Reactivities of zero-valent group 10 complexes toward organic isocyanates: Synthesis of metallacycles containing dimeric isocyanate units, isocyanate cyclotrimerization, and computational chemistry

Article abstract of DOI:10.1039/c9nj03332g

The reactions of [Pd(olefin)(PR₃)₂] (PR₃ = PMe₃, PMe₂Ph) with two equivalents of an aryl or alkyl isocyanate afford cis-[Pd{-N(R)C(O)N(R)C(O)-}(PR₃)₂] (R = 1-naphthyl, 4-phenoxyphenyl), which are five-membered palladacycles bearing dimeric isocyanate units, or cyclic tetramers as assemblies of four five-membered palladacycles, [Pd{C(O)N(R′)C(O)N(R′)}(PMe₃)]₄, (R′ = 3-methylbenzyl, 4-methylbenzyl or 4-methoxybenzyl), depending on the alkyl substituent on R-NCO. Interestingly, these reactions afford cyclic trimers as catalytic products when two equivalents or excess amounts of benzyl isocyanate are used. In contrast, reactions of [Pt(olefin)(PR₃)₂] with two equivalents of an alkyl or aryl isocyanate afford only the five-membered platinacycle, namely cis-[Pt{-N(R)C(O)N(R)C(O)-}(PMe₃)₂] (R = 3-methylbenzyl, 4-methylbenzyl, 4-fluorobenzyl, 4-methoxybenzyl, (S)-(+)-(1-naphthyl)ethyl, (R)-(-)-(1-naphthyl)ethyl, 4-phenoxyphenyl and 2,6-difluorophenyl). Aided by theoretical calculations, we propose mechanisms for the formation of the five-membered palladacycle or platinacycle, the cyclic tetramer, and the cyclotrimerization of the organic isocyanate. In addition, the ligand-exchange reactions between a five-membered platinacycle bearing a chiral substituent such as (S)-(+)-(1-naphthyl)ethyl or (R)-(-)-(1-naphthyl)ethyl) moieties and 1,2-bis(diethylphosphino)ethane (DEPE), a chelating phosphine, clearly afford the corresponding platinacycle bearing a DEPE ligand with retention of chirality. On the other hand, reactions of [Ni(COD)₂] with various organic isocyanates in the presence of tertiary phosphines only afford the corresponding cyclic trimers. In contrast, similar reactions in the presence of N-heterocyclic carbenes (NHC) such as 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) or 1,3-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazol-2-ylidine (SIPr) afford unexpected adducts between R-NCO and the NHC ligand.

Full text of DOI:10.1039/c9nj03332g

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Reactivities of zero-valent group 10 complexes toward organic
isocyanates: synthesis of metallacycles containing dimeric
isocyanate units, isocyanate cyclotrimerization, and
computational chemistry
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
Young-Sung Han,a,b Kang-Yeoun Jung,b Yong-Joo Kim,*a Kyoung Koo Baeck,*a Gang Min Lee,c Soon
W. Leec
The reactions of [Pd(olefin)(PR3)2] (PR3 = PMe3, PMe2Ph) with two equivalents of an aryl or alkyl isocyanate afford cis-[Pd{–
N(R)C(O)N(R)C(O)–}(PR3)2] (R = 1-naphthyl, 4-phenoxyphenyl), which are five-membered palladacycles bearing dimeric
isocyanate units or cyclic tetramers as assemblies of four five-membered palladacycles, [Pd{C(O)N(R′)C(O)N(R′)}(PMe3)]4,
(R′ = 3-methylbenzyl, 4-methylbenzyl or 4-methoxybenzyl), depending on the alkyl substituent on R–NCO. Interestingly,
these reactions afford cyclic trimers as catalytic products when two equivalents or excess amounts of benzyl isocyanate
are used. In contrast, reactions of [Pt(olefin)(PR3)2] with two equivalents of an alkyl or aryl isocyanate afford only the five-
membered platinacycle,namely cis-[Pt{–N(R)C(O)N(R)C(O)–}(PMe3)2] (R = 3-methylbenzyl, 4-methylbenzyl, 4-fluorobenzyl,
4-methoxybenzyl, (S)-(+)-(1-naphthyl)ethyl, (R)-(−)-(1-naphthyl)ethyl, 4-phenoxyphenyl and 2,6-difluorophenyl). Aided by
theoretical calculation, we propose mechanisms for the formation of the five-membered palladacycle or platinacycle, the
cyclic tetramer, and the cyclotrimerization of the organic isocyanate. In addition, the ligand-exchange reactions between a
five-membered platinacycle bearing a chiral substituent such as (S)-(+)-(1-naphthyl)ethyl or (R)-(−)-(1-naphthyl)ethyl)
moieties and 1,2-bis(diethylphosphino)ethane (DEPE), a chelating phosphine clearly afford the corresponding platinacycle
bearing a DEPE ligand with retention of chirality. On the other hand, reactions of [Ni(COD)2] with various organic
isocyanates in the presence of tertiary phosphines only afford the corresponding cyclic trimers. In contrast, similar
reactions in the presnec of N-heterocyclic carbene (NHC) such as 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) or
1,3-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazol-2-ylidine (SIPr) afford unexpected adducts between R–NCO and the
NHC ligand.
that are finally converted into organic olefinic compounds. Paul
and coworkers22 studied the Pd(0)-catalyzed cyclotrimerization of
R–NCO both computationally and experimentally. The above-
mentioned reports suggest that various metallacycles including a
five-membered ring composed of organic isocyanate units might be
key intermediates in the catalytic cyclotrimerization of R–NCO;
however, only a few palladacycles bearing dimeric organic
isocyanate units have been reported so far.
We recently observed that low-valent Pd or Pt complexes react with
organic isocyanates to afford Pd(II) or Pt(II) metallacycles, that
contain dimeric organic isocyanate units.23 We also reported that
the reaction of [Pd(styrene)L2] with benzyl isocyanate affords a
cyclic tetramer, that is an assembly of four five-membered
palladacycles, together with cyclic trimers of the organic isocyanate;
however, the mechanistic details of their formation were not
explored. In this context, we decided to investigate the mechanism
for the conversions of metallacycles into their cyclic tetramers and
organic isocyanurates, which depend on the metal or the organic
substituent on the isocyanate.
Introduction
Metallacycles containing organic isocyanate units (R–NCO) are a key
intermediates in the main-group-, rare-earth-, and transition metal-
catalyzed cyclotrimerizations of organic isocyanates.1−22 Although
such reactions have been studied on multiple occasions, synthetic
routes to five-membered metallacycles that possess dimeric organic
isocyanate units are relatively rare. For example, Misono and co-
workers18 reported the Ni(II)-catalyzed cyclotrimerization of R–NCO,
while Hoberg and co-workers19 also reported that Ni(0) complexes
react with R–NCO in the presence of olefins to afford nickellacycles
a. Department of Chemistry, Kangnung-Wonju National University, Gangneung 210-
702, Korea. Corresponding authors. (Y.J.K.) Tel: + 82-33-640-2308. Fax: + 82 -33-
640-2264. E-mail: yjkim@ kangnung.ac.kr. (For theoretical part, K.K.B.) baeck@
gwnu.ac.kr; Tel: + 82-33-640-2307.
b. Department of Biochemical Engineering, Kangnung-Wonju National University,
Gangneung 210-702, Korea
c. Department of Chemistry, Sungkyunkwan University, Suwon 440-746, Korea
† Electronic Supplementary Information (ESI) available: CCDC 1922154-1922158
contain the supplementary crystallographic data for compounds 10, 16, 17, 18 and
19. For ESI and crystallographic data in CIF or other electronic materials such as
the calculated energy data, details of atomic coordinates, and spectral data {1H,
13C{1H}, and 31P-NMR} of the complexes see DOI: 10.1039/x0xx00000x
In this work, we report the formation of various metallacycles by
reacting low-valent group 10 metal complexes, namely [L2M(olefin)]
(M = Pd or Pt), depending on the alkyl or aryl isocyanates and
examine metallacyclic formation or unexpected reactions between
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[Ni(COD)2] and various organic (alkyl or aryl) isocyanates in the to afford the corresponding five-membered platinacycles, namely
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presence of tertiary phosphines or N-heterocyclic carbenes [1,3- cis-[Pt{–N(R)C(O)N(R)C(O)–}(PMe3)2] (9−16).DInOIc:o1n0.t1r0a3s9t/tCo9tNhJe03332G
R
bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) or 1,3-bis(2,6-
Ph
Et
L
L
L
L
N
O
R
diisopropylphenyl)-4,5-dihydroimidazol-2-ylidine (SIPr)]. In addition,
we describe the conversion of the metallacycles into the
corresponding cyclic tetramers bearing dimeric organic isocyanate
units and the cyclic trimerization of R–NCO by computational
calculation.
R-NCO (2equiv.)
Pd
L2Pd
Pd
55 0
C
N
Ph
Et
L = PMe3, PMe2Ph
O
62 ~ 93%
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Results and discussion
NCO
OCN
OCN
(previous work)23
Cl
OCN
O
Reactions of [Pd(olefin)L2] with R–NCO. In order to synthesize five-
1
2
membered
metallacycles,
we
first
converted
diethylbis(phosphine)Pd(II) complexes into Pd(0)–olefin complexes,
which were subsequently treated with several aryl isocyanates
(Scheme 1). All of these reactions produced five-membered
palladacycles possessing a dimeric isocyanate unit (Scheme 1).
In contrast, similar reactions with alkyl isocyanate such as various
benzyl derivatives afforded cyclic tetramers of four five-membered
palladacycles, namely [Pd(PMe3){–C(O)N(R)C(O)N(R)–}]4 {R = 3-
methylbenzyl (3); R = 4-methylbenzyl (4); R = 4-methoxybenzyl (5)},
as well as organic cyclic trimers, (R–NCO)3 (R = 3-methylbenzyl; R =
4-methylbenzyl; R = 4-methoxybenzyl) (Scheme 2). On the other
hand, the products of the reactions with ethyl, cyclohexyl, and allyl
isocyanates as well as 4-methoxybenzyl isocyanate instantly or
slowly decomposed during isolation. The electronic or steric nature
of the organic isocyanate seems to affect the formation of the
corresponding five-membered metallacycle, which depends on the
isocyanate substituent and may induce the dissociation of one
phosphine from the five-membered palladacycle to afford cyclic
tetramers of four palladacycles. The 1H-NMR spectra of the
Scheme 1. Reactions of [Pd(styrene)L2] with aryl isocyanates.
