Functionalised organometallic photoswitches containing dihydropyrene units

Functionalising organic molecular photoswitches with metal complexes has been shown to alter and enhance their switching states. These organometallic photoswitches provide a promising basis for novel smart molecular materials and molecular electronic devices. We have detailed the synthesis and characterisation of mono- and bimetallic half-sandwich ruthenium and iron complexes functionalised with alkynyl dihydropyrenes (DHP). Their electronic and photophysical properties were determined by the use of chemical, electrochemical and spectroelectrochemical techniques. The introduction of the metal alkynyl moiety allows access to additional redox and protonation states not accessible by the DHP alone. An additional metal alkynyl moiety inhibits observable photochromic switching. Analysis of the NIR and IR bands in the mixed valence complexes suggests there is a high degree of charge delocalisation across the DHP.

Estimation of Electron Distribution over Dinuclear Organometallic Molecular Wires by "IR Tag" Analysis of Ancillary Acyl-Cp Ligands

Understanding the details of electronic properties of mixed-valence (MV) states of organometallic molecular wires is essential to gain insights into electron transfer phenomena. Although the field of MV chemistry is matured, there remain issues to be solved, which cannot be accessed by the conventional analytical methods. Here, we describe the synthesis and properties of diruthenium bridging (diethynylbenzene)diyl wires, (μ-p and m-C≡C-C₆H₄-C≡C){RuCp^R(dppe)}₂ 1, with the acyl-substituted cyclopentadienyl rings [Cp^R: Cp^e; η⁵-C₅H₄COOMe (a-series: ester derivatives), Cp^a; η⁵-C₅H₄COMe (b-series: acetyl derivatives)], which are installed as IR-tags to estimate electron densities at the metal centers in the MV species. The electrochemical and IR/near IR-spectroelectrochemical studies reveal that the two metal centers in the para-isomers p-1a,b ⁺ interact with each other more strongly than those in the meta-isomers m-1a,b ⁺ . Electron-spin resonance study also supports the radicals being delocalized over the Ru-(p-C≡C-C₆H₄-C≡C)-Ru moieties in p-1a,b ⁺ . The spectroelectrochemical IR study shows significant higher-energy shifts of the ν(C=O) vibrations brought about upon 1e-oxidation. Spectral simulation on the basis of the Bloch equations allows us to determine the electron transfer rate constants (k _et) between the two metal centers being in the orders of 10¹² s^-1 ( p-1 ⁺ ) and 10⁹ s^-1 ( m-1 ⁺ ). The shifts of the ν(C=O) bands reveal that the charge densities on the para-isomers p-1a,b ⁺ are widely delocalized over the Ru-(p-C≡C-C₆H₄-C≡C)-Ru linkages in contrast to the meta-isomers m-1a,b ⁺ , where the electron densities are mainly localized on the metal fragments, as supported by the density functional theory and time-dependent density functional theory studies as well as comparison with the reference mononuclear acetylide complexes, C₆H₅-C≡C-RuCp^R(dppe) 2. We have successfully demonstrated that the carbonyl groups (>C=O) in the ancillary Cp ligands also work as IR-tags to report detailed information on the electron densities at the metal centers and the electron distribution over MV complexes as well.

Iron vs. ruthenium: syntheses, structures and IR spectroelectrochemical characterisation of half-sandwich Group 8 acetylide complexes

A synthetic ‘trick’ affording complexes [M(CCR)(dppe)Cp′] (M = Fe, Ru) in high purity directly from the reaction vessel is described.

Tetrel and pnictogen functionalised propargylidynes

The reaction of [W([triple bond, length as m-dash]CC[triple bond, length as m-dash]CSiMe₃)(CO)₂(Tp*)] (Tp* = tris(dimethylpyrazolyl)borate) with AgNO₃ affords {[W([triple bond, length as m-dash]CC[triple bond, length as m-dash]CAg)-(CO)₂(Tp*)][AgNO₃]}_n while [Hg{C[triple bond, length as m-dash]CC[triple bond, length as m-dash]W(CO)₂(Tp*)}₂] with ⁿBuLi affords [W([triple bond, length as m-dash]CC[triple bond, length as m-dash]CLi)(CO)₂(Tp*)]. These anhydrous reagents allow the installation of main group elements (e.g., Si, Sn, Pb, P, As) as propargylidyne termini.

