Calcium Hydride Insertion Reactions with Unsaturated C–C Bonds

Abstract

The dimeric β-diketiminato calcium hydride, [(BDI)CaH] 2 (BDI = HC{(Me)CN-2,6-i-Pr 2 C 6 H 3 } 2 ), reacts with terminal alkenes to provide the corresponding alkyl derivatives. With 1-octene, 3,3-dimethyl-1-butene, 3-phenyl-1propene, and 4-phenyl-1-butene, the ultimate products are dimeric alkyl species, which form sequentially via dinuclear calcium hydrido-alkyl intermediates. Reaction of diphenylacetylene with [(BDI)CaH] 2 provides a tetra-calcium complex in which a stilbene dianion bridges symmetrically between two hydrido-bridged bis-β-diketiminato calcium units, while treatment with trans-stilbene yields a dicalcium benzyl-hydride derivative, [{(BDI)Ca} 2 (H)(PhCHCH 2 Ph)]. Reaction of [(BDI)CaH] 2 and 1,5-hexadiene has previously been observed to provide facile 5-exo-trig cyclization to calcium cyclopentylmethyl derivatives. In contrast, analogous reaction with 1,7-octadiene provides exclusive intermolecular insertion to yield a dimeric open chain calcium oct-7-en-1-yl derivative. Reaction with the internal alkene, norbornene, enables the identification of a highly reactive dinuclear calcium norbornyl-hydride. The greater basicity of the calcium secondary alkyl species is emphasized by the subsequent isolation of a product of intramolecular deprotonation of a BDI iso-propyl methyl substituent.

Calcium Hydride Reduction of Polycyclic Aromatic Hydrocarbons

“…Reactions of 2 with naphthalene,a nthracene and tetracene performed at 350 Kw ithin the cavity of aC WE PR spectrometer provided no evidence for the production of short lived hydrogen radicals.I ne ach case,h owever, signals (17), Ca1-C88 2.651(2), Ca1-C89 2.923(2), Ca1-C94 2.838(2), Ca1-C95 2.624(2), Ca1-C96 3.019(2), Ca2-N3 2.3492 (17),C a2-N4 2.4179(18), Ca2-C96 3.071(2), Ca2-C97 2.981(2), Ca2-C98 2.858(2), Ca2-C99 2.748(2), Ca2-C1002 .712(2), Ca2-C101 2.868(2), Ca3-N5 2.3902(18), Ca3-N6 2.4405 (19),C a3-C89 3.138(2), Ca3-C90 2.995(2), Ca3-C91, 2.875(2) Ca3-C92 2.804(2), Ca3-C93 2.801(2), Ca3-C94 2.964(2); N1-Ca1-N2 78.05 (6), N3-Ca2-N4 77.51(6), N5-Ca3-N6 78.73(6);(11)C a1-N1 2.3290(12), Ca1-N2 2.3412(12), Ca1-C30 2.7127(15), Ca1-C31 2.8973(15), Ca1-C32 2.7097 (14), Ca1-C33 2.7711 (14),C a1-C34 2.7660 (15);N1-Ca1-N2 76.92 (4). Symmetry operations to generate equivalent atoms 1Àx,1 Ày,1 Àz.…”

“…BDI = HC{(Me)CN-2,6-i Pr 2 C 6 H 3 } 2 ), [4,2] b-diketiminate derivatives have been especially prominent. Thes ynthesis of asolvent-free analogue of 1 (2,see Scheme 1) highlights how ar eduction in coordinative saturation at the calcium center can impact significantly on the observed chemistry.…”

“…Thes ynthesis of asolvent-free analogue of 1 (2,see Scheme 1) highlights how ar eduction in coordinative saturation at the calcium center can impact significantly on the observed chemistry. [5] Compound 2 reacts with aw ide range of unactivated terminal alkenes, [4,6] providing n-alkyl derivatives,w hich are sufficiently nucleophilic to effect the heterolytic cleavage of H 2 or even the direct displacement of hydride from benzene. [5,6] Subsequent use of ab ulkier b-diketiminate ligand in the synthesis of [( DIPeP BDI)SrH] 2 (3; DIPeP BDI = HC{(Me)CN-2,6-(Et 2 CH) 2 C 6 H 3 } 2 )has shown that analogous reactivity may be achieved at strontium.…”

Regioselective Hydrosilylation of Olefins Catalyzed by a Molecular Calcium Hydride Cation

“…Only after the hydrosilane was fully consumed or when hydride 3 was dissolved in [D 8 ]THF and pressurized with ethylene (1 bar), was formation of an ethyl calcium species detected by characteristic signals at d À1.02 (q) and 1.26 (t) ppm for the methylene and methyl protons, respectively. [24] After 10 min at 25 8C, higher n-alkyl calcium species were also evident from their charac-teristic resonances, indicating additional insertion of ethylene into the calcium-n-alkyl bond (see the Supporting Information). While oligomerization of ethylene was not observed for solid [CaH 2 ] 1 [23] and [( DIPP BDI)Ca(m-H)] 2 , [24] strontium hydride [( DIPeP BDI)Sr(m-H)] 2 (DIPeP = 2,6-(pent-3-yl) 2 -phenyl) formed oligoethylene at room temperature.…”

“…[24] After 10 min at 25 8C, higher n-alkyl calcium species were also evident from their charac-teristic resonances, indicating additional insertion of ethylene into the calcium-n-alkyl bond (see the Supporting Information). While oligomerization of ethylene was not observed for solid [CaH 2 ] 1 [23] and [( DIPP BDI)Ca(m-H)] 2 , [24] strontium hydride [( DIPeP BDI)Sr(m-H)] 2 (DIPeP = 2,6-(pent-3-yl) 2 -phenyl) formed oligoethylene at room temperature. [20a] Unlike the BDI-stabilized ethyl complexes, the highly reactive cationic n-alkyl calcium derivative of 3 could not be isolated as it readily decomposed in THF solution (t 1/2 < 10 min at 25 8C, 20 min at À20 8C) to give short alkanes (C 2 -C 6 ) and other undefined species.…”