Methyloxy Substituted Heteroleptic Bis(phthalocyaninato) Yttrium Complexes: Density Functional Calculations

The effects of alkyloxy substituents attached to one phthalocyanine ligand of three heteroleptic bis(phthalocyaninato) yttrium complexes Y(Pc)[Pc(α‐OCH₃)₄] ( 1 ), Y(Pc)[Pc(α‐OCH₃)₈] ( 2 ), and Y(Pc)[Pc(β‐OCH₃)₈] ( 3 ), as well as their reduction products {Y(Pc)[Pc(α‐OCH₃)₄]}^? ( 4 ), {Y(Pc)[Pc(α‐OCH₃)₈]}^? ( 5 ), and {Y(Pc)[Pc(β‐OCH₃)₈]}^? ( 6 ) [H₂Pc(α‐OCH₃)₄=1,8,15,22‐tetrakis(methyloxy)phthalocyanine; H₂Pc(α‐OCH₃)₈=1,4,8,11,15,18,22,25‐octakis(methyloxy)phthalocyanine; H₂Pc(β‐OCH₃)₈=2,3,9,10,16,17,23,24‐octakis(methyloxy)phthalocyanine] are studied by DFT calculations. Good consistency is found between the calculated results and experimental data for the electronic absorption, IR, and Raman spectra of 1 and 3 . Introduction of electron‐donating methyloxy groups on one phthalocyanine ring of the heteroleptic double‐deckers induces structural deformation in both phthalocyanine ligands, electron transfer between the two phthalocyanine rings, changes in orbital energy and composition, shift of electronic absorption bands, and different vibrational modes of the unsubstituted and substituted phthalocyanine ligands in the IR and Raman spectra in comparison with the unsubstituted homoleptic counterpart Y(Pc)₂. The calculations reveal that incorporation of methyloxy substituents at the nonperipheral positions has greater influence on the structure and spectroscopic properties of bis(phthalocyaninato) yttrium double‐deckers than at the peripheral positions, which increases with increasing number of substituents. Nevertheless, the substituent effect of alkyloxy substituents at one phthalocyanine ligand of the double‐decker on the unsubstituted phthalocyanine ring and on the whole molecule and the importance of the position and number of alkyloxy substituents are discussed. In addition, the effect of reducing 1 – 3 to 4 – 6 on the structure and spectroscopic properties of the bis(phthalocyaninato) yttrium compounds is also discussed. This systemic DFT study is not only useful for understanding the structure and spectroscopic properties of bis(phthalocyaninato) rare earth metal complexes but also helpful in designing and preparing double‐deckers with tunable structure and properties.     

Sandwich Double‐Decker Lanthanide(III) “Intracavity” Complexes Based on Clamshell‐Type Phthalocyanine Ligands: Synthesis,Spectral, Electrochemical,and Spectroelectrochemical Investigations

Phthalocyanine compounds of novel type based on a bridged bis‐ligand, denoted “intracavity” complexes, have been prepared. Complexation of clamshell ligand 1,1′‐[benzene‐1,2‐diylbis(methanediyloxy)]bis[9(10),16(17),23(24)‐tri‐tert‐butylphthalocyanine] (^clam,tBuPc₂H₄, 1 ) with lanthanide(III) salts [Ln(acac)₃] ? n H₂O (Ln=Eu, Dy, Lu; acetylacetonate) led to formation of double‐deckers ^clam,tBuPc₂Ln ( 2 a – c ). Formation of high molecular weight oligophthalocyanine complexes was demonstrated as well. The presence of an intramolecular covalent bridge affecting the relative arrangement of macrocycles was shown to result in specific physicochemical properties. A combination of UV/Vis/NIR and NMR spectroscopy, MALDI‐TOF mass‐spectrometry, cyclic voltammetry, and spectroelectrochemistry provided unambiguous characterization of the freshly prepared bis‐phthalocyanines, and also revealed intrinsic peculiarities in the structure–property relationship, which were supported by theoretical calculations. Unexpected NMR activity of the paramagnetic dysprosium complex 2 b in the neutral π‐radical form was observed and examined as well.     

