Carbon-Rich Ruthenium Allenylidene Complexes Bearing

Article pubs.acs.org/Organometallics

Carbon-Rich Ruthenium Allenylidene Complexes Bearing Heteroscorpionate Ligands Frank Strinitz,† Johannes Tucher,‡ Johanna A. Januszewski,§ Andreas R. Waterloo,§ Philipp Stegner,† Sebastian Förtsch,† Eike Hübner,∥ Rik R. Tykwinski,§ and Nicolai Burzlaff*,† †

Inorganic Chemistry, Department of Chemistry and Pharmacy & Interdisciplinary Center for Molecular Materials (ICMM), Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Egerlandstraße 1, 91058 Erlangen, Germany ‡ Inorganic Chemistry I, University Ulm, Albert-Einstein-Allee 11, 89081 Ulm, Germany § Organic Chemistry, Department of Chemistry and Pharmacy & Interdisciplinary Center for Molecular Materials (ICMM), Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Henkestraße 42, 91054 Erlangen, Germany ∥ Organic Chemistry, Technical University Clausthal, Leibnizstraße 6, 38678 Clausthal-Zellerfeld, Germany S Supporting Information *

ABSTRACT: A series of ruthenium allenylidene complexes bearing polyaromatic substituents have been prepared starting from [Ru(bdmpza)Cl(PPh3)2] (1) (bdmpza = bis(3,5dimethylpyrazol-1-yl)acetato). Reacting 1 with 1,1-bis(3,5-ditert-butylphenyl)-1-methoxy-2-propyne results in the formation of two structural isomers of an allenylidene complex [Ru(bdmpza)Cl(CCC(PhtBu2)2)(PPh3)] (5A/5B), as well as the related carbonyl complex [Ru(bdmpza)Cl(CO)(PPh3)] (4A/4B). Conversion of 9-ethynyl-9-fluorenol leads to the corresponding allenylidene complex [Ru(bdmpza)Cl(CC(FN))(PPh3)] (7A/7B) (FN = fluorenyl). Based on anthraquinone, a new synthetic route toward 10-ethynyl-10-hydroxyanthracen-9-one via the trimethylsilyl-protected propargyl alcohol is described, and subsequent conversion of this compound to the allenylidene complex ([Ru(bdmpza)Cl(C C(AO))(PPh3)] (12A/12B) (AO = anthrone) is reported. The synthetic route from 7H-benzo[no]tetraphen-7-one to the propargyl alcohol 7-ethynyl-7H-benzo[no]tetraphen-7-ol is described, which is followed by the transformation into the allenylidene complex [Ru(bdmpza)Cl(CC(BT))(PPh3)] (17A/17B) (BT = benzotetraphene). The molecular structures of 4B, 7A, 7B, 12A, 12B, 13A, and 17A have been characterized by single-crystal X-ray crystallography, and these analyses suggest that 17A might function as a “metal-tuned organic field effect transistor”. The electrochemical properties of the allenylidene complexes have been studied via cyclic voltammetry, and time-dependent DFT calculations have been conducted to assign weak absorptions in the NIR region to forbidden MLCT transitions.

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complex trans-[Cl(16-TMC)RuCCC(2-py)2]+ (16TMC = 1,5,9,13-tetramethyl-1,5,9,13-tetraazacyclohexadecane, py = pyridyl),5 or via all carbon linked systems such as trans[Cl(dppe)2Ru−CC−C(CH3)C(H)−C(CH3)CC Ru(dppe)2Cl]BF4, which results from the coupling of the diynyl and allenylidene moieties.6 Nevertheless, classical mononuclear ruthenium allenylidene chemistry still draws significant attention due to the versatile substitution patterns of the propargyl alcohols that can be achieved via alkynylation of a variety of keto derivatives, as shown for examples such as the ferrocenyl substituted allenylidene complexes [RuTp(PPh2iPr)(CCCFc2)]Cl (Fc = ferrocenyl) and [RuCp(dppe)(CCCH(Fc))]PF6.7 For ruthenium complexes, many different ligand systems are able to stabilize allenylidene systems. Already, the simple reagent [RuCl2(PPh3)3] is an important precursor in ruthenium chemistry8 and allows the

INTRODUCTION Organometallic complexes containing allenylidene moieties are of considerable interest due to their characteristic chemical and physical properties.1 The synthesis of cumulene based complexes has benefited immensely from the methodology published by Selegue.2 The reaction of substituted propargyl alcohols with a variety of ruthenium based metal complexes allows for the direct formation of ionic and neutral complexes, and this has dramatically simplified the synthetic demand for such work. π-Conjugated systems based on ruthenium are important in systems that allow exchange of electrons via the cumulenylidene unit between remote terminal groups,3 thus leading to interesting properties and potential applications in molecular-scale electronic, magnetic, and optical devices.4 Special attention has been put on dinuclear compounds that can communicate along the allenylidene unit. The linking between the two metal centers can be achieved either via functionalization of the allenylidene with nitrogen based donor substituents, as in the bis(pyridyl)allenylidene−ruthenium(II) © 2014 American Chemical Society

Received: March 14, 2014 Published: September 11, 2014 5129

dx.doi.org/10.1021/om5002777 | Organometallics 2014, 33, 5129−5144

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Scheme 1. Synthesis of Ruthenium Vinylidene Intermediate [Ru(bdmpza)Cl(CCH(COMe(PhtBu2)(PPh3)] (3), Carbonyl Complexes [Ru(bdmpza)Cl(CO)(PPh3)] (4A, 4B), Allenylidene Complexes [Ru(bdmpza)Cl(CCC(PhtBu2)2)(PPh3)] (5A, 5B), and Representative Labeling of the Heteroscorpionate Ligand (for 5A and 5B)

of our efforts on the synthesis of new 18 VE [Ru(bdmpza)Cl(PPh3)2] based allenylidene complexes derived from a series of polyaromatic propargyl alcohols.

formation of 16 valence electron (VE) allenylidene complexes by dissociation of one triphenylphosphine ligand.9 Alternatively, rigid ligand systems such as the anionic Tp (hydridotris(pyrazol-1-yl)borate),10 Cp (cyclopentadienyl)2,11 and bdmpza (bis(3,5-dimethylpyrazol-1-yl)acetato)12 or neutral PNP (N( n Pr)-(CH 2 CH 2 PPh 2 ) 2 ) 13 and dppe (1,2-bis(diphenylphosphino)ethane)3e,6,14 are more commonly employed for the formation of allenylidene complexes. In particular, the precursor [Ru(bdmpza)Cl(PPh3)2] has shown interesting organometallic chemistry,15 often similar to the chemistry reported for analogous Cp and Tp complexes. The main difference is the formation of structural isomers, which occur due to the reduced symmetry of the N,N,O-coordination motif in comparison to the ligands that show rotational symmetry. For the diphenyl and ditolyl based, neutral bdmpza allenylidene complexes, two structural isomers could be separated, and both are stable toward air and water, which makes them promising candidates for characterization of new carbon-rich ruthenium allenylidene complexes.12 Functionalized acenes have proven to be good candidates for small molecule semiconductor applications, and their properties have been extensively studied over the past decade.16 In some cases, acene derivatives have allowed the realization of largearea, mechanically flexible, and low-cost devices. The corresponding precursors, e.g., pentacenequinones, have also proven useful as organic semiconductors.17 The functionalization of acenes is mainly focused on appending alkyl, aryl, and alkyne residues to the framework in order to tune the HOMO− LUMO gap and the arrangement in the solid state.16a,18 Recently, we have reported on the synthesis of carbon-rich ruthenium allenylidene complexes based on pentacenequinone, which provided molecules with interesting structural and electronic properties.19 Thus, herein, we describe the extension

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RESULTS AND DISCUSSION

Synthesis. Typically, the straightforward synthesis of ruthenium allenylidene complexes following Selegue’s route starts from substituted propargyl alcohols, leading to the dissociation of water from the intermediary hydroxyvinylidene complexes. Depending on the metal fragment used in the reaction, the dissociation of water requires the addition of catalytic amounts of acid, which allows isolation of the labile vinylidene species. For the facially coordinating bdmpza ligand, it has been observed that the intermediate vinylidene complexes can be detected via 1H NMR spectroscopy due to the characteristic vinylidene proton, although the complex cannot be isolated and reacts directly to give the allenylidene complex. Dixneuf et al. have shown that the reversible addition of sodium methoxide to the cationic allenylidene complex trans[(dppm)2ClRu(CCCPh2]PF6 yields the corresponding neutral alkynyl complex trans-[(dppm)2ClRu(−CC−CPh2(OMe)].20 In an attempt to explore the syntheses of cumulenylidene complexes based on [Ru(bdmpza)Cl(PPh3)2] (1) further, we decided to start from the terminal alkyne 2, the methoxy ether of the conventionally used diarylpropargyl alcohol (Scheme 1). This compound has recently been shown to be an effective building block for forming stabilized organic cumulenes with up to ten carbon atoms,21 albeit the presence of the ether group might enhance the formation of the vinylidene complex instead of the allenylidene complex due to the reduced leaving potential of the methanol unit in comparison to the free hydroxyl group.20 5130


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The synthesis of the respective neutral cumulenylidene complex started from [Ru(bdmpza)Cl(PPh3)2] (1) and excess propargyl alcohol 2 in THF (Scheme 1). Initially, no apparent color change was observed. After 3 days, however, a strong purple color was visible, and formation of the allenylidene complexes [Ru(bdmpza)Cl(CCC(PhtBu2)2)(PPh3)] (5A, 5B) was completed by heating for 4 h under reflux. This implies that the reaction might proceed to completeness just by sole heating for some hours. Because of the facial coordinating motif of the bdmpza ligand, the formation of two structural isomers was observed, as has been reported previously. For isomers of types A and B, the pyrazole group next to the remaining phosphine ligand will be marked by a prime (e.g., Me3′) throughout this text (see also Scheme 1). The relatively high stability (no degradation over days was observed) allowed the separation of the isomers via column chromatography under aerobic conditions and afforded a purple (5A) and a red isomer (5B). 13C NMR spectra of 5B reveal characteristic signals for a ruthenium allenylidene complex at 314.7 ppm (d, 2JCP = 18.3 Hz, Cα), 234.6 ppm (Cβ), and 152.4 ppm (Cγ), as well as a singlet in the 31P NMR spectrum at 34.5 ppm. For compound 5A, the 13C NMR spectrum revealed strong contamination with the carbonyl complex [Ru(bdmpza)Cl(CO)(PPh3)] (4A, carbonyl trans to pyrazole group), which can be formed by oxygen-induced bond cleavage of the vinylidene intermediate, as has been shown previously for [Ru(bdmpza)Cl(CCHPh)(PPh3)].12a Unfortunately, all attempts to avoid formation of 4A during synthesis or separation of 5A via column chromatography provided only an impure product. Nevertheless, the assignment of the two structural isomers A and B to the respective symmetry and positions was accomplished based on comparisons to previously reported two-dimensional NMR experiments (ROESY) and APT 13C NMR measurements.12a Namely, type B complexes show cross-peaks between the methyl substituents in the 3- and 3′-positions with the aryl protons of the allenylidene moiety in the ROESY spectrum, which indicate a symmetrical arrangement trans to the carboxylate anchor.12a Attempts to obtain crystals of 5B suitable for X-ray diffraction by layering a solution in dichloromethane with nhexane lead, within several weeks, to bond cleavage of the allenylidene unit with conservation of the relative geometry, providing complex 4B, as illustrated in Figure 1. In comparison to the previously reported complex 4A, the carbonyl ligand in 4B is trans to the carboxylate, and thus, the chlorido and triphenylphosphine ligands are trans to the pyrazole units. This observation is unexpected, since the direct carbonylation of [Ru(bdmpza)Cl(PPh3)2] (1) and decomposition of the resulting vinylidene complexes lead exclusively to the carbonyl complex 4A with the carbonyl trans to a pyrazole.12a The ruthenium(II) center of 4B is facially coordinated by the bdmpza ligand, resulting in a slightly distorted octahedral geometry caused by the rather rigid and strained coordination geometry of the heteroscorpionate ligand (Figure 1). The Ru− C(3) (1.923(5) Å) bond is slightly elongated and C(3)−O(3) (1.009(5) Å) is contracted in comparison to the structural isomer 4A (Ru−C(3) = 1.831(5) Å, C(3)−O(3) = 1.151(6) Å) as a result of the trans orientation of the carboxylate group,12a which acts as a σ donor. This is in contrast to the pyrazolyl donor, which is a σ and π donor, as well as a π acceptor, and shows no trans influence, as previously discussed and supported by DFT calculations for the dissociation energies of N,N,O

