Structural and Photophysical Study on Alkynyl Cyclometalated Pt2Pb2

Article pubs.acs.org/Organometallics

Structural and Photophysical Study on Alkynyl Cyclometalated Pt2Pb2 and Pt2Pb Clusters Á lvaro Díez, Elena Lalinde,* M. Teresa Moreno,* and Santiago Ruiz

Departamento de Química-Centro de Síntesis Química de La Rioja, (CISQ), Universidad de La Rioja, 26006, Logroño, Spain S Supporting Information *

ABSTRACT: Neutralization reactions of (NBu4)[Pt(bzq)(CCR)2] (bzq = 7,8-benzoquinolinyl) with [Pb(HBpz3)]Cl (pz = pyrazolyl) afford tetranuclear neutral Pt2Pb2 derivatives [{Pt(bzq)(CCR)2}{Pb(HBpz3)}]2 (R = Ph, 1; C6H4OMe3, 2) or the anionic trinuclear Pt2Pb cluster (NBu4)[{Pt(bzq)(CCC6H4CF3-4)2}2{Pb(HBpz3)}], 3, stabilized by Pt−Pb and PbII···η2-(CCR) bonding interactions in the solid state, as confirmed by X-ray crystallography. The variable-temperature 1H NMR spectra of 3 confirm the existence of a dynamic equilibrium that averages the “Pt(bzq)(CCC6H4CF3-4)2” groups in solution. 1D 1H PGSE-NMR, 2D DOSY, and 1H variable-temperature NMR experiments for the tetranuclear clusters 1 and 2 indicate that in solution these dimers generate mainly binuclear [{Pt(bzq)(CCR)2}{Pb(HBpz3)}] units by cleavage of the PbII···η2-(CCR) interactions. All clusters exhibit phosphorescent emission in rigid media (solid, glasses) and 3 also in CH2Cl2 solution. The emission maxima of 1 and 2 are slightly blue-shifted in relation to the precursors, being assigned to a mixed 3MLCT/3LC (L = bzq) excited state, perturbed by the Pt−Pb bond. However, the emission maximum of 3 coincides with that of its precursor, indicating little or no involvement of the Pt−Pb bonds in the emissive state.

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are the most represented,10 while the PtII−PbII are notably sparse.11 Therefore, the controlled formation of novel heteropolymetallic PtII−PbII systems and the study of their structure−properties relationship are of great importance in designing functional materials. We note that despite the environmental concerns related to lead, its chemistry has attracted much attention in recent years because of its intriguing structural motifs12 and its possible applications in nonlinear optics,13 birefringence,14 ferroelectrics,15 semiconducting,16 and luminescent materials.11,17 The structural versatility is caused by the stereoactivity of the 6s2 electron pair of the PbII ion,18 which exerts a notable influence in their structures, categorized as hemi- or holodirected. Mixing of 6s and 6p orbitals leads to a stereochemically active lone pair, generating hemidirected structures with a void in the coordination sphere of the PbII, occupied by the stereochemically active lone pair, whereas symmetrical holodirected environments are usually found with high coordination numbers. Regarding this topic, we have previously demonstrated that different degrees of activity of the lone pair produce subtle modifications not only on the structure but also on the photophysical responses to external stimuli.11,17f,g Thus, by reaction of the homoleptic alkynylplatinates with Pb(ClO4)2· 3H2O we isolated tetranuclear clusters [Pt2Pb2(CCR)8]11a

INTRODUCTION Luminescent mono- and multinuclear complexes have attracted much recent research attention, primarily because of their potential applications in optoelectronic materials (photocatalysis,1 sensors,2 nonlinear optics,3 solar energy devices,4 and OLEDs5). In this area, alkynyl ligands with their rich σ/πbonding versatility, complemented with noncovalent metallophilic interactions, have been successfully used for the assembly of closed-shell (d8, d10) homo- and heteropolynuclear complexes with fascinating structures and interesting emissive properties.6 Their photophysical properties are determined primarily by the electronic characteristics of the alkynyl σ/π groups, modulated by the strength of the η···(M) alkyne bonds and the metal−metal interactions in the final aggregate. Interestingly, some of these complexes have also shown interesting concentration- or solvent-induced polymorphism, solid-state mechanochromism, thermochromism, vapochromism, or vapoluminescence, accompanied by large changes in their photophysical properties.7 The most extensively studied polynuclear η2-CCR bridging systems involve d10−d10 coinage ions6a,8 and, to a lesser extent, d8(PtII)−d10 transition metal ions,9 in general having strong σ and/or π alkynyl−metal bonds. However, systems with borderline post-transition closed-shell ions Pt−M (d10s2) have been less explored, due to the lower tendency of these metals to be complexed by π-alkyne interactions. Considering alkynyl Pt−M(d10s2) systems, Pt−TlI aggregates © XXXX American Chemical Society

Received: February 26, 2016

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DOI: 10.1021/acs.organomet.6b00162 Organometallics XXXX, XXX, XXX−XXX

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Organometallics Scheme 1. Synthesis of Complexes 1−3

4, C26) with 1 equiv of [Pb(HBpz3)]Cl27 and NaPF6 (10 equiv), as a chloride abstractor (see Experimental Section for details), are presented in Scheme 1. The precursor (NBu4)[Pt(bzq)(CCC6H4OMe-3)2] (B) was synthesized for this work following a similar procedure to that published by our group for related complexes.26 As is seen in Scheme 1, the results of the reactions depend on the electronic characteristics of the R substituent. Thus, treatment of the phenyl (A) and meta-methoxyphenyl (B) alkynyl derivatives with [Pb(HBpz3)]+ leads to the formation of the tetranuclear clusters 1 and 2. In these systems, the anionic fragment [Pt(bzq)(C CR)2]− (R = Ph, 1; C6H4OMe-3, 2) is neutralized with one [Pb(HBpz3)]+ cation by formation of a Pt→Pb bond, and the bimetallic fragment [{Pt(bzq)(CCR)2}{Pb(HBpz3)}] dimerizes through weak PbII···η2−CC interactions, as confirmed by X-ray (see below). However, the reaction of (NBu4)[Pt(bzq)(CCC6H4CF3-4)2] (C), containing a less electron donating substituent, affords the trinuclear anionic complex (NBu4)[{Pt(bzq)(CCC6H4CF3-4)2}2{Pb(HBpz3)}] (3), in which the cationic entity [Pb(HBpz3)]+ is bonded to two anionic [Pt(bzq)(CCC6H4CF3-4)2]− fragments. Identical results were obtained by using an excess of [Pb(HBpz3)]Cl (2:1 Pt:Pb molar ratio). It should be noted that in relation to the trinuclear Pt2Pb derivatives obtained by reaction of (NBu4)[Pt(bzq)(CCR)2] (R = Ph, C6H4CF3-4) with Pb(ClO4)2·3H2O11b the inclusion of a HBpz3 nitrogen auxiliary ligand coordinated to the Pb center favors the formation of binuclear species PtPb, which further dimerizes to form tetranuclear species Pt2Pb2. In the case of the acceptor C6H4CF3-4 substituent, which reduces the donor capability of the alkynyl ligand, two dialkynylplatinates are still necessary to fulfill the electronic requirements of the “Pb(HBpz3)” unit, giving rise to a final Pt2Pb complex. Complexes 1−3 were characterized by X-ray diffraction and by standard spectroscopic techniques [elemental analysis, mass spectrometry, IR, NMR (1H, 13C{1H}, 19F, and 195Pt)]. Specifically, in order to understand their nature in solution, unidimensional PGSE and bidimensional DOSY NMR 1H spectra were performed for 1 and 2.