Rutheniumethynyl-Triarylamine Organic-Inorganic Mixed-Valence Systems: Regulating Ru-N Electronic Coupling by Different Aryl Bridge Cores

Four rutheniumethynyl-triarylamine complexes 1-4 with different aryl bridge cores were prepared. The solid structures of complexes 2-4 were fully confirmed by X-ray single-crystal diffraction analysis. Two consecutive one-electron oxidation processes of complexes 1-4 were attributed to the ruthenium and nitrogen centers, as revealed by cyclic voltammetry and square-wave voltammogram. Results also showed decreasing potential difference ΔE of complexes 1, 3, and 4, with the largest value for 2. Upon chemical oxidation of complexes 1-4 by 1.0 eq oxidation reagents FcPF₆ or AgSbF₆ , the mixed-valence complexes, except for 2⁺ , show characteristic broad NIR absorptions in the UV-vis-NIR spectroscopic experiments. NIR multiple absorptions were assigned to NAr₂ →RuCp*(dppe) intervalence charge transfer (IVCT) and metal-to-ligand charge transfer transitions by TDDFT calculations. Coupling parameter (H_ab ) from Hush theory revealed that increasing electronic communication in 1⁺ , 3⁺ , and 4⁺ . Electron density distribution of the HOMO for neutral molecules (1, 3, and 4) and spin density distribution of the corresponding single-oxidized states (1⁺ , 3⁺ , and 4⁺ ) increases progressively on the bridge as the size of the aromatic system increases, proving incremental contributions from bridge cores during oxidation.

Mix and (Mis)match: further studies of the electronic structure and mixed-valence characteristics of 1,4-diethynylbenzene-bridged bimetallic complexes

The 1,4-diethynylbenzene motif is commonly employed as a bridging ligand in bimetallic molecular systems intended to show pronounced intramolecular electronic interactions, delocalized electronic structures and 'wire-like' properties between the metal fragments at the ligand termini. In contrast to these expectations, the donor-acceptor compounds [{Cp'(CO)xM'}(μ-C[triple bond, length as m-dash]CC6H4C[triple bond, length as m-dash]C){M(PP)Cp'}]n+ [n = 0, 1; M'(CO)xCp' = Fe(CO)2Cp, W(CO)3Cp*; M(PP)Cp' = Fe(dppe)Cp, Fe(dppe)Cp*, Ru(PPh3)2Cp, Ru(dppe)Cp, Ru(dppe)Cp*] display remarkably little bridge-mediated electronic interaction between the electron-rich {M(PP)Cp'} and electron-poor {M'(CO)xCp'} fragments in the ground state. However, a relatively high-energy (26 000-30 000 cm-1) M-to-M' charge transfer can be identified. One-electron oxidation is largely localized on the {M(C[triple bond, length as m-dash]CR)(PP)Cp'} fragment and gives rise to a new charge transfer band with bridging-ligand-to-{M(PP)Cp'}+ (M'(CO)xCp' = Fe(CO)2Cp) or M'-to-M(+) (M(CO)xCp' = W(CO)3Cp*) character. The localized electronic ground state of these complexes is better revealed through analysis of the IR spectra, taking advantage of the well-resolved ν(C[triple bond, length as m-dash]C) and ν(CO) bands and IR spectroelectrochemical methods, than through the more classical analysis based on the concepts of Marcus-Hush theory and analysis of the putative IVCT electronic transition. The conclusions are supported by DFT calculations using the BLYP35 functional.

Halogenation of A-frame μ-carbido complexes: synthesis of μ2-halocarbynes

The new A-frame μ₂-carbido complexes [Rh₂(μ₂-C)X₂(μ₂-dppm)₂] (X = Cl, Br; dppm = Ph₂PCH₂PPh₂) react with PhICl₂ or [pyH][Br₃] to provide rare examples of μ₂-halocarbyne complexes [Rh₂(μ-CX)(μ-X)X₄(μ-dppm)₂] (X = Cl, Br).

Fluorenylporphyrins functionalized by electrochromic ruthenium units as redox-triggered fluorescence switches

The electrofluorochromic behaviour of two ruthenium-appended porphyrin dyads has been investigated. Differences in response according to the nature of the interposed aryl linker are rationalised with the aid of electrochemistry and TD-DFT calculations.

A [C1 + C2] route to propargylidyne complexes

The reactions of [W(CBr)(CO)₂(Tp*)] with a range of terminal alkynes (RCCH), mediated by [Pd(PPh₃)₄] and CuI, afford new propargylidynes [W(C–CCR)(CO)₂(Tp*)] [R = ^tBu, C₆H₄X (X = H, NH₂, NO₂), APh₃ (A = C, Si, Ge), B(O₂CCH₂)₂NMe].