L
R
N
O
O
N
Pd
O
R
L
N
N
R
N
O
Pd
R
R
Ph
R
R
Et
L
L
O
R-NCO
(2 equiv.)
L
Pd
L2Pd
+
O
N R
O
O
N
R
Ph
Et
Pd
N
N
N
R
L = PMe3
O
Pd
N
O
O
L
R
R-NCO
Me
Me
OMe
OCN
OCN
OCN
(previous work)23a
OCN
5
3
4
compounds formed from 3−5 show magnetic inequivalences for Scheme 2. Reactions of Pd(styrene)L2 with alkyl isocyanate
their methylene protons (N–CH2Ar) at high fields,namely  2.84–
Ph
R
R
O
Et
L
L
2.89 (d) and 3.79–3.97 (d) with germinal coupling constants J =
15.1–15.6 Hz, and at low field:  4.65–4.69 (d, J = 15.1–16.1 Hz) and
6.22–6.73 (dd, J = 17.0 Hz, JHP = 8.3–8.7 Hz). The high-field
methylene protons are assigned to those near the Pd center, and
while the low-field protons are assigned to those two carbonyl
groups, which explains the diastereotopic N-benzylic proton
splittings.
The 13C{1H}-NMR spectra of complexes formed from 3–5 display
two CO carbons at  173.1–173.2 due to their Pd-CO bonds, and at
 164.8–165.1 due to their carbonyl groups that are each
coordinated to a neighboring Pd metal. In order to confirm the
cyclotrimerization of R–NCO, we carried out catalytic reactions
R-NCO (6 eq)
N
Pd
L2Pd
O
N
O
R
55 0
C
Ph
Et
N
R = m-Me-C6H4CH2, 6: 61%
R = p-Me-C6H4CH2, 7: 64%
R = p-MeO-C6H4CH2, 8: 28%
Scheme 3. Catalytic cyclotrimerization of organic isocyanates.
palladium chemistry shown in Scheme 2, analogous reactions with
benzyl isocyanate derivatives afforded only the five-membered
platinacycles, 9 (R = 3-methylbenzyl), 10 (R = 4-methylbenzyl), 11 (R
= 4-fluorobenzyl), and 12 (R = 4-methoxybenzyl). In other words, in
contrast to the Pd chemistry, the expected cyclic tetramers of four
five-membered platinacycles and cyclic trimers of R–NCO, did not
form. In comparison, our recent reactions of [Pt(styrene)(PMe2Ph)2]
with organic isocyanates R–NCO (R = C6H5, p-Cl-C6H4) produced a
mixture of the cyclic trimer (ArNCO)3 as the major product and the
(Scheme 3) with excess R–NCO (R
= 3-methylbenzyl, 4-
methylbenzyl, and 4-methoxybenzyl). The cyclic trimers,
(isocyanurates, (R–NCO)3), were separated by column
chromatography with (ethyl acetate)/hexane as the eluent.
Reactions of Pt(olefin)L2 with R–NCO. On the basis of Schemes 1
and 2, we attempted to synthesize the platinum analogs of the
above-mentioned Pd complexes from [Pt(olefin)L2] and various
isocyanates (Scheme 4).
[Pt(styrene)L2], generated from [PtEt2(PR3)2] and styrene at 80 °C,
slowly reacted with alkyl and aryl isocyanates at room temperature
five-membered
platinacycle,
cis-[Pt{–
N(Ar)C(O)N(Ar)C(O)–}(PMe2Ph)2] as the minor product.23b On the
basis of these results, we speculate that less basic or somewhat
2 | J. Name., 2012, 00, 1-3
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R
hindered PMe2Ph–Pt(II) complexes facilitate the cyclotrimerization
of R–NCO compared to basic phosphine–Pt(II) complexes.
View Article Online
Ph
L
Et
L
N
O
R-NCO (2 eq)DOI: 10.1039/C9NJ03332G
Pt
L2Pt
Pt
80 0
C
N
The
isolated
five-membered
platinacycles
cis-[Pt{–
L
Ph
L
Et
R
N(R)C(O)N(R)C(O)–}(PMe3)2] were readily verified by IR
spectroscopy, which exhibited two strong (CO) bands due to the
dimeric organic isocyanate units. The 31P{1H} NMR spectra of
complexes 9–16 show two doublets each with satellite signals,
indicative of the cis form, and magnetic inequivalence for PMe3
ligands coordinated to the Pt center. Complexes 10 and 16, i.e. cis-
O
55 ~ 90%
Me
Me
Me
O
F
OCN
OCN
OCN
(previous work)23b
OCN
OCN
10
11
12
13
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9
10
NCO
12
11
[Pt{–N(R)C(O)N(R)C(O)–}(PMe3)2](R
=
4-methylbenzyl,
2,6-
Me
NCO
Me
F
difluorophenyl), were structurally characterized by X-ray diffraction.
The molecular structures of complexes 10 and 16 are shown in
Figures 1 and 2, which reveal that each Pt(II) metal has a slightly
distorted square-planar coordination sphere. Each platinum metal
coordinates to two cis trimethylphosphine ligands and a five-
membered platinacycle moiety composed of single dimeric
isocyanate unit, in which one carbon (C7 or C1) and one nitrogen
(N2) are bonded.
In order to determine the molecular structures of the unique five-
membered Pt(II) complexes containing chiral moieties composed of
dimeric isocyanate units, we subjected complexes 13 and 14 to
ligand exchange by treating them with an equivalent of 1,2-
O
OCN
OCN
F
14
13
15
16
Scheme 4. Reactions of Pt(styrene)L2 with organic isocyanate
bis(diethylphosphino)ethane (DEPE),
a
chelating phosphine
(Scheme 5). These reactions proceeded readily to afford the
corresponding cis-[Pt{–N(R)C(O)N(R)C(O)–}(DEPE)] Pt(II) complexes
(17 and 18) in quantitative yields. The molecular structures of
complexes 17 and 18 are provided in Figures 3(a) and (b), which
reveal that the Pt(II) metals have a square-planar coordination
sphere. As expected, the chiral configurations of starting complexes
13 and 14 are retained during the ligand-exchange reaction, which
confirmed the starting (S)-(+) or (R)-(−) form of the 1-
(naphthyl)ethyl moiety. To the best of our knowledge, these are the
first examples of enantiomeric five-membered Pt(II) complexes with
dimeric isocyanate units.
Figure 1. ORTEP drawing of complex 10. Atomic displacement ellipsoids are
shown at the 40% probability level. Selected bond lengths (Å) and bond
angles (°): Pt1–C7 2.053(2), Pt1–N2 2.057(2), Pt1–P2 2.2526(6), Pt1–P1
2.3549(5), N1–C7 1.357(3), N1–C16 1.407(3), N1–C8 1.470(3), N2–C17
1.456(3), C7–O1 1.236(2), C16-O2 1.236(3); C7–Pt1–N2 78.92(7), C7–Pt1–P2
89.97(6), C7–Pt1–P1 164.73(6), N2–Pt1–P2 164.18(5), P2–Pt1–P1 94.84(2),
N2–C16–N1 113.54(2).
R
N
R
N
Et2
P
L
L
O
R
O
Et2PCH2CH2PEt2
Pt
Pt
N
N
P
R
Et2
O
O
80 ~ 86%
L = PMe3
R-NCO
NCO
NCO
Me
Me
(R-)
(S+)
17
18
Scheme 5. Ligand exchange reaction
Figure 2. ORTEP drawing of complex 16. Displacement ellipsoids for
nonhydrogen atoms are shown at the 40% probability level. Selected bond
lengths (Å) and bond angles (º): Pt1–C1 1.985(5), Pt1–N2 2.102(5), Pt1–P2
2.159(2), Pt1–P1 2.264(2), O1–C1 1.281(7), O2–C2 1.227(6), N1–C1 1.407(7),
N1–C2 1.474(8), N2–C2 1.294(8); C1–Pt1–N2 83.4(2), C1–Pt1–P2 161.7(2),
C1–Pt1–P1 91.0(2), P2–Pt1–P1 94.70(6), C2–N2–Pt1 113.9(5), O1–C1–N1
119.9(5), N2–C2–N1 112.1(5).
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DOI: 10.1039/C9NJ03332G
Ph
B
5
6
7
8
Pd
Pd
L
L
A
Ph
C
R
NCO
R
R
O
N
O
N
N
G
O
L
L
R
NCO
O
R
9
C
N
D
10
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R
R
O
NCO
R
L
L
N
O
R
N
O
Pd
(b)
E
N
R
N
R
F
N
O
Pd
R
O
L
L
- L
H
R
NCO
O
L
R
N
O
Pd
O
R
N
O
N
N
Pd
O
R
R
R
R
L
I
L
Pd
N
N
N
O
R
O
Pd
N
O
L
R
Figure 4 Proposed mechanism for the formation of the Pd-cyclic tetramer
Figure 3. Molecular structures of complexes 17 and 18. Displacement and cyclic trimer of R–NCO. For discussion convenience, labels A to I are
ellipsoids for non-hydrogen atoms are shown at the 30% probability level. used to indicate reactants, intermediates, and products.
Selected bond lengths (Å) and bond angles (°). (a) (S)-(+)-(1-naphthyl)ethyl)
(17): Pt1–C36 2.033(6), Pt1–N1 2.051(5), Pt1–P2 2.234(2), Pt1–P1 2.334(2), phosphine ligand H dissociates from the palladacycle to afford the
O1–C23 1.240(7), O2–C36 1.224(7), N1–C23 1.337(8), N2–C36 1.394(7), N2– cyclic tetramer I of the five-membered palladacycle.
