Synthesis, structural, photophysical and electrochemical studies of various d-metal complexes of btp [2,6-bis(1,2,3-triazol-4-yl)pyridine] ligands that give rise to the formation of metallo-supramolecular gels

DOI: 10.1039/C3DT52309H

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Synthesis, structural, photophysical and electrochemical studies of

various d-metal complexes of btp [2,6-bis(1,2,3-triazol-4-yl)pyridine]

ligands that give rise to the formation of metallo-supramolecular gels†

a

a,d

a

b

c

Joseph P. Byrne, Jonathan A. Kitchen, Oxana Kotova, Vivienne Leigh, Alan P. Bell, John J. Boland,

b

a

5

Martin Albrecht and Thorfinnur Gunnlaugsson*

Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX

DOI: 10.1039/b000000x

2

,6-Bis(1,2,3-triazol-4-yl)pyridine (btp) is a terdentate binding

heterocycles. Facile and modular synthesis of such ligands is of

motif that is synthesised modularly via the CuAAC reaction.

Herein, we present the synthesis of ligands 1 and 2 and the

investigation into the coordination chemistry, photophysical

behaviour and electrochemistry of complexes of these with a

number of d-metal ions (e.g. Ru(II), Ir(III), Ni(II) and Pt(II)).

The X-ray crystal structures of ligand 1 and the complexes

[Ru⋅2 ](PF )Cl, [Ni⋅1 ](PF )Cl and [Ir⋅1Cl₃] are also

great interest and has–in recent years–led to increased interest in

the 2,6-bis(1,2,3-triazol-4-yl)pyridine (btp) moiety. Btp-based

‡

1

2

0

5

0

5

6

7

0

5

0

5

0

ligands can be obtained via the Cu(I)-catalysed alkyne –azide

-13

‘

click’ (CuAAC) reaction from a wide range of substrates.

The

CuAAC reaction is a regioselective, high yielding and tolerant

reaction that gives exclusively 1,4-disubstituted 1,2,3-triazole

4-18

products.

The btp binding motif has been shown by Flood et

2

6

2

6

al. to form stable coordination compounds and has been utilised

presented, but all the complexes displayed non-classical

−

in such diverse applications as tuning the optical properties of

triazolyl C–H⋅⋅⋅Cl hydrogen bonding. All but one complex

Ru(II)-polypyridyl complexe s, in the formation of metallo-

showed no metal-based luminescence at room temperature,

while, for example the Pt(II) complexes displayed

luminescence at 77 K. The electrochemistry of the Ru(II)

complexes was also studied and they were found to have

higher oxidation potentials than analogous compounds. The

supramolecular architectures and polymers, binding halide s,

sensitisation of lanthanide luminescence in the solid state and

recently by Yuan et al. in the formation of self-healing metallo-

23

supramolecular gels. Hence, btp is a highly versatile building

block that we have recently started working with. Herein we

report the synthesis of btp ligands 1 and 2 (Scheme 1) and their

coordination chemistry with Ru(II), Ir(III), Ni(II) and Pt(II), as

well as various structural, photophysical and electrochemical

analyses of these complexes. Ru(II) complexes with polypyridyl

ligands have been studied in the past with particular interest being

paid to their electrochemical and photophysical properties. Bis-

2

+

redox behaviour of [RuL₂] complexes with both 1 and 2 was

nearly identical, while [Ru⋅1Cl (DMSO)] was oxidised at

2

significantly lower potential. We also show that the Ru(II)

complex of 2, [Ru2 ](PF )Cl, gave rise to the formation a

2

6

metallo-supramolecular gel; the morphology of which was

studied using by scanning electron and helium ion

microscopy.

2

+

terdentate complexes such as [Ru(terpy)₂] overcome isomerism

and provide more linear structure than tris-bidentate complexes.

Zhang et al. showed that the btp motif has very similar binding

properties to terpy, with similar bond angles and lengths

3

0

Introduction

Transition metal ion complexes are widely studied, particularly

with respect to their photophysical properties, electrochemical

6

properties and potential biological applications. The d metal ions

8

Ru(II) and Ir(III) and d metal ions Ni(II) and Pt(II) have all

3

4

5

0

5

shown significant applications in biological systems, as cellular

imaging agents, DNA binders and in anti-cancer treatment,

but the complexes of these metals are usually kinetically inert and

stable. Pyridine-centred terdentate binding motifs are

a

particularly privileged coordinating environment for such metal

ions. For example, 2,2′:6′,2′′-terpyridine (terpy) and its

derivatives are ubiquitous in the literature, featuring in dye-

3,4

sensitised solar cells, DNA and protein binding, metallo-

7

supramolecular coordination polymers, and in ion sensing.

75

3 2 2 3

Scheme 1 Synthesis of ligands 1 and 2. (i) CuI, (PPh ) PdCl , THF/Et N

These ligand are, however, limited by the synthetic challenge

involved in derivatising them, particularly with regard to

introducing flanking ‘arms’ appended to the non-central

(1:1), trimethylsilylacetylene, 0 °C→rt; (ii) NaN , rt, 1h, DMF/H O; (iii)

3

2

CuSO

4

⋅5H

2

2 3 2

O, Na ascorbate, K CO , DMF/H O, rt, 18h.

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determined by X-ray diffraction therefore making study of such

systems valuable as an analogue for terpy. A number of Ru(II)

complexes with btp have subsequently been recently reported,

showing ind ee d such similar characteristics to the terpy

2,19 ,20 ,25 -27

5

0

5

0

5

analogues.

However, to the best of our knowledge,

there are no examples in the literature of Ir(III) complexes with

btp-containing ligands. Giving that Ir(III) is isoelectronic to

Ru(II) and its complexes have long been of interest, due to their

emission properties, we decided to investigate their formation

herein. The d octahedral Ni(II) complexes are isostructural to

the octahedral d metal complexes. Only one example of the

interaction between the btp motif and the square planar d Pt(II)

ion has been reported, where it was used in the formation of

metallopolymers. The chemistry of Pt(II)-terpy derived systems

is, however, well studied, often as a result of their ability to

exhibit metal⋅⋅⋅metal interactions.

1

2

6

8

Fig. 1 Comparison of the chemical shifts of the proton resonances in

There have only been, to

1

H NMR spectra of (a) Ligand

1

(400 MHz, DMSO-d

); (c) [Ru⋅1 ](PF (600 MHz,

] (400 MHz, DMSO-d ); (e) [Pt⋅1Cl]Cl (400 MHz,

). Peaks are labelled as follows: t (triazolyl CH), u (3- and 5-

), z (–OCH ).

6

); (b)

the best of our knowledge, two btp-based supramolecular gels

previously reported in the literature. One responsive system

exploited the conformational changes that btp undergoes upon

binding a metal (vide infra) to interconvert between a helically

6

0

2

[Ru⋅1Cl (DMSO)] (600 MHz, DMSO-d

6

2

6 2

)

DMSO-d

6

); (d) [Ir⋅1Cl

3

6

pyridyl CH), v (4-pyridyl CH), w and x (phenyl CH), y (CH

2

3

folded polymer and a metallo-supramolecular cross-linked gel,

while the other work described self-healing polymeric

was related to the triazolyl protons. Having made these ligands

we next formed the various d-metal ion complexes of 1 and 2.

The monoleptic Ru(II) complex of 1 was prepared upon

treating ligand 1 with 1 molar equivalent of [RuCl (DMSO) ] in

6

7

8

9

5

0

5

0

5

0

5

materials . Both of these systems involved polymeric poly-btp

components, we herein present the first example of a metallo-

supramolecular gel derived from discrete mono-btp components

2

4

CHCl₃under reflux conditions and [Ru⋅1Cl (DMSO)] was

2

(

i.e. ligand 2). In this article we give full account of our results.

collected upon filtration as a bright red solid in good yield (86%).

1

The H-NMR spectrum (600 MHz, DMSO-d ; Fig. 1(b) and

6

Results and discussion

shown in full in ESI, Fig. S3) showed resonances shifted relative

to the ligand, as well as a new resonance appearing at 3.49 ppm,

arising from the bound DMSO molecule in the structure. MALDI

Synthesis and characterisation

Ligands

1

and

2

were synthesised in

a

one-pot

+

HRMS confirmed this, showing the presence of [M−(DMSO)]

3

4

5

0

5

0

5

0

5

deprotection/‘click’ reaction from the relevant bromide and 2,6-

bis((trimethylsilyl)ethynyl)-pyridine (3) where the azide was

produced with subsequent alkyne d eprotection in situ, following a

paradigm used by Fletcher et al.

washing the reaction mixture with EDTA/NH OH solution, the

species corresponding to m/z = 681.0213 with an isotopic

distribution pattern matching the calculated one (cf. ESI, Fig.

S12).

