An iron dichloride complex [Fe]­Cl2 supported by a pincer phosphine–pyridine–imidazoline (PNNimid) ligand {[Fe]­Cl2 = (PNNimid)­FeCl2}, upon activation with NaHBEt3, catalyzes the isomerization of 1,1-disubstituted alkenyl boronates to synthetically valuable but previously difficult-to-access trisubstituted (Z)-alkenyl boronates with excellent regio- and stereoselectivity. The loading of the catalyst activator relative to iron was found to affect the selectivity and catalytic efficiency. In situ solvent-assisted electrospray ionization mass (SAESI-MS) studies revealed the generation of two catalytically competent species depending on the Fe/NaHBEt3 ratios: the reaction of [Fe]­Cl2 with 1.5 equiv NaHBEt3 predominantly formed a monohydride chloride [Fe]­HCl, while treatment with 3 equiv NaHBEt3 furnished a dihydride [Fe]­H2. In addition, the iron alkyl intermediates resulting from the insertion of the alkenyl boronate into the Fe–H bonds of [Fe]­HCl and [Fe]­H2 were successfully captured by SAESI-MS. The iron hydride catalysts are sensitive to the steric properties of the alkene substrates: the monohydride [Fe]­HCl is efficient for the synthesis of less hindered alkyl-bearing trisubstituted (Z)-alkenyl boronates, whereas the dihydride [Fe]­H2 is a favorable catalyst for generation of sterically more demanding aryl-substituted products. The synthetic utility of these trisubstituted (Z)-alkenyl boronate products was demonstrated by stereoselective synthesis of multisubstituted conjugated dienes and cyercene A.

The asymmetric hydrogenation of vinylsilanes catalyzed by a new C 1-symmetric phosphine–pyridine–oxazoline cobalt complex is described. The method provides an efficient approach to chiral tertiary silanes with enantioselectivities up to 99% ee. Furthermore, the o-methyl-substituted benzylic silane products undergo ruthenium-catalyzed dehydrogenative silylation to produce chiral benzosilolanes in high yields without racemization of the stereogenic center α to the quaternary Si atom.

Main observation and conclusion Stereoselective isomerization of α‐alkyl styrenes is accomplished using a new iron catalyst supported by phosphine‐pyridine‐oxazoline (PPO) ligand. The protocol provides an atom‐efficient and operationally simple approach to trisubstituted alkenes in high yields with excellent regio‐ and stereoselectivities under mild conditions. The results of deuterium‐labelling and radical trap experiments are consistent with an iron‐hydride pathway involving reversible alkene insertion and β‐H elimination.