was determined by H NMR spectroscopy of the crude reaction mixture.
(Ab−Ad), whereas substituted arylamines with electron-
withdrawing haloanilines such as iodo-, bromo-, chloro-,
fluoro-, or nitroanilines exhibiting excellent yield (85−99%)
afforded the desired guanidines within 2 h at room
temperature (Ae−Al). In addition, substituted anilines with
bulkier groups such as 2,6-Me2C6H3NH2 and 2,4,6-
Me3C6H2NH2 could also be converted to the corresponding
products (Am and An) up to 88%. The reaction of a substrate
such as 2-mercaptopyridine, which consisted of amine (NH)
and thiol (SH) groups as different nucleophiles in its two
tautomeric forms, with an equimolar amount of DIC afforded
N,N′-diisopropyl-2-thioxopyridine-1(2H)-carboximidamide
(Ao in Table 2) in high yield, indicating that the reactivity of
the amine group is greater compared to that of the thiols
toward the carbodiimides. All of the products (Aa−Ao) were
fully characterized with the help of NMR spectroscopy and
mass spectrometry (MS) studies (Figures FS66−FS77), and
the yields were calculated from isolated yields.
Further, catalytic hydroalkoxylation of the carbodiimides was
performed with a number of alcohols. The reaction of three
different carbodiimides and aryl, as well as aliphatic, alcohols
catalyzed by complex 6c afforded the corresponding chemo-
selective products (Ba−Bn in Table 3) in excellent yields (80−
99%) within 3 h at room temperature (Figures FS78−FS99).
DIC reacts faster with alcohols compared to dicyclohex-
ylcarbodiimide (DCC) because of greater electron donation of
the cyclohexyl groups than the isopropyl moieties (Ba and Bc
in Table 3). The acidity and steric bulk of the respective
alcohols played a crucial role in determining the reactivity of
hydroalkoxylation. Aryl alcohols with electron-donating groups
such as 2-methylphenol and benzyl alcohol afforded very good
conversion (Ba−Be in Table 3), whereas aryl alcohols with
electron-withdrawing iodo, chloro, and nitro groups could also
be converted to the respective isourea in excellent yield (88−
95%) within 3 h at 60 °C (Bf−Bj in Table 3). Although the
reaction of β-naphthol with DCC did not yield any product, it
reacted with DIC to give the expected product (Bk in Table 3)
in higher conversion, presumably because of the smaller steric
congestion imposed by the β-naphthol and isopropyl groups.
The use of aliphatic alcohols, such as ethanol and 1-butanol,
caused the rate of the hydroalkoxylation reaction with DIC to
increase significantly (Bl−Bn in Table 3) compared to that of
their aryl analogues.
Encouraged by the extraordinarily high catalytic activity of
the dinuclear titanium(IV) complex 6c and its greater
tolerance of amine and alcohol functionality in guanylation
and isourylation reactions, we extended the utilization of
complex 6c as a competent catalyst for the addition of a
number of E−H bonds (E = S, P, C) to carbodiimides (Table
3) in order to explore the generality of catalyst 6c. Thiophenol
was first reacted with DIC in the presence of 6c to afford a
quantitative formation of thioguanidines (Ca and Cb in Table
3 and Figures FS100−FS103). Substituted arylthiols such as 4-
chlorothiophenol and benzothiazole-2-thiol were also con-
verted to the respective thioguanidines in excellent yields (85−
98%) within 3 h at room temperature (Cc−Cf in Table 3 and
Figures FS104−FS110). In contrast, 6-(trifluoromethyl)-
pyridine-2-thiol yielded a bis-insertion product because of its
high reactivity (Cg and Ch in Table 3 and Figures FS111−
FS113) toward carbodiimides under identical reaction
conditions. Thus, it can be said that the pyridyl group present
in 6-(trifluoromethyl)pyridine-2-thiol exhibited no influence
on hydrothiolation, indicating significant tolerance of the
heterocyclic functionalities toward the dinuclear catalyst 6c.
