1,2,3-Triazole based bisphosphine, 5-(diphenylphosphanyl)-1-(2-(diphenylphosphanyl)-phenyl)-4-phenyl-1: H -1,2,3-triazole: An ambidentate ligand with switchable coordination modes

Article abstract of DOI:10.1039/c8ra04086a

The reaction of 1-(2-bromophenyl)-4-phenyl-1H-1,2,3-triazole (1) with Ph₂PCl yielded bisphosphine, 5-(diphenylphosphanyl)-1-(2-(diphenylphosphanyl)phenyl)-4-phenyl-1H-1,2,3-triazole (2). Bisphosphine 2 exhibits ambidentate character in either the κ²-P,N or κ²-P,P coordination mode. Treatment of 2 with [M(CO)₄(piperidine)₂] (M = Mo and W) yielded κ²-P,N and κ²-P,P coordinated Mo⁰ and W⁰ complexes [M(CO)₄(2)] [M = W-κ²-P,N (4); Mo-κ²-P,P (5); W-κ²-P,P (6)] depending on the reaction conditions. Formation and stability of κ²-P,P coordinated Mo⁰ and W⁰ complexes were assessed by time dependent ³¹P{¹H} NMR experiments and DFT studies. The complex 4 on treatment with [AuCl(SMe₂)] afforded the hetero-bimetallic complex [μ-PN,P-{o-Ph₂P(C₆H₄){1,2,3-N₃C(Ph)C(PPh₂AuCl)}-κ²-P,N}W(CO)₄] (7). The 1:1 reaction between 2 and [CpRu(PPh₃)₂Cl] yielded [(η⁵-C₅H₅)RuCl{o-Ph₂P(C₆H₄){1,2,3-N₃C(Ph)C(PPh₂)}}-κ²-P,P] (8), whereas the similar reaction with [Ru(η⁶-p-cymene)Cl₂]₂ in a 2:1 molar ratio produced a cationic complex [(η⁶-p-cymene)RuCl{o-Ph₂P(C₆H₄){1,2,3-N₃C(Ph)C(PPh₂)}}-κ²-P,N]Cl (9). Similarly, treatment of 2 with [M(COD)(Cl)₂] (M = Pd and Pt) in a 1:1 molar ratio yielded Pd^II and Pt^II complexes [{o-Ph₂P(C₆H₄){1,2,3-N₃C(Ph)C(PPh₂)}-κ²-P,P}PdCl₂] (10) and [{o-Ph₂P(C₆H₄){1,2,3-N₃C(Ph)C(PPh₂)}-κ²-P,P}PtCl₂] (11). The reaction of 2 with 2 equiv. of [AuCl(SMe₂)] afforded [Au₂Cl₂{o-Ph₂P(C₆H₄){1,2,3-N₃C(Ph)C(PPh₂)}}-μ-P,P] (12). Most of the complexes have been structurally characterized. Palladium complex 10 shows excellent catalytic activity towards Cu-free Sonogashira alkynylation/cyclization reactions.

Full text of DOI:10.1039/c8ra04086a

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1,2,3-Triazole based bisphosphine, 5-
(diphenylphosphanyl)-1-(2-(diphenylphosphanyl)-
phenyl)-4-phenyl-1H-1,2,3-triazole: an
ambidentate ligand with switchable coordination
modes†
Cite this: RSC Adv., 2018, 8, 25704
*
Latchupatula Radhakrishna, Madhusudan K. Pandey and Maravanji S. Balakrishna
The reaction of 1-(2-bromophenyl)-4-phenyl-1H-1,2,3-triazole (1) with Ph2PCl yielded bisphosphine, 5-
(diphenylphosphanyl)-1-(2-(diphenylphosphanyl)phenyl)-4-phenyl-1H-1,2,3-triazole (2). Bisphosphine 2
exhibits ambidentate character in either the k2-P,N or k2-P,P coordination mode. Treatment of 2 with
[M(CO)4(piperidine)2] (M ¼ Mo and W) yielded k2-P,N and k2-P,P coordinated Mo0 and W0 complexes
[M(CO)4(2)] [M ¼ W-k2-P,N (4); Mo-k2-P,P (5); W-k2-P,P (6)] depending on the reaction conditions.
Formation and stability of k2-P,P coordinated Mo0 and W0 complexes were assessed by time dependent
31P{1H} NMR experiments and DFT studies. The complex 4 on treatment with [AuCl(SMe2)] afforded the
hetero-bimetallic complex [m-PN,P-{o-Ph2P(C6H4){1,2,3-N3C(Ph)C(PPh2AuCl)}-k2-P,N}W(CO)4] (7). The
1 : 1 reaction between
2
and [CpRu(PPh3)2Cl] yielded [(h5-C5H5)RuCl{o-Ph2P(C6H4){1,2,3-N3C(Ph)
C(PPh2)}}-k2-P,P] (8), whereas the similar reaction with [Ru(h6-p-cymene)Cl2]2 in a 2 : 1 molar ratio
produced a cationic complex [(h6-p-cymene)RuCl{o-Ph2P(C6H4){1,2,3-N3C(Ph)C(PPh2)}}-k2-P,N]Cl (9).
Similarly, treatment of 2 with [M(COD)(Cl)2] (M ¼ Pd and Pt) in a 1 : 1 molar ratio yielded PdII and PtII
complexes [{o-Ph2P(C6H4){1,2,3-N3C(Ph)C(PPh2)}-k2-P,P}PdCl2] (10) and [{o-Ph2P(C6H4){1,2,3-N3C(Ph)
C(PPh2)}-k2-P,P}PtCl2] (11). The reaction of 2 with 2 equiv. of [AuCl(SMe2)] afforded [Au2Cl2{o-Ph2P(C6H4)
{1,2,3-N3C(Ph)C(PPh2)}}-m-P,P] (12). Most of the complexes have been structurally characterized.
Palladium complex 10 shows excellent catalytic activity towards Cu-free Sonogashira alkynylation/
cyclization reactions.
Received 14th May 2018
Accepted 6th July 2018
DOI: 10.1039/c8ra04086a
rsc.li/rsc-advances
to phosphine moieties can generate interesting ligand
systems with rich coordination chemistry.6 In this context,
mono- or bisphosphines containing pyridine,7 imidazole,8
pyrazole9 or furan10 moieties have attracted more attention,
whereas triazole based systems have been less explored,11
though they exhibit ambidentate behavior and nd applica-
tion in catalysis.2,12
Recently we reported the synthesis of two triazole based
mono phosphines by exploiting the temperature controlled
Li/H exchange phenomenon and studied their group 11
metals chemistry.13 As a continuation of our work, herein, we
describe the synthesis of C1-symmetric triazole based
bisphosphine 2. We also demonstrate the ambidentate
behavior of ligand 2 with Mo0 and W0 metal centers using
extensive NMR studies and DFT calculations. The coordina-
tion chemistry of ligand 2 with PdII, PtII, RuII and AuI metal
precursors and the catalytic activity of palladium complex 10
in tandem Cu-free Sonagashira coupling/cyclization reac-
tions are also investigated.
Introduction
Chelating ligands having both so- and hard-donor atoms
have drawn considerable interest owing to their ability to
stabilize the metal atoms before and aer the oxidative
addition and reductive elimination reactions, two important
steps in metal mediated homogeneous catalysis.1 If the
ligands possess more than two donor atoms, and unlike
pincer complexes, show exibility in their coordination
behavior to vary the donor atoms under the inuence of
temperature,2 light3 or redox reagents,4 they can also nd
application in molecular switches, logic gates, sensors etc.5
Therefore incorporating heteroaryl groups having donor
atoms such as nitrogen, oxygen or sulphur in close proximity
Phosphorus Laboratory, Department of Chemistry, Indian Institute of Technology
Bombay, Powai, Mumbai 400076, India. E-mail: krishna@chem.iitb.ac.in;
msb_krishna@iitb.ac.in; Fax: +91-22-5172-3480/2576-7152
† Electronic supplementary information (ESI) available. CCDC 1832214,
1832216–1832224. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/c8ra04086a
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is not clear, the large 5JPP value indicates the least possibility of
through bond coupling and does not rule out the possibility of
through-space coupling. C1-symmetric biaryl-bisphosphines14
and imidazole based bisphosphines (Table 1) have shown
through-space coupling with JPP values of similar magnitude.8b
Bischalcogenide derivatives of 2 (2a and 2b; See ESI Scheme
S1†) did not show phosphorus–phosphorus coupling probably
due to the non-availability of phosphorus lone pairs for
through space interaction, thus suggesting the coupling to be
of through-space in nature. The assignment of chemical shis
in 2 are based on previously reported triazole based mono
phosphines.13 The triazole bonded phosphorus is signicantly
shielded compared to the ortho-carbon bound phosphorus
atom.
