Triazolylidene Metal Complexes Tagged with a Bodipy Chromophore

Article pubs.acs.org/Organometallics

Triazolylidene Metal Complexes Tagged with a Bodipy Chromophore: Synthesis and Monitoring of Ligand Exchange Reactions Miquel Navarro,†,‡ Suxiao Wang,‡ Helge Müller-Bunz,‡ Gareth Redmond,‡ Pau Farràs,§ and Martin Albrecht*,†,‡ †

Department für Chemie und Biochemie, Universität Bern, CH−3012 Bern, Switzerland School of Chemistry, University College Dublin, Belfield, Dublin 4, Ireland § School of Chemistry, NUI Galway, Galway, Ireland ‡

S Supporting Information *

ABSTRACT: The alkyne azide “click” reaction was successfully used to prepare new Bodipy-functionalized triazoles and triazolium salts. The Bodipy functionality was compatible with cyclometalation conditions as well as with transmetalation procedures involving a triazolyldene silver intermediate, as demonstrated by the successful formation of a metallacyclic palladium dimer and an iridium chelate. Both complexes were characterized by X-ray diffraction, and spectroscopic studies demonstrate unperturbed photoluminescence of the Bodipy chromophore (emission around 545 nm, quantum yields in the 0.35−0.7 range, and excited-state lifetimes between 3 and 7 ns). The palladium dimer 4 was cleaved using N,N-dimethylaminopyridine (dmap) and acridine to afford monomeric triazolylidene palladium complexes 5 and 6. While dmap is a classical spectator ligand, acridine acts as photoluminescence quencher and quenching constants were determined as KSV = 0.86 and 1.6 × 104 M−1 for complexes 4 and 5, respectively. This dual reactivity of acridine as ligand and quencher was utilized for a ligand displacement assay that allowed modification of the organometallic site of the hybrid complex to be monitored by emission spectroscopy.

■

INTRODUCTION Boron-dipyrromethene (Bodipy) compounds have been extensively studied since the first 4,4-difluoro-4-bora-3a,4adiaza-s-indacene was prepared in 1968.1 Derivatives of Bodipy have since become very valuable functional units and have been applied successfully in both materials science and in biomedical studies.2 The wide range of applications of Bodipy compounds originates from a combination of beneficial properties, including excellent thermal and photochemical stability, high fluorescence quantum yields, accessibility of triplet states, relatively high absorption coefficients, and excitation and emission at wavelengths above 500 nm. These benefits have prompted the use of Bodipy derivatives as building blocks for fabricating, for example, energy transfer cassettes,3 artificial light harvesting complexes,4 fluorescent switches,5 chemosensors,6 and sensitizers for dye-sensitized solar cells.7 A large number of Bodipy derivatives with tunable and hence promising photophysical properties have been prepared over the past few years using a variety of different synthetic strategies.2,8 Recently, transition-metal-containing chromophoric compounds have been prepared by attaching a metal center to the periphery of the Bodipy unit or via incorporation into the π-conjugated core of Bodipy.9,10 These materials feature a © XXXX American Chemical Society

number of options for tuning the properties of the resulting metal Bodipy hybrid species in a well-defined manner. Despite this progress, however, the effect of the metal center on the chromophoric properties of Bodipy materials has been rather limited. Functionalization of Bodipy scaffolds with an N-heterocyclic carbene (NHC) complex offers unique opportunities for exploiting the synergies that arise from combining photoluminescence and transition-metal-centered (catalytic) activity.11 In particular, NHCs generally form robust bonds to transition metals12 and impart high catalytic activity.13 First proofs of concept to link Bodipy fragments to imidazolylidenes have just appeared while our work was ongoing.14 In our efforts to integrate N-heterocyclic carbenes for materials application,15 we have recently focused on triazolylidenes,16 a subclass of the so-called abnormal or mesoionic carbenes.17 The 1,2,3-triazole core of these ligands is synthetically very versatile and can be assembled by highly functional group tolerant [2 + 3] cycloaddition reactions of alkynes and azides.18 Most relevant in this context, “click” chemistry has been used previously to Received: August 22, 2016

