Frustrated Lewis Pair Chemistry Derived from Bulky Allenyl and Propargyl Phosphanes

The dimesitylpropargylphosphanes mes₂P?CH₂?C≡C?R 6 a (R=H), 6 b (R=CH₃), 6 c (R=SiMe₃) and the allene mes₂P?C(CH₃)=C=CH₂ ( 8 ) were reacted with Piers’ borane, HB(C₆F₅)₂. Compound 6 a gave mes₂PCH₂CH=CH(B(C₆F₅)₂] ( 9 a ). In contrast, addition of HB(C₆F₅)₂ to 6 b and 6 c gave mixtures of 9 b (R=CH₃) and 9 c (R=SiMe₃) with the regioisomers mes₂P?CH₂?C[B(C₆F₅)₂]=CRH 2 b (R=CH₃) and 2 c (R=SiMe₃), respectively. Compounds 2 b , c underwent rapid phosphane/borane (P/B) frustrated Lewis pair (FLP) reactions under mild conditions. Compound 2 c reacted with nitric oxide (NO) to give the persistent FLP NO radical 11 . The systems 2 b , c cleaved dihydrogen at room temperature to give the respective phosphonium/hydridoborate products 13 b , c . Compound 13 c transferred the H⁺/H^? pair to a small series of enamines. Compound 13 c was also a metal‐free catalyst (5 mol %) for the hydrogenation of the enamines. The allene 8 reacted with B(C₆F₅)₃ to give the zwitterionic phosphonium/borate 17 . The ‐PPh₂‐substituted mes₂P‐propargyl system 6 d underwent a typical 1,2‐P/B‐addition reaction to the C≡C triple bond to form the phosphetium/borate zwitterion 20 . Several products were characterized by X‐ray diffraction.     

How Frustrated Lewis Acid/Base Systems Pass through Transition‐State Regions: H2 Cleavage by [tBu3P/B(C6F5)3]

We investigate the transition‐state (TS) region of the potential energy surface (PES) of the reaction tBu₃P+H₂+B(C₆F₅)₃→tBu₃P‐H⁽⁺⁾+^(?)H?B(C₆F₅)₃ and the dynamics of the TS passage at room temperature. Owing to the conformational inertia of the phosphane???borane pocket involving heavy tBu₃P and B(C₆F₅)₃ species and features of the PES E(P???H, B???H | B???P) as a function of P???H, B???H, and B???P distances, a typical reactive scenario for this reaction is a trajectory that is trapped in the TS region for a period of time (about 350 fs on average across all calculated trajectories) in a quasi‐bound state (scattering resonance). The relationship between the timescale of the TS passage and the effective conformational inertia of the phosphane???borane pocket leads to a prediction that isotopically heavier Lewis base/Lewis acid pairs and normal counterparts could give measurably different reaction rates. Herein, the predicted quasi‐bound state could be verified in molecular collision experiments involving femtosecond spectroscopy.     

Inherent Stability Limits of Intramolecular Boron Nitrogen Lewis Acid–Base Pairs

The reaction of (C₆F₅)₂BH ( 1 ) with N,N‐dimethylallylamine ( 2 ), N,N‐diethylallylamine ( 3 ) and 1‐allylpiperidine ( 4 ) afforded the five‐membered ring systems (C₆F₅)₂B(CH₂)₃NR₂ (R=Me ( 5 ), Et ( 6 )) and (C₆F₅)₂B(CH₂)₃N(CH₂)₅ ( 7 ) with an intramolecular dative B? N bond. A different product was obtained from the reaction of (C₆F₅)₂BH ( 1 ) with N,N‐diisopropylallylamine ( 8 ), which afforded the seven‐membered ring system (C₆F₅)₂B(CH₂)₃N(iPr)CH(Me)CH₂ ( 9 ) under extrusion of dihydrogen. All compounds were characterised by elemental analysis, NMR spectroscopy and single‐crystal X‐ray diffraction experiments. Density functional theory (DFT) studies were performed to rationalise the different reaction mechanism for the formation of products 6 and 9 . The bonding situation of compound 9 was analysed in terms of its electron density topology to describe the delocalised nature of a borane– enamine adduct.     