Location of the hole and acid proton in neutral nonprotonated and protonated mixed (phthalocyaninato)(porphyrinato) yttrium double-decker complexes: density functional theory calculations

The location of the hole and acid proton in neutral nonprotonated and protonated mixed (phthalocyaninato)(porphyrinato) yttrium double-decker complexes, respectively, is studied on the basis of density functional theory (DFT) calculations on the molecular structures, molecular orbitals, atomic charges, and electronic absorption and infrared spectra of the neutral, reduced, and two possible protonated species of a mixed (phthalocyaninato)(porphyrinato) yttrium compound: [(Pc)Y(Por)], [(Pc)Y(Por)]-, [(HPc)Y(Por)], and [(Pc)Y(HPor)], respectively. When the neutral [(Pc)Y(Por)] is reduced to [(Pc)Y(Por)]-, the calculated results on the molecular structure, atomic charge, and electronic absorption and infrared spectra show that the added electron has more influence on the Pc ring than on its Por counterpart, suggesting that the location of the hole is on the Pc ring in neutral [(Pc)Y(Por)]. Nevertheless, comparison of the calculation results on the structure, orbital composition, charge distribution, and electronic absorption and infrared spectra between [(HPc)Y(Por)] and [(Pc)Y(HPor)] leads to the conclusion that the acid proton in the protonated mixed (phthalocyaninato)(porphyrinato) yttrium compound should be localized on the Por ring rather than the Pc ring, despite the localization of the hole on the Pc ring in [(Pc)Y(Por)]. This result is in line with the trend revealed by comparative studies of the X-ray single-crystal molecular structures between [MIII{Pc(alpha-OC5H11)4}(TClPP)] and [M(III)H{Pc(alpha-OC5H11)4}(TClPP)] (H2TClPP=5,10,15,20-tetrakis(4-chlorophenyl)porphyrin; M=Sm, Eu). The present work not only represents the first systemic DFT study on the structures and properties of mixed (phthalocyaninato)(porphyrinato) yttrium double-decker complexes, but more importantly sheds further light on the nature of protonated bis(tetrapyrrole) rare-earth complexes.     

Studies of "pinwheel-like" bis[1,8,15,22-tetrakis(3-pentyloxy)phthalocyaninato] rare earth(III) double-decker complexes

Homoleptic bis(phthalocyaninato) rare-earth double-deckers complexes [M(III)[Pc(alpha-OC5H11)4]2] (M = Eu, Y, Lu; Pc(alpha-OC5H11)4 = 1,8,15,22-tetrakis(3-pentyloxy)phthalocyaninate) have been prepared by treating the metal-free phthalocyanine H2Pc(alpha-OC5H11)4 with the corresponding M(acac)3.nH2O (acac = acetylacetonate) in refluxing n-octanol. Due to the C4h symmetry of the Pc(alpha-OC5H11)4 ligand and the double-decker structure, all the reactions give a mixture of two stereoisomers with C4h and D4 symmetry. The former isomer, which is a major product, can be partially separated by recrystallization due to its higher crystallinity. The molecular structure of the major isomer of the Y analogue has been determined by single-crystal X-ray diffraction analysis. The metal center is eight-coordinate bound to the isoindole nitrogen atoms of the two phthalocyaninato ligands, forming a distorted square antiprism. Such an arrangement leads to an interesting pinwheel structure when viewed along the C4 axis, which assumes a very unusual S8 symmetry. The major isomers of all these double-deckers have also been characterized with a wide range of spectroscopic methods. A systematic investigation of their electronic absorption and electrochemical data reveals that the pi-pi interaction between the two Pc(alpha-OC5H11)4 rings is weaker than that for the corresponding unsubstituted or beta-substituted bis(phthalocyaninato) analogues.     

