Juliá Hernández, Fabio

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Juliá Hernández, Fabio

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Juliá Hernández, Fabio

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Universidad de Murcia. Departamento de Química Inorgánica

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Open Access
Ferrioxalate Photocatalysis: A Multitasking Platform for Reductive Iron Catalysis
(AAAS, 2001-01-01) Carlos Bernabeu; Sergio Adalid; Sara Colombo; Nojus Cironis; Partha Pratim Sen; Ken Okuno; Fabio Juliá; Juliá Hernández, Fabio; Fabio Juliá; Química Inorgánica; Fabio Juliá; Facultades de la UMU::Facultad de Química
Iron’s abundance motivates its use in sustainable catalyst systems that also offer complementary reactivity manifolds compared to precious metals. However, the challenging reduction of benchmark iron salts to active species hinders their application in reductive transformations. Here we report a photochemical strategy that exploits the innate reactivity of ligand-to-metal charge-transfer (LMCT) excited states of iron oxalate complexes to harness oxalate salts as latent terminal 2-electron reductants in iron catalysis. The investigation of this activation mode has led to the development of a versatile catalytic platform enabling transformations hitherto inaccessible to previous iron catalyst systems. The synthetic value of this tactic is demonstrated on diverse reductive transformations using readily available building blocks with high chemoselectivity, opening new synthetic opportunities.
Open Access
Catalysis in the excited state: bringing innate transition metal photochemistry into play
(American Chemical Society, 2005-03-05) Juliá Hernández, Fabio; Química Inorgánica; Facultad de Química
Transition metal catalysis is an indispensable tool for organic synthesis that has been harnessed, modulated and perfected for many decades by careful selection of metal centers and ligands, giving rise to synthetic methods with unparalleled efficiency and chemoselectivity. Recent developments have demonstrated how light irradiation can also be recruited as a powerful tool to dramatically alter the outcome of catalytic reactions, providing access to innovative pathways with remarkable synthetic potential. In this context, the adoption of photochemical conditions as a mainstream strategy to drive organic reactions has unveiled exciting opportunities to exploit the rich excited-state framework of transition metals for catalytic applications. This Perspective examines the advances on the application of transition metal complexes as standalone photocatalysts, exploiting the innate reactivity of their excited states beyond the common use as photoredox catalysts. An account of relevant examples is dissected to provide a discussion on the electronic reorganization, the orbitals involved and the associated reactivity of different types of excited states. This analysis aims to provide practitioners with fundamental principles and guiding strategies to understand, design and apply light-activation strategies to homogeneous transition metal catalysis for organic synthesis.
Open Access
Developing strongly luminescent platinum(IV) complexes: facile synthesis of bis- cyclometalated neutral emitters
(2016) Juliá Hernández, Fabio; Bautista, Delia; González Herrero, Pablo; Química Inorgánica
A straightforward, one-pot procedure has been developed for the synthesis of bis-cyclometalated chloro(methyl)platinum(IV) complexes with a wide variety of heteroaromatic ligands of the 2-arylpyridine type. The new compounds exhibit phosphorescent emissions in the blue to orange colour range and represent the most efficient Pt(IV) emitters reported to date, with quantum yields up to 0.81 in fluid solutions at room temperature.
Open Access
Exploring Excited-State Tunability in Luminescent Tris-cyclometalated Platinum(IV) Complexes: Synthesis of Heteroleptic Derivatives and Computational Calculations
(2014-10-29) Aullón, Gabriel; Bautista, Delia; Juliá Hernández, Fabio; González Herrero, Pablo; Química Inorgánica
The synthesis, structure, electrochemistry, and photophysical properties of a series of heteroleptic tris-cyclometalated Pt(IV) complexes are reported. The complexes mer-[Pt(C^N)2(C'^N')]OTf, with C^N = C-deprotonated 2-(2,4-difluorophenyl)pyridine (dfppy) or 2-phenylpyridine (ppy), and C'^N' = C-deprotonated 2-(2-thienyl)pyridine (thpy) or 1-phenylisoquinoline (piq), were obtained by reacting bis-cyclometalated precursors [Pt(C^N)2Cl2] with 2 equiv of AgOTf and an excess of the N'^C'H pro-ligand. The complex mer-[Pt(dfppy)2(ppy)]OTf was obtained analogously and photoisomerized to its fac counterpart. The new complexes display long-lived luminescence at room temperature in the blue to orange color range. The emitting states involve electronic transitions almost exclusively localized on the ligand with the lowest π-π* energy gap and have very little metal character. DFT and TD-DFT calculations on mer-[Pt(ppy)2(C'^N')]+ (C'^N' = thpy, piq) and mer/fac-[Pt(ppy)3]+ support this assignment and provide a basis for the understanding of the luminescence of tris-cyclometalated Pt(IV) complexes. Excited states of LMCT character may become thermally accessible from the emitting state in the mer isomers containing dfppy or ppy as chromophoric ligands, leading to strong nonradiative deactivation. This effect does not operate in the fac isomers or the mer complexes containing thpy or piq, for which nonradiative deactivation originates mainly from vibrational coupling to the ground state.