Complex 6c also proved to be a potent catalyst in
hydrophosphorylation with use of the diphenylphosphine
oxide [Ph2P(O)H] and three carbodiimides. Diphenylphos-
phine oxide was smoothly converted to the corresponding
phosphorylguanidine using catalyst 6c in each case (Da−Dc in
Table 3 and Figures FS113−FS120). Moreover, the presence
of two resonance peaks in the 31P NMR spectra in the case of
DIC indicated the formation of E and Z isomers of the
respective phosphorylguanidine products (Figure FS114),
whereas upon changing from DIC to the bulkier carbodiimide
such as DCC and N-ethyl-N′-tert-butylcarbodiimide, we were
able to obtain successfully only one isomer of phosphor-
ylguanidine. Similar results were reported by Westerhausen et
al.20 in hydrophosphorylation catalyzed by alkali metals. We
also extended our study in hydroacetylenation using phenyl-
acetylene with three different carbodiimides such as DIC,
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a
Table 5. Sequential Hydroalkoxylation−Hydroamination to Carbodiimides by Catalyst 6c
a
Reaction conditions: 4 mg of catalyst (0.005 mmol, ∼0.5 mol %); cat./alcohol = 1/100; cat./carbodiimide = 1/100; 550 μL of CDCl3; 60 °C. The
1
yield was determined by H NMR spectroscopy of the crude reaction mixture.
Figure 6. First-order kinetics plot for the reaction of benzyl alcohol with DIC catalyzed by 6c.
DCC, and N-ethyl-N′-tert-butylcarbodiimide at 70 °C to give
the corresponding products in high yield (Da−Dc in Table 3
and Figures FS121−FS124).
phenyl isothiocyanate and substituted phenyl isocyanate as the
heterocumulene source, the insertion of amines, alcohols,
thiols, and diphenylphosphine oxide was studied, and the
results are presented in Table 4 (Fa−Fi in Table 4 and Figures
FS125−FS135). The insertion of N,N-diisopropylamine, 2-
methylaniline, and 2-fluoroaniline proceeded rapidly at room
temperature to give the corresponding inserted products in
quantitative yields (Fa−Fc in Table 4). In an analogous
reaction, the addition of an aliphatic alcohol, 1-butanol,
produced the corresponding product O-butyl phenylcarbamo-
thioate (Fd). A cyclic product (Fe) was obtained within 1 h
when 2-iodophenol was used as the source of alcohol.
Aromatic thiols were smoothly inserted into the phenyl
isothiocyanate to afford phenyl phenylcarbamodithioate (Fh)
and 4-chlorophenyl phenylcarbamodithioate (Fi) in very good
yields. However, the addition of diphenylphosphine oxide into
phenyl isocyanate proved sluggish, and 95% conversion was
obtained after 1 h of reaction time (Fh and Fg in Table 4).
The enhanced reactivity of phenyl isothiocyanate and
However, a dimerized product resulted when a propargylic
substrate such as 3-(N,N-dimethylamino)-1-propyne or 5-
methoxy-1-pentyne was used under identical conditions.48
This observation showed the competition between alkyne
oligomerization and insertion into heterocumulenes, revealing
a lower energy barrier for insertion into the C−C bond,
favoring the former process, rather than insertion into
carbodiimides. However, when this reaction was performed
with simple alkynes, such as 1-hexyne or 1-pentyne, it yielded
the desired insertion product in excellent yield, providing
substituted amidines (Dd−Dg in Table 3). Sterically bulky
acetylene substrates such as ethynyltrimethylsilane required a
longer reaction time (8 h) to achieve complete conversion (Dh
and Di in Table 3). The scope of the catalytic addition of E−H
bonds (E = N, O, S, P) was extended to isothiocyanates and
isocyanates to illustrate the robust nature of catalyst 6c. Using
H
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isocyanate with the various nucleophiles with respect to the
carbodiimides was due to the stronger electrophilic character
of the isothiocyanate C atom, as was already reported in
previously published literature.3−5
than those for the hydroalkoxylation reaction with respect to
each substrate and catalyst (kobs = 0.023 M−1 m−1 for complex
6c in hydroamination and 0.009 M−1 m−1 for complex 6c in
hydroalkoxylation; kobs = 0.011 M−1 m−1 for aniline, 0.0031
M−1 m−1 for benzyl alcohol, and 0.009 M−1 m−1 for DIC in
hydroamination and 0.0039 M−1 m−1 for DIC in hydro-
alkoxylation).