Reactions of some fluoroaromatics with the ethoxide anion

The reactions of sodium ethoxide in ethanol with various fluoroaromatics, C₆F_6?nH_n, C₆F_5?nH_nNO₂, C₆F₅X (X = CF₃, C₆F₅, COCH₃, CH₂Br), C₆Cl₆ and $\text{m}$H₂C₆Cl₄ have been studied. Partial substitution of the aromatic halogen was observed. The new products have been characterized by elemental analysis, NMR (H?1 and F?19), infrared and mass spectroscopy.     

Ab Initio Molecular Dynamics Study of Hydrogen Cleavage by a Lewis Base [tBu3P] and a Lewis Acid [B(C6F5)3] at the Mesoscopic Level—Dynamics in the Solute–Solvent Molecular Clusters

With the help of state‐of‐the‐art ab initio molecular dynamics methods, we investigated the reaction pathway of the {tBu₃P + H₂ + B(C₆F₅)₃} system at the mesoscopic level. It is shown that: i) the onset of H₂ activation is at much larger boron???phosphorus distances than previously thought; ii) the system evolves to the product in a roaming‐like fashion because of quasi‐periodic nuclear motion along the asymmetric normal mode of P???H?H???B fragment; iii) transient configurations of a certain type are present despite structural interference from the solvent; iv) transient‐state configurations with sub‐picosecond lifetime have potentially interesting infrared activity in the organic solvent (toluene) as well as in the gas phase. The presented results should be helpful for future experimental and theoretical studies of frustrated Lewis pair (FLP) activity.     

B(C6F5)3/Chiral Phosphoric Acid Catalyzed Ketimine–Ene Reaction of 2‐Aryl‐3H‐indol‐3‐ones and α‐Methylstyrenes

The enantioselective ketimine–ene reaction is one of the most challenging stereocontrolled reaction types in organic synthesis. In this work, catalytic enantioselective ketimine–ene reactions of 2‐aryl‐3H‐indol‐3‐ones with α‐methylstyrenes were achieved by utilizing a B(C₆F₅)₃/chiral phosphoric acid (CPA) catalyst. These ketimine–ene reactions proceed well with low catalyst loading (B(C₆F₅)₃/CPA=2 mol %/2 mol %) under mild conditions, providing rapid and facile access to a series of functionalized 2‐allyl‐indolin‐3‐ones with very good reactivity (up to 99 % yield) and excellent enantioselectivity (up to 99 % ee). Theoretical calculations reveal that enhancement of the acidity of the chiral phosphoric acid by B(C₆F₅)₃ significantly reduces the activation free energy barrier. Furthermore, collective favorable hydrogen‐bonding interactions, especially the enhanced N?H???O hydrogen‐bonding interaction, differentiates the free energy of the transition states of CPA and B(C₆F₅)₃/CPA, thereby inducing the improvement of stereoselectivity.     

Transfer Hydrocyanation of α‐ and α,β‐Substituted Styrenes Catalyzed by Boron Lewis Acids

A straightforward gram‐scale preparation of cyclohexa‐1,4‐diene‐based hydrogen cyanide (HCN) surrogates is reported. These are bench‐stable but formally release HCN and rearomatize when treated with Lewis acids. For BCl₃, the formation of the isocyanide adduct [(CN)BCl₃]^? and the corresponding Wheland complex was verified by mass spectrometry. In the presence of 1,1‐di‐ and trisubstituted alkenes, transfer of HCN from the surrogate to the C?C double bond occurs, affording highly substituted nitriles with Markovnikov selectivity. The success of this transfer hydrocyanation depends on the Lewis acid employed; catalytic amounts of BCl₃ and (C₆F₅)₂BCl are shown to be effective while B(C₆F₅)₃ and BF₃?OEt₂ are not.     

