Generation and conversion of the transient 1,1-bis(trimethylsilyl)-2-( 2,4,6-triisopropylphenyl)-silene

Treatment of 2,4,6-triisopropylbenzaldehyde with tris(trimethylsilyl)silylmagnesium bromide (2) gives 2,4,6-triisopropylphenyl-tris(trimethylsilyl)silyl-methanol (3) in approximately 70% yield and E-3,4-bis(2,4,6-triisopropylphenyl)-1,1,2,2-tetrakis(trimethylsilyl)-1,2-disilacyclobutane (5) (15%). 5 is the [2 + 2] head-to-head cyclodimer of the transient 1,1-bis(trimethylsilyl)-2-(2,4,6-triisopropylphenyl)silene (4), formed by trimethylsilanolate elimination according to a Peterson mechanism from the magnesium alkoxide, derived from the alcohol 3. Deprotonation of 3 with McLi at low temperature in ether produces a complex mixture of products, the main constituents being the silene dimer 5 (10%) and bis(trimethylsilyl)-2,4,6-triisopropylbenzyl-trimethylsiloxysilane (10) (60%), which is formed by readdition of the eliminated lithiumtrimethylsilanolate at the Si=C bond of 4. The deprotonation of 3 with McMgBr or PhMgBr (activated by LiBr) in THF at room temperature results in the formation of the polysilane (Me₃Si)₃SiSi(SiMe₃)₂CH₂(2,4,6-C₆H₂iPr₃) (13). Its generation indicates that there exists an equilibrium between the magnesium alkoxide derived from the alcohol 3 on one side, and the magnesium silanide 2 and 2,4,6-triisopropylbenzaldehyde on the other side. Possible pathways of the formation of the compounds mentioned, as well as of further by-products, are discussed. The 1,2-disilacyclobutane 5 is characterized by an X-ray crystal structure analysis.     

The first silastannene >si=sn<: a new doubly-bonded system of heavier group 14 elements

The reaction of bis[di-tert-butyl(methyl)silyl]dilithiosilane 1 with dichlorobis(2,4,6-triisopropylphenyl)stannane in THF at room temperature yielded highly air- and moisture-sensitive deep violet crystals of 1,1-bis[di-tert-butyl(methyl)silyl]-2,2-bis(2,4,6-triisopropylphenyl)-1-sila-2-stannaethene 2 with a Si=Sn double bond. The molecular structure of 2 was established by X-ray crystallography, which showed a trans-bent structure (bending angles of 26.2 degrees for the sp2 Si atom and 9.6 degrees for the sp2 Sn atom) with a >Si=Sn< bond length of 2.4188(14) A and a twisting angle of 34.6 degrees . The geometry and regioselectivity of the addition reaction of PhEH (E = O and S) corresponds to the polarity of the double bond Sidelta-=Sndelta+, which is also supported by theoretical calculations on the model silastannene (H3Si)2Si=SnPh2.     

Remote asymmetric trifluoromethylation induced by chiral sulfinyl group: synthesis of enantiomerically pure 1-(2-naphthyl)-2,2,2-trifluoroethanol

The reaction of 1-[(2,4,6-triisopropylphenyl)sulfinyl]-2-naphthaldehyde with (trifluoromethyl)trimethylsilane using tetramethylammonium fluoride gave trifluoromethylated compounds in high yield with high diastereoselectivity. Desilylation and subsequent recrystallization yielded the enantiomerically and diastereomerically pure trifluoroethanol, which afforded chiral 1-(2-naphthyl)-2,2,2-trifluoroethanol after removal of the sulfinyl group.     

Synthesis and Structure of Sterically Crowded Triarylphosphine Bearing 4-Bromo-2,6-Bis(4-tert-Butylphenyl)Phenyl Group

Abstract

A novel sterically crowded triarylphosphine bearing a 2,6-diaryl-4-bromophenyl group, [4-bromo-2,6-bis(4-tert-butylphenyl)phenyl]bis(2,4,6-triisopropylphenyl)phosphine (1), was synthesized. The X-ray crystallography revealed that the bond angles and lengths around the phosphorus atom (110.9°, 1.846 Å) are comparable to those of tris(2,4,6-triisopropylphenyl)phosphine and its derivatives. Triarylphosphine 1 is reversibly oxidized to the radical cation at the potential close to that of the typical sterically crowded (bromoaryl)phosphine, (4-bromo-2,6-diisopropylphenyl)bis(2,4,6-triisopropylphenyl)phosphine, and exhibits the UV absorption at long wavelength (λ_max 332 nm) characteristic of the sterically crowded triarylphosphines. Thus, triarylphosphine 1 can be regarded to be a promising candidate for the key synthetic intermediate or building block to the functional molecules bearing sterically crowded triarylphosphine moieties.     

