New expanded-ring NHC platinum(0) complexes: Synthesis, structure and highly efficient diboration of terminal alkenes

Article abstract of DOI:10.1016/j.jorganchem.2020.121140

The synthesis and structural characterization of a series of novel platinum(0) complexes were reported. A number of (NHC)Pt(dvtms) (dvtms = 1,3-divinyl-1,1,3,3-tetramethyldisiloxane) complexes were investigated in catalytic addition of B₂Pin₂ to terminal alkenes. The novel expanded ring N-heterocyclic carbene complex (7-Dipp)Pt(dvtms) showed highest performance, turnover numbers up to 3800 were achieved. The scope of the reaction was illustrated by 20 examples with a variety of alkyl, alkoxy, halogen, ester, ketone and acetal substituents.

Full text of DOI:10.1016/j.jorganchem.2020.121140

Journal Pre-proof
New expanded-ring NHC platinum(0) complexes: Synthesis, structure and highly
efficient diboration of terminal alkenes
Sergey A. Rzhevskiy, Maxim A. Topchiy, Konstantin A. Lyssenko, Anna N.
Philippova, Maria A. Belaya, Alexandra A. Ageshina, Maxim V. Bermeshev, Mikhail S.
Nechaev, Andrey F. Asachenko
PII:
S0022-328X(20)30041-3
DOI:
https://doi.org/10.1016/j.jorganchem.2020.121140
JOM 121140
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 22 November 2019
Revised Date: 22 January 2020
Accepted Date: 23 January 2020
Please cite this article as: S.A. Rzhevskiy, M.A. Topchiy, K.A. Lyssenko, A.N. Philippova, M.A.
Belaya, A.A. Ageshina, M.V. Bermeshev, M.S. Nechaev, A.F. Asachenko, New expanded-ring NHC
platinum(0) complexes: Synthesis, structure and highly efficient diboration of terminal alkenes, Journal of
Organometallic Chemistry (2020), doi: https://doi.org/10.1016/j.jorganchem.2020.121140.
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New expanded-ring NHC platinum(0) complexes: synthesis, structure
and highly efficient diboration of terminal alkenes
Sergey A. Rzhevskiya, Maxim A. Topchiya, Konstantin A. Lyssenkob, Anna N. Philippovab,
Maria A. Belayac, Alexandra A. Ageshinaa, Maxim V. Bermesheva, Mikhail S. Nechaeva,d, Andrey F.
Asachenkoa,b,*
a
A. V. Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Leninsky
Prospect 29, Moscow, 119991, Russia. E-mail: Andrey F. Asachenko aasachenko@ips.ac.ru
b A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Vavilov
Street 28, Moscow, 119991, Russia
c
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Leninsky Prospect
47, Moscow, 119991, Russia
d M. V. Lomonosov Moscow State University, Leninskie Gory 1 (3), Moscow, 119991, Russia

Abstract
The synthesis and structural characterization of a series of novel platinum(0) complexes were
reported. A number of (NHC)Pt(dvtms) (dvtms = 1,3-divinyl-1,1,3,3-tetramethyldisiloxane)
complexes were investigated in catalytic addition of B2Pin2 to terminal alkenes. The novel expanded
ring N-heterocyclic carbene complex (7-Dipp)Pt(dvtms) showed highest performance, turnover
numbers up to 3800 were achieved. The scope of the reaction was illustrated by 20 examples with a
variety of alkyl, alkoxy, halogen, ester, ketone and acetal substituents.
Graphical abstract
Keywords
Platinum, N-heterocyclic carbenes, alkenes, diboration, catalysis
Highlights
•
A series of fourteen Pt(0) complexes with expanded-ring NHCs and 4,5-disubtituted
NHCs were prepared.
•
•
Structures of the novel complexes were described in solid state.
The catalytic activity of the (NHC)Pt(dvtms) complexes was evaluated for the alkenes
1,2-diboration.