with a dynamic Pt2Pb2 core, which are sensitive to mechanical grinding and donor vapor solvents. By using the dialkynylcycloplatinate derivatives (NBu4)[Pt(bzq)(CCR)2] (R = Ph, C6H4CF3-4) we obtained two different Pt2Pb clusters, depending on the substituent on the alkynyl group. The reaction with R = Ph affords the neutral derivative [{Pt(bzq)(C CPh)2}2Pb], containing a symmetrical hemidirected coordination, whereas the analogous reaction using the substrate with the less electron-donating C6H4CF3-4 substituent evolves with formation of a mixture of the related neutral Pt2Pb cluster and the unusual anionic adduct [{Pt(bzq)(CCC6H4CF3-4)2}2{Pb(O2ClO2}]−, in which the perchlorate present in the reaction media coordinates to the Pb center. Taking into account this result, we decided to explore the coordination of other different donor coligands to the PbII center, with the goal to increase the stability of the final clusters. In this sense, the nitrogen donor poly(pyrazolyl)-borate ligands have been widely used as auxiliary ligands in coordination, organometallic, and bioinorganic chemistry,19 and they have shown an important role in a wide range of topics, such as C−H bond activation,20 catalytic processes,21 models for enzymatic reactions,22 metal extraction,19b,d−f,23 and biomedical applications.22a,24 However, there are very few reports on the influence of these ligands on the photophysical properties of metal complexes.25 In addition, these ligands would be expected to introduce a remarkable steric hindrance, disfavoring undesirable face-to-face intermolecular π···π interactions, which are typical in planar cycloplatinate systems. In this contribution, we report the synthesis, structural characterization, and optical properties of novel alkynyl cyclometalated Pt2Pb2 and Pt2Pb clusters stabilized by a synergistic combination of PbII···η2-(CCR) and PtII−PbII bonding interactions, obtained by reaction of (NBu4)[Pt(bzq)(CCR)2] (R = Ph, C6H4OMe-3, C6H4CF3-4) with [Pb(HBpz3)]Cl (pz = pyrazolyl).

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SYNTHESIS The reactions of the heteroleptic anionic compounds (NBu4)[Pt(bzq)(CCR)2] (R = Ph, A;26 C6H4OMe-3, B; C6H4CF3B


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Organometallics

Figure 1. Molecular structures and coordination environments of the Pb2+ centers in complexes (a) 1 and (b) 2·CH2Cl2.

Figure 2. Molecular structure of the anion [{Pt(bzq)(CCC6H4CF3-4)2}2{Pb(HBpz3)}]− in complex 3·2CHCl3 and the coordination environment of the Pb2+ center.

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CRYSTAL STRUCTURES

complete understanding of the crystal structures of these complexes has special interest because the number of systems described with Pt−Pb bonds is extremely low,11,17a,c−g,28 and these represent one of the few examples described with Pb···η2CC interactions.11 Crystal structures of 1 and 2 (Figure 1,

Single crystals suitable for X-ray analysis were grown by slow diffusion of n-hexane into CH2Cl2 solutions of 1−3 at room temperature (Figures 1 and 2 and Tables 1 and S1−S3). The C


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Organometallics Table 1. Selected Bond Lenghts [Å] and Angles [deg] of 1, 2·CH2Cl2, and 3·2CHCl3 3·2CHCl3 Pt−N Pt−CCyclomet Pt−Cα Cα−Cβ Pb−Cα Pb−Cβ Pt−Pb Pb−Pt−N Pb−Pt−CCyclomet Pb−Pt−Cα Pt−Cα−Cβ Cα−Cβ−Cγ CCyclomet−Pt−N Cα−Pt−Cα

1

2·CH2Cl2

2.065(7) 2.066(7) 2.022(9), 2.008(8) 1.200(12), 1.226(11) 3.027(8), 2.951(9) 3.132(8), 3.142(9) 3.2315(4) 104.10(19) 87.27(18) 95.1(2), 81.7(2) 176.6(7), 168.3(7) 178.4(9), 174.3(9) 80.9(3) 96.4(3)

2.060(6), 2.062(6) 2.049(7), 2.055(7) 1.957(8)−2.019(7) 1.217(11)−1.225(11) 2.951(9)−3.144(8) 2.998(6)−3.429(7) 3.0933(4), 3.3059(4) 100.31(16), 94.07(18) 114.0(2), 99.49(18) 71.0(2)−94.9(2) 167.3(6)−179.7(8) 172.5(8)−177.8(8) 81.4(3), 81.2(3) 97.1(3), 94.2(3)

Pt1 2.083(5) 2.049(6) 1.952(6), 1.957(6) 1.218(8), 1.198(9) 3.111(7) 3.1125(3) 110.04(14) 80.55(17) 71.70(18), 103.21(17) 174(8), 177.0(6) 175.9(7), 175,5(6) 80.0(2) 94.0(2)

Pt2 2.077(6) 2.036(7) 2.028(6), 2.028(7) 1.211(9), 1.214(10) 2.928(6), 2.898(8) 3.057(6), 3.180(8) 3.6214(4)

176.3(6), 174.7(6) 177.3(7), 178.3(7) 81.4(3) 94.7(3)

presence of weak Pb···η2-CC interactions. The Pb···Pb transannular distance [4.5361(4) Å (1); 4.1687 (6) Å (2)] is shorter than those seen in [Pt2Pb2(CCTol)8Sx] (S = solvent) clusters (∼5.089−5.436 Å), but still out of the van der Waals limit (4.04 Å). The central metallic core [Pt 2Pb2] adopts a planar disposition in 1 (torsion angle 0°), with Pb−Pt−Pb [78.38(1)°] and Pt−Pb−Pt [101.62(1)°] angles similar to those described in some related Pt−Tl complexes. 10a,f However, 2 presents a nonplanar rhomboidal metallic core with a torsion angle between the Pt−Pb vectors of 25.21(1)° and Pb−Pt−Pb/Pt−Pb−Pt angles of 69.88(1)°, 70.70(1)°/ 102.14(1)°, and 108.12(1)°. As can be seen in Figure 1, the lead centers present a distorted octahedral environment, with coordination to the three nitrogen atoms of the tris(pyrazolyl)borate ligand, the Pt center of its own unit, and the two alkynyl groups of the other entity. The environment is asymmetric, with Pb−N distances in the range 2.433(6)−2.556(7) Å (1) and 2.464(6)−2.511(6) Å (Pb1); 2.491(6)−2.527(7) (Pb2) (2), transoidal N3/N9−Pb−Pt angles smaller than 180° [168.52(16)° (1); 166.36(14)° (Pb1), 163.20(15)° (Pb2) (2)], and cisoidal N−Pb−N angles smaller than 90° [73.4(2)− 78.0(2)° (1); 73.8(2)−77.0(2)° (Pb1), 72.6(2)−76.4(2)° (Pb2) (2)]. The angles formed by the centroid of the acetylenic carbons, the Pb center, and the corresponding trans N are also smaller than 180° [146.05°, 157.08° (1); 150.16°, 156.91° (Pb1), 152.72°, 153.24° (Pb2) (2)]. The asymmetry in the Pb coordination environment and the relatively long Pb···CC interactions are in agreement with a certain activity of the lone pair located toward the interior of the dimetallacycle and along the transannular Pb···Pb direction.18 The structural data of the [HBpz3]− group are in agreement with those described in other structures with polypyrazolylborate ligands.27,32 In complex 3 the lead completes its coordination with two anionic “[Pt(bzq)(CCC6H4CF3-4)2]−” units, resulting in the formation of a trinuclear Pt2Pb anion (Figure 2, Tables 1 and S3). The two platinum fragments are oriented mutually cis (with an anti disposition of the C and N atoms of the bzq ligands), forming a dihedral angle of 16°, and display a very dissimilar bonding interaction with the lead center. Thus, one of the platinum fragments coordinates to the Pb center through the Pt−Cα unit with a short Pt(1)−Pb distance [3.1125(3) Å] and a relatively long Pb−Cα [Pb···C(14) 3.111(7) Å]. The