A

DOI: 10.1021/acs.organomet.6b00672 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics

ously by the spectroscopic signature of the triazole C−H unit, which appears as a singlet at 7.83 ppm in the 1H NMR spectrum and as a new resonance in the aromatic region at δC 120.0 in the 13C NMR spectrum. Subsequent alkylation of the N3 position was accomplished with MeOTf (OTf = trifluoromethanesulfonate, CF3SO3−). Performing this alkylation in Et2O induced spontaneous precipitation of the pure triazolium salt 3. Diagnostic spectroscopic features for the formation of the triazolium salt were the deshielding of the Ctrz−H singlet by more than 1 ppm (δH 9.03), in addition to the appearance of the N−CH3 resonance at δH 4.35 in the 1H NMR spectrum. Moreover, an X-ray diffraction analysis of suitable single crystals that formed directly from the reaction solution confirmed the formation of 3. Palladation of this hybrid Bodipy triazolium salt 3 was accomplished by reacting 3 with Pd(OAc)2 in the presence of K2CO3 and NaCl (THF solution, reflux temperature for 2 days). The carbonate base was added to facilitate metal coordination as well as a proton-scavenging source,22 while NaCl was added to provide an anionic ligand for metal coordination. This protocol yielded the palladium complex 4 as an orange solid. Purification of this complex was conveniently achieved by column chromatography (CH2Cl2/MeOH, 99/1), affording pure complex 4 in a moderate 47% yield. Spectroscopic analysis is in agreement with the formation of a cyclometalated species and reveals the disappearance of the triazolium CH signal as well as the loss of an aromatic CH resonance of the meso-aryl group that links the Bodipy fragment to the triazolylidene unit. Moreover, the residual aromatic resonances are non symmetry related in the chelate and appear as three distinct signals at δH 7.65, 7.44, and 7.00. The two high-field resonances show a characteristic three-bond coupling (3JHH = 8.0 Hz), while the most up- and downfield resonances are both split by long-range coupling (4JHH = 1.8 Hz). These data allow for an unambiguous assignment and reveal metal coordination in comparison to the two doublets at δH 8.12 and 7.46 ppm in the ligand precursor 3 (Figure S1 in the Supporting Information). Ortho palladation and the formation of a Pd−Caryl bond was also supported by a low-field 13C NMR signal at δC 144.6 in addition to the triazolylidene resonance at δC 152.1. Related cyclopalladation was previously observed in similarly aryl-substituted triazolium23 and imidazolium salts.24 X-ray diffraction analysis of single crystals confirmed the spectroscopically deduced coordination pattern of complex 4 and indicate the formation of a bis-μ2-chlorido-bridged palladium(II) dimer which allows the palladium to adopt a square-planar geometry (Figure 2).23,25 The bridging mode entails a coplanar arrangement of the two Pd(C,C) metallacycles. The molecular structure further illustrates the κ2C,C′ bonding motif of the triazolylidene ligand, which includes the carbenic triazolylidene C atom and one carbon of the aryl ring that links the Bodipy and the triazolylidene ligand. This chelation forces the heterocycle, the ortho-metalated phenyl ring, and the metallacycle into a mutually coplanar arrangement. The bond lengths are in agreement with related carbenearyl ortho-palladated structures,23,25 with the Pd−Ctrz bond distance (Pd1−C24 = 1.994(4) Å, Pd2−C54 = 1.979(4) Å) only marginally shorter than the Pd−Caryl bond distance (Pd1− C20 = 2.003(3) Å, Pd2−C50 = 2.018(4) Å; Table 1). Cleavage of such halide-bridged palladium dimers has been extensively studied and is readily achieved by using N- or Pdonor ligands to afford monometallic species.26 In this work, we have chosen two different N-donor ligands to form

prepare specific Bodipy compounds that are connected to triazoles either via the meso-aryl group or via one of the pyrrole fragments (Figure 1).19 Building on these preliminary results,

Figure 1. Examples of Bodipy triazole compounds prepared by “click” chemistry on the meso-aryl group (left) and directly on the Bodipy core (right).

we here report on the successful synthesis of the first Bodipy mesoionic carbene hybrid complexes and their photophysical properties. The utilization of acridine, which acts both as a ligand and as a quencher,20 has been exploited in order to spectroscopically probe ligand substitution, one of the fundamental metal-centered transformations.