Figure 1. Molecular structure of [Ru(bdmpza)Cl(CO)(PPh3)] (4B). Thermal ellipsoids are drawn at the 50% probability level. Hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and angles (deg): Ru−N(11) = 2.156(3), Ru−N(21) = 2.082(3), Ru− O(1) = 2.119(2), Ru−P(1) = 2.3360(10), Ru−Cl(1) = 2.3880(11), Ru−C(3) = 1.923(5), C(3)−O(3) = 1.009(5); N(11)−Ru−N(21) = 82.68(11), O(1)−Ru−N(11) = 85.60(10), O(1)−Ru−N(21) = 87.15(10), O(1)−Ru−C(3) = 177.34(13), Ru−C(3)−O(3) = 176.0(4).

ligands.22 The observed bond cleavage and subsequent CO complex formation of 4B suggest that the steric demands of the four tert-butyl groups in 5B reduces the stability in comparison to the analogous unsubstituted diphenyl allenylidene complex [Ru(bdmpza)Cl(CCCPh2)(PPh3)], which we reported before.12a Closely related to the diphenyl allenylidene complexes are systems bearing a fluorene group on Cγ. Fluorene based allenylidene complexes have previously been shown to inhibit the rearrangement of the allenylidene moiety into the corresponding indenylidene complex.23 NMR spectroscopic experiments have shown that [(η6-p-cymene)RuCl(C C(FN))(PCy3)]OTf (FN = fluorenyl) reacts upon addition of HOTf to the alkenylcarbyne, but no further transformation could be observed.23 Following the route described above, addition of excess amounts of 9-ethynylfluoren-9-ol (6) to [Ru(bdmpza)Cl(PPh3)2] (1) led to the formation of a deep purple solution (Scheme 2). The increased stability of the product, in comparison to 5A/5B, allowed separation of the structural isomers via column chromatography under aerobic conditions to yield purple (7A, allenylidene trans to pyrazole) and red (7B, allenylidene trans to carboxylate) isomers. For 7A, the characteristic signals for the allenylidene chain are observed in the 13C NMR spectrum at δ 300.6 (d, 2JC,P = 27.6 Hz, Cα), 236.4 (d, 3JC,P = 4.6 Hz, Cβ), and 141.0 (Cγ) with doublets for Cα and Cβ caused by coupling with the phosphorus atom of the triphenylphosphine ligand. Furthermore, the IR spectrum shows an intense band at 1910 cm−1, corresponding to the cumulenylidene ligand. The 31P NMR spectrum consists of one singlet at 34.6 ppm, and ESI MS experiments show the presence of the protonated monocationic species at m/z 825.16 (100%, MH+). Similar spectroscopic values are obtained for the second isomer 7B with signals at δ 314.4 (d, 2JC,P = 19.3 Hz, Cα), 256.2 (Cβ), and 141.6 ppm (Cγ) in the 13C NMR spectrum (P−C coupling observable only for Cα), while the 31P NMR spectrum shows one singlet at 30.9 ppm, which is shifted upfield in comparison to 7A. The IR spectrum shows the 5131


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Scheme 2. Synthesis of bdmpza Based Ruthenium Allenylidene Complexes [Ru(bdmpza)Cl(CC(FN))(PPh3)] (FN = fluorenyl) (7A, 7B)

cumulenic stretch at 1903 cm−1, a slightly lower value than that for 7A, and the ESI MS experiments reveal the main observable signal that is consistent with the protonated monocationic species at m/z 825.16 (100%, MH+). The assignment of the geometries was in accordance to the previously synthesized bdmpza based allenylidene complexes and could be verified by single-crystal X-ray structure determination of both isomers. Crystals of 7A and 7B have been obtained from solutions in dichloromethane layered with n-hexane and represent the first single-crystal X-ray structure determinations of fluorene based allenylidene complexes to the best of our knowledge.10a,14d,20,23,24 Complex 7A crystallizes as an enantiomeric mixture (space group Pbca) as [Ru(bdmpza)Cl(CC(FN))(PPh3)]·H2O with one water molecule bound via a hydrogen bond to the carbonyl moiety of the carboxylate unit (Figure 2). The molecular structure exhibits a slightly distorted octahedral geometry at the Ru(II) center with the allenylidene positioned trans to a pyrazole donor, the triphenylphosphine trans to the second pyrazole donor, and the chlorido ligand trans to the carboxylate anchor. In comparison to the diphenyl allenylidene complex [Ru(bdmpza)Cl(C

CCPh2)(PPh3)], the bdmpza ligand of 7A shows only slight deviations.12a In the alkylidene moiety, the Ru−C(61) bond, at 1.865(3) Å, is similar to that of [Ru(bdmpza)Cl(CC CPh2)(PPh3)] (1.886(5) Å)12a and the octahedral Tp ruthenium allenylidene complex [RuTp(CCCPh2)(PPh3)2]PF6 (1.889(3) Å),10e but this bond is considerably longer than that in pentacoordinated 16 VE ruthenium allenylidene complexes such as [RuCl2(CCCPh2)(PCy3)2] (1.794(11) Å).25 The allenylidene chain also deviates slightly from a linear geometry (∠Ru−C(61)−C(62) = 175.1(3)°, C(61)−C(62)−C(63) = 172.7(3)°). As has been described for the structurally related butatriene 4-(9H-fluoren9-ylidene)-2-methylbuta-2,3-dienal (COH(CH 3 )CC C(FN)),26 the bond lengths of the five-membered ring of the fluorenyl unit of 7A show less bond length alternation than the parent fluorenone,27 which indicates a strong delocalization of the electron density from the allenylidene moiety to the fluorenyl unit. Also notable are strong solid-state π−π stacking interactions between two neighboring fluorenyl units (Figure 3), with an interplanar distance of 3.45 Å, as calculated from the least-squares plane generated from the carbon atoms of one fluorenyl moiety to the plane of its neighbor.

Figure 3. π−π stacking interactions between two molecules of 7A: (a) top view and (b) side view.

The second structural isomer [Ru(bdmpza)Cl(C C(FN))(PPh3)] (7B) shows solid-state characteristics similar to those of 7A, including a distorted octahedral geometry (Figure 4). Compound 7B crystallizes in the space group P1̅ as a racemic mixture. The chlorido and triphenylphosphine ligands are positioned trans to pyrazole donors, placing the allenylidene unit trans to the carboxylate anchor. Therefore, the respective bond lengths differ slightly in comparison to those in 7A. For example, there is shortening of the Ru−C(61) bond to 1.855(5) Å, and a similar contraction of the Ru−N(11) bond, which can be explained by the reduced trans influence in this structural isomer because the π-accepting pyrazole and allenylidene ligands are no longer positioned trans to each other. Additionally, the allenylidene chain of 7B (∠Ru− C(61)−C(62) = 175.7(4)°, C(61)−C(62)−C(63) = 177.2(5)°) is slightly less distorted from linearity than that in

Figure 2. Molecular structure of [Ru(bdmpza)Cl(CC(FN))(PPh3)] (7A). Thermal ellipsoids are drawn at the 50% probability level. Hydrogen atoms and one molecule water have been omitted for clarity. Selected bond lengths (Å) and angles (deg): Ru−N(11) = 2.172(2), Ru−N(21) = 2.231(2), Ru−O(1) = 2.094(2), Ru−P(1) = 2.3121(9), Ru−Cl(1) = 2.3552(9), C(63)−C(67) = 1.472(4), C(63)−C(64) = 1.470(4), C(64)−C(65) = 1.406(4), C(65)−C(66) = 1.466(5), C(66)−C(67) = 1.407(4), Ru−C(61) = 1.865(3), C(61)−C(62) = 1.247(4), C(62)−C(63) = 1.352(4); Ru−C(61)− C(62) = 175.1(3), C(61)−C(62)−C(63) = 172.7(3). 5132


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acetylene with lithium in liquid ammonia, followed by the addition of anthraquinone, leading to the monosubstituted propargyl alcohol 11. This synthesis can be mimicked by the addition of the commercially available suspension of sodium acetylide in xylenes to anthraquinone. These procedures, however, offer low yields of 11 and they are also unattractive because of difficult purification due to the low solubility of 11. An improved route to 11 was thus developed, which allows the high yield synthesis of ketone 11 (Scheme 3).19,30 In the first step of the reaction, a substoichiometric amount of n-BuLi is added to trimethylsilylacetylene in dry THF. In the following step, the lithium acetylide was added dropwise to an excess amount of anthraquinone (9) in THF to avoid the formation of the bis-adduct 9,10-bis((trimethylsilyl)ethynyl)-9,10-dihydroanthracene-9,10-diol (8).31 After aqueous workup, the unreacted anthraquinone can be removed via column chromatography (silica, dichloromethane as eluent), yielding the ketone 10. The propargyl alcohol 11 was then obtained via desilylation with potassium hydroxide in aqueous methanol. The desymmetrization of anthraquinone via acetylide addition leads to the appearance of four aromatic signals in the 1H NMR spectrum of 10 at 8.17, 8.08, 7.71, and 7.51 ppm, with second-order coupling patterns characteristic of an orthosubstituted arene. Furthermore, singlets for the alcohol and TMS groups are observed at 3.16 and 0.16 ppm, respectively. The 13C NMR spectrum shows the moiety at 183.1 ppm and the three characteristic signals for a propargyl alcohol groups at 106.7, 91.5, and 66.4 ppm. The removal of the TMS group from 10 to give 11 leads to no change in the coupling pattern of the aryl protons in the 1H NMR spectrum, while the appearance of an additional signal corresponding to the alkyne proton at 2.71 ppm can be observed concurrent with the loss of the singlet of the TMS group. The solubility of 11 is significantly decreased, however, and a 13C NMR spectrum can be recorded only in DMSO-d6 and shows the terminal alkyne carbon appearing at 76.1 ppm and the keto moiety at 182.4 ppm. Preparation of the corresponding ruthenium allenylidene complexes 12A and 12B was carried out using an excess of propargyl alcohol 11 (Scheme 4). The formation of the intense purple color, characteristic for allenylidene complexes, indicated the successful conversion to 12A/12B, and the appearance of a peak at 1880 cm−1 in the IR spectrum confirmed formation of the allenylidene group. Separation of the two structural isomers was achieved by column chromatography. For the first isomer 12A, the allenylidene carbon atoms Cα (292.1 ppm, d, 2JC,P = 26.8 Hz), Cβ (251.0 ppm, d, 3JC,P = 5.0 Hz), and Cγ (141.4 ppm, d, 4JC,P = 3.0 Hz) appear as doublets in the 13C NMR spectrum, including long-range 4JC,P between the triphenylphosphine ligand and Cγ. A singlet is found in the 31 P NMR spectrum at 30.1 ppm, resulting from the triphenylphosphine ligand, which also supports the suggested

