An Unusual and Facile Synthetic Route to Alumoles

Reaction of the aluminum dialkynyl LAl(CCR)₂ (L=N,N‐chelate ligand and R=organic group) with B(C₆F₅)₃ proceeds through an intermediate with Al⋅⋅⋅η²‐C≡C side‐on coordination to form the alumoles (2, 4, 6). A distinctive reaction pattern indicates a new facile synthetic route to aluminum‐containing heterocycles. The synthetic process is described, and the characterization of compounds and computational calculations were carried out. Furthermore, alumoles 2 and 4 exhibit an aggregation‐induced emission (AIE) of the bright yellow fluorescence.

Stoichiometric and catalytic isomerization of alkenylboranes using bulky Lewis bases

1,1-Carboboration of alkynes with boranes R'B(C₆F₅)₂ (R' = (CH₂)₃Ph, C₆F₅) affords mixtures of the E and Z isomers of RCH = CR'B(C₆F₅)₂ (R = (CH₂)₂Me, (CH₂)₃Me, (CH₂)₂Ph, CH₂CHMe₂, CHMe₂, CMe₃, CH₂OMe, CH₂N(CO)₂C₆H₄), treatment of these alkenylboranes with stoichiometric or catalytic amounts of tBu₂PH or other donors are shown to induce isomerization. The proposed mechanism involving a zwitterionic borataalkene intermediate is supported by computations.

Tin(IV) Compounds with 2-C6F4PPh2 Substituents and Their Reactivity toward Palladium(0): Formation of Tin-Palladium Complexes via Oxidative Addition

The tin(IV) compounds Me_xSn(2-C₆F₄PPh₂)_4-x (1, x = 1; 2, x = 2) and ClSn(2-C₆F₄PPh₂)₃ (3) were obtained from the reactions of 2-LiC₆F₄PPh₂ with MeSnCl₃ (3:1), Me₂SnCl₂ (2:1), or SnCl₄ (3:1), respectively. The reactions of 2-LiC₆F₄PPh₂ with SnCl₄ in different stoichiometric ratios (4:1-1:1) gave 3 as the main product. Compound Cl₂Sn(2-C₆F₄PPh₂)₂ (4) was formed in the transmetalation reaction of 3 and [AuCl(tht)] but could not be isolated. 1 and 2 react with palladium(0) sources {[Pd(PPh₃)₄] and [Pd(allyl)Cp]} by the oxidative addition of one of their Sn-C_Aryl bonds to palladium(0) with formation of the heterobimetallic complexes [MeSn(μ-2-C₆F₄PPh₂)₂Pd(κC-2-C₆F₄PPh₂)] (5) and [Me₂Sn(μ-2-C₆F₄PPh₂)Pd(κ²-2-C₆F₄PPh₂)] (6) featuring Sn-Pd bonds. The reaction of 3 with palladium(0) proceeds via the oxidative addition of the Sn-Cl bond to palladium(0), thus furnishing the complex [Sn(μ-2-C₆F₄PPh₂)₃PdCl] (7) featuring a Sn-Pd bond and a pentacoordinate Pd atom. Transmetalation of Me_xSn(2-C₆F₄PPh₂)_4-x (x = 1-3) with [Pd(allyl)Cl]₂ gave Me_xClSn(2-C₆F₄PPh₂)_3-x and [Pd(allyl)(μ-2-C₆F₄PPh₂)]₂. For x = 1, the compound MeClSn(2-C₆F₄PPh₂)₂ (generated in situ) reacted with another 1 equiv of [Pd(allyl)Cl]₂ by the oxidative addition of the Sn-Cl bond to palladium(0) and the reductive elimination of allyl chloride, thus leading to [MeSn(μ-2-C₆F₄PPh₂)₂PdCl] (8). The reductive elimination of allyl chloride was also observed in the reaction of 3 with [Pd(allyl)Cl]₂, giving [Sn(μ-2-C₆F₄PPh₂)₃PdCl] (7). All compounds have been characterized by means of multinuclear NMR spectroscopy, elemental analysis, single-crystal X-ray diffraction, and selected compounds by ¹¹⁹Sn Mössbauer spectroscopy. Computational analyses (natural localized molecular orbital calculations) have provided insight into the Sn-Pd bonding of 5-8.

