Polyelectrochromic Vinyl Ruthenium-Modified ... - ACS Publications

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Polyelectrochromic Vinyl Ruthenium-Modified Tritylium Dyes Steffen Oßwald, Stefanie Breimaier, Michael Linseis, and Rainer F. Winter* Fachbereich Chemie der Universität Konstanz, Universitätsstraße 10, D-78457 Konstanz, Germany S Supporting Information *

ABSTRACT: A series of four mononuclear and one dinuclear ruthenium styryl complexes with redox active triarylmethylium ligands were prepared. All new compounds were characterized by NMR spectroscopy, MS spectrometry, cyclic voltammetry, and in various oxidation states by IR and UV/vis/NIR and EPR spectroscopy. The increase in conjugation length by the introduction of the vinyl ruthenium entity pushes the electronic absorption to low energy, almost into the near-infrared region. Electrochemical and spectroscopic properties are strongly influenced by the para substituents at the triarylmethylium ligands. The complexes were characterized in up to four different oxidation states up to the trication level and show pronounced electrochromism. The oxidized mixed-valent diruthenium complex 52+ shows a moderate degree of charge and spin delocalization over the styryl ruthenium sites.

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INTRODUCTION Crystal violet and its many derivatives constitute an important class of dyestuffs1,2 owing to their favorable absorption properties. They are also used for medical purposes, e.g., in the Gram staining of bacteria,3 DNA staining in agarose gels,4 and the staining of tissue culture monolayers.5 Crystal violet itself exhibits antibacterial, antifungal, antitypanosomal, antiviral, and antiangiogenic properties,6 which has led to applications in the treatment of oral candidiasis in HIVinfected patients7 or in low-budget burn wound management.8 Besides their optical and biological properties, triarylmethylium (tritylium) compounds also possess intriguing electrochemical properties.9 Despite their structural simplicity, these compounds are capable of forming extended redox series that connect Ar3C+ cations to neutral Ar3C• radicals and, upon further one-electron reduction, to Ar3C− anions. Numerous accounts have devised and exploited elaborate schemes that relate the potentials of the +/0 and 0/− redox couples to fundamental thermodynamic properties of these amphihydric, trivalent carbon species. Examples are the pKR+ values, where KR+ denotes the equilibrium constant of the reaction Ar3C+ + OH2 ⇌ Ar3C-OH + H+, the hydride affinities of Ar3C+, the free enthalpies for homo- or heterolytic dissociation of the Ar3C-X bond, the pKa values of the corresponding triarylmethanes Ar3C-H, or the absolute hardness of the Ar3C• radicals.9b−f In these studies, correlations between the +/0 redox potentials E1/2 and Taft’s σ+ parameter and those of the 0/− redox couple and the σ− parameter have been noted. Particularly electronrich tritylium ions with two or three strong NR2 donors are even capable of undergoing further oxidation to persistent radical dications, which extends the Ar3C-based redox series to four interconvertible members.10 Further elongation of the conjugated π-system of tritylium dyes by styryl (Ph−CHCH-) or tolanyl (Ph−CC-) groups © XXXX American Chemical Society

has been reported to shift the wavelength of the maximum absorption to lower energies, partly down to the near-infrared region (NIR), and to further increase the extinction coefficients.9g,11 Although there are several reports on ferrocenyl-substituted tritylium dyes with the cyclopentadienyl ring of a ferrocene as an aryl substituent at the carbonium center or as a pendant in vinylogously extended analogues,11b,12 other examples of metal organic derivatives of triarylmethylium dyes are rare. They include mixed ruthenium sandwich complexes where the lactone of crystal violet is η6-bonded to one or two Cp*Ru fragments (Cp* = η5-C5Me5)13 and rhenium carbonyl complexes of pyridine- or 2,2′-bipyridinemodified tritylium ligands.14 Most relevant to the present work are the ruthenium complexes of Lin and co-workers with one, two, or three NEt2 groups of ethyl violet (4-Et2N−C6H4)3C+ replaced by Cp(PPh3)2Ru−CC- moieties.15 A sizable redshift of the prominent low-energy band from 587 nm for ethyl violet to 855, 897, or 974 nm on successive substitutions was noted. No attempts were made, however, to exploit the redox activity inherent to the triarylmethylium core and the halfsandwich ruthenium entities in redox switching the absorptions of these dyes and probing their electrochromism. We became interested in alkenyl ruthenium-modified tritylium dyes as part of our ongoing program on organometallic electrochromic materials with (PiPr3)2Cl(CO)Ru− CHCH- ({Ru}-CHCH-) as an electroactive and strongly auxochromic tag.16 Thus, alkenyl ruthenium-appended triarylamines, tetraphenylethenes, and bridged bis(alkenyl ruthenium)arylenes undergo up to four reversible oxidations, depending on the number of {Ru}-CHCH- entities, and the number of further bridge-based redox processes. Their Received: March 14, 2017

A

DOI: 10.1021/acs.organomet.7b00194 Organometallics XXXX, XXX, XXX−XXX

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Organometallics

benzophenone failed in our hands because of the inherent inertness of the latter ketone. Removal of the trimethylsilyl protecting group from the ethynyl functions was achieved by K2CO3 or KOH in methanol. NMR spectra of the organic precursors are collected as Figures S1−S24. The final step involved the formation of the respective tritylium cation under acidic conditions with a slight excess of Brookhart’s acid [H(Et2O)2]+ [tetrakis{3,5-bis(trifluoromethyl)phenyl}borate]−19 in diethyl ether. Excess acid was carefully neutralized with 1,8-bis(dimethylamino)naphthalene (proton sponge). This step is crucial as the final alkenyl ruthenium complexes are highly sensitive toward acids. The subsequent hydroruthenation with HRu(CO)Cl(PiPr3)2 was carried out in benzene and provided the target complexes in yields of 46−93%. All new complexes were readily identified by characteristic signals in their 1 H- and 31 P{ 1 H}-NMR spectra (see Experimental Section and Figures S25−S43). The latter show only one singlet for the phosphine ligands in the region between 40 and 47 ppm. Particularly indicative are the doublet signals of the vinyl protons. Of note is the pronounced highfield shift of the α-vinyl proton H1 to 10−13 ppm when compared to other alkenyl ruthenium complexes, where the corresponding resonance is observed at approximately 8.2−8.7 ppm.16b,20 In contrast, the neighboring vinyl proton H2 resonates in the normal range at 6.36 to 6.67 ppm. The 13C NMR resonance of the methylium carbon atom is known to be particularly sensitive to the electronic properties of the 4substituents at the aryl rings with a shift range of approximately 34 ppm between the tris(4-tolyl) (δ = 212.7 ppm) and tris(4N,N-dimethylanilino) derivatives (δ = 179.0 ppm).21 The corresponding resonances of complexes 1a−5a appear in a rather narrow range of 178.8−181.9 ppm. Comparison of complexes 1+ and 2+ with the bis- or tris(4-anisyl)methylium cations on one hand (δ = 201.0 and 194.0 ppm) and of complexes 3+−5+ (δ = 179.3−179.6 ppm) with the tris(4NMe2) derivative (δ = 179.0 ppm) shows that the vinyl ruthenium moiety is a much better donor than an OMe group and almost as strong a donor as the NMe2 group. On the other hand, its donor capabilities are slightly inferior to those of the Cp(PPh3)2Ru−CC- half-sandwich moiety, which shifts the respective resonance further upfield to 176.7 ppm.15 Similar conclusions can be drawn from the positioning of the most red-shifted electronic transition. The HOMO of tritylium cations tends to localize on the most electron-rich aryl substituent(s), whereas the LUMO is usually biased to the methylium center and to a lesser extent to the aryl group(s).22 This is also borne out by our calculations on the full models of complexes 1+−4+ as is evident from the contour plots of these MOs in Figure 1 and Figures S44−S49. Thus, the HOMO of all complexes is dominated by the ruthenium styryl group as the strongest electron donor (>80%), whereas the LUMO has

