Catalyzed M-C coupling reactions in the synthesis of s-(pyridylethynyl)dicarbonylcyclopentadienyliron complexes

Article abstract of DOI:10.1039/d0ra02333g

The reactions between terminal ethynylpyridines, (trimethylsilyl)ethynylpyridines and cyclopentadienyliron dicarbonyl iodide were studied under Pd/Cu-catalyzed conditions to develop a synthetic approach to the s-alkynyl iron complexes Cp(CO)₂Fe-C?C-R (R =ortho-,meta-,para-pyridyl). Depending on the catalyst and reagents used, the yields of the desired s-pyridylethynyl complexes varied from 40 to 95%. In some cases the reactions withortho-ethynylpyridine gave as byproduct the unexpected binuclear FePd μ-pyridylvinylidene complex [Cp(CO)Fe{μ₂-?¹(C_a):?¹(C_a)-?¹(N)-C_a?C_?(H)(o-C₅H₄N)}(μ-CO)PdI]. The conditions, catalysts, and reagents that provide the highest yields of the desired s-pyridylethynyl iron compounds were determined. The methods developed allowed the synthesis of the corresponding s-4-benzothiadiazolylethynyl complex Cp(CO)₂Fe-C?C-(4-C₆H₃N₂S) as well. Eventually, synthetic approaches to s-alkynyl iron complexes of the type Cp(CO)₂Fe-C?C-R (R =ortho-,meta-,para-pyridyl, 4-benzothiadiazol-2,1,3-yl) based on the Pd/Cu-catalyzed cross-coupling reactions were elaborated.

Full text of DOI:10.1039/d0ra02333g

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Catalyzed M–C coupling reactions in the synthesis
of s-(pyridylethynyl)
Cite this: RSC Adv., 2020, 10, 17014
dicarbonylcyclopentadienyliron complexes†
a
b
*
Victor V. Verpekin,
Oleg V. Semeikin,
Alexander D. Vasiliev,cd
Alexander A. Kondrasenko,a Yuri A. Belousov
and Nikolai A. Ustynyuk
b
b
*
The reactions between terminal ethynylpyridines, (trimethylsilyl)ethynylpyridines and cyclopentadienyliron
dicarbonyl iodide were studied under Pd/Cu-catalyzed conditions to develop a synthetic approach to the
s-alkynyl iron complexes Cp(CO)2Fe–C^C–R (R ¼ ortho-, meta-, para-pyridyl). Depending on the catalyst
and reagents used, the yields of the desired s-pyridylethynyl complexes varied from 40 to 95%. In some
cases the reactions with ortho-ethynylpyridine gave as byproduct the unexpected binuclear FePd m-
pyridylvinylidene complex [Cp(CO)Fe{m2-h1(Ca):h1(Ca)-k1(N)-Ca]Cb(H)(o-C5H4N)}(m-CO)PdI]. The
conditions, catalysts, and reagents that provide the highest yields of the desired s-pyridylethynyl iron
compounds were determined. The methods developed allowed the synthesis of the corresponding s-4-
benzothiadiazolylethynyl complex Cp(CO)2Fe–C^C–(4-C6H3N2S) as well. Eventually, synthetic
approaches to s-alkynyl iron complexes of the type Cp(CO)2Fe–C^C–R (R ¼ ortho-, meta-, para-
pyridyl, 4-benzothiadiazol-2,1,3-yl) based on the Pd/Cu-catalyzed cross-coupling reactions were
elaborated.
Received 12th March 2020
Accepted 20th April 2020
DOI: 10.1039/d0ra02333g
rsc.li/rsc-advances
Cl).28–34 However, in some cases, such reactions may give low
yields of desired products and a range of by-products, for
Introduction
example, complexes in which the copper or the silver fragments
are p-coordinated to the transferred alkynyl ligand.35–38
Metal s-alkynyl complexes displaying such peculiar character-
istics as linear geometry, high stability, and p-unsaturated
character have been demonstrated to constitute promising
building blocks for the design of materials, which can possess
such properties as optical nonlinearity,1–5 light-emission,6–12
and electrical conductivity.13–18 Moreover, they are an important
class of coordination compounds because of their relevance in
synthetic chemistry19–24 and proton reduction catalysis.25–27
A variety of methods for the synthesis of transition metal
acetylides have been developed.24 The most common synthetic
route to them is transmetallation, where a generated [M–C^C–
R] species [M ¼ Cu(I), Ag(I), Au(I), alkali-metal (Li, Na), or an
alkaline-earth-metal (MgX, etc.)] acts as an alkynyl transfer
reagent to transition-metal halide complexes LnMX (X ¼ I, Br,
Other general strategy to the preparation of transition metal
acetylides takes advantage of the facility of some transition
metal complexes to catalyze M–C coupling reactions. The most
general route to group 10 metal s-alkynyl derivatives is based on
copper(I)-catalyzed dehydrogalogenation reactions between an
appropriate metal halide complex and a terminal alkyne in an
amine solvent.39–42 This method is applicable to the synthesis of
alkynyl, polyynyls, and polyyndiyls of tungsten, molybdenum,
iron, ruthenium, rhodium, and iridium.5,43–47 In some cases, the
CuI-catalyzed reactions of transition metal halides with stannyl
acetylenes may be performed in the absence of amines.48–51
Palladium catalysts, currently being an indispensable tool of
organic synthesis, can also be used in the M–C^C– bond
formation. The team of Claudio Lo Sterzo demonstrated that,
similarly to organic electrophiles, transition metal iodides
undergo coupling with trialkyltin acetylides, in the presence of
palladium to form alkynyl complexes of ruthenium, iron,
tungsten, and molybdenum.52–55 The role of palladium catalysts
in promoting these transformations was also investigated.52,56–59
Although, the Lo Sterzo approach was shown to be a valuable
route to alkynyl complexes, the need for preparation of tin
reagents and removal of tin impurities limits the appeal of this
method. To overcome these disadvantages, one can use an
organometallic analogue of the Sonogashira protocol,60,61 where
aInstitute of Chemistry and Chemical Technology SB RAS, Krasnoyarsk Research
Center, Siberian Branch of the Russian Academy of Sciences, Akademgorodok 50-24,
Krasnoyarsk, 660036, Russian Federation. E-mail: vvv@sany-ok.ru
bA. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of
Sciences, ul. Vavilova 28, Moscow 119991, Russian Federation. E-mail: ustynyuk@
ineos.ac.ru
cInstitute of Physics SB RAS, Krasnoyarsk Research Center, Siberian Branch of the
Russian Academy of Sciences, Akademgorodok, 50-38, Krasnoyarsk, 660036, Russia
dSiberian Federal University, Svobodny Prospect, 79, Krasnoyarsk, 660041, Russia
† Electronic supplementary information (ESI) available. CCDC 1973678, 1973917,
1973260 and 1982510. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/d0ra02333g
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transition metal halides react with terminal alkynes to form pyridylethynyl iron complexes 1–3 from Cp(CO)2FeI and ethy-
metal alkynyls via the Pd/Cu- or Pd-catalyzed dehydrohaloge- nylpyridines under the Oshima conditions was primarily caused
nation route, which provides milder reaction conditions and by a suppression of the formation and transfer of pyridylethynyl
facilitates purication of products. Despite the seeming avail- moieties to the palladium atom (Pd/Cu-catalyzed reactions) or
ability of this approach for the synthesis of metal acetylides, it of the formation of this moiety at the Fe–Pd center from the p-
was exploited only once by Oshima62 in the synthesis of s- coordinated alkyne (Cu-free reaction). Here we report on the
alkynyl iron complexes Cp(CO)2Fe–C^C–Ar.
