CHARACTERIZATION OF GALLIUM-NITROGEN ADDUCTS BY X-RAY STRUCTURAL AND NMR SPECTRAL STUDIES. CRYSTAL STRUCTURE OF [(PhMe2CCH2)2GaCI]2 AND OF ITS MONOMERIC t-BUTYLAMINE ADDUCT, (PhMe2CCH2)2GaCI[NH2(t-Bu)]

Abstract

The nature of [(PhMe₂CCH₂)₂GaCl]₂ and its adducts with NH₂(t-Bu) and NH₂(n-Pr) have been investigated. [(PhMe₂CCH₂)₂GaCl]₂ crystallizes in the monoclinic space group P2₁/c with a=11.2495(16)Å, b = 21.4977(32)A, c = 7.8337(15)Å, β = 93.489(14)°, V= 1891.0(5)ų and D(calcd.)= 1.305 Mg/m³ for Z = 2. The structure was refined to R(F) = 4.2% for 1672 reflections above 6[sgrave](F). The molecule has perfect C_i symmetry, a planar Ga(μ-Cl)₂Ga core and an expanded C(α)-Ga-C(α) angle of 137.9(3)° between the neophyl ligands. (PhMe₂CCH₂)₂-GaCl[NH₂(t-Bu)] crystallizes in the monoclinic space group P2₁/n with a = 6.4023(10) A, b= 17.4274(25) A, c = 22.2389(38) Å, β = 94.939(13)°, V= 2472.2(7)ų and D(calcd.) = 1.225 Mg/m³ for Z = 4. This structure was refined to R(F) = 3.9% for 1700 reflections above 6[sgrave](F). The crystal structure is stabilized by intermolecular Cl … H-N hydrogen bonds and the central Ga(III) atom has a distorted tetrahedral geometry. A benzene solution of (PhMe₂-CCH₂)₂GaCl[NH₂(t-Bu)] is in equilibrium with [(PhMe₂CCH₂)₂GaCl]₂[NH₂(t-Bu)] and free amine according to ¹HNMR studies. In contrast to this, a solution of (PhMe₂CCH₂)-GaCl₂[NH₂(t-Bu)] is in equilibrium with [(PhMe₂CCH₂)GaCl₂]₂[NH₂(t-Bu)], free [(PhMe₂-CCH₂)-GaCl₂]₂ and free amine. Solutions of (PhMe₂CCH₂)₂GaCI[NH₂(n-Pr)] and (PhMe₂CCH₂)GaCl₂[NH₂(n-Pr)] show no evidence for similar equilibria.     

Cumulated double bond systems as ligands : IV. 1H and 13C NMR studies of the intra- and inter-molecular exchange processes of cationic dialkylsulfurdiimine compounds of RhI,IrI and PtII

The preparation and properties are described of trans-[(Ph₃P)₂(CO)M(RNSNR)] [ClO₄] (M  Rh^I, Ir^I; R  Me, Et, i-Pr, t-Bu) and of cis- or trans-[L₂Pt(RNSNR)X] [ClO₄] (X  Cl^?, L  Et₂S, PhMe₂As, PhMe₂P, R  Me, t-Bu; X  CH₃, L  PhMe₂P, R  Me).¹H and ¹³C NMR data show the existence of various isomers in solution which may interconvert via intra- and inter-molecular exchange processes. A general reaction scheme for the intramolecular exchange processes is discussed.     

Silyl-titanation of acetylenes and 1,3-dienes

A Ti^IIISi active species, Cp₂TiSiMe₂Ph, is formed either by the reaction of Cp₂TiCl₂ with two equivalents of PhMe₂SiLi or by the reaction of Cp₂TiCl with one equivalent of PhMe₂SiLi. Highly regio- and stereo-selective silyltitanation by this species has been observed with acetylenes and 1,3-dienes.     

Palladium(0)‐Catalyzed Directed syn‐1,2‐Carboboration and ‐Silylation: Alkene Scope,Applications in Dearomatization,and Stereocontrol by a Chiral Auxiliary

We report the development of palladium(0)‐catalyzed syn‐selective 1,2‐carboboration and ‐silylation reactions of alkenes containing cleavable directing groups. With B₂pin₂ or PhMe₂Si‐Bpin as nucleophiles and aryl/alkenyl triflates as electrophiles, a broad range of mono‐, di‐, tri‐ and tetrasubstituted alkenes are compatible in these transformations. We further describe a directed dearomative 1,2‐carboboration of electron‐rich heteroarenes by employing this approach. Through use of a removable chiral directing group, we demonstrate the viability of achieving stereoinduction in Heck‐type alkene 1,2‐difunctionalization. This work introduces new avenues to access highly functionalized boronates and silanes with precise regio‐ and stereocontrol.     