■

RESULTS AND DISCUSSION Synthesis of Bodipy Triazolylidene Palladium Complexes. The availability of the azide-functionalized Bodipy derivative 1 provided direct access to Bodipy-functionalized triazolylidene complexes (Scheme 1).10 Thus, coupling of 1 with 1-hexyne via dipolar [2 + 3] cycloaddition (“click” chemistry),21 which was performed in the presence of CuSO4 and sodium ascorbate under biphasic conditions (H2O/tBuOH; 1/1 ratio), afforded triazole 2 containing a Bodipy unit in a remote position. Product formation was indicated unambiguScheme 1. General Synthesis of Bodipy-Functionalized Mesoionic Triazolium Ligand 3 and ORTEP Diagram of Triazolium Salt 3a

a

Thermal ellipsoids in the ORTEP drawing are given at the 50% probability level; hydrogen atoms and the cocrystallized CHCl3 molecule are omitted for clarity. B


Article

Organometallics

complexes at 744.2969 and 801.2866 amu, respectively (theoretical values 744.2989 and 801.2880 amu, respectively). Morever, the 1H NMR spectra show the appearance of a new set of signals in the aromatic region corresponding to 1 equiv of coordinated dmap and acr, respectively, as well as a new singlet at δH 2.53, which is characteristic for the two NCH3 groups of the dmap ligand in complex 5. Imine coordination and dimer cleavage induced a diagnostic upfield shift of the 1H NMR resonance attributed to the phenyl proton in an ortho position relative to palladium (Figure S2 in the Supporting Information). Upon dmap coordination, this resonance appears a full 1 ppm upfield: viz. δH 7.65 in complex 4 in comparison to δH 6.65 in complex 5. This shift is even more pronounced upon acridine coordination, and the CH resonance appears at a remarkable 1.95 ppm higher field (δH 5.70). In contrast, the other two phenyl protons of the same aromatic system experience only marginal changes (Δδ < 0.15 ppm), suggesting a through-space rather than an electronic origin for the observed shift. These data therefore suggest a trans arrangement of the triazolylidene and aromatic imine ligand and a strong aromatic ring current that affects the resonance frequency of the ortho proton of the cyclometalated phenyl group due to a perpendicular orientation of the acridine and dmap ligands with respect to the palladium coordination plane. Such a ring current is expected to be more pronounced for the larger aromatic system acridine than for dmap, in agreement with the more pronounced upfield shift.27 Moreover, 1H NMR spectroscopy indicated the presence of a minor component (7), suggesting this minor component to be the cis isomer. These structural assignments were confirmed by an X-ray diffraction analysis of suitable crystals of complex 6. The ORTEP representation reveals a palladium center in a slightly distorted square planar geometry with the acridine ligand positioned trans to the triazolylidene and cis to the aryl ligand (Figure 3). The Pd−Ctrz (carbene) and the Pd−Caryl bond lengths are essentially unaltered in comparison to those in the dimeric structure 4 (Pd−C1 = 1.9919(18) Å and Pd−C8 = 2.0112(18) Å), indicating that these bond lengths are predominantly governed by the chelate bonding mode and much less by the trans-positioned ligand. The Pd−Nacr distance (Pd−N6 = 2.1209(15) Å) is larger than those of related complexes reported in the literature,28 presumably due to the high trans effect induced by the triazolylidene ligand. As surmised from the NMR spectroscopic shifts, the acridine ligand is positioned almost perpendicular to the palladium

Figure 2. ORTEP diagram of palladium dimer 4. Thermal ellipsoids are given at the 50% probability level; hydrogen atoms are omitted for clarity.

Table 1. Selected Bond Lengths (Å) and Angles (deg) of the Two Pd Units in the Dimetallic Complex 4a Pd−Ctrz Pd−CPh Pd−Cltrans Pd−Clcis Ctrz−Pd−CPh Ctrz−Pd−Clcis CPh−Pd−Cltrans Clcis−Pd−Cltrans a

Pd1

Pd2

1.994(4) 2.003(3) 2.4014(8) 2.4231(9) 80.22(14) 99.21(10) 95.28(10) 85.38(3)

1.979(4) 2.018(4) 2.3874(8) 2.4156(9) 80.74(15) 98.19(11) 95.14(10) 85.86(3)

Clcis and Cltrans relative to Ctrz

monometallic palladium Bodipy complexes: namely, 4dimethylaminopyridine (dmap) and acridine (acr). These ligands were selected because of their easy availability, their strong binding to palladium, and specifically for their distinct photophysical implications. Acridine has been demonstrated to act as an efficient photoluminescence quencher,20 while dmap has no reported photophysical effects. Hence, the photoluminescent properties can serve as a probe for specific metal− ligand modifications. Exposure of dimeric complex 4 to stoichiometric quantities of dmap or acridine readily yielded the corresponding monomeric palladium complexes 5 and 6, respectively (Scheme 2). Bonding of the imine ligand was confirmed by HR-MS analysis, which displayed the expected [M − Cl]+ ionic mass for the molecular ion for dmap and acr