The activation parameters for the hydroalkoxylation and
hydroamination reactions were determined from the Eyring
and Arrhenius plots, with ΔH⧧, ΔS⧧, and Ea values of 11.22(4)
kJ mol−1, −243.43(7) J mol−1, and 13.88 kJ mol−1 and
10.64(3) kJ mol−1, −241.77(5) J mol−1, and 12.89 kJ mol−1,
respectively (Figures 7 and FS44−FS46 and FS53−FS56),
Sequential Hydroelementation Reaction. We also
wanted to explore the hydroamination and hydroalkoxylation
reactions in a sequential manner using titanium catalyst 6c
(Ga−Gd in Table 5 and Figures FS136−FS145). The
sequential hydroalkoxylation−hydroamination of carbodii-
1
mides was monitored by H NMR spectra. In the initial step,
benzyl alcohol was reacted with DIC in a 1:1 molar ratio in the
presence of 5 mol % catalyst 6c, followed by the addition of 1
equiv of arylamine, leading to the formation of the
corresponding products (Ga and Gb in Table 5) in good
yields. Because of the greater nucleophilic character of alcohol
compared to amine, we presumed that the alcohol would
initially react with DIC to afford an isourea derivative, which
eventually reacted with the amine to produce 1-methoxy-
N,N′,N″-trialkylmethanetriamine (Ga and Gb in Table 5),
yielding up to 95% of the product within 6 h at 60 °C
1
temperature. The H NMR spectrum of Ga exhibits three
separate broad resonances assigned to the NH peaks at δΗ
5.2−4.8 (Figure FS136). A similar NMR spectral observation
was noted in the case of N-tert-butyl-N′-ethylcarbodiimide,
which began as the heterocumulene source (Gb in Figure
FS139).
Kinetic Study. To determine the initial rates of the
hydroalkoxylation and hydroamination reactions, kinetic
experiments were performed with respect to the starting
material and catalyst 6c. Reactions were performed with
variable concentrations of catalyst 6c, as well as DIC and
benzyl alcohol while the other reagents’ concentrations
remained unchanged. Hence, in situ NMR spectroscopy
experiments were carried out by loading complex 6c (0.03,
0.04, 0.05, 0.06, and 0.07 M) from a stock solution and adding
DIC (0.126 g, 1.0 mmol), PhCH2OH (0.108 g, 1.0 mmol),
and CDCl3 (1 mL) to it. The temperature of the solution
mixture was set at 50 °C. At indicated time intervals, the
solution was analyzed by 1H NMR spectroscopy, which
revealed that the rate law of the reactions displayed a first-
order dependence on complex 6c (Figures FS36−FS38). The
reaction rate increased linearly with an increase in the amount
of catalyst (Figure 6). The increase of the amount of DIC and
PhCH2OH also led to linear acceleration of the reaction
(Figures FS39−FS43). The rate of the reaction also displayed a
first-order dependence on DIC (Figure FS43), PhCH2OH
(Figure FS41), and complex 6c (Figure FS38), giving rise to
the following kinetic rate equation:
Figure 7. Eyring plots of ln(kobs/T) (M m−1 K−1) versus 1/T (K−1)
titanium (6c)-catalyzed reactions of PhNH2 and DIC in CDCl3 (0.4
ML) at various temperatures (1 equiv of aniline is present with
respect to DIC). Reaction conditions: 6c = 0.05 M, [DIC] = 1.0 M,
and [PhNH2] = 1.0 M in CDCl3 (0.4 mL) having ΔH⧧ = 10.64(4) kJ
mol−1 and ΔS⧧ = −241.77(3) J mol−1 K−1.
displaying a higher activation barrier (Ea) for the hydro-
alkoxylation reaction over the hydroamination reaction. The
large negative entropy values signify high-order transition
states (TSs) at the rate-determining step.
The reaction of DIC with a series of substituted anilines
revealed the effect of electronic substitution on the hydro-
amination reaction (Table TS22). Aniline substitution at both
the meta (3-F) and para (4-Cl, 4-Br, 4-NO2, 4-OMe, and
NMe2) positions with respect to DIC was studied under the
standard protocol. It was observed that the rate of the
hydroamination reaction was dependent on the electronic
effect of the substituents of arylamines. The formation of the
guanidine derivatives from these different substituted anilines
was studied with respect to time (Table TS22, entries 1−7,
and Figures FS57−FS63).