3,34

as shown in Scheme 1. Upon

The dileptic complex [Ru⋅1 ](PF ) was prepared upon heating

2

6 2

4

2

equivalents of ligand 1 with 1 equivalent of RuCl ⋅xH O under

3 2

ligands were obtained in high purity (confirmed by elemental

analysis), which eliminated the need of any further purification

microwave irradiation to 120 °C for 40 minutes, and isolated by

1

counterion exchange to the PF salt. The H-NMR spectrum (600

6

(such as the use of chromatography) and moderate yields of 53%

MHz, DMSO-d ) is shown in Fig. 1(c). The doublet and triplet

6

and 63%, respectively,

associated with pyridyl protons (u and v) are clearly resolved in

this spectrum, at 7.71 and 7.64 ppm, respectively, not overlapping

with any other resonances. The [Ru⋅2 ](PF ) complex was

Due to the C -symmetry in both 1 and 2, only a few resonances

2

1

were observed in the H-NMR spectra. The spectrum of 1 was

recorded in both DMSO-d and CDCl solutions (both shown in

2

6 2

6

3

prepared in an identical manner and so was the Ni(II) complex

^E^S^I⁾^.^T^h^e^s^p^e^c^t^r^u^m^s^h^o^wⁿⁱⁿ^Fⁱ^g^.¹⁽^a⁾⁽⁴⁰⁰^M^H^z^,^D^M^S^O^-^d6⁾

8

[

Ni⋅1 ](PF ) , using NiCl ⋅xH O as the metal source. The d

2 6 2 2 2

displayed the expected number of resonances for 1. The triazolyl

1

Ni(II) ion is paramagnetic, hence the signals in the H-NMR (600

peak appeared as a well resolved singlet at 8.72 ppm (marked t in

Fig. 1), a multiplet at 7.91–8.07 ppm was made up from the

overlap of the pyridyl signals with one of the phenyl signals. The

other resonance from the phenyl ring was observed at 7.45 ppm

MHz, CD CN) spectrum were broadened and shifted. One signal

3

was shifted as far downfield as 56.46 ppm. All three of these

complexes were observed in MALDI HRMS and their recorded

isotopic distribution patterns matched calculated ones (see ESI).

(marked x) and two singlets (y and z) at 5.81 and 3.84 ppm arose

The formation of the monoleptic complex [Ir⋅1Cl ] was

3

from the methylene and methyl ester moieties, respectively.

achieved using conditions modified from those previously

reported by Collin et al. for analogous terpy ligands (heating

under microwave irradiation to 160 °C in (CH OH) for 20

The carboxylic acid ligand 2 was found to have poor solubility

1

in organic solvents. The H-NMR spectrum (600 MHz, DMSO-

d₆) was once again very simple (ESI Fig. S3). The resonance at

5

related to four of the eight phenyl CH protons, the multiplet from

7.88–8.06 ppm resulted from the overlap of the remaining phenyl

signal and the two pyridyl resonances, the singlet at 8.74 ppm

2

35

minutes). This complex showed very poor solubility in a range

of solvents. However, the H-NMR spectrum (400 MHz, DMSO-

.80 ppm arose from the methylene linker, a doublet at 7.45 ppm

1

d₆) was successfully recorded in a dilute solution (Fig. 1(d)). This

00 complex was found not to be stable and was shown to decompose

over a period two weeks. It was also shown to dissociated rapidly

1

2

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Fig. 3 Coordination sphere of [Ru⋅2

2

](PF

6

)Cl with thermal ellipsoids at

Fig. 2 (a) Crystal structure of 1 shown with thermal ellipsoids at 50%

probability. Hydrogen atom positions were calculated; (b) The

interlocking’ packing structure of the ligand in the solid state.

2

5

50% probability. Ligand ‘arms’, solvents and counterions have been

omitted to more clearly show the atoms of interest. The btp motifs are

arranged in a pseudo-octahedral geometry about the Ru(II) centre. Angles

and bond lengths are given in Table 2. Full structure is shown in Fig. 4.

‘

5

0

5

in DMSO solution. Though not stable, it is the first example of an

Ir(III)-btp complex to be reported to date.

Monoleptic Pt(II) complexes of both 1 and 2 were successfully

yellow plate-like crystals, from which the solid-state X-ray

structure was determined at 108 K. The ligand crystallised in the

low-symmetry triclinic space group P−1. The molecule, as

displayed in Fig. 2(a), adopted a ‘horseshoe’ configuration,

which is in keeping with the anti-anti conformation shown

3

4

0

5

0

5

obtained by reaction of the relevant ligand with cis-

1

[

PtCl (DMSO) ] ( H-NMR spectra and HRMS of both Pt(II)

2

1

complexes are shown in ESI). The H-NMR spectrum of

Pt⋅1Cl]Cl (400 MHz, DMSO-d ) is shown in Fig. 1(e). Unlike

[

13,25

6

prevoiously. for a structurally similar btp ligands.

. This is a

the spectra of the other complexes, there were no overlapping

resonances; the triplet arising from the 4-pyridyl proton (marked

v in Fig. 1) being shifted further downfield than the other pyridyl

protons (u in Fig. 1). The [Pt⋅1Cl]Cl complex was found to have

limited solubility in most common solvents and it was shown to

dissociate in DMSO solution over short time.

result of electrostatic repulsion between the lone pairs of the

pyridyl and 3-triazolyl nitrogen atoms; resulting in the triazolyl

protons pointing into the cavity. Moreover, the plane of the btp

motif was approximately orthogonal to the planes of the phenyl

rings (88.29° and 88.38°). The molecules pack in an interdigitated

manner (Fig. 2(b)) as a result of π–π interactions between the

phenyl rings in the ligand’s ‘arms’. The planar btp motifs are also

arranged parallel to each other. Moreover, hydrogen-bonding

interactions between three of the four methylene CH protons with

triazolyl nitrogen atoms as well as an interaction of the 5-pyridyl

CH with the triazolyl nitrogen, are also observed. These

1

X-ray crystal structure analysis

A number of crystal structures were obtained for the complexes

formed above, the general crystallographic data and structure

refinements being provided in Table 1. Single crystals of 1 were

2

0

grown by slow evaporation of a solution in CHCl , yielding

3

Table 1 Selected crystallographic data and structure refinements

Compound

1

[Ru⋅2

2

](PF

6

3 2

)Cl(CH CN)(H O)0.50 [Ni⋅1

2

](PF

6

)Cl(H

2

O)(CH

3

CN)

3 2 2 6 2 0.25

[Ir⋅1Cl ](H O)0.25(C H O )

(EtOH)1.25(Et

2

O)0.50

Formula

CCDC code

Formula weight

T (K)

Crystal system

Space group

a (Å)

C

27

H

23

N

7

O

4

C

56.50

H

54.50ClF

6

N

15

O10.25PRu

C

56

H

51ClF

6

N

9

15NiO P

27.50 3 7 4.75

C H25Cl IrN O

956219

509.52

108(2)

956220

1398.14

108(2)

Triclinic

P−1

12.235(2)

17.491(4)

17.627(4)

105.76(3)

105.52(3)

93.49(3)

3461.4(12)

2

956222

1317.25

108(2)

Triclinic

P−1

956221

808.07

100(2)

Triclinic

Monoclinic

P2 /c

P−1

1

6.3501(13)

12.965(3)

14.859(3)

92.45(3)

101.17(3)

100.30(3)

1176.9(4)

2

14.4083(10)

14.8238(11)

16.2001(12)

108.541(3)

91.506(3)

115.862(3)

2896.2(4)

2

15.4149(18)

14.1809(19)

15.627(2)

90

105.781(9)

90

b (Å)

c (Å)

α (°)

β (°)

γ (°)₃

V (Å )

3287.2(7)

4

Z

F(000)

532

1.438

1421

1.333

1356

1.510

1620

1.673

−

3

D

c

(Mg⋅m

)

−1

μ (mm )

0.101

1.214

0.367

1.103

1.952

1.039

10.497

1.072

2

GOF on F

R

wR

1

[I>2σ(I)]

2

[I>2σ(I)]

0.0639

0.1262

0.0705

0.2099

0.0497

0.1257

0.0470

0.1226

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Fig. 4 A ball and stick model of the X-ray crystal structure of [Ru⋅2

2

](PF

6 3

)Cl, showing hydrogen-bonding interactions. Uninvolved molecules of CH CN

−

and Et O and PF counterion as well as hydrogen atoms are omitted for clarity.

2 6

interactions are all of the order of 2.59(5) Å in length and at

angles of 162(4)° (Details of these interactions are shown in ESI).

pyridyl nitrogen atoms and the Ru(II) centre are slightly shorter

than those between the triazolyl nitrogen atoms and the metal.

Selected bond lengths and angles between the coordinating

5

Yellow crystals of complex [Ru⋅2 ](PF )Cl were grown by

2

6

diffusion of diethyl ether into CH CN. The [Ru⋅2 ](PF )Cl 20 nitrogen atoms and the Ru(II) centre are shown in Table 2. The

3

2

6

crystallised in the triclinic space group P−1. When compared with

the structure of ligand 1, the triazole rings have rotated, with the

N(3), N(5), N(43) and N(45) atoms coordinating the Ru(II) ion

mean planes of the two coordinating ligands’ btp motifs were

nearly orthogonal, at an angle of 87.99°. This geometry is broadly

in agreement with bond angles and lengths reported for similar

1

0

2,25

(see Fig. 3). The Ru(II) adopts an N6 coordination sphere and is

btp structures previously reported,

and also much like the

distorted significantly from an octahedral geometry. The angle 25 geometry of the well-studied [Ru(terpy) ](PF ) . Similarly to

2

6 2

formed between the pyridyl nitrogen atoms and the Ru(II) centre

is only slightly distorted at 176.5°, while the intraligand triazolyl

N–Ru–N angles are all approximately 157°; deviating

significantly from the ideal of 180°. The distances between the

the terpy analogue, the pyridyl N–Ru bond lengths are shorter

than the triazolyl N–Ru distances. However, the difference

between these two measurements is less significant than for terpy

with variations of less than 0.06 Å, as opposed to nearly 0.10 Å.

