Sulfinylamid-Metathese und Nitren-Transfer an Komplexen des sechswertigen Molybdäns und Wolframs

Sulfinylamide Metathesis and Nitrene Transfer at Complexes of Hexavalent Molybdenum and Tungsten Protolysis of tungsten hexachloride with tosyl amide offers a direct access to [W(NTos)₂Cl₂]_n ( 1 a) . In presence of donor ligands coordination polymer 1 a can be converted into molecular complexes, e. g. [W(NTos)₂Cl₂(dme)] ( 1 b ), [W(NTos)₂Cl₂(PMe₃)₂] ( 1 c ) and [W(NTos)₂Cl₂(4,4′-Me₂bipy)] ( 1 d ). The synthesis of the homologous molybdenum compound [Mo(NTos)₂Cl₂]_n ( 2 a) can be achieved via metathesis of [Mo(O)₂Cl₂]_n with sulfinyl amide Tos-NSO. An attempt to synthesize a molybdenum phosphine complex in an analogous manner as 1 c , but starting from 2 a or its base adduct [Mo(NTos)₂Cl₂(dme)] ( 2 b ), leads to nitrene transfer to the phosphine. Me₃P=NTos can be detected and the d² molybdenum complex [Mo(NTos)Cl₂(PMe₃)₃] ( 3 ) is isolated. 3 is characterized by a crystal structure analysis. In phosphine complex 1 c , a similar nitrene abstraction is inhibited, in contrast 1 d is reacting with PMe₃ under nitrene abstraction to yield [W(NTos)Cl₂(4,4′-Me₂bipy)(PMe₃)₂] ( 4 ). This observation is in accord with a nitrene transfer induced via direct attack of the phosphine on the nitrogen atom of 1 d .     

Komplexe des Chroms und Molybdäns mit Aminoarsan-Liganden. III

Complexes of Chromium and Molybdenum with Aminoarsanes as Ligands. III The reaction of the norbornadien complexes (CO)₄MC₇H₈ (M = Cr, Mo) with aminoarsanes Me_mAs(NMe₂)_n (m = 2, 1; n = 1, 2) is examined. The substitution reaction results in the formation of complexes of the formula cis-(CO)₄M(aminoarsane)₂. These complexes rearrange to a mixture of hexacarbonyles M(CO)₆ and monosubstituted complexes (CO)₅M-aminoarsane. The cleavage of the As? N bond in the coordinated aminoarsane ligand with acid molecules as ethanol, thioethanol, or glycol yields complexes of the type (CO)₄M[AsMe_n)? X_m]₂.     

Carbonyl-Monoolefin-Derivate des Chroms,Molybdäns und Wolframs. I. Tetracarbonyl-Phosphin-Olefin-Komplexe

Carbonyl Monoolefin Derivatives of the Group VI Transition Metals. I. Tetracarbonyl Phosphine Olefin Complexes Monoolefin complexes cis-M(CO)₄(PR₃)(olefin) (M ? Cr, Mo, W; R ? Et, Bu, Prⁱ, Ph; olefin ? maleic anhydride, dimethyl maleate, dimethyl fumarate, bis(trimethylsilyl) fumarate, ethylene) are obtained from the ionic compounds Et₄N[R₃PM(CO)₄Cl] either via ethanol or acetonitrile derivatives M(CO)₄(PR₃)L, or directly in a two phase system. The olefins are displaced by Lewis-bases such as amines or phosphines under mild conditions.     

Komplexe des Chroms,Molybdäns und Wolframs mit Aminoarsan-Liganden

Complexes of Chromium, Molybdenum, and Tungsten with Aminoarsanes as Ligands The aminoarsanes Me₂As? NMe₂, MeAs(NMe₂)₂, and As(NMe₂)₃ form with the carbonyles of the sub-group VI metals complexes of the general formula (CO)₅M? L (L = aminoarsane; M ? Cr, Mo, W). The cleavage of the As? N bond by reactions with acids HX results in the formation of complexes of the general formula (CO)₅M? As(Me₂)? X, (CO)₅M? As(Me)X₂, and (CO)₅M? AsX₃.     

