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. 2025 Feb 5;44(4):582-594.
doi: 10.1021/acs.organomet.4c00479. eCollection 2025 Feb 24.

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

Matthew D Haynes  1 , Clement G Collins Rice  1 , Louis J Morris  1 , Zoë R Turner  1 , Dermot O'Hare  1
Affiliations

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

Matthew D Haynes et al. Organometallics. .

Abstract

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 (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 Ph3 LH2 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-d 8 confirmed their conversion into the monomeric thf-d 8 adducts [(R3 L)Ae(thf-d 8) n ]; crystallographic verification of the structural motif was provided by the X-ray crystal structure of [(Ph3 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 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.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Chart 1
Chart 1. Selected Examples of Complexes Supported by Dianionic Chelating Ligands with Rigid Naphthalene Backbones
Scheme 1
Scheme 1. Synthesis of 1–6via the 2:1 Reaction of R3LH2 (R3 = Ph2Me and Ph3) with [AeN″2]2 (Ae = Ca, Sr and Ba) in Benzene
Scheme 2
Scheme 2. “Structural Snapshots” of the Transition of a “Relaxed” Nitrogen-Bridged [(R3L)Ae]2 Dimer into a “Contracted” Naphthalene-Bridged form via an Intermediate Species in Which Both Interactions are Present
Figure 1
Figure 1
Thermal displacement ellipsoid drawings (30% probability) of [(Ph2MeL)Ca]2 (1), [(Ph2MeL)Sr]2 (2), [(Ph2MeL)Ba]2 (3), and [(Ph3L)Ca]2 (4). All hydrogen atoms have been omitted, and wireframes are used for clarity.
Figure 2
Figure 2
Illustrations of the deformation density of the principal interacting orbital in dimeric complexes 1–6 computed by EDA-NOCV relative to isolated monomeric species. Blue and yellow represent donating and accepting orbitals, respectively. The dominance of the Ae–N interaction in 1, 2, and 4 is contrasted with the Ae-arene π-facial interactions in 5 and 6.
Figure 3
Figure 3
Thermal displacement ellipsoid drawings (30% probability) of [(Ph3L)Sr]2 (5) and [(Ph3L)Ba]2 (6). All hydrogen atoms have been omitted for clarity.
Scheme 3
Scheme 3. Synthesis of [(R3L)Ae(thf)n] from [(R3L)Ae]2 (1–6); Illustrated for [(Ph3L)Sr(thf)3] (7) Which was also Verified in the Solid State
Figure 4
Figure 4
Thermal displacement ellipsoid drawing (30% probability) of [(Ph3L)Sr(thf)3] (7). All hydrogen atoms have been omitted, and phenyl groups are shown in ball-and-stick form for clarity.
See this image and copyright information in PMC

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