C23 1.337(8); C36–Pt1–N1 79.9(2), N1–Pt1–P2 170.3(1), N1–Pt1–P1 In order to support our proposed mechanism, we optimized the
102.5(2), P2–Pt1–P1 85.41(6), C23–N1–Pt1 115.4(4), C36–N2–C23 118.7(5). geometries of all relevant reactants, intermediates, and products
(b) R = (R)-(−)-(1-naphthyl)ethyl) (18): Pt1–C36 2.032(6), Pt1–N1 2.055(4), for both the palladium and platinum systems at the
Pt1–P2 2.230(2), Pt1–P1 2.330(2), O1–C23 1.244(6), O2–C36 1.224(7), N1– wB97XD/lanl2DZ level of theory. The relative energies associated
C23 1.336(7), N2–C36 1.389(7), N2–C23 1.403(7); C36–Pt1–N1 79.9(3), N1– with each sequential step and the corresponding reaction energies
Pt1–P2 170.5(1), N1–Pt1–P1 102.6(1), P2–Pt1–P1 85.35(5), C23–N1–Pt1 were calculated using the equations given in the caption to Figure 5.
114.5(4), C36–N2–C23 119.0(4).
The relative energy at the very initial stage of the overall process,
i.e., a mixture of the organic isocyanate and [Pd(styrene)L2], was set
Computational studies. Based on the experimental studies into the to 0.0 kcal/mol (see Figure 5). The main features of the optimized
formation of palladacycles bearing dimeric organic isocyanate units structures of the [Pd(styrene)(PR3)2] (B), and
as well as cyclic isocyanate trimers, we propose the following [Pd(C6H5CH2NCO)(PR3)2] (D) -bonded intermediates, as well as the
mechanism for their formation (Figure 4). To aid in the discussion, seven-membered [Pd(C6H5CH2NCO)3(PR3)2] palladacycle (F) are
labels A to I are used to denote the reactants, products, and shown in Figure 6, because their structures have not been
intermediates in Figure 4; these labels are also used in Figure 5.
experimentally determined. The possible transition structures that
First, an organic isocyanate (benzyl or aryl isocyanate, A) adds to connect reactants, intermediates, and products in each step have
[Pd(styrene)L2] (B) to afford the Pd(0) intermediate, [Pd(R–NCO)L2] not been calculated; because that task is beyond the scope of the
(D), with concomitant dissociation of styrene C. Subsequent present study. Nevertheless, the energy profile shown in Figure 5
addition of R–NCO affords the five-membered palladacycle E, with seems sufficiently reasonable to support the discussions below.
final insertion of R–NCO into the Pd–C bond resulting in the In an earlier work, Paul and co-workers22b examined the
formation of the seven-membered palladacycle F, which undergoes (diamine)Pd(0)-catalyzed cyclotrimerization of Ar–NCO and
reductive elimination to form the cyclic trimer G of R–NCO, with the suggested the mechanism by the neutral and zwitter-ionic
Pd(0) intermediate D regenerated. At the same time, depending on pathways based on the reaction of [Pd(dba)(N–N)] (dba =
the isocyanate, one
dibenzylidene acetone) with Ar–NCO. The first step in our
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DOI: 10.1039/C9NJ03332G
O
R
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step
(I)
Figure 5. Energetic relationships (in kcal/mol) in the proposed mechanism.a
different solvents could be another reason for the inefficient
a)Labels A to I are the same as those used in Figure 4. M is for either Pd or Pt. stabilization. The -intermediate
undergoes isocyanate
The numeric values are reaction energies in kcal/mol and are calculated
using the equations given below with the total energies listed in Table-SM2
in the ESI.
D
cycloaddition in step-2 to afford the five-membered palladacycle (or
platinacycle) E. Moving forward, the metallacycle E can follow one
of two pathways. In the first, R–NCO inserts into the five-membered
ring (step-3) to afford a seven-membered metallacycle F, which
then undergoes reductive C–N elimination to produce the cyclic
isocyanate trimer G (step-4), with the initial M(0) intermediate D
regenerated to complete one catalytic cycle.
-------------------------------------------------------------------------------------------------
(A) RNCO = C6H5CH2NCO
(B) L2M∙∙∙PhEt = [(CH3)3P]2M∙∙∙C6H5CH=CH2
(C) PhEt = C6H5CH=CH2
(D) L2M∙∙∙R-NCO = [(CH3)3P]2M∙∙∙C6H5CH2NCO
(E) L2M∙∙∙(RNCO)2 = [(CH3)3P]2M∙∙∙[C6H5CH2NCO]2
(F) L2M∙∙∙(RNCO)3 = [(CH3)3P]2M∙∙∙[C6H5CH2NCO]3
(G) (RNCO)3 = [C6H5CH2NCO]3
On the other hand, in an alternative second pathway (step-5), one
phosphine ligand H dissociates from the metallacycle E; subsequent
tetramerization of the [M{–C(O)N(R)C(O)N(R)–}(PR3)] units forms
the cyclic tetramer I through M–O bond coordination. The energy
diagram in Figure 5 clearly shows that the formation of the cyclic
tetramer from the five-membered metallacycle is energetically
feasible for both the palladium and platinum systems. In contrast to
the computational results, the reaction of [Pt(olefin)L2] with R–NCO
produces only a five-membered platinacycle, with the formation of
the cyclic tetramer not observed experimentally. These results
suggest that while cyclotetramerization is thermodynamically
feasible, the actual process may be under kinetic control. In other
words, the activation barrier for cyclotetramerization step-5 might
be sufficiently low in the palladium system, but too high in the
platinum system. Unfortunately, calculating these activation
energies by optimizing the transition-state structures involved in
tetramerization (step-5) is beyond the scope of the present work.
We recently demonstrated an alternative method for the formation
of the cyclic tetramer, which involves the abstraction of one
phosphine ligand by a sulfur atom, resulting in the phosphine ligand
dissociation in the form of trimethylphosphine sulfide (Me3P=S)
when platinacycle E is treated with sulfur powder, with the
subsequent assembly of the four five-membered platinacycles
(H) L = (CH3)3P
(I) [LM∙∙∙(RNCO)2]4 = {(CH3)3PM∙∙∙[C6H5CH2NCO]2}4
-------------------------------------------------------------------------------------------------
Estep-1 = [E0(L2M∙∙∙RNCO) + E0(PhEt)] – [E0(L2M∙∙∙PhEt)
Estep-2 = [E0(L2M∙∙∙(RNCO)2) + E0(PhEt)] – [E0(L2M∙∙∙PhEt) + 2 x E0(RNCO)]
Estep-3 = [E0(L2M…(RNCO)3) + E0(PhEt)] – [E0(L2M..PhEt) + 3 x E0(RNCO)]
Estep-4 = [E0((RNCO)3) – 3 x E0(RNCO)]
Estep-5 = [(1/4) x E0(LM ∙∙∙RNCO) + E0(PhEt) + E0(L)] – [E0(L2M ∙∙∙PhEt)
+ 2 x E0(RNCO)]
------------------------------------------------------------------------------------------------
mechanism, however, does not involve the M{+C(O)N−-R}L2, zwitter
ion,22b,24 because the [M(R–NCO)(PR3)2] -complex D is much lower
in energy than the corresponding zwitter ionic compound.
According to our ab initio calculations, the zwitter ionic structure in
the first step (step-1) is actually unstable and collapses to the
neutral -complex D. In this study, the stabilization of the excess
negative charge on the N-atom of the zwitter ionic form by benzyl
groups may not be as efficient as that previously reported for
phenyl groups.22b The different environmental effects, ie., the
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(Scheme 6).23b This practical synthesis is in good agreement with
our computational results for the formation of the Pt-cyclic
tetramer.
Figure 6. Showing the main features of the calculatedVigeewoAmrtiectleriOesnlinoef
DOI: 10.1039/C9NJ03332G
selected intermediates in Figures 4 and 5. Hydrogen atoms are omitted for
clarity. Full structural data are provided in Table-SM3 in ESI.
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L
R
N
Reactions of [Ni(COD)2] with R-NCO. We also examined the
reactivity of the Ni(0) complex toward R-NCO with the expectation
that the metallacycle or cyclic trimer of the isocyanate will be
formed, as was observed for Pd and Pt. However, we were unable
to prepare the [Ni(styrene)(PR3)2] Ni(0) complex because the
starting complex [NiEt2(PR3)2] is thermally unstable; therefore, we
used [Ni(COD)2] in the presence of excess PR3. Hoberg19 and
Yamamoto25 reported Ni(0)-catalyzed reactions of R–NCO in the
presence of olefins in which the Ni(0) complexes contained less
basic phosphines such as PPh3 or PCy3. In addition, Misono and co-
workers18 reported that [Ni(PPh3)4]-catalyzed reactions of R–NCO
afforded cyclic isocyanate trimers.
In this study, we treated [Ni(COD)2] with various organic
isocyanates in the presence of basic tertiary phosphines (2–4
equivalents) at room temperature, which afforded the
corresponding cyclic isocyanate trimers as shown in Scheme 7.
These results suggest that an excess amount of a basic tertiary
phosphine (PMe3 or PMe2Ph) induces the dissociation COD from
[Ni(COD)2] to create vacant sites for R–NCO coordination, which
may lead to a five or seven-membered nickellacycle intermediate.
The intermediate then reductively eliminates to form the cyclic
isocyanate trimers. However, the expected five-membered
nickellacycle was not observed.
The above Ni(0) reactions resulted in rather poor yields. Therefore,
we examined selective or efficient reactions for R-NCO
cyclotrimerization using a supporting ligand other than PR3. N-
heterocyclic carbene (NHCs) are well-known effective alternatives
to tertiary phosphine ligands. Hence, we decided to introduce (an
IPr) or (SIPr) NHC ligand as the supporting group (Scheme 8). These
reactions afforded only the NHC/R-NCO adduct, with the nickel
complexes not observed. In contrast, Wolf and co-workers26
showed that [(IPr)Ni(styrene)2] reacts with Ph–NCO to afford a
nickellacyclic complex composed of Ph–NCO and one styrene, which
is closely related to the heteronickellacyclic complexes previously
reported by the groups of Hoberg19 and Yamamoto.25
The molecular structure of [SIPrBenzyl-NCO] (19) is shown in
Figure 7, which clearly illustrates the steric congestion around the
carbene carbon (C1) due to the presence of the two bulky 2,6-
diisopropylphenyl groups. The C1–C4 bond (1.514(2) Å) is
somewhat shorter than a normal C–C bond (1.54 Å), and the N3–C4
bond (1.289(2) Å) is significantly shorter than a normal N–C bond
(1.45 Å). In fact, several research groups have reported direct
adduct formation between NHC ligands and R–NCO.27−29
O
O
N
Pt
O
R
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N
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R
R
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R
R
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R
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- L=S
N
Pt
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N
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O
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N
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O
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R
L = PMe3 R = Benzyl, 37%
Scheme 6. Formation of a Pt-cyclic tetramer upon treatment with elemental
sulfur.