1

3

5

0

Table 2 Selected bond lengths [Å], angles [°] and distortion parameters [°] for Ru(II), Ni(II) and Ir(III) complexes and their terpy analogues

a

c

[

Ru⋅2

2

](PF

6

)Cl [Ru(terpy)

2

](PF

6

)

2

[Ni⋅1

2

](PF

6

)Cl [Ni(terpy)

2

]_b(ClO )

4 2

[Ir⋅1Cl

3

]

3

[Ir(terpy)Cl ]

2

⋅H O

M(1)-N(4)

M(1)-N(44)

M(1)-N(3)

M(1)-N(43)

M(1)-N(5)

2.021(4)

2.023(4)

2.051(4)

2.057(4)

2.078(4)

176.50(14)

156.79(15)

156.60(15)

102.5

1.974(7)

1.981(7)

2.065(7)

2.076(6)

2.065(6)

2.067(6)

178.8(3)

158.4(3)

159.1(2)

93.3

2.046(2)

2.036(2)

2.088(2)

2.122(2)

2.078(2)

2.132(2)

175.43(8)

154.31(8)

154.24(8)

121.4

2.024(8)

1.984(9)

2.146(11)

2.116(10)

2.113(11)

2.108(10)

177.4(6)

156.1(4)

155.3(4)

107.0

Ir(1)-N(4)

Ir(1)-N(3)

Ir(1)-N(5)

Ir(1)-Cl(3)

Ir(1)-Cl(1)

1.996(5)

2.057(5)

2.022(5)

2.3543(18)

2.3559(17)

2.3585(17)

175.83(16)

159.3(2)

179.27(6)

52.1

1.927(3)

2.044(3)

2.049(3)

2.370(1)

2.3556(7)

2.3466(8)

177.34(8)

161.3(1)

179.51(3)

44.4

M(1)-N(45)

Ir(1)-Cl(2)

N(4)-M(1)-N(44)

N(3)-M(1)-N(5)

N(43)-M(1)-N(45)

N(4)-Ir(1)-Cl(2)

N(3)-Ir(1)-N(5)

Cl(3)-Ir(1)-Cl(1)

d

Σ

a

36 b

37 c

38 d

Data from Lashgari et al . Data from Rae et al. Data from Sheldrick and co-workers. Distortion parameter Σ=Σ|(90°−θ)| for cis-N–M–N angles.

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similar pseudo-octahedral geometry to that discussed above.

However, the ‘arms’ were uninfluenced by any intermolecular

interactions, with two distinct conformations of the complex

being present in the unit cell.

Table 3 Hydrogen bonds for [Ru⋅2

2

](PF

6

)Cl [Å and °].

D–H⋅⋅⋅A

d(D–H) d(H⋅⋅⋅A) d(D⋅⋅⋅A) ∠(DHA)

O(2)-H(2X)⋅⋅⋅O(200)

O(111)-H(11X)⋅⋅⋅O(100)

O(41)-H(41)⋅⋅⋅O(3)

O(4)-H(4X)⋅⋅⋅Cl(1)

O(44)-H(44X)⋅⋅⋅O(90)

O(200)-H(200)⋅⋅⋅O(2)

O(90)-H(90X)⋅⋅⋅Cl(1)

C(17)-H(17)⋅⋅⋅Cl(1)

0.85

0.92

0.84

0.90

0.91

0.85

0.86

0.95

2.40

2.62

1.93

2.08

1.68

2.57

2.18

2.857

3.26(4)

3.390(19)

2.766(6)

2.980(4)

2.573(6)

3.26(4)

179.0

141.3

172.9

176.8

165.2

137.4

178.6

134.7

3

5

Lilac crystals of the Ni(II) complex of ligand 1 were obtained

upon ether diffusion into a CH CN solution. The [Ni⋅1 ](PF )Cl

3

2

6

complex also crystallised in the triclinic space group P−1 with

one molecule in the asymmetric unit. The structure has a distorted

octahedral geometry around the metal centre, with cis-N–Ni–N

bond angles ranging from 77.15(8)°–106.93(8)° and trans-N–Ni–

N angles ranging from 154.24(8)°– 175.43(8)°. This structure is

more distorted from octahedral geometry than the [Ru⋅2 ](PF )Cl

40

3.048(6)

3.589(5)

2

6

The angles are also more distorted from octahedral than the terpy

structure, with a distortion parameter of 121.4°. The comparison

analogue by approximately 2° in each case and the distortion 45 of this structure to a terpy analogue (Table 2), showed that the

5

0

5

0

parameter, Σ , for this structure (equal to the sum of the

deviations of each cis-N–Ru–N angle from the ideal of 90°) is

1

geometry is significantly more distorted from octahedral, the

average pyridyl N–Ni bond lengths are slightly longer and the

average triazolyl N–Ni bonds are slightly shorter (2.105 Å

02.5°, which is more distorted from the ideal than the terpy

structure, for which Σ is 93.3°, cf. Table 2.

The ‘arms’ of each ligand were arranged differently as shown 50 terpy structure is also lower, with a value of 107.0°. The packing

in Fig. 4, with all of the terminal carboxylic acid groups being

involved in hydrogen bonding in the solid state. One carboxylic

group CO(1)O(2)H hydrogen bonds to a water molecule

HO(500)H, which in turn hydrogen bonds to an ethanol molecule

O(200)). The two ligands show intermolecular hydrogen 55 atoms of the interstitial water molecule display hydrogen bonding

bonding between CO(4)O(3)H and CO(42)O(41)H with a donor–

acceptor distance O(41)⋅⋅⋅O(3) measuring 2.766(6) Å. O(4) also

interacts with the Cl counterion (O(4)-H(4X)⋅⋅⋅Cl(1)

7

compared to 2.121 Å for terpy). The distortion parameter of the

1

2

of the [Ni⋅1 ](PF )Cl complex is shown in Fig. 5. In contrast to

2 6

the carboxylic acid ‘arms’ in the structure of [Ru⋅2 ](PF )Cl

2

6

above, the methyl ester ligand ‘arms’ of ligand 1 do not have any

hydrogen bonding interactions with each other. Both hydrogen

(

interactions to the chloride ions in the structure (O(100)–

H⋅⋅⋅Cl(1) = 3.193(2) and 3.221(3) Å, ∠(O(100)–H⋅⋅⋅Cl(1)) =

169.3 and 169.6°), while the chloride also interacts with one of

triazolyl protons C(10)H (vide infra). There is also a solvent⋅⋅⋅π

−

=

2

.980(4) Å, 176.8°). CO(43)O(44)H hydrogen bonds to the

hydroxyl group (O(90)) of one disordered ethanol molecule, 60 interaction between the water molecule and N(7) of one of the

−

which also shows interactions with the Cl ion, leading to a

repeatable coordination network. Triazolyl C(17)H displays an

interaction with Cl(1) which will be discussed in more detail

below. Selected hydrogen bonding distances and angles are

shown in Table 3.

triazole rings. The lone pair on O(100) of the water molecule

points towards the ring. This interaction has an O⋅⋅⋅centroid

distance of 3.297 Å. Selected bond lengths and angles are

provided in ESI.

65

3

Fig. 6 X-ray crystal structure of [Ir⋅1Cl ]. Thermal ellipsoids at 50%

probability. Selected bond lengths and angles are shown in Table 2.

Small single crystals of the [Ir⋅1Cl ] complex were grown by

3

2

5

vapour diffusion of diethyl ether into a DMF solution. [Ir⋅1Cl₃]

Fig. 5 Capped stick model of the packing structure of [Ni⋅1

2 6

](PF )Cl.

70

crystallised in the monoclinic space group P2 /c with one

1

molecule in the asymmetric unit as shown in Fig. 6. The structure

contains one quarter occupancy ethylene glycol and one quarter

occupancy water molecule. One of the ester groups was

disordered over two sites with relative occupancies of 50% for

each site disorder, only one position is shown in Fig. 6 and full

A crystal structure of [Ru⋅1 ](PF ) in the triclinic space group

2

6 2

P−1 was also obtained. The data was, however, not of sufficient

quality to fully resolved, but clear connectivity could be

ascertained, and picture of this structure is shown in the ESI (Fig.

S22). The coordination sphere about the Ru(II) ion clearly had

3

0

75

This journal is © The Royal Society of Chemistry [year]

[journal], [year], [vol], 00–00 | 5

DOI: 10.1039/C3DT52309H

Dalton Transactions

Page 6 of 14

refinement details are provided in the ESI. The Ir(III) adopts a

distorted octahedral geometry, with an N Cl coordination sphere.

3

The intraligand triazolyl trans-N–Ir–N angle, much like the

structures already discussed, is distorted from purely octahedral

geometry by 159.3(2)°. The pyridyl N–Ir distance (1.996(5) Å)

was shorter than the triazolyl N–Ir distances (2.057(5) and

5

0

5

0

5

0

5

2

.022(5) Å). The bond lengths and angles in the complexes are

comparable to those in an analogous terpy structure as shown in

Table 2. Comparison of the distortion parameters for both

1

2

3

structures shows that [Ir⋅1Cl ] is more distorted (Σ = 52.1°) from

3

pure octahedral than the terpy analogue (Σ = 44.4°). No crystals

of the Pt(II) complexes suitable for X-ray crystallography were

obtained; this was due mostly to the poor solubility of these

complexes in most common solvents.

The structures of the three complexes [Ru⋅2 ](PF )Cl,

2

6

[

Ni⋅1 ](PF )Cl and [Ir⋅1Cl ] all displayed non-classical hydrogen

2 6 3

bonding interactions between the acidic triazole CH and chloride

ions present in the structures, Table 4. As well as binding cations,

such as d-block metals, it has been shown that 1,2,3-triazole

ligands are capable of recognising anions. Anion receptors have

been reported which take advantage of these interactions, either

to simultaneously bind both metal ions and halide from salts such

as KCl,

macrocycle ,

encapsulate chloride ions in the cavity of

a

or template the formation of interlocked

structures. Despite their potential for interesting interactions,

however, triazole C–H⋅⋅⋅Cl bonds have not been widely

−

investigated, but studies published with structural data

consistently report donor–acceptor distances of the order of

4-45

−

3

.5 Å.

The bond lengths and angles for the C–H⋅⋅⋅Cl bonds

in our structures (as shown in Table 4) are very similar to each

−

other, with H⋅⋅⋅Cl distances of 2.6–2.8 Å and with donor–

−

acceptor distances being between 3.3–3.6 Å. The Cl being

located about 134° out of the plane of the C–H bond in all cases.