New asymmetric reactions of 2-formyl- and 2-acyl-1-[(2,4, 6-triisopropylphenyl)sulfinyl]naphthalenes via diastereomeric rotamers

Nucleophilic reactions with Grignard reagents and the Mukaiyama aldol reactions of the naphthaldehydes having the (2,4, 6-triisopropylphenyl)sulfinyl group produced products with high stereoselectivity. In these reactions, the stereochemistry of the major products changes depending on the Lewis acids used. Reduction of the 2-acyl-1-[(2,4,6-triisopropylphenyl)sulfinyl]naphthalenes also proceeds with high stereoselectivity but with a different stereochemistry depending on the reducing agents. We have demonstrated, by the mechanistic consideration based on the X-ray crystal structures as well as the (1)H and (13)C NMR spectral data, that the extremely high and specific stereoselectivities of these reactions are due to the predominant rotamer around the C(naph)-S axis. Synthesis of enantiomerically pure 2-naphthylmethanol is provided as an example.     

Siliciumverbindungen mit starken intramolekularen sterischen wechselwirkungen : XLIX. Disilane und ein disilen mit unsymmetrischer substitution an den siliciumatomen

Treatment of chlorobis(2,4,6-triisopropylphenyl)silane (Ar₂SiHCl) with lithium naphthalenide and subsequent addition of the chlorosilanes R₂SiHCl (R = ⁱPr, ^tBu, Mes) gives the unsymmetrical disilanes R₂HSiSiHAr₂ which are smoothly converted into the 1,2-dichlorodisilanes 8–10. The X-ray structure analysis of the 1,1-dimesityldisilane 10 reveals a staggered conformation with the chlorine atoms disposed in an anti orientation. Whilst the reductive chloride elimination from the 1,1-dialkyldichlorodisilanes 8 and 9 did not give the corresponding disilenes, the same reaction of 10 provided bright yellow crystals of 1,1-dimesityl-2,2-bis(2,4,6-triisopropylphenyl)disilene, the structure of which was confirmed by a complete NMR study.     

Stereoselective synthesis of (E)-1-iodo-1-selenoalkenes via hydroalumination-iodination of 1-alkynyl selenides

syn-Hydroalumination of 2,4,6-triisopropylphenylselanyl-1-alkynes 22 with DIBAL-H, followed by Al/I exchange with I₂, afforded selectively the corresponding (E)-1-iodo-1-selenoalkenes in good yields. The sterically hindered 2,4,6-triisopropylphenyl group proved to be mandatory and prevented the formation of undesired by-products.     

Study of the reactivity of organonickel sigma-complexes towards nitriles

The reactivity of organonickel sigma-complexes of type [NiBr(Ar)(bpy)], where Ar = 2,6-dimethylphenyl (Xyl), 2,4,6-trimethylphenyl (Mes), 2,4,6-triisopropylphenyl (Tipp), 2,4,6-tricyclohexylphenyl (Tchp), bpy = 2,2´-bipyridine, towards nitriles (acetonitrile, propionitrile, chloroacetonitrile, benzonitrile) has been investigated. This reaction leads to imines by formation of new carbon—carbon bond between aromatic fragment and nitrile group C≡N.     

A highly efficient catalytic system for cross-coupling of aryl chlorides and bromides with malononitrile anion by palladium carbene complexes

Six imidazolium chlorides (1-6) as precursors of 1,3-diaryl substituted N-heterocyclic carbene ligands were synthesized and evaluated in palladium-catalyzed cross-coupling reactions of aryl chlorides and bromides with malononitrile in the presence of NaH. Among them, 1,3-bis(2,4,6-triethylphenyl)imidazolium chloride (5) and 1,3-bis(2,4,6-triisopropylphenyl)imidazolium chloride (6) are novel. The catalytic system combining Pd(0) with imidazolium salts 4, 5 and 6 with bulky aryl groups in pyridine is found to be superior over others and afforded alpha-arylmalononitriles in high yields when employing a wide variety of substrates.     

