β-(Z) Selectivity Control by Cyclometalated Rhodium(III)-Triazolylidene Homogeneous and Heterogeneous Terminal Alkyne Hydrosilylation Catalysts

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β‑(Z) Selectivity Control by Cyclometalated Rhodium(III)−

Triazolylidene Homogeneous and Heterogeneous Terminal Alkyne

Hydrosilylation Catalysts

́

Beatriz Sanchez-Page, Julen Munarriz, M. Victoria Jimenez,* Jesus J. Perez-Torrente,* Javier Blasco,

́

Gloria Subias, Vincenzo Passarelli, and Patricia Alvarez

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ABSTRACT: The cyclometalated Rh(III)−NHC compounds

[Cp*RhI(C,C′)-Triaz] (Triaz = 1,4-diphenyl-3-methyl-1,2,3-triazol-5-

ylidene) and [Cp*RhI(C,C′)-Im] (Im = 1-phenyl-3-methyl-imidazol-2-

ylidene) are eﬃcient catalysts for the hydrosilylation of terminal alkynes

with complete regio- and stereoselectivity toward the thermodynamically

less stable β-(Z)-vinylsilane isomer at room temperature in chloroform or

acetone. Catalyst [Cp*RhI(C,C′)-Triaz] shows a superior catalytic

performance in terms of activity and has been applied to the

hydrosilylation of a range of linear 1-alkynes and phenylacetylene

derivatives with diverse hydrosilanes, including HSiMePh₂, HSiMe₂Ph,

HSiEt₃, and the bulkier heptamethylhydrotrisiloxane (HMTS), to aﬀord

the corresponding β-(Z)-vinylsilanes in quantitative yields. The graphene-

based hybrid material TRGO-Triaz-Rh(III), featuring cyclometalated

[Cp*RhI(C,C′)-Triaz] (Triaz = 1,4-diphenyl-3-methyl-1,2,3-triazol-5-ylidene) rhodium(III) complexes covalently immobilized through the

triazolylidene linker, has been prepared by metalation of the trimethylsilyl-protected 3-methyl-4-phenyl-1,2,3-triazolium iodide functionalized

graphene oxide material, TRGO-Triaz, with [Cp*RhCl₂]₂using sodium tert-butoxide as base. The coordination sphere of the supported

rhodium(III) complexes has been determined by means of XPS and extended X-ray absorption ﬁne structure (EXAFS) spectroscopy, showing the

replacement of the iodido ligand by O-functionalities on the carbon wall. In sharp contrast with the homogeneous catalyst, the heterogeneous

hybrid catalyst TRGO-Triaz-Rh(III) is not active at room temperature although it shows an excellent catalytic performance at 60 °C. In addition,

the hybrid catalyst TRGO-Triaz-Rh(III) has shown an excellent recyclability, allowing at least six catalytic runs in the hydrosilylation of oct-1-yne

with HSiMePh₂in acetone with complete selectivity to the β-(Z)-vinylsilane product. The reaction mechanism for the molecular catalyst

[Cp*RhI(C,C′)-Triaz] has been explored by means of DFT calculations, pointing to a metal−ligand bifunctional mechanism involving reversible

cyclometalation that is competitive with a noncooperative pathway. The proposed mechanism entails the Rh−C_Arassisted hydrosilane activation to

aﬀord a reactive Rh−silyl intermediate that leads to a (E)-silylvinylene intermediate after alkyne insertion and a metallacyclopropene-driven

isomerization. The release of the β-(Z)-vinylsilane product can occur by a reversible cyclometalation mechanism involving σ-CAM with the C_Ar−H

bond or, alternatively, the Si−H bond of an external hydrosilane. The energy barrier for the latter is 1.2 kcal·mol⁻¹lower than that of the C_Ar−H

bond, which results in a small energy span diﬀerence that makes both pathways competitive under catalytic conditions.

KEYWORDS: graphene, covalent functionalization, N-heterocyclic carbenes, rhodium, hydrosilylation, reaction mechanism

regio- and stereoselectivity along the H−Si addition process is

still a major challenge.

The hydrosilylation of terminal alkynes can aﬀord three

INTRODUCTION

■

Catalysis is a key enabling technology for developing feasible

solutions toward a sustainable chemical production.¹In this

context, the hydrosilylation of carbon−carbon multiple bonds is

one of the most remarkable methods for the construction of Si−

C bonds. In particular, the hydrosilylation of alkynes provides a

straightforward and atom-economical access to vinylsilanes,

which are useful intermediates in organic synthesis,²such as

coupling partners in Hiyama cross coupling reactions,³or

industrial reagents to synthesize cross-linked silicone polymers.⁴

Despite major advances over the last years, the developing of

transition-metal hydrosilylation catalysts for the control of the

possible vinylsilane isomers, namely, the linear β-(Z) and β-(E)

Received: July 28, 2020

Revised: October 18, 2020

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isomers resulting from the syn- and trans-anti-Markovnikov

addition, respectively, and the branched α-vinylsilanes from the

Markovnikov addition. Besides, the formation of silylalkyne

derivatives, resulting from the competitive dehydrogenative

silylation process, is occasionally observed for some catalytic

systems (Scheme 1).⁵Although the β-(E)-vinylsilane formation

generally occurs with high selectivity,⁶the selective synthesis of

α-⁷and β-(Z)-isomers⁸is more challenging. Furthermore, the

isomerization of β-(Z)-vinylsilanes to thermodynamically more

stable β-(E)-vinylsilanes under the typical conditions of

Chart 1. Leading Catalysts for β(Z) Stereoselective

Hydrosilylation of Terminal Alkynes

Scheme 1. Possible Products for the Hydrosilylation of

Terminal Alkynes

zol-5-ylidene) as a catalyst for the hydrosilylation of a range of

terminal and internal alkynes with good β-(Z) and syn

selectivities, respectively, which constitutes the ﬁrst example of

a triazolylidene-based catalyst for this transformation.²²

Furthermore, we have set up a strategy for the immobilization

of Rh(I)−triazolylidene complexes by making use of a bottom-

up approach involving a stepwise solid phase synthesis of the

corresponding triazolium fragments through the epoxy

functionalities on thermally reduced graphene oxides

(TRGO). This hybrid catalyst eﬃciently catalyzed the hydro-

silylation of alkynes, showing the same good selectivity as the

related [RhI(cod)(Triaz)] homogeneous catalyst. Noticeably,

the good recyclability of the hybrid catalyst demonstrates the

strength of the C−N covalent bond of the triazolylidene linker to

the graphitic wall under hydrosilylation conditions. In this

context, it is worth mentioning that a rather limited number of

heterogenized rhodium hydrosilylation catalysts have been

previously described in the literature.^23,24To the best of our

knowledge, there are only two examples of Rh(I)−NHC

catalysts covalently supported on carbonaceous materials, one

of which showed moderate catalytic activity in the hydro-

silylation of internal alkynes.²⁵However, pyrene-tagged

rhodium NHC complexes anchored onto reduced graphene

oxide were found to be only moderately active for the

hydrosilylation of terminal alkynes, and exhibited very limited

recyclability.²⁶

Keeping in mind the above results, we foresee the potential of

cyclometalated rhodium(III) complexes, such as [Cp*RhI-

(C,C′)-Triaz] or [Cp*RhI(C,C′)-Im)] (Im = 1-phenyl-3-

methyl-imidazolylide), as alkyne hydrosilylation catalysts. The

combination of a supporting Cp* ligand with a strong donor

NHC moiety engaged in a ﬁve-membered metalacycle, resulting

from the ortho metalation of the phenyl substituent, provides a

stable structural framework with possible application in

hydrofunctionalization reactions. In particular, the Rh−C_Ar

bond is a reactive site that could participate in the precatalyst

activation by reaction with the hydrosilane²⁷or the alkyne,^11a

thus aﬀording reactive hydrosilylation intermediates.²⁸Interest-

ingly, reversible cyclometalation has been proposed as a possible

metal−ligand bifunctional mechanism in catalysis.²⁹In fact,

computational studies have shown that the cooperativity of a

cyclometalated metal−ligand fragment could be operative in the

transition-metal-catalyzed reactions constitutes an additional

diﬃculty that hinders the development of β-(Z)-selective

catalysts.^5,9So far, a number of β-(Z)-selective noble-metal-

based catalysts bearing Rh,¹⁰Ir,¹¹and Ru,¹²have been

developed. However, many of them show either low reactivity

or substrate-dependent selectivity, and usually produce a

mixture of vinylsilane isomers. In addition, a few earth-abundant

transition-metal based catalytic systems, such as Co,¹³Fe¹⁴and

Mn,¹⁵have been recently reported to aﬀord similar outcomes. A

selection of β(Z)-stereoselective catalysts for terminal alkyne

hydrosilylation is shown in Chart 1. However, these examples

are still scarce, and therefore, the development of much more

eﬃcient catalysts to access the less thermodynamic stable β-(Z)-

vinylsilane derivatives with wider applicability remains neces-

sary.

Ligand design and mechanistic understanding are pivotal for

the rational development of more eﬃcient hydrosilylation

catalysts. N-heterocyclic carbenes (NHCs) have been con-

solidated as powerful ligands for boosting catalytic activity

owing to their strong coordination ability and tunable character,

which enables the control of the steric and electronic properties

at the metal center.¹⁶In this regard, considerable attention has

been paid to the development of alkyne hydrosilylation rhodium

catalysts based on functionalized NHC^6a,c,17and bis-

NHC^7d,11b,18ligands exhibiting diﬀerent degrees of selectivity

and eﬃciency. In particular, 1,2,3-triazolylidene (Triaz) ligands

have emerged as a versatile subclass of NHCs with increased σ-

donor properties, compared to classical Arduengo-type

imidazol-2-ylidene ligands, and an electronic ﬂexibility because

of their mesoionic character derived from 1,3-disubstitution of

the heterocyclic ring.^19,20These properties make them powerful

tools for catalyst design and have found application in a range of

catalytic transformations including cross coupling, oleﬁn

metathesis, water oxidation, and the hydrosilylation of carbonyl

compounds.²¹We have recently reported the eﬃciency of

[RhI(cod)(Triaz)] (Triaz = 1,4-diphenyl-3-methyl-1,2,3-tria-

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catalytic dehydrogenation of ammonia-borane and formic

acid,³⁰as well as in dehydrogenative silylation or transfer

hydrogenation catalytic reactions.³¹

The selective C−H activation of the N-bound phenyl group

proposed for 1 was unambiguously conﬁrmed by an X-ray

diﬀraction analysis on a single crystal of the complex. The crystal

structure of 1 shows a pseudotetrahedral environment at the

metal center (Figure 1a) similar to that already reported for the

iridium-chlorido analogues.³²The reduced bite angle of the

cyclometalated triazolylidene ligand [C(1)−Rh−C(7)

78.6(3)°] distorts the coordination of both the C(1)−N(2)−

N(3)−N(4)−C(5) and C(6)−C(7)−C(8)−C(9)−C(10)−

Herein, we report on the synthesis and characterization of a

graphene-based hybrid catalyst featuring [Cp*RhI(C,C′)-

Triaz] complexes covalently immobilized through the triazoly-

lidene linker as well as its application as heterogeneous catalyst

for the hydrosilylation of a range of terminal alkynes with diverse

hydrosilanes. In addition, we have carried out recyclability

studies and a comparative study of its catalytic activity with that

of related [Cp*RhI(C,C′)-NHC] homogeneous catalysts.

Moreover, the reaction mechanism for the molecular catalyst

has been investigated by theoretical calculations at the Density

Functional Theory (DFT) level. On the basis of such

calculations, a metal−ligand bifunctional mechanism involving

reversible cyclometalation could be feasible.

RESULTS AND DISCUSSION

■

Synthesis and Characterization of N-Heterocyclic

Carbene Rhodium(III) Complexes [Cp*RhI(C,C′)-Triaz]

(1) and [Cp*RhI(C,C′)-Im] (2). Cyclometalated Rh(III)−

NHC compounds 1 and 2 were prepared by reaction of the

corresponding azolium salts, 1,4-diphenyl-3-methyl-1,2,3-tria-

zolium iodide and 1-phenyl-3-methyl-imidazolium iodide, with

half equivalent of the dimer compound [Cp*RhCl₂]₂in the

presence of sodium tert-butoxide (Scheme 2).

The formation of 1 proceeds through the mixed-halogen

intermediate species [Cp*RhICl(Triaz)], which was observed

when the reaction was conducted in the presence of 1 equiv of

NaOtBu (see Supporting Information, SI). It is worth noting

Scheme 2. Synthesis of Cyclometalated Complexes

[Cp*RhI(C,C′)-NHC] (NHC = Triaz, 1; Im, 2)

Figure 1. ORTEP views of [Cp*RhI(C,C′)-NHC] with the thermal

ellipsoids at 50% probability. Most hydrogen atoms are omitted for

clarity. Selected bond lengths (Å) and angles (deg): a) 1: C(1)−Rh

2.005(6), C(7)−Rh 2.048(7), Rh−I 2.6630(7), Rh−Ct 1.8577(5),

C(1)−Rh−C(7) 78.6(3), C(1)−Rh−I 89.65(16), C(7)−Rh−I

88.89(17), Ct−Rh−C(7) 130.06(18), Ct−Rh−I 123.38(2), Ct−Rh−

C(1) 131.47(18). b) 2: C(1)−Rh 2.000(3), C(12)−Rh 2.049(3), Rh−

I 2.6847(3), Rh−Ct 1.8702(2), C(1)−Rh−C(12) 77.96(12), C(1)−

Rh−I 91.82(8), C(12)−Rh−I 95.47(8), Ct−Rh−C(1) 130.26(8),

Ct−Rh−I 123.121(12), Ct−Rh−C(12) 125.56(8), and C(1)−Rh−

C(12) 77.96(12). Ct, centroid of the C₅ring of the Cp* moiety.

that the related chlorido compound [Cp*RhCl(C,C)-Triaz]

had previously been prepared by transmetalation of the

triazolylidene silver compound to [Cp*RhCl₂]₂without any

base.³²However, regarding the covalent immobilization of this

type of complexes on solid supports, the use of NaOtBu is much

more convenient as it avoids the use of a silver salt, as well as the

problems associated with the removal of the insoluble AgCl

byproduct. Compound 1 was obtained as an orange solid in 73%

yield and fully characterized by elemental analysis, HRMS and

NMR spectroscopy (see the SI).