Table 1) reveal the dimerization of the binuclear PtPb unit, forming the final tetranuclear [{Pt(bzq)(CCR)2}{Pb(HBpz3)}]2 (R = Ph, 1; C6H4OMe-3, 2) aggregates, through opposite Pb···η2-CC interactions. 1 presents a C2 axis, which makes the two [{Pt(bzq)(C CPh)2}{Pb(HBpz3)}] fragments equivalent, while in 2 the two bimetallic fragments are not related by symmetry, exhibiting distinct metric data. Accordingly, 1 presents only one Pt−Pb distance [3.2315(4) Å], while 2 shows two asymmetric intermetallic bond lengths [Pt(1)−Pb(1) 3.0933(4), Pt(2)− Pb(2) 3.3059(4) Å]. These distances are notably shorter than the sum of the van der Waals radii (3.77 Å)29 and within the range described for other PtII−PbII compounds (2.642−3.313 Å).11,17d−g,28 In particular, the Pt−Pb lengths are slightly larger than those found in [{Pt(bzq)(CCPh)2}2Pb] [2.9182(5), 2.9759(5) Å],11b which might be attributed to the lower formal charge of the lead in 1 and 2 due to its coordination to the [HBpz3]− ligand. The Pt−Pb vectors are slightly tilted with respect to the Pt coordination plane [12.34(13)° (1), 11.82(11)° and 21.82(13)° (2)], with the Pb ion located essentially above the corresponding Pt atom, thus enhancing the donor−acceptor Pt→Pb bonding interaction. As aforesaid, the Pb center interacts with both alkynyl ligands of the other PtPb unit, with the Pb···Cα distances slightly shorter than the Pb···Cβ [Pb···Cα/Cβ 3.027(8), 2.951(9)/ 3.132(8), 3.142(9) Å, 1; 2.951(9)−3.144(8)/2.998(6)− 3.429(7) Å, 2], with the Pb(2)···C(63)C(64) bond in 2 [Pb···Cα/Cβ 3.115(8)/3.429(7) Å] being the most asymmetric. The asymmetry is similar to that previously observed by us in other derivatives11 (with a shorter Pb−Cα interaction), but the observed Pb−C distances are significantly longer (i.e., [Pt2Pb2(CCTol)8]·CH2Cl2, Pb···Cα/Cβ 2.69(2)−2.72(2)/ 2.74(2)−2.83(2) Å),11a suggesting a relatively weak Pb···η2CC interaction. However, these distances are smaller than the sum of the van der Waals radii of Csp (1.78 Å)30 and the covalent radii of Pb (1.47 Å) (sum 3.25 Å),31 being, in fact, responsible for the stabilization of the dimers in the solid state. In the aggregate, the lead centers are located at 0.481 Å (1) and 0.515 Å (Pb1) and 0.631 Å (Pb2) (2) from the [Pt(CCR)2] coordination plane of the other unit, and the Pt−Pb′ distances [Pt(1)−Pb(1′) 3.9002(4) Å (1) and Pt(1)−Pb(2)/Pt(2)− Pb(1) 3.9979(5)/3.9195(6) Å (2)] are larger than the van der Waals limit (3.77 Å), reinforcing the idea that the stabilization of the tetranuclear clusters in the solid state is due to the D


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Organometallics second Pt fragment increases the PbII coordination number up to seven, with the two alkynyl units [Pb···Cα 2.898(8), 2.928(6) Å, Pb···Cβ 3.057(6), 3.180(8) Å] and a long secondary contact with the platinum [Pt(2)−Pb 3.6214(4) Å]. The Pt−Pb and Pb···η2-CC distances are larger than those found in the perchlorate adduct (NBu4)[{Pt(bzq)(CCC6H4CF3-4)2}2{Pb(O2ClO2)}],11b in accordance with the coordination of the capping tris(pyrazolyl)borate ligand, [HBpz3]−, which is more electron donating and produces a greater steric hindrance than the bidentate perchlorate O2ClO2− ligand around the PbII ion. The asymmetric coordination geometry around the lead suggests that the lone pair in 3 is also stereochemically active.18 The benzoquinolinyl ligands, although displaced, are partially eclipsed with a minimum separation between them of 3.365 Å, in the range of those described for π··· π interactions, which might contribute to the stability of the anion (Figure 2). The supramolecular structures of 1, 2·CH2Cl2, and 3· 2CHCl3 evidence different packing. While in 1 the dimers pack through weak Hpz···πbzq, Cpz···Hbzq, CPh···Hbzq, CPh···Cbzq, and Cpz···HPh secondary interactions (Figure S1), in 2·CH2Cl2 the tetranuclear clusters aggregate giving rise to chains, which are additionally connected by π···π interactions of consecutive cyclometalating bzq rings (3.348−3.376 Å) (Figure S2a,b) forming sheets. In 3·2CHCl3 each [Pt2Pb]− anion contacts through displaced bzq···bzq interactions (3.233 Å), forming dimers (Figure S3a), which interact through weak CC··· NBu4, HNBu4···Hbzq, Hpq···FCF3, HNBu4···FCF3, and HPh/ C,HNBu4/FCF3/πbzq/πPh···CHCl3 interactions.

