Dichloro(ethylenediamine)platinum(II), a water-soluble analog of the antitumor cisplatin, as a heterogeneous catalyst for a stereoselective hydrosilylation of alkynes under neat conditions

Article abstract of DOI:10.1016/j.tetlet.2020.152300

A stereoselective method for the hydrosilylation of internal and terminal alkynes under heterogeneous catalysis by dichloro(ethylenediamine)platinum(II) is discussed. This commercially available platinum complex operates under neat conditions at 90 °C, pr

Full text of DOI:10.1016/j.tetlet.2020.152300

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Dichloro(ethylenediamine)platinum(II), a water-soluble analog of the antitu‐
mor cisplatin, as a heterogeneous catalyst for a stereoselective hydrosilylation
of alkynes under neat conditions
Jean Fotie, Mercy Enechojo Agbo, Fengrui Qu, Trevor Tolar
PII:
DOI:
Reference:
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https://doi.org/10.1016/j.tetlet.2020.152300
TETL 152300
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Please cite this article as: Fotie, J., Enechojo Agbo, M., Qu, F., Tolar, T., Dichloro(ethylenediamine)platinum(II),
a water-soluble analog of the antitumor cisplatin, as a heterogeneous catalyst for a stereoselective hydrosilylation
of alkynes under neat conditions, Tetrahedron Letters (2020), doi: https://doi.org/10.1016/j.tetlet.2020.152300
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Dichloro(ethylenediamine)platinum(II), a water-soluble analog of the antitumor
cisplatin, as a heterogeneous catalyst for a stereoselective hydrosilylation of alkynes
under neat conditions
Jean Fotie,a* Mercy Enechojo Agbo,a Fengrui Qu,b and Trevor Tolara
aDepartment of Chemistry and Physics, Southeastern Louisiana University, SLU 10878, Hammond, LA
70402-0878, USA
bDepartment of Chemistry and Biochemistry, The University of Alabama, Tuscaloosa, AL 35487, USA
Abstract
A stereoselective method for the hydrosilylation of internal and terminal alkynes under
heterogeneous catalysis by dichloro(ethylenediamine)platinum(II) is discussed. This commercially
available platinum complex operates under neat conditions at 90 oC, producing exclusively the (trans)
Z-isomer with symmetrical internal alkynes, while terminal alkynes produce a mixture of α- and β(E)-
hydrosilylated products. No β(Z)-hydrosilylated product was observed during this study, and the
selectivity between the α- and β(E)-hydrosilylated products appears to be influenced to a certain
degree by the nature of the hydrosilanes. The catalyst was recyclable up to five runs under gram scale
conditions without any loss of the catalytic activity.
Key words: Dichloro(ethylenediamine)platinum(II), Alkynes, Stereoselective Hydrosilylation,
Heterogeneous Catalysis.
_______________
*Corresponding author. Tel.: (+1) 985-549-5112, Fax: (+1) 985-549-5126
E-mail address: jean.fotie@southeastern.edu (Jean Fotie)
1

Introduction
Metal-catalyzed hydrosilylation of alkynes is arguably one of the most powerful, convenient and
atom-efficient method for the synthesis of alkenylsilanes and vinylsilanes.1 Owing to their unique
reactivity, these are valuable intermediates in organic chemistry, with a wide range of applications in
a number of important transformations such as Hiyama-type couplings,2 Heck couplings,3 coupling
with aldehydes,4 Friedel-Crafts reactions,5 and served as dienophiles in Diels-Alder reactions.6
Due to their high catalyst turnovers, platinum complexes are by far the most explored catalysts for
the hydrosilylation of olefins and acetylenes, with the Speier system (H2PtCl6/iPrOH)7 and Karstedt
complex ([Pt2(dvtms)3], dvtms = 1,3-divinyl-1,1,3,3-tetramethyldisiloxane)8 being the most commonly
used in industrial settings. These latter catalysts are well known to form colloidal platinum particles
during the course of the reaction, and to address these shortcomings, a number of platinum
complexes bearing a wide range of ligands including bulky phosphines, N-heterocyclic carbenes or
chelating acyclic aminocarbenes have been explored.9 In addition, less reactive but highly selective
ruthenium complexes,6, 10 as well as some rhodium(I)11 and palladium complexes12 are also reported
in the chemical litterature.
The constant need for more selective, robust and recyclable catalysts has resulted in the development
of heterogenous hydrosilylation methods, primarily based on metal nanoparticles.1d, 13 This includes
13h
13i
super-microporous silica-supported platinum nanoparticles,1d,
ligand-free Pt3 clusters,13e,
polysiloxane stabilized platinum nanoparticles, as well as platinum nanodispersed in organically
modified silicates from our research group,13g all used as heterogeneous catalysts for the
hydrosilylation of olefins and acetylenes. In our contineous effort to develop heterogenous catalytic
systems for the hydrosilylation of olefins and acetylenes, we here report the stereoselective
2

