Synthesis, structure and reactivity of Pd and Ir complexes based on new lutidine-derived NHC/phosphine mixed pincer ligands

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Synthesis, structure and reactivity of Pd and Ir complexes based

on new lutidine-derived NHC/phosphine mixed pincer ligands

Práxedes Sánchez,^aMartín Hernández-Juárez,^aEleuterio Álvarez,^aMargarita Paneque,^a,* Nuria

Rendón^aand Andrés Suárez^a,*

Received 00th January 20xx,

Accepted 00th January 20xx

DOI: 10.1039/x0xx00000x

Coordination studies of new lutidine-derived hybrid NHC/phosphine ligands (CNP) to Pd and Ir have been performed.

Treatment of the square-planar [Pd(CNP)Cl](AgCl₂) complex 2a with KHMDS produces the selective deprotonation at the

CH₂P arm of the pincer to yield the pyridine-dearomatised complex 3a. A series of cationic [Ir(CNP)(cod)]⁺complexes 4 has

been prepared by reaction of the imidazolium salts 1 with Ir(acac)(cod). These derivatives exhibit in the solid state, and in

solution, a distorted trigonal bipyramidal structure in which the CNP ligands adopt an unusual C_(axial)-N_(equatorial)-P_(equatorial)

coordination mode. Reactions of complexes 4 with CO and H₂yield the carbonyl species 5a(Cl) and 6a(Cl), and the

dihydrido derivatives 7, respectively. Furthermore, upon reaction of complex 4b(Br) with base, selective deprotonation at

the methylene CH₂P arms is observed. The, thus formed, deprotonated Ir complex 8b reacts with H₂in a ligand-assisted

process leading to the trihydrido complex 9b, which can also be obtained by reaction of 7b(Cl) with H₂in the presence of

KO^tBu. Finally, the catalytic activity of Ir-CNP complexes in the hydrogenation of ketones has been briefly assessed.

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Pidko´s group, is that the increased flexibility of the CNC pincer

results in enhanced reactivities towards H₂and CO₂in

Introduction

Metal complexes based on lutidine-derived PNP pincer ligands

have gained considerable attention due to their applications in

organometallic chemistry and catalysis (Fig. 1a).¹In these

derivatives metal-ligand cooperativity, triggered by

deprotonation of the methylene arms of the ligand

accompanied by dearomatisation of the pyridine ring, has led

to unique reactivity in the activation of a diversity of X-H (X =

H, C, O, N) bonds. While significantly less studied, analogous

complexes based on CNC pincers (C stands for a N-heterocyclic

carbene, NHC) have also been described (Fig. 1b).^2-4As shown

with Ru-CNC complexes,^3,4these derivatives can also be

deprotonated at the methylene CH₂N bridges, and participate

in metal-ligand cooperation processes. Furthermore, the larger

Py-CH₂-NHC linkage, which forms 6-membered metallacycles

upon coordination, confers a greater flexibility on the ligand in

comparison to 5-membered rings formed in PNP pincers. This

flexibility should permit stabilizing metal complexes in a

variety of coordination geometries, a relevant issue in catalysis

where the intermediates in the catalytic cycle may need to

adopt different structural arrangements. For example, while

PNP ligands have only exhibited meridional coordination

modes, facial coordination of CNC ligands in Ru complexes has

been observed.³More remarkable, as demonstrated by the

comparison to Ru-PNP systems.^4b

a)

b)

N

[M]

R₂P

[M]

PR₂

N

R

M-PNP

M-CNC

c)

d)

N

PR₂

[M]

PR₂

[M]

N

R

N

R

M-CNP

Danopoulos, Braunstein et al.

M-CNP (this work)

(2015)

Fig. 1 General structure of metal complexes with a) lutidine-

derived PNP ligands, b) lutidine-derived CNC ligands, c)

deprotonated picoline-derived CNP ligands, and d) lutidine-

derived CNP ligands (this work).

In addition, non-symmetric pincer ligands, i.e. having two

inequivalent flanking donor groups, allow for

a larger

electronic and steric diversity derived from the potential

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tuning of two different side donors.⁵With respect to lutidine- P-donor fragment, followed by phosphine deprotection by

derived pincer complexes, some examples of PNP’⁶and CNC’^4asimple treatment with refluxing MeOH. The CNP ligands

derivatives have been reported. Unsymmetrical PNX and CNX precursors were obtained with moderate to good yields (55-

pincer complexes have also been described, although these 85%) as white to brown solids.

derivatives are usually of the type PNN¹and CNN⁷where

hemilabile coordination of the N-donor flanking group has

Synthesis and deprotonation of Pd-CNP complex 2a

been proposed. In marked contrast, complexes based on CNP

For an evaluation of the coordination capabilities of these

new CNP ligands, we initially studied the formation of Pd

derivatives. Thus, salt 1a(Cl) was reacted with Ag₂O in CH₂Cl₂,

followed by addition of PdCl₂(cod) to yield complex 2a

(Scheme 2).¹⁰The spectroscopic data support the formation of

a complex in which the CNP ligand is coordinated to the metal

ligands having a pyridine central moiety and in which the two

side functionalities are two significantly different strong

σ

-

donors, such as a phosphine and a NHC, have not been

investigated. In fact, a limited number of hybrid tridentate

ligands possessing both phosphine and NHC donors have been

reported, and these have either a ligand backbone based on a

1,3-disubstituted phenyl ring,^8aor a different arrangement of

the donor moieties, where the NHC group is the central unit of

the pincer ligand.^8b-fAlso, recently Danopoulos, Braunstein et

al. have prepared Co and Cr complexes based on deprotonated

1

centre as a pincer. For example, its H NMR spectrum shows

distinctly two signals for the bridging methylenes. The CH₂P

2

protons appear at 4.32 ppm (d, J_HP= 11.3 Hz), whereas the

NCH₂hydrogens produce a singlet at 6.05 ppm. The ¹³C{¹H}

NMR spectrum exhibits a doublet at 166.4 ppm with a large

²J_CP(183 Hz, carbene carbon, C², of the NHC moiety), indicating

the trans disposition of the NHC and phosphine moieties.

NHC/phosphine mixed pincer ligands having a central picoline

9

motif (Fig. 1c)

.

Based on these precedents, we aimed to develop a new

class of ligands having NHC and phosphine side donors and a

lutidine central fragment (CNP, Fig. 1d). A fundamental

difference of these ligands with the previous picoline-based

pincer derivatives reported by Danopoulos, Braunstein et al.

resides in the presence of a methylene linker between the

pyridine and the NHC functionalities, which could also be

susceptible to deprotonation and should enhance pincer

flexibility. In this contribution, we report on the synthesis of

the precursors of these ligands as well as their coordination to

Pd and Ir complexes. In particular, the ability of CNP ligands to

adapt to different coordination geometries and participate in

ligand-assisted processes has been assessed.

Scheme 2 Synthesis and reactivity of Pd complex 2a

.

A single crystal X-ray diffraction study of 2a confirmed the

proposed structure (Fig. 2). Thus, complex 2a in the solid state

is comprised of a Pd atom in an square-planar coordination

geometry, with the carbene and phosphine fragments of the

pincer disposed trans to each other (C²(NHC)-Pd-P = 168.65^o),

and the chloride ligand trans to the pyridine (N(Py)-Pd-Cl =

175.03^o). The NHC-Pd-Py chelate ring has a boat conformation

as determined by the torsion angle C(14)-N(3)-Pd(1)-C(1) of

32.4^o, whereas the 5-membered ring involving the phosphine

donor has an envelope conformation with a C(18)-N(3)-Pd(1)-

P(1) torsion angle of 28.4^o.

X

N

i)

N

X

N

PPh₂

N

1a(Cl)

; Ar = Mes, X = Cl

Ar

1b(Cl); Ar = 3,5-Xyl, X = Cl

1b(Br); Ar = 3,5-Xyl, X = Br

Since it can be expected that CNP ligands can be

deprotonated in either the CH₂P or CH₂-NHC arms, the

acid/base responsiveness of 2a was tested by adding KHMDS

to a suspension of the complex in THF.¹¹In the ¹H NMR

spectrum of the resulting product 3a, a significant up-field shift

for the signals of the pyridine protons (5.55-6.46 ppm) in

accord with the dearomatisation of this moiety is observed.

Meanwhile, the =CHP fragment produces a singlet signal at

3.41 ppm (integrating to 1H) in the ¹H NMR spectrum and a

doublet at 63.3 ppm (¹J_CP= 66 Hz) in the ¹³C{¹H} NMR

experiment, evidencing the selective deprotonation of the CNP

ligand at the CH₂P arm.

i) for 1a(Cl): Ph₂PH + KO^tBu in MeCN/THF

for 1b(Cl) and 1b(Br): Ph₂P(BH₃)H + KO^tBu in MeCN/THF; then MeOH, reflux

Scheme 1 Syntheses of CNP ligands precursors.

Results and discussion

Syntheses of imidazolium salts 1

Syntheses of imidazolium salts 1a(Cl), 1b(Cl) and 1b(Br)

were effected as shown in Scheme 1. Derivative 1a(Cl) was

prepared by reaction of the corresponding 2-chloromethyl-6-

imidazolylmethyl-pirydine with diphenyl phosphine in the

presence of KO^tBu. Alternatively, in the case of salts 1b(Cl) and

1b(Br), higher product yields were obtained when diphenyl

phosphine-borane adduct was used for the introduction of the

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observed.¹³Finally, as observed with other pentacoordinated

diolefin Ir complexes,¹³the distance from the Ir atom to the

centroid of the C=C bonds is slightly longer for the alkene

coordinated trans to the NHC than for the olefin placed in the

meridional position (ꢀd(Ir-centroid C=C) = 0.14 Å).

Fig. 2 ORTEP drawing at 30% ellipsoid probability of the

cationic component of complex 2a. Hydrogen atoms and

solvent molecules have been omitted for clarity. Selected bond

lengths [Å] and angles [^o]: Pd(1)-C(1) 2.038(6), Pd(1)-N(3)

2.071(4), Pd(1)-P(1) 2.2623(15), Pd(1)-Cl(1) 2.2758(14), C(1)-

Pd(1)-P(1) 168.65(16), N(3)-Pd(1)-Cl(1) 175.03(14), P(1)-Pd(1)-

Cl(1) 93.97(5), P(1)-Pd(1)-N(3) 81.34(14), C(1)-Pd(1)-Cl(1)

95.93(16), C(1)-Pd(1)-N(3) 88.6(2).