associated radical cations and higher oxidized forms exhibit strong absorption in the NIR or the low-energy régime of the visible (vis) region, as long as efficient conjugation between the {Ru}-CHCH- moieties and the parent organic π-system is maintained.16a,17 Similar complexes of the mer-(PMe3)3Cl(CO)Ru-CHCH- fragment have also been reported but seem to suffer from somewhat lower stabilities and less intense low-energy absorptions of their oxidized forms.18 We report here on four mono- and one bis(alkenyl ruthenium) triarylmethylium dyes and their electronic, electrochemical, and spectroscopic properties of their various oxidized (up to the trication level) and singly reduced forms.

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RESULTS AND DISCUSSION Synthesis and Characterization. Tritylium cations are generally accessible from substituted benzophenones (Scheme 1, route A) or benzoic acid esters (Scheme 1, route B) and one Scheme 1. Synthesis of Complexes 1−5

or two equivalents of an aryl lithium reagent. Starting from benzophenones with two different aryl groups, the former approach can also be used to synthesize CAr3+ derivatives with three different aryl substituents. Triarylmethanol precursors 1a and 3a were prepared accordingly from 4-trimethylsilylethynyl benzophenone and the phenyllithium reagent generated in situ from 4-bromoanisole or 4-bromo-N,N-dimethylaniline, and 2a, 4a, and 5a were prepared from 4-bromoanisole (2a), 4-bromoN,N-dimethyaniline (4a), or 4-bromo-1-trimethylsilylethynylbenzene (5a) and the respective benzoic acid ester. The alternative approach to 5a of adding 4-lithiated N,Ndimethylaminoaniline to bis(4-trimethysilylethynyl)-

Figure 1. Contour plots of the calculated HOMO (left) and LUMO (right) of complex 1+ (PBE1PBE/6-31G(d)PCM(CH2Cl-CH2Cl). B


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Organometallics

large red shift of the prominent absorption band of complexes 3+ and 4+ when compared to (4-Me2NC6H4)(C6H5)2C+ (λmax = 461 nm) or (4-Me2NC6H4)2(C6H5)C+ (λmax = 623 nm, c.f. λmax = 753 nm for 3+ and 682 nm for 4+). The slight blue shift in the order 1+, 2+ < 3+ < 4+ complies with the known tendency of the most electron-rich aryl substituent (the styryl ruthenium moiety for 1+, 2+, and the 4-Me2NC6H4 moiety for the other complexes) to maximize its overlap with the empty pπ orbital of the central methylium carbon atom.22 This means that the more extended π-conjugated Ru-CHCH-C6H4 arm of complexes 3+ and 4+ conjugates less well with the tritylium carbon atom than in complexes 1+ and 2+. The various degrees of conjugation and electron-donation of the styryl ruthenium moiety to the electron-deficient tritylium core can also be discerned from the energy of the Ru-CO stretching vibration ν(CO). The positioning of that band mirrors the electron density at the ruthenium atom. As the compilation of Table 2 shows, ν(CO) generally appears at

larger contributions from the methylium center (∼30%) and the attached aryl rings with higher contributions from the substituted ones (e.g., 29% for the dimethylaminopheny, 27% for the styryl, and 13% for the phenyl ring of 3+; for a more detailed fragment decomposition according to an NBO analysis, see Tables S1−S3). The electronic absorption data of the complexes are compiled in Table 1. They display a structured intense band Table 1. UV/vis/NIR Dataa of Complexes 1n+−5n+ complex

λmax in nm (ε in L mol−1 cm−1)

1 1+ 12+ 2 2+ 22+

347 (9000), 393 (4700), 458 (7800) 393 (11500), 441 (13700), 773 (63100) 371 (5500), 450 (20800), 488 (18900), 586 (26400), 1180 (1500) 385 (12700), 457 (21300) 420 (16600), 465 (33200), 511 (8500), 766 (88700) 423 (6400), 470 (7700), 497 (31200), 518 (62700), 568 (33100), 781 (3700), 1500 (1300) 452 (9600), 751 (5600) 324 (16500), 366 (16000), 491 (18000), 753 (54200) 383 (16900), 452 (25000), 623 (34100), 1127 (2900) 306 (38800), 338 (35000), 400 (24700), 460 (19800), 605 (13400) 327 (33500), 418 (20200), 610 (97400), 682 (48400), 448 (33200), 611 (23300), 950 (−), 1430 (−) 323 (50000), 446 (24000), 607 (7300), 689 (15400), 786 (12000) 289 (52000), 370 (21500), 472 (5000), 658 (26800), 690 (48400), 768 (47800) 289 (58800), 368 (17900), 439 (7000), 620 (12000), 658 (15700), 689 (17000), 754 (34400), 966 (11300) 290 (48000), 293 (102600), 300 (42000), 349 (25700), 622 (19000), 705 (22900)

3 3+ 32+ 4 +

4 42+ 5 5+ 52+ 53+

Table 2. IR Data of Complexes 1n+−5n+ in Their Various Oxidation Statesa complex

1+

2+

1n 2n 3n 4n 5n

1945 1937 1924 1921 1922

1987 1986 1981 1980 1927, 1978

3+

0

1960 1982

1911 1912 1913 1911 1913

All band positions given in cm−1. Measured in 1,2-C2H4Cl2/0.25 mM NBu4+ B{C6H3(CF3)2}4− at 293 (±3) K. a