Figure 4. Molecular structure of [Ru(bdmpza)Cl(CC(FN))(PPh3)] (7B). Thermal ellipsoids are drawn at the 50% probability level. Hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and angles (deg): Ru−N(11) = 2.146(4), Ru−N(21) = 2.081(4), Ru−O(1) = 2.144(3), Ru−P(1) = 2.3552(12), Ru−Cl(1) = 2.4077(11), C(63)−C(67) = 1.466(7), C(63)−C(64) = 1.469(7), C(64)−C(65) = 1.408(7), C(65)−C(66) = 1.463(8), C(66)−C(67) = 1.407(7), Ru−C(61) = 1.855(5), C(61)−C(62) = 1.247(7), C(62)−C(63) = 1.363(7); Ru−C(61)−C(62) = 175.7(4), C(61)− C(62)−C(63) = 177.2(5).

7A. The change in the relative positions around the ruthenium center also leads to reduced distances between the fluorenyl moiety and one phenyl ring of the triphenylphosphine ligand of the complex. This close proximity of the phenyl rings appears to hinder the π−π stacking interaction between two neighboring fluorenyl units in the solid state, which also seems to result in smaller angles ∠Ru−Cα−Cβ and ∠Cα−Cβ− Cγ of 7A. Although heteroatom substituted allenylidene complexes based on 4,5-diazafluorene14a,b and cyclopentadithiophene have been reported,28 little is known about allenylidene complexes with larger polyaromatic substituents. To date, only few complexes are discussed in the literature, such as, for example, trans,trans-[(dppe)2Ru(Cl)(CCC(bianth)C CC)(Cl)Ru(dppe)2](OTf)2, that is based on the extended conjugated system [9,9′]bianthracenylidene-10,10′-dione.3f Notably, in this system, the close proximity of the protons of two anthrone units of the bianthrone moiety results in significant strain and a nonplanar organic spacer. For further studies on the π−π stacking interactions between polyaromatic allenylidene units, the anthraquinone (AQ) based 10-ethynyl-10hydroxyanthracen-9-one was targeted (11, Scheme 3). Although compound 11 is known, an appealing high yield synthesis is missing.29 The classic approach to 11 begins with the formation of a lithium acetylide, via reaction of gaseous

Scheme 3. Synthesis of the TMS-Ethynyl Alcohol 10 and the Deprotected Propargyl Alcohol 11

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Scheme 4. Synthesis of [Ru(bdmpza)Cl(CC(AO))(PPh3)] (AO = Anthrone) (12A, 12B)

structure. ESI-MS experiments again show the major observable signal resulting from the protonated monocationic species at m/z 863.14 (100%, MH+). For the structural isomer 12B, with the allenylidene unit positioned trans to the carboxylate, the 13C NMR spectrum shows a downfield shift for Cα (309.6 ppm, d, 2 JC,P = 19.8 Hz) and Cβ (277.0 ppm) relative to 12A. The third allenylidene carbon Cγ appears almost unchanged at 140.5 ppm, and a signal at 29.1 ppm in the 31P NMR spectrum confirms the triphenylphosphine ligand. In the ESI-MS experiments, the signal for a monocationic complex from 12B is, as expected, observed at m/z 863.14 (4%, MH+). In the IR absorption spectrum, the change in coordination geometry gives rise to an increase of 16 cm−1 in the cumulene vibration (1896 cm−1) compared to 12A. For the ruthenium allenylidene complexes reported within this work, no clear trend for the allenylidene absorptions in the IR spectrum could be observed regarding A and B type isomers. In the cases of 12A/12B, the difference of 16 cm−1 might be explainable by a reduced linearity of the allenylidene moiety as described below. The assignment of the relative geometry could be verified for complexes 12A and 12B by X-ray crystal structure analysis, performed on crystals obtained from solutions in dichloromethane layered with n-hexane (Figure 5). Complex 12A (allenylidene trans to pyrazole) crystallizes as a racemic mixture [Ru(bdmpza)Cl(CC(AO))(PPh3)]·CH2Cl2 in space group P1̅ with one solvent molecule disordered over three positions. The distorted octahedral geometry is affected by the strained bdmpza ligand that shows values comparable to those of the fluorenyl allenylidene complex 7A discussed above. The change from the central 5-membered ring in the fluorenyl moiety to the 6-membered ring in the anthraquinone based system in complex 12A leads to increased steric repulsion between the anthrone moiety and the triphenylphosphine ligand. This results in a smaller bond angle ∠O(1)−Ru−P(1) in 12A (83.9°) compared to that in 7A (92.7°), and a considerable greater ∠P(1)−Ru−Cl(1) angle for 12A (100.5°) than for 7A (92.1°). The allenylidene unit shows rather unremarkable values of Ru−C(31) = 1.868(3) Å, ∠Ru− C(31)−C(32) = 177.0(3)°, and ∠C(31)−C(32)−C(33) = 175.2(4)°. Similar to complex 7A, π−π stacking interactions between two anthrone units are observed (Figure 6), with a mean interplanar distance of 3.37 Å, as calculated between the leastsquares plane generated from the carbon atoms of one anthrone moiety to the plane of its neighbor. For comparison, it is noted that anthraquinone shows a similar slipped stack arrangement in the solid state, with a mean interplanar distance of 3.48 Å.32 The structural isomer 12B (allenylidene trans carboxylate, Figure 7), crystallizes in space group P1̅. Similar to the solid-

Figure 5. Molecular structure of [Ru(bdmpza)Cl(CC(AO))(PPh3)] (12A). Thermal ellipsoids are drawn at the 50% probability level. Hydrogen atoms and solvent molecules have been omitted for clarity. Selected bond lengths (Å) and angles (deg): Ru−N(11) = 2.138(3), Ru−N(21) = 2.193(3), Ru−O(1) = 2.077(2), Ru−P(1) = 2.3325(8), Ru−Cl(1) = 2.3761(8), Ru−C(31) = 1.868(3), C(31)− C(32) = 1.243(5), C(32)−C(33) = 1.362(5); Ru−C(31)−C(32) = 177.0(3), C(31)−C(32)−C(33) = 175.2(4).

Figure 6. π−π stacking interactions between two molecules of 12A: (a) top view and (b) side view.

state structures discussed above, the positioning of the π-donor and π-acceptor pyrazole trans to the chlorido ligand, and the allenylidene trans to the carboxylate anchor, leads to a loss of the trans influence for both ligands. This change in the coordination sphere leads to a shortened Ru−N(21) bond with 2.0740(18) Å and a similar Ru−C(61) bond with 1.862(2) Å. The bond angles of the allenylidene chain are slightly reduced compared to those in 12A, in contrast to the fluorenyl system (7A/7B), with Ru−C(61)−C(62) = 174.4(2)° and C(31)− C(32)−C(33) = 169.8(3)° The explanation for the bent allenylidene unit of 12B can be suggested from the solid-state packing motif of two neighboring complexes (Figure 8). The 5134


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Figure 7. Molecular structure of [Ru(bdmpza)Cl(CC(AO))(PPh3)] (12B). Thermal ellipsoids are drawn at the 50% probability level. Hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and angles (deg): Ru−N(11) = 2.1355(19), Ru−N(21) = 2.0740(18), Ru−O(1) = 2.1367(15), Ru−P(1) = 2.3546(6), Ru− Cl(1) = 2.4100(6), Ru−C(61) = 1.862(2), C(61)−C(62) = 1.232(3), C(62)−C(63) = 1.354(3); Ru−C(61)−C(62) = 174.4(2), C(61)− C(62)−C(63) = 169.8(3).

Figure 9. Molecular structure of [Ru(bdmpza)Cl(CC(PCO))(PPh3)] (13A). Thermal ellipsoids are drawn at the 50% probability level. Hydrogen atoms and two molecules of dichloromethane have been omitted for clarity. Selected bond lengths (Å) and angles (deg): Ru−N(11) = 2.142(3), Ru−N(21) = 2.196(3), Ru−O(1) = 2.079(2), Ru−P(1) = 2.3325(10), Ru−Cl(1) = 2.3770(9), Ru−C(61) = 1.859(3), C(61)−C(62) = 1.244(5), C(62)−C(63) = 1.365(5); Ru−C(61)−C(62) = 172.8(3), C(61)−C(62)−C(63) = 179.0(4).

with the typical distorted coordination sphere of the bdmpza ligand (Figure 9). The pentacenone of unit 13A shows an almost planar geometry with slight deviations at one terminal phenyl ring. The packing motif in the solid state shows that 13A has a structure that is almost identical to the analogous anthraquinone based complex 12A, although only partial overlap of four phenyl rings can be observed for 13A (Figure 10). For a possible application of pentacene- or pentacenequinone based compounds in, for example, field effect transistors, efficient overlap of the planar π systems is crucial in order to allow for charge transport along this axis.16a To investigate the effects of the size of the carbon-rich ligand in comparison to its geometry, an allenylidene complex was synthesized based on the commercially available benzotetraphene-7-one (Scheme 5). Starting from 7H-benzo[no]tetraphen-7-one (14), the addition of lithiated TMS-acetylene (excess) led to the quantitative formation of the corresponding propargyl alcohol 15, as indicated by the characteristic singlets of the alcohol proton (2.59 ppm) and the TMS group (0.23 ppm) in the 1H NMR spectrum. In the 13C NMR spectrum of compound 15, the two relevant alkyne signals appear at 107.6 and 93.2 ppm, while that of the tetrahedral carbon is observed at 69.9 ppm. The product gives a signal at m/z 413.11 in the negative mode of ESI-MS analysis that can be attributed to a chloride adduct of 15 (18%, [M + Cl]−). Deprotection of the alkyne is achieved in methanol with potassium hydroxide. 7-Ethynyl-7H-benzo[no]tetraphen-7-ol (16) shows the additional signal of the alkyne proton at 2.91 ppm in the 1H NMR spectrum, while the singlet of the TMS group is lost. In the 13C NMR spectrum, the loss of the methyl resonance from the TMS group and the shift of the terminal alkyne carbon to 76.4 ppm support the successful transformation from 15 to 16.