Komplexe des Chroms,Molybdäns und Wolframs mit Aminoarsan-Liganden. II [1]

Complexes of Chromium, Molybdenum, and Tungsten with Aminoarsanes as Ligands. II The cleavage of the As? N bond in aminoarsane ligands with acids is examined and the reactivity of the As? N bond in the aminoarsane molecule and in the aminoarsane ligand is compared. The results confirme the σ-donor-π-acceptor model of the complex bonding as well as the mechanism of the cleavage of the As? N bond.     

Substituierte Halogenocarbonylmetallate des Chroms,Molybdäns und Wolframs. IV. Die Kristallstruktur von Tetramethylammonium-Chloropentacarbonylwolframat

Substituted Halocarbonyl Metallates of Chromium, Molybdenum, and Tungsten. IV. Crystal Structure of Tetramethylammonium Chloropentacarbonyltungstate The structure of tetramethylammonium chloropentacarbonyltungstate has been determined from single crystal X-ray data. The compound crystallizes with four formula units in the monoclinic unit cell (space group P2₁/c) of the dimensions a = 1111.3(4) pm, b = 1110.3(4) pm c = 1204.1(3) pm, β = 99.63(3)°, V = 1464.8 × 10⁶ pm³ (R = 0.028). The anion possesses approximately C_4v symmetry with the principal interatomic distances d(W–C(cis)) = 203 pm, d(W–C(trans)) = 197 pm d(W–Cl) = 256.6 pm. No unusual contacts between cation and anion have been found.     

Penicillamin-Komplexe des Nickels,Chroms und Molybdäns — Strukturelle Besonderheiten und biologische/medizinische Relevanz

Penicillamine Complexes of Nickel, Chromium, and Molybdenum — Structural Particularity and Biological/Medical Relevance The compounds Tl₂[Ni^II(H₂O)₆][Ni^II(D-pen)(L-pen)]₂[Ni^II(SCN)₂(H₂O)₄] 1 , Tl[Ni^II(D-pen)₂H] · H₂O 2 , Tl[Cr^III(D-pen)₂] 3 , and Na₂[MoO₄(pen)₂] · 3 CH₃OH · 3 H₂O 4 have been prepared by the reaction of nickel nitrate (for 1 ), nickel acetate (for 2 ), potassium chromate (for 3 ), and sodium molybdate (for 4 ) with D- and D, L-penicillamine, respectively. They were characterized by single-crystal X-ray structure analysis and other physical methods. Whereas penicillamine acts as a bidentate (N, S)-ligand in 1 and 2 , Cr^III (in 3 ), and Mo^V (in 4 ) are coordinated to the three ligand atoms N, O, and S. The presence of three different types of Ni^II-complexes a cationic, a neutral, and an anionic one in 1 is remarkable. For crystal data see Inhaltsübersicht.     

Phosphinsubstituierte Chelatliganden. XVIII. Penta- und Tetracarbonylmetall-Komplexe des Chroms,Molybdäns und Wolframs mit sekundären und tertiären Phosphinothioformamid-Liganden

Phosphine Substituted Chelate Ligands. XVIII. Penta- and Tetracarbonylmetal Complexes of Chromium, Molybdenum, and Tungsten with Secondary and Tertiary Phosphinothioformamide Ligands Mono- and bidentately coordinated phosphinothioformamide complexes are obtained by photochemical substitution of the metal hexacarbonyls M(CO)₆ (M ? Cr ( a ), Mo ( b ), W ( c )). The M(CO)₅ · THF adducts react with secondary thioamides under exclusion of light to give the P-coordinate pentacarbonyl complexes [(CO)₅MPPh₂C(S)NHR¹] (R¹ ? Ph ( 1a – c ), Me ( 2a )). The photoreaction of M(CO)₅ · THF with secondary and tertiary thioamides at low temperatures leads to the formation of the P, S-chelate complexes . The corresponding N-silylated complexes 6a – c (R¹ ? Me₃Si, R² ? Ph) are obtained by direct photosubstitution of M(CO)₆ in cyclohexane solution. The labile bis(thioformamide) complexes [(CO)₄M(PPh₂C(S)NHMe)₂] ( 7a – c , cis-trans isomers) are synthesized in low yields according to the same procedure. The attempted alkylation of the chelate complexes 3a – c remains unsuccessful, whereas the secondary thioformamides react with n-BuLi/CH₂Br₂ to give the methylene bis(thioformirnidoesters) [Ph₂PC(NR¹)S]₂CH₂ (R¹ ? Ph (8), Me ( 9 )) in quantitative yields.     

