Stannyl Group Research Articles

Structure and Natural Bond Orbital Analysis of Oxiranes Substituted with a Group 14 Element. A Comment of SN2 Regioselectivity

Abstract Crystal structure analysis of oxiranes substituted with a group 14 element revealed that silyl and stannyl groups lengthened their α C–O bonds. Natural bond orbital analysis showed that silyl group raised the energy level of α C–O σ orbital and lowered that of α C–O σ* orbital. It was suggested that the former might lengthen the α C–O bond and that the latter should affect the regioselectivity in ring-opening reactions.

Diverging Effects of Steric Congestion on the Reaction of Tributylstannyl Radicals with Areneselenols and Aryl Bromides and Their Mechanistic Implications.

The effects of bulky ortho,ortho' groups on the reactions of aryl bromides and areneselenols with tributylstannane have been studied. Bulky ortho,ortho' groups accelerate the reaction of the bromides with the stannane but retard the reactions of the selenols. On the other hand, ab initio and force field calculations show that introducing bulky ortho substituents into selenols causes a greater increase in strain than in the corresponding bromides. Two possible explanations for the divergent reactivity patterns are advanced. On one hand, it is possible that bromine abstraction by stannyl radicals from aryl bromides proceeds in a single step through a linear transition state whereas the abstraction of SeH from the selenols involves a T-shaped, hypervalent intermediate. Alternatively, it may be that both reactions are concerted with the bromine abstraction having a late transition state and the SeH abstraction an early one. Approximate second-order rate constants for the reaction of tributylstannane with a range of hindered aryl bromides are derived from competition reactions. 2,4,6-Tri-tert-butylbenzeneselenol is able to function moderately well as a catalyst for the stannane-mediated reactions of vinyl bromides. The X-ray crystal structure of bis(2,4,6-triisopropylphenyl) diselenide is presented.

Radical Cyclization in Heterocycle Synthesis. 6.(1) A New Entry to Cyclic Amino Alcohols via Stannyl Radical Cyclization of Oxime Ethers Connected with Aldehydes or Ketones.

Oxime ethers connected by a tether to aldehydes or ketones efficiently cyclize via stannyl radical addition-cyclization to provide a new entry to cyclic amino alcohols. Upon treatment with tributyltin hydride in the presence of AIBN, oxime ethers connected with either an aldehyde or a ketone via a nitrogen atom smoothly underwent stannyl radical addition-cyclization to give five- to seven-membered cis- and trans-heterocyclic amino alcohols of which the trans-isomers were major products. The newly found radical cyclization provides a novel method for preparing not only bifunctionalized heterocyclic compounds but also adjacently functionalized amino alcohols carrying two quaternary carbons.

Temperature Effect on the Kinetics for the Reaction of Stannyl Anion with Primary Butyl Bromide

The decay of the tributylstannyl anion in the presence of primary butyl bromide were measured with a modified stopped-flow apparatus at low temperatures. The investigation for the differences between that decay at 10°C and −60°C revealed the formation of the stannyl radical as the intermediate of this reaction.

Carbonyllithium chemistry. Intramolecular conversion of an acyllithium via the utilization of an anionic 1,2-stannyl rearrangement

The reaction of α-stannylmethyllithium with CO (1 atm) generates the acyllithium that smoothly undergoes anionic 1,2-stannyl rearrangement at −78°C to give the enolate derivative of acyltin. The rearrangement of the stannyl group is much faster than that of the silyl group.

Reactivity of a Cationic Phosphenium Complex of Tungsten Containing an Alkyl or a Stannyl Group

The treatment of Cp(CO)2MeW{PN(Me)CH2CH2NMe(OMe)} with BF3OEt2, followed by PPh3, yields trans-[Cp(CO)2(PPh3)W{PN(Me)CH2CH2NMe(Me)}] BF4, suggesting that a cationic phosphenium complex is first formed and then migratory insertion of the phosphenium ligand into a W-alkyl bond takes place. In the reaction of the stannyl containing complex, Cp(CO)2(SnR3)W{PN(Me)CH2CH2N-Me(OMe)}, with TMSOTf, an alkyl migration from Sn to a phosphenium P occurs to give a stannylene complex.

Reactivity of a Cationic Phosphenium Complex of Tungsten Containing an Alkyl or a Stannyl Group

The treatment of Cp(CO)2MeW{PN(Me)CH2CH2NMe(OMe)} with BF3OEt2, followed by PPh3, yields trans-[Cp(CO)2(PPh3)W{PN(Me)CH2CH2NMe(Me)}] BF4, suggesting that a cationic phosphenium complex is first formed and then migratory insertion of the phosphenium ligand into a W-alkyl bond takes place. In the reaction of the stannyl containing complex, Cp(CO)2(SnR3)W{PN(Me)CH2CH2N-Me(OMe)}, with TMSOTf, an alkyl migration from Sn to a phosphenium P occurs to give a stannylene complex.

