Synthesis, Structure, and Coordination Chemistry of Phosphine-Functionalized Imidazole/Imidazolium Salts and Cleavage of a C-P Bond in an NHC-Phosphenium Salt using a Pd(0) Precursor

Article abstract of DOI:10.1021/acs.organomet.5b00336

A simple method involving metal-halogen exchange reaction(s) to prepare various phosphine-functionalized imidazole/imidazolium salts and their coordination chemistry with different metal precursors has been described. Interestingly, the reaction of 1,3-dimethyl-2-(diphenylphosphino)-4-iodoimidazolium iodide (6) with Pd₂(dba)₃ in the presence of triphenylphosphine affords a Pd(II)-NHC complex which involves the cleavage of a C-P bond presumably occurring via oxidative addition of Pd(0) to a C-I bond to afford an in situ generated Pd(II) species, which subsequently reacts with another 1 equiv of 6 through the phosphine center to form an adduct followed by a dephosphinylation reaction. (Chemical Equation Presented).

Full text of DOI:10.1021/acs.organomet.5b00336

Article
pubs.acs.org/Organometallics
Synthesis, Structure, and Coordination Chemistry of Phosphine-
Functionalized Imidazole/Imidazolium Salts and Cleavage of a C−P
Bond in an NHC−Phosphenium Salt using a Pd(0) Precursor
Vedhagiri Karthik, Vivek Gupta, and Ganapathi Anantharaman*
Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, India
*
S Supporting Information
ABSTRACT: A simple method involving metal−halogen
exchange reaction(s) to prepare various phosphine-function-
alized imidazole/imidazolium salts and their coordination
chemistry with different metal precursors has been described.
Interestingly, the reaction of 1,3-dimethyl-2-(diphenylphosphi-
no)-4-iodoimidazolium iodide (6) with Pd (dba)3 in the
2
presence of triphenylphosphine affords a Pd(II)−NHC
complex which involves the cleavage of a C−P bond
presumably occurring via oxidative addition of Pd(0) to a
C−I bond to afford an in situ generated Pd(II) species, which
subsequently reacts with another 1 equiv of 6 through the phosphine center to form an adduct followed by a dephosphinylation
reaction.
INTRODUCTION
zole (1) and 1,3-dimethyl-4,5-diiodoimidazolium iodide (5)
using chlorodiphenylphosphine as the source of the electrophile
to afford a phosphine-functionalized imidazole/imidazolium
salt at the backbone position for the former case and at the 2-
position for the latter. The coordination chemistry of the
aforementioned phosphines (3, 4, and 6) with various metal
precursors and, in addition, a rare example of C−P bond
cleavage in an NHC−phosphenium salt using a Pd(0)
precursor to afford a palladium(II)−carbene complex are
discussed.
■
Phosphines and N-heterocyclic carbenes (NHCs) have played a
pivotal role in the development of organometallic chemistry,
and stitching these two classes of neutral, two-electron σ-donor
ligands together would further foster their application as ligands
for transition metals which may prove valuable in catalysis. In
view of this, several approaches to append a phosphine group
1
,2
to the NHC skeleton have been made and metalation via
both functionalities was successfully achieved.3 A detailed
2
account of this subject has appeared recently. Phosphines
attached to the imidazolium (NCN) carbon center are better
described as NHC−phosphenium adducts and act as poor
donors toward transition metals. The dative and labile nature of
the C−P bond is echoed in their reactivity toward weak
nucleophiles such as chloride ion, which results in heterolytic
cleavage of the C−P bond in such systems to give
chlorodiphenylphosphine and free NHC which, although not
isolated, has been successfully trapped by Chauvin and co-
RESULTS AND DISCUSSION
■
Synthesis and General Characterization of Function-
alized Imidazole/Imidazolium Salts and Their Metal
Complexes. The phosphine-functionalized imidazole(s) 2 and
3
were synthesized starting from 1 using sequential metal−
halogen exchange reactions. The synthesis of 2 was previously
described, and compound 3 was synthesized by subjecting 2
8b
4
workers. A similar reactivity pattern was observed in the
to another metal−halogen exchange reaction followed by
addition of chlorodiphenylphosphine. Compound 3, isolated as
a colorless solid, is stable to air and moisture and show two
coordination sphere of metal complexes (Pd, Rh, Cu, etc.) to
4
,5
afford metal−NHC complexes. Also, cleavage of a C−P bond
in NHC−phosphenium salts with an electron-rich metal center
such as Pt(0) was reported by Baker and co-workers involving a
nonoxidative addition pathway.
Metal−halogen exchange reactions with diiodoimidazole are
31
doublets at −36.2 and −29.3 ppm in its P NMR spectrum.
Compound 3 on methylation with trimethyloxonium tetra-
fluoroborate in dichloromethane gave the corresponding
imidazolium salt 4 in moderate yield (Scheme 1). The
imidazolium salt 4, with triflate as counteranion, was previously
reported by Ruiz and Mesa with a different procedure involving
6
7
particularly handy to achieve functionalization at the backbone
position(s) of imidazole and imidazolium salts with mild
reagents and conditions. We have recently reported backbone-
functionalized imidazolium salts which act as precursors for
synthesizing the metal complexes of both normal and
2c
the intermediacy of free carbenes. On the other hand, metal−
8
mesoionic carbenes. In this contribution, we report metal−
Received: April 23, 2015
halogen exchange reaction(s) with 1-methyl-4,5-diiodoimida-
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.5b00336
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Article
Scheme 1. Synthesis of Phosphine-Functionalized
Imidazole/Imidazolium Salts
of 3.060(3) and 3.032(1) Å in two crystallographically
independent Au−phosphine complexes in the asymmetric unit.