higher energies than in neutral styryl ruthenium complexes 4RC6H4−CHCH-{Ru}, where ν(CO) varies from ∼1908 cm−1 (R = NMe2, NH2) to 1917 cm−1 (R = CF3, NO2) depending on the electronic properties of R.24 It even approaches values that were found for oxidized styryl ruthenium complexes where the unipositive charge is shared by a secondary redox site as is the case for [{Ru}-CHCHC6H4-4-NMe2]+ (ν(CO) = 1950 cm−1) or [{Ru}-CHCHC6H4−N(C6H4OMe-4)2]+ (1944 cm−1).17d,24b The latter radical cations resemble our present complexes insofar as they also exhibit an electron vacancy at the pπ atomic orbital of the central atom E of an EAr3+ unit. The energy ordering of ν(CO) 4 ≈ 5+ < 3+ < 2+ < 1+ mirrors the degree by which the electron demand of the tritylium core is satisfied by the vinyl ruthenium moiety. Electrochemistry. Ruthenium styryl complexes with additional redox-active constituents generally exhibit one chemically and electrochemically reversible oxidation per {Ru} moiety plus additional redox processes inherent to the parent scaffold. This also holds here. As displayed in Figures S50−S55, cyclic voltammograms of monoruthenium complexes 1+−3+ exhibit two reversible redox processes that correspond to the +/2+ and the +/0 couples. Diruthenium complex 5+ and the bis(4-N,Ndimethylamino)-substituted monoruthenium complex 4+ as the most electron-rich representatives of the present complexes even exhibit a further anodic wave due to the 2+/3+ redox couple (see Figure 2). The expected 0/− couple that is commonly observed for other tritylium systems is shifted to outside the cathodic discharge limit of our CH2Cl2-based electrolyte (c.f. approximately −2.04 V for (C6H4NMe2-4)3C• or −1.85 V for (C6H4OMe-4)3C• in DMSO/NBu4+ClO4−;9b note that the Ag/AgCl reference couple has a half-wave

a

All band positions are given in nm, and extinction coefficients are given in L mol−1 cm−1. Measured in 1,2-C2H4Cl2/0.25 mM NBu4+ [B{C6H3(CF3)2}4]− at 293 (±3) K.

at low energy in the vis region with the lowest energy absorption maximum at λ = 682−773 nm and ε values in the range of 48400−97400 L mol−1 cm−1, endowing them with deep green to blue coloration. TD-DFT calculations assign the lowest energy band to the HOMO−LUMO transition (see Table S4 and the graphical display of crucial MOs in Table S5). That transition consequently involves some degree of chargetransfer from the styryl ruthenium to the C+Ar2 entity. Introduction of the styryl ruthenium moiety generally induces a sizable red-shift of λmax as a consequence of the efficient integration of the {Ru}-CHCH- entity ({Ru} = Ru(CO)Cl(PiPr3)2) into the conjugated π-system. Thus, complexes 1+ and 2+ absorb at much larger wavelengths (lower energies, λmax = 773 nm) than (4-OMeC6H4)2(C6H5)C+ (λmax = 497 nm),21 (4OMeC6H4)3C+ (λmax = 486 nm),23 and even the vinylogously extended tritylium dyes (4-OMeC6H4−CHCH-C6H4)(C6H5)2C+ (λmax = 678 nm) and (4-OMeC6H4−CHCHC6H4)2(C6H5)C+ (λmax = 726 nm).11a This demonstrates once more the equivalency (if not superiority) of the {Ru} moiety to a conjugated phenyl ring in terms of increasing the conjugation length of the parent organic π-system.17c,d On the other hand, the {Ru} moiety of the present complexes again appears slightly inferior to CpRu(PPh3)2-CC-. Thus, the corresponding absorption band in the monoruthenium complex Ph(4-OMeC6H4)C+(C6H4−CC−Ru(PPh3)2Cp), analogous to 1+, is further red-shifted by 725 cm−1 to λmax = 819 nm.15 The strong hyperchromic effect of the {Ru} moiety is also evident from the C


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Organometallics

E1/2+/2+ of complex 3+ is approximately 110 mV lower than that of malachite green (4-Me2NC6H4)2(C6H5)C+,10a whereas those of complexes 4+ and 5+ appear approximately 270 or 200 mV cathodic of the +/2+ couple of crystal violet itself.10b These observations let us conclude that the 4-styryl ruthenium moiety outperforms the 4-NMe2C6H4 substituent when it comes to stabilizing a further positive charge by resonance despite being the weaker electron donor. This becomes particularly manifest in the lowering of E1/2 for the 2+/3+ couple of diruthenium complex 5 + by 340 mV when compared to that of monoruthenium complex 4+ (Table 3). Similar trends also hold for the E1/2 of the +/0 couple. The comparison of the half-wave potential of complex 2+ of −0.965 with that of −0.770 V for (4-OMeC6H4)3C+ in the same electrolyte again defines the -CHCH-{Ru} moiety as the superior electron donor. Substitution of the methoxy group of complex 1+ by the NMe2 donor in complex 3+ induces nearly the same cathodic potential shift as was observed for the +/2+ couple. Likewise, introducing another 4-NMe2 donor substituent to complex 3+ results in a significantly larger cathodic shift of E1/2+/0 than that caused by a CHCH-{Ru} moiety (c.f. complexes 4+ and 5+, Table 3). IR Spectroelectrochemistry. Our electrochemical data indicate that the vinyl ruthenium moiety is particularly efficient at stabilizing an additional positive charge by resonance. Thus, the electron loss upon further oxidation to the associated dications should be preferably compensated by that entity. The charge-sensitive Ru(CO) IR label can be advantageously used to probe for such effects as competition of the oxidized tritylium core with the CO π* orbitals for back bonding should lead to a sizable blue shift of ν(CO). To probe for such effects, we performed IR spectroelectrochemical (IR SEC) experiments by electrolyzing samples of the complexes in an optically transparent thin-layer cell26 under IR monitoring. The results of that study are listed in Table 2 and are graphically depicted in Figure 3 and Figures S56−S61. Oxidation of the complexes to their associated dications accordingly induces a sizable blue shift of the Ru(CO) band to 1980−1987 cm−1. As for the monocationic precursors, ν(CO) is higher for the less electron-rich complexes and decreases somewhat in complexes 32+ and 42+ bearing one or two NMe2 donors. The basically identical energy of ν(CO) in the latter two complexes shows that the second NMe2 donor substituent in 42+ does not contribute to a detectable extent to stabilizing the additional positive charge. This is a manifestation of the well-known saturation effect, which arises from the fact that it is impossible to rotate all three aryl groups to a conformation that would allow them to overlap with the empty pπ orbital of the central atom and the prevalence of conformations, where the most electron-rich aryl ring(s) achieve greater coplanarity with the electron-deficient center.9a,22,27 Of note is the much smaller span of ν(CO) energies covered by the four monoruthenium complexes of 7 cm−1 when compared to the parent cations, where it amounts to 23 cm−1. This shows that the -CHCH{Ru} entity carries most of the burden of electron loss from the tritylium cations, thus attenuating the impact of the electronic properties of the other aryl substituents. An even larger attenuation is observed upon reduction of the tritylium ions to their corresponding neutral radicals, which removes the electron deficiency of the carbenium center. Blocking π-conjugation eliminates the impact of the 4substituents on the other aryl groups such that the ν(CO) values fall in a narrow range of 1911−1913 cm−1, basically