hydrosilylation of internal and terminal alkynes under neat conditions using
dichloro(ethylenediamine)platinum(II). Unlike many discrete metal complexes which operate
preferentially under homogeneous catalysis, this commercially available platinum complex proceeds
via heterogeneous catalysis. Furthermore, despite platinum complexes being well explored for their
catalytic activities in hydrosilylation reactions,9 this water-soluble analog of the antitumor cisplatin
has been investigated primarily for its anticancer properties,14 which is the result of its DNA-damaging
effects via a selective binding mechanism.15 As such, its catalytic capability remains unexplored. This
work represents a rare and to the best of our knowledge, unprecedented glimpse into its potential as
a catalyst in chemical transformations. In addition, the catalytic system developed during the course
of this study works equally well with internal and terminal alkynes, producing exclusively the (trans)
Z-isomer with symmetrical internal alkynes, while terminal alkynes produce a mixture of α- and β(E)-
hydrosilylated products. The nature of the hydrosilanes seems to influence somewhat the selectivity
between the α- and β(E)-hydrosilylated products, and with no β(Z)-vinylsilane observed.
Results and Discussion
As part of our continue efforts to develop more efficient and sustainable hydrosilylation methods,13g,
16
we noticed that dichloro(ethylenediamine)platinum(II), Pt(en)Cl2, was able to catalyze the
hydrosilylation of diphenylacetylene in the presence of diphenylsilane in refluxing toluene in 18 h as
illustrated in Scheme 1. These initial reaction conditions were adapted from a previous study from
our research group,13g and a quick optimization was undertaken as summarized in Table 1. It appears
that the reaction goes to completion in toluene at 100 oC, in presence of 1 mol% of Pt(en)Cl2 (entry
3), but not when refluxed in either CH3CN or THF (entries 4 and 5) with the same catalyst load.
3

H2N NH2
Pt
Ph
Ph
Cl
Cl
Ph2SiH2
Ph
Ph
+
SiHPh2
Scheme 1. Hydrosilylation of diphenylacetylene by diphenylsilane in the presence of
dichloro(ethylenediamine)platinum(II).
Table 1. Exploration of the reaction conditions using diphenylacetylene and diphenylsilane
Entries
Ph2SiH2
(eq.a)
Pt(en)Cl2
(mol%)
Solvent
Temperature Time (h)
oC
Percent
conversion (%)b
0.5
1
1.2
Toluene
reflux
18
65
2
3
1.2
1.2
1.2
1.2
1.2
2.0
1.0
1.2
1.2
1.2
1.2
1.2
1.0
1.0
1.0
1.0
1.0
1.0
1.0
0.5
1.0
1.0
none
1.0
Toluene
Toluene
CH3CN
THF
60
100
reflux
reflux
90
18
18
18
18
18
18
18
18
18
18
18
6
78
98c
37
4
5
84
6
neat
97c
98c
80
7
neat
90
8
neat
90
9
neat
90
63
10
11
12
13
neat
rt
32
neat
60
76
neat
90
N.Rd
73
neat
90
Reactions were performed under a nitrogen atmosphere, using 100 mg of diphenylacetylene. aIn relationship to the number of moles
b
c
of diphenylacetylene. Percent conversions determined by GC-MS, using tridecane as an internal standard. No starting material was
present upon reaction completion as indicated by GC-MS. dN.R. = No Reaction.
All these reactions were performed under a nitrogen atmosphere, and when neat conditions were
o
implemented with a similar catalyst load and 1.2 eq. of hydrosilane at 90 C for 18 h, no starting
4