Allylmetal-directed addition of 1O2: Scope, mechanism and synthetic utility

Allylic silyl and stannyl groups strongly influence the regio- and stereochemistry of alkene oxygenations by 1O2, even within functionalized systems. Allylstannanes undergo anti-SE2′ oxygenation to form both Z-stannylalkenyl hydroperoxides and 4-stannyl-1,2-dioxolanes; the ene-like reaction is generally preferred unless limited by allylic strain. The alkenylstannane products, as well as the derived iodides, are effective substrates for palladium-mediated cross-couplings, additions, carbonylations, and acylations to form peroxydienes, peroxyenones, and peroxyenoates. Allylsilanes are less effective directing groups, possessing reactivity surprisingly similar to simple alkenes, and undergoing oxidation to form regioisomeric mixtures of hydroperoxides. The different reactivities and product distributions observed for allylstannanes and allylsilanes reflect different nucleophilicities of the ground state alkenes as well as variable polarization of the developing perepoxides by the neighboring C–Sn or C–Si bond. The observed selectivity for production of Z-alkenylmetals appears to result from the preferential formation of a single perepoxide pyramidal isomer and the tendency for this perepoxide to abstract the inside hydrogen on the metal-bearing carbon at a rate which is faster than either perepoxide inversion or single bond rotation to deliver the outside hydrogen for abstraction.

From 1,2,4-Triazines and Tributyl(ethynyl)tin to Stannylated Bi- and Terpyridines: The Cycloaddition Pathway

Recently, we reported on cycloadditions between electron-deficient heterodienes and tributyl(ethynyl)tin, which provide a new pathway to stannylated pyridazines and, in one special case, pyridines. In order to broaden the synthetic scope of these reactions, we have developed hetero [4+2] cycloaddition reactions between a number of tailor-made 1,2,4-triazines 5–9 (acting as heterodienes), and tributyl(ethynyl)tin (acting as dienophile). The desired 1,2,4-triazines are readily available, in moderate to very good yields, by the condensation reactions of appropiate carbamidrazones and glyoxals. These cycloadditions open up a novel route to regiospecifically stannylated 2,2′-bi- and 2,2′,6′,2′′-terpyridines 1–4, 11 in good yields. The stannanes 1–4, 11 are versatile synthetic intermediates, and with this strategy various substituents can be incorporated directly by substitution of the stannyl group, as was shown for halogens and carbon electrophiles under Stille conditions.

MonomericN-Lithioaryl- andN-Lithioborylstannylamines from Distannylamines

8-Aminoquinoline reacts with (dimethylamino)trimethylstannane in a 2:1 molar ratio, undergoing transamination to the distannylamine 1a. The 9-[bis(trimethylstannyl)amino]-9-borabicyclo[3.3.1]nonane (1b) is obtained by the stannazane cleavage reaction of tris(trimethylstannyl)amine with 9-chloro-9-BBN. The cleavage of one Sn–N bond of the distannylamines 1a and 1b with MeLi yields the first two monomeric N-lithioaminostannanes, 2a and 2b, which can be stored at ambient temperature without decomposition. The molecular structures of 1a, 1b, 2a, and 2b have been determined by multinuclear magnetic resonance spectra in solution, as well as by X-ray structure analysis. Characteristic features are the intramolecular adduct formation of the quinoline ring nitrogen atom with one of the stannyl groups in 1a, as well as with the lithium cation in 2a, and the surprisingly short bonds between the central nitrogen atom and the adjacent elements [d(NSn): 2.02 A, d(NB): 1.38 A, d(NC): 1.34 A, d(NLi): 1.95 A] detected in the molecular structures of the lithium salts.

Reactivity of the 1-azavinylidene cluster [Ru 3( μ-H)( μ-NCPh 2)(CO) 10] with hydrogen, tertiary silanes and tertiary stannanes

The reactivity of the 1-azavinylidene cluster [Ru 3( μ-H)( μ-NCPh 2)(CO) 10] ( 1) with hydrogen, tertiary silanes and tertiary stannanes has been investigated. The reaction of 1 with hydrogen (1 atm, 110°C) gives [Ru 4( μ-H) 4(CO) 12] and H 2NCHPh 2 as end-products, proceeding via the imido and amido intermediates [Ru 3( μ-H) 2( μ 3-NCHPh 2)(CO) 9] ( 2) and [Ru 3( μ-H)( μ-HNCHPh 2)(CO) 10] ( 3), respectively. Although no reaction is observed between compound 1 and tertiary organosilanes at 110°C, 1 reacts readily with tertiary organostannanes to give [Ru 3( μ-H) 2( μ-NCPh 2)(SnR 3)(CO) 9] ( 4: R=Ph; 5: R=Bu). 1H-NMR spectroscopy and the X-ray structure of the triphenylstannyl derivative 4 demonstrate that the addition of the stannane reagents to 1 takes place on the cluster metal framework. No transfer of the stannyl group from the metal to the azavinylidene ligand is observed at 110°C. This is in contrast with the results obtained in the hydrogenation of 1, where reduction of the azavinylidene ligand is observed under comparable reaction conditions.

