Dipolar Sesquifulvalene Compounds with (Tetraaryl-Î·4

Article pubs.acs.org/Organometallics

Dipolar Sesquifulvalene Compounds with (Tetraaryl‑η4‑cyclobutadiene)(η5- cyclopentadienediyl)cobalt(I) Complex Units as Electron Donors Sven Dabek,† Marc Heinrich Prosenc,*,‡ and Jürgen Heck*,§ †

Deutsches Patentamt München, Zweibrückenstraße 12, 80331 München, Germany Fachbereich Chemie, Technische Universität Kaiserslautern, Erwin-Schrödinger-Straße 52, 67663 Kaiserslautern, Germany § Fachbereich Chemie, Universität Hamburg, Martin-Luther-King-Platz 6, 20146 Hamburg, Germany ‡

S Supporting Information *

ABSTRACT: Mononuclear monohydro sequifulvalene complexes of cobalt and their vinylogous derivatives [(Ar4CBD)Co(Cp-Z-C7H7)] (Ar4CBD = C4Ar4; Ar = p-X-C6H4; X = H, Z = − (4); X = H, −C2H2− (9a); X = Cl, Z = −C2H2− (9b); X = Me, Z = −C2H2− (9c); X = OMe, Z = −C2H2− (9d); X = NMe2, Z = −C2H2− (9e); X = H, Z = −(C2H2)2− (10); X = H, Z = −(C2H2)3− (11)) were synthesized and transformed by hydride abstraction to the corresponding dipolar sesquifulvalene complexes of [(Ar4CBD)Co(Cp-Z-C7H6)]+ (Ar4CBD = C4Ar4; Ar = p-X-C6H4; X = H, Z = − (5); X = H, Z = −C2H2− (12a); X = Cl, Z = −C2H2− (12b); X = Me, Z = −C2H2− (12c); X = H, Z = −(C2H2)2− (13)) featuring a (tetraaryl-η4-cyclobutadiene)(η5-cyclopentadienediyl)cobalt(I) sandwich complex as an electron donor and the cationic tropylium part as an electron acceptor. Hydride abstraction to form the complexes [(Ar4-η4-CBD)Co{(η5-C5H4)Z(C7H6)]+ (Ar = p-C6H4X; X = OMe, NMe2; Z = −C2H2−) and [(Ar4-η4CBD)Co{(η5-C5H4)Z(C7H6)}]+ (Ar = C6H5; Z = −(C2H2)3− (14)) failed and led to decomposition. The mononuclear archetypal sesquifulvalene complex 5 was obtained by nucleophilic addition of the monolithiated complex (Ar4CBD)Co(CpLi) (3) to tropylium cation and subsequent hydride abstraction from the seven-membered ring. The vinylogous derivatives 9a−e, 10, and 11 were prepared by Horner−Wadsworth−Emmons (HWE) reactions of the suitable carbaldehydes (Ar4CBD)Co(Cp-ZCHO) (Z = −(C2H2)n−) with the HWE reagent cyclohepta-1′,3′,5′-trien-1′-ylmethylphosphonate diethyl ester in a phase transfer catalyzed reaction. The donor−acceptor interaction was studied by means of 1H and 13C NMR and UV−vis spectroscopy, cyclic voltammetry, X-ray structure determination, and hyper-Rayleigh scattering (HRS) measurements. For analysis of electronic excitations DFT calculations were performed on the complexes, revealing the cyclobutadiene metal complex fragment to be the donor and the metal complex Cp-bridge-cycloheptatrienylium fragment to be the acceptor.

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INTRODUCTION The concept of employing dipolar organometallic complexes for compounds with nonlinear optical (NLO) properties,1 e.g. second harmonic generation (SHG), has been shown to be very fruitful. In a simplified model, these complexes are commonly composed of an organometallic electron-donating and/or -accepting group connected by a π bridge, which enables electronic communication between them. For organometallic electron-accepting groups carbonyl and nitrosyl complexes were applied2 as well as Fischer-type carbene complexes3 and cationic compounds of organic π ligands.4 The most widely used organometallic donating units are half-sandwich5 and sandwich complexes and in particular ferrocenes and ruthenocenes, due to their inertness and facile synthetic availability of derivatives.6 Isoelectronic with ferrocene are sandwich complexes of the type (η4-cyclobutadiene)(η5cyclopentadienyl)cobalt(I), which are stable in air as well and can be electronically fine-tuned by the aryl substituents at the cyclobutadiene ligand. However, a (η4-cyclobutadiene)(η5cyclopentadienyl)cobalt(I) unit has not been reported as an © 2012 American Chemical Society

electron donor yet in dipolar complexes directed toward NLO properties, except for a short note in a review article.1l In a previous paper we presented a strategy to build up mononuclear and dinuclear sesquifulvalene complexes and vinylogous congeners on the basis of ferrocene and ruthenocene derivatives. These are synthesized straightforwardly by starting with the appropriate cyclopentadienyl carboxaldehyde sandwich complex. Subsequent Horner−Wadsworth−Emmons (HWE) reactions are used to extend the olefinic bridge between the donor and the acceptor of a dipolar sesquifulvalene complex.1l,4h,6e In this paper we present the syntheses, molecular structures, and spectroscopic properties of dipolar mononuclear sesquifulvalene cobalt complexes and their vinylogous derivatives with a (tetraaryl-η4-cyclobutadiene)(η5-cyclopentadiendiyl)cobalt(I) entities as electron-donating groups. Moreover, to fine-tune the electronic properties, the cyclobutadiene ligands are provided Received: July 27, 2012 Published: September 24, 2012 6911

dx.doi.org/10.1021/om300710x | Organometallics 2012, 31, 6911−6925

Organometallics

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demonstrated in Scheme 2, the corresponding tropylium compounds were obtained by hydride abstraction. When the cycloheptatriene compounds were treated with trityl cation, decomposition was observed for 11 with n = 3 and for 9d,e. The instability of 11 with the hexatriene linker between the donor and the acceptor is in agreement with the instability of the corresponding ferrocene derivative.6e The decomposition of 9d,e may be due to an increasing oxidation sensitivity, which ends up in an irreversible (vide infra) oxidation reaction of the (Ar4CBD)CoCp entity. In principle, there are two different paths concerning the mechanism of the hydride abstraction. For easily oxidized complexes such as ferrocenes, the hydride abstraction proceeds presumably via an oxidation of the metal complex first, followed by an intermolecular hydrogen abstraction.12 If the oxidized complex is sufficiently stable, as for ferrocenium cation, it is even possible to isolate and characterize it.1l,13 For complexes with a higher oxidation potential such as ruthenocene or (Ar4CBD)CoCp complexes (Ar = phenyl)14 with less electron releasing aryl substituents (vide infra), the hydride abstraction is assumed to occur directly.12 This mechanism needs more free space around the hydride for abstraction and explains the necessity to isomerize the cycloheptatriene substituent of cobalt complexes, bringing the hydridic function via a 1,5-hydrogen shift13 in a more distant position relative to the ipso carbon atom of the sevenmembered ring. While the hydride abstraction via the redox mechanism mostly needs low temperature to stabilize the radical cation, the direct hydride elimination can be performed at room temperature. Solid-State Structure. For two tropylium compounds (5 and 12c) crystals could be obtained suitable for X-ray structure determination (Figures 2−4). The sesquifulvalene complex 12c crystallizes in the triclinic space group P1̅, and for 5 the monoclinic space group P21/c is found. The molecular structure of complex 12c reveals a disorder in the sesquifulvalene part. Both structures of the complexes 5 and 12c display very similar Co−CCBD distances (1.987(2)− 2.013(2) Å for 5 and 1.982(6)−2.002(6) Å for 12c). The Co−C distances of the CBD part are distinctly shorter than for the cobalt−cyclopentadienyl coordination (2.053(3)−2.095(3) Å for 5 and 2.000(10)−2.083(8) A for 12c) (Table 1). The structural data of the sandwich core of 5 and 12c are quite comparable to those of other molecular structures of (η4cyclobutadiene)(η5-cyclopentadienyl)cobalt(I) complexes reported in the literature.15−18 The difference in Co−C bond lengths suggests a stronger cobalt bonding to the C4-ring than

with four aryl substituents whose para position is modified by different groups X (Figure 1).

Figure 1. Mononuclear sesquifulvalene complexes of (tetraaryl-η4cyclobutadiene)(η5-cyclopentadienediyl)cobalt(I) units and vinylogous derivatives as target compounds.

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RESULTS AND DISCUSSION Synthesis. From earlier work it was known that a direct coupling between a five- and seven-membered ring receiving an archetypal sesquifulvalene ligand is successful, when the metallocene is monometalated and acts as a nucleophile upon addition to the tropylium ring.1l,6e Since an application of a direct monometalation of the Cp ring in 1 by organolithium compounds failed, a chloromercuration reaction was performed first to obtain the monomercurated complex 2.7 After a mercury−lithium exchange reaction the lithiated complex 3 was subjected to a nucleophilic addition on tropylium hexafluorophosphate (Scheme 1). The product yielded the cycloheptatrienyl-substituted complex 4 contaminated with 10% of the starting material 1, which could not be separated from the desired compound 4 by means of recrystallization or column chromatography. However, the formation of the compound 5 as a salt allows an easy separation, due to different solubilities of the neutral, weakly polar complex 1 in comparison to the salt of 5. Former results indicate that a hydride abstraction is more easily performed from the seven-membered ring to form the tropylium compound 5, when the cycloheptatriene is linked to the Cp ligand through an sp2 carbon atom.8 Hence, compound 4 was heated in mesitylene, to induce isomerization via a 1,5hydrogen migration.9 The synthesis of the vinyloguous sesquifulvalene complexes was performed by reaction of the appropriate carbaldehyde10 with the HWE reagent cycloheptatrienylmethyl phosphonate diethyl ester6e in a phase transfer catalysis11 (Scheme 2). As

Scheme 1. Synthesis of the Archetypal Sesquifulvalene Complex 5 with (Ar4CBD)(Cp)Co as the Electron-Donating Complex

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Scheme 2. Synthesis of Dipolar, Mononuclear, Vinylogous Sesquifulvalene Complexes with a (Ar4CBD)Co(Cp) Unit As Electron Donor

reason for the relatively small tilt angle of about 20° for the aryl substituent C10−C15 of derivative 5 (see Figure 3) may be caused by the steric demand of the tropylium substituent, which is tilted only about 14° relative to the best plane of the Cp ligand and is placed in an almost van der Waals contact with this aryl substituent (compare Table 2). It is interesting to note that the crystal packing of compound 12c forms a layered structure, wherein the sesquifulvalene moieties of one layer of molecules is facing the sesquifulvalene parts of another layer of molecules. The same holds true for the cyclobutadiene entity (Figure 5). Spectroscopic and Electrochemical Properties of the Tropylium Compounds. All sandwich compounds under study have been characterized by 1 H and 13 C NMR spectroscopy. The assignment of the resonance signals has been done by means of one- and two-dimensional NMR spectroscopy. For the neutral monohydro sesquifulvalene complexes 4, 9a−e, 10, and 11 the proton resonance signals of the sevenmembered ring appear in the range of 5.2−7.3 ppm and the signals of the Cp protons in the range of 4.58−4.72 ppm (Table 3). The corresponding two shift ranges are found for the 13C signals (Table 4). The resonance signals of the hydrogenbearing carbon nuclei of these neutral compounds range from 80 to 85 ppm for the Cp ligands and from 122 to 131 ppm for the cycloheptatriene moiety, respectively. A distinct highfrequency shift of all of these signals is observed upon hydride abstraction, which is caused by the positive charge of the cationic tropylium unit. The signals of the Cp protons shift about 1 ppm to higher frequency. The degree of high-frequency shift Δδ of the Cp protons depends on the conjugation length of the π linker between donor and acceptor: i.e., for n = 0, Δδ = ∼1 ppm, for n = 1, Δδ = 0.7 ppm, and for n = 2, Δδ = ∼0.5 ppm (Table 3). The tendency of decreasing interaction upon increasing conjugation lengths is also verified by 13C NMR results (Table 4). Even on the 13C resonance signal of the CBD ligand a small effect of the conjugation length can be considered for the sesquifulvalene cation. The shift of the

Figure 2. Molecular structure of the archetypal sesquifuvalene complex 5. The counterion and the hydrogen atoms are omitted for clarity.

to the C5-ring ligand, which is in agreement with theoretical calculations.10,19,20 In contrast, the distance between the Co atom and the centroid Xcp of the five-membered ring is slightly reduced (1.684 Å for 5 and 1.683 and 1.682 Å for 12c) compared to the distance between the Co atom and the centroid of the C4-ring (1.704 Å for 5 and 1.683 12c, respectively) (Table 2). Due to the larger ring size, the fivemembered ring immerses better into the coordination sphere of the Co center than the four-membered ring. The aryl substituents of the cyclobutadiene ligands in 5 and 12c are all tilted in the ranges of 22.7−64.7 and 23.2−51.8°, respectively, relative to the plane of the four-membered ring, and form a four-bladed propeller as found for other arylated η4cyclobutadiene ligands in Co complexes (Figure 2).10,15,18 The 6913


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Figure 3. Top view of the molecular structure of the archetypal sesquifulvalene complex 5, illustrating the relative position of the tropylium ring and the obverse arene substituent. The remaining arene substituents, the counterion, and hydrogen atoms are omitted for clarity.

