Half-sandwich ruthenium(ii) complexes with tethered arene-phosphinite ligands: Synthesis, structure and application in catalytic cross dehydrogenative coupling reactions of silanes and alcohols

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Half-sandwich ruthenium(II) complexes with

tethered arene-phosphinite ligands: synthesis,

structure and application in catalytic cross

dehydrogenative coupling reactions of silanes

and alcohols†

Cite this: Dalton Trans., 2020, 49,

210

Rebeca González-Fernández,

Pascale Crochet * and Victorio Cadierno

*

The preparation of the tethered arene-ruthenium(II) complexes [RuCl₂{η⁶:κ¹(P)-C₆H₅(CH₂)_nOPR₂}] (R = Ph,

i

n = 1 (9a), 2 (9b), 3 (9c); R = Pr, n = 1 (10a), 2 (10b), 3 (10c)) from the corresponding phosphinite ligands

i

R₂PO(CH₂)_nPh (R = Ph, n = 1 (1a), 2 (1b), 3 (1c); R = Pr, n = 1 (2a), 2 (2b), 3 (2c)) is presented. Thus, in a

ﬁrst step, the treatment at room temperature of tetrahydrofuran solutions of dimers [{RuCl(μ-Cl)(η⁶-

arene)}₂] (arene = p-cymene (3), benzene (4)) with 1-2a-c led to the clean formation of the corresponding

mononuclear derivatives [RuCl₂(η⁶-p-cymene){R₂PO(CH₂)_nPh}] (5-6a-c) and [RuCl₂(η⁶-benzene){R₂PO

(CH₂)_nPh}] (7-8a-c), which were isolated in 66–99% yield. The subsequent heating of 1,2-dichloroethane

solutions of these compounds at 120 °C allowed the exchange of the coordinated arene. The substitution

process proceeded faster with the benzene derivatives 7-8a-c, from which complexes 9-10a-c were gen-

erated in 61–82% yield after 0.5–10 h of heating. The molecular structures of [RuCl₂(η⁶-p-cymene)

{ⁱPr₂PO(CH₂)₃Ph}] (6c) and [RuCl₂{η⁶:κ¹(P)-C₆H₅(CH₂)_nOPⁱPr₂}] (n = 1 (10a), 2 (10b), 3 (10c)) were unequi-

vocally conﬁrmed by X-ray diﬀraction methods. In addition, complexes [RuCl₂{η⁶:κ¹(P)-C₆H₅(CH₂)_nOPR₂}]

(9-10a-c) proved to be active catalysts for the dehydrogenative coupling of hydrosilanes and alcohols

under mild conditions (r.t.). The best results were obtained with [RuCl₂{η⁶:κ¹(P)-C₆H₅(CH₂)₃OPⁱPr₂}] (10c),

which reached TOF and TON values up to 117 600 h⁻¹and 57 000, respectively.

Received 15th November 2019,

Accepted 2nd December 2019

DOI: 10.1039/c9dt04421c

rsc.li/dalton

decades. A special subset of (η⁶-arene)-ruthenium(II) complexes

are the so-called tethered derivatives (Fig. 1), in which the η⁶-

Introduction

Since the pioneering work of Winkhaus and Singer in 1967,¹coordinated arene ligand is linked to a pendant donor atom

the chemistry of half-sandwich (η⁶-arene)-ruthenium(II) com- which also coordinates to the metal center (polydentate

plexes has exponentially expanded, representing nowadays one examples involving two or three σ-donor units are obviously

of the most versatile and widely studied families of organo- known).⁶In comparison with their non-tethered counterparts,

metallic ruthenium complexes.²Relevant applications of this these complexes gain robustness and rigidity from the chelate

type of compounds in catalysis,³biomedicine⁴and supramole- eﬀect, which has found to be advantageous in the field of

cular chemistry⁵have been described during the last two homogeneous catalysis as they can be used at higher tempera-

tures, over prolonged reaction periods, and also because they

allow a better stereodiscrimination in asymmetric processes.⁷

Laboratorio de Compuestos Organometálicos y Catálisis (Unidad Asociada al CSIC),

A large number of tethered arene-ruthenium(II) complexes

Centro de Innovación en Química Avanzada (ORFEO-CINQA), Departamento de

featuring C-,⁸N-,⁹O-,¹⁰S-,¹¹As-,¹²and P-donor^6,13units are

Química Orgánica e Inorgánica, Instituto Universitario de Química Organometálica

currently known, with the latter being by far the most numer-

“Enrique Moles”, Facultad de Química, Universidad de Oviedo, Julián Clavería 8,

E-33006 Oviedo, Spain. E-mail: crochetpascale@uniovi.es, vcm@uniovi.es;

Fax: +(34)985103446; Tel: +(34) 985103453

†Electronic supplementary information (ESI) available: Copies of the NMR

spectra of all the ruthenium complexes synthesized in this work and the alkoxy-

silanes isolated in the catalytic experiments. Kinetic profile of the dehydrogena-

tive cross-coupling reaction of Me₂PhSiH with MeOH catalyzed by 0.005 mol% of

10c. CCDC 1958494 (6c), 1958495 (10a), 1958496 (10b) and 1958497 (10c). For

ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/

c9dt04421c

Fig. 1 Generic structure of tethered arene-ruthenium(II) complexes.

210 | Dalton Trans., 2020, 49, 210–222

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ous. However, the vast majority of examples involves phos-

phine-type ligands, typically containing two- or three carbon

spacers connecting the phosphorus atom and the arene

group.^6,13The use of other phosphorus donors remains almost

unexplored. In this regard, complexes A,¹⁴

B

¹⁵and C ¹⁶are the

only ruthenium(^II) complexes incorporating η⁶-arene-κ¹-phos-

phinite ligands quoted to date in the literature (see Fig. 2).^17–19

Interestingly, while the synthesis of complexes A and B was Scheme 1 Synthesis of the phosphinite ligands R₂PO(CH₂)_nPh (1-2a-c).

accomplished in two steps from the corresponding phosphi-

nite ligand and appropriate dimeric precursor, i.e. [{RuCl(μ-Cl)

(η⁶-C₆H₅CO₂Me)}₂] or [{RuCl(μ-Cl)(η⁶-p-cymene)}₂], via initial

cleavage of the chloride bridges by the phosphinite and sub-

sequent intramolecular exchange of the arene on the resulting

κ¹-(P) mononuclear adducts,^14,15compounds [RuCl₂{η⁶:κ¹(P)-

C₆H₅CH₂CH₂CH₂OPR₂}] (C) were generated in modest yield

(25–44%) by reacting the 3-phenylpropanol-ruthenium(^II)

derivative [RuCl₂{η⁶:κ¹(O)-C₆H₅CH₂CH₂CH₂OH}] with the

corresponding chlorophosphine R₂PCl in the presence of

base.^17,20

(CH₂)_nPh}] (7-8a-c), featuring a κ¹-(P) coordination of the

ligands,²³by treatment of the corresponding dimeric precursor

[{RuCl(μ-Cl)(η⁶-arene)}₂] (arene = p-cymene (3), benzene (4))²⁴

with 2.7 equivalents of 1-2a-c (Scheme 2). The reactions, which

were performed in tetrahydrofuran at room temperature,

aﬀorded 5-8a-c as air-stable orange solids in 66–90% yield. As

a consequence of the lower solubility of dimer [{RuCl(μ-Cl)(η⁶-

benzene)}₂] (4) in THF with respect to its p-cymene analogue 3,

longer reaction times were systematically required in the synth-

eses of the benzene derivatives 7-8a-c (12 h vs. 1 h in the case

of 5-6a-c).

As expected, the formation of all these complexes could be

conveniently monitored by ³¹P{¹H} NMR spectroscopy, the

spectra showing a slight shift of the phosphorus signal to high

fields (Δδ from −1.1 to −3.6 ppm) in comparison to the corres-

ponding uncoordinated R₂PO(CH₂)_nPh ligand (see Table 1).

The ¹H and ¹³C{¹H} NMR spectra obtained also exhibited

signals in accordance with the proposed formulations, and

satisfactory elemental analyses were in all the cases obtained

(see details in the Experimental section).

In this contribution, an alternative and more eﬃcient syn-

thesis of complexes C, as well as that of related species con-

taining shorter carbon spacers between the oxygen atom

and the phenyl group, i.e. compounds [RuCl₂{η⁶:κ¹(P)-

C₆H₅CH₂CH₂OPR₂}] and [RuCl₂{η⁶:κ¹(P)-C₆H₅CH₂OPR₂}] (R =

i

Ph, Pr), is presented employing the preformed phosphinites

as starting materials. In addition, all the tethered complexes

were evaluated as potential catalysts for the dehydrogenative

cross-coupling of hydrosilanes with alcohols, showing excel-

lent activities under mild conditions.²¹

In addition, single crystals of [RuCl₂(η⁶-p-cymene){ⁱPr₂PO

(CH₂)₃Ph}] (6c) suitable for X-ray diﬀraction analysis could be

obtained by slow diﬀusion of n-hexane into a saturated solu-

tion of the complex in tetrahydrofuran, thus allowing to

unequivocally confirm the structures proposed for 5-8a-c. An

ORTEP-type view of the molecule is shown in Fig. 3 along with

selected bonding parameters. The complex features a typical

three-legged piano-stool geometry, with the ruthenium atom

surrounded by the η⁶-bonded p-cymene ring, two chlorides,

and the phosphorus atom of the phosphinite ligand. The Ru–

Cl bond lengths (2.404(1) and 2.410(1) Å) and Cl(1)–Ru–Cl(2)

angle (85.83(2)°) fall within the expected range for [RuCl₂(η⁶-p-

Results and discussion

Our investigations started with the preparation of the phosphi-

nite ligands Ph₂PO(CH₂)_nPh (n = 1 (1a), 2 (1b), 3 (1c)) and

ⁱPr₂PO(CH₂)_nPh (n = 1 (2a), 2 (2b), 3 (2c)). They were obtained

in 50–77% yield by following the route described by

Mukaiyama and co-workers,²²based on the initial deprotona-

n

tion of the corresponding primary alcohol with BuLi in tetra-

hydrofuran, and subsequent addition of chlorodiphenylphos-

phine or chlorodiisopropylphosphine to the resulting alcoho-

late solution (Scheme 1).