cross-coupling of terminal ethynylpyridines and (trimetylsilyl)
As a part of our studies on proton reduction catalysis,25 we ethynylpyridines with cyclopentadienyliron dicarbonyl iodide
searched for a facile synthetic route to a series of s-pyr- under different Pd/Cu-catalyzed conditions to obtain the target
idylethynyl iron complexes Cp(CO)2Fe–C^C–(n-C5H4N) (n ¼ iron pyridylethynyl complexes.
ortho (1), meta (2), para (3)) containing two Lewis base centers
(Cb of ethynyl and N atom of pyridine). The efficient preparation
of the iron arylethynyls complexes Cp(CO)2Fe–C^C–Ar by Pd/
Cu-catalyzed cross-coupling of Cp(CO)2FeI with terminal aryla-
cetylenes62 inspired us to apply the Oshima protocol for the
Results and discussion
Development of Pd/Cu-catalyzed approaches to the synthesis
of Cp(CO)2Fe–C^C–(n-C5H4N) (n ¼ ortho (1), meta (2), para
(3)) and Cp(CO)2Fe–C^C–(4-C6H3N2S) (5)
preparation of 1–3. Unfortunately, our rst attempt to obtain
the ortho-pyridylethynyl iron complex Cp(CO)2Fe–C^C–(2- Following on from the hypothesized reasons of the inability to
C5H4N) (1) using the Oshima conditions did not give the target obtain the ethynylpyridyl iron complexes Cp(CO)2Fe–C^C–(n-
substance. Upon an increase in the reaction temperature to C5H4N) (n ¼ ortho (1), meta (2), para (3)), we realized that
60 ꢀC an unexpected binuclear FePd m-pyridylvinylidene facilitation of the transmetallation step (the formation and the
complex
[Cp(CO)Fe{m2-h1(Ca):h1(Ca)-k1(N)-Ca]Cb(H)(2- transfer of acetylide species) in Pd/Cu-catalyzed reaction
C5H4N)}(m-CO)PdI] (4) was obtained in yield of 2%, but still between Cp(CO)2FeI and ethynylpyridines should allow the
without traces of 1 (Scheme 1). The 12% yield of complex 4 was preparation of the desired products 1–3. Therefore, two
achieved by using one equivalent of PdCl2 without copper approaches were proposed to solve this problem: (i) the use of
iodide and pure diisopropylamine as a solvent63 (Scheme 1). (trimethylsilyl)ethynylpyridines that in the presence of uoride
Attempts to synthesize the iron derivatives of meta- and para- ion generate anionic pentacoordinate silicate species [Me3Si(F)–
pyridylethynyles under described conditions62 were also C^C–Pyr]ꢁ, in which the alkynyl group is more nucleophilic
unsuccessful; the iron acetylide compounds were obtained in and should be smoothly transferred to a palladium catalyst
very low yields (less than 5%) although no formation of the side (Hiyama coupling);64 (ii) the application of stronger base than
binuclear FePd products was observed in these cases.
secondary and tertiary amines such as 1,8-diazabicyclo[5.4.0]
For that reasons, we became interested in developing undec-7-ene (DBU) to facilitate the acetylide species formation
a simple and reliable synthetic approach to s-acetylide iron in Pd/Cu-catalyzed reactions of Cp(CO)2FeI with terminal ethy-
complexes 1–3 based on the Pd/Cu-catalyzed cross-coupling nylpyridines. Our preliminary experiments suggested that both
reactions. We proposed that the inability to obtain the approaches can be used.
The palladium(II) complexes bis(triphenylphosphine)palla-
dium(II) dichloride PdCl2(PPh3)2 and bis(acetonitrile)palladium
dichloride PdCl2(NCMe)2, as well as tris(dibenzylideneacetone)
dipalladium(0) Pd2(dba)3 were tested as catalysts in this study.
However, in our rsts experiments an application of PdCl2(-
PPh3)2 as catalyst was found to results in an unexpected
substitution of CO ligands by PPh3 in [Cp(CO)2Fe] fragments to
give the side-products Cp(CO)(PPh3)FeI and Cp(CO)(PPh3)Fe–
C^C–(2-C5H4N), thereby making the separation of the reaction
mixture more difficult. Therefore, in our following experiments
we applied only such palladium catalysts that do not contain
ligands capable to substitute carbonyl groups in the initial and
the target compounds, namely Pd2(dba)3 and PdCl2(NCMe)2.
The inuence of the presence of CuI cocatalyst on the reaction
outcome was also examined.
The application of the “(trimethylsilyl)ethynylpyridine”
approach resulted in only moderate yields (up to 60%) of the
target complexes 1–3; the radical dimerization product
[Cp(CO)2Fe]2 (in 23–37% yield) and the corresponding 1,4-di(n-
pyridyl)buta-1,3-diynes65 (trace amounts) were also obtained.
The nature of the palladium catalyst (PdCl2(NCMe)2 or
Pd2(dba)3) didn't affect the yields of 1–3 here, as well as the
presence of CuI as cocatalyst (Table 1). However, a source of
Scheme 1 Reactions of terminal arylacetylenes62 and 2-ethynylpyr-
idine with Cp(CO)2FeI under Oshima conditions; unexpected forma-
tion of binuclear m-pyridylvinylidene complex 4. (i) PdCl2(PPh3)2
i
2.5 mol%, CuI 5 mol%, Pr2NH–THF 1 : 2, 25 ꢀC, 30 min; (ii) PdCl2(-
i
PPh3)2 5 mol%, CuI 2.5 mol%, Pr2NH–THF 1 : 2, 25 ꢀC, 30 min; (iii) 1
equiv. PdCl2, iPr2NH, 60 ꢀC, 1 h.