1. Introduction
Boronic acids and their derivatives proved to be useful reagents for a wide range of reactions,
in particular, for the C-C, C-O and C-N bonds formation [1-5]. While aryl boronic acids and their
derivatives have been well studied in organic synthesis, aliphatic boronic acids derivatives have
received considerably less attention. Alkyl 1,2-bis(boronates) are of particular interest due to their
feasibility toward synthesis of multi-functionalized compounds [6-16].
A number of catalysts have been proposed for the 1,2-diborylalkanes synthesis via 1,2-
diboration of alkenes. The most promising among them are platinum-based catalytic systems, such as
Pt/TiO2 [5], Pt(dba)2 [17, 18], Pt(COD)2, Pt(NBE)3, [19], Pt(COD)Cl2 [20] and Pt2(dba)3+taddol-
derived phosphonite ligands [21]. Transition metal complexes of N-heterocyclic carbenes (Ag, Au,
Cu, Pd and Rh) are also shown to be active catalysts in alkenes 1,2-diboration [22-31]. Despite
reported 1,2-diboration of alkenes catalyzed by (NHC)Pt(0) complexes [32], the influence of the
NHC-ligand structure on the complexes activity was not shown.
We believe that expanded-ring (NHC)Pt(0) complexes may show enhanced catalytic
performance in alkenes 1,2-diboration due to the unique steric and electronic properties of expanded-
ring NHCs. In the course of our ongoing studies on the development of new NHC-based metal
complexes for the application in catalytic reactions under environmentally benign conditions [33-46],
herein, we report our findings on diboration of terminal alkenes catalyzed by expanded-ring NHC
platinum(0) complexes.
2. Experimental
Materials and methods
All reactions were carried out using standard Schlenk technique under argon atmosphere.
Tetrahydrofuran and toluene were distilled over sodium-benzophenone under argon. All alkenes and
Bis(pinacolato)diboron (B2Pin2) were purchased from Sigma-Aldrich. Chemicals and solvents were
obtained from commercial sources and used without further purification. NMR spectra were obtained
1
on a Bruker “Avance 600” (600 MHz H, 151 MHz 13C). The chemical shifts are frequency
referenced relative to the residual undeuterated solvent peaks. Coupling constants J are given in
Hertz as positive values regardless of their real individual signs. The multiplicity of the signals is
indicated as ‘‘s”, ‘‘d”, “t” or ‘‘m” for singlet, doublet, triplet or multiplet, respectively. The
abbreviation ‘‘br” is given for broadened signals.
X-ray diffraction data were collected on a APEX II DUO CCD diffractometer using
molybdenum radiation [λ(MoKα) = 0.71072 Å, ω-scans]. The substantial redundancy in data allowed
empirical absorption correction to be applied with SADABS by multiple measurements of equivalent