C(11) rings, bringing about notable yaw angles ψ,³³namely

13.7° and 5.5°, respectively. Alternatively, reduced pitch angles

are observed [C(6)−C(7)−C(8)−C(9)−C(10)−C(11), pitch,

θ 1.8°; C(1)−N(2)−N(3)−N(4)−C(5), pitch, θ 0.1°].

Furthermore, the steric release as well as the C(17)−H(17)···I

contact (Figure 1a, C(17)−H(17) 0.95 Å, H(17)···I 3.04 Å,

C(17)···I 3.954(6) Å, C(17)−H(17)−I 162°) should be

responsible for the dihedral angle C(1)−C(5)−C(12)−C(17)

of 41.6(1.1)°.

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a b

,

Table 1. Hydrosilylation of 1-Alkynes Catalyzed by [Cp*RhI(C,C′)-NHC] (NHC = Triaz, 1; Im, 2)

entry

1-alkyne/hydrosilane

solvent

CDCl₃

T (°C)

catalyst

t (min)

conv (%)

β-(Z) (%)

β-(E) (%)

α (%)

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

n-HexCCH/HSiMe₂Ph

25

60

25

60

25

60

1

2

1

2

1

2

1

2

1

20

360

15

110

300

20

120

54

150

70

48

20

18

22

50

85

45

40

98

99

98

99

98

97

99

98

99

97

96

99

98

99

24

99

acetone-d₆

n-HexCCH/HSiMePh₂

CDCl₃

acetone-d₆

n-HexCCH/HSiEt₃

PhCCH/HSiMe₂Ph

CDCl₃

acetone-d₆

CDCl₃

acetone-d₆

CDCl₃

acetone-d₆

PhC≡CH/HSiEt₃

MeOC₆H₄−CCH/HSiMe₂Ph

CF₃C₆H₄−C≡CH/HSiMe₂Ph

CyCCH/HSiMe₂Ph

CyCCH/HSiEt₃

20

240

1000

t-BuCCH/HSiMe₂Ph

n-HexCCH/HMTS

68

8

acetone-d₆

98

b

a

1

Conversions and selectivities (%) were calculated by H NMR using anisole as internal standard. Experiments were carried out in CDCl₃or

acetone-d₆(0.5 mL) using a HSiR₃/alkyne/catalyst ratio of 100/100/1, [catalyst]_o= 1 × 10⁻³M.

The cyclometalated iodido complex [Cp*RhI(C,C′)-Im] (2)

had already been prepared by Choudhury et al.³⁴using NaOAc

as base instead of NaOtBu. Although the crystal structure of 2

was also reported, the poor quality of that determination, carried

out at 293 K, e.g., R₁= 0.1211 [I > 2σ(I)], wR₂= 0.4370 (all

data), prompted us to perform a signiﬁcantly more accurate

study at 100 K. Both at 100 and 293 K, the space group was

P2₁/c, with slightly diﬀerent unit cells. The ORTEP view of the

crystal structure of 2 and a selection of bond lengths and angles

are given in Figure 1b. It is worth mentioning that, due to the

small bite angle of the phenyl-imidazolylidene metalated ligand

[C(1)−Rh−C(12) 77.96(12)°], both the imidazolylidene

moiety and the metalated phenyl ring deviate from the ideal

arrangement at Rh−C(1) and Rh−C(12) bonds, respectively.

In particular, they render the following pitch and yaw angles:

C(7)−C(8)−C(9)−C(10)−C(11)−C(12), pitch, θ 7.4°, yaw,

ψ 6.8°; C(1)−N(2)−C(3)−C(4)−N(5), pitch, ψ 0.7°, yaw, ψ

10.5°.³³

Hydrosilylation of 1-Alkynes Catalyzed by [Cp*RhI-

(C,C′)-NHC]. Compounds [Cp*RhI(C,C′)-Triaz] (1) and

[Cp*RhI(C,C′)-Im] (2) were tested as catalyst precursors for

the hydrosilylation of a range of aliphatic and aromatic terminal

alkynes, including oct-1-yne, phenylacetylene derivatives, and

3,3-dimethyl-but-1-yne; using HSiMePh₂, HSiMe₂Ph, and

HSiEt₃as hydrosilanes (see Table 1). The reactions were

performed in CDCl₃or acetone-d₆, at 25 or 60 °C, with standard

catalyst loads of 1 mol % and were routinely monitored by ¹H

NMR spectroscopy using anisole as internal standard.

solvent. However, catalyst 1, bearing the cyclometalated

triazolylidene ligand, is more active than 2. In fact, 1 catalyzes

the hydrosilylation of oct-1-yne at room temperature either in

chloroform or acetone, and signiﬁcantly longer reaction times

are needed for 2 (Table 1, entries 1−4). To our delight, the

frequently observed isomerization of β-(Z)-vinylsilane to the

more thermodynamically stable β-(E)-vinylsilane isomer once

the alkyne substrate has been completely exhausted is not

observed here.^22,35Further, the hydrosilylation reactions of oct-

1-yne with less reactive hydrosilanes, such as HSiMePh₂or even

HSiEt₃, proceed eﬃciently with both catalysts, aﬀording

complete selectivity for the β-(Z)-vinylsilane isomer (Table 1,

entries 5−11). In general, hydrosilylation reactions with catalyst

1 are faster in acetone-d₆than in CDCl₃at room temperature,

although the reaction speeds up signiﬁcantly in CDCl₃at 60 °C

(entries 5 and 6).

The excellent catalytic performance of 1 in acetone-d₆

prompted us to study the substrate scope with this catalyst.

Full conversion to the β-(Z)-vinylsilane product was attained in

the hydrosilylation of phenylacetylene with HSiMe₂Ph or

HSiEt₃in acetone-d₆in about 20 min (entries 13 and 14). In

contrast, the related Rh(I) catalyst [RhI(cod)Triaz] exhibited

moderate catalytic activity and poor selectivity for the

hydrosilylation of phenylacetylene.²²The hydrosilylation of

phenylacetylene derivatives having either an electron-donating

(−OMe) or an electron-withdrawing (−CF₃) substituent at the

para position with HSiMe₂Ph is slightly slower, especially for the

latter, although complete selectivity to the β-(Z)-vinylsilane

products was achieved with both substrates (entries 15 and 16).

The hydrosilylation of cyclohexylacetylene, a secondary alkyl

substituted alkyne, with HSiMe₂Ph and HSiEt₃in CDCl₃or

acetone-d₆also proceeds eﬃciently at 25 °C to give the

Noteworthy, both catalysts are eﬀective for the hydro-

silylation of oct-1-yne with HSiMe₂Ph, aﬀording full conversion

and complete selectivity for the less thermodynamically stable β-

(Z)-vinylsilane isomer using either acetone-d₆or CDCl₃as

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Figure 2. DFT calculated Gibbs energy reaction proﬁle (in kcal·mol⁻¹relative to D′ and isolated molecules) for the hydrosilylation of phenylacetylene

with HSiMe₂Ph catalyzed by [Cp*RhI(C,C′)-Triaz] (1).

Figure 3. Possible reaction pathways to be undertaken for intermediate E (in kcal·mol⁻¹relative to D′ and isolated molecules).

corresponding β-(Z)-vinylsilane products (entries 17 and 19).

Alternatively, the hydrosilylation of a bulky aliphatic alkyne such

as t-Bu-CCH is much slower, even at 60 °C, and pretty

unselective, aﬀording 68% of the β-(E)-vinylsilane (Table 1,

entry 20), which is in agreement with the observed trend for

related Rh(I)−NHC catalysts.^17c,18Gratifyingly, the hydro-

silylation of oct-1-yne with the least reactive and bulkier

heptamethylhydrotrisiloxane (HMTS) takes place slowly at 60

°C with complete selectivity to the β-(Z)-vinylsilane product

(Table 1, entry 21).

To our delight, the hydrosilylation reaction can be carried out

on a preparative scale as has been demonstrated for the synthesis

of (Z)-dimethyl(oct-1-en-1-yl)(phenyl)silane by three consec-

utive catalytic cycles using catalyst 1 (see Experimental Section).

We have studied the hydrosilylation of phenylacetylene with

the hydrosilanes Ph₂SiH₂and PhSiH₃catalyzed by 1 at 60 °C in

CDCl₃. Both reactions are unselective due to the formation of

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Figure 4. DFT-optimized structures and selected distances of (a) TS-EC, (b) TS-ED, (c) TS-GC, and (d) TS-GD. Notice that nonrelevant hydrogen

atoms have been omitted for clarity.

multiaddition products,³⁶which is consistent with the high

activity exhibited by catalyst 1. Hydrosilylation of phenyl-

acetylene with PhSiH₃or Ph₂SiH₂(1:1) aﬀorded a mixture of

mono- and dialkenylsilane products with complete regioselec-

tivity for the β-styryl derivatives, although the Z stereoselectivity

is lost. Phenylacetylene reacted with PhSiH₃(3:1 molar ratio, 4

h) to the give the tris-styrylsilane product (87%) as the ZEE

(53%) and EEE (34%) stereoisomers. In contrast, the

hydrosilylation of phenylacetylene with Ph₂SiH₂(2:1) gave

diphenyl((Z)-styryl)silane (47%) and diphenyl((Z)-styryl)-

((E)-styryl)silane (53%) in 40 min, thereby suggesting that

under these experimental conditions the ﬁrst hydrosilylation

proceeds with β-(Z) stereoselectivity (see SI).

Mechanistic Insights on the Hydrosilylation of 1-

Alkynes Catalyzed by 1. In order to shed light on the

mechanism of the hydrosilylation of terminal alkynes catalyzed

by 1, and understand its outstanding activity and selectivity, we

performed a complete theoretical study. In particular, we applied

DFT at the B3LYP-D3BJ/def2-TZVP//def2-SVP (PCM,

acetone) level of theory (see the Experimental Section for

more details). We selected HSiMe₂Ph and phenylacetylene as

hydrosilane and alkyne models, respectively. The active catalyst

(complex 1) was considered in its totality, without including

geometrical simpliﬁcations, as it bears reactive and bulky ligands

that are likely to have a relevant eﬀect in the reaction

pathways.^37,38For the sake of a clear understanding, the

reaction intermediates and transition states are referred to by

capital letters starting by A (which corresponds to the catalyst,

1). Notice that we have set the energy reference at D′, as this

species is the most likely starting point for successive catalytic

cycles. The lowest-in-energy reaction pathway is shown in

Figure 2, while other discarded alternatives are provided in

Figure 3.

The ﬁrst step consists of the ligand exchange between the

iodido ligand and a hydrosilane molecule. This happens through

intermediate B, which is 14.3 kcal·mol⁻¹less stable than A, and

yields intermediate C, which is 7.4 kcal·mol⁻¹higher in energy

than A. Notice that the aforementioned process is facilitated by

the coordination ﬂexibility of the Cp* ligand, which changes its

coordination mode form η⁵to η¹,^39,40as we previously reported

for structurally related catalysts.³⁷Then, the hydrosilane H−Si

bond is activated by means of a σ-complex assisted metathesis

(σ-CAM) mechanism involving the H−Si and Rh−C_Arbond,

thus forming new Rh−Si and C_Ar−H bonds.^41,42This step

proceeds via TS-CD (see Figure S34 in the SI), and is required

to surmount an energy barrier of 14.5 kcal·mol⁻¹(with respect

to A, feasible under the working conditions), leading to the silyl

intermediate D, whose relative energy is 1.2 kcal·mol⁻¹higher

than that of C. We note that we also explored the classical inner-

sphere mechanisms that involve the hydrosilane oxidative

addition to the metal center,⁴³but we could not ﬁnd any stable

intermediate. In fact, the oxidative addition on Rh(III) species A

(and C) would lead to an Rh(V) intermediate, which, with very

few exceptions,⁴⁴has been extensively reported to be unstable.

As D bears a coordination vacancy, both the hydrosilane and

the alkyne could occupy it. The coordination of the hydrosilane

would lead to D′, 2.3 kcal·mol⁻¹more stable than D; however,

this pathway could not further evolve as the oxidative addition of

the hydrosilane into the Rh(III) center would lead to an Rh(V)

intermediate. Also notice that the signiﬁcant steric repulsions

within the complex hinder the hydrosilane coordination, thereby

resulting in a stabilization energy of only 2.3 kcal·mol⁻¹. The

ligand exchange between the hydrosilane and the alkyne leads to

D′′, 2.4 kcal·mol⁻¹less stable than D′, which has not been

included in Figure 2 for simplicity. Nonetheless, this step is

necessary for the alkyne insertion into the Rh−Si bond, which

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Scheme 3. Mechanistic Proposal for the Hydrosilylation of Phenylacetylene with HSiMe₂Ph Catalyzed by [Cp*RhI(C,C′)-Triaz]

(1) on the Basis of DFT Calculations

takes place via TS-DE (see Figure S34 in the SI) and yields the

(Z)-silylvinylene intermediate E, with a relative energy of −15.9

kcal·mol⁻¹with respect to D′. The process requires overcoming

an energy barrier of 20.6 kcal·mol⁻¹(with respect to A) for the

ﬁrst catalytic cycle, and 14.3 kcal·mol⁻¹(with respect to D′) for

successive cycles (see below).