Lanthanide(III) Bis(phthalocyaninato)–[60]Fullerene Dyads: Synthesis,Characterization, and Photophysical Properties

A novel series of double‐decker lanthanide(III) bis(phthalocyaninato)–C₆₀ dyads [Ln^III(Pc)(Pc′)]–C₆₀ (M=Sm, Eu, Lu; Pc=phthalocyanine) ( 1 a – c ) have been synthesized from unsymmetrically functionalized heteroleptic sandwich complexes [Ln^III(Pc)(Pc′)] (Ln=Sm, Eu, Lu) 3 a – c and fulleropyrrolidine carboxylic acid 2 . The sandwich complexes 3 a – c were obtained by means of a stepwise procedure from unsymmetrically substituted free‐base phthalocyanine 5 , which was first transformed into the monophthalocyaninato intermediate [Ln^III(acac)(Pc)] and further reacted with 1,2‐dicyanobenzene in the presence of 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU). ¹H NMR spectra of the bis(phthalocyaninato) complexes 3 a – c and dyads 1 a – c were obtained by adding hydrazine hydrate to solutions of the complexes in [D₇]DMF, a treatment that converts the free radical double‐deckers into the protonated species, that is, [Ln^III(Pc)(Pc′)H] and [Ln^III(Pc)(Pc′)H]–C₆₀. The electronic absorption spectra of 3 a – c and 1 a – c in THF exhibit typical transitions of free‐radical sandwich complexes. In the case of dyads 1 a – c , the spectra display the absorption bands of both constituents, but no evidence of ground‐state interactions could be appreciated. When the UV/Vis spectra of 3 a – c and 1 a – c were recorded in DMF, typical features of the reduced forms were observed. Cyclic voltammetry studies for 3 a – c and 1 a – c were performed in THF. The electrochemical behavior of dyads 1 a – c is almost the exact sum of the behavior of the components, namely the double‐decker [Ln^III(Pc)(Pc′)] and the C₆₀ fullerene, thus confirming the lack of ground‐state interactions between the electroactive units. Photophysical studies on dyads 1 a – c indicate that only after irradiation at 387 nm, which excites both C₆₀ and [Ln^III(Pc)(Pc′)] components, a photoinduced electron transfer from the [Ln^III(Pc)(Pc′)] to C₆₀ occurs.     

A Phosphorus Analogue of Bis(η4‐cyclobutadiene)iron(0)

P makes it possible : The convenient oxidative synthesis of the 16‐electron organophosphorus iron sandwich complex [Fe(η⁴‐P₂C₂tBu₂)₂] (see structure) suggests that the elusive all‐carbon complex [Fe(η⁴‐C₄H₄)₂] is a viable synthetic target.

     

Tuning the Dipolar Second‐Order Nonlinear Optical Properties of Cyclometalated Platinum(II) Complexes with Tridentate N^C^N Binding Ligands

Appropriate functionalization of the cyclometalated ligand, L , and the choice of the ancillary ligand, X, allows the dipolar second‐order nonlinear optical response of luminescent [Pt L X] complexes—in which L is an N^C^N‐coordinated 1,3‐di(2‐pyridyl)benzene ligand and X is a monodentate halide or acetylide ligand—to be controlled. The complementary use of electric‐field‐induced second‐harmonic (EFISH) generation and harmonic light scattering (HLS) measurements demonstrates how the quadratic hyperpolarizability of this appealing family of multifunctional chromophores, characterized by a good transparency throughout much of the visible region, is dominated by an octupolar contribution.     

Cover Picture: A Phosphorus Analogue of Bis(η4‐cyclobutadiene)iron(0) (Angew. Chem. Int. Ed. 17/2009)

A rare phosphorus analogue of the elusive complex bis(η⁴‐cyclobutadiene)iron(0) is reported by K. Lammertsma et al. in their Communication on page 3104 ff. The background of the cover picture shows John Montagu (1718–1792), 4th Earl of Sandwich and 1st Lord of the Admiralty, who certainly would not have dreamt that an important class of organometallic compounds, sandwich complexes, would bear his name one day. The synthesis of [Fe(P₂C₂tBu₂)₂] shows that sandwich complexes are still topical objects of research.