reflections. The structures were solved by direct methods and refined by the full-matrix least-squares
technique against F2 in the anisotropic-isotropic approximation. C-H hydrogen atoms in all structures
were placed in calculated positions and refined within the riding model. All calculations were
performed with the SHELXTL software package [47]. Crystal data and structure refinement
parameters for complexes IPrMePt(dvtms) (2g, CCDC 1573639), IPrClPt(dvtms) (2h, CCDC
1573640), IPrBrPt(dvtms) (2j, CCDC 1573637) and (7-Dipp)Pt(dvtms) (4d, CCDC 1573638) are
listed in supporting information (Table S1). Crystallographic data for the structures reported in this
paper have been deposited to the Cambridge Crystallographic Data Centre. These data can be
obtained
free
of
charge
from
The
Cambridge
Crystallographic
Data
via
www.ccdc.cam.ac.uk/data_request/cif.
All products were characterized using NMR, IR spectroscopy and HRMS and details are
given in the supporting information.
Synthesis of azolium and cyclic amidinum salts
Imidazolium salt ICy·HBF4 was synthesized via direct condensation of glyoxal,
paraformaldehyde, appropriate amine and 48% aqueous HBF4 in toluene solution. Imidazolium salts
IPr·HCl and IMes·HCl were obtained via cyclization of N,N'-diarylethylenediimine under action of
the paraformaldehyde and chlorotrimethylsilane in ethyl acetate solution [48]. The analogous
corresponding bisimines cyclization under action of the paraformaldehyde solution in 4M HCl in 1,4-
dioxane gave salts IPrMe·HBF4 and IMesMe·HBF4 [49]. Halogenated imidazolium salts IPrCl·HCl and
IPrBr·HCl were obtained by treatment of free NHC with CX4 (X=Cl or Br) [50-52]. Imidazolinium
salts SIPr·HCl and SIMes·HCl were prepared by cyclization of corresponding N,N'-
diarylethylenediammonium dichlorides with triethyl orthoformate. Highly hindered imidazolium salts
IPr*·HCl and IPrOMe*·HCl were obtained according to literature procedures [48, 53, 54]. Precursors
of the expanded-ring NHC were synthesized via solvent-free alkylation of N,N'-diarylformamidines
with 1,3-dibromopropane or 1,4-dibromobutane [55, 56].
General procedure for preparation of (NHC)Pt(dvtms)
A 10 ml Schlenk flask equipped with a magnetic stir bar was charged with 1.2 mmol (1.2 eq.)
of corresponding azolium (or amidinium) salt and evacuated to 0.1-0.2 mmHg. The Schlenk flask
was heated at 100 °C/0.1 mmHg for 1h. The flask was filled with argon and allowed to cool to room
temperature followed by addition of 6 ml of dry THF. The reaction mixture was stirred for 5 min and
1.2 ml of a 1M NaHMDS in THF was added (2.4 ml for (7-Dipp)Pt(dvtms)). The reaction mixture
was allowed to stir for 1 h at room temperature and 1.0 mmol of Pt2(dvtms)3 in dvtms was added. The
light yellow solution was stirred overnight, and then it was transferred to a 100 ml round-bottomed
flask with dichloromethane and evaporated to dryness. The solids were triturated with 20 ml of

dichloromethane and filtered through a 1 cm pad of silica gel eluting with 3x20 ml of CH2Cl2. The
filtrate was evaporated to dryness; the solids were triturated with 3x1 ml of n-pentane to give a pure
complex as white microcrystalline solid.
General procedure for alkene diboration.
A screw cap vial equipped with magnetic stir bar was charged with freshly distilled alkene (1
mmol) and B2Pin2 (1.1 mmol) followed by 4 ml of heptane. (7-Dipp)Pt(dvtms) (4 mg) was added and
the reaction mixture was allowed to stir at room temperature for 20 h. The reaction mixture was
evaporated to dryness. The residue was purified by column chromatography (EtOAc/hexanes as
eluent).
3. Results and discussion
A series of N-heterocyclic carbene platinum(0) complexes (NHC)Pt(dvtms) was synthesized
for investigation diboration reaction of alkenes. Synthesis of imidazolium salts was performed
according to previously reported techniques (see supplementary information) [48, 49, 53-56].
Platinum(0) complexes were obtained by direct interaction of Karstedt's catalyst Pt2(dvtms)3 with
free carbenes in THF solution (Scheme 1) [57].
Scheme 1. Synthesis of N-heterocyclic carbene platinum(0) complexes
Previously reported complexes bearing five-membered ring NHCs IСyPt(dvtms) (2a, 88%),
IPrPt(dvtms) (2b, 47%), SIPrPt(dvtms) (2c, 50%), SIMesPt(dvtms) (2d, 87%) [58], IPr*Pt(dvtms)
(2e, 64%), IPrOMe*Pt(dvtms) (2f, 70%) [59], as well as expanded six- and seven-membered ring
NHCs 6-MesPt(dvtms) (4a, 42%), (6-Dipp)Pt(dvtms) (4b, 61%), and (7-Mes)Pt(dvtms) (4c, 51%)
[60] were prepared (structures of ligands are shown on Scheme 2). We also performed synthesis of
five new platinum NHC complexes: IPrMePt(dvtms) (2g, 88%), IPrClPt(dvtms) (2h, 63%),
IMesMePt(dvtms) (2i, 93%), IPrBrPt(dvtms) (2j, 53%), (7-Dipp)Pt(dvtms) (4d, 59%).

