Reactivity of Bis(guanidinate) Magnesium Hydride and Alkyl Complexes: Mg-E (E = S, Se, Te) Bond Formation and Structural Diversification

Abstract

The reactivity of the bis(guanidinate) magnesium hydride complex [L1 MgH]2 (1) [L1 = {(ArHN)(ArN)–C = N–C(NAr)(NHAr)}; Ar = 2,6-iPr2C6H3] toward sulfur-, selenium-, and tellurium-based reagents has been investigated. Reactions of complex 1 with sulfur-containing reagents such as p-MePhSH, Ph2S2, afforded the magnesium thiolate complexes [L1 MgSAr]2 (Ar = 4-Me-C6H4; 2 and Ar = Ph; 3), while treatment with phosphine chalcogenides [Ph3P = E; E = S, Se] generated the bridging chalcogenide species [{L1 Mg}2(μ-E)] (E = S, 4; Se, 5). Further extension to selenium and tellurium chemistry furnished the magnesium aryl selenolate and tellurolate complexes [L1 MgEPh]2 (E = Se, 6; Te, 8) together with the neutral bis(guanidine)-supported bis(arylchalcogenolate) derivatives [L1(H)Mg(EPh)2] (E = Se, 7; Te, 9). Control experiments support a stepwise sequence for the formation of such complexes involving initial formation of magnesium aryl chalcogenolates, followed by further aryl chalcogenol-promoted chalcogen incorporation. Beyond the successful sulfur-, selenium-, and tellurium-transfer chemistry, the versatility of the bis(guanidinate) magnesium platforms was further demonstrated by the isolation of chloride- and hydroxide-bridged complexes, [L1 Mg(μ-Cl)]2 (10) and [L2 Mg(μ–OH)]2 (11) [L2 = {(ArHN)(ArN)–C = N–C(NAr)(NHAr)}; Ar = 2,6-Et2C6H3]. Additionally, complex 1 undergoes solvent-mediated ligand transformation in THF, to furnish the disubstituted guanidinate magnesium complex 12. All complexes were isolated and characterized by standard spectroscopic techniques and single-crystal X-ray diffraction analysis.