Dehydrogenative Diboration of Alkynes Catalyzed by Ir/CO/tBuNC System

Article abstract of DOI:10.1016/j.jorganchem.2020.121614

Catalytic dehydrogenative diboration (DHDB) of alkyne with HBpin was achieved using [Ir(COD)Cl]₂ and other related Ir precursors under CO atmosphere. The selectivity for DHDB over hydroboration was higher in less polar solvents and under higher

Full text of DOI:10.1016/j.jorganchem.2020.121614

Journal Pre-proof
Dehydrogenative Diboration of Alkynes Catalyzed by Ir/CO/tBuNC
System
Qingheng Lai , Oleg V. Ozerov
PII:
S0022-328X(20)30517-9
DOI:
Reference:
https://doi.org/10.1016/j.jorganchem.2020.121614
JOM 121614
To appear in:
Journal of Organometallic Chemistry
Received date:
Revised date:
Accepted date:
21 September 2020
11 November 2020
12 November 2020
Please cite this article as: Qingheng Lai , Oleg V. Ozerov , Dehydrogenative Diboration of
Alkynes Catalyzed by Ir/CO/tBuNC System, Journal of Organometallic Chemistry (2020), doi:
https://doi.org/10.1016/j.jorganchem.2020.121614
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition
of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of
record. This version will undergo additional copyediting, typesetting and review before it is published
in its final form, but we are providing this version to give early visibility of the article. Please note that,
during the production process, errors may be discovered which could affect the content, and all legal
disclaimers that apply to the journal pertain.
© 2020 Published by Elsevier B.V.

Dehydrogenative Diboration of Alkynes
Catalyzed by Ir/CO/tBuNC System
Qingheng Lai and Oleg V. Ozerov*
Department of Chemistry, Texas A&M University, 3255 TAMU, College Station, TX 77842.
ozerov@chem.tamu.edu
ABSTRACT. Catalytic dehydrogenative diboration (DHDB) of alkyne with HBpin was achieved
using [Ir(COD)Cl]2 and other related Ir precursors under CO atmosphere. The selectivity for DHDB
over hydroboration was higher in less polar solvent and under increasing CO pressure. It was further
t
improved when catalytic amount of BuNC was added to the reaction. It was possible to achieve
DHDB of both terminal and internal alkynes with selectivity for DHDB of up to 9:1 under the best
conditions. Some DHDB products were isolated on the preparative scale.
KEYWORDS. Iridium, catalysis, alkynes, diboration, hydroboration.
1

1. Introduction
1,2-Diboration of alkynes is a reaction that produces 1,2-diborylalkenes [1],which are useful
building blocks for the syntheses of polysubstituted alkenes [2-6]. It is typically conceived
stoichiometrically as a formal addition of the B-B bond in a diborane across a triple bond of an
alkyne [7,8]. The diborane usually carries heteroatom substituents on the borons, with the B2pin2
and B2cat2 being the most common reagents. This reaction has been catalyzed by a transition
metal complexes such as Pt [9-16] or Cu [17-19], by strong bases for certain substrates [20],via
organocatalysis [21,22],and has even been shown to proceed without a catalyst for some
diboranes [23]. An Ir catalyst for diboration using a B-B reagent has also been reported [24].
Figure 1. Top: conventional diboration of alkynes with a B-B reagent. Bottom: dehydrogenative
diboration of alkynylboronates with HBpin using a (SiNN)Ir catalyst.
2

In 2015, we reported on tandem catalysis of the conversion of terminal alkynes into
triborylalkenes by the Ir complexes supported by the SiNN ligand [25]. The first step of the
transformation is the dehydrogenative borylation of terminal alkynes (DHBTA), on which we
and others extensively reported separately [ 26-36 ]. DHBTA results in the formation of
alkynylboronates which are diborated in the second step to yield triborylalkenes by a (SiNN)Ir
catalysts modified by the addition of CO. The unusual part of this reaction was that the
diboration was not of a kind depicted at the top of Figure 1 but instead used HBpin as the boron
substrate and thus was net dehydrogenative. This is potentially an attractive alternative to the
diboration with diboranes because it relies on a simpler boron starting material. We were not
able to establish the mechanism by which this dehydrogenative diboration (DHDB) happens, but
did isolate a (SiNN)Ir(CO) complex which was itself a competent catalyst. The selectivity for
the diboration was not perfect and competitive hydroboration also took place to some extent.
Fortuitously, alkenes with three -Bpin substituents proved to be less soluble and were easily
isolated by recrystallization out of mixtures containing tri- and diboryl alkenes.
We desired to explore whether an analogous DHDB can be applicable to alkynes other than
alkynylboronates and also if the selectivity towards diboration could be improved. Although we
intended to focus on the Ir complexes of the SiNN ligand, this report describes how it was
discovered that the SiNN ligand was not necessary and that a simpler catalyst formulation was
possible.
3

