Synthesis, Structural Characterization, and Reactivity of Zirconium Complexes Containing Trimethylenemethane-Based Ligands

General synthetic routes to zirconium metallocene-like complexes containing derivatives of the dianionic trimethylenemethane (TMM) ligand are presented. One approach consists of reacting the dilithium salts of TMM, tribenzylidenemethane (TBM), tert-butyltribenzylidenemethane (t-Bu-TBM), and dibenzylidenemethylenemethane (DBM) with either Cp*ZrCl3 or CpZrCl3(DME). In the case of the small TMM fragment, the product is the zwitterionic Cp*(TMM)Zr(μ-Cl)2Li(TMEDA) (1). Larger TMM derivatives give discrete salts such as [Cp*(TBM)ZrCl2][Li(TMEDA)2] (2), [Cp(TBM)ZrCl2][Li(TMEDA)2] (3), [Cp(t-Bu-TBM)ZrCl2][Li(TMEDA)2] (4), [Cp*(t-Bu-TBM)ZrCl2][Li(TMEDA)2] (5), and [Cp*(exo-endo-DBM)ZrCl2][Li(TMEDA)2] (6). The reaction of TBM(LiTMEDA)2 with Cp*ZrCl2CH2Ph affords [Cp*(TBM)ZrCl(CH2Ph)][Li(TMEDA)2] (9); thus the retention of LiCl(TMEDA)2 by zirconium is strong. Structural characterization of these complexes reveals crowded environments around the zirconium, especially when both TBM and Cp* are coordinated. It is also possible to take advantage of intramolecular σ-bond metathesis reactions to convert coordinated allyl ligands to TMM-related fragments. For example, [Cp*(TMM)Zr]2(μ-CH2) (10) is derived from Cp*(η3-CH2C(Me)CH2)ZrMe2, and Cp*(TBM)ZrMe(THF) (12) is from Cp*(PhCH2C(CHPh)2)ZrMe2 (11). Formation of the methylpropargyl complex Cp*(TBM)Zr(η3-CH2CCMe) (13) from Cp*(TBM)ZrMe(THF) and 2-butyne instead of a butenyl derivative is a consequence of steric constraints. Activation of 2−6 with methylaluminoxane affords homogeneous catalyst mixtures for polymerization of ethylene and 1,5-hexadiene and copolymerization of ethylene with 1-hexene. There is a strong correlation between catalyst precursor structure and reactivity. Polyethylene can also be prepared by pressurizing a vessel containing only Cp*(TBM)ZrMe(THF)

Interpolyelectrolyte Complexes of Conjugated Copolymers and DNA: Platforms for Multicolor Biosensors

Interchain interactions modulate the frequency of emission from a cationic water-soluble conjugated polymer. The polymer, PFPB, is obtained by a Suzuki copolymerization of p-phenylenebisboronic acid with a 95:5 mixture of 2,7-dibromo-9,9-bis(6‘-bromohexyl)fluorene and 4,7-dibromo-2,1,3-benzothiadiazole, followed by quarternization of the pendant groups by addition of NMe3. The structure of PFPB contains 5% of the 2,1,3-benzothiadiazole (BT) chromophore within a cationic poly(fluorene-co-phenylene) polymer chain. The emission of PFPB is blue under dilute conditions (-6 M in repeat units) and green at higher concentrations. Energy transfer to dye-labeled ss-DNA is more efficient, relative to the parent polymer poly(9,9-bis(6‘-N,N,N,-trimethylammonium)hexyl)fluorene-co-alt-1,4-phenylene) dibromide (PFP), as a result of improved spectral overlap. By using a peptide nucleic acid (PNA-C*) labeled with a red-emitting chromophore one can obtain three different emission colors, depending on the nature of the substrate under interrogation. If no ss-DNA is present, the solution emits blue. With a ss-DNA that is noncomplementary to PNA-C*, green emission is observed. Red emission occurs upon addition of ss-DNA complementary to the PNA sequence

Synthesis, Structural Characterization, and Reactivity of Zirconium Complexes Containing Trimethylenemethane-Based Ligands

