Unexpected Formation of Ferrocenyl (vinyl) benzoquinoline Ligands

Article pubs.acs.org/Organometallics

Unexpected Formation of Ferrocenyl(vinyl)benzoquinoline Ligands by Oxidation of an Alkyne Benzoquinolate Platinum(II) Complex Jesús R. Berenguer, Julio Fernández, Nora Giménez, Elena Lalinde,* M. Teresa Moreno, and Sergio Sánchez* Departamento de Quı ́mica-Centro de Sı ́ntesis Quı ́mica de La Rioja (CISQ), Universidad de La Rioja, 26006 Logroño, Spain S Supporting Information *

ABSTRACT: Oxidation of [Pt(bzq-κN,κC10 )(C 6 F 5 )(η 2 HCCFc)] (1) with PhICl2 and I2 affords the unusual halideferrocenyl(vinyl)benzoquinoline PtII derivatives [Pt{bzqκN-η2-CHC(X)Fc}(C6F5)X] (X = Cl (4a), I (4b)), arising from C−X and C−C coupling processes, together with small amounts of the corresponding PtIV products [{Pt(bzqκN,κC10)(C6F5)X(μ-X)}2] (X = Cl (5a), I (5b)), respectively. Complexes 4 are very stable but they undergo easy displacement reactions with PPh3, yielding trans-[Pt(C6F5)X(PPh3)2] and the corresponding new functionalized (vinyl)benzoquinoline ligands [(Z)-bzq-CHC(X)Fc] (X = Cl (6a), I (6b)). The dinuclear PtIV derivatives 5 are alternatively obtained in high yield by oxidation of the solvate [Pt(bzq-κN,κC10)(C6F5)(CH3COCH3)] (2). Treatment of 5 with dmso or direct oxidation of [Pt(bzq-κN,κC10)(C6F5)(tht)] (3) provides mononuclear [Pt(bzq-κN,κC10)(C6F5)X2(L)] (L = dmso (7a−c), tht (8a−c)) as a mixture of cis and trans isomers.

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INTRODUCTION Direct carbon−carbon and carbon−halogen bond formation caused by transition metals has become a topic of tremendous interest, owing to their importance in the design of efficient and selective processes.1−9 In this field, significant achievements with remarkable selectivity have been obtained via C(sp2)−H activation of substrates having a directing group able to form ortho-metalated complexes as initial or transient species.3,4 Among different metals, palladium and platinum complexes have been extensively investigated in both stoichiometric and catalytic modes in conjunction with strong oxidants (e.g. hypervalent iodine reagents, electrophilic halogenating reagents, ...).5−9 In these processes, reductive elimination from a high oxidation state (mononuclear MIV, dinuclear PdIII) has been proposed as a key step of the carbon−carbon and carbon−halide bond-forming reactions.5−11 Thus, in PtII chemistry the general mechanism for the formation of new bonds under oxidative conditions usually involves the initial oxidation of the Pt center giving rise to a PtIV intermediate, which undergoes subsequent reductive elimination to produce C−C or C−halide bonds.11−13 En route, diplatinum(III) complexes14 and even paramagnetic mononuclear PtIII species15 have been rarely found as short-lived precursors of the PtIV intermediates. Direct attack of the electrophilic reagent at the ligand is very rare, although some examples of fluorination, chlorination, and bromination have been reported when the axial site at Pt is sterically protected.16 Here we report the synthesis of unusual (Z)-10-[1-X,1-ferrocenyl(vinyl)]benzoquinoline ligands (X = Cl, I) generated by simple reaction of the alkyne complex [Pt(bzq-κN,κC10)(C6F5)(η2HCCFc)] (1), containing the redox-active ferrocenyl group, © 2013 American Chemical Society

with oxidants (PhICl2 and I2). In this context, it is worth noting that, although the mechanisms of redox transformations at dinuclear complexes are far from being understood, the potential of utilizing the cooperation between two centers to allow access to new reaction pathways has been long recognized.9,17,18 Interest in platinum(II) cycloplatinated complexes containing rigid conjugated ligands such as benzo[h]quinoline has been mainly focused on the study of their exceptional luminescent properties with potential applications in many areas such as light-emitting materials,19 photocatalysts,20 and biosensors,21 and less attention has been devoted to their reactivity.22 In the course of our current research on luminescent benzoquinolate platinum complexes, we recently reported the synthesis of the neutral solvate complex [Pt(bzqκN,κC10)(C6F5)(CH3COCH3)] (2), which allowed us to form the alkyne derivative [Pt(bzq-κN,κC10)(C6F5)(η2-HCCFc)] (1).23 Due to the presence of a very stable “Pt(bzqκN,κC10)(C6F5)” framework and two close redox centers (PtII and FeII) connected through the unsaturated η2-alkyne unit, we thought it could be of interest to examine its reactivity toward halogenated sources. Halogenation reactions of mononuclear and dinuclear PtII complexes with cyclometalated C−N ligands have been well studied. They have shown to proceed to give rise to both stable diplatinum species (PtIII−PtIII and PtII− PtIV)7,14,24,25 and final PtIV complexes.26−29 However, due to the presence of the ferrocenyl(alkyne) ligand in [Pt(bzqκN,κC10)(C6F5)(η2-HCCFc)] (1), its oxidation with PhICl2 Received: May 17, 2013 Published: July 5, 2013 3943

dx.doi.org/10.1021/om4004384 | Organometallics 2013, 32, 3943−3953

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Scheme 1

or I2 leads mainly to the final PtII complexes [Pt{bzq-κN-η2CHCFcX}(C6F5)X] (X = Cl (4a), I (4b)) containing the new (Z)-10-[1-X,1-ferrocenyl(vinyl)] functionalized benzoquinoline molecules, which can be also easily obtained as the free ligands (Z)-10-[1-X,1-ferrocenyl(vinyl)]benzoquinoline (X = Cl (6a), I (6b)). For comparative purposes, the halogenation reactions of the solvate precursor 2 and [Pt(bzq-κN,κC10)(C6F5)(tht)] (3) have been also examined, giving rise to new pentafluorophenyl cycloplatinate PtIV derivatives.

benzoquinolate ligand in relation to the precursor (see Figure S1 in the Supporting Information for 4b), supporting the occurrence of a formal reduction of the alkyne unit to an olefin with involvement of the bzq ligand. The vinyl signal exhibits in both complexes a 2JPt−H coupling of 75 Hz, which is consistent with η2 bonding to a PtII center.31−33 The presence of four different CH(C5H4) proton resonances ascribed to the ferrocenyl (Fc) group together with five distinct fluorine resonances (2Fo, Fp, 2Fm) with 3JPt‑oF couplings in the expected range (218−309 Hz) indicates a low symmetry with remarkable steric congestion, leading to restricted C−Fc and PtII− Cipso(C6F5) rotation in both complexes. Evaporation at room temperature of a solution of 4a in a 1/2 mixture of CH2Cl2 and n-hexane yielded red crystals suitable for X-ray crystallography. Two molecules with identical bond lengths and angles, within experimental error (3σ criterion), were found in the asymmetric unit; therefore, only the data of one of them are given here (molecule A, Figure 1, Table 1). For the data of

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RESULTS AND DISCUSSION Formation of Ferrocenyl(vinyl)benzoquinoline Systems. The complex [Pt(bzq-κN,κC10)(C6F5)(η2-HCCFc)] (1) was found to react with 1 equiv of iodobenzene dichloride (PhICl2) and with I2, yielding the two new types of products 4 and 5, respectively (Scheme 1). The relative proportions of both products are dependent on the reaction temperature. In fact, treatment of a suspension of 1 at low temperature (0 °C) with PhICl2 yields a red solution from which only 4a is isolated as a microcrystalline red solid. At room temperature, along with 4a, a small amount (∼12%) of 5a also precipitates as a yellow solid. In contrast, the reactions of 1 with Cl2 (solution of Cl2 in CCl4 or CH2Cl2) and Br2 were found to give complicated mixtures. In the reaction with chlorine the expected 4a was only detected (19F NMR spectroscopy) as a minor component and 5a separated out in very low yield (∼6%). Complexes 5 are very insoluble, but they were definitively identified as dinuclear PtIV derivatives by mass spectrometry, elemental analysis, and IR spectroscopy. Their formation is likely due to the occurrence of alkyne loss in solution followed by a fast attack at the Pt center. In fact, both [{Pt(bzq-κN,κC10)(C6F5)X(μ-X)}2] (X = Cl (5a), I (5b)) and the bromide analogue [{Pt(bzqκN,κC10)(C6F5)Br(μ-Br)}2] (5c) are independently obtained by treatment of the solvate precursor [Pt(bzq-κN,κC10)(C6F5)(CH3COCH3)] (2) with the corresponding oxidant (PhICl2, I2, or Br2). In this context, it should be noted that two similar iodide dimeric complexes [Pt(phpy)ArI(μ-I)2]2 (phpy = phenylpyridinate, Ar = C6H3Me2, C6H3(CF3)2) have recently been reported by Yagyu et al.,30 formed by oxidative addition of I2 to the dmso or acetonitrile precursors [Pt(phpy)Ar(S)] (S = dmso, NCMe). Interestingly, the retention of the meridional disposition of the phpy and Ar groups on both Pt centers was confirmed by X-ray crystallography, and therefore, complexes 5 are suggested to have a similar structure. Complexes 4a,b have been identified as PtII complexes on the basis of analytical data, NMR spectroscopy, and X-ray crystallography for 4a. Their 1H NMR spectra display a characteristic singlet of a vinyl group (δ 6.44, 4a; δ 6.46, 4b) and distinctive downfield shifts for H2 and H9 of the