2. Results and Discussion
2.1. Optimization of DHDB of 1-phenyl-1-butyne.
We selected 1-phenyl-1-butyne as the test substrate to examine whether DHDB can be extended
to internal, carbon-substituted alkynes. Application of 1% (SiNN)Ir(COE) as the catalyst under
conditions similar to those we reported in 2015 resulted in the formation of the predominantly
DHDB product along with two isomeric hydroboration products. Performing a control
experiment with 1 mol% [Ir(COD)Cl]2 as the catalyst (all molar percentages refer to the Ir
content, not the molar amount of the dimeric precursor), we found that it furnished essentially
the same product distribution. This was surprising because our control experiment with 5 mol%
[Ir(COE)2Cl]2 in the 2015 paper led primarily to hydroboration and to little or no diboration
products. The culprit in this instance was that 5 mol% Ir is a high catalyst loading and the
introduction of CO via freeze-pump-thaw cycles takes some time (that the 2015 experiment did
not control for) after the mixing the alkyne, HBpin, and the Ir catalyst. Thus, it is possible to
consume the reagents (primarily via hydroboration) before CO is properly introduced.
Having realized this, we examined a series of simple Ir precursors (Table 1) at 1 mol% Ir loading
and taking care to minimize the exposure time prior to the introduction of CO. Except for
[Ir(COD) Br]2 and [Ir(COD)I]2, all the entries in Table 1 resulted in approximately the same
distribution of DHDB/hydroboration products. This suggests that the same active species was
generated in entries 1, 2, and 5-7 and that implies that the anionic ligand attached to Ir in the
precursor (Cl, OH, or OMe) was replaced with another. We hypothesize that the HBpin reagent
undergoes metathesis with the Ir-O and Ir-Cl bonds to replace them with Ir-H, which may further
react with H-Bpin to give rise to Ir-B and H2 (as byproduct of DHDB was shown in Figure S18),
but that such metathesis is ineffective with Ir-Br or Ir-I.
4

Table 1. Alkyne diboration with different iridium precursorsa
Yield of A1-
Yield of
A1-BpinH
14%
Yield of A1-
HBpin
7%
entry
[Ir]
Bpin2
77%
74%
5%
1
2
3
4
5
6
7
(SiNN)IrCOE
[Ir(COD)Cl]2
[Ir(COD)Br]2
[Ir(COD)I]2
17%
7%
85%
8%
10%
71%
72%
76%
75%
14%
[Ir(COD)OH]2
[Ir(COD)OMe]2
[Ir(COE)2Cl]2
17%
10%
16%
10%
14%
8%
a. All reactions performed at 50 °C in heptane with 0.08 mmol 1-phenyl-1-butyne, 0.28 mmol
HBpin, and 1 mol% catalyst loading under 1 atm CO. b. Yields were determined by 1H NMR
integration versus 1,4-dioxane as an internal standard.
We selected [Ir(COD)Cl]2 for the next set of experiments aimed at improving the selectivity
of the reaction towards DHDB. The results are summarized in Table 2. The selectivity for
DHDB increased modestly but steadily as the polarity of the solvent decreased (entries 1-4, 9,
10). It was also noted that the selectivity increased with increased pressure of CO (entries 4, 18,
19). We surmise that these two facts are related. CO is more soluble in less polar solvents [37]
and thus the effective concentration of CO is influenced by both the nature of the solvent and by
the CO pressure introduced into the reaction vessel. Increasing the reaction temperature (entries
4-6) decreased the selectivity for DHDB. Although CO solubility may increase with temperature
[38,39], it is possible that the binding of CO to Ir is less favorable at higher temperatures.
5

Although we have not established the identity of the Ir species in the catalytic mixture, it seems
reasonable to propose that DHDB requires binding of one or more CO ligands to Ir, and that the
“last” CO binding to Ir is not bound very strongly, such that its concentration is affected by
temperature, solvent polarity and CO pressure. Hydroboration does proceed without CO, and it
may also proceed via species with CO bound to Ir, but with fewer CO ligands than may be
required for DHDB.
The effect of other additives was also explored. Adding tricyclohexylphosphine or pyridine had
a negligible effect on the outcome of the reaction (entries 12 and 13). The use of tBuNC instead
t
of CO did not lead to any DHDB products (entry 18); however, the use of BuNC in addition to
CO resulted in the improvement of selectivity. Finally, it should be noted that performing the
reaction in the presence of liquid mercury did not affect the outcome (entry 11), suggesting that
the catalysis proceeds homogeneously.
Table 2. Summary of the optimization of alkyne diboration
A1-Bpin2/(A1-
BpinH+A1-HBpin)b
entry
Solvent
Additive
CO pressure
1
2
3
THF
PhF
42/58
52/48
57/43
none
none
none
1 atm
1 atm
1 atm
toluene
6

