As part of a program directed at the development of palladium-and nickel-catalyzed couplings of alkyl electrophiles, 1 we have been exploring the possibility of achieving a variant of the Heck reaction wherein an alkyl, rather than an aryl, electrophile is coupled with an olefin. In an initial study, we were pleased to discover that such a transformation can indeed be accomplished, albeit in very poor yield (1.2%; eq 1). Interestingly, however, control reactions established that carbon-carbon bond formation proceeds more efficiently in the absence of palladium (24%; eq 1)! Our mechanistic hypothesis for this unanticipated carbene-catalyzed cyclization is outlined in Figure 1. 2,3 Thus, the catalyst (Nu:) adds to the electrophilic β carbon of the α, β-unsaturated ester, generating an enolate (A). Tautomerization then affords B ,4 in which the β carbon is now nucleophilic (umpolung5 ,6 ). An intramolecular S N 2 reaction provides C, which undergoes elimination to furnish the observed product and to regenerate the catalyst (Nu:).For most of the previously described nucleophile-catalyzed reactions of Michael acceptors, the initial adduct (e.g., A) reacts with electrophiles in the α position (e.g., the Morita-BaylisHillman reaction 7 ). Indeed, we have only been able to identify one previous report of a process wherein conjugate addition of a catalyst leads to the β carbon serving as a nucleophile. 8 Furthermore, an interesting contrast is provided by the recent work of Krafft, who has established that enones/enals that bear pendant halides undergo cyclization in the α position when treated with stoichiometric PMe 3 or PBu 3 and then KOH (e.g., eq 2). 9

Key to the isolation of the first alkyl strontium complex was the synthesis of a strontium hydride complex that is stable towards ligand exchange reactions. This goal was achieved by using the super bulky β‐diketiminate ligand DIPePBDI (CH[C(Me)N‐DIPeP]2, DIPeP=2,6‐diisopentylphenyl). Reaction of DIPePBDI‐H with Sr[N(SiMe3)2]2 gave (DIPePBDI)SrN(SiMe3)2, which was converted with PhSiH3 into [(DIPePBDI)SrH]2. Dissolved in C6D6, the strontium hydride complex is stable up to 70 °C. At 60 °C, H–D isotope exchange gave full conversion into [(DIPePBDI)SrD]2 and C6D5H. Since H–D exchange with D2 is facile, the strontium hydride complex served as a catalyst for the deuteration of C6H6 by D2. Reaction of [(DIPePBDI)SrH]2 with ethylene gave [(DIPePBDI)SrEt]2. The high reactivity of this alkyl strontium complex is demonstrated by facile ethylene polymerization and nucleophilic aromatic substitution with C6D6, giving alkylated aromatic products and [(DIPePBDI)SrD]2.

A Ni/Pybox catalyst achieves the asymmetric cross-coupling of secondary alpha-bromo amides with organozinc reagents. The process tolerates a variety of functional groups and affords the desired product in good yield and in high enantiomeric excess.

Alkaline earth metal amides (AeN'' : Ae=Ca, Sr, Ba, N''=N(SiMe ) ) catalyze alkene hydrogenation (80-120 °C, 1-6 bar H , 1-10 mol % cat.), with the activity increasing with metal size. Various activated C=C bonds (styrene, p-MeO-styrene, α-Me-styrene, Ph C=CH , trans-stilbene, cyclohexadiene, 1-Ph-cyclohexene), semi-activated C=C bonds (Me SiCH=CH , norbornadiene), or non-activated (isolated) C=C bonds (norbornene, 4-vinylcyclohexene, 1-hexene) could be reduced. The results show that neutral Ca or Ba catalysts are active in the challenging hydrogenation of isolated double bonds. For activated alkenes (e.g. styrene), polymerization is fully suppressed due to fast protonation of the highly reactive benzyl intermediate by N''H (formed in the catalyst initiation). Using cyclohexadiene as the H source, the first Ae metal catalyzed H-transfer hydrogenation is reported. DFT calculations on styrene hydrogenation using CaN'' show that styrene oligomerization competes with styrene hydrogenation. Calculations also show that protonation of the benzylcalcium intermediate with N''H is a low-energy escape route, thus avoiding oligomerization.

A new, convenient procedure for the addition reaction of trimethylsilylacetylene to imines is described. Simply treating a solution of aldimine and trimethylsilyl acetylene with catalytic [IrCl(COD)](2) furnishes the adduct in preparatively useful yields. Interestingly, the reaction may be conducted in the absence of solvent. [reaction: see text]