Figure 1. Molecular structure of [Pt{bzq-κN-η2-CHC(Cl)Fc}(C6F5)Cl] (4a, molecule A).

molecule B see the Supporting Information (Figure S2 and Table S1). Both molecules are engaged by π···π interactions associated with the bzq units, a feature not unusual with these types of groups.23 The crystal structure reveals the formation of the new substituted (Z)-10-[1-chloro, 1-ferrocenyl(vinyl)]benzoquinoline, which is acting as a chelating κN:η2 ligand to a “Pt(C6F5)Cl” fragment. In addition to the Pt−Cl bond, the formation of the new C(vinyl)−Cl and C(bzq)−C(vinyl) bonds implies a formal carbohalogenation of the η 2 ferrocenylacetylene, giving rise to the neutral olefin (Z)C(bzq)HCFcCl, in which the chlorine and Fc groups adopt a final geminal disposition. The new carbon−chlorine (C(16)− 3944


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corresponding Pt−Cipso and C−C(Fc) bonds, evident in the 1H and 19F NMR spectra. In the formation of complexes 4a,b there are several points worth noting. First, several groups have recently developed approaches to form diverse 10-substituted benzo[h]quinoline molecules2,6,7,9,17,34 by metal-catalyzed C−H activation, as effective alternatives to more traditional ortho-lithiation electrophilic procedures, but as far as we are aware, this is the first occasion in which an halide−vinyl fragment, CH CXR, is incorporated. Second, the formation of the final ligands implies a formal C−C coupling between the initial η2-alkyne and the benzoquinolate group. In this context, we note that, although the insertion of alkynes into cyclometalated complexes has become an increasingly important tool for the construction of nitrogen-containing heterocycles,3,35 the insertion of alkynes into a benzoquinolate ligand has been observed in only a few instances.36,37 Jones et al. have recently reported the synthesis of an isoquinoline salt, which takes place via an initial insertion reaction of dimethyl acetylenedicarboxylate with Cp*M(bzq)Cl (M = Rh, Ir), affording the corresponding vinyl complexes as intermediate complexes.36 A similar insertion reaction has been also reported by Cabeza et al.37 on a triruthenium carbonyl cluster having a 2-amino-7,8benzoquinolate ligand and the alkynes HCCCH2X (X= OH, SiMe3), affording in this case allyl-type η3-C3 functionalization at the C10 site of the ligand. Third, in organoplatinum chemistry, although migratory insertions of unsaturated molecules such as CO, CNR, alkenes, and even alkynes into Pt−H and Pt−R are well documented,31,33 to our knowledge a similar insertion into the very robust Pt−C(bzq) cycloplatinate bond has never been reported. Finally, coordination of a terminal alkyne to a PtII complex usually makes the ligand more electrophilic and, therefore, it is commonly involved in facile metal-mediated nucleophilic attacks, giving new, often interesting, molecules.33,38 Consequently, the observed direct reaction of the electrophilic oxidant with the coordinated η2-alkyne, likely mediated by the presence of the electron-rich ferrocenyl unit, is rather striking and opens a new metal reaction pathway. In platinum chemistry it is worth mentioning the interesting formation of the bzqPPh2 ligand by reductive C(bzq)−P coupling on the mixed-valence diplatinum phosphide complex (NBu4)[PtII(C6F5)2(PPh2)2PtIV(bzq)I2],24 recently reported by Fortuño et al., and the serendipentious generation of [Pt(bzqκN-η2-CCFc)(C6F5)(μ−κCα:η2-CCFc)Pt(bzq-κN,κC10)(C6F5)] found by slow crystallization of 1.23 Previous DFT calculations on the alkyne precursor complex [Pt(bzq-κN,κC10)(C6F5)(η2-HCCFc)] (1) revealed that the two highest occupied molecular orbitals are close in energy (HOMO, −5.49 eV; HOMO-1, −5.54 eV) and are essentially located on the ferrocenyl alkyne ligand.23 In addition, the complex exhibits a quasi-reversible oxidation wave (see Figure S3, Supporting Information) at 0.70 V, which is attributed to the Fc/Fc+ redox couple. This assignment is in agreement with previous observations on PtII cycloplatinated complexes, which usually exhibit metal-centered irreversible waves (PtII to PtIII or PtIV) at higher potentials.39 On these bases, although the exact mechanism of formation of complexes 4 remains unclear, a plausible reaction sequence illustrated with PhICl2 is presented in Scheme 2. The reaction could be driven by initial oxidation of the ferrocenyl group with formation of Cl• atoms and Cl− ions giving a transient cage species of type A. Subsequent addition of Cl• to the triple bond with a concerted associated redox process involving Fc+ to Fc reduction and PtII to PtIV

Table 1. Selected Distances (Å) and Angles (deg) for Complexes [Pt{bzq-κN-η2-CHC(Cl)Fc}(C6F5)Cl]·0.5(hexane) (4a·0.5(hexane), molecule A) Pt(1)−C(15) 2.098(5) Pt(1)−C(16) 2.185(5) Pt(1)−C(27) 2.024(6) Pt(1)−Cl(2) 2.3048(15) Pt(1)−N(1) 2.095(4) C(15)−C(16) 1.398(8) C(16)−Cl(1) 1.770(5) C(16)−C(17) 1.478(8) C(15)−C(10) 1.485(7) C(27)−Pt(1)−Cl(2) 86.2(2) Cl(2)−Pt(1)−N(1) 90.7(1) C(10)−C(15)−C(16) 129.2(5) C(15)−C(16)−Cl(1) 120.0(4) C(15)−C(16)−C(17) 123.6(5) N(1)−Pt(1)−C(27) 175.6(2) trans-[Pt(bzq-κN,κC10)(C6F5)Br2(dmso)]·0.5(hexane) (trans-7c(dmsoκO)·0.5(hexane)) Pt(1)−C(10) 2.011(6) Pt(1)−N(1) 2.111(5) Pt(1)−O(1) 2.197(4) Pt(1)−C(15) 2.050(6) Pt(1)−Br(1) 2.4504(8) Pt(1)−Br(2) 2.4654(7) S(1)−O(1) 1.544(4) C(10)−Pt(1)−N(1) 81.5(2) N(1)−Pt(1)−O(1) 89.6(2) O(1)−Pt(1)−C(15) 92.4(2) C(10)−Pt(1)−C(15) 96.8(3) Br(1)−Pt(1)−C(10) 86.0(2) Br(1)−Pt(1)−N(1) 91.8(1) Br(1)−Pt(1)−O(1) 91.1(1) Br(1)−Pt(1)−C(15) 93.6(2) Br(2)−Pt(1)−C(10) 94.8(2) Br(2)−Pt(1)−N(1) 83.3(1) Br(2)−Pt(1)−O(1) 87.4(1) Br(2)−Pt(1)−C(15) 91.4(2) S(1)−O(1)−Pt(1) 121.1(2) cis-[Pt(bzq-κN,κC10)(C6F5)I2(tht)] (cis-8b) Pt(1)−C(10) 2.049(9) Pt(1)−N(1) 2.119(8) Pt(1)−S(1) 2.386(2) Pt(1)−C(15) 2.067(9) Pt(1)−I(1) 2.6479(7) Pt(1)−I(2) 2.7550(7) C(10)−Pt(1)−N(1) 82.3(3) C(10)−Pt(1)−S(1) 88.2(2) C(10)−Pt(1)−I(1) 84.8(2) N(1)−Pt(1)−S(1) 84.9(2) N(1)−Pt(1)−I(1) 86.5(2) C(15)−Pt(1)−S(1) 93.4(3) C(15)−Pt(1)−I(1) 94.6(3) C(15)−Pt(1)−C(10) 92.1(4) C(15)−Pt(1)−I(2) 90.7(3) S(1)−Pt(1)−I(2) 91.03(6) I(1)−Pt(1)−I(2) 95.55(2) N(1)−Pt(1)−I(2) 94.9(2) cis-[Pt(bzq-κN,κC10)(C6F5)Br2(tht)]·0.25(acetone)·0.25H2O (8c·0.25(acetone)·0.25H2O) Pt(1)−C(10) Pt(1)−S(1) Pt(1)−Br(1) C(10)−Pt(1)−N(1) C(10)−Pt(1)−Br(1) N(1)−Pt(1)−Br(1) C(15)−Pt(1)−Br(1) C(15)−Pt(1)−Br(2) Br(1)−Pt(1)−Br(2)

2.050(4) 2.363(1) 2.4677(5) 81.1(2) 84.6(1) 85.2(1) 92.3(2) 90.1(1) 95.25(2)

Pt(1)−N(1) 2.112(4) Pt(1)−C(15) 2.044(5) Pt(1)−Br(2) 2.5682(5) C(10)−Pt(1)−S(1) 96.6(1) N(1)−Pt(1)−S(1) 92.7(1) C(15)−Pt(1)−S(1) 89.8(1) C(15)−Pt(1)−C(10) 95.2(2) S(1)−Pt(1)−Br(2) 83.34(3) N(1)−Pt(1)−Br(2) 93.6(1)