Ionic liquids containing the triply negatively charged tricyanomelaminate anion and a B(C6F5)3 adduct anion

Room‐temperature ionic liquids containing the triply charged tricyanomelaminate (tcmel) ion [C₃N₆(CN)₃]^3? were synthesized. The 1‐methyl‐3‐methylimidazolium (MMIm), 1‐ethyl‐3‐methylimidazolium (EMIm), and 1‐butyl‐3‐methylimidazolium (BMIm) salts of the tricyanomelaminate ion have glass transition temperatures (?6, ?20, and ?30 °C) similar to those found for the analogous monomeric dicyanoamide salts. They are thermally stable up to over 200 °C and dissolve in polar organic solvents. Addition of B(C₆F₅)₃ to M₃[tcmel] (M=Na, MMIm, EMIm, BMIm) yields salts containing the very voluminous adduct ion [C₃N₆{CN ? B(C₆F₅)₃}₃]^3? (tcmel_3B). The solid‐state structure of [MMIm]₃[tcmel] shows only long cation ??? anion contacts but in large number, while the solid‐state structure of [Na(THF)₃]₃[tcmel_3B] ? 1.76 THF displays strong interactions of the sodium cation with the amido nitrogen atoms of the anion. Hence this adduct anion cannot be regarded as a weakly coordinating anion. A similar situation is found for the MMIm salt, [MMIm]₃[tcmel_3B] ? 2.66 CH₂Cl₂, in which weak hydrogen bonds with the acidic proton of the MMIm ion are observed. On the basis of computations the energetics, structural trends, and charge transfer of adduct anion formation were studied.     

Pentafluorphenyliod(III)-Verbindungen. 2. Fluor-Aryl Substitution an Iodtrifluorid: Synthese von Pentafluorphenylioddifluorid C6F5IF2 und Bis(pentafluorphenyl)iodonium Pentafluorphenylfluoroboraten [(C6F5)2I]+[(C6F5)nBF4−n]−

Pentafluorophenyliodine(III) Compounds. 2. Fluorine-Aryl Substitution Reactions on Iodinetrifluoride: Synthesis of Pentafluorophenyliodinedifluoride C₆F₅IF₂ and Bis(pentafluorophenyl)iodonium Pentafluorophenylfluoroborates[(C₆F₅)₂I]⁺[(C₆F₅)_nBF_4?n]^? Mono- and disubstitution can be achieved in the fluorine-aryl substitution reaction on the low-temperature phase IF₃ in CH₂Cl₂ at ?78°C depending on the aryl transfer reagent. With B(C₆F₅)₃ [(C₆F₅)₂I]⁺ [(C₆F₅)_nBF_4?n]^? (68% yield) and with Cd(C₆F₅)₂ C₆F₅IF₂ (97% yield) is obtained whereas with C₆F₅SiMe₃ no fluorine-aryl substitution takes place on IF₃ even under basic conditions (EtCN or F^? addition). At ?78°C in EtCN solution IF₃ does not disproportionate but attacks the solvent under formation of HF.     

Influence of Cyclopentadienyl Ring‐Tilt on Electron‐Transfer Reactions: Redox‐Induced Reactivity of Strained [2] and [3]Ruthenocenophanes