Reaction of 3 with tetrakis(acetonitrile)copper(I) tetrafluor-
oborate in a 2/1 ratio in dichloromethane afforded the
homoleptic complex 11, in which copper adopts a highly
distorted tetrahedral geometry due to the smaller bite angle of
a
3
. The 31P NMR of 11 shows two broad signals at −15.4 and
−
19.9 ppm, indicating the nonequivalence of two phosphorus
centers. Additionally, the molecular ion peak at m/z 963.2128
−
+
(
M − BF ) in the ESI-MS spectrum indicates the stability of
4
11 in the solution state.
a
i
Reagents and conditions: (a) PrMgCl, LiCl, THF; (b) PPh Cl; (c)
2
The coordinating properties of 4 are only marginally different
(
CH ) O(BF ), DCM; (d) CH I, CH CN, reflux; (e) PhSSO Ph in
3 3 4 3 3 2
in comparison to 3, and noteworthy and confounding is the
nonreactivity of 4 toward nickel chloride or palladium chloride
under experimental conditions similar to those used for the
synthesis of 8 or 9. The ligand 4 is the phosphine analogue of
the “Y”-shaped tris(imidazolium) salt reported by Peris and co-
workers which afforded homo- and heterodimetallic complexes
THF.
halogen exchange reaction with 5, followed by quenching with
electrophile, resulted in the formation of 2-substitued
imidazolium salts 6 and 7, which could be purified by
crystallization with methanol. The reaction is envisaged to
occur via migration of initially formed carbanion at a backbone
center to a more stable NCN carbon center. The products were
thoroughly characterized, and their identities were unambigu-
ously established by single-crystal X-ray crystallography
11
with different coordination environments. Reaction of 4 with
cuprous chloride in a 1/1 metal to ligand ratio afforded two
products, 12 and 13, in which 13 is the major product; both the
complexes were thoroughly characterized (Scheme 3).
Complex 12 shows a broad signal centered at −27.4 ppm in
(
Figures S1 and S2 in the Supporting Information). The C−
31
its P NMR spectrum, and all 12 methyl protons appear as a
P bond distance (1.857(8) Å) in 6 is within the range of those
1
9
,5c
singlet in its H NMR spectrum. The molecular structure of 12
observed for similarly known compounds, and crystals of 7
contain a triiodide counteranion plausibly obtained by aerial
oxidation of iodide ion during crystallization.
consists of a four-membered chloro-bridged dicopper structure
with a Cu···Cu bond distance of 2.916(1) Å, and the dihedral
angle between the two CuCl planes in Cu Cl is 25.54(5)°
2
2
2
The coordination chemistry of 3 was explored with different
metal precursors preferring different coordination geometries,
and all of the complexes were structurally characterized
(
Figure 2 and Table 2). The bite angle (P−Cu−P) indicates
severe distortion from a regular tetrahedral geometry, and the
values are comparable to those of DHP (deer-head phosphine,
o-phenylenebis(diisopropylphosphine), with a bite angle of
(Scheme 2 and Figure 1). Complexes 8 and 9 (Figure S3 in
12
9
2.44(3)°) and 12 crystallizes with one CuCl unit and a BF
a
2 4
Scheme 2. Various Binding Modes of 3 with Metals
anion. However, the other product 13 was a homoleptic
complex similar to 11 with bite angles of 93.26(5)° (P(1)−
Cu−P(2)) and 93.38(5)° (P(3)−Cu−P(4)) and was charac-
3
1
terized by a single broad peak at −15.2 ppm in its P NMR
spectrum.
Interestingly, reaction of 4 with tetrakis(acetonitrile)copper-
(
I) tetrafluoroborate in a 1/1 ratio in dichloromethane afforded
complex 14, in which copper is bound to only one bis-
phosphine ligand and the other two coordinating sites are
occupied by acetonitrile molecules. The coordinated acetoni-
trile molecules are labile and can be substituted by nitrogen-
containing linkers to afford discrete systems or coordination
polymers. When complex 14 was treated with 2 equiv of linear
linker 4,4′-bipyridine (4,4′-bpy), a discrete Cu tetramer (15)
4
was obtained, which was structurally characterized (Figure 3
and Table 3). The asymmetric unit of complex 15 consists of a
dinuclear copper complex with two types of Cu centers
separated by a distance of 11.088(2) Å, and the tetramer is
related by inversion symmetry. The four coordination sites are
fulfilled by a bis-phosphine unit and two nitrogen atoms from
two different 4,4′-bpy units in Cu(2) (crystallographic
numbering), while Cu(1) is bound to two nitrogen donor
ligands, namely 4,4′-bpy and acetonitrile molecule, in addition
to the bis-phosphine ligand 4.
a
Reagents and conditions: (a) NiCl ·6H O, EtOH + DCM; (b)
2
2
PdCl , CH CN + DCM; (c) AuCl, DCM; (d) [Cu(CH CN) ]BF ,
DCM.
2
3
3
4
4
the Supporting Information) are isostructural, with the central
metal atom in a square-planar disposition and the five-
membered metallacycle almost coplanar to the imidazole ring
with the dihedral angles of 5.337(10) and 5.351(9)°,
respectively. The bite angles in 8 and 9 were found to be
C−P Bond Cleavage. Baker and co-workers observed the
cleavage of a C−P bond when a NHC−phosphenium adduct
was treated with Pt(PPh ) to afford a three-coordinate
9
0.4 and 88.9°, respectively (Table 1), and the values are
10
comparable to those of diphenylphosphinopropane (dppp).
3
3
The molecular structure of digold complex 10 shows almost
two linear P−Au−Cl bonds which are skewed to show
intramolecular aurophilic interactions with a Au···Au distances
platinum phosphenium complex via a nonoxidative addition
6
pathway, plausibly with the intermediacy of a NHC−
4b
diaminophosphenium−platinum complex.
B
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Article
Figure 1. ORTEP diagrams showing 30% probability thermal ellipsoids and selected atom labels for complexes 8 (left), 10 (middle), and 11 (right).
Hydrogen atoms, counteranions, and solvent(s) of crystallization have been omitted for clarity.
Table 1. Selected Bond Lengths (Å) and Angles (deg) in Complexes 8−11
8
9
10
11
N1−C1
N2−C1
C2−C3
N(1)−C(1)−N(2)
P(1)−Ni−P(2)
1.335(5)
1.328(5)
1.347(5)
113.7(3)
90.38(4)
N1−C1
N2−C1
C2−C3
N(1)−C(1)−N(2)
P(1)−Pd−P(2)
1.364(4)
1.329(4)
1.375(5)
113.0(3)
88.89(3)
N1−C1
N2−C1
C2−C3
N(1)−C(1)−N(2)
P(1)−Au(1)−Cl(1)
P(2)−Au(2)−Cl(2)
1.347(13)
1.314(14)
1.364(15)
114.5(10)
175.45(11)
172.28(11)
N1−C1
N2−C1
C2−C3
N(1)−C(1)−N(2)
P(1)−Cu(1)−P(2)
P(3)−Cu(1)−P(4)
1.367(11)
1.306(12)
1.382(11)
112.3(7)
93.29(8)
93.20(7)
a
Scheme 3. Coordination Chemistry of Phosphine-Functionalized Imidazolium Salt 4
a
Reagents and conditions: (a) CuCl, THF; (b) [Cu(CH CN) ] BF , DCM; (c) 4,4′−bipyridine, CH CN.
