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

A series of (DIPPnacnac)CaN(SiMe3)(2 center dot)S complexes (DIPPnacnac = HC[C(Me)N(2,6-iPr-C6H3)](2); S = solvent) could be obtained by the addition of S = THF, DME or N-Me-morpholine (Morph) to (DIPPnacnac) CaN(SiMe3)(2)center dot 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 Et2O. Bulkier and weaker Lewis bases like the tertiary amines Et3N, 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)center dot(S) with PhSiH3 gave [(DIPPnacnac) CaH center dot S] for S = THF, Et2O 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 center dot THF](2) in aromatic solvents or in THF. Thermal decomposition of [(DIPPnacnac) CaH center dot THF](2) (release of H-2 at 200 degrees C) is compared to that of Mg and Zn analogues. Weakly coordinating Et2O in [(DIPPnacnac) CaH center dot OEt2](2) could be replaced by THF, Morph or DABCO but not with Et3N. The addition of TMEDA led to the formation of CaH2 and unidentified products. The addition of DME led to the decomposition of Et2O and complex [(DIPPnacnac) CaOEt](2) was obtained. Crystal structures of the following compounds are presented: (DIPPnacnac) CaN(SiMe3)(2)center dot S (S = Morph, DME), [(DIPPnacnac) CaH center dot S](2) (S = Et2O, Morph and DABCO) and [(DIPPnacnac) CaOEt](2). Although bulkyligands 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.