Fig. 3 ORTEP drawing at 30% ellipsoid probability of the

cationic component of complex 4b(BAr_F). Hydrogen atoms and

solvent molecules have been omitted for clarity. Selected bond

lengths [Å] and angles [^o]: Ir(1)-C(1) 2.029(4), Ir(1)-N(3)

2.253(3), Ir(1)-P(1) 2.3412(9), Ir(1)-C(31) 2.263(4), Ir(1)-C(32)

2.217(4), Ir(1)-C(35) 2.140(3), Ir(1)-C(36) 2.101(4), C(1)-Ir(1)-

P(1) 95.61(10), N(3)-Ir(1)-P(1) 75.98(8), N(3)-Ir(1)-C(1)

81.07(13).

Synthesis and structural features of Ir-CNP complexes

Reaction of imidazolium salts

1 with Ir(acac)(cod) provided

cationic olefin complexes 4, isolated as yellow to orange solids

in moderate to good yields (30-80%) (Scheme 3). These

derivatives are stable in the solid state to the atmospheric

agents, and have been fully characterised by NMR. For

1

example, in the H NMR spectrum of 4b(Br), the CH₂P protons

As exemplified with complex 4a(Cl), a dynamic behaviour

in solution for complexes

NMR spectra of 4a(Cl) registered in the temperature range

4

has been evidenced by NMR. VT-¹H

are diastereotopic and appear as doublet of doublets at

(²J_HP= 2.1 Hz) and 4.17 ppm (²J_HH= 15.5 Hz and ²J_HP= 11.6 Hz).

δ 3.36

o

Similarly, protons for the CH₂N bridge produce two doublets at

between 50 and −80 C show sharp signals for the resonances

attributable to the CNP ligand. In contrast, broad signals at

δ

5.65 and 6.91 (²J_HH= 14.1 Hz). The ¹³C{¹H} NMR spectrum

shows a doublet at 164.8 ppm for the C²NHC carbon with a

very small ²J_CPcoupling constant of 8 Hz. These data suggest a

cis coordination of the phosphine and NHC donors, also

confirmed in the solid state by a single crystal X-ray diffraction

study of 4b(BAr_F) (Fig. 3), obtained by anion exchange in

complex 4b(Br) with NaBAr_F.

2.98 and 3.49 ppm, integrating for two protons each, are

observed for the olefinic protons at 25 C. H-¹H COSY and H-

¹H NOESY experiments indicate that each signal is produced by

protons of different olefinic moieties; i.e. H^b1,H^b2and H^a1,H^a2

produce signals at 2.98 and 3.49 ppm, respectively (Fig. 4a). In

addition, these signals broaden upon lowering the

o

1

The structure of complex 4b(BAr_F) is best described as

adopting a distorted trigonal bipyramidal geometry despite the

acute P-Ir-N(Py) bond angle of 75.98(8)^o. The CNP ligand

exhibits a facial coordination, with the NHC donor in the apical

position (P-Ir-C(NHC) angle of 95.61(10)^o). In addition, the six-

membered chelate ring involving the NHC and pyridine donors

adopts a boat–like conformation as defined by the dihedral

angle C(13)-N(3)-Ir(1)-C(1) of −50.6^o, while the chelate ring

containing the phosphine fragment exhibits an envelope

conformation with a C(17)-N(3)-Ir(1)-P(1) angle of 29.5^o. This

facial coordination mode is unprecedented in M-PNP

complexes and may be ascribed to the larger flexibility of the

six-membered Py-M-NHC chelate ring, as previously observed

temperature and eventually split at temperatures below

^oC into two sets of two signals each, appearing at 2.23 (H^b2)

and 3.39 (H^b1), and 2.86 (H^a2) and 3.90 (H^a1), respectively. An

approximate value of

G^‡= 10.9 kcal mol^-1at the coalescence

−25

δ

ꢀ

temperature (244 K) can be estimated for the fluxional

process. This dynamic behaviour can be ascribed to alkene site

exchange allowed by the decoordination of the C=C fragment

trans to the NHC moiety to produce the distorted tetrahedral

intermediate A, followed by re-coordination of the free olefin

moiety to the opposite side without a net change of the fac

coordination mode of the CNP ligand (Fig. 4a).

In addition, the ¹H,¹H-exchange spectroscopy (EXSY)

experiment of 4a(Cl) registered at 50 ^oC demonstrates the

existence of additional dynamic processes with higher energy

barriers. Thus, intense exchange cross-peaks between the

signals for the olefinic protons appearing at 2.98 and 3.49 ppm

are observed, which can be explained by the formal rotation of

in Ru-CNC complexes.³In addition, the C_(axial)-N_(equatorial)

-

P_(equatorial)coordination mode of the pincer differs significantly

from previously reported pentacoordinated d⁸pincer

complexes,¹²for which an eq-ax-eq distribution is usually

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the diolefin ligand allowed by the decoordination of one of the the complex. Previously, mirror-image isomer exchange

Ir-alkene bonds (Fig. 4a). Furthermore, the observation of involving a pseudo-Berry rotation has been observed for

strong correlation peaks between the resonances of the o-, m- pentacoordinated pincer Ir complexes containing diolefin

and p- protons of one of the PPh groups with the aromatic ligands.^13cHowever, this process should not be possible in

protons of the other phenyl group, as well as between the complexes

signals of the methylene protons in each of the CH₂P and CH₂N mode of the pincer. Since, as discussed above, olefin

arms, indicates that the CNP pincer in complexes also decoordination seems facile, the observed fluxional process

undergoes structural changes, which could be assigned to a could likely involve the intermediacy of the square-planar

slow interconversion between the two enantiomeric forms of structure (Fig. 4b).

4 due to the C_(axial)-N_(equatorial)-P_(equatorial)coordination

4

B

Scheme 3 Synthesis and reactivity of Ir-CNP complexes 4.

Fig. 4 Proposed dynamic processes in solution operating in the cationic part of complexes

4 (positive charges have been

supressed for clarity; PR₂= PPh₂, Ar = mesityl or 3,5-xylyl).

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To evaluate the donating properties of the CNP ligands, we Hz) and –23.30 ppm (²J_HP= 18.9 Hz) due to the hydrido ligands

prepared the carbonyl derivative 5a(Cl) by bubbling CO placed trans to the pyridine and trans to the chloride,

through a CH₂Cl₂solution of complex 4a(Cl) (Scheme 3). respectively. In the ¹³C{¹H} NMR spectrum, the C²NHC appears

1

Signals of the bridging CH₂P and CH₂N protons in the H NMR at 172.9 ppm as a doublet signal (²J_CP= 119 Hz). Exposure of a

spectrum support a planar coordination of the CNP pincer. sample of 7a(Cl) in CD₂Cl₂to deuterium gas (2 bar) or addition

Thus, the CH₂P protons produce a doublet signal at 4.18 ppm of CD₃OD causes fast H/D exchange of the hydrido ligands.

(²J_HP= 10.0 Hz) while the CH₂N hydrogens appear as a singlet

Furthermore, the structural features of complex 7a(Cl)

at 6.11 ppm. In the IR spectrum, the carbonyl ligand absorbs at have been studied in the solid state by single crystal X-ray

1985 cm^-1, which is

higher frequency than that diffraction (Fig. 6). This derivative has an octahedral geometry

a

corresponding to the (^tBu-PNP)-Ir analogue (1964 cm^-1),¹⁴with the two hydrido ligands occupying mutually cis positions

suggesting a lower electron density at the metal centre in the and the CNP ligand adopting a meridional coordination, as

Ir-CNP system. The CO ligand is detected in the ¹³C{¹H} NMR defined by the C(1)-Ir(1)-P(1) angle value of 166.5(3)^o. The

spectrum by the appearance of a doublet signal at 177.2 ppm chelate ring incorporating the NHC fragment has a boat-like

(²J_CP= 10 Hz), while the C²NHC carbon appears at 178.1 ppm conformation as shown by the C(14)-N(3)-Ir(1)-C(1) torsion

(²J_CP= 99 Hz).

angle of –26.5(9)^o, whereas an envelope conformation for the

Interestingly, complex 5a(Cl) reversibly coordinates a new N(Py)-Ir-P ring is observed with a C(18)-N(3)-Ir(1)-P(1) dihedral

CO molecule yielding complex 6a(Cl), as inferred from the angle of –14.9(8)^o.

absorption bands corresponding to the CO ligands, which

1

appear in the IR spectrum at 1946 and 2021 cm^-1.¹⁵In the H

NMR spectrum of 6a(Cl), the presence of a singlet signal at

6.09 ppm (2H) for the CH₂N arm and a doublet at 4.29 ppm

2

(2H, J_HP= 10.9 Hz) attributable to the CH₂P moiety suggests

the existence of a symmetry plane containing the CNP-Ir

coordination plane and points out to a meridional coordination

of the pincer ligand,^13bat variance with the coordination

geometry in the also pentacoordinated compounds 4.

As determined by VT-¹H NMR spectroscopy (see SI),

carbonyl complexes 5a(Cl) and 6a(Cl) exhibit a dynamic

behaviour in solution, which equilibrates the two otherwise

diastereotopic hydrogens of both methylene bridges. In

square-planar Pd¹⁶and octahedral Ru complexes incorporating

CNC ligands,^3bsimilar dynamic processes have been ascribed

to

a slow interconversion between the two twisted Fig. 6 ORTEP drawing at 30% ellipsoid probability of complex

conformations adopted by both C²(NHC)-N(Py)-M chelate rings 7a(Cl). Hydrogen atoms, except hydrido ligands, and solvent

of the pincer ligand. Similarly, the observed fluxionality in molecules have been omitted for clarity. Selected bond lengths

derivatives 5a(Cl) and 6a(Cl) can be attributed to the fast [Å] and angles [^o]: Ir(1)-C(1) 2.037(10), Ir(1)-N(3) 2.192(9), Ir(1)-

atropoisomerism between the two limiting enantiomeric P(1) 2.262(3), Ir(1)-H(1)Ir 1.600, Ir(1)-H(2)Ir 1.599, Ir(1)-Cl(1)

forms shown in Fig. 5.

2.509(3), C(1)-Ir(1)-P(1) 166.5(3), N(3)-Ir(1)-H(1)Ir 173.9, P(1)-

Ir(1)-H(1)Ir 92.7, P(1)-Ir(1)-N(3) 82.2(3), C(1)-Ir(1)-H(1)Ir 95.4,

C(1)-Ir(1)-N(3) 89.0(4).

Deprotonation and ligand-assisted H₂activation

We have also explored the deprotonation of the Ir-CNP

complexes 4 ¹⁷Treatment of 4b(Br) with KO^tBu produces the

.

selective deprotonation of the CH₂P arm (Scheme 4). The

1

resulting complex 8b is characterised in the H NMR spectrum

by the presence of significantly high-field shifted signals for the

Fig. 5 Interconversion between the limiting conformations of

pyridine

protons

(5.6-6.4

ppm),

evidencing

the

5a(Cl) and 6a(Cl)

.

dearomatisation of the pyridine ring. The =CHP proton appears

as a singlet at 3.86 ppm, while the CH₂-NHC hydrogens

generate two doublets at 4.93 and 5.29 ppm (²J_HH= 13.6 Hz). In

the ¹³C{¹H} NMR spectrum, the resonance caused by the C²

NHC carbon appears as an overlapped doublet at 170.6 ppm.