In contrast to ruthenocene [Ru(η⁵‐C₅H₅)₂] and dimethylruthenocene [Ru(η⁵‐C₅H₄Me)₂] ( 7 ), chemical oxidation of highly strained, ring‐tilted [2]ruthenocenophane [Ru(η⁵‐C₅H₄)₂(CH₂)₂] ( 5 ) and slightly strained [3]ruthenocenophane [Ru(η⁵‐C₅H₄)₂(CH₂)₃] ( 6 ) with cationic oxidants containing the non‐coordinating [B(C₆F₅)₄]^? anion was found to afford stable and isolable metal?metal bonded dicationic dimer salts [Ru(η⁵‐C₅H₄)₂(CH₂)₂]₂[B(C₆F₅)₄]₂ ( 8 ) and [Ru(η⁵‐C₅H₄)₂(CH₂)₃]₂[B(C₆F₅)₄]₂ ( 17 ), respectively. Cyclic voltammetry and DFT studies indicated that the oxidation potential, propensity for dimerization, and strength of the resulting Ru?Ru bond is strongly dependent on the degree of tilt present in 5 and 6 and thereby degree of exposure of the Ru center. Cleavage of the Ru?Ru bond in 8 was achieved through reaction with the radical source [(CH₃)₂NC(S)S?SC(S)N(CH₃)₂] (thiram), affording unusual dimer [(CH₃)₂NCS₂Ru(η⁵‐C₅H₄)(η³‐C₅H₄)C₂H₄]₂[B(C₆F₅)₄]₂ ( 9 ) through a haptotropic η⁵–η³ ring‐slippage followed by an apparent [2+2] cyclodimerization of the cyclopentadienyl ligand. Analogs of possible intermediates in the reaction pathway [C₆H₅ERu(η⁵‐C₅H₄)₂C₂H₄][B(C₆F₅)₄] [E=S ( 15 ) or Se ( 16 )] were synthesized through reaction of 8 with C₆H₅E?EC₆H₅ (E=S or Se).     

Metal‐Free Hydrogenation Catalyzed by an Air‐Stable Borane: Use of Solvent as a Frustrated Lewis Base

In recent years ‘frustrated Lewis pairs’ (FLPs) have been shown to be effective metal‐free catalysts for the hydrogenation of many unsaturated substrates. Even so, limited functional‐group tolerance restricts the range of solvents in which FLP‐mediated reactions can be performed, with all FLP‐mediated hydrogenations reported to date carried out in non‐donor hydrocarbon or chlorinated solvents. Herein we report that the bulky Lewis acids B(C₆Cl₅)_x(C₆F₅)_3?x (x=0–3) are capable of heterolytic H₂ activation in the strong‐donor solvent THF, in the absence of any additional Lewis base. This allows metal‐free catalytic hydrogenations to be performed in donor solvent media under mild conditions; these systems are particularly effective for the hydrogenation of weakly basic substrates, including the first examples of metal‐free catalytic hydrogenation of furan heterocycles. The air‐stability of the most effective borane, B(C₆Cl₅)(C₆F₅)₂, makes this a practically simple reaction method.     

Stable Borane Adducts of Alcoholates and Carboxylates

Six adducts of B(C₆F₅)₃ and archetypical alcoholates and carboxylates, were prepared and isolated as crystalline sodium crown ether salts, [Na(15‐crown‐5)][CH₃O · B(C₆F₅)₃] ( 1 ), [Na(15‐crown‐5)][CH₃CH₂O · B(C₆F₅)₃] ( 2 ), [Na(15‐crown‐5)][HCO₂ · B(C₆F₅)₃] ( 3 ), [Na(15‐crown‐5)][(H₃CCO₂ · B(C₆F₅)₃] ( 4 ), [Na(15‐crown‐5)][(F₃CCO₂ · B(C₆F₅)₃] ( 5 ), and [Na₂(15‐crown‐5)₃][C₂O₄ · 2 B(C₆F₅)₃] ( 6 ). All compounds were fully characterized by multinuclear NMR‐ and IR spectroscopy, ESI MS spectrometry, and X‐ray crystallography.     

