Klaus Eichele Publication Abstracts 2023

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M. Auer, J. Bolten, K. Eichele, H. Schubert, C. P. Sindlinger, L. Wesemann Heavy Metalla Vinyl-Cations show Metal-Lewis Acid Cooperativity in Reaction with Small Molecules (NH3, N2H4, H2O, H2), Chem. Sci. 2022, accepted. DOI: 10.1039/D2SC05620H

Halide abstraction from tetrylidene complexes [TbbE(Br)IrH(PMe₃)₃] [E =Ge (1), Sn (2)] and [Ar*E(Cl)IrH(PMe₃)₃] gives the salts [TbbEIrH(PMe₃)₃][BArF₄] [E =Ge (3), Sn (4)] and [Ar*EIrH(PMe₃)₃][BArF₄] [E = Ge (3'), E = Sn (4')] (Tbb = 2,6-[CH(SiMe₃)₂]₂-4-(t-Bu)C₆H₂, Ar* = 2,6-Trip₂C₆H₃, Trip = 2,4,6-triisopropylphenyl). Bonding analysis suggests their most suitable description as metalla-tetrela vinyl cations with a Ir=E double bond and a near linear coordination at the Ge/Sn atoms. Cationic complexes 3 and 4 oxidatively add NH₃, N₂H₄, H₂O, HCl*Et₂O, and H₂ selectively to give: [TbbGe(NH₂)IrH₂(PMe₃)₃][BArF₄] (5), [TbbE(NHNH₂)IrH₂(PMe₃)₃][BArF₄] [E = Ge (7), Sn(8)], [TbbE(OH)IrH₂(PMe₃)₃][BArF₄] [E = Ge (9), Sn(10)], [TbbE(Cl)IrH₂(PMe₃)₃][BArF₄] [E = Ge (11a), Sn(12a)], [TbbGe(H)IrH₂(PMe₃)₃][BArF₄] (13), [TbbSn(μ-H₃)Ir(PMe₃)₃][BArF₄] (14), and [TbbSnHIrH₂(PMe₃)₃][BArF₄] (15). 14 isomerizes to give 15 via an 1,2-H shift reaction. Hydride addition to cation 3 gives a mixture of products [TbbGeHIrH(PMe₃)₃] (16) and [TbbGeIrH₂(PMe₃)₃] (17) and a reversible 1,2H-shift between 16 and 17 was studied. In the tin case 4 the dihydride [TbbSnIrH₂(PMe₃)₃] (18) was isolated exclusively. The PMe₃ and PEt₃ derivatives, 18 and [TbbSnIrH₂(PEt₃)₃] (19), respectively, could also be synthesized in reaction of [TbbSnH₂]- with the respective chloride [(R₃P)nIrCl] (R = Me n = 4, R = Et n = 3). Reaction of complex 19 with CO gives the substitution product [TbbSnIrH₂(CO)(PEt₃)₂] (20). Further reaction with CO results in hydrogen transfer from the iridium to the tin atom to give [TbbSnH₂Ir(CO)₂(PEt₃)₂] (21). The reversibility of this ligand induced reductive elimination transferring 20 to 21 is shown.

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R. H. Kern, M. Schneider, K. Eichele, H. Schubert, H. F. Bettinger, L. Wesemann, Boradigermaallyl: (4 + 3) Cycloaddition-Initiated Boron Insertion into Benzene, Angew. Chem. Int. Ed. 2023, 62, e202301593. DOI: 10.1002/anie.202301593

The 2π electron 1,3-dipole boradigermaallyl, valence-isoelectronic to an allyl cation, is synthesized from a bis(germylene). It reacts with benzene at room temperature by insertion of a boron atom into the benzene ring. Computational investigation of the mechanism shows the boradigermaallyl reacting with a benzene molecule in a concerted (4+3) or [π4s+π2s] cycloaddition reaction. Thus, the boradigermaallyl acts as a highly reactive dienophile in this cycloaddition reaction with nonactivated benzene as diene unit. This type of reactivity provides a novel platform for ligand assisted borylene insertion chemistry.

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M. Zweigart, C. Wenzel, K. Eichele, H. Schubert, L. Wesemann, Stiba-, Arsa- and Phosphastannenes: Syntheses and Reactivities, Angew. Chem. Int. Ed. 2023, 62, e202304200. DOI: 10.1002/anie.202304200

A facile synthesis for unprecedented stibastannene (10) featuring a Sn=Sb-double bond together with the homologous arsa- (9) and phosphastannenes (8) is presented. Chloride abstraction from respective stannyl pnictinidenes [E=P (5), As (6), Sb (7)], which were made accessible by reduction of ECl₃ addition products at an intramolecular phosphine-stabilized stannylene, gave the pnictastannenes in moderate yields. The pnictastannenes coordinate Pd(PPh₃)₂ fragments (12-14) and the phosphastannene forms also a nickel coordination compound with the Ni(PPh₃)₂-fragment (11). 2,3-Dimethylbutadiene shows a [2+4]-cycloaddition (15-17) in reaction with the pnictastannenes (8-10). Products of a [2+2]-addition (18, 19) were isolated as the phosphaalkyne reaction products for 8 and 9. Addition of an O-H bond at the Sn=P-bond was found in reaction of water with phosphastannene 8. Reaction with ammonia afforded the NH₃-adducts (21-23) at the tin atom for pnictastannenes 8-10. Only in the case of the arsastannene an azide reaction product featuring a three membered Sn-As-N-ring was obtained.