Although the J_CPvalue cannot be unambiguously calculated, a

Complexes 4a(Cl) and 4b(Cl) react with H₂producing the

dihydrido derivatives and cyclooctene (Scheme 3). At room

7

1

temperature, the H NMR spectrum of complex 7a(Cl) shows

two doublets of doublets at –20.19 (²J_HP= 13.8 Hz, J_HH= 7.0

2

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value of 2 to 20 Hz is estimated, suggesting a cis coordination cyclic ketone,

of the phosphine and NHC fragments. This coordination mode (entry 10).

is further supported by the existence of strong NOE contacts

between the protons of the xylyl and PPh₂groups.

α

-tetralone, proceeded with a high conversion

Deprotonated complex 8b reacts with H₂at 0 ^oC to produce

Conclusions

the trihydrido derivative 9b in a ligand-assisted process leading

to the re-aromatisation of the pyridine fragment. Complex 9b

is only stable under an atmosphere of H₂and can be also

obtained by reaction of 7b(Cl) with KO^tBu followed by

In summary, Pd and Ir complexes based on novel lutidine-

derived CNP pincer ligands have been synthesised. The

flexibility of the chelating Py-CH₂-NHC fragment of the ligands

allows for both facial and meridional coordination modes in

five- and six-coordinated Ir-CNP complexes. Furthermore,

selective deprotonation of the CH₂P arm in Ir-CNP complexes

promotes ligand-assisted H-H activation, leading to active

species in ketone hydrogenation. Further studies involving the

application of metal complexes based on CNP ligands in X-H (X

= H, C, heteroatom) bond activation and as catalysts in the

(de)hydrogenation of polar substrates are currently in progress

in our laboratory.

exposure to H₂. The trihydrido complex 9b shows in the ¹H

2

NMR spectrum a doublet of doublets at –9.98 ppm (2H, J_HP

=

2

18.2 Hz, J_HH= 4.8 Hz) due to the apical hydrido ligands and a

doublet of triplets at –19.64 ppm (1H, ²J_HP= 14.4 Hz) produced

by the hydride trans to the pyridine N. The C²of the NHC

fragment appears in the ¹³C{¹H} NMR spectrum as a doublet at

176.9 ppm with a large ²J_CP(121 Hz), in agreement with a trans

disposition of the NHC and phosphine donors of the CNP

ligand.

Table 1 Hydrogenation of ketones catalysed by Ir-CNP complexes^a

Entry

1^b

Ketone

Ir-CNP

T (^oC) Conv. (%)

4a(Cl)

30

60

95

93

2^b,c

3

Acetophenone

>99

98

4

4b(Cl)

5a(Cl)

5

43

6

7

4´-Methoxiacetophenone 4a(Cl)

4´-Chloroacetophenone

80

96

>99

99

8

2´-Bromoacetophenone

9

2´-Fluoroacetophenone

82

Scheme 4 Selective deprotonation of complex 4b(Br), and

formation of complex 9b

.

10

α-Tetralone

89

a

Reaction conditions, unless otherwise noted: 1 bar of H₂, 2-

Hydrogenation of ketones catalysed by Ir-CNP complexes

methyltetrahydrofuran, S/C/B = 100/1/15, base: KO^tBu, 16 h.

[S] = 0.13 M. Conversion was determined by ¹H NMR

spectroscopy. ^b4 bar of H₂. ^cS/C/B = 250/1/15.

In order to assess the catalytic potential of these Ir-CNP

complexes, their performance in the hydrogenation of ketones

was studied (Table 1).¹⁸In the presence of KO^tBu, complex

4a(Cl) smoothly catalysed the hydrogenation of acetophenone

under 4 bar of H₂at 30 ^oC in 2-methyltetrahydrofuran, using a

S/C/B ratio of 100/1/15 (entry 1). By using the same pressure,

catalyst loading could be decreased to a S/C ratio of 250 after

heating to 60 ^oC (entry 2). Also, at this temperature, a lower H₂

pressure (1 bar) could be employed (entry 3). Under the latter

conditions, complex 4b(Cl) was found to be slightly less active,

whereas a significantly lower catalytic activity was obtained

with the carbonyl derivative 5a(Cl) (entries 4 and 5). Finally,

the hydrogenation of a series of ketones was performed with

complex 4a(Cl). High conversions were obtained in the case of

acetophenone derivatives substituted with p-methoxi, p-

chloro and o-bromo substituents (entries 6-8). Alternatively,

the presence of fluoro substituents seems somewhat

detrimental since 2-fluoroacetophenone was reduced with a

slightly lower yield (entry 9). Also, the hydrogenation of a

Experimental

General procedures

All reactions and manipulations were performed under nitrogen or

argon, either in a Braun Labmaster 100 glovebox or using standard

Schlenk-type techniques. All solvents were distilled under nitrogen

with the following desiccants: sodium-benzophenone-ketyl for

diethyl ether (Et₂O) and tetrahydrofuran (THF); sodium for hexane,

pentane and toluene; CaH₂for dichloromethane (CH₂Cl₂) and

acetonitrile (CH₃CN); and NaOMe for methanol (MeOH). 1-(3,5-

dimethylphenyl)-1H-imidazole and 1-(2,4,6-trimethylphenyl)-1H-

imidazole were prepared as previously described.¹⁹Ir(acac)(cod)²⁰

21

and NaBAr_Fwere synthesized according to literature procedures.

All other reagents were purchased from commercial suppliers and

6 | J. Name., 2012, 00, 1-3

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ARTICLE

used as received. NMR spectra were obtained on Bruker DPX-300, 7.36 (m, 4H, 4 H arom PPh), 7.28 (m, 6H, 6 H arom PPh), 7.12 (s, 1H,

DRX-400, AVANCEIII/ASCEND 400R or DRX-500 spectrometers. H arom Imid), 7.03 (d, ³J_HH= 7.7 Hz, 1H, H arom Py), 7.01 (s, 2H, 2 H

³¹P{¹H} NMR shifts were referenced to external 85% H₃PO₄, while arom Mes), 5.94 (s, 2H, CH₂N), 3.59 (s, 2H, CH₂P), 2.33 (s, 3H, CH₃),

¹³C{¹H} and ¹H shifts were referenced to the residual signals of

2.01 (s, 6H, 2 CH₃). ³¹P{¹H} NMR (202 MHz, CD₂Cl₂):

NMR (126 MHz, CD₂Cl₂): 158.8 (d, J_CP= 8 Hz, C_qarom), 152.7 (C_q

arom), 141.4 (C_qarom), 138.7 (d, J_CP= 3 Hz, CH arom), 138.5 (d, J_CP

δ

−11.7. ¹³C{¹H}

deuterated solvents. All data are reported in ppm downfield from

δ

o

Me₄Si. All NMR measurements were carried out at 25 C, unless

=

otherwise stated. NMR signal assignations were confirmed by 2D

15 Hz, 2 C_qarom), 137.9 (CH arom), 134.7 (2 C_qarom), 133.0 (d, J_CP

= 19 Hz, 4 CH arom), 131.2 (C_qarom), 129.9 (2 CH arom), 129.0 (2

CH arom), 128.7 (d, J_CP= 7 Hz, 4 CH arom), 124.0 (d, J_CP= 5 Hz, CH

arom), 123.9 (CH arom), 122.7 (CH arom), 121.3 (d, J_CP= 2 Hz, CH

arom), 53.7 (CH₂N), 38.3 (d, J_CP= 17 Hz, CH₂P), 21.1 (CH₃), 17.7 (2

CH₃). HRMS (ESI): m/z 476.2243 [(M−Cl)⁺] (exact mass calculated for

C₃₁H₃₁N₃P: 476.2256).

NMR spectroscopy (¹H-¹H COSY, H-¹H NOESY, H-¹³C HSQC and H-

¹³C HMBC). HRMS data were obtained on a JEOL JMS-SX 102A mass

spectrometer at the Instrumental Services of Universidad de Sevilla

(CITIUS). ESI-MS experiments were carried out in a Bruker 6000

apparatus by the Mass Spectrometry Service of the Instituto de

Investigaciones Químicas. Elemental analyses were run by the

Analytical Service of the Instituto de Investigaciones Químicas in a

Leco TrueSpec CHN elemental analyzer. IR spectra were acquired on

a Bruker Tensor 27 instrument.

1

[2-(Diphenylphosphinyl)methyl-6-(3-(3,5-xylyl)imidazolium-1-

yl)methyl]pyridine chloride, 1b(Cl)

A solution of 2,6-bis(chloromethyl)pyridine (3.96 g, 22.5 mmol) and

1-xylyl-1H-imidazole (1.93 g, 11.2 mmol) in THF (20 mL) was heated

to 45 °C for 7 days. The solution was reduced to half the initial

volume by solvent evaporation, and Et₂O (10 mL) was added to

precipitate the product. The solid was filtered, washed with Et₂O (2

x 10 mL) and pentane (3 x 5 mL) and dried under vacuum. [2-

Chloromethyl-6-(3-(3,5-xylyl)imidazolium-1-yl)methyl]pyridine

Synthesis of imidazolium salts 1

Imidazolium salts 1 were synthesised in two steps from the

corresponding 2,6-bis(halomethyl)pyridines and imidazoles as

shown below.

[2-(Diphenylphosphinyl)methyl-6-(3-mesitylimidazolium-1-

yl)methyl]pyridine chloride, 1a(Cl)

1

chloride was isolated as a white solid (2.21 g, 57%). H NMR (400

A solution of 2,6-bis(chloromethyl)pyridine (4.00 g, 22.7 mmol) and

1-mesityl-1H-imidazole (2.12 g, 11.4 mmol) in toluene (80 mL) was

refluxed for 7 days. The precipitate was filtered, washed with cold

THF (2 x 20 mL) and pentane (3 x 20 mL), and dried under vacuum

MHz, CDCl₃):

H arom Py), 8.09 (s, 1H, H arom Imid), 7.89 (dd, J_HH= 8.0 Hz, J_HH

δ

11.09 (s, 1H, H arom Imid), 8.19 (d, ³J_HH= 7.2 Hz, 1H,

3

=

7.2 Hz, 1H, H arom Py), 7.54 (m, 2H, H arom Py + H arom Imid), 7.23

(s, 2H, 2 H arom Xyl), 7.11 (s, 1H, H arom Xyl), 6.10 (s, 2H, CH₂N),

4.69 (s, 2H, CH₂Cl), 2.36 (s, 6H, 2 CH₃). ¹³C{¹H} NMR (101 MHz,

to

yl)methyl]pyridine chloride as a brown solid (2.91 g, 70%). H NMR

(400 MHz, CDCl₃): 10.56 (s, 1H, H arom Imid), 8.13 (s, 1H, H arom

yield

[2-chloromethyl-6-(3-mesitylimidazolium-1-

1

CDCl₃):

δ 156.1 (C_qarom), 151.7 (C_qarom), 140.9 (CH arom), 140.5

δ

(2 C_qarom), 136.4 (CH arom), 134.3 (CH arom), 132.1 (CH arom),

125.2 (CH arom), 124.1 (C_qarom), 123.8 (CH arom), 120.31 (CH

arom), 119.58 (2 CH arom), 52.7 (CH₂N), 45.4 (CH₂Cl), 21.4 (2 CH₃).