9.95/31.3 Hz/8.24 B; 9.76/28.7 Hz/7.91 3 vs 10.03/28.7 Hz/ 8.19 C). For complex 3, the variable-temperature 1H NMR spectra confirm the occurrence of a dynamic process that averages the “Pt(bzq)(CCC6H4CF3-4)2” fragments in solution. Thus, by decreasing the temperature, most of the signals corresponding to the bzq ligand broaden. As is shown in Figure S4, the coalescence for the H2 signal is observed at ∼235 K, and at lower temperatures two different H2 resonances (δ 9.96; 9.32) corresponding to two distinct bzq ligands are resolved, in accordance with a rigid trinuclear Pt2Pb complex. Due to the low solubility of these complexes, only the 13 C{1H} NMR spectra of 2 and 3 have been registered, but with low resolution despite prolonged accumulation. Notwithstanding, both complexes show signals due to the bzq and HBpz3− ligands, with the metalated C2 resonance for the bzq (δ 150.5, 2; 150.2, 3) and the C4′ (δ 104.4) for the HBpz3 ligand being the most characteristic. The 195-platinum resonance for the most soluble complex 2 was found as a singlet at δ −3208, remarkably deshielded in relation to the precursor (δ −3845), consistent with the decrease of the electron density of the Pt atom due to the formation of the Pt−Pb bond. Unfortunately, despite prolonged accumulation, lead satellites were not resolved. As noted above (structural studies), the tetranuclear species 1 and 2 are formed by two binuclear PtPb entities, which interact through weak PbII···η2-CCR interactions, which could be broken in solution. In order to understand the behavior of these entities in solution, an analysis using onedimensional 1H PGSE-NMR (pulse field gradient spin echo),33 two-dimensional DOSY, (diffusion ordered spectroscopy),33c,34 and diffusion and variable-temperature 1H NMR experiments for 1 were carried out. With the PGSE technique it is possible to estimate the self-diffusion coefficient (D) for a molecule in solution, which can be related to its hydrodynamic radius (rH) through the Stokes−Einstein equation (see the Experimental Section). The hydrodynamic radius, calculated in this way in solution, allows an estimation of the molecular size, which can be compared with the radius obtained for the molecule in the solid state by X-ray diffraction studies (rX‑ray).33 Figure 3a shows a section of the 1H PGSE-NMR spectra for 1. As can be observed, the resonance intensity of the selected signal located at 7.56 ppm (H5′ pyz, H7,8 bzq) and that of the residual proton of the CDCl3 solvent decrease upon increasing the pulsed-field gradient. Figure 3b shows the graphical representation of the intensity of the signal located at 7.56 ppm (I) as a function of the gradient (g), which allows obtaining a value for the diffusion coefficient D (7.781 × 10−10 m2/s). The 2D version of 1H PGSE experiments (DOSY, diffusionordered spectroscopy)33c,34 has been also successfully applied in the characterization of organometallic compounds in solution,35 analysis of mixtures,36 identification of hydrogen bonding,37 chemical exchanges,38 or characterization of molecular aggregates and polymeric species.35b,39 In order to check the validity of D, obtained from the unidimensional 1H PGSE-NMR spectra, we also performed a DOSY study for 1, which is shown in Figure S5. The 2D-DOSY spectrum for 1 shows the chemical shifts along the horizontal axis and separated diffusion coefficient of complex 1 and of the solvent along the vertical axis (logarithmic scale). As expected, the solvent (log D = −8.569; D = 2.698 × 10−9 m2/s) diffuses faster than 1 (log D = −9.108; D = 7.798 × 10−10 m2/s). The value of the diffusion coefficient obtained for 1 (D = 7.798 × 10−10 m2/ s) is similar to that calculated by the 1H-PGSE experiment (D =

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CHARACTERIZATION AND DIFFUSION EXPERIMENTS 1 and 2 show several ν(CC) bands in the range 2085−2060 cm−1. These bands are slightly shifted to lower frequencies compared to those observed in the precursors (2103, 2090 cm−1 R = Ph;26 2096, 2077 cm−1 R = C6H4OMe-3), pointing to a weakening of the CC triple bonds caused by the π interaction of the Pb center with the alkynyl fragments. 3 shows three bands in the range 2111−2070 cm−1 with a shoulder at 2040 cm−1 (precursor 2105, 2082 cm−1),26 consistent with the presence of two terminal alkynyl groups and two CC groups that interact with the PbII ion. The molar conductivity of the anionic derivative 3 (98 Ω−1 cm2 mol−1, CH3CN) is slightly lower than that expected for a 1:1 electrolyte, while 1 and 2 do not show conductivity, indicating that neutral units remain in solution. MALDI−TOF(+) of 1 and 2 show peaks due to the tetranuclear fragments [{Pt(bzq)(CCR)2}2{Pb(HBpz3)}Pb]+ ([M − HBpz3]+), in agreement with a dimeric formulation, and also peaks that fit well to the binuclear [{Pt(bzq)(CCR)2}{Pb(HBpz3)}]+ unit. However, in both complexes, the most intense peak is due to the trinuclear ions [{Pt(bzq)(CCR)2}{Pb(HBpz3)}2]+ (m/z 1416, 1; 1476, 2), which might be formed by loss of a platinum [Pt(bzq)(C CR)2]− fragment. The MALDI−TOF(−) of 3 shows the molecular peak corresponding to the anion [{Pt(bzq)(C CC6H4CF3-4)2}2{Pb(HBpz3)}]− ([M − NBu4]−, m/z 1843). The 1H NMR spectra of all complexes, assigned with the aid of 1H−1H COSY experiments, show only one group of signals for the bzq and HBpz3 ligands. The corresponding H2 and H4 resonances appear slightly shifted to lower frequencies in relation to those observed in the precursors (NBu4)[Pt(bzq)(CCR)2] (A−C),26 but with similar J195Pt−H coupling constants for the H2 signal (δ H2/JPt−H/δ H4 CDCl3: 9.82/ 29.6 Hz/8.15 1 vs 10.08/28 Hz/8.22 A; 9.80/31.2 Hz/8.14 2 vs E


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those expected for the tetranuclear clusters and closer to the values estimated for the binuclear units points to the occurrence of a fast dissociation process, in which the binuclear units could be predominant, according to Scheme 2. Scheme 2. Proposed Equilibrium between the Tetra- and Binuclear Entities for 1 and 2

A further support of the involvement of this equilibrium between the tetranuclear and binuclear units is demonstrated by variable-temperature 1H NMR studies. Thus, as shown in Figure 4, upon lowering the temperature, the proton resonances due to H2 and H4 of the bzq ligand, H4′ of the tris(pyrazolyl)borate group, and Hortho of the CCPh fragments gradually shift to low frequencies (δ 9.82, H2bzq, 8.15, H4bzq, 6.00, H4′pz, 6.68, H2Ph 298 K vs 9.69, 8.06, 5.85, 6.46, 233 K). These upfield shifts are consistent with the expected mutual electronic effect of the involved aromatic groups, as shown by X-ray (Figure 1), when the Pb(HBpz3) fragment in the binuclear species moves close to the bzq of its own unit and the phenyl alkynyl substituents of the opposite one in the tetranuclear aggregate. Therefore, according to entropic considerations, upon decreasing the temperature, the equilibrium is displaced to the formation of the tetranuclear aggregates through the association of binuclear units.

Figure 3. (a) Section of the 1H PGSE-NMR spectra in CDCl3 for 1. The resonance intensity of the signal at 7.56 ppm and that of the solvent decrease upon increasing the pulsed-field gradient (g). (b) Graphical representation of the I of this signal vs g to obtain the diffusion coefficient D for 1.