Results and discussion
Synthesis of 5-(diphenylphosphanyl)-1-(2-
(diphenylphosphanyl)phenyl)-4-phenyl-1H-1,2,3-triazole (2)
The temperature-controlled lithiation of 1-(2-bromophenyl)-4-
phenyl-1H-1,2,3-triazole (1), followed by the treatment of
Ph2PCl resulted in two different 1,2,3-triazole functionalized
monophosphines
[o-Ph2PC6H4{1,2,3-N3C(Ph)C(H)}]
and
[C6H5{1,2,3-N3C(Ph)C(PPh2)}] depending on the reaction
conditions.13 This method was employed to synthesize triazole
based new bisphosphine in one or two step reactions. Treat-
ment of 1-(2-bromophenyl)-4-phenyl-1H-1,2,3-triazole (1) with
two equivalents of nBuLi, followed by the addition of two
equivalents of Ph2PCl yielded bisphosphine [o-Ph2P(C6H4)
{1,2,3-N3C(Ph)C(PPh2)}] (2) (Scheme 1). Alternately, 1-(2-bro-
mophenyl)-4-phenyl-1H-1,2,3-triazole (1) on treatment with
Single crystals of 2 suitable for X-ray diffraction analysis were
obtained from an ethanol solution of 2 kept at 0 ꢁC for 24 h. The
phosphorus centers exhibit distorted trigonal pyramidal geom-
etry with both the phosphorus atoms being orthogonal to each
n
one equivalent of BuLi followed by the addition of Ph2PCl at
ꢁ
ꢀ78 C afforded kinetically stable triazole based mono phos-
phine A, which on further treatment with nBuLi followed by
the addition of Ph2PCl at room temperature produced
bisphosphine [o-Ph2P(C6H4){1,2,3-N3C(Ph)C(PPh2)}] (2) as
shown in Scheme 1. The 31P{1H} NMR spectrum of 2 showed
two doublets at ꢀ30.4 and ꢀ17.5 ppm with a JPP coupling of
22.3 Hz. The existence of coupling between the two phos-
phorus atoms, which are ve bonds apart, was conrmed by
31P–31P COSY experiment. Although, the origin of the coupling
˚
other as shown in Fig. 1. The P2–C7 [1.830(3) A] bond distance is
˚
little shorter compared to P1–C2 (1.859(3) A) bond distances due
to the better electron withdrawing nature of the triazole ring.
Coordination chemistry of bisphosphine 2
Recently, we demonstrated the coordination behavior of tri-
azole based monophoshines towards group 11 metals, in which
ligand showed mono-, di- as well as tridentate coordinating
Scheme 1 Synthesis of triazole based phosphorus ligand 2.
Table 1 The 31P NMR data for C1-symmetric bisphosphines
Compounda
R
dP
JPP (Hz)
Reference
b
OCH3
CH3
Cl
C6H5
N(CH3)2
ꢀ13.6 (d), ꢀ14.0 (d)
ꢀ12.8 (d), ꢀ14.6 (d)
ꢀ12.0 (d), ꢀ14.1 (d)
ꢀ13.9 (d), ꢀ15.1 (d)
ꢀ14.4 (d), ꢀ14.5 (d)
18.3
27.1
22.5
11.4
5.3
14
14
14
14
14
[o-Ph2P(C6H4){1-N(CH)2-4-NC(PPh2)}]
[o-Ph2P(C6H4){1-N(CH)2-4-N(CH3)
C(PPh2)}]OTf
ꢀ18.0 (d), ꢀ30.3 (d)
ꢀ19.6 (d), ꢀ22.6 (d)
24.3
27.9
8b
8b
[o-Ph2P(C6H4){1,2,3-N3C(Ph)C(PPh2)}] (2)
[o-Ph2P(O)(C6H4){1,2,3-N3C(Ph)C((O)
PPh2)}] (2a)
[o-Ph2P(Se)(C6H4){1,2,3-N3C(Ph)C((Se)
PPh2)}] (2b)
ꢀ17.5 (d), ꢀ30.4 (d)
22.3
This paper
This paper
c
28.5 (s), 12.7 (s)
31.6 (s) 1JPSe ¼ 754 (Hz), 18.5 (s) 1JPSe ¼ 752 (Hz)
This paper
c
a
b
c
In all these compounds phosphorus atoms are ve bonds apart. d in ppm. Not observed.
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Scheme 2 Synthesis of Mo0 and W0 complexes 4–6.
P,P (I) and k-P, k-P-coordination (IV) via phosphorus atoms are
the most common and preferred modes for 2, it can also show
chelating [k2-P,N] (II), as well as chelating-cum-bridging [k2-P,N
and m-PN,P] (III) modes to perform as a tridentate ligand.
However the possibility of 2 showing other coordinating modes
V–IX is less likely (Chart 1), but are not precluded, as appro-
priate metal precursors might enable these coordination
modes. Therefore, it would be interesting to study the coordi-
nation chemistry of 2 with various transition metal precursors.
Treatment of bisphosphine 2 with [Mo(piperidine)2(CO)4] in
Fig.
1 Molecular structure of 2 with 50% ellipsoid probability.
Hydrogen atoms were omitted for clarity. Selected bond distances (A˚)
and bond angles (ꢁ) of 2: P1–C2 1.859(3), P1–C15 1.835(3), P2–C7
1.830(3), P2–C27 1.827(3), N1–N2 1.352(3), N2–N3 1.312(3), C2–P1–
C15 101.42(12), C2–P1–C21 101.18(12), C15–P1–C21 103.93(12), C7–
P2–C27 103.14(12), C7–P2–C33 101.64(12), C27–P2–C33 103.12(12),
N1–N2–N3 106.7(2).
modes.13 Although, bidentate mode is common with the triazole
based phosphines, the reports on the participation of two CH2Cl2 at room temperature resulted in [{o-Ph2P(C6H4){1,2,3-
nitrogen atoms in coordination is rare. Bisphosphine 2 can act N3C(Ph)C(PPh2)}-k2-P,P}Mo(CO)4] (5) with ligand showing k2-
as a potential tetradentate ligand. The plausible coordinating P,P coordination. The same reaction with [W(piperidine)2(CO)4]
modes for the ligand 2 are listed in Chart 1. Although, simple k2- afforded initially k2-P,N coordinated complex, [{o-Ph2P(C6H4)
Chart 1 Possible coordinating modes for bisphosphine 2.
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Fig. 2 Time dependent 31P{1H} NMR spectral data for the isomerization of complex 3 to 5.
Fig. 3 Time dependent 31P{1H} NMR spectral data for the isomerization of complex 4 to 6.
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Fig. 4 Molecular structures of 4, 5 and 6. All hydrogen atoms and solvent molecules were omitted for clarity.
Table 2 Energy (eV) of the selected MOs and MO contributions of
bound phosphorus atom, probably along with one of the tri-
compounds 3–6a
azole nitrogen atoms and triazolyl phosphorus atom being le
uncoordinated. The 31P{1H} NMR spectrum of complex 5
Contribution of
HOMO (%)
Contribution of
LUMO (%)
2
consists of two doublets at 35.6 and 23.7 ppm with a JPP
19 Hz indicating k2-P,P coordination to molybdenum.
z
HOMO (eV)
LUMO (eV)
M
CO
2
M
CO
2
To gain some insight into the stability of complexes 3 and 4,
we have examined the DG values obtained from DFT calcula-
tions. The energy difference (DG) between the k2-P,N coordi-
3
4
5
6
ꢀ5.15
ꢀ5.05
ꢀ5.67
ꢀ5.61
ꢀ1.52
ꢀ1.61
ꢀ1.27
ꢀ1.32
60
56
64
60
27
30
24
26
13
14
12
14
5
5
15
14
4
4
4
5
92
91
80
81
nated W0 complex
4
and the k2-P,N coordinated Mo0
intermediate 3 is ꢀ175.1 kcal molꢀ1, which clearly indicates
relatively more stability of 4. Similarly, the energy difference
(DG) between the complexes 3 and 5 is ꢀ6.6 kcal molꢀ1 and the
same between 4 and 6 is ꢀ6.4 kcal molꢀ1. Therefore, the
kinetically controlled k2-P,N-complex isomerizes to k2-P,P-
complex. A dichloromethane solution of k2-P,N coordinated
complex 4 on stirring at room temperature for 72 h or the
reaction of 2 with [W(piperidine)2(CO)4] in toluene under reux
conditions for 12 h yielded k2-P,P-complex 6 in quantitative
yield. The 31P{1H} NMR spectrum of 6 shows two doublets at
18.9 ppm (1JWP z 238.3 Hz, 2JPP z 12.8 Hz) and 6.9 ppm (1JWP
z 247.3 Hz, 2JPP z 12.8 Hz). The course of the reaction was also
monitored by time dependent 31P{1H} NMR spectroscopy.
a
M ¼ Mo (3 and 5), W (4 and 6).