Having structurally characterised the aforementioned complexes,

2

+

we next investigated the supramolecular properties of [Ru⋅2 ] .

2

Table 4 Non-classical hydrogen bond lengths [Å] and angles [°] for all

three complexes. (D=donor, A=acceptor)

Metal

D-H⋅⋅⋅A

d(D-H) d(H⋅⋅⋅A) d(D⋅⋅⋅A) ∠(DHA)

Ru(II) C(17)-H(17)⋅⋅⋅Cl(1)

Ni(II) C(10)-H(10A) ⋅⋅Cl(1)

Ir(III) C(18)-H(18A) ⋅⋅Cl(2)

0.950

2.857 3.589(5)

2.7042 3.434(3)

2.623 3.358(8)

134.7

134.1

134.4

55

Fig. 7 HIM images of Ru(II) gel (a, b) showing its fibrous microstructure.

The inset in (a) shows the formation of the metallogel in ethanol.

(

e.g. NaCl, KCl and KI) while others have used this idea to

create optically healable supramolecular polymers or potential

luminescent reporters for micro-environmental changes.

Here the supramolecular metallogel of [Ru⋅2 ](PF )Cl was

0

4

0

Formation of supramolecular metallogels

The structural analysis of [Ru⋅2 ](PF )Cl discussed above (Fig. 4)

6

7

0

5

0

2

6

2

6

formed in several steps by preparing an ethanol solution of the

dichloride complex followed by addition of a saturated aqueous

solution of NH PF with subsequent formation of a precipitate

suggests the potential of this compound for the formation of

supramolecular metallogels due to the presence of polymer chains

within its crystal structure through hydrogen bond interactions

between the carboxylic groups and chloride anions. There

currently exists a great interest within the field of supramolecular

and materials chemistry in the search for such new materials with

various functional properties that are different from their

4

6

(

the bis-(PF ) complex). The supranatant was then decanted off

6

4

5

and left to stand overnight resulting in the formation of viscous

yellow soft material, which was identified as gel by a simple

51

“

inversion test”. The gel exhibited luminescence similar to that

1

of the ligand (vide infra). H-NMR (400MHz, DMSO-d ) and

HRMS confirmed that the gel contained [Ru⋅2₂] (Fig. S7 and

6

4

6

monomeric components. We have recently shown the use of

lanthanide ions for the formation of luminescent organic

metallogels (or supramolecular gels) and self-assembly

2+

5

0

S15 in ESI).

The fibrous nature of the gels was revealed by scanning

electron microscopy (SEM) (see ESI) and helium ion (HIM)

7

Langmuir-Blodget films. The former we have recently shown

can be used as a matrix for the growth of inorganic salt nanowires

6

| Journal Name, [year], [vol], 00–00

This journal is © The Royal Society of Chemistry [year]

DOI: 10.1039/C3DT52309H

Page 7 of 14

Dalton Transactions

Dynamic Article Links ►

Journal Name

Cite this: DOI: 10.1039/c0xx00000x

www.rsc.org/xxxxxx

ARTICLE TYPE

Fig. 8 Emission spectra of (a) [Ru⋅1Cl

cut where a different filter had to be applied. In (c) the green trace is the emission spectrum of glass at 77 K with concentration of ~10 M.

2 3

(DMSO)], (b) [Ir⋅1Cl ] and (c) [Pt⋅1Cl]Cl at room temperature (blue) and 77 K (red). In (a) and (c), the spectrum is

−6

microscopy (Fig. 7). Both analyses showed similar structure of

the material but HIM allowed us to obtain higher quality data

compared to SEM. We believe that the fibres consist of Ru(II)

complexes connected together through hydrogen bonding

forming in a similar manner to the network found by structural

analysis (Fig. 4) involving carboxylic groups, chloride anions and

solvent molecules. The average width of the fibres was found to

be in a range of 100 25 nm; while the secondary order

arrangement of the fibres can be found under higher

magnification with a width of 20 5 nm (Fig. 7(b)). Structural

analysis of any of the other d-metal complexes investigated in

this work did not suggest the formation of supramolecular

was observed. This band exhibited a lifetime of ~2.5 ns. Ligand 2

had almost identical spectroscopic behaviour (see ESI).

5

0

5

0

5

45

The absorbance spectrum of [Ru⋅1 ](PF ) in CH CN showed

2

6 2

3

bands similar to those of the ligand, but blue-shifted, only slightly

in the case of the band centred at 232 nm, but by ~15 nm for the

band at 286 nm, the band associated with the binding triazoles.

The spectrum also exhibits a new MLCT band at 395 nm.

1

2

+

50

Bis-terdentate Ru(II) complexes (including [Ru(terpy) ] ) are

2

often practically non-luminescent, due to thermal population from

3

their MLCT excited states to a close-lying non-emitting metal

centred (MC) excited states. It has been reported that modifying

the ligand structures can, however, raise the energy of the MC

metallogels; and this was indeed verified as the attempts to obtain 55 state and hence, increase the luminescence arising from such

similar materials for them was, on all occasions, not successful.

However, simple structural modification of these ligands by, for

instance, incorporating functional groups, such as large polymer

chains, either at the central pyridyl unit or on the arms

structurally modified complex. Perfect octahedral geometry about

the metal ion is thought to increase the MC energy by leading to a

strong ligand field. However, as it has been shown in the

structural studies above that the coordination environment in

themselves, or by simply employing coordination with other 60 these complexes is distorted significantly from pure octahedral

metal ions, such as the f-metal ions, or the use of mixed transition

and lanthanide metal ions, would open up an avenue for the

creation of new materials with various functional properties, such

as luminescent and magnetic properties, and we are currently

geometry (Σ

= 102.5°), we did not necessarily expect

[Ru⋅1 ](PF ) to be highly luminescent in solution. Indeed, as has

2

6 2

been the case with most btp-based ligands as well as simple

terpy-based ligands, [Ru⋅1 ](PF ) showed no long-lived

2

6 2

investigating these avenues of research in greater detail using 65 luminescence at room temperature, as only a ligand-centred

such structural analogues of 1 and 2.

fluorescence band at 335 nm (τ ≈ 2.5 ns) similar to that of the

ligand was observed. Moreover, degassing the solution led to

only a slight enhancement of luminescence intensity; confirming

the above. The excitation spectrum observed was also similar to

Photophysical investigations

Having structurally characterised the Ru(II) and Ir(III) complexes

3

4

0

5

0

of 1 and 2, we next investigated their various physical properties, 70 that of the ligand. In light of this, luminescence emission spectra

and that of the ligands; beginning by investigating their

photophysical properties since both Ru(II) and Ir(III) complexes,

in particular, are often found to possess desirable luminescence.

of [Ru⋅1 ](PF ) were also recorded at 77 K, but unfortunately, no

2 6 2

emission was observed. Similarly, the spectroscopic properties of

[Ru⋅2 ](PF ) were found to follow the almost identical path;

2

6 2

The same properties for the [Ru⋅1Cl (DMSO)], [Pt⋅1Cl]Cl and

[Ru⋅1 ](PF ) only giving rise to very weak luminesce (see ESI).

2

2 6 2

[Pt⋅2Cl]Cl, complexes (for which X-ray crystal structures were 75 A sample of the metallogel derived from this species was

not obtained), were also investigated in a similar manner. All the

photophysical properties were investigated in spectroscopic grade

immobilised on a quartz slide and the solid state luminescence

measured at room temperature, and as had been seen for both the

,

CH CN solution.

[Ru⋅1 ](PF ) and [Ru⋅2 ](PF ) complexes, only ligand-centred

3

2

6 2

2

6 2

The UV-Vis absorbance spectrum of ligand 1 at room

emission (centred at 310 nm) was observed for the metallogel

temperature displayed two bands with maxima at 235 nm (ε 80 (see ESI Fig. S32).

−1

4

5000 L mol cm ) and 300 nm (ε 8700 L mol cm ) upon

Monoleptic complex [Ru⋅1Cl (DMSO)] had quite different

2

excitation of this ligand, a broad emission band centred at 335 nm

properties to those seen above. The absorbance bands recorded

This journal is © The Royal Society of Chemistry [year]

[journal], [year], [vol], 00–00 | 7

DOI: 10.1039/C3DT52309H

Dalton Transactions

Page 8 of 14

for [Ru⋅1Cl (DMSO)] were centred at 230, 302, 354 and 450 nm

Table 5 Half-wave potentials and anodic–cathodic peak separations of

redox curves for Ru(II) complexes.

2

60

and [Ru⋅1Cl (DMSO)] displayed an emission centred at 335 nm

2

as well as a very broad but significantly less intense luminescence

with its maximum at 475 nm, upon excitation at room

temperature. At 77 K, the emission was, however, found to be

centred at 285 nm with a broad band of comparable intensity

being also observed at longer wavelengths; being centred at 475

nm.

Complex

E

1/2 [V]

ΔE

p

[mV]

a

[

Ru⋅1

Ru⋅2

2

](PF

6

)

2

⁺¹^.⁴²a

70

60

58

5

0

5

0

5

0

5

2

6

2

⁺¹^.⁴²b

[

2

Ru⋅1Cl (DMSO)]

+0.75

a

–1

sweep rate 100 mV s , [NBu

4

6

]PF as supporting electrolyte (1 mM),

+

potentials vs SCE using Fc /Fc as internal standard (E1/2 = +0.40 V (ΔE

p

=

The absorbance profile of [Ir⋅1Cl ] displayed a band at 232 nm

b

2+

3+

3

3 3

72 mV); [Ru(bpy) ] /[Ru(bpy) ] as internal standard (E₁_/₂= +1.39V

1

2

3

with a shoulder at 260 nm. A band centred at 293 nm tailed off

until 480 nm. At room temperature, there was a luminescence

band observed at 330 nm, while at 77 K, a broad luminescence

centred at 450 nm became much more apparent; the fluorescence

band at 335 nm being seen as a shoulder in the spectrum.