Intermediate E may undertake three diﬀerent processes,

which are summarized in Figure 3. One possibility is a direct σ-

CAM between the C_Ar−H and Rh−C bonds to directly yield the

β-(E)-vinylsilane products (via TS-EC Figure 4a) and C (blue

pathway). This process requires overcoming an energy barrier of

16.1 kcal·mol⁻¹, determined by the energy diﬀerence between E

and the transition structure TS-EC. The second possibility

would be σ-CAM with a newly coordinated hydrosilane, i.e.,

between the H−Si and the Rh−C bonds, to yield the β-(E)-

vinylsilane product and D, by means of TS-ED (Figure 4b), as

shown in the red pathway. This pathway requires overcoming an

energy barrier of 23.8 kcal·mol⁻¹(the energy diﬀerence between

TS-ED and E). Alternatively, E can isomerize to intermediate G,

with a relative energy of −23.0 kcal·mol⁻¹, 7.1 kcal·mol⁻¹more

stable than E (black pathway). This process may take place via a

metallacyclopropene intermediate F, also named η²-vinylsilane

metal species,⁴⁵with a relative energy of −6.2 kcal·mol⁻¹(9.7

kcal·mol⁻¹higher than E). Notice that the energetic proﬁle of

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Scheme 4. Stepwise Synthesis and Structure of the Graphene-Based Rh(III)−Triazolylidene Hybrid Catalyst TRGO-Triaz-

Rh(III) (See the SI for Details)

this process is signiﬁcantly lower than that involving the direct β-

(E)-vinylsilane formation (9.7 kcal·mol⁻¹vs 23.8 kcal·mol⁻¹and

16.1 kcal·mol⁻¹), and thus the isomerization pathway will be the

preferred one. On balance, intermediate F leads to the

isomerization of the (Z)-silylvinylene into the more stable

(E)-silylvinylene intermediate. We associate the feasibility of the

formation of the three-membered metallacycle intermediate to

the presence of a coordination vacancy in the 16e⁻intermediate

E, which facilitates the coordination of a second carbon atom to

the metal center, thus forming intermediate F.

Finally, there would be two diﬀerent possibilities for the

generation of the β-(Z)-vinylsilane product from G by means of

σ-CAM processes, which are analogous to those reported for the

formation of the β-(E)-vinylsilane isomer (see Figure 2). The

ﬁrst one consists of the cyclometalation via σ-CAM between H−

C_Arand Rh−C bonds through TS-GC (Figure 4c), with an

energy barrier of 13.2 kcal·mol⁻¹(dictated by the energy

diﬀerence between TS-GC and G), which would regenerate

intermediate C and yield the β-(Z)-vinylsilane (blue pathway in

Figure 2). The second alternative (red pathway) involves the

coordination of another hydrosilane molecule and the σ-CAM

between the H−Si and the Rh−C bonds (via TS-GD, Figure

4d), with an energy barrier of 12.0 kcal·mol⁻¹(determined by

the diﬀerence between TS-GD and G). This pathway leads to

the β-(Z)-vinylsilane and intermediate D′ (upon coordination

of a hydrosilane in the coordination vacancy of D).

Overall, the process is very favorable from a thermodynamic

point of view, with a ΔG of −39.2 kcal·mol⁻¹with respect to D′

(and −32.9 kcal·mol⁻¹with respect to A) for the β-(Z)-

vinylsilane product. We calculated the eﬀective energy span

(ΔG^⧧) for the cycle by means of the method proposed by

Kozuch et al.⁴⁶According to this framework, the ﬁrst catalytic

cycle features ΔG^⧧of 20.6 kcal·mol⁻¹, which is determined by

the energy diﬀerence between TS-DE (the alkyne insertion into

the Rh−Si bond) and A. However, since the lowest-in-energy

pathway leads to D′, we set the zero of energies at this point as it

is the starting point for subsequent cycles. Thus, the energy span

for the subsequent reaction cycles would be ΔG^⧧= 12.0 kcal·

mol⁻¹, which corresponds to the ﬁnal σ-CAM between the H−Si

hydrosilane bond and the Rh−C bond of the (Z)-silylvinylene

(G).⁴⁷

The proposed mechanism for the hydrosilylation of phenyl-

acetylene with HSiMe₂Ph catalyzed by [Cp*RhI(C,C′)-Triaz]

(1) on the basis of theoretical calculations is summarized in

Scheme 3. The release of the β-(Z)-vinylsilane product from the

(E)-silylvinylene intermediate can occur by a reversible

cyclometalation mechanism involving σ-CAM with the C_Ar−H

bond (outer catalytic cycle),^30aor the Si−H bond of an external

hydrosilane (inner catalytic cycle). Since the energy barrier for

the σ-CAM pathway involving the Si−H bond is 1.2 kcal·mol⁻¹

lower than that of the C−H bond, both pathways could be

operative under the experimental reaction conditions.

Remarkably, TS-GD is 1.2 kcal·mol⁻¹more stable than TS-

GC, pointing toward the σ-CAM between the H−Si and the

Rh−C bonds is preferred to the reversible cyclometalation;

however, the very small energy diﬀerence between both

pathways indicates that both will contribute to the overall

reaction ensemble. It is also noticeable that the transition state

for cyclometalation was 7.7 kcal·mol⁻¹more stable than the σ-

CAM with the hydrosilane for the (E)-silylvinylene intermediate

(E), while it is 1.2 kcal·mol⁻¹less favorable for the (Z)-

silylvinylene intermediate (G). We attribute this feature to the

higher steric hindrance in E, which disfavors the hydrosilane

coordination (see Figure 4).

In order to analyze in depth, the role of steric eﬀects in the

reaction mechanism, we recomputed the aforementioned

reaction pathways for an alky-substituted NHC−Rh complex

in which we have replaced the phenyl moiety in the NHC

scaﬀold by a methyl group. For analogy with catalyst 1, we called

this one 1-Me, which corresponds to intermediate A-Me in the

theoretically computed reaction pathways (see Figures S35 and

S36 in the SI). The results showed that a similar reaction

mechanism takes place when the bulkier phenyl group is

substituted by a methyl one (Figures S35 and S36), with minor

changes in the energy barriers, as a consequence of the lower

steric hindrance of the Me group. Namely, the energy span for

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Figure 5. (a) HRTEM, (b) STEM (I), and EDX mapping images of Rh (II), N (III), and O (IV) for TRGO-Triaz-Rh(III), and high resolution XPS

spectra of (c) N 1s and (d) O 1s for TRGO-Triaz (blue curves) and TRGO-Triaz-Rh(III) (red curves).

the alkyne insertion in the Rh−Si bond (determined by TS-DE-

Me and D′-Me for the second catalytic cycle) is 9.6 kcal·mol⁻¹,

i.e., 4.7 kcal·mol⁻¹lower than that derived from the original

catalyst (1). On the contrary, the energy diﬀerence between the

η²-vinylsilane metal intermediate (F-Me) and the β(E)-

vinylsilane formation by σ-CAM-driven orthometalation (TS-

EC-Me) is 6.8 kcal·mol⁻¹, only 0.4 kcal·mol⁻¹higher than that of

1 (Figures 3 and S36); thus indicating that both catalysts will

undertake the same isomerization process to yield the β(Z)-

vinylsilane isomer. Probably, the most remarkable diﬀerence is

that the energy splitting between the two possibilities for the

release of the ﬁnal product (energy diﬀerence between TS-GD-

Me and TS-GC-Me, Figure S35) is signiﬁcantly higher for 1-Me,

the σ-CAM between the H−Si hydrosilane bond and the Rh−C

bond of G-Me being 5.6 kcal·mol⁻¹more favorable than the

orthometalation, while it is only 1.2 kcal·mol⁻¹for 1. As a

consequence, we only expect the former process to take place.

We attribute this diﬀerence to the lower steric hindrance in 1-

Me. As TS-GD(-Me) is more sterically impeded, the

substitution of the phenyl moiety by a methyl one, relieves the

steric repulsion, making this transition structure signiﬁcantly

lower in energy than that of TS-GC(-Me), in which the steric

repulsion eﬀect is less important as its coordination sphere is less

crowded (it misses the extra silane present in TS-GD(-Me))

Synthesis and Characterization of Graphene-Based

Rhodium(III)−Triazolylidene Hybrid Catalyst. The remark-

able alkyne hydrosilylation performance of the cyclometalated

[Cp*RhI(C,C′)-Triaz] (1) compound prompted us to prepare

a related graphene-oxide-supported Rh(III)−triazolylidene

hybrid material. A 3-methyl-4-phenyl-1,2,3-triazolium iodide

functionalized graphene oxide material having trimethylsilyl-

protected hydroxy groups recently reported by us, TRGO-

Triaz, has been used for this purpose (Scheme 4). According to

our previous experience, the protection of all −OH groups in the

triazolium functionalized material is required for the successful

metalation that leads to triazolylidene rhodium complexes

anchored to the carbon nanomaterial. In fact, the TMS-

protected Rh(I)−triazolylidene (TMS = trimethylsilyl) hybrid

material has shown excellent stability and good recyclability for

alkyne hydrosilylation, thereby conﬁrming the strength of the

C−N covalent bond of the triazolylidene to the graphitic wall.²²

The graphene supported Rh(III)−triazolylidene hybrid

material, TRGO-Triaz-Rh(III), was prepared by reaction of

TRGO-Triaz with [Cp*RhCl₂]₂in the presence of sodium tert-

butoxide. The rhodium content of the new hybrid material, 5.7

wt %, was determined by means of ICP−MS. HRTEM images

(Figure 5a) and STEM-EDX mapping (Figure 5b, I−IV) of

TRGO-Triaz-Rh(III) establish the homogeneous distribution

of the rhodium atoms (black spots of size between 0.7 and 1.2

nm, Figure 5a) all along the graphene basal planes (Figure 5b,

II).^22,48Similarly, nitrogen and oxygen are also homogeneously

distributed in the graphene material (Figure 5b, III−IV,

respectively) although silicon was almost undetectable. A similar

result was obtained by the analysis of this sample by XPS (see SI

Table S1) conﬁrming that the silicon content observed in the

parent TRGO-Triaz material (5.3%) have disappeared after

rhodium anchoring. The presence of Rh(III) in TRGO-Triaz-

Rh(III) was evidenced by the doublet signal in the high-

resolution XPS Rh 3d spectrum with an average separation

between the maxima of ∼4.6 eV and with the maximum of the

3d5/2 peak centered at ∼310.1 eV (SI Figure S9).⁴⁹

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Alternatively, the anchorage of rhodium to the triazolylidene

moieties was evidenced by a change in the XPS N 1s spectra

(Figure 5c). Not only is the maximum of the signal shifted to

lower binding energies (from 400.2 to 399.5 eV), but also there

is a narrowing of the signal observed with full widths at half-

maximum, fwhm, of 1.6 and 3.3 eV for TRGO-Triaz-Rh(III)

and TRGO-Triaz, respectively. These eﬀects were also observed

in the XPS N 1s spectra of the previously reported TRGO-

Triaz-Rh(I) compared to that of TRGO-Triaz.²²Surprisingly,

when analyzing the high resolution XPS O 1s spectra (Figure

5d), a shift in the maximum toward lower binding energies is

also seen after rhodium anchoring. This signiﬁcant fact is

consistent with the elimination of the C−O−Si bonds involving

the protective TMS groups, which is in accordance with the

observed absence of Si in the hybrid material. Besides, the higher

intensity at lower binding energies in that spectrum does not

discard the formation of Rh−O bonds. Moreover, the

deconvolution of the high resolution XPS C 1s spectra conﬁrms

a substantial increase in the Csp³content after rhodium

anchoring (from 15.5% to 34.5% for TRGO-Triaz and

TRGO-Triaz-Rh(III), respectively; see Table S1). All in all,

the signiﬁcant increment in the Csp³content after rhodium

anchoring seems to be related to the release of the TMS

protecting groups from TRGO-Triaz as Me₃SiOH due to the

protonation with the tert-butanol generated in the formation of

the triazolylidene rhodium complex. As a consequence, tert-

butoxy moieties are linked to the graphitic wall of TRGO-Triaz-

Rh(III) as ether groups. The elimination of the TMS protective

groups was also indirectly conﬁrmed by XPS analysis of the

TRGO-Triaz′ material. Such a system was obtained by

treatment of TRGO-Triaz at the same experimental conditions

as those used to prepare TRGO-Triaz-Rh(III) but in the

absence of [Cp*RhCl₂]₂, that is, with NaOtBu in THF and

additional washing with methanol. The resulting material

TRGO-Triaz′, exhibits a negligible XPS Si content. Moreover,

the same eﬀect was observed when the material TRGO-Triaz

was treated directly with t-BuOH. The XPS of this washed

material TRGO-Triaz′′ conﬁrms the lability of the protective

groups under the experimental conditions.

hybrid material. This behavior is similar to that previously

observed for [RhI(cod)Triaz] and the TMS-protected TRGO-

Triaz-Rh(I) hybrid material.²²

The EXAFS ﬁt was performed in the R-space between 1.1 and

3.1 Å for TRGO-Triaz-Rh(III) and between 1.1 and 3.9 Å for 1.