Chlorthionitrenkomplexe des Molybdäns

Chlorothionitrene Complexes of Molybdenum Molybdenum pentachloride reacts with trimer thiazylchloride, (NSCl)₃, forming the chlorothionitrene complex \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm Cl}_4 {\rm Mo} = \mathop {\rm N}\limits^ \oplus = \mathop {{\rm SCl}}\limits^ \ominus $\end{document}, in which the chlorothionitrene ligand is to be understood as (NSCl)^2? group. I reacts with phosphorylchloride forming the solvate Cl₃PO? Mo(Cl₄)(NSCl) ( II ) that can also be obtained directly from MoCl₅ · OPCl₃ and trithiazylchloride. II reacts with chloride ions giving the anionic chlorothionitrene complex [Cl₅Mo(NSCl)]? ( III ). Thermal decomposition of I leads to MoNCl₃ under SCl₂ cleavage, while reaction of I with chloride ions gives [MoNCl₄]?. Both reactions prove chlorothionitrene complexes to be excellent precursors for the syntheses of nitrido complexes. The complexes I—III have been characterized by IR spectroscopy.     

Neue Calix[4]aren‐Komplexe des vierwertigen Molybdäns

Novel Calix[4]arene Complexes of Tetravalent Molybdenum The reaction of p‐tert.‐Butylcalix[4]aren Cax(OH)₄ with [Mo(NMe₂)₄] in equimolar amounts at 80°C in toluene affords after extraction into acetonitrile a mixture of [CaxO₄Mo(NHMe₂)(NCMe)] ( 1(NCMe) ) and [(CaxO₄Mo)₂(NCMe)₂] ( 2(NCMe)₂ ). If the same reaction is carried out in acetonitrile or in mixtures of toluene and acetonitrile instead of toluene, the formation of 2(NCMe)₂ is suppressed and only 1(NCMe) has been isolated. Both compounds have been characterized by X ray crystal structure determinations. 1(NCMe) : space group: C2/c, lattice constants: a = 37, 987(8)Å, b = 13, 012(3)Å, c = 20, 271(4)Å, β = 103, 39°; 2(NCMe)₂ : space group: P2₁/n, lattice constants: a = 11, 937(2)Å, b = 21, 078(4)Å, c = 19, 620(4)Å, β = 107, 31(3)°. The molybdenum atom in 1(NCMe) is coordinated with four oxygen atoms of the calix[4]arene ligand, a nitrogen atom of the amine ligand, and the nitrogen atom of the endohedrally coordinated acetonitrile molecule in a slightly distorted octahedron. Two of these monomer units are linked via hydrogen bridges. In 2(NCMe)₂ two complex fragments [CaxO₄Mo(NCMe)] are linked via phenolate units of the calix[4]arene. The Mo‐Mo′ distance of 261.2(1)pm is in accordance with a Mo‐Mo double bond. EH‐, DFT‐, und MP2‐ calculations have been performed on model complexes [CaxO₄Mo(NH₃)(NCH)] ( 1′(NCH) ) and [(p‐H‐CaxO₄Mo)₂(NCH)₂] ( 2′(NCH)₂ ) for a closer inspection of the binding in these compounds. The results of the calculations suggest that addition of the electron rich, basic oxygen atom is the structure determining feature of 2′(NCH)₂ and not a metal metal bond.     

[MoN(NPPh3)3] – ein monomerer Nitrido-Komplex des Molybdäns

[MoN(NPPh₃)₃] – a Monomeric Nitrido Complex of Molybdenum [MoN(NPPh₃)₃] ( 1 ) has been prepared from [MoCl₃(N₃S₂)]₂ and LiNPPh₃ in toluene suspension in good yields. From n-hexane/dichloromethane solutions 1 · 2 CH₂Cl₂ crystallizes as colourless single crystals, which were suitable for a crystal structure determination. 1 forms monomeric molecules with a Mo≡N distance of 166.6 pm for the nitrido ligand, which corresponds to a triple bond, and MoN-bonds of 193.6 pm on average of the NPPh₃^–-ligands, corresponding to shortened single bonds.     