With compounds R₂PO(CH₂)_nPh (1-2a-c) in hands, we next

explored their coordination to ruthenium. In particular, we

initially synthesized the mononuclear complexes [RuCl₂(η⁶-p-

cymene){R₂PO(CH₂)_nPh}] (5-6a-c) and [RuCl₂(η⁶-benzene){R₂PO

Fig. 2 Structure of the η⁶-arene-κ¹-phosphinite-ruthenium(II) com-

plexes A–C.

Scheme 2 Synthesis of the arene-ruthenium(II) complexes 5-8a-c.

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Table 1 ³¹P{¹H} NMR data for the phosphinite ligands 1-2a-c and the ruthenium(II) complexes 5-10a-c ^a

Comp.

δ_P

Comp.

δ_P

Comp.

δ_P

Comp.

δ_P

1a

1b

1c

2a

2b

2c

114.5

112.6

112.1

154.5

152.2

151.4

5a

111.6

110.1

109.5

151.9

150.7

150.3

7a

7b

7c

8a

8b

8c

111.2

109.0

109.3

150.9

148.5

148.0

9a

158.6

121.5

119.3

206.2

159.8

156.3

5b ^b

5c ^b

6a

9b

9c ^b

10a

10b

10c

6b

6c

^aUnless otherwise stated, the spectra were recorded in CDCl₃at r.t. δ_Pin ppm. ^bSpectra recorded in CD₂Cl₂at r.t.

cymene bond^24,27allowed the high yield preparation of com-

pounds 9a–c from [RuCl₂(η⁶-benzene){Ph₂PO(CH₂)_nPh}] (7a–c)

(Scheme 3). Interestingly, the reactions times needed for the

complete consumption of the starting materials were found to

be strongly influenced by the number of carbon atoms con-

necting the phosphinite and phenyl units, with a time increas-

ing with the spacer’s length (from 2 h for 7a to 10 h for 7c).

Concerning the preparation of their diisopropylphosphinite

counterparts, i.e. compounds [RuCl₂{η⁶:κ¹(P)-C₆H₅(CH₂)_nOPⁱPr₂}]

(10a–c), we found that they can be conveniently accessed

employing both [RuCl₂(η⁶-p-cymene){ⁱPr₂PO(CH₂)_nPh}] (6a–c)

and [RuCl₂(η⁶-benzene){ⁱPr₂PO(CH₂)_nPh}] (8a–c) as starting

materials, with only minor diﬀerences in yields and reaction

times between them (see Scheme 4). The greater reactivity of

these derivatives in comparison to that of compounds 5a–c

and 7a–c can be ascribed to the higher electron density of the

metal center, which labilizes the ruthenium–arene bond

through back-donation from the occupied d ruthenium orbi-

tals to the empty π* arene ones.²⁸On the other hand, although

to a lesser extent, the eﬀect of the length of the spacer on the

reaction rates was also observed in these cases. The η⁶:κ¹(P)-

coordination of the phosphinite ligands was reflected in the

³¹P{¹H} NMR spectra of complexes 9-10a-c by a downfield shift

of the phosphorus signals with respect to those of their non-

tethered precursors (Δδ = 6–56 ppm; see Table 1). The

greatest deshielding eﬀect was observed for [RuCl₂{η⁶:κ¹(P)-

C₆H₅CH₂OPR₂}] (R = Ph (9a), ⁱPr (10a)), which according to the

X-ray data (see below) contain the more strained chelate ring.²⁹

Fig. 3 ORTEP-type view of the structure of complex 6c showing the

crystallographic labelling scheme. Hydrogen atoms have been omitted

for clarity. Thermal ellipsoids are drawn at the 30% probability level.

Selected bond distances (Å) and angles (°): Ru–C* = 1.712(2); Ru–Cl(1) =

2.404(1); Ru–Cl(2) = 2.410(1); Ru–P(1) = 2.351(1); P(1)–O(1) = 1.619(2);

P(1)–C(11) = 1.839(2); P(1)–C(14)

=

1.850(1); O(1)–C(17)

= 1.452(2);

C*–Ru–P(1) 126.78(2); C*–Ru–Cl(1)

=

124.95(2); C*–Ru–Cl(2) =

124.43(1); Cl(1)–Ru–Cl(2) = 85.83(2); Cl(1)–Ru–P(1) = 90.01(2); Cl(2)–

Ru–P(1) = 93.21(2); Ru–P(1)–O(1) = 105.28(5); Ru–P(1)–C(11) = 121.12(7);

Ru–P(1)–C(14) = 114.88(7); C(11)–P(1)–C(14) = 103.60(9); C(11)–P(1)–

O(1)

= 104.15(9); C(14)–P(1)–O(1) = 106.57(9); P(1)–O(1)–C(17) =

127.5(1); C* denotes the centroid of the p-cymene unit (C(2), C(3), C(4),

C(5), C(6) and C(7)).

cymene)(PR₃)]-type complexes, and the Ru–P(1) and P(1)–O(1)

distances (2.351(1) and 1.619(2) Å, respectively) are comparable

to those recently found by Balakrishna and co-workers in the

solid-state crystal structure of the related phosphinite-ruthe-

nium(^II) derivative [RuCl₂(η⁶-p-cymene)(Ph₂POCH₂CH₂{1,2,3-

N₃C(Ph)C(H)})] (Ru–P = 2.301(1) Å and P–O = 1.615(2) Å).²⁵

Complexes 5-8a-c were found to be perfectly stable in solu-

tion at room temperature for long periods, not observing,

regardless of the solvent employed, the displacement of the

p-cymene or benzene ligands. In the search of suitable experi-

mental conditions for the generation of the corresponding

tethered complexes, we performed a series of experiments with

CH₂Cl₂, tetrahydrofuran, 1,2-dichloroethane and toluene solu-

tions of [RuCl₂(η⁶-p-cymene){Ph₂PO(CH₂)_nPh}] (5a–c) at

diﬀerent temperatures. We could only observe the selective

formation of the desired complexes [RuCl₂{η⁶:κ¹(P)-

C₆H₅(CH₂)_nOPPh₂}] (9a–c) working in 1,2-dichloroethane

(DCE) at 120 °C (reactions performed in a sealed tube).²⁶

However, the conversions were very low (≤30%) even after 48 h

of heating. To our delight, employing the same experimental

1

The H NMR spectra of 9-10a-c confirmed the coordination of

the pendant phenyl unit of the phosphinite ligands to ruthe-

nium, displaying three well-separated signals: two triplets at

δ_H6.15–6.49 and 5.76–6.12 ppm and one doublet at

δ_H5.09–5.54 ppm with integrated intensities of 1 : 2 : 2 and

3

mutual J_HHcoupling constants of 4.5–6.0 Hz, assigned to the

Scheme 3 Synthesis of the tethered arene-ruthenium(II) complexes

conditions, the more labile character of the Ru-benzene vs. Ru- 9a–c.

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Fig. 5 ORTEP-type view of the structure of complex 10b showing the

crystallographic labelling scheme. Hydrogen atoms have been omitted

for clarity. Thermal ellipsoids are drawn at the 30% probability level.

Selected bond distances (Å) and angles (°): Ru–C* = 1.713(1); Ru–Cl(1) =

2.414(1); Ru–Cl(2) = 2.421(1); Ru–P(1) = 2.306(1); P(1)–O(1) = 1.630(2);

P(1)–C(9)

C*–Ru–P(1)

=

1.843(3); P(1)–C(12)

=

1.834(3); O(1)–C(8)

= 1.443(3);

Scheme 4 Synthesis of the tethered arene-ruthenium(II) complexes

10a–c.

=

126.29(2); C*–Ru–Cl(1)

=

123.99(2); C*–Ru–Cl(2) =

127.51(2); Cl(1)–Ru–Cl(2) = 87.17(2); Cl(1)–Ru–P(1) = 92.43(2); Cl(2)–Ru–

P(1) = 87.55(2); Ru–P(1)–O(1) = 111.04(7); Ru–P(1)–C(9) = 114.76(9); Ru–

P(1)–C(12) = 116.73(9); C(9)–P(1)–C(12) = 107.9(1); C(9)–P(1)–O(1) =

para, meta and ortho protons, respectively. The chemical equiv-

alence of the ortho and meta carbons was also evidenced in the

¹³C{¹H} NMR spectra, which featured in all the cases four

signals for the η⁶-coordinated phenyl group in the δ_Crange

84.5–108.8 ppm (see details in the Experimental section).

To confirm the spectroscopic information and to have a

better insight into the structure of the complexes synthesized,

X-ray diﬀraction studies were carried out on [RuCl₂{η⁶:κ¹(P)-

C₆H₅CH₂OPⁱPr₂}] (10a), [RuCl₂{η⁶:κ¹(P)-C₆H₅CH₂CH₂OPⁱPr₂}]

(10b) and [RuCl₂{η⁶:κ¹(P)-C₆H₅CH₂CH₂CH₂OPⁱPr₂}] (10c).

Views of the molecular structures, along with selected bonding

distances and angles, are shown in Fig. 4–6. All the complexes

exhibit the expected pseudo-octahedral three-legged piano-

stool geometry with the ruthenium atoms bound to two chlor-

104.8(1); C(12)–P(1)–O(1)

=

99.9(1); P(1)–O(1)–C(8)

=

116.3(1);

C* denotes the centroid of the η⁶-coordinated arene unit (C(1), C(2),

C(3), C(4), C(5) and C(6)).

Fig. 6 ORTEP-type view of the structure of complex 10c showing the

crystallographic labelling scheme. Hydrogen atoms have been omitted

for clarity. Thermal ellipsoids are drawn at the 30% probability level.

