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1.
Simple strategies to obtain magnesium complexes with the soft chelating diylidic ligand [Ph2PCHPPh2(fluorenylidene)]? (dppmflu?) were developed to evaluate the influence of the hard acid (cation) and soft base (anion) mismatch on the stability and reactivity of the formed derivatives. Deprotonation of the precursor Ph2PCH2PPh2(flu) (dppmfluH) by an alkylmagnesium derivative or magnesium amide provided access to [{Mg(dppmflu)(μ‐nBu)}2], [Mg(dppmflu){N(SiMe3)2}], and [{Mg(dppmflu)(μ‐Me)}2], which were used as starting materials for further investigations. The reaction of [{Mg(dppmflu)(μ‐nBu)}2] with PhSiH3 in the presence of THF allowed isolation of the magnesium hydride complex [{Mg(dppmflu)(μ‐H)(thf)}2] without a stabilizing nitrogen donor ligand. Prolonged heating enforced ligand redistribution and [{Mg(dppmflu)(μ‐H)(thf)}2] was converted to [Mg(dppmflu)2] and MgH2. The homoleptic derivative [Mg(dppmflu)2], in which the magnesium center is in a very soft ligand environment, can open a THF molecule by frustrated Lewis pair reactivity to give [{Mg(dppmflu)(μ‐OC4H8dppmflu)}2].  相似文献   

2.
    
Salt metathesis of 1-methyl-2,4,6-triphenylphosphacyclohexadienyl lithium and chlorobis(pentafluorophenyl)borane affords a 1-phospha-7-bora-norbornadiene derivative 2 . The C≡N triple bonds of nitriles insert into the P−B bond of 2 with concomitant C−B bond cleavage, whereas the C≡C bonds of phenylacetylenes react with 2 to form λ4-phosphabarrelenes. Even though 2 must formally be regarded as a classical Lewis adduct, the C≡N and C≡C activation processes observed (and the mild conditions under which they occur) are reminiscent of the reactivity of frustrated Lewis pairs. Indeed, NMR and computational studies give insight into the mechanism of the reactions and reveal the labile nature of the phosphorus–boron bond in 2 , which is also suggested by detailed NMR spectroscopic studies on this compound. Nitrile insertion is thus preceded by ring opening of the bicycle of 2 through P−B bond splitting with a low energy barrier. By contrast, the reaction with alkynes involves formation of a reactive zwitterionic methylphosphininium borate intermediate, which readily undergoes alkyne 1,4-addition.  相似文献   

3.
    
Alkyne complexes with vicinal substitution by a Lewis acid and a Lewis base at the coordinated alkyne are prospective frustrated Lewis pairs exhibiting a particular mutual distance and, hence, a specific activation potential. In this contribution, investigations on the generation of a WII alkyne complex bearing a phosphine as Lewis base and a carbenium group as Lewis acid are presented. Independently on potential substrates added, an intramolecular cyclisation product was always isolated. A subsequent deprotonation step led to an unprecedented side-on λ5-phosphinyne complex, which is interpreted as highly zwitterionic according to visible absorption spectroscopy supported by TD-DFT. Low-temperature 31P NMR and EPR spectroscopic measurements combined with time-dependent IR-spectroscopic monitoring provided insights in the mechanism of the cyclisation reaction. Decomposition of the multicomponent IR spectra by multivariate curve resolution and a kinetic hard-modelling approach allowed the derivation of kinetic parameters. Assignment of the individual IR spectra to potential intermediates was provided by DFT calculations.  相似文献   

4.
    
This contribution reports an unprecedentedly efficient dimerization and the first successful polymerization of lignocellulose‐based β‐angelica lactone (β‐AL) by utilizing a selective Lewis pair (LP) catalytic system, thereby establishing a versatile bio‐refinery platform wherein two products, including a dimer for high‐quality gasoline‐like biofuel (C8–C9 branched alkanes, yield=87 %) and a heat‐ and solvent‐resistant acrylic bioplastic (Mn up to 26.0 kg mol?1), can be synthesized from one feedstock by one catalytic system. The underlying reason for exquisite selectivity of the LP catalytic system toward dimerization and polymerization was explored mechanistically.  相似文献   

5.
    