Figure 8. Space-filling model of complex 12B; phenyl ring highlighted in dark gray (right molecule), anthrone moiety highlighted in light gray (left molecule).

space-filling model clarifies that only a small overlap of two anthrone units is observed due to the presence of one phenyl ring (dark gray) of the triphenylphosphine ligand on top of the anthrone moiety, which thus blocks the π−π interactions, as observed for 12A, and forces the neighboring allenylidene chain into a slightly bent structure in the solid state. Recently, we reported on the synthesis of the pentacenequinone based allenylidene complex [Ru(bdmpza)Cl(C C(PCO))(PPh3)] (13A/13B) (PCO = pentacenone, Figure 9 shows 13A) starting from 13-ethynyl-13-hydroxypentacen-6one. The large pentacenone moieties show strong π−π stacking interactions in the solid state, leading to a strongly bent allenylidene chain with ∠Ru−C(61)−C(62) = 167.78(17)° and ∠C(C61)−C(C62)−C(C63) = 163.2(2)° for 13B. Initially, purification as column chromatography did not allow clean separation of both isomers,19 but a single-crystal Xray structure of the second structural isomer 13A has now been obtained from a dichloromethane solution layered with nhexane. The solid-state analysis shows an almost linear arrangement of the allenylidene unit trans to the pyrazole 5135


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Figure 10. π−π stacking interactions between two molecules of 13A from (a) top view and (b) side view.

Scheme 5. Synthesis of the TMS-Ethynyl Alcohol 15 and the Deprotected Propargyl Alcohol 16 Based on 7HBenzo[no]tetraphen-7-one (14)

Scheme 6. Synthesis of [Ru(bdmpza)Cl(CC(BT))(PPh3)] (17A, 17B)

1907 cm−1. The PPh3 ligand shows a singlet at 32.3 ppm in the P NMR spectrum of 17B, confirming the assignment that the allenylidene is positioned trans to the carboxylate anchor. These values are overall in good agreement with the previously observed NMR chemical shifts for type B isomers in comparison to the type A isomers.12a ESI-MS experiments show the appearance of a signal at m/z 934.18 (100%, M+) that is characteristic for the ionized complex. Layering a solution of 17A in dichloromethane with n-pentane gives crystals of the complex suitable for a single-crystal X-ray structure determination. The compound crystallizes as a racemic mixture in the space group P1̅ with two disordered molecules of dichloromethane in the asymmetric unit. A graphical presentation of the compound is illustrated in Figure 11. As mentioned previously for type A isomers, the typical strained κ3 coordination of the bdmpza ligand is observed for 17A, and the allenylidene unit is coordinated trans to a pyrazole group, which leaves the PPh3 ligand trans to the second pyrazole and the chlorido ligand trans to the carboxylate anchor. The main feature of the structure of 17A is the nearly linear allenylidene moiety with ∠Ru−C(61)−C(62) = 174.1(5)° and ∠C(61)−C(62)−C(63) = 176.0(6)°. The benzotetraphene group is nonplanar, due to hydrogen−hydrogen repulsion that forces the phenalene and naphthalene portions out of planarity. The overall arrangement of the benzotetraphene groups for complex 17A in the solid state is that of a staircase arrangement

The preparation of the corresponding benzotetraphene (BT) based ruthenium allenylidene complexes 17A/17B was carried out by combining equimolar amounts of propargyl alcohol 16 and complex 1 (Scheme 6). The reaction mixture turns to deep blue, similar to the reaction to give pentacenequinone based allenylidene complexes 13A/13B, indicating in both cases a strong influence of the aromatic group on the color of the allenylidene complex. The separation of the two structural isomers 17A and 17B was achieved by column chromatography, as described for the anthraquinone based allenylidene complexes 12A/12B. For the major isomer 17A, Cα shows a characteristic signal in the 13C NMR spectrum at 273.6 ppm with a coupling constant of JC,P = 19.2 Hz. For Cβ (221.1 ppm, d, 3JC,P = 3.5 Hz) and Cγ (139.8 ppm, d, 4JC,P = 1.7 Hz), the signals are shifted upfield in comparison to the fluorenone (7A), anthraquinone (12A), and pentacenequinone (13A) based systems. The allenylidene stretch appears in the IR spectrum at 1903 cm−1. A singlet in the 31P NMR spectrum of 17A is found at 35.2 ppm for the PPh3 ligand, supporting the assignment of the allenylidene trans to a pyrazole moiety. ESIMS experiments confirm the formation of the complex through detection of the molecular ion at m/z 934.18 (100%, M+). For the isomer 17B, signals are also shifted upfield in the 13C NMR spectrum relative to the other derivatives (7B, 12B, 13B) for Cα (289.5 ppm, d, 2JC,P = 18.4 Hz), Cβ (237.2 ppm), and Cγ (138.0 ppm). The IR spectrum reveals an allenylidene stretch at

31

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voltammograms recorded in acetonitrile lead to irreversible oxidations and reductions, indicating side reactions of the allenylidene complexes with acetonitrile. The voltammograms recorded in dichloromethane, on the other hand, feature exclusively reversible and quasi-reversible processes with n Bu4NPF6 (0.1 M) as electrolyte and referenced to the ferrocene/ferrocenium couple as internal standard (scan rate of 100 mV/s). For [Ru(bdmpza)Cl(PPh3)2] (1), one reversible oxidation event is observed at 394 mV, which is attributed to the Ru(II)/Ru(III) couple. For the ferrocene/ferrocenium couple, the literature reports a peak separation of 78 mV (83 mV in our setup) in dichloromethane,35 which is a good indication that the peak separation of 73 mV and the peak current ratio ipa/ipc = 0.80 for 1 arise from a reversible oneelectron oxidation. For the ruthenium allenylidene complex [Ru(bdmpza)Cl(CCC(PhtBu2)2)(PPh3)] (5B), two quasi-reversible redox processes can be observed. The oxidation of the ruthenium center occurs at a lower potential of 265 mV compared to 1, indicating a possible electron releasing effect from the allenylidene ligand in comparison to the PPh3 ligand. The reduced peak current ratio indicates, however, that the reversibility of this event is lower in comparison to 1. A second redox process at −1631 mV for 5B can be attributed to the quasi-reversible reduction (ipa/ipc = 0.67) of the allenylidene moiety, as reported previously for analogous systems [Cl(dppe)2Ru(CCCPh2)](PF6) (−1.03 V) and [Cl(16TMC)Ru(CCCPh2)](PF6) (−1.27 V).36 It is, thus, obvious that the two redox couples of the neutral bdmpza allenylidene complex 5B are more cathodic in comparison to the aforementioned cationic allenylidene complexes (Δ = 0.60 V/0.36 V). The fluorene based allenylidene complexes [Ru(bdmpza)Cl(CC(FN))(PPh3 )] (7A, 7B) show a reversible oxidation at 389 and 371 mV, respectively, indicating a positive shift in peak potential in comparison to 5B. Unlike 5B, which shows only a single reduction event, two reductions are observed for 7A and 7B. The reduction at −1273 mV for each 7A and 7B is again attributed to the reduction of the allenylidene moiety and appears more anodic in comparison to 5B. A second, quasi-reversible reduction appears at −1932 mV (7A) and −1937 mV (7B), which is assigned to the reduction of the fluorenyl moiety. Although the position of the allenylidene moiety trans to either the pyrazole or the

Figure 11. Molecular structure of [Ru(bdmpza)Cl(CC(BT))(PPh3)] (17A). Thermal ellipsoids are drawn at the 50% probability level. Hydrogen atoms and two molecules of dichloromethane have been omitted for clarity. Selected bond lengths (Å) and angles (deg): Ru−N(11) = 2.159(5), Ru−N(21) = 2.199(5), Ru−O(1) = 2.091(4), Ru−P(1) = 2.2936(17), Ru−Cl(1) = 2.3803(16), Ru−C(61) = 1.878(6), C(61)−C(62) = 1.239(8), C(62)−C(63) = 1.374(8); Ru− C(61)−C(62) = 174.1(5), C(61)−C(62)−C(63) = 176.0(6).

with an extended stacking motif that includes several π−π stacking interactions (Figure 12). The mean distance between two neighboring phenalene units is 3.39 Å, nearly identical to the separation of pentacenequinone in the solid state at ∼3.4 Å.33 For the naphthalene unit, three short contact interactions between 3.25 and 3.62 Å to the neighboring phenalene unit are observed. Electrochemistry, Absorption Spectroscopy, and TDDFT Calculations. Cyclic voltammetric analyses have been performed on the precursor 1 and on all resulting allenylidene complexes and feature the typical facile oxidation process of the Ru(II) center and several substituent-dependent reduction processes, as previously reported for several mono- and bimetallic ruthenium allenylidene complexes.3f,28,34 The electrochemical data are summarized in Table 1. All cyclovoltammograms are depicted in the Supporting Information. The reversibility of the redox processes shows strong dependence on the solvent that is used. For examples,

Figure 12. π−π stacking interactions between two molecules of 17A from (a) side view and (b) top view. 5137


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Table 1. Summary of the Half-Wave Potentials, Peak-to-Peak Separations, and the Peak Current Ratios Obtained from Cyclic Voltammetry Measurementsa reduction processes compound

E1/2 (mV)

ΔEp (mV)

ipa/ipc

1 5B 7A 7B 12A 12B 17A 17B

−1631 −1932 −1937 −1479 −1315 −1914 −1859

92 85 74 74 91 82 64

0.67 0.45 0.96 0.99 0.88 0.83 0.97

Ru(II)/Ru(III)

E1/2 (mV)

−1273 −1273 −1013 −870 −1228 −1168

ΔEp (mV)

64 64 73 82 83 73

ipa/ipc

E1/2 (mV)

ΔEp (mV)

ipa/ipc

0.76 0.64 0.94 0.94 0.71 0.61

394 265 389 371 466 641 87 188

73 82 73 73 64 83 73 72

0.80 0.71 0.94 0.91 0.98 0.95 0.86 0.97

Cyclic voltammograms were recorded at 20 °C in dichloromethane, with nBu4NPF6 (0.1 M) as electrolyte; potentials are given relative to the ferrocenium/ferrocene couple used as internal standard. All measurements were acquired at a scan rate of 100 mV/s.