Scheme 2. Synthesis of 5 and 6 by Cleavage of the Palladium Dimer 4

C


Article

Organometallics

Figure 3. ORTEP diagram of palladium complex 6. Thermal ellipsoids are given at the 50% probability level; hydrogen atoms are omitted for clarity. Selected bond lengths (Å): Pd−C1 1.9919(18), Pd−C8 2.0112(18), Pd−N6 2.1209(15), Pd−Cl 2.4044(5). Selected bond angles (deg): C1−Pd−C8 80.79(8), C1−Pd−Cl 95.21(5), C8−Pd− N6 91.47(7), N6−Pd−Cl 92.51(4).

Figure 4. Normalized absorption (blue) and emission (red) spectra of complex 4 (CH2Cl2 solution).

square plane (dihedral angle C8−Pd−N6−C43 = 75.32(15)°). The ortho proton of the aryl linker is directed toward the acridine aromatic system with a short C9−H···(centroid of the nitrogen-containing ring of acridine) distance of 3.029(9) Å. Photophysical Properties. Compounds 2−6 are all redorange solids that are stable in air and soluble in common organic solvents such as CH2Cl2, MeCN, acetone, and alcohols, giving pink-orange fluorescent solutions. Their UV−vis absorption spectra (CH2Cl2 solution) are dominated by a strong band around 530 nm, assigned to the Bodipy core (Table 2).2,29 The absorption shifts slightly hypsochromic upon

Titration of Palladium Complexes using Acridine as a Fluorescence Quencher. Modulation of the fluorescence properties of Bodipy has been used previously for targeting specific metal ions such as Zn2+, Cu2+, and Hg2+ 31 and also small anions as well as biomolecules.2a,32 The use of organic molecules for quenching or enhancing the Bodipy emission has been less investigated,20,33 and we were therefore interested in establishing the interaction of acridine with the Bodipy scaffold. Hence, complex 4 was titrated with different amounts of acridine in CH2Cl2. The emission intensity decreased gradually, providing evidence for acridine to serve as a quencher for Bodipy (Figure 5).34 While the emission changes were

Table 2. Photophysical Data of Compounds 2−6a compound

λabs (nm)

ε (10−4 L mol−1 cm−1)

λem (nm)

Φc

τ (ns)

2 3b 4 5 6

528 532 523 524 525

7.7 4.3 11.1 6.6 5.9

542 546 538 536 537

0.56 0.40 0.61 0.67 0.53

3.25 3.10 6.52 5.97 6.28

All data 1.0 × 10−6 M in CH2Cl2 except as noted otherwise. b7.5 × 10−6 M. cQuantum yields and excited-state lifetimes determined with λex 488 nm and λem 540 nm.

a

palladation of the triazolium unit, suggesting a small electronic influence of the substituent on the meso-aryl group on the Bodipy properties. However, modification of the ligand coordination sphere around palladium has no effect and all three complexes 4−6 show an absorption maximum at 524(±1) nm. A strong emission was observed for all compounds with a maximum in the 542−550 nm range, indicating a characteristically small Stokes shift in the 12−15 nm range for these Bodipy derivatives (Figure 4).30 All compounds have long excited-state life times in the nanosecond time range (Figure S6 in the Supporting Information) and good quantum yields (Φ = 0.40−0.67), which compare very well with reported Bodipy chromophores.9,10 Accordingly, the photophysical properties are governed by the Bodipy core and are not perturbed by the organometallic unit. The high spectroscopic similarity of all compounds suggests that the linker efficiently separates electronic modifications at the triazole and metal coordination unit from the photoactive Bodipy system.

Figure 5. Decrease of emission spectra of complex 4 upon titration with different amounts of acridine. The inset shows the corresponding Stern−Volmer plot (the linear regression is 0.975).

moderate, they were consistent and allowed for quantifying the potential of acridine to induce intermolecular excited state quenching. The quenching constant (KSV) of acridine for complex 4 was determined via the Stern−Volmer equation35 (eq 1) from plotting the fluorescence ratio F0/F against the concentration of acridine (Figure 5, inset). Accordingly, a quenching constant of (8.6 ± 2) × 103 M−1 was obtained for complex 4. Applying the same procedure and titration of acridine into solutions of complexes 5 gave the corresponding quenching constants KSV = (1.6 ± 2) × 104 M−1 for complex 5. D