Cl(1) = 1.770(5) Å) and carbon−carbon bond distances (C(15)−C(10) = 1.485(7) Å) lie within the typical range observed for single-bond distances. Although the final sixmembered ring of the chelating ligand is rather constrained, as is evidenced by the torsion angle of 53.8(5)° between the planes N(1)−C(12)−C(11) and C(10)−C(15)−C(16), the olefin is essentially perpendicular to the Pt coordination plane (87.4°), as is typical for PtII complexes.31−33 The Pt−C(olefin) distances are relatively short (2.098(5), 2.185(5) Å), likely due to the very low trans influence of the chloride ligand (Pt(1)− Cl(2) = 2.3048(15) Å). These distances and the CC bond length (1.398(8) Å) fall within the typical range of an η2-olefin bonded to PtII.31−33 In the final complex, the C6F5 ring lies close to the very sterically demanding ferrocenyl group, which rationalizes the hindered rotation of these groups about the 3945


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Scheme 2

oxidation and concomitant coordination of X− would result in the formation of the pentacoordinated chloroferrocenyl(vinyl) PtIV complex B. Fast isomerization of B, likely favored by the strong trans influence of the metalated carbon atom, would give C, which is required for the final reductive C−C coupling. The last two steps have many precedents in PtII/PtIV systems involving halogenated oxidants.8−13 On the other hand, the well-known reluctance of Pt−C(C6F5) bonds to undergo insertion and coupling processes could explain the observed selective C−C(bzq) coupling. The regioselective formation of the ligand (Z)-bzqCHCClFc is associated with the more favored initial addition of the chlorine to the internal alkyne carbon, leading to the less sterically hindered vinyl intermediate having the two bulky groups (Fc and Cl) away from the platinum. Although a direct electrophilic attack of X+ (Cl+ or I+) at the electron-rich alkyne unit to afford B cannot be completely discarded, we believe that the initial oxidation of the Fc group promotes this attack, a fact consistent with its electrochemical oxidation. Furthermore, the electrophilic attack at the triple bond does not occur in the reaction between the free HCCFc and PhICl2, which gives rise to the oxidation of the ferrocenyl group, supporting that the first step in the reaction is the oxidation of the Fc group in 1. Aiming to obtain an additional insight, we also investigated the reactions of the related alkyne complexes [Pt(bzq-κN,κC10)(C6F5)(η2-HC CR)] (R = Ph, tBu) with PhICl2. Under similar conditions, we found that these reactions evolve slowly, generating the insoluble diplatinum PtIV complex 5a and mixtures of more soluble unknown species, but no signals of (vinyl)benzoquinoline species were observed. These results were not unexpected, due to the lability of the alkyne ligand in solution, and it is further evidence of the role of Fc in this transformation. Functionalized rigid benzoquinones are valuable molecules due to their recognized use in photophysical applications40 and catalysis41 and their biological42 properties. We sought to obtain the free ligands (Z)-10-[1-X,1-ferrocenyl(vinyl)]-

benzoquinoline (X = Cl (6a), Br (6b)), which were easily liberated from the platinum by treatment of 4a,b with an excess of PPh3 ligand. The reactions evolve with formation of trans[Pt(C6F5)X(PPh3)2] complexes, as confirmed by 31P{1H} and 19 F NMR spectroscopy (eq 1). After elimination of the platinum complexes, the ligands 6a,b were isolated as pure orange solids and fully characterized (see the Experimental Section).

The most significant feature is the olefinic proton signal, which is seen at δ 8.31 (6a) and 8.19 (6b), respectively. These values are in good agreement with the relatively few available data for 10-(vinyl)benzoquinolines (δ ∼8.6),43 as expected, shifted significantly downfield (by ca. 2 ppm) with respect to the precursors, indicative of decoordination. The CH vinylic carbon appears close in both ligands (δ 127.1 (6a), 126.0 (6b)), whereas the halogenated CXFc resonance exhibits the expected tendency (δ 134.8 (6a) vs 137.3 (6b)). Crystals of [(Z)-bzq-CHC(Cl)Fc] (6a) were obtained and subjected to 3946


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possible, only two are observed by NMR (1H and 19F) in the molar ratio ca. 1:1, which are ascribed to the cis(dmso-κS) (tentatively) and trans(dmso-κO) species. Optimization of the structures by DFT calculations for the dichloride derivative 7a reveals that there are only small differences in the ground state energies between the cis and the trans isomers (see Figure S4 and Tables S2 and S3 in the Supporting Information). From the two cis isomers, cis7a(dmso-κS) is slightly more stable than cis-7a(dmso-κO) (7.2 kJ/mol), whereas the calculated energies of the two trans isomers are approximately similar, taking into consideration the error of the DFT calculations (trans-7a(dmso-κO) vs trans7a(dmso-κS) by 4.0 kJ/mol). These results are in accordance with previous observations for similar cyclometalated PtIV complexes with dmso ligands, which suggest that the most favorable isomer has the oxygen atom trans to the cyclometalated carbon (better σ donor and π acceptor). Similarly, theoretical calculations have shown that the S coordination of the dmso ligand is favored when it is in a trans disposition to an halogen atom in PtIV complexes (in coherence with the softer character of the S atom in relation to oxygen).27 After many attempts, an small number of crystals of 7c were grown from acetone/n-hexane. A single-crystal analysis stablished unambiguously that these crystals were the trans isomer with an oxygenbound dmso ligand trans to the cyclometalated carbon (Figure 3, Table 1). It is interesting that although some dmso-κO PtIV

X-ray diffraction. Although the crystal data were of moderate quality and are not amenable for a detailed discussion, they clearly confirmed the connectivity of the atoms and the retention of the geometry with the geminal disposition of the Fc and chlorine (Figure 2). Vinyl halides have found

Figure 2. Molecular structure of [(Z)-bzq-CHC(Cl)Fc] (6a).

widespread utility as substrates for a variety of cross-coupling reactions. Therefore, the presence of chlorine or iodine in these ligands opens the possibility of further functionalization, allowing the synthesis of new olefinic ligands containing bzq and Fc groups. These types of molecules would also be expected to have potential properties as fluorescent sensor switches, on the basis of the usual stability of the Fc/Fc+ redox pair.44 Preparation of [Pt(bzq-κN,κC10)(C6F5)X2(L)] (L = dmso, tht) Complexes. PtIV complexes have attracted considerable interest, mainly because of their relevance as intermediate species in mechanistic studies related with C−H activation and subsequent functionalization through reductive C−X (X = halide, C, O, N, P, ...) bond eliminations.8−13 In this context, access to stable PtIV compounds is desirable because they will provide further insights for understanding the reactivity of such intermediate species. As noted above, complexes 5 are very insoluble in usual organic solvents; however, we found that in the strong donor solvent dmso, the dimethyl sulfoxide molecules react with the dimers [{Pt(bzq-κN,κC10)(C6F5)X(μ-X)}2] (5) to give the more soluble dmso monomers [Pt(bzq-κN,κC10)(C6F5)X2(dmso)] (7; eq 2). The reaction was

Figure 3. Molecular structure of trans-[Pt(bzq-κN,κC10)(C6F5)Br2(dmso-κO)] (trans-7c(dmso-κO)).

species have been proposed as intermediates in bromination reactions in dmso solution,45 the number of crystallographically characterized platinum complexes containing dmso-κO donors27,46 are very scarce. The Pt center shows a slightly distorted octahedral geometry with both Br atoms in a trans disposition (Pt(1)−Br(1) = 2.4504(8) Å, Pt(1)−Br(2) = 2.4654(7) Å). The most significant distances, Pt(1)−O(1) (2.197(4) Å) and S(1)−O(1) (1.544(4) Å), compare well with those reported for other published examples,27 whereas the S(1)−O(1)−Pt(1) angle (121.1(2)°) is slightly greater. The Pt(1)−C(10) (2.011(6) Å) distance is comparable to those in the related cis-8b and 8c. Notwithstanding, the Pt−C(C6F5) distance (2.050(6) Å) is slightly shorter than those reported in other reported pentafluorophenyl PtIV complexes (trans[Pt(C6F5)4Br(NCPh)]−, 2.106(8)−2.129(9) Å),47 due to the low trans influence of the N donor atom. The presence of the mixture of cis-7(dmso-κS) and trans7(dmso-κO) in solution is inferred from NMR spectroscopy. Thus, at low temperature the 19F NMR spectra showed two sets of five different signals due to C6F5 groups indicating, not unexpectedly, restricted rotation around the Pt−C6F5 bonds in

very slow at room temperature but goes to completion upon moderate heating (∼50 °C) in a few minutes. Treatment of the final solution with water causes the precipitation of 7 as pale yellow (X = Cl (7a), Br (7c)) and orange (X = I (7b)) solids, respectively. Although the formation of different isomers is 3947


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Figure 4. Molecular structures of (left)[cis-Pt(bzq-κN,κC10)(C6F5)I2(tht)] (cis-8b) and (right) [cis-Pt(bzq-κN,κC10)(C6F5)Br2(tht)] (8c).

