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A Congested Ru(dps) 2 or Ru(dprs) 2 Core (dps = di‐2‐pyridyl sulfide; dprs = di‐2‐pyrimidinyl sulfide) Promotes Sulfur Inversion of N , S ‐Chelate Thioethers Containing CH 2 R and 2‐Pyridyl or 2‐Pyrimidinyl Groups
Author(s) -
Tresoldi Giuseppe,
Lo Schiavo Sandra,
Lanza Santo,
Cardiano Paola
Publication year - 2002
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/1099-0682(20021)2002:1<181::aid-ejic181>3.0.co;2-g
Subject(s) - chemistry , sulfide , sulfur , ruthenium , medicinal chemistry , stereocenter , stereochemistry , chelation , inorganic chemistry , catalysis , organic chemistry , enantioselective synthesis
The thioethers L [L = 4‐methylbenzyl 2‐pyridyl sulfide ( L 1 ), 4‐chlorobenzyl 2‐pyridyl sulfide ( L 2 ), 3‐chlorobenzyl 2‐pyridyl sulfide ( L 3 ), 1,4‐bis(2‐pyridylthiomethyl)benzene ( L 4 ), 4‐methylbenzyl 2‐pyrimidinyl sulfide ( L 5 ), and 4‐chlorobenzyl 2‐pyrimidinyl sulfide ( L 6 )], containing a CH 2 R group bonded to the sulfur atom, were prepared and characterized. Compounds L 1 , L 2 , L 3 , and L 4 reacted with cis ‐Ru( N , N ‐dprs) 2 Cl 2 or cis ‐Ru( N , N ‐dps) 2 Cl 2 (dprs = di‐2‐pyrimidinyl sulfide, dps = di‐2‐pyridyl sulfide) leading to the complexes [Ru( N , N ‐dprs) 2 ( N , S ‐L)][PF 6 ] 2 and [Ru( N , N ‐dps) 2 ( N , S ‐L)][PF 6 ] 2 . Similar products were obtained from [Ru( N , N ‐dps) 2 (NO 2 )(NO)][PF 6 ] 2 and L 5 or L 6 . As a consequence of the L ligand N , S ‐chelation, all the complexes contain the four‐membered ring RuSCN( Ru−N ). Since the ruthenium and sulfur atoms are stereogenic centres, with Δ and Λ, and R and S configurations, respectively, they led to four isomers, including the enantiomers. NMR investigations show that the sulfur inversion produces an exchange between the diastereoisomers Δ R and Δ S , as well as Λ S and Λ R . The one‐dimensional band‐shape analysis of the exchanging methylene proton signals showed that the inversion barriers (Δ G ‡ 298 K ) for the dprs complexes are in the 54.9−53.8 kJ mol −1 range, with the two invertomers exhibiting similar abundance. Substitution of dprs with dps affects the relative invertomer population leaving the magnitude of Δ G ‡ 298 K (52.0−50.6 kJ mol −1 ) practically unchanged. Conversely, the substitution of the pyridine thioethers ( L 1 , L 2 ) with pyrimidine thioethers ( L 5 , L 6 ) influences the inversion barriers, and Δ G ‡ 298 K values of 47.5 and 47.0 kJ mol −1 were found for [Ru( N , N ‐dps) 2 ( N , S ‐ L 5 )][PF 6 ] 2 and [Ru( N , N ‐dps) 2 ( N , S ‐ L 6 )][PF 6 ] 2 , respectively. An intramolecular mechanism without any bond rupture is suggested on the basis of the Δ S ‡ values (negative or close to zero) and the NMR spectra, temperature‐reversible and concentration‐independent. The contemporary presence of the congested Ru( N , N ‐dps) 2 or Ru( N , N ‐dprs) 2 core and sterically demanding N , S ‐coordinated thioether ligands is invoked to explain the low energy barrier of the process. This hypothesis is also corroborated by the different behaviour observed for the complex [Ru(bipy) 2 ( N , S ‐ L 1 )][PF 6 ] 2 .