Palladium(0)‐Catalyzed Directed syn‐1,2‐Carboboration and ‐Silylation: Alkene Scope,Applications in Dearomatization,and Stereocontrol by a Chiral Auxiliary

We report the development of palladium(0)‐catalyzed syn‐selective 1,2‐carboboration and ‐silylation reactions of alkenes containing cleavable directing groups. With B₂pin₂ or PhMe₂Si‐Bpin as nucleophiles and aryl/alkenyl triflates as electrophiles, a broad range of mono‐, di‐, tri‐ and tetrasubstituted alkenes are compatible in these transformations. We further describe a directed dearomative 1,2‐carboboration of electron‐rich heteroarenes by employing this approach. Through use of a removable chiral directing group, we demonstrate the viability of achieving stereoinduction in Heck‐type alkene 1,2‐difunctionalization. This work introduces new avenues to access highly functionalized boronates and silanes with precise regio‐ and stereocontrol.     

Synthesis and catalytic properties of polynuclear molybdenum silicon-containing carbene complexes

The molybdenum silicon-containing carbene complexes PhMe₂Si—CH=Mo(NAr)(OR)₂ (1), Ph₂Si[CH=Mo(NAr)(OR)₂]₂ (2), and (RO)₂(ArN)Mo=CH—(SiMe₂)₂—CH=Mo(NAr)(OR)₂ (Ar = 2,6-Prⁱ ₂C₆H₃; R = CMe₂CF₃) were synthesized by the reaction of the R′— CH=Mo(NAr)(OR)₂ compounds (R′ = Bu^t or PhMe₂C) with silicon-containing vinyl reagents. The structures of complexes 1 and 2 and the known PhMe₂C—CH=Mo(NAr)(OCMe₂CF₃)₂ compound were established by X-ray diffraction. The catalytic properties of the silicon-containing carbene complexes in homometathesis of hex-1-ene and metathesis polymerization of cyclooctene were studied. The catalytic activity of these complexes and the stereoregularity of the resulting polyoctenamers substantially depend on the nature of the substituent at the carbene carbon atom. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 247–252, February, 2007.     

Electrophilic Bromination of N‐Acylated Cyclohex‐3‐en‐1‐amines: Synthesis of 7‐Azanorbornanes

The intramolecular bromo‐amidation and the dibromination‐cyclisation of the N‐acylcyclohex‐3‐en‐1‐amines 4, 8, 9, 11, 13, 14 , and 16 was studied in view of the synthesis of bicyclic amines that are of interest as building blocks and potential glycosidase inhibitors. The trifluoroacetamides 4, 9 , and 14 reacted with N‐bromosuccinimide (NBS) in AcOH to give dihydro‐1,3‐oxazines in good yields. The stereoselectivity of the dibromination of the alkenes 8 and 9 depends on the nature of the protecting group, the reagent, and the reaction conditions. Br₂ in CH₂Cl₂ transformed the alkenes 8 and 9 predominantly into diaxial trans,trans‐dibromides. Bromination of 9 with PhMe₃NBr₃ or with Br₂ in the presence of Et₄NBr gave predominantly the diequatorial trans,cis‐ 27 besides some trans,trans‐ 28 . A similar bromination of the C(5)‐substituted N‐acyl‐4‐aminocyclohexenes 11, 13, 14 , and 16 with PhMe₃NBr₃ was accompanied by intramolecular side reactions that were suppressed by the addition of excess Et₄NBr. Under these conditions, 11 gave diastereoselectively trans‐dibromides, while its reaction with Br₂ gave trans‐dibromides along with the dihydrooxazinone 31 . Also the carbamate 13 reacted with PhMe₃NBr₃/Et₄NBr selectively to the trans‐dibromide 32 and with Br₂ to the trans‐dibromides 32 and 33 , the dihydrooxazinone 34 , and the bicyclic ether 35 . Similarly, the trifluoroacetamide 14 provided the dibromide 36 (89%), while its reaction with Br₂ led to the dihydrooxazine 22 , and the dibromides 36 and 37 . The N‐benzyl‐N‐Boc derivative 16 did not yield any dibromide; it reacted with PhMe₃NBr₃/Et₄NBr to the dihydrooxazinone 38 , and with Br₂ to the oxazinone 38 and the bicyclic ether 39 . The high stereoselectivity of the bromination with PhMe₃NBr₃/Et₄NBr suggests an anchimeric assistance of the NHR substituent. Deprotection, cyclisation, and carbamoylation transformed the dibromides 27, 29 , and 32 into the 7‐azanorbornanes 42, 49 , and 53 . The diols 45 and 57 were obtained from 42 and 53 via HBr elimination and stereoselective dihydroxylation; they proved weak inhibitors of several glycosidases. In no case could the formation of a bicyclic azetidine (6‐azabicyclo[3.1.1]heptane) from the dibromides 26 and 30 be observed.     