{1,2,3-N3C(Ph)C(PPh2)}-k2-P,N}W(CO)4] (4) which on prolonging
the reaction time, yielded k2-P,P coordinated complex [{o-
Ph2P(C6H4){1,2,3-N3C(Ph)C(PPh2)}-k2-P,P}W(CO)4] (6) as shown
in Scheme 2. The complexes 4 and 5 were characterized by 31P
{1H} NMR spectroscopy and their structures were conrmed by
single crystal X-ray analysis. The 31P{1H} NMR spectrum of
complex 4 shows two singlets at 23 (1JWP z 239.2 Hz) and
ꢀ23.9 ppm, clearly indicating the coordination of aryl group
Fig. 5 Frontier molecular orbitals of compounds 3–6.
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Scheme 3 Synthesis of W, Au complex 7.
Initially in the case of molybdenum, two resonances were M06/6-31G**,16 lanl2dz level of theory17 for complexes 3–6.
observed at 34.1 and ꢀ24.9 ppm, corresponding to coordinated Crystal structure data were used for coordinates while per-
and uncoordinated phosphorus atoms indicating the formation forming the DFT calculations.18 The computed geometric
of k2-P,N coordinated complex 3. However, within 30 minutes parameters of complexes 4–6 are in good agreement with the
50% of the k2-P,N complex transformed into k2-P,P complex, single crystal X-ray crystallographic structures (see ESI: Tables
and the isomerization was complete within 2 h (Fig. 2). In the S1 and S2†). The HOMO and LUMO energy values are tabu-
case of tungsten, isomerization starts aer 12 h and 50% lated in Table 2.19 In all these complexes, the HOMO level is
conversion was observed aer 40 h and the isomerization was majorly contributed by the metal center and carbonyl groups,
complete aer 72 h (Fig. 3). These NMR studies clearly show the whereas the LUMO level is majorly contributed by the ligand
formation of thermodynamically favored k2-P,P coordination (Fig. 5).20 The HOMO of k2-P,P coordinated complexes 5 and 6
complexes via isomerization of initially formed k2-P,N coordi- are slightly higher in energy as compared to the k2-P,N coor-
nated complexes.
dinated complexes 3 and 4.21 The HOMO–LUMO energy
The IR spectrum of complex 4 showed three nCO bands at differences between k2-P,P in 5 and 6 (4.4 eV and 4.29 eV) are
1850, 1887 and 2013 cmꢀ1, whereas those of 5 and 6 are even more compared to the k2-P,N coordinated complexes 3
appended at 1901, 2023 cmꢀ1 and 1892, 2018 cmꢀ1, respec- and 4 (3.63 eV and 3.44 eV). It clearly suggests that the
tively. The nCO features are similar to those of analogous complexes 5 and 6 are more stable compared to the corre-
complexes of the type cis-[M(CO)4(LL)] (M ¼ Mo and W; LL ¼ sponding k2-P,N coordinated complexes 3 and 4.
dppm and dppe).15
The X-ray quality crystals of complexes 4–6 were obtained by
solvent diffusion methods. The molecular structures of
complexes 4–6 are shown in Fig. 4. The crystal structure of
complex 4 reveals distorted octahedral geometry around tung-
sten center anked by one of the triazolyl nitrogens (N2),
phosphorus atom and four carbonyl groups. The P1–W1–N2
(75.10(9)ꢁ) angle is considerably smaller despite the formation
of six-membered chelate ring which may be due to the relative
orientation of N and P lone pairs. All P–Mo–C and N–Mo–C
bond angles are greater than 90ꢁ, with the largest deviations
being 97.74(15)ꢁ and 96.93(18)ꢁ for P1–W1–C40 and N2–W1–
C39, respectively. The W–C bond distances of mutually trans
˚
˚
carbonyls [W1–C41, 2.039(5) A and W1–C42, 2.021(5) A] are
slightly longer than the W–C bond distances for the carbonyls
˚
trans to phosphorus and nitrogen (W1–C39 (1.972(5) A) and
˚
W1–C40 (1.978(5) A)), due to the poor p acceptor ability of
phosphorus and triazolyl nitrogen moieties compared to the
carbonyls. The P1–M–P2 bond angles in 5 and 6 are 87.76(3)ꢁ
and 87.81(4)ꢁ, respectively. In 5 and 6, the M–C bond distances
for the carbonyl trans to the phosphorus [Mo (1.997(4) and
˚
1.998(4) A) and W (2.000(6) and 2.006(6))] is shorter than the
M–C bond distances of mutually trans carbonyls [Mo (2.030(4)
˚
˚
and 2.044(4) A) and W (2.027(5) and 2.039(5) A)].
In order to gain some insight into the preference between
the k2-P,N and the k2-P,P coordinating modes in Mo and W–
carbonyl complexes, calculations were performed using the
Fig.
6 Molecular structure of 7 with 50% ellipsoid probability.
Hydrogen atoms were omitted for clarity.
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Scheme 4 Synthesis of Ru(II) complexes 8 and 9.
2
The complex 4 can function as a metalloligand due to the consists of two doublets at 54.3 and 36.3 ppm with a JPP
¼
presence of one uncoordinated phosphorus atom. The reaction 51.9 Hz, indicating k2-P,P coordination. The 1H NMR spectrum
of 4 with [AuCl(SMe2)] in dichloromethane resulted in hetero- of 8 shows a singlet at 4.25 ppm for cyclopentadienyl protons.
bimetallic complex 7 as shown in Scheme 3. The 31P{1H} NMR Reaction of 2 with 0.5 [Ru(h6-p-cymene)Cl2]2 in dichloro-
spectrum of 7 shows two singlets at 22.9 (1JWP z 237.5 Hz) and methane yielded a red colored cationic complex [(h6-p-cymene)
12.8 ppm. A shi in the 31P{1H} NMR signal of the triazole RuCl{o-Ph2P(C6H4){1,2,3-N3C(Ph)C(PPh2)}}-k2-P,N]Cl (9) as
bound phosphorus (DdP ¼ 33) indicates its coordination to shown in Scheme 4. Complex 9 showed two singlets in its 31P
gold. The nCO of complex 7 is similar to that of 4 and shows four {1H} NMR spectrum at 35.5 and ꢀ21.3 ppm, indicating k2-P,N
nCO bands at 1857, 1888 and 1901 cmꢀ1 and 2010 cmꢀ1
.
coordination keeping the triazolyl phosphorus (ꢀ21.3 ppm)
The molecular structure of complex 7 is shown in Fig. 6. The uncoordinated. The 1H NMR spectrum of 9 showed four
crystal structure of complex 7 reveals distorted octahedral doublets at 6.53, 6.42, 5.92 and 5.25 ppm for the cymene group.
geometry around tungsten and linear geometry around gold The aliphatic protons of the cymene group showed septet at
atom. The P1–W1–N2 and P1–Au1–Cl1 bond angels are 3.10 ppm and two doublets at 1.07 and 1.24 ppm with a 3JHH
76.14(9)ꢁ and 175.86(5)ꢁ, respectively. The W1–N2 and W2–P1 6.5 Hz for the isopropyl group and a singlet at 1.71 ppm for
¼
˚
˚
bond distances are 2.244(5) A and 2.5080(15) A, whereas W–C methyl group.