Article

Organometallics Scheme 3. Displacement Reaction of Complex 6 with dmap

Bodipy-Functionalized Triazolylidene Iridium Complexes. The versatility of this approach to functionalize catalytically active complexes with a fluorescent probe was further investigated by the synthesis of Bodipy-tagged triazolylidene iridium complexes containing a pyridyl unit as a potentially chelating donor group. Such Ctrz,Npyr-bidentate chelation enhances the stability of the metal complexes.39 Moreover, the corresponding iridium(III) complexes have demonstrated excellent catalytic activity in water oxidation, hydrosilylation, and ether formation,39a,40 thus providing an attractive target for labeling studies to allow for fluorescence monitoring. For this purpose, the Bodipy azide 1 was “clicked” with 2-ethynylpyridine to form the triazole 7 in excellent yield (Scheme 4). Subsequent alkylation was less straightforward than the alkylation of 2 because of the presence of two possible sites for methylation: i.e. Ntrz and Npyr. While strategies for the selective methylation of the triazole nitrogen have been suggested by protecting the pyridyl site as an N-oxide,41 the final deprotection has continuously failed in our hands. Therefore, a nonselective alkylation was performed using 1 equiv of MeOTf. This procedure yielded a mixture of pyridinium and triazolium salt (2/1 ratio of 8a and 8b), in good agreement with previous reports.42 The mixture was separated by column chromatography (CH2Cl2/MeOH 95/5), affording pure 8a as the first fraction and subsequently the pyridinium salt 8b. The two isomers are readily distinguished by the substantial shift differences of the aromatic resonances in the 1H NMR spectrum (Figure S3 in the Supporting Information), including a more pronounced deshielding of the triazole-bound proton for 8a (Δδ = 1.57 ppm). Large shift differences ranging from 0.29 to 0.67 ppm were observed for the pyridyl protons upon pyridine methylation (8b), while only small differences (0.10−0.22 ppm) were noted for these protons upon triazole alkylation (8a). A single-crystal structure determination of 8b unambiguously confirmed the alkylation on the pyridine N atom (Scheme 4). Reaction of 8a with [IrCp*Cl2]2 and Ag2O induced formation of the iridium(III) complex 9,16,43 which was purified by column chromatography to yield a shiny red solid in moderate yield. Complex 9 was unambiguously characterized by 1H NMR spectroscopy. The absence of the triazole proton at δH 10.27 ppm and the new signal at δC 155.7 ppm for the iridium-bound carbon suggest substitution of one proton at the triazolium ring by an [IrCp*Cl] fragment. Furthermore, the deshielding of the Hpyr in a position ortho to the triazole ring and the shielding of the Hpyr in a para position are indicative of pyridine coordination to the metal center. The two doublets corresponding to the mesoaryl group linking the triazolylidene and the Bodipy unit remain unchanged, confirming that no cylcometalation has occurred. For this iridium complex 9, analogous spectroscopic analyses were performed. In comparison to the ligand precursors 7 and 8, smaller differences in the absorption maxima were noted and

These constants are about 1−2 orders of magnitude lower than the quenching constants deduced for cationic quenching.36

F0 = 1 + KSV[acr] (1) F Luminescent Changes in Ligand Displacement Experiments. While both dmap and acridine successfully cleave the dimeric structure of complex 4, their donor properties are different (cf. also the different pKas of dmap and acridine: 9.6 and 5.6, respectively).37 Accordingly, the stronger donor ability of dmap induces displacement of the acridine ligand in complex 6 (Scheme 3). Due to the quenching properties of acridine, this substitution reaction can be conveniently monitored by fluorescence spectroscopy. Hence, recording the emission spectrum of a CH2Cl2 solution of complex 6 upon titration with a dmap solution affords a plot which shows a linear increase of the fluorescence intensity up to the addition of 1 equiv of dmap with respect to complex 6 (Figure 6).38 Addition

Figure 6. Emission intensity changes upon titration of complex 6 with dmap (blue diamonds).

of further amounts of dmap did not change the fluorescence properties further, and the emission intensity remained unchanged. This behavior indicates complete substitution rather than formation of an equilibrium. Such complete substitution was also observed by NMR spectroscopy of complex 4 upon addition of 1 equiv of acridine per palladium center. The spectrum shows complete ligand displacement within the time required for the NMR spectrometer to start recording spectra (less than 3 min). Likewise, addition of 6 equiv of acridine to complex 4 at once induces an immediate quench of luminescence, which indicates an instantaneous exchange. Accordingly, this emission provides a useful probe to monitor ligand displacement events from 6, and this probe may become appealing for investigating catalytic transformations when using complex 6 as precursor. E