H NMR spectra of cis-8 display the characteristic H9 proton from the bzq flanked by platinum satellites at relatively high field (δ 7.30−7.45). This fact is indicative of shielding caused by the proximity of this proton to the ring current of the C6F5 group and coherent with the meridional disposition of the “Pt(C∧N)C6F5” fragment having the two carbon donors mutually cis. The lower values of 3JPt−H9 (8a,b, 35 Hz; 8c, 40 Hz) in comparison to that of the precursor 3 (δ 6.76, 3JPt−H9 = 62 Hz) support the coordination of the bzq to PtIV. Remarkable steric hindrance to the rotation of the C6F5 ring is inferred from the 19F NMR spectra, which show five distinct fluorine signals with very different chemical environments for o-F (and also mF) in the range from 223 to 298 K (Figure S11, Supporting Information). The observed 3JPt‑oF values (75−113 Hz) are typical of pentafluorophenylplatinum(IV) complexes,47−49 showing an important decrease with respect to the values found in complexes 123 and 350 (∼510 Hz). 1

both isomers. When the temperature was increased (see Figures S5−S7 in the Supporting Information), for 7a,c, the two sets of o-F and also m-F signals broaden, coalesce, and simultaneously average into one (Tcoalescence(o-F): 293 K, 7a; 313 K, 7c), whereas for the most voluminous iodide derivative 7b four o-F are still observed at room temperature. Two sets of bzq groups, with some of the signals overlapping, are disclosed in the proton spectra, which supports the retention of the meridional Pt(bzq-κN,κC10)(C6F5) unit. In particular, the proton close to the orthometalated C (H9) appears upfield (δ 7.32 (7a), 7.23 (cis-7b(dmso-κS)), 7.29 (trans-7b(dmsoκO)), 7.29 (cis-7c(dmso-κS)), 7.31 (trans-7c(dmso-κO))), indicative of strong shielding due to its proximity to the aromatic current of the C6F5 group (Figure S8, Supporting Information). The 3JPt−H values dropped considerably (35−39 Hz) in relation to the precursors 1 and 2 (∼70 Hz), which is consistent with the change from PtII to PtIV. At room temperature, the methyl resonances of the dmso ligand in both isomers are found as well-separated singlet resonances (broad in cis-7b(dmso-κS)), remarkably more deshielded in the cis-7(dmso-κS) isomers (3.05−3.07 ppm) than in the trans-7(dmso-κO) isomers (2.53−2.55 ppm), a feature that has been previously observed in related PtIV complexes featuring Oand S-bound dmso.45 Upon cooling, the resonance due to cisκS broadens and finally splits into the expected two distinct singlets (δ 3.09, 3.03 (7a), 3.16, 2.99 (7b), 3.15, 3.01 (7c)), while the singlet due to the trans-7(dmso-κO) isomers remains unchanged. Unfortunately, no satellites were observed in any of the methyl signals. Confirmation of the κS coordination of the dmso ligand in the cis isomers was obtained by a sequence of NOESY and NOE experiments between the H2 proton of the bzq and the Me resonances of the dmso (Figures S9 and S10 (Supporting Information) for 7c). The lack of NOE coupling between the methyl and the aromatic H2 protons for the second isomer confirms that the dmso is coordinated through the oxygen atom. Interestingly, though the ratio between both isomers does not change noticeably once they are formed, we observed that increasing the reaction time in dmso leads always to higher proportions of trans-7(dmso-κO). By way of comparison, the oxidation reactions of [Pt(bzq-κN,κC10)(C6F5)(tht)] (3) with PhICl2, I2, and Br2 were also examined. These reactions evolve with retention of the meridional disposition of the “Pt(bzq-κN,κC10)(C6F5)” fragment and formation of [Pt(bzq-κN,κC10)(C6F5)X2(tht)] (8a−c) as a cis derivative (8c) or a mixture of cis and trans isomers, (cis:trans ≈ 7:1 (8a) 5:1 (8b)) (eq 3), from which the cis isomers can be separated as pure complexes by crystallization. As expected, the

Slow diffusion of n-hexane into chloroform or acetone solutions of the cis isomers 8b,c, respectively, produced X-rayquality crystals (Figure 4). Remarkably, a search of the Cambridge Crystallograpic Database reveals that, although tht is a common ligand for PtII complexes, there is only one reported crystal structure of a PtIV derivative.51 Both structures (cis-8b and cis-8c) are similar and confirm that the bzq and C6F5 groups retain the meridional disposition of the precursor. The platinum shows a distortedoctahedral geometry of a PtIV complex with both iodide (8b) and bromide (8c) atoms in a mutually cis disposition and bond distances and angles (Table 1) in the usual range observed in other PtIV derivatives with the same ligands.13,28−30,52 In both compounds, the Pt−X distance trans to the tetrahydrothiophene ligand (Pt(1)−I(1) = 2.6479(7) Å and Pt(1)−Br(1) = 2.4677(5) Å) is remarkably shorter than the distance trans to the C(bzq) metalate carbon (Pt(1)−I(2) = 2.7550(7) Å and Pt(1)−Br(2) = 2.5682(5) Å), in agreement with the lower trans influence of the sulfur atom. As expected, the Pt−C (2.044(5)− 2.067(9) Å) and Pt−N (2.119(8), 2.112(4) Å) distances are 3948


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Ag/AgCl reference electrode) on a Voltalab PST 050 instrument. The ferrocene/ferrocenium couple served as internal reference (+0.46 V vs Ag/AgCl). 7,8-Benzo[h]quinoline (Hbzq) was purchased from SigmaAldrich, and [Pt(bzq-κN,κC10)(C6F5)(η2-HCCFc)],23 [Pt(bzqκN,κC10)(C6F5)(CH3COCH3)],23 and [Pt(bzq-κN,κC10)(C6F5)(tht)]50 were prepared as reported previously. Preparation of [Pt{bzq-κN-η2-CHC(Cl)Fc}(C6F5)Cl] (4a). To a suspension of [Pt(bzq-κN,κC10)(C6F5)(η2-HCCFc)] (1; 0.200 g, 0.266 mmol) in CH2Cl2 (20 mL) at 0 °C was added iodobenzene dichloride (0.073 g, 0.266 mmol). The mixture was stirred for 3 h, and the obtained red solution was evaporated to dryness. Treatment of the residue with n-hexane (5 mL) afforded 4a as a red solid (0.172 g, 79%). When the reaction was carried out at 298 K during 3 h, a pale yellow solid precipitated and was identified as [{Pt(bzq-κN,κC10)(C6F5)Cl(μ-Cl)}2] (5a) and separated by filtration (0.019 g, 12%). The red filtrate was evaporated to dryness and treated with n-hexane (5 mL) to give 4a (0.129 g, 59%). IR (cm−1): ν(CC) 1373 (s); ν(C6F5)X‑sens 809 (m). Anal. Calcd for C31H18Cl2F5FeNPt: C, 45.33; H, 2.21; N 1.71. Found: C, 45.06; H, 2.18; N, 1.67. MALDI-TOF (+): m/z (%) 821 [M]+ (52); 786 [M − Cl]+ (40). 1H NMR (400.1 MHz, CDCl3, 20 °C, δ): 9.79 (d, J = 4.7 H2, bzq), 8.50 (d, J = 6.4, H4, bzq), 8.15 (d, J = 7.7, H7, bzq), 8.01 (m, 2H, H9, H5,6, bzq), 7.89 (t, J = 7.7, H8, bzq), 7.80 (d, J = 8.7, H5,6, bzq), 7.74 (dd, J = 7.8, J = 5.0, H3, bzq), 6.44 (s, 3JPt−H = 75, 1H, bzq-CHCFcCl), 4.85 (s, 1H, C5H4), 4.47 (s, 1H, C5H4), 4.02 (s, 5H, Cp), 3.97 (s, 1H, C5H4), 3.63 (s, 1H, C5H4). 19F NMR (282.4 MHz, CDCl3, 20 °C, δ): −119.7 (d, JPt‑oF = 218, 1o-F), −126.5 (d, JPt‑oF = 305, 1o-F), −161.1 (t, 1p-F), −163.2 (m, 1m-F), −164.2 (m, 1m-F). E1/2 = 0.67 V (vs Ag/AgCl). Preparation of [Pt{bzq-κN-η2-CHC(I)Fc}(C6F5)I] (4b). To a suspension of [Pt(bzq-κN,κC10)(C6F5)(η2-HCCFc)] (0.170 g, 0.227 mmol) in CH2Cl2 (20 mL) was added 0.058 g of I2 (0.227 mmol) at 25 °C. After 3 h of stirring, the orange solid that precipitated was filtered and indentified as [{Pt(bzq-κN,κC10)(C6F5)I(μ-I)}2] (5b; 0.042 g, 23%). The red filtrate was evaporated to dryness and treated with n-hexane (5 mL) to give 4b as a maroon solid (0.101 g, 44%). At 0 °C, 5b and 4b were also isolated in 50% and 27% yields, respectively. IR (cm−1): ν(CC) 1377 (m), ν(C6F5)X‑sens 805 (m). Anal. Calcd for C31H18I2F5FeNPt: C, 37.08; H, 1.81; N 1.39. Found: C, 36.99; H, 1.78; N, 1.27. MALDI-TOF (+): m/z (%) 1004 [M]+ (100), 750 [M − I2] + (18). 1H NMR (300.1 MHz, CDCl3, 20 °C, δ): 10.10 (d, J = 5.0, H2, bzq), 8.52 (d, J = 7.8, H4, bzq), 8.15 (d, J = 7.1, H7, bzq), 8.03 (d, J = 8.7, H5,6, bzq), 7.89 (m, 2H, H8, H9, bzq), 7.79 (d, J = 8.7, H5,6, bzq), 7.73 (t, J = 9.6, H3, bzq), 6.46 (s, 3JPt−H = 75, 1H, bzq-CH CFcI), 4.75 (s, 1H, C5H4), 4.48 (s, 1H, C5H4), 4.07 (s, 5H, Cp), 4.02 (s, 1H, C5H4), 3.86 (s, 1H, C5H4). 19F NMR (282.4 MHz, CDCl3, 20 °C, δ): −115.9 (d, JPt‑oF = 223, 1o-F), −125.5 (d, JPt‑oF = 309, 1o-F), −161.2 (t, 1p-F), −163.7 (m, 1m-F), −164.7 (m, 1m-F). E1/2 = 0.69 V (vs Ag/AgCl). Preparation of [{Pt(bzq-κN,κC10)(C6F5)X(μ-X)}2] (X = Cl (5a), I (5b), Br (5c)). To a solution of [Pt(bzq-κN,κC 10 )(C 6 F 5 )(CH3COCH3)] (2) in CH2Cl2 (15 mL) at 0 °C was added 1 equiv of the corresponding oxidant (PhICl2, I2, and Br2, respectively). After 3 h of stirring, the suspension that was obtained was filtered, giving 5 as pale yellow (5a), red (5b), and orange (5c) solids. As noted above, the complexes [{Pt(bzq-κN,κC10)(C6F5)X(μ-X)}2] (X = Cl (5a), I (5b)) can be alternatively synthesized in low yield (12% (5a), 23% (5b)) by reaction of [Pt(bzq-κN,κC10)(C6F5)(η2-HCCFc)] (1) and the corresponding oxidant (PhICl2 (5a), I2 (5b)) at 25 °C. Data for [{Pt(bzq-κN,κC10)(C6F5)Cl(μ-Cl)}2] (5a). [Pt(bzq-κN,κC10)(C6F5)(CH3COCH3)] (2; 0.100 g, 0.167 mmol) and iodobenzene dichloride (PhICl2, 0.046 g, 0.167 mmol) were used (yield of 5a: 0.063 g, 61%). IR (cm−1): ν(C−F) 1075 (s), 969 (s); ν(C)X‑sens 800 (s); ν(Pt−Cl) 367 (m), 306, 300 (w). Anal. Calcd for C38H16Cl4F10N2Pt2: C, 37.33; H, 1.32; N 2.29. Found: C, 37.02; H, 1.25; N, 1.98. MALDITOF (+): m/z (%) 1221 [M]+ (1), 1187 [M − Cl]+ (33), 826 [Pt2Cl(bzq)2]+ (100). 1H NMR (400.1 MHz, dmso-d6, 20 °C, δ): 9.22 (dd, J = 5.3, J = 1.0, 3JPt−H = 19, H2, bzq), 8.77 (dd, J = 8.1, JH−H = 1.1, H4, bzq), 8.07−7.94 (m, H3, H5, H6, bzq), 7.75 (d, J = 7.8, H7, bzq), 7.51 (t, J = 7.8, H8, bzq), 7.12 (d, J = 7.8, 3JPt−H = 35, H9, bzq). 19F

