Abstract
Bimetallic 1,8-bis(silylamido)naphthalene alkaline earth complexes [((R(3)) L)Ae](2) ([(R(3)) L](2-) = [1,8-{(R(3)Si)N}(2)C(10)H(6))](2-), where R(3) = Ph(2)Me, Ae = Ca (1), Sr (2), and Ba (3); R(3) = Ph(3), Ae = Ca (4), Sr (5), and Ba (6) were prepared via protonolysis reactions of the phenyl-substituted proligands (Ph(3)) LH(2) and (Ph(2)Me)LH(2) with [AeN″(2)](2) (N″ = [N(SiMe(3))(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-d (8) confirmed their conversion into the monomeric thf-d (8) adducts [((R(3)) L)Ae(thf-d (8)) (n) ]; crystallographic verification of the structural motif was provided by the X-ray crystal structure of [((Ph(3)) L)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 Sr(2+) and Ba(2+) 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.