(B) [(CH3)3P]2PdM...C6H5-CH=CH2
(D) [(CH3)3P]2Pd...C6H5-CH2-NCO
(F) [(CH3)3P]2Pd[C6H5-CH2-NCO]3
R
O
N
O
R-NCO ( 2 eq.)
N
N
Ni
+ PR3 (2 eq. to 4 eq.)
O
R
R
L = PMe3, R = Phenyl, 81%
L = PMe2Ph, R = Phenyl, 26%
L = PMe3, R = Benzyl, 43%, 26%( 2 eq.)
L = PMe2Ph, R = Benzyl, 15%
L = PMe3, R = p-Methoxybenzyl, 27%
L = PMe3, R = p-Methylphenyl, 21%,
Scheme 7 Reactions of the Ni(0) complex with R–NCO in the presence of PR3
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[Ni(styrene)(PR3)2] starting material and the metallacyclic Ni(II)
DOI: 10.1039/C9NJ03332G
intermediate containing the organic isocyanate units. Instead, we
examined the cyclotrimerization of R–NCO.
View Article Online
O
N
2
R-NCO
N
N
O
N
N
N
or
+ 2 NHC
Ni
R
R
Experimental
8
9
R = Ph, 20
R = Benzyl, 19
All manipulations of air-sensitive compounds were performed
under N2 or Ar by Schlenk-line techniques. Solvents were distilled
from Na–benzophenone. The analytical laboratories at Basic
Science Institute (Seoul) of Korea and at Kangnung–Wonju National
University carried out elemental analyses. IR spectra were recorded
on a Perkin Elmer BX spectrophotometer. NMR (1H, 13C{1H}, and
31P{1H}) spectra were obtained in CDCl3 on a JEOL Lamda 300, JNM-
ECZ 400s, and ECA 600 MHz spectrometer. Chemical shifts were
referenced to internal SiMe4 and to external 85% H3PO4. X-ray
reflection data were obtained at either the Korea Basic Science
Institute (Seoul Center) and the Cooperative Center for Research
Facilities at Sungkyunkwan University. Complexes trans-[PdEt2L2] (L
= PMe3 and PMe2Ph)30 and trans-[PtEt2L2] (L = PMe3 and PMe2Ph)31
were prepared by the literature methods.
Scheme 8 Reactions of the Ni(0) complex with R–NCO in the presence of
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NHC ligands.
Synthesis of five-membered palladacycles (1–2). To a Schlenk flask
containing trans-[PdEt2(PMe3)2] (0.224 g, 0.70 mmol) at 0 °C,
styrene (162 μL, 1.41 mmol) and tetrahydrofuran (THF, 3 mL) were
added in that order. The mixture was heated at 55 °C for 1 h to give
a pale yellow solution. 1-Naphthyl isocyanate (203 μL, 1.41 mmol)
was added to the mixture at room temperature, and then the
yellow solution turned into a yellow suspension. After stirring for 2
h at room temperature, the volatiles were completely removed
under vacuum, and then the remaining residue was washed with n-
hexane (2 mL × 3) to obtain yellow solids. The crude solids were
recrystallized from CH2Cl2/(diethyl ether) to afford pure product of
cis-[Pd{–N(Ar)C(O)N(Ar)C(O)–}(PR3)2 (PR3 = PMe3, Ar = 1-naphthyl)
(1, 0.307 g, 93%).
Anal. calc. for C28H32N2O2P2Pd (596.93): C, 56.34; H, 5.40; N, 4.69.
Found: C, 56.33; H, 5.45; N, 4. 63. IR (KBr/cm−1): 1654, 1605 (CO). 1H
NMR (300 MHz, CDCl3, δ): 0.49 (dd, 9H, J = 7.5 Hz, 6.8 Hz, P(CH3)3),
1.51 (d, 9H, J = 9.9 Hz, P(CH3)3), 7.34–7.58 (m, 9H), 7.74–7.81 (m,
3H), 7.98 (d, 1H, J = 7.7 Hz), 8.75 (dd, 1H, J = 7.7 Hz, 30. 8 Hz).
13C{1H} NMR (75 MHz, CDCl3, δ): 15.2 (dd, J = 1.6 Hz, 19.0 Hz,
P(CH3)3), 17.1 (d, J = 30.5 Hz, P(CH3)3), 124.0, 124.2, 124.3 (d, J = 7.5
Hz), 124.7, 125.1 (d, J = 11.8 Hz), 125.2 (d, J = 5.8 Hz), 125.6 (d, J =
6.8 Hz), 125.9 (d, J = 6.2 Hz), 126.2 (d, J = 6.2 Hz), 12 7.1 (d, J = 8.1
Hz), 127.9 (d, J = 4.4 Hz), 128.1 (d, J = 7.5 H z), 128.3 (d, J = 2.5 Hz),
131.2 (d, J = 7.5 Hz), 132.0, 134.5, 1 34.6 (d, J = 3.1 Hz), 137.1 (dd, J
= 7.5 Hz, 3.7 Hz), 148.4 (dd, J = 2.8 Hz, 17.7 Hz), 163.6 (d, JCP = 4.4
Hz, CO), 184.9 (dd, JCP = 11.2, 157 Hz, Pd-CO). 31P{1H} NMR (120
MHz, CDCl3, δ): −29.1 (d, J = 11.1 Hz), −7.7 (s).
Figure 7. ORTEP drawing of compound 19. Displacement ellipsoids for non-
hydrogen atoms are shown at the 40% probability level. Selected bond
lengths (Å) and bond angles (º): O1–C4 1.250(2), N1–C1 1.324(2), N1–C3
1.481(2), N2–C1 1.321(2), N2–C2 1.478(2), N3–C4 1.289(2), N3–C5 1.463(2),
C1–C4 1.515(2), C2–C3 1.519(2); C1–N1–C3 110.9(1), C1–N2–C2 110.5(1),
C4–N3–C5 115.3(2), N2–C2–C3 102.5(1), N1–C3–C2 101.7(1), O1–C4–N3
134.0(2), N3–C5–C6 114.0(2).
Conclusions
In summary, new five-membered palladacycles containing
dimeric organic isocyanate units were prepared from
[Pd(styrene)(PR3)2] and aryl isocyanate. Cyclic tetramers of four
five-membered
palladacycles,
namely
[Pd{C(O)N(R′)C(O)N(R′)}(PR3)]4 (R′ = 3-methylbenzyl, 4-methylbenzyl
and 4-methoxybenzyl), as well as the coresponding organic cyclic
trimer (isocyanurate) were formed when benzyl derivatives were
similarly treated with the Pd(0) complex. In contrast,
[Pt(olefin)(PR3)2] reacted with two equiv. of an alkyl or aryl
isocyanate to afford only the corresponding five-membered
platinacycle. We proposed a catalytic process for the formation of
the cyclic trimer (isocyanurate) and cyclic tetramers of four five-
membered metallacycles. In support of the proposed pathways, all
the reactants, products, and intermediates were optimized using
quantum chemical calculations, which provided computational data
in good agreement with the experimental results. Furthermore, the
calculated -complex intermediates, namely, [M(styrene)(PR3)2]
and [M(R–NCO)(PR3)2] and the seven-membered metallacycles
containing three R–NCO units, which have not been verified
experimentally to date, are included in our proposed mechanism.
Although the catalytic efficiency achieved in this study is lower than
Cis-[Pd{–N(Ar)C(O)N(Ar)C(O)–}(PR3)2 (PR3
= PMe3, Ar = 4-
phenoxyphenyl), 2 was analogously prepared. Complex 2 (70 %):
Anal. calc. for C32H36N2O4P2Pd (681.01): C, 56.44; H, 5.33; N, 4.11.
Found: C, 56.09; H, 5.25; N, 3. 97. IR (KBr/cm−1): 1654, 1607 (CO). 1H
NMR (600 MHz, CDCl3, δ): 1.01 (d, 9H, J = 7.3 Hz, P(CH3)3), 1.59 (d,
9H, J = 10.1 Hz, P(CH3)3), 6.92 (t, 1H, J = 2.8 Hz), 6.93 (t, 1H, J = 2.8
Hz), 6.96–6.99 (m, 4H), 7.01–7.08 (m, 4H), 7.23 (t, 1H, J = 2.8 Hz),
7.24 (t, 1H, J = 2.5 Hz), 7.27–7.31 (m, 4H), 7.34 (s, 1H), 7.35 (s, 1H).
13C{1H} NMR (150 MHz, CDCl3, δ): 15.6 (d, J = 19.1 Hz, P(CH3)3), 16.8
that reported by a previous work,22b the effects of different side
groups and solvents on efficiency can be studied further
investigated. Unfortunately, we were unable to synthesize the
nickel analogs, due to the difficulty in isolating the required
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(d, J = 29.5 Hz, P(CH3)3), 117.7, 118.7, 119.0, 119.4, 122.5, 1 23.1, 8, could not give the exact yield from the contVaiiemwiAnrtaictlieoOnnlionef
DOI: 10.1039/C9NJ03332G
128.4, 129.7, 130.0, 134.3, 147.9, 152.2, 155.6, 157.5, 15 8.4, decomposed 5.
163.5(s, CO), 183.9 (d, JCP = 161 Hz, Pd-CO). 31P{1H} NMR (242 MHz,
CDCl3, δ): −28.6 (s), −6.7 (s).