Ph
Ph
Ph
Ph
N
N
N
N
N
N
N
N
N
N
Ph
Ph
Ph
Ph
IPr*
SIMes
ICy
SIPr
IPr
OMe
Ph
Ph
Ph
N
N
Ph
N
N
N
N
N
N
Ph
Ph
Ph
Ph
N
N
OMe
IPr*OMe
6-Mes
6-Dipp
7-Mes
7-Dipp
Cl
Cl
Br
Br
N
N
N
N
N
N
N
N
IPrMe
IPrBr
IMesMe
IPrCl
Scheme 2. Structures of NHC ligands.
Earlier, formation of air stable free carbenes IPrCl and IPrBr upon halogenation of a free
carbene with tetrahalomethane has been reported [50-52]. Introduction of halogen atoms (chlorine
and bromine) at 4- and 5-positions of NHC leads to complex specific changes in the donor capability
and steric properties of the carbene with respect to IPr. Therefore, we decided to study the effect of
halogen atoms in NHCs on the catalytic properties of platinum complexes.
IPrClPt(dvtms) (2h) and IPrBrPt(dvtms) (2j) complexes were obtained similarly to techniques
described previously (Scheme 3 and 4) [61]. In situ generated free carbenes were treated with CX4 (X
= Cl or Br) to obtain 4,5-dihalocarbenes. In case of IPrCl, solution of chlorinated carbene was treated
with HCl solution in 1,4-dioxane to isolate IPrCl·HCl. Then, platinum(0) complex was obtained

according to the above-mentioned technique using sodium bis(trimethylsilyl)amide and Karstedt's
catalyst Pt2(dvtms)3 (Scheme 3).
Scheme 3. Synthesis of the IPrClPt(dvtms) (2h) complex.
In case of IPrBr, formation of a mixture of mono-, di-, and tri-bromoderivatives IPrBrX·HCl
takes place (see Supporting Information). Therefore, the technique was modified (Scheme 3): to the
solution of a free carbene IPr, solution of 2.4 eq. of CBr4 in THF was added dropwise and the
mixture was stirred for 2 h. Then, Karstedt's catalyst Pt2(dvtms)3 was added. The idea was to obtain a
platinum complex that would differ from IPrBr3 (bromoiminium salt) by polarity. Mono-
bromoderivative would be converted into target dibromide with small excess of CBr4 and long-term
aging of the reaction mixture.
1) NaHMDS, THF
Br
SiMe2
O
SiMe2
N
N
N
N
2) 2.4 eq. CBr4
3) Pt2(dvtms)3
Cl
Pt
Br
1c
2j, 53%
Scheme 4. Synthesis of the IPrBrPt(dvtms) (2j) complex.
All the obtained (NHC)Pt(dvtms) complexes are white powders stable in air. They were
1
characterized by H and 13C NMR spectroscopy. In 13C NMR spectra, signals of ylidene carbon
atoms appear in the region 179–212 ppm evidencing the platinum complex formation. Formation of
1
the complexes was also indicated by the disappearance of the amidinium protons in H NMR.
Splitting of the SiMe2 group signal into two distinct signals at –0.5 and 0.3 ppm, respectively, was