Article

Organometallics

Scheme 4. Synthesis of Bodipy-Functionalized Triazolylidene Iridium Complex 9 and ORTEP Diagram of the Pyridinium Cation of 8ba

a

Ellipsoids in the ORTEP drawing are given at the 50% probability level; hydrogen atoms and the OTf− anion are omitted for clarity.

metal center in the iridium complex 9 is not interacting with the aryl linker, the photophysical properties of the Bodipy fragment are essentially unaltered. Likewise, the excited state lifetime in the nanosecond time range (τ = 4 ns) and the moderate quantum yield (Φ = 0.37) are similar to the properties of the palladium complexes and the ligand precursors. A slightly reduced quantum yield (cf. >0.53 in the palladium complexes) may indicate some quenching due to the iridium center. Nonetheless, the photophysical properties of complex 9 suggest that such Bodipy-functionalized triazolylidene ligands provide attractive features as fluorescent tags for monitoring organometallic transformations.

all compounds have a peak absorption between 528 and 532 nm. As for the palladium complexes, a strong emission was observed for iridium complex 9 and its ligand precursor with a maximum in the 542−548 nm range (Figure 7 and Table 3).

■

Figure 7. Normalized absorption (blue) and emission (red) spectra of complex 9 (CH2Cl2 solution).

Table 3. Photophysical Data of Compounds 7−9a compound

λabs (nm)

ε (10−4 L mol−1 cm−1)

λem (nm)

Φb

τ (ns)

7 8a 9

528 531 532

9.0 8.1 2.6

542 548 547

0.56 0.12 0.37

5.01 2.05 3.96

CONCLUSIONS

We have developed an approach to covalently link triazolylidene metal complexes with a Bodipy functionality as a fluorescent probe. The approach is based on a p-phenylene linker that connects the meso position of the Bodipy chromophore and the N1 position of the triazolylidene fragment. Fluorescent probing and organometallic reactivity studies such as cyclometalation indicate that both functional units are independently operational: i.e., the two functionalities are not mutually influencing reactivity patterns. Such functional independence of the active sites will be advantageous for labeling studies: for example, in biological tissue or on solid supports. One of the appealing benefits of combining organometallic triazolylidene entities with Bodipy groups is the ability to monitor reactions at the organometallic site by fluorescence measurements, which are in contrast to other spectroscopic probes typically unperturbed by other functional entities.44 Such a monitoring application has been demonstrated by a ligand displacement assay using acridine as a photoluminescent quencher and spectator ligand on palladium and extraneous dmap as a more strongly binding ligand. Similar monitoring will be attractive for monitoring, for example, catalytic reactions.

Conditions: CH2Cl2 solutions, 1.0 × 10−5 M (7), 7.5 × 10−6 M (8a), 1 × 10−6 M (9). bQuantum yields and excited-state lifetimes determined with λex 488 nm and λem 540 nm. a

This range is the same as for the palladium complexes and suggests that the aryl linker is efficiently insulating electronic interactions with the Bodipy chromophore. Even though the F