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Table 1 Coupling reactions of cyclopentadienyliron dicarbonyl iodide and [(trimethylsilyl)ethynyl]pyridinesa
Yield of products, %
#
1
Pyr
[Pd]
CuI, mol% Conditions
Conversionb, % Target complex Byproducts
[Cp(CO)2Fe]2 (3%); Cp(CO)(PPh3)FeI (3%);
[–C^C–(2-C5H4N)]2 (5%);
PdCl2(PPh3)2, 10 mol%; 20
40 ꢀC; 120 min 70
1 – 58%
Cp(CO)(PPh3)Fe–C^C–(2-C5H4N) (3%)
[Cp(CO)2Fe]2 (32%); [–C^C–(2-C5H4N)]2 (2%)
[Cp(CO)2Fe]2 (28%); [-C^C–(2-C5H4N)]2 (5%)
[Cp(CO)2Fe]2 (37%)
[Cp(CO)2Fe]2 (27%); [–C^C–(2-C5H4N)]2 (3%)
[Cp(CO)2Fe]2 (23%)
[Cp(CO)2Fe]2 (32%); [–C^C–(4-C5H4N)]2 (6%)
[Cp(CO)2Fe]2 (34%); [–C^C–(4-C5H4N)]2 (5%)
[Cp(CO)2Fe]2 (30%); [–C^C–(4-C5H4N)]2 (3%)
[Cp(CO)2Fe]2 (37%)
[Cp(CO)2Fe]2 (27%); [–C^C–(3-C5H4N)]2 (1%)
[Cp(CO)2Fe]2 (36%)
2
3
4
5
6
7
8
9
Pd2(dba)3, 10 mol%
Pd2(bda)3, 10 mol%
Pd2(bda)3, 2 mol%
20
—
—
36 ꢀC; 90 min 98
36 ꢀC; 90 min 98
60 ꢀC; 90 min 97
36 ꢀC; 90 min 95
50 ꢀC; 90 min 93
36 ꢀC; 90 min 96
36 ꢀC; 90 min 98
36 ꢀC; 90 min 97
50 ꢀC; 90 min 92
36 ꢀC; 90 min 93
50 ꢀC; 90 min 95
1 – 58%
1 – 60%
1 – 44%
1 – 58%
1 – 61%
3 – 49%
3 – 54%
3 – 44%
3 – 40%
2 – 56%
2 – 48%
PdCl2(NCMe)2, 10 mol% 20
PdCl2(NCMe)2, 5 mol%
Pd2(bda)3, 10 mol%
Pd2(bda)3, 10 mol%
PdCl2(NCMe)2, 10 mol% 20
PdCl2(NCMe)2, 5 mol%
Pd2(bda)3, 10 mol%
—
20
—
10
11
12
—
—
—
PdCl2(NCMe)2, 5 mol%
a
All reactions were carried out with use of 1 equiv. Cp(CO)2FeI, 1.5 equiv. Me3Si–C^C–(n-C5H4N), in the presence of 1.5 equiv. TBAF (1 M in THF) in
THF. b Conversion was calculated from the amount of unreacted Cp(CO)2FeI recovered by column chromatography.
tetrabutylammonium uoride is important; the coupling reac- free conditions here, the yield of the target complexes decreased
tions of Cp(CO)2FeI and [(trimethylsilyl)ethynyl]pyridines per- by about 20%, while the yield of [Cp(CO)2Fe]2 increased to 20%
formed with tetrabutylammonium uoride trihydrate gave only and, also, m-pyridylvinylidene complex 4 was obtained in the
half of the pyridylethynyl complex's yield obtained in the reac- case of the reaction of Cp(CO)2FeI and H–C^C–(2-C5H4N)
tions with 1 M solution of TBAF in THF.
(Table 3, entries 2 and 4). Thus, the binuclear complex 4 is also
The “ethynylpyridine” approach was found to be much more produced under the conditions of catalytic formation of
effective, the complexes 1–3 were obtained in yields from 67 to complex 1. It should be noted that for the reactions between
96%. The best catalytic system in this case was PdCl2(NCMe)2/ Cp(CO)2FeI and ethynylpyridines we decided to apply the same
CuI, with which iron-ethynylpyridine coupling proceeds effi- temperature and Pd2(dba)3 loadings that gave the highest yields
ciently at room temperature in 20 minutes (2 mol% of Pd of 1–3 in the ethynylation of Cp(CO)2FeI with [(trimethylsilyl)
ꢀ
catalysts and 20 mol% of CuI) or at 60 C in 30 minutes with ethynyl]pyridines (entries 3, 8, 11 in Table 1).
reduced catalysts loadings (1 and 5 mol%, respectively)
(Table 2).
Therefore, all reactions given in Table 3 were conducted at
36 C with 10 mol% of Pd2(dba)3.
ꢀ
The presence of CuI in these conditions is important for
To emphasize the applicability of the Pd/Cu-catalyzed pyr-
high-yield synthesis of 1–3. The pyridylethynylation smoothly idylethynylation of Cp(CO)2FeI to the synthesis of similar
proceeds only for the Pd(II)/CuI-catalyzed reactions, whereas in compounds, we tried to prepare the corresponding s-4-benzo-
the absence of CuI cocatalyst (Table 2, entries 5, 9 and 13) the thiadiazolylethynyl complex Cp(CO)2Fe–C^C–(4-C6H3N2S) (5).
conversion and the yield of corresponding s-pyridylethynyl Following the developed strategies, we investigated the
complex decreased, but the yield of the dimerization product coupling reactions of Cp(CO)2FeI with 4-(trimethylsilyl)ethynyl-
[Cp(CO)2Fe]2 increased. Moreover, in these conditions the 2,1,3-benzothiadiazole and 4-ethynyl-2,1,3-benzothiadiazole. In
reaction with 2-ethynylpyridine gave m-pyridylvinylidene all experiments performed using both approaches complex 5
complex 4 as a side product in 4% yield.
was obtained. However, its highest yield 94% was achieved only
Similar results were obtained for the reactions between in the coupling of Cp(CO)2FeI and H–C^C–(4-C6H3N2S) at 60 ꢀC
Cp(CO)2FeI and ethynylpyridines catalyzed by the zero-valent using 1 mol% of PdCl2(NCMe)2 and 5 mol% of CuI (Scheme 2,
palladium complex Pd2(dba)3 (Table 3). When the Pd2(dba)3/ entry 3).