Heterobimetallische Komplexe mit Chelatliganden aus mehrzähnigen Aminen und 1,1-Bis(diphenylphosphan)ethen

Heterobimetallic Complexes with Chelate Ligands from Multidentate Amines and 1,1-Bis(diphenylphosphine)ethene By an addition reaction of bidentate amines Me₂N(CH₂)_nNH₂ (n = 2, as-4C2N; 3, as-5C2N) and vinylidene derivatives with an activated double bond CH₂ = C(PPh₂)₂M(CO)₄ (M = Cr, Mo, W) were synthesized in dichlormethane unsymmetrical chelate ligands of the type as-4C2N (or as-5C2N)PPM(CO)₄. They gave with divalent salts M′Y₂ (Y = ac, M′ = Cu, Ni. Y = Cl, M′ = Zn, Cd, Hg) the coloured bimetallic complexes M′Y(as-4C2N) (or as-5C2N)PPM(CO)₄ which were characterized by means of IR-, UV/VIS spectroscopic and ¹H, ¹³C and ³¹P NMR measurements. The molecular structures of the complexes Cuac₂(as-5C2N)PPCr(CO)₄, I and that of CdCl₂(as-4C2N)PPCr(CO)₄, II , were acertained by results of single crystal X-ray determinations. In the crystals of I—II , the coordination polyhedron of each chromium(0) central atom containing two phosphorous donor atoms in a four-membered chelate ring and four terminal CO ligands is octahedrally distorted. This coordination sphere is connected at the carbon ring atom via a methylen chain group (spacer) with the bidentate amine ligand, which has a secondary and a tertiary nitrogen donor atom. Both nitrogen atoms are coordinated with the Cuac₂ under formation of a new kind of [4 + 2]-coordination in a trischelate complex. The six-membered diamine chelat ring in I has a chair-like conformation. The chromium-cadmium complex II is dimer from which the Cd central atoms obtain the rare coordination number of five. The related five-membered diamine chelate ring has δ conformation.     

Diimido‐, Imido(oxo)‐, Dioxo‐ und Imido(alkyliden)‐Halbsandwich‐Verbindungen über selektive Hydrolyse und α—H‐Abstraktion an Organylkomplexen des sechswertigen Molybdäns und Wolframs

Diimido, Imido Oxo, Dioxo, and Imido Alkylidene Halfsandwich Compounds via Selective Hydrolysis and α—H Abstraction in Molybdenum(VI) and Tungsten(VI) Organyl Complexes Organometal imides [(η⁵‐C₅R₅)M(NR′)₂Ph] (M = Mo, W, R = H, Me, R′ = Mes, tBu) 4 — 8 can be prepared by reaction of halfsandwich complexes [(η⁵‐C₅R₅)M(NR′)₂Cl] with phenyl lithium in good yields. Starting from phenyl complexes 4 — 8 as well as from previously described methyl compounds [(η⁵‐C₅Me₅)M(NtBu)₂Me] (M = Mo, W), reactions with aqueous HCl lead to imido(oxo) methyl and phenyl complexes [(η⁵‐C₅Me₅)M(NtBu)(O)(R)] M = Mo, R = Me ( 9 ), Ph ( 10 ); M = W, R = Ph ( 11 ) and dioxo complexes [(η⁵‐C₅Me₅)M(O)₂(CH₃)] M = Mo ( 12 ), M = W ( 13 ). Hydrolysis of organometal imides with conservation of M‐C σ and π bonds is in fact an attractive synthetic alternative for the synthesis of organometal oxides with respect to known strategies based on the oxidative decarbonylation of low valent alkyl CO and NO complexes. In a similar manner, protolysis of [(η⁵‐C₅H₅)W(NtBu)₂(CH₃)] and [(η⁵‐C₅Me₅)Mo(NtBu)₂(CH₃)] by HCl gas leads to [(η⁵‐C₅H₅)W(NtBu)Cl₂(CH₃)] 14 und [(η⁵‐C₅Me₅)Mo(NtBu)Cl₂(CH₃)] 15 with conservation of the M‐C bonds. The inert character of the relatively non‐polar M‐C σ bonds with respect to protolysis offers a strategy for the synthesis of methyl chloro complexes not accessible by partial methylation of [(η⁵‐C₅R₅)M(NR′)Cl₃] with MeLi. As pure substances only trimethyl compounds [(η⁵‐C₅R₅)M(NtBu)(CH₃)₃] 16 ‐ 18 , M = Mo, W, R = H, Me, are isolated. Imido(benzylidene) complexes [(η⁵‐C₅Me₅)M(NtBu)(CHPh)(CH₂Ph)] M = Mo ( 19 ), W ( 20 ) are generated by alkylation of [(η⁵‐C₅Me₅)M(NtBu)Cl₃] with PhCH₂MgCl via α‐H abstraction. Based on nmr data a trend of decreasing donor capability of the ligands [NtBu]^2— > [O]^2— > [CHR]^2— ? 2 [CH₃]^— > 2 [Cl]^— emerges.     