4
C6D6
C6D6
59/41
70/16e
17/83f
N/Ag
0/0h
none
none
1 atm
1 atm
5
6
C6D6
none
1 atm
7
C6D6
none
1 atm Ar
1atm
8
C6D6
none
9
isooctane
heptane
C6D6
69/31
78/22
58/42
55/42
57/43
65/35
73/27
75/25
86/14
0/50
none
1 atm
10
11
12
13
14
15
16
17
18
19
20
21
none
1 atm
Hg drop
1 atm
C6D6
4 mol% P(c-C6H11)3
4 mol% pyridine
1.1 mol% tBuNC
2.1 mol% tBuNC
4.1 mol% tBuNC
3 mol% tBuNC
4.1 mol% tBuNC
none
1 atm
C6D6
1 atm
C6D6
1 atm
C6D6
1 atm
C6D6
1 atm
heptane
C6D6
1 atm
1 atm Arc
2 atmd
3 atmd
1 atm
heptane
heptane
C6D6
86/14
91/9
59/41i
none
none
a. All reactions performed at 50 °C with 0.08 mmol 1-phenyl-1-butyne, 0.28 mmol HBpin, and 1 mol% catalyst loading
1
in a J. Y tube for 5 h. b. Yields were determined by H NMR integration versus 1,4-dioxane as an internal standard. c.
The reaction was conducted under 1 atm Ar instead of CO. d. The reaction was conducted in a top-screw capped
schlenk flask. e. The reaction was performed at room temperature (25 °C) for 3 d. f. The reaction was performed at 80
°C. g. All of the alkyne was converted into a mixture of hydroboration, hydrogenation and other unidentified products.
h. B2Pin2 was used as boron source. i. After all the A1 was consumed, 1 mol % [Ir(COD)Cl] was loaded to the reaction
mixture. Then the resulting mixture was degassed and back-filled with CO, then heated at 50 °C for 15 h.
2.2. Exploration of the scope of DHDB.
Next, we examined the reaction of 1-phenyl-1-butyne with boranes other than HBpin (Table 3).
The use of HBCat (entry 2) resulted in similar selectivity for DHDB, while the use of HBneop
7

(entry 4) led to predominantly hydroboration, with only 9% of the DHDB product. Reactions
with HBdan and HBdaz (entry 3&5) did not lead to any DHDB at all.
Table 3. DHDB with different boranes.
H-[B]
A1-[B]2/(A1-
Alkyne
entry
H-[B]
abbreviation
[B]H+A1-H[B])
conversion
1
2
HBpin
HBcat
74/26
72/28
100%
100%
3
4
HBdaz
0/100
9/91
52%
HBneop
100%
5
HBdan
0/100
20%
8

The alkyne substrate scope of Ir/CO/tBuNC system was briefly examined and is outlined in
Figure 3. Although lower temperature increased the DHDB selectivity, the reaction at RT was
too slow, requiring days for completion. Because of this, we elected to perform the reactions at
50 °C and with 1 atm of CO for convenience. Heptane was used as solvent to improve CO
solubility. It was found that alkyl- and aryl-substituted internal and terminal alkynes can be
diborylated with HBpin to yield cis-diborylalkenes with modest to high selectivity.
Bis(trimethylsilyl)acetylene did not engage in the reaction, possibly owing to the steric
hindrance. The diboration products derived from A3 and A7 were easily isolated as pure white
solids by removing the volatiles at the end of the reaction, followed by recrystallization from a
toluene solution layered with pentane at -35 °C. For terminal alkynes, the diboration products
could be isolated by column chromatography.
9

a. All the reaction performed at 50 °C with 0.08 mmol 1-phenyl-1-butyne, 0.28 mmol HBpin, and 1 mol% catalyst loading in a J.
Y tube for 5 h b. b. Yields were determined by 1H NMR integration versus 1,4-dioxane as an internal standard and were given in
the following order: A-Bpin2/A-BPinH/A-HBpin. c. isolated yield in 2.0 mmol scale were given in parenthesis. d. without
tBuNC.
Figure 3. DHDB with different alkynes.a
10

3. Conclusion
We have expanded the substrate scope of Ir-catalyzed dehydrogenative diboration
(DHDB) to non-alkynylboronate alkynes from an earlier report utilizing (SiNN)Ir complexes. In
the present work, we discovered that the SiNN pincer ligand is not required and that a precatalyst
as simple as [Ir(COD)2Cl]2 can be used under the right conditions. The DHDB reaction is in
competition with hydroboration which is also catalyzed by Ir. Although hydrogen is presumably
produced as a result of DHDB, hydrogenation of the carbon-carbon double or triple bonds was
not observed. For some substrates, the selectivity for DHDB was as high as 9:1. A variety of
terminal or internal alkynes produced diboration products under optimized conditions and some
diboration products were isolated in a pure form. Although we did not pursue the
characterization of the Ir compounds present in the catalytic reaction mixture, the experimental
data suggest that DHDB is favored by increasing competitive coordination of CO to Ir.
11