The cyclic triemrs, 6–8 were independently prepared by the
below reactions. Similar reactions of [Pd(styrene)(PMe3)2] with
= PMe3, R = 3- ethyl, cycohexyl, and allyl isocyanates could not give any suitable
Synthesis of [Pd(PMe3){-C(O)N(R)C(O)N(R)-}]4 (L
methylbenzyl, 4-methylbenzy and 4-methoxybenzyl). To a Schlenk complexes.
flask containing trans-[PdEt2(PMe3)2] (0.225 g, 0.71 mmol) at 0 °C, Synthesis of (R–NCO)3 (R = 3-methylbenzyl, 4-methylbenzyl and 4-
styrene (163 μL, 1.42 mmol) and tetrahydrofuran (THF, 3 mL) were methoxybenzyl). To a Schlenk flask containing trans-[PdEt2(PMe3)2]
added sequentially. The mixture was heated at 55 °C for 1 h to give (0.106 g, 0.33 mmol) at 0 °C, styrene (76 μL, 0.66 mmol) and
a pale yellow solution. 3-Methylbenzyl isocyanate (199 μL, 1.42 tetrahydrofuran (THF, 3 mL) were added in that order. The mixture
mmol) was added to the mixture at room temperature, and then was heated at 55 °C for 1 h to give a pale yellow solution. 3-
the yellow solution turned into a yellow suspension. After stirring Methylbenzyl isocyanate (280 μL, 1.99 mmol) was added to the
for 4 h at room temperature, the volatiles were completely mixture at room temperature. After stirring for 16 h at room
removed under vacuum, and then the remaining residue was temperature, the volatiles were completely removed, and then the
washed with n-hexane (2 mL × 3) to obtain yellow solids. The crude remaining residue was chromatographed over silica gel, eluting
solids were recrystallized twice from CH2Cl2/hexane to afford pure with ethyl acetate/hexane (1:3). The final product, (R–NCO)3 (R = 3-
product of [Pd(PMe3){-C(O)N(R)C(O)N(R)-}]4 (L = PMe3, R = 3-methylbenzyl) methylbenzyl, 5) was obtained in 61% yield. Compound 6: Anal. calc.
(3, 0.166 g, 49%). Anal. calc. for C84H108N8O8P4Pd4 (1907.38): C, for C27H27N3O3 (441.52): C, 73.45; H, 6.16; N, 9.52. Found: C, 73.15;
52.89; H, 5.71; N, 5.87. Found: C, 52.80; H, 5.73; N, 5. 87. IR H, 6.27; N, 9.64. IR (KBr/cm–1): 1682 (CO). 1H NMR (600 MHz, CDCl3,
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(KBr/cm−1): 1652, 1580 (CO). H NMR (600 MHz, CDCl3, δ): 0.85 (d, δ): 2.32 (s, 9H, CH3), 5.01 (s, 6H, CH2), 7.10 (d, 3H, J = 7.3 Hz),
36H, J = 10.1 Hz, P(CH3)3), 2.25 (s,12H), 2.34 (s, 12H), 2.88 (d, 4H, J = 7.19~7.24 (m, 9H). 13C{1H} NMR (150 MHz, CDCl3, δ): 21.6 (s, CH3),
15.6 Hz, CH2), 3.79 (d, 4H, J = 15.6 Hz, CH2), 4.65 (d, 4H, J = 16.1 Hz, 46.4 (s, CH2), 126.2, 12 8.7, 129.1, 129.7, 136.0, 138.5, 149.3 (s, CO).
CH2), 6.73 (dd, 4H, JHP = 8.7 Hz, J = 17.0 Hz, CH2), 6.82 (s, 8H, Ph),
Compounds 7 and 8 were analogously prepared. Complex 7
6.88 ( d, 4 H, J = 7.3 Hz), 7.00–7.05 (m, 8 H), 7.21–7.28 (m. 12H) 91 (64 %): Anal. calc. for C27H27N3O3 (441.52): C, 73.45; H, 6.16; N, 9.52.
(t, 8H, J = 9.0 Hz). 13C{1H} NMR (150 MHz, CDCl3, δ): 13.5 (d, J = 29.5 Found: C, 73.51; H, 6.15; N, 9.37. IR (KBr/cm−1): 1690 (CO). H NMR
1
Hz), 21.6 (CH3), 21. 8 (CH3), 43.9 (CH2), 49.1 (CH2), 122.8, 124.1, (300 MHz, CDCl3, δ): 2.32 (s, 9H, CH3), 4.98 (s, 6H, CH2), 7.12 (d, 6H,
126.8, 126.8, 126. 9, 127.6, 127.9, 128.2, 137.4, 137.7, 140.2, 142.5, J = 8.1 Hz), 7.35 (d, 6H, J = 8.1 Hz).13C{1H} NMR (150 MHz, CDCl3, δ):
165.1(s, CO), 173.1 (d, JCP = 6.9 Hz, Pd-CO). 31P{1H} NMR (242 MHz, 21.4 (s, CH3), 46.2 (s, CH2), 129.3, 12 9.5, 133.0, 138.1, 149.3 (s, CO).
CDCl3, δ): −4.0. The collected filtrates were chromatographed over
Compound 8 (38%): Anal. calc. for C27H27N3O6 (489.52): C, 66.25;
silica gel, eluting with ethyl acetate/hexane (1:3). The final product, H, 5.56; N, 8.58. Found: C, 66.16; H, 5.57; N, 8.71. IR (KBr/cm−1):
1
(R–NCO)3 (R = 3-methylbenzyl), 6 was obtained in 14% yield.
Complex [Pd(PMe3){–C(O)N(R)C(O)N(R)–}]4 (L PMe3,
1689 (CO). H NMR (600 MHz, CDCl3, δ): 3.79 (s, 9H, OCH3), 4.96 (s,
4- 6H, CH2), 6.84 (d, 6H, J = 8.4 Hz), 7.41 (d, 6H, J = 8.4 Hz).13C{1H} NMR
=
R
=
methylbenzyl) (4) was analogously prepared. Complex 4 (15 % yield (150 MHz, CDCl3, δ): 45.9 (s, CH2), 55.5 (s, OCH3), 114.1, 128.3,
1
by NMR sepctroscopy): IR (KBr/cm−1): 1653, 1586 (CO). H NMR 131.0, 149.3, 169.0 (s, CO).
(600 MHz, CDCl3, δ): 0.88 (d, 18H, J = 10.6 Hz, P(CH3)3), 2.24 (s, 12H, Synthesis
of
five-membered
platinacycles,
cis-[Pt{–
CH3), 2.32 (s, 12H, CH3), 2.84 (d, 4H, J = 15.6 Hz, CH2), 3.86 (d, 4 H, J N(R)C(O)N(R)C(O)–}(PMe3)2] (R = 3-methylbenzyl, 4-methylbenzyl,
= 15.6 Hz, CH2), 4.65 (d, 4H, J = 16.1 Hz, CH2), 6.22 (dd, 4H, JHP = 8.3 4-fluorobenzyl, 4-methoxybenzyl, (S)-(+)-1-(1-naphthyl)ethyl, (R)-
Hz, J = 17 Hz, CH2), 7.11 (d, 8H, J = 7.8 Hz, P h), 7.12(d, 8H, J = 7.8 (−)-1-(1-naphthyl)ethyl, 4-phenoxyphenyl and 2,6-difluorophenyl)
Hz), 7.31 (d, H, J = 7.8 Hz), 7.34 (d, 2 H, J = 8.3 Hz). 13C{1H} NMR (150 (7–14). To a Schlenk flask containing cis-[PtEt2(PMe3)2] (0.297 g,
MHz, CDCl3, δ): 13.5 (d, J = 29.5 Hz, P(CH3)), 21.0 (C H3), 21.1 (CH3), 0.73 mmol), styrene (168 μL, 1.46 mmol) and toluene (3 mL) were
43.5 (CH2), 48.6 (CH2), 126.9, 128.4, 128.7, 13 5.0, 135.2, 137.1, added sequentially. The mixture was heated at 80 °C for 18 h to
139.2, 149.1, 164.9 (s, CO), 173.2 (d, JCP = 8.7 Hz, Pd-CO). 31P{1H} give a colorless solution. 3-Methylbenzyl Isocyanate (209 μL, 1.46
NMR (242 MHz, CDCl3, δ): −3.7. We could not separate complex 4 mmol) was then added to the mixture at room temperature. After
and (R–NCO)3 (R = 4-methylbenzyl), 7 (53% NMR yield) due to the stirring for 4 h at room temperature, the volatiles were completely
quite similar solubility.
removed under vacuum, and then the remaining residue was
Complex [Pd(PMe3){–C(O)N(R)C(O)N(R)–}]4 (L
=
PMe3,
R
=
4- solidified with n-hexane to obtain a white solid. The crude solid was
methoxybenzyl) (5, 70%) was analogously prepared. IR (KBr/cm−1): recrystallized from CH2Cl2/n-hexane to afford pure product of cis-
1654, 1582 (CO). 1H NMR (600 MHz, CDCl3, δ): 0.90 (d, 18H, J = 10.2 [Pt{–N(R)C(O)N(R)C(O)–}(PMe3)2] (R = 3-methylbenzyl) (9, 0.301g,
Hz, P(CH3)3), 2.89 (d, 4H, J = 15.1 Hz, CH2), 3.73 (s, 12H, OCH3), 2.32 64%). Anal. calc. for C24H36N2O2P2Pt (641.58): C, 44.93; H, 5.66; N,
(s, 12H, OCH3), 3.97 (d, 4 H, J = 15.1 Hz, CH2), 4.58 (d, 4H, J = 16.1 4.37. Found: C, 44.82; H, 5.73; N, 4.44. IR (KBr/cm–1): 1640, 1582
Hz, CH2), 6.58 (dd, 4H, JHP = 8.3 Hz, J = 17 Hz, CH2), 6.70 (d, 8H, J = (CO). 1H NMR (300 MHz, CDCl3, δ): 1.26 (d, 9H, J = 8.4 Hz, JPtH = 24.6
8.4 Hz, P h), 6.87 (d, 8H, J = 8.7 Hz, Ph), 6.95 (d, H, J = 8.4 Hz, Ph), Hz, P (CH3)3), 1.68 (d, 9H, J = 10.3 Hz, JPtH = 22.7 Hz, P(CH3)3), 2.3 0 (d,
7.33 (d, 2 H, J = 8.3 Hz, Ph). 13C{1H} NMR (150 MHz, CDCl3, δ): 13.5 6H, J = 2.9 Hz, CH3), 4.65 (s, 2H, CH2), 5.02 (s, 2H, CH2), 6.96 (t, 2H, J
(d, J = 30 Hz, P(CH3)3), 43.3 (CH2), 48.1 (CH2), 55.2 (s, OCH3), 55.5 (s, = 6.9 Hz), 7.12–7.15 (m, 2H), 7.20–7.22 (m, 3H), 7.29 (s, 1H, br).