Selected bond distances (Å) and angles (°): Ru–C* = 1.723(1); Ru–Cl(1) =

2.417(1); Ru–Cl(2) = 2.417(1); Ru–P(1) = 2.356(1); P(1)–O(1) = 1.621(2);

P(1)–C(10) = 1.847(3); P(1)–C(13) = 1.838(3); O(1)–C(9) = 1.448(4); C*–

Ru–P(1) = 131.96(2); C*–Ru–Cl(1) = 122.09(2); C*–Ru–Cl(2) = 126.64(2);

Cl(1)–Ru–Cl(2) = 87.36(3); Cl(1)–Ru–P(1) = 90.47(3); Cl(2)–Ru–P(1) =

84.89(3); Ru–P(1)–O(1) = 112.99(8); Ru–P(1)–C(10) = 115.1(1); Ru–P(1)–

C(13) = 116.4(1); C(10)–P(1)–C(13) = 106.8(1); C(10)–P(1)–O(1) = 103.0(1);

C(13)–P(1)–O(1)

= 100.3(1); P(1)–O(1)–C(9) = 116.9(1); C* denotes

the centroid of the η⁶-coordinated arene unit (C(1), C(2), C(3), C(4), C(5)

and C(6)).

Fig. 4 ORTEP-type view of the structure of complex 10a showing the

crystallographic labelling scheme. Hydrogen atoms have been omitted

for clarity. Thermal ellipsoids are drawn at the 30% probability level.

Selected bond distances (Å) and angles (°): Ru–C* = 1.694(1); Ru–Cl(1) =

2.420(1); Ru–Cl(2) = 2.414(1); Ru–P(1) = 2.303(1); P(1)–O(1) = 1.641(3);

ide anions, and to the phosphorus atom and tethered phenyl

ring of the respective phosphinite ligand. The Ru–Cl, Ru–P

and Ru–C* distances are almost identical ( 0.05 Å) in the three

structures, and very similar to those found for the non-teth-

ered complex [RuCl₂(η⁶-p-cymene){ⁱPr₂POCH₂CH₂CH₂Ph}] (6c)

discussed above (see Fig. 3). Concerning the interligand angles

Cl(1)–Ru–Cl(2), Cl(1)–Ru–P(1) and Cl(2)–Ru–P(1), and those

between the centroid of the η⁶-coordinated phenyl ring C* and

the legs, the most noticeable diﬀerence was the increase in

P(1)–C(8)

=

1.847(4); P(1)–C(11)

=

1.828(4); O(1)–C(7)

= 1.445(5);

C*–Ru–P(1)

=

120.22(3); C*–Ru–Cl(1)

=

125.30(3); C*–Ru–Cl(2) =

128.19(3); Cl(1)–Ru–Cl(2) = 85.77(4); Cl(1)–Ru–P(1) = 95.56(4); Cl(2)–

Ru–P(1) = 91.87(4); Ru–P(1)–O(1) = 106.0(1); Ru–P(1)–C(8) = 117.7(1);

Ru–P(1)–C(11) = 122.2(1); C(8)–P(1)–C(11) = 104.5(2); C(8)–P(1)–O(1) =

104.2(2); C(11)–P(1)–O(1)

= 99.3(2); P(1)–O(1)–C(7) = 107.2(3);

C* denotes the centroid of the η⁶-coordinated arene unit (C(1), C(2),

C(3), C(4), C(5) and C(6)).

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Table 2 Dehydrogenative coupling of dimethylphenylsilane with

methanol catalyzed by complexes [RuCl₂{η⁶:κ¹(P)-C₆H₅(CH₂)_nOPR₂}]

(9-10a-c)^a

11.7° of the C*–Ru–P(1) angle when passing from

[RuCl₂{η⁶:κ¹(P)-C₆H₅CH₂OPⁱPr₂}] (10a) to [RuCl₂{η⁶:κ¹(P)-

C₆H₅CH₂CH₂CH₂OPⁱPr₂}] (10c). Interestingly,

a

detailed

inspection of the Ru–C bond distances indicated that the η⁶-

coordinated phenyl ring is, in all the complexes, slightly

inclined (not completely perpendicular to the Ru–C* axis),

with the free end of the ring being further away from the ruthe-

nium atom. This inclination decreases with increasing the

spacer’s length (e.g. Ru–C(1) bond distances of 2.284(2), 2.264

(3) and 2.242(3) Å for 10a, 10b and 10c, respectively). In

addition, contrary to the case of 10b and 10c, the C(7) carbon

in 10a was found to deviate significantly from the mean C(1)-

to-C(6) plane (−0.222(5) Å). Taken together, these observations

indicate a higher strain of the chelate ring in 10a vs. 10b,c.

On the other hand, very similar P(1)–O(1) bond lengths

were observed in the three structures, with values (1.621(2)–

1.641(3) Å) comparable to those previously found in the struc-

tures of the tethered complexes A and B (1.633(2) and 1.625(2)

Å, respectively; see Fig. 2) or in that of the non-tethered deriva-

tive [RuCl₂(η⁶-p-cymene){ⁱPr₂POCH₂CH₂CH₂Ph}] (6c) (1.619(2)

Å). On the contrary, the Ru–P–O and P–O–C angles were

aﬀected by the spacer’s length, increasing from 106.0(1)° and

99.3(8)° to 112.99(8)° and 116.9(1)°, respectively, when passing

from [RuCl₂{η⁶:κ¹(P)-C₆H₅CH₂OPⁱPr₂}] (10a) to [RuCl₂{η⁶:κ¹(P)-

C₆H₅CH₂CH₂CH₂OPⁱPr₂}] (10c).

Entry Catalyst mol% Ru Time (min) Conv.^b(%) Yield^b(%)

1

2

3

4

5

6

7

8

9a

9b

9c

10a

10b

10c

9a

9b

9c

10a

10b

10c

0.1

0.01

0.005

0.001

10

5

>99

60

99

5

98 (85)^c

99

120

100

50

70

40

5

98

57

9

10

11

12

13

14

60

2880

^aReactions were performed under argon atmosphere employing

5 mmol of Me₂PhSiH and 1 mL of MeOH. ^bDetermined by GC.

Diﬀerences between conversions and yields correspond to the disilox-

ane Me₂PhSiOSiPhMe₂. ^cIsolated yield after work-up (see the

Experimental section).

Finally, the catalytic potential of the tethered complexes

[RuCl₂{η⁶:κ¹(P)-C₆H₅(CH₂)_nOPR₂}] (9-10a-c) was investigated. silane after only 5–10 min (entries 1–6). The selectivity of the

As the catalytic reaction we choose the cross dehydrogenative process was also very high in all the cases, the desired

coupling of hydrosilanes and alcohols (Scheme 5), a process of methoxydimethyl(phenyl)silane being formed in ≥98% GC

high interest since it represents an attractive method for the yield. Only trace amounts of a byproduct, i.e. the disiloxane

preparation of useful alkoxysilane reagents.^21,30Also of note is Me₂PhSiOSiPhMe₂, were detected by GC.³³In a second

the fact that this process is gaining relevance in the field of set of experiments, performed with ruthenium loadings of

hydrogen storage and production.³¹Several studies have 0.01 mol%, diﬀerences in activity were observed between the

shown the utility of ruthenium-based catalysts in this type of complexes (entries 7–12), thus allowing to establish some

transformations,³²including the arene-ruthenium(II) com- structure–activity relationships. In particular, the following

plexes [{RuCl(μ-Cl)(η⁶-p-cymene)}₂] (3)^32b,c,fand [RuCl₂(η⁶-p- trends were observed: (i) the activity increases with the length

cymene)(NHC)] (11; NHC = 1-methyl-3-(pyren-1-ylmethyl)-imi- of the spacer within the two series of complexes and (ii) the

dazol-2-ylidene).^32gHowever, we would like to remark here that catalytic performances shown by the diisopropylphosphinite

there are no previous precedents about the use of tethered- derivatives 10a–c were higher than those of their corres-

type derivatives.

ponding diphenylphosphinite counterparts 9a–c (entries 10 vs.

Initial experiments were performed using dimethyl- 7, 11 vs. 8 and 12 vs. 9).^34,35In particular, the best results were

phenylsilane and methanol as model substrates, employing obtained with [RuCl₂{η⁶:κ¹(P)-C₆H₅(CH₂)₃OPⁱPr₂}] (10c), which

the latter also as the solvent. Thus, in a typical experiment, the was able to generate the alkoxysilane Me₂PhSiOMe in 98%

corresponding ruthenium complex 9-10a-c (0.1 mol%) was GC-yield after only 5 min (entry 12), thereby leading to TOF

added under inert atmosphere to a 5 M solution of Me₂PhSiH and TON values of 117 600 h⁻¹and 9800, respectively.

in MeOH at room temperature, monitoring the course of the Reduction of the catalyst loading to 0.005 mol% still produced

reaction by gas chromatography (GC) at 5 minutes intervals. Me₂PhSiOMe in 98% yield after 1 h (entry 13; TON of 19 600; a

The results obtained are collected in Table 2.

kinetic profile of this reaction is given in the ESI file†), but

To our delight, all the complexes showed a remarkable further decrease to 0.001 mol% led to an incomplete trans-

activity leading to the complete conversion of the starting formation with a maximum 57% yield after 48 h (entry 14;

TON of 57 000). Remarkably, the eﬀectiveness shown by

complex [RuCl₂{η⁶:κ¹(P)-C₆H₅(CH₂)₃OPⁱPr₂}] (10c) in this reac-

tion compares favorably with that reported for [{RuCl(μ-Cl)(η⁶-

p-cymene)}₂] (3) (91% yield of Me₂PhSiOMe after 5 min

employing a ruthenium loading of 1 mol%; TOF = 1092 h^{−1 32c}

)

Scheme 5 The catalytic cross dehydrogenative coupling of silanes and

alcohols.

and [RuCl₂(η⁶-p-cymene)(NHC)] (11) (>99% yield of

214 | Dalton Trans., 2020, 49, 210–222

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Me₂PhSiOMe after 10 min employing a ruthenium loading of

0.1 mol%; TOF = 6000 h⁻¹).^32g

The scope of [RuCl₂{η⁶:κ¹(P)-C₆H₅(CH₂)₃OPⁱPr₂}] (10c) was

next explored varying the nature of the alcohol (Scheme 6). For

convenience, we decided to use a catalyst loading of 0.1 mol%

in all the experiments. The results obtained showed that the

eﬃciency of this ruthenium catalyst is markedly influenced by

the steric constrains associated to the substrates. Thus,

although the reactions of dimethylphenylsilane with other

primary alcohols also generated the corresponding alkoxy-

silanes in high yield (>92% by GC, with isolated yields ≥84%),

longer reaction times were systematically required.

