Comparative Coordination Chemistry of PNP and SNS Pincer Ruthenium Complexes

Abstract

Ruthenium carbonyl complexes supported by PNP pincer ligands are prominent catalysts for a range of hydrogenation and dehydrogenation reactions. Recently, Ru complexes with cheaper, more air stable SNS pincer ligands have emerged as attractive alternatives for the development of improved catalysts. However, there is currently a paucity of information on how the replacement of the phosphine donors in PNP ligands with the sulfur donors in SNS ligands influences the synthesis, structure, and electronic properties of the resulting metal complexes. Herein, the coordination chemistry of a series of Ru carbonyl complexes with SNS pincer ligands has been systematically compared with related PNP-ligated species. Three different SNS pincer ligands were explored including a pyridyl based NC 5 H 3 {CH 2 (S t Bu)} 2 ligand and two aliphatic ligands, HN{CH 2 CH 2 (S t Bu)} 2 and NCH 3 {CH 2 CH 2 (S t Bu)} 2 , along with different combinations of monodentate ancillary ligands. The geometric structures of the SNS and PNP Ru complexes were studied using NMR spectroscopy and X-ray crystallography. Additionally, the redox properties and electronic structures of these complexes were probed through a combination of cyclic voltammetry and DFT calculations. Overall, differences between SNS and PNP complexes extend well beyond simply modulating inductive donation to the metal and include changes in synthetic outcomes, as well as variations in geometry that impact redox behavior. Our study reveals fundamental information about the coordination chemistry of the SNS ligand, which may aid in interpreting catalytic results.

Intramolecular 1,2 C−H Addition of o‐Methyl Groups to Form Unique Ruthenium Pincer Tuck‐in Complexes

“…FTIR spectroscopy of 7 in a Nujol mull shows that the major ν C=O stretch appears at 1956 cm −1 and that a minor signal appears as a slightly red shifted shoulder at ∼1953 cm −1 . This is similar to what was observed by Bernskoetter and coworkers for the i PrPN H PRu(CO)Cl 2 complex which has FTIR signals of 1931 and 1928 cm −1 for the cis chloride and trans chloride isomers, respectively [39] . The FTIR signals of 7 are blue shifted relative to i PrPN H PRu(CO)Cl 2 as expected due to the electron withdrawing nature of the aryl rings.…”

“…This is similar to what was observed by Bernskoetter and coworkers for the i PrPN H PRu(CO)Cl 2 complex which has FTIR signals of 1931 and 1928 cm À 1 for the cis chloride and trans chloride isomers, respectively. [39] The FTIR signals of 7 are blue shifted relative to i PrPN H PRu(CO)Cl 2 as expected due to the electron withdrawing nature of the aryl rings. Analysis of crystals grown in dichloromethane layered with pentane suggests that the cis dichloride isomer is likely the major isomer in 7 (Figure 5A).…”

Quantifying Variations in Metal–Ligand Cooperative Binding Strength with Cyclic Voltammetry and Redox-Active Ligands

“…The Ru–N bond distances range from 1.991(2) to 2.024(2) Å and are consistent with the relatively short Ru–N bonds expected due to the π-donor properties of the amido groups. The Ru–S bonds in 1b and 2 range from 2.315(1) to 2.331(1) Å and are typical of Ru II –thioether distances . Likewise, the Ru–N quin distances associated with the flanking quinoline groups in 3 are 2.088(5) and 2.103(4) Å, which compare well to those observed in Ru­(II) complexes containing a quinoline-based pincer ligand .…”

Design and Syntheses of Ruthenium ENE (E = S, Se) Pincer Complexes: A Versatile System for Catalytic and Biological Applications

“…The halfway potential (E 1/2 ) values for complexes C1 and C2 are 0.56 V and 0.53 V, respectively, which were assigned to the oxidation of Ru 2+ to Ru 3+ . The anodic peak was observed at 0.62 V (I a ) for complex C1 and 0.60 V for complex C2 [55] . The observed Ru 2+ to Ru 3+ potentials showed that oxidation of C2 was slightly more favourable than C1 which may be attributed to the slightly better donor ability of Se over S.…”

“…The anodic peak was observed at 0.62 V (I a ) for complex C1 and 0.60 V for complex C2. [55] The observed Ru 2 + to Ru 3 + potentials showed that oxidation of C2 was slightly more favourable than C1 which may be attributed to the slightly better donor ability of Se over S.…”