Figure 4. Molecular structure of 12c. The counterion and the hydrogen atoms are omitted for clarity. Note the disorder in the sesquifulvalene part!

electronic arrangement of the ground state has to be taken into account in the order Me > H > Cl, indicating a slight decrease of electron-donating capability in this order, which is in agreement with the order of the Hammett parameters σp (Table 5).21 A comparable behavior is found for the redox activity. The cyclic voltammograms of the cationic tropylium compounds reveal an electrochemically irreversible oxidation and an irreversible reduction step. The oxidation occurs in the characteristic range for (tetraaryl-η4 -cyclobutadiene)(η 5cyclopentadienyl)cobalt(I) complexes10,22,23 and illustrates an influence of the aryl substituents X, as is observed for the corresponding carbonyl complexes 6a−e.10 The change of X = Me to X = Cl induces an anodic shift of the oxidation potential of about 220 mV, due to the −I effect of the Cl and the +I hyperconjugative influence of the methyl group. As a result of the increasing conjugation length between the electron-donating complex entity and the electron-accepting tropylium fragment in the complexes 5, 12a and 13 the electronic interaction decreases in this order. The potential gap

protons of the seven-membered ring amounts to 7.9−8.6 ppm. A high-frequency shift of more than 20 ppm in comparison to the neutral complexes is induced by the positive charge for the signals of the 13C nuclei of the cationic species. As for sesquifulvalenes themselves, the bonding situation in their vinylogous derivatives can in principle be described in terms of two mesomeric forms: the bis-aromatic form A and the cross-conjugated form B, which is composed of a η6-fulvene complex and a cycloheptatriene moiety (Figure 6). In order to get a deeper insight into the electronic effects of the aryl substituents X on the ground-state electronic arrangement, the 1 H41−1H42 coupling constants across the C41−C42 bond linking the five- and seven-membered rings of the vinylogous sesquifulvalene unit have been determined, since the proton coupling constant 3J(1H41−1H42) increases as the C41−C42 bond order increases.4g From Table 5 a subtle change of 3 1 J( H41−1H42) can be found in the order X = Cl > H > Me, which goes along with the corresponding Hammett parameter σp.21 Considering the two limiting mesomeric forms A and B (Figure 6), a small contribution of the mesomeric form B to the 6914


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Table 1. Selected Bond Lengths (Å) of the Tropylium Complexes 5 and 12ca 5

12c

Cp ring

exptl

DFT

exptl (A)

exptl (B)

DFT

13 DFT

Co−C(1) Co−C(2) Co−C(3) Co−C(4) Co−C(5) C(6)−C(10) C(7)−C(16) C(8)−C(22) C(9)−C(28) Co−C(6) Co−C(7) Co−C(8) Co−C(9) C(34)−C(35) C(34)−C(40) C(35)−C(36) C(36)−C(37) C(37)−C(38) C(38)−C(39) C(39)−C(40)

2.073(2) 2.095(3) 2.092(3) 2.077(3) 2.053(3) 1.465(3) 1.471(3) 1.479(3) 1.477(3) 2.013(2) 1.987(2) 1.988(2) 1.990(2) 1.415(4) 1.411(4) 1.374(4) 1.406(5) 1.354(6) 1.400(5) 1.369(4)

2.1352 2.1160 2.1343 2.1363 2.1114 1.4640 1.4641 1.4656 1.4639 2.0098 2.0125 1.9974 2.0025 1.4238 1.4238 1.3717 1.4120 1.3692 1.4118 1.3718

1.999(8) 2.016(9) 2.109(8) 2.148(8) 2.083(8)

2.062(8) 2.074(9) 2.081(8) 2.083(8) 2.046(8)

2.1244 2.1150 2.1412 2.1167 2.1291 1.449 1.4584 1.4680 1.4678 1.9867 2.0057 2.0140 2.0282 1.4310 1.4304 1.3673 1.4178 1.3647 1.4191 1.3663

2.1416 2.1161 2.1268 2.1278 2.1162 1.467 1.4608 1.4653 1.4607 1.9899 2.0049 2.0143 2.0191 1.4315 1.4332 1.3654 1.4202 1.3631 1.4215 1.3647

1.448(9) 1.464(9) 1.458(9) 1.480(9) 1.991(6) 2.002(6) 1.991(7) 1.982(6) 1.457(7) 1.430(7) 1.368(11) 1.151(13) 1.546(6) 1.578(9) 1.542(8)

1.457(2) 1.368(2) 1.557(3) 1.328(4) 1.557(3) 1.587(3) 1.352(2)

a The notations A and B define the two disordered fragments in the asymmetric unit. The errors for 12c correspond to a restraint to the distances of the other disordered fragment (see also the Experimental Section).

Table 2. Selected Interatomic Distances (Å) and Angles (deg) of the Tropylium Complexes 5 and 12ca 5 CBD(6−9)/Ph(16−21)b CBD(6−9)/Ph(22−27)b CBD(6−9)/Ph(28−33)b Cp(1−5)/CBD(6−9)b Cp(1−5)/Trop(34−40)b XCp−C(1)−C(34)c XTrop−C(34)−C(1)c XCp−C(1)−C(41)c XTrop−C(34)−C(42)c Co−Cp(1−5)b Co−CBD(6−9)b XPh(10−15)−XTropc XPh(10−15)−C(34)c C(10)−C(34) XPh(16−21)−C(41)c XPh(16−21)−C(42)c C(16)−C(34)

22.70 39.80 31.30 64.70 6.50 13.90 175.20 179.60

1.689 1.704 3.975 4.159 3.721

12c (A)

12c (B) 33.40 23.20 51.80 36.00

177.00

177.50

175.00 177.50 1.683

177.50 178.30 1.682 1.697

Figure 5. Crystal packing of 12c.

fragment orbital. The major contribution to the LUMO comes from a C5 bridge−C7 π fragment orbital. In the HOMO the C4 ring and two of the phenyl π orbitals dominate together with a Co dxz orbital. The C5 bridge−C7 π orbitals have also significant coefficients in the HOMO, which is in accord with the electrochemical studies which revealed the oxidation as well as the reduction to be dependent on the length of the bridge between the five- and seven-membered rings. Along these lines are the electrochemical data for complexes 12a−c, in which the shift of the oxidation potential is within the expected direction of electronic influence of the phenyl substituents, which is 220 mV for the oxidation and only about 40 mV for the reduction potential. Electronic Excitation. The most remarkable feature during the synthesis of the dipolar mononuclear tropylium complexes is the dramatic change of color upon hydride abstraction. In all

3.774 3.770 3.328

a The notations A and B define the disordered fragments within the asymmetric unit. bAngles between the best planes of CBD, Cp, phenyl, and tropylium. cX = centroid of the corresponding cycle: XCp = centroid of the C5-ring ligand; XCBD = centroid of the C4-ring ligand; Xtrop = centroid of the tropylium ring.

for 13 is found to be about ∼480 mV smaller than observed for 5 (Table 6, Figure7) Calculation of the molecular orbitals of the complexes revealed the frontier orbitals depicted in Figure 8. The LUMO results from a combination of a Co dz2 type orbital with the z axis in the equatorial plane spanned by the C4 and C5 ring ligands and a small contribution of a nonbonding C4 ring π 6915


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Table 3. 1H NMR Shifts of the Cyclopentadienyl Signals of the Neutral Cycloheptatriene and Cationic Tropylium Compounds cycloheptatrienea c

d

n

X =H

0

4.63 4.86 4.66 4.72 4.67 4.69 4.67 4.70

1 2 3 a

X = Cl

X = Me

4.65 4.71

tropyliumb X = OMe

4.64 4.67

X = NMe2

X=H

X = Cl

X = Me

4.58 4.64

5.62 5.88 5.36 5.42 5.16 5.25

5.36 5.46

5.35 5.39

4.63 4.68

Measured in dichloromethane-d2. bMeasured in nitromethane-d3. cn = number of C−C double bonds between the five- and seven-membered ring. X = substituent in para position of the aryl group.

d

Table 4. 13C NMR Shifts of the Cyclopentadienyl Signals of the Neutral Cycloheptatriene and Cationic Tropylium Compounds cycloheptatrienea Cp nc

Xd = H

0

79.7 85.2 80.9 85.3 81.3 84.9

1 2 a

X = Cl

tropyliumb CBD

X = Me

X=H

X = Cl

Cp X = Me

75.6 81.1 85.2

80.6 84.8

75.9

74.7

75.4

76.0

X=H 85.8 94.5 85.9 91.7 85.1 90.6

X = Cl

CBD X = Me

X=H

X = Cl

X = Me

78.9

80.9

82.2 86.1 92.2

85.9 92.1

80.6 79.8

Measured in dichloromethane-d2. bMeasured in nitromethane-d3. cn = number of C−C double bonds between the five- and seven-membered rings. X = substituent in para position of the aryl group.

d

Figure 6. Bis-aromatic (A) and cross-conjugated (B) mesomeric forms of the dipolar mononuclear vinylogous sesquifulvalene derivatives of (η4-cyclobutadiene)(η5-cyclopentadienyl)cobalt(I).

Table 5. Correlation between the 1H NMR Coupling Constants and the σp Values of the Aryl Substituents X 12aa 12ba 12ca a

X

σpb

H Cl CH3

0 0.23 −0.17

3

Figure 7. Cyclic voltammograms of the tropylium compounds 5, 12a, and 13.

J (Hz) 15.48 15.63 15.14

hexafluoridophosphate is added to a solution of the cycloheptatriene compounds. The color change is in accord with a strong increase of the donor−acceptor interaction.4a,6c The enhancement of the electronic communication between electron donor and acceptor can be observed in UV−vis studies, which were performed with solutions of different solvent polarities, i.e. dichloromethane and nitromethane, to

In CD2Cl2. bσp values from ref 21.

cases the color immediately changes from orange-red to dark blue or green, when the light yellow solution of trityl

Table 6. Cyclic Voltammetric Data of the Tropylium-Substituted (Tetraaryl-η4-cyclobutadiene)(η5-cyclopentadiendiyl)cobalt(I) Complexes compd

X

n

σpb

Epa (mV)c,e

Epc (mV)c,f

ΔE (mV)d

ΔE(LUMO−HOMO) (hartree)

5 12a 13 12b 12c

H H H Cl CH3

0 1 2 1 1

0 0 0 0.23 −0.17

841 626 535 781 558

−779 −660 −611 −635 −678

1620 1286 1146 1416 1236

0.076 0.067 0.060 0.064

Scan rate 200 mV s−1. bσp values from ref 21. cCondtions: vs FcH/FcH+ in MeNO2, 0.4 M [n-Bu4N][PF6], room temperature, reference electrode Ag/AgCl. dΔE = Epa − Epc. eIrreversible oxidation. fIrreversible reduction.

