Oligosilanylated Silocanes

A number of mono- and dioligosilanylated silocanes were prepared. Compounds included silocanes with 1-methyl-1-tris(trimethylsilyl)silyl, 1,1-bis[tris(trimethylsilyl)silyl], and 1,1-bis[tris(trimethylsilyl)germyl] substitution pattern as well as two examples where the silocane silicon atom is part of a cyclosilane or oxacyclosilane ring. The mono-tris(trimethylsilyl)silylated compound could be converted to the respective silocanylbis(trimethylsilyl)silanides by reaction with KO^tBu and in similar reactions the cyclosilanes were transformed to oligosilane-1,3-diides. However, the reaction of the 1,1-bis[tris(trimethylsilyl)silylated] silocane with two equivalents of KO^tBu leads to the replacement of one tris(trimethylsilyl)silyl unit with a tert-butoxy substituent followed by silanide formation via KO^tBu attack at one of the SiMe₃ units of remaining tris(trimethylsilyl)silyl group. For none of the silylated silocanes, signs of hypercoordinative interaction between the nitrogen and silicon silocane atoms were detected either in the solid state. by single crystal XRD analysis, nor in solution by ²⁹Si-NMR spectroscopy. This was further confirmed by cyclic voltammetry and a DFT study, which demonstrated that the N-Si distance in silocanes is not only dependent on the energy of a potential N-Si interaction, but also on steric factors and through-space interactions of the neighboring groups at Si and N, imposing the orientation of the p_z(N) orbital relative to the N-Si-X axis.     

A Unified Mechanism to Account for Manganese- or Ruthenium-Catalyzed Nitrile α-Olefinations by Primary or Secondary Alcohols: A DFT Mechanistic Study

Acceptorless dehydrogenative coupling (ADC) reactions generally involve a nucleophile (e.g., amine) as a coupling partner. Intriguingly, it has been reported that nitriles could also act as nucleophiles in ADC reactions, achieving the α-olefination of nitriles with primary or secondary alcohols by employing a manganese or ruthenium pincer complex as the catalyst, respectively. Although different mechanisms have been postulated for the two catalytic systems, the results of our DFT mechanistic study, reported herein, have allowed us to propose a unified mechanism to account for both nitrile α-olefinations. The reactions take place in four stages, namely alcohol dehydrogenation, nitrile activation to generate a nucleophilic metal species, coupling of an aldehyde or ketone with the metal species to form a C−C bond and to transfer a nitrile (C^α−)H atom to the carbonyl group, and dehydration by transferring the protonic (N−)H to the hydroxy group. A notable feature of the coupling stage is the activation of water or alcohol to give an intermediate featuring an OH⁻- or OR⁻-like group that activates a nitrile C^α−H bond. Moreover, the mechanism can even be applied to the base (KOtBu, modeled by the (KOtBu)₄ cluster)-catalyzed Knoevenagel condensation of nitriles with ketones, which further indicates the generality of the mechanism and the resemblance of the metal pincer complexes to the (KOtBu)₄ base. We expect these in-depth mechanistic insights and the finding of the resemblance of the metal pincer complexes to the (KOtBu)₄ cluster could assist the development of new ADC reactions.     

Radical and Ionic Mechanisms in Rearrangements of o-Tolyl Aryl Ethers and Amines Initiated by the Grubbs–Stoltz Reagent,Et3SiH/KOtBu

Rearrangements of o-tolyl aryl ethers, amines, and sulfides with the Grubbs–Stoltz reagent (Et₃SiH + KO^tBu) were recently announced, in which the ethers were converted to o-hydroxydiarylmethanes, while the (o-tol)(Ar)NH amines were transformed into dihydroacridines. Radical mechanisms were proposed, based on prior evidence for triethylsilyl radicals in this reagent system. A detailed computational investigation of the rearrangements of the aryl tolyl ethers now instead supports an anionic Truce–Smiles rearrangement, where the initial benzyl anion can be formed by either of two pathways: (i) direct deprotonation of the tolyl methyl group under basic conditions or (ii) electron transfer to an initially formed benzyl radical. By contrast, the rearrangements of o-tolyl aryl amines depend on the nature of the amine. Secondary amines undergo deprotonation of the N-H followed by a radical rearrangement, to form dihydroacridines, while tertiary amines form both dihydroacridines and diarylmethanes through radical and/or anionic pathways. Overall, this study highlights the competition between the reactive intermediates formed by the Et₃SiH/KO^tBu system.     

