Pyridinium-phosphonium dications: highly electrophilic phosphorus-based Lewis acid catalysts.

Using commercially available 2-pyridyldiphenylphosphine (o-NC5H4)PPh2, a family of electrophilic phosphonium cations [(o-NC5H4)PFPh2](+) (2) and dications [(o-MeNC5H4)PRPh2](2+) (R = F (4); Me (5)) were prepared. The Lewis acidity of these pyridinium-phosphonium dications was probed in Friedel-Crafts dimerization, hydrodefluorination, hydrosilylation, dehydrocoupling and hydrodeoxygenation reactions. The influence of the counterion on the catalytic activity of the electrophilic phosphonium cations is also discussed.

[((Cl)Im(Dipp))P=P(Dipp)][GaCl4]: a polarized, cationic diphosphene.

The reaction of the neutral diphosphanide [((Cl)Im(Dipp))P-P(Cl)(Dipp)] (6) ((Cl)Im(Dipp) = 4,5-dichloro-1,3-bis(Dipp)-imidazol-2-yl; Dipp = 2,6-di-iso-propylphenyl) with methyl triflate (MeOTf) leads to the formation of cationic diphosphane [((Cl)Im(Dipp))(Me)P-P(Cl)(Dipp)](+) (8+) in a stereoselective methylation. In contrast, reacting with the Lewis acid GaCl3 yields cationic diphosphene [((Cl)Im(Dipp))P=P(Dipp)](+) (7+), which is explained by a low P-Cl bond dissociation energy. The significantly polarized P=P double bond in 7+ allows for its utilization as an acceptor for nucleophiles - the reaction with Cl(-) regenerates diphosphanide and the reaction with PMe3 gives cation [((Cl)Im(Dipp))P-P(PMe3)(Dipp)] (9+).

Phosphine and carbene azido-cations: [(L)N] and [(L)N].

The cationic N-species [(-HCF)PN] () featuring a perfluoro-arene phosphonium group serves as a N-source in stoichiometric reactions with several Lewis bases (L) allowing for the stepwise formation of [(L)N] and [(L)N] cations (L = phosphine, carbene) with liberation of (-HCF)P. X-Ray diffraction analysis and computational studies provide insight into the bonding in these remarkably stable azido-cations.

Catalytic Ketone Hydrodeoxygenation Mediated by Highly Electrophilic Phosphonium Cations.

Ketones are efficiently deoxygenated in the presence of silane using highly electrophilic phosphonium cation (EPC) salts as catalysts, thus affording the corresponding alkane and siloxane. The influence of distinct substitution patterns on the catalytic effectiveness of several EPCs was evaluated. The deoxygenation mechanism was probed by DFT methods.

1,2-Diphosphonium dication: a strong P-based Lewis acid in frustrated lewis pair (FLP)-activations of B-H, Si-H, C-H, and H-H bonds.

A highly Lewis acidic diphosphonium dication [(C10H6)(Ph2P)2](2+) (1), in combination with a Lewis basic phosphine, acts as a purely phosphorus-based frustrated Lewis pair (FLP) and abstracts hydride from [HB(C6F5)3](-) and Et3SiH demonstrating the remarkable hydridophilicity of 1. The P-based FLP is also shown to activate H2 and C-H bonds.

Electrophilic bis-fluorophosphonium dications: Lewis acid catalysts from diphosphines.

Stepwise oxidation of 1,8-bis(diphenylphosphino)naphthalene and a series of (oligo)methylene-linked diphosphines with XeF followed by fluoride abstraction yields a family of compounds featuring phosphine, phosphonium and phosphorane moieties in close proximity. The bisphosphonium ions [(CH)(PhPF)] () and [CH(PhPF)] () exhibit remarkable Lewis acidity arising from the proximity of the phosphonium centers. The effectiveness of bisphosphonium dications (, ) is examined in a series of Lewis acid catalysed transformations.

B(C6F5)3-mediated transformations and hydrogenation of carbodiimides.

The reactivity of a series of carbodiimides RNCNR (R=tBu (1 a), iPr (1 b), SiMe3 (1 c), and Dipp (2,6-di-iso-propylphenyl (1 d)) with B(C6 F5 )3 was investigated. After initial adduct formation, several distinct reaction pathways were identified. These pathways involve either isomerization of the carbodiimide to cyanamide derivatives or insertion of a carbodiimide into a BC bond of B(C6 F5 )3 to yield four-membered heterocycles.

Phosphinimine-substituted boranes and borenium ions.