Oxo-Phosphaniminato-Komplexe von Molybdän und Wolfram. Die Kristallstrukturen von [Mo(O)2(NPPh3)2] und [WO(NPPh3)3]2[W6O19]

Oxo-phosphoraneiminato Complexes of Molybdenum and Tungsten. Crystal Structures of [Mo(O)₂(NPPh₃)₂] and [WO(NPPh₃)₃]₂[W₆O₁₉] The dioxo-phosphoraneiminato complexes [Mo(O)₂(NPPh₃)₂] ( 1 ) and [W(O)₂(NPPh₃)₂] ( 2 ) originate from hydrolysis of the nitrido complexes [MN(NPPh₃)₃] (M = Mo, W). They form colourless crystals, which are characterized by IR and NMR spectroscopy as well as by mass spectrometry. According to the crystal structure analysis of 1 (space group Fdd2, Z = 8; lattice dimensions at –83 °C: a = 1953.3(1), b = 3275.8(3), c = 953.4(1) pm) there are monomeric molecules with tetrahedrally coordinated molybdenum atoms. The distances MoO of 171.2 pm and MoN of 185.9 pm correspond to double bonds. In dichloromethane solution 2 undergoes further hydrolysis with colourless crystals of [WO(NPPh₃)₃]₂[W₆O₁₉] ( 3 ) originating, which are characterized crystallographically (space group Pbcn, Z = 4; lattice dimensions at –50 °C: a = 3225.1(6), b = 1803.6(3), c = 1811.9(3) pm). 3 consists of cations [WO(NPPh₃)₃]⁺ with tetrahedrally coordinated tungsten atoms and of the known [W₆O₁₉]^2– anions. The tungsten atoms of the cations show distances WO of 171.8 pm and WN of 182 pm which correspond to double bonds as in 1 .     

Sigma‐ versus Pi‐Koordination in Bis‐indenyl‐ und Bis‐2‐methallyl‐Imidokomplexen des sechswertigen Molybdäns und Wolframs: DF‐Rechnungen und Kristallstrukturanalyse

Sigma‐ versus Pi‐Coordination in Bis‐indenyl‐ and Bis‐2‐methallyl Imido Complexes of Hexavalent Molybdenum and Tungsten: DF‐Calculations and Crystal Structure Analysis Bis‐indenyl and bis‐2‐methallyl imido complexes [(C₉H₇)₂M(NR)₂] (M = Mo, W; R = tert‐butyl, mesityl) 1 — 4 and [(H₃C‐C₃H₄)₂M(NtBu)₂] (M = Mo, W) 6 , 7 have been prepared starting from [Mo(NtBu)₂Cl₂] or [M(NR)₂Cl₂L₂] (M = W, R = tBu, L = py; M = Mo, W, R = Mes, L₂ = dme) and indenyl lithium or 2‐methallyl magnesium bromide, respectively. According to spectroscopic data and the crystal structure of 4 there are two different coordination modes of the indenyl ligands, [(η³‐C₉H₇)M(NR)₂(η¹‐C₉H₇)], in solution as well as in the solid state. These compounds show fluxional rearrangements in solution, namely σ, π‐exchange of η¹‐ and η³‐coordinated ligands. Similar behavior has been observed for the 2‐methallyl complexes 6 and 7 in solution. In agreement with experimental observations, DF calculations on models of 6 strongly suggest a (σ+π)‐coordination mode of the η³‐coordinated ligand.     