General synthetic routes to zirconium metallocene-like complexes containing derivatives of the dianionic trimethylenemethane (TMM) ligand are presented. One approach consists of reacting the dilithium salts of TMM, tribenzylidenemethane (TBM), tert-butyltribenzylidenemethane (t-Bu-TBM), and dibenzylidenemethylenemethane (DBM) with either Cp*ZrCl3 or CpZrCl3(DME). In the case of the small TMM fragment, the product is the zwitterionic Cp*(TMM)Zr(μ-Cl)2Li(TMEDA) (1). Larger TMM derivatives give discrete salts such as [Cp*(TBM)ZrCl2][Li(TMEDA)2] (2), [Cp(TBM)ZrCl2][Li(TMEDA)2] (3), [Cp(t-Bu-TBM)ZrCl2][Li(TMEDA)2] (4), [Cp*(t-Bu-TBM)ZrCl2][Li(TMEDA)2] (5), and [Cp*(exo-endo-DBM)ZrCl2][Li(TMEDA)2] (6). The reaction of TBM(LiTMEDA)2 with Cp*ZrCl2CH2Ph affords [Cp*(TBM)ZrCl(CH2Ph)][Li(TMEDA)2] (9); thus the retention of LiCl(TMEDA)2 by zirconium is strong. Structural characterization of these complexes reveals crowded environments around the zirconium, especially when both TBM and Cp* are coordinated. It is also possible to take advantage of intramolecular σ-bond metathesis reactions to convert coordinated allyl ligands to TMM-related fragments. For example, [Cp*(TMM)Zr]2(μ-CH2) (10) is derived from Cp*(η3-CH2C(Me)CH2)ZrMe2, and Cp*(TBM)ZrMe(THF) (12) is from Cp*(PhCH2C(CHPh)2)ZrMe2 (11). Formation of the methylpropargyl complex Cp*(TBM)Zr(η3-CH2CCMe) (13) from Cp*(TBM)ZrMe(THF) and 2-butyne instead of a butenyl derivative is a consequence of steric constraints. Activation of 2−6 with methylaluminoxane affords homogeneous catalyst mixtures for polymerization of ethylene and 1,5-hexadiene and copolymerization of ethylene with 1-hexene. There is a strong correlation between catalyst precursor structure and reactivity. Polyethylene can also be prepared by pressurizing a vessel containing only Cp*(TBM)ZrMe(THF)

Hydrogenation of Borollide−Tantalum Complexes: Low-Valent Intermediates and the Effect of Exocyclic Substituents

Hydrogenation of Borollide−Tantalum Complexes:  Low-Valent Intermediates and the Effect of Exocyclic Substituent

Synthesis, Structural Characterization, and Reactivity of Zirconium Complexes Containing Trimethylenemethane-Based Ligands

General synthetic routes to zirconium metallocene-like complexes containing derivatives of the dianionic trimethylenemethane (TMM) ligand are presented. One approach consists of reacting the dilithium salts of TMM, tribenzylidenemethane (TBM), tert-butyltribenzylidenemethane (t-Bu-TBM), and dibenzylidenemethylenemethane (DBM) with either Cp*ZrCl3 or CpZrCl3(DME). In the case of the small TMM fragment, the product is the zwitterionic Cp*(TMM)Zr(μ-Cl)2Li(TMEDA) (1). Larger TMM derivatives give discrete salts such as [Cp*(TBM)ZrCl2][Li(TMEDA)2] (2), [Cp(TBM)ZrCl2][Li(TMEDA)2] (3), [Cp(t-Bu-TBM)ZrCl2][Li(TMEDA)2] (4), [Cp*(t-Bu-TBM)ZrCl2][Li(TMEDA)2] (5), and [Cp*(exo-endo-DBM)ZrCl2][Li(TMEDA)2] (6). The reaction of TBM(LiTMEDA)2 with Cp*ZrCl2CH2Ph affords [Cp*(TBM)ZrCl(CH2Ph)][Li(TMEDA)2] (9); thus the retention of LiCl(TMEDA)2 by zirconium is strong. Structural characterization of these complexes reveals crowded environments around the zirconium, especially when both TBM and Cp* are coordinated. It is also possible to take advantage of intramolecular σ-bond metathesis reactions to convert coordinated allyl ligands to TMM-related fragments. For example, [Cp*(TMM)Zr]2(μ-CH2) (10) is derived from Cp*(η3-CH2C(Me)CH2)ZrMe2, and Cp*(TBM)ZrMe(THF) (12) is from Cp*(PhCH2C(CHPh)2)ZrMe2 (11). Formation of the methylpropargyl complex Cp*(TBM)Zr(η3-CH2CCMe) (13) from Cp*(TBM)ZrMe(THF) and 2-butyne instead of a butenyl derivative is a consequence of steric constraints. Activation of 2−6 with methylaluminoxane affords homogeneous catalyst mixtures for polymerization of ethylene and 1,5-hexadiene and copolymerization of ethylene with 1-hexene. There is a strong correlation between catalyst precursor structure and reactivity. Polyethylene can also be prepared by pressurizing a vessel containing only Cp*(TBM)ZrMe(THF)