3
4
4
3
1
4
On the other hand when the NHC−phosphenium iodide 6
was treated with tris(dibenzylideneacetone)dipalladium(0) in
the presence of 2 equiv of triphenylphosphine, the palladium−
NHC complex 16 was isolated (Scheme 4). In the solid-state
structure of 16 (Figure 4), palladium adopts a square-planar
Albrecht, and it is comparable to those of IMe ([Ir(IMe)-
−1
15
(CO) Cl]; TEP 2051 cm ).
2
The reaction was envisaged to occur via an initial oxidative
16
II
addition of Pd(0) to the C−I bond to afford a Pd −MIC
species (A) (MIC = mesoionic carbene) as an intermediate,
which subsequently reacts with another 1 equiv of 6 to form an
adduct (B). The proposed intermediates could not be isolated,
although an ion peak corresponding to A (m/z 1037.1063) was
observed in the crude reaction mixture through ESI-MS
recorded in positive mode (Supporting Information). In the
presence of water, the Pd−MIC bond in adduct B cleaves to
afford the imidazolium salt 17, and the concomitant
nucleophilic attack of hydroxide ion on any one of the possible
geometry with a Pd−C
bond length of 1.996(13) Å, which
carbene
13
is in the range of those reported in the literature. The two
triphenylphosphine groups coordinated to palladium are trans
to each other, consistent with the single sharp peak observed in
their 31P NMR spectrum.
The donor ability of this NHC ((I)IMe) on the basis of δ(P)
−1
−1
was calculated (TEP 2051 cm (CD Cl ) and 2052 cm
2
2
(
DMSO-d )) using the TEP equation proposed by Iglesias and
6
C
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Article
Figure 2. ORTEP diagrams showing 30% probability thermal ellipsoids and selected atom labels for complexes 12 (left), 13 (middle), and 14
right). Hydrogen atoms, counteranions, and solvent(s) of crystallization have been omitted for clarity.
(
Table 2. Selected Bond Lengths and Angles in Complexes 12 and 13
1
2
13
bond length (Å)
bond angle (deg)
bond length (Å)
bond angle (deg)
C(2)−C(3)
1.374(6)
P(1)−Cu(1)−P(2)
92.99(5)
93.51(5)
77.31(5)
76.94(4)
100.98(5)
100.09(5)
C2−C3
1.360(6)
N(1)−C(1)−N(2)
109.8(5)
110.4(5)
93.26(5)
93.38(5)
124.72(5)
123.05(5)
Cu(1)−P(1)
Cu(1)−P(2)
Cu(1)−Cl(1)
Cu(1)−Cl(2)
Cu···Cu
2.2705(14)
2.2691(14)
2.3217(14)
2.3414(14)
2.9164(10)
P(3)−Cu(1)−P(4)
Cu(1)−Cl(1)−Cu(2)
Cu(1)−Cl(2)−Cu(2)
Cl(1)−Cu(1)−Cl(2)
Cl(2)−Cu(2)−Cl(1)
C31−C32
Cu−P(1)
Cu−P(2)
Cu−P(3)
Cu−P(4)
1.344(7)
N(3)−C(30)−N(4)
P(1)−Cu−P(2)
P(3)−Cu−P(4)
P(1)−Cu−P(3)
P(2)−Cu−P(4)
2.2740(14)
2.2773(13)
2.2721(14)
2.2690(15)
a
Scheme 4. Formation of Pd−NHC Complex 16
Figure 3. ORTEP diagram showing 30% probability thermal ellipsoids
and selected atom labels for complex 15. Hydrogen atoms,
counteranion, and solvent(s) of crystallization have been omitted for
clarity.
4a
centers (P/Ccarbene/Pd) in B led to the cleavage of a C−P
bond to afford the Pd−NHC complex 16.
a
Reagents and conditions: (a) Pd (dba) , PPh , DCM; (b) H O.
The formation of 17 was supported by ESI-MS (m/z
2
3
3
2
3
1
3
1
Legend: (‡) values in parentheses correspond to P NMR δ values in
ppm recorded in CD Cl .
2
81.1201), and a signal at −25.1 ppm in the P NMR
2
2
spectrum compares well with that of 6 and similarly known
Table 3. Selected Bond Lengths and Angles in Complexes 14 and 15
1
4
15
bond length (Å)
bond angle (deg)
bond length (Å)
bond angle (deg)
N(1)−C(1)
1.322(4)
1.361(7)
2.2738(9)
1.957(4)
2.006(4)
N(1)−C1−N(1)#
P(1)−Cu−P(1)#
N(2)−Cu−N(3)
N(3)−Cu−P(1)
C(2)−P(1)−Cu(1)
110.5(4)
C2−C3
1.361(6)
N(1)−C(1)−N(2)
110.6(4)
C2−C2#
Cu−P(1)
Cu−N(2)
Cu−N(3)
94.11(5)
Cu(1)−P(1)
Cu(1)−P(2)
Cu(1)−N(3)
Cu(1)−N(4)
2.2981(13)
2.2663(13)
1.984(4)
P(1)−Cu(1)−P(2)
N(3)−Cu(1)−N(4)
N(4)−Cu(1)−P(1)
N(3)−Cu(1)−P(2)
93.87(4)
112.78(15)
103.40(7)
99.94(11)
115.09(15)
100.88(11)
115.04(11)
2.055(3)
D
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glovebox. All other reagents were used as received; isopropylmagne-
sium chloride was freshly prepared before use.