material was observed in the reaction mixture as indicated by GC-MS (entry 6). The increase of the
equivalence of diphenylsilane from 1.2 to 2.0 did not have any noticeable impact on the reaction
outcome (entry 7). However, any decrease in the equivalence of diphenylsilane (entry 8), catalyst load
(entry 9), temperature (entry 11) or reaction time (entry 13) appear to negatively impact the reaction,
with no product observed in the absence of the catalyst (entry 12). It should be mentioned that the
reaction proceeds at room temperature, although only a modest yield was obtained in 18 h (entry
10). As a result, the conditions in entry 6 were selected for the exploration of the scope of the reaction.
Diphenylacetylene was thus reacted with a number of hydrosilanes, including triethoxysilane,
benzyldimethylsilane, triethylsilane and triphenylsilane, in the presence of 1 mol% of Pt(en)Cl2 at 90
oC for 18 h under neat conditions, to produce compounds 2 – 5 respectively, in good to excellent yields
(Fig 1). The reaction also works well with hex-3-yne in the presence of either diphenylsilane or
triethoxysilane to produce compounds 6 and 7 respectively.
Si
Si(OEt)3
(76%)
SiHPh2
(81%)
Me
Ph
1:
Me
2:
3:
(86%)
H
Ph
Ph
Si
Si(OEt)3
SiEt3
(88%)
SiPh3
(96%)
5:
7:
(72%)
4:
6:
(75%)
Fig. 1. Dichloro(ethylenediamine)platinum(II) catalyzed hydrosilylation of diphenylacetylene and hex-3-
yne using a range of hydrosilanes (isolated yields from 200 mg reactions).
5

All these reactions with symmetrical alkynes produced exclusively a single isomer of the expected
1
product as indicated by the GC-MS and NMR spectra. A careful analysis of the H-, 13C-NMR, HSQC,
HMBC and NOESY spectra of 4, used as an example, indicated that this compound is the Z-isomer
(trans). In fact, no NOESY correlation was observed between the vinylic proton of the alkene and any of
the protons of the triethylsilane group, indicating that this proton was not spatially close to the
triethylsilane group. Instead, this proton show correlations only with the protons from the benzenes
rings, confirming that the vinylic proton and the triethylsilane group are not on the same side of the
double bond (see supplementary information). The same pattern was observed in the NMR data of all
the other compounds.
A number of terminal alkynes with various electronic features, including phenylacetylene,
trimethylsilylacetylene, p-tolyacetylene, 4-ethynylanisole, 1-bromo-4-ethynylbenzene and 1-ethynyl-4-
(trifluoro)benzene were also explored under this catalytic system, and the reaction appears to work
equally well as summarized in Table 2. However, unlike symmetrical internal alkynes that produced
exclusively the (trans) Z-isomer, terminal alkynes produce a mixture of α- and β(E)-hydrosilylated
products, with no β(Z)-vinylsilane observed during this study. Although many of these mixtures were
inseparable by conventional column chromatography, their constituents, namely α-vinylsilane and β(E)-
vinylsilane isomers were rather easily characterized by 1H-NMR and GC-MS. In fact, the large coupling
constant (J = 19.2 Hz) between the trans vinylic protons in the β(E)-vinylsilane isomer in the 1H-NMR of
the mixture stands in clear contrast to the small coupling constant (J = 3.2 Hz) between the two germinal
protons of the α-vinylsilane isomer. These four distinguishable doublets of 1H each (2 from each isomer)
consistently appeared at different chemical shifts, thus enabling an easy determination of the α:β
isomeric ratio.
6

Table 2. Summary of reactions with terminal alkynes (isolated yields from 200 mg reactions)
Starting material
Silane
Products (α:β ratio)
% yield
88
H2SiPh2
SiHPh2
Si(OEt)3
SiEt3
SiHPh2
8ab (57:43)
HSi(OEt)3
HSiEt3
86
75
Si(OEt)3
9b
(60%)
9a
(26%)
(3:7) (the mixture was resolved)
SiEt3
10ab (59:41)
Me
Me
Ph
Si
HSi(Me)2Bn
Si
Ph
73
Me
Me
11ab (52:48)
7