Figure 2. Comparison of cyclic voltammograms (v = 100 mV/s) of 4+ (top) and 5+ (bottom) in CH2Cl2 at T = 293 (±3) K with the 0.1 mM [NBu4]+ [B{C6H3(CF3)2}4]− electrolyte.

potential E1/2 of 0.005 V vs SCE; for conversions to the ferrocene/ferrocenium scale used here, see ref 25). The voltammetric data in Table 3 and their comparison to those of closely related organic tritylium dyes reveal some Table 3. Electrochemical Data for All Complexesa E1/2

ΔEp

E1/2

ΔEp

E1/2

ΔEp

complex

(0/+)

(0/+)

(+/2+)

(+/2+)

(2+/3+)

(2+/3+)

1 2 3 4 5

−720 −965 −890 −1160 −980

59 59 63 71 86

710 700 530 405 470

66 83 86 110

930 590

100

a

All potentials in mV (±3 mV) in CH2Cl2 at T = 293(±3) K relative to the Cp2Fe0/+ couple (E1/2 = 0.000 V). Supporting electrolyte: NBu4+ [B{C6H3(3,5-CF3)2}4]−.

interesting details. The half-wave potential of the +/2+ couple is largely determined by the quality of the strongest aryl donor but is less dependent on the absolute number of donor substituents. For complexes 1+ and 2+, the strongest donor is the 4-styryl ruthenium moiety. Unfortunately, we could find no potential data for the further oxidation of exclusively methoxysubstituted tritylium dyes to their corresponding dications in the literature, which precludes a direct comparison between the methoxy and the vinyl ruthenium groups. The cathodic shift of E1/2+/2+ of 180 mV between complexes 3+ and 1+, however, suggests that the vinyl ruthenium entity is a less powerful donor when compared to that of the 4-NMe2 substituent. The effects of substituting the remaining phenyl substituent of 3+ by either the 4-NMe2C6H4 (4+) or the 4-{Ru}-CHCH-C6H4 “substituent” in 5+ point in the same direction, albeit in an attenuated fashion. Nevertheless, the half-wave potential D


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Figure 4. Changes of IR spectra of complex 5+ (1,2-C2H4Cl2, [NBu4]+ [B{C6H3(CF3)2}4]−, T = 293(±3) K) in the Ru(CO) and aryl C−C stretching region during the oxidation (blue to red).

positive charge is fully absorbed by the second -CHCH-{Ru} moiety. Complex 4+ also offers an additional one-electron oxidation albeit at rather positive potential (Table 3 and Figure 2). Attempts to also investigate that process by IR spectroelectrochemistry allowed partial conversion to 4 3+ before irreversible decomposition set in as indicated by the loss of isosbestic points and only partial recovery of 42+ and 4+ upon back reduction. As shown in Figure S59, further oxidation of 42+ to 43+ is surprisingly accompanied by a red shift of the IR band from 1980 to 1960 cm−1. This suggests that the further oxidation of 42+ to 43+ induces a redistribution of electron density such that the positive charge shifts from the styryl ruthenium moiety to the dimethylamino-substituted phenyl rings. EPR Spectroscopy. Electron paramagnetic resonance spectroscopy is a powerful tool to experimentally probe spin density distribution in paramagnetic species. Owing to the accessibility of two or even three paramagnetic states, the neutral radicals and the dications as well as the trications of complexes 4+ and 5+, complexes 1+−5+ constitute particulary interesting study objects. The EPR results are compiled in Table 4, and Figures 5 and 6 display the spectra obtained for 1, 12+, and 42+ as well as 43+ as representative examples. EPR spectra of all other paramagnetic species can be found in Figures S62−S71. Samples of the dicationic complexes as well as of 53+ were generated by chemically oxidizing their cationic precursors with magic blue (tris(4-bromophenyl)ammoniumyl hexafluoroantimonate), whereas the neutral radicals were prepared by using cobaltocene as reducing agent (1−3) or by in situ electrolysis in an EPR tube (4, 5, 43+). The neutral, one-electron reduced forms of all complexes show the characteristic isotropic signal of a trityl radical at g-values close to the Landé factor ge of 2.002319 (Table 4).31 None of the neutral complexes show any resolved hyperfine interaction with the I = 1/2 31P or, for 3−5, the 14N nuclei, showing that the donor sites bear only little spin density. These experimental results agree well with our quantum chemical calculations on monoruthenium complexes 1−3 as is exemplarily shown by the spin density plot of 1 at the right-hand side of Figure 7 (for similar plots of 2−4, see Figures S72−S79). Our calculations place only 2−3% of the overall spin density on the {Ru} entity, whereas the majority (60%) rests on the central carbyl carbon atom with the remainder

Figure 3. Changes of IR spectra of complex 2+ (1,2-C2H4Cl2, [NBu4]+ [B{C6H3(CF3)2}4]−, T = 293(±3) K) in the Ru(CO) and aryl C−C stretching region during the oxidation (blue to red, top) and the reduction (blue to yellow, bottom).

identical to that of the simple styryl complex Ru(CO)Cl(PiPr3)2(CHCH-C6H5).20b Of further note are the increases in the intensities of the aryl C−C stretching bands at 1550 to 1620 cm−1 upon oxidation to the dications and their intensity loss upon reduction to the neutral radicals. These alterations can be explained by the greater changes of dipole moment in a more extended conjugated system for the cations and dications as opposed to the neutral radicals.28 Diruthenium complex 5+ offers a further peculiarity as its associated dication constitutes a mixed-valent system where the additional electron hole may either be equally distributed over two vinyl ruthenium entities or preferably localized on just one of them. IR spectroscopy offers a snapshot of the intrinsic valence distribution on the short vibrational time scale. As shown in Figure 4, 52+ exhibits a pattern of two widely spaced Ru(CO) bands at 1927 and 1978 cm−1. Upon further oxidation to 53+, these two bands merge to one strong Ru(CO) band, which is now located at 1982 cm−1 (Figure 4 and Figure S60). Following Geiger’s approach,29 the relative CO band shifts as calculated from the displacement of the low-energy Ru(CO) band of 52+ from that of 5+ and that of the high-energy Ru(CO) band of 52+ with respect to 53+ provide insight into how the additional positive charge distributes over the two donor sites. The derived charge distribution parameter Δρ of 0.08 implies only a modest degree of ground state delocalization, rendering 52+ a weakly to moderately coupled mixed-valent system of Class II according to Robin and Day.30 Quite remarkably, the energy of the Ru(CO) stretching band of 53+ is still in the same energy regime as those for the dications of the monoruthenium complexes, showing that the additional E


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Organometallics Table 4. EPR Parameters of the Complexesa complex

g-value

1 2 3 4 5 12+ 22+ 32+ 42+ 52+

2.0117 2.0112 2.0014 2.0135 2.0000 2.0493 2.0491 2.0421 2.0552 2.0286

43+c 53+

2.0146 2.0526

A (31P)b

18.6 18.6 20.0 19.6 12.5 7.9

(2) (2) (2) (2) (2) (2)