Continuous sampling was undertaken over the course of 0.5
h, and the conversions were determined by 1H NMR
spectroscopy analysis. Kinetic experiments showed a first-
order rate equation with respect to substituted amine
derivatives. A Hammett analysis was carried out (Figures
FS64 and FS65) to establish the role of the electronic effects of
the substituents on the reaction rate.49 In a Hammett-type
analysis, plots of the logarithmic values of the relative rate
constants against a set of standard σ− values (Hansch and
dp/dt = kobs[DIC]1[PhCH2OH]1[6c]1
We observed this in the case of the hydroamination reaction
also. The rate of the reaction displayed first-order dependence
on DIC (Figure FS53), PhNH2 (Figure FS51), and complex 6c
(Figure FS49), giving rise to the following kinetic rate
equation:
dp/dt = kobs[DIC]1[PhNH2]1[6c]1
The rate constants for the hydroamination and hydro-
alkoxylation reactions catalyzed by complex 6c are given in
Table TS12. This allows us to directly compare the kobs values
of each substrate and catalyst for two different reactions. The
k
obs values for the hydroamination reaction are relatively higher
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+
colleagues) as well as against σp (the Brown−Okamoto
Scheme 4. Plausible Mechanism of the Titanium-Mediated
Catalytic Insertion of E−H Moieties into Carbodiimides
constant σp ) were made50 (Figures FS63 and FS64). A better
+
correlation was found with the latter, having ρ values of 0.60
and 0.38 for σp+ and σ−, respectively. The positive slope values
suggest 0 < ρ < 1, the reaction is comparatively less sensitive to
substituents than simple aniline, and a negative charge is built
up at the reaction center. A positive slope with a ρ value of
0.60 was obtained (Figure 8), consistent with the formation of
Figure 8. Hammett plot for the hydroamination reaction of DIC with
various substituted amines on the basis of σ−, ρ = 0.602.
a rapid equilibrium (step 2), which produces complex II, that
follows a protonolytic cleavage (step 3), with an additional
molecule of the E−H species. This completes the catalytic
cycle with the concomitant release of the target product and
regeneration of the active species.
negative charge/depletion of positive charge in the turnover-
determining TS. A positive slope indicates that the rate of the
reaction is consequently accelerated by the presence of an
electron-withdrawing group, which helps to effectively stabilize
the negatively charged TS.51,52 Also, moving to the more
delocalized 2-aminonaphthalene group, we observed a
significant slowdown of the rate compared to any other
systems (Figures FS146−FS148).
Most Plausible Mechanism. To explore the most
plausible mechanism of the catalytic addition of E−H (E =
O, N, C, S, P) to carbodiimides, we performed some
controlled reactions. The stoichiometric reaction of catalyst
6c with aniline, benzyl alcohol, and 2,4-di-tert-butylphenol
independently showed that the complete displacement of the
methyl peak of dimethylamidotitanium complexes occurred in
each case by either anilide or alkoxide groups, respectively, at
room temperature (Figures FS19−FS26).
However, the reaction of DIC with catalyst 6c did not
proceed at room temperature and needed 90 °C and 12 h to be
completed (Figures FS27−FS29). The molecular structure of
the titanium(IV) complex 7 formed by the complete
displacement of the dimethylamino group of complex 6c by
DIC was isolated and confirmed by single-crystal X-ray
diffraction analysis (Figure FS4). From these controlled
experiments, we concluded that activation of the precatalyst
is achieved by the addition of the nucleophile (E) moiety to
generate the catalytically active species. On the basis of the
above study, a plausible mechanism is presented in Scheme 4.
The first step in this mechanism is the rapid protonolysis of
catalyst 6c by the E−H moiety, with displacement of the
dimethylamine group, producing the active species (I).
Migratory insertion of DIC to the corresponding Ti−E is in
CONCLUSION
■
In summary, we have synthesized and characterized a series of
mono- and dinuclear titanium(IV) complexes and established
their solid-state structures. The dinuclear titanium(IV)
complex 6c acts as an efficient catalyst for the addition of
E−H bonds (E = N, O, S, P, C) to heterocumulenes such as
carbodiimides compared to the mononuclear analogues. More
importantly, we have shown for the first time that the dinuclear
titanium(IV) complex 6c acts as a single competent catalyst for
the chemoselective insertion of electron-rich alcohols, amines,
phosphine oxide, and thiols with carbodiimides at ambient
conditions with high degrees of conversion. The titanium
catalyst 6c displayed an unusual tolerance toward heteroatoms
and functional groups, giving the corresponding insertion
products in high yields and selectivity. The most plausible
mechanisms of the catalytic addition of electron-rich E−H
bonds (E = O, N, C, S, P) to carbodiimides are also described.