Synthesis of 3. To a stirred suspension of 2 (3.24 g, 8.26 mmol)
and lithium chloride (0.39 g, 9.1 mmol) in dry THF (25 mL) was
added a solution of freshly prepared isopropylmagnesium chloride (9.1
mmol) in THF (7 mL) at −20 °C, and after the cold bath was
removed, the reaction mixture was stirred for 1.5 h followed by
addition of chlorodiphenylphosphine (1.48 mL, 8.26 mmol) at −20
°
C. The reaction mixture was further stirred for 3 h, and then all the
volatiles were removed under vacuum. The residue was dissolved in
DCM, a half-saturated aqueous ammonium chloride solution (40 mL)
was added to this solution, the mixture was stirred for a few minutes,
and then the layers were separated. The aqueous layer was extracted
with DCM (4 × 30 mL), and the combined organic layers were dried
over anhydrous MgSO and filtered. The filtrate was concentrated to
4
dryness to give an off-white solid. The compound was purified by
performing column chromatography (silica gel, 100−200 mesh, eluted
using a solvent mixture of 30% ethyl acetate in hexane). Yield: 1.9 g
(51%). Mp: 126−130 °C. Anal. Calcd for C H N P : C, 74.66; H,
Figure 4. ORTEP diagram showing 30% probability thermal ellipsoids
and selected atom labels for complex 16. Hydrogen atoms,
counteranion (I ), and solvent of crystallization (dichloromethane)
2
8
24
2 2
1
5.37; N, 6.22. Found: C, 74.38; H, 5.50; N, 6.11. H NMR (CDCl
3
,
−
500 MHz; δ, ppm): 3.19 (s, 3H, N-CH ), 7.26−7.43 (m, 20H, C H ),
3
6
5
7.74 (s, 1H, NCHN). 13C NMR (CDCl , 100 MHz; δ, ppm): 34.1,
have been omitted for clarity. Selected bond lengths (Å) and angles
3
(
deg): N1−C1 = 1.369(15), N2−C1 = 1.321(16), C2−C3 = 1.33(2),
128.2, 128.3, 128.5, 128.7, 132.0, 132.2, 133.6, 133.8, 134.6, 138.1,
144.7. 31P NMR (CDCl 202.49 MHz; δ, ppm): −36.2 (d), −29.3 (d).
Pd−C1 = 1.996(13), Pd−I2 = 2.6345(11), Pd−P1 = 2.3433(17); N1−
C1−N2 = 105.8(11), C1−Pd−I2 = 170.8(4).
3,
−1
IR (KBr, cm ): 3047 (w, br), 1582 (w), 1479 (m), 1431 (m), 1347
(
9
(
w), 1318 (w), 1268 (w), 1235 (w), 1194 (m), 1092 (w), 998 (w),
65 (w), 910 (w), 860 (w), 751 (s), 739 (vs), 696 (vs), 543 (m), 525
w), 510 (w), 495 (m), 458 (m), 438 (w). ESI-MS: 451.1493 (M +
9
,17
+ +
H ) .
Synthesis of 4. To a stirred solution of 3 (0.98 g, 2.18 mmol) in
compounds.
In addition, diphenylphosphinic acid, which
could be identified from the crude product mixture using mass
+
dry DCM was added trimethyloxonium tetrafluoroborate (0.32 g, 2.18
mmol) at room temperature, and the mixture was stirred for 16 h.
After that, all the volatiles were removed under vacuum to afford a
white flaky solid, which was purified by column chromatography (silica
gel 100−200 mesh, eluted using a solvent mixture of 5% methanol in
DCM) to afford the title compound as a white solid. Yield: 0.78 g
(65%). Mp: 132−138 °C. Anal. Calcd for C H BF N P : C, 63.07;
spectrometry (m/z 219.0594 (M + H) (Figure S5 in the
3
1
Supporting Information) and P NMR (δ 28.7 ppm (CD Cl ),
2
2
δ 28.1 ppm (DMSO-d )), and palladium black were also
6
observed. When a similar reaction was attempted with
imidazolium salt 7, no addition product was detected,
indicating the crucial role of the iodide counteranion. The
scope of this method to generate a metal−NHC complex with
other low-valent metals and detailed mechanistic aspects of the
reaction are currently being studied in our laboratory.
2
9
27
4
2 2
1
H, 4.93; N, 5.07. Found: C, 62.80; H, 4.74; N, 5.17. H NMR (CDCl ,
3
4
9
1
00 MHz; δ, ppm): 3.39 (s, 6H, N-CH ), 7.28−7.35 (m, 20 H, PPh ),
3
2
.19 (s, 1H, NCHN). 13C NMR (CDCl , 100 MHz; δ, ppm): 36.7,
3
31
29.4, 129.8, 131.0, 132.1, 132.2, 132.3, 145.1. P NMR (CDCl 162
3
,
−1
MHz; δ, ppm): −29.8. IR (KBr, cm ): 3439 (w, br), 3160 (w), 3053
CONCLUSIONS
■
(w), 2923 (w), 1571 (w), 1481 (w), 1435 (s), 1284 (w), 1203 (w),
In summary, we have described the synthesis of various
phosphine-functionalized imidazole/imidazolium salts using
metal−halogen exchange reactions and their coordination
chemistry with different metal precursors. Reaction of 4 with
various copper(I) precursors afforded different mono- and
dinuclear copper complexes (12−14), and reaction of 14 in the
presence of a linker such as 4,4′-bpy gave the interesting
tetranuclear complex 15. In addition the first example of C−P
bond cleavage in an NHC−phosphenium salt (6) using a Pd(0)
precursor to afford a Pd−NHC complex (16) is reported.
1
059 (vs), 849 (w), 795 (w), 743 (vs), 696 (vs), 616 (w), 560 (w),
5
17 (w), 499 (w), 477 (w), 447 (w). ESI-MS: m/z 465.1646 (M −
4
−
+
BF ) .
Synthesis of 5. To a stirred solution of 1 (0.67 g, 2 mmol) in dry
acetonitrile (20 mL) was added methyl iodide (0.25 mL, 4 mmol)
dropwise at 0 °C. The solution was refluxed for 14 h, during which a
colorless precipitate was obtained. The reaction mixture was again
cooled to 0−5 °C for complete precipitation. The precipitate obtained
after filtration was washed with diethyl ether and dried under vacuum.