a

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Figure 10 displays the influence of the conjugation length n between the donor and the acceptor: with the increase of the conjugation length n, the absorption maxima shift to lower wavelength. Remarkably, the extinction coefficient ε of the lowenergy absorption grows with the extent of the bathochromic shift, which is in accord with the results from the solvatochromic measurements. The ratio of charge localization (dipole) and delocalization in the excited state would lead to an increased transition dipole moment and thus to a higher extinction coefficient. In accordance with the results of others27 and from our results28 with a ferrocene and ruthenocene moiety and in particular with our MO calculations (vide supra) of the (Ar4CBD)CoCp complexes as the electron donor, the highenergy absorption band is assigned to a metal-donor-ligand to acceptor charge-transfer (DL-A CT) transition, whereas the low-energy absorption band is caused by a cyclobutadienemetal-donor to acceptor charge-transfer (DM-A CT) transition. An experimental indication for the assignment of the highenergy absorption band to the DL-A CT band is the influence of the conjugation length on the solvatochromic effect, which almost doubles on going from the archetypal sesquifulvalene complex 5 (Δν = −689 cm−1) to the butadiene-bridged derivative 13 (Δν = −1357 cm−1), since the polarizability is increased with growing conjugation length of the π-bonding system, whereas the low-energy CT absorption reveals a change of Δν = −1139 cm−1 for 5 and Δν = −1526 cm−1 for 13. A comparison of the positions of the absorption maxima for the cobalt sandwich compounds illustrates a weak dependence of λmax on the electron-releasing capability of the aryl substituent X (Figure 10). However, a closer look at the UV−vis spectroscopic data (Table 7) discloses that the absorption coefficient of the low-energy absorption band is considerably stronger for the Co species in comparison to the Fe congeners. The extinction coefficient of the long-wavelength absorption of the chromophore 13 exceeds that of the corresponding Fe complex by a factor of 2.6e This must have a strong influence on the first hyperpolarizability β, since the electronic transition moment directly depends on the absorption coefficient and, according to the two-level model, the first hyperpolarizability β is proportional to the square of the electronic transition moment. To reveal information on the character of electronic excitations, we performed calculations on the density functional level of theory on optimized structures in the gas phase (see below). The resulting calculated excitations are in good agreement with the experimental data and are given in Table 7. For interpretation a natural transition orbital analysis was performed,38 revealing orbitals depicted in Figure 10 for the low-energy and Figure 11 for the high-energy transition. While for the low-energy transition an almost pure one natural orbital to one natural orbital transition is found, the high-energy transition consists of two transitions with contributions of 83% and 11% (Figure 11). Some conclusions can be drawn from the calculations. In the low-energy transition the cyclobutadiene ligand as well as the metal center and the C5 bridge−C7 fragment contribute to the hole of the transition, while the particle is mainly located on the acceptor site with small contributions of the metal center and cyclobutadiene ligand. Upon extension of the bridge the hole appears to be more localized on the metal complex site while the particle remains from the metal center to the acceptor fragment. A strong

Figure 8. LUMO (top) and HOMO (bottom) of complex 12c.

elucidate solvatochromism, which gives a clue to the dipole change Δμ between the ground and excited states upon electronic excitation24 and is thus relevant for the first hyperpolarizability β according to the two-level approximation.25 The UV−vis spectra of the complexes under study contain two strong absorption bands in the visible and near-UV region, which are characteristic for dipolar sandwich complexes bearing NLO chromophores. The solvatochromism of the cobalt complexes is negative and is quite similar to those found for the corresponding ferrocene derivatives (Figure 9, Table 7).6c This implies the positive charge to be mainly localized on the seven-membered ring in the electronic ground state, whereas it is delocalized over the complex entity in the electronic excited state.26

Figure 9. UV−vis spectra of the vinylogous sesquifulvalene complex 12a recorded in solvents of different polarities to illustrate the solvatochromic effect. 6917


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Table 7. UV−Vis Data of the Dipolar, Mononuclear Sesquifulvalene CBDCo Complexes DL-A CT

5 12a 13 12b 12c 13c a

X

n

H H H Cl CH3 CH3

0 1 2 1 1

CH2Cl2 ν̃maxa (ε)b 25 907 22 075 19 920 22 222 21 277

(21 420) (17 577) (21 646) (35 870) (25 426)

CH3NO2 ν̃maxa (ε)b 26 596 23 041 21 277 23 364 22 321

(14 745) (8 276) (18 589) (15 393) (15 228)

DM-ACT Δν̃ −689 −966 −1357 −1142 −1044

TD-DFT nm, cm−1 414, 24 155 433 23 095 457 21 882 436, 22 936 499, 20 040

CH2Cl2 ν̃maxa (ε)b 15 528 13 908 12 821 14 164 13 228

(8 526) (19 427) (40 385) (35 656) (23 530)

CH3NO2 ν̃maxa (ε)b 16 667 15 128 14 347 15 383 14 327

(7 135) (9578) (32 918) (15 335) (14 163)

Δν̃ −1139 −1220 −1526 −1221 −1099

TD-DFT nm, cm−1 719, 13908 786, 12 723 808, 12 376 832, 12 019 852, 11 737

In cm−1. bIn M−1 cm−1. cΔν̃ = 1/λmax(CH2Cl2) − 1/λmax(CH3NO2).

state) of the transition. Generally, in the MO picture an extension of a π system will lower the energy of the LUMO and increase the energy of the HOMO. Here an extension of the bridge leads to a large effect on the low-energy transition due to stabilization of the LUMO and also on the high-energy transition due to an increase of the HOMO and decrease of the LUMO upon bridge extension as well as variation of substituents on the phenyl rings of the cyclobutadiene ring (Figure 12). Figure 10. Representative UV−vis spectra of the mononuclear cationic vinylogous sesquifulvalene complexes with different conjugation lengths n.

Figure 12. Natural transition orbital pairs of DL-A CT transition in 13. The natural orbital pairs contribute 11% (top) and 83% (bottom) to the excitation.

Figure 11. Natural transition orbital pairs of DMA-CT transitions. The natural orbital pairs contribute to 96% (5), 98% (12a) and 98% (13) to the excitations. Figure 13. UV−vis spectra of [Ar4(CBD)Co(Cp-Z-C7H6)]+ complexes with different aryl substituents X and the same olefinic linker (Z = −(C2H2)−).

influence of the phenyl substituents on the hole and thus on the transition is anticipated, since only one state is influenced. This is in agreement with the observed bathochromic shift upon extension of the π-conjugated bridge. These influences to a different extent can be observed in a significant decrease of the HOMO−LUMO (Table 6). For the high-energy transition a mixture of two transitions with strong metal complex contribution in the hole and strong π-acceptor orbitals on the particle site was found from the natural transition orbital analysis. In accord with previous conclusions the influence of the bridge length on the highenergy transition can be envisaged due to the different contributions of metal complex fragment and the C5 bridge− C7 fragment to the hole (ground state) and the particle (excited

Nonlinear Optical Studies. The low-lying excited states, the facile polarizability concluded from the pronounced solvatochromism, and the assignment of the intense charge transfer transition bands in the near-UV and, in particular, the visible region, which are both assigned to donor−acceptor transitions, make these sesquifulvalene cobalt complexes very promising for second harmonic generation (SHG). Therefore, these cationic complexes were subjected to hyper-Rayleigh scattering (HRS)29 studies, which is the only method for determining the first hyperpolarizability β of charged compounds. However, an intrinsic drawback of this method 6918


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Figure 14. Absorption and emission spectra of compounds 12a (A), 13 (B), and 12b (C).

is the fluorescence due to two-photon absorption. This problem has been discussed in previous publications4e,6e and can be partially solved, among other means,30 by introducing band-pass filters with peak transmittance at different wavelengths in front of the photomultiplier of the HRS setup.1l,4e The broad fluorescence signal, which reveals the emission maximum at λ/2 of the fundamental wavelength, is easily discriminated from the narrow second harmonic signal. Figure 14 displays the absorption spectra and the emission spectra obtained from HRS experiments, which indicate that a weak intensity of fluorescence is overlapping the λ/2 signal. As a consequence, the β values in Table 8, which are very large compared to those of other sandwich-type NLO chromophores, are too large when calculated. However, another important conclusion can be drawn from the HRS study: the low-energy CT transition plays an important role in the SHG effect. It is quite obvious that in more polar solvents the SHG

Table 8. First Hyperpolarizability β of the Compounds 11, 12a−c, and 13 Determined by HRS Measurements compd

X

n

solvent

λmax (nm)

β (10−30 esu)

CH2Cl2 MeNO2 CH2Cl2 MeNO2 CH2Cl2 MeNO2 CH2Cl2 MeNO2 CH2Cl2 MeNO2

386/644 376/600 453/719 434/661 502/780 470/697 450/706 428/650 470/756 448/698

b b −504a −600a −448a −881a −400a −665a −498 −613a

11

H

0

12a

H

1

13

H

2

12b

Cl

1

12c

CH3

1

a

Two-photon absorption−fluorescence. bNo HRS intensity detectable.

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signal is distinctly larger (Table 8). This effect is caused by the resonance enhancement due to the hypsochromic shift of the low-energy CT transition, which thus becomes less separated from the λ/2 value and contributes more to the intensity of the SHG signal.

excitation in the near-UV and vis region is coupled with a dipole change.

■

■

EXPERIMENTAL SECTION

Manipulations were carried out under a dry nitrogen atmosphere using standard Schlenk techniques. All solvents were saturated with nitrogen. Diethyl ether (Et2O), tetrahydrofuran (THF), n-hexane, and toluene were freshly distilled from the appropriate alkali metal or metal alloy. Dichloromethane (CH2Cl2) and nitromethane (MeNO2) were dried over calcium hydride. NMR: Varian Gemini 200 BB; Bruker AM 360; measured at 295 K relative to TMS. UV−vis: Perkin-Elmer Model 554. IR: KBr pellets, FT-IR, Perkin-Elmer Model 325. MS: Finnigan MAT 311 A (EI-MS). Elemental analyses: CHN-O-Rapid, Fa. Heraeus, Zentrale Elementanalytik, Fachbereich Chemie, Universität Hamburg. The (tetraaryl-η4-cyclobutadiene)(η5-cyclopentadienyl)cobalt(I) carbaldehyde complexes 6a−e,10 cycloheptatrienylmethyl phosphonate diethyl ester,6e and (tetraphenyl-η4-cyclobutadiene)(chloromercurioη5-cyclopentadienediyl)cobalt(I) (2)7 were synthesized as published. X-ray Structure Determination. Crystals of the compounds 5 and 12c suitable for a structure determination were obtained by gasphase diffusion of Et2O into a CH2Cl2 solution of the corresponding complex. The data were collected on a Hilger and Watts Y290 fourcircle diffractometer at 293 K (5) and 173 K (12c) (Mo Kα radiation, λ = 0.710 73 Å). The structures were solved by direct methods (SHELXS-86), and the refinement on F2 was carried out by full-matrix least-squares techniques (SHELXL-97).31 All non-hydrogen atoms were refined with anisotropic thermal parameters. The hydrogen atoms were refined with a fixed isotropic thermal parameter related by a factor of 1.2 to the value of the equivalent isotropic parameter of their carrier atom. Weights were optimized in the final refinement cycles. For the structure of compound 12c the disorder was resolved and disordered fragments were constrained to have similar distances within σ = 0.001. Crystallographic data for the structures reported in this paper (see also Table 9 in the Supporting Information) have been deposited at the Cambridge Crystallographic Data Centre as supplementary publication nos. CCDC-891916 (5) and CCDC-891923 (12c). Copies of the data can be obtained free of charge on application to the CCDC, 12 Union Road, Cambridge CB2 1EZ, U.K. (fax, (internat.) +44-1223/336-033; e-mail, [email protected]]. Hyper-Rayleigh Scattering. Hyper-Rayleigh scattering measurements were performed with a pulsed Nd:YAG laser at a wavelength of λ 1064 nm. For the experimental setup see ref 29. Solutions of the complexes in MeNO2 with concentrations in the range of 10−4−10−6 M were used with p-nitroaniline as a reference (β(MeNO2) = 34.6 × 10−30 esu).32 Fluorescence checks were made by replacement of the interference filter at the entrance of the photomultiplier tube using filters with transmittances at 400, 450, 500, 532, 560, 600, 650, and 700 nm.6e DFT Calculations. Geometry optimization of complex 5, 12c, and 13 revealed the geometrical parameters given in Table 1 in agreement with experimental data. To reveal information on bonding and charge transfer in these complexes, NBO analyses were performed.33 For all calculations at the density functional theory level, the program Gaussian09 was used.34 For geometry optimization the energies were corrected for nonlocal exchange and for nonlocal correlation according to Becke's three-parameter functional B3LYP.35 The def2-TZVP-split valence basis set was used for all atoms.36 Optical excitations were calculated employing the TD-DFT37 method on optimized geometries of complexes 5, 12c, and 13. All stationary points were checked by second-derivative calculations, revealing no imaginary frequencies. Cyclic Voltammetry. Measurements were performed in MeNO2 with 0.4 M [N(n-Bu)4]PF6 as supporting electrolyte. An Amel 5000 system was used with a Pt wire as working electrode and a Pt plate (0.6 cm2) as an auxiliary electrode. The potentials were measured against Ag/AgCl and are referenced against E1/2([Fe(C5H5)2]/[Fe(C5H5)2]+) = 0.