(ΔE

p

= 55 mV)

+

6

7

5

0

5

with 4-iodophenyl ‘arms’ (E = +1.06 vs Fc/Fc , that is, +1.46 V

1

/2

vs SCE). This similarity suggests a minor influence of the

triazole substituent on the metal oxidation potential, which is in

agreement with the weaker orbital alignment between btp and the

octahedral ruthenium centre as compared to terpy-type systems.

Planar Pt(II) complexes have been reported to have

complicated emission behaviour, particularly at low temperature,

as a result of the potential for stacking in solution, leading to

Pt(II)–Pt(II) interactions, as well as interactions between the

As expected, neutral [Ru⋅1Cl (DMSO)] was much easier oxidised

E₁_/₂= +0.75) than the cationic complexes. The CH CN oxidation

3

potential is slightly higher than that reported for the analogous

2

(

aromatic ligands; the emission spectra for complexes such as

+

terpy complex [Ru(terpy)Cl (DMSO)] at +0.68 V (recorded in

2

[Ru(terpy)Cl] being known to vary with concentration as well.

5

4

DMSO). CV spectra of [Ru⋅1Cl (dmso)] in both CH CN and

2

3

In the case of [Pt⋅1Cl]Cl a broad absorbance profile was observed

CH NO were identical, (shown in ESI†) suggesting that

3

2

in CH CN, with a sharp maximum at 222 nm and tailing to

3

potential solvent exchange reactions due to the coordinating

4

00 nm. At room temperature, only the ligand centred emission

nature of CH CN are irrelevant. [Ir⋅1Cl ] showed no oxidation up

3

was observed for [Pt⋅1Cl]Cl, being centred at 333 nm. However,

−5

to solvent discharge potential.

when recorded in CH CN glasses (concentration of ~10 M) at

3

7

5

7 K, two broad emission bands were observed at 442 nm and

78 nm, for [Pt⋅1Cl]Cl. Bands of similar energies have been

Conclusions

assigned to π-π* emission and interligand π-π interactions

8

9

0

5

0

5

In this article we have developed novel terdentate btp ligands 1

and 2, by using ‘click’ chemistry. These were characterised using

various spectroscopic techniques, and their behaviour with d-

block metal ions explored. The X-ray crystal structures of ligand

3

1

respectively for the analogous terpy complex. More dilute

−6

glasses (concentration of ~10 M) show a ligand centred

emission band at 335 nm as well as a weakly structured emission

around 450 nm. This emission spectrum closely resembles the

spectra for the other monoleptic complexes discussed above.

Complex [Pt⋅2Cl]Cl displayed similar photophysical behaviour

with concentrated glasses displaying emission at 460 and 572 nm

and at lower concentrations, two overlapping bands at 340 and

1

and three of the resulting complexes, allowed investigation into

coordination geometry of these ligands with Ru(II), Ni(II) and

Ir(III). The coordination sphere of these structures closely

resembled the distorted octahedral geometry of analogous terpy

structures. The triazole rings played an important role in these

structures, with the nitrogen atoms acting as hydrogen bond

acceptors and the CH acting as a hydrogen bond donor.

The three complexes showed non-classical triazolyl C–H⋅⋅⋅Cl

hydrogen bonding interactions with C–H⋅⋅⋅Cl distances of

.364(6)–3.589(5) Å and bond angles of 134°. The photophysical

behaviour of these complexes in solution was also studied; and

only the ligand-centred fluorescence was observed at room

3

55 nm, the details being given in the ESI.

Electrochemistry

−

In addition to photophysical properties, the electrochemical

properties of transition metal complexes such as those above, are

regularly studied. The electrochemistry of the Ru(II) complexes

−

4

5

0

5

0

5

3

was investigated by cyclic voltammetry in CH CN solution. Both

3

the [Ru⋅1 ](PF ) and [Ru⋅2 ](PF ) showed fully reversible

2

6 2

2

6 2

temperature for all complexes except [Ru⋅1Cl (DMSO)]. Low

temperature studies showed no emission for the dileptic complex,

and a broad band centred at ~450 nm for each of the monoleptic

2

metal-centred oxidation of Ru(II) to Ru(III) at a potential of 1.42

V vs SCE (saturated calomel electrode). Variation of the ligand

‘arms’ from 4-(methylcarboxy)benzyl to 4-(carboxy)benzyl had

complexes [Ru⋅1Cl (DMSO), [Ir⋅1Cl₃] and [Pt⋅1Cl]Cl.

2

almost no impact on the donor properties of the chelating ligand,

which is in agreement with the remote location of these

functional groups and their similar electronic impact. The

oxidation potentials are higher than those reported for terpy-type

1

00 Concentrated glasses of [Pt⋅1Cl]Cl and [Pt⋅2Cl]Cl showed new

emission bands consistent with stacking behaviour.

Electrochemical measurements of Ru(II) complexes showed that

these compounds had higher oxidation potentials than similar and

complexes, e.g. +1.30 (vs SCE) for [Ru(terpy) ](PF ) , which

2

6 2

analogous compounds in the literature.

may be a direct consequence of the five- vs six-membered

peripheral heterocycles and the ensuing better mutual alignment

of metal coordination axes and the lone pairs in the terpy system.

2+

05

The X-ray crystal structure of complex [Ru⋅2₂] showed an

extensive hydrogen-bonding network involving the carboxylic

acid ‘arms’ of the ligand, chloride anions and solvent molecules.

This complex was shown to form gels in EtOH solution and

microscopy images (using both scanning electron microscopy and

2

+

While a related [Ru(btp)₂] complex with alkyl substituents at

the triazole units featured a redox behaviour similar to

+ 12

[

Ru(terpy)] , Hecht and co-workers reported very similar

10 helium ion microscopy) of these gels showed a fibrous structure

oxidation potentials to those observed here for a btp complex

8

| Journal Name, [year], [vol], 00–00

This journal is © The Royal Society of Chemistry [year]

DOI: 10.1039/C3DT52309H

Page 9 of 14

Dalton Transactions

with fibre widths in the range of 100±25 nm. When immobilised

charge on quoting the deposition numbers 956219-956222.

on a quartz slide, this gel exhibited ligand-centred emission much

like that seen for the complex in solution. Such systems suggest a

vast potential for application as materials with various functions

Microscopy studies of the gels

To image the gel samples by scanning electron microscopy

5

including surface healing or oxidation–reduction response, and 60 (SEM), they were deposited manually onto clean silicon samples

we are investigating these at present.

with a thick silicon dioxide layer. The spatula and glass pipettes

used for dosing and silicon pieces used as substrates were all

cleaned thoroughly by sonication in HPLC grade acetone

followed by HPLC grade propan-2-ol. The gels were manually

drop cast on to the silicon at room temperature and dried during 5

days at ambient conditions. Low kV SEM was carried out using

the Zeiss ULTRA Plus using either an SE2 or in-lens detector and

the Zeiss Orion Plus Helium Ion Microscope using an SE2

detector, both in the Advanced Microscopy Laboratory, CRANN,

Experimental

General methods and materials

6

5

All chemicals were purchased from commercial sources and

unless specified used without further purification. Melting points

were determined using an Electrothermal IA9000 digital melting

point apparatus. Elemental analysis was carried out at the

1

2

3

0

5

0

5

0

Microanalytical Laboratory, School of Chemistry and Chemical 70 Trinity College Dublin. The samples prepared for the imaging did

Biology, University College Dublin. Infrared spectra were

recorded on a Perkin Elmer Spectrum One FT-IR Spectrometer

fitted with a universal ATR sampling accessory. NMR spectra

not have any additional conductive layer cover. Beam energies

for the helium ion were 30–35 kV with probe currents ranging

from 0.1–1.5 pA. A 10 μm beam limiting aperture was employed

for all the images. Images were formed by collecting the

were recorded using a Bruker DPX-400 Avance spectrometer or

1

Agilent DD2/LH spectrometer, operating at 400.13 MHz for H- 75 secondary electrons generated during the helium ion interacting

1

3

NMR, 100.6 MHz for

C-NMR, or

a

Bruker AV-600

with the specimen atoms. Charge control was achieved using an

electron flood gun. After each line scan charge neutralisation was

applied. The image was acquired using either 32 or 64 line

averaging.

1

spectrometer, operating at 600.1 MHz for H-NMR and 150.2

1

3

MHz for

C-NMR. All spectra were recorded using

commercially-available deuterated solvents, and were referenced

to solvent residual proton signals. Electrospray mass spectra were

measured on a Micromass LCT spectrometer calibrated using a

leucine enkephaline standard. MALDI Q-Tof mass spectra were

carried out on a MALDI Q-Tof Premier (Waters Corporation,

Micromass MS technologies, Manchester, UK) and high-

resolution mass spectrometry was performed using Glu-Fib as an

internal reference (peak at m/z 1570.677). All microwave

reactions were carried out in 2–5 mL or 10–20 mL Biotage

Microwave Vials in a Biotage Initiator Eight EXP microwave

reactor.

80

Cyclic voltammetry

Electrochemical studies were carried out using a Metrohm

Autolab Potentiostat Model PGSTAT101 employing a gastight

three electrode cell under an argon atmosphere. A platinum disk

2

with 7.0 mm surface area was used as the working electrode and

85

polished before each measurement. The reference electrode was

Ag/AgCl, the counter electrode was a Pt foil. In all experiments

Bu NPF (0.1 M in dry CH CN) was used as supporting

4

6

3

electrolyte with analyte concentrations of approximately 1 mM.