Yield: 0.90 g (95%). Mp: 230−232 °C dec. Anal. Calcd for C H I N :
5
7 3
2
1
C, 12.62; H, 1.48; N, 5.89. Found: C, 12.80, H, 1.50; N, 5.92. H
NMR (DMSO-d 500 MHz; δ, ppm): 3.78 (s, 6H, CH ), 9.38 (s, 1H,
6
3
EXPERIMENTAL SECTION
13
NCHN). C NMR (DMSO-d 125 MHz; δ, ppm): 39.4, 95.1, 141.2.
■
6
−1
General Procedures. All reactions were carried out under an inert
atmosphere of nitrogen using a standard Schlenk line technique, and
solvents were dried according to the standard literature procedures
IR (KBr, cm ): 3104 (w), 3017 (m), 2934 (w), 1641 (w), 1549 (s),
1501 (w), 1426 (m), 1202 (s), 1099 (s), 769 (w), 608 (w), 463 (w)
cm . ESI-MS: 348.8691 (M − I ) .
−1
− +
1
13
31
and freshly distilled prior to use. H, C, and P NMR spectra were
recorded on JEOL (400 and 500 MHz) spectrometers in CDCl3/
CD Cl /DMSO-d /CD CN as a solvent. The chemical shifts were
Synthesis of 6. To a stirred suspension of 5 (4.71 g, 9.9 mmol)
and lithium chloride (0.46 g, 10.9 mmol) in dry THF (50 mL) was
added a solution of isopropylmagnesium chloride (10.9 mmol) in
THF (9 mL) at −20 °C. The cold bath was removed, and the reaction
mixture was stirred further for 1 h 15 min, followed by addition of
chlorodiphenylphosphine (1.8 mL, 9.9 mmol) at −20 °C, and stirred
for another 4 h, after which all volatiles were removed under vacuum.
The residue was dissolved in DCM, and an aqueous half-saturated
ammonium chloride solution (40 mL) was added. The resulting
mixture was filtered through a frit containing a pad of Celite, and the
organic layer was dried over magnesium sulfate and filtered. The
2
2
6
3
1
31
referenced with respect to TMS and 85% H PO for H and P NMR,
respectively. The ESI mass spectra were recorded on a Waters QTOF
instrument. IR spectra were recorded in KBr pellets using an FTIR
spectrophotometer operating from 400 to 4000 cm . The melting
points reported are uncorrected. Phenyl benzenethiosulfonate and
tetrakis(acetonitrile)copper(I) tetrafluoroborate
according to the literature procedures, and the former was subjected
to azeotropic distillation twice in dry toluene and was stored in a
3
4
−1
1
8a
1
8b
were prepared
E
DOI: 10.1021/acs.organomet.5b00336
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
filtrate was concentrated to give a light brown oil, which was triturated
with diethyl ether to give a powdery yellow solid. The solid on washing
with cold methanol (three to four times) gave a white solid, which was
crystallized in methanol. Yield: 2.8 g (53% excluding crystallization
losses). Mp: 150−155 °C dec. Anal. Calcd for C H I N P: C, 38.23;
134.5, 134.7. 31P NMR (CD CN, 162 MHz; δ, ppm): 4.4 (d), 14.5
3
−
1
(d). IR (KBr, cm ): 3433 (br, w), 3094 (w), 3056 (w), 1586 (w),
1494 (w), 1481 (w), 1436 (s), 1357 (w), 1309 (w), 1252 (w), 1207
(w), 1184 (w), 1127 (w), 1101 (m), 1027 (w), 997 (w), 875 (w), 750
(s), 717 (s), 690 (vs), 634 (w), 619 (w), 578 (vs), 554 (m), 522 (w),
502 (s), 492 (s), 412 (w). ESI-MS: sample does not give a satisfactory
ESI-MS analysis.
1
7
17 2
2
1
H, 3.21; N, 5.24. Found: C, 38.27; H, 3.10; N, 5.28. H NMR
DMSO-d , 500 MHz; δ, ppm): 3.55 (s, 3H, N-CH ), 3.58 (s, 3H, N-
(
6
3
13
CH ), 7.41−7.53 (m, 10H, PPh ), 8.20 (s, 1H, NCHN). C NMR
Synthesis of Complex 11. To a dichloromethane solution of 3
(0.14 g, 0.32 mmol) was added tetrakis(acetonitrile)copper(I)
tetrafluoroborate (0.050 g, 0.16 mmol) as a solid, and the reaction
mixture was stirred for 3 h followed by filtration with a medium-
porosity frit to give a clear solution. The filtrate was concentrated to
dryness under vacuum to afford the title compound as a colorless solid.
Yield: 0.15 g (93%). Mp: >250 °C. Anal. Calcd for C H BCuF N P :
3
2
(
DMSO-d , 125 MHz; δ, ppm): 36.5, 37.8, 128.1, 129.9, 130.1, 131.6,
6
3
1
1
31.7, 132.5, 139.9. P NMR (DMSO-d6, 202.49 MHz; δ, ppm):
23.6. IR (KBr, cm ): 3049 (m), 1636 (w), 1546 (w), 1468 (m),
434 (s), 1310 (w), 1198 (m), 1090 (m), 918 (w), 819 (m), 744 (vs),
00 (s), 688 (vs), 668 (m), 627 (w), 536 (m), 506 (s), 455 (w), 433
m). ESI-MS: 407.0175 (M − I ) .