12.5 (2)

A (99/101Ru)b

7.1 (1) 7.1 (1) 7.1 (1)

10.7 (2)

the exception of 12+, the 99/101Ru nucleus. The 31P hfs constants of approximately 19−20 G are basically identical to those observed for simple styryl ruthenium complexes,17c,f,20b,24b,32 indicating that the majority of the spin density resides on the -CHCH-{Ru}-substituted phenyl ring. This also follows from the deviation of the g-values of 2.0421 and 2.0552 from ge. As graphically demonstrated in Figure 7 and Figures S72, S74, S76, and S78 (for details, see Table S6), the calculated spin density at the {Ru} site amounts to 45−50% with a total contribution of the styryl ruthenium moiety of 88−92%. Upon further oxidation of complex 42+ to 43+, the EPR signal changes to a three line spectrum, which can be simulated with a hyperfine coupling to one 14N nucleus. The loss of the A (31P) hyperfine interactions matches with our IR spectroscopic observations and likewise indicates a shift of the primary redox site away from the styryl ruthenium moiety to the two 4NMe2-substituted phenyl rings. On the basis of these observations, the dication is best viewed as containing two noninteracting or very weakly coupled oxidized dimetahylaminophenyl rings. According to IR spectroscopy, the mixed-valent dication 52+ was classified as a mixed-valent system of Class II with a modest degree of charge delocalization over the two styryl ruthenium moieties (vide infra). Our EPR results on 52+ indicate that spin densities are also unevenly distributed over the two {Ru} sites. The obtained spectrum shows hyperfine couplings to two different sets of two phosphorus nuclei each, indicating that both ruthenium vinyl moieties contribute to the SOMO but to a different degree (see Figure S69). Charge and spin density distributions need not necessarily be identical, and the time scales inherent to EPR (∼10−8 s) and IR spectroscopy (∼10−12 s) differ.33 In the present case, the hfs constants of 12.5 and 7.9 G differ less than expected from the charge density distribution parameter of just 8% (i.e., one of the two styryl ruthenium moieties carries 92% and the other only 8% of the overall charge lost from both of these sites on one-electron oxidation). After further oxidation to 53+•, the spectrum is best fit by assuming hfs to two equivalent phosphorus atoms, two inequivalent hydrogen atoms, and one 99/101Ru nucleus. Because of the lower resolution, the derived hfs constants should, however, be regarded as only tentative. UV/Vis/NIR Spectroelectrochemistry. One characteristic asset of tritylium ions is their intense coloration. The prospect of disrupting the conjugated π-system by one-electron reduction or of altering the electronic properties of the aryl substituents by one-electron oxidation offers the promise of multiple color switching by redox chemistry or application of a suitable potential. This aspect has been underutilized in tritylium chemistry, in particular their metal organic derivatives,15 despite the favorable redox properties of ferrocenyl or the Cp(L)2Ru−CC- fragment (L = PR3 or a chelating diphosphine).34 In exploring the multistate electrochromism (polyelectrochromism)35 of the present complexes, we again resorted to spectroelectrochemical methods. The outcomes of these experiments are depicted in Figure 8 and Figures S80−S84, and the pertinent data are compiled in Table 1. As one expects from the behavior of common tritylium dyes, the intense lowenergy vis absorption bleaches upon reduction to the neutral radicals, giving way to red coloration. According to our TDDFT calculations, the underlying transitions of the neutral radicals involve charge-transfer (CT) from the CAr2 units with the 4-NMe2- or OMe-substituted or nonsubstituted phenyl

A (1H)b

8.6 8.6 7.9 8.6

(1) (1) (1) (1)

9.6 (1), 7.9 (1)

a

In CH2Cl2 solution; all hyperfine coupling constants are given in G. The number of interacting nuclei is given in parentheses. cA (14N) = 8.2 G.

b

Figure 5. Experimental (top curve) and simulated (bottom curve) EPR spectrum of 12+ (left) and experimental spectrum of 1 (right) in CH2Cl2 solution at rt.

Figure 6. Experimental (top curve) and simulated (bottom curve) EPR spectrum of 42+ (left) and 43+ (right) in CH2Cl2 solution at rt.

Figure 7. Contour plots of the calculated spin densities of 12+ and 1 (PBE1PBE/6-31G(d)PCM(CH2Cl-CH2Cl)).

being distributed over the aryl rings to slightly varying extents (7−19% per ring; for details, see Table S6). In contrast, the paramagnetic dications 12+−42+ of the monoruthenium complexes show hyperfine splittings (hfs) to two equivalent phosphorus nuclei, the α vinyl proton and, with F


Article

Organometallics

Figure 9. Colors of complex 1n+ in its various redox states (from left to right: 1, 1+, 12+).

Figure 8. Changes of UV/vis/NIR spectra of complex 3+ (1,2C2H4Cl2, NBu4+ B{C6H3(CF3)2}4−, T = 293(±3) K) during the oxidation (blue to red, top) and the reduction (blue to yellow, bottom).

rings to the ruthenium-bonded styryl unit within the αmanifold (α-HOMO → α-LUMO + 1) or minor charge transfer from the styryl ruthenium and the 4-NMe2-substituted phenyl ring to the less-electron-rich one(s) for MOs of the β manifold (β-HOMO → β-LUMO, see Tables S4 and S5). Oxidation, on the other hand, preferably involves the strongest aryl donor substituent and thereby decreases the energy of the HOMO while affecting that of the LUMO to a lesser extent. As a consequence, the Vis absorption is shifted to higher energies with a concomitant decrease in overall intensity. The dications nevertheless have an intense purple or blue coloration. Figure 9 demonstrates the reversible three-state color changes at the example of redox series 1/1+/12+. Our TDDFT calculations also indicate that the prominent vis absorption of the dications is dominated by the α-HOMO → α-LUMO transition, which closely resembles the HOMO → LUMO transition of the closed-shell cations along with a minor C+Ar2 → styryl ruthenium component in the β-manifold (see Tables S5 and S6). Dicationic diruthenium complex 52+ offers another peculiarity in the form of a rather intense absorption band (ε = 11300 L mol−1 cm−1) at 966 nm (see Figure 10). This band is most likely due to charge transfer from the reduced to the oxidized styryl ruthenium moiety within this

Figure 10. Changes of UV/vis/NIR spectra of complex 5+ (1,2C2H4Cl2, NBu4+ B{C6H3(CF3)2}4−, T = 293 (±3) K) during the first oxidation (blue to red, top) and the second oxidation (red to green, bottom).

mixed-valence species. It consequently vanishes upon further oxidation to 53+ (see Figure 10). Quite interestingly, similar yet considerably weaker bands (ε = 2900 L mol−1 cm−1) are also observed for 32+ at even lower energy (λ = 1127 nm, see Figure 8). Complex 42+ even shows two weak NIR bands (see Figure S84) at λ = 950 and 1430 nm. These bands have like character and involve charge-transfer from the aryl rings of the C+Ar2 entity (β-HOMO) to the styryl ruthenium (β-LUMO) or the Ru(CO)Cl(PiPr3)2 moieties (β-LUMO+1) or, in the case of 42+, also from the metal-based β-HOMO − 1 to β-LUMO.

