Iron Dihydride Complex as the Pre-catalyst for Efficient Hydrosilylation of Aldehydes and Ketones Under Visible Light Activation

Visible Light-Induced Unactivated δ-C(sp3 )-H Amination of Alcohols Catalyzed by Iron

An iron-catalyzed remote C(sp³ )-H amination of alcohols through 1,5-hydrogen atom transfer is developed. This protocol provides a method to generate δ-C(sp³ )-N bonds from primary, secondary, and tertiary alcohols under mild conditions. A wide substrate scope and a good functional group tolerance are presented. Mechanistic studies show that a LMCT course of an Fe-OR species and a chlorine radical-induced hydrogen abstraction of an alcohol are possible to generate the alkoxy radical intermediate.

Radical Addition of Dihydroquinoxalin-2-ones to Trifluoromethyl Ketones under Visible-Light Photoredox Catalysis

A visible-light photocatalytic radical addition reaction of dihydroquinoxalin-2-ones to trifluoromethyl ketones has been established using Ru(bpy)₃Cl₂ as photocatalyst, acetonitrile as solvent, and HP Single Blue LED as the source of light. The reaction provides a straightforward approach to the synthesis of dihydroquinoxalin-2-ones bearing a trifluoromethyl-substituted tertiary alcohol moiety in moderate to good yields under mild conditions.

Iron-Catalyzed Photoinduced Remote C(sp3)-H Amination of Free Alcohols

We report a general photocatalytic protocol for the remote C(sp³)-H bond amination of free aliphatic alcohols. The electron transfer between the abundant and inexpensive catalyst FeCl₃ and simple alkanols under blue LED irradiation enables the alkoxy radical formation under mild redox-neutral conditions, with no need for additional oxidant and prefunctionalization. The subsequent selective 1,5-hydrogen atom transfer (HAT) and amination provide a simple and efficient way to access molecular complexity from readily available and bulk alcohols.

Metallaphotoredox: The Merger of Photoredox and Transition Metal Catalysis

The merger of photoredox catalysis with transition metal catalysis, termed metallaphotoredox catalysis, has become a mainstay in synthetic methodology over the past decade. Metallaphotoredox catalysis has combined the unparalleled capacity of transition metal catalysis for bond formation with the broad utility of photoinduced electron- and energy-transfer processes. Photocatalytic substrate activation has allowed the engagement of simple starting materials in metal-mediated bond-forming processes. Moreover, electron or energy transfer directly with key organometallic intermediates has provided novel activation modes entirely complementary to traditional catalytic platforms. This Review details and contextualizes the advancements in molecule construction brought forth by metallaphotocatalysis.

Reaction of Diisobutylaluminum Borohydride, a Binary Hydride, with Selected Organic Compounds Containing Representative Functional Groups

The binary hydride, diisobutylaluminum borohydride [(iBu)₂AlBH₄], synthesized from diisobutylaluminum hydride (DIBAL) and borane dimethyl sulfide (BMS) has shown great potential in reducing a variety of organic functional groups. This unique binary hydride, (iBu)₂AlBH₄, is readily synthesized, versatile, and simple to use. Aldehydes, ketones, esters, and epoxides are reduced very fast to the corresponding alcohols in essentially quantitative yields. This binary hydride can reduce tertiary amides rapidly to the corresponding amines at 25 °C in an efficient manner. Furthermore, nitriles are converted into the corresponding amines in essentially quantitative yields. These reactions occur under ambient conditions and are completed in an hour or less. The reduction products are isolated through a simple acid-base extraction and without the use of column chromatography. Further investigation showed that (iBu)₂AlBH₄ has the potential to be a selective hydride donor as shown through a series of competitive reactions. Similarities and differences between (iBu)₂AlBH₄, DIBAL, and BMS are discussed.

Oxidative α-C-C Bond Cleavage of 2° and 3° Alcohols to Aromatic Acids with O2 at Room Temperature via Iron Photocatalysis

The selective α-C-C bond cleavage of unfunctionalized secondary (2°) and tertiary alcohols (3°) is essential for valorization of macromolecules and biopolymers. We developed a blue-light-driven iron catalysis for aerobic oxidation of 2° and 3° alcohols to acids via α-C-C bond cleavages at room temperature. The first example of oxygenation of the simple tertiary alcohols was reported. The iron catalyst and blue light play critical roles to enable the formation of highly reactive O radicals from alcohols and the consequent two α-C-C bond cleavages.

Visible Light Induced Reduction and Pinacol Coupling of Aldehydes and Ketones Catalyzed by Core/Shell Quantum Dots

We present an efficient and versatile visible light-driven methodology to transform aryl aldehydes and ketones chemoselectively either to alcohols or to pinacol products with CdSe/CdS core/shell quantum dots as photocatalysts. Thiophenols were used as proton and hydrogen atom donors and as hole traps for the excited quantum dots (QDs) in these reactions. The two products can be switched from one to the other simply by changing the amount of thiophenol in the reaction system. The core/shell QD catalysts are highly efficient with a turn over number (TON) larger than 4 × 10⁴ and 4 × 10⁵ for the reduction to alcohol and pinacol formation, respectively, and are very stable so that they can be recycled for at least 10 times in the reactions without significant loss of catalytic activity. The additional advantages of this method include good functional group tolerance, mild reaction conditions, the allowance of selectively reducing aldehydes in the presence of ketones, and easiness for large scale reactions. Reaction mechanisms were studied by quenching experiments and a radical capture experiment, and the reasons for the switchover of the reaction pathways upon the change of reaction conditions are provided.

Organic synthesis with the most abundant transition metal–iron: from rust to multitasking catalysts

The promising aspects of iron in synthetic chemistry are being explored for three-four decades as a green and eco-friendly alternative to late transition metals. This present review unveils these rich iron-chemistry towards different transformations.

Iridium-Catalyzed Transfer Hydrogenation of Ketones and Aldehydes Using Glucose as a Sustainable Hydrogen Donor

A new catalytic system for transfer hydrogenation of carbonyl compounds using glucose as a hydrogen donor was developed. Various ketones and aldehydes were efficiently converted to corresponding alcohols with two equivalents of glucose in the presence of a small amount (0.1 to 1.0 mol%) of iridium catalyst that had a functional ligand. In this catalytic system, transfer hydrogenation reactions proceeded based on the cooperativity of iridium and a functional ligand. It should be noted that environmentally benign water could have been used as a solvent in the present catalytic system for the reduction of various carbonyl substrates. Furthermore, the reaction scope could be extended by using N,N-dimethylacetamide as a reaction solvent.

Synthesis, characterization, and catalytic application in aldehyde hydrosilylation of half-sandwich nickel complexes bearing (κ1-C)- and hemilabile (κ2-C,S)-thioether-functionalised NHC ligands

Ni complexes bearing thioether-functionalised NHCs; hemilabile ligands for catalytic aldehyde hydrosilylation.

Synthesis and catalytic application of [PPP]-pincer iron, nickel and cobalt complexes for the hydrosilylation of aldehydes and ketones

The catalytic performance of [PPP]-pincer hydrido Fe, Ni and Co complexes for the hydrosilylation of aldehydes and ketones was explored.

Constructing reactive Fe and Co complexes from isolated picolyl-functionalized N-heterocyclic carbenes

The Fe(ii) and Co(ii) complexes prepared from the isolated free carbene form of the picolyl-NHC ligands display excellent catalytic activity towards the hydrosilylation of ketones.

Visible light-induced transition metal-catalyzed transformations: beyond conventional photosensitizers

Employment of simple transition metal (TM = Co, Fe, Cu, Pd, Pt, Au)-based photocatalyst (PC) has led to the dramatic acceleration of known TM-catalyzed reactions, as well as to the discovery of unprecedented chemical transformations. Compared to the conventional cooperative/dual photocatalysis (type B), this new class of unconventional PCs operates via a single photoexcitation/catalytic cycle, where the TM complex plays a "double duty" role by harvesting light and catalyzing the chemical transformation. Also, these TM photocatalysts participate in the bond-forming/breaking event in the transformation via a substrate-TM interaction, an aspect that is uncommon for conventional photocatalysis (type A). This tutorial review highlights the recent advances in this emerging area.

Utilization of a Trimethylsilyl Group as a Synthetic Equivalent of a Hydroxyl Group via Chemoselective C(sp3)-H Borylation at the Methyl Group on Silicon

A conversion of trimethylsilylalkanes into the corresponding alcohols is established based on an iridium-catalyzed, chemoselective C(sp³)-H borylation of the methyl group on silicon. The (borylmethyl)silyl group formed by C(sp³)-H borylation is treated with H₂O₂/NaOH, and the resulting (hydroxymethyl)silyl group is converted into a hydroxyl group by Brook rearrangement, followed by oxidation of the resulting methoxysilyl group under Tamao conditions. An alternative route proceeding through the formylsilyl group formed from a (hydroxymethyl)silyl group by Swern oxidation is also established. The method is applicable to substituted trimethylsilylcycloalkanes and 1,1-dimethyl-1-silacyclopentane for conversion into the corresponding stereodefined cycloalkyl alcohols and 1,4-butanediol.

Direct synthesis of dicarbonyl PCP-iron hydride complexes and catalytic dehydrogenative borylation of styrene

An efficient method based on the simple metalating reagent Fe(CO)₅ leads to the synthesis of cyclometalled PCP iron carbonyl pincer complexes which are active catalytic precursors for the selective dehydrogenative borylation of styrene.

Iron piano-stool complexes containing NHC ligands outfitted with pendent arms: synthesis, characterization, and screening for catalytic transfer hydrogenation

The reaction of hydroxyl-appended NHC ligands with FpI affords a pair of iron-containing organometallic species with interesting electronic and structural properties.

Syntheses, structures and properties of isonicotinamidium, thionicotinamidium, 2- and 3-(hydroxymethyl)pyridinium nitrates

New salts containing cations of selected pyridine derivatives of the composition [pyH]NO

Iron catalyzed halogenation of benzylic aldehydes and ketones

A simple iron-catalyzed method for halogenation of aromatic carbonyl compounds in one step has been developed, combined with mechanistic investigation.