−
1
−
1
7
−
+
(
5
6
48
4
4 4
1
Synthesis of 7. The same procedure as for 6 was used. 5 (5.23 g,
C, 63.98; H, 4.60; N, 5.33. Found: C, 64.28; H, 4.57; N, 5.53. H
1
(
1.0 mmol), LiCl (0.51 g, 12.1 mmol), isopropylmagnesium chloride
12.1 mmol), and phenyl benzenethiosulfonate (11.0 mmol, 2.75 g) in
5 mL of THF were used. The product was crystallized in methanol as
NMR (CDCl , 500 MHz; δ, ppm): 3.05 (s, 6H, N-CH ), 6.98−7.30
3
3
13
(m, 42H, PPh , NCHN). C NMR (CDCl , 100 MHz; δ, ppm): 34.2,
2
3
1
128.8, 129.6, 129.8, 130.1, 130.5, 130.6, 130.8, 131.1, 132.2, 132.9,
149.5. 31P NMR (CDCl 202.49 MHz; δ, ppm): −15.4 (br), −19.9
brown crystals. Yield: 2.13 g (27%). Mp: 104−110 °C. Anal. Calcd for
C H I N S: C, 18.56; H, 1.70; N, 3.93. Found: C, 18.61; H, 1.59; N,
3,
−1
(br). IR (KBr, cm ): 3445 (w, br), 3054 (w), 1586 (w), 1482 (s),
1435 (s), 1330 (w), 1250 (w), 1210 (w), 1185 (w), 1055 (vs), 998
(m), 741 (s), 711 (m), 692 (vs), 558 (s), 528 (s), 511 (m), 498 (m),
1
1
12 4
2
1
3
7
.96. H NMR (DMSO-d , 500 MHz; δ, ppm): 3.80 (s, 6H, N-CH ),
.40 (br, 5H, SPh), 8.22 (s, 1H, NCHN). C NMR (DMSO-d , 125
6
3
13
6
−
+
MHz; δ, ppm): 37.2, 38.7, 126.1, 129.3, 129.7, 130.6, 130.9, 132.6,
479 (m). ESI-MS: m/z 963.2128 (M − BF ) .
4
−1
1
40.0. IR (KBr, cm ): 3145 (m), 1576 (w), 1543 (w), 1476 (s), 1439
Synthesis of Complexes 12 and 13. To a stirred solution of 4
(0.102 g, 0.185 mmol) in THF (30 mL) was added CuCl (0.018 g,
0.185 mmol) as a solid, and the mixture was stirred overnight (12 h),
during which a colorless solid precipitated out. The residue and the
filtrate were separated, the residue was washed once with THF, and
the washings were combined with the filtrate. Slow diffusion of diethyl
ether into an acetonitrile solution of the residue gave crystals of 12 in
low yield. The filtrate obtained as above was kept for crystallization by
slow evaporation, and colorless crystals of 13 were obtained in THF
after 3 days. Data for complex 12 are as follows. Yield: 6.3 mg (5%).
Mp: >250 °C. Anal. Calcd for C H BCl Cu F N P : C, 51.59; H,
(
(
m), 1427 (m), 1181 (w), 998 (w), 790 (w), 745 (vs), 695 (m), 686
m), 617 (w), 521 (w), 473 (w). ESI-MS: m/z 330.9766 (M − I ) .
−
+
3
Synthesis of Complex 8. To an ethanolic solution (10 mL) of
nickel chloride hexahydrate (0.053 g, 0.22 mmol) was added a
dichloromethane (20 mL) solution of 3 (0.10 g, 0.22 mmol).
Immediately an intensely red solution was formed, which was stirred
further for 1 h. The solution was filtered, and the filtrate was kept for
crystallization under slow evaporation to afford red crystals of 8
suitable for single-crystal X-ray diffraction. Yield: 0.084 g (65%). Mp:
>
250 °C. Anal. Calcd for C H Cl N NiP : C, 57.98; H, 4.17; N,
28 24 2 2 2
1
58 54
4
3
4
4 4
1
4
.83. Found: C, 57.60; H, 4.20; N, 4.81. H NMR (CD Cl , 400 MHz;
4.03; N, 4.15. Found: C, 51.82, H, 4.09; N, 4.16. H NMR (CD CN,
2
2
3
δ, ppm): 3.19 (s, 3H, N-CH ), 7.43−8.01 [m, 21H, 2(PPh ), NCHN].
500 MHz; δ, ppm): 3.23 (s, 12H, N-CH ), 7.44−7.53 (m, 40H, PPh ),
3
2
3
2
1
3
13
C NMR (CD Cl , 100 MHz; δ, ppm): 29.7, 128.6, 128.7, 129.3,
8.71 (s, 2H, NCHN). C NMR (CD CN, 125 MHz; δ, ppm): 36.5,
2
2
3
31
31
1
31.6, 132.2, 133.5, 133.6, 134.2. P NMR (CD Cl 162 MHz; δ,
ppm): 9.1 (d), 13.9 (d). IR (KBr, cm ): 3401 (m, br), 1623 (w),
127.3, 129.5, 131.0, 132.6, 146.7. P NMR (CD CN, 202.49 MHz; δ,
3
2
2,
−1
−1
ppm): −27.4. IR (KBr, cm ): 3451 (br, w), 3162 (w), 3054 (w), 2250
(w), 1562 (m), 1515 (w), 1483 (m), 1435 (s), 1373 (w), 1208 (w),
1099 (m), 1084 (s), 1059 (s), 916 (w), 855 (w), 791 (w), 748 (vs),
695 (vs), 612 (w), 539 (m), 517 (m), 500 (m), 475 (m). ESI-MS:
1
482 (m), 1434 (s), 1339 (w), 1256 (w), 1216 (m), 1187 (m), 1136
(
(
m), 1096 (s), 1028 (w), 998 (w), 855 (w), 760 (m), 746 (s), 710
vs), 691 (vs), 620 (w), 583 (vs), 531 (vs), 507 (s), 487 (s). ESI-MS:
m/z 575.0400 (M − Cl + CH OH) .
−
+
− +
1215.1224 [M − (CuCl
Yield: 0.10 g (86%). Mp: >250 °C. Anal. Calcd for
: C, 55.51; H, 4.34; N, 4.46. Found: C, 55.82;
H, 4.11; N, 4.20. H NMR (CD CN, 400 MHz; δ, ppm): 3.11 (s, 12H,
) ] . Data for complex 13 are as follows.
3
2
Synthesis of Complex 9. To a suspension of palladium chloride
(
0.021 g, 0.12 mmol) in acetonitrile (10 mL) was added a
C H B CuF12N P
58 54 3 4 4
1
dichlormethane solution (15 mL) of 3 (0.054 g, 0.12 mmol). The
resulting orange solution was stirred for 1 h and was filtered to give a
clear solution, which was kept for crystallization. Slow evaporation led
to the formation of yellow crystals suitable for single-crystal X-ray
diffraction. Yield: (0.060 g, 80%). Mp: >250 °C. Anal. Calcd for
C H Cl N P Pd: C, 53.57; H, 3.85; N, 4.46. Found: C, 53.87; H,
3
1
3
N-CH ), 7.18−7.41(m, 40H, PPh ), 8.99 (s, br, 2H, NCHN).