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M. Zweigart, K.Eichele, H. Schubert, C. P. Sindlinger, L. Wesemann, Authentic Sn=B-Double Bonds in Polar Stannaborene Derivatives, J. Am. Chem. Soc. 2023, 145, 12452-12458. DOI: 10.1021/jacs.3c03744

We report on the synthesis of an authentic Sn=B-moiety realized in a stannaborenyl anion and stannaborenium cation. Starting with an oxidative addition of boron tribromide to a stannylene-phosphine Lewis pair [o-C₆H₄(Ar*BrSn-BBr₂-PPh₂)] (2a) [Ar* = C₆H₃(2,6-Trip)₂, Trip = 2,4,6-C₆H₂iPr₃] was synthesized. Reduction of 2a with magnesium yields the Grignard-type stannaborene [o-C₆H₄(Ar*Sn=B{PPh₂}MgBr{thf})]₂ (3)₂ featuring a Sn=B double bond and a B-Mg interaction. Following an alternative protocol, hydride substitution at 2a yields the tinhydride [o-C₆H₄(Ar*HSn-BBr₂-PPh₂)] (4a). HBr elimination of 4a in reaction with MeNHC (MeNHC = 1,3,4,5-tetramethylimidazol-2-ylidene) gives the carbene and phosphine stabilized stannyl-borylene [o-C₆H₄(Ar*BrSn-B{PPh₂}{MeNHC})] (5) after simultaneous bromide transfer from boron to tin. In reaction of 5 with Li[Al(OC{CF₃}₃)₄] or Na[BArF₄] in a mixture of o-DFB/benzene a stannaborene [o-C₆H₄(Ar*Sn=B{PPh₂}{MeNHC})]+ [6] stabilized by the respective weakly coordinating anion was isolated (ArF = C₆H₃-3,5-(CF₃)₂, o-DFB = o-difluorobenzene). The phosphine and NHC-supported stannaborenium cation 6 adds ammonia at room temperature under splitting of a N-H bond and formation of Sn-NH₂ and B-H bonds to give [o-C₆H₄(Ar*{H₂N}Sn-BH{PPh₂}{MeNHC})]+ (7).

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M. Auer, K. Zwettler, K. Eichele, H. Schubert, C. P. Sindlinger, L. Wesemann, Synthesis of Cobalt-Tin and -Lead Tetrylidynes - Reactivity Study of the Triple Bond, Angew. Chem. Int. Ed. 2023, 62, e202305951. DOI: 10.1002/anie.202305951

Tetrylidynes [TbbSnCo(PMe₃)₃] (1a) and [TbbPbCo(PMe₃)₃] (2) (Tbb = 2,6-[CH(SiMe₃)₂]₂-4-(t-Bu)C₆H₂) are accessed for the first time via a substitution reaction between [Na(OEt₂)][Co(PMe₃)₄] and [Li(thf)₂][TbbEBr₂] (E = Sn, Pb). Following an alternative procedure the stannylidyne [Ar*SnCo(PMe₃)₃] (1b) was synthesized by hydrogen atom abstraction using AIBN from the paramagnetic hydride complex [Ar*SnH=Co(PMe₃)₃] (4) (AIBN = azobis(isobutyronitrile)). The stannylidyne 1a adds two equivalents of water to yield the dihydroxide [TbbSn(OH)₂CoH₂(PMe₃)₃] (5). In reaction of the stannylidyne 1a with CO₂ a product of a redox reaction [TbbSn(CO₃)Co(CO)(PMe₃)₃] (6) was isolated. Protonation of the tetrylidynes occurs at the cobalt atom to give the metalla-stanna vinyl cation [TbbSn=CoH(PMe₃)₃][BArF₄] (7a) [ArF = C₆H₃-3,5-(CF₃)₂]. The analogous germanium and tin cations [Ar*E=CoH(PMe₃)₃][BArF₄] (E = Ge 9, Sn 7b) (Ar* = C₆H₃(2,6-Trip)₂, Trip = 2,4,6-C₆H₂iPr₃) were also obtained by oxidation of the paramagnetic complexes [Ar*EH=Co(PMe₃)₃] (E = Ge 3, Sn 4), which were synthesized by substitution of a PMe₃ ligand of [Co(PMe₃)₄] by a hydridoylene (Ar*EH) unit.