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CONCLUSIONS A series of four mononuclear and one dinuclear vinyl ruthenium-modified triarylmethylium dyes have been synthesized by treatment of the corresponding ethynyl-substituted triphenyl methanol precursors with [H(Et2O)2]+ [tetrakis{3,5G


Article

Organometallics bis(trifluoromethyl)phenyl}borate]− and subsequent hydroruthenation with HRu(CO)Cl(PiPr3)2. Blending well-known crystal violet-type dyes with vinyl ruthenium tags leads to intense low-energy electronic absorption bands that even approach the near-infrared region. By changing the substitution pattern at the tritylium unit, the wavelength of maximum absorption can be tuned over the range of 682−773 nm−1, i.e., by 1725 cm−1. Introducing the electroactive {Ru}-CHCHtag(s) additionally endows these complexes with reversible oxidation. This adds the di- and, for the most electron-rich representatives 4+ and 5+, even the tricationic species to the list of accessible redox states while shifting the reduction to the closed-shell anion out of the accessible solvent window. Reduction to the neutral trityl radicals or oxidation to the corresponding dications bleach the prominent Vis absorption band, leaving behind the red tint of neutral styryl ruthenium complexes or a still intense purple-to-bluish coloration of the dications. Our results from accompanying IR and EPR spectroscopic and spectroelectrochemical measurements as well as our quantum chemical calculations indicate that the vinyl ruthenium-modified phenyl ring carries most of the burden of one-electron oxidation, even when nominally better 4-NMe2C6H4 donors are present. This somewhat counterintuitive behavior results from the superior ability of the styryl ruthenium entity to stabilize an additional positive charge and the surplus spin density by resonance. Thus, after one-electron oxidation, the energy of the Ru(CO) stretch becomes much less sensitive toward the substituents at the other rings. Likewise, hyperfine splitting constants to the 31P nuclei at the ruthenium coordination center are nearly identical to those of oxidized styryl ruthenium complexes [4-RC6H4−CHCH{Ru}]+. Reduction, on the other hand, mainly involves the methylium center with smaller contributions from the attached aryl rings.

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a home-built cylindrical vacuum-tight one-compartment cell. A spiralshaped Pt wire and a Ag wire as the counter and pseudoreference electrodes are sealed into glass capillaries and fixed by Quickfit screws via standard joints. A platinum electrode is introduced as the working electrode through the top port via a Teflon screw cap with a suitable fitting. It is polished with first 1 μm and then 0.25 μm diamond paste before measurements. The cell can be attached to a conventional Schlenk line via a side arm equipped with a Teflon screw valve, allowing experiments to be performed under an argon atmosphere with approximately 5 mL of analyte solution. NBu 4 + [B{C6H3(CF3)2}4]− (0.1 mM) was used as the supporting electrolyte. Referencing was done with addition of an appropriate amount of ferrocene (Cp2Fe) as an internal standard to the analyte solution after all data of interest had been acquired. Representative sets of scans were repeated with the added standard. Electrochemical data were acquired with a computer-controlled BASi CV50 potentiostat. The optically transparent thin-layer electrochemical (OTTLE) cell was home-built and followed the design of Hartl et al.26 It comprised a Pt working and counter electrode and a thin silver wire as a pseudoreference electrode sandwiched between two CaF2 windows of a conventional liquid IR cell. The working electrode was positioned in the center of the spectrometer beam. Mass spectra were recorded on a Bruker micrOTOF II instrument. Quantum Chemical Calculations. The ground state electronic structures were calculated by density functional theory (DFT) methods using the Gaussian 09 program package.39 For computational time to be reduced to a reasonable limit, PiPr3 ligands were replaced by PMe3. Open shell systems were calculated by the unrestricted Kohn− Sham approach (UKS). Geometry optimization followed by vibrational analysis was made either in vacuum or in solvent media. The quasirelativistic Wood−Boring small-core pseudopotentials (MWB)40 and the corresponding optimized set of basis functions for Ru41 and 631G(d) polarized double-ζ basis sets42 for the remaining atoms were employed together with the Perdew, Burke, Ernzerhof exchange and correlation functional (PBE0).43 Solvent effects were described by the polarizable conductor continuum model (PCM) with standard parameters for 1,2-dichloroethane.44 Further DFT calculations were performed with the TURBOMOLE program package (version 6.5)45 using the PBE0 exchange-correlation functional43 with the def2-TZVP basis set.46 Tests with the larger def-TZVP basis set showed only minor changes. Solvent effects were treated by the COSMO-RS model.47 Synthesis, characterization details can be found in the Supporting Information, and NMR spectra of precursors 1a−5a and 1b−5b are given in Figures S1−S24. Ethynylated tritylium dyes 3c+−5c+ were only generated in situ and directly converted to the corresponding complexes. [4-Ethynyl-4′-methoxytriphenylmethylium]+ [BArF]− (1c+). To a stirred solution of [H(Et2O)2]+ tetrakis[{3,5-bis(trifluoromethyl)phenyl}borate]− (475 mg, 0.46 mmol, 1.0 equiv) in 5 mL of dry diethyl ether was slowly added a solution of 4-trimethylsilylethynyl-4′methoxytriphenylmethanol (144 mg, 0.46 mmol, 1.0 equiv) in 10 mL of dry diethyl ether. After stirring the resulting red solution for 15 min, the solvent was removed, yielding [4-ethynyl-4′-methoxytriphenylmethylium]+ [BArF]− in quantitative yield (533 mg). 1H NMR (400 MHz, CDCl3): δ 7.99−7.95 (m, 1H, Har), 7.77−7.75 (m, 2H, Har), 7.70−7.64 (m, 12H, Har, HBArF), 7.48 (s, 4H, HBArF), 7.43−7.41 (m, 4H, Har), 7.21−7.17 (m, 2H, Har), 4.06 (s, 3H, H9), 3.69 (s, 1H, H1) ppm. 19F NMR (377 MHz, CDCl3): δ −62.5 ppm.