OCH3), 113.2, 113.6, 126.5, 128.1, 132.2, 134.4, 157.9, 158.0, 164.8 13C{1H} NMR (150 MHz, CDCl3, δ): 17.3 (d, J = 15.6 Hz, P(CH3)3), 17.5
(s, CO), 173.1 (d, JCP = 6.9 Hz, Pd-CO). 31P{1H} NMR (242 MHz, CDCl3, (d, J = 27.7 Hz, P(CH3)3), 21.6 (s, CH3), 21.7 (s, CH3), 44.7 (s, CH2),
δ): −3.6. The final organic product, (R–NCO)3 (R = 4-methoxybenzyl), 53.6 (s, CH2), 123.6, 125.3, 126.6, 127.0, 127.3, 128.0 (d, J = 5.2 Hz),
8 | J. Name., 2012, 00, 1-3
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129.0, 137.4, 137.5, 140.0, 143.5, 167.8 (s, CO), 182.3 (d, JCP = 142 125.0, 125.2, 125.3, 125.4, 1 25.7, 125.8, 125.9, 126.8V,i1ew26Ar.t9ic,le1O2n8l.in1e,
Hz, Pt-CO). 31P{1H} NMR (242 Hz, CDCl3, δ): −24.1 (d, J = 19.7 Hz, JPtP 129.1, 131.9, 133.6, 13 4.2, 139.0, 141.6, 166.0 (s, CO), 181.7 (br, Pt-
DOI: 10.1039/C9NJ03332G
= 1740 Hz), −23.1 (d, J = 19.7 Hz, JPtP = 3430 Hz).
Complexes 10–16 were prepared in the similar way. cis-[Pt{– (s, JPtP = 1700 Hz).
N(R)C(O)N(R)C(O)–}(PMe3)2] (R = 4-methylbenzyl) (10, 66%): Anal. Cis-[Pt{–N(R)C(O)N(R)C(O)–}(PMe3)2]
CO). 31P{1H} NMR (242 Hz, CDCl3, δ): −23.6 (s, JPtP = 3510 Hz), −23.2
(R
=
(R)-(−)-1-(1-
calc. for C24H36N2O2P2Pt (641.58): C, 44.93; H, 5.66; N, 4.37. Found: naphthyl)ethyl) (14, 70%): Anal. Calcd. for C32H40N2O2P2Pt (741.70):
1
C, 45.41; H, 5.75; N, 4.45. IR (KBr/cm−1): 1641, 1596 (CO). H NMR C, 51.82; H, 5.44; N, 3.78. Found: C, 51.66; H, 5.46; N, 3.60. IR
(600 MHz, CDCl3, δ): 1.25 (d, 9H, J = 8.3 Hz, P(CH3)3), 1.67 (d, 9H, J = (KBr/cm−1): 1635, 1588 (CO). 1H NMR (600 MHz, CDCl3, δ): 1.33 (dd,
10.6 Hz, JPtH = 39.9 Hz, P(CH3)3), 2.28 (d, 6H, J = 6.0H z, (CH3)2), 4.63 18H, J = 7.8 Hz, JPtH = 14.1 Hz, P(CH3)3), 1.86 (d, 3H, J = 6.9 Hz, CH3),
(s, 2H, CH2), 4.99 (s, 2H, CH2), 7.05 (t, 4H, J = 6.9 Hz), 7.31 (t, 4H, J = 2.08 (d, 3H, J = 6.9 H z, CH3), 5.35 (q, 2H, = 6.9 Hz, CH), 6.77 (t, 1H, J
7.3 Hz). 13C{1H} NMR (150 MHz, CDCl3, δ): 17.4 (d, J = 15.6 Hz, = 7.3 Hz), 7.25 (t, 1H, J = 7.1 Hz), 7.29~7.32 (m, 1H), 7.42 (dd, 2H, J =
P(CH3)3), 17.7 (d, J = 27.7 Hz, P(CH3)3), 21.2 (s, CH3), 21.3 (s, CH3), 8.0 Hz, 15.8 Hz), 7.53 (t, 1H, J = 7.6 Hz), 7.62 (d, 1H, J = 8.3 Hz), 7.70
44.5 (s, CH2), 53.5 (s, CH2), 126.6 (d, J = 3.5 Hz), 128.6 (d, J = 5.2 H z), (d, 1H, J = 7.8 Hz), 7.76 (t, 2H, J = 6.9 Hz), 7.82 (d, 1H, J = 8.7 Hz),
128.9 (dd, J = 3.5 Hz, 8.6 Hz), 135.4, 135.7, 137.3, 140.5, 167.8(s, 7.90 (dd, 2H, J = 7.6 Hz, 13.1 Hz), 8.54 (d, 1 H, J = 8.3Hz). 13C{1H}
CO), 182.0 (d, JCP = 144 Hz, Pt-CO). 31P{1H} NMR (242 MHz, CDCl3, δ): NMR (150 MHz, CDCl3, δ): 17.2 (d, J = 38.2 Hz, P(CH3)3), 17.7 (d, J =
−24.2 (d, J = 13.6 Hz, JPtP = 1730 Hz), −23.2 (d, J = 19.7 Hz, JPtP = 3421 26.0 Hz, P(CH3)3), 17.8 (s, CH3), 21.7 (CH3), 49.6 (CH), 61.8 (CH),
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Hz).
124.7, 124.8, 124.9, 125.0, 125.2, 125.3, 125.4, 125. 7, 125.8, 125.9,
Cis-[Pt{–N(R)C(O)N(R)C(O)–}(PMe3)2] (R = 4-fluorobenzyl) (11 126.8, 126.9, 128.1, 129.1, 131.9, 133.7, 134.2, 139.6, 141.6, 166.1
76%): Anal. Calcd. for C22H30F2O2N2P2Pt (649.51) : C, 40.68; H, 4.66; (s, CO), 181.2 (d, JCP = 141 Hz, Pt-CO). 31P{1H} NMR (242 Hz, CDCl3,
N, 4.31. Found: C, 41.17; H, 4.77; N, 4. 35. IR (KBr/cm−1): 1640, 1584 δ): −23.7 (s, JPtP = 3500 Hz), −23.3 (s, JPtP = 1700 Hz).
1
(CO). H NMR (600 MHz, CDCl3, δ): 1.31 (d, 9H, J = 8.43 Hz, JPtH
=
Cis-[Pt{–N(R)C(O)N(R)C(O)–}(PMe3)2] (R = 4-phenoxyphenyl) (15,
36.4 Hz, P (CH3)3), 1.69 (d, 9H, J = 10.6 Hz, JPtH = 38.8 Hz, P(CH3)3), 93%): Anal. Calcd. for C32H36N2O4P2Pt (769.66): C, 49.94; H, 4.71; N,
4.62 (s, 2H, CH2), 4.97 (s, 2H, CH2), 6.91 (t, 2H, J = 9.0 Hz), 6.95 (t, 3.64. Found: C, 49.63; H, 4.70; N, 3.59. IR (KBr/cm−1): 1655, 1587
1
2H, J = 8.8 Hz), 7.34–7.37 (m, 4H). 13C{1H} NMR (150 MHz, CDCl3, δ): (CO). IR (KBr) : 1587, 1655 (CO). H NMR (600 MHz, CDCl3, δ): 1.15
17.5 (d, J = 13.9 Hz, P(CH3)3), 17.7 (d, J = 26.0 Hz, P(CH3)3), 44.1 (s, (d, 9H, J = 8.3 Hz), 1.76 (d, 9H, J = 10.6 Hz), 6.94 (d, 2H, J = 8.7 Hz),
CH2), 53.4 (s, CH2), 114.9 (d, JCF = 20.8 Hz), 115.0 (d, JCF = 22.5 Hz), 6.98 (t, 4H, J = 8.3 Hz), 7.0 2 (d, 2H, J = 8.7 Hz), 7.04–7.07 (m, 2H),
127.9 (d, JCF = 6.9 Hz), 130.1 (d, JCF = 8.7 Hz), 135.9, 139.0, 160.9 (d, 7.24 (d, 2H, J = 8.7 Hz), 7.29 (t, 4H, J = 8.0 Hz), 7.39 (d, 2H, J = 8.7
JCF = 43.4 Hz), 162.5 (d, JCF = 43.4 Hz), 167.7 (s, CO), 182.4 (br, Pt- Hz). 13C{1H} NMR (150 MHz, CDCl3, δ): 16.5 (d, J = 27.7 Hz), 17.2 (d, J
CO). 31P{1H} NMR (242 MHz, CDCl3, δ): −25.6 (d, J = 13.5 Hz, JPtP
1720 Hz), −24.6 (d, J = 13.2 Hz, JPtP = 3420 Hz).
=
= 89. 9 Hz), 118.0, 119.0, 119.1, 119.3, 122.7, 123.1, 129.1, 129.8, 1
30.2, 134.3, 147.9, 153.0, 155.6, 157.7, 158.4, 163.0 (s, CO), 181.8
Cis-[Pt{–N(R)C(O)N(R)C(O)–}(PMe3)2] (R = 4-methoxybenzyl) (12, (d, JCP = 146 Hz, Pt-CO). 31P{1H} NMR (242 MHz, CDCl3, δ): −23.4 (d, J
57%): Anal. Calcd. for C24H36N2O4P2Pt (673.58) : C, 42.79; H, 5.39; N, = 19.7, JPtP = 1760 Hz), −22.6 (d, J = 19.7, JPtP = 3440 Hz).