The ferrocenium/ferrocene redox couple was used as an internal

X-ray Crystallography

57

90

reference (E₁_/₂= 0.40 V vs. SCE).

X-ray data (Table 1) were collected on either a Rigaku Saturn

Photophysical measurements

3

4

5

0

5

0

5

724 CCD Diffractometer (for 1 and [Ru·2 ](PF )Cl) using

2

6

UV-Visible absorbance spectra were measured in 1 cm quartz

cuvettes on a Varian Cary 50 spectrophotometer. Baseline

correction was applied for all spectra. Emission spectra were

measured on a Varian Cary Eclipse luminescence spectrometer.

graphite-monochromated Mo-Kα radiation (λ = 0.71073 Å) or a

Bruker Apex2 Duo (for [Ni·1 ](PF )Cl and [Ir·1Cl ]) using a high

2

6

3

intensity Cu-Kα radiation source (λ = 1.54178 Å). The data sets

from the Rigaku Saturn-724 diffractometer were collected using

Crystalclear-SM 1.4.0 software. Data integration, reduction and

correction for absorption and polarisation effects were all

performed using the Crystalclear-SM 1.4.0 software. Space group

determination, was obtained using Crystalstructure ver.3.8

software. The datasets collected on the Bruker Apex2 Duo were

processed using Bruker APEXv2011.8-0 software. All structures

were solved by direct methods (SHELXS-9 7) and refined against

9

5

All the stock solutions were prepared in CH CN.

3

Some emission spectra were also recorded on a Fluorolog FL-

3

−22 spectrometer from Horiba-Jobin-Yvon Ltd. A Jobin Yvon

FluoroHub single photon counting controller fitted with an

1

00 appropriate wavelength Jobin Yvon NanoLED was used to

measure lifetimes, which were determined from the observed

decays using DataStation v2.4.

2

55,56

all F data (SHELXL-97) using shelXle.

All H-atoms, except

Syntheses of ligands and metal ion complexes

for O–H protons, were positioned geometrically and refined using

a riding model with d(CH_a_r_o) = 0.95 Å, Uiso = 1.2Ueq (C) for

2

,6-Bis((trimethylsilyl)ethynyl)pyridine (3). Protected bis-

1

05 alkyne 3 was prepared from 2,6-dibromopyridine by Sonogashira

aromatic, d(CH) = 0.99 Å, Uiso = 1.2Ueq (C) for CH and 0.98

2

8,59

coupling using a modified literature procedure.

The reaction

Å, Uiso = 1.2Ueq (C) for CH . O–H protons were found from the

3

mixture was stirred at room temperature under argon atmosphere

difference map and fixed to the attached atoms with U = 1.2U .

H

O

for 24 hours, using a dry 1:1 Et N:THF solvent system. The

Crystallographic data for these structures has been deposited

with the Cambridge Crystallographic Data Centre, (CCDC, 12

3

solution was diluted with ethyl acetate and stirred vigorously with

1

10 a solution of EDTA/NH OH for 1 hour. The reaction mixture was

Union

Road,

Cambridge

CB21EZ,

UK;

4

then extracted with ethyl acetate and washed with saturated

http://www.ccdc.cam.ac.uk). Copies can be obtained free of

This journal is © The Royal Society of Chemistry [year]

Journal Name, [year], [vol], 00–00 | 9

DOI: 10.1039/C3DT52309H

Dalton Transactions

Page 10 of 14

1

NaHCO₃solution and brine before drying over MgSO₄and

18.76. Found C = 57.39, H = 3.75, N = 18.92. H NMR (600

concentrating under reduced pressure, yielding a brown solid. 60 MHz, DMSO): δ (ppm) = 5.80 (s, 4H, CH ), 7.45 (d, 4H, J = 8.7

2

Crude product was filtered through a silica plug, washing in

hexane/CH Cl (1:1) and the eluent concentrated under reduced

Hz, Ph CH), 7.91–8.03 (m, 7H, Ph CH and pyr CH), 8.74 (s, 2H,

1

3

triazolyl CH); C NMR (150 MHz, DMSO-d ): δ (ppm) = 52.8

2

6

5

0

5

0

5

0

5

0

5

0

5

pressure, yielding 3 as a tan coloured solid (3.10 g, 11.410 mmol,

(CH ), 118.7 (3- and 5-pyr CH), 124.1 (triazolyl CH), 128.2

(phenyl CH), 129.9 (Ph CH), 130.6 (Ph qt), 138.1 (4-pyr CH),

2

0

6

8%). m.p. 90.3–98.7 °C (Lit. m.p. 97–99 °C). HRMS (m/z)

+

(ESI ): Calculated for C H NSi m/z = 272.1291 [M+H] . 65 140.8 (Ph qt), 147.5 (triazolyl qt), 149.8 (2- and 4-pyr qt), 167.03

15 22 2

1

−1

Found m/z = 272.1299; H NMR (400 MHz, CDCl ): δ = 0.28 (s,

(C=O); IR ν_m_a_x(cm ): 3083 (ar C–H st), 2938 (C–H st), 1719,

3

1

8H, TMS), 7.41 (d, 2H, J = 7.8 Hz, 3- and 5-pyridyl CH), 7.62

1692 (C=O st), 1642, 1614, 1531, 1467, 1420, 1400, 1285, 1242,

1198, 1176, 1106, 1047, 942, 822, 800, 725.

-

1

2

3

4

5

(t, 1H, J = 7.8 Hz, 4-pyridyl CH); IR ν_m_a_x(cm ): 3052 (strong),

2

962, 2900, 2154 (C≡C), 1558, 1440, 1249, 1206, 1163, 1082,

9

85, 953, 836, 811 (strong), 759, 734, 702, 656.

70 Monoleptic Ru(II) complex ([Ru⋅1Cl (DMSO)]). Precursor cis-

2

[

RuCl (DMSO) ] was prepared in a microwave reaction

2 4

General procedure for synthesis of btp ligands 1 and 2

To a solution of the relevant bromide (4.65 mmol) in 15 mL

DMF/water (4:1) was added sodium azide (0.332 g, 4.65 mmol)

according to a literature procedure from RuCl xH O. To this

3 2

complex (0.029 g, 0.059 mmol) was added the ligand 1 (0.030 g,

0.059 mmol) and 5 mL CHCl₃and the mixture refluxed in

and the reaction mixture stirred for 1 hour, yielding the azide 75 darkness for 10 hours before isolating the product complex upon

derivative, which was not isolated, and therefore used without

further purification.** To this solution was added 3 (0.631 g,

2.33 mmol). CuSO ·5H O (0.232 g, 0.93 mmol) and sodium

filtration and washing with ether, yielding a bright red solid

(0.039 g, 0.051 mmol, 86%). Product decomposed over 216 °C.

+

HRMS (m/z) (MALDI): Calculated for C H N O Cl Ru m/z =

4

2

27 23

7

4

2

+

ascorbate (0.368 g, 1.86 mmol) were added to the reaction

681.0232 [M−(DMSO)] . Found m/z = 681.0213; Calculated for

mixture, followed by anhydrous K CO (0.650 g, 4.70 mmol) and 80 C H N O SRuCl ⋅0.5CHCl , C = 43.25, H = 3.63, N = 11.97.

2

3

29 29

7

5

2

3

1

stirred at room temperature for 18 hours in a further 15 mL 4:1

Found C = 43.60, H = 3.39, N = 11.83; H NMR (600 MHz,

DMF/water. EDTA/NH OH solution was added to the reaction

DMSO-d ): δ (ppm) = 3.49 (s, 6H, coordinated DMSO), 3.86 (s,

4

6

mixture and stirred for 1 hour before isolating the product.

6H, –OCH ), 5.92 (s, 4H, CH ), 7.54 (d, 4H, Ph CHs, J = 8.0 Hz),

3

2

8

.01 (d, 4H, Ph CHs, J = 8.0 Hz), 8.07–8.18 (m, 3H, pyr CH),

1

3

2

,6-Bis(1-(4-(methylcarboxy)benzyl)-1,2,3-triazol-4-

85 9.16 (s, 2H, triazolyl CH); C NMR (150 MHz, DMSO-d ): δ =

6

yl)pyridine (1). Ligand 1 was prepared according to the general

procedure above from methyl 4-(bromomethyl)benzoate and was

46.8 (coordinated DMSO), 52.6 (–OCH ), 54.3 (CH ), 119.0 (pyr

3

2

CH), 125.7 (triazolyl CH), 128.9 (Ph CH), 130.1 (Ph CH), 137.8

isolated upon extraction with CHCl , washing the organic layer

(pyr CH), 140.2 (qt), 149.9 (qt), 150.9 (qt), 166.1 (qt); IR ν

(cm ): 3443 (br), 3011, 2925, 1715 (strong), 1614, 1580, 1418,

3

max

−1

with brine. Concentration under reduced pressure and trituration

with cold CH OH followed by recrystallisation from boiling 90 1283 (strong), 1185, 1108 (strong), 1085, 1018, 993, 961, 931,

3

CH OH yielded ligand

1

as an off-white solid (1.27 g,

809, 749, 718, 677.