Excitation spectra of dibenzoborole containing pi-electron systems: controlling the electronic spectra by changing the p(pi)-pi* conjugation

We report time-dependent density functional theory calculations of the vertical excitation energies for the singlet states of three-coordinate 5H-dibenzoborole (DBB) derivatives and four-coordinate 5-fluoro-5H-dibenzoborole ion (FDBB) derivatives. These molecules show remarkable hypsochromic (blue) shifts in their fluorescence spectra and bathochromic (red) shifts in their absorption spectra when the bridging boron atoms change their coordination number from three to four. We constructed a series of derivatives of DBB and FDBB and studied how the energies of the electronic excitations change. The states with prominent oscillator strength in all of the DBB and FDBB derivatives show similar shifts of their excitation energies upon coordination. The three-coordinate DBB derivative 5-(2,4,6-triisopropylphenyl)-2,8-dimethoxy-3,7-bis[p-(N,N-diphenylamino)phenyl]-5H-dibenzo[d,b]borole has an intense absorption at 3.25 eV, which shifts in the four-coordinate FDBB derivative 5-fluro-5-(2,4,6-triisopropylphenyl)-2,8-dimethoxy-3,7-bis[p-(N,N-dip henylamino)phenyl]-5H-dibenzo[d,b]borole ion to 3.17 eV. The experimental absorption peaks are 3.43 and 3.31 eV, respectively. In addition, we investigated and analyzed the nature of these electronic excitations using attachment/detachment density plots, with which we characterized the changes in electron density that arose from the excitations.     

PREPARATION AND SPECTRAL PROPERTIES OF SYMMETRICAL S-ARYL ARENESULFONOTHIOATES (THIOSULFONATES)

Abstract

Arenesulfinyl chlorides (4-XC₆H₄S(O)Cl); × = H, CH₃, F, Cl, Br) react with activated zerovalent zinc in benzene at 6 to 8°C to give symmetrical S-aryl arenesulfonothioates (thiosulfonates) in good to excellent yields. 2-and 3-Substituted arenesulfinyl chlorides (X = Cl, CH₃) give a mixture of products (disulfide, thiosulfinate, and/or thiosulfonate). 2,4,6-Triisopropylbenzenesulfinyl chloride reacts with zinc in 1,2-dimethoxyethane to give S-(2,4,6-triisopropylphenyl) 2,4,6-triisopropylbenzenesulfinothioate and bis(2,4,6-triisopropylphenyl) disulfide. Possible mechanisms for the reactions, the ¹H and ¹³C NMR spectra, and the chemical ionization and electron impact mass spectra of the thiosulfonates are discussed. The para carbon substituent chemical shifts (C_p-SCS) for the thiosulfonates and for symmetrical diaryl disulfides have been subjected to several dual substituent parameter (DSP) correlations.     

Electrochemical synthesis and catalytic activity of organonickel sigma-complexes

A new industrially applicable method of organonickel sigma-complexes production is developed. The technique is based on the reaction of the oxidative addition of ortho-substituted aromatic bromides to electrochemically generated nickel(0)-2,2′-bipyridyl complexes. Electrolysis is performed in undivided electrolyser supplied with sacrificial nickel anode with a periodic or continuous electrolyte loading. The electrochemically obtained organonickel sigma-complexes of type [NiBr(Ar)(bpy)], where Ar is 2,4,6-trimethylphenyl, 2,4,6-triisopropylphenyl, 2,6-dimethylphenyl, are highly effective precatalysts for ethylene oligomerization process, leading to the formation of linear alpha-olefines of C4–C12 fractions     

Synthesis, characterization and oxidizing properties of a diorgano tellurone carrying bulky aromatic substituents

Bis(2,4,6-triisopropylphenyl) tellurone (Tip(2)TeO(2)) was prepared, fully characterized by spectroscopic and X-ray crystallographic analyses, as well as theoretical calculations, and found to be an effective oxidizing agent that was capable of converting alcohols into carbonyl compounds under mild reaction conditions.     