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PHOTOPHYSICAL PROPERTIES Absorption and emission data of 1−3 in CH2Cl2 and in the solid state are summarized in Tables S4 and 2, respectively. Selected spectra are compiled in Figures 5 and 6. For comparative purposes, the data and selected spectra of the precursors are also included (Table S5, Figure S6).26 All Pt−Pb heterometallic complexes 1−3 show high-energy absorptions (∼220−316 nm), which can be attributed to ligand-centered 1 ππ* transition (bzq, CCR).40 In the low-energy region they exhibit less intense broad features with two maxima, which are blue-shifted in relation to their corresponding precursors (i.e., 338, 375 nm 1, 2 vs ∼350, 400 nm A, B; 330, 382 nm 3 vs 346, 392 nm C). According to previous assignments in related heterometallic systems,11 these bands are assigned to a platinum-alkynyl to ligand (bzq) charge transfer transition (1ML′LCT), in which the presence of Pt−Pb bonding interactions increases the electrophilicity of the Pt center, provoking a blue-shift for the transition. This effect is less pronounced in 3, probably due to the occurrence of weaker platinum−lead interactions. For complexes 1 and 2, a less intense shoulder at 421 nm (1) and 424 nm (2) is clearly resolved, which is absent in the precursors. The peak is tentatively attributed to a charge transfer from the electron donor fragment “Pt(CCR)2” toward an excited state that is likely a mixture of the bzq and the “Pb(HBpz3)” groups 1 L′LCT/1ML′M′CT (L, L′ = bzq, CCR; M, M′ = Pt, Pb). All complexes in the solid state at 298 K exhibit broad asymmetric emissions [λmax 505 (1 and 2), 520 nm (3), Figure

7.781 × 10−10 m2/s). The hydrodynamic radius rH, obtained by using the D value obtained from 1H-PGSE experiment and the Stokes−Einstein equation (see the Experimental Section), was 5.48 Å. Two different approximations were used to estimate the radius of the tetranuclear aggregate 1, by using the X-ray diffraction data. In the first one, we estimated the diameter of the hypothetical sphere generated by the tetranuclear unit by averaging the separation between the two bzq groups and the distance between the two boron atoms (∼13.4 Å), giving rise to a molecular radius for the cluster of approximately 6.5 Å. The second approximation to estimate the theoretical volume of the tetranuclear cluster was based on the division of the volume of the crystallographic cell by the number of tetranuclear (2) entities present. As was expected, this method gives a higher value of 8.82 Å, but we assume that this value is overestimated. By using this approximation and taking into account the presence of four binuclear Pt−Pb units in the unit cell, a lower radius of 5.78 Å was estimated for a discrete binuclear “{Pt(bzq)(CCPh)2}{Pb(HBpz3)}” complex. For 2, the theoretical radius calculated was 9.27 for the tetranuclear and 7.36 Å for the binuclear, again larger than the hydrodynamic rH in solution obtained by 1H-PGSE-NMR experiments (6.34 Å). The fact that the hydrodynamic radii in solution are lower than F


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Organometallics

Figure 4. Sections of the 1H NMR spectra (in CDCl3) of 1 at different temperatures, showing the different shifts of the signals assigned to H2, H9, and H4 of the bzq group (red), H2 of the phenyl ring (green), and H4′ of the tris(pyrazolyl)borate (blue).

Table 2. Photophysical Data for Complexes 1−3 in the Solid State and CH2Cl2 Solutions at 298 and 77 K compound 1

2

3

a

medium (T/K) solid (298) solid (77) 5 × 10−5 M solid (298) solid (77) 5 × 10−5 M solid (298) solid (77) 5 × 10−5 M 5 × 10−5 M

(77)a

(77)a

(298) (77)

505max, 505max, 485max, 505max, 505max, 485max, 520max, 515max, 510max, 491max,

λem/nm (λexc/nm)

τ/μs

ϕ (%)

545sh (330−475) 543, 580 (365−450) 523, 560, 620sh (365−450) 560shb (365−480) 541, 585 (365−450) 523, 560, 625sh (365−430) 575shb (330−480) 550, 595 (365−480) 540shb (320−400) 527, 570, 605 (365−460)

7.4 19.7

5.2

11.1 46.2

1.2

7.1 30.4

4.6

No emission in CH2Cl2 solution at 298 K (5 × 10−5 to 10−3 M). bTail to ca. 650 (1, 2), 700 nm (3).

Figure 5. UV−vis absorption spectra of 5 × 10−5 M CH2Cl2 solutions of (a) 2 and (b) 3 and their precursors. Inset: low-energy region.

6], with long lifetimes (7.4 1, 11.1 2, 7.1 μs 3) and low quantum yields (5.2 1, 1.2 2, 4.6% 3). At 77 K the bands become clearly structured, although the maxima remain essentially unchanged (λmax 505 1, 2, 515 nm 3), increasing the lifetimes (19.7 1, 46.2 2, 30.4 μs 3). The emission patterns do not depend on the excitation wavelength, and they show

vibronic spacing typical of the bzq groups, suggesting their involvement in the emissive state. The change of the alkynyl substituents on the emission maxima for 1 (R = Ph) and 2 (R = C6H4OMe-3) is minimal, but in both clusters the emissions are slightly blue-shifted in relation to the corresponding precursor (Δ ∼20 nm), reflecting the stabilization of the HOMO due to the formation of the G


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Organometallics

Figure 6. Normalized emission spectra of 1−3 in the solid state (λex 365 nm) at (a) 298 K and (b) 77 K.

PtII···Pb(HBpz3) bond. However, the λmax in 3 is coincident with that of its precursor C. In contrast to the precursors, 1 and 2 are not emissive in fluid CH2Cl2 solution. The observed quenching could tentatively be related to relaxation due to their dynamic behavior in solution. Upon freezing at 77 K, both complexes exhibit intense and structured bands (λmax 485 nm), slightly blue-shifted in relation to the solid (Δ ∼20 nm) and to their precursors (Δ ∼20 nm 1, 12 nm 2) (Figure S7). On the basis of these observations, the emission for 1 and 2 is mainly assigned as a mixed 3MLCT/3LC transition, with strong ligandcentered contribution and slightly perturbed by the Pt−Pb bond. The trinuclear complex 3 exhibits in CH2Cl2 solution at 298 K an asymmetrical broad band, which becomes structured and blue-shifted upon decreasing the temperature (510, 298 K vs 491 nm 77 K) (Figure S7), which is practically coincident with that observed in the precursor C (Tables 2 and S5), probably due to the presence of weaker Pt−Pb interactions. Therefore, the emission for 3 is attributed to a platinum−alkynyl to ligand 3 ML′LCT 3[Pt(d)/π(CCR)→π*(bzq)] phosphorescence with little or no participation of the Pt−Pb bond. The small band that appears at 605 nm in glasses (Figure S7), related to a different excitation spectrum, could be tentatively assigned to the formation of excimers, favored by the presence of short π···π interactions between the bzq groups, as is observed in the crystal structure. The behavior of these clusters contrasts with the optical properties previously observed in the sandwich-type neutral [{Pt(bzq)(CCR)2}2Pb] (R = Ph, C6H4CF3-4) and anionic (NBu4)[{Pt(bzq)(CCC6H4CF3-4)2}2{Pb(O2ClO2}] related complexes.11b Thus, and probably due to the strong aggregation quenching effect caused by π···π interactions, any of these complexes were found to be emissive in solid state at room temperature. At 77 K, these trinuclear complexes display broad red-shifted bands in the orange region (neutral Pt2Pb, 607 nm R = Ph; 620, 660 nm, R = C6H4CF3-4; anionic, 600 nm), which were attributed to a 3MLM′CT 3[Pt(d)/π(C CR)→Pt(pz)/Pb(sp)/π*(CCR)] excited state, modified by metal−metal interactions, in view of the strong η2-alkynyl−Pb2+ bonds and short Pt−Pt and Pt−Pb distances.11b Interestingly, the emission of these complexes in fluid solution is quenched by increasing the concentration, a fact that was attributed to the formation of dimers through intermolecular (π···π) bzq interactions, similar to those observed in the solid state (Xray). Therefore, in the solid state the presence of the bulky HBpz3− ligands in 1−3 seems to avoid deactivation pathways,

but probably due to the presence of weaker Pt−Pb and alkynyl···Pb(HBpz3) interactions, its influence in the emitting excited state is negligible.