Room-temperature nickel-catalyzed amination of heteroaryl/aryl chlorides with Ni(II)-(σ-Aryl) complex as precatalyst

The room-temperature cross-coupling of heteroaryl and aryl chlorides with secondary cyclic amines can be effected using Ni(II)-(σ-aryl) complex as pre-catalyst. Some useful aromatic and heteroaromatic amine derivatives were readily synthesized in moderate to good yields in the presence of the Ni(II)-(σ-aryl) complex/NHC/KO^tBu/toluene system.     

Synthesis and Antibacterial Activity of Benzazolyl Azolyl Sulfamoyl Acetamides

A new class of benzazolyl azolyl sulfamoyl acetamides was prepared from azolyl sulfamoyl acetates and benzazolyl amines in the presence of KO^tBu in tetrahydrofuran. Compounds with benzothiazole‐thiazole, benzimidazole‐thiazole, benzothiazole‐imidazole, and benzimidazole‐imidazole moieties exhibited excellent antibacterial activity against Bacillus subtilis.     

Comparative Study of Bifunctional Mononuclear and Dinuclear Amidoiridium Complexes with Chiral C−N Chelating Ligands for the Asymmetric Transfer Hydrogenation of Ketones

A series of new bifunctional C?N chelating Ir complexes possessing a metal/NH group was synthesized by cyclometalation of optically active primary benzylic amines such as O‐silylated (S)‐2‐amino‐2‐phenylethanols ( 1 a and 1 a’ ), (R)‐5‐amino‐6,7,8,9‐tetrahydro‐5H‐benzocycloheptene ( 1 b ), and (R)‐1‐phenyl‐2,2‐dimethylpropylamine ( 1 c ). Although treatment of KOtBu with the amine complexes originating from 1 a and 1 a’ afforded amido‐bridged dinuclear complexes ( 3 a and 3 a’ ), more sterically hindered complexes were solely transformed into the coordinatively unsaturated mononuclear amido complexes ( 3 b and 3 c ), which can serve as real catalyst species in the asymmetric transfer hydrogenation. The structural difference in the C?N chelate framework markedly affected the catalytic performance. Among them, amido complex 3 c showed a pronounced ability to catalyze the transfer hydrogenation of acetophenone in 2‐propanol, even at a low temperature of ?30 °C. A hydridoiridium complex ( 4 c ) was also identified in the reaction of 3 c in 2‐propanol, which provides mechanistic insights into the enantiodiscriminating step in the hydrogen transfer to prochiral ketones.     

EINIGE NEUE THIOPHOSPHINSÄUREAMIDE R2P(S)NHR': SYNTHESE UND KERNRESONANZSPEKTROSKOPISCHE UNTERSUCHUNGEN

Abstract

P.P-Dialkylthiophosphinsäureamide R₂P(S)NHR' (R=Me, 'Pr, 'Bu; R'=Me, Et, ⁱPr. ^cHex. ^tBu. Ph. etc.) wurden erhalten durch Umsetzung von R₂PNHR' mit Schwefel oder durch Reaktion von Me₂P(S)CI mit primaren Aminen. Ihre ³¹P- und ¹³C-NMR-Spektren werden diskutiert. Insbesondere die Di-t-butylthiophosphinsäureamide sind auszilg;ergewöhnlich stabil gegen Hydrolyse und Luftsauerstoff. P,P-Dialkylthiophosphinic acid amides R₂P(S)NHR' (R=Me. ⁱPr. ^tBu; R'=Me, Et, ⁱPr, ^cHex. ^tBu, Ph. etc.) have been obtained by reaction of the corresponding aminophosphines with sulfur or by reaction of dimethylthiophosphorylhalides with primary amines. Their ³¹P- and ¹³C-NMR spectra are discussed. The di-t-butylthiophosphinic compounds proved to be remarkably stable against moisture and oxygen.     