Article

Organometallics

■

NCH3), 3.00 (t, 3JHH = 7.5 Hz, 2H, CtrzCH2), 2.50 (s, 6H, CpyrrCH3), 2.33 (q, 3JHH = 7.5 Hz, 4H, CpyrrCH2), 1.91−1.77 (m, 2H, CH2 Bu), 1.60−1.47 (m, 2H, CH2 Bu), 1.33 (s, 6H, CpyrrCH3), 1.04−1.00 (m, 3H, CH3 Bu), 0.98 (t, 3JHH = 7.5 Hz, 6H, Cpyrr CH2CH3). 13C{1H} NMR (100 MHz, CD2Cl2): δ 155.2 (Cpyrr), 146.9 (Ctrz), 140.4 (CPh), 138.7 (Cpyrr), 137.6 (Cpyrr), 135.8 (CPh), 134.1 (Cpyrr), 131.5 (CPhH), 130.8 (Cpyrr), 127.2 (CtrzH), 122.7 (CPhH), 38.7 (NCH3), 29.6 (CtrzCH2), 23.8 (CH2 Bu), 22.8 (CH2 Bu), 17.5 (CpyrrCH2), 14.9 (CpyrrCH2CH3 Et), 13.8 (CH3 Bu), 12.9, 12.5 (2 × CpyrrCH3 Me). 19F NMR (282.2 MHz, CDCl3): δ −79.0 (s), −145.7 (q, JBF = 33.0 Hz). Anal. Calcd for C31H39BF5N5O3S: C, 55.78; H, 5.89; N, 10.49. Found: C, 55.33; H, 5.68; N, 10.36. HR-MS: m/z calculated for C30H39BF2N5 [M − OTf]+ 518.3267; found 518.3250. Bodipy Triazolylidene Palladium Dimer (4). Under an atmosphere of N2, triazolium triflate 3 (67 mg 0.10 mmol), Pd(OAc)2 (22 mg, 0.10 mmol), NaCl (17 mg, 0.30 mmol), and K2CO3 (37 mg, 0.30 mmol) were dissolved in dry THF (15 mL). The mixture was heated to reflux temperature and stirred for 48 h. The reaction mixture was cooled to room temperature, and all volatiles were removed under reduced pressure. The residual dark pink solid was purified via column chromatography (SiO2; CH2Cl2/MeOH 99/1). The solvents were removed under vacuum, giving 4 as an orange solid (31 mg, 47%). 1 H NMR (300 MHz, CDCl3): δ 7.65 (d, 4JHH = 1.8 Hz, 1H, HPh), 7.44 (d, 3JHH = 8.0 Hz, 1H, HPh), 7.00 (dd, 3JHH = 8.0, 4JHH = 1.8 Hz, 1H, HPh), 4.06 (s, 3H, NCH3), 2.97 (t, 3JHH = 7.8 Hz, 2H, CtrzCH2), 2.53 (s, 6H, CpyrrCH3), 2.30 (q, 3JHH = 7.6 Hz, 4H, CpyrrCH2), 1.67− 1.51 (m, 2H, CH2 Bu), 1.41 (s, 6H, CpyrrCH3), 1.33−1.22 (m, 2H, CH2 Bu), 0.98 (t, 3JHH = 7.6, 6H, CpyrrCH2CH3), 0.70 (t, 3JHH = 7.3, 3H, CH3 Bu). 13C{1H} NMR (100 MHz, CDCl3): δ 153.4 (Cpyrr), 152.1 (CtrzPd), 146.7 (Ctrz), 145.5 (CPh), 141.3 (Cpyrr), 141.1 (CPh), 138.9 (Cpyrr), 135.5 (CPhH), 134.9 (CPh), 132.6 (Cpyrr), 130.9 (Cpyrr), 124.6 (CPhH), 113.7 (CPhH), 36.1 (NCH3), 31.7 (CtrzCH2), 23.8 (CH2 Bu), 22.4 (CH2 Bu), 17.2 (CpyrrCH2), 14.8 (CpyrrCH2CH3), 13.4 (CH3 Bu), 12.6, 12.3 (2 × CpyrrCH3). 19F NMR (282.2 MHz, CDCl3): δ −145.8 (br s). Anal. Calcd for C60H74B2Cl2F4N10Pd2: C, 54.73; H, 5.67; N, 10.64. Found: C, 54.22; H, 5.28; N, 9.48. Bodipy Triazolylidene dmap Palladium Complex (5). Compound 4 (26 mg, 0.02 mmol) was stirred in the presence of dmap (5 mg, 0.04 mmol) in CH2Cl2 (5 mL) at room temperature for 3 h. All volatiles were removed in vacuo, and the residue was suspended in Et2O (25 mL). The suspension was filtered through a short path of Celite and the residue washed with copious amounts of Et2O. The residue was then extracted with CH2Cl2 (10 mL) and the extract filtered through Celite. This CH2Cl2 fraction was collected, and all volatiles were removed under reduced pressure, yielding compound 5 as a red solid (20 mg, 63%). Microanalysis indicated correct CH values but an N value that was too low.46 1 H NMR (300 MHz, CDCl3): δ 8.27 (d, 2H, 3JHH = 7.3 Hz, Hdmap), 7.52 (d, 1H, 3JHH = 7.9 Hz, HPh), 6.96 (dd, 3JHH = 7.9 Hz, 4JHH = 1.7 Hz, 1H, HPh), 6.65 (d, 4JHH = 1.7 Hz, 1H, HPh), 6.44 (d, 3JHH = 7.3 Hz, 2H, Hdmap), 4.08 (s, 3H, NtrzCH3), 3.31 (t, 3JHH = 7.3 Hz, 2H, CtrzCH2), 3.00 (s, 6H, NdmapCH3), 2.48 (s, 6H, CpyrrCH3), 2.28 (q, 3 JHH = 7.3 Hz, 4H, CpyrrCH2), 1.71 (quintet, 3JHH = 7.9 Hz, 2H, CH2 Bu), 1.58−1.46 (m, 2H, CH2 Bu), 1.37 (s, 6H, CpyrrCH3), 1.00− 0.93 (m, 9H, CpyrrCH2CH3 + CH3 Bu). 13C{1H} NMR (100 MHz, CDCl3): δ 154.5 (Cdmap), 153.6 (CtrzPd), 153.3 (Cpyrr), 150.6 (CdmapH), 148.3 (Ctrz), 146.8 (CPh), 144.7 (Cpyrr), 141.4 (CPh), 138.7 (Cpyrr), 135.1 (CPh), 134.6 (CPhH), 132.6 (Cpyrr), 130.9 (Cpyrr), 124.2 (CPhH), 113.8 (CPhH), 107.7 (CdmapH), 39.3 (NdmapCH3), 35.9 (NtrzCH3), 32.0 (CtrzCH2), 24.0 (CH2 Bu), 22.7 (CH2 Bu), 17.2 (CpyrrCH2), 14.8 (CpyrrCH2CH3), 14.1 (CH3 Bu), 12.6 (t, JCF = 2.4 Hz, CpyrrCH3), 11.9 (CpyrrCH3). HR-MS: m/z calculated for C37H47BF2N7Pd [M − Cl]+ 744.2989; found 744.2969. Bodipy Triazolylidene acr Palladium Complex (6). Following the same synthetic procedure as described for 5 but using acridine (7 mg, 0.04 mmol) instead of dmap, compound 6 was obtained as an orange solid (17 mg, 51%). No correct microanalysis could be obtained even after repeated precipitation and crystallization attempts. 1 H NMR (500 MHz, CDCl3): δ 9.60 (d, 3JHH = 7.8 Hz, 2H, Hacr), 8.96 (s, 1H, Hacr), 8.01 (d, 3JHH = 7.8 Hz, 2H, Hacr), 7.78 (t, 3JHH = 7.8