Scheme 7 Dehydrogenative coupling of Et₃SiH and Ph₃SiH with

methanol catalyzed by 10c.

The cross dehydrogenative coupling of Me₂PhSiH with

2-propanol was also satisfactorily achieved after 2 h employing

0.1 mol% of 10c, but when bulkier secondary alcohols

(2-butanol or cycloheptanol) were employed, an increase in the

catalyst loading to 1 mol% was required to generate the corres-

ponding alkoxysilanes in high yield (employing 0.1 mol% of

10c incomplete reactions were observed even after 24 h). An

increase of the ruthenium loading to 1 mol% was also needed

in the reaction of Me₂PhSiH with propargyl alcohol, for

which a surprisingly clean transformation occurred without

any side-reaction associated with the activation of the terminal

CuC bond.³⁶The eﬀect of sterics on the activity of complex

10c was also evidenced in the dehydrogenative coupling reac-

tions of triethylsilane and triphenylsilane with methanol

(Scheme 7), requiring, when compared to Me₂PhSiH, a longer

reaction time in the first case, and an increase of the catalyst

loading in the second, to obtain the desired alkoxysilanes in

high yields.

Conclusions

In summary, we have synthesized and structurally character-

ized a series of half-sandwich ruthenium(^II) complexes featur-

ing tethered arene-phosphinite ligands, species underrepre-

sented to date in the literature. The synthesis of compounds

[RuCl₂{η⁶:κ¹(P)-C₆H₅(CH₂)_nOPR₂}] (9-10a-c) was easily accom-

plished in two steps from the readily accessible phosphinite

ligands R₂PO(CH₂)_nPh and dimers [{RuCl(μ-Cl)(η⁶-arene)}₂]

(arene = p-cymene, benzene). Given the greater lability of the

benzene vs. p-cymene ligand, the use of dimer [{RuCl(μ-Cl)(η⁶-

benzene)}₂] resulted in general more convenient, allowing

faster arene exchange processes. The catalytic utility of com-

plexes [RuCl₂{η⁶:κ¹(P)-C₆H₅(CH₂)_nOPR₂}] (9-10a-c) was also

demonstrated, finding that they are able to promote eﬃciently

and under mild conditions the cross dehydrogenative coupling

of hydrosilanes and alcohols. To the best of our knowledge,

the involvement of tethered species in this catalytic transform-

ation is unprecedented. Interestingly, the most active complex

found in this study, namely [RuCl₂{η⁶:κ¹(P)-C₆H₅(CH₂)₃OPⁱPr₂}]

(10c), was more eﬀective than other (η⁶-arene)-ruthenium(II)-

type catalysts previously described.

Experimental

General methods

Synthetic procedures were performed under an atmosphere of

dry argon using vacuum-line and standard Schlenk or sealed-

tube techniques. Organic solvents were dried by standard

methods and distilled under argon before use.³⁷All reagents

were obtained from commercial suppliers and used without

further purification with the exception of the phosphinite ligands

R₂PO(CH₂)_nPh (1-2a-c),²²and the ruthenium(II) complexes

[{RuCl(μ-Cl)(η⁶-arene)}₂] (arene = p-cymene (3), benzene (4)) and

Scheme 6 Dehydrogenative coupling of Me₂PhSiH with diﬀerent alco-

hols catalyzed by 10c.

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Dalton Transactions

[RuCl₂(η⁶-p-cymene)(PPh₃)],²⁴which were prepared by following CH_orthoor CH_metaof PPh), 130.7 (s, CH_paraof PPh), 129.3 and

the methods reported in the literature. NMR spectra were 128.5 (s, CH_orthoand CH_metaof Ph), 127.7 (d, J_PC= 10.1 Hz,

recorded at 25 °C on Bruker DPX-300 or AV400 instruments. CH_orthoor CH_metaof PPh), 126.6 (s, CH_paraof Ph), 110.9 and

¹³C{¹H} and ¹H NMR chemical shifts were referenced to the 98.0 (s, C of p-cymene), 90.1 (d, ²J_PC= 3.5 Hz, CH of p-cymene),

2

residual signal of deuterated solvent. All data are reported in 87.7 (d, J_PC= 5.4 Hz, CH of p-cymene), 68.0 (d, J_PC= 4.0 Hz,

ppm downfield from (CH₃)₄Si. ³¹P{¹H} NMR chemical shifts OCH₂), 37.1 (d, ³J_PC= 7.6 Hz, CH₂Ph), 30.2 (s, CHMe₂), 21.6 (s,

were referenced to 85% H₃PO₄as external standard. DEPT CHMe₂), 17.2 (s, Me) ppm. Elemental analysis calcd (%) for

experiments have been carried out for all the compounds C₃₀H₃₃Cl₂OPRu: C 58.83, H 5.43; found: C 58.75, H 5.37. (5c):

reported in this paper. GC measurements were made on a Yield: 0.327 g (87%). ³¹P{¹H} NMR (CD₂Cl₂): δ = 109.5 (s) ppm.

Hewlett Packard HP6890 apparatus (Supelco Beta-Dex™ 120 ¹H NMR (CD₂Cl₂): δ = 7.95–7.89 (m, 4H, Ph), 7.43–7.20 (m,

3

column, 30 m length, 250 μm diameter). Elemental analyses 11H, Ph), 5.24 and 5.17 (d, 2H each, J_HH= 5.7 Hz, CH of

were provided by the Analytical Service of the Instituto de p-cymene), 3.82–3.77 (m, 2H, OCH₂), 2.76 (t, 2H, ³J_HH= 7.5 Hz,

3

Investigaciones Químicas (IIQ-CSIC) of Seville. For column CH₂Ph), 2.61 (sept, 1H, J_HH= 6.9 Hz, CHMe₂), 2.03–1.96 (m,

3

chromatography, Merck silica gel 60 (230–400 mesh) was 2H, CH₂), 1.81 (s, 3H, Me), 1.10 (d, 6H, J_HH= 6.9 Hz, CHMe₂)

employed.

ppm. ¹³C{¹H} NMR (CD₂Cl₂): δ = 141.5 (s, C_ipsoof Ph), 136.6 (d,

¹J_PC= 48.1 Hz, C_ipsoof PPh), 132.5 (d, J_PC= 10.8 Hz, CH_orthoor

CH_metaof PPh), 130.7 (s, CH_paraof PPh), 128.4 (s, CH_orthoand

CH_metaof Ph), 127.7 (d, J_PC= 10.0 Hz, CH_orthoor CH_metaof

PPh), 125.9 (s, CH_paraof Ph), 110.9 and 97.5 (s, C of p-cymene),

General procedure for the preparation of complexes [RuCl₂(η⁶-

p-cymene){R₂PO(CH₂)_nPh}] (R = Ph, n = 1 (5a), 2 (5b), 3 (5c);

R = ⁱPr, n = 1 (6a), 2 (6b), 3 (6c)) and [RuCl₂(η⁶-benzene){R₂PO

(CH₂)_nPh}] (R = Ph, n = 1 (7a), 2 (7b), 3 (7c); R = ⁱPr, n = 1 (8a),

2 (8b), 3 (8c))

2

90.6 (d, J_PC= 3.6 Hz, CH of p-cymene), 87.6 (d, J_PC= 5.4 Hz,

2

3

CH of p-cymene), 66.7 (d, J_PC= 3.9 Hz, OCH₂), 32.2 (d, J_PC

=

A suspension of the corresponding dimer [{RuCl(μ-Cl)(η⁶- 7.1 Hz, CH₂), 32.1 (s, CH₂Ph), 30.2 (s, CHMe₂), 21.6 (s,

arene)}₂] (arene = p-cymene (3), benzene (4); 0.3 mmol) and CHMe₂), 17.3 (s, Me) ppm. Elemental analysis calcd (%) for

phosphinite ligand R₂PO(CH₂)_nPh (1-2a-c; 0.8 mmol) in tetra- C₃₁H₃₅Cl₂OPRu: C 59.43, H 5.63; found: C 59.24, H 5.64. (6a):

hydrofuran (20 mL) was stirred for 1 (starting from 3) or 12 h Yield: 0.255 g (80%). ³¹P{¹H} NMR (CDCl₃): δ = 151.9 (s) ppm.