longer than those reported recently for the precursor 3 (Pt−C = 2.000(7)−2.003(8) Å, Pt−N = 2.078(7) Å), which is consistent with the increase in the coordination number. The Pt−C(C6F5) distances (8b, 2.067(9) Å; 8c, 2.044(5) Å) are slightly shorter than those reported in other pentafluorophenyl PtIV complexes,47 due to the very low trans influence of the N donor atom. Along the same line, the Pt−S bond lengths (2.386(2), 2.363(1) Å) do not deviate significantly from that seen in 3 (2.3719(19) Å).50 This fact can also be attributed to the nature of the trans ligands. The lower trans influence of the halide in the PtIV species 8 in relation to that of C(bzq) in the PtII species 3 is balancing the change in oxidation state. On the basis of literature precedents for analogous oxidation reactions of PtII complexes with halogenated oxidants, we propose that the first step is a two-electron oxidation to form a cationic PtIV intermediate, followed by reaction with X− to yield the final complexes.8−13,28,47−49 It should be noted that a rearrangement of the pentacoordinate species is required to render the final cis isomers. Similar isomerizations have been previously observed.8−11,48 The preference for the cis isomer, which locates the sulfur cis to the metalate C(bzq) carbon atom, is in accordance with the so-called “transphobia” effect.53

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CONCLUDING REMARKS In summary, we have disclosed that the oxidation of the ferrocenyl group in the η2-ferrocenyl alkyne complex [Pt(bzqκN,κC10)(C6F5)(η2-HCCFc)] (1) induces a formal electrophilic addition to the unsaturated alkyne with concomitant C− C bond formation, thus forming the final PtII complexes [Pt{bzq-κN-η2-CHC(X)Fc}(C6F5)X] (4). The new functionalized (vinyl)benzoquinoline ligands can be easily liberated from metal by a displacement reaction with PPh3. These results reveal a novel reactivity pattern in both the well-known PtIV/ PtII redox systems and in the usual reactivity of alkynes in platinum chemistry and illustrate the potential of utilizing the cooperation between two redox centers to allow access to new reaction pathways. Furthermore, the study of related oxidation reactions using as precursors the labile substrates [Pt(bzq-κN,κC10)(C6F5)(η2HCCPh)], [Pt(bzq-κN,κC10)(C6F5)(CH3COCH3)] (2), or [Pt(bzq-κN,κC10)(C6F5)(tht)] (3) has allowed us to prepare new benzoquinolatepentafluorophenyl PtIV complexes (5, 7, and 8), which could be relevant for understanding mechanistic processes or as precursors to develop novel d6 luminescent materials.

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EXPERIMENTAL SECTION

General Comments. All reactions were carried out under an atmosphere of dry argon, using standard Schlenk techniques. Solvents were obtained from a solvent purification system (M-BRAUN MB SPS-800). NMR spectra were recorded at 293 K on a Bruker ADX 400 spectrometer. Chemical shifts are reported in ppm relative to external standards (SiMe4, CFCl3), and all coupling constants are given in Hz. The NMR spectral assignments of the benzoquinolate ligand (bzq) follow the numbering scheme shown in Figure S12 (Supporting Information). IR spectra were obtained on a Nicolet Nexus FT-IR spectrometer, using Nujol mulls between polyethylene sheets. Elemental analyses were carried out with Perkin-Elmer 2400 CHNS/O and Carlo Erba EA1110 CHNS-O microanalyzers. Mass spectra were recorded on a Microflex MALDI-TOF Bruker (MALDI) spectrometer operating in the linear and reflector modes using dithranol as matrix. Cyclic voltammetry was carried out in 0.1 M NBu4PF6 solutions as supporting electrolyte, using a three-electrode configuration (Pt disk as working electrode, Pt-wire counter electrode, 3949