CONCLUSIONS A series of cationic monometallic dipolar sesquifulvalene complexes [(Ar4-η4-CBD)Co{(η5-C5H4)Z(C7H6)]+ (Ar = pC6H4X, X = Cl, H, Me; Z = −(C2H2)n−, n = 0−2) were synthesized and spectroscopically and (for two of them, 5 and 12c) also structurally characterized. Attempts to prepare the complexes [(Ar4-η4-CBD)Co{(η5-C5H4)Z(C7H6)}]+ (Ar = pC6H4X, X = OMe, NMe2; Z = −C2H2−) and [(Ar4-η4CBD)Co{(η5-C5H4)Z(C7H6)}]+ (Ar = C6H5; Z = −(C2H2)3−) failed and led to decomposition of the products, probably due to an irreversible oxidation and sensitivity to strong Lewis acidity, respectively. In the sesquifulvalene complexes the sandwich units (Ar4CBD)CoCp act as electron donors and the positively charged tropylium moieties as electron acceptors. From NMR spectroscopic and cyclic voltammetric data a decreased donating ability of the sandwich unit is concluded: 12c (X = Me) > 12a (X = H) > 12b (X = Cl). The decreased donating capability in this order is confirmed by the UV−vis measurements, where two strong absorption bands are recorded and absorption maxima are slightly bathochromically shifted with growing donor capability. In accordance with our DFT calculations, the high-energy band is assigned to a donor ligand (DL)−acceptor ligand (A) charge transfer (CT) transition while the low-energy band is caused by a donor cyclobutadiene metal (DM)−A CT transition. It is worth mentioning that the extinction coefficient for the DM-A CT transition for 13 (X = H, Z = −(CHCH)2−) is about 2 times more intense than for the DM-A CT transition of the corresponding ferrocene derivative. The spectroscopic results indicate that NLO chromophores with (CBD)CoCp as donor functionalities are very promising. The SHG effect was measured at the fundamental wavelength of λ = 1064 nm by means of hyper-Rayleigh scattering (HRS) and reveal values for the first hyperpolarizabilities β, which belong to the largest ever obtained for sandwich-type NLO chromophores despite a weak fluorescence overlapping at λ/2. The reason for the exceptionally large SHG effect is a strong resonance enhancement caused by two CT transitions which are coupled with a large dipole change. The results from the DFT calculations and subsequent natural transition orbital analysis further allow a reliable assignment of the electronic excitation. The DFT calculations confirm the HOMOs to be mainly donor localized, whereas the LUMOs are predominantly acceptor based. The cyclobutadiene ligand has a strong influence on the donor orbitals, while the tropylium ligand has a strong influence on the acceptor unit. Thus, the absorption depends on the substituents on the cyclobutadiene ligand. The length of the bridge has an influence on the hole and particle orbitals. Upon extension of the bridge the hole orbital becomes destabilized while the particle state becomes more stabilized, resulting in a bathochromic shift of the excitations. Due to the strong charge transfer character from the cyclobutadiene metal donor to the Cp bridge tropylium acceptor, the transition dipole moment increases upon extension of the bridge, thus increasing the absorption intensity of the electronic excitation. Hence, every electronic 6920


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(Tetraphenyl-η4-cyclobutadiene)(cyclohepta-2′,4′,6′-trien1′-yl-η5-cyclopentadienyl)cobalt(I) (4a). [{(C6H5)4CBD}Co(CpHgCl)] (2; 140 mg, 0.20 mmol) was dissolved in diethyl ether (15 mL) and cooled to −70 °C. A hexane solution of Li-n-Bu (1.5 M, 0.26 mL, 0.39 mmol) was added at −70 °C. The reaction mixture was warmed to room temperature and was stirred for an additional 15 min. The yellow solution was cooled again to −70 °C. Tropylium hexafluorophosphate (47 mg, 0.20 mmol) was added, and the reaction mixture was warmed to room temperature. After the mixture was stirred for an additional 3 h the solvent was evaporated. The solid residue was purified by column chromatography (Al2O3 neutral, 5% water, hexane). A 1H NMR spectrum (see Chart 1 for numbering scheme) of the product revealed a mixture of (tetraphenyl-η4-cyclobutadiene)-

5.97 (dd, 3J = 9.40 Hz, 6.00 Hz, H-3′ (4b)), 6.40 (d, 3J = 6.20 Hz, H2′ (4b)), 7.11−7.25 (m, Hm,p (4b,c), Hm,p (1)), 7.34−7.55 (m, Ho (4b,c), Ho (1)). Since the product consists of three different complexes, assignment of the number of hydrogen atoms was not carried out. 13C NMR: (50 MHz, CD2Cl2, δ in ppm): 28.01 (C-5′ (4b)), 75.56 (CBD (4b,c), CBD (1)), 79.74 (Cp (4b,c)), 83.50 (Cp (1)), 85.18 (Cp (4b,c)), 93.80 (Cq-Cp (1)), 100.05 (Cq-Cp (4b)), 120.64 (C-4′ (4b)), 120.70 (C-6′ (4b)), 126.40 (Cp (4b,c)), 126.40 (C-2′ (4b)), 126.45 (C-7′ (4b)), 126.60 (Cp (1)), 126.87 (C-3′ (4b)), 128.25 (Cm (4b,c)), 128.28 (Cm (1)), 129.06 (Co (4b,c)), 129.18 (Co (1)), 135.78 (C-1′ (4b)), 136.31 (Ci (4b,c), Ci (1)). General Synthesis of the Vinylogous Cycloheptatriene Complexes: [{(4-XC6H4)4CBD}Co{Cp-(E)-(CHCH)nCHT}] (n = 1, X = H, Cl, Me, OMe, NMe2; n = 2, X = H; n = 3, X = H). The aldehyde complexes (6a − 6e, 7, 8) and two equivalents of cyclohepta1′,3′,5′-trien-1′-ylmethyl-phosphonate diethylester are dissolved in benzene. The same volume of soda lye (50%) and a small amount of tetrabutylammonium bromide was added. The reaction mixture was vigorously stirred under reflux for 2.5 until 10 h. The progress of the reaction was monitored by thin layer chromatography. Finally, the reaction mixture was hydrolyzed and extracted with diethyl ether. The organic layers were combined, dried over magnesium sulfate, concentrated and chromatographed. The numbering scheme is given in Chart 2.

Chart 1. Numbering Scheme of the Cycloheptatrienyl Substituent and the Related Isomers 4a−c

(cyclohepta-2′,4′,6′-trien-1′-yl-η5-cyclopentadienediyl)cobalt(I) (4a) and the starting material (tetraphenyl-η 4 -cyclobutadiene)(η 5 cyclopentadienyl)cobalt(I) (1) in a ratio of 9:1. Yield: 60 mg of a mixture of [{(C6H5)4CBD}Co(Cp-2′,4′,6′-CHT)] (4a; CHT = cacloheptatriene) and [{(C6H5)4CBD}CoCp] (1). Since the solubilities of the starting compound 1 and the desired cation 5 would be quite different, further purification of complex 4a was not carried out. 1 H NMR (200 MHz, CD2Cl2, δ in ppm): 2.21 (t, 3J = 5.74 Hz, 1 H, H-1′ (4a)), 4.56 (m, 2 H, Cp (4a)), 4.63 (s, Cp (1)), 4.68 (m, 2 H, Cp (4a)), 5.02 (dd, 3J = 8.79 Hz, 5.86 Hz, 2 H, H-2′/7′ (4a)), 5.91 (m, 2 H, H-3′/6′ (4a)), 6.55 (dd, 3J = 3.41 Hz, 2.69 Hz, 2 H, H-4′/5′ (4a)), 7.15−7.26 (m, 12 H, Hm,p (4a), Hm,p (1)), 7.39−7.47 (m, Ho (4a), Ho (1)). For the remaining starting material 1 and in cases when the resonance signals of the desired complex 4a display a superposition with the signals of compound 1, no number of protons are assigned. 13 C NMR: (50 MHz, CD2Cl2, δ in ppm): 37.53 (C-1′ (4a)), 75.17 (CBD (4a), CBD (1)), 81.52 (Cp (4a)), 83.48 (Cp (1)), 83.71 (Cp (4a)), 101.68 (Cq-Cp (4a)), 124.13 (C-3′/6′ (4a)), 125.83 (C-2′/7′ (4a)), 126.44 (Cp (4a), Cp (1)), 128.26 (Cm (4a), Cm (1)), 129.14 (Co (4a), Co (1)), 131.05 (C-4′/5′ (4a)), 136.68 (Ci (4a), Ci (1)). EIMS (m/z (%)): 570 (47) [M+ (4a)], 480 (56) [M− -CHT (4a), M+ (1)], 415 (12) [{(C6H5)4-CBD}Co+], 214 (67) [CoCpCHT+], 91 (34) [CHT+ (26)], 58 (26) [Co+]. Isomerization of (Tetraphenyl-η 4 -cyclobutadiene)(cyclohepta-2′,4′,6′-trien-1′-yl-η5-cyclopentadienediyl)cobalt(I) (4a) to (Tetraphenyl-η4-cyclobutadiene)(cyclohepta-1′,3′,6′trien-1′-yl-η5-cyclopentadienediyl)cobalt(I) (4b) and (Tetraphenyl-η4-cyclobutadiene)(cyclohepta-1′,3′,5′-trien-1′-yl-η5cyclopentadienyl)cobalt(I) (4c). The isomer [{(C6H5)4CBD}Co(Cp-2′,4′,6′-CHT)] (4a; 15 mg, 0.03 mmol) was dissolved in p-xylene (2 mL). After the mixture was heated at 140 °C for 1 day, the solvent was stripped off in vacuo. 1H NMR spectra show that a mixture of (tetraphenyl-η4-cyclobutadiene)(cyclohepta-1′,3′,6′-trien-1′-yl-η5-cyclopentadienediyl)cobalt (4b), (tetraphenyl-η4-cyclobutadiene)(cyclohepta-1′,3′,5′-trien-1′-yl-η5-cyclopentadienediyl)cobalt (4c), and (tetraphenyl-η4-cyclobutadiene)(η5-cyclopentadienyl)cobalt (1) is formed in a ratio of 8:1:1. For 4c not all resonance signals could be assigned, due to low content and superposition with other signals. Yield: 15 mg of a mixture of [{(C6H5)4CBD}Co(Cp-1′,3′,6′CHT)] (4b), [{(C 6 H 5 ) 4 CBD}CoCp-1′,3′,5′-CHT] (4c) and [{(C6H5)4CBD}CoCp] (1)). EI-MS (m/z (%)): 570 (100) [M+ (4b,c)], 480 (12) [M+ − CHT (4b,c), M+ (1)]. 1H NMR (200 MHz, CD2Cl2, δ in ppm): 1.96 (t, 3J = 6.80 Hz, H-5′exo/endo (4b), 2.07 (d, 3J = 7.08 Hz, H-7′exo/endo (4c)), 4.63 (m, Cp (4b,c), Cp (1)), 4.86 (m, Cp (4b,c)), 5.14 (dt, 3J = 9.60 Hz, 7.00 Hz, H-6′ (4b)), 5.35 (dt, 3 J = 9.20 Hz, 6.80 Hz, H-4′ (4b)), 5.87 (d, 3J = 9.52 Hz, H-7′ (4b)),

Chart 2. Numbering Scheme for the Unsaturated Bridge Connecting the Five- and Seven-Membered Rings and for the Cycloheptatrienyl Substituent

(E)-1-[(Tetraphenyl-η4-cyclobutadiene)(η5-cyclopentadienediyl)cobalt(I)]-2-(cyclohepta-1′,3′,5′-trien-1′-yl)ethene (9a): [{(C6H5)4CBD}CoCpCHO] (6a; 526 mg, 1.03 mmol), cyclohepta1′,3′,5′-trien-1′-ylmethylphosphonate diethyl ester (498 mg, 2.06 mmol), benzene (25 mL), soda lye (50%) (5 mL), 9 h reflux, column chromatography Al2O3 neutral, 5% water, hexane/diethyl ether 2/1. Yield: 466 mg (0.78 mmol, 75.5%) orange-red solid material of 9a. Anal. Calcd for C42H33Co (596.5): C, 84.54; H, 5.58. Found: C, 84.38; H, 5.86. Mp: 164 °C. IR (KBr, cm−1): 3080, 3059, 3019 (CH)Ph, 2953, 2922, 2874 (CH2), 1676 (CC), 1596, 1498, 1443 (CC)Ph, 1125, 1026 (CC)Cp, 970 (CCH), 747, 706 (CH). EI-MS (m/z, (%)): 597 (5) [M+], 357 (16) [{(C6H5)4CBD}+], 180 (4) [Cp(CH CH)CHT+], 124 (23) [CpCo+]. 1H NMR (200 MHz, CD2Cl2, δ in ppm): 2.30 (d, 3J = 7.1 Hz, 2 H, H-7′exo/endo), 4.66 (m, 2 H, Cp), 4.72 (m, 2 H, Cp), 5.20 (dt, 3J = 9.28 Hz, 7.08 Hz, 1 H, H-6′), 5.98 (d, 3J = 5.13 Hz, 1 H, H-2′), 6.07 (d, 3J = 16.11 Hz, 1 H, H-2), 6.17 (dd, 3J = 9.52 Hz, 4.40 Hz, 1 H, H-5′), 6.18 (d, 3J = 16.11 Hz, 1 H, H-1), 6.53 (2dd, 3J = 9.90 Hz, 5.01 Hz, 4.39 Hz, 2 H, H-3′/4′), 7.16−7.23 (m, 12 H, Hm,p), 7.37−7.43 (m, 8 H, Ho). 13C NMR (50 MHz, CD2Cl2, δ in ppm): 27.84 (C-7′), 75.94 (CBD), 80.93 (Cp), 85.30 (Cp), 95.96 (Cq-Cp), 122.33 (C-6′), 123.59 (C-2), 125.53 (C-2′), 126.55 (Cp), 127.60 (C-1), 128.28 (Cm), 129.06 (Co), 129.93 (C-4′), 130.08 (C5′), 131.05 (C-3′), 132.31 (C-1′), 136.34 (Ci). (E,E)-1-[(Tetraphenyl-η4-cyclobutadiene)(η5-cyclopentadienediyl)cobalt(I)]-4-(cyclohepta-1′,3′,5′-trien-1′-yl)-1,3-butadiene (10): {(C 6 H 5 ) 4 CBD}CoCp-(E)-(CHCH)CHO (7; 134 mg, 0.24 mmol), cyclohepta-1′,3′,5′-trien-1′-ylmethylphosphonate diethyl ester (121 mg, 0.48 mmol), benzene (15 mL), soda lye (50%) (5 mL), 6 h reflux, column chromatography Alox neutral, 5% water, hexane/diethyl ether 5/1. Yield: 124 mg (0.20 mmol, 79.5%) orange-red solid material. Anal. Calcd for C44H35Co(H2O) (640.71): C, 82.48; H, 5.82. Found: C, 6921