An octahedral stannylmanganese stannylene complex

Treatment of decacarbonyldimanganese with the alkylarylstannylene RR′Sn ( 2), R=2,4,6- tBu 3C 6H 2, R′=CH 2C(CH 3) 2-3,5- tBu 2C 6H 3, furnishes the tetracarbonyl-stannylmanganese stannylene complex 3, in which the tin atom of the stannyl group is part of a stannaindan ring system. Reaction of 2 with [(OC) 2Fe(NO) 2] yields the tetrahedral iron stannylene complex [OC(NO) 2Fe=SnRR′] ( 4). The structures of 3 and 4 were determined by X-ray crystallography.

Direct Observation of a Stannyl Radical in the Reactions of the Tributylstannyl Anion with Alkyl Halides by a Stopped-Flow Technique

The reaction intermediate in reactions of the tributylstannyl anion with alkyl halides in THF was studied by a stopped-flow technique. The tributylstannyl radical was observed directly in the reactions of sec- and tert-butyl bromides and iodides. Generation of the stannyl radical suggests that electron transfer from the stannyl anion to alkyl halides is taking place.

Synthesis and Characterization of the First Niobocene Germyl Complexes and Reactivity of Triphenylsilyl-, Triphenylgermyl-, and Triphenylstannylniobocene Derivatives. X-ray Molecular Structures of d0 Nb(η5-C5H4SiMe3)2(H)2(EPh3) (E = Ge, Sn)

Thermal treatment of Nb(η5-C5H4SiMe3)2(H)3 (1) with the appropriate organogermanium hydrides (HGeR3) and HSnPh3 gives the corresponding niobocene germyl hydrides Nb(η5-C5H4SiMe3)2(H)2(GeR3), GeR3GePh3 (2), GePh2H (3), GeEt3 (4), Ge(C6H13)3 (5), GeiAm3 (iAm = CH2CH2CH(CH3)2) (6), Ge(C6H13)2Cl (7), GeiAm2Cl (8), Ge(C6H13)2H (9), GeiAm2H (10), and Nb(η5-C5H4SiMe3)2(H)2(SnPh3) (11) in good yields. Spectroscopic data indicate the presence of only one of the two possible structural isomers in which the germyl or stannyl group is in the equatorial plane with a symmetrical structure. Reactivity studies on the series Nb(η5-C5H4SiMe3)2(H)2(ER3), E = Si (12), Ge (2), Sn (11), were carried out. 12 reacts with H2 to give 1, but 2 and 11 were unreactive toward this reagent. Furthermore, a similar behavior was observed with CO and CN(2,6-Me2C6H3). Thus, 12 reacts with these reagents to give rise, after elimination of HSiPh3, to Nb(η5-C5H4SiMe3)2(H)(CO) and Nb(η5-C5H4SiMe3)2(H)(CN(2,6-Me2C6H3)), respectively, while 2 and 11 do not react. Reactions of 12 with HGePh3 and HSnPh3 and of 2 with HSnPh3 gave σ-bond metathesis products, but no reactions were observed between 2 and HSiPh3 or between 11 and HSiPh3 or 11 and HGePh3. The kinetics of these processes have been studied by 1H NMR spectroscopy and indicated the following reactivity trends Nb−SiPh3 > Nb−GePh3 > Nb−SnPh3 for the different processes considered. The X-ray molecular structures of 2 and 11 were established by diffraction studies. The two isostructural complexes show a bent-sandwich coordination with the two hydrides flanking either side of the Nb−Ge and Nb−Sn bonds (2.710(1), 2.830(1) Å in 2 and 11, respectively).

Equilibria in Free-Radical Chemistry: An Ab Initio Study of Hydrogen Atom Transfer Reactions between Silyl, Germyl, and Stannyl Radicals and Their Hydrides