EXPERIMENTAL SECTION

Materials and Methods. All manipulations were carried out at room temperature under a nitrogen atmosphere using standard Schlenk techniques, unless stated otherwise. Solvents were predried, distilled by standard procedures, and degassed by saturation with nitrogen prior to use. The starting materials HRu(CO)Cl(PiPr3)2,20a 4-(trimethylsilylethynyl)benzophenone,15 4-trimethylsilylethynyl-benzoic acid methyl ester,36 and 4-dimethylamino-benzoic acid methyl ester37 were prepared by the procedures described in the literature. The syntheses of the carbinols and the trimethylsilyl-protected alkynes can be found in the Supporting Information. All other chemicals were obtained from commercial sources and used without further purification. 1H NMR (400 MHz), 13C{1H} NMR (101 MHz), and 31 1 P{ H} NMR (162 MHz) spectra were measured on a Bruker Avance III 400 spectrometer as CD2Cl2 solutions at room temperature or in the solvent indicated. The spectra were referenced to the residual protonated solvent (1H) or the solvent signal (13C). For the sake of clarity, the 13 C NMR resonances of the tetrakis[{3,5-bis(trifluoromethyl)phenyl}borate]− anion are reported separately. 13 C{1H} NMR (152 MHz, CD2Cl2): δ 162.4 (1:1:1:1 pattern, 1JB−C = 50.3 Hz, Cipso), 135.4 (Cortho), 129.6 (q, 2JF−C = 31.6 Hz, Cmeta), 126.1 (CCF3), 118.1 (Cpara) ppm. FT-IR spectra were recorded on a Thermo iS10 instrument. UV/vis/NIR spectra were recorded on a TIDAS fiber optic diode array spectrometer (combined MCS UV/ NIR and PGS NIR instrumentation) from J&M in HELLMA quartz cuvettes with 0.1 cm optical path lengths. Electron paramagnetic resonance (EPR) experiments were performed on a MiniScope MS 400 table-top X-band spectrometer from Magnettech. Simulation of the experimental EPR spectra was performed with the MATLAB EasySpin program.38 All electrochemical experiments were executed in H


Article

Organometallics [4-{Ru(CO)Cl(PiPr3)2(CHCH)}-4′-methoxy-triphenylmethylium]+ [BArF]− (1+). Compound 1b (90 mg, 0.08 mmol. 1.0 equiv) was dissolved in 29 mL of dry benzene and stirred over molecular sieves (4 Å) for 5 min. 1,8-Bis(dimethylamino)naphthalene (proton sponge; 5.1 mg, 0.02 mmol, 0.25 equiv) was added to neutralize excess acid, and the red solution was stirred for 90 min. Addition of HRu(CO)Cl(PiPr3)2 (37.8 mg, 0.08 mmol, 1.0 equiv) led to an immediate color change from red to green. The reaction was completed by stirring for 60 min. After removing the solvent and washing four times with 5 mL of n-hexane, 1+ was obtained in 46% yield (61 mg). 1H NMR (400 MHz, C6D6): δ 13.20 (d, 3JH−H = 13.0 Hz, 1H, H1), 8.37 (s, 8H, HBArF), 7.66 (s,4H, HBArF), 7.00−6,94 (m, 4H, Har), 6.92−6.87 (m, 1H, Har), 6.81−6.74 (m, 5H, Har), 6.54−6.50 (m, 1H, Har), 6.48−6.44 (m, 2H, Har, H2), 3.19 (s, 3H, H15), 2.51−2.39 (m, 6H, H17), 1.03− 0.93 (m, 36H, H18) ppm. 13C{1H} NMR (101 MHz, CD2Cl2): δ 203.9 (C ≡ O), 183.1 (C1), 178.8 (C16), 166.9 (C14), 144.9 (C7) 140.8 (C3), 139.2 (C2), 138.6 (C12), 135.8 (C5), 135.5 (C6), 135.4 (C4), 134.6 (C11), 132.3 (C10), 130.8 (C8), 123.8 (C9), 115.8 (C13), 56.8 (C15), 25.7 (C17), 20.0 (C18) ppm. 31P{1H} NMR (162 MHz, C6D6): δ 47.5 ppm. 19F{1H} NMR (377 MHz, C6D6): δ −62.9 ppm. MS (ESI[+], MeOH): calcd for 1+-Cl−-PiPr3 + CH3O− = 619.1922, found 619.1979; calcd for 1+-Cl− + CH3O− = 779.3267, found 779.3287.

3c+ (73 mg, 0.06 mmol, 1.0 equiv), and the resulting green solution was stirred for 30 min. The residue left after solvent removal was washed with n-hexane, yielding 3+ in 71% yield (70 mg). 1H NMR (400 MHz, CD2Cl2): δ 10.72 (d, 3JH−H = 13.2 Hz, 1H, H1), 7.72 (s, 8H, HBArF), 7.77−7.70 (m, 3H, H9,H10), 7.58 (d, 3JH−H = 7.5 Hz, 2H, H5), 7.55 (s, 4H, HBArF), 7.36 (d, 3JH−H = 7.5 Hz, 2H, H4), 7.28 (d, 3 JH−H = 8.6 Hz, 2H, H13), 7.19 (d, 3JH−H = 8.6 Hz, 2H, H12), 6.97 (d, 3 JH−H = 9.5 Hz, 2H, H8), 6.50 (d, 3JH−H = 13.2 Hz 1H, H2), 3.36 (s, 6H, H15), 2.83−2.74 (m, 6H, H17), 1.33−1.25 (m, 36H, H18) ppm. 13 C{1H} NMR (101 MHz, CD2Cl2): δ 179.3 (C16), 177.3 (C1), 143.0 (C7), 141.4 (C3), 157.3 (C14), 138.5 (C13), 137.5 (C5), 134.9 (C8), 134.7 (C2), 133.9 (C11), 133.7 (C6), 132.6 (C10), 124.2 (C12), 123.6 (C4), 41.1 (C15), 24.7 (C17), 19.7 (C18) ppm. The resonance signal of the CO ligand could not be detected. 31P{1H} NMR (162 MHz, CD2Cl2): δ 41.3 ppm. 19F{1H} NMR (377 MHz, CD2Cl2): δ −62.9 ppm.

[4-{Ru(CO)Cl(PiPr3)2(CHCH)}-4′,4″-bis-dimethylamino-triphenylmethylium]+ [BArF]− (4+). A Schlenk tube was charged with molecular sieves (4 Å) and 1,8-bis(dimethylamino)naphthalene (11.2 mg, 0.06 mmol, 0.4 equiv) dissolved in dry benzene. Alkyne 4c+ (200 mg, 0.16 mmol, 1.0 equiv) in benzene was added, and the resulting solution was stirred for 5 min. Then, HRu(CO)Cl(PiPr3)2 (90.0 mg, 0.19 mmol, 1.1 equiv) was added, causing the solution to turn intensely dark blue. The solvent was removed, and the residue was washed three times with 10 mL aliquots of n-hexane to provide complex 4+ in 52% yield (138 mg) as a blue solid. 1H NMR (600 MHz, CD2Cl2): δ 10.05 (d, 3JH−H = 13.5 Hz, 1H, H1), 7.77−7.68 (m, 8H, HBArF), 7.56 (s, 4H, HBArF), 7.40 (d, 3JH−H = 9.0 Hz, 4H, H8), 7.24 (d, 3JH−H = 8.3 Hz, 2H, H5), 7.20 (d, 3JH−H = 8.3 Hz, 2H, H4), 6.85 (d, 3JH−H = 9.0 Hz, 4H, H9), 6.36 (d, 3JH−H = 13.5 Hz, 1H, H2), 3.23 (s, 12H, H11), 2.83−2.72 (m, 6H, H13), 1.33−1.27 (m, 36H, H14). 13 C{1H} NMR (CD2Cl2, 151 MHz): δ 202.6 (C15), 179.6 (C12), 174.4 (t, 3JH−P = 10.2 Hz, C1), 156.9 (C10), 144.0 (C3), 141.0 (C8), 138.3 (C5), 135.4 (C2), 134.5 (C6), 127.7 (C7), 124.2 (C4), 113.2 (C9), 41.0 (C11), 25.3 (C13), 20.3, 19.9 (C14) ppm. 31P{1H} NMR (CD2Cl2, 243 MHz): δ 40.01 ppm. MS (ESI[+], MeOH): calcd for 42+-Cl− = 402.1928, found 402.1958; calcd for 4+-Cl− + HCOO− = 849.3834, found 849.3915.