a

at negative voltage for each complex is observed at −1228 and −1168 mV, respectively, for 17A and 17B and is assigned to a reduction involving the allenylidene moiety; both reductions are best described as quasi-reversible due to lower peak current ratios. A fully reversible reduction of the benzotetraphene unit appears at even lower potential, −1914 mV (17A) and −1859 mV (17B). The UV/vis spectra of the bdmpza based systems synthesized herein have been recorded in dichloromethane and share several common features for ruthenium allenylidene complexes, as previously reported.5,12a,14b,19 The strong absorptions at wavelengths less than ∼450 nm are assigned to ligand-centered (LC) π−π* transitions involving the PPh3 and bdmpza ligands. An additional metal-perturbed π−π* transition can be observed for each complex at higher wavelength with a strong dependence on the corresponding allenylidene substituent and its position relative to the bdmpza ligand. The smallest aromatic system, 5B, shows this signal at 506 nm, and the wavelength of this absorption red-shifts to 654 nm for 17B. In comparison to the allenylidene complexes of type B, a further increase in absorption energy can be observed for the systems with the allenylidene unit positioned trans to the pyrazole moiety (e.g., 708 nm for 17A). A detailed overview of all relevant transitions is given in the Supporting Information (Table S5). Further inspection of the spectra reveals a series of weak, broad transitions in the lower energy region between 700 and 1350 nm that can be attributed to HOMO → LUMO, HOMO-1 → LUMO, and HOMO-2 → LUMO excitations, which are MLCT transitions (Table 2). The longest wavelength transitions in ruthenium allenylidene complexes have been assigned to MLCT transitions previously.37 Similar transitions have been observed previously for the pentacenequinone based allenylidene complex,19 and timedependent DFT (TD-DFT) calculations of the excited states revealed that two absorption bands are located at the edge of the NIR region. Thus, we performed TD-DFT calculations of the excited states on the basis of crystal structures of 7A, 12A, 12B, 13A, and 17A, and theory predicts comparable results for all five of these complexes (Table 2). Hence, we will focus on the details of the benzotetraphene based complex 17A. The results of the calculations of the excited states revealed two absorption bands at 1058 nm (1.17 eV) and 905 nm (1.37 eV) that can be assigned to metal-to-ligand charge-transfer transitions, which are in good agreement with the experimental values (1097 and 989 nm). The first absorption correlates mainly to the HOMO → LUMO transition with the second

carboxylate moiety strongly influences the physical and chemical properties of the complex, as described earlier, no obvious differences in electrochemical properties could be observed for these two structural isomers. For the anthraquinone based allenylidene complexes [Ru(bdmpza)Cl(C C(AO))(PPh3)] (12A, 12B), the influence of the anthrone unit is clearly visible and the difference between both structural isomers is obvious (Figure 13). Three reversible redox

Figure 13. Cyclic voltammogram for [Ru(bdmpza)Cl(C C(AO))(PPh3)] (12A) in CH2Cl2 with nBu4NPF6 (0.1 M) as supporting electrolyte at a scan rate of 100 mV/s (vs Fc/Fc+).

processes can be observed and can be attributed to the Ru(II)/Ru(III) couple (466 mV/641 mV), the allenylidene moiety (−1013 mV/−870 mV), and the anthrone moiety (−1479 mV/−1315 mV). Apparently, the facile reduction of the anthrone unit leads to a positive shift for all three redox events, and this effect is especially pronounced in the B type isomer with the allenylidene moiety trans to the pyrazole unit. The voltammograms of the benzotetraphene based complexes [Ru(bdmpza)Cl(CC(BT))(PPh3)] (17A, 17B) show similarities to fluorene based allenylidene complexes 7A and 7B, although the potentials again vary according to the structural isomer. A reversible oxidation process involving the Ru(II) center appears at either 87 mV (17A) or 118 mV (17B), indicating a more cathodic process due to the electron releasing properties of the benzotetraphene unit. The first redox process 5138


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Table 2. Calculated and Measured Transitions for HOMO → LUMO and HOMO-1 → LUMO in the NIR Regiona observed values

calculated values

compound

wavelength (nm)

5B

1024 733

absorption coefficient (M 151 142

1053 919b

226 175

1201 944 1131

174 133 184

1331 939

155 204

1097 989b 1312 938

764 708 284 503

−1

−1

cm )

wavelength (nm)

transition dipole moment (debye)

transition

906 813

0.12 0.54

HOMO → LUMO HOMO-2 → LUMO

997 879 1204 905 972 858 1058 905

0.85 0.25 0.68 0.24 0.95 0.37 1.54 0.51

HOMO → LUMO HOMO-1 → LUMO HOMO → LUMO HOMO-1 → LUMO HOMO → LUMO HOMO-1 → LUMO HOMO → LUMO HOMO-1 → LUMO

7A

7B

12A 12B 13A 17A 17B a

UV/vis spectra recorded in dichloromethane; details for calculated values are listed in the Experimental Section. bTransition appears as a shoulder of the neighboring peak.

one assignable to the HOMO-1 → LUMO transition. The HOMO and HOMO-1 orbitals are mainly described as ruthenium d orbitals with small contributions from the chlorido ligand and the carboxylate anchor of the bdmpza ligand (Figure 14). For the HOMO, electron density extends toward the

absorption coefficients that are observed experimentally (764 and 708 M−1 cm−1). Furthermore, the HOMO−LUMO gap, calculated as the difference between the calculated orbital energies of the ground state (DFT) of 17A, correlates well with the experimental CV data (calculated 2.0 eV, observed 1.4 eV). All computational details for complexes 7A, 12A, 12B, and 13A are given in the Supporting Information (Figures S1−S4).

■

SUMMARY A series of carbon-rich ruthenium allenylidene complexes bearing heteroscorpionate ligands have been prepared. Starting with the 9-ethynyl-9-fluorenol, complexes [Ru(bdmpza)Cl( CC(FN))(PPh3)] (7A/7B) have been realized. A larger polyaromatic propargyl alcohol is accessible from anthraquinone via ethynylation to afford 10-ethynyl-10-hydroxyanthracen-9-one (11), which is then converted to the complexes [Ru(bdmpza)Cl(CC(AO))(PPh3)] (12A/ 12B). An analogous reaction with the propargyl alcohol of the larger acene pentacenequinone yields the corresponding complexes [Ru(bdmpza)Cl(CC(PCO))(PPh 3 )] (13A/13B), while the benzotetraphenone-derived propargyl alcohol reacts to give the complexes [Ru(bdmpza)Cl(C C(BT))(PPh3)] (17A/17B). It has been shown that strong delocalization of electron density along the allenylidene chain leads to forbidden transitions in the NIR region that have been assigned via TD-DFT calculations to MLCT transitions. Cyclovoltammetric studies of the complexes show that the larger polyaromatic substituents lead to additional cathodic processes, in addition to the anodic Ru2+/Ru3+ redox couple, which involve the aromatic systems and the allenylidene moieties. The anthraquinone based allenylidene complexes [Ru(bdmpza)Cl(C C(AO))(PPh3)] (12A/12B) feature two easily accessible and reversible reductions. Complexes of type A, with the allenylidene units positioned trans to a pyrazole unit, typically show strong π−π stacking

Figure 14. Orbital diagrams of the LUMO (−2.9 eV), HOMO (−4.9 eV), HOMO-1 (−5.1 eV), and HOMO-2 (−5.3 eV) of 17A.

allenylidene chain. For the LUMO, a high degree of delocalization along the allenylidene unit into the phenalene moiety of the benzotetraphene unit is observed. Overall, this results in a rather low-energy LUMO, leading to a small energy difference between the occupied and unoccupied orbitals, and thus, long-wave absorptions are observed. The small transition dipole moments that are calculated (1.54 and 0.51 debye) indicate forbidden transitions, which correlate well with the low 5139