A Combined “Electrochemical–Frustrated Lewis Pair” Approach to Hydrogen Activation: Surface Catalytic Effects at Platinum Electrodes

Herein, we extend our “combined electrochemical–frustrated Lewis pair” approach to include Pt electrode surfaces for the first time. We found that the voltammetric response of an electrochemical–frustrated Lewis pair (FLP) system involving the B(C₆F₅)₃/[HB(C₆F₅)₃]^? redox couple exhibits a strong surface electrocatalytic effect at Pt electrodes. Using a combination of kinetic competition studies in the presence of a H atom scavenger, 6‐bromohexene, and by changing the steric bulk of the Lewis acid borane catalyst from B(C₆F₅)₃ to B(C₆Cl₅)₃, the mechanism of electrochemical–FLP reactions on Pt surfaces was shown to be dominated by hydrogen‐atom transfer (HAT) between Pt, [Pt?H] adatoms and transient [HB(C₆F₅)₃] ^? electrooxidation intermediates. These findings provide further insight into this new area of combining electrochemical and FLP reactions, and proffers additional avenues for exploration beyond energy generation, such as in electrosynthesis.     

Ti Group Metallocene-Catalyzed Synthesis of 1-Hexene Dimers and Tetramers

1-Hexene transformations in the catalytic systems L₂MCl₂–XAlBuⁱ₂ (L = Cp, M = Ti, Zr, Hf; L = Ind, rac-H₄C₂[THInd]₂, M = Zr; X = H, Bu ⁱ) and [Cp₂ZrH₂]₂-ClAlR₂ activated by MMAO-12, B(C₆F₅)₃, or (Ph₃C)[B(C₆F₅)₄] in chlorinated solvents (CH₂Cl₂, CHCl₃, o-Cl₂C₆H₄, ClCH₂CH₂Cl) were studied. The systems [Cp₂ZrH₂]₂-MMAO-12, [Cp₂ZrH₂]₂-ClAlBuⁱ₂-MMAO-12, or Cp₂ZrCl₂-HAlBuⁱ₂-MMAO-12 (B(C₆F₅)₃) in CH₂Cl₂ showed the highest activity and selectivity towards the formation of vinylidene head-to-tail alkene dimers. The use of chloroform as a solvent provides further in situ dimer dimerization to give a tetramer yield of up to 89%. A study of the reaction of [Cp₂ZrH₂]₂ or Cp₂ZrCl₂ with organoaluminum compounds and MMAO-12 by NMR spectroscopy confirmed the formation of Zr,Zr-hydride clusters as key intermediates of the alkene dimerization. The probable structure of the Zr,Zr-hydride clusters and ways of their generation in the catalytic systems were analyzed using a quantum chemical approach (DFT).     

The Bis(pentafluoroethyl)germylene Trimethylphosphane Adduct (C2F5)2Ge⋅PMe3: Characterization,Ligand Properties,and Reactivity

The synthesis of the germylene phosphane adduct (C₂F₅)₂Ge?PMe₃ is described. Starting from (C₂F₅)₃GeH in an excess of PMe₃, heating was applied, whereupon reductive elimination of C₂F₅H occurred. The molecular structure was ascertained by X‐ray diffraction and compared with information obtained by quantum chemical methods. The ligand properties were derived by studying the IR spectrum of the nickel(0) complex [Ni(CO)₃{Ge(C₂F₅)₂(PMe₃)}] in the CO region. (C₂F₅)₂Ge?PMe₃ turned out to be a π‐accepting ligand comparable to PMe₃, in terms of Tolman's electronic parameter. Furthermore a [2+4] cycloaddition reaction with 2,3‐dimethyl‐1,3‐butadiene, and σ‐bond insertion reactions were recorded. Activation of the C?Cl bond in dichloromethane gives rise to the formation of the phosphonium ylide complex [(C₂F₅)₂Cl₂Ge‐CH₂PMe₃], which was fully characterized by X‐ray diffraction.     