The phosphinimines R3PNSiMe3 (R = t-Bu: 1a, R = Cy: 1b, R = Et: 1c, R = Ph: 1d) are reacted with a series of chloro and fluoroboranes (9Cl-9-BBN, (C6F5)2BCl, PhBCl2 and Mes2BF) to access a family of phosphinimine-substituted boranes (2a-d, 3b-d, 4c,d and 6a,b) via Me3SiX elimination (X = Cl, F). The steric and electronic factors governing the formation of monomeric or dimeric products (7c,d) are presented. In addition, in some cases a Lewis acid mediated exchange of Si-bonded methyl groups for a chloro-substituent was observed (5a,b).

Frustrated Lewis pair-mediated C-O or C-H bond activation of ethers.

Protocols for the FLP-mediated transformation of ethers are presented. Distinct reaction pathways involving either C-O or C-H bond activation occur depending on the application of oxophilic B(C6F5)3 or hydridophilic tritylium ions as the Lewis acid.

The highly Lewis acidic dicationic phosphonium salt: [(SIMes)PFPh₂][B(C₆F₅)₄]₂.

The dicationic imidazolium-phosphonium salt [(SIMes)PFPh2][B(C6F5)4]2 has been prepared and shown to exhibit remarkable Lewis acidity in stoichiometric reactions and acting as an effective Lewis acid catalyst for the hydrodefluorination of fluoroalkanes and the hydrosilylation of olefins.

The chemistry of cationic polyphosphorus cages--syntheses, structure and reactivity.

The aim of this review is to provide a comprehensive view of the chemistry of cationic polyphosphorus cages. The synthetic protocols established for their preparation, which are all based on the functionalization of P4, and their intriguing follow-up chemistry are highlighted. In addition, this review intends to foster the interest of the inorganic, organic, catalytic and material oriented chemical communities in the versatile field of polyphosphorus cage compounds.

[3+2] Fragmentation of an [RP(5)Cl](+) cage cation induced by an N-heterocyclic carbene.

The cage compound [DippP5 Cl][GaCl4 ] (Dipp=2,6-diisopropylphenyl) reacts with an NHC (N-heterocyclic carbene) by an unprecedented [3+2] fragmentation of the P5 (+) core. This yields an imidazoliumyl-substituted P3 species featuring a triphosphaallyl anion motif and a neutral P2 compound. The mechanism of the fragmentation reaction was elucidated by means of experimental and quantum chemical methods.

Synthesis of cationic R2P5(+) cages and subsequent chalcogenation reactions.

Cationic R2P5(+) cage compounds (1(+)) have been synthesized by the stoichiometric reaction of R2PCl, GaCl3 and P4. The reaction conditions depend on the substituent R. Alkyl-substituted derivatives (1 a-1 d[GaCl4]) are best synthesized under solvent-free conditions, whereas aryl-substituted derivatives (1 e-1 h[GaCl4]) are formed in C6H5F.

Formation of cationic [RP5Cl](+)-cages via insertion of [RPCl](+)-cations into a P-P bond of the P4 tetrahedron.

Fluorobenzene solutions of RPCl(2) and a Lewis acid such as ECl(3) (E = Al, Ga) in a 1:1 ratio are used as reactive sources of chlorophosphenium cations [RPCl](+), which insert into P-P bonds of dissolved P(4). This general protocol represents a powerful strategy for the synthesis of new cationic chloro-substituted organophosphorus [RP(5)Cl](+)-cages as illustrated by the isolation of several monocations (21a-g(+)) in good to excellent yields. For singular reaction two possible reaction mechanisms are proposed on the basis of quantum chemical calculations.

Zwitterionic and cationic P(5)-clusters from four-membered phosphorus-nitrogen-metal heterocycles.

A general route for the functionalization of P(4) mediated by four-membered phosphorus-nitrogen-metal heterocycles is introduced yielding novel phosphorus-rich clusters.

Preparation of the [(DippNP)2(P4)2]2+-dication by the reaction of [DippNPCl]2 and a Lewis acid with P4.

The controlled activation of white phosphorus, P(4), provides a key entry point into many aspects of phosphorus chemistry. The activation and functionalization of P(4) by N-heterocyclic carbenes and carbene-like main group element fragments is of considerable current interest. In this communication, we report on the first use of a disguised bifunctional Lewis acid [DippNP](2)(2+) obtained from the cyclo-1,3-diphospha-2,4-diazane [DippNPCl](2) for P(4) functionalization.