HSiPh3
SiPh3
Me
65
88
SiPh3
(27%)
12b
(38%)
12a
(42:58) (The mixture was resolved)
Me
Me Si
Me Me
Me
Me Si
HSi(Me)2Bn
Ph
Si
Ph
Me Si
Si
Me
Me
Me Me
Me
13ab (1:1)
Me
Me
Me
HSiPh3
SiPh3
70
79
Me Si
Me
Me Si
Me
SiPh3 Me Si
Me
14ab (41:59)
HSi(OEt)3
Me
Me
Si(OEt)3
Si(OEt)3
Me
Me
15ab (28:72)
HSiEt3
SiEt3
73
SiEt3
Me
Me
16ab (64:36)
8

Me
Si
Ph
Me
Si
HSi(Me)2Bn
Ph
Me
79
Me
Me
Me
Me
17ab (51:49)
HSi(OEt)3
HSiEt3
MeO
MeO
MeO
Si(OEt)3
75
76
84
Si(OEt)3
(24%)
18a
18b
(51%)
MeO
MeO
(32:68) (The mixture was resolved)
SiEt3
SiEt3
MeO
MeO
19ab (64:36)
Me
Me
Si
Ph
HSi(Me)2Bn
Si
Ph
Me
Me
MeO
Br
MeO
20ab (48:52)
HSi(OEt)3
Br
Si(OEt)3
71
Si(OEt)3
Br
21ab (42:58)
9

HSiEt3
SiEt3
Br
Br
72
87
SiEt3
Br
Br
22ab (72:28)
Me
Si
Me
Si
HSi(Me)2Bn
Ph
Ph
Me
Me
Br
Br
23ab (53:47)
HSi(OEt)3
F3C
F3C
F3C
Si(OEt)3
SiEt3
81
75
84
Si(OEt)3
F3C
F3C
24ab (47:53)
HSiEt3
SiEt3
F3C
F3C
25ab (65:35)
Me
Me
Ph
HSi(Me)2Bn
Si
Ph
Si
Me
Me
F3C
F3C
26ab (61:39)
10

Furthermore, the two isomers also appeared to have different retention times on the gas
chromatographs, allowing to record a separate mass spectrometry spectrum for each isomer (see
supplemental data). The combination of 1H and 13C-NMR on one hand and GC-MS on the other permit
a full characterization of the components within each mixture. More importantly, the resolution of
three of these mixtures by column chromatography resulting in the isolation and full characterization
of pure isomers in each case, namely 9a, 9b, 12a, 12b, 18a and 18b, provide additional data to support
these observations. The structure of 12b, obtained as a clear crystalline material, was further confirmed
by single crystal X-ray diffraction, and the molecular structure with thermal ellipsoid representation at
50% probability level is shown in Fig. 2.
Fig. 2. The molecular structure of 12b, showing 50% probability ellipsoids. The single crystal X-ray data
for 12b (CCDC 2007037) is deposited in the Cambridge database, and copies of these materials can be
obtained free of charge from CCDC, 12 Union Road, Cambridge CB2 1EZ, UK,
https://www.ccdc.cam.ac.uk/.
While the nature and the electronic profile of alkynes and hydrosilanes do not appear to significantly
affect the overall yield of the reaction, they do have some impact on the α:β isomeric ratio. For example,
triphenylsilane produced similar isomeric ratios with both with phenylacetylene (12ab, 42:58) and
11