C
3
2
NMR (CD CN, 100 MHz; δ, ppm): 36.4, 129.8, 131.1, 131.2, 131.3,
131.4, 131.6. P NMR (CD CN, 162 MHz; δ, ppm): −15.2 (br). IR
(KBr, cm ): 3557 (w), 3613 (w), 3400 (m, br), 3145 (w), 3074 (w),
2959 (w), 2861 (w), 1634 (w), 1562 (m), 1482 (m), 1438 (s), 1285
(w), 1213 (m), 1055 (vs, br), 997 (s), 793 (w), 745 (s), 696 (s), 613
(w), 559 (w), 544 (m), 513 (m), 499 (m), 478 (m), 460 (m). ESI-MS:
3
31
3
−
1
2
8
24
2
2 2
1
3
.70; N, 4.55. H NMR (DMSO-d , 400 MHz; δ, ppm): 3.25(s, 3H,
N-CH ), 7.49−7.84 (m, 20 H, PPh ), 8.46 (s, 1H, NCHN). C NMR
DMSO-d , 100 MHz; δ, ppm): 34.5, 126.6, 129.4, 129.5, 130.0, 130.1,
6
13
3
2
−
3+
(
1
m/z 331.0806 [(M − 3BF ) /3].
6
4
3
1
32.6, 133.3, 133.9, 134.0, 134.2. P NMR (DMSO-d 162 MHz; δ,
Synthesis of Complex 14. The imidazolium salt 4 (0.20 g, 0.37
6,
−1
ppm): 18.1 (d), 22.4 (d). IR (KBr, cm ): 3441 (w, br), 1481 (m),
434 (vs), 1338 (w), 1257 (w), 1217 (m), 1187 (w), 1144 (w), 1097
vs), 997 (w), 983 (w), 857 (w), 761 (w), 746 (s), 711 (vs), 690 (vs),
21 (w), 587 (vs), 532 (vs), 507 (s), 465 (w). ESI-MS: m/z 632.0416
mmol) and [Cu(CH CN) ]BF (0.12 g, 0.37 mmol) were combined
3
4
4
1
(
6
(
in a Schlenk flask, and dichloromethane (20 mL) was added. The
reaction mixture was stirred for 3 h and then filtered under nitrogen
using a frit. The filtrate, obtained as a clear solution, was concentrated
to dryness to give the title compound as a colorless solid. The
compound was crystallized by layering an acetonitrile solution of 14
with diethyl ether at 0 °C. Yield: 0.27 g (94%). Mp: 202−207 °C dec.
Anal. Calcd for C H B CuF N P : C, 50.51; H, 4.24; N, 7.14.
−
+
M − Cl + CH CN) .
3
Synthesis of Complex 10. To a stirred solution of 3 (0.15 g, 0.33
mmol) in DCM was added AuCl (0.155 g, 0.66 mmol) as a solid, and
the reaction mixture was stirred for 3 h and filtered to give a clear
colorless solution. The filtrate was concentrated to dryness under
vacuum to afford the title compound as a colorless solid. Yield: 0.29 g
3
3
33
2
8
4 2
1
Found: C, 50.52; H, 4.22; N, 7.24. H NMR (CD Cl , 400 MHz; δ,
2
2
ppm): 2.12 [s, 6H, 2(CH CN)], 3.37 (s, 6H, N-CH ), 7.48−7.54 (m,
3
3
13
(
3
94%). Mp: 165−170 °C. Anal. Calcd for C H Au Cl N P : C,
20H, PPh ), 8.86 (s, 1H, NCHN). C NMR (CD Cl , 100 MHz; δ,
2
8
24
2
2
2
2
2
2
2
1
31
6.74; H, 2.64; N, 3.06. Found: C, 36.68; H, 2.59; N, 2.99. H NMR
ppm): 2.2, 36.8, 125.7, 130.1, 131.5, 131.9, 132.0, 132.1, 148.0.
P
−1
(
2
CD CN, 500 MHz; δ, ppm): 2.96 (s, 3H, N-CH ), 7.47−7.64 (m,
NMR (DMSO-d , 202.49 MHz; δ, ppm): −26.9. IR (KBr, cm ):
3443 (w, br), 3174 (w), 2964 (w), 2275 (w), 1631 (w), 1568 (w),
1483 (w), 1438 (w), 1262 (s), 1217 (w), 1094 (vs), 1031 (vs), 863
3
3
6
13
0H, PPh ), 7.86 (s, 1H, NCHN). C NMR (CD CN, 100 MHz; δ,
2
3
ppm): 35.4, 129.0, 129.1, 129.8, 130.0, 132.1, 132.6, 133.2, 133.3,
F
DOI: 10.1021/acs.organomet.5b00336
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(
w), 801 (vs), 745 (w), 695 (m), 613 (w), 559 (w), 500 (w), 481 (w).
ACKNOWLEDGMENTS
−
+
■
ESI-MS: m/z 656.1272 [M − (BF ) − CH CN] .
4
3
This work was supported by the Department of Science and
Technology (DST) and the Council of Scientific and Industrial
Research (CSIR), Government of India. V.K. and V.G. thank
the CSIR and University Grants Commission (UGC) for
fellowships.
Synthesis of Complex 15. To an acetonitrile solution of complex
4 (0.040 g, 0.05 mmol) was added 4,4′-bpy (0.016 g, 0.10 mmol) as a
1
solid, the mixture was stirred for 5 h, and a clear colorless solution was
obtained. The reaction mixture was concentrated to one-third of its
volume and filtered, and the filtrate was layered with diethyl ether and
kept at 0 °C. Pale yellow crystals were obtained after 1 week, which
were collected, washed with diethyl ether, and dried under vacuum.
Yield: 0.036 g (84%). Mp: 140−145 °C. Anal. Calcd for
REFERENCES
■
2
C
H B Cu F N P : C, 53.72; H, 4.21; N, 6.64. Found: C,
3.98; H, 4.30; N, 7.02. IR (KBr, cm ): 3439 (w, br), 3057 (w), 1605
1
51 141 8 4 32 16 8
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−1
5
(
m), 1564 (w), 1532 (w), 1484 (w), 1437 (m), 1411 (w), 1285 (w),
1
5
218 (w), 1057 (vs), 914 (w), 809 (m), 747 (m), 697(m), 620 (w),
42 (w), 478 (w).