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Article

NMR (282.4 MHz, dmso-d6, 20 °C, δ): −114.2 (s, br, 2o-F), −158.5 (t, 1p-F), −162.8 (m, 2m-F); at 55 °C, −113.8 (s, 2o-F), −159.4 (t, 1p-F), −163.6 (m, 2m-F). Data for [{Pt(bzq-κN,κC10)(C6F5)I(μ-I)}2] (5b). [Pt(bzq-κN,κC10)(C6F5)(CH3COCH3)] (2; 0.100 g, 0.167 mmol) and I2 (0.042 g, 0.167 mmol) were used (yield of 5b: 0.107 g, 80%). IR (cm−1): ν(C− F) 1071 (s), 967 (s); ν(C6F5)X‑sens 792 (m), 770 (m); ν(Pt−I) 225 (w), 220 (w). Anal. Calcd for C38H16I4F10N2Pt2: C, 28.74; H, 1.02; N, 1.76. Found: C, 28.56; H, 0.98; N, 1.46. MALDI-TOF (+): m/z (%) 1461 [M − I]+ (9). 1H NMR (400.1 MHz, dmso-d6, 20 °C, δ): 9.26 (d, J = 5.6, JPt−H = 20, H2, bzq), 8.69 (d, J = 7.9, H4, bzq), 8.01 − 7.94 (m, H3, H5, H6, bzq), 7.57 (d, J = 7.7, H7, bzq), 7.50 (t, J = 7.7, H8, bzq), 7.08 (dd, J = 7.7, 3JPt−H = 36, H9, bzq). 19F NMR (282.4 MHz, dmso-d6, 20 °C, δ): −99.5 (s, 1o-F), −104.7 (s, 1o-F), −159.2 (t, 1pF), −162.3 (m, 1m-F), −163.7 (m, 1m-F). Data for [{Pt(bzq-κN,κC10)(C6F5)Br(μ-Br)}2] (5c). [Pt(bzq-κN,κC10)(C6F5)(CH3COCH3)] (2; 0.100 g, 0.167 mmol) and Br2 (9 μL, 0.167 mmol) were used (5c: 0.087 g, 74%). IR (cm−1): ν(C−F) 1074 (s), 967 (s); ν(C6F5)X‑sens 795 (s); ν(Pt−Br) 268 (m), 248, 234 (m). Anal. Calcd for C38H16Br4F10N2Pt2: C, 32.67; H, 1.16; N, 2.01. Found: C, 32.05; H, 1.31; N, 2.00. MALDI-TOF (+): m/z (%) 1321 [M − Br]+ (22). 1H NMR (400.1 MHz, dmso-d6, 20 °C, δ): 9.29 (d, J = 5.2, JPt−H = 19, H2, bzq), 8.81 (d, J = 7.9, H4, bzq), 8.01 − 7.94 (m, H3, H5, H6, bzq), 7.75 (d, J = 7.8, H7, bzq), 7.58 (t, J = 7.7, H8, bzq), 7.16 (m, 3 JPt−H = 38.9, H9, bzq). 19F NMR (282.4 MHz, dmso-d6, 20 °C, δ): −107.3 (s, br, 1o-F), −112.3 (s, br, 1o-F), −159.0 (t, 1p-F), −163.1 (m, 2m-F). Preparation of [bzq-CHC(Cl)Fc] (6a). To a cooled (0 °C) solution of [Pt{bzq-κN-η2-CHC(Cl)Fc}(C6F5)Cl] (4a; 0.129 g, 0.157 mmol) in CH 2 Cl 2 (20 mL) was added 2 equiv of triphenylphosphine (0.082 g, 0.314 mmol). After 1 h of stirring, the solvent was removed and the residue treated with Et2O (20 mL), giving a solid which was filtered and identified as trans-[Pt(C6F5)Cl(PPh3)2] (0.040 g, 28%). The orange filtrate was concentrated to a small volume (2 mL) and purified by column chromatography (SiO2, n-hexane/CH2Cl2 8/2) to give 6a as an orange solid (0.021 g, 32%). IR (cm−1): ν(CC) 1374 (s). MALDI-TOF (+): m/z (%) 423 [M]+ (100). Anal. Calcd for C25H18ClFeN: C, 70.87; H, 4.28; N, 3.31. Found: C, 70.41; H, 3.89; N, 3.52. 1H NMR (400.1 MHz, CDCl3, 20 °C, δ): 9.12 (dd, J = 4.2, J = 1.6, H2, bzq), 8.31 (s, 1H, bzq-CH CFcCl), 8.19 (d, J = 8, H4, bzq), 7.96 (d, J = 7.9, H7/9, bzq), 7.92 (d, J = 7.9, H7/9, bzq), 7.85 (d, J = 8.8, H5/6, bzq), 7.73 (t, J = 7.9, H8, bzq), 7.70 (d, J = 8.8, H5/6, bzq), 7.53 (dd, J = 4.2, J = 8.1, H3, bzq), 4.83 (s, 2H, C5H4), 4.36 (s, 2H, C5H4), 4.30 (s, 5H, Cp). 13C{1H} NMR (100.6 MHz, CDCl3, 20 °C, δ): 148.0 (s, C12, bzq), 147.5 (s, C2, bzq), 135.5 (s, C4, bzq), 134.8 (s, =C(Cl)Fc), 131.2 (s, C7/9, bzq), 129.2 (s, bzq), 128.7 (s, C5/6, bzq), 128.0 (s, C7/9, bzq), 127.7 (s, bzq), 127.3 (s, C8, bzq), 127.1 (s, CHC(Cl)Fc), 126.7 (s, bzq), 125.6 (s, C5/6, bzq), 121.1 (s, C3, bzq), 69.7 (s, 5C, Cp), 69.1 (s, 2C, C5H4), 67.3 (s, 2C, C5H4). E 1/2 = 0.55 V (vs Ag/AgCl) (more waves due to electrogenerated by products are seen at higher potentials). Preparation of [bzq-CHC(I)Fc] (6b). Following the same procedure as that for 6a, starting from [Pt{bzq-κN-η2-CHC(I)Fc}(C6F5)I] (4b; 0.093 g, 0.093 mmol) and PPh3 (0.049 g, 0.186 mmol), 6b was obtained as an orange solid after purification by column chromatography (SiO2, n-hexane/CH2Cl2 8/2) (0.014 g, 29%). IR (cm−1): ν(CC) 1374 (s). MALDI-TOF (+): m/z (%) 515 [M]+ (82), 388 [M − I]+ (100). Anal. Calcd for C25H18IFeN: C, 58.29; H, 3.52; N, 2.72. Found: C, 57.91; H, 3.29; N, 2.51. 1H NMR (400.1 MHz, CD3COCD3, 20 °C, δ): 9.16 (dd, J = 4.3, J = 1.4, H2, bzq), 8.39 (d, J = 8.1, H4, bzq), 8.19 (s, 1H, bzq-CHCFcI), 8.05 (m, H8, bzq), 7.98 (d, J = 8.7, H5/6, bzq), 7.86 (d, J = 8.7, H5/6, bzq), 7.78−7.73 (m, 2H, H7, H9, bzq), 7.67 (m, H3, bzq), 4.86 (s, 2H, C5H4), 4.44 (s, 2H, C5H4), 4.31 (s, 5H, Cp). 13C{1H} NMR (100.6 MHz, CD3COCD3, 20 °C, δ) 148.5 (s, C12, bzq), 147.9 (s, C2, bzq), 137.3 (s, =C(I)Fc), 135.8 (s, C4, bzq), 131.2 (s, C7/9, bzq), 130.5 (s, bzq), 128.4 (s, C5/6, bzq), 128.3 (s, C8, bzq), 127.1 (s, C7/9, bzq), 126.8 (s, bzq), 126.0 (s, CH C(I)Fc), 125.8 (s, C5/6, bzq), 123.5 (s, bzq), 121.5 (s, C3, bzq), 69.7 (s, 5C, Cp, Fc), 69.3 (s, 2C, C5H4, Fc), 68.9 (s, 2C, C5H4, Fc). E1/2 =