HRMS (ESI): m/z 312.1256 [(M−Cl)⁺] (exact mass calculated for

C₁₈H₁₉ClN₃: 312.1268).

3

Imid), 8.06 (d, J_HH= 7.7 Hz, 1H, H arom Py), 7.84 (dd, J_HH= 7.7 Hz,

³J_HH= 7.7 Hz, 1H, H arom Py), 7.48 (d, ³J_HH= 7.7 Hz, 1H, H arom Py),

7.10 (s, 1H, H arom Imid), 6.99 (s, 2H, 2 H arom Mes), 6.24 (s, 2H,

CH₂N), 4.63 (s, 2H, CH₂Cl), 2.33 (s, 3H, CH₃), 2.04 (s, 6H, 2 CH₃).

¹³C{¹H} NMR (125 MHz, CDCl₃):

δ 156.0 (C_qarom), 151.9 (C_qarom),

In a subsequent step, to a solution of Ph₂P(BH₃)H (0.288 g, 1.44

mmol) in THF (10 mL) was added a solution of KO^tBu (0.161 g, 1.44

mmol) in THF (5 mL). The mixture was stirred for 10 min, and added

to a suspension of [2-chloromethyl-6-(3-(3,5-xylyl)imidazolium-1-

yl)methyl]pyridine chloride (0.500 g, 1.44 mmol) in MeCN (10 mL).

The resulting suspension was stirred overnight, and MeOH (10 mL)

was added to quench the reaction. The solvent was evaporated

under vacuum, and the solid was extracted with CH₂Cl₂(3 x 10 mL).

Solvent removal followed by washings with Et₂O (2 x 10 mL) yields a

light orange solid which should correspond to the borane adduct of

1b(Cl). This solid was dissolved in MeOH (10 mL), and the solution

was transferred to a Fisher-Porter vessel and heated to 75 ^oC for 24

h. Volatiles were removed under vacuum, and MeOH (10 mL) was

newly added and the previous procedure repeated. The resulting

solid was washed with toluene (2 x 5 mL) and Et₂O (3 x 5 mL) to give

141.5 (C_qarom), 140.8 (CH arom), 138.9 (CH arom), 134.3 (2 C_q

arom), 130.8 (C_qarom), 130.0 (2 CH arom), 125.1 (CH arom), 124.1

(CH arom), 124.0 (CH arom), 122.8 (CH arom), 52.3 (CH₂N), 45.1

(CH₂Cl), 21.2 (CH₃), 17.7 (2 CH₃). HRMS (ESI): m/z 326.1411

[(M−Cl)⁺] (exact mass calculated for C₁₉H₂₁ClN₃: 326.1424).

In subsequent step, to a solution of PPh₂H (1.08 g, 5.80 mmol)

in THF (10 mL) was added a solution of KO^tBu (0.650 g, 5.80 mmol)

in THF (10 mL). The resulting mixture was stirred for 5 min, and

added to a solution of [2-chloromethyl-6-(3-mesitylimidazolium-1-

yl)methyl]pyridine chloride (2.00 g, 5.52 mmol) in MeCN (40 mL).

The suspension was stirred overnight, and MeOH (15 mL) was

added to quench the reaction. Solvent was evaporated, and the

residue was extracted with CH₂Cl₂(2 x 15 mL). The solid obtained

after removal of the solvent was washed with diethyl ether (3 x 20

mL) and pentane (3 x 20 mL). Imidazolium salt 1a(Cl) was isolated as

an off-white solid (0.444 g, 62%). ¹H NMR (400 MHz, CD₂Cl₂):

δ

a light brown solid (2.40 g, 85%). ¹H NMR (500 MHz, CDCl₃):

δ 10.30

3

11.28 (s, 1H, H arom Imid), 7.74 (d, J_HH= 7.6 Hz, 1H, H arom Py),

(s, 1H, H arom Imid), 7.85 (s, 1H, H arom Imid), 7.60 (d, ³J_HH= 7.5 Hz,

1H, H arom Py), 7.54 (dd, ³J_HH= 7.6 Hz, ³J_HH= 7.6 Hz, 1H, H arom Py),

3

7.64 (dd, J_HH= 7.7 Hz, J_HH= 7.7 Hz, 1H, H arom Py), 7.55 (d, J_HH

=

1.1 Hz, 1H, H arom Imid), 7.44 (m, 4H, 4 H arom), 7.36 (m, 7H, 7 H

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δ δ 159.0 (d, J_CP= 8

−11.7. ¹³C{¹H} NMR (125 MHz, CD₂Cl₂):

arom), 7.29 (s, 2H, 2 H arom Xyl), 7.21 (s, 1H, H arom Xyl), 7.12 (d,

CD₂Cl₂):

Hz, C_qarom), 152.3 (C_qarom), 141.0 (2 C_qarom), 138.4 (d, J_CP= 15

³J_HH= 7.8 Hz, 1H, H arom Py), 5.91 (s, 2H, CH₂N), 3.69 (s, 2H, CH₂P),

2.45 (s, 6H, 2 CH₃). ³¹P{¹H} NMR (121 MHz, CD₂Cl₂):

δ

−11.8. ¹³C{¹H} Hz, 2 C_qarom), 137.9 (CH arom), 135.9 (CH arom), 134.8 (C_qarom),

132.9 (d, J_CP= 19 Hz, 4 CH arom), 131.9 (CH arom), 129.1 (2 CH

arom), 128.7 (d, J_CP= 7 Hz, 4 CH arom), 124.2 (d, J_CP= 5 Hz, CH

arom), 123.9 (CH arom), 121.6 (CH arom), 120.3 (CH arom), 119.7 (2

CH arom), 54.0 (CH₂N), 38.3 (d, J_CP= 16 Hz, CH₂P), 21.3 (2 CH₃).

HRMS (ESI): m/z 462.2089 [(M−Br)⁺] (exact mass calculated for

C₃₀H₂₉N₃P: 462.2099).

NMR (101 MHz, CD₂Cl₂): 159.0 (d, J_CP= 8 Hz, C_qarom), 152.6 (C_q

δ

arom), 141.0 (2 C_qarom), 138.5 (d, J_CP= 15 Hz, 2 C_qarom), 138.0

(CH arom), 136.6 (CH arom), 134.9 (C_qarom), 133.0 (d, J_CP= 19 Hz, 4

CH arom), 131.9 (CH arom), 129.1 (2 CH arom), 128.7 (d, J_CP= 7 Hz,

4 CH arom), 124.2 (d, J_CP= 5 Hz, CH arom), 123.7 (CH arom), 121.8

(CH arom), 120.2 (CH arom), 119.7 (2 CH arom), 54.0 (CH₂N), 38.3

(d, J_CP= 16 Hz, CH₂P), 21.3 (2 CH₃). HRMS (ESI): m/z 462.2082

[(M−Cl)⁺] (exact mass calculated for C₃₀H₂₉N₃P: 462.2094).

Synthesis of Pd-CNP complexes 2a and 3a

Complex 2a. A solution of 1a(Cl) (0.100 g, 0.20 mmol) in CH₂Cl₂

(7 mL) was added Ag₂O (0.049 g, 0.21 mmol). The suspension was

stirred for 24 h, and filtered. To the resulting solution was added

PdCl₂(cod) (0.057 g, 0.20 mmol). After stirring for 4 h, solvent was

removed under vacuum, and the residue was washed with Et₂O (2 ×

5 mL), extracted with CH₂Cl₂(2 × 5 mL), and crystallized from a

CH₂Cl₂/toluene solvent mixture. Pale yellow solid (0.096 g, 60%).

Anal. calcd (%) for C₃₁H₃₀AgCl₃N₃PPd: C 46.8; H 3.8; N 5.3; found: C

[2-(Diphenylphosphinyl)methyl-6-(3-(3,5-xylyl)imidazolium-1-

yl)methyl]pyridine bromide, 1b(Br)

A solution of 1-(3,5-xylyl)-1H-imidazole (1.00 g, 5.81 mmol) in THF

(20 mL) was added to a solution of 2,6-bis(bromomethyl)pyridine

(3.08 g, 11.6 mmol) in THF (20 mL). The solution was stirred for 7

days at room temperature. The resulting precipitate was filtered,

washed with cold THF (2 x 10 mL) and hexane (2 x 10 mL), and dried

1

3

to

give

[2-bromomethyl-6-(3-(3,5-xylyl)imidazolium-1- 47.2; H 3.7; N 4.8. H NMR (500 MHz, CD₂Cl₂): δ 8.30 (d, J_HH= 7.6

yl)methyl]pyridine bromide as a light brown solid (2.00 g, 79%). H Hz, 1H, H arom Py), 8.21 (s, 1H, H arom NHC), 8.05 (dd, ³J_HH= 7.5 Hz,

1

3

³J_HH= 7.5 Hz, 1H, H arom Py), 7.92 (d, J_HH= 7.6 Hz, 1H, H arom Py),

NMR (500 MHz, CD₂Cl₂):

δ

10.86 (s, 1H, H arom Imid), 7.98 (s, 1H, H

7.73 (dd, ³J_HP= 12.1 Hz, ³J_HH= 8.1 Hz, 4H, 4 H arom PPh), 7.58 (t, ³J_HH

= 7.5 Hz, 2H, 2 H arom PPh), 7.50 (m, 4H, 4 H arom PPh₂), 7.03 (s,

2H, 2 H arom Mes), 6.95 (s, 1H, H arom NHC), 6.05 (s, 2H, CH₂N),

3

arom Imid), 7.80 (d, J_HH= 7.6 Hz, 1H, H arom Py), 7.75 (s, 1H, H

3

arom Imid), 7.72 (dd, J_HH= 7.7 Hz, J_HH= 7.6 Hz, 1H, H arom Py),

3

7.42 (d, J_HH= 7.6 Hz, 1H, H arom Py), 7.34 (s, 2H, 2 H arom Xyl),

2

4.32 (d, J_HP= 11.3 Hz, 2H, CH₂P), 2.39 (s, 3H, CH₃), 2.17 (s, 6H, 2

7.12 (s, 1H, H arom Xyl), 5.98 (s, 2H, CH₂N), 4.51 (s, 2H, CH₂Br), 2.36

CH₃). ³¹P{¹H} NMR (121 MHz, CD₂Cl₂):

