Iridium Pincer Catalysts for Silane Dehydrocoupling: Ligand Effects on Selectivity and Activity

Catalytic reactions of bisphosphinite pincer-ligated iridium compounds <i>p</i>-X^<i>R</i>(POCOP)­IrHCl (POCOP) [2,6-(R₂PO)₂C₆H₃, R = ^<i>i</i>Pr, X = H (<b>1</b>); R = ^<i>t</i>Bu, X = COOMe (<b>2</b>); = H (<b>3</b>); = NMe₂ (<b>4</b>)] with primary and secondary silanes have been performed. Complex <b>1</b> is primarily a silane redistribution precatalyst, but dehydrocoupling catalysis is observed for sterically demanding silane substrates or with aggressive removal of H₂. The bulkier compounds (<b>2</b>–<b>4</b>) are silane dehydrocoupling precatalysts that also undergo competitive redistribution with less hindered substrates. Products generated from reactions utilizing <b>2</b>–<b>4</b> include low molecular weight oligosilanes with varying degrees of redistribution present or disilanes when employing more sterically demanding silane substrates. Selectivity for redistribution versus dehydrocoupling depends on the steric and electronic environment of the metal but can also be affected by reaction conditions

Iridium Pincer Catalysts for Silane Dehydrocoupling: Ligand Effects on Selectivity and Activity

Catalytic reactions of bisphosphinite pincer-ligated iridium compounds <i>p</i>-X^<i>R</i>(POCOP)­IrHCl (POCOP) [2,6-(R₂PO)₂C₆H₃, R = ^<i>i</i>Pr, X = H (<b>1</b>); R = ^<i>t</i>Bu, X = COOMe (<b>2</b>); = H (<b>3</b>); = NMe₂ (<b>4</b>)] with primary and secondary silanes have been performed. Complex <b>1</b> is primarily a silane redistribution precatalyst, but dehydrocoupling catalysis is observed for sterically demanding silane substrates or with aggressive removal of H₂. The bulkier compounds (<b>2</b>–<b>4</b>) are silane dehydrocoupling precatalysts that also undergo competitive redistribution with less hindered substrates. Products generated from reactions utilizing <b>2</b>–<b>4</b> include low molecular weight oligosilanes with varying degrees of redistribution present or disilanes when employing more sterically demanding silane substrates. Selectivity for redistribution versus dehydrocoupling depends on the steric and electronic environment of the metal but can also be affected by reaction conditions

Zirconium-Catalyzed Amine Borane Dehydrocoupling and Transfer Hydrogenation

κ⁵-(Me₃SiNCH₂CH₂)₂N­(CH₂CH₂NSiMe₂CH₂)Zr (<b>1</b>) has been found to dehydrocouple amine borane substrates, RR′NHBH₃ (R = R′ = Me; R = ^<i>t</i>Bu, R′ = H; R = R′ = H), at low to moderate catalyst loadings (0.5–5 mol %) and good to excellent conversions, forming mainly borazine and borazane products. Other zirconium catalysts, (N₃N)­ZrX [(N₃N) = N­(CH₂CH₂NSiMe₂CH₂)₃, X = NMe₂ (<b>2</b>), Cl (<b>3</b>), and O^<i>t</i>Bu (<b>4</b>)], were found to exhibit comparable activities to that of <b>1</b>. Compound <b>1</b> reacts with Me₂NHBH₃ to give (N₃N)­Zr­(NMe₂BH₃) (<b>5</b>), which was structurally characterized and features an η² B–H σ-bond amido borane ligand. Because <b>5</b> is unstable with respect to borane loss to form <b>2</b>, rather than β-hydrogen elimination, and <b>2</b>–<b>4</b> do not exhibit X ligand loss during catalysis, dehydrogenation is hypothesized to proceed <i>via</i> an outer-sphere-type mechanism. This proposal is supported by the catalytic hydrogenation of alkenes by <b>2</b> using amine boranes as the sacrificial source of hydrogen

Zirconium Metal–Organic Frameworks Assembled from Pd and Pt P^NN^NP Pincer Complexes: Synthesis, Postsynthetic Modification, and Lewis Acid Catalysis

Carboxylic acid-functionalized Pd and Pt P^NN^NP pincer complexes were used for the assembly of two porous Zr metal–organic frameworks (MOFs), 2-PdX and 2-PtX. Powder X-ray diffraction analysis shows that the new MOFs adopt cubic framework structures similar to the previously reported Zr₆O₄(OH)₄[(P^OC^OP)­PdX]₃, [P^OC^OP = 2,6-(OPAr₂)₂C₆H₃); Ar = <i>p</i>-C₆H₄CO₂^–, X = Cl^–, I^–] (1-PdX). Elemental analysis and spectroscopic characterization indicate the presence of missing linker defects, and 2-PdX and 2-PtX were formulated as Zr₆O₄(OH)₄(OAc)_2.4[M­(P^NN^NP)­X]_2.4 [M = Pd, Pt; P^NN^NP = 2,6-(HNPAr₂)₂C₅H₃N; Ar = <i>p</i>-C₆H₄CO₂^–; X = Cl^–, I^–]. Postsynthetic halide ligand exchange reactions were carried out by treating 2-PdX with Ag­(O₃SCF₃) or NaI followed by PhI­(O₂CCF₃)₂. The latter strategy proved to be more effective at activating the MOF for the catalytic intramolecular hydroamination of an <i>o</i>-substituted alkynyl aniline, underscoring the advantage of using halide exchange reagents that produce soluble byproducts