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CONCLUSIONS In summary, we report on the synthesis, structures, and optical properties of two neutral Pt2Pb2 clusters [{Pt(bzq)(C CR)2}{Pb(HBpz3)}]2 (R = Ph, 1; C6H4OMe-3, 2) and one anionic Pt2Pb derivative, (NBu4)[{Pt(bzq)(CCC6H4CF34)2}2{Pb(HBpz3)}] (3), stabilized by PtII−PbII bonds with relatively short Pt−Pb distances. X-ray diffraction studies reveal that for 1 and 2 the neutral [{Pt II (bzq)(CCR) 2 }{PbII(HBpz3)}] unit dimerizes by weak Pb···η2-CCR interactions, giving rise to tetranuclear Pt2Pb2 entities, whereas in the trinuclear derivative 3, the lead center of the [Pb(HBpz3)]+ unit is complexed by two [Pt(bzq)(C CC6H4CF3-4)2]− fragments. Although the contribution of distinct supramolecular noncovalent forces between the platinum fragments also plays a role, we think that the formation of cluster 3 seems to be mainly governed by the electronic effect of the alkynyl group. The presence of the acceptor C6H4CF3 substituent reduces the donor capability of the alkynyl ligands, and thus, two platinum−alkynyl fragments are required to fulfill the electronic requirements of the lead ion in the [Pb(HBpz3)]+ unit in 3 instead of one platinum fragment for each Pb unit present in 1 and 2, having more donor substituents (Ph, C6H4OMe-3). Therefore, these results represent an example of the influence of the alkynyl substituents in the final structures of the heteropolymetallic clusters. According to diffusion NMR spectroscopy (1D 1H PGSE-NMR and 2D-DOSY experiments) and variable-temperature 1H NMR studies, we suggest that the clusters 1 and 2 establish a fast equilibrium in solution with the corresponding binuclear Pt−Pb species through the cleavage of the Pb···η2CCR interactions. Clusters 1 and 2 display emission profiles in rigid media (solid, glass) similar to those of the precursors with slight blue shifts in their maxima, being associated with a mixed 3MLCT/3LC (L = bzq) transition, barely perturbed by the Pt−Pb bond. In contrast, the emission maxima of complex 3 coincide with that of the precursors, indicating the negligible or null influence of the Pt−Pb bond in the emissive state.

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EXPERIMENTAL SECTION

General Comments. All reactions were carried out under an atmosphere of dry argon, using standard Schlenk techniques and solvents from a solvent purification system (MBraun MB SPS-800). H


