MLCT and LMCT Transitions in Acetylide Complexes. Structural, Spectroscopic, and Redox Properties of Ruthenium(II) and -(III) Bis(σ-arylacetylide) Complexes Supported by a Tetradentate Macrocyclic Tertiary Amine Ligand

Abstract

Ruthenium(II) complexes trans-[Ru(16-TMC)(C⋮CC6H4X-p)2] (X = OMe (1), Me (2), H (3), F (4), Cl (5); 16-TMC = 1,5,9,13-tetramethyl-1,5,9,13-tetraazacyclohexadecane) are prepared by the reaction of [RuIII(16-TMC)Cl2]Cl with the corresponding alkyne and NaOMe in the presence of zinc amalgam. Low ν(C⋮C) stretching frequencies are observed for 1−5 and are attributed to the σ-donating nature of 16-TMC. The molecular structures of 1, 3, and 5 have been determined by X-ray crystal analyses, which reveal virtually identical Ru−C and C⋮C bond distances (mean 2.076 and 1.194 Å, respectively). The cyclic voltammograms of 1−5 show quasi-reversible RuIII/II and RuIV/III oxidation couples. Oxidative cleavage of the acetylide ligand in 3 by dioxygen affords [Ru(16-TMC)(C⋮CPh)(CO)]+ (6). Ruthenium(III) derivatives trans-[Ru(16-TMC)(C⋮CC6H4X-p)2]+ are generated in situ by electrochemical oxidation in dichloromethane or by chemical oxidation of 1−5 with Ce(IV). Their UV−visible absorption spectra show a vibronically structured absorption band with λmax at 716−768 nm. The vibrational progressions, which range from 1730 to 1830 cm-1, imply that the electronic transition involves distortion of the acetylide ligand in the excited state. An assignment of pπ(ArC⋮C) → dπ *(RuIII) charge transfer is proposed for this transition.

Mixed‐Valence Ruthenium Complexes Rotating through a Conformational Robin–Day Continuum

“…In the present cases of [ 1 ] + and [ 2 ] + , the interpretation of the NIR spectra (Figure 3) in terms of a series of overlapping IVCT transitions and a formally Ru II/III d 6 /d 5 MV system (at or near the class II–III borderline) might account for the overlapping transitions that comprise the NIR band envelope, either in terms of multiple IVCT transitions or the presence of closely lying MLCT/LMCT transitions. Alternatively, the appearance of additional features on the NIR band envelope might arise from a vibronic progression due to coupling with the ν(C≡C) vibrational modes 51. However, both the increasing intensity of the higher‐energy features in a closely related series of 1,4‐naphthyl‐ and 9,10‐anthryl‐bridged complexes24 and the IR spectra of [ 1 ] + and [ 2 ] + are difficult to reconcile with this interpretation.…”

Synthesis and charge transfer characteristics of a ruthenium–acetylide complex

“…More recently, their charge transfer behaviour was investigated by various methods, including mechanically controllable break junction (MCBJ), where this class of complexes demonstrated high conductivity 1,2 and spectro-electrochemical analysis, in which their redox responsiveness and different charge transfer modes such as metal-toligand charge-transfer (MLCT), ligand-to-metal charge-transfer (LMCT) and even inter valence charge transfer (IVCT) were studied. [3][4][5] Yet while the through-bond charge transfer behaviours were investigated by the above-mentioned methods, their through-space (or inter-molecular) charge transfer ability still remains ambiguous despite of its importance for organic electronic applications. Furthermore, unlike other Ru-compounds, which have been used as dopants for (organic) semiconductors, the doping ability of ruthenium-acetylide complexes is still unclear.…”

Syntheses and molecular structures of trans-bis(alkynyl) tetrakis-triethylphosphite ruthenium complexes

“…The chemistry of trans-bis(alkynyl) complexes of ruthenium has been extensively developed over the past decades, and whilst the vast majority are supported by ancillary phosphine ligands, [1][2][3][4] examples with other supporting ligand sets, including, for example, mixed phosphine-carbonyl [5,6] or N-heterocyclic carbenecarbonyl [7] ligand sets, macrocyclic amines and dioxodiazamacrocyles [8,9] are also known. In addition to finding extensive application as building blocks and donors for the construction of NLO active materials, [10,11] including chemically and redoxswitchable examples, [12,13] donor molecules within solar cells [14][15][16] and applications as sensors, [17] trans-[Ru(C≡CR) 2 (dppe) 2 ] [dppe = 1,2bis(diphenylphosphino)ethane] complexes systems commonly feature in designs of metal-containing molecular wires.…”