(starting from 4) at room temperature. The resulting solution ¹H NMR (CDCl₃): δ = 7.42 (br s, 5H, Ph), 5.47 and 5.40 (d, 2H

3

was then evaporated to dryness, the oily residue formed dis- each, J_HH= 5.9 Hz, CH of p-cymene), 5.00 (d, 2H, J_PH= 3.6

solved in the minimum amount of CH₂Cl₂(ca. 5 mL), and the Hz, OCH₂), 2.98–2.87 (m, 3H, CHMe₂and PCHMe₂), 2.10 (s,

product precipitated by adding 20 mL of a diethyl ether/ Me), 1.48–1.30 (m, 18H, CHMe₂and PCHMe₂) ppm. ¹³C{¹H}

3

hexane mixture (1 : 1 v/v). The same precipitation procedure NMR (CDCl₃): δ = 137.7 (d, J_PC= 6.4 Hz, C_ipsoof Ph), 128.7

was repeated twice more and the reddish orange solid was and 127.1 (s, CH_orthoand CH_metaof Ph), 128.1 (s, CH_paraof Ph),

2

finally washed with diethyl ether (5 mL) and dried in vacuo. 108.4 and 97.5 (s, C of p-cymene), 88.5 (d, J_PC= 3.2 Hz, CH of

Characterization data for the resulting complexes 5-8a-c are as p-cymene), 87.7 (d, ²J_PC= 4.2 Hz, CH of p-cymene), 69.2 (d, ²J_PC

1

follows: (5a): Yield: 0.298 g (83%). ³¹P{¹H} NMR (CDCl₃): δ = = 9.2 Hz, OCH₂), 30.5 (s, CHMe₂), 30.2 (d, J_PC= 20.5 Hz,

111.6 (s) ppm. ¹H NMR (CDCl₃): δ = 8.03–7.96 (m, 4H, Ph), PCHMe₂), 22.1 (s, CHMe₂), 18.1 and 17.8 (s, PCHMe₂), 18.0 (s,

3

7.43–7.32 (m, 11H, Ph), 5.25 and 5.20 (d, 2H each, J_HH= 5.9 Me) ppm. Elemental analysis calcd (%) for C₂₃H₃₅Cl₂OPRu: C

3

Hz, CH of p-cymene), 4.86 (d, 2H, J_PH= 5.1 Hz, OCH₂), 2.69 52.08, H 6.65; found: C 52.15, H 6.71. (6b): Yield: 0.251 g

(sept, 1H, ³J_HH= 6.9 Hz, CHMe₂), 1.83 (s, 3H, Me), 1.08 (d, 6H, (77%). ³¹P{¹H} NMR (CDCl₃): δ = 150.7 (s) ppm. ¹H NMR

³J_HH= 6.9 Hz, CHMe₂) ppm. ¹³C{¹H} NMR (CDCl₃): δ = 137.8 (CDCl₃): δ = 7.39–7.25 (m, 5H, Ph), 5.32 and 5.27 (d, 2H each,

3

1

3

(d, J_PC= 8.5 Hz, C_ipsoof Ph), 136.3 (d, J_PC= 48.4 Hz, C_ipsoof ³J_HH= 6.2 Hz, CH of p-cymene), 4.23 (td, 2H, J_HH= 6.3 Hz,

PPh), 132.5 (d, J_PC= 11.1 Hz, CH_orthoor CH_metaof PPh), 130.9 ³J_PH= 3.9 Hz, OCH₂), 3.04 (t, 2H, J_HH= 6.3 Hz, CH₂Ph),

3

(s, CH_paraof PPh), 128.5 and 127.0 (s, CH_orthoand CH_metaof 2.89–2.77 (m, 3H, CHMe₂and PCHMe₂), 2.06 (s, Me), 1.38–1.19

Ph), 127.9 (d, J_PC= 10.2 Hz, CH_orthoor CH_metaof PPh), 127.8 (s, (m, 18H, CHMe₂and PCHMe₂) ppm. ¹³C{¹H} NMR (CDCl₃): δ =

CH_paraof Ph), 111.9 and 97.6 (s, C of p-cymene), 90.6 (d, ²J_PC

3.4 Hz, CH of p-cymene), 87.5 (d, J_PC= 5.5 Hz, CH of Ph), 126.8 (s, CH_paraof Ph), 107.5 and 96.8 (s, C of p-cymene),

=

138.0 (s, C_ipsoof Ph), 128.9 and 128.6 (s, CH_orthoand CH_metaof

2

p-cymene), 68.5 (s, OCH₂), 30.1 (s, CHMe₂), 21.8 (s, CHMe₂), 88.8 (d, J_PC= 3.2 Hz, CH of p-cymene), 87.7 (d, J_PC= 4.1 Hz,

17.5 (s, Me) ppm. Elemental analysis calcd (%) for CH of p-cymene), 68.0 (d, ²J_PC= 11.3 Hz, OCH₂), 37.6 (d, ³J_PC

=

1

C₂₉H₃₁Cl₂OPRu: C 58.20, H 5.22; found: C 57.93, H 5.33. (5b): 5.6 Hz, CH₂Ph), 30.0 (s, CHMe₂), 29.4 (d, J_PC= 19.7 Hz,

Yield: 0.272 g (74%). ³¹P{¹H} NMR (CD₂Cl₂): δ = 110.1 (s) ppm. PCHMe₂), 22.1 (s, CHMe₂), 17.9 (s, Me), 17.4 (s, PCHMe₂) ppm.

¹H NMR (CD₂Cl₂): δ = 7.87–7.81 (m, 4H, Ph), 7.43–7.28 (m, Elemental analysis calcd (%) for C₂₄H₃₇Cl₂OPRu: C 52.94, H

3

11H, Ph), 5.16 and 5.04 (d, 2H each, J_HH= 6.0 Hz, CH of 6.85; found: C 53.05, H 6.91. (6c): Yield: 0.235 g (70%). ³¹P{¹H}

3

p-cymene), 3.95 (td, 2H, J_HH= 6.0 Hz, J_PH= 5.1 Hz, OCH₂), NMR (CDCl₃): δ = 150.3 (s) ppm. ¹H NMR (CDCl₃): δ =

3

2.96 (t, 2H, J_HH= 6.0 Hz, CH₂Ph), 2.53 (sept, 1H, J_HH= 6.9 7.37–7.14 (m, 5H, Ph), 5.50 and 5.41 (d, 2H each, J_HH= 2.0

3

Hz, CHMe₂), 1.74 (s, 3H, Me), 1.08 (d, 6H, J_HH= 6.9 Hz, Hz, CH of p-cymene), 4.01–3.95 (m, 2H, OCH₂), 2.95–2.77 (m,

CHMe₂) ppm. ¹³C{¹H} NMR (CD₂Cl₂): δ = 138.7 (s, C_ipsoof Ph), 5H, CH₂Ph, CHMe₂and PCHMe₂), 2.13 (s, Me), 2.10–2.04 (m,

136.5 (d, J_PC= 48.0 Hz, C_ipsoof PPh), 132.4 (d, J_PC= 10.8 Hz, 2H, CH₂), 1.31–1.24 (m, 18H, CHMe₂and PCHMe₂) ppm. ¹³C

1

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2

{¹H} NMR (CDCl₃): δ = 141.1 (s, C_ipsoof Ph), 128.6 and 128.4 (s, 126.7 (s, CH_paraof Ph), 88.4 (d, J_PC= 3.0 Hz, C₆H₆),

2

CH_orthoand CH_metaof Ph), 126.2 (s, CH_paraof Ph), 108.2 and 68.6 (d, J_PC= 7.1 Hz, OCH₂), 37.4 (d, J_PC= 7.1 Hz, CH₂Ph),

1

97.0 (s, C of p-cymene), 88.6 (s, CH of p-cymene), 87.7 (d, ²J_PC

=

30.7 (d, J_PC= 23.2 Hz, PCHMe₂), 18.2 and 18.0 (s, PCHMe₂)

2

4.5 Hz, CH of p-cymene), 67.2 (d, J_PC= 10.3 Hz, OCH₂), 32.8 ppm. Elemental analysis calcd (%) for C₂₀H₂₉Cl₂OPRu: C

3

(d, J_PC= 5.8 Hz, CH₂), 32.2 (s, CH₂Ph), 30.1 (s, CHMe₂), 29.9 49.11, H 5.99; found: C 49.22, H 6.01. (8c): Yield: 0.214 g

(d, J_PC= 20.4 Hz, PCHMe₂), 22.1 (s, CHMe₂), 18.0 and 17.6 (s, (71%). ³¹P{¹H} NMR (CDCl₃): δ = 148.0 (s) ppm. ¹H NMR

1

PCHMe₂), 17.9 (s, Me) ppm. Elemental analysis calcd (%) for (CDCl₃): δ = 7.38–7.22 (m, 5H, Ph), 5.61 (s, 6H, C₆H₆),

C₂₅H₃₉Cl₂OPRu: C 53.76, H 7.04; found: C 53.71, H 7.11. (7a): 3.92–3.86 (m, 2H, OCH₂), 2.98–2.90 (m, 2H, PCHMe₂), 2.77 (t,

3

Yield: 0.277 g (85%). ³¹P{¹H} NMR (CDCl₃): δ = 111.2 (s) ppm. 2H, J_HH= 7.5 Hz, CH₂Ph), 2.05–1.98 (m, 2H, CH₂), 1.40–1.25

¹H NMR (CDCl₃): δ = 8.04–7.97 (m, 4H, Ph), 7.47–7.35 (m, 11H, (m, 12H, PCHMe₂) ppm. ¹³C{¹H} NMR (CDCl₃): δ = 141.2 (s,

3

Ph), 5.42 (d, 6H, J_HH= 1.0 Hz, C₆H₆), 4.96 (d, 2H, J_PH

=

C_ipsoof Ph), 128.5 and 128.4 (s, CH_orthoand CH_metaof Ph),

5.7 Hz, OCH₂) ppm. ¹³C{¹H} NMR (CDCl₃): δ = 137.6 (d, J_PC

126.1 (s, CH_paraof Ph), 88.4 (s, C₆H₆), 67.1 (d, J_PC= 6.6 Hz,

3

2

8.1 Hz, C_ipsoof Ph), 136.4 (d, ¹J_PC= 51.6 Hz, C_ipsoof PPh), 132.3 OCH₂), 32.3 (d, J_PC= 6.6 Hz, CH₂), 32.0 (s, CH₂Ph), 30.9

3

1

(d, J_PC= 11.2 Hz, CH_orthoor CH_metaof PPh), 131.2 (s, CH_paraof (d, J_PC= 24.0 Hz, PCHMe₂), 18.2 (s, PCHMe₂) ppm. Elemental

PPh), 128.6 and 127.4 (s, CH_orthoand CH_metaof Ph), 128.2 (d, analysis calcd (%) for C₂₁H₃₁Cl₂OPRu: C 50.20, H 6.22; found:

J_PC= 10.4 Hz, CH_orthoor CH_metaof PPh), 128.0 (s, CH_paraof C 50.11, H 6.24.

2

Ph), 90.1 (d, J_PC= 3.2 Hz, C₆H₆), 69.0 (s, OCH₂) ppm.