trimethylsilylacetylene (14ab, 41:59), with an excess of the β-(E)isomer, while benzyldimethylsilane
produced a 1:1 isomeric ratio with every alkyne tested regardless of their electronic profile;
phenylacetylene (11ab, 52:48), trimethylsilylacetylene (13ab, 50:50), p-tolyacetylene (17ab, 51:49), 4-
ethynylanisole (20ab, 48:52) and 1-bromo-4-ethynylbenzene (23ab, 53:47), except for 1-ethynyl-4-
(trifluoro)benzene (26ab, 61:39) that produced a larger excess of the α-isomer. Interestingly, while
triethoxysilane produced mixtures with an excess of the β-(E)-isomer, which appears to be more
pronounced with alkynes with an electron-donating groups, triethylsilane does exactly the opposite by
producing mixtures with an excess of the α-isomer, which appeared to be more pronounced with
alkynes with an electron-withdrawing groups.
From a mechanistic perspective, the presence of the Markovnikov (α-isomer) and the anti-Markovnikov
(β-isomer) in the product mixtures implies two competitive pathways well accepted for the
hydrosilylation of alkynes and alkenes. As such, the key step that determines the regioselectivity of the
reaction is the migratory insertion, which proceeds either through hydroplatination to produce the β-
isomer or through silylplatination resulting in the α-isomer,9a, 9c, 17 following a Chalk–Harrod mechanism
recently modified by Corma and coworkers,13e as illustrated in Scheme 2. According to this recent study,
the Pt species formed in situ determines the observed selectivity, with Pt nanoparticles inducing the
production of β-vinylsilanes, while small Pt clusters of 3-4 atoms control the formation of α-
vinylsilanes.13e These observations are consistent with a previous study from our research group in
which Pt nanoparticles dispersed and stabilized in organically modified silicates produced exclusively
the β-vinylsilane products during the hydrosilylation of alkenes and alkynes, with no α-isomer
observed.13g The study from the Corma’s research group clearly showed that small Pt clusters preferably
produced the α-isomer, and also enable the identification of alternative intermediates, labelled in
Scheme 2 as modified Chalk-Harrod species.13e Taken together, these studies suggest that the presence
12

of both the α-isomer and the β-isomer within the same reaction mixture implies the formation of two
different Pt catalytic species, namely Pt nanoparticles (which exclusively produces β-vinylsilanes) and
small Pt clusters (which exclusively produces α-vinylsilanes), from the same initial Pt precatalyst
(Scheme 2). It is still unclear how the electronic profile of the alkyne starting materials and the nature
of hydrosilanes contribute to the formation of either of these catalytic species, if at all. One thing for
sure is that they have some influence on the selectivity observed during the course of this study,
indicating that further investigations are still needed.
-conditions
Pt precatalyst
-conditions
R1
R3Si
R1
SiR3
Pt
Pt3
R1
H
H
R3Si
SiR3
Pt
SiR3
H
Pt
Pt3
Pt
Pt3
Pt3
SiR3
R1
H
R1
R1
Chalk-Harrod
Modified
Chalk-Harrod
R1
Chalk-Harrod
R
1 R1
Modified
Chalk-Harrod
R3Si
R1
H
R3Si
R1
H
Pt
Pt3
HSiR3
Scheme 2. Possible pathways for the hydrosilylation of alkynes leading to either the α-isomer (right) or
the β-isomer (left) through both Chalk-Harrod and modified Chalk-Harrod mechanism.13e
Nevertheless, since the reaction proceeds via heterogeneous catalysis, it was necessary to investigate
the reusability of the catalyst. This study was carried out at a gram scale, using hex-3-yne and
triethoxysilane as the starting materials. Not only the yield of the reaction was similar at a larger scale,
the same catalyst was recycled up to five runs with no loss of catalytic activities, as illustrated in Fig. 3.
13

However, it should be mentioned that the reaction proceeded via homogeneous catalysis whenever a
solvent such as toluene, CH3CN or THF was used.
100%
80%
60%
80
82
77
78
79
40%
20%
0%
1
2
3
4
5
Number of cycles
Fig. 3. Study of the reusability of dichloro(ethylenediamine)platinum(II) using hex-3-yne and
triethoxysilane in the preparation of 7 (these are isolated yields from 1 gram scale reactions).
Conclusion
Dichloro(ethylenediamine)platinum(II), a water-soluble analog of the antitumor cisplatin, has been
proven to be a catalyst procursor for an efficient and robust hydrosilylation of acetylenes. Unlike many
discrete metal complexes which operate preferentially under homogeneous catalysis, this commercially
available platinum complex proceeds via heterogeneous catalysis under neat conditions, and works well
with both internal and terminal alkynes. While symmetrical internal alkynes produced exclusively the
(trans) Z-isomer, terminal alkynes produced a mixture of α- and β(E)-vinylsilanes, with no β(Z)-
hydrosilylated product observed during this study. The electronic profile of the alkynes as well as the
nature of the hydrosilanes also appeared to have some influence on the observed selectivity. As for
possible mechanistic pathways, the presence of both the α-isomer and the β-isomer within the same
14