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5B: Yield: 18 mg (0.017 mmol, 5%); 1H NMR (CDCl3, 300 MHz): δ = 7.68 (s, 3H, Ph), 7.61 (s, 3H, Ph), 7.57 (m, 6H, m-PPh3), 7.57 (m, 6H, m-PPh3), 7.16 (m, 3H, p-PPh3), 7.03 (m, 6H, o-PPh3), 6.71 (s, 1H, CH), 5.83 (s, 1H, H4′), 5.70 (s, 1H, H4), 2.52 (s, 3H, Me5′), 2.47 (s, 3H, Me5), 2.25 (s, 3H, Me3), 1.40 (s, 3H, Me3′), 1.24 (s, 36H, tBu) ppm; 13C NMR (CDCl3, 75 MHz): δ = 314.7 (d, 2JCP = 18.3 Hz, Cα), 234.6 (Cβ), 165.9 (CO2−), 155.6 (C3′), 154.8 (C3), 152.4 (Cγ), 151.2 (m-Ph), 146.3 (i-Ph), 141.3 (C5′), 139.5 (C5), 134.5 (d, 2JCP = 9.2 Hz, o-PPh3), 133.5 (d, 1JCP = 46.8 Hz, i-PPh3), 129.3 (p-PPh3), 127.5 (d, 3 JCP = 9.2 Hz, m-PPh3), 123.9 (o-Ph), 123.6 (p-Ph), 108.4 (C4′), 108.3 (C4), 69.7 (CH), 34.9 (Met‑Bu), 14.6 (Me3′), 13.9 (Me3), 11.6 (Me5′), 11.1 (Me5) ppm; 31P NMR (CDCl3, 122 MHz): δ = 34.5 ppm; IR (KBr): ν̃ 1907 (m, CCC), 1666 (s, as-CO2−), 1559 (m, CN) cm−1; MS (ESI-TOF, MeCN) m/z (%): 1025.46 (100) [M − Cl]+, 1061.43 (12) [M + H]+. [Ru(bdmpza)Cl(CC(FN))(PPh3)] (7A/7B). To a suspension of [Ru(bdmpza)Cl(PPh3)2] (1.614 g, 1.78 mmol) in THF (50 mL) was added 9-ethynyl-9-fluorenol (550 mg, 2.67 mmol), and the mixture was stirred for 48 h at room temperature and finally heated to reflux for 6 h. The isomeric mixture was purified according to the general method, yielding a purple isomer 7A (allenylidene trans to pyrazole) and a red isomer 7B (allenylidene trans to carboxylate). Nomenclature of the fluorenyl moiety is according to IUPAC nomenclature. 7A: Yield: 738 mg (0.885 mmol, 49%); 1H NMR (CDCl3, 300 MHz): δ = 7.56 (m, 6H, m-PPh3), 7.46 (m, 3H, p-PPh3), 7.34 (m, 6H, o-PPh3), 7.27 (m, 2H, FN−H1 & FN−H8), 7.23 (m, 2H, FN−H4 & FN−H5), 7.00 (m, 2H, FN−H3 & FN−H6), 6.91 (m, 2H, FN−H2 & FN−H7), 6.69 (s, 1H, CH), 6.04 (s, 1H, pz−H4′), 6.00 (s, 1H, pz− H4), 2.57 (s, 3H, pz−Me5′), 2.50 (s, 3H, pz−Me5), 2.45 (s, 3H, pz− Me3), 1.92 (s, 3H, pz−Me3′) ppm; 13C NMR (CDCl3, 75 MHz): δ = 300.6 (d, 2JC,P = 27.6 Hz, Cα), 236.4 (d, 3JC,P = 4.6 Hz, Cβ), 166.6 (CO2−), 156.1 (pz−C3′), 154.6 (pz−C3), 144.1 (FN−C4b), 143.9 (FN−C4a), 141.0 (FN−C9), 141.0 (pz−C5′), 139.6 (pz−C5), 136.2 (FN−C8a), 136.2 (FN−C9a), 134.3 (d, 2JC,P = 9.6 Hz, o-PPh3), 132.9 (d, 1JC,P = 47.0 Hz, i-PPh3), 129.8 (p-PPh3), 129.3 (FN−C2 & FN− C7), 129.2 (FN−C3 & FN−C6), 128.0 (d, 3JC,P = 10.3 Hz, m-PPh3), 121.7 (FN−C1 & FN−C8), 121.2 (FN−C4 & FN−C5), 109.4 (pz− C4′), 108.6 (pz−C4), 69.0 (CH), 14.5 (pz−Me3′), 13.6 (pz−Me3), 11.4 (pz−Me5′), 11.2 (pz−Me5) ppm; 31P NMR (CDCl3, 122 MHz): δ = 34.6 ppm; mp.: 230−235 °C (dec.); IR (KBr): ν̃ 1910 (m, C CC), 1664 (s, as-CO2−), 1560 (w, CN) cm−1; MS (ESI-TOF, MeCN) m/z (%): 755.19 (17) [M − Cl − CO2]+, 825.16 (100) [M + H]+; Elemental analysis calcd. (%) for C45H38ClN4O2PRu: C 64.78, H 4.59, N 6.72; found: C 64.71, H 4.34, N 6.71. 7B: Yield: 228 mg (0.273 mmol, 15%); 1H NMR (CDCl3, 300 MHz): δ = 7.64 (m, 6H, m-PPh3), 7.50 (m, 3H, p-PPh3), 7.38 (m, 6H, o-PPh3), 7.24 (m, 2H, FN−H1 & FN−H8), 7.18 (m, 2H, FN−H4 & FN−H5), 7.16 (m, 2H, FN−H3 & FN−H6), 6.99 (m, 2H, FN−H2 & FN−H7), 6.75 (s, 1H, CH), 5.90 (s, 1H, pz−H4′), 5.71 (s, 1H, pz− H4), 2.55 (s, 3H, pz−Me5′), 2.51 (s, 3H, pz−Me5), 2.19 (s, 3H, pz− Me3), 1.42 (s, 3H, pz−Me3′) ppm; 13C NMR (CDCl3, 75 MHz): δ = 314.4 (d, 2JC,P = 19.3 Hz, Cα), 256.2 (Cβ), 165.8 (CO2−), 155.7 (pz− C3′), 154.9 (pz−C3), 145.1 (FN−C4b), 143.5 (FN−C4a), 141.6 (FN− C9), 140.0 (pz−C5′), 139.9 (pz−C5), 136.5 (FN−C8a), 136.5 (FN− C9a), 134.5 (d, 2JC,P = 9.6 Hz, o-PPh3), 132.5 (d, 1JC,P = 47.6 Hz, iPPh3), 129.7 (p-PPh3), 129.7 (FN−C2 & FN−C7), 129.4 (FN−C3 & FN−C6), 127.8 (d, 3JC,P = 10.2 Hz, m-PPh3), 122.1 (FN−C1 & FN− C8), 121.1 (FN−C4 & FN−C5), 108.4(pz−C4′), 108.3 (pz−C4), 69.6 (CH), 14.3 (pz−Me3′), 13.9 (pz−Me3), 11.8 (pz−Me5′), 11.2 (pz− Me5) ppm; 31P NMR (CDCl3, 122 MHz): δ = 30.9 ppm; mp.: 235− 240 °C (dec.); IR (KBr): ν̃ 1903 (m, CCC), 1666 (s, as-CO2−), 1564 (w, CN) cm−1; MS (ESI-TOF, MeCN) m/z (%): 755.19 (17) [M − Cl − CO2]+, 825.16 (100) [M + H]+; Elemental analysis calcd. (%) for C45H38ClN4O2PRu: C 64.78, H 4.59, N 6.72; found: C 64.89, H 4.28, N 6.71. 10-Hydroxy-10-((trimethylsilyl)ethynyl)anthracen-9(10H)one (10). To a solution of trimethylsilylacetylene (1.39 mL, 0.98 g, 10.0 mmol) in THF (20 mL), which was cooled to −40 °C, was added dropwise n-BuLi (1.6 M in hexanes, 4.90 mL, 7.80 mmol). The

interactions in the solid state, as documented in their singlecrystal X-ray structure determinations. The benzotetraphenonederived complex [Ru(bdmpza)Cl(CC(BT))(PPh3)] (17B) shows a staircase arrangement that might allow the use in organometallic metal−semiconductor field-effect transistors (OMESFETs). In combination with favorable solid-state packing, the inherent high stabilities of all bdmpza based ruthenium allenylidene complexes, in combination with the electron-accepting ability and low-energy absorption characteristics, might allow future applications in molecular electronics. For example, future studies in this regard will explore if some of these compounds can act as molecular slides for single-walled carbon nanotubes (SWCNTs) either to accept electrons from these or to load electron on these, similar to previous reports based on SWCNTs/pyrene/porphyrin nanohybrids.38

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EXPERIMENTAL SECTION

All operations were carried out under a N2 atmosphere by applying conventional Schlenk techniques. The yields refer to analytically pure substances. All commercial materials were of reagent quality and used as received. 7H-Benzo[no]tetraphen-7-one was purchased from Aldrich. Elemental analyses were determined with a Euro EA 3000 (Euro Vector) and an EA 1108 (Carlo Erba) instrument (σ = ± 1% of the measured content). UV/vis spectroscopy was performed with a Varian Cary 5000 spectrometer. IR spectra were recorded with an Excalibur FTS- 3500 FTIR in CaF2 cuvettes (0.2 mm) or as KBr pellets. 1H and 13C NMR spectra were measured with a Bruker AVANCE DRX400 WB and a Bruker AVANCE DPX300 NB instrument. The δ values are given relative to tetramethylsilane (1H) or the deuterated solvent (13C). ESI-MS spectra were recorded on a Bruker Daltonics maXis ultrahigh resolution ESI-Time-Of-Flight MS. Peaks were identified using simulated isotopic patterns created within the Bruker Data Analysis software. X-ray structure determinations were carried out on a Bruker-Nonius Kappa-CCD diffractometer. Hbdmpza, [RuCl2(PPh3)3], [Ru(bdmpza)Cl(PPh3)2], 1,1-bis(1,3-ditert-butylphenyl)-1-methoxy-2-propyne, 13-hydroxy-13-ethynylpentacen-6-one, and [Ru(bdmpza)Cl(CCC(PCO))(PPh3)] (PCO = pentacenone) (13A/13B) were prepared according to the literature.8f,19,21,39 The following abbreviations are used for the organic substituents: FN (fluorenyl), AO (anthrone), PCO (pentacenone), BT (benzotetraphene). General Purification Method. The isomeric mixture was dissolved in CH2Cl2 (5 mL) and loaded on a column (silica, length 15 cm, Ø 4 cm), washed with a mixture of Et2O/n-pentane (1:1 v/v), and eluted with CH2Cl2/acetone (1:1 v/v), and the solvent was removed in vacuum. Separation of isomers was achieved on a second column (silica, length 25 cm, Ø 4 cm) with CH2Cl2/acetone (1:1 v/v). [Ru(bdmpza)Cl(CCC(PhtBu2)2)(PPh3)] (5A/5B). To a suspension of [Ru(bdmpza)Cl(PPh3)2] (205 mg, 0.226 mmol) in THF (50 mL) was added 1,1-bis(3,5-di-tert-butylphenyl)-1-methoxy2-propyne (150 mg, 0.336 mmol). The suspension was stirred for 72 h at room temperature and subsequently heated for 4 h under reflux. The solvent of the purple solution was removed under vacuum, yielding the crude product. The isomeric mixture was purified according to the general method, yielding a purple isomer 5A (allenylidene trans to pyrazole) that could not be completely separated from the formed carbonyl complex [Ru(bdmpza)Cl(CO)(PPh3)2] (4A) and a red isomer 5B (allenylidene trans to carboxylate). 5A (data extracted from spectra containing the carbonyl complex 4A): Yield: 52 mg (0.049 mmol, 22%); 1H NMR (CDCl3, 300 MHz): δ = 7.66 (s, 4H, o-Ph), 7.61 (s, 2H, p-Ph), 7.57 (m, 6H, m-PPh3), 7.16 (m, 3H, p-PPh3), 7.00 (m, 6H, o-PPh3), 6.69 (s, 1H, CH), 5.81 (s, 1H, H4′), 5.69 (s, 1H, H4), 2.59 (s, 3H, Me5′), 2.46 (s, 3H, Me5), 2.33 (s, 3H, Me3), 1.35 (s, 3H, Me3′), 1.24 (s, 36H, tBu) ppm; 31P NMR (CDCl3, 122 MHz): δ = 37.6 ppm; IR (KBr): ν̃ 1912 (m, CCC), 1672 (s, as-CO2−), 1565 (w, CN) cm−1; MS (ESI-TOF, MeCN) m/ z (%): 1025.46 (100) [M − Cl]+, 1061.43 (12) [M + H]+. Attempts to obtain characteristic 13C data of 5A failed. 5140