˚
bond distances vary from 1.964(6) to 2.035(6) A. Further,
The crystals of complex 8 were obtained by diffusion of
complex 7 shows weak Au/Carene interaction between gold and petroleum ether into a saturated solution of 8 in chloroform.
triazole (N1) attached phenyl group. The Au/Carene separation The unit cell contains two independent molecules with iden-
˚
˚
is 3.40 A for ipso C1 and 3.480 A for ortho C6, which lies within tical bond parameters. In 8, ruthenium atom adopts a pseudo-
˚
the range of Au–Carene interactions (3.07–3.55 A) reported in the octahedral geometry (Fig. 7). The P1–Ru1–P2, P1–Ru–Cl1 and
literature.22
P7–Ru–Cl1 bond angels are 91.86(4), 88.72(4) and 93.59(4)ꢁ,
The reaction of bisphosphine 2 with one equvivalent of [(h5- respectively. It species slight deviation from the ideal octahe-
C5H5)Ru(PPh3)2Cl] in toluene under reux conditions afforded dral angle. The Ru–P, Ru–Cl and Ru–C bond distances are in the
mononuclear complex [(h5-C5H5)RuCl{o-Ph2P(C6H4){1,2,3- range expected for typical half-sandwich complexes.8c The
N3C(Ph)C(PPh2)}}-k2-P,P] (8). The 31P{1H} NMR spectrum of 8 phosphorus (P2) attached phenyl hydrogen (H34) is involved in
Fig. 7 Molecular structures of 8 and 9. Hydrogen atoms and solvent molecule were omitted for clarity.
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weak intermolecular hydrogen bonding with triazole nitrogen
˚
(N3) with a N3/H34 distance of 2.50 A. This interaction plays
a major role in bulk crystal packing (see ESI Fig. S1†).
In complex 9, the ruthenium center shows pseudo-
octahedral geometry with p-cymene, one of the nitrogen (N2)
of triazole group, phosphorus atom (P2) and chloride ion
occupying the coordinating sites (Fig. 7). The P1–Ru1–N2
(80.42(16)ꢁ), P1–Ru1–Cl1 (89.85(7)ꢁ) and N2–M–Cl1 (88.30(16)ꢁ)
bond angles clearly indicate the distorted octahedral geometry
around the ruthenium atom. The Ru1–P1, Ru1–N1 and Ru1–Cl1
˚
bond distances are 2.3060(19), 2.136(6) and 2.4074(19) A,
˚
respectively. The Ru1–C (2.237 A) mean distance is comparable
to the same in analogues complexes such as: [(h6-p-cymene)
i
2
RuCl{2-NMe2-3- Pr2P-indene}-k -P,N]BF4 (2.226 A) and [(h6-p-
23
˚
cymene)RuCl{PR1R2}-k2-P,N]ClO4 R1 ¼ (O–C10H6–C10H6–O) R2
24
˚
¼ [O–C6H4{2-C(NN(Me)CH)CH}] (2.242 A).
The reactions of [M(COD)Cl2] (M ¼ Pd, Pt) with 2 in 1 : 1
molar ratio in dichloromethane afforded [MCl2(2)] (M ¼ Pd (10);
Pt (11)) in good yield. The 31P{1H} NMR spectra of 10 and 11
conrm the k2-P,P coordination. Interestingly palladium
complex did not show 2JPP coupling, whereas platinum complex
showed 2JPP and 1JPtP couplings of 17.52 Hz and 3582 & 3721 Hz,
respectively.
The suitable crystals of complexes 10 and 11 were obtained
from chloroform solution layered with petroleum ether. Both
palladium and platinum atoms adopt square planar geometry
(Fig. 8). The P1–M–P2 bond angles in 10 and 11 are 94.72(3)ꢁ
and 94.11(16)ꢁ, respectively. Triazole nitrogen atoms N3 and N2
show weak intermolecular hydrogen bonding with phenylene
hydrogen atoms H25 and H14 of two other molecules (See ESI
Fig. S2†) which is evident from the N3/H25 and N2/H14 bond
Fig.
9
Molecular structure of 12 with 50% ellipsoid probability.
Hydrogen atoms and solvent molecule were omitted for clarity.
Selected bond distances (A˚) and bond angles (ꢁ): P1–Au1 2.2224(11),
P2–Au2 2.2101(11), P1–C2 1.814(4), P2–C7 1.806(4), Au1–Cl1
2.2834(11), Au2–Cl2 2.2703(11), Au1–Au2 3.3406(3), P1–Au1–Cl1
174.27(4), P2–Au2–Cl2 174.94(5), C2–P1–Au1 115.02(15), C7–P2–Au2
111.46(14), N1–N2–N3 107.6(3).
˚
separation of 3.3406(3) A, indicating intramolecular auro-
philic interaction. The Au/Au distance is within the range (ca.
2.50–3.50 A) and less than the sum of the van der Waals radii
(3.8 A) reported in the literature.
˚
25
˚
Sonogashira coupling and sequential cyclization of alkyne
and 2-halophenols to form synthetically useful 2-substituted
benzofuran-type frameworks is an important methodology as
these compounds constitute ubiquitous core structure in
natural products and pharmaceuticals.26 For the preparation
of benzofurans, a palladium catalyst in the presence copper
salt as co-catalyst is generally employed for tandem
alkynylation/cyclization reactions of terminal alkynes with o-
hydroxy aryl halides.27 However, Cu-free Sonogashira alkyny-
lation and sequential cyclization methods are scant in the
literature.28 In order to assess the catalytic efficiency of palla-
dium complex 10, tandem Cu-free Sonogashira alkynylation/
cyclization reactions were performed.
˚
˚
distances of 2.570 A and 2.553 A, respectively. No such inter-
actions were observed in platinum complex 11.
The reaction of 2 with two equivalents of [AuCl(SMe2)] in
dichloromethane yielded digold complex, [Au2Cl2{o-Ph2P(C6H4)
{1,2,3-N3C(Ph)C(PPh2)}}-m-P,P] (12). The 31P{1H} NMR spectrum
of 12 exhibits two resonances at 24.5 and 12.2 ppm. The mass
spectrum of complex 12 shows a peak at 1018.0853 corre-
sponding to [M ꢀ Cl]+.
A perspective view of the molecular structure of 12 is shown
in Fig. 9. The bond angels P1–Au1–Cl1 (174.94(5)ꢁ) and P2–
Au2–Cl2 (174.27(4)ꢁ) are almost linear but orthogonal to each
other. AuI centers display linear geometry with an Au/Au
Fig. 8 Molecular structures of 10 and 11. All hydrogen atoms and solvent molecule were omitted for clarity.
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Table 3 Optimization of reaction conditionsa
Entry
Solvent
Base
Time (h)
Conversion (%)a
1
2
3
4
5
6
7
8
9
Dioxane
Dioxane/H2O(1 : 1)
CH3CN
CH3CN/H2O(1 : 1)
DMF
Toluene
DMSO
DMSO
DMSO
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
K2CO3
12
12
12
12
12
12
12
6
55
68
60
76
85
48
74
Cs2CO3
Cs2CO3
99 (95b)
78c
12
a
Conversion determined by GC-MS using 2-iodophenol as internal standard. b Isolated yield. c 0.5 mol% catalyst used.
Chart 2 Substrate scope for tandem Cu-free Sonagashira alkynylation/cyclization reaction. Conditions: 2-iodophenol 0.5 mmol, alkynes
0.6 mmol, DMSO 3 mL, Cs2CO3 0.75 mmol, 80 ꢁC, catalyst (1 mol%). Isolated yield.
Initially, the reaction of 2-iodophenol with phenyl acetylene
was tested with 1 mol% of palladium catalyst 10 in various
Conclusions
solvents. An excellent yield of 2-phenylbenzofuran was observed
when Cs2CO3 was used as a base in dimethyl sulfoxide at 80 ꢁC
for 12 h. The yield was lowered considerably in other solvents
(Table 3, entries 1–6). The coupling reaction was strongly
inuenced by the base as well as catalyst loading. Replacing
Cs2CO3 with K2CO3 gave only moderate conversion (Table 3,
entry 7). Catalyst loading of 0.5 mol% resulted in lower
conversion rate (Table 3, entry 9). On decreasing the reaction
time to 6 h, the conversion was not signicantly affected (Table
3, entry 8). Under the optimized reaction conditions, various
combinations of substituted o-iodophenols and alkynes were
subjected to the tandem coupling/cyclization reaction to
produce 2-substituted benzofurans in good to excellent yields.
The results of the tandem Cu-free Sonogashira alkynylation/
cyclization reaction are summarized in Chart 2. Both aromatic
and aliphatic acetylene were tolerated in this conversion. In
contrast, the coupling reaction of 2-iodophenol with 2-ethe-
nylpyridine was not successful and resulted in negligible
conversion.