The B(C6F5)3 Boron Lewis Acid Route to Arene‐Annulated Pentalenes

4,5‐Dimethyl‐1,2‐bis(1‐naphthylethynyl)benzene ( 12 ) undergoes a rapid multiple ring‐closure reaction upon treatment with the strong boron Lewis acid B(C₆F₅)₃ to yield the multiply annulated, planar conjugated π‐system 13 (50 % yield). In the course of this reaction, a C₆F₅ group was transferred from boron to carbon. Treatment of 12 with CH₃B(C₆F₅)₂ proceeded similarly, giving a mixture of 13 (C₆F₅‐transfer) and the product 15 , which was formed by CH₃‐group transfer. 1,2‐Bis(phenylethynyl)benzene ( 8 a ) reacts similarly with CH₃B(C₆F₅)₂ to yield a mixture of the respective C₆F₅‐ and CH₃‐substituted dibenzopentalenes 10 a and 16 . The reaction is thought to proceed through zwitterionic intermediates that exhibit vinyl cation reactivities. Some B(C₆F₅)₃‐substituted species ( 26 , 27 ) consequently formed by in situ deprotonation upon treatment of the respective 1,2‐bis(alkynyl)benzene starting materials ( 24 , 8 ) with the frustrated Lewis pair B(C₆F₅)₃/P(o‐tolyl)₃. The overall formation of the C₆F₅‐substituted products formally require HB(C₆F₅)₂ cleavage in an intermediate dehydroboration step. This was confirmed in the reaction of a thienylethynyl‐containing starting material 21 with B(C₆F₅)₃, which gave the respective annulated pentalene product 23 that had the HB(C₆F₅)₂ moiety 1,4‐added to its thiophene ring. Compounds 12 – 14 , 23 , and 26 were characterized by X‐ray diffraction.     

Synthesis and reactivity of alkynyl-linked phosphonium borates

The phosphine tBu₂PC?CH ( 1 ) was reacted with B(C₆F₅) to give the zwitterionic species tBu₂P(H)C?CB(C₆F₅)₃ ( 2 ). The analogous species tBu₂P(Me)C?CB(C₆F₅)₃ ( 3 ), tBu₂P(H)C?CB(Cl)(C₆F₅)₂ ( 4 ), tBu₂P(H)C?CB(H)(C₆F₅)₂ ( 5 ), and tBu₂P(Me)C?CB(H)(C₆F₅) ₂ ( 6 ) were also prepared. The salt [tBu₂P(H)C?CB(C₆F₅)₂(THF)][B(C₆F₅)₄] ( 7 ) was prepared through abstraction of hydride by [Ph₃C][B(C₆F₅)₄]. Species 5 reacted with the imine tBuN?CHPh to give the borane–amine adduct tBu₂PC?CB[tBuN(H)CH₂Ph](C₆F₅)₂ ( 8 ). The related phosphine Mes₂PC?CH ( 9 ; Mes=C₆H₂Me₃) was used to prepare [tBu₃PH][Mes₂PC?CB(C₆F₅)₃] ( 10 ) and generate Mes₂PC?CB(C₆F₅)₂. The adduct Mes₂PC?CB(NCMe)(C₆F₅)₂ ( 11 ) was isolated. Reaction of Mes₂PC?CB(C₆F₅)₂ with H₂ gave the zwitterionic product (C₆F₅)₂(H)BC(H)?C[P(H)Mes₂][(C₆F₅)₂BC?CP(H)Mes₂] ( 12 ). Reaction of tBu₂PC?CB(C₆F₅)₂, a phosphine–borane generated in situ from 5 , with 1‐hexene gave the species [tBu₂PC?CB(C₆F₅)₂](CH₂CHnBu)[tBu₂PC?CB(C₆F₅)₂] ( 13 ) and subsequent reaction with methanol or hexene resulted in the formation of [tBu₂P(H)C?CB(C₆F₅)₂](CH₂CHnBu)[tBu₂PC?CB(C₆F₅)₂](OMe) ( 14 ) or the macrocycle {[tBu₂PC?CB(C₆F₅)₂](CH₂CH₂nBu)}₂ ( 15 ), respectively. In a related fashion, the reaction of 13 with THF afforded the macrocycle [tBu₂PC?CB(C₆F₅)₂](CH₂CHnBu)[tBu₂PC?CB(C₆F₅)₂][O(CH₂)₄] ( 16 ), although treatment of tBu₂PC?CB(C₆F₅)₂ with THF lead to the formation of {[tBu₂PC?CB(C₆F₅)₂][O(CH₂)₄]}₂ ( 17 ). In a related example, the reaction of Mes₂PC?CB(C₆F₅)₂ with PhC?CH gave {[Mes₂PC?CB(C₆F₅)₂](CH?CPh)}₂ ( 18 ). Compound 5 reacted with AlX₃ (X=Cl, Br) to give addition to the alkynyl unit, affording (C₆F₅)₂BC(H)?C[P(H)tBu₂](AlX₃) (X=Cl 19 , Br 20 ). In a similar fashion, 5 reacted with [Zn(C₆F₅)₂] ? C₇H₈, [Al(C₆F₅)₃] ? C₇H₈, or HB(C₆F₅)₂ to give (C₆F₅)₃BC(H)?C[P(H)tBu₂][Zn(C₆F₅)] ( 21 ), (C₆F₅)₃BC(H)?C[P(H)tBu₂][Al(C₆F₅)₂] ( 22 ), or [(C₆F₅)₂B]₂HC?CH[P(H)tBu₂] ( 23 ), respectively. The implications of this reactivity are discussed.     