In order to have an appropriate model to analyze the spectrum of

1, we have made use of the crystallographic data for this

compound to calculate phases and amplitudes of the diﬀerent

paths, as indicated in the Experimental Section. Figure 6a shows

the experimental spectrum and the best ﬁt obtained for this

sample. The analysis is in accordance with the crystallographic

data and the Rh presents a piano stool geometry formed by the

Cp* ligand, two shorter Rh−C distances which belong to the

orthometalated N-phenyl group and to the carbene of the

triazolylidene ligand, and a iodine atom for the last coordination

In order to shed more light on the local structure of the

Rh(III) atoms in the hybrid material TRGO-Triaz-Rh(III),

Extended X-ray Absorption Fine Structure (EXAFS) spectra at

the Rh K edge were measured. EXAFS analysis was also related

with that of the molecular complex [Cp*RhI(C,C′)-Triaz] (1)

and compared with those of the known [RhI(cod)Triaz] (cod =

1,5-cyclooctadiene) rhodium(I) molecular compound and the

TMS-protected TRGO-Triaz-Rh(I) hybrid material.²²Focus-

ing on the properties of TRGO-Triaz-Rh(III) and 1, their

EXAFS spectra (EXAFS signals and the Fourier transforms

(FT), see Figure S12) clearly indicate diﬀerent environments for

the Rh(III) atoms in both samples. The FT allows us to

determine a strong peak at a distance of about 1.65 Å (without

phase shift correction) for TRGO-Triaz-Rh(III) that agrees

with Rh−C or Rh−O interatomic distances. Contributions

beyond this ﬁrst coordination shell are weak, suggesting the lack

of heavier atoms close to the Rh centers. However, the FTs of 1

show two peaks of similar intensity at distances of 1.65 and 2.40

Å. The ﬁrst peak is less intense with respect to the previous

samples, indicating either a smaller coordination number or a

greater disorder in the Rh−C (or O) coordination shell. The

second distance is in agreement with an Rh−I interatomic

distance, suggesting that the iodido ligand is in the ﬁrst

coordination shell for the molecular complexes, but not for the

Figure 6. Best ﬁts (lines) and experimental (circles) FTs curves (open

for moduli and dark for the real parts) for (a) [Cp*RhI(C,C′)-Triaz]

(1) and (b) TRGO-Triaz-Rh(III); (c) structural model for the hybrid

TRGO-Triaz-Rh(III) material.

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a b

,

Table 2. Hydrosilylation of 1-Alkynes Catalyzed by the Hybrid Catalyst TRGO-Triaz-Rh(III)

entry

1-alkyne/hydrosilane

solvent

CDCl₃

T (°C)

t (min)

conv (%)

β-(Z) (%)

β-(E) (%)

α (%)

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

n-HexCCH/HSiMe₂Ph

25

60

25

60

25

60

25

60

30

40

30

36

100

90

30

240

30

76

300

0

99

0

99

0

99

0

99

0

acetone-d₆

CDCl₃

n-HexCCH/HSiMePh₂

n-HexCCH/HSiEt₃

98

0

99

0

acetone-d₆

99

97

98

99

98

97

99

25

CDCl₃

acetone-d₆

PhCCH/HSiMe₂Ph

PhC≡CH/HSiEt₃

MeOC₆H₄−C≡CH/HSiMe₂Ph

CF₃C₆H₄−C≡CH/HSiMe₂Ph

t-BuCCH/HSiMe₂Ph

n-HexCCH/HMTS

66

9

1100

99

b

a

Conversions and selectivities (%) were calculated by ¹H NMR spectroscopy using anisole as internal standard. Experiments were carried out in

CDCl₃or acetone-d₆(0.5 mL) using a HSiR₃/alkyne/catalyst ratio of 100/100/1, 1 mol % of Rh calculated according to ICP-MS measurements.

position. Regarding the analysis of TRGO-Triaz-Rh(III), it is

clear that the previous model fails to account for the local

environment of the Rh center, as no iodido is found in the ﬁrst

coordination shell. Following previous results on rhodium and

iridium carbon supported materials,^22,48we have replaced the I

atom by an O in the Rh neighborhood. To our delight, the ﬁt

quickly converges, reaching the outcome shown in the Figure 6b.

This result reveals that the iodine has been replaced by an

oxygen in the Rh coordination sphere. The most likely

possibility is that the oxygen belongs to one of the −OH or

−O-tBu groups on the carbon wall to complete the rhodium

coordination, instead of the iodido, which is clearly not present

in the immediate vicinity of Rh atoms in this hybrid material (see

Figure 6c). The reﬁned parameters of both ﬁts are summarized

in Table S3.

Catalytic Activity in Hydrosilylation of 1-Alkynes and

Recycling of the Hybrid Catalyst TRGO-Triaz-Rh(III). The

catalytic activity of the heterogeneous graphene-based catalyst

TRGO-Triaz-Rh(III) in the hydrosilylation of terminal alkynes

has been studied and compared with that of the molecular

homogeneous catalyst [Cp*RhI(C,C′)-Triaz] (1) (Table 2).

The reactions were carried out in CDCl₃or acetone-d₆using a

catalyst load of 1 mol % of Rh (calculated according to the

rhodium content of 5.7 wt % from ICP−MS) and monitored by

¹H NMR spectroscopy.

acetylene derivatives having electronically dissimilar substitu-

ents at the para position in acetone-d₆at 60 °C (entries 13 and

14). These results contrast with the performance of the related

Rh(I) hybrid catalyst TRGO-Triaz-Rh(I), for which extensive

phenylacetylene polymerization was observed.⁵⁰As can be

observed in the reaction proﬁles for the hydrosilylation of 4-R-

C₆H₄−CCH derivatives (R = H, MeO, and CF₃) with

HSiMe₂Ph (Figure 7), the presence of an −OMe electron-

donating group resulted in a slight increase in the catalytic

activity compared to phenylacetylene. However, the hydro-

silylation of the phenylacetylene derivative with an electron-

withdrawing substituent such as CF₃is much slower. According

to the negative slope of the Hammett plot (ρ = −0.63 for

TOF₅₀) a buildup of positive charge in the transition state of the

reaction is occurring and consequently a rate increase by

electron-donor groups is observed due to resonance stabilization

(see Figure S29).^21b

As observed for the homogeneous catalyst 1, the hydro-

silylation of the bulky t-BuCCH with HSiMe₂Ph by TRGO-

In contrast to 1, TRGO-Triaz-Rh(III) showed no catalytic

activity at room temperature, neither in acetone-d₆nor in

CDCl₃. However, at 60 °C, the hybrid catalyst is an eﬀective

catalyst for the hydrosilylation of oct-1-yne with hydrosilanes

such as HSiMe₂Ph or HSiMePh₂aﬀording full conversion and

complete selectivity for the β-(Z)-vinylsilane isomer in less than

40 min in both solvents (entries 1−8). Remarkably, although the

hydrosilylation of oct-1-yne with HSiEt₃requires around 100

min it proceeds with excellent selectivity in both solvents

(entries 9 and 10).

TRGO-Triaz-Rh(III) eﬃciently catalyzed the hydrosilyla-

tion of aromatic alkynes. Phenylacetylene was selectively

transformed into the corresponding β-(Z)-vinylsilane product

in acetone-d₆at 60 °C using HSiMe₂Ph or HSiEt₃in 30 and 240

min, respectively (entries 11 and 12). Interestingly, complete β-

(Z) selectivity was attained in the hydrosilylation of phenyl-

Figure 7. Reaction proﬁle obtained from ¹H NMR data for the

hydrosilylation of arylacetylenes derivatives 4-R-C₆H₄−CCH (R =

H, purple; MeO, red; and CF₃, brown) with HSiMe₂Ph (1:1), catalyzed

by TRGO-Triaz-Rh(III) in acetone-d₆(0.5 mL) at 60 °C with 1 mol %

of Rh calculated according to ICP−MS measurements.

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Triaz-Rh(III) was unselective, aﬀording a similar product

distribution with β-(E)-vinylsilane as the major reaction

outcome (entry 15). Notice that the hydrosilylation of oct-1-

yne with heptamethylhydrotrisiloxane (HMTS) is β-(Z)-

selective although, as for catalyst 1, a much longer reaction

time (18 h) is required (entry 16). Importantly, no β-(Z) to β-

(E) vinylsilane isomerization was observed in the catalyzed

hydrosilylation of oct-1-yne with HSiMe₂Ph neither with

TRGO-Triaz-Rh(III) nor with 1, even when heating during

long reaction times.

loss of the initial Rh content was observed after the ﬁrst run. This

is consistent with the removal of physisorbed rhodium species,

not eliminated by the standard material washing, but likely

removed under the catalytic reaction conditions. Remarkably,

no rhodium leaching was detected in the following runs (Figure

8) thereby conﬁrming the stability of the graphene-based

rhodium(III)-triazolylidene hybrid catalyst.

Catalyst recycling experiments with TRGO-Triaz-Rh(III) for

the hydrosilylation of oct-1-yne with both HSiMePh₂and

HSiMe₂Ph have been carried out in acetone-d₆at 60 °C using a

catalyst load of 1 mol % of Rh. The recycling experiments (run

n) were carried out by evaporating the solvent under vacuum,

washing the residue with fresh n-hexane (3 × 1 mL) and then,

adding a new load of hydrosilane/oct-1-yne/acetone-d₆(Table

3). Remarkably, the recovered heterogeneous catalyst after the

catalysis runs exhibited identical performance as the fresh

catalyst after 5 consecutive cycles for both hydrosilanes. The

recycling runs were performed under an argon atmosphere,

except for the last run that was carried out on air (entries 6 and

1

12). The catalytic reactions were monitored by H NMR and

showed very similar kinetic proﬁles in the successive recycling

Figure 8. Recycling of TRGO-Triaz-Rh(III) in the hydrosilylation of

oct-1-yne with HSiMePh₂in acetone-d₆for six catalytic runs (reaction

time of 40 min). Oct-1-yne conversion and Rh percentage in the

recycled material in base of the Rh content, analyzed by ICP−MS, of

the ﬁltrate and washings after each run.

Table 3. Catalyst Recycling Experiments for the

Hydrosilylation of Oct-1-yne Catalyzed by the Hybrid

a b

,

Catalyst TRGO-Triaz-Rh(III)

n-HexCCH/

entry

hydrosilane

HSiMePh₂

t (min) conv (%) β-(Z) (%)

CONCLUSIONS

■

1

2

3

4

5

6

7

8

9

run 1

40

30

99

98

99

98

99

98

>99

The cyclometalated Rh(III)−NHC compound[Cp*RhI(C,C′)-

Triaz](Triaz = 1,4-diphenyl-3-methyl-1,2,3-triazol-5-ylidene) is

an eﬃcient catalyst for the hydrosilylation of terminal alkynes

with complete regio- and stereoselectivity toward the

thermodynamically less stable β-(Z)-vinylsilane isomer at

room temperature both in chloroform and acetone. Linear 1-

alkynes, such as oct-1-yne, tert-butylacetylene, and phenyl-

acetylene derivatives undergo hydrosilylation with diverse

hydrosilanes, including HSiMePh₂, HSiMe₂Ph, HSiEt₃, and

the bulkier heptamethylhydrotrisiloxane (HMTS), to aﬀord the

corresponding β-(Z)-vinylsilanes in quantitative yields.

run 2

run 3

run 4

run 5

run 6

run 1

run 2

run 3

run 4

run 5

run 6

c

HSiMe₂Ph

10

11

12

c

We have applied our strategy for the immobilization of Rh(I)-

triazolylidene compounds on carbonaceous materials, which has

demonstrated the strength of the C−N covalent bond of the

triazolylidene linker to the graphitic wall under hydrosilylation

conditions, to prepare a Rh(III)-triazolylidene hybrid catalyst.

The graphene-based hybrid material featuring covalently

immobilized cyclometalated [Cp*RhI(C,C′)-Triaz] complexes

through the triazolylidene linker, TRGO-Triaz-Rh(III), has

been prepared by metalation of the trimethylsilyl-protected 3-

methyl-4-phenyl-1,2,3-triazolium iodide functionalized gra-

phene oxide material, TRGO-Triaz, with [Cp*RhCl₂]₂using

sodium tert-butoxide as base. The coordination sphere of the

supported rhodium(III) complexes has been determined by

means of XPS and extended X-ray absorption ﬁne structure

(EXAFS) spectroscopy showing the replacement of the iodido

ligand by O-functionalities on the carbon wall. Furthermore,

experimental studies in combination with XPS measurements

evidence the elimination of the trimethylsilyl protective groups

which are replaced by tert-butoxy moieties linked to the graphitic

wall as ether groups. The heterogeneous TRGO-Triaz-Rh(III)

hybrid catalyst is not active at room temperature although it

a

Conversions and selectivities (%) were calculated by ¹H NMR using

b

anisole as internal standard. Experiments were carried out in

acetone-d₆(0.5 mL) at 60 °C, using a HSiR₃/oct-1-yne/catalyst ratio

of 100/100/1, 1 mol % of Rh calculated according to the ICP

c

measurements. Recycling experiment carried out on air.

experiments, even for the last cycle. The recycled heterogeneous

catalyst recovered after the successive catalysis runs, TRGO-

Triaz-Rh(III)-R, was characterized by means of XPS.

Interestingly, the N 1s and Rh 3d spectra, accounting only for

the supported organometallic moiety, are similar to that of the

parent TRGO-Triaz-Rh(III). This analysis conﬁrms structural

similarities for the metal center before and after the catalytic

cycles, which points toward similar oxidation states and the

maintenance of the C−N moieties (see the SI). Finally, in order

to control the stability of the immobilized rhodium(III) complex

in the TRGO-Triaz-Rh(III) hybrid catalyst, the possible

rhodium leaching along the catalytic runs was investigated. We

did so by means of ICP−MS analysis of the ﬁltrate and washings

after each run in the hydrosilylation of oct-1-yne with HSiMePh₂

(Table 3, entries 1−6) to determine their Rh content. A 0.5%

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shows an excellent catalytic performance in acetone at 60 °C,

comparable to that of the homogeneous catalyst [Cp*RhI-

(C,C′)-Triaz], and excellent recyclability, as it has been reused

in six consecutive cycles without loss of activity while

maintaining the selectivity.

CHNS/O microanalyzer or a LECO−CHNS-932 micro-

analyzer equipped with a LECO-VTF-900 furnace coupled to

the microanalyzer.