4.16. Found: C, 41.60; H, 5.28; N, 3.92. IR (KBr/cm−1): 1640, 1587
Cs-[Pt{–N(R)C(O)N(R)C(O)–}(PMe3)2] (R = 2,6-difluorophenyl) (16,
69%): Anal. Calcd. for C20H24F4N2O2P2Pt (657.44): C, 36.54; H, 3.68;
1
(CO). H NMR (600 MHz, CDCl3, δ): 1.27 (d, 9H, J = 8.35 Hz, JPtH
=
19.4 Hz, P (CH3)3), 1.68 (d, 9H, J = 10.1 Hz, JPtH = 30.2 Hz, P(CH3)3), N, 4.26. Found : C, 36.98; H, 3.83; N, 4.33. IR (KBr/cm−1): 1665, 1622
1
3.76 (s, 3H, OCH3), 3.77 (s, 3H, OCH3), 4.60 (s, 2H, CH2), 4.97 (s, 2H, (CO). H NMR (600 MHz, CDCl3, δ): 1.12 (d ,9H, J = 8.7 Hz, P(CH3)3),
CH2), 6.78 (d, 2H, J = 8.7 Hz), 6.81 (d, 2H, J = 8.7 Hz), 7.32 (d, 2 H, J = 1.75 (d, 9H, J = 10.6 Hz, JPtH = 42.6 Hz, P(CH3)3), 6.89 (tt, 4H, J = 7.8
8.7 Hz), 7.37 (d, 2H, J = 8.7 Hz). 13C{1H} NMR (150 MHz, CDCl3, δ): Hz, 19.7 Hz), 7.01–7.06 (m, 1H), 7.19–7.24 (m, 1H). 13C{1H} NMR
17.4 (d, J = 12.1 Hz, P(CH3)3), 17.7 (d, J = 24.3 Hz, P(CH3)3), 44.1 (s, (150 MHz, CDCl3, δ): 15.8 (d, J = 27.7 Hz, P(CH3)3), 17.2 (d, J = 39.9
OCH3), 53.2 (s, OCH3), 53.7 (s, JPtC = 12.1 Hz, CH2), 55.5 (dd, JCP = 5.2, Hz, P(CH3)3), 111.4, 111.5 (d, JCF = 3.5 Hz), 125.1 (d. JCF = 8.7 Hz),
15.6 Hz, CH2), 113. 6 (d, J = 24.3 Hz), 127.6, 129.9, 132.6, 135.6, 125.2 (d. JCF = 10.4 Hz), 128.4 (d, JCF = 10.4 Hz), 128.5 (d, JCF = 8.7
158.0, 158.2, 167.8 (s, CO), 182.1 (d, JCP = 142 Hz, Pt-CO). 31P{1H} Hz), 158.6 (dd, JCF = 4.3, 114 Hz), 16 0.2 (dd, JCF = 4.3 Hz, 108 Hz),
NMR (242 MHz, CDCl3, δ): −24.1 (d, J = 13.2 Hz, JPtP = 1730 H z), 162.4 (s, CO), 180.5 (br, Pt-CO). 31P{1H} NMR (242 MHz, CDCl3, δ):
−23.1 (d, J = 13.2 Hz, JPtP = 3420 Hz).
Cis-[Pt{–N(R)C(O)N(R)C(O)–}(PMe3)2]
−24.2 (d, J = 19.7 Hz, JPtP = 1820 Hz), −23.5 (d, J = 19.7 Hz, JPtP = 3540
(S)-(+)-1-(1- Hz).
(R
=
naphthyl)ethyl) (13, 90%): Anal. Calcd. for C32H40N2O2P2Pt (741.70): Ligand exchange reactions of cis-[Pt{–N(R)C(O)N(R)C(O)–}(PMe3)2]
C, 51.82; H, 5.44; N, 3.78. Found: C, 51.93; H, 5.41; N, 3.64. IR (R = (S)-(+)-1-(1-naphthyl)ethyl or (R)-(-)-1-(1-naphthyl)ethyl). To a
1
(KBr/cm−1): 1634, 1588 (CO). H NMR (600 MHz, CDCl3, δ): 1.34 (d, CH2Cl2 (3 ml) solution containing 13 (0.082 g, 0.11 mmol), DEPE (26
9H, J = 8.3 Hz, P(CH3)3), 1.35 (d, 9H, J = 8.3 Hz, P(CH3)3), 1.86 (d, 3H, μL, 0.11 mmol) was added. After stirring for 2 h at room
J = 6.9 Hz, CH3), 2.09 (d, 3H, J = 6.9 Hz, CH3), 5.36 (q, 1H, J = 6.9 Hz, temperature, the volatiles were removed under vacuum, and then
6.4 Hz, CH), 5.94 (q, 1H, J = 6.9 Hz, 6.9 Hz, CH), 6.77 (t, 1H, J = 7.6 the remaining residue was washed with n-hexane (2 mL × 3) to
Hz), 7.26 (t, 1H, J = 7.6 Hz), 7.29–7.32 (m, 1H), 7.40–7.44, (m, 2H), obtain white solids. The crude solid was recrystallized from
7.54 (t, 1H, J = 7.8 Hz), 7.63 (d, 1H, J = 8.3 Hz), 7.70 (d, 1H, J = 7.8 CH2Cl2/n-hexane to afford white crystals of Pt(DEPE){–
Hz), 7.76 (d, 2H, J = 7.8 Hz), 7.82 (d, J = 8.7 Hz), 7.90 (dd, 2H, J = 7.8 N(R)C(O)N(R)C(O)–} {R = (S)-(+)-1-(1-naphthyl)ethyl}, 17 (0.086 g, 98%).
Hz, 10.6 Hz), 8.55 (d, 1H, J = 8.7 Hz). 13C{1H} NMR (150 MHz, CDCl3, Anal. Calcd. for C36H46N2O2P2Pt (795.79): C, 54.33; H, 5.83; N, 3.52.
δ): 17.2 (d, J = 38.2 Hz, P(CH3)3), 17.7 (d, J = 26.0 Hz, P(CH3)3), 17.8, Found: C, 54.23; H, 5.85; N, 3.29. IR (KBr/cm–1): 1637, 1590 (CO). 1H
(s, CH3), 21.6 (s, CH3), 49.5 (C H), 61.7 (CH), 124.7, 124.8, 124.9, NMR (400 MHz, CDCl3, δ): 0.47 (m, 3H), 0.63 (dt, 3H, J = 7.8 Hz, 16. 5
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Hz), 0.95–1.06 (m, 7H), 1.18–1.84 (m, 10H), 1.90 (d, 3H, J = 6.9 Hz),
(R–NCO)3 (R = benzyl), 43−15 %: 1H NMR (300 MHz, CDCl3, δ): 5.03
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2.05 (d, 3H, J = 6.4 Hz), 2.17 (m, 1H), 5.64 (bq, 1H, J = 5.7 Hz), 6.02 (s, 6H, CH2), 7.28–7.35 (m, 10H), 7.45 (dd,D5OHI,: 1J0=.1073.97/CH9zN, J10.833H32zG).
(q, 1H J = 6.9 Hz), 7.12 (t, 1H, J = 7.3 Hz), 7.24 (t, 1H), 7.33 (t, 1 H, J = 13C{1H} NMR (150 MHz, CDCl3, δ): 46.5 (s, CH2), 128.4, 128.8, 129.3,
7.3 Hz), 7.39 (t, 1H, J = 7.3 Hz), 7.43 (t, 1H, J = 7.3 Hz), 7.51 (t, 1H, J = 13 6.0, 149.3 (s, CO).
7.3 Hz), 7.65 (d, 1H, J = 7.8 Hz), 7.73 (d, 1 H, J = 8.3 Hz), 7.75 (d, 1H, J
(R–NCO)3 (R = 4-methoxybenzyl), 27 % ( see compound 8). (R–
1
= 8.3 Hz), 7.79 (d, 1H, J = 7.3 Hz), 7.84 (d, 1H, J = 8.7 Hz), 7.86 (d, 1H, NCO)3 (R = p-tolyl), 21 %: H NMR (600 MHz, CDCl3, δ): 2.33 (s, 9H,
J = 8.7 Hz), 8.06 (d, 1H, J = 8.7 Hz), 8.20 (d, 1H, J = 8.3 Hz). 13C{1H} CH3), 7.14 (d, 6H, J = 7.8 Hz), 7.2 2 (d, 6H, J = 8.3 Hz). 13C{1H} NMR
NMR (100 MHz, CDCl3, δ): 8.3 (s, PCH2CH3), 8.6 (s, PCH2CH3), 8. 9 (s, (150 MHz, CDCl3, δ): 21.5 (s, CH3), 130.2, 130.3 ,133.6 ,1 37.2 ,153.5
PCH2CH3), 9.0 (s, PCH2CH3), 17.5 (d, J = 38.2 Hz, PCH2), 17.7 (s, CH3), (s, CO).
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18
19
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23
24
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30
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32
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35
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18.1 (d, J = 36.4 Hz, PCH2), 18.4 (s, PCH2), 18.8 (d, J = 24.3 Hz, PCH2),
Reactions of [Ni(COD)2] with R–NCO in the presence of NHC (N-
22.1 (s, CH3), 22.5 (dd, J = 12.1 Hz, 34.7 Hz, PCH2), 24.7 (dd, J = 8.7 heterocyclic carbene). To a Schlenk flask containing [Ni(COD)2]
Hz, 31.2 Hz, PCH2), 48.7 (s, CH), 63.3 (s, CH), 124.5(d, J = 6.9 Hz), (0.068 g, 0.25 mmol) at 0 °C, SIPr (1,3-bis(2,6-diisopropylphenyl)-
124.7, 125. 0, 125.1, 125.3, 125.4, 125.6, 125.7, 126.5, 126.7, 128.0, 4,5-dihydroimidazol-2-ylidine, 0.217 g, 0.56 mmol) dissolved in
128.8, 131.7, 132.0, 133.8, 134.2, 139.1, 142.1, 166.4 (s, CO), 187.6 tetrahydrofuran (4 mL) was added. The mixture was stirred for 30
(d, JCP = 137 Hz, Pt-CO). 31P{1H} NMR (160 MHz, CDCl3, δ): 42.2 (s, min at room temperature. Benzyl isocyanate (69 μL, 0.56 mmol)
JPtP = 1690 Hz), 46.7 (s, JPtP = 3330 Hz).
was added to the mixture. After stirring for 3 h at room
[Pt(DEPE){–N(R)C(O)N(R)C(O)–}] {R = (R)-(−)-1-(1-naphthyl)ethyl} 18 (86%) temperature, the volatiles were removed, and then the remaining
was analogously prepared. Anal. Calcd. for C36H46N2O2P2Pt (795.79): residue washed with n-hexane (2 mL × 3) to obtain crude solids. The
C, 54.23; H, 5.85; N, 3.29. Found: C, 54.41; H, 5.85; N, 3.49. IR crude solid was recrystallized from THF/(diethyl ether) to afford
1
(KBr/cm–1): 1638, 1594 (CO). H NMR (600 MHz, CDCl3, δ): 0.48 (m, white crystals of [SIPrBenzyl-NCO], 19 (0.222 g, 76%). Anal. Calcd.