CuI pair was applied, the target pyridylethynyl complexes 1–3
were produced in high yields (84, 86 and 87% for 1, 2 and 3,
respectively) and the yields of the dimerization product
The proposed catalytic cycles
Previously, the Lo Sterzo group clearly demonstrated a close
[Cp(CO)2Fe]2 were in a range of 6–8%. However, under copper-
analogy between the Pd-catalyzed carbon–carbon and metal–
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Table 2 Pd(II)/CuI- and Pd(II)-catalyzed coupling reactions of cyclopentadienyliron dicarbonyl iodide and ethynylpyridinesa
Yield of products, %
#
1
Pyr
[Pd]
CuI, mol% Conditions
Conversion, % Target complex Byproducts
Cp(CO)(PPh3)FeI (3%);
PdCl2(PPh3)2, 10 mol%; 20
40 ꢀC; 30 min 86
1 – 66%
Cp(CO)(PPh3)Fe–C^C–(2-C5H4N) (8%)
2
3
4
5
6
7
8
9
10
11
12
13
PdCl2(NCMe)2, 10 mol% 20
PdCl2(NCMe)2, 2 mol% 20
24 ꢀC; 20 min 98
24 ꢀC; 20 min 97
60 ꢀC; 30 min 98
60 ꢀC; 90 min 29
24 ꢀC; 20 min 97
24 ꢀC; 20 min 96
60 ꢀC; 30 min 99
60 ꢀC; 90 min 75
24 ꢀC; 20 min 99
24 ꢀC; 20 min 98
60 ꢀC; 30 min 99
60 ꢀC; 90 min 74
1 – 91%
1 – 94%
1 – 92%
1 – 15%
3 – 91%
3 – 92%
3 – 96%
3 – 67%
2 – 83%
2 – 93%
2 – 95%
2 – 66%
[Cp(CO)2Fe]2 (5%);
[Cp(CO)2Fe]2 (2%);
PdCl2(NCMe)2, 1 mol%
PdCl2(NCMe)2, 5 mol%
5
—
[Cp(CO)2Fe]2 (4%);
[Cp(CO)2Fe]2 (9%); 4 – 3% [Fe], 55% [Pd]b
PdCl2(NCMe)2, 10 mol% 20
PdCl2(NCMe)2, 2 mol% 20
—
—
—
PdCl2(NCMe)2, 1 mol%
PdCl2(NCMe)2, 5 mol%
5
—
[Cp(CO)2Fe]2 (7%)
[Cp(CO)2Fe]2 (13%)
—
—
PdCl2(NCMe)2, 10 mol% 20
PdCl2(NCMe)2, 2 mol% 20
PdCl2(NCMe)2, 1 mol%
PdCl2(NCMe)2, 5 mol%
5
—
[Cp(CO)2Fe]2 (6%)
a
All reactions were carried out with use of 1 equiv. Cp(CO)2FeI, 1.5 equiv. H–C^C–(n-C5H4N), in the presence of 1.5 equiv. DBU in THF. b Isolated
yield of 4 based on Cp(CO)2FeI and PdCl2(NCMe)2 consumption.
Table 3 Pd(0)/CuI- and Pd(0)-catalyzed coupling reactions of cyclopentadienyliron dicarbonyl iodide and ethynylpyridinesa
Yield of products, %
#
Pyr
[Pd], mol% CuI, mol% Conditions
Conversion, % Target complex Byproducts
1
2
10
10
20
—
36 ꢀC; 90 min 96
1 – 84%
1 – 64%
[Cp(CO)2Fe]2 (8%); [–C^C–(2-C5H4N)]2 (3%)
36 ꢀC; 90 min 95
[Cp(CO)2Fe]2 (17%); 4 – 7% [Fe], 72% [Pd]b
3
4
10
10
20
—
36 ꢀC; 90 min 95
36 ꢀC; 90 min 96
3 – 86%
3 – 67%
[Cp(CO)2Fe]2 (6%); [–C^C–(4-C5H4N)]2 (2%)
[Cp(CO)2Fe]2 (20%); [–C^C–(4-C5H4N)]2 (4%)
5
10
20
36 ꢀC; 90 min 96
2 – 87%
[Cp(CO)2Fe]2 (7%); [–C^C–(3-C5H4N)]2 (3%)
a
All reactions were carried out with use of 1 equiv. Cp(CO)2FeI, 1.5 equiv. H–C^C–(n-C5H4N), in the presence of 1.5 equiv. DBU in THF. b Isolated
yield of 4 based on Cp(CO)2FeI and Pd2(dba)3 consumption.
carbon bond formation mechanisms through reactions between reactions between Cp(CO)2FeI and 2-ethynylpyridine. The
[h5-(1-diphenylphosphino-2,4-diphenyl)cyclopentadienyl](CO)3-
formation of the binuclear FePd m-pyridylvinylidene complex 4 in
MI (M ¼ Mo, W) and PdCl2(NCMe)2 with a following treatment of the reactions under Cu-free conditions (Table 2 entries 5, 9, 13
the resulting binuclear MPd oxidation addition complexes with and Table 3 entries 2, 4) clearly shows that the reaction pathways
4-nitro-1-[2-(tributhylstannyl)ethynyl]benzene.57,59 The mecha- leading to 1 and 4 may have common intermediates. Moreover,
nism of the Pd/Cu- and Pd-catalyzed pyridylethynylation of one can assume that in the reaction performed with the stoi-
cyclopentadienyliron dicarbonyl iodide should be apparently chiometric ratios of Pd2(dba)3, Cp(CO)2FeI and H–C^C–(2-
analogous to that of the carbon–carbon coupling reactions. Some C5H4N), the ratio of 1 to 4 should change in favor of the latter.
additional clues to the mechanisms of the formation of the Indeed, the reaction of Cp(CO)2FeI with 2-ethynylpyridine in the
complexes 1–3, 5 may be provided by a consideration of the presence of 1 equiv. of Pd2(dba)3 in triethylamine as a solvent
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Scheme 2 The results on the Pd/Cu-catalyzed synthesis of Cp(CO)2Fe–C^C–(4-C6H3N2S) (5).
gave complex 4 in yield of 78% (Scheme 3). However, the trace a decrease of yields of 2 and 3, and didn't give any binuclear
amount (3% yield) of the 2-pyridylethynyl complex 1 was ob- products (Table 2 entries 9 and 13).