δ

34.8. ¹³C{¹H} NMR (126

(s, 6H, 2 CH₃). ¹³C{¹H} NMR (125 MHz, CD₂Cl₂):

δ

157.4 (C_qarom),

152.9 (C_qarom), 141.0 (2 C_qarom), 138.9 (CH arom), 136.1 (CH MHz, CD₂Cl₂):

δ

166.4 (d, J_CP= 183 Hz, C-2 NHC), 161.9 (d, J_CP= 7 Hz,

arom), 134.7 (C_qarom), 132.0 (CH arom), 124.0 (CH arom), 123.9 C_qarom), 155.1 (C_qarom), 142.1 (CH arom), 139.6 (C_qarom), 135.8

(CH arom), 123.6 (CH arom), 120.7 (CH arom), 119.7 (2 CH arom), (C_qarom), 135.5 (2 C_qarom), 133.3 (d, J_CP= 11 Hz, 4 CH arom),

53.9 (CH₂N), 34.0 (CH₂Br), 21.2 (2 CH₃). HRMS (ESI): m/z 356.0751 132.7 (2 CH arom), 129.7 (d, J_CP= 12 Hz, 4 CH arom), 129.0 (2 CH

[(M−Br)⁺] (exact mass calculated for C₁₈H₁₉BrN₃: 356.0757).

arom), 126.6 (d, J_CP= 46 Hz, 2 C_qarom), 126.4 (CH arom), 125.4 (d,

In a subsequent step, to a solution of Ph₂P(BH₃)H (0.483 g, 2.42 J_CP= 10 Hz, CH arom), 124.0 (d, J_CP= 5 Hz, CH arom), 123.4 (d, J_CP= 5

mmol) in THF (10 mL) was added a solution of KO^tBu (0.271 g, 2.42 Hz, CH arom), 55.2 (CH₂N), 41.7 (d, J_CP= 28 Hz, CH₂P), 21.3 (CH₃),

mmol) in THF (10 mL). The resulting mixture was stirred for 10 min, 18.6 (2 CH₃). MS (ESI, CH₂Cl₂): m/z (%): 616 (100) [(M−AgCl₂)⁺].

and added to

a

solution of [2-bromomethyl-6-(3-(3,5-

Complex 3a. To a suspension of 2a (0.025 g, 0.04 mmol) in THF

xylyl)imidazolium-1-yl)methyl]pyridine bromide (1.01 g, 2.39 mmol) (2 mL) was added KHMDS (0.007 g, 0.04 mmol). The mixture was

in MeCN (20 mL). The suspension was stirred overnight, and MeOH stirred for 30 min, and solvent was evaporated under reduced

(15 mL) was added to quench the reaction. The solvent was pressure. The residue was washed with Et₂O (2 x 2 mL) and

evaporated under vacuum, and the resulting solid was extracted extracted with THF (2 x 2 mL). Solvent removal under vacuum

with CH₂Cl₂(3 x 10 mL). Solvent removal followed by washings with provides complex 3a as an orange solid (0.020 g, 85%). An analytical

Et₂O (2 x 10 mL) yields a light orange solid which should correspond pure sample of 3a could not be obtained due to significant

to the borane adduct of 1b(Br). This solid was dissolved in MeOH decomposition of the complex during purification.

(10 mL), and the solution was transferred to a Fisher-Porter vessel

and heated to 75 ^oC for 24 h. Volatiles were removed under

vacuum, and MeOH was newly added and the previous procedure

was repeated. The resulting solid was washed with toluene (10 mL)

1

and Et₂O (10 mL) to give an off-white solid (0.693 g, 55% yield). H

NMR (500 MHz, CD₂Cl₂):

δ

10.77 (s, 1H, H arom Imid), 7.65 (d, ³J_HH

=

¹H NMR (400 MHz, THF-d₈):

δ 7.71 (m, 4H, 4 H arom PPh₂), 7.44 (s,

7.6 Hz, 1H, H arom Py), 7.61 (t, ³J_HH= 1.2 Hz, 1H, H arom Imid), 7.56 1H, H arom NHC), 7.22 (m, 6H, 6 H arom PPh₂), 6.98 (s, 1H, H arom

(m, 2H, H arom Py + H arom Imid), 7.38 (m, 4H, 4 H arom PPh), 7.32 NHC), 6.87 (s, 2H, 2 H arom Mes), 6.46 (ddd, ³J_HH= 8.9 Hz, ³J_HH= 6.4

(s, 2H, 2 H arom Xyl), 7.29 (m, 6H, 6 H arom PPh), 7.13 (s, 1H, H Hz, ⁵J_HP= 2.8 Hz, 1H, H^c), 6.30 (d, ³J_HH= 8.7 Hz, 1H, H^b), 5.55 (d, ³J_HH

3

arom Xyl), 7.07 (d, J_HH= 7.6 Hz, 1H, H arom Py), 5.84 (s, 2H, CH₂N), = 6.3 Hz,1H, H^d), 4.87 (s, 2H, CH₂N), 3.41 (s, 1H, H^a), 2.30 (s, 3H,

3.62 (s, 2H, CH₂P), 2.37 (s, 6H, 2 CH₃). ³¹P{¹H} NMR (202 MHz,

CH₃), 2.08 (s, 6H, 2 CH₃). ³¹P{¹H} NMR (162 MHz, THF-d₈):

δ 25.3.

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2

3

¹³C{¹H} NMR (126 MHz, THF-d₈):

δ 175.1 (d, J_CP= 166 Hz, C-2 NHC),

arom Py), 7.20 (d, J_HH= 12.0 Hz, 1H, NCHH), 7.05 (td, J_HH= 7.6 Hz,

⁵J_HP= 1.2, 1H, H arom PPh), 6.84 (d, ³J_HH= 4.0 Hz, 1H, H arom NHC),

6.83 (s, 1H, H arom Xyl), 6.76 (m, 2H, 2 H arom PPh), 6.53 (s, 2H, 2 H

arom Xyl), 5.59 (d, ²J_HH= 12.0 Hz, 1H, NCHH), 5.43 (dd, ³J_HH= 7.7 Hz,

³J_HH= 7.7 Hz, 2H, 2 H arom PPh), 4.19 (dd, ²J_HH= 15.6 Hz, ²J_HP= 11.6,

174.8 (d, J_CP= 26 Hz, C_qarom), 150.0 (C_qarom), 138.7 (C_qarom),

137.9 (C_qarom), 137.4 (d, J_CP= 8 Hz, 2 C_qarom), 136.2 (2 C_qarom),

133.3 (d, J_CP= 11 Hz, 4 CH arom), 132.7 (C^c), 129.6 (2 CH arom),

129.0 (2 CH arom), 128.2 (d, J_CP= 11 Hz, 4 CH arom), 123.4 (d, J_CP= 5

Hz, CH arom), 121.2 (d, J_CP= 4 Hz, CH arom), 117.0 (d, J_CP= 21 Hz,

C^b), 102.9 (C^d), 63.3 (d, J_CP= 66 Hz, C^a), 56.9 (CH₂N), 21.2 (CH₃), 18.6

(2 CH₃).

2

1H, PCHH), 3.46 (br, 2H, 2 CH= COD), 3.35 (dd, J_HH= 15.6 Hz, J_HP

=

3.2 Hz, 1H, PCHH), 2.96 (br, 2H, 2 CH= COD), 2.32 (m, 4H, 4 CHH

COD), 2.12 (s, 6H, 2 CH₃), 1.94 (m, 2H, 2 CHH COD), 1.39 (m, 2H, 2

CHH COD). ³¹P{¹H} NMR (162 MHz, CD₂Cl₂):

δ

19.9. ¹³C{¹H} NMR

Synthesis of Ir-CNP complexes 4-9

(126 MHz, CD₂Cl₂): 164.5 (d, J_CP= 8 Hz, C-2 NHC), 160.3 (d, J_CP= 4.0

δ

Complex 4a(Cl). A solution of 1a(Cl) (0.769 g, 1.50 mmol) in

CH₂Cl₂(8 mL) was added to a solution of Ir(acac)(cod) (0.600 g, 1.50

mmol) in CH₂Cl₂(8 mL). The resulting solution was stirred overnight.

Solvent was evaporated, and the solid was recrystallized from cold

THF. The obtained solid was washed with Et₂O (2 x 10 mL) and

Hz, C_qarom), 159.0 (d, J_CP= 6 Hz, C_qarom), 139.5 (2 C_qarom), 139.2

(C_qarom), 138.4 (CH arom), 135.2 (d, J_CP= 25 Hz, C_qarom), 134.4 (d,

J_CP= 13 Hz, 2 CH arom), 131.8 (d, J_CP= 2 Hz, CH arom), 129.6 (CH

arom), 129.4 (m, 3 CH arom), 129.2 (d, J_CP= 10 Hz, 2 CH arom),

129.0 (d, J_CP= 8 Hz, 2 CH arom), 128.5 (d, J_CP= 47 Hz, C_qarom),

124.6 (d, J_CP= 4 Hz, CH arom), 124.1 (CH arom), 123.4 (d, J_CP= 2 Hz,

pentane (2 x 10 mL). Yellow solid (0.682 g, 56%). ¹H NMR (400 MHz,

3

CD₂Cl₂):

δ

8.46 (s, 1H, H arom NHC), 8.33 (d, J_HH= 7.5 Hz, 1H, H CH arom), 122.1 (2 CH arom), 121.8 (CH arom), 66.1 (br, 4 CH=

arom Py), 7.88 (dd, ³J_HH= 7.5 Hz, ³J_HH= 7.5 Hz, 1H, H arom Py), 7.79 COD), 59.1 (NCH₂), 44.7 (d, J_CP= 27 Hz, PCH₂), 38.4 (d, J_CP= 6 Hz, 2

(dd, ³J_HP= 8.5 Hz, ³J_HH= 8.5 Hz, 2H, 2 H arom PPh), 7.62 (m, 3H, 3 H CH₂COD), 28.3 (2 CH₂COD), 21.3 (2 CH₃).

arom), 7.38 (d, ³J_HH= 7.5 Hz, 1H, H arom Py), 7.12 (d, ²J_HH= 14.0 Hz,

Complex 4b(Br). A solution of Ir(acac)(cod) (0.368 g, 0.92 mmol)

3

1H, NCHH), 7.08 (t, J_HH= 7.5 Hz, 1H, H arom), 6.89 (m, 3H, 3 H in CH₂Cl₂was added a solution of 1b(Br) (0.500 g, 0.92 mmol) in

arom), 6.75 (s, 1H, H arom), 6.65 (s, 1H, 1H, H arom NHC), 5.87 (dd, CH₂Cl₂, and the solution was stirred overnight. Solvent was