Kinetic studies, together with Hammet analysis of the
hydroamination reaction, indicate that protonolysis is the
rate-determining step of the reaction.
EXPERIMENTAL SECTION
■
General Methods. All manipulations involving air- and moisture-
sensitive compounds were carried out under argon using the standard
Schlenk technique or an argon-filled glovebox. Hydrocarbon solvents
(n-pentane and toluene) were distilled under nitrogen from LiAlH4
and stored in the glovebox. CH2Cl2 was dried over P2O5 and distilled
J
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under reflux conditions. Tetrahydrofuran was dried and deoxygenated
by distillation over sodium benzophenone ketyl under argon and then
distilled and dried over CaH2 prior to being stored in the glovebox.
1H (400 MHz), 13C{1H} (100 MHz), and 31P{1H} (100 MHz) NMR
spectroscopy spectra were measured on a Bruker AVANCE III-400
spectrometer. Elemental analyses were performed on a Bruker EURO
elemental analyzer at the Indian Institute of Technology Hyderabad.
[{Ph2P(X)NH}2C6H4] (1a and 1b), [trans-C6H10{Ph2P(X)NH}2] [X
= S (2a) and Se (2b)] and [HN(Ph2PSe)2] (5b) were prepared
according to published procedures,34−36 and Ti(NMe2)4 was
purchased from Sigma-Aldrich India. NMR spectroscopy solvent
C6D6 was purchased from Sigma-Aldrich India, dried over sodium/
potassium, distilled, and stored in the glovebox.
3.74−3.30 (m, 2H, CHN), 236−1.83 (m, 3H, CH2), 1.52.1.49 (m,
5H, CH2), 1.33−1.08 (m, 1H, CH2). 13C{1H} NMR (100 MHz,
C6D6): δC 132.4 (P−ArC), 132.3 (o-ArC), 130.8 (m-ArC), 129.2 (p-
ArC), 47.5 (CHN), 44.7 (N−CH3), 31.8 (CH2), 25.4 (CH2), 22.9
(CH2). 31P{1H} NMR (161.9 MHz, C6D6): δP 73.4. Elem anal. Calcd
for C34H42N4P2Se2Ti (774.5): C, 52.73; H, 5.47; N, 7.23. Found C,
52.21; H, 5.11; N, 6.98.
Preparation of [{κ2-N(PPh2Se)2}2Ti(NMe2)2] (6b). In a 25 mL dry
Schlenk flask, 100 mg (0.179 mmol) of the protic ligand
[{Ph2P(Se)}2NH] (5b) was placed, and 5 mL of dry toluene was
added to it. To this solution was added a mixture of [Ti(NMe2)4]
(20.1 mg, 0.089 mmol) and 5 mL of toluene. The resulting solution
immediately turned red. This solution was kept under stirring
conditions for another 6 h at ambient temperature. The solvent was
thereafter evaporated in a vacuum to obtain a red solid, which was
recrystallized from toluene into deep-red crystals at a temperature of
−35 °C.
Preparation of [κ3-[C6H4{NPh2P(Se)}2Ti(NMe2)2]] (3b). In a 25
mL dry Schlenk flask, 100 mg (0.157 mmol) of ligand 1b was placed,
and 5 mL of dry toluene was added to it. To this solution was added
dropwise at ambient temperature a mixture of [Ti(NMe2)4] (35 mg,
0.157 mmol) and 5 mL of toluene. The resulting solution turned red
immediately. The reaction mixture was kept under stirring conditions
for another 6 h at ambient temperature. The solvent was thereafter
evaporated in a vacuum to obtain a red solid, which was recrystallized
from toluene into deep-red crystals at room temperature.
1
Yield: 210 mg (98%). H NMR (400 MHz, C6D6): δH 7.83−7.77
(m, 4H, ArH), 6.85−6.80 (m, 12H, ArH), 6.46−6.44 (m, 4H, ArH),
2.85 (s, 12H, NMe2). 13C{1H} NMR (100 MHz, C6D6): δC 139.4
(P−ArC), 137.4 (P−ArC), 132.4 (o-ArC), 132.2 (o-ArC), 127.7 (m-
and p-ArC), 121.6 (p-ArC), 120.8 (p-ArC), 46.9 (N−CH3). 31P{1H}
NMR (161.9 MHz, C6D6): δP 55.8. Elem anal. Calcd for
C59H59N4P4Se4Ti (1311.7): C, 54.02; H, 4.53; N, 4.27. Found: C,
53.72; H, 4.19; N, 3.96.
