β-Diketiminate calcium hydride complexes: the importance of solvent effects.

A series of (DIPPnacnac)CaN(SiMe)·S complexes (DIPPnacnac = HC[C(Me)N(2,6-iPr-CH)]; S = solvent) could be obtained by the addition of S = THF, DME or N-Me-morpholine (Morph) to (DIPPnacnac)CaN(SiMe)·OEt or (DIPPnacnac)CaN(SiMe). Crystal structures for complexes with S = DME and Morph are compared to literature-known structures with S = none, THF or EtO. Bulkier and weaker Lewis bases like the tertiary amines EtN, TMEDA and DABCO did not interact with (DIPPnacnac)CaN(SiMe). The reaction of (DIPPnacnac)CaN(SiMe) with PhSiH gave conversion to a calcium hydride complex that dismutated in (DIPPnacnac)Ca and CaH. The reaction of (DIPPnacnac)CaN(SiMe)·S with PhSiH gave [(DIPPnacnac)CaH·S] for S = THF, EtO or N-Me-morpholine (Morph). For S = DME, high reaction temperatures were needed and dismutation into (DIPPnacnac)Ca and CaH was observed. Extensive NMR investigations (VT-NMR and PGSE) confirm the dimeric nature of [(DIPPnacnac)CaH·THF] in aromatic solvents or in THF. Thermal decomposition of [(DIPPnacnac)CaH·THF] (release of H at 200 °C) is compared to that of Mg and Zn analogues. Weakly coordinating EtO in [(DIPPnacnac)CaH·OEt] could be replaced by THF, Morph or DABCO but not with EtN. The addition of TMEDA led to the formation of CaH and unidentified products. The addition of DME led to the decomposition of EtO and complex [(DIPPnacnac)CaOEt] was obtained. Crystal structures of the following compounds are presented: (DIPPnacnac)CaN(SiMe)·S (S = Morph, DME), [(DIPPnacnac)CaH·S] (S = EtO, Morph and DABCO) and [(DIPPnacnac)CaOEt]. Although bulky ligands have long been thought to be the key to the stabilization of calcium hydride complexes, the presence of a polar, strongly coordinating, co-solvent is also crucial.