Revisiting oxo-centered carbonyl-triruthenium clusters: investigating CO photorelease and some spectroscopic and electrochemical correlations

Abstract

We synthesized and characterized a series of oxo-centered carbonyl-triruthenium complexes with the general formula [RuO(CHCOO)(L)(CO)], where L = 2,6-dimethylpyrazine (dmpz) (1), isonicotinamide (adpy) (2), 4-acetylpyridine (acpy) (3), 3-methylpyridine (3-pic) (4), 4-methylpyridine (4-pic) (5), 4-tert-butylpyridine (4-tbpy) (6), 4-(dimethyl)aminopyridine (dmap) (7), or 4-aminopyridine (ampy) (8); we also investigated the photoreactivity of these complexes. Single-crystal X-ray diffraction helped to elucidate the structures of 1·HO, 7·CHCl, and 8. The unit cell of 8 is composed of four cluster units; the hydrogen bonds between the amino groups of the terminal ligand of a neighboring molecule and the oxygen atoms of CO or acetate bridging ligands hold these cluster units together. The spectroscopic (NMR, UV-visible, and IR) and the electrochemical properties (cyclic voltammetry) of these complexes correlated with the ancillary ligands in terms of their σ-donating and π-accepting characteristics. The molecular orbital and the electronic localized description of the [RuO]-CO unit helped to rationalize the correlations. The photoreactivity of compounds 1-8 was investigated by laser excitation at 377 nm. Given the CO photorelease quantum yields, σ-donor ligands and aqueous medium (more polar) stabilized the charge-transfer excited state that culminated in CO photosubstitution, leading to higher Φ values.

Structural and electrochemical comparison of trinuclear ruthenium oxo clusters [Ru3(OAc)6O(L)3]+and [Ru3(OAc)6O(L)2(CO)] (L = imidazole, benzimidazole, and 4-phenylpyridine)

“…The Ru-O bonds for the CO-bound Ru atom are slightly longer, around 2.05 Å , than the other two Ru-O bonds (1.90 Å ). At about 1.85 Å , the Ru-C bond lengths are comparable to those in other reported [Ru 3 (OAc) 6 O(L) 2 (CO)] structures (Moreira et al, 2016). The Ru-N bond lengths are only marginally shorter in 1-CO than in 3-CO and other similar structures.…”

A pyrazine‐bridged trimer of oxo‐centered triruthenium–carbonyl clusters and the supramolecular assembly built from multiple noncovalent contacts

“…We find that the CO-attached Ru atoms (Ru1, Ru4, and Ru7) show longer Ru-O eq distances than the pyrazine-attached Ru-O eq distances, suggesting that the CO stabilizes Ru in the lower valence than the pyrazine does. In the literature, [26,36,37,[41][42][43] crystallographic characterizations of the [Ru 3 O(RCOO) 6 (CO)L 2 ] complexes are reported for variable terminal ligands L with N-or Oheterocycles such as 1-azabicyclo[2,2,2]octane (abco), [26] THF, [36] and 1-methyl-4,4 0 -bipyridinium ion. [37] The triangular cores observed in all of these complexes show identical structural features to those in 1.…”

Acetatos trinucleares de rutênio coordenados a ligantes fenazínicos: estudos sobre síntese, reatividade, interações com DNA e avaliação do potencial tripanocida

“…Com base na teoria de Combinação Linear Adaptada por Simetria (do inglês Symmetry-Adappted Linear Combination, SALC), um diagrama de orbitais moleculares (DOM) foi proposto por Baumann em 1978, para explicar as transições eletrônicas em complexos simétricos, pertencentes ao grupo de ponto D3h -quando todos os ligantes periféricos são iguais. Mais tarde, Alexiou mostrou um segundo diagrama, fruto do desdobramento daquele sob simetria C2v -quando um terceiro ligante L' é diferente dos dois outros (ALEXIOU, 1993;BAUMANN et al, 1978;COTTON et al, 1972 (BAUMANN et al, 1978;MOREIRA et al, 2016).…”

“…quanto mais densidade eletrônica os ligantes piridínicos doam, maior o efeito da retrodoação na ligação Ru II -CO; como resultado líquido, as energias dos orbitais dπ do metal variam muito pouco (MOREIRA et al, 2016). Porém os efeitos de sigmadoação e π-acidez dos ligantes ficam mais acentuados quando se analisa as bandas de transferência de carga cluster-ligante (TCCL).…”

“…Porém os efeitos de sigmadoação e π-acidez dos ligantes ficam mais acentuados quando se analisa as bandas de transferência de carga cluster-ligante (TCCL). Quanto maior a capacidade σdoadora do ligante, mais ele desestabiliza os níveis dπ do metal, incluindo aqueles que não possuem simetria adequada para interagir com o ligante CO (e que não sofrem efeito push-pull); consequentemente, as energias das transições π* dπ diminuem (MOREIRA et al, 2016). As bandas mais finas e intensas abaixo de 273 nm são transições intrínsecas π*  π dos ligantes (IL).…”