Cerium Fluorenyl Complexes Including CC Coupling Reactions

Abstract

The first structurally characterized fluorenyl (Flu) complexes of cerium are reported, bearing one, two, and three fluorenyl ligands. The reaction of CeX 3 (THF) x (X = Cl and I) with KFlu led to the half-sandwich complexes FluCeX 2 (THF) 3 . The chloride derivative was utilized in salt metathesis reactions, affording complexes FluCeR 2 (THF) x with R = OtBu, OSiMe 3 , OC 6 H 3 iPr 2 -2,6, Me 2 Pz, and Cp (x = 1 or 2; Me 2 Pz = 3,5dimethylpyrazolato, Cp = C 5 H 5 ). The mono(fluorenyl) complexes FluCeR 2 (THF) x are prone to ligand redistribution at ambient temperature, leading to the respective sandwich complexes Flu 2 CeR(THF). Utilization of K(2,10-tBu 2 Flu) (KFlu tBu ) afforded tris(fluorenyl) complex Flu tBu 3 Ce(THF) instead, showcasing two η 5 -and one η 1 -bound fluorenyl ligands. Treatment of FluCeCl 2 (THF) 3 with halogenating oxidants such as C 2 Cl 6 , I 2 , or TeBr 4 did not afford stable cerium(IV) species but mixtures of 9halogenidofluorene and 1,1′-bifluorene. Selective fluorenyl coupling reactions could be achieved for C 2 Cl 6 . Respective investigations with lanthanum and neodymium complexes support σ-bond metathesis as the main reaction path for C−C-bond formation.

Rare‐Earth‐Metal Alkyl and Aryl Compounds in Organic Synthesis

“…Fluorenyl complex FluCeCl 2 (thf) 3 (55 Ce ) resembles the Imamoto reagent CeCl 3 /RLi (RCeCl 2 (thf) x , 20 Ce,Cl ) due to the feasibility of a η 5 !η 3 !η 1 coordination switch of the weakly bonded fluorenyl ligand. [130] Compound 55 Ce (19) with benzyl bromide produced the respective dibenzyl derivative. [73b] A closely related σ-bond metathesis was observed in the reaction of sterically crowded complexes Ln(C 5 Me 5 ) 3 with PhSSPh, likewise involving a η 5 !η 1 coordination switch of the pentadienyl ligand.…”

“…Fluorenyl complex FluCeCl 2 (thf) 3 ( 55 Ce ) resembles the Imamoto reagent CeCl 3 /RLi (RCeCl 2 (thf) x , 20 Ce,Cl ) due to the feasibility of a η 5 →η 3 →η 1 coordination switch of the weakly bonded fluorenyl ligand [130] . Compound 55 Ce readily reacts with halogenating oxidants like C 2 Cl 6 via displacement of the fluorenyl ligand.…”

Benz[e]indenyl and benz[f]indenyl molybdenum compounds: evidence of the η3-coordination mode

“…These rearrangements have been investigated on Cp and few congeners with annulated benzene rings (Cp 0 ), mainly on indenyl (Ind = C 9 H 7 ) [4][5][6][7][8][9][10][11][12] and fluorenyl (Flu = C 13 H 9 ). [12][13][14] Electronically saturated transition metal complexes with Z 5 -bonded extended aromatic systems exhibit a substantial increase in the reaction rates of substitution reactions, when compared to their Z 5 -Cp counterpart that has given rise to the term ''indenyl effect''. [15][16][17][18] It is usually interpreted in terms of the M-Cp 0 bond strength in the two relevant hapticity modes.…”