X-ray photoemission spectroscopy (XPS) spectra were

performed on a SPECS system operating under a pressure of

10⁻⁷Pa with a Mg Kα X-ray source. The functional groups in the

graphene-based materials were quantiﬁed by deconvolution of

the corresponding high resolution XPS peaks using a peak

analysis procedure that employs a combination of Gaussian and

Lorentzian functions and a Shirley baseline.⁵⁴The spectra did

not require charge neutralization and were subsequently

calibrated to the C 1s line at 284.5 eV. The binding energy

proﬁles for the C 1s spectra were deconvoluted as follows:

undamaged structures of Csp²-hybridized carbons (284.5 eV),

damaged structures or Csp³-hybridized carbons (285.5 eV), C−

OH groups (286.5 eV), O−C−O functional groups (287.7 eV),

and C(O)OH groups at 288.7 eV. The O 1s spectra were

deconvoluted using the components CO/COO (531.7 eV),

C−O (533.5 eV), and C−O−Si (533.6 eV). For the N 1s

spectra, diﬀerent components were used depending on the

nature of the material analyzed and includes −NN− (400.0

eV), −N− (401.1 eV) and N⁺ (402.8 eV). The amount of

rhodium in the hybrid catalysts was determined by means of

Inductively Coupled Plasma Mass Spectrometry (ICP−MS) in

an Agilent 7700x instrument.⁵⁵Raman spectroscopy was

performed on a Renishaw 2000 Confocal Raman Microprobe

using a 514.5 nm argon ion laser. Spectra were recorded from

750 to 3500 cm⁻¹.

DFT studies on the reaction mechanism in the process

involving the molecular catalyst [Cp*RhI(C,C′)-Triaz] have

shown two feasible (and competitive) mechanistic scenarios: (i)

a metal−ligand bifunctional mechanism involving reversible

cyclometalation and (ii) a noncooperative pathway. The

proposed cooperative pathway entails the Rh−C_Arassisted

hydrosilane activation to aﬀord a reactive Rh−silyl intermediate.

Regioselective 2,1-alkyne insertion into the Rh−Si bond aﬀords

a (Z)-silylvinylene intermediate which is isomerized to the (E)-

silylvinylene through a metallacyclopropene intermediate with

the relief of steric strain between the Cp*Rh metal fragment and

the adjacent silyl as the driving force of the process. Finally, the

H-transfer from the ﬂanking phenyl ring to the (E)-silylvinylene

by means of a σ-CAM with the C_Ar−H bond leads to the β-(Z)-

vinylsilane product restoring the Rh−C bond. However, the

release of the β-(Z)-vinylsilane product from the (E)-

silylvinylene intermediate can also occur by a mechanism

involving σ-CAM with the Si−H bond of an external

hydrosilane. It has been found that the energy barrier for the

σ-CAM pathway involving the Si−H bond is only 1.2 kcal·mol⁻¹

lower than that of the C−H bond. As the turnover-determining

transition state is determined by the energy barrier of the σ-

CAM processes, the energy span diﬀerence between both

mechanisms is also small and thus, both pathways are likely to be

competent under catalytic conditions. For comparison, we also

computed the reaction pathways for the catalysis resulting of the

substitution of the phenyl substituent in 1 by a methyl group (1-

Me). The calculations point toward the same reaction

mechanism taking place with 1-Me. However, in this case, the

energy barrier for the σ-CAM pathway involving the Si−H bond

is 5.6 kcal·mol⁻¹lower than that of the C−H bond, so we expect

that only the former alternative would take place.

X-ray absorption spectroscopy (XAS) measurements at the

Rh K edge were recorded at room temperature on the CLAESS

beamline⁵⁶at the ALBA synchrotron (Cerdanyola del Valles,

̀

Spain). The storage ring was operating at 3 GeV with a current of

120 mA. The EXAFS spectra were measured with a Si (311)

double crystal monochromator, and harmonic rejection was

carried out with a Pt strip in the vertical collimator. Estimated

energy resolution, ΔE/E, at the Rh K edge was better than 10⁻⁴.

The XAS spectra were measured in the transmission mode using

pellets diluted with cellulose, if necessary, to optimize the

absorption jump. The XAS spectra were normalized to unity

edge jump and the k weighted EXAFS signals, k²χ(k), were

obtained using the Athena software from the Demeter

package.⁵⁷The FT curves of the k²χ(k) signals were obtained

for the 2.8 ≤ k ≤ 15 Å⁻¹range, using a sinus window. The

EXAFS structural analysis was performed using theoretical

phases and amplitudes calculated by the FEFF-6 code,⁵⁸and ﬁts

to the experimental data were carried out in R-space with the

Artemis program of the Demeter package.⁵⁷

EXPERIMENTAL SECTION

■

General Considerations. All reactions were carried out

under under argon using Schlenk techniques. Solvents were

distilled immediately prior to use from the appropriate drying

agents or obtained from a Solvent Puriﬁcation System

(Innovative Technologies). The azolium salts, 1,4-diphenyl-3-

methyl-1,2,3-triazolium iodide⁵¹and 1-phenyl-3-methyl-1,3-

imidazolium iodide,⁵²and the rhodium starting material

53

[Cp*RhCl₂]₂were prepared according to the literature

¹H and ¹³C{¹H} NMR spectra were recorded on a Bruker

Advance 300 (300.1276 and 75.4792 MHz) at room temper-

ature in CDCl₃or acetone-d₆. NMR chemical shifts are reported

in ppm relative to tetramethylsilane and referenced to partially

deuterated solvent resonances. Coupling constants (J) are given

in Hertz. NMR assignments are based on homo- and

heteronuclear shift correlation spectroscopy. The adopted

atom numbering in the cyclometalated compounds starts at

the metal-bound carbon (C1), circles toward the nitrogen-

bound carbon (C2), and ﬁnishes at C6, the carbon ortho to the

metal-bound carbon. Electrospray mass spectra (ESI−MS) were

recorded on a Bruker Esquire 3000+ spectrometer using sodium

formiate as reference.

methods. The trimethylsilyl-protected, 3-methyl-4-phenyl-

1,2,3-triazolium iodide functionalized graphene oxide material,

TRGO-Triaz, was prepared from a thermally partially reduced

graphene oxide by a three step solid-phase procedure followed

by the protection of the −OH groups by reaction with

trimethylsilylimidazole (see the SI).²²All other reagents were

commercially available and used as-received.

Speciﬁc Equipment. Thermogravimetric analyses (TGA)

were performed on a TA SDT 2960 analyzer. The procedure was

as follows: 3 mg of sample was heated in the thermobalance to

1000 °C at 10 °C min⁻¹using a nitrogen/air ﬂow (1:1) of 200

mL min⁻¹. High-resolution transmission electron microscopy

(HRTEM) images were obtained using a JEOL JEM-2100F

transmission electron microscope, equipped with a ﬁeld-

emission-gun (FEG) that operated at 200 kV. Elemental

analyses were carried out on a Perkin-Ekmer 2400 Series-II

Single crystals of [Cp*RhI(C,C′)-Triaz] (1) and [Cp*RhI-

(C,C′)-Im] (2)⁵⁹for the X-ray diﬀraction studies were grown by

slow diﬀusion of n-hexane into a chloroform (1) or dichloro-

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methane (2) solution of the complex. X-ray diﬀraction data were

collected at 100(2) K on the diﬀractometers Bruker APEX DUO

CCD (1) and SMART APEX CCD (2) with graphite-

monochromated Mo−Kα radiation (λ = 0.71073 Å) using ω

rotations. Intensities were integrated and corrected for

absorption eﬀects with SAINT−PLUS⁶⁰and SADABS⁶¹

programs, both included in the APEX2 package. The structures

were solved by the Patterson method with SHELXS-97⁶²and

reﬁned by full matrix least-squares on F²with SHELXL-2014,⁶³

under WinGX.⁶⁴

Crystal Data and Structure Reﬁnement for 1.

C₂₅H₂₇IN₃Rh·CHCl₃, M = 718.67 g mol⁻¹, monoclinic, P2₁/c,

a = 17.6520(18) Å, b = 12.0217(12) Å, c = 14.0368(14) Å, β =

113.1940(10)°, V = 2738.0(5) Å³, Z = 4, D_calc= 1.743 g cm⁻³, μ

= 2.064 mm⁻¹, F(000) = 1416, prism, orange, 0.180 × 0.120 ×

0.030 mm³, θ_min/θ_max2.108/26.372°, index ranges: − 22 ≤ h ≤

22, − 15 ≤ k ≤ 15, − 17 ≤ l ≤ 17, reﬂections collected/

independent 27926/5598 [R(int) = 0.0821], data/restraints/

parameters 5598/0/313, GOF = 1.065, R₁= 0.0554 [I > 2σ(I)],

wR₂= 0.1110 (all data), largest diﬀ. peak/hole 1.256/−1.225

e·Å⁻³. CCDC deposit number 1982114.

Crystal Data and Structure Reﬁnement for 2.

C₂₀H₂₄IN₂Rh, M = 522.22 g mol⁻¹, monoclinic, P2₁/c, a =

14.0181(11) Å, b = 8.4600(7) Å, c = 16.4369(13) Å, β =

102.7530(10)°, V = 1901.2(3) Å³, Z = 4, D_calc= 1.824 g cm⁻³, μ

= 2.526 mm⁻¹, F(000) = 1024, prism, orange, 0.170 × 0.120 ×

0.020 mm³, θ_min/θ_max1.489/27.097°, index ranges −17 ≤ h ≤

17, − 10 ≤ k ≤ 10, − 21 ≤ l ≤ 20, reﬂections collected/

independent 22270/4189 [R(int) = 0.0457], data/restraints/

parameters 4189/0/223, GOF = 1.018, R₁= 0.0251[I > 2σ(I)],

wR₂= 0.0522 (all data), largest diﬀ. peak/hole 0.689/−0.514

e Å⁻³. CCDC deposit number 1982113.

were reacted in a mixture of THF/MeOH (1:1, 25 mL) at room

temperature for 12 h. After that time, the solution was brought to

dryness under vacuum and the resulting solid extracted with

CH₂Cl₂(2 × 15 mL). The resulting brown solution was ﬁltered

and concentrated to ∼2 mL under reduced pressure. Slow

addition of pentane (8 mL) gave a microcrystalline orange solid

which was separated by decantation, washed with pentane (2 × 3

mL) and dried in vacuum. Yield: 84.3 mg, 0.148 mmol, 85%. ¹H

NMR (300 MHz, 298 K, CDCl₃): δ 7.69 (dd, 1H, J_H−H= 7.3,

1.3, H⁶Ph), 7.34 (d, 1H, J_H−H= 2.1, CH Im), 7.13 (dd, J_H−H

=

7.3, 1.3, H³Ph), 6.97 (d, 1H, J_H−H= 2.1, CH Im), 6.96−6.87 (m,

2H, H⁵, H⁴Ph), 3.87 (s, 3H, NCH₃), 1.91 (s, 15H, CH₃, Cp*).

HRMS (ESI+, CH₃CN, m/z): Calcd. for C₂₀H₂₄N₂RhI: 522.23,

[M]⁺. Found for C₂₀H₂₄N₂Rh: 395.1018, [M−I]⁺.

Synthesis of TRGO-Triaz-Rh(III). TRGO-Triaz (60 mg)

was dispersed in anhydrous THF (20 mL) in an ultrasonic bath

for 30 min. Then, [Cp*RhCl₂]₂(25 mg, 0.040 mmol) and

NaOt-Bu (15.36 mg, 0.16 mmol) were sequentially added and

the suspension was stirred at room temperature for 24 h. The

black solid was washed with MeOH (2 × 15 mL), THF (2 × 10

mL), and Et₂O (1 × 5 mL), with the help of an ultrasonic bath/

centrifuge, and dried under vacuum.

TRGO-Triaz Treatments. (a) TRGO-Triaz (51.5 mg) was

dispersed in anhydrous THF (10 mL) in an ultrasonic bath for

30 min. Then, NaOt-Bu (20.34 mg, 0.218 mmol) was added,

and the suspension stirred at room temperature for 12 h. The

black solid was ﬁltered, washed with MeOH (3 × 7 mL) and

Et₂O (1 × 5 mL), with the help of an ultrasonic bath/centrifuge,

and dried under vacuum to aﬀord the material TRGO-Triaz′.

(b) TRGO-Triaz (40 mg) was dispersed in a mixture of t-

BuOH/H₂O (1:1, 10 mL) in an ultrasonic bath for 30 min. The

suspension was stirred at room temperature for 12 h, washed

with MeOH (3 × 7 mL) and Et₂O (1 × 5 mL), with the help of

an ultrasonic bath/centrifuge, and dried under vacuum to aﬀord

the material TRGO-Triaz′′.

Synthesis of [Cp*RhI(C,C′)-Triaz] (1). 1,4-Diphenyl-3-

methyl-1,2,3-triazolium iodide (100 mg, 0.270 mmol),

[Cp*RhCl₂]₂(83.4 mg, 0.135 mmol) and NaOtBu (51.9 mg,

0.540 mmol) were reacted in THF (25 mL) at room

temperature for 12 h. After that time, the solution was ﬁltered

and then evaporated to dryness under vacuum. The organo-

metallic compound was extracted with CH₂Cl₂(15 mL), and the

resulting dark orange solution was ﬁltered and concentrated to

∼2 mL under reduced pressure. Slow addition of pentane (12

mL) aﬀorded an orange solid which was separated by

decantation, washed with pentane (2 × 3 mL) and dried in

vacuum. Recrystallization from dichloromethane/pentane gave

the compound as a microcrystalline orange solid. Yield: 60.5 mg,

0.101 mmol, 73%. ¹H NMR (300 MHz, 298 K, CDCl₃): δ 7.92

(d, 2H, J_H−H= 8.1, H_oPh), 7.82 (d, 1H, J_H−H= 7.4, H⁶NPh),

General Procedure for Catalytic Alkyne Hydrosilyla-

tion Reactions. Hydrosilylation catalytic tests were carried out

in NMR tubes, under an argon atmosphere, in CDCl₃or

acetone-d₆. In a typical procedure, an NMR tube was charged

under argon with the catalyst (1 × 10⁻³mmol, 1 mol %),

deuterated solvent (0.5 mL), the corresponding alkyne (0.1

mmol), hydrosilane (0.1 mmol), and anisole (0.01 mmol) as an

internal standard. The solution was kept at room temperature or

1

in a thermostated bath at 60 °C and monitored by H NMR

spectroscopy. The weight of the supported catalysts used in each

experiment was calculated according to ICP measurements

assuming that all the rhodium in the hybrid materials

corresponds to active catalyst sites.