A new triazole-based bisphosphine 2 has been synthesized. The
ambidentate bisphosphine 2 shows k2-P,P, k2-P,N-chelation as
well as m-(k2-P,N, k-N) and m-(k-P, k-P) bridging coordination
modes to act as di- or tridentate ligand. The kinetically
controlled k2-P,N coordination modes in Mo0 and W0
complexes “switched” to the thermodynamically preferred k2-
P,P coordination modes and the isomerization process was
monitored by time dependent 31P{1H} NMR studies and further
supported by DFT studies. The palladium complex 10 is found
to be an efficient catalyst for tandem Cu-free Sonagashira
alkynylation/cyclization reaction. Further catalytic investigation
are under active investigation in our laboratory.
Experimental section
General procedures
All the air sensitive compounds were handled and stored in the
MBRAUN Glove box. All reactions were performed under an
inert atmosphere of dry nitrogen or argon, using standard
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Schlenk techniques. All the solvents were dried by conventional ꢀ15 ꢁC to get analytically pure product of 2 as white crystalline
methods and distilled prior to use. The compounds solid. Yield: 62% (0.9 g).
[M(piperidine)2(CO)4] (M ¼ Mo and W),33 [(h5-C5H5)Ru(PPh3)2-
Mp: 167–170 ꢁC. Anal. calcd for C38H29N3P2: C, 77.41; H,
Cl],34 [Ru(h6-p-cymene)Cl2]2,35 [M(COD)Cl2] (M ¼ Pd or Pt),36 4.96; N, 7.13. Found C, 77.26; H, 5.38; N, 7.22% H NMR (500
[AuCl(SMe2)],37 5-(diphenylphosphino)-1,4-diphenyl-1H-1,2,3- MHz, CDCl3): d 7.39 (td, J ¼ 7.6, 1.3 Hz, 2H), 7.34–7.29 (m, 7H),
triazole,13 1-(2-(diphenylphosphanyl)phenyl)-4-phenyl-1H-1,2,3- 7.28–7.24 (m, 5H), 7.24–7.18 (m, 9H), 7.13 (dd, J ¼ 7.3, 4.1 Hz,
triazole (A)13 and 2-iodo-4,6-dimethylphenol38 were prepared 4H), 7.11–7.06 (m, 1H), 7.01–6.97 (m, 2H).13C NMR (126 MHz,
according to the published procedures. Other reagents were CDCl3) d 152.69, 135.38, 133.98, 133.83, 132.92, 131.00, 130.51,
obtained from commercial sources and used aer purication. 129.68, 129.27, 129.03, 128.95, 128.67, 128.61, 128.46, 127.73,
127.59. 31P{1H} NMR (202 MHz, CDCl3): d ꢀ17.52 (d, JPP ¼ 22.3
1
Hz), ꢀ30.43 (d, JPP ¼ 22.3 Hz). HRMS (ES) m/z calcd for
Instrumentation methods
C
38H30N3P2 ([M + H]+) 590.1907; found 590.1909.
The solution NMR spectra were recorded on a Bruker FT spec-
trometers (Advance-400 or 500) MHz at ambient probe
temperatures. 13C{1H} and 31P{1H} NMR spectra were acquired
using broad band decoupling method. The spectra were recor-
ded in CDCl3 solutions with CDCl3 as an internal lock; chemical
shis of 1H and 13C NMR spectra are reported in ppm downeld
from TMS, used as an internal standard. The chemical shis of
31P{1H} NMR spectra are referred to 85% H3PO4 as an external
standard. Positive values indicate downeld shis. Infrared
spectra were recorded on a PerkinElmer 400 FTIR instrument in
KBr disk. The microanalyses were performed using a Carlo Erba
Model 1112 elemental analyzer. Mass spectra were recorded
using Waters Q-Tof micro (YA-105). Melting points of all
compounds were determined on a Veego melting point appa-
ratus and are uncorrected. GC-MS analyses were carried out in
Agilent 7890A GC system.
Synthesis of [{o-Ph2P(C6H4){1,2,3-N3C(Ph)C(PPh2)}-k2-P,N}
W(CO)4] (4)
A solution of 2 (0.03 g, 0.051 mmol) and [W(CO)4(piperidine)2]
(0.024 g, 0.051 mmol) in dichloromethane (8 mL) was stirred for
4 h at room temperature. Then, the solvent was evaporated
under reduced pressure, washed with petroleum ether (3 ꢂ 5
mL) and dried under vacuo to give analytically pure product of 4
as a yellow solid. Yield: 80% (0.036 g). Mp: 212–215 ꢁC. IR (KBr
disk): nCO
¼
2013, 1887, 1850 cmꢀ1
. Anal. calcd for
C
42H29N3O4P2W: C, 56.97; H, 3.36; N, 4.75. Found C, 56.43; H,
3.68; N, 5.13%. 1H NMR (400 MHz, CDCl3): d 7.76–7.68 (m, 2H),
7.63–7.50 (m, 10H), 7.46 (dd, J ¼ 13.4, 5.9 Hz, 4H), 7.21 (t, J ¼
7.2 Hz, 1H), 7.03–6.97 (m, 1H), 6.96–6.81 (m, 7H), 6.71 (td, J ¼
7.8, 1.9 Hz, 2H), 6.22 (t, J ¼ 7.5 Hz, 2H). 31P{1H} NMR (162 MHz,
CDCl3): d 23.01 (1JWP ¼ 239.2), ꢀ23.94. HRMS (ES) m/z calcd for
Synthesis of [o-Ph2P(C6H4){1,2,3-N3C(Ph)C(PPh2)}] (2)
C
42H30N3O4P2W ([M + H])+ 886.1222; found 886.1222.
Method A. To a Schlenk ask charged with 2-bromophenyl-
n
triazole (2.5 g, 8.33 mmol) and THF (50 mL) at ꢀ78 C, BuLi Synthesis of [{o-Ph2P(C6H4){1,2,3-N3C(Ph)C(PPh2)}-k2-P,P}
ꢁ
(11.5 mL, 18.33 mmol, 1.6 M solution in hexane) was added Mo(CO)4] (5)
ꢁ
dropwise and the reaction mixture was stirred at ꢀ78 C for 1
A solution of 2 (0.03 g, 0.051 mmol) and [Mo(CO)4(piperidine)2]
hour, warmed to room temperature and stirring was continued
(0.019 g, 0.051 mmol) in dichloromethane (8 mL) was stirred for
for 4ꢁh. The resulting reddish coloured solution was cooled to
4 h at room temperature. The solvent was evaporated under
ꢀ78 C and the THF (10 mL) solution of PPh2Cl (3.87 g, 17.5
vacuum, and the residue was washed with petroleum ether (3 ꢂ
mmol) was added dropwise through a cannula. The resulting
5 mL) and dried under vacuo to give analytically pure product of
5 as a colorless solid. Yield: 79% (0.034 g). Mp: 202–205 C. IR
mixture was slowly warmed to room temperature and stirred for
further 12 h and ltered through celite to remove LiCl. The
solvent was removed under reduced pressure and the yellow oily
residue obtained was washed with petroleum etꢁher, dissolved in
minimum amount ethanol and stored at ꢀ15 C to get analyt-
ically pure product of 2 as a white crystalline solid. Yield: 56%
(2.75 g).
Method B. To a Schlenk ask charged with 1-(2-(diphenyl-
phosphanyl)phenyl)-4-phenyl-1H-1,2,3-triazole (A) (1 g, 2.47
mmol) in THF (40 mL) at ꢀ78 ꢁC, was added dropwise a hexane
solution of nBuLi (1.7 mL, 2.7 mmol, 1.6 M solution in hexane).
The mixture was allowed to warm to room temperature and was
stirred for 5 h. Again the solution was cooled to ꢀ78 ꢁC and the
THF (5 mL) solution of PPh2Cl (0.54 g, 2.47 mmol) was added
dropwise through a cannula. The resulting mixture was slowly
ꢁ
(KBr disk): nCO ¼ 2023, 1925, 1901 cmꢀ1. Anal. calcd for C42-
H29MoN3O4P2$0.5CH2Cl2: C, 60.76; H, 3.59; N, 5.00. Found C,
60.98; H, 3.67; N, 5.25%. 1H NMR (500 MHz, CDCl3): d 7.68–7.62
(m, 2H), 7.53–7.47 (m, 2H), 7.47–7.42 (m, 3H), 7.39–7.32 (m,
5H), 7.31–7.27 (m, 4H), 7.24–7.15 (m, 5H), 7.00 (t, J ¼ 7.4 Hz,
1H), 6.95 (dd, J ¼ 7.7, 6.2 Hz, 1H), 6.90 (t, J ¼ 7.7 Hz, 2H), 6.86–
6.79 (m, 4H). 31P{1H} NMR (202 MHz, CDCl3): d 35.58 (d, 2JPP
¼
2
19.0 Hz), 23.67 (d, JPP ¼ 19.0 Hz). HRMS (ES) m/z calcd for
C
42H30N3O4P2Mo ([M + H])+ 800.0770; found 800.0770.