Aggregation-Mediated Optical Properties of pH-Responsive Anionic Conjugated Polyelectrolytes

Conjugated polyelectrolyte copolymers containing 2,1,3-benzothiadiazole- (BT) and oligo(ethylene oxide)-substituted fluorene and phenylene units have been designed and synthesized. The phenylene pendent groups also have carboxylic acid functionalities, which allow probing the effect of pH on optical properties. The BT content in the backbone can be regulated at the synthesis stage. Dynamic light scattering studies show that polymers aggregate in water at low pH. Increased interchain contacts give rise to a lowering of the photoluminescence (PL) efficiency via self-quenching when the BT units are absent and increased levels of FRET from the phenylene−fluorene segments to BT. Furthermore, the PL efficiency of BT increases in the aggregated structures. Examination of solvent effects indicates that the increased BT efficiencies are likely due to decreased contact with water. The changes in PL efficiencies are reversible, showing that the aggregates are dynamic and not kinetically constrained

Synthesis, Characterization, and Spectroscopy of 4,7,12,15-[2.2]Paracyclophane Containing Donor and Acceptor Groups: Impact of Substitution Patterns on Through-Space Charge Transfer

This paper reports the synthesis of 4,7,12,15-tetra(4‘-dihexylaminostyryl)[2.2]paracyclophane (1), 4-(4‘-dihexylaminostyryl)-7,12,15-tri(4‘ ‘-nitrostyryl)[2.2]paracyclophane (2), 4,7-bis(4‘-dihexylaminostyryl)-12,15-bis(4‘ ‘-nitrostyryl)-[2.2]paracyclophane (3), 4,7,12-tris(4‘-dihexylaminostyryl)-15-(4‘ ‘-nitrostyryl)[2.2]paracyclophane (4), 4,15-bis(4‘-dihexylaminostyryl)-7,12-bis(4‘ ‘-nitrostyryl)[2.2]paracyclophane (5), and 4,12-bis(4‘-dihexylaminostyryl)-7,15-bis(4‘ ‘-nitrostyryl)[2.2]paracyclophane (6). These molecules represent different combinations of bringing together distyrylbenzene chromophores containing donor and acceptor groups across a [2.2]paracyclophane (pCp) bridge. X-ray diffraction studies show that the lattice arrangements of 1 and 3 are considerably different from those of the parent chromophores 1,4-bis(4‘dihexylaminostyryl)benzene (DD) and 1,4-di(4‘-nitrostyryl)benzene (AA). Differences are brought about by the constraint by the pCp bridge and by virtue of chirality in the “paired” species. The absorption and emission spectra of 1−6 are also presented. Clear evidence of delocalization across the pCp structure is observed. Further, in the case of 2, 3, and 4, emission from the second excited state takes place

Hydrogenation of Borollide−Tantalum Complexes: Low-Valent Intermediates and the Effect of Exocyclic Substituents

Hydrogenation of Borollide−Tantalum Complexes:  Low-Valent Intermediates and the Effect of Exocyclic Substituent