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Cl − CO2]+, 824.21 (13) [M − Cl − CO2 + MeCN]+, 863.14 (100) [M + H]+; Elemental analysis calcd. (%) for C46H38ClN4O3PRu: C 64.07, H 4.44, N 6.50; found: C 63.83, H 4.42, N 6.51. 12B: Yield: 56 mg (0.065 mmol, 16%); 1H NMR (CDCl3, 300 MHz, 25 °C): δ = 8.18 (d, 3JH,H = 7.5 Hz, 2H, AO−H), 7.98 (t, 3JH,H = 7.4 Hz, 2H, AO−H), 7.77 (d, 3JH,H = 7.8 Hz, 2H, AO−H), 7.64 (m, 6H, m-PPh3), 7.47 (m, 6H, o-PPh3, 2H, AO−H), 7.13 (m, 3H, pPPh3), 6.84 (s, 1H, CH), 5.89 (s, 1H, pz−H4′), 5.74 (s, 1H, pz−H4), 2.60 (s, 3H, pz−Me5′), 2.54 (s, 3H, pz−Me5), 2.06 (s, 3H, pz−Me3), 1.39 (s, 3H, pz−Me3′) ppm; 13C NMR (CDCl3, 75 MHz): δ = 309.6 (d, 2JC,P = 19.8 Hz, Cα), 277.0 (Cβ), 187.8 (CO), 165.9 (CO2−), 155.4 (pz−C3′), 154.7 (d, 3JC,P = 2.0 Hz, pz−C3), 141.6 (Cγ), 140.5 (pz−C5′), 140.1 (d, 4JC,P = 2.0 Hz, pz−C5), 134.4 (2 × AO−CH), 134.3 (2 × AO−CH), 133.0 (d, 1JC,P = 35.7 Hz, i-PPh3), 132.1 (d, 3JC,P = 9.9 Hz, o-PPh3), 132.0 (d, 4JC,P = 3.0 Hz, p-PPh3), 131.9 (2 × AO− C), 129.2 (2 × AO−C), 128.0 (d, 2JC,P = 11.9 Hz, o-PPh3), 127.8 (2 × AO−CH), 127.7 (2 × AO−CH), 108.3 (pz−C4′), 108.3 (pz−C4), 69.6 (CH), 14.0 (pz−Me3′), 13.5 (pz−Me3), 11.7 (pz−Me5′), 11.2 ppm (pz−Me5); 31P NMR (CDCl3, 122 MHz): δ = 29.1 ppm; IR (CH2Cl2): ν̃ 1896 (m, CCC), 1667 (s, as-CO2−), 1605 (w, C N) cm−1; MS (ESI-TOF, MeCN) m/z (%): 412.11 (62) [M − Cl − CO2 + MeCN]2+, 687.11 (31) [Ru(bdmpza)Cl(PPh3)(MeCN)]+, 783.18 (88) [M − Cl − CO2]+, 824.21 (100) [M − Cl − CO2 + MeCN]+, 863.14 (4) [M + H]+; Elemental analysis calcd. (%) for C46H38ClN4O3PRu: C 64.07, H 4.44, N 6.50; found: C 63.38, H 4.41, N 6.40. 7-((Trimethylsilyl)ethynyl)-7H-benzo[no]tetraphen-7-ol (15). To a solution of trimethylsilylacetylene (99.0 μL, 68.3 mg, 0.713 mmol) in THF (20 mL) cooled to −80 °C was added dropwise nBuLi (1.6 M in hexanes, 401 μL, 0.642 mmol). The solution was allowed to stir for 30 min before being transferred slowly via cannula into a solution of 7H-benzo[no]tetraphen-7-one (14) (50.0 mg, 0.178 mmol) in THF (20 mL) at room temperature. The reaction mixture was stirred for 16 h at room temperature. The reaction was cooled to 0 °C and quenched via the addition of water (3 mL). The solvent was removed under vacuum, and the crude product was dissolved in CH2Cl2 and dried (Na2SO4) to yield 15 as a yellow powder. Yield: 66.0 mg (0.174 mmol, 98%); 1H NMR (300 MHz, CDCl3): δ = 8.70 (m, 1H), 8.38 (d, 3JH,H = 7.4 Hz, 1H), 8.30 (m, 2H), 7.94 (m, 4H), 7.68 (m, 2H), 7.54 (m, 2H), 2.59 (s, 1H, OH), 0.23 (s, 9H, TMS) ppm; 13C NMR (75 MHz, CDCl3): δ = 135.6 (C), 135.6 (C), 135.1 (C), 133.4 (C), 130.2 (C), 129.1 (CH), 128.8 (CH), 128.7 (CH), 128.7 (C), 128.3 (CH), 127.8 (C), 127.7 (CH), 127.5 (CH), 126.7 (CH), 126.6 (CH), 126.5 (CH), 126.2 (CH), 126.0 (CH), 125.7 (CH), 107.6 (C), 93.2 (C), 69.9 (C−OH), 0.01 (C−Si(CH3)3) ppm (one tertiary carbon atom not observed); MS (ESI-TOF, MeCN) m/z (%): 413.11 (18) [M + Cl]−. 7-Ethynyl-7H-benzo[no]tetraphen-7-ol (16). To a solution of 15 (66.0 mg, 0.174 mmol) in methanol (20 mL) was added potassium hydroxide (0.5 mL, 4.0 M in H2O). The resulting mixture was stirred for 3 h at ambient conditions. The solvent was removed under vacuum, the crude product was extracted with CH2Cl2 (50 mL), washed with H2O (3 × 25 mL), and dried (Na2SO4), and the solvent was removed under vacuum to yield 7-ethynyl-7H-benzo[no]tetraphen-7-ol (16) as an orange-brown powder. Yield: 37.3 mg (0.122 mmol, 70%); 1H NMR (300 MHz, CDCl3): δ = 8.67 (m, 1H), 8.29 (m, 3H), 7.91 (m, 4H), 7.67 (m, 2H), 7.52 (m, 2H), 2.92 (s, 1H, OH), 2.91 (s, 1H) ppm; 13C NMR (75.5 MHz, CDCl3): δ = 135.7 (C), 135.3 (C), 135.2 (C), 135.0 (C), 133.3 (C), 130.0 (C), 128.9 (C), 129.0 (CH), 128.9 (CH), 128.6 (CH), 128.3 (CH), 128.3 (CH), 127.5 (CH), 127.4 (CH), 126.6 (CH), 126.5 (CH), 126.2 (CH), 126.2 (C), 125.7 (CH), 125.5 (CH), 86.6 (C), 76.4 (CH), 69.1 (C− OH) ppm; MS (ESI-TOF, MeCN) m/z (%): 289.10 (48) [M − OH]+. [Ru(bdmpza)Cl(CC(BT))(PPh 3 )] (17A/17B). [Ru(bdmpza)Cl(PPh3)2] (111 mg, 0.122 mmol) and 7-ethynyl-7Hbenzo[no]tetraphen-7-ol (16) (37.3 mg, 0.122 mmol) were suspended in THF (80 mL) and stirred at room temperature for 72 h. The solvent of the deep blue solution was removed under vacuum, yielding the crude product. The isomeric mixture was purified according to the

solution was allowed to stir for 30 min before being transferred slowly via cannula into a suspension of anthraquinone (2.09 g, 10.1 mmol) in THF (40 mL) at room temperature. The reaction mixture was stirred for 40 h at room temperature, cooled to 0 °C, and quenched via the addition of water (10 mL). The suspension was filtered off, washed with water/THF (2 × 4 mL, H2O:THF = 1:1) and pure THF (3 × 10 mL), and saturated aqueous NH4Cl (100 mL) was added to the filtrate. The aqueous phase was extracted with CH2Cl2 (3 × 100 mL) and dried (Na2SO4), and the solvent was removed under vacuum to yield a red powder. The crude product was separated from unreacted anthraquinone via column chromatography with CH2Cl2 as eluent (silica, length 15 cm, Ø 4 cm) to obtain 10 as a pink solid. Yield: 2.74 g (8.95 mmol, 89%); 1H NMR (300 MHz, CDCl3): δ = 8.17 (m, 2H, AO−H), 8.08 (d, 3JH,H = 7.7 Hz, 2H, AO−H), 7.71 (m, 2H, AO−H), 7.51 (m, 2H, AO−H), 3.16 (s, 1H, OH), 0.16 (s, 9H, Si(CH3)3) ppm; 13 C NMR (75 MHz, CDCl3): δ = 183.1 (CO), 143.7, 134.3, 129.4, 129.2, 128.4, 127.3, 106.7 (Calkyne−Si), 91.5 (Calkyne), 66.4 (C−OH), −0.2 (Si(CH3)3) ppm; IR (KBr): ν̃ 3072 (w, CH), 2957 (w, CH), 2899 (w, CH), 2172 (w, CC), 1649 (vs, CO), 1599 (s), 1582 (s), 1456 (m) cm−1; MS (ESI-TOF, MeCN) m/z (%): 305.10 (100) [M − H]−; Elemental analysis calcd (%) for C19H18O2Si: C 74.47, H 5.92; found: C 74.64, H 5.91. 10-Ethynyl-10-hydroxyanthracen-9(10H)-one (11). To a solution of the trimethylsilyl-protected propargyl alcohol 10 (1.00 g, 3.26 mmol) in MeOH (20 mL) was added KOH (5 mL, 4.0 M in H2O). The resulting mixture was stirred for 2 h at room temperature under ambient conditions. The solvent was removed under vacuum, the crude product was extracted with CH2Cl2 (200 mL), washed with H2O (3 × 100 mL), and dried (Na2SO4), and the solvent was removed under vacuum to obtain 11 as a gray powder. Yield: 649 mg (2.77 mmol, 85%); 1H NMR (300 MHz, CDCl3): δ = 8.26 (m, 2H, AO−H), 8.11 (d, 3JH,H = 7.9 Hz, 2H, AO−H), 7.74 (m, 2H, AO−H), 7.55 (m, 2H, AO−H), 2.98 (s, 1H, OH), 2.71 (s, 1H, CH) ppm; 1H NMR (300 MHz, DMSO-d6): δ = 8.09 (m, 4H, AO−H), 7.83 (m, 2H, AO−H), 7.60 (m, 2H, AO−H), 7.15 (s, 1H, OH), 3.70 (s, 1H, CH) ppm; 13C NMR (75 MHz, DMSO-d6): δ = 182.4 (CO), 145.1, 134.3 (2 × CH), 128.9 (CH), 128.4, 128.4 (2 × CH), 126.2 (CH), 87.1 (Calkyne), 76.1 (Calkyne−H), 64.2 (C−OH) ppm; IR (KBr): ν̃ 3256 (m, OH & alkynyl CH), 2956 (s, CH), 2918 (vs, CH), 2849 (s, CH), 2112 (w, CC), 1772 (m, CO), 1733 (m), 1656 (m) cm−1; MS (ESITOF, MeCN) m/z (%): 233.06 (19) [M − H]−; Elemental analysis calcd (%) for C16H10O2: C 82.04, H 4.30; found: C 82.36, H 4.30. [Ru(bdmpza)Cl(CC(AO))(PPh 3 )] (12A/12B). [Ru(bdmpza)Cl(PPh3)2] (341 mg, 0.400 mmol) and 10-ethynyl-10hydroxyanthracen-9(10H)-one (11) (300 mg, 1.28 mmol) were suspended in THF (80 mL) and stirred at room temperature for 48 h. The solvent of the purple solution was removed under vacuum, yielding the crude product. The isomeric mixture was purified according to the general method, yielding a purple isomer 12A (allenylidene trans to pyrazole) and a red isomer 12B (allenylidene trans to carboxylate). 12A: Yield: 185 mg (0.215 mmol, 54%); 1H NMR (CDCl3, 300 MHz, 25 °C): δ = 8.18 (d, 3JH,H = 7.5 Hz, 2H, AO−H), 7.94 (t, 3JH,H = 7.4 Hz, 2H, AO−H), 7.78 (m, 2H, AO−H), 7.54 (m, 6H, m-PPh3), 7.32 (m, 3H, p-PPh3), 7.25 (m, 6H, o-PPh3), 7.18 (m, 2H, AO−H), 6.77 (s, 1H, CH), 6.08 (s, 1H, pz−H4′), 5.98 (s, 1H, pz−H4), 2.60 (s, 3H, pz−Me5′), 2.55 (s, 3H, pz−Me5), 2.21 (s, 3H, pz−Me3), 2.00 (s, 3H, pz−Me3′) ppm; 13C NMR (CDCl3, 75 MHz): δ = 292.1 (d, 2JC,P = 26.8 Hz, Cα), 251.0 (d, 3JC,P = 5.0 Hz, Cβ), 187.1 (CO), 166.3 (CO2−), 156.3 (pz−C3′), 154.7 (pz−C3), 141.4 (d, 4JC,P = 3.0 Hz, Cγ), 141.1 (pz−C5′), 139.8 (d, 4JC,P = 2.0 Hz, pz−C5), 134.3 (2 × AO− CH), 134.1 (d, 3JC,P = 6.9 Hz, o-PPh3), 133.3 (d, 1JC,P = 38.6 Hz, iPPh3), 132.4 (2 × AO−C), 132.0 (2 × AO−C), 130.0 (d, 4JC,P = 2.0 Hz, p-PPh3), 128.8 (2 × AO−CH), 128.3 (2 × AO−CH), 128.2 (2 × AO−CH), 128.0 (d, 2JC,P = 9.9 Hz, o-PPh3), 109.5 (pz−C4′), 108.2 (pz−C4), 69.1 (CH), 14.5 (pz−Me3′), 13.2 (pz−Me3), 11.4 (pz− Me5′), 11.1 (pz−Me5) ppm; 31P NMR (CDCl3, 122 MHz): δ = 30.1 ppm; IR (CH2Cl2): ν̃ 1880 (m, CCC), 1666 (s, as-CO2−), 1592 (m, CN) cm−1; UV/vis (CH2Cl2): λmax (log(ε)): 363 nm (3.17), 580 nm (3.44); MS (ESI-TOF, MeCN) m/z (%): 783.18 (12) [M − 5141