Synthesis of complexes [RuCl₂{η⁶:κ¹(P)-C₆H₅(CH₂)_nOPPh₂}]

(n = 1 (9a), 2 (9b), 3 (9c))

Elemental analysis calcd (%) for C₂₅H₂₃Cl₂OPRu: C 55.36, H

4.27; found: C 55.29, H 4.39. (7b): Yield: 0.300 g (90%). ³¹P{¹H}

NMR (CDCl₃): δ = 109.0 (s) ppm. ¹H NMR (CDCl₃): δ = In Teflon-capped sealed tube, 0.1 mmol of the correspond-

7.92–7.86 (m, 4H, Ph), 7.43–7.28 (m, 11H, Ph), 5.21 (s, 6H, ing ruthenium complex [RuCl₂(η⁶-benzene){Ph₂PO(CH₂)_nPh}]

C₆H₆), 4.07 (td, 2H, ³J_HH= 6.0 Hz, ³J_PH= 4.5 Hz, OCH₂), 2.97 (t, (7a–c) were dissolved in 20 mL of 1,2-dichloroethane and the

3

2H, J_HH= 6.0 Hz, CH₂Ph) ppm. ¹³C{¹H} NMR (CDCl₃): δ = resulting solution stirred at 120 °C for the indicated time (see

1

139.0 (s, C_ipsoof Ph), 136.3 (d, J_PC= 51.2 Hz, C_ipsoof PPh), below). The mixture was then evaporated to dryness, the oily

132.2 (d, J_PC= 11.0 Hz, CH_orthoor CH_metaof PPh), 131.1 (s, residue formed dissolved in the minimum amount of CH₂Cl₂

CH_paraof PPh), 129.3 and 128.6 (s, CH_orthoand CH_metaof Ph), (ca. 0.5 mL), and the product precipitated by adding 20 mL of

128.0 (d, J_PC= 10.2 Hz, CH_orthoor CH_metaof PPh), 126.7 (s, a diethyl ether/hexane mixture (1 : 1 v/v). The same precipi-

CH_paraof Ph), 90.0 (s, C₆H₆), 68.4 (s, OCH₂), 37.2 (d, ³J_PC= 10.0 tation procedure was repeated twice more and the brown solid

Hz, CH₂Ph) ppm. Elemental analysis calcd (%) for was finally washed with diethyl ether (5 mL) and dried

C₂₆H₂₅Cl₂OPRu: C 56.12, H 4.53; found: C 56.03, H 4.48. (7c): in vacuo. Characterization data for the resulting complexes 9a–c

Yield: 0.287 g (84%). ³¹P{¹H} NMR (CDCl₃): δ = 109.3 (s) ppm. are as follows: (9a): Reaction time: 2 h. Yield: 0.028 g (61%).

1

¹H NMR (CDCl₃): δ = 7.97–7.92 (m, 4H, Ph), 7.45–7.18 (m, 11H, ³¹P{¹H} NMR (CDCl₃): δ = 158.6 (s) ppm. H NMR (CDCl₃): δ =

Ph), 5.39 (s, 6H, C₆H₆), 3.95–3.89 (m, 2H, OCH₂), 2.76 (t, 2H, 7.77–7.46 (m, 10H, PPh), 6.41 (br, 1H, CH_paraof Ph), 6.10 (br,

³J_HH= 7.5 Hz, CH₂Ph), 2.01–1.96 (m, 2H, CH₂) ppm. ¹³C{¹H} 2H, CH_metaof Ph), 5.39 (br, 2H, CH_orthoof Ph), 4.74 (d, 2H,

NMR (CDCl₃): δ = 141.3 (s, C_ipsoof Ph), 136.6 (d, ¹J_PC= 51.5 Hz, ³J_PH= 16.2 Hz, OCH₂) ppm. ¹³C{¹H} NMR (CD₂Cl₂): δ = 134.0

1

C

_ipsoof PPh), 132.2 (d, J_PC= 10.7 Hz, CH_orthoor CH_metaof PPh), (d, J_PC= 54.0 Hz, C_ipsoof PPh), 132.2 (s, CH_paraof PPh), 131.5

131.1 (s, CH_paraof PPh), 128.5 (s, CH_orthoand CH_metaof Ph), (d, J_PC= 10.5 Hz, CH_orthoor CH_metaof PPh), 128.1 (d, J_PC= 11.4

128.1 (d, J_PC= 10.0 Hz, CH_orthoor CH_metaof PPh), 126.0 (s, Hz, CH_orthoor CH_metaof PPh), 108.8 (s, C_ipsoof Ph), 98.1, 94.1

CH_paraof Ph), 90.0 (s, C₆H₆), 67.2 (s, OCH₂), 32.2 (s, CH₂and and 80.6 (s, CH of Ph), 67.8 (s, OCH₂) ppm. Elemental analysis

CH₂Ph) ppm. Elemental analysis calcd (%) for C₂₇H₂₇Cl₂OPRu: calcd (%) for C₁₉H₁₇Cl₂OPRu: C 49.15, H 3.69; found: C 49.22,

C 56.85, H 4.77; found: C 56.78, H 4.69. (8a): Yield: 0.188 g H 3.76. (9b): Reaction time: 5 h. Yield: 0.039 g (82%). ³¹P{¹H}

(66%). ³¹P{¹H} NMR (CDCl₃): δ = 150.9 (s) ppm. ¹H NMR NMR (CDCl₃): δ = 121.5 (s) ppm. ¹H NMR (CDCl₃): δ =

(CDCl₃): δ = 7.40 (br s, 5H, Ph), 5.66 (s, 6H, C₆H₆), 5.02 (d, 2H, 7.88–7.82 (m, 4H, PPh), 7.41–7.38 (m, 6H, PPh), 6.49 (t, 1H,

3

³J_PH= 4.8 Hz, OCH₂), 3.11–3.00 (m, 2H, PCHMe₂), 1.46–1.30 ³J_HH= 6.0 Hz, CH_paraof Ph), 5.88 (t, 2H, J_HH= 6.0 Hz, CH_meta

3

(m, 12H, PCHMe₂) ppm. ¹³C{¹H} NMR (CDCl₃): δ = 138.0 (s, of Ph), 5.24 (d, 2H, J_HH= 6.0 Hz, CH_orthoof Ph), 4.36 (dt, 2H,

C_ipsoof Ph), 128.7 and 126.4 (s, CH_orthoand CH_metaof Ph), ³J_PH= 19.8 Hz, ³J_HH= 4.8 Hz, OCH₂), 2.63 (t, 2H, ³J_HH= 4.8 Hz,

2

127.9 (s, CH_paraof Ph), 88.6 (d, J_PC= 2.4 Hz, C₆H₆), 68.9 (s, CH₂Ph) ppm. ¹³C{¹H} NMR (DMSO-d₆): δ = 136.5 (d, ¹J_PC= 54.6

1

OCH₂), 31.2 (d, J_PC= 23.5 Hz, PCHMe₂), 18.4 (s, PCHMe₂) Hz, C_ipsoof PPh), 132.3 (d, J_PC= 11.1 Hz, CH_orthoor CH_metaof

ppm. Elemental analysis calcd (%) for C₁₉H₂₇Cl₂OPRu: PPh), 131.1 (s, CH_paraof PPh), 128.1 (d, J_PC= 10.6 Hz, CH_ortho

C 48.11, H 5.74; found: C 48.24, H 5.80. (8b): Yield: 0.208 g or CH_metaof PPh), 102.2 (d, ²J_PC= 11.3 Hz, C_ipsoof Ph), 92.6 (d,

(71%). ³¹P{¹H} NMR (CDCl₃): δ = 148.5 (s) ppm. ¹H NMR ²J_PC= 4.6 Hz, CH of Ph), 91.3 and 85.9 (s, CH of Ph), 68.0 (s,

(CDCl₃): δ = 7.39–7.33 (m, 5H, Ph), 5.48 (s, 6H, C₆H₆), 4.09 (td, OCH₂), 29.5 (s, CH₂Ph) ppm. Elemental analysis calcd (%) for

3

2H, J_HH= 6.0 Hz, J_PH= 3.3 Hz, OCH₂), 2.97 (t, 2H, J_HH

=

C₂₀H₁₉Cl₂OPRu: C 50.22, H 4.00; found: C 50.31, H 3.98.

6.0 Hz, CH₂Ph), 2.95–2.86 (m, 2H, PCHMe₂), 1.35–1.21 (m, (9c):¹⁶Reaction time: 10 h. Yield: 0.039 g (79%). ³¹P{¹H} NMR

12H, PCHMe₂) ppm. ¹³C{¹H} NMR (CDCl₃): δ = 138.7 (s, (CD₂Cl₂): δ = 119.3 (s) ppm. ¹H NMR (CD₂Cl₂): δ = 7.90–7.85

3

C_ipsoof Ph), 129.2 and 128.5 (s, CH_orthoand CH_metaof Ph), (m, 4H, PPh), 7.42–7.39 (m, 6H, PPh), 6.28 (t, 1H, J_HH= 4.5

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Dalton Transactions

3

Hz, CH_paraof Ph), 5.82 (t, 2H, J_HH= 4.5 Hz, CH_metaof Ph), General procedure for the catalytic cross dehydrogenative

3

5.09 (d, 2H, J_HH= 4.5 Hz, CH_orthoof Ph), 4.90 (dt, 2H, J_PH

=

coupling of hydrosilanes and alcohols using complex

12.6 Hz, J_HH= 4.5 Hz, OCH₂), 2.79 (t, 2H, J_HH= 5.1 Hz, [RuCl₂{η⁶:κ¹(P)-C₆H₅(CH₂)₃OPⁱPr₂}] (10c)

3

CH₂Ph), 2.24–2.18 (m, 2H, CH₂) ppm. ¹³C{¹H} NMR (CD₂Cl₂):

Under inert atmosphere, the corresponding hydrosilane

1

δ = 137.7 (d, J_PC= 54.5 Hz, C_ipsoof PPh), 131.5 (d, J_PC

=

(5 mmol), alcohol (1 mL) and complex 10c (0.005–0.05 mmol;

0.1–1 mol%) were introduced in a Schlenk tube equipped with

a bubbler, and the reaction mixture stirred at room tempera-

ture until complete conversion of the starting hydrosilane. The

course of the reaction was monitored regularly taking samples

of ca. 5 μL which, after dilution with CH₂Cl₂, were analyzed by

GC. For the isolation of the alkoxysilane products, the reaction

mixture was first subjected to a flash chromatography over

silica gel, eluting with hexanes, and subsequently to vacuum-

line evaporation or Kugelrohr distillation to eliminate all the

volatiles. The identity of the alkoxysilanes was assessed by

comparison of their NMR spectroscopic data with those

10.8 Hz, CH_orthoor CH_metaof PPh), 130.5 (s, CH_paraof PPh),

127.7 (d, J_PC= 10.7 Hz, CH_orthoor CH_metaof PPh), 97.9

(d, ²J_PC= 10.5 Hz, CH of Ph), 96.0 (s, C_ipsoof Ph), 93.4 and 84.5

(s, CH of Ph), 66.0 (s, OCH₂), 26.9 and 24.1 (s, CH₂and

CH₂Ph) ppm.