EXPERIMENTAL SECTION

General Considerations. The metal precursor salt [IrCp*Cl2]245 and the azide 110 were synthesized as reported in the literature. All other reagents were commercially available and were used as received. All microwave experiments were carried out using a Biotage Initiator 2.5 instrument, operating at 0−400 W irradiation power. Unless specified otherwise, NMR spectra were recorded at 25 °C on Varian spectrometers operating at 300 or 400 MHz (1H NMR) and 100 MHz (13C NMR), respectively. Chemical shifts (δ in ppm, coupling constants J in Hz) were referenced to residual solvent signals (1H, 13 C). Assignments are based on homo- and heteronuclear shift correlation spectroscopy. The purity of bulk samples of the complexes has been established by NMR spectroscopy and, when possible, by elemental analysis. Elemental analyses were performed at UCD Microanalytic Laboratory using an Exeter Analytical CE-440 elemental analyzer; residual solvent was confirmed by NMR spectroscopy and also by X-ray structure determinations. High-resolution mass spectrometry was carried out with a Micromass/Waters Corp. USA liquid chromatography time-of-flight spectrometer equipped with an electrospray source. UV−vis absorption spectra were acquired using a double-beam spectrophotometer (V-650; Jasco, Inc.). Photoluminescence spectra were acquired using a QuantaMaster 40 instrument (Photon Technology International (PTI), Inc.) equipped with a pulsed Xe short arc discharge lamp and Czerny−Turner monochromators. Absolute photoluminescence quantum yield (PL QY) data were obtained by using the QuantaMaster 40 instrument (PTI, Inc.) equipped with an integrating sphere (Labsphere, Inc.), coupled by a fiber bundle to the collection monochromator, and a 5 mm path length cylindrical quartz cuvette (120-QS; Hellma GmbH & Co. KG). Photoluminescence lifetime measurements were measured by the system FluoroCube-01-NL (Jobin Yvon, Horiba Ltd.), equipped with a semiconductor pulsed light emitting diode (emission wavelength of 488 nm;

Triazolylidene Metal Complexes Tagged with a Bodipy Chromophore

Recommend Documents