7.64−7.52 (m, 5H, H³NPh, and H_m, H_pPh)_,7.15 (t, 1H, J_H−H

=

7.3, H⁵NPh), 7.05 (t, 1H, J_H−H= 7.3, H⁴NPh), 4.12 (s, 3H,

The vinylsilane reaction products derived from 1-alkynes were

unambiguously characterized on the basis of the coupling

patterns and constants of vinylic protons in the ¹H NMR spectra

and subsequent comparison to literature values.⁶⁵Values for J

ranged from 17 to 19 Hz for β-(E), 13 to 16 Hz for β-(Z), and 1

to 3 Hz for α-vinylsilanes.

The recycling of the heterogeneous catalyst was carried out by

evaporating the deuterated solvent under vacuum. The residue

was washed with hexane (3 × 1 mL) using a centrifuge to

remove the organic products and dried in vacuum. Then,

another load of reactants and deuterated solvent were added to

perform a new catalytic cycle under the same experimental

conditions.

NCH₃), 1.55 (s, 15H, CH₃Cp*). ¹³C{¹H} NMR (75 MHz, 298

K, CDCl₃) δ: 165.9 (d, J_C−Rh= 55.5, C_Triaz), 159.7 (d, J_C−Rh

=

35.8, C¹NPh), 145.1 (d, J_C−Rh= 3.4, C²NPh), 144.9 (C_TriazPh),

140.2 (C⁶NPh), 131.0 (C_o, Ph), 129.8 (C_p, Ph), 129.0 (C_m, Ph),

128.2 (C_ipsoPh),127.9 (C⁵NPh), 122.5 (C⁴NPh), 113.9 (C³

NPh), 97.5 (d, J_C−Rh= 4.9, C Cp*), 37.3 (NCH₃), 10.2, (CH₃

Cp*). Anal. Calc. for C₂₅H₂₇N₃RhI: C, 50.10; H, 4.54; N, 7.01.

Found C, 50.20; H, 4.73; N, 7.20. HRMS (ESI+, CH₃CN, m/z):

Calcd. for C₂₅H₂₇N₃RhI: 599.3129, [M]⁺. Found for

C₂₅H₂₇N₃Rh: 472.1247, [M-I]⁺. Found for C₁₅H₁₃N₃:

236.1172, [Triaz]⁺.

Synthesis of [Cp*RhI(C,C′)-Im] (2). 1-Phenyl-3-methyl-

1,3-imidazolium iodide (100 mg, 0.350 mmol), [Cp*RhCl₂]₂

(108 mg, 0.175 mmol) and NaOtBu (67.3 mg, 0.700 mmol)

Synthesis of (Z)-Dimethyl(oct-1-en-1-yl)(phenyl)-

silane. A Schlenk tube with a screw cap was charged with

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catalyst 1 (9.5 mg, 0.0158 mmol), acetone (5 mL), oct-1-yne

(1.58 mmol, 241 μL), and HSiMe₂Ph (1.58 mmol, 248 μL). The

solution was stirred at room temperature for 30 min until

complete consumption of the reactants (NMR) and then a new

load of reactants was added. After three consecutive catalytic

cycles, the yellow solution was passed through a silica gel column

to give (Z)-dimethyl(oct-1-en-1-yl)(phenyl)silane as a colorless

liquid (1.13 g, 97%) with only trace amounts of the β-(E)

vinylisomer after elimination of the solvent.

Computational Details. DFT calculations were performed

with the Gaussian09 suite, revision D.01.⁶⁶We selected the

B3LYP exchange-correlation functional,⁶⁷with D3BJ dispersion

corrections⁶⁸and the “ultraﬁne” grid. Geometry optimizations

were carried out using the df2-SVP basis set, with further energy

reﬁnements by means of single point calculations with def2-

TZVP.⁶⁹We also applied a PCM implicit model for the solvent

(acetone), which we included in both gradients and energy

calculations.⁷⁰The nature of the stationary points has been

conﬁrmed by analytical frequency analysis. Moreover, we

removed the translational entropy contribution to the Gibbs

energy as by Morokuma and co-workers.⁷¹The motivation for

the method selection is based on our previous studies on

hydrosilylation reactions catalyzed by Rh- and Ir-based

complexes, in which the aforementioned methodology has

been demonstrated to perform well and provide results in

agreement with experimental observations.^37,72Structure graph-

ical representations were made by means of CylView software.⁷³

Julen Munarriz − Department of Chemistry & Biochemistry,

University of CaliforniaLos Angeles, Los Angeles, California

́

90095, United States; Departamento de Quımica Fısica and

́

Instituto de Biocomputacion y Fısica de Sistemas Complejos

(BIFI), Universidad de Zaragoza, Facultad de Ciencias, 50009

Zaragoza, Spain; orcid.org/0000-0001-6089-6126

́

Javier Blasco − Instituto de Nanociencia y Materiales de Aragon

(INMA), CSIC - Universidad de Zaragoza, 50009 Zaragoza,

́

Spain; Departamento de Fısica de la Materia Condensada,

Universidad de Zaragoza, Zaragoza 50009, Spain;

orcid.org/0000-0002-9706-3272

Gloria Subias − Instituto de Nanociencia y Materiales de Aragon

(INMA), CSIC - Universidad de Zaragoza, 50009 Zaragoza,

́

Spain; Departamento de Fısica de la Materia Condensada,

Universidad de Zaragoza, Zaragoza 50009, Spain;

orcid.org/0000-0002-9029-1977

Vincenzo Passarelli − Centro Universitario de la Defensa, ES-

50090 Zaragoza, Spain; orcid.org/0000-0002-1735-6439

́

Patricia Alvarez − Instituto de Ciencia y Tecnologıa del Carbono,

INCAR, CSIC, 33080 Oviedo, Spain; orcid.org/0000-0001-

9676-0546

Complete contact information is available at:

https://pubs.acs.org/10.1021/acscatal.0c03295

Author Contributions

The manuscript was written through the contributions of all

authors. All authors have given approval to the ﬁnal version of

the manuscript.

ASSOCIATED CONTENT

* Supporting Information

The Supporting Information is available free of charge at

https://pubs.acs.org/doi/10.1021/acscatal.0c03295.

■

Notes

sı

The authors declare no competing ﬁnancial interest.

ACKNOWLEDGMENTS

■

Synthesis of TRGO-Triaz, TG, Raman, XPS, and STEM-

EDX characterization of TRGO-based materials, detailed

XAS analysis of rhodium complexes, NMR analysis and

reaction proﬁles for selected hydrosilylation reactions,

and DFT energetic data and optimized coordinates for

catalytic intermediates and transition states (PDF)

The authors express their appreciation for the ﬁnancial support

from MICINN/FEDER, projects PID2019-103965GB-100,

CTQ2016-75884-P and RTI2018-098537-B-C22, DGA/

́

FEDER 2014-2020 “Building Europe from Aragon” (groups

E42_20R and E12_20R), and Principado de Asturias/FEDER

(IDI/2018/000121). The authors also acknowledge ALBA

Synchrotron for granting beamtime and the collaboration of the

CLAESS beamline staﬀ.

Optimized geometries for the 1-catalyzed cycle (XYZ)

Optimized geometries for the 1-Me-catalyzed cycle

(XYZ)

REFERENCES

■

Crystallographic data (CIF)

(1) Lanzafame, P.; Perathoner, S.; Centi, G.; Gross, S.; Hensen, E. J.

M. Grand challenges for catalysis in the Science and Technology

Roadmap on Catalysis for Europe: moving ahead for a sustainable

future. Catal. Sci. Technol. 2017, 7, 5182−5194.

(2) Somfai, P.; Seashore-Ludlow, B. Organosilicon reagent: vinyl-,

alkynyl-, and arylsilanes. In Comprehensive Organic Synthesis; Springer:

Amsterdam, The Netherlands, 2014.

(3) Komiyama, T.; Minami, Y.; Hiyama, T. Recent Advances in

Transition-Metal-Catalyzed Synthetic Transformations of Organo-

silicon Reagents. ACS Catal. 2017, 7, 631−651.

AUTHOR INFORMATION

Corresponding Authors

M. Victoria Jimenez − Departamento de Quımica Inorganica,

■

́

Instituto de Sıntesis Quımica y Catalisis Homogenea-ISQCH,

Universidad de Zaragoza-C.S.I.C., 50009 Zaragoza, Spain;

orcid.org/0000-0002-0545-9107; Email: vjimenez@

unizar.es

(4) Pouget, E.; Tonnar, J.; Lucas, P.; Lacroix-Desmazes, P.;

Ganachaud, F.; Boutevin, B. Well-Architectured Poly-

(dimethylsiloxane)-Containing Copolymers Obtained by Radical

Chemistry. Chem. Rev. 2010, 110, 1233−1277.

́

Jesus J. Perez-Torrente − Departamento de Quımica Inorganica,

́

Instituto de Sıntesis Quımica y Catalisis Homogenea-ISQCH,

Universidad de Zaragoza-C.S.I.C., 50009 Zaragoza, Spain;

orcid.org/0000-0002-3327-0918; Email: perez@unizar.es

́

(5) Perez-Torrente, J. J.; Nguyen, D. H.; Jimenez, M. V.; Modrego, F.

́

J.; Puerta-Oteo, R.; Gomez-Bautista, D.; Iglesias, M.; Oro, L. A.

Hydrosilylation of Terminal Alkynes Catalyzed by a ONO-Pincer

Iridium(III) Hydride Compound: Mechanistic Insights into the

Hydrosilylation and Dehydrogenative Silylation Catalysis. Organo-

metallics 2016, 35, 2410−2422.

Authors

́

Beatriz Sanchez-Page − Departamento de Quımica Inorganica,

́

Instituto de Sıntesis Quımica y Catalisis Homogenea-ISQCH,

Universidad de Zaragoza-C.S.I.C., 50009 Zaragoza, Spain;

orcid.org/0000-0002-2449-7459

(6) For examples of selective β-(E)-alkenylsilane formation, see:

́

(a) Dierick, S.; Vercruysse, E.; Berthon-Gelloz, G.; Marko, I. E. User-

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pubs.acs.org/acscatalysis

Research Article

Friendly Platinum Catalysts for the Highly Stereoselective Hydro-

Hydrosilylation of Terminal Alkynes. Org. Chem. Front. 2017, 4, 1517−

1521. (c) Teo, W. J.; Wang, C.; Tan, Y. W.; Ge, S. Cobalt-Catalyzed Z-

Selective Hydrosilylation of Terminal Alkynes. Angew. Chem., Int. Ed.

2017, 56, 4328−4332. (d) Sun, J.; Deng, L. Cobalt Complex-Catalyzed

Hydrosilylation of Alkenes and Alkynes. ACS Catal. 2016, 6, 290−300.

(14) (a) Challinor, A. J.; Calin, M.; Nichol, G. S.; Carter, N. B.;

Thomas, S. P. Amine-Activated Iron Catalysis: Air- and Moisture-

Stable Alkene and Alkyne Hydrofunctionalization. Adv. Synth. Catal.

2016, 358, 2404−2409. (b) Greenhalgh, M. D.; Frank, D. J.; Thomas, S.

P. Iron-Catalysed Chemo-, Regio-, and Stereoselective Hydrosilylation

of Alkenes and Alkynes using a Bench-Stable Iron(II) Pre-Catalyst. Adv.

Synth. Catal. 2014, 356, 584−590.

(15) Liang, H.; Ji, Y.-X.; Wang, R.-H.; Zhang, Z.-H.; Zhang, B. Visible-

Light-Initiated Manganese-Catalyzed E-Selective Hydrosilylation and

Hydrogermylation of Alkynes. Org. Lett. 2019, 21, 2750−2754.

(16) Peris, E. Smart N-Heterocyclic Carbene Ligands in Catalysis.

Chem. Rev. 2018, 118 (19), 9988−10031.

(17) (a) Tyagi, A.; Yadav, S.; Daw, P.; Ravi, C.; Bera, J. K. A Rh(I)

complex with an annulated N-heterocyclic carbene ligand for E-

selective alkyne hydrosilylation. Polyhedron 2019, 172, 167−174.

silylation of Alkynes and Alkenes. Chem.Eur. J. 2015, 21, 17073−

́

17078. (b) Cano, R.; Yus, M.; Ramon, D. J. Impregnated platinum on

magnetite as an efficient, fast, and recyclable catalyst for the

hydrosilylation of alkynes. ACS Catal. 2012, 2, 1070−1078.

́

(c) Berthon-Gelloz, G.; Schumers, J.-M.; de Bo, G.; Marko, I. E.

Highly β -(E)-Selective Hydrosilylation of Terminal and Internal

Alkynes Catalyzed by a (IPr)Pt(diene) Complex. J. Org. Chem. 2008,

73, 4190−4197. (d) Takeuchi, R.; Nitta, S.; Watanabe, D. A Selective

Synthesis of (E)-Vinylsilanes by Cationic Rhodium Complex-

Catalyzed Hydrosilylation of 1-Alkynes and Tandem Hydrosilyla-

tion/Isomerization Reaction of Propargylic Alcohols to β -Silyl Ketones.

J. Org. Chem. 1995, 60, 3045−3051.

(7) For examples of selective F-alkenylsilane formation, see: (a) Xie,

X.; Zhang, X.; Gao, W.; Meng, C.; Wang, X.; Ding, S. Iridium-catalyzed

Markovnikov hydrosilylation of terminal alkynes achieved by using a

trimethylsilyl-protected trihydroxysilane. Commun. Chem. 2019, 2, 101.