reaction mixture suggests the creation of two different Pt catalytic species; the Pt nanoparticles
enabling the formation of β-vinylsilanes and small Pt clusters allowing for the production of α-
vinylsilanes, both from the same initial Pt precatalyst. This catalyst was recyclable up to 5 runs under a
gram scale conditions without any loss of the catalytic activity.
Acknowledgement
We thank NSF CHE MRI-1828078 for the SC XRD instrument at the University of Alabama (Tuscaloosa)
used for the single crystal X-ray diffraction analysis. J.F. is also grateful for the financial support from
the Louisiana Biomedical Network, and NSF CHE-1954734.
Appendix A. Supplementary data
1
Supplementary information associated with this article including the experimental data, H and 13C-
NMR, and the GC-MS spectra featuring the isomeric ratios in each of the mixtures reported can be found
in the online version, at
References
1. (a) D. Troegel, J. Stohrer, Coord. Chem. Rev. 255 (2011) 1440–1459; (b) S.-L. Shi, Z.L. Wong, S.L.
Buchwald, Nature 532 (2016) 353–356; (c) Z. Mo, J. Xiao, Y. Gao, L. Deng, J. Am. Chem. Soc. 136
(2014) 17414–17417; (d) M. Planellas, W. Guo, F. Alonso, M. Yus, A. Shafir, R. Pleixats, T. Parella, Adv.
Synth. Catal. 356 (2014) 179–188; (e) A. Garcia-Rubia, J.A. Romero-Revilla, P. Mauleon, R. Gomez
Arrayas, J.C. Carretero, J. Am. Chem. Soc. 137 (2015) 6857–6865; (f) A. Simonneau, M. Oestreich,
Nat. Chem. 7 (2015) 816–822. (g) A. Rivera-Hernandez, B.J. Fallon, S. Ventre, C. Simon, M.-H.
15

Tremblay, G. Gontard, E. Derat, M. Amatore, C. Aubert, M. Petit, Org. Lett. 18 (2016) 4242–4245; (h)
J. Guo, Z. Lu, Angew. Chem., Int. Ed. 55 (2016) 10835–10838.
2. (a) Y. Hatanaka, T. Hiyama, Synlett (12) (1991) 845–53; (b) T. Hiyama, J. Organomet. Chem. 653 (2002)
58–61; (c) L. Cornelissen, V. Cirriez, S. Vercruysse, O. Riant, Chem. Commun. 50 (2014) 8018–8020,
(d) L. Cornelissen, M. Lefrancq, O. Riant, Org. Lett. 16 (2014) 3024–3027.
3. (a) K. Itami, Y. Ushiogi, T. Nokami, Y. Ohashi, J.-I. Yoshida, Org. Lett. 6 (2004) 3695–3698, (b) A.
Battace, T. Zair, H. Doucet, M. Santelli, J. Organomet. Chem. 690 (2005) 3790–3802.
4. M.C. McIntosh, S.M. Weinreb, J. Org. Chem. 56 (1991) 5010–5012.
5. L.A. Paquette, W.E. Fristad, D.S. Dime, T.R. Bailey, J. Org. Chem. 45 (1980) 3017–3028.
6. B.M. Trost, Z.T. Ball, J. Am. Chem. Soc. 127 (2005) 17644–17655.
7. (a) J.L. Speier, J.A. Webster, G.H. Barnes, J. Am. Chem. Soc. 79 (1957) 974–979; (b) J.L. Speier, R.
Zimmerman, J. Webster, J. Am. Chem. Soc. 78 (1956) 2278–2281.
8. (a) B.D. Karstedt, DE2307085A1, 1973. (b) B.D. Karstedt, DE1941411A, 1970. (c) B.D. Karstedt,
FR1548775, 1968.
9. (a) G. Berthon-Gelloz, J.-M. Schumers, G. De Bo, I.E. Marko, J. Org. Chem. 73 (2008) 4190–4197; (b)
M. Blug, X.-F. Le Goff, N. Mezailles, P. Le Floch, Organometallics 28 (2009) 2360–2362 ; (c) J.-X. Xu,
M.-Y. Chen, Z.-J. Zheng, J. Cao, Z. Xu, Y.-M. Cui, L.-W. Xu, ChemCatChem 9 (2017) 3111–3116; (d) G.F.
Silbestri, J.C. Flores, E. de Jesus, Organometallics 31 (2012) 3355–3360; (e) P. Zak, M. Bolt, M. Kubicki,
C. Pietraszuk, Dalton Trans. 47 (2018) 1903–1910; (f) R.S. Chay, B.G.M. Rocha, A.J.L. Pombeiro, V.Y.
Kukushkin, K.V. Luzyanin, ACS Omega 3 (2018) 863–871; (g) L. Ortega-Moreno, R. Peloso, C. Maya, A.
Suarez, E. Carmona, Chem. Commun. 51 (2015) 17008–17011.
10. (a) Y. Na, S. Chang, Org. Lett. 2 (2000) 1887–1889; (b) C. Menozzi, P.I. Dalko, J. Cossy, J. Org. Chem.
70 (2005) 10717-10719; (c) B.M. Trost, Z.T. Ball, J. Am. Chem. Soc. 123 (2001) 12726–12727.
16