0.57 V (vs Ag/AgCl) (more waves due to electrogenerated by products are seen at higher potentials). Preparation of [Pt(bzq-κN,κC10)(C6F5)X2(dmso)] (X = Cl (7a), I (7b), Br (7c)). General Procedure. A suspension of [{Pt(bzqκN,κC10)(C6F5)X(μ-X)}2] (5) in 2 mL of dmso was heated to 50 °C for 5 min and stirred until complete dissolution of the corresponding complex. The solution was poured into 400 mL of H2O, and the obtained precipitate was filtered to give 7. Data for [Pt(bzq-κN,κC10)(C6F5)Cl2(dmso)] (7a). Starting from [{Pt(bzq-κN,κC10)(C6F5)Cl(μ-Cl)}2] (5a; 0.050 g, 0.041 mmol), 7a was obtained as a pale yellow solid (0.046 g, 82%). IR (cm−1): ν(C− F) 1073 (s), 970 (s); ν(C6F5)X‑sens 798 (m); ν(Pt−Cl) 349 (m), 325 (w). Anal. Calcd for C21H14Cl2F5NOPtS: C, 36.59; H, 2.05; N, 2.03; S, 4.65. Found: C, 36.10; H, 2.19; N, 2.26; S, 3.97. MALDI-TOF (−): m/z (%) 646 [M − dmso + Cl]− (100), 610 [M − dmso]− (35), 576 [Pt(bzq)(C6F5)Cl]− (62). 1H NMR (400.1 MHz, CD3COCD3, −30 °C, cis:trans isomers ∼1:1.5, δ): cis-7a(dmso-κS) 9.42 (d, J = 5.0, H2, bzq), 8.81 (d, J = 8.6, H4, bzq), 8.10 (m, 3H, H5, H6, H3, bzq), 7.82 (t, J = 8.0, H8, bzq), 7.59 (d, J = 7.3, H7, bzq), 7.32 (t, J = 8.4, JPt−H = 39, H9, bzq), 3.09 (s, 3H, CH3, dmso), 3.03 (s, 3H, CH3, dmso); trans7a(dmso-κO) 9.40 (d, J = 5.1, H2, bzq), 8.85 (d, J = 8.1, H4, bzq), 8.15−8.04 (m, 3H, H5, H6, H3, bzq), 7.82 (t, J = 8.0, H8, bzq), 7.59 (d, J = 7.3, H7, bzq), 7.32 (t, J = 8.4, J Pt−H = 39, H9, bzq), 2.54 (s, 6H, dmso). When the temperature was increased, the two Me signals of the cis isomer broadened and averaged into one at 3.05 ppm. 19F NMR (376.5 MHz, CD3COCD3, −50 °C, δ): cis-7a(dmso-κS) −112.2 (d, JPt‑oF = 102, 1o-F), −119.0 (d, JPt‑oF = 105, 1o-F), −160.8 (t, 1p-F), −164.1 (m, 1m-F), −165.1 (m, 1m-F); trans-7a(dmso-κO) −112.6 (d, JPt‑oF = 104, 1o-F), −117.6 (d, JPt‑oF = 116, 1o-F), −161.0 (t, 1p-F), −164.4 (m, 1m-F), −166.0 (m, 1m-F). 19F NMR (25 °C, δ): −115.0 (br), −161.6 (t, p-F, trans), −161.9 (t, p-F, cis), −165.5 (m, br, m-F, trans), −165.9 (m, br, m-F, cis). Data for [Pt(bzq-κN,κC10)(C6F5)I2(dmso)] (7b). Starting from [{Pt(bzq-κN,κC10)(C6F5)I(μ-I)}2] (5b; 0.040 g, 0.025 mmol), 7b was obtained as an orange solid (0.039 g, 88%). IR (cm−1): ν(C−F) 1066 (m), 967 (m); ν(C6F5)X‑sens 791 (m); ν(Pt−I) 247 (w), 224 (w). Anal. Calcd for C21H14I2F5NOPtS: C, 28.92; H, 1.62; N, 1.61; S, 3.68. Found C, 28.39; H, 0.97; N, 1.71; S, 3.08. MALDI-TOF (−): m/z (%) 667 [Pt(bzq)(C6F5)I]− (100). MALDI-TOF (+): m/z (%) 744 [M − I]+ (17). 1H NMR (400.1 MHz, CD3COCD3, −50 °C, cis:trans isomers ∼1:1, δ): cis-7b(dmso-κS) 9.47 (d, J = 6.0, H2, bzq), 8.75 (d, J = 8.1, H4, bzq), 8.15−8.05 (m, 3H, H5, H6, H3, bzq), 7.66−7.57 (m, 2H, H7, H8, bzq), 7.23 (d, J = 7.5, J Pt−H = 37, H9, bzq), 3.16 (s, 3H, CH3, dmso), 2.99 (s, 3H, CH3, dmso); trans-7b(dmso-κO) 9.44 (d, J = 5.1, H2, bzq), 8.78 (d, J = 8.0, H4, bzq), 8.15−8.05 (m, 3H, H5, H6, H3, bzq), 7.66−7.57 (m, 2H, H7, H8, bzq), 7.29 (d, J = 7.2, JPt−H = 39, H9, bzq), 2.53 (s, 6H, CH3, dmso). When the temperature was increased, the two Me signals of the cis isomer broadened and averaged into one at 3.06 ppm. 19F NMR (376.5 MHz, CD3COCD3, −50 °C, δ): cis-7b(dmso-κS) −100.2 (d, JPt‑oF = 111, 1o-F), −106.4 (d, JPt‑oF = 122, 1o-F), −160.9 (t, 1p-F), −163.7 (m, 1m-F), −165.1 (m, 1m-F); trans-7b(dmso-κO) −101.1 (d, JPt‑oF = 107, 1o-F), −105.1 (d, JPt‑oF = 126, 1o-F), −161.2 (t, 1p-F), −164.1 (m, 1m-F), −165.9 (m, 1m-F). 19 F NMR (25 °C, δ): −99.5 (s, br, o-F, cis), −100.7 (s, br, o-F, trans), −161.9 (t, p-F, cis + trans), −164.8 (m, br, m-F, cis + trans), −166.0, −166.4 (m, br, m-F, cis + trans). Data for [Pt(bzq-κN,κC10)(C6F5)(dmso)Br2] (7c). Starting from [{Pt(bzq-κN,κC10)(C6F5)Br(μ-Br)}2] (5c; 0.050 g, 0.036 mmol), 7c was obtained as a pale yellow solid (0.044 g, 79%). IR (cm−1): ν(C− F) 1077 (m), 971 (m); ν(C6F5)X‑sens 793 (m); ν(Pt−Br) 268 (w), 232 (w). Anal. Calcd for C21H14Br2F5NOPtS: C, 32.41; H, 1.81; N, 1.80; S, 4.12. Found: C, 32.13; H, 1.51; N, 2.32; S, 3.75. MALDI-TOF (−): m/z (%) 779 [M]− (25), 770 [M − dmso]− (10), 620 [M − dmso − Br]− (100). 1H NMR (400.1 MHz, CD3COCD3, −50 °C, cis:trans isomers ∼2:1, δ): cis-7c(dmso-κS) 9.46 (d, J = 5.2, JPt−H = 18, H2, bzq), 8.82 (d, J = 7.8, H4, bzq), 8.08 (m, 3H, H3, H5, H6, bzq), 7.76 (d, J = 8.0, H7, bzq), 7.59 (t, J = 8.0, H8, bzq), 7.29 (d, J = 7.1, JPt−H = 35, H9, bzq), 3.15 (s, 3H, CH3, dmso), 3.01 (s, 3H, CH3, dmso); trans7c(dmso-κO) 9.42 (d, J = 5.2, JPt−H = 17, H2, bzq), 8.85 (d, J = 7.9, H4, bzq), 8.17 (t, J = 5.5, H3, bzq), 8.16 (m, H5, H6, bzq), 7.77 (d, J = 3950


Organometallics

Article

Data for [Pt(bzq-κN,κC10)(C6F5)Br2(tht)] (8c). [Pt(bzq-κN,κC10)(C6F5)(tht)] (3; 0.136 g, 0.216 mmol) and Br2 (11 μL, 0.216 mmol) were used to obtain cis-8c as a yellow solid (0.080 g, 47%). IR (cm−1): ν(C−F) 1074 (s), 974 (s); ν(C6F5)X‑sens 791 (s); ν(Pt−Br) 234 (w). Anal. Calcd for C23H16Br2F5NPtS: C, 35.04; H, 2.05; N, 1.78; S, 4.07. Found: C, 34.84; H, 2.26; N, 2.18; S, 4.35. MALDI-TOF (+): m/z (%) 790 [M]+ (30), 710 [M − Br]+ (100). 1H NMR (400.1 MHz, CD3COCD3, 25 °C, δ): 10.00 (d, J = 8, JPt−H = 18, H2, bzq), 8.87 (d, J = 8.1, H4, bzq), 8.13 (m, 2H, H3, H5/6, bzq), 8.05 (d, J = 8.0, H5/6, bzq), 7.90 (d, J = 7.8, H7, bzq), 7.69 (t, J = 7.8, H8, bzq), 7.42 (t, J = 7.8, JPt−H = 40, H9, bzq), 3.13 (m, 1H, α-CH2, tht), 3.06 (m, 1H, αCH2, tht), 2.20 (m, 1H, α-CH2, tht), 1.80 (m, 1H, α-CH2, tht), 1.77 (m, 1H, β-CH2, tht), 1.57 (m, 1H, β-CH2, tht), 1.04 (m, 1H, β-CH2, tht), 0.97 (m, 1H, β-CH2, tht). 19F NMR (376.5 MHz, CD3COCD3, −50 °C, δ): −103.3 (d, JPt‑oF = 87, 1o-F), −115.5 (d, JPt‑oF = 90, 1o-F), −160.3 (t, 1p-F), −164.0 (m, 1m-F), −164.7 (m, 1m-F). X-ray Crystallography. Table S4 (Supporting Information) reports details of the structural analysis for the complexes 4a, trans7c(dmso-κO), cis-8b and 8c. Red crystals of complex 4a were obtained by slow evaporation at room temperature of a solution of the complex in a 1:2 mixture of CH2Cl2 and hexane, while yellow (trans7c(dmso-κO), 8c) and orange (cis-8b) crystals were obtained by slow diffusion of hexane into saturated solutions of the corresponding compounds in acetone (trans-7c(dmso-κO), 8c, −30 °C) and CH2Cl2 (cis-8b, room temperature). X-ray intensity data have been collected with a NONIUS-κCCD area-detector diffractometer, using graphitemonochromated Mo Kα radiation (λ(Mo Kα) = 0.71071 Å), and the images were processed using the DENZO and SCALEPACK suite of programs.54 The structures were solved by Patterson and Fourier methods using DIRDIF9955 (4a) or SHELXS-9756 (trans-7c(dmsoκO), cis-8b and 8c) and refined by full-matrix least squares on F2 with SHELXL-97.56 The absorption corrections were performed using MULTI-SCAN,57 with the WINGX program suite.58 All nonhydrogen atoms were assigned anisotropic displacement parameters. The hydrogen atoms were constrained to idealized geometries fixing isotropic displacement parameters of 1.2 times the Uiso value of their attached carbons for aromatic and methylene hydrogens and 1.5 times for the methyl groups. For complex 4a, the olefinic hydrogen atoms H15 and H46 were assigned from the Fourier map and refined with a fixed distance of 0.93 Å to their attached carbon atoms. Complexes 4a and trans-7c(dmso-κO) crystallize with half a molecule of hexane (4a·0.5(hexane) and trans-7c(dmso-κO)·0.5(hexane)), but we have been not able to model the crystallization solvent present in the structure of complex 8c. Examination with SQUEEZE59 revealed the presence of two voids of 116 Å3 containing a total of 40 e, which fits well for the presence in the unit cell of one molecule of acetone and water. Therefore, we have included them in the empirical formula as crystallization solvent (8c·0.25(acetone)·0.25H2O). For complex 4a, five restraints have been used to model the hexane molecule found in the asymmetric unit (4a·0.5(hexane)). The structures present some residual peaks greater than 1 e Å−3 in the vicinity of the metal atoms or solvent molecules, but with no chemical meaning. Computational Details for Theoretical Calculations. DFT calculations were carried out using the Gaussian 09 package.60 All calculations applied the functional of Perdew, Burke, and Ernzerhof61 that uses 25% exchange and 75% correlation weighting and is denoted as PBE0. The basis set used was the LanL2DZ effective core potential62 for the metal center (Pt) and 6-31G(d,p) for the ligand atoms. All isomers were optimized without considering solvent effects, and no negative values were found in the results of the vibrational frequency analysis.