Advanced 1,1-carboboration reactions with pentafluorophenylboranes

The advanced 1,1-carboboration reaction converts alkynes to alkenylboranes and allows a variety of sequential ring forming reactions of bis(alkynyl) compounds.

The 1,1 carboboration reaction of a variety of metal-substituted alkynes with simple trialkylboranes R₃B yields the respective alkenylboranes (Wrackmeyer reaction). The use of the strongly electrophilic R-B(C₆F₅)₂ reagents allows for much milder reaction conditions and gives good yields of the respective bulky alkenylboranes from conventional terminal alkynes by means of 1,2-hydride migration. Even internal alkynes undergo 1,1-carboboration with the R-B(C₆F₅)₂ reagents, in this case yielding alkenylboranes by means of C–C bond cleavage. Phosphorus, sulfur or even boron containing substituents can serve as the migrating alkynyl substituents in the advanced 1,1-carboboration reactions using the R-B(C₆F₅)₂ reagents. Sequential 1,1-carboboration of geminal bis(alkynyl) derivatives of these elements with the R-B(C₆F₅)₂ boranes yields boryl substituted phospholes, thiophenes or even boroles in quite a variety. Vicinal bis(alkynyl)arenes or heteroarene substrates undergo benzannulation reactions in this way. Many of the -B(C₆F₅)₂ substituted 1,1-carboboration products can be used as reagents in cross coupling reactions. A recently disclosed organometallic analogue, namely a 1,1-carbozirconation reaction is described.

Functionalization of Intramolecular Frustrated Lewis Pairs by 1,1-Carboboration with Conjugated Enynes

The vicinal P/B frustrated Lewis pair (FLP) Mes2PCH2CH2B(C6F5)2 undergoes 1,1-carboboration reactions with the Me3Si-substituted enynes to give ring-enlarged functionalized C3-bridged P/B FLPs. These serve as active FLPs in the activation of dihydrogen to give the respective zwitterionic [P]H(+)/[B]H(-) products. One such product shows activity as a metal-free catalyst for the hydrogenation of enamines or a bulky imine. The ring-enlarged FLPs contain dienylborane functionalities that undergo "bora-Nazarov"-type ring-closing rearrangements upon photolysis. A DFT study had shown that the dienylborane cyclization of such systems itself is endothermic, but a subsequent C6F5 migration is very favorable. Furthermore, substituted 2,5-dihydroborole products are derived from cyclization and C6F5 migration from the photolysis reaction. In the case of the six-membered annulation product, a subsequent stereoisomerization reaction takes place and the resultant compound undergoes a P/B FLP 1,2-addition reaction with a terminal alkyne with rearrangement.

1,1-Carboboration to tellurium–boron intramolecular frustrated Lewis pairs

The tellurium acetylide Ph(CH₂)₂TeCCPh reacts with boranesvia1,1-carboboration to give a series of borylated vinyl telluroethers.

Intramolecular 1,1-carboboration versus intermolecular FLP addition in reactions of boranes and bis(phenylethynyl)telluroether

Reactions of boranes with Te(CCPh)₂ proceed via initial intermolecular 1,1-carboboration followed by either an intramolecular carboboration or an FLP addition to a second molecule, yielding 1-bora-4-tellurocyclohexa-2,5-diene heterocycles or tricylic derivatives of 1,4-ditellurocyclohexa-2,5-diene, respectively.

Highly tin-selective stille coupling: synthesis of a polymer containing a stannole in the main chain

The incorporation of heavier Group 14 element heteroles into semiconducting polymers leads to unusual optoelectronic properties. However, polymers containing stannoles have not been accessible to date. We report a synthetic route to a well-defined, stannole-containing polymer, the first example of this class of π-conjugated polymers. This route was made possible by developing difunctionalized stannole monomers and highly tin-selective Stille coupling reactions that leave the tin in the stannole untouched. Compared to poly(3-n-hexylthiophene), the resulting polymer displays a remarkable bathochromic shift in its absorption.