3H), 0.64 (dt, 3H, J = 7.3 Hz, 17. 0 Hz), 0.97–1.05 (m, 7H), 1.21–1.30 for C35H45N3O (523.74): C, 80.26; H, 8.66; N, 8.02. Found: C, 80.44;
(m, 2H), 1.40–1.63 (m, 6 H), 1.75–1.84 (m, 2H), 1.90 (d, 3H, J = 6.9 H, 8.70; N, 8.11. H NMR (300 MHz, CDCl3, δ): 1.30 (t, 24H, J = 7.3
1
Hz), 2.05 (d, 3H, J = 6.4 Hz), 2.13–2.21 (m, 1H), 5.64 (t, 1H, J = 5.7 Hz), 3.18 (sep, 4H, J = 7.0 Hz), 4.09 (s, 2H), 4.15 (s, 4H), 6.47–6.50
Hz), 6.02 (d, 1H J = 6.4 Hz), 7.12 (t, 1H, J = 7.3 Hz), 7.24 (t, 1H, dr), (m, 2H), 6.91 (dd, 3H, J = 5.1 Hz, 2.2 Hz), 7.21 (d, 4H, J = 7.7 Hz), 7.39
7.33 (t, 1H, J = 7.8 Hz), 7.39 (t, 1H, J = 7.3 Hz), 7.43 (t, 1H, J = 7. 3 (t, 2H, J = 7.8 Hz). 13C{1H} NMR (75 MHz, CDCl3, δ): 24.3 (s, CH3), 25.4
Hz), 7.51 (t, 1H, J = 7.3 Hz), 7.66 (d, 1H, J = 8.3 Hz), 7.73 (d, 1H, J = (s, CH3), 29.5 (s, CH), 48.8 (s, CH2), 52.3 (s, SIPr CH2), 124.5, 124.7,
7.8 Hz), 7.75 (d, 1H, J = 8.3 Hz), 7.79 (d, 1H, J = 7.3 Hz), 7.84 (d, 1H, J 127.2, 127.8, 129.8, 132.9, 144.7, 146.4, 153.1 (s, NCN), 167.3 (s,
= 8.7 Hz), 7.86 (d, 1H, J = 7.8 Hz), 8.06 (d, 1H, J = 8.7 Hz), 8.20 (d, 1H, CO).
J = 8.3 Hz). 13C{1H} NMR (150 MHz, CDCl3, δ): 8.5 (s, PCH2CH3), 8.8 (s,
An analogous reaction with phenyl isocyanate with [Ni(COD)2] in
PCH2CH3), 9.2 (s, PCH2CH3), 9.3 (s, PCH2CH3), 17.7 (d, J = 39.9 Hz, the presence of 2 equiv IPr (1,3-bis(2,6-diisopropylphenyl)imidazol-
PCH2), 18.0 (s, CH3), 18.1 (d, J = 36.4 Hz, PCH2), 18.5 (d, J = 22.5 Hz, 2-ylidene) was performed. [IPrPhenyl-NCO], 20 (42%): Anal. Calcd.
PCH2), 19.1 (d, J = 22.5 Hz, PCH2), 22.3 (s, CH3), 22.8 (dd, J = 11.3 Hz, for C34H41N3O (523.78): C, 80.43; H, 8.14; N, 8.28. Found: C, 79.98;
1
3 3.8 Hz, PCH2), 25.0 (dd, J = 8.7, 31.2 Hz, PCH2), 49.0 (s, CH), 63.5 (s, H, 7.78; N, 8.68. H NMR (300 MHz, CDCl3, δ): 1.22 (d, 12H, J = 7.0
CH), 124.8( d, J = 5.2 Hz), 124.9, 125.1, 125.2, 12 5.3, 125.4, 125.5, Hz), 1.29 (d, 12H, J = 7.0 Hz), 2.66 (sep, 4H, J = 7.0 Hz), 6.65 (t, 1H, J
125.8, 126.0, 126.7, 126.9, 128.3, 129.0, 131. 7, 132.0, 133.8, 134.2, = 7.0 Hz), 6.88–6.98 (m, 4H), 7.07 (s, 2H), 7.28 (d, 4H, J = 7.7 Hz),
139.3, 142.3, 166.4 (s, CO), 187.6 (d, JCP = 135 Hz, Pt-CO). 31P{1H} 7.46 (t, 2H, J = 7.7 Hz). 13C{1H} NMR (75 MHz, CDCl3, δ): 23.6 (s, CH3),
NMR (242 Hz, CDCl3, δ): 40.7 (s, JPtP = 1690 Hz), 45.2 (s, JPtP = 3330 24.7 (s, CH3), 29.5 (s, CH), 120.4, 122.1, 124.2, 124.3, 127.8, 130.5,
Hz).
133.6, 1 44.9, 149.4, 150.5 (s, CO), 151.3 (s, NCN).
Reactions of [Ni(COD)2] with R–NCO in the presence of PR3. To a
Schlenk flask containing [Ni(COD)2] (0.219 g, 0.80 mmol) at 0 °C,
tetrahydrofuran (3 mL) and PMe3 (328 μL, 3.18 mmol) were added
in that order. The mixture was stirred for 30 min to give a yellow
solution. Phenyl isocyanate (173 μL, 1.59 mmol) was added to the
mixture at room temperature. After stirring for 4 h at room
temperature, the volatiles were removed under vacuum, and then
the remaining residue was chromatographed over silica gel, by
eluting with ethyl acetate/hexane (1:3). The final product, (R–NCO)3
(R = phenyl) was obtained in 81% yield.
X-Ray Crystallography
Single crystals of 10, 16, 17, 18, and 19 for X-ray crystallography
were grown from CH2Cl2/ n-hexane (or ether) at −35 °C. All X-ray
data were collected at 200(2) K with the use of a Bruker Smart
diffractometer equipped with a Mo X-ray tube. Collected data were
corrected for absorption with SADABS based upon the Laue
symmetry by using equivalent reflections.32 All calculations were
carried out with SHELXTL programs.33 All structures were solved by
direct methods. The remaining non-hydrogen atoms were refined
anisotropically. All hydrogen atoms were generated in ideal
positions and refined in a riding mode. Details of crystal data,
intensity collection, and refinement details are given in Table SM1.
Analogous reactions with benzyl, 4-methoxybenzyl, and p-tolyl
isocyanates with [Ni(COD)2] in the presence of 2 equiv or 4 equiv
PMe3 or PMe2Ph were performed. Organic isocyanurates, (Ar–
NCO)3 (Ar = benzyl, 4-methoxybenzyl, and p-tolyl ), were obtained
in 15–43% yields.
Details of Computations
1
(R–NCO)3 (R = phenyl): H NMR (600 MHz, CDCl3, δ): 7.40 (d, 6H, J
The geometry of reactants, intermediates, and products were
optimized by the wB97XD34 density-functional-theory (DFT)
functional forms implemented in the Gaussian09 suit of programs,35
= 7.3 Hz), 7.44 (t, 3H, J = 7.3 Hz), 7.49 (t, 6H, J = 7.6 Hz). 13C{1H} NMR
(150 MHz, CDCl3, δ): 128.6, 129.6, 133.8, 148.9 (s, CO).
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in conjunction with the Lanl2DZ basis sets.36 Up to the 28 and 60
core-electrons of Pd and Pt, respectively, are replaced by effective-
core-potentials in the Lanl2DZ sets as in other usual computational
works for compounds containing the heavy elements.37 All of the
optimized structures were confirmed to be a stationary structure
having no imaginary frequencies and the zero-point-energy (ZPE) is
calculated by using the harmonic frequencies with no scaling factor.
For clarity, all of the molecules of the present computations were
designated by indices from (A) to (I), as shown in Figures 4 and 5.
The total energies including the ZPE correction were collated in
Table-SM2 of Electronic Supplementary Information (ESI), and the
reaction energies were calculated by the equations summarized in
the footnote of Figure 5. The main features of geometrical
structures of (B), (D), and (F) are shown in Figure 6 without
hydrogen atoms for brevity. The full details of atomic coordinates
are given in Table-SM3 of ESI.
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Conflicts of interest
There are no conflicts to declare.
Acknowledgements
This work was supported by the Basic Science Research Program
through the National Research Foundation of Korea (NRF) funded
by the Ministry of Education, Science and Technology (NRF-
2016R1D1A3B03932228).
Notes and references
‡ Footnotes relating to the main text should appear here. These
might include comments relevant to but not central to the
matter under discussion, limited experimental and spectral data,
and crystallographic data.
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Table of contents
Reactivities of zero-valent group 10 complexes toward organic
isocyanates: synthesis of metallacycles containing dimeric isocyanate
units, isocyanate cyclotrimerization, and computational chemistry
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Young-Sung Han, Kang-Yeoun Jung, Yong-Joo Kim, Kyoung Koo Baeck, Gang Min Lee and Soo
n W. Lee
L
R
N
O
O
N
M
O
R
N
M = Pd
R
L
N
N
R
R
O
N
O
M
L
L
N
N
R
R
O
R
R
R
O
M
L
O
R
M
O
S
N
N
N
N
R
O
M = Pt
O
M
N
O
O
L
R
Five-membered metallacycles involving dimeric isocyanate units converted into cyclic tetramers and isocyanurates,
depending on the central metal or organic isocyanates, and their synthetic and theoretical studies were carried out.