Exploring the Nuclearity and Structural Motifs of Phenoxyimine Alkaline Earth Complexes

TL;DR

This paper investigates how different ligands and metals affect the structure of alkaline earth metal complexes.

Contribution

The study reveals how ligand design and synthetic methods influence the nuclearity and structural motifs of these complexes.

Findings

Changing N-imine substituent size does not affect protonolysis reactions in Mg and Ca complexes.

Equimolar reactions produce heteroleptic complexes without ligand redistribution.

Smaller substituents lead to multimetallic clusters in Ca and Sr complexes.

Abstract

The nuclearity and
structural motifs of alkaline earth complexes
supported by bidentate phenoxyimine ligands has been explored by modulation
of the stereoelectronic profile of the ligand, the atomic number of
the metal, and the synthetic protocol. Changing the size of the N-imine substituents was found to have no effect on protonolysis
reactions between [MgN″2]2 or CaN″2(thf)2 (N″ = N(SiMe3)2) and HtBu2,ArL
(1-OH-2-CH = NAr-4,6-tBu-C6H2; Ar = 2,6-iPr–C6H3 = Dipp or 2,6-CHPh2-4-Me-C6H2 = Ar*) regardless of reaction stoichiometry, with homoleptic bis(ligand) complexes (tBu2,DippL)2Mg (1), (tBu2,Ar*L)2Mg (2), (tBu2,DippL)2Ca(thf) (3) and (tBu2,Ar*L)2Ca(thf)
(4) isolated. The importance of reaction protocol was
demonstrated by the facile isolation of heteroleptic complex (tBu2,Ar*L)MgI(OEt2) (5) from the reaction of equimolar amounts
of HtBu2,Ar*L and
MeMgI. Importantly, no subsequent ligand redistribution was observed
when complex 5 readily reacted with KN” or KODipp
to form (tBu2,Ar*L)Mg{N(SiMe3)2}(OEt2) (6) and (tBu2,Ar*L)Mg(ODipp)(thf) (7). When small 4,6-phenoxide substituents
were considered (HH2,DippL), multimetallic clusters
were afforded: (H2,DippL)3Ca2(N″)(thf) (8) and (H2,DippL)6Sr3 (9).

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