Organometallics

Article

82.63; H, 5.88. Mp: 130 °C. IR (KBr, cm−1): 3022 (CH)Ph, 2924, 2851 (CH2), 1596, 1498, 1443 (CC)Ph, 1025 (CC)Cp, 979 (CCH), 744, 705 (CH). EI-MS m/z (%): 623 (79) [M+], 416 (94) [{(C6H5)4CBD}Co+], 266 (67) [CoCp(CHCH)2CHT+]. 1H NMR (200 MHz, CD2Cl2, δ in ppm): 2.59 (d, 3J = 7.08 Hz, 2 H, H-7′exo/endo), 4.67 (m, 3J = 2.00 Hz, 2 H, Cp), 4.69 (m, 2 H, Cp), 5.44 (m, 7.20 Hz, 1 H, H-6′), 5.75 (d, 3J = 15.63 Hz, 1 H, H-4), 6.02−6.32 (m, 5 H, H-1/2/3, H-2′/5′), 6.56 (2dd, 3J = 10.07 Hz, 5.86 Hz, 4.27 Hz, 2 H, H-3′/4′), 7.16−7.24 (m, 12 H, Hm,p), 7.36−7.42 (m, 8 H, Ho). 13C NMR (50 MHz, CD2Cl2, δ in ppm): 28.18 (C-7′), 76.00 (CBD), 81.29 (Cp), 84.88 (Cp), 96.06 (Cq-Cp), 122.74 (C-6′), 126.01 (C-4), 126.52 (Cp), 127.06, 127.88, 128.84, 130.32, 132.97 (C2′/5′, C-1,2,3), 128.28 (Cm), 129.10 (Co), 131.12 (C-3′/4′), 132.63 (C-1′), 136.24 (Ci). (E,E,E)-1-[(Tetraphenyl-η4-cyclobutadiene)(η5cyclopentadienediyl)cobalt(I)]-6-(cyclohepta-1′,3′,5′-trien-1′-yl)1,3,5-hexatriene (11): {(C6H5)4CBD}CoCp-(E)-(CHCH)2CHO (8; 41 mg, 0.07 mmol), cyclohepta-1′,3′,5′-trien-1′-ylmethylphosphonate diethyl ester (34 mg, 0.14 mmol), benzene (4 mL), soda lye (50%) (4 mL), 4 h reflux, column chromatography Al2O3 neutral, 5% water, hexane/diethyl ether 3/1. Yield: 41 mg (0.06 mmol, 91%) orange-red solid material. Anal. Calcd for C46H37Co (4H2O) (720.79): C, 76.65; H, 6.29. Found: C, 76.70; H, 6.47. Mp: 129 °C. IR (KBr, cm−1): 3079, 3055, 3021 (CH)Ph, 2924, 2850 (CH2), 1724, 1675 (CC), 1597, 1498, 1443 (CC)Ph, 1156, 1026 (CC)Cp, 993 (CCH), 744, 705 (CH). EIMS (m/z (%)): 648 (17) [M+], 415 (13) [{(C6H5)4CBD}Co+], 356 (55) [{(C6H5)4CBD}+], 278 (14) [CoCp(CHCH)3C6H6+]. 1H NMR (200 MHz, CD2Cl2, δ in ppm): 2.63 (d, 3J = 7.14 Hz, 2 H, H7′exo/endo), 4.67 (m, 2 H, Cp), 4.70 (m, 2 H, Cp), 5.44 (dt, 3J = 8.80 Hz, 6.80 Hz, 1 H, H-6′), 5.75 (d, 3J = 14.00 Hz, 1 H, H-6), 6.02−6.37 (m, 6 H, H-2′/5′, H-2/3/4/5), 6.53−6.61 (m, 3 H, H-1, H-3′/4′), 7.14−7.25 (m, 12 H, Hm,p), 7.36−7.43 (m, 8 H, Ho). 13C NMR (50 MHz, CD2Cl2, δ in ppm): 28.14 (C-7′), 75.94 (CBD), 81.11 (Cp), 85.12 (Cp), 96.03 (Cq-Cp), 122.70 (C-6′), 126.49 (Cp), 126.49, 127.88, 128.93, 132.06, 133.51, 134.44 (C-2′/5′, C-2/3/4/5), 126.83 (C-6), 128.25 (Cm), 129.05 (Co), 130.53 (C-1), 130.91 (C-4′), 131.04 (C-3′), 132.81 (C-1′), 136.21 (Ci). (E)-1-[(Tetrakis(4-chlorophenyl)-η 4 -cyclobutadiene)(η 5 cyclopentadienediyl)cobalt(I)]-2-(cyclohepta-1′,3′,5′-trien-1′-yl)ethene (9b). {(4-ClC6H4)4CBD}CoCpCHO (6b; 100 mg, 0.15 mmol), cyclohepta-1′,3′,5′-trien-1′-ylmethylphosphonate diethyl ester (90 mg, 0.36 mmol), benzene (4 mL), 50% soda lye (4 mL), 2.5 h reflux, column chromatography Al2O3 neutral, 5% water, hexane/ diethyl ether 5/1. Yield: 110 mg (0.15 mmol, 96.5%) orange-red solid material. Anal. Calcd for C42H29Cl4Co (0.5H2O) (M = 743.45): C, 67.85; H, 3.98. Found: C, 67.99; H, 4.24. Mp: 190 °C. IR (KBr, cm−1): 3017 (CH)Ph, 2922, 2851 (CH2), 1601, 1495, 1443 (CC)Ph, 1117, 1011 (C C)Cp, 1081 (CCl), 952 (CCH), 818 (CH). EI-MS (m/z (%)): 736 (2), 734 (6), 732 (4) [M+ − (Cl, isotopic pattern) 722 (2), 720 (6), 718 (4) [M+ − CH2 − (Cl-isotopic pattern)], 91 (100) [CHT+]. 1H NMR (200 MHz, CD2Cl2, δ in ppm): 2.36 (d, 3J = 7.08 Hz, 2 H, H7′exo/endo), 4.65 (m, 2 H, Cp), 4.71 (m, 2 H, Cp), 5.25 (dt, 3J = 9.00 Hz, 7.10 Hz, 1 H, H-6′), 6.01 (dd, 3J = 4.15 Hz, 2.00 Hz, 1.71 Hz, 1 H, H-2′), 6.04 (d, 3J = 16.11 Hz, 1 H, H-2), 6.15 (d, 3J = 16.11 Hz, 1 H, H-1), 6.21 (ddd, 3J = 9.34 Hz, 3.60 Hz, 2.00 Hz, 1 H, H-5′), 6.55 (2dd, 3 J = 8.85 Hz, 4.40 Hz, 3.15 Hz, 2 H, H-3′/4′), 7.17 (d, 3J = 8.79 Hz, 8 H, Hm), 7.28 (d, 3J = 8.79 Hz, 8 H, Ho). 13C NMR (50 MHz, CD2Cl2, δ in ppm): 27.69 (C-7′), 74.66 (CBD), 81.05 (Cp), 85.22 (Cp), 96.23 (Cq-Cp), 122.30 (C-2), 127.84 (C-6′), 126.24 (C-2′), 127.84 (C-5′), 128.73 (Cm), 130.12 (Co), 130.44 (C-4′), 130.58 (C-1), 131.09 (C3′), 131.85 (C-1′), 132.26 (Ci), 134.330 (Cp). (E)-1-[(Tetra-p-tolyl-η4-cyclobutadiene)(η5-cyclopentadienediyl)cobalt(I)]-2-(cyclohepta-1′,3′,5′-trien-1′-yl)ethene (9c): {(4CH3C6H4)4CBD}CoCpCHO (6c) (40 mg, 0.07 mmol), Cyclohepta-1′,3′,5′-trien-1′-ylmethylphosphonate diethyl ester (40 mg, 0.16 mmol), benzene (5 mL), 50% soda lye (5 mL), 6 h reflux, column chromatography Al2O3 neutral, 5% water, hexane/diethyl ether 2/1.