4. Experimental Section.
4.1. General considerations.
Unless otherwise specified, all reactions and manipulations were carried out under an argon
atmosphere using glove box or Schlenk line techniques. Solvents were dried and deoxygenated
via the solvent purification system and stored over molecular sieves in the glove box filled with
argon. Heptane, THF, toluene, C6H5F, C6D6 were dried over NaK /Ph2CO/18-crown-6, distilled
and stored over molecular sieves in an Ar-filled glove box. Fluorobenzene and C6D5Br were
dried over CaH2, distilled and stored over molecular sieves in an Ar-filled glove box.
[Ir(COD)Cl]2 [40], [Ir(COD)Br]2 [41], [Ir(COD)I]2 [42], [Ir(COE)2Cl]2 [43], [Ir(COD)OH]2 [44],
[Ir(COD)OMe]2 [ 45 ], (SiNN)Ir(COE) [26] were prepared according to previous literature.
Alkynes were deoxygenated by three freeze-pump-thaw cycles or dried under vacuum overnight
prior transferring into an Ar-filled glove box. All other chemicals were used as received from
commercial vendors. Benzodiazaborole (HBdaz) [46], neopentylglycolborane (HBnpg) [47], and
1,8-naphthalenediaminatoborane (HBdan) [48] were prepared according to published procedures.
13
NMR spectra were recorded on a Varian iNova 300 spectrometer (1H NMR, 299.951 MHz, C
31
NMR, 75.413 MHz, P NMR, and 121.425 MHz), Varian Inova 400 (1H NMR, 399.535 MHz;
13
11B NMR, 128.185 MHz) and NMRS 500 (1H NMR, 499.703 MHz; C NMR, 125.697 MHz)
1
spectrometer. Chemical shifts are given in δ (ppm). H NMR and 13C NMR spectra were
referenced using the solvent signals.
4.2. Precatalyst screening for DHDB of 1-phenyl-1-butyne with pinacolborane.
A 64 μL stock solution of Ir catalyst (0.0125 M in C6H6, 0.00080 mol) was added to a J. Young
tube. After removing C6H6 under vacuum, 11.3 μL 1-phenyl-1-butyne (0.080 mol), 42 μL
pinacolborane (0.28 mol) and 450 μL heptane was loaded via syringe. The J. Young tube was
12

degased via freeze-pump-thaw 3 cycles, and then refilled with 1 atm CO. the resulting mixture
was heated in 50 °C for 15 h. The solvent was removed under vacuum and 500 μL 0.08 M 1,4-
dioxane in C6D6 was added. The yields of the diboration and hydroboration products were
1
determined via H NMR analysis (500 MHz, C6D6, Entry 2 is shown as an example in Figure
S1). Diboration product A1-Bpin2 [49]: δ 7.35 – 7.33 (m, PhH, 2H), 7.18 (t, JH-H = 7.7 Hz, PhH,
2H), 7.03 (tt, JH-H = 7.2, 1.4 Hz, PhH, 1H), 2.42 (q, JH-H = 7.5 Hz, CH2CH3, 2H), 1.17 (s, BpinH,
12H), 1.13 (t, JH-H = 7.5 Hz, CH2CH3, 3H). 1.12 (s, BpinH, 12H). Hydroboration product A1-
BpinH: δ 7.39 – 7.37 (m, PhH, 2H) 7.24 (t, JH-H = 7.7 Hz, PhH, 2H), 7.12 (t, JH-H = 7.7 Hz, PhH,
1H) 6.96 (t, JH-H = 7.3 Hz, PhCCH, 1H), 2.16 (p, JH-H = 7.5 Hz, CH2CH3, 2H), 1.06 (s, BpinH,
12H), 0.84 (t, JH-H = 7.5 Hz, CH2CH3, 3H); The reason we assigned the resonances to A1-BpinH
is that for compound A1-BpinH the ethyl CH2 proton would couple to both the CH3 proton and
alkenyl protons, thus giving rise to a quintet instead of quartet resonances for the CH2 protons,
and triplet instead of singlet resonance for the alkenyl proton [50]. The assignment was also
consistent with other reactions that afford different A1-BpinH/A1-HBpin ratios. Hydroboration
product A1-HBpin: δ 2 PhH resonances are overlapping with product A1-Bpin2, 7.72 (s,
PhCHC, 1H), 7.08 (t, JH-H = 7.4 Hz, 1H), 1.4 Hz, PhH, 1H), 2.65 (q, JH-H = 7.6 Hz, CH2CH3,
2H), 1.27 (t, JH-H = 7.5 Hz, CH2CH3, 3H), 1.12 (s, BpinH, 12H);
4.3. Solvent screening for DHDB of 1-phenyl-1-butyne with pinacolborane.
A 64 μL stock solution of [Ir(COD)Cl]2 (0.0125 M in C6H6, 0.00080 mol) was added to a J.
Young tube. After the benzene was removed under vacuum, 11.3 μL 1-phenyl-1-butyne (0.080
mol), 42 μL pinacolborane (0.28 mol) and 450 μL solvent was loaded via syringe. The J. Young
tube was degased through freeze-pump-thaw 3 cycles, and then refilled with 1 atm CO. the
resulting mixture was heated in 50 °C for 15 h. The solvent was removed under vacuum and 500
13

