Hydrogen can be selectively removed from organotin trihydrides to generate the corresponding organohydrostannylene intermediates. Depending on the size of the substituent and the mode of generation, the intermediates undergo further reactions. Herein, we report on the formation of a variety of organotin hydrides with tin in the oxidation states Sn(II) , Sn(I) -Sn(III) and Sn(III) -Sn(III) , all accessed by the controlled removal of hydrogen from the tetravalent Ar'Sn(IV) trihydride (Ar'=2,6-dimesitylphenyl, mesityl=2,4,6-trimethylphenyl).
Alkyltin trihydride [(Me Si) CHSnH ] was synthesized and the reductive elimination of hydrogen from this species was investigated. A methyl-substituted N-heterocyclic carbene reacts with the organotrihydride in dependence on stoichiometry and solvent to give a series of products of the reductive elimination and dehydrogenative tin-tin bond formation. Besides characterization of the carbene adduct of the alkyltin(II) hydride, a Sn chain was also isolated, encompassing two stannyl-stannylene sites, which are stabilized each as NHC-adducts. Complete dehydrogenation resulted to give either a carbene-stabilized distannyne or a metalloid Sn -cluster salt. Reductive elimination of hydrogen was also achieved with an excess of diethylmethylamine to give the alkyltin(II) hydride as a Lewis base free tetramer [(RSnH) ]. The method of cluster formation at low temperatures by hydrogen elimination was also transferred to the mesityl-substituted tin trihydride MesSnH . In this case [(MesSn) ], showing a [5]prismane structure, was isolated in good yield and characterized. NMR spectroscopic features of the propellane-type cluster [Trip Sn ] are reported.
Bulkily substituted organodihydrogermylium and ‐stannylium cations [Ar*EH2]+ (E=Ge, Sn; Ar*=2,6‐Trip2C6H3, Trip=2,4,6‐triisopropylphenyl) were characterized as salts of the weakly coordinating perfluorinated alkoxyaluminate anion [Al{OC(CF3)3}4]−. At room temperature, the stannylium cation liberates hydrogen to generate the low valent organotin cation [Ar*Sn]+. In contrast, the dihydrogermylium cation transfers the hydrogen atoms to an aryl moiety of the terphenyl ligand and oxidatively adds either hydrogen under an atmosphere of hydrogen or a sp2 CH unit of the 1,2‐difluorobenzene solvent.
The reaction of NHC (NHC = 1,3,4,5-tetramethylimidazolylidene, where NHC = N-heterocyclic carbene) adducts to organotin(II) hydrides Ar*SnH and Ar'SnH [Ar* = 2,6-TripCH, where Trip = 2,4,6-triisopropylphenyl; Ar' = 2,6-MesCH, where Mes = 2,4,6-trimethylphenyl)] with Lewis acids such as B(CF) or [CPh] allows the abstraction of hydride and thus the generation of cationic, dicoordinate bis(σ-C)-substituted stannylenes [ArSn(NHC)]. The supposedly dicoordinate constitution of this cationic stannylene was investigated by NMR spectroscopy and further supported by density functional theory computations. For Ar'SnH(NHC), the generated cation was found to be inadequately sterically encumbered, allowing the formation of an adduct, [Ar'(NHC)Sn-Sn(H)(NHC)Ar'], which can be described as the protonated bis(NHC) adduct to the formal 1,2-distannyne.
A bulky substituted stannane Ar*SnH (Ar*=2,6-(2',4',6'-triisopropylphenyl)phenyl) was treated with the well-known frustrated Lewis pair (FLP) PtBu /B(C F ) in varying stoichiometries. To some degree, hydride abstraction and adduct formation is observed, leading to [Ar*SnH (PtBu )] which is rather unreactive toward further dehydrogenation. In a competing process, the FLP proved to be capable of completely striping-off hydrogen and hydrides to generate the first cationic phosphonio-stannylene [Ar*Sn(PtBu )] . This behavior provides insight into the activation/abstraction mechanism processes involved in these Group 14 hydride derivatives.
Adamantylisonitrile and benzonitrile were reacted with bulky substituted organotin trihydride [Ar*SnH 3 ] [Ar* = (C 6 H 3 -2,6-Trip 2 ), Trip = 2,4,6-triisopropylphenyl]. They do not show any reaction at room temperature as well as at 80 °C. After activation of the organotin trihydride with diethylmethylamine in the isonitrile case three hydrogen atoms were transferred from the tin atom to the isonitrile unit and a carbon tin bond was formed to give an intramolecular adduct between a diorganostannylene and a dialkylamine. Benzonitrile as well as adamantylisonitrile react both with low-valent organotin hydride [Ar*SnH] 2 . Benzonitrile shows an insertion reaction with the low-valent organotin hydride to yield a dimeric insertion product, whereas the isonitrile carbon atom of adamantylisonitrile abstracts three hydrogen atoms from the low-valent organotin hydride to give an equimolar mixture between (adamantylmethylamido)organostannylene and a bis(isonitrile)distannyne adduct.
Ein sterisch anspruchsvoll substituiertes Stannan Ar*SnH3 (Ar*=2,6‐(2′,4′,6′‐Triisopropylphenyl)phenyl) wurde mit dem bekannten frustrierten Lewis‐Paar (FLP) PtBu3/B(C6F5)3 in verschiedenen stöchiometrischen Zusammensetzungen umgesetzt. Unter anderem wurde die Hydridabstraktion und Adduktbildung beobachtet, die zum SnIV‐Kation [Ar*SnH2(PtBu3)]+ führt. Dieses zeigte sich gegenüber weiterer Wasserstoffabstraktion reaktionsträge. In einem hierzu konkurrierenden Prozess wurde hingegen vollständige Entfernung der Wasserstoffatome beobachtet, was zum ersten kationischen Phosphoniostannylen [Ar*Sn(PtBu)]+ führt. Dieses Reaktionsverhalten lässt Rückschlüsse auf die involvierten Prozesse der Wasserstoff‐/Hydridabstraktion dieser Gruppe‐14‐Hydridderivate zu.
Following the alkane‐elimination route, the reaction between tetravalent aryl tintrihydride Ar*SnH3 and trivalent rare‐earth‐metallocene alkyls [Cp*2Ln(CH{SiMe3}2)] gave complexes [Cp*2Ln(μ‐H)2SnAr*] implementing a low‐valent tin hydride (Ln=Y, Lu; Ar*=2,6‐Trip2C6H3, Trip=2,4,6‐triisopropylphenyl). The homologous complexes of germanium and lead, [Cp*2Ln(μ‐H)2EAr*] (E = Ge, Pb), were accessed via addition of low‐valent [(Ar*EH)2] to the rare‐earth‐metal hydrides [(Cp*2LnH)2]. The lead compounds [Cp*2Ln(μ‐H)2PbAr*] exhibit H/D exchange in reactions with deuterated solvents or dihydrogen.
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