³J_HP= 8.0 Hz, ³J_HH= 8.0 Hz, 2H, 2 H arom PPh), 5.56 (d, ²J_HH= 14.0 Hz, evaporated, and the residue was extracted with CH₃CN (5 mL). The

2

1H, NCHH), 3.97 (dd, J_HH= 14.8 Hz, J_HP= 11.5 Hz, 1H, PCHH), 3.45 solution was brought to dryness, and the resulting solid was washed

(m, 3H, 2 CH= COD + PCHH), 2.93 (br, 2H, 2 CH= COD), 2.31 (s, 3H, with toluene (7 mL) and Et₂O (7 mL) and dried. Pale orange solid

CH₃), 2.05 (br, 4H, 4 CHH COD), 1.75 (s, 3H, CH₃), 1.71 (br, 2H, 2 CHH (0.238 g, 31%). Anal. calcd (%) for C₃₈H₄₀BrIrN₃P: C 54.2, H 4.8, N

COD), 1.28 (br, 2H, 2 CHH COD), 0.98 (s, 3H, CH₃). ³¹P{¹H} NMR (162

MHz, CD₂Cl₂): 164.4 (d, J_CP(d, J_HH= 7.7 Hz, 1H, H arom Py), 8.26 (d, J_HH= 1.5 Hz, 1H, H arom

16.9. ¹³C{¹H} NMR (126 MHz, CD₂Cl₂):

5.00; found: C 54.4, H 5.05, N 4.7. ¹H NMR (400 MHz, CD₂Cl₂):

δ 8.28

3

δ

= 8 Hz, C-2 NHC), 160.1 (d, J_CP= 4 Hz, C_qarom), 158.5 (d, J_CP= 6 Hz, NHC), 7.92 (dd, ³J_HH= 7.7 Hz, ³J_HH= 7.7 Hz, 1H, H arom Py), 7.83 (dd,

C_qarom), 139.5 (CH arom + C_qarom), 137.7 (C_qarom), 136.8 (d, J_CP³J_HP= 8.9 Hz, ³J_HH= 8.9 Hz, 2H, 2 H arom PPh), 7.64 (m, 3H, 3 H arom

= 18 Hz, C_qarom), 135.9 (C_qarom), 135.3 (C_qarom), 134.0 (CH PPh), 7.49 (d, ³J_HH= 7.8 Hz, 1H, H arom Py), 7.09 (t, ³J_HH= 7.5 Hz, 1H,

2

3

arom), 133.8 (CH arom), 131.6 (d, J_CP= 2 Hz, CH arom), 130.3 (d, J_CPH arom PPh), 6.91 (d, J_HH= 14.1 Hz, 1H, NCHH), 6.88 (d, J_HH= 1.5

3

= 10 Hz, 2 CH arom), 130.1 (d, J_CP= 2 Hz, CH arom), 130.1 (d, J_CP= 39 Hz, 1H, H arom NHC), 6.85 (s, 1H, H arom Xyl), 6.79 (dd, J_HH= 6.6

Hz, C_qarom), 129.3 (d, J_CP= 10 Hz, 2 CH arom), 129.2 (d, J_CP= 8 Hz, 2 Hz, ³J_HH= 6.6 Hz, 2H, 2 H arom PPh), 6.53 (s, 2H, 2 H arom Xyl), 5.65

2

3

CH arom), 128.8 (d, J_CP= 10 Hz, 2 CH arom), 125.0 (d, J_CP= 5 Hz, CH (d, J_HH= 14.1 Hz, 1H, NCHH), 5.45 (dd, J_HH= 8.4 Hz, J_HH= 8.4 Hz,

2

arom), 124.7 (CH arom), 124.3 (CH arom), 123.6 (d, J_CP= 2 Hz, CH 2H, 2 H arom PPh), 4.17 (dd, J_HH= 15.5 Hz, J_HP= 11.6 Hz, 1H,

arom), 63.5 (br, 4 CH= COD), 59.5 (NCH₂), 44.3 (d, J_CP= 29 Hz, PCH₂), PCHH), 3.49 (br, 2H, 2 CH= COD), 3.36 (dd, J_HH= 15.7 Hz, ²J_HP= 2.1

2

37.7 (d, J_CP= 6 Hz, 2 CH₂COD), 28.8 (br, 2 CH₂COD), 21.0 (CH₃), 18.0 Hz, 1H, PCHH), 2.98 (br, 2H, 2 CH= COD), 2.35 (br, 4H, 2 CH₂COD),

(CH₃), 17.5 (CH₃). MS (ESI, CH₂Cl₂): m/z (%): 776 (100) [(M–Cl)⁺] 2.14 (s, 6H, 2 CH₃), 1.92 (br, 2H, CH₂COD), 1.42 (br, 2H, CH₂COD).

(fragmentation of ion m/z 776: 666 (100) [(M–HCl–C₈H₁₂)⁺]). HRMS

(ESI): m/z 776.2740 [(M−Cl)⁺] (exact mass calculated for C₃₉H₄₂N₃IrP:

776.2746).

³¹P{¹H} NMR (162 MHz, CD₂Cl₂):

δ

20.0. ¹³C{¹H} NMR (101 MHz,

CD₂Cl₂): 164.8 (d, J_CP= 8 Hz, C-2 NHC), 160.4 (d, J_CP= 3 Hz, C_q

δ

arom), 158.8 (d, J_CP= 6 Hz, C_qarom), 139.6 (CH arom), 139.2 (C_q

arom), 138.5 (2 C_qarom), 135.3 (d, J_CP= 25 Hz, C_qarom), 134.5 (d,

J_CP= 13 Hz, 2 CH arom), 131.9 (CH arom), 129.8 (CH arom), 129.7

(CH arom), 129.5 (d, J_CP= 9 Hz, 2 CH arom), 129.3 (d, J_CP= 10 Hz, 2

CH arom), 129.1 (d, J_CP= 8 Hz, 2 CH arom), 128.6 (d, J_CP= 43 Hz, C_q

arom), 124.7 (d, J_CP= 4 Hz, CH arom), 123.8 (CH arom), 123.4 (CH

arom), 122.3 (2 CH arom), 122.2 (CH arom), 66.0 (br, 4 CH= COD),

59.4 (CH₂N), 44.7 (d, J_CP= 28 Hz, CH₂P), 38.5 (d, J_CP= 6 Hz, 2 CH₂

COD), 28.4 (2 CH₂COD), 21.4 (2 CH₃). MS (ESI, CH₂Cl₂): m/z (%): 762

(100) [(M–Br)⁺] (fragmentation of ion m/z 762: 654 (100) [(M–Br–

C₈H₁₂)⁺]).

Complex 4b(Cl). To a solution of Ir(acac)(cod) (0.269 g, 0.67

mmol) in CH₂Cl₂(5 mL) was added 1b(Cl) (0.335 g, 0.67 mmol) in

CH₂Cl₂(8 mL), and the reaction mixture was stirred for 4 h. After

solvent evaporation, the solid was extracted with CH₃CN (5 mL). The

solvent was removed in vacuo, and the resulting solid was washed

with toluene (3 x 3 mL) and Et₂O (3 x 5 mL), and dried. Orange-

yellow solid (0.412 g, 77%). Anal. calcd (%) for C₃₈H₄₀ClIrN₃P·CH₂Cl₂:

C 53.1, H 4.8, N 4.8; found: C 53.4, H 5.0, N 4.75. ¹H NMR (400 MHz,

CD₂Cl₂):

Hz, 1H, H arom Py), 7.90 (dd, ³J_HH= 8.0 Hz, ³J_HH= 8.0 Hz, 1H, H arom

δ

8.42 (d, ³J_HH= 4.0 Hz, 1H, H arom NHC), 8.32 (d, ³J_HH= 8.0

3

4

Py), 7.83 (ddd, J_HP= 10.4 Hz, J_HH= 8.0 Hz, J_HH= 1.6 Hz, 2H, 2 H

arom PPh), 7.63 (m, 3H, 3 H arom PPh), 7.51 (d, ³J_HH= 8.0 Hz, 1H, H

Complex 4b(BAr_F). A solution of 4b(Br) (0.100 g, 0.12 mmol) in

CH₂Cl₂(5 mL) was added to a solution of NaBAr_F(0.105 g, 0.12

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mmol) in CH₂Cl₂(5 mL). The resulting suspension was stirred for 4 h. (d, J_CP= 3 Hz, CH arom), 122.0 (d, J_CP= 3 Hz, CH arom), 54.6 (CH₂N),

The precipitate was filtered off, and the solvent was removed under 42.7 (d, J_CP= 31 Hz, CH₂P), 21.2 (CH₃), 18.5 (2 CH₃).

vacuum to yield the complex as an orange solid (0.164 g, 85%).

Complex 6a(Cl). In a J. Young valved NMR tube, a solution of

Crystals of complex 4b(BAr_F) suitable for X-ray diffraction analysis 5a(Cl) (0.011 g, 0.01 mmol) in CD₂Cl₂(0.7 mL) was pressurised with

were grown by layering pentane over a CH₂Cl₂solution. Anal. calcd 1 bar of CO. The solution was analyzed by NMR spectroscopy. IR

1

(CH₂Cl₂): 1946, 2021 cm^-1(ν_CO). H NMR (400 MHz, CD₂Cl₂):

δ 8.57

(%) for C₇₀H₅₂BF₂₄IrN₃P: C 51.7, H 3.2, N 2.6; found: C 51.6, H 3.25, N

1

3

2.5. H NMR (500 MHz, CD₂Cl₂):

δ

7.86 (dd, J_HH= 7.6 Hz, J_HH= 7.6 (d, ³J_HH= 0.8 Hz, 1H, H arom NHC), 8.41 (d, ³J_HH= 7.5 Hz, 1H, H arom

3

Hz, 1H, H arom Py), 7.81 (dd, J_HH= 8.5 Hz, J_HP= 6.7 Hz, 2H, 2 H Py), 7.98 (dd, J_HH= 7.6 Hz, J_HH= 7.6 Hz, 1H, H arom Py), 7.74 (d,

arom PPh), 7.76 (s, 8H, 8 H arom BAr_F), 7.66 (m, 4H, 3 H arom PPh + ³J_HH= 7.7 Hz, 1H, H arom Py), 7.47 (m, 10H, 10 H arom PPh), 7.01 (d,

H arom Py), 7.58 (s, 4H, 4 H arom BAr_F), 7.48 (d, ³J_HH= 7.7 Hz, 1H, H ³J_HH= 0.8 Hz, 1H, H arom NHC), 6.98 (s, 2H, 2 H arom Mes), 6.09 (s,

3

2

arom Py), 7.33 (d, J_HH= 2.0 Hz, 1H, H arom NHC), 7.11 (t, J_HH= 7.5 2H, CH₂N), 4.29 (d, J_HP= 10.9 Hz, 2H, CH₂P), 2.32 (s, 3H, CH₃), 2.03

3

(s, 6H, 2 CH₃). ³¹P{¹H} NMR (162 MHz, CD₂Cl₂):

δ

26.8. ¹³C{¹H} NMR

Hz, 1H, H arom PPh), 6.95 (d, J_HH= 2.0 Hz, 1H, H arom NHC), 6.93

3

4

(s, 1H, H arom Xyl), 6.82 (ddd, J_HH= 8.1 Hz, J_HH= 8.1 Hz, J_HP= 1.9

Hz, 2H, 2 H arom PPh), 6.49 (s, 2H, 2 H arom Xyl), 5.86 (d, ²J_HH= 14.2

(126 MHz, CD₂Cl₂): 177.4 (CO), 161.5 (C_qarom), 161.3 (d, J_CP= 94

δ

Hz, C-2 NHC), 155.1 (C_qarom), 140.5 (CH arom), 140.2 (C_qarom),

136.1 (2 C_qarom), 135.7 (C_qarom), 132.5 (d, J_CP= 12 Hz, 4 CH

arom), 131.1 (2 CH arom), 129.5 (d, J_CP= 11 Hz, 4 CH arom), 129.4

(d, J_CP= 55 Hz, 2 C_qarom), 129.4 (2 CH arom), 125.2 (CH arom),

124.4 (CH arom), 124.0 (d, J_CP= 9 Hz, CH arom), 122.8 (CH arom),

56.7 (CH₂N), 44.9 (d, J_CP= 37 Hz, CH₂P), 21.2 (CH₃), 18.1 (2 CH₃).