Synthesis of [{o-Ph2P(C6H4){1,2,3-N3C(Ph)C(PPh2)}-k2-P,P}
W(CO)4] (6)
Method A. A solution of 2 (0.03 g, 0.051 mmol) and
warmed to room temperature and stirred for 12 h and LiCl was [W(CO)4(piperidine)2] (0.024 g, 0.051 mmol) in dichloro-
ltered off. The solvent was removed under reduced pressure methane (8 mL) was stirred for 72 h at room temperature. Then
and the yellow oily residue obtained was washed with petroleum the solvent was evaporated under reduced pressure and the
ether, dissolved in minimum amount ethanol and stored at residue obtained was washed with petroleum ether (3 ꢂ 5 mL)
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and dried under vacuo to give analytically pure product of 6 as 4.25 (s, 5H). 31P{1H} NMR (202 MHz, CDCl3): d 54.36 (d, J ¼ 51.9
2
colorless solid. Yield: 76% (0.034 g).
Hz), 36.34 (d, JPP ¼ 51.9 Hz). HRMS (ES): m/z calcd for C43-
Method B. A solution of 2 (0.03 g, 0.051 mmol) and H35ClN3P2Ru ([M + H]+): 792.1041; found: 792.1042.
[W(CO)4(piperidine)2] (0.024 g, 0.051 mmol) in toluene (15 mL)
was reuxed for 12 h and then the reaction mixture was cooled Synthesis of [(h6-p-cymene)RuCl{o-Ph2P(C6H4){1,2,3-N3C(Ph)
to room temperature. The solvent was completely removed C(PPh2)}}-k2-P,N]Cl (9)
under reduced pressure and the residue obtained was washed
A solution of [Ru(h6-p-cymene)Cl2]2 (0.0174 g, 0.0285 mmol) in
with petroleum ether (3 ꢂ 5 mL) and dried under vacuo to give
dichloromethane (3 mL) was added drop wise to a solution of 2
analytically pure product of 6 as a colorless solid Yield: 90%
(0.0338 g, 0.057 mmol) also in dichloromethane (4 mL) and
stirred for 4 h at room temperature. The solvent was removed
under reduced pressure and the residue obtained was washed
(0.04 g).
Mp: 217–220 ꢁC. IR (KBr disk): nCO ¼ 2018, 1918, 1892 cmꢀ1
Anal. calcd for C42H29O4N3P2W: C, 56.97; H, 3.3; N, 4.75. Found
with petroleum ether (3 ꢂ 5 mL) and dried under vacuo to give
1
C, 56.63; H, 3.35; N, 4.57%. H NMR (400 MHz, CDCl3): d 7.63
compound 9 as a red solid. Yield 93% (0.048 g) Mp: 257–260 ꢁC.
(ddd, J ¼ 11.7, 7.5, 1.8 Hz, 2H), 7.51–7.41 (m, 5H), 7.39–7.27 (m,
Anal. calcd for C48H43Cl2N3P2Ru: C, 64.36; H, 4.84; N, 4.69.
8H), 7.27–7.20 (m, 5H), 7.16 (dd, J ¼ 13.1, 5.4 Hz, 2H), 7.01 (t, J ¼
Found C, 64.19; H, 4.53; N, 4.36%. 1H NMR (500 MHz, CDCl3):
d 8.15 (dd, J ¼ 12.7, 7.7 Hz, 1H), 7.88–7.62 (m, 7H), 7.57 (s, 4H),
7.48–7.40 (m, 4H), 7.34 (t, J ¼ 7.6 Hz, 1H), 7.18–7.16 (m, 2H),
6.97 (dt, J ¼ 40.8, 7.1 Hz, 6H), 6.73 (t, J ¼ 7.0 Hz, 2H), 6.54 (d, J ¼
3.7 Hz, 1H), 6.43 (d, J ¼ 4.7 Hz, 1H), 6.03 (t, J ¼ 8.0 Hz, 2H), 5.93
(d, J ¼ 6.0 Hz, 1H), 5.25 (d, J ¼ 6.0 Hz, 1H), 3.18–3.03 (m, 1H),
7.4 Hz, 1H), 6.97–6.86 (m, 3H), 6.86–6.79 (m, 3H). 31P NMR (162
MHz, CDCl3): d 18.9 (1JWP ¼ 238.3 Hz, 2JPP ¼ 12.8 Hz), 6.9 (1JWP
¼
2
247.3 Hz, JPP
¼
12.8 Hz). HRMS (ES) m/z calcd for
C
42H30N3O4P2W ([M + H])+ 886.1222; found 886.1222.
1.72 (s, 3H), 1.24 (d, J ¼ 6.5 Hz, 3H), 1.08 (d, J ¼ 6.7 Hz, 3H). 31
P
Synthesis of [m-PN,P{o-Ph2P(C6H4){1,2,3-N3C(Ph)
C(PPh2AuCl)}-k2-P,N}W(CO)4] (7)
{1H} NMR (202 MHz, CDCl3): d 35.52 (s), ꢀ21.34 (s). HRMS (ES):
m/z Calcd. for C48H43ClN3P2Ru ([M ꢀ Cl]+): 860.1669; found:
860.1667.
To a solution of complex 4 (0.051 g, 0.0576 mmol) in dichloro-
methane (5 mL) was added dropwise a solution of [AuCl(SMe2)]
(0.017 g, 0.0576 mmol) in the same solvent (5 mL) and stirred
for 4 h at room temperature. The solvent was aerward evapo-
rated under vacuum; the residue obtained was washed with
petroleum ether (2 ꢂ 5 mL) and dried under vacuo to give
analytically pure product of 7 as an orange red solid. Yield: 84%
(0.057 g). Mp: 222–225 ꢁC. IR (KBr disk): nCO ¼ 2010, 1901, 1888,
1857 cmꢀ1 Anal. calcd for C42H29AuClO4N3P2W: C, 45.12; H,
Synthesis of [{o-Ph2P(C6H4){1,2,3-N3C(Ph)C(PPh2)}-k2-P,P}
PdCl2] (10)
To a stirred solution of [Pd(COD)Cl2] (0.015 g, 0.051 mmol) in
dichloromethane (4 mL) was added drop wise a solution of 2
(0.03 g, 0.051 mmol) also in dichloromethane (4 mL) and the
reaction mixture was stirred for 4 h at room temperature. The
solvent was removed under reduced pressure and the residue
obtained was washed with petroleum ether (2 ꢂ 5 mL) and
dried under vacuo to give compound 10 as a yellow solid. Yield:
1
2.61; N, 3.76. Found C, 45.09; H, 2.35; N, 3.94%. H NMR (500
MHz, CDCl3): d 8.10 (ddd, J ¼ 10.8, 7.4, 2.2 Hz, 2H), 7.84–7.71
(m, 5H), 7.69–7.61 (m, 4H), 7.57 (dt, J ¼ 6.2, 3.1 Hz, 5H), 7.23
(dd, J ¼ 11.7, 4.4 Hz, 2H), 7.07 (ddd, J ¼ 6.6, 5.8, 4.2 Hz, 2H), 6.92
(t, J ¼ 7.8 Hz, 2H), 6.82 (ddd, J ¼ 9.6, 7.3, 3.2 Hz, 3H), 6.74 (dd, J
¼ 8.1, 1.1 Hz, 2H), 6.27 (dd, J ¼ 14.6, 7.3 Hz, 2H). 31P NMR (202
MHz, CDCl3): d 22.89 (1JWP ¼ 237.5 Hz), 12.75.
ꢁ
85% (0.0331 g). Mp: 271–274 C. Anal. calcd for C38H29 Cl2N3-
P2Pd: C, 59.51; H, 3.81; N, 5.48. Found C, 59.57; H, 3.44; N,
1
5.12%. H NMR (500 MHz, CDCl3): d 8.02 (s, 2H), 7.86 (dd, J ¼
13.0, 7.4 Hz, 2H), 7.63 (dd, J ¼ 11.3, 8.2 Hz, 3H), 7.57–7.49 (m,
3H), 7.48–7.41 (m, 3H), 7.33 (dd, J ¼ 12.1, 7.8 Hz, 5H), 7.23 (d, J
¼ 7.6 Hz, 1H), 7.18–7.10 (m, 2H), 7.09–7.02 (m, 2H), 6.99 (t, J ¼
7.6 Hz, 2H), 6.85 (td, J ¼ 7.8, 3.2 Hz, 2H), 6.62 (d, J ¼ 7.2 Hz, 2H).
31P{1H} NMR (202 MHz, CDCl3): d 25.9 (s), 12.9 (s). HRMS (ES)
m/z calcd for C38H29N3P2PdCl ([M ꢀ Cl])+ 730.0565; found
730.0565.