Synthesis of complexes [RuCl₂{η⁶:κ¹(P)-C₆H₅(CH₂)_nOPⁱPr₂}]

(n = 1 (10a), 2 (10b), 3 (10c))

Complexes 10a–c, isolated as brown solids, were prepared as

described for 9a–c starting from 0.1 mmol of the corres-

ponding ruthenium complex [RuCl₂(η⁶-p-cymene){ⁱPr₂PO

(CH₂)_nPh}] (6a–c; method A) or [RuCl₂(η⁶-benzene){ⁱPr₂PO

(CH₂)_nPh}] (8a–c; method B). Characterization data are as

follows: (10a): Reaction time: 1 h (method A) or 0.5 h (method

B). Yield: 0.026 g (65%) (method A) or 0.024 g (62%) (method

1

reported in the literature (copies of the H and ¹³C{¹H} NMR

spectra of the products obtained are included in the ESI file†).

X-ray crystal structure determination of compounds 6c and

10a–c

1

B). ³¹P{¹H} NMR (CDCl₃): δ = 206.2 (s) ppm. H NMR (CD₂Cl₂):

3

δ = 6.35 (t, 1H, J_HH= 5.7 Hz, CH_paraof Ph), 6.01 (t, 2H, J_HH

=

Crystals of 6c and 10a,c suitable for X-ray diﬀraction analysis

5.7 Hz, CH_metaof Ph), 5.23 (d, 2H, J_HH= 5.7 Hz, CH_orthoof were obtained by slow diﬀusion of n-hexane into a saturated

3

Ph), 4.60 (d, 2H, J_PH= 13.5 Hz, OCH₂), 2.61–2.49 (m, 2H, solution of the complexes in tetrahydrofuran or dichloro-

PCHMe₂), 1.16–1.40 (m, 12H, PCHMe₂) ppm. ¹³C{¹H} NMR methane, respectively. For 10b, the crystals were obtained by

(CDCl₃): δ = 110.2 (s, C_ipsoof Ph), 100.0 and 75.6 (s, CH of Ph), slow diﬀusion of diethyl ether into a saturated solution of the

2

91.7 (d, J_PC= 13.4 Hz, CH of Ph), 72.2 (s, OCH₂), 30.2 complex in dichloromethane. The most relevant crystal and

(d, J_PC= 25.5 Hz, PCHMe₂), 16.9 and 16.2 (s, PCHMe₂) ppm. refinement data are collected in Table 3. In all the cases, data

1

Elemental analysis calcd (%) for C₁₃H₂₁Cl₂OPRu: C 39.40, collection was performed with a Rigaku-Oxford Diﬀraction

H 5.34; found: C 39.22, H 5.30. (10b): Reaction time: 1.5 h Xcalibur Onyx Nova single-crystal diﬀractometer using Cu-Kα

(method A) or 1 h (method B). Yield: 0.027 g (67%) (method A) radiation (λ = 1.5418 Å). Images were collected at a fixed

or 0.029 g (70%) (method B). ³¹P{¹H} NMR (CDCl₃): δ = crystal-to-detector distance of 62 mm using the oscillation

159.8 (s) ppm. ¹H NMR (CD₂Cl₂): δ = 6.38 (t, 1H, ³J_HH= 5.7 Hz, method, with 1.20° oscillation and 4.5–11.0 s variable exposure

3

CH_paraof Ph), 5.80 (t, 2H, J_HH= 5.7 Hz, CH_metaof Ph), 5.16 time per image for 6c and 30.0–130.0 s for 10c. For 10a and

3

(d, 2H, J_HH= 5.7 Hz, CH_orthoof Ph), 4.07 (dt, 2H, J_PH

=

10b, the oscillation method was used with 1.10° oscillation,

3

16.2 Hz, J_HH= 4.8 Hz, OCH₂), 3.00–2.89 (m, 2H, PCHMe₂), and 2.0–4.5 s or 7.5–17.0 s variable exposure time per image,

3

2.45 (t, 2H, J_HH= 4.8 Hz, CH₂Ph), 1.19–1.27 (m, 12H, respectively. Data collection strategy was calculated with the

PCHMe₂) ppm. ¹³C{¹H} NMR (CDCl₃): δ = 98.1 (d, J_PC= 11.0 program CrysAlis^ProCCD.³⁸Data reduction and cell refinement

2

Hz, CH of Ph), 95.9 (s, C_ipsoof Ph), 95.3 and 81.5 (s, CH of Ph), were performed with the program CrysAlis^ProRED.³⁸An

1

67.7 (s, OCH₂), 29.3 (s, CH₂Ph), 27.7 (d, J_PC= 26.7 Hz, empirical absorption correction was applied using the SCALE3

PCHMe₂), 18.5 and 16.6 (s, PCHMe₂) ppm. Elemental analysis ABSPACK algorithm as implemented in the program

calcd (%) for C₁₄H₂₃Cl₂OPRu: C 40.99, H 5.65; found: C 41.10, CrysAlis^ProRED.³⁸The software package WINGX was used for

H 5.55. (10c):¹⁶Reaction time: 2 h (method A) or 1.5 h space group determination, structure solution, and refine-

(method B). Yield: 0.030 g (72%) (method A) or 0.033 g (79%) ment.³⁹The structures were solved by Patterson interpretation

1

(method B). ³¹P{¹H} NMR (CDCl₃): δ = 156.3 (s) ppm. H NMR and phase expansion using SIR92 (6c and 10a)⁴⁰or

3

(CD₂Cl₂): δ = 6.15 (t, 1H, J_HH= 5.6 Hz, CH_paraof Ph), 5.76 (t, DIRDIF2008 (10b and 10c).⁴¹Isotropic least-squares refine-

3

2H, J_HH= 5.6 Hz, CH_metaof Ph), 5.54 (d, 2H, J_HH= 5.6 Hz, ment on F²using SHELXL97 was performed.⁴²During the

3

CH_orthoof Ph), 4.32–4.24 (m, 2H, J_PH= 13.8 Hz, J_HH= 5.4 Hz, final stages of the refinements, all the positional parameters

OCH₂), 3.05–2.97 (m, 2H, PCHMe₂), 2.77 (t, 2H, J_HH= 6.0 Hz, and the anisotropic temperature factors of all non-H atoms

3

CH₂Ph), 2.14–2.06 (m, 2H, CH₂), 1.31–1.16 (m, 12H, PCHMe₂) were refined. All H atoms were geometrically located and their

2

ppm. ¹³C{¹H} NMR (CDCl₃): δ = 100.3 (d, J_PC= 7.7 Hz, CH of coordinates were refined riding on their parent atoms. The

Ph), 94.3 (s, C_ipsoof Ph), 89.0 and 87.7 (s, CH of Ph), 64.7 (d, function minimized was {∑[ω(F_o− F_c) ]/∑[ω(F_o) ]}^1/2where

2

2 2

¹J_PC= 3.6 Hz, OCH₂), 29.6 (d, J_PC= 23.9 Hz, PCHMe₂), 29.4 ω = 1/[σ²(F_o) + (aP)²+ bP] (a and b values are given in Table 3)

and 25.1 (s, CH₂and CH₂Ph), 18.8 (d, J_PC= 2.6 Hz, PCHMe₂), with σ(F_o) from counting statistics and P = [max (F_o, 0) +

1

2

17.9 (s, PCHMe₂) ppm.

2F_c]/3. Atomic scattering factors were taken from

218 | Dalton Trans., 2020, 49, 210–222

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Table 3 Crystal data and structure reﬁnement for compounds 6c and 10a–c

6c

10a

10b

10c

Empirical formula

Formula weight

Temperature/K

Wavelength/Å

Crystal system

Space group

Crystal size/mm

a/Å

b/Å

c/Å

α (°)

β (°)

C₂₅H₃₉Cl₂OPRu

558.50

150(2)

1.54184

Monoclinic

P2₁/n

0.11 × 0.06 × 0.05

9.3696(1)

15.1236(2)

18.3093(2)

90

98.796(1)

90

C₁₃H₂₁Cl₂OPRu

396.24

150(2)

1.54184

Triclinic

ˉ

P1

0.40 × 0.19 × 0.05

7.2966(3)

7.6884(3)

15.4349(6)

85.087(3)

81.257(4)

62.338(4)

2

C₁₄H₂₃Cl₂OPRu

410.26

150(2)

1.54184

Orthorhombic

Pbca

0.20 × 0.13 × 0.08

8.8108(1)

13.2483(2)

27.2268(4)

90

C₁₅H₂₅Cl₂OPRu

424.29

293(2)

1.54184

Orthorhombic

Pbca

0.11 × 0.04 × 0.03

8.9634(2)

13.7539(3)

27.5000(6)

90

8

3390.2(2)

1.663

11.215

γ (°)

Z

4

8

Volume/Å³

Calculated density/g cm⁻³

µ/mm⁻¹

2563.95(5)

1.447

7.557

757.89(6)

1.736

12.494

3178.13(8)

1.715

11.941

F(000)

θ range/°

Index ranges

1160

400

1664

1728

3.80–69.47

−11 ≤ h ≤ 11

−17 ≤ k ≤ 18

−22 ≤ l ≤ 20

99.0%

5.76–69.22

−7 ≤ h ≤ 8

−9 ≤ k ≤ 9

−18 ≤ l ≤ 18

99.6%

3.71–69.41

−10 ≤ h ≤ 10

−15 ≤ k ≤ 15

−32 ≤ l ≤ 32

99.7%

10 246

2953 (R_int= 0.0282)

176/0

5.88–69.46

−8 ≤ h ≤ 10

−15 ≤ k ≤ 16

−33 ≤ l ≤ 31

99.9%

Completeness to θ_max

No. of reflns. collected

No. of unique reflns.