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Organometallics

2096 (m), 2077 (m). ΛM (CH2Cl2): 104.2 Ω−1 cm2 mol−1. 1H NMR (δ, 300.13 MHz, CDCl3): 10.03 (d, JH−H = 4.8, JPt−H = 28.7, H2bzq), 8.56 (d, JH−H = 5.6, JPt−H = 38.8, H9bzq), 8.19 (d, JH−H = 7.8, H4bzq), 7.68 (d, JH−H = 8.7, H5bzq), 7.48 (m, 3H, Hbzq, HC6H4), 7.37 (m, 1H, Hbzq, HC6H4), 7.00 (m, 6H, Hbzq, HC6H4), 6.63 (m, 2H, HC6H4), 3.76 (s, 6H, OMe), 3.23 (m, 8H, NBu4), 1.33 (m, 8H, NBu4), 1.09 (m, 8H, NBu4), 0.66 (t, 3JH−H = 7.1, 12H, NBu4). 13C{1H} NMR (δ, 75.5 MHz, CDCl3): 163.3 (s, C10bzq), 158.9 (s, C3, C6H4), 158.8 (s, C3, C6H4), 157.8 (s, 2JPt−C = 57.2, C12), 149.8 (s, 2JPt−C = 30.0, C2bzq), 143.5 (s, C10bzq), 135.4 (s, C4bzq), 134.7 (s, C9bzq), 133.0 (s, C13bzq), 131.7 (s, C14bzq), 131.0 (s, C7bzq), 130.1 (s, tentatively assigned to C C), 129.2 (s, 3JPt−C = 44.3, C8bzq), 128.2 (s, C5, C6H4), 128.1 (s, C5, C6H4), 126.0 (s, C1C6H4), 123.9 (s, C6, C6H4), 123.6 (s, C6, C6H4), 122.0 (s, 3JPt−C = 62.0, C3bzq), 120.7 (s, C5bzq), 119.7 (s, C6bzq), 116.1 (s, C2, C6H4), 116.0 (s, C2, C6H4), 110.1 (s, C4, C6H4), 110.0 (s, C4, C6H4), 106.2 (s, tentatively assigned to CC), 103.3 (s, tentatively assigned to CC), 99.0 (s, tentatively assigned to CC), 58.0 (s, N−CH2), 54.8 (s, COMe), 54.7 (s, COMe), 23.6 (s, CH2), 19.0 (s, CH2), 13.2 (s, CH3). 195Pt{1H} NMR (δ, 86.02 MHz, CDCl3): −3845 (s). Preparation of [{Pt(bzq)(CCPh)2}{Pb(HBpz)3}]2 (1). To a yellow solution of (NBu4)[Pt(bzq)(CCPh)2] (0.200 g, 0.244 mmol) in acetone (15 mL) were added 0.112 g (0.244 mmol) of [Pb(HBpz3)]Cl and 0.300 g (2.44 mmol) of NaClO4. After 30 min of reaction, a yellow solid was filtered and washed with H2O (5 mL) and EtOH (5 mL) (0.175 g, 72%). Anal. Calcd for [C38H28N7BPtPb]2 (1991.53): C, 45.83; H, 2.83; N, 9.85. Found: C, 45.72; H, 2.80; N, 9.75. MALDI-TOF (+): m/z (%) calcd for [{Pt(bzq)(CCPh)}{Pb(HBpz)3}]+ (C30H23N7BPtPb) 894.64, found 894 (24); calcd for [{Pt(bzq)(CCPh) 2}{PbHB(pz)3 }] (C38H28 N7BPtPb) 995.75, found, 996 (4); calcd for [{Pt(bzq)(CCPh)2}{PbHB(pz)3}2]+ (C47H38N13B2PtPb2) 1415.99, found 1416 (45); calcd for [{Pt(bzq)(CCPh)}2{PbHB(pz)3}Pb]+ (C67H46N8BPt2Pb2) 1778.50, found 1778 (20). IR (cm−1): ν(CC) 2094 (s), 2086 (s), 2070 (s), 2060 (s). ΛM (CH3CN): 0 Ω−1 cm2 mol−1. 1H NMR (δ, 400.17 MHz, CDCl3): 9.82 (d, JH−H = 2.6, JPt−H = 29.6, H2bzq), 8.60 (s, JPt−H = 38.9, H9bzq), 8.15 (d, JH−H = 6.2, H4bzq), 7.70 (d, JH−H = 8.8, H5/6bzq), 7.59 (m, Ph), 7.56 (m, H7bzq, H8bzq, H5′pz), 7.42 (d, JH−H = 8.8, H5/6bzq),7.31 (s, H3bzq), 6.92 (s, H3′pz, Ph), 6.68 (s, Ph), 5.92 (s, H4′pz). The low solubility of this complex precludes its characterization by 13C{1H} and 195Pt{1H} NMR. Preparation of [{Pt(bzq)(CCC6H4OMe-3)2}{Pb(HBpz)3}]2 (2). To a yellow solution of (NBu4)[Pt(bzq)(CCC6H4OMe-3)2] (0.150 g, 0.171 mmol) in acetone (15 mL) were added [Pb(HBpz3)]Cl (0.078 g, 0.171 mmol) and NaClO4 (0.209 g, 1.71 mmol). After 4 h of stirring, a yellow solid was filtered and washed with H2O (5 mL) and EtOH (5 mL) (0.101 g, 56%). Anal. Calcd for [C40H32N7O2BPtPb]2 (2111.63): C, 45.50; H, 3.05; N, 9.29. Found: C, 45.62; H, 3.01; N, 9.26. MALDI-TOF (+): m/z (%): calcd for [{Pt(bzq)(C CC6H4OMe-3)}{Pb(HBpz)3}]+ (C31H25N7BOPtPb) 924.66, found, 924 (52); calcd for [{Pt(bzq)(CCC6H4OMe-3)2}{PbHB(pz)3}] (C40H32N7BO2PtPb) 1055.82, found 1056 (14); calcd for [{Pt(bzq)(CCC 6 H 4 OMe-3) 2 }{PbHB(pz) 3 } 2 ] + (C 49 H 42 N 13 B 2 O 2 PtPb 2 ) 1476.04, found 1476 (45); calcd for [{Pt(bzq)(CCC6H4OMe3)}2{PbHB(pz)3}Pb]+ (C71H54N8BO4Pt2Pb2) 1898.60, found 1899 (20). IR (cm−1): ν(CC) 2085 (m, br), 2060 (m). ΛM(CH3CN): 0 Ω−1 cm2 mol−1. 1H NMR (δ, 400.17 MHz, CDCl3): δ 9.80 (d, JH−H = 5.1, JPt−H = 31.2, H2bzq), 8.58 (d, JH−H = 5.4, JPt−H = 38.6, H9bzq), 8.14 (d, JH−H = 6.9, H4bzq), 7.67 (d, JH−H = 8.6, H5/6bzq), 7.58 (m, H7bzq, H8bzq), 7.55 (m, H5′pz, C6H4), 7.40 (d, JH−H = 8.6, H5/6bzq),7.33 (t, JH−H = 6.4, H3bzq), 6.93 (m, H3′pz, C6H4), 6.64 (d, JH−H = 7.7, C6H4), 6.55 (d, JH−H = 8.0, C6H4), 6.50 (d, JH−H = 7.3, C6H4), 6.02 (s, C6H4), 5.94 (s, H4′pz), 5.87 (s, C6H4), 3.35 (s, OMe). 13C{1H} NMR (δ, 75.5 MHz, CDCl3): 159.0 (s, C3, C6H4), 158.8 (s, C3, C6H4), 150.5 (s, C2bzq), 142.1 (s, C3′pz), 136.8 (s, C4bzq), 135.7 (s, C5/6bzq), 134.9 (s, C9bzq, C5′pz), 130.1 (s, C7bzq), 129.5 (s, C5/6bzq), 128.7 (s, C5, C6H4), 128.5 (s, C5, C6H4), 127.7 (s, C1, C6H4), 126.6 (s, C1, C6H4), 124.9 (s, C6, C6H4), 124.4 (s, C6, C6H4), 122.6 (s, C3bzq), 122.0 (s, C8bzq), 121.1 (s, C2, C6H4), 115.4 (s, C2, C6H4), 114.0 (s, C4, C6H4), 113.9 (s, C4, C6H4), 104.4 (s, C4′pz), 54.9 (s, COMe), 54.7 (s, COMe). 195Pt{1H} NMR (δ, 75.5 MHz, CDCl3): −3208 (s).

NMR spectra were recorded at 293 K on Bruker ARX 300 or Bruker ADVANCE 400 spectrometers. Chemical shifts are reported in ppm relative to external standards (SiMe4, CFCl3, and Na2[PtCl6]), and all coupling constants are given in Hz. The NMR spectral assignments of the benzoquinolyl ligands (bzq) follow the numbering scheme shown in Scheme S1. 1H PGSE-NMR experiments were recorded on a Bruker AVANCE 400 equipped with a BBI H-BB Z-GRD probe at 298 K without spinning, using the “double stimulated echo pulse sequence” (double STE).41 In these conditions, the dependence of the resonance intensity (I) on a constant waiting time and on a varied gradient strength (G) is described by eq 1.

I = Io exp[− D(2πγδG)2 (Δ − δ /3)× 104]

(1)

where I = intensity of the observed spin−echo, Io = intensity of the spin−echo without gradients, D = diffusion coefficient, Δ = diffusion time, δ = gradient length, γ = gyromagnetic ratio. The pulse sequence was composed of 90° pulses. The duration of the gradients (δ) was 2 ms, the delay (Δ) was 200 ms, and the strength (G) was varied during the experiment. The spectra were performed with 0.2 mM solutions in CDCl3 at 298 K using the solvent as internal standard, and using 32 K (K = 1000) points. The exponential plots of I vs G were fitted using a standard exponential algorithm implemented in TOPSPIN software. Using the obtained diffusion coefficient D of the sample and the internal standard and through the Stokes−Einstein equation (eq 2), an accurate value of the hydrodynamic radius rH can be obtained in each case.42

