Deca-Arylsamarocene: An Unusually Inert Sm(II) Sandwich Complex

Abstract

Samarocene sandwich complexes with superbulky penta-arylcyclopentadienyl ligands have been prepared and were structurally characterized: [(4-EtC 6 H 4 ) 5 C 5 ] 2 Sm (1) and [(4-iPrC 6 H 4 ) 5 C 5 ] 2 Sm (2). Analogous to the previously reported synthesis of [(4-nBuC 6 H 4 ) 5 C 5 ] 2 Sm, reaction of (DMAT) 2 Sm• (THF) 2 (DMAT = 2-Me 2 N-α-Me 3 Si-benzyl) and the appropriate Ar 5 C 5 H ligand gave 1 (66% yield) and 2 (59% yield). In contrast to the high reactivity of Cp* 2 Sm, complex 1 has been shown to be surprisingly stable toward reaction with a large variety of reagents. Even under forcing conditions, no reaction with N 2 , CO, CO 2 , pyrazine, trans-stilbene, pyridine, P 4 , and benzophenone was observed. Complex 1 reacts with cuminil ArC(O)C(O)Ar (Ar = 4-iPrC 6 H 4 ) to yield the Sm(III) sandwich complex [(4-EtC 6 H 4 ) 5 C 5 ] 2 Sm[ArC(O)C(O)Ar] (3), which could be isolated in 83% yield as a dark-red crystalline material. Complex 2 reacts with oxygen in the presence of phenazine to yield the bimetallic Sm(III) complex [(4-iPrC 6 H 4 ) 5 C 5 Sm(η 1 -phenazine)] 2 (μ:η 2 -η 2 -O 2 ) 2 (4) in 25% yield as dark-red crystals. The unusually high redox-stability of deca-arylsamarocenes originates from steric hindrance of the Sm metal center.

Super‐Bulky Penta‐arylcyclopentadienyl Ligands: Isolation of the Full Range of Half‐Sandwich Heavy Alkaline‐Earth Metal Hydrides

“…Sandwich or half‐sandwich complexes incorporating penta‐arylcyclopentadienyl ligands exist across the Periodic Table . The suitable selection of an aryl group (Ar=4‐R‐C 6 H 4 , R=Me, Et, i Pr, n Bu; Ar=3,5‐R 2 C 6 H 3 , R=Me, t Bu) for substitutions on the C 5 carbocycle has led to the corresponding complexes with improved solubility and better crystallinity. Previously, Harder et al.…”

“…Sandwich or half-sandwich complexes incorporating penta-arylcyclopentadienyl ligands exist across the Periodic Table. [12] Thes uitable selection of an aryl group (Ar = 4-R-C 6 H 4 ,R= Me, [13] Et, i Pr, [14] n Bu; [15] Ar = 3,5-R 2 C 6 H 3 ,R= Me, t Bu [16] )f or substitutions on the C 5 carbocycle has led to the corresponding complexes with improved solubility and better crystallinity.Previously,Harder et al reported that protonolysis of heavy alkaline-earth-metal dibenzyl complexes AeR 2 (R = benzyl) with (Cp BIG )H (Cp BIG = (4-n Bu-C 6 H 4 ) 5 -cyclopentadienyl) gave sandwich (Cp BIG ) 2 Ae,n ot the desired heteroleptic (Cp BIG )AeR complexes. [15] Inspired by these results,w ed eliberately synthesized an ew penta-arylcyclopentadienyl ligand with i Pr groups in the meta positions of the Ph rings,( Cp Ar )H (Cp Ar = C 5 Ar 5 ,A r = 3,5-i Pr 2 -C 6 H 3 )t o increase the steric hindrance.Herein, we report the synthesis and structures of (Cp Ar )Ae[CH(SiMe 3 ) 2 ](THF) (1-Ae)(Ae = Ca, Sr, Ba).…”

“…2-Sr and 4-Sr exhibited comparable activities towards alkenes hydrogenation, indicating that THF and DABCO played asimilar effect on catalytic reactions.Compared with 2-Ca, 4-Sr and 4-Ba showed higher reactivity as well as wider substrate scope (entry [13][14][15][16][17][18][19][20]. Di-substituted conjugated alkenes (trans-stilbene and a-Me-styrene) and tri-substituted activated alkenes (trans-1,2-diphenylpropene and phenylcyclohexene) could be fully converted within 1-10 hw ith the highly reactive 4-Ba (entry 14,16,18,20). It is noteworthy that 4-Ba could also catalyze the hydrogenation of tetrasubstituted conjugated alkene,tetraphenylethylene,although the conversion was low (5 %, 24 h, entry 21).…”

Synthesis and Structures of s- and p-Block Metal Complexes Containing Sterically Demanding Pentaarylcyclopentadienyl Substituents

“…A promising method to overcome this experimental problem is the use of para-alkyl-substituted pentaarylcyclopentadienyl ligands C5(p-alkyl-Ph)5 [16][17][18][19] such as pentakis-(4-n-butylphenyl)cyclopentadienyl (Cp Big = C5(p-n-Bu-Ph)5) [16] as well as the corresponding pentakis-(4-ethylphenyl)cyclopentadienyl (C5(p-Et-Ph)5) and pentakis-(4-ipropylphenyl)cyclopentadienyl derivatives (C5(p-i-Pr-Ph)5). [20] In addition, the introduction of (bulky) substituents in para-position furthermore enhances the steric bulk of the ligand. Scheme 1: Symmetrically alkyl-substituted pentaaryland pentabenzylcyclopentadienes.…”

“…Scheme 1: Symmetrically alkyl-substituted pentaaryland pentabenzylcyclopentadienes. [13,[20][21][22][23][24][25] These sterically demanding cyclopentadienyl ligands were successfully applied in the synthesis of decaarylmetallocenes M[C5(p-R-Ph)5]2, which were found to form relatively strong "merry-go-round" hydrogen bond networks between the neighboring pentaarylcyclopentadienyl ligands, thus favoring the homoleptic and linear coordination of a metal center by two cyclopentadienyl ligands. Quantum chemical calculations at the DFT+D-level of theory showed a combined interaction energy of −87.2 kJ mol -1 for all ten hydrogen bonds.…”