2
2
010, 75, 7141−7145. (c) Edwards, P. G.; Hahn, F. E. Dalton Trans.
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́
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2
3
3
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6
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(
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g, 0.20 mmol) in dichloromethane through a cannula; the reaction
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filtrate was washed with water (4 × 30 mL), and the organic layer was
dried over anhydrous magnesium sulfate and filtered. The filtrate was
concentrated to dryness and washed with pentane to afford the title
compound as a yellow solid. Slow evaporation of a dichloromethane
solution of 16 afforded single crystals suitable for X-ray diffraction.
Yield: 0.105 g (47% with respect to Pd (dba) ). Mp: 90−95 °C dec.
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(
2
g) Consorti, C. S.; Aydos, G. L. P.; Ebeling, G.; Dupont, J. Org. Lett.
008, 10, 237−240. (h) Dumrath, A.; Wu, X.; Neumann, H.;
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4
9, 8988−8992. (i) Azouri, M.; Andrieu, J.; Picquet, M.; Cattey, H.
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7
1
265. (k) Majhi, P. K.; Streubel, R. Inorg. Chem. 2012, 51, 10408−
0416. (l) Majhi, P. K.; Sauerbrey, S.; Leiendecker, A.; Schnakenburg,
2
3
G.; Arduengo, A. J., III; Streubel, R. Dalton Trans. 2013, 42, 13126−
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Anal. Calcd for C H I N P Pd: C, 44.49; H, 3.37; N, 2.53. Found: C,
4
4
1
37 3
2 2
1
4.79; H, 3.43; N, 2.51. H NMR (DMSO-d , 500 MHz; δ, ppm): 3.03
6
(
(
1
1
s, 3H, N-CH ), 3.35 (s, 3H, N-CH ), 6.92 (s, 1H, C H), 7.42−7.55
3
3
5
13
m, 30H, PPh ). C NMR (DMSO-d , 100 MHz; δ, ppm): 37.7, 38.1,
3
6
26.1, 128.9, 129.0, 129.1, 129.2, 129.4, 129.5, 131.6, 131.9, 132.0,
31
32.6, 133.7, 134.5, carbene carbon signal could not be detected.
P
−1
(2) (a) Bates, J. I.; Kennepohl, P.; Gates, D. P. Angew. Chem., Int. Ed.
NMR (DMSO-d , 162 MHz; δ, ppm): 18.3. IR (KBr, cm ): 3434 (w,
6
2
009, 48, 9844−9847. (b) Mendoza-Espinosa, D.; Donnadieu, B.;
br), 3051 (w), 1649 (w), 1617 (w), 1585 (w), 1572 (w), 1479 (m),
1
(
Bertrand, G. Chem. - Asian J. 2011, 6, 1099−1103. (c) Ruiz, J.; Mesa,
A. F. Chem. - Eur. J. 2012, 18, 4485−4488.
434 (vs), 1389 (w), 1337 (w), 1310 (w), 1265 (w), 1182 (m), 1095
s), 1026 (w), 998 (w), 743 (m), 693 (vs), 616 (w), 542 (w), 521 (s),
11 (s), 494 (m), 458 (w), 425 (w). ESI-MS: m/z 978.9639 (M −
(
3) Gaillard, S.; Renaud, J. L. Dalton Trans. 2013, 42, 7255−7270.
5
−
+
(4) (a) Abdellah, I.; Lepetit, C.; Canac, Y.; Duhayon, C.; Chauvin, R.
Chem. - Eur. J. 2010, 16, 13095−13108. (b) Maaliki, C.; Lepetit, C.;
Canac, Y.; Bijani, C.; Duhayon, C.; Chauvin, R. Chem. - Eur. J. 2012,
I ) .
1
9
X-ray Structure Solution and Refinement. The crystal data
were collected on a Bruker Apex Smart diffractometer. Data were
collected using graphite-monochromated Mo Kα radiation (λ =
1
(
8, 7705−7714.
5) (a) Newkome, G. R.; Evans, D. W.; Fronczek, F. R. Inorg. Chem.
0
.71073 Å). All of the structures were solved by direct methods using
2
1987, 26, 3500−3506. (b) Abdellah, I.; Canac, Y.; Mboyi, C. D.;
SHELXS-97 and refined by full-matrix least squares on F . All
hydrogen atoms were included in idealized positions, and a riding
model was used. Non-hydrogen atoms were refined with anisotropic
displacement parameters. One of the disordered counteranions BF4
present in the crystal structure of 13 and disordered solvent molecules
in 11, 13, and 15 were treated by squeeze refinement using
Duhayon, C.; Chauvin, R. J. Organomet. Chem. 2015, 776, 149−152.
(
c) Debono, N.; Canac, Y.; Duhayon, C.; Chauvin, R. Eur. J. Inorg.
−
Chem. 2008, 2008, 2991−2999.
6) Hardman, N. J.; Abrams, M. B.; Pribisko, M. A.; Gilbert, T. M.;
Martin, R. L.; Kubas, G. J.; Baker, R. T. Angew. Chem., Int. Ed. 2004,
43, 1955−1958.
7) Knochel, P.; Dohle, W.; Gommermann, N.; Kneisel, F. F.; Kopp,
(
20
PLATON.
(
F.; Korn, T.; Sapountzis, I.; Vu, V. A. Angew. Chem., Int. Ed. 2003, 42,
4302−4320.
ASSOCIATED CONTENT
Supporting Information
Figures, a table, and CIF files giving crystal structure diagrams
of 6, 7, and 9, isotopic distributions of 16, NMR spectra, and
crystallographic data. The Supporting Information is available
free of charge on the ACS Publications website at DOI:
■
(
8) (a) Karthik, V.; Bhat, I. A.; Anantharaman, G. Organometallics
*
S
2
013, 32, 7006−7013. (b) Karthik, V.; Gupta, V.; Anantharaman, G.
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416.
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(
̈
1
(
1
0.1021/acs.organomet.5b00336.
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DOI: 10.1021/acs.organomet.5b00336
Organometallics XXXX, XXX, XXX−XXX