Promoting π-Facial Interactions in Phenyl-Substituted 1,8-Bis(silylamido)naphthalene Alkaline Earth Complexes

Bimetallic 1,8-bis(silylamido)naphthalene alkaline earth complexes [(^R₃ L)Ae]₂ ([^R₃ L]^2- = [1,8-{(R₃Si)N}₂C₁₀H₆)]^2-, where R₃ = Ph₂Me, Ae = Ca (<b>1</b>), Sr (<b>2</b>), and Ba (<b>3</b>); R₃ = Ph₃, Ae = Ca (<b>4</b>), Sr (<b>5</b>), and Ba (<b>6</b>) were prepared <i>via</i> protonolysis reactions of the phenyl-substituted proligands ^Ph₃ LH₂ and ^Ph₂MeLH₂ with [AeN″₂]₂ (N″ = [N(SiMe₃)₂]^-) in benzene. X-ray crystallographic analysis showed that <b>1</b>, <b>2</b>, and <b>4</b> crystallize as nitrogen-bridged dimers. Conversely, <b>5</b> and <b>6</b> display a naphthalene-bridged motif, while the structure of <b>3</b> is intermediate between the two distinct classes. NMR spectroscopic analysis of isolated samples of <b>1</b>-<b>6</b> in thf-<i>d</i> ₈ confirmed their conversion into the monomeric thf-<i>d</i> ₈ adducts [(^R₃ L)Ae(thf-<i>d</i> ₈) _<i>n</i> ]; crystallographic verification of the structural motif was provided by the X-ray crystal structure of [(^Ph₃ L)Sr(thf)₃] (<b>7</b>). The structural range of dimers <b>1</b>-<b>6</b> was influenced by the electron-withdrawing nature of the phenyl substituents of the ligand and the ability to form "soft" multihaptic π-facial interactions with the metal ions, which was preferential for the larger Sr²⁺ and Ba²⁺ cations as well as the relative strength of the metal-N bonds. This has been rationalized through complementary computational studies. This work provides insight into the structure and bonding preferences of heavy alkaline earth complexes with rigid bis(amido) ligands.