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

Bimetallic 1,8-bis(silylamido)naphthalene alkaline earth complexes [(R3L)Ae]2 ([R3L]2– = [1,8-{(R3Si)N}2C10H6)]2–, where R3 = Ph2Me, Ae = Ca (1), Sr (2), and Ba (3); R3 = Ph3, Ae = Ca (4), Sr (5), and Ba (6) were prepared via protonolysis reactions of the phenyl-substituted proligands Ph3LH2 and Ph2MeLH2 with [AeN″2]2 (N″ = [N(SiMe3)2]−) in benzene. X-ray crystallographic analysis showed that 1, 2, and 4 crystallize as nitrogen-bridged dimers. Conversely, 5 and 6 display a naphthalene-bridged motif, while the structure of 3 is intermediate between the two distinct classes. NMR spectroscopic analysis of isolated samples of 1–6 in thf-d8 confirmed their conversion into the monomeric thf-d8 adducts [(R3L)Ae(thf-d8)n]; crystallographic verification of the structural motif was provided by the X-ray crystal structure of [(Ph3L)Sr(thf)3] (7). The structural range of dimers 1–6 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.