1,3-Migration of a phenyl group in the conversion of (Me3Si)2(PhMe2Si)CSiMePhX into (Me3Si)2(Ph2MeSi)CSiMe2Y species

The finding that compounds of the type (Me₃Si)₂(PhMe₂Si)CSiMePhX react with electrophiles to give very predominantly rearranged products (Me₃Si)₂(Ph₂MeSi)CSiMe₂Y, which would be expected to be thermodynamically disfavoured, can be rationalized in terms of a mechanism in which the anchimerically-assisted departure of X⁻ gives the Ph-bridged cation [(Me₃Si)₂

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MePh]⁺ which is attacked by the nucleophile at the less hindered centre bearing two Me groups rather than that bearing one Me and one Ph group, with the outcome determined by kinetic rather than thermodynamic factors. Both (Me₃Si)₂(Ph₂MeSi)CSiMe₂Br and its isomer (Me₃Si)₂(PhMe₂Si)CSiMePhBr react with AgBF₄ in CH₂Cl₂ or Et₂O to give >95% of the fluoride (Me₃Si)₂(Ph₂MeSi)CSiMe₂F. Reaction of the bromide (Me₃Si)₂(PhMe₂Si)CSiMePhBr with AgO₂CCF₃ in Et₂O, and that of the hydride (Me₃Si)₂(PhMe₂Si)CSiMePhH with ICl in CCl₄, likewise give >95% of the rearranged (Me₃Si)₂(Ph₂MeSi)CSiMe₂O₂CCF₃ and (Me₃Si)₂(Ph₂MeSi)CSiMe₂Cl, respectively.     

Electrochemical synthesis of organosilicon compounds

Electrochemical reduction of allyl, vinyl, and aryl halides in the presence of a silylating agent (Me₃SiCl, HMe₂SiCl, or PhMe₂SiCl) afforded the corresponding organosilicon compounds offering a valuable method for introduction of a silyl group into organic molecules.     

Kinetic studies on the hydrosilylation of phenylacetylene with R3SiH (R3 = PhMe2, Ph2Me,Ph3, Et3) using bis(1,2‐diphenylphosphinoethane)norbornadiene rhodium(I) hexafluorophosphate as catalyst

Product distribution and kinetic studies on the hydrosilylation of phenylacetylene by Ph₃SiH, Ph₂MeSiH, PhMe₂SiH and Et₃SiH were performed using bis‐[1,2‐diphenylphosphinoethane]norbornadienerhodium(I) hexafluorophosphate, 1, as catalyst. Pre‐equilibration of the catalyst with the acetylene produced hydrosilylations, pre‐equilibration with the silane did not. The catalyst showed a pronounced selectivity for cis‐addition to form β‐products, t‐PhCH­CHSiR₃, unlike most hydrosilylation catalysts. The kinetic studies showed a hydrosilylation reaction that is zero order with respect to both acetylene and the silane, with a dependency upon catalyst concentration. The k_obs value is directly influenced by the substituents on the silane: k(PhMe₂SiH) > k (Et₃SiH > k (Ph₂MeSiH) > k (Ph₃SiH). Intercalation of the catalyst in hectorite was not useful, since either no reaction occurred in non‐polar solvents, or extraction of the catalyst occurred in polar solvents to produce the same product distributions. Copyright © 2000 John Wiley & Sons, Ltd.     