(b) Wu, G.; Chakraborty, U.; von Wangelin, A. J. Regiocontrol in the

cobalt catalyzed hydrosilylation of alkynes. Chem. Commun. 2018, 54,

12322−12325. (c) Guo, J.; Lu, Z. Highly chemo-, regio-, and

stereoselective cobalt-catalyzed Markovnikov hydrosilylation of

alkynes. Angew. Chem., Int. Ed. 2016, 55, 10835−10838. (d) Iglesias,

́

(b) Morales-Ceron, J. P.; Lara, P.; Lopez-Serrano, J.; Santos, L. L.;

́

Salazar, V.; Alvarez, E.; Suarez, A. Rhodium(I) Complexes with Ligands

Based on N-Heterocyclic Carbene and Hemilabile Pyridine Donors as

Highly E Stereoselective Alkyne Hydrosilylation Catalysts. Organo-

́

M.; Aliaga-Lavrijsen, M.; Sanz Miguel, P. J.; Fernandez-Alvarez, F. J.;

́

Perez-Torrente, J. J.; Oro, L. A. Preferential α -Hydrosilylation of

́

metallics 2017, 36, 2460−2469. (c) Jimenez, M. V.; Perez-Torrente, J.

Terminal Alkynes by Bis-N-Heterocyclic Carbene Rhodium(III)

Catalysts. Adv. Synth. Catal. 2015, 357, 350−354. (e) Trost, B. M.;

Ball, Z. T. Alkyne Hydrosilylation Catalyzed by a Cationic Ruthenium

Complex: Efficient and General Trans Addition. J. Am. Chem. Soc.

2005, 127, 17644−17655.

́

J.; Bartolome, M. I.; Gierz, V.; Lahoz, F. J.; Oro, L. A. Rhodium(I)

Complexes with Hemilabile N-Heterocyclic Carbenes: Efficient Alkyne

Hydrosilylation Catalysts. Organometallics 2008, 27, 224−234.

́

(18) (a) Puerta-Oteo, R.; Munarriz, J.; Polo, V.; Jimenez, M. V.; Perez-

Torrente, J. J. Carboxylate-Assisted β -(Z) Stereoselective Hydro-

silylation of Terminal Alkynes Catalyzed by a Zwitterionic Bis-NHC

Rhodium(III) Complex. ACS Catal. 2020, 10, 7367−7380. (b) Iglesias,

(8) For examples of selective β-(Z)-alkenylsilane formation, see:

(a) Mutoh, Y.; Mohara, Y.; Saito, S. (Z)-Selective Hydrosilylation of

Terminal Alkynes with HSiMe(OSiMe3)2 Catalyzed by a Ruthenium

Complex Containing an N-Heterocyclic Carbene. Org. Lett. 2017, 19,

5204−5207. (b) Martín, M.; Sola, E.; Lahoz, F. J.; Oro, L. A. Trans

Additions of Silanes to 1-Alkynes Catalyzed by Ruthenium Complexes:

Role of in Situ Formed Polynuclear Aggregates. Organometallics 2002,

21, 4027−4029.

́

M.; Sanz Miguel, P. J.; Polo, V.; Fernandez-Alvarez, F. J.; Perez-

Torrente, J. J.; Oro, L. A. An Alternative Mechanistic Paradigm for the

β -Z Hydrosilylation of Terminal Alkynes: The Role of Acetone as a

Silane Shuttle. Chem. - Eur. J. 2013, 19, 17559−17566.

(19) Marichev, K. O.; Patil, S. A.; Bugarin, A. Recent advances in the

synthesis, structural diversity, and applications of mesoionic 1,2,3-

triazol-5-ylidene metal complexes. Tetrahedron 2018, 74, 2523−2546.

(20) Crabtree, R. H. Abnormal, Mesoionic and Remote N-H

heterocyclic Carbene Complexes. Coord. Chem. Rev. 2013, 257, 755−

766.

(21) See, for example: (a) Vivancos, A.; Segarra, C.; Albrecht, M.

Mesoionic and Related Less Heteroatom-Stabilized N-Heterocyclic

Carbene Complexes: Synthesis, Catalysis, and Other Applications.

Chem. Rev. 2018, 118, 9493−9586. (b) Mazloomi, Z.; Pretorius, R.;

(9) (a) Gao, R.; Pahls, D. R.; Cundari, T. R.; Yi, C. S. Experimental and

Computational Studies of the Ruthenium Catalyzed Hydrosilylation of

Alkynes: Mechanistic Insights into the Regio- and Stereoselective

Formation of Vinylsilanes. Organometallics 2014, 33, 6937−6944.

(b) Jun, C.-H.; Crabtree, R. H. Dehydrogenative Silation, Isomerization

and the Control of Syn- vs. Anti-addition in the Hydrosilation of

Alkynes. J. Organomet. Chem. 1993, 447, 177−187.

(10) Zhao, X.; Yang, D.; Zhang, Y.; Wang, B.; Qu, J. Highly β (Z)-

Selective Hydrosilylation of Terminal Alkynes Catalyzed by Thiolate-

Bridged Dirhodium Complexes. Org. Lett. 2018, 20, 5357−5361.

̀

́

Pamies, O.; Albrecht, M.; Dieguez, M. Triazolylidene Iridium

Complexes for Highly Efficient and Versatile Transfer Hydrogenation

of C = O, C = N, and C = C Bonds and for Acceptorless Alcohol

Oxidation. Inorg. Chem. 2017, 56, 11282−11298. (c) Wei, Y.; Liu, S.-X.;

Mueller-Bunz, H.; Albrecht, M. Synthesis of Triazolylidene Nickel

Complexes and Their Catalytic Application in Selective Aldehyde

Hydrosilylation. ACS Catal. 2016, 6, 8192−8200.

́

(11) (a) Corre, Y.; Werle, C.; Brelot-Karmazin, L.; Djukic, J.-P.;

Agbossou-Niedercorn, F.; Michon, C. Regioselective hydrosilylation of

terminal alkynes using pentamethylcyclopentadienyl iridium(III)

metallacycle catalysts. J. Mol. Catal. A: Chem. 2016, 423, 256−263.

́

(b) Iglesias, M.; Perez-Nicolas, M.; Sanz Miguel, P. J.; Polo, V.;

́

Fernandez-Alvarez, F. J.; Perez-Torrente, J. J.; Oro, L. A. A synthon for a

14-electron Ir(III) species: catalyst for highly selective β -(Z)

hydrosilylation of terminal alkynes. Chem. Commun. 2012, 48, 9480−

9482. (c) Sridevi, V. S.; Fan, W. Y.; Leong, W. K. Stereoselective

Hydrosilylation of Terminal Alkynes Catalyzed by [Cp *IrCl2]2: A

Computational and Experimental Study. Organometallics 2007, 26,

1157−1160.

́

(22) Sanchez-Page, B.; Jimenez, M. V.; Perez-Torrente, J. J.; Passarelli,

V.; Blasco, J.; Subias, G.; Granda, M.; Alvarez, P. Hybrid Catalysts

́

Comprised of Graphene Modified with Rhodium-Based N-Hetero-

cyclic Carbenes for Alkyne Hydrosilylation. ACS Appl. Nano Mater.

2020, 3, 1640−1655.

(23) Wang, W.; Cui, L.; Sun, P.; Shi, L.; Yue, C.; Li, F. Reusable N-

Heterocyclic Carbene Complex Catalysts and Beyond: A Perspective

on Recycling Strategies. Chem. Rev. 2018, 118, 9843−9929.

̈

(12) (a) Conifer, C.; Gunanathan, C.; Rinesch, T.; Holscher, M.;

Leitner, W. Solvent-Free Hydrosilylation of Terminal Alkynes by

Reaction with a Nonclassical Ruthenium Hydride Pincer Complex. Eur.

J. Inorg. Chem. 2015, 2015, 333−339. (b) Na, Y.; Chang, S. Highly

Stereoselective and Efficient Hydrosilylation of Terminal Alkynes

Catalyzed by [RuCl2(p-cymene)]2. Org. Lett. 2000, 2, 1887−1889.

(13) (a) Chen, J.; Guo, J.; Lu, Z. Recent Advances in Hydro-

metallation of Alkenes and Alkynes via the First Row Transition Metal

Catalysis. Chin. J. Chem. 2018, 36, 1075−1109. (b) Du, X.; Hou, W.;

Zhang, Y.; Huang, Z. Pincer Cobalt Complex-Catalyzed Z-selective

́

(24) (a) Lazaro, G.; Fernandez-Alvarez, F. J.; Iglesias, M.; Horna, C.;

Vispe, E.; Sancho, R.; Lahoz, F. J.; Iglesias, M.; Perez-Torrente, J. J.;

Oro, L. A. Heterogeneous Catalysts Based on Supported Rh-NHC

Complexes: Synthesis of High Molecular Weight Poly(silylether)s by

Catalytic Hydrosilylation. Catal. Sci. Technol. 2014, 4, 62−70.

(b) Jankowska-Wajda, M.; Bartlewicz, O.; Szpecht, A.; Zajac, A.;

Smiglak, M.; Maciejewski, H. Platinum and Rhodium Complexes

Ligated by Imidazolium-Substituted Phosphine as Efficient and

13349

https://dx.doi.org/10.1021/acscatal.0c03295

ACS Catal. 2020, 10, 13334−13351

ACS Catalysis

pubs.acs.org/acscatalysis

Research Article

Recyclable Catalysts for Hydrosilylation. RSC Adv. 2019, 9, 29396−

Torrente, J. J. Mechanistic Insights on the Functionalization of CO2

with Amines and Hydrosilanes Catalyzed by a Zwitterionic Iridium

Carboxylate-Functionalized Bis-NHC Catalyst. ChemCatChem 2019,

29404.

(25) (a) Binding, S. C.; Pernik, I.; Gonca̧ les, V. R.; Wong, C. M.;

Webster, R. F.; Cheong, S.; Tilley, R. D.; Garcia-Bennett, A. E.;

Gooding, J. J.; Messerle, B. A. Simultaneous Functionalization of

Carbon Surfaces with Rhodium and Iridium Organometallic Com-

plexes: Hybrid Bimetallic Catalysts for Hydroamination. Organo-

metallics 2019, 38, 780−787. (b) Wong, C. M.; Walker, D. B.; Soeriyadi,

A. H.; Gooding, J. J.; Messerle, B. A. A Versatile Method for the

Preparation of Carbon-Rhodium Hybrid Catalysts on Graphene and

Carbon Black. Chem. Sci. 2016, 7, 1996−2004.

11, 5524−5535.

́

(38) Iglesias, M.; Fernandez-Alvarez, F. J.; Oro, L. A. Non-classical

Hydrosilane Mediated Reductions Promoted by Transition Metal

Complexes. Coord. Chem. Rev. 2019, 386, 240−266.

(39) Pitman, C. L.; Finster, O. N. L.; Miller, A. J. M. Cyclopentadiene-

Mediated Hydride Transfer from Rhodium Complexes. Chem.

Commun. 2016, 52, 9105−9108.

(40) Hallam, B. F.; Pauson, P. L. Ferrocene Derivatives. Part III.

Cyclopentadienyl Iron Carbonyls. J. Chem. Soc. 1956, 3030−3037.

(41) Perutz, R. N.; Sabo-Etienne, S. The sigma-CAM Mechanism:

sigma complexes as the basis of sigma-bond metathesis at late-

transition-metal centers. Angew. Chem., Int. Ed. 2007, 46, 2578−2592.

(42) Julian, A.; Guzman, J.; Jaseer, E. A.; Fernandez-Alvarez, F. J.;

Royo, R.; Polo, V.; Garcia-Orduna, P.; Lahoz, F. J.; Oro, L. A.

Mechanistic Insights on the Reduction of CO2 to Silylformates

Catalyzed by Ir-NSiN species. Chem. - Eur. J. 2017, 23, 11898−11907.

(43) Chalk, A. J.; Harrod, J. F. Homogeneous Catalysis. II. The

Mechanism of the Hydrosilation of Olefins Catalyzed by Group VIII

Metal Complexes. J. Am. Chem. Soc. 1965, 87, 16−21.

(26) Ruiz-Botella, S.; Peris, E. Immobilization of Pyrene-Adorned N-

Heterocyclic Carbene Complexes of Rhodium(I) on Reduced

Graphene Oxide and Study of their Catalytic Activity. ChemCatChem

2018, 10, 1874−1881.

́

(27) Ríos, P.; Fouilloux, H.; Díez, J.; Vidossich, P.; Lledos, A.;

Conejero, S. R-Silane Platinum(II) Complexes as Intermediates in C-Si

Bond-Coupling Processes. Chem.- Eur. J. 2019, 25, 11346−11355.

(28) (a) Pannetier, N.; Sortais, J.-B.; Issenhuth, J.-T.; Barloy, L.; Sirlin,

C.; Holuigue, A.; Lefort, L.; Panella, L.; de Vries, J. G.; Pfeffer, M.

Cyclometalated Complexes of Ruthenium, Rhodium and Iridium as

Catalysts for Transfer Hydrogenation of Ketones and Imines. Adv.

Synth. Catal. 2011, 353, 2844−2852. (b) Espada, M. F.; Esqueda, A. C.;

́

(44) Vasquez-Cespedes, S.; Wang, X.; Glorius, F. Plausible Rh(V)

Intermediates in Catalytic C-H Activation Reactions. ACS Catal. 2018,

8, 242−257.

́

Campos, J.; Rubio, M.; Lopez-Serrano, J.; Alvarez, E.; Maya, C.;

Carmona, E. Cationic (η 5-C5Me4R)RhIII Complexes with Metalated

Aryl Phosphines Featuring η 4-Phosphorus plus Pseudo-Allylic

Coordination. Organometallics 2018, 37, 11−21.

(45) Frohnapfel, D. S.; Templeton, J. L. Transition metal η 2-vinyl

complexes. Coord. Chem. Rev. 2000, 206, 199−235.

