Homoleptic Trigonal Planar Lanthanide Complexes Stabilized by Superbulky Silylamide Ligands

The lithium silylamides [Li­(μ³-NHSiMe₂Bu^t)]₆ (<b>1</b>) and [Li­(μ-NHSiPrⁱ₃)­(THF)]₂ (<b>2</b>) were reacted with ClSiMe₃, ClSiMe₂Bu^t, or ClSiPrⁱ₃ to prepare a series of secondary silylamines by salt metathesis reactions. These were deprotonated with KH to afford the group 1 transfer agents [K­{μ-N­(SiMe₂Bu^t)­(SiMe₃)}­(C₇H₈)]₂ (<b>3</b>), [{K­[μ-N­(SiPrⁱ₃)­(SiMe₃)]}₂]_∞ (<b>4</b>), [{K­[μ-N­(SiMe₂Bu^t)₂]}₂­(C₇H₈)]_∞ (<b>5</b>), [K­{N­(SiPrⁱ₃)­(SiMe₂Bu^t)}]_∞ (<b>6</b>), [K­{N­(SiPrⁱ₃)₂}]_∞ (<b>7</b>), and [K­{N­(SiPrⁱ₃)₂}­(THF)₃] (<b>8</b>). The synthetic utility of these group 1 transfer agents has been demonstrated by their reactions with [Ln­(I)₃(THF)₄] (Ln = La, Ce) in various stoichiometries to yield heteroleptic [La­{N­(SiMe₂Bu^t)­(SiMe₃)}₂(μ-I)]₂ (<b>9</b>) and homoleptic [Ln­{N­(SiMe₂Bu^t)­(SiMe₃)}₃] (Ln = La <b>10</b>, Ce <b>11</b>) and [La­{N­(SiMe₂Bu^t)₂}₃] (<b>12</b>). The very bulky silylamide ligands described herein can impart unusual geometries to their lanthanide complexes. Complexes <b>10</b>–<b>12</b> remarkably exhibit approximate planarity in the solid state rather than the more common trigonal pyramidal shapes observed in previously reported neutral homoleptic lanthanide silylamide complexes. Complexes <b>1</b>–<b>12</b> have been variously characterized by X-ray crystallography, NMR spectroscopy, FTIR spectroscopy, and CHN microanalysis