Tuning coordination modes of pyridine/thioether Schiff base (NNS) ligands to mononuclear manganese carbonyls

Abstract

We have investigated the coordination modes of NNS Schiff base, thioether ligands to manganese (I) carbonyls. The ligands contain ortho substituted pyridines (H, CH 3 , OCH 3 , fluorophenyl) and varying substituents (H, CH 3 ) at the Schiff base linkage. In general, reaction of [Mn(CO) 5 Br] with a tridentate NNS ligand in CH 2 Cl 2 affords species in which the thioether-S may be bound or unbound to the manganese center, depending on the steric and electronic substitution in the ligand framework; as a result, the complexes exhibit two or three carbonyl ligands, respectively. Aldehyde-derived ligand frames ( tricarbonyl motif. We highlight that coordination of these NNS ligands to Mn(I) carbonyls occurs on a soft conformational landscape, and that ligand substituents can be rationally employed to favor the desired coordination mode.

Synthesis and Reactivity of Mn–CF3 Complexes

“…Even after halide abstraction with Lewis acids such as AgPF 6 , addition of CF 3 anions was unsuccessful. Moving to a Mn (I) source, (CO) 5 MnBr, allowed for an easy exchange of CO groups with various ligands [39][40][41][42] but displacement of Br with CF 3 again was problematic, even after abstraction with AgPF 6 . While we chose to avoid toxic and difficult to prepare Cd(CF 3 ) 2 , this may offer an alternate route to Mn-CF 3 complexes with soft donors such as phosphines.…”

“…Further workup was unnecessary as we found that ligand substitution on the acyl complex was accompanied by rapid decarbonylation at room temperature. Moving to a Mn (I) source, (CO)5MnBr, allowed for an easy exchange of CO groups with various ligands [39][40][41][42]…”

“…Attempted reactions of the Mn(CO) 5 CF 3 /Mn(CO) 5 COCF 3 mixture with various bi-and tridentate P-donor ligands, including: PPh 3 , PMe 3 , DPPE, DPPF, DMPE, Tripod, Triphos, P(O i Pr) 3 , P(OPh) 3 were unsuccessful as soft donor ligands appeared ineffective at displacing the strongly held carbonyls unlike the similar complexes (CO) 5 Mn-X complexes (X = Br, I, Me) which have a rich coordination chemistry with soft ligands [39][40][41][42]. Hard donor ligands gave moderate success but reactions required harsh conditions (100 • C, 48 h reaction time) to afford mixtures of starting material and the desired products.…”

“…Reaction of 2 with bipyridine (Bpy) and phenanthroline (Phen) furnished complexes (3) and (4) respectively (50 °C, 12 h, Scheme 4). This method was also utilized with a tridentate mixed-donor NNS Schiff Base [2-(methylthio)-N-(1-(pyridin-2-yl)ethylidene)aniline] [39] to give (7) in 40% yield (Scheme 5). In contrast, reactions of (2) and (5) with soft phosphine ligands gave mixtures of products, again showing the significant effect of the CF 3 group given that Mn-X complexes (X = Br, Cl) readily coordinate soft donors [39][40][41][42].…”

Transition metal complexes of a dihydroquinazoline-containing ligand: synthesis, crystal structures and physical properties

“…Since the properties of such complexes are heavily influenced by the nature of the ligands [10], much attention has been given to the design and synthesis of chelating ligands. Tridentate Schiff base ligands often exhibit versatile chelating modes, such as NNN, NNO, NNS and ONO [11][12][13][14][15][16]. Hence, the design and synthesis of such ligands remains an interesting area of current research.…”