μL 0.08 M 1,4-dioxane in C6D6 was added. The yields of the diboration and hydroboration
products were determined via 1H NMR analysis.
4.4. Control experiments.
4.4.1. Reaction of 1-phenyl-1-butyne with bis(pinacolato)diboron catalyzed by [Ir(COD)Cl]2 at 1
atm CO.
To a J. Young tube, 32 μL stock solution of [Ir(COD)Cl]2 (0.0125 M in C6D6, 0.00040 mol), 140
μL stock solution of B2Pin2 (1.0 M in C6D6, 0.28 mol), and 160 μL stock solution of 1-phenyl-1-
butyne/1,4-dioxane ([alkyne]: 0.5 M in C6D6, 0.080 mol; 1,4-dioxane: 0.25 M in C6D6 as internal
standard) were loaded via syringe. The J. Young tube was degassed by 3 cycles of freeze-pump-
thaw, and then back filled with 1 atm CO. No reaction between alkyne and boron reagents after
the tube was heated in 50 °C for 15 h.
4.4.2. Reaction of 1-phenyl-1-butyne with pinacolborane catalyzed by [Ir(COD)Cl]2 at 1 atm Ar.
To a J. Young tube, 32 μL stock solution of [Ir(COD)Cl]2 (0.0125 M in C6D6, 0.00040 mol), 280
μL stock solution of borane (1.0 M in C6D6, 0.28 mol), and 160 μL stock solution of 1-phenyl-1-
butyne/1,4-dioxane ([alkyne]: 0.5 M in C6D6, 0.080 mol; 1,4-dioxane: 0.25 M in C6D6 as internal
standard) were loaded via syringe. The resulting mixture was heated in 50 °C for 18 h. No
diboration product A2-Bpin2 was detected by 1H NMR spectroscopy.
4.4.3. Reaction of 1-phenyl-1-butyne with pinacolborane catalyzed by [Ir(COD)Cl]2 at 1 atm
CO, where additional 0.5% [Ir(COD)Cl]2 was added after all the alkyne was converted into
diboration and hydroboration products.
14

A 32 μL stock solution of [Ir(COD)Cl]2 (0.0125 M in C6D6, 0.00040 mol) was added to a J.
Young tube. Then 240 μL 0.50 M stock solution of 1-phenyl-1-butyne (0.080 mol) in C6D6 and
280 μL 1.0 M stock solution of pinacolborane (0.28 mol) in C6D6 was loaded via syringe. The J.
Young tube was degased via freeze-pump-thaw 3 cycles, and then refilled with 1 atm CO. the
resulting mixture was heated in 50 °C for 15 h. 32 μL (0.00040 mol) of iridium catalyst stock
solution was added to the resulting mixture followed by the same CO refilling process. The
reaction mixture was heated at the same oil bath for another 15 h before the solvent was removed
under vacuum and 500 μL 0.08 M 1,4-dioxane in C6D6 was added, the ratio of diboration product
to hydroboration products remained unchanged.
4.5. tBuNC-assisted DHDB of 1-phenyl-1-butyne.
To a J. Young tube, 32 μL stock solution of [Ir(COD)Cl]2 (0.0125 M in C6D6, 0.00040 mol), 32
t
μL stock solution of BuNC (0.0500 M in C6D6, 0.0016 mol), 240 μL stock solution of borane
(1.0 M in C6D6, 0.24 mol), and 160 μL stock solution of 1-phenyl-1-butyne/1,4-dioxane
([alkyne]: 0.5 M in C6D6, 0.080 mol; 1,4-dioxane: 0.25 M in C6D6 as internal standard) were
loaded via syringe. The J. Young tube was degased via freeze-pump-thaw 3 times, and then
refilled with 1 atm CO. The resulting mixture was heated in 50 °C for 15 h. The yields of the
diboration and hydroboration products were determined via 1H NMR analysis.
4.6. Borane substrate scope for DHDB of 1-phenyl-1-butyne.
4.6.1. General procedure.
To a J. Young tube, 64 μL stock solution of [Ir(COD)Cl]2 (0.0125 M in C6D6, 0.00080 mol), 280
μL stock solution of borane (1.0 M in C6D6, 0.28 mol), and 160 μL stock solution of 1-phenyl-1-
butyne/1,4-dioxane ([alkyne]: 0.5 M in C6D6, 0.080 mol; 1,4-dioxane: 0.25 M in C6D6 as internal
15

standard) were loaded via syringe. The J. Young tube was degassed via freeze-pump-thaw 3
times, and then refilled with 1 atm CO. The resulting mixture was heated in 50 °C for 15 h. The
yields of the diboration and hydroboration products were determined via 1H NMR analysis.
4.6.2. Selected NMR data for the products and other reaction observations.
HBcat as boron source (Figure S2): A1-Bcat2: δ 7.31 – 7.29 (m, aromaticH, 2H), 7.19 (t, JH-H
=
7.7 Hz, aromaticH, 2H), 7.08 (tt, JH-H = 7.2, 1.4 Hz, aromaticH, 1H) 6.93 (dd, JH-H = 5.8, 3.3 Hz,
BcatH, 2H), 6.85 (dd, JH-H = 5.9, 3.4 Hz, BcatH, 2H), 6.76 (dd, JH-H = 5.9, 3.3 Hz, BcatH, 2H),
6.70 (dd, JH-H = 5.9, 3.2 Hz, BcatH, 2H), 2.49 (q, JH-H = 7.6 Hz, CH2CH3, 2H), 1.06 (t, JH-H = 7.6
Hz, CH2CH3, 3H). A1-BcatH: δ aromatic resonances (aromaticH) of A1-BcatH cannot be
differentiated from that of A1-HBcat, 2.11 (p, JH-H = 7.5 Hz, CH2CH3, 2H), 0.83 (t, JH-H = 7.5
Hz, CH2CH3, 3H). A1-HBcat: δ aromatic resonances of A1-HBcat cannot be differentiated
from that of A1-BcatH, 7.82 (s, ArCHC, 1H), 2.65 (q, JH-H = 7.6 Hz, CH2CH3, 2H), 1.23 (t, JH-H
= 7.5 Hz, CH2CH3, 3H).
HBdaz as boron source (Figure S3): around 52% alkyne was converted into a mixture of
unidentified products.
HBnpg as boron source (Figure S4): A1-BnpgH: δ 7.31 – 7.25 (m, aromaticH, 2H), 7.29 – 7.15
(m, aromaticH, 2H), 7.14 – 7.08 (m, aromaticH, 1H), 6.87 (t, J = 7.3 Hz, ArCCH, 1H), 3.26 (s,
BnpgCH2, 4H), 2.09 (p, J = 7.5, CH2CH3, 2H), 0.84 (t, J = 7.5 Hz, CH2CH3, 3H), 0.52 (s,
BnpgCH3, 6H). A1-HBnpg: δ 7.65 (s, ArCHC, 1H), 7.39 – 7.30 (m, aromaticH, 2H), 7.08 – 7.01
(m, aromaticH, 2H), 3.32 (s, BnpgCH2, 4H), 2.62 (q, J = 7.4 Hz, CH2CH3, 2H), 1.24 (t, J = 7.5
Hz, CH2CH3, 3H), 0.51 (s, BnpgCH3, 6H). Around 91% of hydroboration products were formed.
16

