Half-Sandwich Ruthenium(II) Complexes of Click Generated 1,2,3-Triazole Based Organosulfur/-selenium Ligands: Structural and Donor Site Dependent Catalytic Oxidation and Transfer Hydrogenation Aspects

1-Benzyl-4-((phenylthio)-/(phenylseleno)­methyl)-1H-1,2,3-triazole (L1/L2) and 4-phenyl-1-((phenylthio)-/(phenylseleno)­methyl)-1H-1,2,3-triazole (L3/L4) synthesized
using the click reaction have been reacted for the first time with
[{(η6-C6H6)­RuCl­(μ-Cl)}2] and NH4PF6 to design the half-sandwich
complexes [(η6-benzene)­RuLCl]­PF6 (1–4 for L = L1–L4), which have been characterized
by single-crystal X-ray diffraction and explored for the catalytic
oxidation of alcohols with N-methylmorpholine N-oxide (NMO) and transfer hydrogenation of ketones with
2-propanol. There is a pseudo-octahedral “piano-stool”
disposition of donor atoms around Ru in 1–4. In 1 and 2, N(3) of the triazole
skeleton coordinates with Ru, whereas in other complexes the nitrogen
involved is N(2). The Ru–S and Ru–Se bond distances
are 2.3847(11)/2.3893(10) and 2.497(5)/2.4859(9) Å, respectively.
The catalytic processes are more efficient with 3 and 4 (compared to 1 and 2), in which
N(2) of the triazole is involved in coordination with Ru. The nature
of the chalcogen and steric factors together also appear to affect
the efficiency of complexes. HOMO–LUMO energy gaps are lower
for 3 and 4 than for 1 and 2. The formation of RuIVO species probably
results in oxidation and transfer hydrogenation involves an intermediate
containing Ru–H. Bond distances and angles based on DFT calculations
are generally consistent with experimental values.