D=

KBT 6πηrH

(2)

where KB = Boltzmann constant, T = temperature in kelvin, and η = solvent viscosity. For DOSY experiments, data processing was performed with Bruker TOPSPIN 2.1 using the included diffusion-ordered spectroscopy routine. IR spectra were obtained on a Nicolet Nexus FT-IR spectrometer, using Nujol mulls between polyethylene sheets. Elemental analyses were carried out with a Carlo Erba EA1110 CHNS-O microanalyzer. Mass spectra were recorded on a Microflex MALDI-TOF Bruker (MALDI) spectrometer operating in the linear and reflector modes using dithranol as matrix. Conductivities were measured using a Crison GLP31 conductimeter. The optical absorption spectra were recorded using a Hewlett-Packard 8453 spectrophotometer in the visible and near-UV ranges. Diffuse reflectance UV−vis data of pressed powders diluted with SiO2 or KBr were recorded on a Shimadzu (UV-3600) spectrophotometer with a Harrick Praying Mantis accessory and recalculated following the Kubelka−Munk function. Emission and excitation spectra were obtained on a Jobin-Yvon Horiba Fluorolog 3-11 Tau-3 spectrofluorimeter, with the lifetimes measured in the phosphorimeter mode (with an F1-1029 lifetime emission PMT assembly, using a 450 W Xe lamp). Quantum yields in the solid state were measured using an F3018 integrating sphere mounted on a Fluorolog 3-11 Tau 3 spectrofluorimeter. The starting materials [Pt(bzq)(μ-Cl)]2,43 (NBu4)[Pt(bzq)(CCPh)2] (A),26 (NBu4)[Pt(bzq)(CCC6H4-CF3-4)2] (C),26 and [Pb(HBpz3)]Cl27 were prepared according to reported procedures. Preparation of (NBu4)[Pt(bzq)(CCC6H4OMe-3)2] (B). [Pt(bzq)(μ-Cl)]2 (0.500 g, 0.611 mmol) was added to a solution of LiCCC 6 H 4 OMe-3 (4.893 mmol), prepared from HC CC6H4OMe-3 (0.622 mL, 4.893 mmol) and LiBun (3.06 mL, 1.6 N, 4.893 mmol) in diethyl ether/n-hexane (30 mL) at −20 °C, and the mixture was stirred at room temperature for ca. 1 h. The solvent was evaporated to dryness, and the orange solid residue was extracted with cold i-PrOH (30 mL). The mixture was filtered under Ar through Celite, and the filtrate stirred with a solution of NBu4Br (0.394 g, 1.223 mmol) in 5 mL of deoxygenated H2O to yield B as a yellow solid (0.595 g, 64%). Anal. Calcd for C47H58N2O2Pt (878.05): C, 64.29; H, 6.66; N, 3.19. Found: C, 64.40 H, 6.62; N, 3.16. MALDITOF (−): m/z (%) calcd for [Pt(bzq)(CCC6H4OMe-3)2]− (C47H58N2O2Pt) 878.05, found 878 (100). IR (cm−1): ν(CC) I


Article

Organometallics Preparation of (NBu 4 )[{Pt(bzq)(CCC 6 H 4 CF 3 -4) 2 } 2 {Pb(HBpz3)}] (3). To a yellow solution of (NBu4)[Pt(bzq)(C CC6H4CF3-4)2] (0.150 g, 0.157 mmol) in acetone (15 mL) were added [Pb(HBpz3)]Cl (0.072 g, 0.157 mmol) and NaClO4 (0.193 g, 1.57 mmol). After 4 h of reaction, a gray precipitate was filtered. The filtrate was evaporated to dryness, and the yellow residue treated with 5 mL of H2O, giving 3 as a yellow solid (0.147 g, 90%). Anal. Calcd for C87H78N9F12BPt2Pb (2085.76): C, 50.10; H, 3.77; N, 6.04. Found: C, 50.04; H, 3.66; N, 6.10. MALDI-TOF (−) m/z (%): calcd for [{Pt(bzq)(CCC6H4CF3-4)2}2{Pb}]− (C62H34N2F12Pt2Pb) 1632.32, found 1632 (3); calcd for [{Pt(bzq)(CCC6H4CF3-4)2}2{Pb(HBpz)3}]− (C71H42N8F12BPt2Pb) 1843.29; found 1843 (3). IR (cm−1): ν(CC) 2111 (s), 2088 (s), 2070 (s), 2040 (sh). ΛM (CH3CN) = 98 Ω−1 cm2 mol−1. 1H NMR (δ, 400.17 MHz, CDCl3): 9.67 (d, JH−H = 3.8, JPt−H = 28.7, H2bzq), 8.40 (d, JH−H = 6.9, JPt−H = 37.7, H9bzq), 7.91 (d, JH−H = 6.2, H4bzq), 7.60 (d, JH−H = 8.7, H5/6bzq), 7.54 (m, H7bzq, H8bzq), 7.48 (m, H5′pz), 7.24 (d, JH−H = 8.7, H5/6bzq), 7.16 (s, H3bzq), 7.05 (d, JH−H = 7.4, C6H4), 6.84 (d, JH−H = 7.4, C6H4), 6.83 (s, H3′pz), 5.80 (s, H4′pz), 3.20 (m, NCH2, NBu4), 1.43 (m, −CH2−, NBu4), 1.18 (q, −CH2−, NBu4), 0.77 (t, −CH3, NBu4). 13 C{1H} NMR (δ, 75.5 MHz, CDCl3): 150.2 (s, C2bzq), 144.2 (s), 142.0 (s), 136.3 (s), 135.2 (s), 134.8 (s), 133.8 (s), 131.4 (s), 129.8 (s), 129.4 (s), 126.7 (s), 124.6 (s), 124.3 (s), 122.6 (s), 121.5 (s), 121.3 (s), 104.4 (s), 59.1 (s, NCH2, NBu4), 24.2 (s, −CH2−, NBu4), 19.6 (s, −CH2−, NBu4), 13.6 (s, −CH3, NBu4). 19F NMR (δ, 282.48 MHz, CDCl3): −62.2 (s, CF3). X-ray Crystallography Experimental Details. Details of the structural analyses for all complexes are summarized in Table S6. Yellow crystals were obtained by slow diffusion at −30 °C (1, 3· 2CHCl3) or 4 °C (2·CH2Cl2) of n-hexane into solutions of the complexes in CH2Cl2 (1, 2) or CHCl3 (3). In all cases, graphitemonochromatic Mo Kα radiation was used, data collection were performed on a NONIUS-κCCD area-detector diffractometer, and the images were processed using the DENZO and SCALEPACK suite of programs,44 carrying out the absorption correction at this point for 2· CH2Cl2. The absorption correction for 1 and 3·2CHCl3 was performed using MULTI-SCAN45 with the WINGX program suite.46 The structures were solved by direct and Patterson methods using SIR200447 (1, 3·CHCl3) or by Intrinsic Phasing using SHELXT (2·CH2Cl2)48 and refined by full-matrix least-squares on F2 with SHELXL-97.49 All hydrogen atoms were constrained to idealized geometries fixing isotropic displacement parameters 1.2 times the Uiso value of their attached carbon for the aromatic carbons and 1.5 times for the methyl groups. For 3·2CHCl3, disordered crystallization molecules of CHCl3 were observed and modeled. Finally, the structures show some residual peaks greater than 1 e A−3 in the vicinity of the platinum or lead atoms (1, 2·CH2Cl2, and 3·2CHCl3) and the crystallization molecules of CHCl3 (3·2CHCl3), but with no chemical meaning.

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Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Spanish MINECO (Project CTQ2013-45518-P).

ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.6b00162. Further details of X-ray crystallography (Tables S1−S3 and S6, Figures S1−S3), selected NMR spectra (Figures S4, S5 and Scheme 1 for labeling), and some photophysical data and figures (Tables S4, S5 and Figures S6, S7) for compounds reported in this work (PDF) Crystallographic data (CIF)

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