Synthesis of [(h5-C5H5)RuCl{o-Ph2P(C6H4){1,2,3-N3C(Ph)
C(PPh2)}}-k2-P,P] (8)
A solution of [(h5-C5H5)Ru(PPh3)2Cl] (0.0369 g, 0.051 mmol) in
toluene (8 mL) was added slowly to a solution of 2 (0.030 g, 0.051
mmol) in toluene (8 mL) at room temperature. The reaction
mixture was reuxed at 100 ꢁC for 12 h to give a clear yellow
solution. The solvent was removed under vacuum and the
residue obtained was washed with hot petroleum ether (3 ꢂ 8
Synthesis of [{o-Ph2P(C6H4){1,2,3-N3C(Ph)C(PPh2)}-k2-P,P}
PtCl2] (11)
mL) and dissolved in chloroform and layered with petroleum A solution of Pt(COD)Cl2 (0.019 g, 0.051 mmol) in dichloro-
ether, which on slow diffusion gave red colour crystals of 8. methane (4 mL) was added drop wise to a solution of 2 (0.03 g,
Yield 74% (0.03 g). Mp: 270–273 ꢁC. Anal. calcd for C43H34- 0.051 mmol) also in dichloromethane (4 mL) and the solution
ClN3P2Ru: C, 65.27; H, 4.33; N, 5.31. Found C, 65.41; H, 3.97; N, was stirred for 4 h at room temperature. The solvent was
1
5.05%. H NMR (500 MHz, CDCl3): d 7.70 (s, 2H), 7.60 (dd, J ¼ removed under reduced pressure and the residue obtained was
18.2, 10.2 Hz, 3H), 7.50 (t, J ¼ 6.5 Hz, 4H), 7.43 (s, 5H), 7.30 (t, J washed with petroleum ether (2 ꢂ 5 mL) and concentrated to
¼ 7.5 Hz, 1H), 7.26–7.20 (m, 2H), 7.19–7.10 (m, 2H), 6.93 (t, J ¼ a small bulk and 2 mL of chloroform was added and stored at
7.4 Hz, 1H), 6.85 (t, J ¼ 7.1 Hz, 1H), 6.76 (t, J ¼ 7.1 Hz, 2H), 6.70 25 ꢁC to give 11 as a colorless crystalline solid. Yield: 79%
(t, J ¼ 6.5 Hz, 2H), 6.66–6.60 (m, 2H), 6.45 (d, J ¼ 7.0 Hz, 2H), (0.0362
g).
Mp:
260–263
ꢁC.
Anal.
calcd
for
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Table 4 Crystallographic Information for compounds 2 and 4–7
2
4
5
6
7
Formula
Formula weight
T (K)
C
38H29N3P2
C42H29N3O4P2W
885.47
150
C43H30Cl3MoN3O4P2
916.93
150
C43H30Cl3N3O4P2W
1004.84
100
C42H29AuClN3O4P2W
1117.89
150
589.58
150
Crystal system
Space group
Monoclinic
P21/n
15.5170(11)
11.9307(7)
18.3226(15)
90
111.801(9)
90
3149.4(4)
4
Triclinic
P1
Monoclinic
P21/c
14.1841(3)
11.2966(2)
25.2699(6)
90
97.008(2)
90
4018.80(15)
4
Monoclinic
P21/c
14.1865(3)
11.2881(3)
25.1974(9)
90
97.169(2)
90
4003.53(19)
4
Monoclinic
P21/n
12.5915(3)
20.0214(6)
15.3286(4)
90
92.147(2)
90
3861.62(18)
4
ꢀ
˚
a, A
12.6150(6)
13.3420(9)
14.0151(8)
71.437(5)
69.756(5)
65.940(5)
1977.1(2)
2
˚
b, A
˚
c, A
a, deg
b, deg
g, deg
3
˚
V, A
Z
rcalcg/cm3
1.243
0.169
1232
1.487
3.046
876
1.515
0.653
1856
1.667
3.213
1984
1.923
6.97
2136
M (MoKa)/mmꢀ1
F(000)
Crystal size (mm3)
Theta range (deg)
Reections collected
0.151 ꢂ 0.14 ꢂ 0.065 0.171 ꢂ 0.146 ꢂ 0.108 0.314 ꢂ 0.154 ꢂ 0.095 0.224 ꢂ 0.119 ꢂ 0.097 0.168 ꢂ 0.053 ꢂ 0.039
4.33 to 49.994
21 113
4.082 to 50
22 276
6935
4.624 to 49.998
42 569
7077
3.958 to 49.996
21 398
6857
4.112 to 49.998
18 829
6764
Independent reections 5544
S
R1
wR2
1.059
0.0555
0.1586
1.054
0.0336
0.0861
1.033
0.0472
0.1198
1.04
0.0379
0.0949
1.034
0.0323
0.0781
a
b
R ¼ S||Fo| ꢀ |Fc||/S|Fo|. b wR2 ¼ [Sw(Fo ꢀ Fc2)2/Sw(Fo2)2]1/2 w ¼ 1/[s2(Fo2) + (xP)2] where P ¼ (Fo + 2Fc2)/3.
a
2
2
2
C38H29Cl2N3P2Pt$0.5CH2Cl2: C, 51.49; H, 3.37; N, 4.68. Found C, 1JPt–P ¼ 3720.7 Hz, JPP ¼ 17.7 Hz). HRMS (ES) m/z calcd for
1
51.70; H, 3.40; N, 4.59%. H NMR (400 MHz, CDCl3): d 7.96 (s,
2H), 7.79 (dd, J ¼ 13.1, 7.5 Hz, 2H), 7.66–7.48 (m, 7H), 7.48–7.39
(m, 3H), 7.35–7.27 (m, 4H), 7.22 (d, J ¼ 7.5 Hz, 1H), 7.18–7.10
(m, 2H), 7.09–7.03 (m, 2H), 6.99 (t, J ¼ 7.7 Hz, 2H), 6.83 (td, J ¼
7.8, 3.2 Hz, 2H), 6.61 (d, J ¼ 7.2 Hz, 2H). 31P{1H} NMR (202 MHz,
C
38H29N3P2PtCl ([M ꢀ Cl])+ 819.1171; found 820.1162.
Synthesis of [Au2Cl2{ o-Ph2P(C6H4){1,2,3-N3C(Ph)C(PPh2)}}-m-
P,P] (12)
A dichloromethane (5 mL) solution of AuCl(SMe2) (0.030 g,
0.102 mmol) was added drop wise to a solution of 2 (0.030 g,
1
2
CDCl3): d 8.04 (d, JPt–P ¼ 3581.7 Hz, JPP ¼ 17.7 Hz), ꢀ4.06 (d,
Table 5 Crystallographic Information for compounds 8–12
8
9
10
11
12
Formula
Formula weight
T (K)
C
87H69Cl5N6P4Ru2
C48H43Cl2N3P2Ru
895.76
150
C39H30Cl5N3P2Pd
887.25
150
C39H30Cl5N3P2Pt
974.94
150
C39H30Au2Cl5N3P2
1173.78
150
1701.75
150
Crystal system
Space group
Triclinic
P1
Triclinic
P1
Monoclinic
P21/c
13.3510(4)
11.0729(2)
25.9296(6)
90
95.690(2)
90
3814.38(17)
4
Orthorhombic
P212121
10.2544(3)
12.3816(4)
28.9853(11)
90
90
90
3680.1(2)
4
1.76
Monoclinic
P21/c
12.7791(5)
14.3916(6)
20.6657(8)
90
95.247(4)
90
3784.7(3)
4
ꢀ
ꢀ
˚
a, A
13.7636(3)
14.7629(4)
22.1839(5)
76.1417(19)
85.9054(18)
85.3961(19)
4355.90(17)
2
12.7908(7)
15.2107(10)
15.2959(10)
114.525(6)
103.851(5)
102.567(5)
2453.6(3)
2
˚
b, A
˚
c, A
a, deg
b, deg
g, deg
3
˚
V, A
Z
rcalcg/cm3
1.297
0.619
1732
1.212
0.526
920
1.545
0.954
1784
2.06
8.216
2232
M (MoKa)/mmꢀ1
F(000)
4.297
1912
Crystal size (mm3)
Theta range (deg)
Reections collected
0.123 ꢂ 0.102 ꢂ 0.065 0.176 ꢂ 0.153 ꢂ 0.098 0.222 ꢂ 0.091 ꢂ 0.05 0.175 ꢂ 0.157 ꢂ 0.072 0.17 ꢂ 0.07 ꢂ 0.05
4.17 to 50
83 601
3.174 to 49.994
47 691
8624
4.178 to 49.994
36 825
6721
3.29 to 49.994
24 542
6484
4.272 to 50
30 848
6649
Independent reections 15 315
S
R1
wR2
1.054
0.0582
0.1493
1.037
0.084
0.2392
1.053
0.0406
0.0835
1.109
0.0562
0.134
1.025
0.0269
0.065
a
b
a
2
2
R ¼ S||Fo| ꢀ |Fc||/S|Fo|. b wR2 ¼ [Sw(Fo ꢀ Fc2)2/Sw(Fo2)2]1/2 w ¼ 1/[s2(Fo2) + (xP)2] where P ¼ (Fo + 2Fc2)/3.
