Reduction of Ketimines by Samarium(II) Complexes. Isolation and Structural Characterization of Samarium(III) η¹-Amine/η¹-Ketimido and η²-Ketimine Complexes

Abstract

The reaction of (C 5 Me 5 ) 2 Sm(THF) 2 with 2 equiv of benzophenone imine (Ph 2 CdNH) in THF at room temperature gave the samarocene(III) amine/ketimido complex (C 5 Me 5 ) 2 Sm-(NdCPh 2 )(NH 2 CHPh 2 ) (1) in 58% isolated yield. The use of 1 equiv of Ph 2 CdNH also afforded 1 as the only isolable product, albeit in a lower yield (ca. 20%). Deuterium-labeling experiments suggest that 1 is formed via hydrogen abstraction by the in-situ-generated imine radical anion species, followed by acid-base reaction between the resulting amido species and another molecule of Ph 2 CdNH. The reactions of 2 equiv of Sm(OAr) 2 (THF) 3 (Ar ) C 6 H 2t Bu 2 -2,6-Me-4) with N-phenyl benzophenone imine (Ph 2 CdNPh) and N-phenyl fluorenone imine (C 12 H 8 CdNPh) yielded the Sm(III) η 2 -imine-dianion/aryloxide complexes Sm(η 2 -Ph 2 -CNPh)(OAr)(THF) 3 (3, 65%) and Sm(η 2 -C 12 H 8 CNPh)(OAr)(THF) 3 (4, 77%), respectively, together with the byproduct Sm(OAr) 3 . The reaction of 1 equiv of Sm(OAr) 2 (THF) 3 with Ph 2 CdNPh also gave the imine-dianion complex 3, whereas an imine radical anion species was not observed. Similarly, the reactions of 2 equiv of Sm{N(SiMe 3 ) 2 } 2 (THF) 2 with Ph 2 -CdNPh and C 12 H 8 CdNPh yielded the η 2 -imine-dianion/silylamido complexes Sm(η 2 -Ph 2 -CNPh){N(SiMe 3 ) 2 }(THF) 3 (5, 87%) and Sm(η 2 -C 12 H 8 CNPh){N(SiMe 3 ) 2 }(THF) 3 (6, 71%), respectively. Complexes 3-6 represent the first examples of structurally characterized trivalent lanthanide η 2 -imine complexes.

A Deca‐9‐Fluorenolato‐deca‐Samarium Oxide Cage

“…For the ligands bridging between two metals, the κ(C#F)–Sm bond lengths are considerably shorter than the Sm–C#F bond lengths involved in η 5 coordination (Table ), and are more related to Sm–C σ‐bonds that have been crystallographically characterized {e.g. Sm–C: 2.564(4) Å in [9‐(phenylimino)fluorenyl‐C,N]‐(2,6‐di‐ tert ‐butyl‐4‐methylphenoxy)‐tris(tetrahydrofuran)‐samarium} . It should be noted that there is a significant difference in the bond length of Sm–O4/O7 from that of Sm–O3/O8, despite both being coordinated to Sm III .…”

Rare-earth metal bis(alkyl) complexes bearing pyrrolidinyl-functionalized cyclopentadienyl, indenyl and fluorenyl ligands: synthesis, characterization and the ligand effect on isoprene polymerization

“…13 The central metal in 6 is five-coordinated by one fluorenyl ligand in Z 1 , k 1 -modes, two CH 2 SiMe 3 groups, and one oxygen atom of THF to adopt a distorted-trigonal-bipyramidal geometry. If the ionic radius is considered, 14 the C Flu -Lu distance (2.529( 12) Å) in 6 is comparable with those in Sm(Z 2 -C 12 H 8 CNPh)(OAr)(THF) 3 , 12 but is much longer than those in (FluCH 2 -Py)Lu(CH 2 SiMe 3 ) 2 (THF) (av. C Flu -Lu = 2.357 Å), in which the fluorenyl ligand is bound to the central metal in an Z 5 -fashion.…”

“…Such a Z 1 -bonding mode in rare-earth metal complexes is scarce. 12,13 For instance, in Sm(Z 2 -C 12 H 8 CNPh)(OAr)(THF) 3 the fluorenyl moieties are bound to samarium ions via the bridgehead atom in a Z 1 -fashion, 12 while in [(Z 3 :Z…”

Mechanistic Vistas of Trivalent Nitrogen Compound Reduction by Samarium Diiodide

“…Comparison of reactivity showed that SmI 2 ‐water‐amine is the strongest reductant compared to other reagents, which achieved higher yields [16] . In a different study, Cp* 2 Sm(THF) 2 , a more powerful reductant than SmI 2 , was employed for the reduction of ketimines where the crystal structure of the product showed that the amine is coordinated to Sm 3+ [17] . The reduction of tert ‐butanesulfinyl imine was used to synthesize six‐membered rings with high stereochemical outcome [18] .…”