A Dicerium(IV) Nitride Complex with a Linear CeNCe Core Stabilized by Bulky Cyclohexyltriamide Ligands.

Lanthanide nitrides remain rare, being restricted to the singular example with a CeN(Li2)Ce core stabilized by two Lewis acidic lithium ions. Here, we introduce a new cyclohexyltriamide ligand [TachDMBS] to lanthanide chemistry, which enables us to isolate a lanthanide nitride complex [{(TachDMBS)Ce}2(μ-N)][Na(12-crown-4)2] (6) with a linear CeNCe core without any alkali metal interaction. Complex 6 was prepared by the reaction of a rare dinuclear tuck-in-tuck-over cerium(IV) metallacycle [{(CH2CHNSiMe2tBu)2(CHNSiMetBu(μ-CH2)Ce}2] (4) with one equivalent of NaNH2 in benzene in the presence of two equivalents of 12-crown-4, yielding 48%. The Ce-N(nitride) bond distances in 6 (2.051(19) Å) are close to the shortest Ce-N bonds reported so far, and a linear Ce-N-Ce bond angle in 6 (180.00°) is disclosed. The isostructural oxo analogue [{(TachDMBS)Ce}2(μ-O)] (7) was prepared for comparison. Computational analysis of 6 and 7 reveals Ce═N multiple-bonding character consisting of two 2c-2e σ-bonds and two orthogonal 3c-2e π-bonds in 6, showing a similar bonding trend to that in the known CeN(Li2)Ce linkage, but single bonds for Ce-O in 7, confirming the stronger donating capability of N3- vs O2- in the bridging mode and highlighting the importance of supporting ligands in stabilizing the unsupported CeNCe core.