Synthesis of Diaryl Ethers: A Long-Standing Problem Has Been Solved

A breakthrough in the synthesis of diaryl ethers has been achieved as shown in Equation (1). The coupling of phenols with aryl boronic acids in the presence of copper(II ) acetate and a base proceeds under very mild conditions (room temperature) as described simultaneously by Evans et al. and Chan et al. Examples: R¹=2-Cl, 2-I, 2-OMe, 4-tBu, 4-CH₂CH(NHCOOtBu)CO₂Me, 3,5-tBu₂; R²=2-Me, 3-OMe, 3-NO₂, 4-H, 4-F, 4-OMe.     

Elementorganische Amin/Imin-Verbindungen,XXXI. Cyclometallierung bei N-tert-Butyl-Phosphor-Stickstoff-Iridiumkomplexen

Element-Organic Amine/Imine Compounds, XXXI. - Cyclometallation with N-tert-Butyl-Phosphorus-Nitrogen Iridium Complexes The interaction of R¹R²N–PNR³ ( 1 ) (R¹  SiMe₃, tBu, iC₃H₇; R²  R³  SiMe₃, tBu) with [M(COD)(μ-Cl)]₂ ( 2 ), M  Rh, Ir, affords the amino(imino)phosphane complexes 3 , whose PN bond adds methanol with formation of the diamidophosphite complexes 4 . Already below 0°C the iridium compounds of 4 undergo cyclometallation of a tBu methyl group (R²) with formation of the hydrido-iridium metallaheterocycles 5 . The structures of 4b and 5a are elucidated by X-ray analyses.     

On the Ambiphilic Reactivity of Geometrically Constrained Phosphorus(III) and Arsenic(III) Compounds: Insights into Their Interaction with Ionic Substrates

The ambiphilic nature of geometrically constrained Group 15 complexes bearing the N,N‐bis(3,5‐di‐tert‐butyl‐2‐phenolate)amide pincer ligand (ONO^3?) is explored. Despite their differing reactivity towards nucleophilic substrates with polarised element–hydrogen bonds (e.g., NH₃), both the phosphorus(III), P(ONO) ( 1 a ), and arsenic(III), As(ONO) ( 1 b ), compounds exhibit similar reactivity towards charged nucleophiles and electrophiles. Reactions of 1 a and 1 b with KOtBu or KNPh₂ afford anionic complexes in which the nucleophilic anion associates with the pnictogen centre ([(tBuO)Pn(ONO)]^? (Pn=P ( 2 a ), As ( 2 b )) and [(Ph₂N)Pn(ONO)]^? (Pn=P ( 3 a ), As ( 3 b )). Compound 2 a can subsequently be reacted with a proton source or benzylbromide to afford the phosphorus(V) compounds (tBuO)HP(ONO) ( 4 a ) and (tBuO)BzP(ONO) ( 5 a ), respectively, whereas analogous arsenic(V) compounds are inaccessible. Electrophilic substrates, such as HOTf and MeOTf, preferentially associate with the nitrogen atom of the ligand backbone of both 1 a and 1 b , giving rise to cationic species that can be rationalised as either ammonium salts or as amine‐stabilised phosphenium or arsenium complexes ([Pn{ON(H)O}]⁺ (Pn=P ( 6 a ), As ( 6 b )) and [Pn{ON(Me)O}]⁺ (Pn=P ( 7 a ), As ( 7 b )). Reaction of 1 a with an acid bearing a nucleophilic counteranion (such as HCl) gives rise to a phosphorus(V) compound HPCl(ONO) ( 8 a ), whereas the analogous reaction with 1 b results in the addition of HCl across one of the As?O bonds to afford ClAs{(H)ONO} ( 8 b ). Functionalisation at both the pnictogen centre and the ligand backbone is also possible by reaction of 7 a / 7 b with KOtBu, which affords the neutral species (tBuO)Pn{ON(Me)O} (Pn=P ( 9 a ), As ( 9 b )). The ambiphilic reactivity of these geometrically constrained complexes allows some insight into the mechanism of reactivity of 1 a towards small molecules, such as ammonia and water.     