Lewis Acid Adducts of Narrow Band Gap Conjugated Polymers

We report on the interaction of Lewis acids with narrow band gap conjugated copolymers containing donor and acceptor units. Examination of the widely used poly[(4,4-bis(2-ethylhexyl)cyclopenta-[2,1-b:3,4-b′]dithiophene)-2,6-(diyl-alt-benzo[2,1,3]thiadiazole)-4,7-diyl] (1) shows weaker binding with B(C6F5)3 when compared with a small molecule that contains a cyclopenta-[2,1-b:3,4-b′]dithiophene (CDT) unit flanked by two benzo[2,1,3]thiadiazole (BT) fragments. Studies on model compounds representative of 1, together with a comparison between B(C6F5)3 and BBr3, indicate that the propensity for Lewis acid coordination is decreased because of steric encumbrance surrounding the BT nitrogen sites. These observations led to the design of chromophores that incorporate an acceptor unit with a more basic nitrogen site, namely pyridal[2,1,3]thiadiazole (PT). That this strategy leads to a stronger B−N interaction was demonstrated through the examination of the reaction of B(C6F5)3 with two small molecules bis(4,4-bis(hexyl)-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)-4,7-pyridal[2,1,3]thiadiazole (8) and bis{2-thienyl-(4,4-bis(hexyl)-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)}-4,7-pyridal[2,1,3]thiadiazole (9) and two polymer systems (poly[(4,4-bis(2-ethylhexyl)cyclopenta-[2,1-b:3,4-b′]dithiophene)-2,6-diyl-alt-([1,2,5]thiadiazolo[3,4-c]pyridine)-4,7-diyl] (10) and poly[(4,4-bis(2-ethylhexyl)cyclopenta-[2,1-b:3,4-b′]dithiophene)-2,6-diyl-alt-(4′,7′-bis(2-thienyl)-[1,2,5]thiadiazolo[3,4-c]pyridine)-5,5-diyl] (11). From a materials perspective, it is worth pointing out that through the binding of B(C6F5)3, new NIR-absorbing polymers can be generated with band gaps from 1.31 to 0.89 eV. A combination of studies involving ultraviolet photoemission spectroscopy and density functional theory shows that the narrowing of the band gap upon borane coordination to the pyridal nitrogen on PT is a result of lowering the energies of both the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the optically relevant fragments; however, the LUMO is decreased to a greater extent, thereby giving rise to the narrowing of the gap

Synthesis, Characterization, and Spectroscopy of 4,7,12,15-[2.2]Paracyclophane Containing Donor and Acceptor Groups: Impact of Substitution Patterns on Through-Space Charge Transfer

This paper reports the synthesis of 4,7,12,15-tetra(4‘-dihexylaminostyryl)[2.2]paracyclophane (1), 4-(4‘-dihexylaminostyryl)-7,12,15-tri(4‘ ‘-nitrostyryl)[2.2]paracyclophane (2), 4,7-bis(4‘-dihexylaminostyryl)-12,15-bis(4‘ ‘-nitrostyryl)-[2.2]paracyclophane (3), 4,7,12-tris(4‘-dihexylaminostyryl)-15-(4‘ ‘-nitrostyryl)[2.2]paracyclophane (4), 4,15-bis(4‘-dihexylaminostyryl)-7,12-bis(4‘ ‘-nitrostyryl)[2.2]paracyclophane (5), and 4,12-bis(4‘-dihexylaminostyryl)-7,15-bis(4‘ ‘-nitrostyryl)[2.2]paracyclophane (6). These molecules represent different combinations of bringing together distyrylbenzene chromophores containing donor and acceptor groups across a [2.2]paracyclophane (pCp) bridge. X-ray diffraction studies show that the lattice arrangements of 1 and 3 are considerably different from those of the parent chromophores 1,4-bis(4‘dihexylaminostyryl)benzene (DD) and 1,4-di(4‘-nitrostyryl)benzene (AA). Differences are brought about by the constraint by the pCp bridge and by virtue of chirality in the “paired” species. The absorption and emission spectra of 1−6 are also presented. Clear evidence of delocalization across the pCp structure is observed. Further, in the case of 2, 3, and 4, emission from the second excited state takes place