observed [58]. The obtained complexes were also characterized by elemental analysis and IR
spectrometry.
We were unable to obtain signals corresponding to ylidene carbon atoms in 13C NMR spectra
of the complexes (7-Mes)Pt(dvtms) (4c) and (7-Dipp)Pt(dvtms) (4d) in CDCl3. However, it became
possible when CDCl3 was substituted with 1,2-dichlorobenzene-d4 at 70°C. Signals of CNHC atoms
appeared at 230.80 ppm for (7-Mes)Pt(dvtms) (4c), and 235.95 ppm for (7-Dipp)Pt(dvtms) (4d). We
1
have also obtained H-13C HMBC spectra of these compounds. Notably, coupling between ylidene
carbon and 195Pt was observed (1JPt-C = 705 (4c) and 716 (4d) Hz).
Previously not reported complexes IPrMePt(dvtms) (2g), IPrClPt(dvtms) (2h), IPrBrPt(dvtms)
(2j), and (7-Dipp)Pt(dvtms) (4d) were characterized by X-ray crystallography (Figure 1). Crystals for
X-ray crystallography were obtained by slow evaporation from CH2Cl2–pentane, 1:5. Structures of
the complexes are presented in the figures below. The main geometric parameters of the complexes
are presented in Table 1.
IPrClPt(dvtms) (2h)
IPrMePt(dvtms) (2g)
IPrBrPt(dvtms) (2j)
(7-Dipp)Pt(dvtms) (4d)

Figure 1. General view of IPrMePt(dvtms) (2g), IPrClPt(dvtms) (2h), IPrBrPt(dvtms) (2j), and (7-
Dipp)Pt(dvtms) (4d) in representation of atoms by thermal ellipsoids (p=50%).
Table 1. Main geometric parameters of the Pt(0) NHC complexes.
No.
1
Complex
R(CNHC-Pt), Å N–CNHC–N
Ref.
[58]
ICyPt(dvtms) (2a)
IPrPt(dvtms) (2b)
SIPrPt(dvtms) (2c)
IPrMePt(dvtms) (2g)
IPr*Pt(dvtms) (2e)
IPr*OMePt(dvtms) (2f)
IPrClPt(dvtms) (2h)
IPrBrPt(dvtms) (2j)
(6-Mes)Pt(dvtms) (4a)
2.026
2.068
2.053
2.051
2.054
2.048
2.042
2.052
2.066
2.070
2.071
103.8°
103.9°
107.0°
103.3°
104.1°
103.9°
104.2°
103.9°
116.0°
117.1°
117.7°
2
[58]
3
[58]
4
this work
[59]
5
6
[59]
7
this work
this work
[60]
8
9
10 (7-Mes)Pt(dvtms) (4c)
11 (7-Dipp)Pt(dvtms) (4d)
[60]
this work
The N–CNHC–N angle in the NHC ligand increases when transferring from five- to seven-
membered cyclic salts. Values of the parameter for platinum(0) complexes with five-membered
carbenes are practically the same independently of the presence of substituents. The table also
evidences that Pt–CNHC bond lengths in platinum(0) complexes with five-, six-, and seven-membered
carbenes are close to each other and lie within the range of 2.042–2.071 Å.
Our preliminary studies showed that (NHC)Pt(dvtms), bis(pinacolato)diboron, starting
substances and products are stable towards air, thus all catalytic reactions were performed under
ambient atmosphere. Aliphatic solvents, such as hexane, heptane and cyclohexane are among the
most favorable solvents for industrial applications due to their properties such as cost, stability,
toxicity, corrosivity, and environmental hazard [44, 45, 62, 63]. In this regard, heptane was chosen as
reaction solvent. The reactions were performed in air by using 1 mol% of platinum catalyst loading,
styrene as substrate and heptane as solvent (Table 2).
Table 2. Diboration of styrene catalyzed by (NHC)Pt(dvtms).