A bulky substituted stannane Ar*SnH3 (Ar*=2,6‐(2′,4′,6′‐triisopropylphenyl)phenyl) was treated with the well‐known frustrated Lewis pair (FLP) Pt Bu3/B(C6F5)3 in varying stoichiometries. To some degree, hydride abstraction and adduct formation is observed, leading to [Ar*SnH2(Pt Bu3)]+ 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(Pt Bu3)]+. This behavior provides insight into the activation/abstraction mechanism processes involved in these Group 14 hydride derivatives.  相似文献   

6.
    
The chemistry of dicationic diboranes with two BII atoms that are engaged in direct B−B bonding is by enlarge unexplored, although these molecules have intriguing properties due to their combined Lewis acidic and electron-donor properties. Unsymmetric dicationic diboranes are extremely rare, but especially attractive due to their polarized B−B bond. In this work we report the directed synthesis of several stable unsymmetric dicationic diboranes by reaction between the electron-rich ditriflato-diborane B2(hpp)2(OTf)2 (hpp=1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-α]pyrimidinate) and phosphino-pyridines, establishing B−N and B−P bonds with the diborane concomitant with triflate elimination. In the case of 2-((ditertbutylphosphino)methyl)pyridine, the B−N bond is formed instantly, but the B−P bond formation requires (due to steric constraints) several days at ambient conditions for completion, creating an intermediate that could be used for frustrated Lewis pair (FLP)-like chemistry. Here we test its reaction with an aldehyde, and propose a new type of FLP-like chemistry.  相似文献   

7.
    
The germylene species (CH{(CMe)(2,6-iPr2C6H3N)}2)GePCO 1 is shown to react with the Lewis acids (E(C6F5)3 E=B, Al). Nonetheless, 1 participates in FLP chemistry with electron deficient alkynes or olefins, acting as an intramolecular FLP. In contrast, in the presence of B(C6F5)3 and an electron rich alkyne, 1 behaves as Ge-based nucleophile to effect intermolecular FLP addition to the alkyne. This reactivity demonstrates that the reaction pathway is controlled by the nature of the electrophile and nucleophile generated in solution, as revealed by extensive DFT calculations.  相似文献   

8.
    
The concept of frustrated Lewis pairs (FLPs) has been widely applied in various research areas, and metal‐free hydrogenation undoubtedly belongs to the most significant and successful ones. In the past decade, great efforts have been devoted to the synthesis of chiral boron Lewis acids. In a sharp contrast, chiral Lewis base derived FLPs have rarely been disclosed for the asymmetric hydrogenation. In this work, a novel type of chiral FLP was developed by simple combination of chiral oxazoline Lewis bases with achiral boron Lewis acids, thus providing a promising new direction for the development of chiral FLPs in the future. These chiral FLPs proved to be highly effective for the asymmetric hydrogenation of ketones, enones, and chromones, giving the corresponding products in high yields with up to 95 % ee. Mechanistic studies suggest that the hydrogen transfer to simple ketones likely proceeds in a concerted manner.  相似文献   

9.
    
Electrophilic fluorophosphonium triflates bearing pyridyl ( 3 [OTf]) or imidazolyl ( 4 [OTf])-substituents act as intramolecular frustrated Lewis pairs (FLPs) and reversibly form 1 : 1 adducts with CO2 ( 5 + and 6 +). An unusual and labile spirocyclic tetrahedral intermediate ( 7 2+) is observed in CO2-pressurized (0.5–2.0 bar) solutions of cation 4 + at low temperatures, as demonstrated by variable-temperature NMR studies, which were confirmed crystallographically. In addition, cations 3 + and 4 + actively bind carbonyls, nitriles and acetylenes by 1,3-dipolar cycloaddition, as shown by selected examples.  相似文献   

