Michael D. Fryzuk

We report the first bottleable enantiopure P-chiral secondary phosphines from the rhodium-catalyzed asymmetric hydrogenation of phosphaalkenes. Catalytic asymmetric hydrogenation, a reaction of broad academic and industrial importance for C═C, N═C, and O═C bonds, has not previously been reported for the P═C bond. The hydrogenation of ArP═CR₂ (Ar = Mes, m-Xyl and TMOP; R = Ph, 4-C₆H₄F) affords four unprecedented P-stereogenic secondary phosphines in 76%-90% isolated yields with 91%-97% enantiomeric excess (ee). These isolable P-chiral secondary phosphines are configurationally stable indefinitely in the solid state and show only modest loss in ee when kept in solution for over a month at room temperature.

The synthesis and reactivity of the bimetallic rhodium–copper complex, Rh(COE)[P ₂ N ₂ ]Cu, which is stabilized by the P ₂ N ₂ macrocycle, is reported.

The reaction of the dilithium diamido–diphosphine macrocycle, Li₂[N(SiMe₂CH₂P(Ph)CH₂SiMe₂)₂N] (Li₂[P₂N₂]) with [Rh(COD)Cl]₂ generates the dirhodium macrocyclic compound, [P₂N₂][Rh(COD)]₂ (where COD = η⁴-1,5-cyclooctadiene), wherein both rhodium-COD units are syn to each other and have square planar geometries. While this dirhodium derivative does react with H₂, no clean products could be isolated. Upon reaction of Li₂[P₂N₂] with [Rh(COE)₂Cl]₂ (where COE is η²-cyclooctene), the dilithium–dihodium derivative ([Rh(COE)][P₂N₂]Li)₂(dioxane) forms, which was characterized by single-crystal X-ray analysis and NMR spectroscopy. The cyclooctene derivative reacts with dihydrogen in benzene to generate the dilithium–dirhodium-dihydride complex ([Rh(H)₂][P₂N₂]Li)₂(dioxane); also formed is the dilithium–dirhodium–phenylhydride complex ([Rh(C₆H₅)H][P₂N₂]Li)₂(dioxane) via oxidative addition of a C–H bond of the solvent. The phenyl-hydride is eventually converted to the dihydride derivative via further reaction with H₂. This process is complicated by adventitious H₂O, which leads to the isolation of the amine-dihydride, Rh[P₂N₂H](H)₂; drying of the H₂ eliminates this side product. Nevertheless, careful addition of H₂O to ([Rh(COE)][P₂N₂]Li)₂(dioxane) results in protonation of one of the amido units and the formation of the rhodium–amine cyclooctene derivative, Rh[P₂N₂H](COE), which upon reaction with H₂ generates the aforementioned amine-dihydride, Rh[P₂N₂H](H)₂. The mechanism by which dihydrogen and C–H bonds of benzene are activated likely involves initial dissociation of cyclooctene from the 18-electron centers in ([Rh(COE)][P₂N₂]Li)₂(dioxane), followed by H–H and C–H bond activation. The ability of one of the amido units of the P₂N₂ macrocycle to be protonated is a potentially useful proton storage mechanism and is of interest in other bond activation processes.

The coordination chemistry of the new NNP pincer ligand framework (QuiNacNacP) is explored with cobalt. Upon treatment of the cobalt(II) complex Co[QuiNacNacP]Cl with KC₈, the formation of cobalt(I) dinitrogen complex Co[QuiNacNacP]N₂ was observed. Co[QuiNacNacP]N₂ crystallizes as a square planar (S = 0) complex with an essentially unactivated N₂ ligand. In solution, the dinitrogen complex is in equilibrium with the paramagnetic T‐shaped complex Co[QuiNacNacP] (S = 1). The ability of Co[QuiNacNacP]Cl to act as a catalyst precursor in the reductive silylation of dinitrogen was also briefly explored. Reaction of ≈ 1000 equivalents KC₈ with ≈ 1500 equivalents Me₃SiCl (relative to Co[QuiNacNacP]Cl) under 1 atm of N₂ furnished roughly 40 equivalents of N(SiMe₃)₃.

The redox behaviour of the dimeric tetrairon complex, ([fc(NPⁱPr₂)₂]Fe)₂ (where fc(NPⁱPr₂)₂ = 1,1′-(C₅H₄NPⁱPr₂)₂Fe) has been investigated.

The reaction of CS₂with the side-on end-on dinitrogen complex ([NPN^Si]Ta)₂(μ–η¹:η²-N₂)(μ-H)₂generates two products, the ratio of which depends on the concentration of added CS₂.

A low-coordinate iron hydride complex bearing an unsymmetrical NpN (enamido–phosphinimine) ligand scaffold was synthesized and fully characterized. Insertion reactivity with azobenzene, 3-hexyne, and 1-azidoadamantane was explored, and the isolated products were analogous to previously reported β-diketiminate iron hydride insertion products. Surprisingly, the NpN iron hydride displays unprecedented reactivity toward hexafluorobenzene, affording an NpN iron fluoride complex and pentafluorobenzene as products. The NpN iron hydride is a precatalyst for catalytic hydro-defluorination of perfluorinated aromatics in the presence of silane. Kinetic studies indicated that the rate-determining step during catalysis involved silane.