Due to the difficulties on purification of HBnpg as well as low diboration yield, no further study
was conducted using this boron source.
HBdan as boron source (Figure S5): A1-BdanH: 6.75 (t, J = 7.3 Hz, ArCCH, 1H), 6.01 (dd, J =
6.3, 2.0 Hz, BdanH, 2H), 1.99 (p, J = 7.4 Hz, CH2CH3, 2H), 0.86 (t, J = 7.5 Hz, CH2CH3, 3H).
A1-HBdan: δ 6.05 (dd, J = 5.9, 2.5 Hz, BdanH, 2H), 2.21 (q, J = 8.4 Hz, CH2CH3, 2H). With
only 20% of the alkyne was converted, alkenyl proton resonances of hydroboration product A1-
HBdan could be overlapped with aromatic proton resonances, which make it difficult to
conclude whether A1-HBdan or A1-Bdan2 is formed. However, based on the ratio of CH2
resonance to Bdan resonance (1:1), it is more likely the hydroboration product A1-HBdan (9%).
According to the coupling between alkenyl proton and ethyl CH2 proton in A1-BdanH, it would
be reasonable to claim that 11% of A1-BdanH was formed. Therefore, for this borane no DHDB
product was formed.
4.7. Alkyne substrate scope of DHDB.
4.7.1. General procedure.
To a J. Young tube, 20 μL stock solution of [Ir(COD)Cl]2 (0.010 M in C6D6, 0.00020 mol), 40
μL stock solution of tBuNC (0.040 M in C6D6, 0.00160 mol), 44 μL (0.30 mol) HBpin, 0.1 mmol
of alkyne and 400 μL isooctane were loaded via syringe in the Glove box. The J. Young tube
was degased via freeze-pump-thaw 3 cycles, and then refilled with 1 atm CO. The resulting
mixture was heated in 50 °C for 15 h. The yield of diboration and hydroboration was revealed by
1H NMR analysis.
4.7.2. Selected product data.
17

A2-Bpin2 (Figure S6): 1H NMR (500 MHz, C6D6): δ 7.65-7.63 (m, ArH, 2H), 7.13 (t, JH-H = 7.6
Hz, ArH, 2H), 7.00 (m, ArH, 1H), 6.63 (s, ArCCH, 1H), 1.23 (s, BpinH, 12H), 1.12 (s, BpinH,
12H). A5-Bpin2 (Figure S9): 1H NMR (500 MHz, C6D6): δ 7.65-7.64 (m, ArH, 2H), 7.23-7.22
t
(m, ArH, 2H), 6.69 (s, ArCCH, 1H), 1.27 (s, BpinH, 12H), 1.17 (s, BuH, 9H), 1.13 (s, BpinH,
12H). A6-Bpin2 (Figure S10): 1H NMR (500 MHz, C6D6): δ 7.60-7.59 (m, ArH, 2H), 6.93-6.91
t
(m, ArH, 2H), 6.61 (s, ArCCH, 1H), 1.26 (s, BpinH, 12H), 1.16 (s, BuH, 9H), 1.13 (s, BpinH,
12H).
4.8 Preparative-scale of DHDB.
4.8.1. General procedure.
To a 25 mL PTFE-valved gas-tight flask, 6.7 mg (0.01 mmol) [Ir(COD)Cl]2, 11 μL (0.08 mmol)
tBuNC, 2.0 mmol alkyne and 871 μL (6.0 mmol) HBpin was loaded in an Argon-filled glove
box. The flask was taken out of the box and degassed via freeze-pump-thaw 3 times, and then
refilled with 1 atm CO. The resulting mixture was heated in 50 °C for 15 h. The flask was
transferred to the box, and the volatile was removed under vacuum. The diboration product was
then isolated by the following methods. For A3 and A7: the residue was dissolved with toluene
and filtered through a short pad of Celite. Toluene solution was concentrated and then layered
with pentane. Crystalline solid A3-Bpin2 and A7-Bpin2 were collected after slow diffusion
overnight at -35 °C freezer. For A4: A4-Bpin2 was purified by chromatography on silica gel
with 2:1 hexane:acetone.
4.8.2. Product yields and NMR data.
A3-Bpin2: white solid, isolated yield: 528 mg (61%) 1H NMR (500 MHz, CDCl3, Figure S12) δ
13
7.01-7.08 (m, 6H, ArH), 6.95-6.96 (m, 4H, ArH), 1.32 (s, 24H, Bpin CH3). C NMR (125 Hz,
18