No. of parameters/restraints

Refinement method

Goodness-of-fit on F²

Weight function (a, b)

R₁[I > 2σ(I)]^a

14 073

5736

9404

4781 (R_int= 0.0272)

278/0

2819 (R_int= 0.0613)

167/0

3147 (R_int= 0.0318)

181/0

Full-matrix least-squares on F²

1.030

0.0267, 0.0925

0.0216

1.059

0.1116, 0.0000

0.0504

1.044

0.0367, 1.6410

0.0262

1.118

0.0570, 0.2256

0.0302

wR₂[I > 2σ(I)]^a

0.0507

0.1376

0.0647

0.0892

R₁(all data)

0.0253

0.0527

0.287, −0.520

0.0517

0.1405

0.998, −1.790

0.0294

0.0672

0.575, −0.737

0.0324

0.0918

0.366, −0.753

R₂(all data)

Largest diﬀ. peak and hole/e Å⁻³

^aR₁= ∑(|F_o| − |F_c|)/∑|F_o|; wR₂= {∑[w(F_o²− F_c²)²]/∑[w(F_o²)²]}^1/2

.

International Tables for X-ray Crystallography, Volume C.⁴³

Geometrical calculations related to the centroids C* were

made with PARST.⁴⁴The crystallographic plots were made with

DIAMOND.⁴⁵

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Conﬂicts of interest

There are no conflicts to declare.

Acknowledgements

Financial support from the Spanish Ministry of Economy,

Industry and Competitiveness (MINECO project CTQ2016-

75986-P) and the University of Oviedo (project PAPI-18-GR-2011-

0032) is gratefully acknowledged. R. G.-F. thanks MECD of Spain

for the award of a FPU fellowship (FPU17/00230).

Notes and references

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15 M. K. Pandey, J. T. Mague and M. S. Balakrishna, Inorg.

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Organometallics, 2018, 37, 48; (f) T. J. Prior, H. Savoie,

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10 For representative examples, see: (a) Y. Miyaki, T. Onishi, 19 (a) Igau and co-workers reported some examples of teth-

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220 | Dalton Trans., 2020, 49, 210–222

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20 (a) Although Kurosawa and co-workers originally referred 32 See, for example: (a) S. V. Maifeld, R. L. Miller and D. Lee,

to [RuCl₂{η⁶:κ¹(O)-C₆H₅CH₂CH₂CH₂OH}] as a dimer, i.e.

[{RuCl(µ-Cl)(η⁶-C₆H₅CH₂CH₂CH₂OH)}₂] (see ref. 16), its

monomeric tethered structure was later established by

Winter and co-workers through single-crystal X-ray diﬀrac-

tion studies (see ref. 10c); (b) The same approach had

been previously employed for the preparation of com-

pounds [Cr(CO)₂{η⁶:κ¹(P)-C₆H₅(CH₂)_nOPPh₂}] (n = 1, 2, 3)

from [Cr(CO)₃{η⁶-C₆H₅(CH₂)_nOH}]: W. R. Jackson, I. D. Rae

and M. G. Wong, Aust. J. Chem., 1984, 37, 1563.

Tetrahedron Lett., 2002, 43, 6363; (b) R. L. Miller,

S. V. Maifeld and D. Lee, Org. Lett., 2004, 6, 2773;

(c) Y. Ojima, K. Yamaguchi and N. Mizuno, Adv. Synth.

Catal., 2009, 351, 1405; (d) D. V. Gutsulyak,

S. F. Vyboishchikov and G. I. Nikonov, J. Am. Chem. Soc.,

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W. Y. Fan, J. Organomet. Chem., 2012, 717, 9; (f) K. Kanno,

Y. Aikawa and S. Kyushin, Tetrahedron Lett., 2017, 58, 9;

(g) D. Ventura-Espinosa, A. Carretero-Cerdán, M. Baya,

H. García and J. A. Mata, Chem. – Eur. J., 2017, 23, 10815;

(h) J. Kaźmierczak, K. Kuciński, D. Lewandowski and

G. Hreczycho, Inorg. Chem., 2019, 58, 1201.

21 For a recent review article on the catalytic formation of

silicon-heteroatom bonds, covering the cross dehydrogena-

tive coupling of hydrosilanes with alcohols and highlight-

ing the synthetic utility of the alkoxysilane products, see: 33 Formation of this byproduct, arising from the presence of

K. Kuciński and G. Hreczycho, ChemCatChem, 2017, 9,

1868.

22 (a) K. Masutani, T. Minowa, Y. Hagiwara and

T. Mukaiyama, Bull. Chem. Soc. Jpn., 2006, 79, 1106;

adventitious water, was previously observed by us while

studying the same coupling reaction with platinum-based

catalysts: J. Francos, J. Borge, S. Conejero and V. Cadierno,

Eur. J. Inorg. Chem., 2018, 3176.

(b) T. Shintou, W. Kikuchi and T. Mukaiyama, Bull. Chem. 34 Although we have not carried out mechanistic studies, we

Soc. Jpn., 2003, 76, 1645.

assume that the reaction proceeds through the same

pathway proposed for [RuCl₂(η⁶-p-cymene)(NHC)] (11), in

which the alcohol molecule attacks the silane once co-

ordinated to the cationic fragment [RuCl(η⁶-p-cymene)

(NHC)]⁺(see ref. 32g). According to this, the higher reactiv-

ity of the diisopropylphosphinite derivatives 10a–c vs. their

diphenylphosphinite counterparts 9a–c is probably related

to the greater electronic density of the metal center in the

former, which facilitates the dissociation of one of the

chloride ligands.

23 The only previous examples of metal complexes containing

these ligands coordinated in a κ¹-(P) manner are [Ni

(Ph₂POCH₂Ph)₄], trans-[PdX₂(Ph₂POCH₂Ph)₂] (X = Cl, CN)

and cis-[PdCl₂(Ph₂POCH₂Ph)(L)] (L = PhPMe₂, PhP(OMe)₂):

(a) A. W. Verstuyft and J. H. Nelson, Synth. React. Inorg.

Met.-Org. Chem., 1975, 5, 69; (b) A. W. Verstuyft,

D. A. Redfield, L. W. Cary and J. H. Nelson, Inorg. Chem.,

1976, 15, 1128; (c) A. W. Verstuyft, L. W. Cary and

J. H. Nelson, Inorg. Chem., 1976, 15, 3161;

(d) C. W. Weston, A. W. Verstuyft, J. H. Nelson and 35 For comparative purposes we performed the same reaction

H. B. Jonassen, Inorg. Chem., 1977, 16, 1313;

(e) A. W. Verstuyft, D. A. Redfield, L. W. Cary and

J. H. Nelson, Inorg. Chem., 1977, 16, 2776.

employing 0.01 mol% of the non-tethered derivative

[RuCl₂(η⁶-benzene){Ph₂PO(CH₂)₃Ph}] (7c). It also showed a

good catalytic activity, but its eﬀectiveness was lower than

that of [RuCl₂{η⁶:κ¹(P)-C₆H₅(CH₂)₃OPPh₂}] (9c) (130 min

were needed to attain the complete conversion of the start-

ing silane; to be compared with entry 9 in Table 2). This

result points to a positive eﬀect of the tethered structure on

the catalytic activity. In addition, we also carry out the reac-

tion using the known complex [RuCl₂(η⁶-p-cymene)(PPh₃)]

as catalyst (0.01 mol%). After 2 h at r.t., only 5% conversion

was observed, indicating that the nature of the P-donor

ligand (phosphinite vs. phosphine) exerts a strong eﬀect

on this catalytic transformation.

24 M. A. Bennett and A. K. Smith, J. Chem. Soc., Dalton Trans.,

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25 B. Choubey, P. S. Prasad, J. T. Mague and

M. S. Balakrishna, Eur. J. Inorg. Chem., 2018, 1707.

26 In toluene at 120 °C, minor amounts of complexes

[RuCl₂{η⁶:κ¹(P)-C₆H₅(CH₂)_nOPPh₂}] (9a–c) are also formed,

along with species of type [RuCl₂(η⁶-toluene){Ph₂PO

(CH₂)_nPh}] resulting from the displacement of the

p-cymene ligand by the toluene solvent.

27 E. L. Muetterties, J. R. Bleeke and A. C. Sievert,

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type complexes. See, for example: (a) M. I. Bruce, Chem.

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29 P. E. Garrou, Chem. Rev., 1981, 81, 229.

30 For general reviews on catalytic dehydrocoupling processes,

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31 See, for example: D. Ventura-Espinosa, S. Sabater, 39 L. J. Farrugia, J. Appl. Crystallogr., 2012, 45, 849.

A. Carretero-Cerdán, M. Baya and J. A. Mata, ACS Catal., 40 A. Altomare, G. Cascarano, C. Giacovazzo and A. Gualardi,

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222 | Dalton Trans., 2020, 49, 210–222

Article Doi

Half-sandwich ruthenium(ii) complexes with tethered arene-phosphinite ligands: Synthesis, structure and application in catalytic cross dehydrogenative coupling reactions of silanes and alcohols

DOI: 10.1039/c9dt04421c

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