Dennis P. Arnold

Efficient photocatalytic Suzuki cross-coupling reactions on Au–Pd alloy nanoparticles under visible light irradiation

We report herein highly efficient photocatalysts comprising supported nanoparticles (NPs) of gold (Au) and palladium (Pd) alloys, which utilize visible light to catalyse the Suzuki cross-coupling reactions at ambient temperature. The alloy NPs strongly absorb visible light, energizing the conduction electrons of NPs which produce highly energetic electrons at the surface sites. The surface of the energized NPs activates the substrates and these particles exhibit good activity on a range of typical Suzuki reaction combinations. The photocatalytic efficiencies strongly depend on the Au : Pd ratio of the alloy NPs, irradiation light intensity and wavelength. The results show that the alloy nanoparticles efficiently couple thermal and photonic energy sources to drive Suzuki reactions. Results of the density functional theory (DFT) calculations indicate that transfer of the light-excited electrons from the nanoparticle surface to the reactant molecules adsorbed on the nanoparticle surface activates the reactants. The knowledge acquired in this study may inspire further studies of new efficient photocatalysts and a wide range of organic syntheses driven by sunlight.

Infra-red spectra of phthalocyanine and naphthalocyanine in sandwich-type (na)phthalocyaninato and porphyrinato rare earth complexes

Abstract The infra-red spectroscopic data for a series of 88 sandwich-type (na)phthalocyaninato and porphyrinato rare earth complexes, including heteroleptic double- and triple-deckers, have been collected and systematically studied. The IR characteristics for unsubstituted and substituted (na)phthalocyaninato monoradical anion Pc′⋅− (Pc′=Pc, Pc*), Nc′⋅− (Nc′=Nc, Nc*), and dianion Pc′2− (Pc′=Pc, Pc*) are thus comparatively described.

Porphyrin Dimers Linked by Conjugated Butadiynes

Abstract 1,3-Butadiynes RCCCCR, where R = 5′-substituted nickel(II) octaethylporphyrin (NiOEP) ( 1e ), 2′-substituted nickel(II) 5′, 10′, 15′, 20′-tetraphenylporphyrin (NiTPP) ( 4e ), and 2′-substituted nickel(II) heptaethylporphyrin (NiHEP) ( 5d ), have been prepared from the respective bromovinyl species by dehydrobromination and oxidative coupling. The published synthesis of ( 1e ) has been improved to achieve a 40% yield for four steps from NiOEP. The metal-free bis(OEP) diyne was prepared by acid treatment of ( 1e ), while more strenuous conditions led to a novel furan substituted at the 2- and 5-positions with OEP units. The visible absorption spectra of the 5′- and 2′-substituted diynes differ markedly, the former compounds exhibiting split absorption bands and red shifts indicative of extensive chromophore interaction.

The preparation of novel porphyrins and bis(porphyrins) using palladium catalysed coupling reactions

Abstract The palladium(0) catalysed coupling of alkynyl porphyrins with either aryl iodides or a β- bromovinylporphyrin leads to symmetrical and unsymmetrical bis(porphyrins) incorporating various unsaturated bridges. Some novel porphyrins bearing enyne and alkyne substituents are also described.

Infrared spectra of phthalocyanine and naphthalocyanine in sandwich-type (na)phthalocyaninato and porphyrinato rare earth complexes. Part 3. The effects of substituents and molecular symmetry on the infrared characteristics of phthalocyanine in bis(phthalocyaninato) rare earth complexes