1
Yield: 120 mg (99%). H NMR (400 MHz, C6D6): δH 8.01−7.95
(m, 8H, ArH), 7.11−6.93 (m, 10H, ArH), 6.64−6.54 (m, 6H, ArH),
2.97 (s, 12H, NMe2). 13C{1H} NMR (100 MHz, C6D6): δC 136.7
(P−ArC), 135.9 (P−ArC), 132.2−132.0 (o-ArC), 130.8 (o-ArC),
127.8−127.6 (m- and p-ArC), 45.1 (N−CH3). 31P{1H} NMR (161.9
MHz, C6D6): δP 59.7. Elem anal. Calcd for C34H36N4P2Se2Ti (768.4):
C, 53.14; H, 4.72; N, 7.29. Found C, 52.73; H, 4.52; N, 7.01.
Preparation of [κ3-[C6H4{(NPh2PS)(N)}Ti(NMe2)]2] (3c). In a 25
mL dry Schlenk flask, 100 mg (0.185 mmol) of ligand 1a was placed,
and 5 mL of dry toluene was added to it. To this solution was added
dropwise a mixture of [Ti(NMe2)4] (21 mg, 0.0925 mmol) and 5 mL
of toluene. The resulting solution immediately turned red. The
reaction mixture was kept under stirring conditions for another 12 h
at ambient temperature. The solvent was thereafter evaporated in a
vacuum to obtain a red solid, which was recrystallized from toluene
into deep-red crystals at a temperature of −35 °C.
Preparation of [{κ2-N(PPh2Se)}Ti(NMe2)2]2 (6c). In a 25 mL dry
Schlenk flask 100 mg (0.183 mmol) of ligand, 5b was placed, and 5
mL of dry toluene was added to it. To this solution was added a
mixture of [Ti(NMe2)4] (21 mg, 0.0915 mmol) and 5 mL of toluene.
The resulting solution immediately turned red. This solution was kept
under stirring conditions for another 12 h at ambient temperature.
The solvent was thereafter evaporated in a vacuum to obtain a red
solid, which was recrystallized from toluene into deep-red crystals at a
temperature of −35 °C.
1
Yield: 146 mg (96%). H NMR (400 MHz, C6D6): δH 8.01−7.96
(m, 8H, ArH), 7.04−7.01 (m, 12H, ArH), 6.64−6.54 (m, 6H, ArH),
3.07 (s, 12H, NMe2). 13C{1H} NMR (100 MHz, C6D6): δC 136.7
(P−ArC), 135.9 (P−ArC), 132.2 (o-ArC), 132.1 (o-ArC), 130.8 (m-
ArC), 130.8 (m-ArC), 127.7 (p-ArC), 45.1 (N−CH3). 31P{1H} NMR
(161.9 MHz, C6D6): δP 59.7. Elem anal. Calcd for C32H44N6P2Se2Ti2
(828.3): C, 46.40; H, 5.35; N, 10.15. Found: C, 46.09; H, 4.99; N,
9.87.
1
Yield: 146 mg (95%). H NMR (400 MHz, C6D6): δH 7.99−7.94
(m, 8H, ArH), 7.14−7.11 (m, 2H, ArH), 6.99−6.96 (m, 16H, ArH),
6.62−6.61 (m, 2H, ArH), 2.97 (s, 12H, NMe2). 13C{1H} NMR (100
MHz, C6D6): δC 137.7 (P−ArC), 132.3 (o-ArC), 132.2 (o-ArC),
129.2 (m-ArC), 128.4 (m-ArC), 125.6 (p-ArC), 44.6 (N−CH3).31P-
{1H} NMR (161.9 MHz, C6D6): δP 61.8. Elem anal. Calcd for
C54H56N6P2S2Ti2 (1010.9): C, 64.16; H, 5.58; N, 8.31. Found: C,
63.82; H, 5.13; N, 8.04.
