Hydrocarbon‐Soluble Calcium Hydride: A “Worker‐Bee” in Calcium Chemistry

Abstract

The reactivity of the hydrocarbon-soluble calcium hydride complex [{CaH(dipp-nacnac)(thf)}(2)] (1; dipp-nacnac=CH{(CMe)(2,6-iPr(2)C(6)H(3)N)}(2)) with a large variety of substrates has been investigated. Addition of 1 to C=O and C=N functionalities gave easy access to calcium alkoxide and amide complexes. Similarly, reduction of the C[triple chemical bond]N bond in a cyanide or an isocyanide resulted in the first calcium aldimide complexes [Ca{N=C(H)R}(dipp-nacnac)] and [Ca{C(H)=NR}(dipp-nacnac)], respectively. Complexation of 1 with borane or alane Lewis acids gave the borates and alanates as contact ion pairs. In reaction with epoxides, nucleophilic ring-opening is observed as the major reaction. The high reactivity of hydrocarbon-soluble 1 with most functional groups contrasts strongly with that of insoluble CaH(2), which is essentially inert and is used as a common drying agent. Crystal structures of the following products are presented: [{Ca{OC(H)Ph(2)}(dipp-nacnac)}(2)], [{Ca{N=C(H)Ph}(dipp-nacnac)}(2)], [{Ca{C(H)=NC(Me)(2)CH(2)C(Me)(3)}(dipp-nacnac)}(2)], [{Ca{C(H)=NCy}(dipp-nacnac)}(2)], [Ca(dipp-nacnac)(thf)](+)[H(2)BC(8)H(14)](-) and [{Ca(OCy)(dipp-nacnac)}(2)]. The generally smooth and clean conversions of 1 with a variety of substrates and the stability of most intermediates against ligand exchange make 1 a valuable key precursor in the syntheses of a wide variety of beta-diketiminate calcium complexes.

Reduction of Ketones with Hydrocarbon‐Soluble Calcium Hydride: Stoichiometric Reactions and Catalytic Hydrosilylation

“…Deviations from symmetrical bridging of the alkoxide ligands is only found for 2 and is supposedly correlated to intramolecular Ph(π)···Ca interaction. [2] The crystal structure of 3 shows the centrosymmetric (R,S)-diastereomer ( Figure 1). Like in 2, the coordination sphere of Ca 2+ is completed by interaction with the Ph ring of the alkoxide ligand.…”

“…[2] As benzophenone is not prone to any of the side reactions summarized in Scheme 1, we screened a variety of α-hydrogen containing ketones. Scheme 2. Reactions of these selected ketones with 1 were generally fast and gave full conversion.…”

“…In most cases well-defined calcium complexes could be isolated and have been characterized by crystal structure determinations. [2] Since the nucleophilic addition to ketones is one of the most versatile reactions in organic syntheses, [3] we now expand the scope of this new hydride cium 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.…”

Heterofunctionalization catalysis with organometallic complexes of calcium, strontium and barium

“…Despite a report by Spielmann & Harder (2007) documenting that 17 readily reacts with alternative substrates, including benzonitrile, cyclohexene oxide, 2-methylpropene oxide, 1,1,3,3-tetramethylbutyl isonitrile and diphenylmethyl-N -phenylimine, via insertion of unsaturated carbon-nitrogen and carbon-oxygen bonds into the calcium-hydride bond of the organometallic reagent, catalytic preparations for the hydrosilylation (or hydrogenation) of these substrates with Group II reagents have yet to be reported.…”

Heterolysis of Dihydrogen by Nucleophilic Calcium Alkyls

“…Like the aforementioned organolanthanides, the calcium center of 1 possesses a formal d 0 configuration and was found to engage in polarized insertion reactivity with a variety of unsaturated substrates 18, 19. Although compound 1 helped stimulate widespread interest in the isolation of heavy s‐block hydrides, its reactivity with C=C bonds was limited to the conjugated and more activated alkenes, 1,3‐cyclohexadiene,19 myrcene, and 1,1‐diphenylethene 20.…”