The infra-red (IR) spectroscopic data for a series of 45 homoleptic unsubstituted and substituted bis(phthalocyaninato) rare earth complexes M(Pc)2 and M(Pc*)2 [M=Y, La...Lu except Pm; H2Pc=phthalocyanine; H2Pc*=2,3,9,10,16,17,24,25-octakis(octyloxy)phthalocyanine (H2OOPc) and 2(3),9(10),16(17),24(25)-tetra(tert-butyl)phthalocyanine (H2TBPc)] have been collected with resolution of 2 cm(-1). The IR spectra for M(Pc)2 and M(OOPc)2 are much simpler than those of M(TBPc)2, revealing the relatively higher symmetry of the former two compounds. For M(Pc)2 the Pc-* marker band at 1312-1323 cm(-1), attributed to the pyrrole stretching, and the isoindole stretching band at 1439-1454 cm(-1) are found to be dependent on the central rare earth size, shifting slightly to the higher energy along with the decrease of rare earth radius. The frequency of the vibration at 876-887 cm(-1) is also dependent on the rare earth ionic size. The metal size-sensitivity of this band and theoretical studies render it possible to re-assign it to the coupling of isoindole deformation and aza vibration. The nature of another metal-sensitive vibration mode at 1110-1116 cm(-1), which was previously assigned to the C-H bending, is now re-assigned as an isoindole breathing mode with some small contribution also from C-H in-plane bending. These assignments are supported by comparative studies of the IR spectra of substituted bis(phthalocyaninato) analogues M(OOPc)2 and M(TBPc)2. By comparison between the IR spectra of unsubstituted and substituted bis(phthalocyaninato) rare earth analogues and according to the IR characteristics of alkyl groups, some characteristic vibrational fundamentals due to the Pc rings and the substituents can be separately identified. In conclusion, all the metal size-dependent IR absorptions are composed primarily of the vibrations of pyrrole or isoindole stretching, breathing or deformation or aza stretching of the Pc ring.

Synthesis and Spectroscopic Properties of Homoleptic Bis[octakis(octyloxy)phthalocyaninato] Rare Earth(III) Sandwich Complexes

A series of homoleptic bis[2,3,9,10,16,17,23,24-octakis(octyloxy)phthalocyaninato] rare earth(III) sandwich complexes {M[Pc(OC8H17)8]2 (M = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Y, Ho, Er, Tm) (1) and (3)–(13), and HCe[Pc(OC8H17)8]2 (2)} has been prepared by the cyclic tetramerization of 4,5-di(octyloxy)phthalonitrile on the template of M(acac)3·nH2O in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene. Their spectroscopic properties were systematically investigated by ultraviolet–visible, near-infrared, infrared, and mass spectroscopy, and the effects of ionic radius on the inter-ring electronic communication are described.

Sandwich complexes of naphthalocyanine with the rare earth metals

Over the past two decades and in particular the past five years, numerous sandwich-type rare earth complexes containing naphthalocyanine ligands have been synthesized. The more extended delocalized π-electron system of naphthalocyanine in comparison with phthalocyanine generates unique physical, spectroscopic, electrochemical and photoelectrochemical properties which have aroused significant research interest in these compounds. This review summarizes recent progress in research on this important class of molecular materials and overviews the current status of the field.

Functionalization of 5,15-Diphenylporphyrin: Preparation and X-Ray Crystal Structures of meso Nitro, Bromo, and Trimethylsilylethynyl Derivatives

Substitutions on 5,15-diphenylporphyrin led to the isolation of mono- and di-bromo and mono- and di-nitro derivatives, which were converted into their respective nickel(II) complexes. Reaction of the bromoporphyrins with iodine/silver nitrite resulted in nitrodebromination as well as conventional nitration. The nickel(II) complex of 5-nitro-10,20-diphenylporphyrin was reduced to the 5-amino derivative. The nickel(II) complexes of the bromoporphyrins were converted into the respective mono- and bis-(trimethylsilylethynyl) species. The crystal structures of 5-nitro-10,20-diphenylporphyrin, 5-bromo- 10,20-diphenylporphyrinatonickel(II), and 10,20-diphenyl-5-(trimethylsilylethynyl)porphyrinatonickel(II) were determined.