Factors determining transformations of silicon-containing aroxyls. Communication 2. Change in stability in the series of o-trimethylsilyl-, o-phenyldimethylsilyl-, and o-methyldiphenylsilyl-containing aroxyls

Conclusions In the dimerization-rearrangement of silicon-containing aroxyls, the relative migration ability of o-organosilyl substituents decreases in the series PhMe₂Si > Me₃Si > MePh₂Si > Ph₃Si.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2344–2346, October, 1984.     

Darstellung und IR-spektroskopische Untersuchungen von Siloxysilanolen

Preparation and I.R. Spectroscopic Investigations of Siloxysilanols The preparation of siloxanols of the typs (RMe₂SiO)₃SiOH, (Me_3?nPh_nSiO)(Me₃SiO)₂SiOH, (PhMe₂SiO)_n(Me₃SiO)_3?nSiOH and Me_3?n(R′Me₂SiO)_nSiOH (n = 1?3) is described. The position of the OH-stretching vibration in carbon tetrachloride and the shift Δν of this band at assoziation with tetrahydrofuran and diethylether have been measured. The position of ν_OH band and Δν values are determined by n and by the substituents. The Δν values correlate with the σ* constants of the substituents R. Intramolecular interaction between the hydroxy group and the π electrons of phenyl substituents resp. lone pair electrons of the halogen atoms proceed in the siloxanols (XCH₂Me₂SiO)₃SiOH (X = Cl, Br, Ph) and Me_3?n(PhMe₂SiOSiMe₂O)_nSiOH (n = 1?3).     

Regularities of ring-opening metathesis polymerization of cyclooctene in the presence of molybdenum catalysts

At the initial stages the polymerization of cis-cyclooctene in the bulk with the catalysts Me₃C-CH=Mo(NAr)(OCMe₂CP₃)₂, PhMe₂C-CH=Mo(NAr)(OCMe₂CP₃)₂, Me₃Si-CH=Mo(NAr)(OCMe₂CP₃)₂, and PhMe₂Si-CH=Mo(NAr)(OCMe₂CP₃)₂ predominantly affords cis-polyoctenamers. The content of the trans- units in the polymer increases with an increase in the conversion. The sharpest increase in the trans- unit content observed for conversions higher than 80% is related to secondary metathesis reactions. The number-average molecular weights of the polymers increase linearly with the conversion. At conversions above 80% the molecular weights decrease due to the increasing contribution of chain transfer reactions. Polyoctenamers with the increased content of trans- units crystallize in two modifications.     

Boraformylation and Silaformylation of Allenes

The boraformylation of allenes with B₂(pin)₂ and a formate ester as boron and formyl source, respectively, proceeds in the presence of a copper catalyst. The reaction selectively affords the corresponding β‐boryl β,γ‐unsaturated aldehydes in good to high yields. Furthermore, the silaformylation of allenes was achieved with a formate ester and PhMe₂Si−B(pin) as the silicon source.     

Transition metal reactions of silanes II. The reaction of cycloalkenes with various hydrosilanes and carbon monoxide catalyzed by Co2(CO)8

The reaction of cycloalkenes(cyclopentene, cyclohexene, cycloheptene, cyclooctene, 1-methylcyclohexene, and norbornene) with Et₂MeSiH and carbon monoxide in the presence of Co₂(CO)₈ gave the corresponding diethylmethylsiloxymethylenecycloalkenes. In such reactions of cyclohexene, the following hydrosilanes gave the corresponding siloxymethylenecyclohexanes: Me₃SiH, EtMe₂SiH, Et₂MeSiH, Et₃SiH, PhMe₂SiH, Ph₂MeSiH. Effects of the reaction conditions(the pressure of carbon monoxide, the temperature, and the molar ratio of cyclohexene to Et₂MeSiH) were examined. The yield of diethylmethylsiloxymethylenecyclohexane increased remarkably with increasing molar ratio of cyclohexene to Et₂MeSiH. At higher temperature, the yield of the isomerization product, 1-(diethylmethylsiloxymethyl)-cyclohex-1-ene, increased.     