[4-{Ru(CO)Cl(PiPr3)2(CHCH)}-4′4″-dimethoxy-triphenylmethylium]+ [BArF]− (2+). To a stirred solution of 2c+ (88.7 mg, 0.07 mmol, 1.0 equiv) in 20 mL of dry benzene were added 1,8-bis(dimethylamino)naphthalene (5.6 mg, 0.03 mmol, 0.4 equiv) and molecular sieves (4 Å), and the mixture was stirred for 5 min. Upon addition of HRu(CO)Cl(PiPr3)2 (36.3 mg, 0.07 mmol, 1.0 equiv), the color of the solution turned from red to intense green. The solvent was removed, and the resulting solid was washed seven times with 4 mL aliquots of n-hexane to yield 2+ in 43% yield (54 mg). 1H NMR (400 MHz, CD2Cl2): δ 12.32 (d, 3JH−H = 13.2 Hz, 1H, H1), 8.34 (s, 8H, HBArF), 7.63 (s, 4H, HBArF), 7.50−7.40 (m, 6H, H5, H8), 7.27−7.20 (m, 2H, H4), 7.13−7.08 (m, 4H, H9), 6.67 (d, 3JH−H = 13.2 Hz 1H, H2), 3.20 (s, 6H, H11), 2.55−2.43 (m, 6H, H13), 1.07−0.97 (m, 36H, H14) ppm. 13C{1H} NMR (101 MHz, CD2Cl2): δ 200.2 (C ≡ O), 183.3 (C1), 181.9 (C12), 167.5 (C10), 145.6 (C3), 142.2 (C5), 139.8 (C8), 137.1 (C2), 135.3 (C6), 133.2 (C7), 126.6 (C4), 115.8 (C9), 56.7 (C11), 25.7 (C13), 20.3 (C14) ppm. 31P{1H} NMR (162 MHz, CD2Cl2): δ 45.0 ppm. 19F{1H} NMR (377 MHz, CD2Cl2): δ −62.9 ppm. MS (ESI[+], MeOH): calcd for 2+-Cl−-PiPr3 + CH3O− = 649.1992, found 649.2081; calcd for 2+-Cl− + CH3O− = 809.3445, found 809.3360.

[4,4′-Bis-{Ru(CO)Cl(PiPr3)2(CHCH)}-4″-dimethylamino-triphenylmethylium]+ [BArF]− (5+). 1,8-Bis(dimethylamino)naphthalene (35 mg, 0.16 mmol, 0.3 equiv) was added to a solution of 5c+ (830 mg, 0.62 mmol. 1.0 equiv) in 18 mL of dry diethyl ether. After the addition of molecular sieves (4 Å), the reaction was stirred for 5 min. Then, a solution of HRu(CO)Cl(PiPr3)2 (602 mg, 1.48 mmol, 2.05 equiv) in dichloromethane was added dropwise, upon which the solution color changed instantaneously to dark green. After 10 min, the solvent was

4-[{Ru(CO)Cl(PiPr3)2(CHCH)}-4′-dimethylamino-triphenylmethylium]+ [BArF]− (3+). To a solution of HRu(CO)Cl(PiPr3)2 (33.2 mg, 0.07 mmol, 1.1 equiv) in dry dichloromethane was added alkyne I


Article

Organometallics removed, and the green crude product was washed with n-hexane yielding 5+ as a green solid in 93% (1.26 g). 1H NMR (CD2Cl2, 400 MHz): δ 10.32 (d, 3JH−H = 13.5 Hz, 1H, H1), 7.79−7.67 (m, 8H, HBArF), 7.56 (s, 4H, HBArF), 7.48 (d, 3JH−H = 9.1 Hz, 2H, H8), 7.28 (d, 3 JH−H = 8.3 Hz, 4H, H5), 7.19 (d, 3JH−H = 8.3 Hz, 4H, H4), 6.87 (d, 3 JH−H = 9.1 Hz, 2H, H9), 6.42 (d, 3JH−H = 13.5 Hz, 1H, H2), 3.27 (s, 6H, H11), 2.87−2.70 (m, 6H, H13), 1.52−1.12 (m, 72H, H14) ppm. 13 C{1H} NMR (CD2Cl2, 101 MHz): δ 202.4 (C ≡ O), 179.5 (C12), 179.0 (t, 3JH−P = 10.0 Hz, C1), 157.7 (C10) 142.0 (C8), 141.0 (C3), 138.7 (C5), 135.4 (C2), 128.8 (C7), 126.5 (C6), 124.8 (C4), 114.1 (C9), 41.3 (C11), 25.3 (C13), 20.3 (C14) ppm. 31P{1H} NMR (CD2Cl2, 162 MHz): δ 40.42 ppm. MS (ESI[+], MeOH): calcd for 5+ = 1306.4698, found 1306.4592.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.7b00194. Synthesis and characterization of the carbinols and the ethynylated trityium dyes; figures displaying NMR spectra, cyclic voltammograms, and the outcomes of IR and UV/Vis/NIR spectroelectrochemical and EPR studies; and details of the quantum chemical calculations, including charge and spin density distributions in the various oxidation states and displays of crucial frontier MOs of full models of complexes 1+−4+ (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Rainer F. Winter: 0000-0001-8381-0647 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work is dedicated to Walter Frank on the occasion of his 60th birthday. We greatly appreciate financial support of this work by Deutsche Forschungsgemeinschaft (DFG) (Grant Wi1262/9-2) and the DFG and the State of BadenWürttemberg for providing us with access to the computational facilities of the bw_For network (JUSTUS HPC Facility, University of Ulm). We also thank Denis Runge and Eva Schiebel for their contributions during advanced student’s laboratories and Alexander Klaiber for his help with the recording of mass spectra.

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REFERENCES

(1) (a) Kern, A.; Caro, H. Manufacture of dye-stuff, US 290856, 1883. (b) Kern, A. Manufacture of purple dye-stuff, US 290892, 1883. J


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