CDCl3, Figure S13)  141.38, 129.43, 127.53, 125.90, 84.17, 25.00. HR-MS (EI) calcd for
C26H35B2O4: 433.2716; found 433.2709. The NMR data were consistent with literature values
[9].
A7-Bpin2: white solid, isolated yield: 622 mg (63%) 1H NMR (500 MHz, CDCl3, Figure S16) δ
3
7.18 (d, JH-H = 8.1 Hz, 2H, ArH), 7.03 (d, J = 7.8 Hz, 2H, ArH) 2.29 (s, 3H, ArCH3), 1.30 (s,
12H, BpinCH3), 1.27 (s, 12H, BpinCH3), 1.10 (s, 12H, BpinCH3). 13C NMR (125 Hz, CDCl3,
Figure S17)  142.41, 136.36, 128.44, 127.75, 83.90, 83.47, 83.22, 25.02, 24.94, 24.64, 21.31.
HR-MS (EI) calcd for C27H44B3O6: 496.3448; found 496.3405.The NMR data were consistent
with literature values [25].
1
A4-Bpin2: colorless oil, yield: 340 mg (50%); H NMR (500 Hz, CDCl3, Figure S14)  0.87 (t,
3JH-H = 6.8 Hz, 3H), 1.26 (s, 12H, BpinCH3), 1.31 (s, 12H, BpinCH3), 1.19-1.31 (m, 6H), 1.34-
1.45 (m, 2H), 2.21 (t, 3JH-H = 7.1Hz, 2H), 5.85 (s, 1H). 13C NMR (125 Hz, CDCl3, Figure S15) 
83.72, 83.35, 39.67, 30.91, 25.03, 25.00, 22.56, 14.10. HR-MS (EI) calcd for C18H35B2O4:
337.2716; found 337.2708. The NMR data were consistent with literature values [Error!
Bookmark not defined.].
Acknowledgments.
We are thankful for the support of this work by the US National Science Foundation (grant CHE-
1565923 to O.V.O.). We are grateful to Dr. Chun-I Lee for the preparation of (SiNN)Ir(COE).
Appendix A. Supplementary data.
Supplementary data to this article can be found online.
19

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.
Graphical abstract
20

References
[1] S. Krautwal, M. J. Bezdek, P. Chirik, J. Am. Chem. Soc. 139 (2017) 3868–3875.
[2] T. Ishiyama, M. Yamamoto, N. Miyaura, Chem. Lett. 25 (1996) 1117-1118.
[3] M. Shimizu, C. Nakamaki, K. Shimono, M. Schelper, T. Kurahashi, T. Hiyama, J. Am.
Chem. Soc. 127 (2005) 12506-12507.
[4] Y. Nishihara, M. Miyasaka, M. Okamoto, H. Takahashi, E. Inoue, K. Tanemura, T. Takagi,
J. Am. Chem. Soc. 129 (2007) 12634-12635.
[5] N. Iwadate, M. Suginome, J. Am. Chem. Soc., 132 (2010) 2548-2549.
[6] E.C. Neeve, S.J. Geier, I.A.I. Mkhalid, S.A. Westcott, T.B. Marder, Chem. Rev. 116 (2016)
9091-9161.
[7] F. Zhao, X. Jia, P. Li, J. Zhao, Y. Zhou, H. Liu, Org. Chem. Front. 4 (2017) 2235-2255.
[8] T.B. Marder and N.C. Norman, Top. Catal. 5 (1998) 63-73.
[9] T. Ishiyama, N. Matsuda, N. Miyaura, A. Suzuki, J. Am. Chem. Soc. 115 (1993) 11018-
11019.
[10] J. Takaya, N. Iwasawa, ACS Catal. 2 (2012) 1993-2006.
[11] T. Ishiyama, N. Matsuda, M. Murata, F. Ozawa, A. Suzuki, N. Miyaura, Organometallics
15 (1996) 713-720.
[12] G. Lesley, P. Nguyen, N. J. Taylor, T. B. Marder, A. J. Scott, W. Clegg, N. C. Norman,
Organometallics 15 (1996) 5137-5154.
[13] R. L. Thomas, F. E. S. Souza, T. B. Marder, J. Chem. Soc., Dalton Trans. (2001) 1650-
21