No.
Complex
Yield, %
1
3
IСyPt(dvtms) (2a)
IPrPt(dvtms) (2b)
34
0
4
5
6
7
8
9
10
11
12
13
14
15
SIPrPt(dvtms) (2c)
38
traces
43
0
0
75
0
72
83
>99
63
>99
SIMesPt(dvtms) (2d)
IPrMePt(dvtms) (2g)
IPr*Pt(dvtms) (2e)
IPr*OMePt(dvtms) (2f)
IPrClPt(dvtms) (2h)
IMesMePt(dvtms) (2i)
IPrBrPt(dvtms) (2j)
(6-Mes)Pt(dvtms) (4a)
(6-Dipp)Pt(dvtms) (4b)
(7-Mes)Pt(dvtms) (4c)
(7-Dipp)Pt(dvtms) (4d)
Reagents and conditions: styrene (1 equiv.), B2Pin2 (1.1 equiv.), catalyst (1 mol%). Yields by 1H NMR
spectroscopy with BHT as Internal Standard.
Catalyst screening showed that structure of NHC-ligand strongly affects yield of diboration
product. Catalytic activity of corresponding platinum(0) complexes seems to related with several
factors, such as electronic and steric effects of NHC carbene ligand. Our experiments have shown
that catalytic activity increases primarily due to expansion of carbene cycle in order: SIPrPt(dvtms)
(2c) < (6-Dipp)Pt(dvtms) (4b) ≤ (7-Dipp)Pt(dvtms) (4d). We suppose that observed increase in
activity related with N–CNHC–N angle expansion and increase of ligand steric bulk (Table 1). Among
the expanded ring complexes the highest activities were found for six- and seven- membered ligands
decorated with bulky 2,6-diisopropylphenyl-substituents (7-Dipp)Pt(dvtms) (4b) and (6-
Dipp)Pt(dvtms) (4d). In comparison with them complexes (6-Mes)Pt(dvtms) (4a) and (7-
Mes)Pt(dvtms) (4c) with less-bulky mesityl- substituents demonstrated decreased activity. The same
trend was observed for SIPrPt(dvtms) (2c) and SIMesPt(dvtms) (2d) couple (Table 2).
Five-membered imidazol-2-ylidene complexes were generally less active in diboration of
styrene. Whereas the IMes and backbone-substituted IMesMe complexes were inactive, IPr-based
complexes showed moderate to good activity; catalytic activity increased in order: H (2b) << CH3
(2g) < Br (2j) ≈Cl (2h). Such effect may be attributed to the increase in %Vbur for IPr-ligands bearing
substituents at C4 and C5 atoms of imidazole ring [49], larger steric bulk on NHC ligand resulted in
higher activity. Interestingly, further increase of NHC steric bulk in complexes 2e and 2f resulted in
the loss of catalytic activity.

Next, we evaluated activities of (7-Dipp)Pt(dvtms) (4b) and (6-Dipp)Pt(dvtms) (4d) under
low loadings (Table 3). To our delight, decreasing the catalyst loading from 1 to 0.1ꢀmol% did not
significantly affect the yields of the desired product for both catalysts. However, when the catalyst
loading was further decreased to 0.025ꢀmol%, much lower product yield (67%) was obtained with (6-
Dipp)Pt(dvtms) (4b), whereas 0.025 mol% of (7-Dipp)Pt(dvtms) (4d) afforded product in near-
quantitative yield (TON = 3800). Thus, these conditions were selected as the standard conditions for
the substrate screening.
Table 3. Detailed comparison of 4b and 4d activity
Catalyst
loading, mol%
No.
1
Catalyst
Yield, %
1
0.5
0.1
>99
>99
98
(7-Dipp)Pt(dvtms) (4d)
0.025
0.005
1
0.5
0.1
95
20.5
>99
>99
97
2
(6-Dipp)Pt(dvtms) (4b)
0.025
67
Reagents and conditions: styrene (1 equiv.), B2Pin2 (1.1 equiv.), catalyst (x mol%).
Next, we evaluated performance of catalyst 4d in diboration of terminal alkenes (Table 4).
The elaborated catalyst allowed diboration of styrenes bearing alkyl- and alkoxy- substituents and
gave products 5b-e in near quantitative yields. Halogen-substituted styrenes were also suitable
substrates, products 5f-g were obtained with 98-99% yields.

