Lanthanide/actinide differentiation with sterically encumbered N-heterocyclic carbene ligands

Abstract

A study is reported on the relative stability of trivalent bis(ligand) complexes of the form [M(L(R))(2)N''] for trivalent group 3, lanthanide and actinide cations, using the sterically demanding N-heterocyclic carbene ligand L(R) = [OCMe(2)CH(2){CNCH(2)CH(2)NR}] (R = (i)Pr L(P), Mes L(M), Dipp L(D); N'' = N(SiMe(3))(2)). For the small Y(III) cation (r(6-coord) = 1.040 A) and the smallest L(R), R = (i)Pr, mono, bis, and tris(L(P)) complexes can be made; [Y(L(P))(2)N''] and [Y(L(P))(3)] have been characterised. For the larger ligands, L(M) and L(D), only the mono(L(R)) complexes [Y(L(M))N''(2)] and [Y(L(D))N''(2)] can be made. For the larger Ce(III) (r(6-coord) = 1.15 A), mono(L(R)) and bis(L(R)) complexes [Ce(L(M))N''(2)], [Ce(L(D))N''(2)], [Ce(L(M))(2)N''], and [Ce(L(D))(2)N''] can be made; structural characterisation of the latter two confirm the high degree of steric congestion. The new complex [U(L(M))N''(2)] has also been isolated. Despite the very similar radii of Ce(III) and U(III) (r(6-coord) = 1.165 A), the complexes [U(L(R))(2)N''] cannot be isolated; a surprising display of the difference between the 4f and 5f metal series. However, the six-coordinate, bis(ligand) U(IV) complexes can readily be isolated if smaller ancillary ligands are used; [U(L(M))(2)I(2)] and [U(L(D))(2)I(2)] have been fully, including structurally, characterised.

Influence of Pyrazolate vs N-Heterocyclic Carbene Ligands on the Slow Magnetic Relaxation of Homoleptic Trischelate Lanthanide(III) and Uranium(III) Complexes

“…N -heterocyclic carbene ligands are well-known for their strongly σ-donating character and have found utility in stabilizing high-valent transition metal complexes, homogeneous catalysis, and even actinide–lanthanide differentiation . However, N -heterocyclic carbene complexes of the f-elements are still fairly sparse, found primarily in heteroleptic systems in which the carbene is tethered to an alkyl chain or stabilized by bulky heteroatom substituents .…”

Recent Advances in Catalysis Involving Bidentate N-Heterocyclic Carbene Ligands

“…There are several review articles reported in the past decade, which are dedicated to NHC ligands bearing one additional donor group [ 7 , 8 , 9 , 10 ]. Included in these review articles are bidentate NHC ligands with phosphorous tether [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ], nitrogen [ 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 ], and oxygen tethers [ 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 ,…”

Dioxo-, Oxo-imido-, and Bis-imido-Molybdenum(VI) Complexes with a Bis-phenolate-NHC Ligand

“…However, since previous studies showed that these complexes can be quite challenging in their synthesis, we sought for NHC ligands with anionic linker atoms, which facilitate the metal binding of the NHC ligand and enforce a stronger bonding of the NHC to the metal center. Employing this strategy has led to the isolation of various unusual main group, − early transition metal, − late transition metal ,− and f-element NHC complexes − with unique reactivity patterns and spectroscopic as well as electrochemical properties. In our search for a NHC ligand that is capable of forcing the metal center to bind to the NHC moiety by using anionic linker groups, we came across the bis-phenol benzimidazolium chloride [H 3 L 1 ]­Cl introduced by Bercaw et al and by Bellemin-Lapponnaz .…”