Open Access
Synthesis and Photophysical Properties of Cyclometallated Pt(II) 1,2-Benzenedithiolate Complexes and Heterometallic Derivatives Obtained from the Addition of [Au(PCy3)]+ Units
(American Chemical Society, 2012-04-13) Juliá Hernández, Fabio; Jones, Peter G.; González Herrero, Pablo; Química Inorgánica
The cyclometalated compounds [Pt(C^N)(HC^N)Cl] [HC^N = 2-phenylpyridine (Hppy; 1a), 1-(4-tert-butylphenyl)isoquinoline (Htbpiq; 1b)] react with 1,2-benzenedithiol, t-BuOK, and Bu4NCl in a 1:1:2:1 molar ratio in CH2Cl2/MeOH to give the complexes Bu4N[Pt(C^N)(bdt)] [bdt = 1,2-benzenedithiolate; C^N = ppy (Bu4N2a), tbpiq (Bu4N2b)]. In the absence of Bu4NCl, the same reactions afford solutions of K2a and K2b, which react with [AuCl(PCy3)] to give the neutral heterometallic derivatives [Pt(C^N)(bdt){Au(PCy3)}] [C^N = ppy (3a), tbpiq (3b)]. The cationic derivatives [Pt(C^N)(bdt){Au(PCy3)}2]ClO4 [C^N = ppy (4a), tbpiq (4b)] are obtained by reacting 3a and 3b with acetone solutions of [Au(OClO3)(PCy3)]. The crystal structures of 3b and 4b reveal the formation of short Pt···Au metallophilic contacts in the range 2.929–3.149 Å. Complexes 3b, 4a, and 4b undergo dynamic processes in solution that involve the migration of the [Au(PCy3)]+ units between the S atoms of the dithiolate. Complexes Bu4N2a and 2b display a moderately solvatochromic band in their electronic absorption spectra that can be ascribed to a transition of mixed ML′CT/LL′CT character (M= metal; L = bdt; L′ = C^N; CT = charge transfer), while their emissions are assignable to transitions of the same orbital parentage but from triplet excited states. The successive addition of [Au(PCy3)]+ units to the anions 2a and 2b results in an increase in the absorption and emission energies attributable to lower highest occupied molecular orbital energies. Additionally, the characteristics of the absorption and emission spectra of the heterometallic derivatives indicate a gradual loss of LL′CT character in the involved electronic transitions, with a concomitant increase of the L′C and ML′CT contributions.
Open Access
Homoleptic tris-cyclometalated platinum(iv) complexes: a new class of long-lived, highly efficient 3LC emitters
(2014) Bautista, Delia; Fernández-Hernández, Jesus Miguel; Juliá Hernández, Fabio; González Herrero, Pablo; Química Inorgánica
The synthesis of meridional and facial isomers of tris-cyclometalated Pt(IV) complexes, [Pt(C^N)3]OTf, where C^N is a C-deprotonated 2-phenylpyridine-based ligand or 1-phenylpyrazole, is reported for the first time. The facial isomers exhibit high-energy emissions from essentially 3LC excited states, characterized by lifetimes of hundreds of microseconds and quantum yields up to 0.49 at room temperature in fluid solution, the highest ever found for Pt(IV) complexes. Stern–Volmer studies demonstrate the high sensitivity of the facial isomers toward oxygen and their electrochemical characterization reveals large redox gaps and a strong oxidizing character in the excited state.