tained, thereby conrming that the catalytic 2-pyr-
idylethynylation of Cp(CO)2FeI occurs even under these mechanistic aspects of the cross-coupling reactions, a noncon-
conditions, although in a much lesser degree. tradictory mechanistic scheme of the pyridylethynylation of
Taking into account the data obtained and the known
Obviously, one of these common intermediates in the cyclopentadienyliron dicarbonyl iodide was proposed (Scheme
reaction pathways to 1 and 4 is binuclear FePd species 4), which explains the reaction pattern and the possibility of
(Scheme 4, A) formed by an oxidative addition of Cp(CO)2FeI to alternative reaction pathway. For the Pd/Cu-catalyzed reactions
catalytically active Pd0 species. In the absence of an efficient (pathway A), the rst step of the catalytic cycle would be an
transmetallating agent, such as the copper acetylide or anionic oxidative addition of the Cp(CO)2FeI to the catalytically active
pentacoordinate silicate adduct [Me3Si(F)–C^C–(2-C5H4N)] Pd0L2 species to give a binuclear FePd intermediate A. A
NBu4, a p-coordination of the alkyne to A can occur resulting subsequent transmetallation, where transfer of the pyr-
in complex A0. Without a strong base A0 rearrange into the m- idylacetylide moiety from the Cu-acetylide formed in the
pyridylvinylidene complex 4. To reveal the mechanism of this copper-cycle to the FePd complex A led to a complex B, which
process, an additional study is needed, since there are several undergoes trans to cis isomerization to give a complex B0,
possible reaction pathways for its proceeding. It is worth a following reductive elimination of the latter results in the Fe–
noting that the examples of the acetylene-to-vinylidene C cross-coupling products Cp(CO)2Fe–C^C–(n-C5H4N) (n ¼
tautomerism involving two adjacent metal centers are known ortho (1), meta (2), para (3)). The initial oxidative addition and
and described in several works,66–70 but they are much less the nal reductive elimination steps of a mechanism for the Cu-
studied in contrast to the well-understood acetylene-to- free reaction (pathway B) are the same as for the Pd/Cu-
vinylidene rearrangement mediated by
a single metal catalyzed one. However, an alternative ligand L substitution in
center.71,72 It is also worth to note that the ortho-position of the the intermediate A by the alkyne can take place resulting in p-
nitrogen atom in 2-ethynylpyridine plays an important role in alkyne complex A0. Its subsequent deprotonation then occurs to
the process of formation of the binuclear FePd m-pyr- give the complex B0. The generation of the complex 4 in this
idylvinylidene complex 4, as the Pd-catalyzed reactions of context can be considered as a side pathway C of the Pd-
Cp(CO)2FeI with 3- and 4-ethynylpyridines simply resulted in catalyzed reaction between Cp(CO)2FeI and 2-ethynylpyridine
Scheme 3 Reaction of high yield synthesis of the binuclear FePd m-pyridylvinylidene complex 4.
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Scheme
4
Proposed mechanism of Pd/Cu- and Pd-catalyzed coupling reactions of cyclopentadienyliron dicarbonyl iodide and
ethynylpyridines.
that is facilitated by the absence of transmetallating agents or
appropriate base, and ortho-position of the nitrogen atom in the
pyridine ring of the alkyne. The catalytic cycle for the complex 5
formation should be the same as for 1–3.
The results obtained in the case of the “(trimethylsilyl)ethy-
nylpyridine” demonstrated that pyridylethynylation of
Cp(CO)2FeI should proceed according to the reaction pathway
commonly accepted for the Hiyama coupling, i.e. transfer of the
pyridylacetylide moiety to the FePd complex A should goes
through anionic pentacoordinate silicate species64 (Scheme 5).
Characterization of the complexes
The IR and the 1H and 13C{1H} NMR data for the complexes 1–3
and 5 were obtained. The NMR signals were assigned on the
basis of 1H–13C correlations measured through HSQC and
HMBC experiments, respectively (Table 4). The structure of the
complexes can be deduced from the combined NMR and IR
data.
The IR spectra of 1–3 in CH2Cl2 solution show two very
strong absorptions at about 2043 and 1996 cmꢁ1 that
Scheme 5 Proposed mechanism of Pd-catalyzed coupling reactions of cyclopentadienyliron dicarbonyl iodide and [(trimethylsilyl)ethynyl]
pyridines.
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Table 4 IR and NMR (d, ppm [J, Hz]) spectroscopic data for the Cp(CO)2Fe–C^C–(n-C5H4N) [n ¼ ortho (1), meta (2), para (3)] and Cp(CO)2Fe–
C^C–(4-C6H3N2S) (5)
NMR (d, ppm [J, Hz], CD2Cl2)
1H
13C
–Ca^Cb–R
C5H5
Ca
Cb
95.4
95.7
102.0
102.9
C5H5
CO
IR, cmꢁ1 (CH2Cl2)
1
2
3
5
5.14
5.13
5.13
5.20
116.7
112.3
114.3
112.3
85.4
85.3
85.6
85.6
212.2
212.4
212.3
212.3
2112 (nC^C), 2043, 1997 (nCO
2111 (nC^C), 2044, 1996 (nCO
2110 (nC^C), 2044, 1998 (nCO
2100 (nC^C), 2042, 1997 (nCO
)
)
)
)
correspond to the n(C^O) stretching modes of carbonyl groups
The proximity of crystals 1 and 2 cell parameters (Table S3†)
at the iron atom. An additional absorption with strong intensity and small differences in the sequence of atoms in their mole-
at about 2111 cmꢁ1 is attributed to the n(C^C) stretching cules suggest that there are small differences in a packing of
frequencies of the alkynyl ligand. The n(CO) and the n(C^C) molecules. Indeed, the structures 1 and 2 are mirror-like each
frequencies of the complex
5
with s-4-ethynyl-2,1,3- other, and the mirror plane is perpendicular to the cell axis b.
benzothiadiazole ligand are insignicantly shied to low- The iron atom in 1–3 and 5 is coordinated by a cyclopentadienyl
frequency in comparison with 1–3.
The 13C nuclei of a- and b-alkynyl carbons of 1–3 and 5
resonate in the regions d 112–117 and 95–103 ppm, respectively.
It is noteworthy that these signals slightly vary with the nature
of the substituents in s-alkynyl ligands. The downeld shi of
Ca nuclei by approximately 2 ppm is observed on moving from
the meta- to para- and to ortho-pyridylethynyl iron complexes.
However, this trend doesn't hold for the Cb nuclei, here only the
signal of 3 is downeld shied by 7 ppm compared with those
of the 1 and 2. These correlations are apparently due to changes
in p-electron distribution induced by the electronic effect of the
pyridyl fragments. However, these effects can't be reduced to
a single parameter (like only inductive or mesomeric effects), as
was showed by Claude Lapinte team for cationic complexes of
the type [Cp*(dppe)Fe–C^C–(n-C5H4N)][PF6] (n ¼ 2, 3, 4).73 At
the same time, the 13C chemical shis of the cyclopentadienyl
and carbonyl groups coordinated to the iron atom are almost
independent of their nature (Table 4). The presence of the
pyridyl substituents in 1–3 are indicated by signals between 7.02
and 8.50 ppm in 1H NMR spectra, and between 119 and
152 ppm in 13C NMR spectra of the complexes. The carbon and
hydrogen atoms of the 2,1,3-benzothiadiazole group in 5 reso-
nate in the regions d 118–156 and d 7.48–7.76 ppm in 13C and 1H
NMR spectra, respectively. So, overall the IR and NMR spectra
parameters of 1–3 and 5 are similar to those found for analo-
gous cyclopentadienyliron dicarbonyl complexes with different
s-alkynyl ligands.34,54,62
The molecular structures of the complexes Cp(CO)2Fe–
C^C–(2-C5H4N) (1), Cp(CO)2Fe–C^C–(3-C5H4N) (2), Cp(CO)2-
Fe–C^C–(4-C5H4N) (3), and Cp(CO)2Fe–C^C–(4-C6H3N2S) (5)
were solved on the basis of X-ray diffractometry data. Suitable
crystals of 1–3 and 5 were grown from dichloromethane/hexane
mixtures. The views of the structures are shown in Fig. 1,
selected bond lengths and angles are given in Table 5. The
Fig. 1 Molecular structures of 1 (a), 2 (b), 3 (c), and 5 (d) with the
thermal ellipsoids set at the 50% probability level.
crystal data and renement parameters are included in the
ESI.†
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Table 5 The selected bond distances (A˚) and angles (ꢀ) for the complexes 1–3 and 5
1
2
3
5
˚
Distances, A
Fe–C3
C3–C9
C9–C10
Fe–Cp
1.9159(17)
1.204(2)
1.436(2)
1.919(2)
1.200(3)
1.437(3)
1.7200(11)
1.906(3)
1.203(5)
1.423(4)
1.7186(19)
1.917(3)
1.208(4)
1.435(4)
1.7222(16)
1.7223(8)
Bond angles, ꢀ
Fe–C3–C9
C3–C9–C10
C3–Fe–C1
175.94(16)
176.54(19)
89.26(8)
174.3(2)
176.8(3)
86.8(1)
89.4(1)
179.4(4)
177.7(5)
89.68(17)
89.07(16)
178.6(3)
174.6(4)
88.80(15)
89.56(14)
C3–Fe–C2
87.11(8)
Angles between planes, ꢀ
h5-Cp:ringa
84.51(7)
81.38(6)
84.58(8)
80.97(7)
68.64(14)
88.27(8)
71.22(12)
81.40(8)
(O1–C1–Fe–C2–O2):ringa
a
The angles between appropriate plane and plane of the substituent's ring (pyridine in 1–3 and benzothiadiazole in 5) of the s-alkynyl ligands are
given.
ring in h5-fashion, two terminal CO ligands, and by s-alkynyl 1 mol% of PdCl2(NCMe)2 and 5 mol% of CuI and heating at
ꢀ
ligand to adopt a typical pseudo-octahedral geometry. The bond 60 C for 30 minutes. In case of the Cu-free coupling between
lengths and angles in 1–3 and 5 are close to each other and to Cp(CO)2FeI and 2-ethynylpyridine, there was an additional side-
those found in the known complexes of the type Cp(CO)2Fe– reaction, which resulted in traces of the binuclear complex
C^C–R.74–77 The differences in geometry of the complexes' [Cp(CO)Fe{m2-h1(Ca):h1(Ca)-k1(N)-Ca]Cb(H)(2-C5H4N)}(m-CO)
molecules are associated with the position of C^C–R moiety PdI] (4). The oxidative addition species Cp(CO)2Fe-[PdL2]-I (A in
relative to the iron fragment. The pyridylethynyl ligands in 1 Scheme 4) are supposed to be a key intermediate in the catalytic
and 2, and the 4-ethynyl-2,1,3-benzothiadiazolyl ligand in 5 lean cycle of the s-alkynyl complexes formation, however in the
slightly toward one of the carbonyl group of the iron atom in absence of effective transmetallating agents or appropriate base
such a way that the planes between ring of the substituent and A is assumed to become a precursor to 4.
[Fe(CO)2] fragment exhibit angles about 81ꢀ. At the same time,
The developed methodology can be extended to the synthesis
in the complex 3 the para-pyridylethynyl ligand is almost of other s-alkynyl complexes of iron. So, the coupling of cyclo-
perpendicular to the plane formed by two carbonyl ligands and pentadienyliron dicarbonyl iodide and 4-ethynyl-2,1,3-
the iron atom. Moreover, the angles between the planes of the benzothiadiazole under the same condition as above was
substituent's ring in the s-alkynyl and the cyclopentadienyl found to proceed efficiently resulting in the complex Cp(CO)2-
ligands are about 70ꢀ in 3 and 5, whereas the analogous angles Fe–C^C–(4-C6H3N2S) (5). The spectroscopic and structural
in 1 and 2 are ca. 85ꢀ. It is also of interest that the pyridyl features of 1–3, 5 were described.
substituents in 1 and 2 differ in their orientations: when the
nitrogen atom in 1 is oriented to Cp ring, that in the complex 2
the nitrogen is placed opposite, i.e. oriented to carbonyl groups.
Experimental
General considerations
All operations and manipulations were carried out under an
Conclusions
argon atmosphere. Solvents (dichloromethane, petroleum
In this paper, two approaches were developed for the pyr- ether, ethyl acetate, hexane, triethylamine) were puried by
idylethynylation of cyclopentadienyliron dicarbonyl iodide distillation from the appropriate drying agents and stored
based on Pd/Cu- and Pd-catalyzed Fe–C coupling of (trime- under argon. THF was dried by reuxing over sodium/
thylsilyl)ethynylpyridines and ethynylpyridines with Cp(CO)2- benzophenone ketyl and freshly distilled prior to use. The
FeI. Although these two approaches differ only in the nature of course of reactions was monitored by TLC on Silica gel (Alu
species participating in the transmetallation step (transfer of foils, Sigma-Aldrich) and IR spectroscopy. Neutral silica gel
the pyridylacetylide moiety to catalytically active species), the (silica 60, 0.2–0.5 mm, Macherey-Nagel) was used for column
second “ethynylpyridine” approach was found to be much more chromatography. Pd(Cl)2(PPh3)2,78 Pd(Cl)2(NCMe)2,79 Pd2(-
effective compared with the rst “(trimethylsilyl)ethynylpyr- dba)3$CHCl3,80 and Cp(CO)2FeI81 were prepared according to
idine” one. For example, the s-pyridylethynyl iron complexes literature procedures. Ortho-, meta-, para-[(trimethylsilyl)
Cp(CO)2Fe–C^C–(n-C5H4N) (n ¼ ortho (1), meta (2), para (3)) ethynyl]pyridines82 and 4-(trimethylsilyl)ethynyl-2,1,3-benzo-
were obtained in highest yields (about 95%) in the reaction of thiadiazole83 were prepared from ethynyltrimethylsilane. Ortho-
ethynylpyridines with Cp(CO)2FeI in THF in the presence of 1,8- and para-ethynylpyridines were synthesised from 2-methyl-4-(n-
diazabicyclo[5.4.0]undec-7-ene as a base upon the catalysis with pyridyl)but-3-yn-2-ols by elimination of acetone, according to
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published procedures.65 Meta-ethynylpyridine and 4-ethynyl- yield (218 mg, 0.781 mmol) from cyclopentadienyliron dicar-
2,1,3-benzothiadiazole were obtained by desilylation of meta- bonyl iodide (250 mg, 0.822 mmol) and 3-ethynylpyridine
[(trimethylsilyl)ethynyl]pyridine84 and 4-(trimethylsilyl)ethynyl- (127 mg, 1.223 mmol) with the use of THF (8 mL), DBU (0.18
2,1,3-benzothiadiazole.83 Tetrabutylammonium uoride solu- mL, 183 mg, 1.204 mm), PdCl2(NCMe)2 (2 mg, 0.008 mmol), and
tion (1 M solution in THF, Aldrich), 1,8-diazabicyclo[5.4.0] CuI (8 mg, 0.042 mmol). 1H NMR (CD2Cl2, 25 ꢀC) d, ppm [J, Hz]:
3
3
undec-7-ene (Aldrich), and catalyst CuI (“Vekton-M” Ltd.) were 5.13 (s, 5H, C5H5); 7.14 (dd, 1H, JHH ¼ 7.3 Hz, JHH ¼ 5.0 Hz,
purchased and used directly. The synthetic procedures for the Hmeta of (3-Pyr) (H5)); 7.54 (d, 1H, 3JHH ¼ 8.0 Hz, Hpara of (3-Pyr)
3
preparation of 1–3 and 5 providing the highest yields are (H6)); 8.30 (d, 1H, JHH ¼ 3.2 Hz, Hortho of (3-Pyr) (H4)); 8.49 (s,
described in the experimental part (Table 2, entries 4, 8, and 12; 1H, N–C–Hortho of (3-Pyr) (H2)). 13C{1H} NMR (CD2Cl2, 25 ꢀC)
Scheme 2, entry 3), the detailed isolation procedures and d, ppm [J, Hz]: 85.3 (s, C5H5); 95.7 (s, ^C2–); 112.3 (s, –C1^);
characterization of the products can be found in the ESI.†
122.4 (s, Cmeta of (3-Pyr) (C5)); 124.6 (s, Cipso of (3-Pyr)) 137.3 (s,
Physical-chemical characteristics were obtained in the Cpara of (3-Pyr) (C6)); 145.3 (s, Cortho of (3-Pyr) (C4)); 152.1 (s, N–
Krasnoyarsk Regional Centre of Research Equipment, Siberian Cortho of (2-Pyr) (C2)) 212.4 (s, 2Fe–CO). IR (CH2Cl2 n/cmꢁ1):
Branch of the Russian Academy of Sciences. The IR spectra were 2111s (nC^C), 2044vs, 1996vs (nCO), 1580w, 1561w, 1474w (nC]C
recorded on the Shimadzu IR Tracer-100 spectrometer (Japan). and nC]N). IR (KBr n/cmꢁ1): 2103s (nC^C), 2038vs, 1994vs (nCO),
1H, 13C{1H}, 31P{1H}, HSQC, and HMBC NMR spectra were ob- 1572w, 1555w, 1473w (nC]C and nC]N). Anal. found: C, 60.21%;
tained using NMR spectrometer AVANCE III 600 (Bruker, Ger- H, 3.26%; N, 5.00%. Calc. for C14H9FeNO2 (279): C, 60.25%; H,
many). Chemical shis are reported in ppm units referenced to 3.25%; N, 5.02%.
residual solvent resonances for 1H, 13C{1H}, HSQC, and HMBC
spectra or to an external 85% H3PO4(aq) standard for 31P{1H}
Synthesis of Cp(CO)2Fe–C^C–(4-C5H4N) (3)
spectra. The X-ray data for 1–3 and 5 were obtained with the
Similarly, Cp(CO)2Fe–C^C–(4-C5H4N) (3) was obtained from
Smart Photon II diffractometer (Bruker AXS, Germany).
cyclopentadienyliron dicarbonyl iodide (339 mg, 1.115 mmol)
and 4-ethynylpyridine (173 mg, 1.680 mmol) with the use of
THF (10 mL), DBU (0.25 mL, 255 mg, 1.678 mmol), PdCl2(-
Synthesis of Cp(CO)2Fe–C^C–(2-C5H4N) (1)
Cyclopentadienyliron dicarbonyl iodide (315 mg, 1.036 mmol) NCMe)2 (3 mg, 0.012 mmol), and CuI (11 mg, 0.052 mmol) was
and 2-ethynylpyridine (0.155 mL, 158 mg, 1.534 mmol) were dis- obtained Cp(CO)2Fe–C^C–(4-C5H4N) (3) (299 mg, 1.072 mmol,
solved in freshly distilled THF (10 mL), then DBU (0.23 mL, 96%). 1H NMR (CD2Cl2, 25 ꢀC) d, ppm [J, Hz]: 5.13 (s, 5H, C5H5);
234 mg, 1.539 mmol), PdCl2(NCMe)2 (3 mg, 0.012 mmol), and CuI 7.11 (dd, 2H, 3JHH ¼ 5.4 Hz, Hmeta of (4-Pyr)); 8.39 (d, 2H, 3JHH
¼
(10 mg, 0.052 mmol) were added. The reaction mixture was stirred 4.7 Hz, Hortho of (4-Pyr)).13C{1H} NMR (CD2Cl2, 25 ꢀC) d, ppm [J,
at 60 ꢀC for 30 minutes, and then was evaporated to dryness; the Hz]: 85.6 (s, C5H5); 102.1 (s, ^C2–); 114.2 (s, –C1^); 125.5 (s,
residue was dissolved in dichloromethane and passed through Cortho of (4-Pyr)); 135.3 (s, Cipso of (4-Pyr)); 149.3 (s, Cmeta of (3-
a pad (0.5 cm) of silica gel by using ethyl acetate as an eluent. The Pyr)); 212.3 (s, 2Fe–CO). IR (CH2Cl2 n/cmꢁ1): 2110s (nC^C),
ltrate was concentrated in vacuo and chromatographed on silica 2044vs, 1998vs (nCO), 1591s (nC]C and nC]N). IR (KBr n/cmꢁ1):
gel (9 ꢂ 2 cm). A dark-yellow fraction containing the s-alky- 2109s (nC^C), 2037vs, 1992vs (nCO), 1589s, 1526w, 1487w (nC]C
nylpyridine iron complex was eluted with petroleum ether-ethyl and nC]N). Anal. found: C, 60.39%; H, 3.24%; N, 5.04%. Calc.
acetate (3 : 7) mixture and subsequently with ethyl acetate. The for C14H9FeNO2 (279): C, 60.25%; H, 3.25%; N, 5.02%.
complex Cp(CO)2Fe–C^C–(2-C5H4N) (1) was isolated as brown-
Synthesis of [Cp(CO)Fe{m2-h1(Ca):h1(Ca)-k1(N)-Ca]Cb(H)(2-
yellow solid aer evaporation of the solvent (266 mg,
0.953 mmol, 92%). 1H NMR (CD2Cl2, 25 ꢀC) d, ppm [J, Hz]: 5.14 (s,
C5H4N)}(m-CO)PdI] (4)
3
3
4
5H, C5H5); 7.02 (ddd, 1H, JHH ¼ 7.6 Hz, JHH ¼ 5.3 Hz, JHH
¼
Cyclopentadienyliron dicarbonyl iodide (162 mg, 0.533 mmol)
and Pd2(dba)3$CHCl3 (277 mg, 0.268 mmol) were dissolved in
triethylamine (8 mL). 2-Ethynylpyridine (0.055 mL, 0.545 mmol)
was added to the vigorously stirred mixture, which was then
stirred for 1 hour at room temperature. Aer removal of NEt3 by
evaporation, dichloromethane was added and the solution was
ltered through a pad (0.5 cm) of silica gel by using ethyl acetate
as an eluent. The ltrate was concentrated to about 1 mL
volume and chromatographed on a silica gel column (8 ꢂ 1 cm).