Alkali-Metal-Alkoxide Powered Zincation of Fluoroarenes Employing Zinc Bis-Amide Zn(TMP)2

Reminiscent of Lochmann-Schlosser superbase recipes, the addition of two molar equivalents of KOtBu to Zn(TMP)₂ (TMP=2,2,6,6-tetramethylpiperidide) transforms this mild zinc bis-amide base to a powerful metalating agent able to perform facile regioselective zincation of a wide range of sensitive fluoroarenes. Structural authentication of the intermediates post Zn−H exchange demonstrates activation of both TMP groups to form a range of higher order bis-aryl potassium zincates, isolable as solids and further functionalized in electrophilic interception reactions. Studies assessing the role of KOtBu reveal that the first equivalent undergoes co-complexation with Zn(TMP)₂, enabling kinetic activation of the amide groups; whereas the second equivalent stabilizes the metalated intermediate preventing ligand redistribution. Showcasing its metalating power, this bimetallic KOtBu/Zn(TMP)₂ partnership, can effect zincation of toluene and benzene at room temperature.     

From Anilines to Aryl Ethers: A Facile,Efficient, and Versatile Synthetic Method Employing Mild Conditions

We have developed a simple and direct method for the synthesis of aryl ethers by reacting alcohols/phenols (ROH) with aryl ammonium salts (ArNMe₃⁺), which are readily prepared from anilines (ArNR′₂, R′=H or Me). This reaction proceeds smoothly and rapidly (within a few hours) at room temperature in the presence of a commercially available base, such as KO^tBu or KHMDS, and has a broad substrate scope with respect to both ROH and ArNR′₂. It is scalable and compatible with a wide range of functional groups.     

From Anilines to Aryl Ethers: A Facile,Efficient, and Versatile Synthetic Method Employing Mild Conditions

We have developed a simple and direct method for the synthesis of aryl ethers by reacting alcohols/phenols (ROH) with aryl ammonium salts (ArNMe₃⁺), which are readily prepared from anilines (ArNR′₂, R′=H or Me). This reaction proceeds smoothly and rapidly (within a few hours) at room temperature in the presence of a commercially available base, such as KO^tBu or KHMDS, and has a broad substrate scope with respect to both ROH and ArNR′₂. It is scalable and compatible with a wide range of functional groups.     

DFT/TDDFT studies of the ancillary ligand effects on structures and photophysical properties of rhenium (I) tricarbonyl complexes with the imidazo[4,5‐f]‐1,10‐phenanthroline ligand

The seven rhenium (I) tricarbonyl complexes having a general formula fac‐[ReBr(CO)₃(R₁,R₂,R₃‐N^{^}N)] (N^{^}N = imidazo[4,5‐f]‐1,10‐phenanthroline; R₁ = ? ^tBu, R₂ = R₃ = ? H, 1 ; R₁ = ? C?CH, R₂ = R₃ = ? H, 2 ; R₁ = ? ^tBu, R₂ = ? C?CH, R₃ = ? H, 3 ; R₁ = ? ^tBu, R₂ = R₃ = ? C?CH, 4 ; R₁ = ? ^tBu, R₂ = ? CH₃, R₃ = ? H, 5 ; R₁ = ? ^tBu, R₂ = R₃ = ? CH₃, 6 ; R₁ = ? ^tBu, R₂ = ? OCH₃, R₃ = ? H, 7 ) have been investigated theoretically by density functional theory (DFT) and time‐dependent density functional theory (TDDFT) methods. The different substituted groups on N^{^}N ligand induce changes on the electronic structures and photophysical properties for these complexes. It is found that the introduction of ? C?C decreases the energy level of lowest unoccupied molecular orbital (LUMO) while the introduction of ? CH₃ or ? OCH₃ lead to increase the energy level of LUMO. The order of LUMO energy level rising is in line with the increasing of donating abilities of substituted groups; and the influence of R₂ position is greater than that of R₁ position on LUMO energy level. The lowest energy absorption bands have changes in the order of 7 < 6 < 5 < 1 < 2 < 3 < 4 . These results of electronic affinity (EA), ionization potential (IP), and reorganization energy (λ) indicate that all of these complexes can be used as electron transporting materials. Moreover, the smallest difference between λ_electron and λ_hole of 4 indicates that it is better to be used as an emitter in the organic light‐emitting diodes. © 2015 Wiley Periodicals, Inc.     