1656.
[14] H. A. Ali, A. E. A. Al Quntar, I. Goldberg, M. Srebnik, Organometallics 21 (2002) 4533-
4539.
[15] V. Lillo, J. Mata, J. Ramírez, E. Peris, E. Fernandez, Organometallics 25 (2006) 5829-
5831.
[16] H. Prokopcová, J. Ramírez, E. Fernández, C. O. Kappe, Tetrahedron Lett. 49 (2008)
4831-4835.
[17] A. Grirrane, A. Corma, H. Garcia, Chem. Eur. J. 17 (2011) 2467-2478.
[18] V. Lillo, M. R. Fructos, J. Ramírez, A. A. C. J. Braga, F. Maseras, M. M. Díaz-Requejo, P.
J. Pérez, E. Fernández, Chem. Eur. J. 13 (2007) 2614-2621.
[19] H. Yoshida, S. Kawashima, Y. Takemoto, K. Okada, J. Ohshita, K. Takaki, Angew.
Chem. Int. Ed. 51 (2012) 235-238.
[20] C. Kojima, K.-H. Lee, Z. Lin, M. Yamashita, J. Am. Chem. Soc. 138 (2016) 6662–6669.
[21] K. Nagao, H. Ohmiya M. Sawamura, Org. Lett. 17 (2015) 1304–1307
[22] A. Yoshimura, Y. Takamachi, L.-B. Han A. Ogawa, Chem. – Eur. J. 21 (2015) 13930–
13933.
[23] C. Kojima, K.-H. Lee, Z. Lin M. Yamashita, J. Am. Chem. Soc. 138 (2016) 6662–6669.
[24] N. Iwadate M. Suginome, J. Am. Chem. Soc. 132 (2010) 2548–2549.
22

[25] C.-I. Lee, W. -C. Shih, J. Zhou, J. H. Reibenspies, O. V. Ozerov, Angew. Chem. Int. Ed. 54
(2015) 14003-14007.
[26] C-I. Lee, J. Zhou, O. V. Ozerov, J. Am. Chem. Soc. 135 (2013) 3560-3566.
[27] C. J. Pell, O. V. Ozerov, Inorg. Chem. Front. 2 (2015) 720-724.
[28] C.-I. Lee, J. C. DeMott, C. J. Pell, A. Christopher, J. Zhou, N. Bhuvanesh, O. V. Ozerov,
Chem. Sci. 6 (2015) 6572-6582.
[29] C. J. Pell, O. V. Ozerov, J. Organomet. Chem. 912 (2020) 121143.
[30] B. J. Foley, O. V. Ozerov, Organometallics 13 (2020) 2352–2355.
[31] J. Zhou, C.-I. Lee, O. V. Ozerov, ACS Catal. 8 (2018) 536-545.
[32 B. J. Foley, N. S. Bhuvanesh, J. Zhou O. V. Ozerov, ACS Catal. 10 (2020) 9824-9836.
[33] T. Tsuchimoto, H. Utsugi, T. Sugiura, S. Horio, Adv. Synth. Catal. 357 (2015) 77-82.
[34] E. A. Romero, R. Jazzar, G. Bertrand, Chem. Sci. 8 (2017) 165-168.
[35] D. Wei, B. Carboni, J.-B. Sortais, C. Darcel, Adv. Synth. Catal. 360 (2018) 3649-3654.
[36] R. J. Procter, M. Uzelac, J. Cid, P. J. Rushworth, M. J. Ingleson, ACS Catal. 9 (2019)
5760-5771.
[ 37 ] CO mol fraction data at 25 °C: 0.0000628 (chlorobenzene); 0.0000674 (benzene);
0.0000798 (toluene); 0.00173 (heptane) a. J. C. Gjaldbaek, Acta. Chem. Scand. 1952, 6,
623; 0.0000486 (1,4-dioxane at 23 °C) b. W. Krauss, and W. Gestrich, Chem. -Tech.
(Heidelberg) 1977, 6, 513.
[38] J. Horiuti, Sci. Pap. Inst. Phys. Chem. Res. (Jpn) 17 (1931) 125.
23

[39] F. T. Liu A. Yabe, J. Chem. Eng. Data 41 (1996) 589–592.
[40 J. L. Herdé, J. C. Lambert, C. V. Senoff, Inorg. Synth. 15 (1974) 18-20.
[41] B. Bjoern, G. Y. Cristina, R. Frank, H. Guenter, Eur. J. Inorg. Chem. 10 (2002) 2569-2586.
[42] S. M. Socol, C. Yang, D. W. Meek, R. Glaser, Can. J. Chem. 70 (1992) 2424-2433.
[43] A. Van der Ent, A. L. Onderdelinden, Inorg. Synth. 14 (1973) 92-95.
[44] L. M. Green, D. W. Meek, Organometallics 8 (1989) 659-666.
[45] R. Uson, L. A. Oro, J. A. Cabeza, Inorg. Synth. 23 (1985) 126-130.
[46 S. W. Hadebe, R. S. Robinson, Eur. J. Org. Chem. 21 (2006) 4898-4904.
[47] C. A. Incerti–Pradillos, M. A. Kabeshov, A. V. Malkov, Angew. Chem. Int. Ed. 52 (2013)
5338-5341.
[48] N. Iwadate, M. Suginome, J. Organomet. Chem. 694 (2009) 1713-1717.
[49] Y. Zhou, W. You, K. B. Smith M. K. Brown, Angew. Chem. Int. Ed. 126 (2014) 3543-
3547.
[50] G.-M. Ho, L. Segura, I. Marek, Chem. Sci. 11 (2020) 5944-5949.
24