3

+

2

.49 mmol, 53%). m.p. 221.1–223.5 °C. HRMS (m/z) (ESI ):

+

Calculated for C H N O Na m/z = 532.1709 [M+Na] . Found

General procedure for synthesis of dileptic Ru(II) and Ni(II)

complexes. To the relevant ligand (2 equiv.) was added 5 mL

2

7

23

7

4

m/z = 532.1711; Calculated for C H N O , C = 63.65, H = 4.55,

2

7

23

7

4

1

N = 19.24. Found C = 63.38 H = 4.52 N = 19.29. H NMR (400 95 aqueous ethanol solution (70% v/v). The solution was degassed

MHz, DMSO): δ = 3.84 (s, 6H, –OCH ), 5.81 (s, 4H, CH ), 7.45 and RuCl ⋅xH O or NiCl ⋅xH O (1 equiv.) added. This was stirred

3

2

3

2

(

d, 4H, J = 8.2 Hz, Ph CH), 7.91–8.07 (m, 7H, Ph CH and pyr

for 40 minutes at 120 °C under microwave irradiation. The

yellow reaction mixture was filtered through celite and

concentrated under reduced pressure. Ethanol was added to

1

3

CH), 8.72 (s, 2H, triazolyl CH); C NMR (150 MHz, CDCl ): δ

3

=

52.4 (–OCH ), 53.8 (CH ), 119.4 (3- and 5-pyridyl CH), 122.1

3 2

(triazolyl CH), 127.8 (phenyl CH), 130.3 (phenyl CH), 130.6 (qt, 100 solubilise the complex before centrifuging. The supernatant was

phenyl), 137.8 (4-pyridyl CH), 139.3 (qt, phenyl), 148.8 (qt,

decanted off and a few drops of NH PF were added before

4 6

centrifuging again. The solution was decanted off and the solid

triazolyl), 149.7 (qt, 2- and 6-pyridyl), 166.3 (C=O). IR ν

(cm ): 3154, 3078 (ar C–H st), 3010, 2956 (C–H st), 2845 (O–

max

−1

which had formed was dissolved in CH CN and concentrated

3

CH st), 2101, 1729 (C=O st), 1608 and 1572 (C–C γ), 1511,

under reduced pressure, yielding a solid.

3

1

436, 1426, 1314, 1278, 1236, 1214, 1196, 1155, 1109, 1085, 105

044, 1022, 991, 973, 843, 820, 797, 782, 756, 732, 687, 667.

Dileptic Ru(II) complex of

1 ([Ru⋅1 ](PF ) ). Complex

2 6 2

[

Ru⋅1 ](PF ) was prepared according to the general procedure

2

6 2

2,6-Bis(1-(4-(carboxy)benzyl)-1,2,3-triazol-4-yl)pyridine (2).

Like 1 above, carboxylic acid ligand 2 was synthesised from 4-

for dileptic complexes outlined above, from ligand 1 (0.056 g,

0.11 mmol) and RuCl ⋅xH O (0.012 g, 0.05 mmol), yielding a

3

2

(bromomethyl) benzoic acid. It was isolated upon acidification of 110 bright yellow solid (0.015 g, 0.01 mmol, 28%). This was

the EDTA/NH OH solution by dropwise addition of concentrated

dissolved in CH CN and crystallised via ether diffusion. m.p.

4

3

HCl solution until pH 7 was reached. 2 was collected as a beige

236.1–238.0 °C. HRMS (m/z) (MALDI): Calculated for

+

solid upon suction filtration (0.705 g, 1.46 mmol, 63%). Product

C H N O F PRu m/z = 1265.2308 [M−PF ] . Found m/z =

54 46 14 8 6 6

−

+

decomposed over 284 °C. HRMS (m/z) (ESI ): Calculated for

1265.2323; Calculated for C H N O F P RuNa m/z =

54 46 14 8 12 2

−

+

C H N O m/z = 480.1426 [M−H] . Found m/z = 480.1423; 115 1433.1848. Found m/z = 1433.1832. [M+Na] ; Calculated for

2

5

18

7

4

Calculated for C H N O ⋅0.5H O, C = 57.46, H = 3.86, N =

C H N O RuP F ⋅3H O, C = 44.30, H = 3.58, N = 13.39.

54 46 14 8 2 12 2

2

5

19

7

4

2

1

0

| Journal Name, [year], [vol], 00–00

DOI: 10.1039/C3DT52309H

Page 11 of 14

Dalton Transactions

1

Found C = 44.22, H = 3.17, N = 13.39; H NMR (600 MHz,

(0.210 g, 0.41 mmol) and IrCl ⋅xH O (0.130 g, 0.41 mmol) were

3 2

DMSO-d ): 3.75 (s, 6H, –OCH ), 5.35 (s, 4H, CH ), 6.62 (d, 4H, 60 suspended in ethylene glycol (5 mL). The reaction mixture was

6

3

2

J = 7.0 Hz, Ph CH), 7.18 (d, 4H, J = 7.0 Hz, Ph CH), 7.64 (t, 1H,

J = 6.9 Hz, 4-pyr CH), 7.71 (d, 2H, J =6.8 Hz, 3- and 5-pyr CH),

8.41 (s, 2H, triazolyl CH); C NMR (150 MHz, DMSO-d ): δ

6

degassed before heating at 160 °C in darkness for 20 minutes

under microwave irradiation. The reaction mixture was allowed

to cool to room temperature before filtering to collect precipitate.

The precipitate was washed with ethanol, H O and Et O, yielding

1

3

5

0

5

0

5

0

5

0

5

0

5

(

ppm) = 52.6 (–OCH ), 54.5 (CH ), 120.8 (4-pyr CH), 127.2

3 2

2

(

triazolyl CH), 128.4 (Ph CH), 130.0 (Ph CH), 138.4 (3-, 5-pyr 65 complex [1⋅IrCl ] as a yellow solid (0.166 g, 0.21 mmol, 50%).

3

1

9

+

CH), 139.4 (Ph qt), 150.3 (triazolyl qt), 165.9 (carbonyl qt);

F

Product decomposed over 330 °C. HRMS (m/z) (ESI ):

Calculated for C H N O Cl IrNa m/z = 830.0404 [M+Na] .

27 23 7 4 3

+

NMR (376 MHz, DMSO-d ): δ = −70.6 (d, J = 706.1 Hz, PF );

6

3

1

2

3

4

5

P NMR (162 MHz, DMSO-d ): δ = −142.98 (apparent quin, J =

11.4 Hz); IR ν_m_a_x(cm ): 3322, 1711, 1640, 1618, 1572, 1646,

Found m/z = 830.0373; Calculated for C H N O IrCl ⋅C H O ,

27 23 7 4 3 2 6 2

6

−1

7

1

C = 40.03, H = 3.36, N = 11.27. Found C = 39.37, H = 3.05, N =

1

428, 1281, 1191, 1111, 828 (strong), 730.

70 10.99; H NMR (400 MHz, DMSO-d ): δ = 3.86 (s, 6H, –OCH ),

6

3

6

.08 (s, 4H, CH ), 7.61 (d, 4H, J = 8.4 Hz, phenyl CH), 8.05 (d,

2

Dileptic Ru(II) complex of

[Ru⋅2 ](PF ) was prepared according to the general procedure for

dileptic complexes outlined above, using dicarboxylate

2

([Ru⋅2 ](PF ) ). Complex

4H, J = 8.2 Hz, Ph CH), 8.15 (t, 1H, J = 7.7 Hz, 4-pyr CH), 8.30

(d, 2H, J = 7.8 Hz, 3- and 5-pyr CH), 9.33 (s, 2H, triazolyl CH);

C NMR (150 MHz, DMSO-d , assigned from CH COSY): δ =

6

2

6 2

2

6 2

1

3

2

(0.100 g, 0.21 mmol) and RuCl ⋅xH O (0.023 g, 0.11 mmol), 75 52.7 (–OCH ), 55.2 (CH ), 120.4 (3-, 5-pyr CH), 127.5 (triazolyl

3

2

3

2

yielding a bright yellow solid (0.069 g, 0.06 mmol, 26%). This

was re-dissolved in a 1:1 mixture of CH CN and ethanol and

crystallised via ether diffusion. A large yellow crystal was formed

and structure determined by X-ray diffractometry. m.p. 206.5–

2

C H N O Ru m/z = 1063.1962 [M−2(PF )−H]+ . Found m/z =

1

H = 3.15 N = 13.93. Found C = 42.05 H = 2.58 N = 13.70; H

NMR (400 MHz, DMSO-d ): δ = 5.67 (s, 8H, CH ), 7.19 (d, 8H,

J = 8.3 Hz, Ph CH), 7.86 (d, 8H, J = 8.2 Hz, Ph CH), 8.36 (t, 2H, 85 purification. To this complex (1 equiv.) was added ligand 1 or 2

J = 7.7 Hz, 4-pyr CH), 8.45 (d, 4H, J = 7.7 Hz, 3- and 5-pyr CH),

9

53.8 (CH ), 120.0 (3-, 5-pyr CH), 126.3 (triazolyl CH), 127.7 (Ph

CH), 129.7 (Ph CH), 131.0 (Ph qt), 137.5 (4-pyr CH), 137.8 (Ph

qt), 149.0 (pyr qt), 149.5 (triazolyl qt), 166.3 (C=O qt); F NMR 90 Pt(II) complex of 1 ([Pt⋅1Cl]Cl). According to the general

(

CH), 129.2 (Ph CH), 130.2 (Ph CH), 141.1 (4-pyr CH); IR ν

max

−1

(cm ): 3498, 3124, 2955, 1723 (strong), 1615, 1594, 1478, 1431

(strong), 1349, 1277 (strong), 1219, 1187, 1110 (strong), 1085,

1074, 1052, 1022, 953, 869, 807, 770, 753, 726 (strong), 713,

3

09.6 °C. HRMS (m/z) (MALDI): Calculated for 80 687, 658, 634, 622.

+

5

0

37 14

8

6

063.1998; Calculated for C H N O RuP F ⋅3H O, C = 42.65

General procedure for preparation of Pt(II) complexes.

5

0

38 14

8

2

12

2

1

Precursor cis-[PtCl (DMSO) ] was prepared from K [PtCl ]

2

4

according to a literature procedure and used without further

6

2

(1 equiv.) and the suspension refluxed in CH OH in darkness for

5 hours. The reaction mixture was cooled over ice before

isolation of the product.

