Reactions of the dimeric calcium hydride complex[(DIPP‐nacnac)CaH · thf] 2 { 1 ; DIPP‐nacnac = CH[(CMe)(2,6‐ i Pr 2 C 6 H 3 N)] 2 } with the α ‐hydrogen containing ketones acetophenone, acetone, dibenzylketone and 2‐adamantone are smooth. In most cases not only addition but also substantial enolization is observed as a side reaction and in some cases also aldol condensation was found. Despite this unselectivity, the addition products could be isolated crystalline pure. Crystal structures of [(DIPP‐nacnac)CaOCH(Me)Ph] 2 ( 3 ), [(DIPP‐nacnac)CaOCH(CH 2 Ph) 2 ] 2 ( 6 ) and [(DIPP‐nacnac)Ca(2‐adamantoxide)] 2 ( 7 ) have been determined. The calcium hydride complex 1 is an effective catalyst in the hydrosilylation of ketones. Independent from the silane/ketone ratio, a strong preference for formation of bis ‐alkoxy silanes [PhSiH(OR) 2 ] is observed. In most cases no enoxy groups have been found in the product. This indicates that the mechanism does not involve addition of the calcium hydride to the ketone functionality. A concerted addition of silane to ketone through a six‐coordinate hypervalent silicon intermediate is proposed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
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Spielmann et al. (2008) studied this question.