Yield: 31 mg (0.05 mmol) orange-red solid material (67.4%). Mp: 230 °C. Anal. Calcd for C46H41Co (H2O) (M = 670.78): C, 82.37; H, 6.46. Found: C, 82.44; H, 6.82. IR (KBr, cm−1): 3084, 3025 (CH)Ph, 2918, 2855 (CH3), 1654 (CC), 1618, 1516, 1438 (CC)Ph, 1380 (CH3), 1110, 1018 (CC)Cp, 952 (CCH), 809 (CH). EI-MS (m/z (%)): 652 (100) [M+], 471.6 (43) [{(4-CH3C6H4)4CBD}Co+], 240.3 (91) [CoCp-(CHCH)CHT+], 57 (79) [Co+]. 1H NMR (200 MHz, CD2Cl2, δ in ppm): 2.26 (s, 12 H, CH3), 2.30 (d, 3J = 7.10 Hz, 2 H, 1 H-7′exo/endo), 4.62 (m, 2 H, Cp), 4.67 (m, 2 H, Cp), 5.21 (dt, 3J = 9.03 Hz, 7.20 Hz, 1 H, H-6′), 5.93 (d, 3J = 5.10 Hz, 1 H, H-2′), 6.09 (s, 2 H, H-1/2), 6.18 (dd, 3J = 9.28 Hz, 3.78 Hz, H, C-5′), 6.52 (2dd, 3J = 9.77 Hz, 4.88 Hz, 4.30 Hz, 2 H, H-3′/4′), 6.98 (d, 3J = 7.81 Hz, 8 H, Hm), 7.26 (d, 3J = 8.06 Hz, 8 H, Ho). 13C NMR (50 MHz, CD2Cl2, δ in ppm): 21.21 (CH3); 27.51 (C-7′), 75.42 (CBD), 80.64 (Cp), 84.77 (Cp), 95.32 (Cq-Cp), 122.01 (C-6′), 123.60 (C-2), 125.02 (C-2′), 127.29 (C-5′), 128.62 (Cm), 128.67 (Co), 129.08 (C-1), 129.57 (C4′), 130.81 (C-3′), 132.20 (C-1′), 133.05 (Cp), 135.93 (Ci). (E)-1-[{Tetrakis(4-methoxyphenyl)-η 4 -cyclobutadiene}(η 5 cyclopentadienediyl)cobalt(I)]-2-(cyclohepta-1′,3′,5′-trien-1′-yl)ethene (9d): {(4-MeOC6H4)4CBD}CoCpCHO (6d; 30 mg, 0.05 mmol), cyclohepta-1′,3′,5′-trien-1′-ylmethylphosphonate diethyl ester (27 mg, 0.11 mmol), benzene (3 mL), 50% soda lye (3 mL), 4 h reflux, column chromatography Al2O3 neutral, 5% water/95% toluene. Yield: 32 mg (0.04 mmol, 93.6%) orange-red solid material. Mp: 226 °C. Anal. Calcd for C46H41CoO4 (Et2O) (M = 790.88): C, 75.93; H, 6.50. Found: C, 75.69; H, 6.78. EI-MS (m/z (%)): 716.5 (100) [M+], 702 (M+ − CH2), 535.2 (12) [{(4-CH3OC6H4)4CBD}Co+], 240.1 (52) [CoCp(CHCH)CHT+]. IR (KBr, cm−1): 2999, 2952, 2928 (CH2, CH3), 2833 (COCH3), 1607, 1513, 1450 (CC)Ph, 1382 (CH3), 1243 (COCH3), 1173, 1033 (CC)Cp, 954 (CCH), 809 (CH). 1H NMR (200 MHz, CD2Cl2, δ in ppm): 2.34 (d, 3J = 7.08 Hz, 2 H, H-7′exo/endo), 3.77 (s, 12 H, OCH3), 4.62 (m, 2 H, Cp), 4.68 (m, 2 H, Cp), 5.24 (dt, 3J = 9.27 Hz, 7.00 Hz, 1H, H-6′), 5.96 (d, 3J = 5.37 Hz, 1 H, H-2′), 6.07 (d, 3J = 15.78 Hz, 1 H, H-2), 6.16 (d, 3J = 15.78 Hz, 1 H, H-1), 6.18 (dd, 3J = 9.28 Hz, 4.40 Hz, 1 H, C-5′), 6.53 (2dd, 3 J = 10.55 Hz, 5.58 Hz, 4.80 Hz, 2 H, H-3′/4′), 6.72 (d, 3J = 8.79 Hz, 8 H, Hm), 7.30 (d, 3J = 8.79 Hz, 8 H, Ho). 13C NMR (50 MHz, CD2Cl2, δ in ppm): 27.87 (C-7′), 55.54 (OCH3), 75.29 (CBD), 80.70 (Cp), 84.86 (Cp), 95.58 (Cq-Cp), 113.77 (Cm), 122.22 (C-6′), 124.22 (C2), 125.14 (C-2′), 127.65 (C-5′), 128.45 (Ci), 129.13 (C-1), 129.86 (C-4′), 130.07 (Co), 131.14 (C-3′), 132.55 (C-1′), 158.43 (Cp). (E)-1-[Tetrakis(4-dimethylaminophenyl)(η4-cyclobutadiene)(η5cyclopentadienediyl)cobalt(I)]-2-(cyclohepta-1′,3′,5′-trien-1′-yl)ethene (9e). {(4-(CH3)2NC6H4)4CBD}CoCpCHO (6e; 80 mg, 0.12 mmol), cyclohepta-1′,3′,5′-trien-1′-ylmethylphosphonate diethyl ester (57 mg, 0.42 mmol), benzene (6 mL), 50% soda lye (3 mL), 10 h reflux, column chromatography Al2O3 neutral, 5% water, hexane/ diethyl ether 1/1. Yield: 48 mg (0.06 mmol) red solid material (53.1%). Mp: 305 °C. Anal. Calcd for C50H53CoN4 (1/2CH2Cl2) (M = 811.40): C, 74.75; H, 6.71, N 6.90. Found: C, 75.20; H, 6.86, N 7.02. EI-MS (m/z (%)): 767.9 (100) [M+], 586.9 (12) [{(4-(CH3)2NC6H4)4CBD}Co+], 528.1 (26) [{(4-(CH3)2NC6H4)4CBD}+], 240.1 (26) [CoCp(CHCH)CHT+]. IR (KBr, cm−1): 3085, 3015 (CH)Ph, 2993, 2976, 2888, 2850 (CH2,CH3), 1609, 1524, 1444 (CC)Ph, 1388 (CH3), 1195 (CN), 1126, 1004 (CC)Cp, 945 (CCH), 814 (CH). 1H NMR (200 MHz, CD2Cl2, δ in ppm): 2.34 (d, 3J = 7.22 Hz, 2 H, H-7′exo/endo), 2.92 (s, 24 H, N(CH3)2), 4.58 (m, 2 H, Cp), 4.64 (m, 2 H, Cp), 5.24 (dt, 3J = 8.23 Hz, 7.20 Hz, H, H-6′), 5.94 (d, 3J = 5.82 Hz, 1 H, H-2′), 6.07 (d, 3J = 16.00 Hz, H, H-2), 6.10−6.20 (m, H, H-5′), 6.20 (d, 3J = 16.00 Hz, 1 H, H-1), 6.40−6.60 (m, 2 H, H-3′/4′), 6.54 (d, 3J = 11.67 Hz, 8 H, Hm), 7.26 (d, 3J = 11.67 Hz, 8 H, Ho). 13C NMR (50 MHz, CD2Cl2, δ in ppm): 27.99 (C-7′), 40.61 (N(CH3)2), 75.64 (CBD), 80.36 (Cp), 84.54 (Cp), 95.26 (Cq-Cp), 112.10 (Cm), 122.09 (C-6′), 124.40 (Ci), 124.51 (C-2′), 125.35 (C-5′), 127.48 (C-2), 128.31 (C4′), 129.37 (C-3′), 129.72 (Co), 131.22 (C-1), 132.86 (C-1′), 149.12 (Cp). General Synthesis of Cationic, Mononuclear (Ar4CBD)CoCp Complexes with Tropylium Substitution. The cycloheptatrienylsubstituted complexes 4b,c, 9a−e, 10, and 11 were dissolved in 6922


Organometallics

Article

{(C6H5)4CBD}Co{Cp-(E)-(CHCH)2CHT} (10; 60 mg, 0.10 mmol) in dichloromethane (2 mL), trityl hexafluorophosphate (30 mg, 0.08 mmol) in dichloromethane (2 mL), stirring at room temperature for 5 min, color change from orange-red to blue, addition of diethyl ether (20 mL) to provide the desired tropylium salt, recrystallization from dichloromethane solution and gas-phase diffusion of diethyl ether. Yield: 21 mg (0.03 mmol) black-green cubes (28.4%). Mp: 340 °C dec. Anal. Calcd for C44H34CoF6P (M = 766.65): C, 68.93; H, 4.47. Found: C, 68.33; H, 4.53. FAB-MS (m/z (%)): 621 (5) [M+], 415 (3) [{(C6H5)4CBD}Co+], 356 (100) [{(C6H5)4CBD}+]. IR (KBr, cm−1): 1586, 1498, 1437 (CC)Ph, 1124, 1002 (CC)Cp, 929 (CCH), 846, 545 (PF6), 747, 705 (CH). 1H NMR (200 MHz, CD3NO2, δ in ppm): 5.16 (m, 2 H, Cp), 5.25 (m, 2 H, Cp), 6.34 (dd, 3J = 14.89 Hz, 11.23 Hz, 1H, H-2), 6.62 (d, 3J = 14.89 Hz, 1H, H-4), 6.85 (d, 3J = 14.65 Hz, 1H, H-1), 7.24−7.32 (m, 12 1H, Hm,p), 7.44−7.59 (m, 9 H, H-3, Ho), 8.36−8.46 (m, 4 H, H-3′/3′,4′/4′), 8.62 (d, 3J = 9.03 Hz, 2 H, H-2′/2′). 13C NMR (50 MHz, CD3NO2, δ in ppm) 79.75 (CBD), 85.13 (Cp), 90.56 (Cp), 95.80 (Cq-Cp), 128.66 (Cp), 128.82 (C-2), 129.85 (Cm), 130.47 (Co), 131.44 (C-4), 136.54 (Ci), 148.17 (C-2′/ 2′), 148.33 (C-1), 149.60 (C-3′/3′), 150.21 (C-4′/4′), 152.94 (C-3), 167.49 (C-1′). UV−vis (λmax, nm (ε, M−1 cm−1)): in CH2Cl2, 502 (21 646), 780 (40 385); in MeNO2, 470 (18 589), 697 (32 918). Attempt To Synthesize (E,E,E)-1-[(Tetraphenyl-η4cyclobutadiene)(η 5 -cyclopentadienediyl)cobalt]-6-(tropylium)1,3,5-hexatriene Hexafluorophosphate (14): {(C6H5)4CBD}Co{Cp(E)-(CHCH)3CHT} (11; 20 mg, 0.03 mmol) in dichloromethane (2 mL), trityl hexafluorophosphate (11 mg, 0.03 mmol) in dichloromethane (1 mL), stirring at room temperature for 5 min, color change from orange-red to green-brown, addition of diethyl ether (20 mL) revealed a green-brown solid material that is almost insoluble in dichloromethane. The corresponding 1H NMR spectrum gave no indication for the desired product 14. (E)-1-[Tetrakis(4-chlorophenyl)(η 4 -cyclobutadiene)(η 5 cyclopentadienediyl)cobalt(I)]-2-(tropylium)ethene Hexafluorophosphate (12b): {(4-ClC6H4)4CBD}CoCp-(E)-(CHCH)CHT (9b; 63 mg, 0.09 mmol) in dichloromethane (4 mL), trityl hexafluorophosphate (33 mg, 0.08 mmol) in dichloromethane (2 mL), stirring at room temperature for 5 min, color change from orange-red to dark green, addition of diethyl ether (20 mL) to provide the desired tropylium salt 12b, recrystallization from dichloromethane solution and gas-phase diffusion of diethyl ether. Yield: 30 mg (0.03 mmol, 40%) black-green cubes. Mp: 285 °C dec. Anal. Calcd for C42H28Cl4CoF6P (M = 878.39): C, 57.43; H, 3.21. Found: C, 57.95; H, 3.74. FAB-MS (m/z (%)): 735 (55), 733 (92), 731 (68) [M+ − (isotopic pattern of 35/37Cl)], 554 (25), 552 (43), 550 (27) [{(4-ClC6H4)4CBD}Co+(isotopic pattern of 35/37Cl)]. IR (KBr, cm−1): 1598, 1496, 1457 (CC)Ph, 1176, 1012 (CC)Cp, 1082 (CCl), 968 (CCH), 837, 558 (PF6). 1H NMR (200 MHz, CD3NO2, δ in ppm): 5.36 (m, 2 H, Cp), 5.46 (m, 2 H, Cp), 6.69 (d, 3J = 15.38 Hz, 1H, H-2), 7.22 (d, 3J = 6.76 Hz, 8 H, Hm), 7.42 (d, 3J = 6.76 Hz, 8 H, Ho), 7.46 (d, 3J = 15.38 Hz, 1H, H-1), 8.30 (d, 3J = 10.44 Hz, 2 H, H-2′/2′), 8.43−8.52 (m, 4 H, H-3′/3′,4′/4′). 13C NMR (50 MHz, CD3NO2, δ in ppm): 78.90 (CBD), 86.05 (Cp), 92.20 (Cp), 94.80 (Cq-Cp), 127.70 (C-2), 129.91 (Cm), 131.59 (Co), 133.49 (Ci), 134.30 (Cp), 147.51 (C-1), 147.85 (C-2′/2′), 150.02 (C-3′/3′), 151.23 (C4′/4′), 166.11 (C-1′). UV−vis (λmax, nm (ε, M−1 cm−1)): in CH2Cl2, 450 (35 870), 706 (35 656); in MeNO2, 428 (15 393), 650 (15 335). (E)-1-[(Tetra-p-tolyl-η4-cyclobutadiene)(η5-cyclopentadienediyl)cobalt(I)]-2-(tropylium)ethene Hexafluorophosphate (12c): {(4CH3C6H4)4CBD}CoCp-(E)-(CHCH)CHT (9c; 38 mg, 0.06 mmol) in dichloromethane (2 mL), trityl hexafluorophosphate (20 mg, 0.05 mmol) in dichloromethane (1 mL), stirring at room temperature for 5 min, color change from orange-red to blue, addition of diethyl ether (20 mL) to provide the desired tropylium salt. Recrystallization from dichloromethane solution and gas-phase diffusion with diethyl ether. Yield: 30 mg (0.04 mmol, 73%) black-green solid material. Mp: 222 °C dec. Anal. Calcd for C46H40CoF6P(CH2Cl2)(H2O) (M = 899.67): C, 62,65; H, 4,93. Found: C, 62.72; H, 5.23. FAB-MS (m/z (%)): 651

dichloromethane. A solution of trityl hexafluorophosphate (0.9−1 equiv) in dichloromethane was added. The reaction mixture was stirred for 5−10 min at room temperature. During this time the color changed from orange-red to dark green or blue. Afterward diethyl ether was poured into the reaction mixture, to precipitate the tropylium salts. The precipitate was collected on a filter and dried in vacuo. The solid material was recrystallized from dichloromethane solution and gas-phase diffusion with diethyl ether. The numbering scheme is given in Chart 3.