Zur Reaktion von tert-Butyl-phosphaalkin mit Molybdänkomplexen

Reaction of tert -Butyl-phosphaalkyne with Molybdenum Complexes The reaction of tBuC≡P with [(CH₃CN)₃Mo(CO)₃] leads to the complex [Mo(CO)₄〈Mo(CO)₂(η⁴-P₃CtBu){η⁴-P₂(CtBu)₂}〉] 1 as well as to the alkyne complexes [Mo(CO)₄〈{P₃(CtBu)₂}{Mo(CO)₂(CtBu)}{η³-P₂(CtBu)₂}〉] 2 and [Mo(CtBu){η⁴-P₂(CtBu)₂(CO)}{η⁵-P₃(CtBu)₂}] 3 . All compounds are characterized by X-ray structural analysis, by NMR- and IR spectroscopy and by mass spectrometry. In complex 1 a 1,3-diphosphacyclobutadiene and a 1,2,4-triphosphacyclobutadiene are connected by two molybdenum carbonyl centres. In 2 a 1,3-diphosphacyclobutadiene is π- and a novel 1,2,4-triphospholyl ligand is σ-bonded at two Mo centres. A characteristic feature of 3 besides a π co-ordinated 1,2,4-triphospholyl ligand is a 3,4-diphosphacyclopentadienone as ligand, formed via CO insertion during the cyclodimerisation of two phosphaalkynes.     

Carbonyl‐Komplexe von Chrom,Molybdän und Wolfram mit Isocyanacetat. Reaktionen am koordinierten Isocyanacetat. Stabilisierung von Isocyanessigsäure und Isocyanacetylchlorid am Metall. Isocyanopeptide [1]

Carbonyl Complexes of Chromium, Molybdenum and Tungsten with Isocyano Acetate. Reactions of Coordinated Isocyanoacetate. Stabilization of Isocyanoacetic Acid and Isocyanoacetyl Chloride at the Metal Atom. Isocyanopeptides The reactions of [(OC)₅MCNCH₂CO₂Et] (M = Cr, W) with Na[N(SiMe₃)₂] or with KOH afford the isocyanoacetate complexes [(OC)₅MCNCH₂CO₂]^? ( 1,2 ). Similarly, the complex [(OC)₃Mo(CNCH₂CO₂^?Li⁺)₃] ( 4 ) was obtained from [(OC)₃Mo(CNCH₂CO₂Et)₃] ( 3 ) and LiOH. Protonation of 1 and 2 affords the sublimable isocyanoacetic acid complexes [(OC)₅MCNCH₂CO₂H] ( 5 , 6 ; M = Cr, W) in which the functional isocyanide is stabilized at the metal atom. Reactions of [(OC)₅WCNCH₂CO₂^?K⁺] and of [(OC)₃Mo(CNCH₂CO₂^?Li⁺)₃] with oxalyl dichloride give the isocyanoacetyl chloride compounds [(OC)₅WCNCH₂COCl] ( 9 ) (sublimable) and [(OC)₃Mo(CNCH₂COCl)₃] ( 10 ); the latter ( 10 ) was not isolated. Complexes 9 and 10 were reacted in situ with β‐alanine, glycine, phenylalanine and methionine esters as well as the peptide esters GlyGlyOEt, PhePheOMe, Phe‐β‐AlaOMe, and GlyGlyGlyOMe to form the isocyanoacetyl amino acid esters ( 11 ‐ 14 ) and the isocyanoacetyl peptide esters ( 15 ‐ 18 ) which are stabilized at the molybdenum atom.     

Verbindungen des Germaniums und Zinns. 3. Sterisch überladene Alkylarylstannane durch Übertragung und Isomerisierung von 2,4,6-Tri-tert-butylphenylgruppen

Compounds of Germanium and Tin. 3. Sterically Congested Alkylarylstannanes by Transfer and Isomerization of 2,4,6-Tri-tert-butylphenyl Groups Reaction of SnBr₄ and SnI₄ with 2,4,6-tri-tert-butylphenyllithium (ArLi) by rearrangement of two Ar-groups gives the stannanes ArR₂SnBr ( 3 ) and ArR₂SnI ( 4 ), R = 2-methyl-2(3,5-di-tert-butylphenyl)propyl, which by a further transalkylation reaction with methyl lithium yield ArR₂SnCH₃ ( 5 ). However, treatment of 3 and 4 with tert-butyl lithium exclusively leads to ArR₂SnH ( 6 ) which surprisingly is also obtained by reaction of ArRSnCl₂ with tert-butyl lithium, presumably by an intermolecular R-group transfer. The structures of 5 and 6 were confirmed by X-ray crystallography.