ASSOCIATED CONTENT
■
S
* Supporting Information
Preparation of [κ3-[trans-C6H10{NPh2P(S)}2Ti(NMe2)2]] (4a).36
In a 25 mL dry Schlenk flask, 100 mg (0.183 mmol) of ligand 2a was
placed, and 5 mL of dry toluene was added to it. To this solution was
added a mixture of [Ti(NMe2)4] (41 mg, 0.183 mmol) and 5 mL of
toluene. The resulting reaction mixture immediately turned red. This
solution was kept under stirring conditions for another 6 h at ambient
temperature. The solvent was thereafter evaporated in vacuum to
obtain a red-colored solid which was recrystallized from toluene into
deep red crystals at a temperature of −35 °C.
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.8b01766.
1H, 13C{1H}, and 31P{1H} NMR and MS spectra and
combustion analysis of all of the complexes and all of the
insertion products Aa−Ao, Ba−Bn, Ca−Ch, Da−Di,
Ea−Ec, Fa−Fh, and Ga−Gd and also full details of
single-crystal X-ray diffraction analyses of the reported
complexes 3b, 3c, 4b, 6b, and 6c (PDF)
Yield: 118 mg (95%). 1H NMR (400 MHz, C6D6): δH = 8.00−7.73
(m, 8H, ArH), 7.38−7.24 (m, 12H, ArH), 3.24−3.22 (m, 2H, CHN),
3.01 (s, 12H, NMe2), 1.76−1.75 (m, 2H, CH2), 1.44−1.41 (m, 3H,
CH2), 1.39−1.32 (m, 2H, CH2), 1.01−1.00 (m, 1H, CH2) ppm;
13C{1H} NMR (100 MHz, C6D6): δC = 132.5 (P−ArC), 131.7 (o-
ArC), 131.5 (m-ArC), 128.1 (p-ArC), 56.4.1 (CHN), 45.5 (N−CH3),
35.5 (CH2), 24.9 (CH2) ppm; 31P{1H} NMR (161.9 MHz, C6D6): δP
= 66.7 ppm; Elemental Analysis: C34H42N4P2S2Ti (680.7): Calcd C
59.99, H 6.22, N 8.23. Found C 59.39, H 5.85, N 7.79.
Accession Codes
CCDC 1846007−1846011 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.
Preparation of [κ3-[trans-C6H10{NPh2P(Se)}2Ti(NMe2)2]] (4b).
Complex 4b was prepared using a procedure similar to that for the
preparation of complex 4a using 100 mg (0.157 mmol) of ligand 2b
and [Ti(NMe2)4] (35 mg, 0.157 mmol).
AUTHOR INFORMATION
■
1
Corresponding Author
*E-mail: tpanda@iith.ac.in (T.K.P.).
Yield: 120 mg (99%). H NMR (400 MHz, C6D6): δH 7.95−7.93
(m, 8H, ArH), 7.45−7.26 (m, 12H, ArH), 3.99 (s, 12H, TiNMe2),
K
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[BPh4]. Formation of the Alkyne π-Complex [(Et2N)2U(C≡CtBu)-
(η2-HC≡CtBu)][BPh4]. Organometallics 1999, 18, 2407−2409.
(6) Weetman, C.; Hill, M. S.; Mahon, M. F. Magnesium Catalysis for
the Hydroboration of Carbodiimides. Chem. - Eur. J. 2016, 22, 7158−
7162.
ORCID
Hari Pada Nayek: 0000-0003-4247-547X
Tarun K. Panda: 0000-0003-0975-0118
Author Contributions
(7) Alonso, F.; Moglie, Y.; Radivoy, G.; Yus, M. Solvent- and
catalyst-free regioselective hydrophosphanation of alkenes. Green
Chem. 2012, 14, 2699−2702.
All the authors contributed equally.
Notes
The authors declare no competing financial interest.
(8) (a) Ryu, J. S.; Marks, T. J.; McDonald, F. E. Organolanthanide-
Catalyzed Intramolecular Hydroamination/Cyclization/Bicyclization
of Sterically Encumbered Substrates. Scope, Selectivity, and Catalyst
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ACKNOWLEDGMENTS
■
This work was supported by Japan International Cooperation
Agency FRIENDSHIP Project under the Collaboration Kick-
starter Programme ARC2016-2. J.B. and A.H. thank the CSIR
and UGC India, respectively, for their Ph.D. fellowships. We
also thank Prof. Kazushi Mashima and Dr. Hayato Tsurugi,
Osaka University, Japan, for their generous support. We thank
Dr. Dinabandhu Das, Jawaharlal Nehru University, India, for
his support in X-ray crystallography.
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