     

Highly Stereocontrolled Ring‐Opening Polymerization of Racemic Alkyl β‐Malolactonates Mediated by Yttrium [Amino‐alkoxy‐bis(phenolate)] Complexes

Yttrium [amino‐alkoxy‐bis(phenolate)]amido complexes have been used for the ring‐opening polymerization (ROP) of racemic alkyl β‐malolactonates (4‐alkoxycarbonyl‐2‐oxetanones, rac‐MLA^Rs) bearing an allyl (All), benzyl (Bz) or methyl (Me) lateral ester function. The nature of the ortho‐substituent on the phenolate rings in the metal ancillary dictated the stereocontrol of the ROP, and consequently the syndiotactic enrichment of the resulting polyesters. ROP promoted by catalysts with halogen (Cl, Br)‐disubstituted ligands allowed the first reported synthesis of highly syndiotactic PMLA^Rs (P_r ≥ 0.95); conversely, catalysts bearing bulky alkyl and aryl ortho‐substituted ligands proved largely ineffective. All polymers have been characterized by ¹H and ¹³C{¹H} NMR spectroscopy, MALDI‐ToF mass spectrometry and DSC analyses. Statistical and thermal analyses enabled the rationalization of the chain‐end control mechanism. Whereas the stereocontrol of the polymerization obeyed a Markov first‐order (Mk1) model for the ROP of rac‐MLA^Bz and rac‐MLA^All, the ROP of rac‐MLA^Me led to a chain end‐control of Markov second‐order type (Mk2). DFT computations suggest that the high stereocontrol ability featured by catalysts bearing Cl‐ and Br‐substituted ligands does not likely originate from halogen bonding between the halogen substituent and the growing polyester chain.     

Density Functional Theory Investigation on the Second‐Order Nonlinear Optical Properties of Chlorobenzyl‐o‐Carborane Derivatives

The structures and second‐order nonlinear optical (NLO) properties of a series of chlorobenzyl‐o‐carboranes derivatives ( 1 – 12 ) containing different push‐pull groups have been studied by density functional theory (DFT) calculation. Our theoretical calculations show that the static first hyperpolarizability (β_tot) values gradually increase with increasing the π‐conjugation length and the strength of electron donor group. Especially, compound 12 exhibits the largest β_tot (62.404×10^?30 esu) by introducing tetrathiafulvalene (TTF), which is about 76 times larger than that of compound 1 containing aryl. This means that the appropriate structural modification can substantially increase the first hyperpolarizabilities of the studied compounds. For the sake of understanding the origin of these large NLO responses, the frontier molecular orbitals (FMOs), electron density difference maps (EDDMs), orbital energy and electronic transition energy of the studied compounds are analyzed. According to the two‐state model, the lower transition energy plays an important role in increasing the first hyperpolarizability values. This study may evoke possible ways to design preferable NLO materials.     

Chiral Bis(oxazoline) Ruthenium Complexes with Bipyridyl‐Type N‐Heteroaromatics: Comparative Stereochemical and Photochemical Characterization of their Λ‐ and Δ‐Diastereomeric Geminate Isomers

Diastereomeric geminate pairs of chiral bis(2‐oxazoline) ruthenium complexes with bipyridyl‐type N‐heteroaromatics, Λ‐ and Δ‐[Ru(L‐ L)₂(iPr‐biox)]²⁺ (iPr‐biox=(4S,4′S)‐4,4′‐diisopropyl‐2,2′‐bis(2‐oxazoline); L‐ L=2,2′‐bipyridyl (bpy) for 1 Λ and 1 Δ, 4,4′‐dimethyl‐2,2′‐bipyridyl (dmbpy) for 2 Λ and 2 Δ, and 1,10‐phenanthroline (phen) for 3 Λ and 3 Δ), were separated as BF₄ and PF₆ salts and were subjected to the comparative studies of their stereochemical and photochemical characterization. DFT calculations of 1 Λ and 1 Δ electronic configurations for the lowest triplet excited state revealed that their MO‐149 (HOMO) and MO‐150 (lower SOMO) characters are interchanged between them and that the phosphorescence‐emissive states are an admixture of a Ru‐to‐biox charge‐transfer state and an intraligand excited state within the iPr‐biox. Furthermore, photoluminescence properties of the two Λ,Δ‐diastereomeric series are discussed with reference to [Ru(bpy)₃]²⁺.     