Influence of the Homopolar Dihydrogen Bonding CH⋅⋅⋅HC on Coordination Geometry: Experimental and Theoretical Studies

The reaction of the N‐thiophosphorylated thiourea (HOCH₂)(Me)₂CNHC(S)NHP(S)(OiPr)₂ (HL), deprotonated by the thiophosphorylamide group, with NiCl₂ leads to green needles of the pseudotetrahedral complex [Ni(L‐1,5‐S,S′)₂] ? 0.5 (n‐C₆H₁₄) or pale green blocks of the trans square‐planar complex trans‐[Ni(L‐1,5‐S,S′)₂]. The former complex is stabilized by homopolar dihydrogen C?H???H?C interactions formed by n‐hexane solvent molecules with the [Ni(L‐1,5‐S,S′)₂] unit. Furthermore, the dispersion‐dominated C?H??? H?C interactions are, together with other noncovalent interactions (C?H???N, C?H???Ni, C?H???S), responsible for pseudotetrahedral coordination around the Ni^II center in [Ni(L ‐1,5‐S,S′)₂] ? 0.5 (n‐C₆H₁₄).     

Bifunctional Behavior of Unsaturated Intramolecular Phosphane–Borane Frustrated Lewis Pairs Derived from Uncatalyzed 1,4‐Hydrophosphination of a Dienylborane

Three unsaturated C₄‐bridged phospane/borane frustrated Lewis pairs (P/B FLPs) are prepared by uncatalyzed hydrophosphination of a dienylborane. The systems are bifunctional. Consequently, two examples undergo clean hydroboration reactions with HB(C₆F₅)₂ to yield B/B/P systems. The 1,4‐P/B system (C₆F₅)₂B?CH₂CH?CMeCH₂PMes₂ reacts with benzaldehyde initially by allylborane addition, followed by internal P/B FLP addition to the pendant C?C double bond, to yield a bicyclic product. The corresponding reaction of (C₆F₅)₂B?CH₂CH?CMeCH₂PtBu₂ stops at the allylborane/benzaldehyde addition product. The related system (C₆F₅)₂B?CH₂CH?CMeCH₂PPh₂ shows a similar bifunctional reaction pattern, whereby allylborane addition to benzaldehyde is combined with P/B addition to a second aldehyde equivalent to form the eight‐membered heterocyclic 1:2 addition product.