Synthesis and reactivity of alkaline-earth stannanide complexes by hydride-mediated distannane metathesis and organostannane dehydrogenation?

Dalton Transactions Pub Date: 2020-07-09 DOI: 10.1039/D0DT02406F

Abstract

The synthesis of heteroleptic complexes with calcium– and magnesium–tin bonds is described. The dimeric β-diketiminato calcium hydride complex, [(BDI)Ca(μ-H)]2 (ICa) reacts with Ph3Sn–SnPh3 to provide the previously reported μ2-H bridged calcium stannanide dimer, [(BDI)2Ca2(SnPh3)(μ-H)] (3). Computational assessment of this reaction supports a mechanism involving a hypervalent stannate intermediate formed by nucleophilic attack of hydride on the distannane. Monomeric calcium stannanides, [(BDI)Ca(SnPh3)·OPPh3] (8·OPPh3) and [(BDI)Ca(SnPh3)·TMTHF] (8·TMTHF, TMTHF = 2,2,5,5-tetramethyltetrahydrofuran) were obtained from ICa and Ph3Sn–SnPh3, after addition OPPh3 or TMTHF. Both complexes were also synthesised by deprotonation of Ph3SnH by ICa in the presence of the Lewis base. The calcium and magnesium THF adducts, [(BDI)Ca(SnPh3)·THF2] (8·THF2) and [(BDI)Mg(SnPh3)·THF] (9·THF), were similarly prepared from [(BDI)Ca(μ-H)·(THF)]2 (ICa·THF2) or [(BDI)Mg(μ-H)]2 (IMg) and Ph3SnH. An excess of THF or TMTHF was essential in order to obtain 8·TMTHF, 8·THF2 and 9·THF in high yields whilst avoiding redistribution of the phenyl-tin ligand. The resulting Ae–Sn complexes were used as a source of [Ph3Sn]? in salt metathesis, to provide the known tristannane Ph3Sn–Sn(t-Bu)2–SnPh3 (11). Nucleophilic addition or insertion with N,N′-di-iso-propylcarbodiimide provided the stannyl-amidinate complexes, [(BDI)Mg{(iPrN)2CSnPh3}] (12) and [(BDI)Ca{(iPrN)2CSnPh3}·L] (13·TMTHF, 13·THF, L = TMTHF, THF). The reactions and products were monitored and characterised by multinuclear NMR spectroscopy, whilst for compounds 8, 9, 12, and 13·THF, the X-ray crystal structures are presented and discussed.

Graphical abstract: Synthesis and reactivity of alkaline-earth stannanide complexes by hydride-mediated distannane metathesis and organostannane dehydrogenation
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