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general method, yielding the blue isomer 17A (allenylidene trans to pyrazole) and the blue isomer 17B (allenylidene trans to carboxylate). 17A: Yield: 62.6 mg (0.0670 mmol, 55%); 1H NMR (300 MHz, CD2Cl2): δ = 9.11 (d, 3JH,H = 7.4 Hz, 1H, BT−H), 8.92 (d, 3JH,H = 8.5 Hz, 1H, BT−H), 8.70 (d, 3JH,H = 7.9 Hz, 1H, BT−H), 8.42 (d, 3JH,H = 7.9 Hz, 1H, BT−H), 8.13 (d, 3JH,H = 7.4 Hz, 1H, BT−H), 7.98 (d, 3 JH,H = 8.7 Hz, 1H, BT−H), 7.82 (s, 2H, BT−H), 7.57 (m, 8H, PPh3 + BT−H), 7.33 (m, 10H, PPh3 + BT−H), 7.13 (t, 3JH,H = 7.7 Hz, 1H, BT−H), 6.74 (s, 1H, CH), 6.10 (s, 1H, pz−H4′), 6.09 (s, 1H, pz−H4), 2.63 (s, 3H, pz−Me5′), 2.59 (s, 3H, pz−Me5), 2.31 (s, 3H, pz−Me3), 1.93 (s, 3H, pz−Me3′) ppm; 13C NMR (75 MHz, CD2Cl2): δ = 273.6 (d, 2JC,P = 19.2 Hz, Cα), 221.1 (d, 3JC,P = 3.5 Hz, Cß), 166.4 (CO2−), 156.3 (pz−C3′), 154.8 (pz−C3), 141.6 (pz−C5′), 140.5 (pz−C5), 139.8 (d, 4JC,P = 1.7 Hz, Cγ), 139.1 (BT−C), 136.2 (BT−C), 134.6 (d, 2 JC,P = 7.0 Hz, o-PPh3), 134.4 (BT−C), 134.2 (BT−C), 133.8 (BT− C), 132.6 (d, 1JC,P = 48.9 Hz, i-PPh3), 130.5 (BT−CH), 130.0 (d, 4JC,P = 2.6 Hz, p-PPh3), 129.8 (BT−C), 129.7 (BT−CH), 129.7 (BT−CH), 129.1 (BT−C), 129.1 (BT−CH), 128.8 (BT−CH), 128.7 (BT−CH), 128.1 (d, 3JC,P =9.7 Hz, m-PPh3), 127.9 (BT−CH), 127.8 (BT−CH), 127.7 (BT−CH), 127.5 (BT−CH), 126.9 (BT−CH), 126.0 (BT− CH), 109.3 (pz−C4′), 108.4 (pz−C4), 69.4 (CH), 14.4 (pz−Me3′), 13.5 (pz−Me3), 11.5 (pz−Me5′), 11.3 (pz−Me5) ppm; 31P NMR (122 MHz, CD2Cl2): δ = 35.2 ppm; IR (KBr): ν̃ 1903 (m, CCC), 1661 (s, as-CO2−), 1560 (m, CN) cm−1; MS (ESI-TOF, MeCN) m/z (%): 934.18 (100) [M]+, 855.22(23) [M − Cl − CO2]+; Elemental analysis calcd. (%) for C53H42ClN4O2PRu: C 68.12, H 4.53, N 6.00; calcd. (%) for C53H42ClN4O2PRu × 0.1 CH2Cl2: C 67.64, H 4.51, N 5.94; found: C 67.43, H 4.51, N 5.89. Sample contained at least 10% CH2Cl2 according to 1H NMR spectrum. 17B: Yield: 17.1 mg (0.0183 mmol, 15%); 1H NMR (300 MHz, CD2Cl2): δ = 9.12 (d, 3JH,H = 7.5 Hz, 1H, BT−H), 8.93 (d, 3JH,H = 8.6 Hz, 1H, BT−H), 8.71 (d, 3JH,H = 7.9 Hz, 1H, BT−H), 8.44 (d, 3JH,H = 8.1 Hz, 1H, BT−H), 8.24 (d, 3JH,H = 7.5 Hz, 1H, BT−H), 8.03 (d, 3 JH,H = 8.8 Hz, 1H, BT−H), 7.80 (d, 3JH,H = 3.9 Hz, 2H, BT−H), 7.60 (m, 9H, PPh3 + BT−H), 7.38 (d, 3JH,H = 8.8 Hz, 1H, BT−H), 7.19 (m, 9H, PPh3 + BT−H), 6.76 (s, 1H, CH), 5.91 (s, 1H, pz−H4′), 5.74 (s, 1H, pz−H4), 2.59 (s, 3H, pz−Me5′), 2.55 (s, 3H, pz−Me5), 2.20 (s, 3H, pz−Me3), 1.40 (s, 3H, pz−Me3′) ppm; 13C NMR (75 MHz, CD2Cl2): δ = 289.5 (d, 2JC,P = 18.4 Hz, Cα), 237.2 (Cß), 166.4 (CO2−), 156.2 (pz−C3′), 154.8 (pz−C3), 142.4 (pz−C5′), 140.5 (pz− C5), 138.9 (BT−C), 138.3 (BT−C), 138.0 (Cγ), 135.4 (d, 1JC,P = 46.0 Hz, i-PPh3), 134.7 (d, 2JC,P = 9.2 Hz, o-PPh3), 134.2 (BT−C), 133.6 (BT−C), 132.4 (BT−C), 132.2 (BT−CH), 132.0 (BT−C), 131.4 (d, 3 JC,P = 9.2 Hz, m-PPh3), 131.4 (BT−CH), 130.8 (BT−CH), 130.2 (BT−CH), 129.8 (d, 4JC,P = 1.8 Hz, p-PPh3), 129.3 (BT−CH), 128.8 (BT−CH), 128.4 (BT−CH), 127.8 (BT−CH), 127.6 (BT−CH), 126.5 (BT−CH), 108.5 (pz−C4′), 108.3 (pz−C4), 70.0 (CH), 14.4 (pz−Me3′), 13.7 (pz−Me3), 11.9 (pz−Me5′), 11.3 (pz−Me5) ppm; 31 P NMR (122 MHz, CD2Cl2): δ = 32.3 ppm; IR (KBr): ν̃ 1907 (m, CCC), 1662 (s, as-CO2−), 1560 (m, CN) cm−1; MS (ESITOF, MeCN) m/z (%): 934.18 (100) [M]+. Cyclic Voltammetry. Cyclic voltammetry experiments were performed using a AUTOLAB PGSTAT 100. A three-electrode cell was used, using a gold disk working electrode and a platinum wire counter electrode, and a silver wire was used as a pseudo-reference electrode. Cyclic voltammetry was performed in MeCN or CH2Cl2 solution (1.00 mM complex) containing 0.1 M n-Bu4NPF6 as supporting electrolyte. All solutions were deoxygenated with N2 before each experiment, and a blanket of N2 was used over the solution during the experiment. The potential values (E) were calculated using the following equation: E = (Epc + Epa)/2, where Epc and Epa correspond to the cathodic and anodic peak potentials, respectively. Potentials are referenced to the ferrocenium/ferrocene (Fc+/Fc) couple used as an internal standard. Calculations. All density functional theory (DFT) calculations were carried out by using the Jaguar 7.7.107 software running on Linux 2.6.18-238.el5 SMP (x86_64) on two AMD Phenom II X6 1090T processor workstations (Beowulf-cluster) parallelized with OpenMPI. The X-ray crystal structure of the corresponding complex was used as

the starting geometry. Complete geometry optimizations were carried out on the implemented LACVP* (Hay-Wadt effective core potential (ECP) basis on heavy atoms, N31G6* for all other atoms) basis set and with the B3LYP density functional. The calculated structures were proven to be true minima by the absence of imaginary frequencies. Orbital Plots were obtained using Maestro 9.1.207, the graphical interface of Jaguar. UV/vis transitions were obtained by timedependent (TD-DFT) calculations on the geometry of the minimized structure.40 X-ray Structure Determinations. A Bruker-Nonius KappaCCD diffractometer was used for data collection (graphite monochromator, Mo Kα radiation, λ = 0.71073 Å). Single crystals of 4B, 7A, 7B, 12A, 12B, 13A, and 17A were coated with perfluoropolyether, picked with a glass fiber, and immediately mounted in the nitrogen cold gas stream of the diffractometer. The structures were solved by using direct methods and refined with full-matrix least-squares against F2 (Siemens SHELX- 97).41 A weighting scheme was applied in the last steps of the refinement with w = 1/[σ2(Fo2) + (aP)2 + bP] and P = [2Fc2 + max(Fo2,0)]/3. Hydrogen atoms were included in their calculated positions and refined in a riding model. The asymmetric unit of 7A contains one water molecule. The asymmetric unit of 12A contains one dichloromethane disordered over 3 positions. The unit cell of 12B contains one n-hexane molecule that has been treated as a diffuse contribution to the overall scattering without specific atom positions by SQUEEZE/PLATON.42 The asymmetric units of 7B, 13A, and 17A each contain two dichloromethane molecules, and one of these dichloromethane molecules is disordered over two positions with occupancies of 50% each. All details and parameters of the measurements are summarized in Table S1 (Supporting Information). CCDC 991625−991631 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/ data_request/cif. The structure pictures were prepared with the program Diamond 2.1e.43

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ASSOCIATED CONTENT

S Supporting Information *

Tables and CIF files giving crystallographic data and structure refinement details for 4B, 7A, 7B, 12A, 12B, 13A, and 17A; TD-DFT calculations of 7A, 12A, 12B, and 13A; table of all recorded UV/vis transitions; and cyclic voltammograms of all ruthenium allenylidene complexes. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: nicolai.burzlaff@fau.de (N.B.). Tel: (+49) 9131-8528976. Fax: (+49) 9131-85-27387. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Bavarian State Ministry of Science, Research and Arts through the grant “Solar Technologies go Hybrid (SolTech)”.

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REFERENCES

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