11. A. Sato, H. Kinoshita, H. Shinokubo, K. Oshima, Org. Lett. 6 (2004) 2217–2220.
12. (a) Y. Sumida, T. Kato, S. Yoshida, T. Hosoya, Org. Lett. 14 (2012) 1552–1555; (b) H. Zhou, C. Moberg,
Org. Lett. 15 (2013) 1444–1447.
13. (a) H. Miura, K. Endo, R. Ogawa, T. Shishido, ACS Catal. 7 (2017) 1543–1553; (b) R.C. Bal, A.K. Shil,
N.R. Guha, D. Sharma, P. Das, Catal. Lett. 144 (2014) 1530–1536; (c) W.A. Solomonsz, G.A. Rance,
B.J. Harris, A.N. Khlobystov, Nanoscale 5 (2013) 12200–12205; (d) W. Hu, H. Xie, H. Yue, P. Prinsen,
R. Luque, Catal. Commun. 97 (2017) 51–55; (e) M.A. Rivero-Crespo, A. Leyva-Perez, A. Corma, Chem.
- Eur. J. 23 (2017) 1702–1708 ; (f) B.P.S. Chauhan, A. Sarkar, Dalton Trans. 46 (2017) 8709–8715; (g)
B.J. Duke, E.N. Akeroyd, S.V. Bhatt, C.I. Onyeagusi, S.V. Bhatt, B.R. Adolph, J. Fotie, New J. Chem. 42
(2018) 11782–11795 ; (h) G. Fernandez, R. Pleixats, ChemistrySelect 3 (2018) 11486–11493; (i) U.
Diaz, D. Brunel, A. Corma, Chem. Soc. Rev. 42 (2013) 4083–4097.
14. (a) A.P. Jekunen, D.K. Hom, J.E. Alcaraz, A. Eastman, S.B. Howell, Cancer Res. 54 (1994) 2680–2687;
(b) E.F. McClay, K.D. Albright, J.A. Jones, A. Eastman, R. Christen, S.B. Howell, Cancer Res. 52 (1992)
6790-6796.
15. (a) T. Ohmori, T. Morikage, H. Sugimoto, Y. Fujiwara, K. Kasahara, K. Nishio, S. Ohta, Y. Sasaki, T.
Takahashi, N. Saijo, Jpn. J. Cancer Res. 84 (1993) 83–92; (b) V. Murray, H. Motyka, P.R. England, G.
Wickham, H.H. Lee, W.A. Denny, W.D. McFadyen, Biochemistry 31 (1992) 11812–11817; (c) A.
Eastman, Anal. Biochem. 197 (1991) 311–315; (d) A. Eastman, Chem.-Biol. Interact. 61 (1987) 241–
248; (e) A. Eastman, Biochemistry 25 (1986) 3912–15; (f) A. Eastman, Biochemistry 24 (1985) 5027–
5032.
16. (a) S.V. Bhatt, S.V. Bhatt, J. Fotie, American Chemical Society, SERMACS–676, 2018; (b) S.V. Bhatt,
S.V. Bhatt, J. Fotie, Tetrahedron Lett. 60 (2019) 1636–1639.
17

17.
(a) A.J. Chalk, J.F. Harrod., J. Am. Chem. Soc. 87 (1965) 16–21; (b) S. Sakaki, N. Mizoe, M.
Sugimoto, Organometallics 17 (1998) 2510–2523.
18