Raman spectroscopic characteristics of phthalocyanine and naphthalocyanine in sandwich-type (na)phthalocyaninato and porphyrinato rare earth complexes

Abstract The Raman spectroscopic data for a series of 50 phthalocyaninato and/or porphyrinato rare earth complexes including monomeric Tb[T(4-Cl)PP]acac, and sandwich-type RE(Pc′)2 [RE=Ce, Eu, Gd, Tb, Y; Pc′=Pc, Pc(OC5H11)8, Pc(OC8H17)8, Pc(C7H15)8], RE(Nc*)2 [RE=La, Ce, Pr, Nd, Eu, Gd, Tb, Er, Y; Nc*=Nc(tBu)4, Nc(SC12H25)8], (Pc)RE(Pc*)RE(Pc*) [RE=Eu, Tb, Er; Pc*=Pc(OC5H11)8], (Pc)Eu(Pc*)Er(Pc*) [Pc*=Pc(OC8H17)8], Eu(Pc)(Pc*) [Pc*=Pc(OC5H11)8, Pc(C7H15)8], Eu(Por)(Pc′) [Por=TPP, TPyP, T(4-Cl)PP, T(4-OMe)PP, T(4-tBu)PP; Pc′=Pc, Pc(C7H15)8], Eu(Por)(Nc) [Por=TPyP, T(4-Cl)PP], HEu(Por)(Pc), Ce(TPyP)(Pc), RE2(Por)2(Pc) [RE=Ce, Eu; Por=TPP, TPyP, T(4-Cl)PP, T(4-tBu)PP], and RE2(Por)(Pc′)2 [RE=Eu, Ce, Y; Por=TPP, TPyP, T(4-Cl)PP, T(4-OMe)PP, T(4-tBu)PP, OEP; Pc′=Pc, Pc(OC8H17)8, Pc(C7H15)8], and (TPyP)RE(Pc*)RE′(Pc*) [RE≠RE′=Eu, Y; Pc*=Pc(C7H15)8] have been collected in the solid state using a Raman microprobe and excitation at 632.8 nm (and in some cases, 780 nm). The Raman characteristics for unsubstituted and substituted (na)phthalocyaninato mono-radical anions Pc′ − (Pc′=Pc, Pc*), Nc* − and dianions Pc′2− (Pc′=Pc, Pc*) are thus comparatively described. The intense band at ca. 1500 cm−1 was confirmed to be the marker band for Pc′ − and Pc′2− anions.

Porphyrin dimers linked by conjugated butadiyne bridges: preparations, spectra, voltammetry and reductive spectroelectrochemistry of {[M(OEP)](m-C4)[M(OEP)]} (M2 H4, Co2, Ni2, Cu2, Zn2, Pd2, Pt2, Co/Ni, Ni/Cu, Ni/Zn)

A series of derivatives M2P2 (M2 ≡ H4, Co2, Ni2, Cu2, Zn2, Pd2, Pt2, Co/Ni, Ni/Cu, Ni/Zn) of the ligand meso,meso′-bis(octaethylporphyrinyl)butadiyne has been prepared and characterized by 1H NMR, FT Raman and visible absorption spectroscopies as well as by cyclic and a.c. voltammetry in CH2Cl2 solution at 20 and −40 °C. The electronic spectra exhibit multiple Soret bands and the voltammetry reveals successive one-electron reductions indicating the accessibility of ‘mixed valence’ π-radical anions and π-dianions. Using in situ thin layer spectroelectrochemistry, the UV to near-IR spectra of [M2P2]1− and [M2P2]2− (M as above) were recorded at ≤ −40 °C. Apart from the Co complexes (reduced at the metal ion), the bis(porphyrin) anions have spectra which include sharp, intense near-IR bands (e = 50 000–200 000 M−1cm−1) at c. 4500 and 11 500 cm−1([M2P2]1−) and 9500 cm−1([M2P2]2−). An empirically constructed semiquantitative frontier orbital model explains the observed electronic absorption bands. Inter-porphyr...