10.
In order to use H2 as a clean source of electricity, prohibitively rare and expensive precious metal electrocatalysts, such as Pt, are often used to overcome the large oxidative voltage required to convert H2 into 2 H+ and 2 e?. Herein, we report a metal‐free approach to catalyze the oxidation of H2 by combining the ability of frustrated Lewis pairs (FLPs) to heterolytically cleave H2 with the in situ electrochemical oxidation of the resulting borohydride. The use of the NHC‐stabilized borenium cation [(IiPr2)(BC8H14)]+ (IiPr2=C3H2(NiPr)2, NHC=N‐heterocyclic carbene) as the Lewis acidic component of the FLP is shown to decrease the voltage required for H2 oxidation by 910 mV at inexpensive carbon electrodes, a significant energy saving equivalent to 175.6 kJ mol?1. The NHC–borenium Lewis acid also offers improved catalyst recyclability and chemical stability compared to B(C6F5)3, the paradigm Lewis acid originally used to pioneer our combined electrochemical/frustrated Lewis pair approach.  相似文献   

11.
The reactions of the intramolecular frustrated Lewis pair‐adduct Ph2PC(p‐Tol)?C(C6F5)B(C6F5)2(CNtBu) with XeF2 gave Ph2P(F)C(p‐Tol)?C(C6F5)B(F)(C6F5)2 ( 3 ). This species reacts with two equivalents of Al(C6F5)3?C7H8 producing the salt, [Ph2P(F)C(p‐Tol)?C(C6F5)B(C6F5)2][F(Al(C6F5)3)2] ( 4 ), whereas reaction with HSiEt3/B(C6F5)3 gave Ph2P(F)C(p‐Tol)?C(H)B(C6F5)3 ( 5 ). The photolysis of 3 resulted in aromatization affording the phenanthralene derivative Ph2P(F)C(p‐Tol(o‐C6F4))?CB(F)(C6F5)2 ( 6 ).  相似文献   

12.
Hydroboration of dimesitylvinylphosphane with bis[3,5‐bis(trifluoromethyl)phenyl]borane [HB(Fxyl)2] gave the intramolecular ethylene‐bridged P/B frustrated Lewis pair (FLP) Mes2PCH2CH2B(Fxyl)2. The new compound underwent a variety of typical FLP reactions such as P/B‐addition to the carbonyl group of p‐chloro‐benzaldehyde. Cooperative N,N‐addition to nitric oxide gave the respective persistent P/B FLPNO. radical, which readily reacted with 1,4‐cyclohexadiene by H‐atom abstraction to yield the corresponding P/B FLPNOH product. The B(Fxyl)2‐containing FLP reacted as a template for the HB(C6F5)2 reduction of carbon monoxide to the formyl stage to give the respective FLP(η2‐formylborane) product. Most products were characterized by single‐crystal X‐ray crystal structure analysis.  相似文献   

13.
    
Tame d0 phosphidotitanocene cations stabilized with a pendant tertiary phosphane arm are reported. These compounds were obtained by one-electron oxidation of d1 precursors with [Cp2Fe][BPh4]. The electronic structure of these compounds was studied experimentally (EPR, UV/Vis, and NMR spectroscopy, X-ray diffraction analysis) and through DFT calculations. The theoretical analysis of the bonding situation by using the electron localization function (ELF) shows the presence of π-interactions between the phosphido ligand and Ti in the d0 complexes, whereas dπ–pπ repulsion prevents such interactions in the d1 complexes. In addition, CH–π interactions were observed in several complexes, both in solution and in the solid state, between the phosphido ligand and the phosphane arm. The d0 complexes were found to be light sensitive, and decompose through Ti−P bond homolysis to give TiIII species. A naked d0 phosphidotitanocene cation has been trapped by reaction with diphenylacetylene, yielding a Ti/P frustrated Lewis pair (FLP), which was found to be less reactive than a previously reported Zr analog.  相似文献   