Tris(pyrrolyl-alpha-methyl)amines that sterically protect a trigonal metal site

Three substituted tris(pyrrolyl-alpha-methyl)amines (H(3)[Aryl(3)TPA]) (Aryl = 2,4,6-C(6)H(2)Me(3), 2,4,6-C(6)H(2)(i-Pr)(3) (Trip), or 3,5-C(6)H(3)(CF(3))(2)) have been prepared. An X-ray study of [Trip(3)TPA]MoCl shows it to be a distorted trigonal bipyramidal species in which the 2,4,6-triisopropylphenyl substituents surround and protect the apical chloride. Attempts to prepare other Mo, Zr, and Hf complexes yielded species in which one pyrrole-containing arm remained free (Mo) or dimethylamine remained in the coordination sphere of [Aryl(3)TPA](3-) complexes (Zr, Hf).     

1-(2,4,6-triisopropylphenyl)ethylamine: a new chiral auxiliary for the asymmetric synthesis of gamma-amino acid derivatives

The title compound has proven to be an excellent chiral auxiliary for nitrones in SmI2-mediated reductive coupling with alpha,beta-unsaturated esters. A variety of such nitrones, prepared from aldehydes and enantiopure N-hydroxy-1-(2,4,6-triisopropylphenyl)ethylamine, afforded gamma-N-hydroxyamino esters in high yields and diastereomeric purity. These adducts, readily available as either enantiomer, could be transformed into gamma-N-acetoxyamino esters, N-Boc-gamma-amino esters, and gamma-lactams.     

Synthesis, structure, and redox properties of crowded triarylphosphines carrying 2,6-diarylphenyl substituents

Crowded triarylphosphines carrying 2,6-diarylphenyl and 2,4,6-trialkylphenyl groups were synthesized by the reaction of arylcopper(I) reagent with the chlorophosphines. The triarylphosphines had large bond angles and lengths around the phosphorus and were reversibly oxidized at significantly low potentials. X-ray crystallography of bis(2,4,6-triisopropylphenyl)[4-methyl-2,6-di(1-naphthyl)phenyl]phosphine revealed that two 1-naphthyl groups took anti conformation in the crystal.     

Highly active in situ catalysts for anti-Markovnikov hydration of terminal alkynes

The anti-Markovnikov hydration of terminal alkynes to give aldehydes is catalyzed by complexes derived in situ from air-stable [CpRu(eta6-naphthalene)]PF6 (C) and 6-aryl-2-diphenylphosphinopyridines (L). Ligands L are readily available from a modular synthesis. Increasing the size of the ligand C-6 aryl group in the order R = Ph < mesityl < 2,4,6-triisopropylphenyl < (2,4,6-triphenyl)phenyl gave hydration catalysts of highest known activity. [reaction: see text]     

Synthesis of the first fluoro(phosphanyl)- and diphosphanyl-stannanes and surprising formation of [P(SnMe3)4]+ SiF5-

Monophosphanylation of the difluorostannane Is2SnF2 (Is = 2,4,6-triisopropylphenyl) with Si(PH2)4 furnishes the first isolable fluoro(phosphanyl)stannane Is2Sn(F)PH2 1, which readily undergoes unique SiO2-assisted decompostion to [Is2Sn(PH)]2 2 and HF, while further phosphanylation of 1 leads to the remarkably stable diphosphanylstannane Is2Sn(PH2)2 3; the latter reacts with Me3SnF at the glass-wall to give the first perstannylphosphonium pentafluorosilicate [P(SnMe3)4]+ SiF5- 4.     

Reductive Mannich-type reaction using the composite reagents of phosphine and Lewis acid

We found that the combination of Ph₃P and TiCl₄ was the excellent promoter for reductive Mannich-type reaction of S-2,4,6-triisopropylphenyl 2-bromopropanethioate with several imines and that the corresponding products were obtained in good yields with high anti-selectivity.     

Thermolysis,photolysis, and oxidation of an overcrowded 1,3,2-dithiastannetane derivative

Reactions of a sterically crowded 1,3,2-dithiastannetane derivative bearing 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl (=Tbt) and 2,4,6-triisopropylphenyl (=Tip) groups on the tin atom are described. Both thermolysis and photolysis of the 1,3,2-dithiastannetane [Tbt(Tip)SnS₂CPh₂] resulted in the formation of products derived from the corresponding stannanethione [Tbt(Tip)Sn=S], while the oxidation reaction by m -chloroperbenzoic acid gave a novel tincontaining heterocyclic system, an 1,2,4,5-oxadithiastannolane derivative.