Interplay between the Diradical Character and Third‐Order Nonlinear Optical Properties in Fullerene Systems

To reveal new structure–property relationships in the nonlinear optical (NLO) properties of fullerenes that are associated with their open‐shell character, we investigated the interplay between the diradical character (y_i) and second hyperpolarizability (longitudinal component, γ_zzzz) in several fullerenes, including C₂₀ , C₂₆ , C₃₀ , C₃₆ , C₄₀ , C₄₂ , C₄₈ , C₆₀ , and C₇₀ , by using the broken‐symmetry density functional theory (DFT; LC‐UBLYP (μ=0.33)/6‐31G*//UB3LYP/6‐31G*). We found that the large differences between the geometry and topology of fullerenes have a significant effect on the diradical character of each fullerene. On the basis of their different diradical character, these fullerenes were categorized into three groups, that is, closed‐shell (y_i=0), intermediate open‐shell (0<y_i<1), and almost pure open‐shell compounds (y_i?1), which originated from their diverse topological features, as explained by odd‐electron‐density and spin‐density diagrams. For example, we found that closed‐shell fullerenes include C₂₀ , C₆₀ , and C₇₀ , whereas fullerenes C₂₆ and C₃₆ and C₃₀ , C₄₀ , C₄₂ , and C₄₈ are pure and intermediate open‐shell compounds, respectively. Interestingly, the γ_zzzz enhancement ratios between C₃₀ / C₃₆ and C₄₀ / C₆₀ are 4.42 and 11.75, respectively, regardless of the smaller π‐conjugation size in C₃₀ and C₄₀ than in C₃₆ and C₆₀ . Larger γ_zzzz values were obtained for other fullerenes that had intermediate diradical character, in accordance with our previous valence configuration interaction (VCI) results for the two‐site diradical model. The γ_zzzz density analysis shows that the large positive contributions originate from the large γ_zzzz density distributions on the right‐ and left‐extended edges of the fullerenes, between which significant spin polarizations (related to their intermediate diradical character) appear within the spin‐unrestricted DFT level of theory.     

Optically Active Oxo(phthalocyaninato)vanadium(IV) with Geometric Asymmetry: Synthesis and Correlation between the Circular Dichroism Sign and Conformation

Oxovanadium(IV) phthalocyanines (VOPcs) with a single‐handed rotation have been prepared, and their right‐ and left‐handed enantiomers resolved on a chiral HPLC column. These enantiomers gave circular dichroism (CD) spectra of opposite signs; the correlation between the CD sign and conformation was obtained by time‐dependent density functional theory (TDDFT) calculations: an enantiomer showing a negative sign in the Q band was suggested to be the right‐handed conformer viewing from the axial oxygen side, whereas that giving a positive CD sign was assigned to the left‐handed conformer. Although silicon phthalocyanines (SiPcs) with two different alkoxy axial ligands have been resolved similarly, the absence of a meaningful CD difference probably reflects the flat character of the SiPc plane compared to the VOPc plane. Changes in the Q‐band CD, depending on the relative orientation of the peripheral substituents, have been worked out theoretically and the origin of the chiroptical properties is discussed.     

The First Five‐Membered‐Heterocycle‐Fused Subphthalocyanine Analogues: Chiral Tri(benzo[b]thiopheno)subporphyrazines

Two tri(benzo[b]thiopheno)subporphyrazine regioisomers with C₃ and C₁ molecular symmetry have been isolated from the cyclotrimerization of benzo[b]thiophene‐2,3‐dicarbonitrile as the first five‐membered‐heterocycle‐fused subphthalocyanine analogues. Optical resolution of both regioisomers was achieved by using a chiral HPLC technique, affording the first chiral subphthalocyanine analogues.     