Complex 7a(Cl). In a Fisher-Porter vessel, a solution of 4a(Cl)

3

Hz, 1H, NCHH), 5.48 (dd, J_HH= 8.7 Hz, J_HP= 8.7 Hz, 2H, 2 H arom

PPh), 5.44 (d, ²J_HH= 14.2 Hz, 1H, NCHH), 4.16 (dd, ²J_HH= 15.6 Hz, ²J_HP

= 11.3 Hz, 1H, PCHH), 3.55 (br, 2H, 2 CH= COD), 3.39 (dd, ²J_HH= 15.6

Hz, ²J_PH= 3.0 Hz, 1H, PCHH), 3.02 (br, 2H, 2 CH= COD), 2.39 (m, 4H, 4

CHH COD), 2.16 (s, 6H, 2 CH₃), 1.95 (m, 2H, 2 CHH COD), 1.49 (m,

2H, 2 CHH COD). ³¹P{¹H} NMR (202 MHz, CD₂Cl₂):

δ

20.3. ¹³C{¹H}

NMR (125 MHz, CD₂Cl₂):

δ

166.1 (d, J_CP= 8 Hz, C-2 NHC), 162.2 (q, (0.120 g, 0.15 mmol) in CH₂Cl₂(8 mL) was pressurised with 2 bar of

J_CB= 50 Hz, 4 BC_qarom BAr_F), 161.5 (d, J_CP= 3 Hz, C_qarom), 157.5 (d, H₂and stirred overnight. The system was depressurised, solvent

J_CP= 6 Hz, C_qarom), 139.7 (CH arom), 139.0 (d, J_CP= 10 Hz, C_qwas evaporated and the residue was washed with Et₂O (2 x 10 mL)

arom), 139.0 (2 C_qarom), 135.3 (m, 8 CH arom BAr_F), 135.1 and pentane (2 x 10 mL). Yellow solid (0.083 g, 80%). Crystals of

(overlapped, C_qarom), 134.5 (d, J_CP= 14 Hz, 2 CH arom), 132.2 (d, complex 7a(Cl) suitable for X-ray diffraction analysis were grown by

J_CP= 2 Hz, CH arom), 130.5 (CH arom), 130.1 (d, J_CP= 2 Hz, CH layering hexane over a CH₂Cl₂solution. Anal. calcd (%) for

1

arom), 129.7 (d, J_CP= 10 Hz, 2 CH arom), 129.5 (d, J_CP= 10 Hz, 2 CH C₃₁H₃₂ClIrN₃P: C 52.8, H 4.6, N 5.9; found: C 52.9, H 4.7, N 5.4. H

NMR (400 MHz, CD₂Cl₂): δ

7.79 (dd, ³J_HH= 7.8 Hz, ³J_HH= 7.8 Hz, 1H, H

arom), 129.3 (d, J_CP= 8 Hz, 2 CH arom), 129.3 (q, J_CF= 32 Hz, 8 C_q

3

arom Py), 7.73 (dd, J_HP= 10.6 Hz, ³J_HH= 7.9 Hz, 2H, 2 H arom PPh),

arom BAr_F), 128.2 (d, J_CP= 38 Hz, C_qarom), 125.3 (d, J_CP= 5 Hz, CH

arom), 124.8 (q, J_CF= 272 Hz, 8 CF₃), 123.4 (CH arom), 122.6 (2 CH

arom), 122.2 (CH arom), 122.0 (CH arom), 117.9 (m, 4 CH arom

BAr_F), 66.2 (br, 4 CH= COD), 60.7 (NCH₂), 44.7 (d, J_CP= 28 Hz, PCH₂),

38.3 (d, J_CP= 6 Hz, 2 CH₂COD), 28.6 (2 CH₂COD), 21.4 (2 CH₃). MS

(ESI, CH₂Cl₂): m/z (%): 762 (100) [(M–C₃₂H₁₂BF₂₄)⁺] (fragmentation of

ion m/z 762: 654 (100) [(M–C₃₂H₁₂BF₂₄–C₈H₁₂)⁺]).

3

7.57 (d, J_HH= 7.8 Hz, 1H, H arom Py), 7.40 (m, 6H, 6 H arom), 7.33

(m, 4H, 4 H arom), 7.09 (s, 1H, H arom NHC), 7.02 (s, 1H, H arom

2

Mes), 6.97 (s, 1H, H arom Mes), 6.70 (d, J_HH= 14.6 Hz, 1H, NCHH),

2

4.96 (d, J_HH= 14.6 Hz, 1H, NCHH), 4.41 (dd, J_HH= 16.3 Hz, J_HP

=

2

10.4 Hz, 1H, PCHH), 3.38 (dd, J_HH= 16.3 Hz, J_PH= 9.5 Hz, 1H,

PCHH), 2.40 (s, 3H, CH₃), 2.20 (s, 3H, CH₃), 1.92 (s, 3H, CH₃), –20.19

(dd, ²J_HP= 13.8 Hz, ²J_HH= 7.0 Hz, 1H, IrH trans to Py), –23.30 (dd, ²J_HP

Complex 5a(Cl). A solution of 4a(Cl) (0.080 g, 0.10 mmol) in

CH₂Cl₂(10 mL) was bubbled with CO for 5 min, and the solvent was

evaporated. The resulting solid was washed with Et₂O (2 x 10 mL)

and pentane (2 x 10 mL), and crystallized from THF. Orange solid

(0.048 g, 70%). Anal. calcd (%) for C₃₂H₃₀ClIrN₃OP: C 52.6, H 4.1, N

2

= 18.9 Hz, J_HH= 7.0 Hz, 1H, IrH cis to Py). ³¹P{¹H} NMR (162 MHz,

CD₂Cl₂): δ δ 172.9 (d, J_CP= 119

26.8. ¹³C{¹H} NMR (101 MHz, CD₂Cl₂):

Hz, C-2 NHC), 164.8 (d, J_CP= 6 Hz, C_qarom), 156.1 (C_qarom), 138.6

(C_qarom), 138.2 (C_qarom), 136.9 (C_qarom), 136.5 (CH arom), 135.7

(d, J_CP= 50 Hz, C_qarom), 135.4 (C_qarom), 134.7 (d, J_CP= 13 Hz, 2 CH

arom), 132.4 (d, J_CP= 11 Hz, 2 CH arom), 130.5 (d, J_CP= 2 Hz, CH

1

5.75; found: C 52.2, H 4.6, N 5.5. IR (CH₂Cl₂): 1985 cm^-1(ν_CO). H

3

NMR (300 MHz, CD₂Cl₂):

δ

8.41 (s, 1H, H arom NHC), 8.28 (d, J_HH

=

3

7.5 Hz, 1H, H arom Py), 7.97 (dd, J_HH= 7.6 Hz, J_HH= 7.6 Hz, 1H, H arom), 129.5 (CH arom), 129.2 (CH arom), 128.6 (CH arom), 128.3

3

arom Py), 7.77 (d, J_HH= 7.7 Hz, 1H, H arom Py), 7.61 (ddd, J_HP

=

(d, J_CP= 10 Hz, 2 CH arom), 128.0 (d, J_CP= 9 Hz, 2 CH arom), 122.7

11.8 Hz, ³J_HH= 7.7 Hz, ⁴J_HH= 0.6 Hz, 4H, 4 H arom PPh), 7.46 (m, 6H, (CH arom), 122.3 (d, J_CP= 9 Hz, CH arom), 121.2 (d, J_CP= 4 Hz, CH

6 H arom PPh), 7.02 (m, 3H, 2 H arom Mes + H arom NHC), 6.11 (s, arom), 120.4 (d, J_CP= 4 Hz, CH arom), 56.7 (CH₂N), 47.1 (d, J_CP= 33

2

2H, CH₂N), 4.18 (d, J_HP= 10.0 Hz, 2H, CH₂P), 2.34 (s, 3H, CH₃), 2.12 Hz, CH₂P), 21.3 (CH₃), 18.9 (CH₃), 18.5 (CH₃). Signals for one

(s, 6H, 2 CH₃). ³¹P{¹H} NMR (162 MHz, CD₂Cl₂):

δ

45.7. ¹³C{¹H} NMR

quaternary aromatic carbon could not be identified.