Ab initio calculations using a (valence) double-ζ pseudopotential (DZP) basis set, with (MP2, QCISD) and without (SCF) the inclusion of electron correlation, predict that the reactions of silyl, germyl, and stannyl radicals with silane, germane, stannane, trimethylsilane, trimethylgermane, and trimethylstannane proceed via transition states of C3v or D3d symmetry in which the attacking and leaving radical centers adopt a collinear arrangement. For reactions involving •SiH3, •GeH3 and •SnH3, energy barriers of between 23.4 (•SiH3 + SnH4) and 86.0 (•SnH3 + SiH4) kJ•mol-1 are predicted at the QCISD/DZP//MP2/DZP (+ ZPVE) level of theory. Specifically, the identity exchange reaction involving silane and the silyl radical is predicted to involve an energy barrier of some 53.6 kJ•mol-1 at the highest level of theory, in good agreement with the available experimental data. The similar reactions involving germyl (•GeH3 + GeH4) and stannyl radicals (•SnH3 + SnH4) are predicted to have energy barriers of 47.0 and 38.9 kJ•mol-1, respectively, at the same level of theory. Inclusion of alkyl substitution on one of the heteroatoms in each reaction serves to alter the position of the hydrogen atom undergoing translocation in the transition state when compared with the unsubstituted series; the reactions of H3Y• with Me3XH become “later” when compared with the analogous parent reaction (H3Y• with XH4). Energy barriers of between 23.8 (•SiH3 + Me3SnH) and 98.3 (•SnH3 + Me3SiH) kJ•mol-1 are predicted at the MP2/DZP (+ ZPVE) level of theory. The mechanistic implications of these computational data are discussed.

Steric acceleration in the reaction of aryl bromides with tributylstannyl radicals

Approximate absolute rate constants for the abstraction of bromine from a series of aryl bromides by stannyl radicals have been determined: 2,4,6-tri-tert-butylbromobenzene and 2,4,6-triphenylbromobenzene are found to be unusually reactive, most likely owing to steric acceleration.

Sulfones as Radical Progenitors: An Unprecedented Example of Homolytic Sulfone Cleavage Facilitated by o-Stannyl Substitution of Aryl Sulfones(1).

Allylic aryl sulfones bearing an o-allyldialkylstannyl moiety (1b), when converted to stannyl radical 1a, suffer homolytic cleavage via intramolecular attack of the stannyl radical on the sulfone. Allyl radicals generated in this manner can be utilized for further intramolecular radical cyclizations; thus the overall transformation can be viewed as an alkylative desulfonylation reaction. Previously unknown sulfonyl stannane polymer 5 is generated as a byproduct. The o-dibutylstannyl radical derived from nonallylic aryl sulfone 15 does not suffer homolysis but instead forms 9-membered macrocycle 19 via an intramolecular reaction with the phenylacetylene group.

Generation of α-Alkylthio Radicals by Photoinduced One-Electron Oxidation of α-Stannyl Sulfides and Their Use for Carbon-Carbon Bond Formation

Abstract Cation radicals, generated from α-stannyl sulfides by the photoinduced single electron transfer, cleave into α-alkylthio radical intermediates with the elimination of the stannyl group. The α-alkylthio radicals thus formed are utilized for carbon-carbon bond forming reactions.

On the radical Brook and related reactions: an ab initio study of some (1,2)-silyl, germyl and stannyl translocations

Ab initio molecular orbital calculations using a (valence) double-ζ pseudopotential basis set (DZP) with (MP2, QCISD) and without (SCF) the inclusion of electron correlation predict that the transition states (12–14) involved in homolytic (1,2)-translocation reactions of silyl (SiH3), germyl (GeH3) and stannyl (SnH3) groups between carbon centres, between carbon and nitrogen, and between carbon and oxygen proceed via homolytic substitution mechanisms involving front-side attack at the group (IV) heteroatom. While migrations between carbons are predicted to be unlikely, with calculated activation barriers of 71–137 kJ mol–1, depending on the level of theory, migrations from carbon to nitrogen and from carbon to oxygen are predicted to be facile. For example, rearrangement of the (silylmethyl)aminyl radical (H3SiCH2NH˙) to the silylaminomethyl species (H3SiNHCH2˙) is predicted to proceed with a barrier of 50.8–63.2 kJ mol–1 when electron correlation is included, in excellent agreement with experimental data. In addition, the analogous translocation to oxygen in the silylmethoxyl radical (H3SiCH2O˙), the prototypical radical Brook rearrangement, is calculated to require only 19.9 kJ mol–1 at the MP2/DZP + ZPVE level. Somewhat unexpectedly, MP2/DZP calculations predict that the stannylmethoxyl radical (H3SnCH2O˙) rearranges to the stannyloxymethyl radical (H3SnOCH2˙) without barrier.

An Unexpected Trimethylstannylpyrrole from a Stannylated Derivative of Tosylmethyl Isocyanide (TosMIC) and Chalcone

The structure of the title compound, tert-butyl 3-benzoyl-4-phenyl-2-(trimethylstannyl)pyrrole-N-carboxylate, [Sn(CH3)3(C22H20NO3)], is one of the first in which the stannyl group is attached to a C atom of the pyrrole ring. There appears to be an intramolecular interaction between the Sn atom and the carbonyl O atoms of both the benzoyl and the tert-butoxycarbonyl substituents. The compound was prepared by a base-induced cycloaddition of a stannylated derivative of tosylmethyl isocyanide to chalcone.