14.
一直以来寻找直接有效的乙烯基官能化合成方法的研究备受关注. 报道了一种新型的有机胺盐酸盐/B(C6F5)3 (BCF)体系催化炔烃与氢氯酸或羧酸的加成反应方法, 可选择性地在炔烃的C(2)位氯代或羧化. 研究了在有机胺盐酸盐/BCF体系催化下, 不同取代的炔烃与无机酸HCl的氢氯化加成反应. 在2,2,4,4-四甲基哌啶盐酸盐/BCF([TMPH]+[Cl-B(C6F5)3]-)催化下, 等物质的量的炔烃和HCl反应时, 端基芳炔的C(2)位一加成产物的比例可高达90%以上, 而端基烷基炔烃的选择性较芳炔差, 叔丁基乙炔的一加成产物只占到67%. 报道了非金属催化剂路易斯酸BCF催化的炔烃与羧酸CF3COOH的烯醇酯化反应, 端基芳炔的C(2)位烯醇酯化产率可达95%以上, 而二苯基乙炔及非芳香性端基炔的反应活性较低. 首次实现了非金属催化剂FLPs参与催化的炔烃与酸的选择性氢氯化和烯醇酯化加成反应.  相似文献   

15.
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16.
    
The reactivity of the frustrated Lewis pair (FLP) (F5C2)3SnCH2P(tBu)2 ( 1 ) was investigated with respect to the activation of elemental hydrogen. The reaction of 1 at elevated hydrogen pressure afforded the intramolecular phosphonium stannate(II) (F5C2)2SnCH2PH(tBu)2 ( 3 ). It was characterized by means of multinuclear NMR spectroscopy and single crystal X-ray diffraction. NMR experiments with the two isotopologues H2 and D2 showed it to be formed via an H2 adduct (F5C2)3HSnCH2PH(tBu)2 ( 2) and the subsequent formal reductive elimination of pentafluoroethane; this is supported by DFT calculations. Parahydrogen-induced polarization experiments revealed the formation of a second product of the reaction of 1 with H2, [HP(tBu)2Me][Sn(C2F5)3] ( 4 ), in 1H NMR spectra, whereas 2 was not detected due to its transient nature.  相似文献   

17.
A boron‐based catalyst was found to catalyze the straightforward alkylation of amines with readily available carboxylic acids in the presence of silane as the reducing agent. Various types of primary and secondary amines can be smoothly alkylated with good selectivity and good functional‐group compatibility. This metal‐free amine alkylation was successfully applied to the synthesis of three commercial medicinal compounds, Butenafine, Cinacalcet. and Piribedil, in a one‐pot manner without using any metal catalysts.  相似文献   

18.
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19.
    
The active six-membered cyclo-FLP 6 undergoes a rapid P/B addition reaction to carbon dioxide. At elevated temperature, the resulting heterobicyclo[2.2.2]octane derived product 7 undergoes ring opening and equilibrates with the cyclotetramer (7)4 . In the large macrocyclic structure, four monomeric six-membered cyclo-FLP units are connected by four CO2 molecules to form the supramolecular ring system. The P/B cyclo-FLP 6 undergoes a variety of additional cycloaddition reactions.  相似文献   

20.
    
Rare-earth metal cations have been used rarely as Lewis-acidic components in the chemistry of frustrated Lewis pairs (FLPs). Herein, we report the first cerium/phosphorus system ( 2 ) employing a heptadentate N4P3 ligand, which exhibits triple FLP-type reactivity towards a series of organic substrates, including isocyanates, isothiocyanates, diazomethane, and azides on a single rare-earth Lewis acidic Ce center. This result shows that the Ce center and three P atoms in 2 could simultaneously activate three equivalents of small molecules under mild conditions. This study broadens the diversity of FLPs and demonstrates that rare earth based FLP exhibit unique properties compared with other FLP systems.  相似文献   

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