Chart 3. Numbering Scheme of the Tropylium Substituent in 5 and 12−14

(Tetraphenyl-η4-cyclobutadiene)(1′-tropylium-η5cyclopentadienediyl)cobalt(I) Hexafluorophosphate (5): {(C6H5)4CBD}Co(Cp-1′,3′,5′-CHT) (4b) and {(C6H5)4CBD}Co(Cp-1′,3′,6′-CHT) (4c) (132 mg, 0.23 mmol) in dichloromethane (7 mL), trityl hexafluorophosphate (80 mg, 0.21 mmol) in dichloromethane (3 mL), stirring at room temperature for 10 min, color change from orange-red to blue, addition of diethyl ether (20 mL) to provide the desired tropylium salt, recrystallization from dichloromethane solution and gas-phase diffusion of diethyl ether. Yield: 120 mg (0.17 mmol, 81.6%), black blue crystals. Mp: 245 °C dec. Anal. Calcd for C40H30CoF6P (1/4CH2Cl2) (M = 726.70): C, 65.70; H, 4.18. Found: C, 66.04; H, 4.26. FAB-MS (m/z (%)): 569 (100) [M+], 415 (15) [{(C6H5)4CBD}Co+], 213 (15) [CoCpTrop+]. IR (KBr, cm−1): 3052, 3031 (CH)Ph, 1611, 1492, 1442 (CC)Ph, 1126, 1003 (CC)Cp, 834, 547 (PF6), 747, 705 (CH). 1H NMR (200 MHz, CD3NO2, δ in ppm): 5.62 (m, 2 H, Cp), 5.88 (m, 2 H, Cp), 7.18−7.30 (m, 8 H, Ho), 7.34−7.38 (m, 12 H, Hm,p), 7.91−8.02 (m, 2 H, H-3′/3′), 8.14 (d, 3J = 10.62 Hz, 2 H, H-2′/2′), 8.28 (dd, 3J = 10.07 Hz, 4.03 Hz, 2 H, H-4′/4′). 13C NMR: (50 MHz, CD3NO2, δ in ppm): 82.17 (CBD), 85.79 (Cp), 94.51 (Cp), 96.60 (Cq-Cp), 128.83 (Cp), 130.14 (Co,m), 135.01 (Ci), 146.89 (C-2′/2′), 148.64 (C-4′/4′), 150.67 (C-3′/3′), 165.93 (C-1′). UV−vis (λmax, nm (ε, M−1 cm−1)): in CH2Cl2, 386 (21 420), 644 (8526); in MeNO2, 376 (14 745), 600 (7135). (E)-1-[(Tetraphenyl-η 4 -cyclobutadiene)(1′-tropylum-η 5 cyclopentadienediyl)cobalt(I)]-2-(tropylium)ethene Hexafluorophosphate (12e): {(C6H5)4CBD}Co{Cp-(E)-(CHCH)CHT} (9a; 77 mg, 0.13 mmol) in dichloromethane (5 mL), trityl hexafluorophosphate (31 mg, 0.13 mmol) in dichloromethane (2 mL), stirring at room temperature for 5 min, color change from orange-red to blue, addition of diethyl ether (20 mL) to provide the desired tropylium salt, recrystallization from dichloromethane solution and gas-phase diffusion of diethyl ether. Yield: 50 mg (0.07 mmol, 52.3%) black-violet cubes. Mp: 275 °C dec. Anal. Calcd for C42H32CoF6P (1/4CH2Cl2) (M = 752.73): C, 66.61; H, 4.30. Found: C, 66.33; H, 4.44. FAB-MS (m/z (%)): 595 (24) [M + ], 415 (16) [{(C 6 H 5 ) 4 CBD}Co + ], 356 (100) [{(C6H5)4CBD}+]. IR (KBr, cm−1): 3057 (CH), 1599, 1498, 1457 (CC)Ph, 1122, 1025 (CC)Cp, 962 (CCH), 848, 545 (PF6), 749, 708 (CH). 1H NMR (200 MHz, CD3NO2, δ in ppm): 5.36 (m, 2 H, Cp), 5.42 (m, 2 H, Cp), 6.52 (d, 3J = 15.44 Hz, H, H-2), 7.15−7.35 (m, 13 H, H-1, Hm,p), 7.42−7.47 (m, 8 H, Ho), 8.07 (d, 3J = 8.84 Hz, 2 H, H-2′/2′), 8.39−8.49 (m, 4 H, H-3′/3′,4′/4′). 13C NMR (50 MHz, CD3NO2, δ in ppm): 80.57 (CBD), 85.89 (Cp), 91.72 (Cp), 95.08 (Cq-Cp), 126.91 (C-2), 128.47 (Cp), 129.91 (Cm), 130.01 (Co), 135.87 (Ci), 147.73 (C-2′/2′), 148.38 (C-1), 149.23 (C-3′/3′), 150.20 (C-4′/4′), 166.47 (C-1′). UV−vis (λmax, nm (ε, M−1 cm−1)): in CH2Cl2, 453 (17 577) nm, 719 (19427) nm; in MeNO2, 432 (14 868), 670 (16 299). (E,E)-1-[(Tetraphenyl-η4-cyclobutadiene)(η5-cyclopentadienediyl)cobalt]-4-(tropylium)-1,3-butadiene Hexafluorophosphate (13): 6923


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(35) [M+], 471 (100) [{(4-CH3C6H4)4CBD}Co+], 412 (5) [{(4CH3C6H4)4CBD}+]. IR (KBr, cm−1): 2919 (CH3), 1595, 1496, 1455 (CC)Ph, 1385 (CH3), 1129, 1056 (CC)Cp, 962 (CCH), 848, 558 (PF6). 1H NMR (200 MHz, CD3NO2, δ in ppm): 2.23 (s, 12 H, CH3), 5.35 (pt, 3J = 2.10 Hz, 2 H, Cp), 5.39 (pt, 3J = 2.10 Hz, 2 H, Cp), 6.52 (d, 3J = 15.38 Hz, H, H-2), 7.04 (d, 3J = 7.90 Hz, 8 H, Hm), 7.33 (d, 3J = 7.90 Hz, 8 H, Ho), 7.46 (d, 3J = 15.38 Hz, H, H-1), 8.04 (d, 3J = 9.03 Hz, 2 H, H-2′/2′), 8.29−8.33 (m, 4 H, H-3′/3′,4′/4′). 13 C NMR: (50 MHz, CD2Cl2, δ in ppm): 21.62 (CH3), 80.88 (CBD), 85.85 (Cp), 92.10 (Cp), 105.23 (Cq-Cp), 126.86 (C-2), 130.07 (Cm), 130.31 (Co), 132.81 (Cp), 138.55 (Ci), 147.18 (C-2′/2′), 148.48 (C3′/3′), 149.16 (C-1), 149.63 (C-4′/4′), 166.08 (C-1′). UV−vis (λmax, nm (ε, M−1 cm−1)): in CH2Cl2, 470 (25 426), 756 (23 530); in MeNO2, 448 (15 228), 698 (14 163). Attempt To Synthesize (E)-1-[{Tetrakis(p-methoxyphenyl)-η4cyclobutadiene}(η 5 -cyclopentadienediyl)cobalt}-2-(tropylium)ethene Hexafluorophosphate (12d): {(4-CH3OC6H4)4CBD}CoCp(E)-(CHCH)CHT (9d; 42 mg, 0.06 mmol) in dichloromethane (2 mL), trityl hexafluorophosphate (21 mg, 0.06 mmol) in dichloromethane (1 mL), stirring at room temperature for 5 min, color change from orange-red to deep red, addition of diethyl ether (20 mL) revealed a brown solid material, whose 1H NMR spectrum gave no hint of the desired tropylium salt. Attempt To Synthesize (E)-1-[{Tetrakis(4-(dimethylamino)phenyl)-η4-cyclobutadiene}(η5-cyclopentadienediyl)cobalt]-2-(η7tropylium)ethene Hexafluorophosphate (12e): {(4(CH3)2NC6H4)4CBD}CoCp-(E)-(CHCH)CHT (9e; 30 mg, 0.04 mmol) in dichloromethane (2 mL), trityl hexafluorophosphate (13 mg, 0.03 mmol) in dichloromethane (1 mL), stirring at room temperature for 5 min, color change from orange-red to deep red, addition of diethyl ether (20 mL) revealed a brown solid material, whose 1H NMR spectrum gave no hint of the desired tropylium salt.

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1217−1254. (m) Coe, B. J. In Comprehensive Coordination Chemistry; McCleverty, J. A., Meyer, T. J., Eds.; Elsevier Science: Amsterdam, 2003; Chapter 9.14, pp 621−687. (n) Coe, B. J.; Curati, N. R. M. Comments Inorg. Chem. 2004, 25, 147−184. (o) Coe, B. J. Acc. Chem. Res. 2006, 39, 383−393. (p) Cariati, E.; Pizzotti, M.; Roberto, D.; Tessore, F.; Ugo, R. Coord. Chem. Rev. 2006, 250, 1210−1233. (q) Humphrey, M. G.; Samoc, M. Adv. Organomet. Chem. 2008, 55, 61−136. (r) Di Bella, S.; Dragonetti, C.; Pizzotti, M.; Roberto, D.; Tessore, F.; Ugo, R. In Molecular Organometallic Materials for Optics; Le Bozec, H., Guerchais, V., Eds.; Springer Verlag: Berlin, Heidelberg, 2010; Topics in Organometallic Chemistry 28, pp 1−55. (s) Kuzyk, M. G. J. Mater. Chem. 2009, 19, 7444−7465. (t) Maury, O.; Le Bosec, H. In Molecular Materials; Bruce, D. W., O’Hare, D., Walton, I. R., Eds.; Wiley: New York, 2010. (2) For example see: (a) Bourgault, M.; Baum, K.; Le Bosec, H.; Pucetty, G.; Ledouox, I.; Zyss, J. New J. Chem. 1998, 517−522. (b) Mata, J.; Uriel, S.; Peris, E.; Llusar, R.; Houbrechts, S.; Persoons, A. J. Organomet. Chem. 1998, 562, 197−202. (c) Lee, I. S.; Lee, S.; Chung, Y. K.; Kim, D.; Song, N. W. Inorg. Chim. Acta 1998, 279, 243− 248. (d) Briel, O.; Sünkel, K.; Krossing, I.; Nöth, H.; Schmälzlin, E.; Meerholz, K.; Bräuchle, C.; Beck, W. Eur. J. Inorg. Chem. 1999, 483− 490. (e) Cadierno, V.; Conejero, S.; Gamasa, M. P.; Gimeno, J.; Asselberghs, I.; Houbrechts, S.; Clays, K.; Persoons, A.; Borge, J.; Garcia-Granda, S. Organometallics 1999, 18, 582−597. (f) Mata, J. A.; Peris, E.; Asselberghs, I.; van Boxel, R.; Persoons, A. New. J. Chem. 2001, 25, 1043−1046. (3) For example see: (a) Roth, G.; Fischer, H.; Meyer-Friedrichsen, T.; Heck, J.; Houbrechts, S.; Persoons, A. Organometallics 1998, 17, 1511. (b) Licandro, E.; Maiorana, S.; Papagni, A.; Hellier, P.; Capella, L.; Persoons, A.; Houbrechts, S. J. Organomet. Chem. 1999, 583, 111− 119. (c) Jayaprakash, K. N.; Ray, P. C.; Matsuoka, I.; Bhadbhade, M. M.; Puranik, V. G.; Das, P. K.; Nishihara, H.; Sarkar, A. Organometallics 1999, 18, 3851−3858. (d) Ipaktschi, J.; Mohseni-Ala, J.; Dülmer, A.; Steffens, S.; Wittenburg, C.; Heck, J. Organometallics 2004, 23, 4902− 4909. (e) Szesni, N.; Drexler, M.; Maurer, J.; Winter, R. F.; de Montigny, F.; Lapinte, C.; Steffens, S.; Heck, J.; Weibert, B.; Fischer, H. Organometallics 2006, 25, 5774−5787. (4) For example see: (a) Behrens, U.; Brussaard, H.; Hagenau, U.; Heck, J.; Hendrickx, E.; Körnich, J.; van der Linden, J. G. M.; Persoons, A.; Spek, A. L.; Veldman, N.; Voss, B.; Wong, H. Chem. Eur. J. 1996, 2, 98. (b) Hendrickx, E.; Persoons, A.; Samson, S.; Stephenson, G. R. J. Organomet. Chem. 1997, 542, 295. (c) Farrell, T.; Meyer-Friedrichsen, T.; Malessa, M.; Haase, D.; Saak, W.; Asselberghs, I.; Wostyn, K.; Clays, K.; Persoons, A.; Heck, J.; Manning, A. R. Dalton Trans. 2001, 29. (d) Malaun, M.; Kowallick, R.; McDonagh, A. M.; Marcaccio, M.; Paul, R. L.; Asselberghs, I.; Clays, K.; Persoons, A.; Bildstein, B.; Fiorini, C.; Nunzi, J.-M.; Ward, M. D.; McCleverty, J. A. Dalton Trans. 2001, 3025. (e) Farrell, T.; Manning, A. R.; Murphy, T. C.; Meyer-Friedrichsen, T.; Heck, J.; Asselberghs, I.; Persoons, A. Eur. J. Inorg. Chem. 2001, 2365. (f) Meyer-Friedrichsen, T.; Mecker, C.; Prosenc, M. H.; Heck, J. Eur. J. Inorg. Chem. 2002, 239−248. (g) Farrell, T.; Manning, A. R.; Mitchell, G.; Heck, J.; Meyer-Friedrichsen, T.; Malessa, M.; Wittenburg, C.; Prosenc, M. H.; Cunningham, D.; McArdle, P. Eur. J. Inorg. Chem. 2002, 1677−1686. (h) Meyer-Friedrichsen, T.; Wong, H.; Prosenc, M. H.; Heck, J. Eur. J. Inorg. Chem. 2003, 936. (i) Steffens, S.; Prosenc, M. H.; Heck, J.; Asselgerghs, I.; Clays, K. Eur. J. Inorg. Chem. 2008, 1999−2006. (j) Coe, B. J.; Essex-Lopresti, J. P.; Harris, J. A.; Houbrechts, S.; Persoons, A. Chem. Commun. 1997, 1645−1646. (5) For example see: (a) Dias, A. R.; Garcia, M. H.; Robalo, M. P.; Green, M. L. H.; Lai, K. K.; Pulham, A. J.; Klueber, S. M.; Balavoine, G. J. Organomet. Chem. 1993, 453, 241. (b) Dias, A. R.; Garcia, M. H.; Rodriges, J. C.; Green, M. L. H.; Kuebler, S. M. J. Organomet. Chem. 1994, 475, 241. (c) Cifuentes, M. P.; Humphrey, M. G. J. Organomet. Chem. 2004, 689, 3968−3981. (d) Powell, C. E.; Humphrey, M. G. Coord. Chem. Rev. 2004, 248, 725−756. (e) Garcia, M. H.; Florindo, P.; Piedade, M. F. M.; Duarte, M. T.; Robalo, M. P.; Heck, J.;