Ligand Design for Site‐Selective Metal Coordination: Synthesis of Transition‐Metal Complexes with η6‐Coordination of the Central Ring of Anthracene

A polycyclic aromatic ligand for site‐selective metal coordination was designed by using DFT calculations. The computational prediction was confirmed by experiments: 2,3,6,7‐tetramethoxy‐9,10‐dimethylanthracene initially reacts with [(C₅H₅)Ru(MeCN)₃]BF₄ to give the kinetic product with a [(C₅H₅)Ru]⁺ fragment coordinated at the terminal ring, which is then transformed into the thermodynamic product with coordination through the central ring. These isomeric complexes have markedly different UV/Vis spectra, which was explained by analysis of the frontier orbitals. At the same time, the calculations suggest that electrostatic interactions are mainly responsible for the site selectivity of the coordination.     

Controlling the nature of mixed (phthalocyaninato)(porphyrinato) rare-earth(III) double-decker complexes: the effects of nonperipheral alkoxy substitution of the phthalocyanine ligand

The half-sandwich rare-earth complexes [M(III)(acac)(TClPP)] (M = Sm, Eu, Y; TClPP = meso-tetrakis(4-chlorophenyl)porphyrinate; acac = acetylacetonate), generated in situ from [M(acac)3] x n H2O and H2(TClPP), were treated with 1,8,15,22-tetrakis(3-pentyloxy)phthalocyanine [H2{Pc(alpha-OC5H11)4}] (Pc = phthalocyaninate) under reflux in n-octanol to yield both the neutral nonprotonated and protonated (phthalocyaninato)(porphyrinato) rare-earth double-decker complexes, [M(III){Pc(alpha-OC5H11)4}(TClPP)] (1-3) and [M(III)H{Pc(alpha-OC5H11)4}(TClPP)] (4-6), respectively. In contrast, reaction of [Y(III)(acac)(TClPP)] with 1,4,8,11,15,18,22,25-octakis(1-butyloxy)phthalocyanine [H2Pc(alpha-OC4H9)8] gave only the protonated double-decker complex [Y(III)H{Pc(alpha-OC4H9)8}(TClPP)] (7). These observations clearly show the importance of the number and positions of substituents on the phthalocyanine ligand in controlling the nature of the (phthalocyaninato)(porphyrinato) rare-earth double-deckers obtained. In particular, alpha-alkoxylation of the phthalocyanine ligand is found to stabilize the protonated form, a fact supported by molecular-orbital calculations. A combination of mass spectrometry, NMR, UV-visible, near-IR, MCD, and IR spectroscopy, and X-ray diffraction analyses, facilitated the differentiation of the newly prepared neutral nonprotonated and protonated double-decker complexes. The crystal structure of the protonated form has been determined for the first time.     

Stepwise Reduction of 9,10‐Bis(dimesitylboryl)anthracene

Stepwise reduction of 9,10‐bis(dimesitylboryl)anthracene afforded an radical anion and a dianion, accompanied by stepwise changes of the aromaticity of the anthracene moiety. The radical has a planar semiquinoidal structure, while the dianion has a puckered quinoidal structure. The alteration of the geometries of the 9,10‐bis(dimesitylboryl)anthracene upon reduction is rationalized by the nature of the bonding. These results have been confirmed by cyclic voltammetry, X‐ray crystallography, NMR, EPR, and UV‐vis‐NIR spectroscopy, as well as DFT calculations.     

Second‐Order Nonlinear Optical Activity of Dipolar Chromophores Based on Pyrrole‐Hydrazono Donor Moieties

Donor1+donor2→acceptor : The second‐order NLO molecular properties of a class of dipolar chromophores that incorporate the following design elements are investigated: 1) a substituted hydrazono moiety as a strong donor; 2) a pyrrole ring as an auxiliary donor; 3) strong acceptor groups (see figure). Their first hyperpolarisabilities show good promise for use in electro‐optical devices.