Confluence of disparate carbido chemistries: [WRuAu2(μ-C)2Cl2(CO)2(PCy3)2(Tp*)]

The reaction of [Ru(CAuCl)Cl₂(PCy₃)₂] with [W(CSnⁿBu₃)(CO)₂(Tp*)] (obtained from [W(CBr)(CO)₂(Tp*)], ⁿBuLi and ClSnⁿBu₃) affords the heterotetrametallic bis(carbido) complex [WRuAu₂(μ-C)₂Cl₃(CO)₂(PCy₃)₂(Tp*)] in which the two distinct μ-carbido ligands adopt linear and T-shaped geometry at carbon.

Simple generation of a dirhodium μ-carbido complex via thiocarbonyl reduction

The reaction of [RhCl(CS)(PPh₃)₂] with excess catecholborane affords the cumulenic carbido complex [Rh₂(μ-C)Cl₂(PPh₃)₄] which undergoes phosphine and halide substitution to afford a range of complexes in which the RhCRh spine remains intact.

Through-conjugation of two phosphaalkyne (‘CP’) moieties mediated by a bimetallic scaffold

The bis-cyaphide complex [{Ru(dppe)₂}₂{μ-(CC)₂C₆H₄-p}(CP)₂] is the first molecule to incorporate two phosphaalkyne ‘CP’ moieties within a through-conjugated scaffold, and demonstrates interesting redox behaviour.

Multistep Oxidation of Diethynyl Oligophenylamine-Bridged Diruthenium and Diiron Complexes

Homo-dinuclear nonlinear complexes [{M(dppe)Cp*}₂{μ-(-C≡C)₂X}] (dppe = 1,2-bis(diphenylphosphino)ethane; Cp* = η⁵-C₅Me₅; X = triphenylamine (TPA), M = Ru (1a) and Fe (1b); X = N,N,N',N'-tetraphenylphenylene-1,4-diamine (TPPD), M = Ru (2a)) were prepared and characterized by ¹H, ¹³C, and ³¹P NMR spectroscopy and single-crystal X-ray diffraction (1a, 2a). Attempts to prepare the diiron analogue of 2a were not successful. Experimental data obtained from cyclic voltammetry, square wave voltammetry, UV-vis-NIR (NIR = near-infrared) spectro-electrochemistry, and very informative IR spectro-electrochemistry in the C≡C stretching region, combined with density functional theory calculations, afford to make an emphasizing assessment of the close association between the metal-ethynyl termini and the oligophenylamine bridge core as well as their respective involvement in sequential one-electron oxidations of these complexes. The anodic behavior of the homo-bimetallic complexes depends strongly both on the metal center and the length of the oligophenylamine bridge core. The poorly separated first two oxidations of diiron complex 1b are localized on the electronically nearly independent Fe termini. In contrast, diruthenium complex 1a exhibits a significantly delocalized character and a marked electronic communication between the ruthenium centers through the diethynyl-TPA bridge. The ruthenium-ethynyl halves in 2a, separated by the doubly extended and more flexible TPPD bridge core, show a lower degree of electronic coupling, resulting in close-lying first two anodic waves and the NIR electronic absorption of [2a]⁺ with an indistinctive intervalence charge transfer character. Finally, the third anodic waves in the voltammetric responses of the homo-bimetallic complexes are associated with the concurrent exclusive oxidation of the TPA or TPPD bridge cores.

High oxidation state bromocarbyne complexes

Bromination of the carbyne complexes [W(CR)Br(CO)₂(dcpe)] (R = Ph, SiPh₃; dcpe = 1,2-bis(dicyclohexylphosphino)ethane) provides high oxidation state derivatives [W(CPh)Br₃(dcpe)] and [W(CBr)Br₃(dcpe)], the latter via an unprecedented bromodesilylation process.

Asymmetric oxidation of vinyl- and ethynyl terthiophene ligands in triruthenium complexes

Newly synthesized open-triangle triruthenium vinyl and ethynyl terthiophene complexes exhibit stepwise laterally localized oxidation processes, as revealed by UV-vis-NIR and IR spectroelectrochemistry.

New donor–acceptor conjugates based on a trifluorenylporphyrin linked to a redox–switchable ruthenium unit

Spectroelectrochemical studies show four accessible redox states on dyad 3 with the first oxidation process taking place at the Ru(ii) centre and the second oxidation and first reduction processes at the porphyrin centre.