Open Access
Influence of Ancillary Ligands and Isomerism on the Luminescence of Bis-cyclometalated Platinum(IV) Complexes
(ACS, 2016-08-01) Juliá Hernández, Fabio; García-Legaz, María Dulce; Bautista, Delia; González Herrero, Pablo; Química Inorgánica
The synthesis, characterization, and photophysical properties of a wide variety of bis-cyclometalated Pt(IV) complexes featuring a C2-symmetrical or unsymmetrical {Pt(ppy)2} unit (sym or unsym complexes, respectively; ppy = C-deprotonated 2-phenylpyridine) and different ancillary ligands are reported. Complexes sym-[Pt(ppy)2X2] (X = OTf–, OAc–) were obtained by chloride abstraction from sym-[Pt(ppy)2Cl2] using the corresponding AgX salts, and the triflate derivative was employed to obtain homologous complexes with X = F–, Br–, I–, trifluoroacetate (TFA–). Complexes unsym-[Pt(ppy)2(Me)X] (X = OTf–, F–) were prepared by reacting unsym-[Pt(ppy)2(Me)Cl] with AgOTf or AgF, respectively, and the triflate derivative was employed as precursor for the synthesis of the homologues with X = Br–, I–, or TFA– through its reaction with the appropriate anionic ligands. The previously reported complexes unsym-[Pt(ppy)2X2] (X = Cl–, Br–, OAc–, TFA–) are included in the photophysical study to assess the influence of the arrangement of the cyclometalated ligands. Density functional theory (DFT) and time-dependent DFT calculations on selected derivatives were performed for a better interpretation of the observed excited-state properties. Complexes sym-[Pt(ppy)2X2] (except X = I–) exhibit phosphorescent emissions in fluid solutions at 298 K arising from essentially 3LC(ppy) excited states, which are very similar in shape and energy. However, their efficiencies are heavily dependent on the nature of the ancillary ligands, which affect the energy of deactivating ligand-to-ligand charge transfer (LLCT) or ligand-to-metal charge transfer (LMCT) states. The fluoride derivative sym-[Pt(ppy)2F2] shows the highest quantum yield of this series (Φ = 0.398), mainly because the relatively high metal-to-ligand charge transfer admixture in its emitting state leads to a high radiative rate constant. Complexes unsym-[Pt(ppy)2X2] emit from 3LC(ppy) states in frozen matrices at 77 K, but their emissions are totally quenched in fluid solution at 298 K because of the presence of low-lying, dissociative LMCT excited states, which also cause photoisomerization reactions. Complexes unsym-[Pt(ppy)2(Me)X] (X = F–, Cl–, Br–, TFA–) show strong emissions in fluid solutions at 298 K (Φ = 0.52–0.63) because deactivating LMCT states lie at high energies. However, derivative unsym-[Pt(ppy)2(Me)I] is only weakly emissive at 298 K because of the presence of low-lying LLCT [p(I) → π*(ppy)] states.
Open Access
Aromatic C−H Activation in the Triplet Excited State of Cyclometalated Platinum(II) Complexes Using Visible Light
(2016-04-08) Juliá Hernández, Fabio; González Herrero, Pablo; Química Inorgánica
The visible-light driven cyclometalation of arene substrates containing an N-donor heteroaromatic moiety as directing group by monocy-clometalated Pt(II) complexes is reported. Precursors of the type [PtMe(C^N)(N^CH)], where N^CH is 2-phenylpyridine (ppyH) or related compunds with diverse electronic properties and C^N is the corresponding cyclometalated ligand, afford homoleptic cis-[Pt(C^N)2] complexes upon irradiation with blue LEDs at room temperature with evolution of methane. Heteroleptic derivatives cis-[Pt(ppy)(C'^N')] are obtained analogously from [PtMe(ppy)(N'^C'H)], where N'^C'H represents an extended set of heteroaromatic compounds. Experimental and computational studies demonstrate an unprecedented C–H oxidative addition, which is initiated by a triplet excited state of metal-to-ligand charge-transfer (MLCT) character and leads to a detectable Pt(IV) methyl hydride intermediate.