Direct Olefination of Alcohols with Sulfones by Using Heterogeneous Platinum Catalysts

Carbon‐supported Pt nanoparticles (Pt/C) were found to be effective heterogeneous catalysts for the direct Julia olefination of alcohols in the presence of sulfones and KOtBu under oxidant‐free conditions. Primary alcohols, including aryl, aliphatic, allyl, and heterocyclic alcohols, underwent olefination with dimethyl sulfone and aryl alkyl sulfones to give terminal and internal olefins, respectively. Secondary alcohols underwent methylenation with dimethyl sulfone. Under 2.5 bar H_2, the same reaction system was effective for the transformation of alcohol OH groups to alkyl groups. Structural and mechanistic studies of the terminal olefination system suggested that Pt⁰ sites on the Pt metal particles are responsible for the rate‐limiting dehydrogenation of alcohols and that KOtBu may deprotonate the sulfone reagent. The Pt/C catalyst was reusable after the olefination, and this method showed a higher turnover number (TON) and a wider substrate scope than previously reported methods, which demonstrates the high catalytic efficiency of the present method.     

Synthesis and Characterization of Tris(oxazolinyl)borato Copper(II) and Copper(I) Complexes

The reaction of To^MTl (To^M=tris(4,4-dimethyl-2-oxazolinyl)phenylborate) and CuBr₂ in benzene at 60 °C provides To^MCuBr ( 1 ) as an entry-point into tris(oxazolinyl)phenylborato copper chemistry. To^MCuO^tBu ( 2 ) and To^MCuOAc ( 3 ) are prepared by the reactions of To^MCuBr with KO^tBu and NaOAc, respectively. To^MCuO^tBu is transformed into (To^MCuOH)₂ ( 4 ) through hydrolysis. NMR, FT-IR, and EPR spectroscopies are used to determine the electronic and structural properties of these copper(II) compounds, and the solid-state structures were characterized by X-ray crystallography. Reduction of copper is observed upon treatment of To^MCuO^tBu with phenylsilane in an attempt to synthesize monomeric copper(II) hydride. To^MCu ( 5 ) and To^M₂Cu ( 6 ) were independently synthesized and characterized for comparison.     

Enantiomerically Pure Constrained Geometry Complexes of the Rare-Earth Metals Featuring a Dianionic N-Donor Functionalised Pentadienyl Ligand: Synthesis and Characterisation

We report the preparation of enantiomerically pure constrained geometry complexes (cgc) of the rare-earth metals bearing a pentadienyl moiety (pdl) derived from the natural product (1R)-(−)-myrtenal. The potassium salt 1 , [Kpdl*], was treated with ClSiMe₂NHtBu, and the resulting pentadiene 2 was deprotonated with the Schlosser-type base KOtPen/nBuLi (tPen=CMe₂(CH₂Me)) to yield the dipotassium salt [K₂(pdl*SiMe₂NtBu)] ( 3 ). However, 3 rearranges in THF solution to its isomer 3’ by a 1,3-H shift, which elongates the bridge between the pdl and SiMe₂NtBu moieties by one CH₂ unit. This is crucial for the successful formation of various monomeric C₁- or dimeric C₂-symmetric rare-earth cgc complexes with additional halide, tetraborohydride, amido and alkyl functionalities. All compounds have been extensively characterised by solid-state X-ray diffraction analysis, solution NMR spectroscopy and elemental analyses.     

