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

A series of (DIPPnacnac)CaN(SiMe3 )2 ·S complexes (DIPPnacnac = HC[C(Me)N(2,6-iPr-C6 H3 )]2 ; S = solvent) could be obtained by the addition of S = THF, DME or N-Me-morpholine (Morph) to (DIPPnacnac)CaN(SiMe3 )2 ·OEt2 or (DIPPnacnac)CaN(SiMe3 )2 . Crystal structures for complexes with S = DME and Morph are compared to literature-known structures with S = none, THF or Et2 O. Bulkier and weaker Lewis bases like the tertiary amines Et3 N, TMEDA and DABCO did not interact with (DIPPnacnac)CaN(SiMe3 )2 . The reaction of (DIPPnacnac)CaN(SiMe3 )2 with PhSiH3 gave conversion to a calcium hydride complex that dismutated in (DIPPnacnac)2 Ca and CaH2 . The reaction of (DIPPnacnac)CaN(SiMe3 )2 ·S with PhSiH3 gave [(DIPPnacnac)CaH·S]2 for S = THF, Et2 O or N-Me-morpholine (Morph). For S = DME, high reaction temperatures were needed and dismutation into (DIPPnacnac)2 Ca and CaH2 was observed. Extensive NMR investigations (VT-NMR and PGSE) confirm the dimeric nature of [(DIPPnacnac)CaH·THF]2 in aromatic solvents or in THF. Thermal decomposition of [(DIPPnacnac)CaH·THF]2 (release of H2 at 200 °C) is compared to that of Mg and Zn analogues. Weakly coordinating Et2 O in [(DIPPnacnac)CaH·OEt2 ]2 could be replaced by THF, Morph or DABCO but not with Et3 N. The addition of TMEDA led to the formation of CaH2 and unidentified products. The addition of DME led to the decomposition of Et2 O and complex [(DIPPnacnac)CaOEt]2 was obtained. Crystal structures of the following compounds are presented: (DIPPnacnac)CaN(SiMe3 )2 ·S (S = Morph, DME), [(DIPPnacnac)CaH·S]2 (S = Et2 O, Morph and DABCO) and [(DIPPnacnac)CaOEt]2 . 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.