Synthesis of Heteroleptic Cerium(III) Anionic Amido-Tethered N-Heterocyclic Carbene Complexes

The in situ low-temperature (−78 °C) reaction of the amine N-heterocyclic carbene
t-BuNHCH2CH2[C{t-BuN(CHCH)N}] (3, HL1), KMe, and 1/2 equiv of [CeI3THF4] (6) in DME/diethyl ether solutions does not afford [(L1)2CeI] (7a); instead, 6 and H2L1I (8) are isolated
in low yields. H2L1Cp (11) is the only isolable product from the reaction of LiL1 (9) and
TlCp. The N-methyl analogue proligand t-BuNH2CH2CH2[HC{MeN(CHCH)N}]2Br (12, H3L2Br2) and the amine−N-heterocyclic carbene t-BuNHCH2CH2[C{MeN(CHCH)N}] (13, HL2)
have been synthesized. However, attempts to prepare and isolate the lithium amido−N-heterocyclic carbene t-BuNLiCH2CH2[C{MeN(CHCH)N}] (14, LiL2) were unsuccessful.
Transamination of [(HL1)LiBr] (2) with [Ce{N(SiMe3)2}3] successfully affords the compounds
[{(L1)Ce(N[SiMe3]2)(μ-Br)}2] (15) and [(L1)Ce{N(SiMe3)2}2] (16), the former being a product
of ligand exchange of 16 with the LiBr byproduct. The complex [{(L1)Ce(N[SiMe3]2)(μ-I)}2]
(17) is obtained by a ligand exchange reaction between 16 and LiI. Compounds 6, 8, 11, 12,
and 15−17 have been characterized by X-ray crystallography and, variously, by NMR
spectroscopy and CHN microanalysis.