Complex 7b(Cl). In a Fisher-Porter vessel, a solution of 4b(Cl)

(126 MHz, CD₂Cl₂): 178.1 (d, J_CP= 99 Hz, C-2 NHC), 177.2 (d, J_CP

δ

=

(0.100 g, 0.12 mmol) in CH₂Cl₂(5 mL) was pressurised with 5 bar of

10 Hz, CO), 164.7 (d, J_CP= 7 Hz, C_qarom), 156.5 (C_qarom), 141.4 (CH

arom), 140.1 (C_qarom), 136.3 (2 C_qarom), 135.7 (C_qarom), 133.2

(d, J_CP= 12 Hz, 4 CH arom), 131.9 (d, J_CP= 2 Hz, 2 CH arom), 130.3 (d,

J_CP= 53 Hz, 2 C_qarom), 129.4 (d, J_CP= 11 Hz, 4 CH arom), 129.2 (2

CH arom), 125.4 (CH arom), 124.4 (d, J_CP= 10 Hz, CH arom), 123.6

o

H₂and heated to 50 C. After 16 h, the system was cooled to room

temperature and depressurised. The solvent was evaporated and

the residue was washed with Et₂O (3 x 3 mL) and pentane (3 x 3

1

mL). Pale yellow solid (0.073 g, 85%). H NMR (400 MHz, CD₂Cl₂):

δ

10 | J. Name., 2012, 00, 1-3

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7.85 (m, 2H, 2 H arom PPh), 7.74 (dd, ³J_HH= 8.0 Hz, ³J_HH= 8.0 Hz, 1H, broadening. Cis coordination of the phosphine and NHC fragments

H arom Py), 7.56 (d, ³J_HH= 8.0 Hz, 1H, H arom Py), 7.47 (m, 4H, 4 H of the CNP ligand is proposed on the basis of the following NOE

arom), 7.36 (m, 4H, 4 H arom), 7.29 (m, 3H, 3 H arom), 7.24 (d, ³J_HHcontacts:

= 1.5 Hz, 1H, H arom NHC), 7.18 (m, 1H, H arom), 7.11 (s, 1H, H

arom), 6.53 (d, ²J_HH= 14.4 Hz, 1H, NCHH), 4.96 (d, ²J_HH= 14.8 Hz, 1H,

2

NCHH), 4.49 (dd, J_HH= 16.4 Hz, J_HP= 10.4 Hz, 1H, CHHP), 3.54 (dd,

²J_HH= 16.6 Hz, ²J_HP= 10.0 Hz, 1H, CHHP), 2.44 (s, 6H, 2 CH₃), –19.73

(dd, ²J_HP= 16.6 Hz, ²J_HH= 7.2 Hz, 1H, IrH trans to Py), –23.24 (dd, ²J_HP

2

= 18.8 Hz, J_HH= 7.2 Hz, 1H, IrH cis to Py). ³¹P{¹H} NMR (162 MHz,

CD₂Cl₂): δ δ 172.4 (d, J_CP= 122

27.7. ¹³C{¹H} NMR (101 MHz, CD₂Cl₂):

Complex 9b. In a J. Young valved NMR tube, a suspension of

Hz, C-2 NHC), 164.9 (d, J_CP= 5 Hz, C_qarom), 155.8 (C_qarom), 141.9

(C_qarom), 138.5 (2 C_qarom), 136.8 (2 CH arom), 136.3 (d, J_CP= 52

Hz, C_qarom), 134.6 (d, J_CP= 12 Hz, 2 CH arom), 134.2 (d, J_CP= 38 Hz,

C_qarom), 132.9 (d, J_CP= 11 Hz, 2 CH arom), 130.7 (d, J_CP= 2 Hz, CH

arom), 129.8 (d, J_CP= 1 Hz, CH arom), 128.6 (d, J_CP= 10 Hz, 2 CH

arom), 128.2 (d, J_CP= 9 Hz, 2 CH arom), 125.7 (2 CH arom), 122.7

(CH arom), 122.6 (d, J_CP= 9.0 Hz, CH arom), 121.5 (d, J_CP= 4 Hz, CH

arom), 121.4 (d, J_CP= 5 Hz, CH arom), 57.1 (CH₂N), 46.3 (d, J_CP= 32

Hz, CH₂P), 21.6 (2 CH₃). HRMS (ESI): m/z 656.1794 [(M−Cl)⁺] (exact

mass calculated for C₃₀H₃₀N₃IrP: 656.1801).

o

4b(Br) (0.030 g, 0.036 mmol) in THF-d₈(0.7 mL) cooled to 0 C was

treated with KO^tBu (0.004 g, 0.039 mmol). The NMR tube was

charged with 5 bar of H₂and kept to 0 ^oC to avoid thermal

decomposition of the product. The resulting solution was analysed

by NMR spectroscopy.

In a J. Young valved NMR tube, a suspension cooled to −20 ^oC of

7b(Cl) (0.012 g, 0.017 mmol) in THF-d₈(0.7 mL) was treated with

KO^tBu (0.002 g, 0.018 mmol). Immediately, the NMR tube was

charged with 5 bar of H₂and kept to 0 ^oC to avoid thermal

decomposition of the product. After 1 h, the resulting solution was

analysed by NMR spectroscopy.

Complex 8b. In a J. Young valved NMR tube, a suspension of

4b(Br) (0.030 g, 0.036 mmol) in THF-d₈(0.7 mL) was treated with

KO^tBu (0.004 g, 0.039 mmol) forming a dark red solution. The

3

¹H NMR (400 MHz, THF-d₈):

δ 7.78 (dd, J_HP= 8.5 Hz, J_HH= 8.5 Hz,

3

o

4H, 4 H arom PPh), 7.82 (s, 2H, 2 H arom), 7.50 (dd, J_HH= 7.6 Hz,

³J_HH= 7.6 Hz, 1H, H arom Py), 7.35 (m, 2H, 2 H arom), 7.24 (m, 6H, 6

H arom), 7.11 (m, 1H, H arom), 7.07 (s, 1H, H arom NHC), 6.94 (s,

solution was kept to 0 C to avoid thermal decomposition of the

product. Satisfactory elemental analysis could not be obtained due

to the low thermal stability of the product.

2

1H, H arom NHC), 5.18 (s, 2H, NCH₂), 3.98 (d, J_PH= 10.0 Hz, 2H,

PCH₂), 2.38 (s, 6H, 2 CH₃), –9.98 (dd, ²J_HP= 18.2 Hz, ²J_HH= 4.8 Hz, 2H,

IrH cis to Py), –19.64 (dt, ²J_HP= 14.4 Hz, ²J_HH= 4.8 Hz, 1H, IrH trans to

Py). ³¹P{¹H} NMR (162 MHz, THF-d₈):

δ

30.9. ¹³C{¹H} NMR (101 MHz,

THF-d₈): 176.9 (d, J_CP= 121 Hz, C-2 NHC), 164.7 (d, J_CP= 6 Hz, C_q

δ

3

¹H NMR (400 MHz, THF-d₈, 273 K):

δ 7.98 (ddd, J_HH= 7.9 Hz, J_HP=

arom), 155.9 (C_qarom), 143.0 (C_qarom), 139.1 (d, J_CP= 42 Hz, 2 C_q

arom), 137.2 (2 C_qarom), 134.3 (d, J_CP= 13 Hz, 4 CH arom), 134.1

(CH arom), 129.4 (2 CH arom), 128.2 (CH arom), 127.8 (d, J_CP= 10

7.9 Hz, ⁴J_HH= 1.6 Hz, 2H, 2 H arom PPh), 7.50 (d, ³J_HH= 2.0 Hz, 1H, H

arom NHC), 7.45 (m, 3H, 3 H arom PPh), 7.22 (d, ³J_HH= 2.0 Hz, 1H, H

arom NHC), 7.00 (s, 2H, 2 H arom Xyl), 6.92 (td, ³J_HH= 7.4 Hz, J_HP

=

5

Hz, 4 CH arom), 125.5 (2 CH arom), 121.3 (CH arom), 121.1 (d, J_CP

=

1.5 Hz, 1H, H arom PPh), 6.81 (ddd, ³J_HH= 7.7 Hz, ³J_HH= 7.7 Hz, ⁴J_HP

9 Hz, CH arom), 120.5 (CH arom), 120.1 (d, J_CP= 4 Hz, CH arom),

59.9 (CH₂N), 49.2 (d, J_CP= 34 Hz, CH₂P), 21.2 (2 CH₃).

3

1.4 Hz, 2H, 2 H arom PPh), 6.79 (s, 1H, H arom Xyl), 6.65 (dd, J_HH

3

7.5 Hz, J_HP= 7.5 Hz, 2 H, 2 H arom PPh), 6.39 (ddd, J_HH= 8.5 Hz,

³J_HH= 6.3 Hz, J_HP= 1.9 Hz, 1H, H^c), 5.98 (d, J_HH= 8.6 Hz, 1H, H^b),

5

3

Representative procedure for ketone hydrogenation

5.58 (d, J_HH= 6.2 Hz, 1H, H^d), 5.29 (d, J_HH= 13.6 Hz, 1H, NCHH),

3

2

In a glovebox, a Fischer-Porter vessel was charged with a

solution of complex 4a(Cl) (2.0 mg, 2.5 ꢁmol), KO^tBu (2.7 mg, 37

ꢁmol) and acetophenone (30 ꢁL, 0.26 mmol) in 2-

methyltetrahydrofuran (2.0 mL). The reactor was purged three

4.93 (d, J_HH= 13.6 Hz, 1H, NCHH), 3.86 (s, 1H, H^a), 3.09 (br, 2H, 2

2

CH= COD), 2.62 (br, 2H, 2 CH= COD), 2.16 (s, 6H, 2 CH₃), 2.04 (br,

4H, 4 CHH COD), 1.89 (br, 2H, 2 CHH COD), 1.66 (br, 2H, 2 CHH

o

COD). ³¹P{¹H} NMR (162 MHz, THF-d₈, 273 K):

δ

17.7. ¹³C{¹H} NMR

times with H₂, and finally pressurized to 1 bar and heated to 60 C.

After 16 h, the reactor was slowly cooled down to room

temperature, the reaction solution was evaporated, and conversion

was determined by ¹H NMR spectroscopy using mesitylene as

internal standard.

(101 MHz, THF-d₈, 273 K): 170.6 (m, C-2 NHC + C_qarom), 153.6 (d,

δ

J_CP= 6 Hz, C_qarom), 148.8 (d, J_CP= 15 Hz, C_qarom), 140.8 (C_qarom),

138.5 (2 C_qarom), 136.8 (d, J_CP= 53 Hz, C_qarom), 134.0 (d, J_CP= 10

Hz, 2 CH arom), 131.4 (d, J_CP= 2 Hz, C^c), 130.3 (d, J_CP= 11 Hz, 2 CH

arom), 129.2 (m, 2 CH arom), 128.4 (d, J_CP= 8 Hz, 2 CH arom), 128.3

(d, J_CP= 8 Hz, 2 CH arom), 127.1 (CH arom), 122.6 (2 CH arom),

122.0 (CH arom), 121.9 (CH arom), 114.2 (d, J_CP= 14 Hz, C^b), 100.3

(C^d), 76.5 (d, J_CP= 59 Hz, C^a), 61.6 (CH₂N), 37.3 (br d, J_CP= 3 Hz, 2 CH₂

COD), 30.7 (br, 2 CH₂COD), 21.5 (2 CH₃). Signals for the four olefinic

carbons could not be identified probably due to significant line

Acknowledgements

Financial support (FEDER contribution) from the Spanish

MINECO (CTQ2013-45011-P, CTQ2016-80814-R and CTQ2014-

J. Name., 2013, 00, 1-3 | 11

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DOI: 10.1039/C6DT03652J

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12 | J. Name., 2012, 00, 1-3

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Article Doi

Synthesis, structure and reactivity of Pd and Ir complexes based on new lutidine-derived NHC/phosphine mixed pincer ligands

DOI: 10.1039/c6dt03652j

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