Unexpected alkyl isomerization at the silicon ligand of an unsaturated Rh complex: combined experiment and theory.

The formation of dimer [(µ-Cl)Rh-(κ3(P,Si,Si)PhP(o-C6H4CH2SiiPr2)(o-C6H4CH2SiiPrnPr))]2 (Rh-3) with an n-propyl group on one of the silicon atoms as a minor product was affected by the reaction of [RhCl(COD)]2 with proligand PhP(o-C6H4CH2SiHiPr2)2, L1. The major product of the reaction was monomeric 14-electron Rh(III) complex [ClRh(κ3(P,Si,Si)PhP(o-C6H4CH2SiiPr2)2)] (Rh-1). Computations revealed that the monomer-dimer equilibrium is shifted toward the monomer with four isopropyl substituents on the two Si atoms of the ligand as in Rh-1; conversely, the dimer is favored with only one n-propyl as in Rh-3, and with less bulky alkyl substituents such as in [ClRh(κ3(P,Si,Si)PhP(o-C6H4CH2SiMe2)2]2 (Rh-2). Computations on the mechanism of formation of Rh-3 directly from [RhCl(COD)]2 are in agreement with the experimental findings and it is found to be less energetic than if stemming from Rh-1. Additionally, a Si-O-Si complex, [µ-Cl-Rh{κ3(P,Si,C)PPh(o-C6H4CH2SiiPrO SiiPr2CH-o-C6H4)}]2, Rh-4, is generated from the reaction of Rh-1 with adventitious water as a result of intramolecular C-H activation.

Homogeneous versus MOF-supported catalysis: a direct comparison of catalytic hydroboration with Ni tripodal P3E (E = Si, Ge) complexes.

The MOF material NU-1000 was employed to host Ni tripodal complexes prepared from new organometallic precursors [HNi(κ4(E,P,P,P)-E(o-C6H4CH2PPh2)3], E = Si (Ni-1), Ge (Ni-2). The new heterogeneous catalytic materials, Ni-1@NU-1000 and Ni-2@NU-1000, show the advantages of both homogeneous and heterogeneous catalysts. They catalyze the hydroboration of aldehydes and ketones more efficiently than the homogeneous Ni-1 and Ni-2, under aerobic conditions and show recyclability.

14-Electron Rh and Ir silylphosphine complexes and their catalytic activity in alkene functionalization with hydrosilanes.

Herein we report an experimental and computational study of a family of four coordinated 14-electron complexes of Rh(iii) devoid of agostic interactions. The complexes [X-Rh(κ3(P,Si,Si)PhP(o-C6H4CH2SiiPr2)2], where X = Cl (Rh-1), Br (Rh-2), I (Rh-3), OTf (Rh-4), Cl·GaCl3 (Rh-5); derive from a bis(silyl)-o-tolylphosphine with isopropyl substituents on the Si atoms. All five complexes display a sawhorse geometry around Rh and exhibit similar spectroscopic and structural properties. The catalytic activity of these complexes and [Cl-Ir(κ3(P,Si,Si)PhP(o-C6H4CH2SiiPr2)2], Ir-1, in styrene and aliphatic alkene functionalizations with hydrosilanes is disclosed. We show that Rh-1 catalyzes effectively the dehydrogenative silylation of styrene with Et3SiH in toluene while it leads to hydrosilylation products in acetonitrile. Rh-1 is an excellent catalyst in the sequential isomerization/hydrosilylation of terminal and remote aliphatic alkenes with Et3SiH including hexene isomers, leading efficiently and selectively to the terminal anti-Markonikov hydrosilylation product in all cases. With aliphatic alkenes, no hydrogenation products are observed. Conversely, catalysis of the same hexene isomers by Ir-1 renders allyl silanes, the tandem isomerization/dehydrogenative silylation products. A mechanistic proposal is made to explain the catalysis with these M(iii) complexes.

Functionalized NU-1000 with an Iridium Organometallic Fragment: SO2 Capture Enhancement.

A new material, MOF-type [Ir]@NU-1000, was accessed from the incorporation of the iridium organometallic fragment [Ir{κ3(P,Si,Si)PhP(o-C6H4CH2SiiPr2)2}] into NU-1000. The new material incorporates less than 1 wt % of Ir(III) (molar ratio Ir to NU-1000, 1:11), but the heat of adsorption for SO2 is significantly enhanced with respect to that of NU-1000. Being a highly promising adsorbent for SO2 capture, [Ir]@NU-1000 combines exceptional SO2 uptake at room temperature and outstanding cyclability. Additionally, it is stable and can be regenerated after SO2 desorption at low temperature.