Double Phosphinoboration of CO2: A Facile Route to Diphospha-Ureas

The reactions of CO₂ with a series of phosphinoboranes, including R₂PBpin (R=Ph, tBu; pin=pinacol), R₂PBMes₂ (R=Ph, tBu; Mes=2,4,6-Me₃-C₆H₂), and R₂PBcat (R=Ph, tBu, Mes; cat=catechol) are described. Although R₂PBpin and R₂PBMes₂ afford products of the form R₂PCO₂Bpin (R=Ph 1 , tBu 4 ) and R₂PCO₂BMes₂ (R=Ph 2 , tBu 3 ), respectively, R₂PBcat lead to further reaction affording the diphospha-ureas, (R₂P)₂CO (R=Ph 5 , tBu 6 , Mes 7 ), together with O(Bcat)₂. Computational studies provide insight into the mechanism, revealing an intermediate derived from double phosphinoboration of CO₂.     

Ferrocenyl Sulfinylimide and Diferrocenyl Sulfurdiimide,Fc?NSO and Fc(NSN)Fc

1 Abbreviations and Nomenclature: Fc = η¹-ferrocenyl, CpFe(C₅H₄-); Cp = η⁵-cyclopentadienyl, η⁵-C₅H₅. Compounds containing the —NSO group are designated as either thionylimides, sulfinylimides or N-sulfinylamines. The systematic name is imido oxo sulfuranes(IV).

The reactions of ferrocenylamine, Fc? NH₂ ( 1 ), with thionyl chloride and sulfur dichloride in hexane solution in the presence of triethylamine lead to the title compounds Fc? NSO ( 2 ) and Fc(NSN)Fc ( 3 ), respectively, 2 and 3 have also been obtained in reactions of the silylated ferrocenylamine, Fc? NH(SiMe₃) ( 1b ), with thionyl chloride. The ferrocenyl sulfinylimide 2 has been converted to sulfurdiimides such as Fc(NSN)Fc ( 3 ) and Fc(NSN)R (R = ^tBu ( 4a ), SiMe₃ ( 4b )) by reaction with the lithium derivative of silylated amines, LiN(SiMe₃)R (R = Fc, ^tBu, SiMe₃). The new ferrocenyl compounds 2–4 have been characterized by their NMR spectra, and their electrochemical behaviour has been studied. The molecular structure of Fc? NSO ( 2 ) has been determined by an X-ray structure analysis; the sulfinylimide has the Z configuration, and the —NSO group is coplanar with the cyclopentadienyl ring to which it is attached.     

Synthesis of a “Masked” Terminal Nickel(II) Sulfide by Reductive Deprotection and its Reaction with Nitrous Oxide

The addition of 1 equiv of KSCPh₃ to [L^RNiCl] (L^R={(2,6‐iPr₂C₆H₃)NC(R)}₂CH; R=Me, tBu) in C₆H₆ results in the formation of [L^RNi(SCPh₃)] ( 1 : R=Me; 2 : R=tBu) in good yields. Subsequent reduction of 1 and 2 with 2 equiv of KC₈ in cold (?25 °C) Et₂O in the presence of 2 equiv of 18‐crown‐6 results in the formation of “masked” terminal Ni^II sulfides, [K(18‐crown‐6)][L^RNi(S)] ( 3 : R=Me; 4 : R=tBu), also in good yields. An X‐ray crystallographic analysis of these complexes suggests that they feature partial multiple‐bond character in their Ni? S linkages. Addition of N₂O to a toluene solution of 4 provides [K(18‐crown‐6)][L^tBuNi(SN?NO)], which features the first example of a thiohyponitrite (κ²‐[SN?NO]^2?) ligand.