Relative Ease of Hydrogenolysis of Some Organometallic Compounds¹

Abstract

The picrate of I was prepared by adding 0.10 g. of I to 5 ml. of a saturated solution of picric acid in chloroform, heating the mixture to boiling, and allowing it to cool slowly.The precipitate was collected, washed with a little chloro-form, and recrystallized from chloroform to give yellow needles melting at 199-200°( dec.

LiAlH4: From Stoichiometric Reduction to Imine Hydrogenation Catalysis

“…[21] Given the simplicity of these group 2m etal catalysts,w e wondered whether LiAlH 4 ,w hich in imine reduction is normally added stoichiometrically,c ould be catalytically active.A lready in the 1960s,L iAlH 4 was used as ac atalyst for alkyne reduction, [24] however, the very harsh conditions needed (35 mol %c at, 190 8 8C, 80 bar H 2 )d id not encourage follow-up research. Acrucial step is the hydrogenolysis of the metal À Cbond by H 2 ,for which the rate is known to decrease with decreasing bond ionicity:N a À C > Mg À C > Al À C. [25] since it is well-known that RNH 2 and R 2 NH react smoothly with LiAlH 4 to give aluminium amide products and H 2 , [26][27][28][29][30][31] hydrogenolysis of AlÀNbonds to give amines is anticipated to be even more cumbersome.S ubstitution of H 2 for polar borane or silane reductants was therefore al ogical step. Indeed, hydroboration and hydrosilylation reactions were found to be more promising.…”

LiAlH4: From Stoichiometric Reduction to Imine Hydrogenation Catalysis

“…[20] We recently reported simple group 2m etal catalysts of the type MN'' 2 (M = Ca, Sr, Ba;N'' = N(SiMe 3 ) 2 ), which operate efficiently under surprisingly mild conditions (1-6 bar H 2 ,8 0 8 8C) and show af air substrate scope and functional-group tolerance. Acrucial step is the hydrogenolysis of the metal À Cbond by H 2 ,for which the rate is known to decrease with decreasing bond ionicity:N a À C > Mg À C > Al À C. [25] since it is well-known that RNH 2 and R 2 NH react smoothly with LiAlH 4 to give aluminium amide products and H 2 , [26][27][28][29][30][31] hydrogenolysis of AlÀNbonds to give amines is anticipated to be even more cumbersome.S ubstitution of H 2 for polar borane or silane reductants was therefore al ogical step. [23] Also the last s-bond metathesis step in the cycle seemed questionable.Acomprehensive calculational study, however, demonstrated that the metal hydride mechanism shown in Scheme 1isfeasible.…”

Heteronuclear NMR Correlations To Probe the Local Structure of Catalytically Active Surface Aluminum Hydride Species on γ‐Alumina

“…[2] However, main-group-metal alkyls display lower reactivity toward hydrogen: Examples of such reactions usually imply forcing conditions. [10] We reasoned that the strong polarization of the Al À C bond by the electron-deficient support would ease the heterolytic splitting of H 2 . Prolonged heating of 1 at 400 8C under low H 2 pressure (0.733 bar) afforded material 2.…”