7.9, H7, bzq), 7.60 (m, H8, bzq), 7.31 (d, J = 7.9, J Pt−H = 36, H9, bzq), 2.55 (s, 6H, CH3, dmso). When the temperature was increased, the two Me signals of the cis isomer broadened and averaged into one at 3.07 ppm. 19F NMR (376.5 MHz, CD3COCD3, −50 °C, δ): cis7c(dmso-κS) −107.8 (d, JPt‑oF = 108, 1o-F), −114.4 (d, JPt‑oF = 114, 1o-F), −160.7 (t, 1p-F), −163.9 (m, 1m-F), −165.1 (m, 1m-F); trans7c(dmso-κO) −108.3 (d, JPt‑oF = 108, 1o-F), −112.9 (d, JPt‑oF = 113, 1o-F), −160.9 (t, 1p-F), −164.2 (m, 1m-F), −165.9 (m, 1m-F). 19F NMR (25 °C, δ): −108.0 (br, o-F), −112.6 (br, o-F), −161.8 (t, p-F, cis+trans), −165.6 (m, br, m-F, cis + trans). Preparation of [Pt(bzq-κN,κC10)(C6F5)X2(tht)] (X = Cl (8a), I (8b), Br (8c)). General Procedure. To a solution of [Pt(bzqκN,κC10)(C6F5)tht] (3) in CH2Cl2 1 equiv of the corresponding oxidant (PhICl2, I2, or Br2) was added. After 1 h of reaction, the solvent was evaporated to dryness and the residue was treated with Et2O (5 mL) obtaining 8. Data for [Pt(bzq-κN,κC10)(C6F5)Cl2(tht)] (8a). [Pt(bzq-κN,κC10)(C6F5)(tht)] (3; 0.140 g, 0.223 mmol) and PhICl2 (0.061 g, 0.223 mmol) were used to give 8a as a pale yellow solid (0.120 g, 77%). IR (cm−1): ν(C−F) 1079 (s), 967 (s); ν(C6F5)X‑sens 796 (s); ν(Pt−Cl) 348 (s), 345 (w). Anal. Calcd for C23H16Cl2F5NPtS: C, 39.50; H, 2.31; N, 2.00; S, 4.58. Found: C, 39.23; H, 2.29; N, 2.47; S, 4.62. MALDITOF (+): m/z (%) 664 [M − Cl]+ (100), 631 [M − 2Cl]− (16). 1H NMR (400.1 MHz, CDCl3, −30 °C, cis:trans isomers ∼7:1, δ): cis-8a 10.00 (d, J = 7.0, JPt−H = 20, H2, bzq), 8.54 (d, J = 8.0, H4, bzq), 7.96 (d, J = 8.4, H5/6, bzq), 7.90 (t, H3, bzq), 7.80 (m, H5/6, H7, bzq), 7.66 (t, J = 7.8, H8, bzq), 7.45 (t, J = 7.5, JPt−H = 35, H9, bzq), 3.16 (m, 1H, α-CH2, tht), 2.96 (m, 1H, α-CH2, tht), 2.30 (m, 1H, α-CH2, tht), 2.07 (m, 1H, α-CH2, tht), 1.81 (m, 1H, β-CH2, tht), 1.48 (m, 2H, β-CH2, tht), 1.15 (m, 1H, β-CH2, tht); trans-8a 9.08 (d, J = 4, H2, bzq), 8.45 (d, J = 10, H4, bzq), 8.00−7.46 (the rest of the bzq and tht signals are overlapped with signals corresponding to cis-8a). 19F NMR (376.5 MHz, CDCl3, −30 °C, δ): cis-8a −110.4 (d, JPt‑oF = 75, 1o-F), −117.2 (d, JPt‑oF = 85, 1o-F), −156.8 (t, 1p-F), −159.7 (m, 1m-F), −161.8 (m, 1m-F); trans-8a −113.0 (m, JPt‑oF ≈ 80, 1o-F), −119.5 (d, JPt‑oF ≈ 85, 1o-F), −157.4 (t, 1p-F), −160.5 (m, 1m-F), −162.5 (m, 1m-F). A sample was crystallized from CH2Cl2/Et2O giving rise pure cis-8a. 1H NMR (400.1 MHz, CD3COCD3, −30 °C, δ): 10.03 (d, J = 8.0, JPt−H = 20, H2, bzq), 8.94 (d, J = 8.0, H4, bzq), 8.18 (m, H5/6, H3, bzq), 8.11 (d, J = 12.0, H5/6, bzq), 7.95 (d, J = 8.0, H7, bzq), 7.71 (t, J = 7.5, H8, bzq), 7.42 (t, J = 7.5, JPt−H = 35, H9, bzq), 3.08 (m, 2H, α-CH2, tht), 2.25 (m, 1H, α-CH2, tht), 1.74 (m, 2H, tht), 1.53 (m, 1H, β-CH2, tht), 1.02 (m, 1H, β-CH2, tht), 0.66 (m, 1H, β-CH2, tht). Data for [Pt(bzq-κN,κC10)(C6F5)I2(tht)] (8b). [Pt(bzq-κN,κC10)(C6F5)(tht)] (3; 0.150 g, 0.238 mmol) and I2 (0.061 g, 0.238 mmol) were used to give 8b as an orange solid (0.126 g, 63%). IR (cm−1): ν(C−F) 1078 (s), 970 (s); ν(C6F5)X‑sens 795 (s); ν(Pt−I) 224 (w). Anal. Calcd for C23H16I2F5NPtS: C, 31.31; H, 1.83; N, 1.59; S, 3.63. Found C, 30.89; H, 1.97; N, 1.67; S, 3.46. MALDI-TOF (+): m/ z (%) 755 [M − I + 2H]+ (100), 670 [Pt(bzq)(C6F5)I]+ (33). 1H NMR (400.1 MHz, CDCl3, 25 °C, cis:trans isomers ∼5:1, δ): cis-8b 10.44 (d, J = 8.0, JPt−H = 16, H2, bzq), 8.46 (d, J = 8.0, H4, bzq), 7.97 (d, J = 8.0, H5/6, bzq), 7.78 (m, H5/6, H7, bzq), 7.73 (t, J = 7.5, H3, bzq), 7.67 (t, J = 7.5, H8, bzq), 7.31 (t, J = 6.5, JPt−H = 38, H9, bzq), 2.86 (m, 2H, α-CH2, tht), 2.75 (m, 1H, α-CH2, tht), 1.78 (m, 1H, αCH2, tht), 1.55 (m, 2H, β-CH2, tht), 0.92 (m, 2H, β-CH2, tht); trans8b 9.33 (d, J = 5.0, JPt−H = 20, H2, bzq), 8.39 (d, J = 8.0, H4, bzq), 7.93−7.38 (the rest of the bzq and tht signals appear overlapped with other corresponding to cis-8b). 19F NMR (376.5 MHz, CD3COCD3, −50 °C, δ): cis-8b −92.2 (d, JPt‑oF = 109, 1o-F), −113.1 (d, JPt‑oF = 113, 1o-F), −159.6 (t, 1p-F), −162.9 (m, 1m-F), −164.3 (m, 1m-F); trans8b −101.4 (m, 1o-F), −105.2 (d, 1o-F), −160.8 (t, 1p-F), −163.7 (m, 1m-F), −165.5 (m, 1m-F). A sample was crystallized from CHCl3/nhexane to give mainly cis-8b. 1H NMR (400.1 MHz, CD3COCD3, 25 °C, δ): 10.36 (d, J = 8.0, JPt−H = 20, H2, bzq), 8.83 (d, J = 8.0, H4, bzq), 8.11 (m, H5/6, H3, bzq), 8.03 (d, J = 12.0, H5/6, bzq), 7.86 (d, J = 8.0, H7, bzq), 7.71 (t, J = 8.0, H8, bzq), 7.30 (t, J = 7.5, JPt−H = 40, H9, bzq), 2.95 (m, 2H, α-CH2, tht), 1.87 (m, 1H, α-CH2, tht), 1.66 (m, 1H, αCH2, tht), 1.59 (m, 1H, β-CH2, tht), 1.40 (m, 1H, β-CH2, tht), 0.80 (m, 2H, β-CH2, tht).

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ASSOCIATED CONTENT

S Supporting Information *

1

H NMR spectrum of 4b (Figure S1), molecular structure and selected distances and angles for 4a (molecule B) (Figure S2 and Table S1), cyclic voltammetry of 1 (Figure S3), theoretical calculations (Tables S2 and S3 and Figure S4), variabletemperature 19F NMR spectra of 7a−c (Figures S5−S7),

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variable-temperature 1H NMR spectra of 7a (Figure S8), NOESY and NOE experiments for complex 7c at 223 K (Figures S9 and S10), variable-temperature 19F NMR spectra of 8c (Figure S11), numbering Scheme for the bzq ligand (Figure S12), and crystallographic data (CIF files and Table S4). This material is available free of charge via the Internet at http:// pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E.L.: fax, (+34) 941 299 621; e-mail, [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Spanish MICINN (Project CTQ2008-06669-C02-02/BQU). We thank the CESGA for computer support.

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Organometallics

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