Synthesis of heteroleptic cerium(III) anionic amido-tethered N-heterocyclic carbene complexes

The in situ low-temperature (-78 degrees 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 [(L-1)(2)CeI] (7a); instead, 6 and (H2LI)-I-1 (8) are isolated in low yields. (H2LCp)-Cp-1 (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, (H3LBr2)-Br-2) 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 [{(L-1)Ce(N[SiMe3](2))(mu-Br)}(2)] (15) and [(L-1)Ce{N(SiMe3)(2)}(2)] (16), the former being a product of ligand exchange of 16 with the LiBr byproduct. The complex [{(L-1)Ce(N[SiMe3](2))(mu-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.