3

1

3

.26 (s, 4H, triazolyl CH); C NMR (150 MHz, DMSO-d ): δ =

6

2

1

9

3

1

376 MHz, DMSO-d ): δ = −70.6 (d, J = 711.4 Hz, PF );

P

procedure above, ligand 1 (0.081 g, 0.16 mmol) was treated with

cis-[PtCl (DMSO) ] (0.069 g, 0.16 mmol). Product was purified

by filtering the reaction mixture, concentrating the filtrate, re-

6

NMR (162 MHz, DMSO-d ): δ = −142.99 (apparent quin, J =

6

2

−1

711.2 Hz); IR ν_m_a_x(cm ): 3321, 2921, 2850, 1695, 1615, 1576,

421, 1261, 1111, 1056, 1020, 805 (strong).

1

dissolving this in CHCl and centrifuging. The supranatent was

3

95

decanted off and the process repeated until the supranatent was

colourless. The resultant yellow solid was the pure complex

[Pt⋅1Cl]Cl (0.024 g, 0.032 mmol, 20%). Product decomposed

Ni(II) complex of 1 ([Ni⋅1 ](PF ) ). Complex [Ni⋅1 ](PF ) was

prepared according to the general procedure outlined above using

1 (0.100 g, 0.20 mmol) and NiCl ⋅xH O 0.013 g, 0.10 mmol).

Ether diffusion into a CH CN solution yielded lilac needle-like

crystalline solid (0.020 g, 0.014 mmol, 20%). m.p. 189.9–193.8 100 739.1143; Calculated for C H N O PtCl ⋅0.5H O, C = 39.55 H,

°

m/z = 1221.2618. Found m/z = 1221.2644; Calculated for

C H N O NiP F ⋅H O, C = 46.81, H = 3.49, N = 14.15. Found

C = 46.83, H = 2.98, N = 13.78; H NMR (600 MHz, CD CN): δ

2

6 2

2

6 2

+

over 250 °C. HRMS (m/z) (ESI ): Calculated for

2

+

C H N O ClPt m/z = 739.1148 [M−Cl] . Found m/z =

27 23 7 4

3

2

7

23

7

4

2

+

1

C; HRMS (m/z) (MALDI+): Calculated for C H N O NiF P

= 2.84, N = 11.74. Found C = 40.07, H = 2.42, N = 11.70; H

5

4

46 14

8

6

NMR (400 MHz, DMSO-d ): δ = 3.83 (s, 6H, –OCH ), 6.00 (s,

6

3

4H, CH ), 7.57 (d, 4H, J = 8.3 Hz, Ph CH), 8.01 (d, 4H, J = 8.3

5

4

46 14

8

2

12

2

1

Hz, Ph CH), 8.22 (d, 2H, J = 8.0 Hz, 3, 5-pyr CH), 8.47 (t, 1H, J

3

−1

=

5

3.84 (br), 5.49 (br), 6.41 (br), 7.86 (br), 17.48 (br), 29.94 (br), 105 = 8.1 Hz, 4-pyr CH), 9.32 (s, 2H, triazolyl CH); IR ν_m_a_x(cm ):

1

3

6.46 (br); C NMR (150 Hz, CD CN, assigned by CH COSY):

3423, 3076, 2953, 1716 (strong), 1614, 1595, 1579, 1512, 1479,

1434, 1418, 1313, 1280 (strong), 1223, 1184, 1110 (strong),

1074, 1047, 1019, 965, 840, 812, 747, 725 (strong), 687, 659.

3

1

9

δ = 50.2, 126.2; F NMR (376 MHz, CD CN): δ = −73.4 (d, J =

706.6 Hz, PF₆); P NMR (162 MHz, CD CN): δ = −144.6

3

1

3

−1

(apparent quin, J = 706.4 Hz, PF ); IR ν (cm ): 3077, 2615,

6 max

2

1

301, 1714 (strong), 1615, 1592, 1579, 1512, 1474, 1435, 1419, 110 Pt(II) complex of 2 ([Pt⋅2Cl]Cl). According to the general

316, 1279 (strong), 1217, 1183, 1110 (strong), 1065, 1053,

020, 967, 813 (strong), 770, 726 (strong), 619, 604, 589, 576,

procedure above, 2 (0.183 g, 0.38 mmol) was treated with cis-

[PtCl (DMSO) ] (0.161 g, 0.38 mmol). Product was isolated upon

2

555 (strong).

filtration and washed with CH OH, CHCl and Et O, yielding

3 3 2

[Pt⋅2Cl]Cl as a yellow solid (0.212 g, 0.298 mmol, 78%). Product

Ir(III) Complex of 1 ([Ir⋅1Cl ]). Complex [Ir ⋅1 Cl ] was 115 decomposed over 350 °C HRMS (MALDI): Calculated for

3

5,62

+

synthesised using a modified literature procedure.

Ligand 1

C H N O ClPt m/z = 711.0835 [M−Cl] . Found m/z =

25 19 7 4

Journal Name, [year], [vol], 00–00 | 11

DOI: 10.1039/C3DT52309H

Dalton Transactions

Page 12 of 14

6

.

T. Kinoshita, J. T. Dy, S. Uchida, T. Kubo and H. Segawa, Nature

Photonics, 2013, 7, 535-539.

7

11.0859; Calculated for C H N O PtCl ⋅1.5CHCl , C = 34.35,

25 19 7 4 2 3

1

H = 2.23, N = 10.58. Found C = 34.02, H = 2.01, N = 10.33; H

NMR (600 MHz, CD OD): δ (ppm) = 5.96 (s, 4H, CH ), 7.65 (d,

4

CH), 8.39 (t, 1H, J = 8.2 Hz, 4-pyr CH), 9.13 (s, 2H, triazolyl

CH); C NMR (150 MHz, CD OD): δ = 55.7 (CH ), 120.5 (3-

6

7

8

9

5

0

5

0

5

0

5

7. F. S. Han, M. Higuchi, T. Ikeda, Y. Negishi, T. Tsukuda and D. G.

Kurth, J. Mater. Chem., 2008, 18, 4555-4560.

3

2

H, J = 8.3 Hz, Ph CH), 8.06–8.18 (m, 6H, Ph CH and 3-, 5-pyr

8. a) J. A. Kitchen, E. M. Boyle and T. Gunnlaugsson, Inorg. Chim.

Acta, 2012, 381, 236-242. b)P. Wang, Z. Li, G.-C. Lv, H.-P. Zhou, C.

Hou, W.-Y. Sun and Y.-P. Tian, Inorg. Chem. Commun., 2012, 18,

87-91. c) A. M. Nonat, A. J. Harte K. Senechal-David, J. P. Leonard

and T. Gunnlaugsson, Dalton Trans., 2009, 4703.

9. a) R. M. Meudtner, M. Ostermeier, R. Goddard, C. Limberg and S.

Hecht, Chem. Eur. J., 2007, 13, 9834-9840. b) D. Schweinfurth, N.

Deibel, F. Weisser and B. Sarkar, Nachr. Chem., 2011, 59, 937-941.

c) J. Crowley and D. McMorran, Top. Het. Chem., 2012, 28: 31-84.

5

1

3

2

and 5-pyr CH), 127.1 (triazolyl CH), 128.4 (Ph CH), 130.1 (Ph

CH), 131.5 (qt), 142.3 (4-pyr) CH, 148.1 (qt), 151.3 (qt), 151.7

−1

(

qt), 167.3 (C=O qt); IR ν_m_a_x(cm ): 3424, 3077, 2635, 1698

(strong), 1614, 1580, 1480, 1419, 1388, 1279 (strong), 1182,

116 (strong), 1073, 1049, 1017, 818 (strong), 752 (strong), 729

strong).

1

0

1

(

1

0. L. Munuera and R. K. O'Reilly, Dalton Trans., 2010, 39, 388-391.

11. T. El Malah, S. Rolf, S. M. Weidner, A. F. Thünemann and S. Hecht,

Chem. Eur. J., 2012, 18, 5837-5842.

1

2. Y. Li, J. C. Huffman and A. H. Flood, Chem. Commun., 2007, 2692-

2694.

Acknowledgements

3. a) P. Danielraj, B. Varghese and S. Sankararaman, Acta Crystallogr.

Sect. C, 2010, 66, m366-m370. b) D. Zornik, R. M. Meudtner, T. El

Malah, C. M. Thiele and S. Hecht, Chem. Eur. J., 2011, 17, 1473-

1484. c) N. Chandrasekhar and R. Chandrasekar, Angew. Chem. Int.

Ed., 2012, 51, 3556-3561. d) J. D. Crowley, P. H. Bandeen and L. R.

Hanton, Polyhedron, 2010, 29, 70-83.

We thank the Irish Research Council Embark Initiative

(Postgraduate Postgraduate Scholarship JPB, and Postdoctoral

Fellowship to JAK) and Science Foundation Ireland for financial

support (SFI 2010 and 2012 Principal Investigation grants (TG

and JJB, respectively). JPB would like to thank Dr Jennifer E.

Jones, Dr Steve Comby, Samuel Bradberry, Bryan Hogan, Colm

Delaney and Dr Gearóid Ó Máille for useful discussion. We

would like to thank Dr John O’Brien for technical assistance and

useful discussion of NMR results and Prof. Sylvia Draper for use

of low-temperature spectroscopy apparatus.

1

5

1

4. C. W. Tornøe, C. Christensen and M. Meldal, J. Org. Chem., 2002,

6

7, 3057-3064.

2

0

15. V. V. Rostovtsev, L. G. Green, V. V. Fokin and K. B. Sharpless,

Angew. Chem. Int. Ed., 2002, 41, 2596-2599.

1

6. T. R. Chan, R. Hilgraf, K. B. Sharpless and V. V. Fokin, Org. Lett.,

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