Table 4. (NHC)Platinum(0)-catalyzed diboration of terminal alkenes
BPin
4d 0.5 mol%
B2Pin2
+
Bpin
heptane
r.t., air, 20h
R
R
5a-t
BPin
BPin
BPin
BPin
BPin
BPin
5a, 98%
5b, 95%
5c, 98%
BPin
BPin
BPin
BPin
BPin
BPin
MeO
t-BuO
Cl
5d, 97%
BPin
5e, 92%
5f, 98%
BPin
BPin
BPin
BPin
Cl
BPin
Br
5g, 99%
5i, 95%
5h, 98%
BPin
BPin
BPin
BPin
BPin
BPin
OTHP
5j, 86%
BPin
5k,
5l,
90%
82%
BPin
BPin
O
BPin
O
BPin
BPin
O
Br
Cl
5m, 99%
5n, 97%
5o, 97%
BPin
O
BPin
O
O
BPin
BPin
BPin
BPin
O
BPin
O
5p, 92%
5q, 87%
5r,
95%
BPin
BPin
BPin
5s, 89%
5t, 92%
Reagents and conditions: alkene 1 equiv., B2Pin2 1.1 equiv., catalyst 0.5 % mol, r.t., 20h.
Ortho-substituents on the styrene core were also tolerated; products 5h and 5i were isolated in
yields of 95 and 98%, respectively. Diboration of allylbenzene, 1-allylnaphtalene and THP-protected

2-allylphenol gave products 5j (86%), 5k (82%) and 5l (90%), respectively. Allyloxybenzenes were
diborated in 97-99% yields (Table 4, 5m-o).
Addition of B2Pin2 to alkenes, bearing ester, ketone and acetal groups were efficient, products
were obtained in 87-95% yields (Table 4, 5p-r). Simple aliphatic alkenes were tested under reaction
conditions; 1-hexene gave product in 89% yield, whereas 1-vinylcyclohexene was diborated in 92%
yield (Table 4, 5s and 5t respectively).
Conclusions
In conclusion, a series of fourteen (NHC)Pt(dvtms) complexes was prepared. Five complexes
were reported for the first time: IPrMePt(dvtms) (2g), IPrClPt(dvtms) (2h), IPrBrPt(dvtms) (2j),
IMesMePt(dvtms) (2i), (7-Dipp)Pt(dvtms) (4d); four of which (2g, 2h, 2j, and 4d) were characterized
structurally in the solid state using XRD.
Catalytic activities of complexes in diboration of terminal alkenes were evaluated. High
catalytic activity of novel expanded-ring seven-membered NHC complex (7-Dipp)Pt(dvtms) (4d)
was found. Scope and limitations of elaborated catalyst were examined on 20 examples. Combination
of using non-toxic and recoverable alkane solvents, ambient conditions and low loading of catalyst
leading to near-quantitative yields of corresponding products seems to us as highly effective and
atom-economical method of obtaining valuable 1,2-diborylalkanes.
Acknowledgements
Part of this work (synthesis of imidazolium and amidinium salts) was carried out by M. A.
Topchiy and S. A. Rzhevskiy as part of A. V. Topchiev Institute of Petrochemical Synthesis (TIPS)
Russian Academy of Sciences (RAS) State Program. M. V. Bermeshev is thankful to the Russian
Science Foundation (RSF) for financial support (project number 17-19-01595) (synthesis and
catalytic activity studies of five-membered (NHC)Pt complexes). M. S. Nechaev and A. F.
Asachenko are thankful for financial support to Russian Foundation for Basic Research (RFBR),
research project number 16-29-10706 ofi_m. Authors are grateful to the Moscow State University
(Russia) for the opportunity to use the NMR facilities of the Center for Magnetic Tomography and
Spectroscopy. The contribution of the Center for Molecular Composition Studies of INEOS RAS is
also gratefully acknowledged.
Appendix A. Supplementary data
Supplementary data to this article can be found online at

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Highlights
•
A series of fourteen Pt(0) complexes with expanded-ring NHCs and 4,5-
disubtituted NHCs were prepared.
•
•
Structures of the novel complexes were described in solid state.
The catalytic activity of the (NHC)Pt(dvtms) complexes was evaluated for the
alkenes 1,2-diboration.

Declaration of interests
☒ The authors declare that they have no known competing financial interests or personal relationships
that could have appeared to influence the work reported in this paper.
☐The authors declare the following financial interests/personal relationships which may be considered
as potential competing interests: