Terminal Imido Rhodium Complexes

Compounds of the late transition metals with M?X multiple bonds (X=CR₂, NR, O) represent a synthetic challenge, partly overcome by preparative chemists, but with noticeable gaps in the second‐ and third‐row elements. For example, there are no isolated examples of terminal imido rhodium complexes known to date. Described herein is the isolation, characterization, and some preliminary reactivity studies of the first rhodium complexes [Rh(PhBP₃)(NR)] (PhBP₃=PhB{CH₂PPh₂}₃) with a multiple and terminal Rh?N bond. These imido compounds result from reactions of organic azides with the corresponding rhodium(I) complex having a labile ligand, and display a pseudo‐tetrahedral core geometry with an almost linear Rh‐N‐C arrangement [177.5(2)°] and a short Rh? N bond [1.780(2) Å]. We also show that the Rh?N bond undergoes protonation at the nitrogen atom or addition of H₂, and also engages in nitrene‐group transfer and cycloaddition reactions.     

A Persistent 1,2‐Dihydrophosphasilene Adduct

The reaction of the arylchlorosilylene–NHC adduct ArSi(NHC)Cl [Ar=2,6‐Trip₂‐C₆H₃; NHC=(MeC)₂(NMe)₂C] 1 with one molar equiv of LiPH₂^.dme (dme=1,2‐dimethoxyethane) affords the first 1,2‐dihydrophosphasilene adduct 2 (ArSi(NHC)(H)?PH). The latter is labile in solution and can undergo head‐to‐tail dimerization to give [ArSi(H)PH]₂ 3 and “free” NHC. Further stabilization of 2 by complexation with {W(CO)₅} affords the isolable 1,2‐dihydrophosphasilene–tungsten complex 4 [ArSi(NHC)(H)?P(H)W(CO)₅]. Additionally, the new 1‐silyl‐2‐hydrophosphasilene ArSi(NHC)(H)?PSiMe₃ 5 could be synthesized and structurally characterized. DFT studies confirmed that the Si?P bond in 2 and 4 is mostly zwitterionic with drastically decreased double‐bond character.     

Sodium Phosphaethynolate as a Building Block for Heterocycles

Phosphorus‐containing heterocycles have evolved from laboratory curiosities to functional components, such as ligands in catalytically active metal complexes or molecular constituents in electronic devices. The straightforward synthesis of functionalized heterocycles on a larger scale remains a challenge. Herein, we report the use of the phosphaethynolate (OCP)^? anion as a building block for various sterically unprotected and functionalized hydroxy substituted phosphorus heterocycles. Because the resulting heterocycles are themselves anions, they are building blocks in their own right and allow further facile functionalization. This property may be of interest in coordination chemistry and material science.     

1,3‐Dehydro‐o‐Carborane: Generation and Reaction with Arenes

Like the importance of benzyne, witnessed in modern arene chemistry for decades, 1,2‐dehydro‐o‐carborane (o‐carboryne), a three‐dimensional relative of benzyne, has been used as a synthon for generating a wide range of cage, carbon‐functionalized carboranes over the past 20 years. However, the selective B functionalization of the cage still represents a challenging task. Disclosed herein is the first example of 1,3‐dehydro‐o‐carborane featuring a cage C? B bond having multiple bonding characters, and is successfully generated by treatment of 3‐diazonium‐o‐carborane tetrafluoroborate with non‐nucleophilic bases. This presents a new methodology for simultaneous functionalization of both cage carbon and boron vertices.     

Non‐Pincer‐Type Mononuclear Scandium Alkylidene Complexes: Synthesis,Bonding, and Reactivity

The first non‐pincer‐type mononuclear scandium alkylidene complexes were synthesized and structurally characterized. These complexes exhibited short Sc?C bond lengths and even one of the shortest reported to date (2.1134(18) Å). The multiple character of the Sc?C bond was highlighted by a DFT calculation. This was confirmed by experimental reactivity study where the complex underwent [2+1] cycloaddition with elemental selenium and [2+2] cycloaddition with imine. DFT calculation also revealed a strong nucleophilic behavior of the alkylidene complex that was experimentally demonstrated by the C?H bond activation of phenylacetylene.     

[2+2+2] Cycloaddition reaction with the participation of unsaturated ketones catalyzed by an Rh(i)—Sn(ii) system

Codimerization of vinyl ketones with metallylacetone or metallylacetophenone in the presence of [RhCl(C₂H₄)₂]₂-SnCl₂ affords substitutedendo-2-acyl-8-oxabicyclo[3.2.1]octanes, the products of the formal [2+2+2] cycloaddition.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2280–2283, November, 1995.We thank Uve Ihhoff (Moscow Representative of Bruker GmbH) for the provision of their AMX 400 spectrometer.     

Stereospecific Construction of Chiral Tertiary and Quaternary Carbon by Nucleophilic Cyclopropanation with Bis(iodozincio)methane

The reaction of a ketone having a leaving group at the α‐position, such as α,β‐epoxy ketone or α‐sulfonyloxy ketone, with bis(iodozincio)methane affords a zinc alkoxide of cyclopropanol. The reaction proceeds by nucleophilic addition of the dizinc to the carbonyl group and a sequential intramolecular nucleophilic substitution of the introduced iodozinciomethyl group to the adjacent electrophilic carbon that has a leaving group. When an optically active α,β‐epoxy ketone or α‐sulfonyloxy ketone is treated with the dizinc, a zinc alkoxide of cyclopropanol having a chiral tertiary or quaternary carbon in the cyclopropane ring is obtained, and the obtained zinc alkoxide of cyclopropanol acts as a chiral homoenolate. When it is treated with an electrophile in the presence of copper cyanide, it gives an optically active α‐tertiary or ‐quaternary ketone that retains high optical purity.     

Reversible Addition of Carbon Dioxide to Main Group Metal Complexes at Temperatures about 0 °C

The reaction of dialane [LAl-AlL] ( 1 ; L=dianion of 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene, dpp-bian) with carbon dioxide results in two different products depending on solvent. In toluene at temperatures of about 0 °C, the reaction gives cycloadduct [L(CO₂)Al-Al(O₂C)L] ( 2 ), whereas in diethyl ether, the reaction affords oxo-bridged carbamato derivative [L(CO₂)(Et₂O)Al(μ-O)AlL] ( 3 ). The DFT and QTAIM calculations provide reasonable explanations for the reversible formation of complex 2 in the course of two subsequent (2+4) cycloaddition reactions. Consecutive transition states with low activation barriers were revealed. Also, the DFT study demonstrated a crucial effect of diethyl ether coordination to aluminium on the reaction of dialane 1 with CO₂. The optimized structures of key intermediates were obtained for the reactions in the presence of Et₂O; calculated thermodynamic parameters unambiguously testify the irreversible formation of the product 3 .     

Tautomerization‐Mediated Molecular Switching Between Six‐ and Seven‐Membered Rings Stabilized by Hydrogen Bonding

1,3,4,6‐Tetraketones typically undergo keto–enol tautomerism forming bis‐enols stabilized by intramolecular hydrogen bonding in two six‐membered rings. However, 1,3,4,6‐tetraketones derived from the terpene ketone camphor and norcamphor exist as isomers with two distinguishable modes of intramolecular hydrogen bonding, namely, the formation of six‐ or seven‐membered rings. The structural requirements for this so far unknown behavior were investigated in detail by synthesis and comparison of structural analogues. Both isomers of such 1,3,4,6‐tetraketones were fully characterized in solution and in the solid state. Intriguingly, they slowly interconvert in solution by means of tautomerism–rotation cascades, as was corroborated by DFT calculations. The influence of temperature and complexation with the transition metals Pd, Rh, and Ir on the interconversion process was investigated.     

A Chiral Thioxanthone as an Organocatalyst for Enantioselective [2+2] Photocycloaddition Reactions Induced by Visible Light

Thioxanthone 1 , which was synthesized in a concise fashion from methyl thiosalicylate, exhibits a significant absorption in the visible light region. It allows for an efficient enantioselective catalysis of intramolecular [2+2] photocycloaddition reactions presumably by triplet energy transfer.     

Reaction of α,β-unsaturated trifluoromethyl ketones with cyclic enamines

The reactions of ,-unsaturated trifluoromethyl ketones containing aromatic and heteroaromatic substituents with 1-morpholinocyclopentene, 1-morpholinocyclohexene, and 1-methyl-4-morpholino-1,2,5,6-tetrahydropyridine were studied. The reactions proceeded stereospecifically to give the corresponding bicyclo[3.2.1]octane, bicyclo[3.3.1]nonane, and azabicyclo[3.3.1]nonane derivatives.     

Intramolecular [2+2] photocycloaddition of substituted isoquinolones: enantioselectivity and kinetic resolution induced by a chiral template

From simple to complex: Starting from easily accessible isoquinolones 1 (X=Br, OH), complex cyclobutane photoproducts such as compound 2 can be obtained with high enantioselectivity (88-96?%?ee) through the use of a chiral template. Compound 3, which was isolated in 53?%?ee starting from a racemic substrate, is the product of a unique, unprecedented kinetic resolution process.     

Catalytic Asymmetric Synthesis of 8‐Oxabicyclooctanes by Intermolecular [5+2] Pyrylium Cycloadditions

Highly enantioselective intermolecular [5+2] cycloadditions of pyrylium ion intermediates with electron‐rich alkenes are promoted by a dual catalyst system composed of an achiral thiourea and a chiral primary aminothiourea. The observed enantioselectivity is highly dependent on the substitution pattern of the 5π component, and the basis for this effect is analyzed using experimental and computational evidence. The resultant 8‐oxabicyclo[3.2.1]octane derivatives possess a scaffold common in natural products and medicinally active compounds and are also versatile chiral building blocks for further manipulations. Several stereoselective complexity‐generating transformations of the 8‐oxabicyclooctane products are presented.