(29) Ghatak, K.; Mane, M.; Vanka, K. Metal or Nonmetal

Cooperation with a Phenyl Group: Route to Catalysis? A Computa-

tional Investigation. ACS Catal. 2013, 3, 920−927.

(46) Kozuch, S.; Shaik, S. How to Conceptualize Catalytic Cycles?

The Energetic Span Model. Acc. Chem. Res. 2011, 44, 101−110.

(47) Even though G and TS-DE are the lowest- and highest-in-energy

reaction intermediate and transition state, they are not the couple

determining ΔG^⧧, as when the barrier-determining transition state

appears before the intermediate, it is necessary to add the cycle ΔG to

their energy diﬀerence, which in this case would lead to the meaningless

value of ΔG^⧧= 14.3 − (−23.0) + (−39.2) = −1.9 kcal·mol⁻¹for the ﬁrst

cycle. Since we predict that subsequent catalytic cycles start in D′, the

ΔG^⧧value if we consider G and TS-DE as the TOF-determining TS

and intermediate would be G^⧧= 14.3 − (−23.0) + (−32.9) = 4.4 kcal·

mol⁻¹, which is lower than the actual energy span determined by G and

TS-GD (12.0 kcal·mol⁻¹).

(30) (a) Jongbloed, L. S.; de Bruin, B.; Reek, J. N. H.; Lutz, M.; van der

Vlugt, J. I. Reversible cyclometalation at RhI as a motif for metal-ligand

bifunctional bond activation and base-free formic acid dehydrogen-

ation. Catal. Sci. Technol. 2016, 6, 1320−1327. (b) Bhattacharya, P.;

Krause, J. A.; Guan, H. Mechanistic Studies of Ammonia Borane

Dehydrogenation Catalyzed by Iron Pincer Complexes. J. Am. Chem.

Soc. 2014, 136, 11153−11161.

(31) (a) Choi, G.; Tsurugi, H.; Mashima, K. Hemilabile N-Xylyl-N ′-

methylperimidine Carbene Iridium Complexes as Catalysts for C-H

Activation and Dehydrogenative Silylation: Dual Role of N-Xylyl

Moiety for ortho-C-H Bond Activation and Reductive Bond Cleavage.

J. Am. Chem. Soc. 2013, 135, 13149−13161. (b) Ghoochany, L. T.;

Kerner, C.; Farsadpour, S.; Menges, F.; Sun, Y.; Niedner-Schatteburg,

G.; Thiel, W. R. C-H Activation at a Ruthenium(II) Complex-The Key

Step for a Base-Free Catalytic Transfer Hydrogenation? Eur. J. Inorg.

Chem. 2013, 2013, 4305−4317.

́

(48) (a) Nieto, J.; Jimenez, M. V.; Alvarez, P.; Perez-Mas, A. M.;

́

Gonzalez, Z.; Pereira, R.; Sanchez-Page, B.; Perez-Torrente, J. J.;

Blasco, J.; Subías, G.; Blanco, M.; Menendez, R. Enhanced Chemical

́

and Electrochemical Water Oxidation Catalytic Activity by Hybrid

Carbon Nanotube-Based Iridium Catalysts Having Sulfonate-Func-

tionalized NHC ligands. ACS Appl. Energy Mater. 2019, 2, 3283−3296.

(32) Donnelly, K. F.; Lalrempuia, R.; Muller-Bunz, H.; Albrecht, M.

Regioselective Electrophilic C-H Bond Activation in Triazolylidene

Metal Complexes Containing a N-Bound Phenyl Substituent. Organo-

metallics 2012, 31, 8414−8419.

́

(b) Blanco, M.; Alvarez, P.; Blanco, C.; Jimenez, M. V.; Perez-Torrente,

́

J. J.; Oro, L. A.; Blasco, J.; Cuartero, V.; Menendez, R. Enhancing the

Hydrogen Transfer Catalytic Activity of Hybrid Carbon Nanotube-

Based NHC-Iridium Catalysts by Increasing the Oxidation Degree of

the Nanosupport. Catal. Sci. Technol. 2016, 6, 5504−5514.

(49) NIST database: NIST X-ray Photoelectron Spectroscopy

Database. NIST Standard Reference Database 20, Version 4.1.

DOI: 10.18434/T4T88K.

́

(33) Azpíroz, R.; Rubio-Perez, L.; Di Giuseppe, A.; Passarelli, V.;

́

Lahoz, F. J.; Castarlenas, R.; Perez-Torrente, J. J.; Oro, L. A.

Rhodium(I)-N-Heterocyclic Carbene Catalyst for Selective Coupling

of N-Vinylpyrazoles with Alkynes via C-H Activation. ACS Catal. 2014,

4, 4244−4253.

(50) Rhodium(I) complexes can promote undesirable polymerization

of aryl-substituted alkynes such as phenylacetylene. See, for example:

Mori, A.; Takahisa, E.; Yamamura, Y.; Kato, T.; Mudalige, A. P.; Kajiro,

H.; Hirabayashi, K.; Nishihara, Y.; Hiyama, T. Stereodivergent

Syntheses of (Z)- and (E)-Alkenylsilanes via Hydrosilylation of

Terminal Alkynes Catalyzed by Rhodium(I) Iodide Complexes and

Application to Silicon-Containing Polymer Syntheses. Organometallics

2004, 23, 1755−1765.

(34) (a) Ghorai, D.; Choudhury, J. Exploring a unique reactivity of N-

heterocyclic carbenes (NHC) in rhodium(III)-catalyzed intermolecu-

lar C-H activation/annulation. Chem. Commun. 2014, 50, 15159−

15162. (b) Thenarukandiyil, R.; Gupta, S. K.; Choudhury, J. Unraveling

the Competition of Two C-H and Two M-C Bonds in Guiding the

Mechanism of Rhodium(III)-Catalyzed C-H Activation-Annulation.

ACS Catal. 2016, 6, 5132−5137.

(35) Busetto, L.; Cassani, M. C.; Femoni, C.; Mancinelli, M.;

Mazzanti, A.; Mazzoni, R.; Solinas, G. N-Heterocyclic Carbene-Amide

Rhodium(I) Complexes: Structures, Dynamics, and Catalysis. Organo-

metallics 2011, 30, 5258−5272.

(51) Mangione, M. I.; Spanevello, R. A.; Anzardi, M. B. Efficient and

straightforward click synthesis of structurally related dendritic triazoles.

RSC Adv. 2017, 7, 47681−47688.

(52) Liu, J.; Chen, J.; Zhao, J.; Zhao, Y.; Li, L.; Zhang, H. A Modified

Procedure for the Synthesis of 1-Arylimidazoles. Synthesis 2003, 17,

2661−2666.

(36) Yamashita, H.; Uchimaru, Y. Chem. Commun. 1999, 1763−1764.

́

(37) Ojeda-Amador, A. I.; Munarriz, J.; Alaman-Valtierra, P.; Polo, V.;

́

Puerta-Oteo, R.; Jimenez, M. V.; Fernandez-Alvarez, F. J.; Perez-

13350

https://dx.doi.org/10.1021/acscatal.0c03295

ACS Catal. 2020, 10, 13334−13351

ACS Catalysis

pubs.acs.org/acscatalysis

Research Article

(53) White, C.; Yates, A.; Maitlis, P. M.; Heinekey, D. M. (η5-

Pentamethylcyclopentadienyl)Rhodium and -Iridium Compounds. In

Inorganic Syntheses; John Wiley & Sons, Inc: New York, 1992; Vol. 29,

pp 228−234.

(68) (a) Grimme, S.; Antony, J.; Ehrlich, S.; Krieg, H. A consistent and

accurate ab initio parametrization of density functional dispersion

correction (DFT-D) for the 94 elements H-Pu. J. Chem. Phys. 2010,

132, 154104. (b) Johnson, E. R. E.; Becke, A. D. A. A post-Hartree-Fock

model of intermolecular interactions. J. Chem. Phys. 2005, 123, 024101.

(69) Weigend, F.; Ahlrichs, R. Balanced basis sets of split valence,

triple zeta valence and quadruple zeta valence quality for H to Rn:

Design and assessment of accuracy. Phys. Chem. Chem. Phys. 2005, 7,

3297−3305.

(54) Sherwood, P. M. A. In Practical Surface Analysis in Auger and X-

ray Photoelectron Spectroscopy, 2^nded; Briggs, D., Seah, M. P., Eds.;

Wiley: New York, 1990. Vol. 1, p 657.

(55) Elgrabli, D.; Floriani, M.; Abella-Gallart, S.; Meunier, L.; Gamez,

C.; Delalain, P.; Rogerieux, F.; Boczkowski, J.; Lacroix, G.

Biodistribution and Clearance of Instilled Carbon Nanotubes in Rat

Lung. Part. Fibre Toxicol. 2008, 5, 20−33.

(56) Simonelli, L.; Marini, C.; Olszewski, W.; Avila Perez, M.;

Ramanan, N.; Guilera, G.; Cuartero, V.; Klementiev, K. CLÆSS: the

hard x-ray absorption beamline of the ALBA CELLS synchrotron.

Cogent Physics 2016, 3, 1231987.

(57) Ravel, B.; Newville, M. ATHENA, ARTEMIS, HEPHAESTUS:

data analysis for X-ray absorption spectroscopy using IFEFFIT. J.

Synchrotron Radiat. 2005, 12, 537−541.

(58) Rehr, J. J.; Albers, R. C. Theoretical approaches to x-ray

absorption fine structure. Rev. Mod. Phys. 2000, 72, 621−654.

(59) The crystal structure of 2 was previously reported by Choudhury

et al. (ref 34). Nonetheless, the poor quality of that determination {R1 =

0.1211 [I > 2 > (I)], wR₂= 0.4370 (all data)} prompted us to carry out a

signiﬁcantly more accurate determination at 100 K.

(70) Scalmani, G.; Frisch, M. J. Continuous surface charge polarizable

continuum models of solvation. I. General formalism. J. Chem. Phys.

2010, 132, 114110.

(71) Tanaka, R.; Yamashita, M.; Chung, L. W.; Morokuma, K.;

Nozaki, K. Mechanistic Studies on the Reversible Hydrogenation of

Carbon Dioxide Catalyzed by an Ir-PNP Complex. Organometallics

2011, 30, 6742−6750.

́

(72) Lazaro, G.; Fernandez-Alvarez, F. J.; Munarriz, J.; Polo, V.;

́

Iglesias, M.; Perez-Torrente, J. J.; Oro, L. A. Orthometallation of N-

substituents at the NHC ligand of [Rh(Cl)(COD)(NHC)] complexes:

its role in the catalytic hydrosilylation of ketones. Catal. Sci. Technol.

2015, 5, 1878−1887.

́

(73) CYLview, 1.0b; Legault, C. Y., Ed.; Universite de Sherbrooke,

2009 (http://www.cylview.org).

(60) SAINT+: Area-Detector Integration Software, version 6.01; Bruker

AXS: Madison, WI, 2001.

(61) Sheldrick, G. M. SADABS Program; University of Gottingen:

̈

Gottingen, Germany, 1999.

(62) Sheldrick, G. M. SHELXS 97, Program for the Solution of Crystal

̈

Structure; University of Gottingen: Gottingen, Germany, 1997.

(63) Sheldrick, G. M. Crystal structure refinement with SHELXL. Acta

Crystallogr., Sect. C: Struct. Chem. 2015, 71, 3−8.

(64) Farrugia, L. J. WinGX and ORTEP for Windows: an update. J.

Appl. Crystallogr. 2012, 45, 849−854.

(65) (a) Jun, C.-H.; Crabtree, R. H. Dehydrogenative silation,

isomerization and the control of syn- vs. anti-addition in the

hydrosilation of alkynes. J. Organomet. Chem. 1993, 447, 177−187.

(b) Nakamura, S.; Uchiyama, M.; Ohwada, T. Chemoselective

Silylzincation of Functionalized Terminal Alkynes Using Dianion-

Type Zincate (SiBNOL-Zn-ate): Regiocontrolled Synthesis of Vinyl-

silanes. J. Am. Chem. Soc. 2004, 126, 11146−11147. (c) Andavan, G. T.

S.; Bauer, E. B.; Letko, C. S.; Hollis, T. K.; Tham, F. S. Synthesis and

Characterization of a Free Phenylene bis(N-heterocyclic carbene) and

its di-Rh Complex: Catalytic Activity of the di-Rh and CCC-NHC Rh

Pincer Complexes in Intermolecular Hydrosilylation of Alkynes. J.

Organomet. Chem. 2005, 690, 5938−5947. (d) Katayama, H.;

Taniguchi, K.; Kobayashi, M.; Sagawa, T.; Minami, T.; Ozawa, F.

Ruthenium-Catalyzed Hydrosilylation of Terminal Alkynes: Stereo-

divergent Synthesis of (E)- and (Z)-Alkenylsilanes. J. Organomet. Chem.

2002, 645, 192−200.

(66) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;

Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.;

Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.;

Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;

Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima,

T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.;

Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin,

K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.;

Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.;

Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo,

C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A.

J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma,

K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.;

̈

Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V,

Cioslowski, J.; Fox, D. J. Gaussian 09, revision D.01; Gaussian, Inc.;

Wallingford CT, 2009.

(67) Becke, A. D. A new mixing of Hartree-Fock and local density-

functional theories. J. Chem. Phys. 1993, 98, 1372−1377.

13351

https://dx.doi.org/10.1021/acscatal.0c03295

ACS Catal. 2020, 10, 13334−13351

Article Doi

β-(Z) Selectivity Control by Cyclometalated Rhodium(III)-Triazolylidene Homogeneous and Heterogeneous Terminal Alkyne Hydrosilylation Catalysts

DOI: 10.1021/acscatal.0c03295

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Article abstract of DOI:10.1021/acscatal.0c03295

Full text of DOI:10.1021/acscatal.0c03295

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