Metal-organic layers stabilize earth-abundant metal-terpyridine diradical complexes for catalytic C-H activation.

We report the synthesis of a terpyridine-based metal-organic layer (TPY-MOL) and its metalation with CoCl and FeBr to afford CoCl·TPY-MOL and FeBr·TPY-MOL, respectively. Upon activation with NaEtBH, CoCl·TPY-MOL catalyzed benzylic C-H borylation of methylarenes whereas FeBr·TPY-MOL catalyzed intramolecular C -H amination of alkyl azides to afford pyrrolidines and piperidines. X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS), X-ray photoelectron spectroscopy, UV-Vis-NIR spectroscopy, and electron paramagnetic spectroscopy (EPR) measurements as well as density functional theory (DFT) calculations identified M(THF)·TPY-MOL (M = Co or Fe) as the active catalyst with a M-(TPY˙˙) electronic structure featuring divalent metals and TPY diradical dianions.

Successful Coupling of a Bis-Amidoxime Uranophile with a Hydrophilic Backbone for Selective Uranium Sequestration.

The amidoxime group (-RNHNOH) has long been used to extract uranium from seawater on account of its high affinity toward uranium. The development of tunable sorbent materials for uranium sequestration remains a research priority as well as a significant challenge. Herein, we report the design, synthesis, and uranium sorption properties of bis-amidoxime-functionalized polymeric materials (BAP 1-3).

Phenanthroline-based metal-organic frameworks for Fe-catalyzed C-H amination.

We report here the synthesis of a robust and highly porous Fe-phenanthroline-based metal-organic framework (MOF) and its application in catalyzing challenging inter- and intramolecular C-H amination reactions. For the intermolecular amination reactions, a FeBr-metalated MOF selectively functionalized secondary benzylic and allylic C-H bonds. The intramolecular amination reactions utilizing organic azides as the nitrene source required the reduction of the FeBr-metalated MOF with NaBHEt to generate the active catalyst.

Chemoselective single-site Earth-abundant metal catalysts at metal-organic framework nodes.

Earth-abundant metal catalysts are critically needed for sustainable chemical synthesis. Here we report a simple, cheap and effective strategy of producing novel earth-abundant metal catalysts at metal-organic framework (MOF) nodes for broad-scope organic transformations. The straightforward metalation of MOF secondary building units (SBUs) with cobalt and iron salts affords highly active and reusable single-site solid catalysts for a range of organic reactions, including chemoselective borylation, silylation and amination of benzylic C-H bonds, as well as hydrogenation and hydroboration of alkenes and ketones.

Robust and Porous β-Diketiminate-Functionalized Metal-Organic Frameworks for Earth-Abundant-Metal-Catalyzed C-H Amination and Hydrogenation.

We have designed a strategy for postsynthesis installation of the β-diketiminate (NacNac) functionality in a metal-organic framework (MOF) of UiO-topology. Metalation of the NacNac-MOF (I) with earth-abundant metal salts afforded the desired MOF-supported NacNac-M complexes (M = Fe, Cu, and Co) with coordination environments established by detailed EXAFS studies. The NacNac-Fe-MOF catalyst, I•Fe(Me), efficiently catalyzed the challenging intramolecular sp(3) C-H amination of a series of alkyl azides to afford α-substituted pyrrolidines.

Synthesis of Chiral Tertiary Boronic Esters by Oxime-Directed Catalytic Asymmetric Hydroboration.

Chiral boronic esters are useful intermediates in asymmetric synthesis. We have previously shown that carbonyl-directed catalytic asymmetric hydroboration (CAHB) is an efficient approach to the synthesis of functionalized primary and secondary chiral boronic esters. We now report that the oxime-directed CAHB of alkyl-substituted methylidene and trisubstituted alkene substrates by pinacolborane (pinBH) affords oxime-containing chiral tertiary boronic esters with yields up to 87% and enantiomeric ratios up to 96:4 e.

Robust, chiral, and porous BINAP-based metal-organic frameworks for highly enantioselective cyclization reactions.

We report here the design of BINAP-based metal-organic frameworks and their postsynthetic metalation with Rh complexes to afford highly active and enantioselective single-site solid catalysts for the asymmetric cyclization reactions of 1,6-enynes. Robust, chiral, and porous Zr-MOFs of UiO topology, BINAP-MOF (I) or BINAP-dMOF (II), were prepared using purely BINAP-derived dicarboxylate linkers or by mixing BINAP-derived linkers with unfunctionalized dicarboxylate linkers, respectively. Upon metalation with Rh(nbd)2BF4 and [Rh(nbd)Cl]2/AgSbF6, the MOF precatalysts I·Rh(BF4) and I·Rh(SbF6) efficiently catalyzed highly enantioselective (up to 99% ee) reductive cyclization and Alder-ene cycloisomerization of 1,6-enynes, respectively.

Surprisingly Facile C-H Activation in the Course of Oxime-Directed Catalytic Asymmetric Hydroboration.

Deuterium-labeling studies carried out in conjunction with investigations into the directed catalytic asymmetric hydroboration of unsaturated oxime ethers reveal a surprisingly facile -metallation or σ-bond metathesis pathway that that diverts the expected course of CAHB to a tandem C-H activation/hydroboration reaction pathway.

Ligand scaffold optimization of a supramolecular hydrogenation catalyst: Analyzing the influence of key structural subunits on reactivity and selectivity.

Results are reported for the catalytic asymmetric hydrogenation of two prototypical substrates with a series of more than 150 closely related supramolecular catalysts differing in only their ligand/catalyst scaffold. These modular catalysts are constructed from four subunits and vary widely in their reactivity (no reaction to quantitative yield) and enantioselectivity (racemic to 96% ee). Analysis of the ligand/catalyst scaffold optimization data reveals how each subunit contributes to the effectiveness of the modular supramolecular catalyst.

Efficient amide-directed catalytic asymmetric hydroboration.

A series of acyclic beta,gamma-unsaturated amides are shown to undergo highly regio- (>95%) and enantioselective (93-99% ee) rhodium-catalyzed hydroboration with pinacolborane (PinBH) using simple chiral monophosphite or phosphoramidite ligands in combination with Rh(nbd)2BF4. The most effective ligands identified are phosphoramidite 4, derived from BINOL and N-methylaniline, and phosphite 5c, prepared from the (4'-tert-butyl)phenyl TADDOL analogue and phenol. For example, (E)-3-hexenoic acid phenylamide ((E)-1) undergoes rhodium-catalyzed hydroboration with PinBH (0.