Effect of the nature of carbene fragments in the tungsten complexes PhMe2E-CH=W(NAr)(OR′)2 and Me3E-CH=W(NAr)(OR′)2 (E = C, Si) on their catalytic properties in olefin metathesis reactions

Catalytic properties of the silicon-containing carbene complexes of tungsten Me₃Si-CH=W(NAr)(OR′)₂(1) and PhMe₂Si-CH=W(NAr)(OR′)₂ (2) and their hydrocarbon analogs Me₃C-CH=W(NAr)(OR′)₂ (3) and PhMe₂C-CH=W(NAr)(OR′)₂ (4) (Ar = 2,6-Prⁱ ₂C₆H₃, R′ = CMe₂CF₃) were studied in homometathesis of hex-1-ene, metathesis polycondensation of deca-1,9-diene, and ring opening metathesis polymerization of cyclooctene. The nature of the carbene fragment in the tungsten catalysts substantially affects their catalytic activity. Silicon-containing catalysts 1 and 2 were found to be 3−5 times less active than their hydrocarbon analogs 3 and 4. Metathesis polymerization of cyclooctene in the bulk with initiators 1–4 completed within a few minutes to form a block. Stereoregularity of the formed polyoctenamers depends to a considerable extent on the nature of the carbene fragments in the starting initiators. Initiators 1–2 lead to polyoctenamers mainly containing the cis-units, whereas the use of complexes 3 and 4 affords polyoctenamers mainly containing the trans-units. The structures of novel compound 2 and known complexes 1, 3, and 4 were determined by X-ray diffraction analysis. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1840–1845, September, 2008.     

Reactions of group IV organometallic compounds : XXIX. Insertion reactions of (trimethylsilylmethylene)phosphorane with heterocumulenes. Inhibition of Wittig type reactions

A reaction of (trimethylsilylmethylene)dimethylphenylphosphorane, PhMe₂PCHSiMe₃ (I), with phenyl isocyanate affords a 2/1 insertion product, which results from insertion of phenyl isocyanate into both the CSi and CH bonds of I. By way of contrast, a reaction of isothiocyanate and carbon disulfide with I affords 1/1 products by insertion of these heterocumulenes into the CSi bond of I. In these reactions, Wittig-type elimination of dimethylphenylphosphine oxide or sulfide did not occur because of irreversible migrations of the trimethylsilyl group to the anionic centers of the Zwitterionic intermediates.     

Tris(trimethylsilyl)methane and tris(dimethylphenylsilyl)methane: Preparation and comparison of some alkene and cyclopropane derivatives

It is known that metalation of (RMe₂Si)₃CH (R: a = Me, b = Ph) with MeLi in THF yields (RMe₂Si)₃CLi, which when reacted with allyl bromide, (RMe₂Si)₃C-CH₂-CH=CH₂ (1a, 1b) are produced. In this study, although (PhMe₂Si)₃CLi does not react with benzyl bromide, under the same conditions (Me₃Si)₃CLi does, giving the expected product. We found that the bromination of 1b was unsuccessful and the reaction of 1a occurs in low yield due to severe steric hindrance. This idea is supported by our results, which show that, when treated with dichlorocarbene and dibromocarbene, 1a and 1b yield the related dihalocyclopropanes. Furthermore, reduction of the obtained products gives the dehalogenated compounds.     

Progress of olefin polymerization by metallocene catalysts

New C₁‐symmetric metallocenes such as [Me₂C(PhCp)(Flu)ZrCl₂, [Me₃Pen(Flu)]ZrCl₂, [PhMe₃Pen(Flu)]ZrCl₂ were synthesized and used for the polymerization of propene by higher polymerization temperatures. Different polypropylene micro structures were obtained. Important for industrial processes are the high molecular weights of the polymers produced by the pentalenelike catalysts, which are very stable by higher temperatures. For synthesis of syndiotactic polystyrene and new substituted half‐sandwich titanocenes are used such as 1,3‐Me₂‐CpTiCl₃, Me₄CpTiCl₃, PhCpTiCl₃, cyclohexyl‐CpTiCl₃. If they are fluorinated, the activity for the production of syndiotactic polystyrene can be increased 10 times. The synthesized polymer shows a high melting point of 275°C.     

A convenient synthesis and structure of stabilized ylide complexes of palladium(II)

New types of some carbonyl- and cyano-phosphonium ylide complexes of palladium(II) were readily prepared in good yield by treatment of the corresponding bis(phosphonium)hexachlorodipalladate, [R₃P⁺-CH₂-Z]₂[Pd₂Cl₆]^2? (R₃P = Ph₃P, Z = COMe, COOEt, CONH₂ or CN; R₃P = PhMe₂P, Z = COPh), with sodium acetate.