ASSOCIATED CONTENT

S Supporting Information *

CIF files giving crystallographic data for 5 and 12c. This material is available free of charge via the Internet at http:// pubs.acs.org.

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AUTHOR INFORMATION

Notes

The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work was supported by the Deutsche Forschungsgemeinschaft (DFG, HE 1309/3) by the European Community (COST D 14, TMR FMRX-CT-98-0166). M.H.P. thanks the Deutsche Forschungsgemeinschaft for a fellowship (DFG, PR 654/1-1).

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REFERENCES

(1) (a) Williams, D. J. Angew. Chem. 1984, 96, 637; Angew. Chem., Int. Ed. Engl. 1984, 23, 690. (b) Boyd, R. W. In Nonlinear Optics, Academic Press: New York, 1992. (c) Prasad, P. N., Williams, D. J. In Nonlinear Optical Effects In Molecules & Polymers; Wiley: New York, 1991. (d) Nalwa, H. S. Appl. Organomet. Chem. 1991, 5, 349. (e) Wagnière, G. H. In Linear and Nonlinear Optical Properties of Molecules; VCH: Weinheim, Germany, 1993. (f) Laidlaw, W. M.; Denning, R. G.; Verbiest, T.; Chauchard, E.; Persoons, A. Nature 1993, 363, 58−60. (g) Marks, T. J.; Ratner, M. A. Angew. Chem. 1995, 107, 167; Angew. Chem., Int. Ed. Engl. 1995, 34, 155. (h) Long, N. J. Angew. Chem. 1995, 107, 37; Angew. Chem., Int. Ed. Engl. 1995, 34, 21. (i) Nalwa, H. S.; Miyata, S. In Nonlinear Optics of Organic Molecules and Polymers; CRC Press: New York, 1997. (j) Whittall, I. R.; McDonagh, A. M.; Humphrey, M. G.; Samoc, M. Adv. Organomet. Chem. 1998, 42, 291. (k) Coe, B. J. Chem. Eur. J. 1999, 5, 2464. (l) Heck, J.; Dabek, S.; Meyer-Friedrichsen, T.; Wong, H. Coord. Chem. Rev. 1999, 190−192, 6924


Organometallics

Article

Wittenburg, C.; Holtmann, J.; Licandro, E. J. Organomet. Chem. 2008, 693, 2987−2999. (6) For example see: (a) Green, M. L. H.; Marder, S. R.; Thompson, M. E.; Brandy, J. A.; Bloor, D.; Kolinsky, P. V.; Jones, R. J. Nature 1987, 330, 360. (b) Togni, A.; Hayashi, T. Ferrocenes; VCH: Weinheim, Germany, 1995, and references therein. (c) Wong, H.; Meyer-Friedrichsen, T.; Farrell, T.; Mecker, C.; Heck, J. Eur. J. Inorg. Chem. 2000, 631−646. (d) Bildstein, B. Coord. Chem. Rev. 2000, 206− 207, 369. (e) Wong, H.; Meyer-Friedrichsen, T.; Farrell, T.; Mecker, Ch.; Heck, J. Eur. J. Inorg. Chem. 2000, 631. (f) Heck, J.; Dede, M. In Ferrocenes: Ligand, Materials and Biomolecules; Strepnicka, P., Ed.; Wiley: New York, 2008; pp 317−392. (7) (a) Rausch, M. D.; Genetti, R. A. J. Org. Chem. 1970, 35, 3888. (b) Nguyen, H. V.; Yeamine, M. R.; Amin, J.; Motevalli, M.; Richards, C. J. J. Organomet. Chem. 2008, 693, 3668−3676. (8) Meyer-Friedrichsen, T. Ph.D. Thesis, University of Hamburg, 1999, (9) (a) Ter Berg, A. T.; Kloosterziel, H. Recl. Trav. Chim. Pays-Bas 1963, 82, 741. (b) Hubert, A. J.; Reimlinger, H. Synthesis 1970, 405. (10) Dabek, S.; Prosenc, M. H.; Heck, J. J. Organomet. Chem. 2007, 692, 2216−2226. (11) (a) Piechuckie, C. Synthesis 1976, 187. (d) Mandon, D.; Astruc, D. Organometallics 1989, 8, 2372. (b) Dehmlow, E. V. Angew. Chem. 1977, 89, 521. (c) Dehmlow, E. V.; Dehmlow, S. S. Phase Transfer Catalysis, 3rd ed.; VCH: Weinheim, Germany, 1993. (12) Gubin, S. P.; Smirnova, S. A.; Derisovich, L. L.; Gulovich, A. A. J. Organomet. Chem. 1971, 30, 243. (13) Gupta, H. K.; Brydges, S.; McGlinchey, M. J. Organometallics 1999, 18, 115−122. (14) Kölle, U. Inorg. Chim. Acta 1981, 47, 13. (15) (a) Uno, M.; Ando, K.; Komatsuzaki, N.; Tsuda, T.; Tanaka, T.; Sawada, M.; Takahashi, S. J. Organomet. Chem. 1994, 473, 303. (b) Kang, Y. K; Chung, Y. K.; Lee, S. W. Organometallics 1995, 14, 4905. (16) Ortin, Y.; Ahrenstorf, K.; O’Donohue, P.; Foede, D.; MüllerBunz, H.; McArdle, P.; Manning, A. R.; McGlinchey, M. J. J. Organomet. Chem. 2004, 689, 1657. (17) (a) Riley, E.; Davis, R. E. J. Organomet. Chem. 1976, 113, 157. (b) Rausch, M. D.; Westover, G. F.; Mintz, E.; Reisner, G. M.; Bernal, I.; Clearfield, A.; Troup, J. M. Inorg. Chem. 1979, 18, 2605. (c) Villa, A. Ch.; Coghi, L.; Manfredotti, A. G.; Guastini, C. Acta Crystallogr. 1974, B30, 2101. (d) Harrison, R. M.; Brotin, T.; Noll, B. C.; Michl, J. Organometallics 1997, 16, 3401. (e) Jones, G.; Richards, C. J. Organometallics 2001, 20, 1251−1254. (18) Behrendt, C.; Dabek, S.; Heck, J.; Courtney, D.; Manning, A. R.; McGlinchey, M. J.; Müller-Bunz, H.; Ortin, Y. J. Organomet. Chem. 2006, 691, 1183. (19) Clack, D. W.; Warren, K. D. Inorg. Chim. Acta 1978, 27, 105. (20) Mutseneck, E. V.; Loginov, D. A.; Perekalin, D. S.; Starikova, Z. A.; Golovanov, D. G.; Petrovskii, P. V.; Zanello, P.; Corsini, M.; Laschi, F.; Kudinov, A. R. Organometallics 2004, 23, 5944. (21) Hansch, C.; Leo, A.; Taft, R. W. Chem. Rev. 1991, 91, 165. (22) (a) Koelle, U. Inorg. Chim. Acta 1981, 47, 13. (b) Stoll, M. E.; Lovelace, S. R.; Geiger, W. E.; Schimanke, H.; Hyla-Krypsin, I.; Gleiter, R. J. Am. Chem. Soc. 1999, 121, 9343. (23) O’Donohue, P.; McAdam, C. J.; Courtney, D.; Ortin, Y.; MüllerBunz, H.; Manning, A. R.; McGlinchey, M. J.; Simpson, J. J. Organomet. Chem. 2011, 696, 1510−1527. (24) De Martino, R. N.; Choe, E. W; Khanarian, G.; Haas, D.; Leslie, T.; Nelson, G.; Stamatoff, J.; Stutz, D.; Teng, C. C.; Yoon, H. In Nonlinear Optical and Electroactive Polymers; Prasars, P. N., Ulrich, D. R., Eds.; Pulnam: New York, 1988; p 169. (25) Oudar, J. L.; Chemla, D. S. J. Chem. Phys. 1977, 66, 2664. (26) Reichardt, C. In Solvents and Solvent Effects in Organic Chemistry; VCH: Weinheim, Germany, 1990. (27) Barlow, S.; Bunting, H. E.; Ringham, C. R.; Green, J. C.; Bublitz, G. U.; Boxer, S. G.; Perry, J. W.; Marder, S. R. J. Am. Chem. Soc. 1999, 121, 3715. Barlow, S.; Marder, S. R. Chem. Commun. 2000, 1555.

(28) Heck, J.; Prosenc, M. H.; Meyer-Friedrichsen, T.; Holtmann, J.; Walczuk, E.; Dede, M.; Farrell, T.; Manning, A. R.; Kuball, H.-G.; Archetti, G.; Wang, Y.-H.; Liu, K.; Luo, Y. Proc. SPIE 2007, 6653, 66530R. (29) (a) Clays, K.; Persoons, A. Rev. Sci. Instrum. 1992, 63, 3285. (b) Clays, K.; Persoons, A. Rev. Sci. Instrum. 1992, 63, 3285. (30) (a) Stadler, S.; Dietrich, R.; Bourhill, G.; Bräuchle, C. Opt. Lett. 1996, 21, 251−253. (b) Stadler, S.; Bourhill, G.; Bräuchle, C. J. Phys. Chem. 1996, 100, 6927. (c) Pauley, M. A.; Wang, C. H. Rev. Sci. Instrum. 1999, 70, 1277. (d) Clays, K.; Hendricks, H.; Verbiest, T.; Persoons, A. Adv. Mater. 1998, 10, 643. (e) Olbrechts, G.; Munters, T.; Clays, K.; Persoons, A.; Kim, O.-K.; Choi, L.-S. Mater 1999, 12, 221. (31) (a) Sheldrick, G. M. SHELXS-86 Program for Crystal Structure Determination; University of Göttingen, Göttingen, Germany, 1986; (b) Sheldrick, G. M. SHELXL-97 Program for Crystal Structure Refinement; University of Göttingen, Göttingen, Germany, 1997. (32) Verbiest, T.; Clays, K.; Samyn, S.; Wolff, J.; Reinhoudt, D.; Persoons, A. J. Am. Chem. Soc. 1994, 116, 9320. (33) Weinhold, F.; Landis, C. R. Valency and Bonding: A Natural Bond Orbital Donor-Acceptor Perspective; Cambridge University Press: Cambridge, U.K., 2005. (34) . Frisch, M. J. et al. Gaussian 09, Revision A.02; Gaussian Inc., Wallingford, CT, 2009. (35) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. (36) (a) Weigend, F.; Ahlrichs, R. Phys. Chem. Chem. Phys. 2005, 7, 3297. (b) Weigend, F. Phys. Chem. Chem. Phys. 2006, 8, 1057. (37) Burke, K.; Werschnik, J.; Gross, E. K. U. J. Chem. Phys. 2005, 123, 062206. (38) Martin, R. L. J. Chem. Phys. 2003, 118, 4775−4777.

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Dipolar Sesquifulvalene Compounds with (Tetraaryl-Î·4

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