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C, 39.37; H, 2.31; N, 3.65%. 1H NMR: (400 MHz, CDCl3): d 7.80–
7.63 (m, 5H), 7.61–7.45 (m, 13H), 7.25 (d, J ¼ 6.2 Hz, 3H), 7.23–
7.16 (m, 2H), 7.10 (t, J ¼ 7.4 Hz, 1H), 7.00 (ddd, J ¼ 19.3, 11.2,
6.2 Hz, 4H), 6.58 (dd, J ¼ 7.6, 4.7 Hz, 1H). 31P{1H} NMR (202
MHz, CDCl3): d 24.49 (s), 12.18 (s). HRMS (ES): m/z Calcd. for
Table 6 Selected bond distances (A˚) and angels (ꢁ) for compounds 4–
7
4 (M ¼ W)
5 (M ¼ Mo)
6 (M ¼ W)
7 (M ¼ W)
Bond distances
P1–C2
P2–C7
P1–M
P2–M
M–CAvg
N1–N2
N2–N3
C39–O1
C40–O2
M–N2
C
38H29Au2ClN3P2 ([M ꢀ Cl]+): 1018.0851; found: 1018.0853.
1.840(4)
1.824(4)
2.5156(11)
—
2.002(5)
1.369(5)
1.313(5)
1.161(6)
1.156(6)
2.242(3)
—
1.846(3)
1.834(3)
2.5335(9)
2.5245(9)
2.017(4)
1.353(4)
1.303(4)
1.149(5)
1.147(4)
—
1.844(5)
1.828(5)
2.5263(13)
2.5131(13)
2.018(6)
1.354(5)
1.311(6)
1.157(7)
1.146(6)
—
1.854(6)
1.827(6)
2.5080(15)
—
2.009(6)
1.360(6)
1.312(6)
1.141(7)
1.157(7)
2.244(5)
2.2134(15)
2.2893(15)
General procedure for tandem Cu-free Sonagashira
alkynylation/cyclization reaction
The reactions were performed in a closed vessel containing
a mixture of alkyne (1.2 equiv.), substituted 2-iodophenol (1.0
equiv), Cs2CO3 (1.5 equiv) and catalyst 10 (1 mol%) in DMSO (3
mL). The reaction mixture was heated at 80 ꢁC for 6 h. The
solution was diluted with H2O (10 mL) extracted twice with ethyl
acetate (10 mL). The combined organic fractions were dried over
Na2SO4 and the solvent was evaporated under reduced pressure.
The crude product obtained was puried by silica gel column
chromatography using petroleum ether/ethyl acetate.
P2–Au
Au–Cl
—
—
—
—
—
Bond angles
P1–M–P2
P1–M–N2
—
87.76(3)
—
92.21(10)
92.06(10)
—
174.34(11)
—
178.17(10)
174.19(14)
107.4(3)
—
87.81(4)
—
92.27(16)
92.27(16)
—
173.87(15)
—
178.09(14)
174.8(2)
107.2(4)
—
—
75.10(9)
97.74(15)
—
96.93(18)
171.68(15)
172.32(16)
—
173.32(17)
107.3(3)
—
76.14(9)
97.74(15)
—
96.93(18)
166.05(17)
176.10(19)
—
168.8(2)
108.6(4)
175.86(5)
P1–M–C40
P2–M–C39
N2–M–C39
P1–M–C39
N2–M–C40
P2–M–C40
C41–M–C42
N1–N2–N3
P2–Au–Cl
X-ray crystallography
Single crystal X-ray data collection was performed at 100–150 K
using a Rigaku Saturn724 diffractometer (Enhance Mo-Ka X-ray
˚
source, l ¼ 0.71073 A) with a graphite monochromater for
compounds 2 and 4–12 with the u-scan technique. Crystal data
and the details of the structure determination of 2 and 4–12 are
given in Tables 4 and 5, whereas the selected bond parameters
are listed in Tables 6 and 7. The data were reduced using Cry-
salisPro Red 171.38.43 soware. The structures were solved by
Olex2 (ref. 29) with the ShelXT30 structure solution program
using intrinsic phasing and rened with the ShelXL31 rene-
ment package using least squares minimization. All non-
hydrogen atoms were rened anisotropically. Hydrogen atoms
were placed in calculated positions and included as riding
contributions with isotropic displacement parameters tied to
those of the attached non-hydrogen atoms. In compounds 4, 8
and 9 the disordered solvent molecules could not be identied
or modelled to a known solvent hence it was SQUEEZED using
PLATON.32 Crystallographic data for the structures reported in
this paper have been deposited with the Cambridge Crystallo-
graphic Data Centre as supplementary publication no. CCDC
1832214 (compound 2) and CCDC 1832216–1832224
(compounds 4–12).
0.051 mmol) in the same solvent (6 mL) and stirred for 4 h at
room temperature. The solvent was removed under reduced
pressure and the residue obtained was washed dissolved in
a mixture of petroleum ether (5 mL) and chloroform (1 mL) and
stored at room temperature for 24 h to give 12 as a colourless
crystalline solid. Yield: 68% (0.041 g). Mp: >275 ꢁC. Anal. calcd
for C38H29Au2Cl2N3P2$CHCl3: C, 39.91; H, 2.58; N, 3.58. Found
Table 7 Selected bond distances (A˚) and angels (ꢁ) for compounds 8–
12
8 (M ¼ Ru)
Bond distances
9 (M ¼ Ru)
10 (M ¼ Pd)
11 (M ¼ Pt)
P1–M
P2–M
N2–M
M–Cl1
M–Cl2
M–Cavg
P1–C2
P2–C7
N3/H34
2.2851(13)
2.2902(13)
—
2.3060(19)
—
2.136(6)
2.4074(19)
2.2606(9)
2.2549(9)
—
2.3243(9)
2.3507(9)
—
1.835(3)
1.818(3)
—
2.249(4)
2.241(4)
—
2.336(4)
2.352(4)
—
1.834(17)
1.853(19)
—
2.4245(12)
Conflicts of interest
2.2066
1.835(5)
1.827(4)
2.505
2.237
1.825(8)
1.838(8)
—
There are no conicts to declare.
Acknowledgements
We are grateful to the Science & Engineering Research Board,
New Delhi, India, for nancial support of this work through
grant No. SB/S1/IC-08/2014. LR and MKP thank UGC, New Delhi
for the fellowship. We also thank the Department of Chemistry
Instrumentation Facilities, IIT Bombay, for spectral and
analytical data. We thank Dr Debasish Sengupta for verifying
some catalytic data.
Bond angels
P1–M–P2
P1–M–N2
P1–M–Cl1
P1–M–Cl2
P2–M–Cl1
P2–M–Cl2
P1–M–P2
91.86(5)
—
88.72(4)
—
93.59(4)
—
91.86(5)
—
94.72(3)
—
94.11(16)
—
80.42(16)
89.85(7)
—
—
—
—
93.56(3)
168.66(3)
167.96(4)
88.64(3)
94.72(3)
89.09(16)
174.15(16)
171.60(16)
90.92(16)
94.11(16)
25716 | RSC Adv., 2018, 8, 25704–25718
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