Four fractions were successively eluted with petroleum ether-
ethyl acetate (9 : 1), (4 : 1), (3 : 2) mixtures and nally with
ethyl acetate. The rst yellow-brown fraction gave 3 mg of the
initial Cp(CO)2FeI. 167 mg (89%) of dibenzylideneacetone was
obtained from the second bright yellow fraction. The binuclear
FePd complex 4 was isolated in 78% yield (213 mg, 0.415 mmol)
0.8 Hz, Hpara of (2-Pyr) (H4)); 7.22 (d, 1H, 3JHH ¼ 8.0 Hz, Hortho of (2-
Pyr) (H6)); 7.53 (td, 1H, 3JHH ¼ 7.7 Hz, 4JHH ¼ 1.6 Hz, Hmeta of (2-
Pyr) (H5)); 8.40 (d, 1H, JHH ¼ 5.3 Hz, N–C–Hmeta of ^C2(2-Pyr)
3
(H3)). 13C{1H} NMR (CD2Cl2, 25 ꢀC) d, ppm [J, Hz]: 85.4 (s, C5H5);
95.4 (s, ^C2–); 116.7 (s, –C1^); 119.9 (s, Cmeta of (2-Pyr (C5))); 125.9
(s, N–Cmeta of (2-Pyr) (C6)); 135.3 (s, Cpara of (2-Pyr) (C4)); 145.8 (s,
Cipso of (2-Pyr));149.0 (s, Cortho of (2-Pyr) (C3)); 212.2 (s, 2Fe–CO). IR
(CH2Cl2 n/cmꢁ1): 2112s (nC^C), 2043vs, 1997vs (nCO), 1582m,
1556w, 1460m (nC]C and nC]N). IR (KBr n/cmꢁ1): 2108s (nC^C),
2034vs, 1982vs (nCO), 1582m, 1556w, 1457m (nC]C and nC]N).
Anal. found: C, 60.41%; H, 3.26%; N, 5.01%. Calc. for C14H9FeNO2
(279): C, 60.25%; H, 3.25%; N, 5.02%.
Synthesis of Cp(CO)2Fe–C^C–(3-C5H4N) (2)
Following the procedure described for preparation of 1, as a brown solid aer evaporation of the solvent from the third
complex Cp(CO)2Fe–C^C–(3-C5H4N) (2) was obtained with 95% orange fraction. The fourth dark-yellow fraction contained 4 mg
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(0.014 mmol, 3% yield) of Cp(CO)2Fe–C^C–(2-C5H4N) (1). A direct methods and rened by full-matrix least squares on F2,
recrystallization of Cp(CO)2Fe[m-C]CH(2-C5H4N)]PdI from using SHELX programs.86,87 Hydrogen atoms have been placed
CH2Cl2–hexane (1 : 2) mixture gave 176 mg of red-brown in calculated positions and taken into account in the nal
1
ꢀ
microcrystals. H NMR (CD2Cl2, 25 C) d, ppm [J, Hz]: 5.25 (s, stages of renement in the “riding model” approximation.
C5H5); 6.91 (d, JHH ¼ 8.2, Hortho of (2-Pyr)); 7.07 (t, JHH ¼ 5.9,
Hmeta of (2-Pyr)); 7.54s (]C2H); 7.69 (t, JHH ¼ 7.3, Hpara of (2-
Pyr)); 9.41 (d, JHH ¼ 3.4, N–C–Hmeta of (2-Pyr)).13C{1H} NMR
(CD2Cl2, 25 ꢀC) d, ppm [J, Hz]: 88.3 (s, C5H5); 115.2 (s, Cortho of (2-
Pyr)); 121.0 (s, Cmeta of (2-Pyr)); 139.1 (s, Cpara of (2-Pyr)); 140.2 (s,
]C2H); 153.2 (s, N–Cmeta of (2-Pyr)); 171.0 (s, Cipso of (2-Pyr));
206.25 (s, Fe–CO); 230.77 (s, Fe-CObridging); 312.8 (s, m-C1). IR
(CH2Cl2 n/cmꢁ1): 2026s, 1876s (nCO), 1600m, 1582m, 1550m,
1466m (nC]C and nC]N). IR (KBr n/cmꢁ1): 2005s, 1848s (nCO),
1599m, 1583m, 1546m, 1464m (nC]C and nC]N). Anal. found: C,
32.78%; H, 1.95%; N, 2.73%. Calc. for C14H10FeINO2Pd (513): C,
32.75; H, 1.96%; N, 2.73%.
Author contributions
Victor V. Verpekin: conceptualization, data curation, funding
acquisition, investigation, methodology, supervision, visuali-
zation, writing – original dra, writing – review & editing;
Oleg V. Semeikin: perform investigation on Pd(0)-catalyzed
coupling reactions of Cp(CO)2FeI and [(trimethylsilyl)ethynyl]
pyridines; Alexander D. Vasiliev: X-ray diffractometry investi-
gation; Alexander A. Kondrasenko: NMR investigation; Yuri A.
Belousov: resources; Nikolai A. Ustynyuk: conceptualization,
writing – review & editing. All authors have read and agreed to
the published version of the manuscript.
Synthesis of Cp(CO)2Fe–C^C–(4-C6H3N2S) (5)
Following the procedure described for preparation of 1–3,
complex Cp(CO)2Fe–C^C–(4-C6H3N2S) (5) was obtained from
cyclopentadienyliron dicarbonyl iodide (309 mg, 1.016 mmol)
and 4-ethynyl-2,1,3-benzothiadiazole (245 mg, 1.531 mmol)
with the use of THF (9 mL), DBU (0.23 mL, 234 mg, 1.539
mmol), PdCl2(NCMe)2 (3 mg, 0.012 mmol), and CuI (10 mg,
0.052 mmol). The product was isolated from the reaction
Conflicts of interest
There are no conicts to declare.
Acknowledgements
mixture by column chromatography on silica gel (9 ꢂ 2 cm). A This research was funded by a grant from the Russian Science
dark-yellow fraction containing the s-4-benzothiadiazolyle- Foundation (project No. 18-73-00150).
thynyl iron complex was eluted with petroleum ether-ethyl
acetate (4 : 1 and 3 : 2) mixture. The complex Cp(CO)2Fe–
Notes and references
C^C–(4-C6H3N2S) (5) was obtained as brown-yellow solid aer
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H, 2.40%; N, 8.33%.
X-ray diffraction studies
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