A Cation-Captured Palladium(0) Anion: Synthesis, Structure, and Bonding of [PdBr(PPh3)2]− Ligated by an N-Heterocyclic Phosphenium Cation

Caputo, Christine A.; Brazeau, Allison L.; Hynes, Zachery; Price, Jacquelyn T.; Tuononen, Heikki M.; Jones, Nathan D.

doi:10.1021/om9006278

Cited by 54 publications

(54 citation statements)

References 26 publications

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“…We assume that this reaction is likewise initiated by Cl/OTf exchange, but that a hypothetical NHP palladium(0) triflate is unstable and decomposes. This finding is in line with previous results,5,13 which indicated that the “push–pull” effect exerted by a combined action of π‐acceptor and strong σ‐donor ligands is essential for the stabilization of the zero‐valent metal atom in these complexes.…”

Section: Resultssupporting

confidence: 93%

“…The 31 P chemical shifts of 3 – 6 in general fall in the downfield region ( δ > 200 ppm), which is typical of the majority of related phosphenium complexes5–9 but not for IIb , which exhibits a very unusual 31 P chemical shift at δ = 26.9 ppm,7 nearly 200 ppm lower than in the other complexes. We attribute this amazing deviation to the rather special electronic situation7 that presumably makes this compound an outlier.…”

Section: Resultsmentioning

confidence: 80%

“…Cyclic diaminophosphenium ions1,2 (also known as N‐heterocyclic phosphenium ions, NHP) have a long history in coordination chemistry because of their ability to act as σ‐donor/π‐acceptor ligands in transition‐metal complexes 3,4. A particularly interesting sub‐class are complexes with group 10 metal atoms (M = Ni, Pd, Pt) of the general type [MX(NHP)(L) 2 ] ( I )5,6 and [MX(NHP)] 2 ( II ;7,8 L = phosphane, X = halide), which exhibit notable structural diversity and raise some scientifically interesting electron‐counting difficulties (Scheme ) 8. Thus, complexes I exist as two structural varieties in which the phosphorus atom in the NHP unit exists either in a trigonal‐planar coordination sphere with a short P–M bond or in a pyramidal coordination with a lengthened P–M bond.…”

Section: Introductionmentioning

confidence: 99%

“…Thus, complexes I exist as two structural varieties in which the phosphorus atom in the NHP unit exists either in a trigonal‐planar coordination sphere with a short P–M bond or in a pyramidal coordination with a lengthened P–M bond. Structures of the first type are considered to reflect the interaction of a cationic phosphenium ligand with a zero‐valent metal atom to form a double bond in a bonding situation similar to Fischer‐type carbene complexes ( Ia ; Scheme ) 5,8. In contrast, the bonding in complexes of the second type has been interpreted in terms of the interaction of an anionic phosphide ligand with a divalent metal centre ( Ib ; Scheme ), and the dichotomy between the two types of complexes is assumed to reflect a variable electron demand in the phosphenium ligands, which has allowed one to establish an analogy with the “non‐innocent” behaviour of nitrosyl ligands 6…”

Section: Introductionmentioning

confidence: 99%

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Sterically Controlled Synthesis and Nucleophilic Substitution Reactions of Di‐ and Trimeric N‐Heterocyclic Phosphenium Metal(0) Halides

et al. 2014

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The reaction of symmetrical bis(diazaphospholenyl) compounds with [MCl2(cod)] (M = Pd, Pt; cod = 1,5‐cyclooctadiene) has been used to prepare N‐heterocyclic phosphenium (NHP) metal(0) halides [M(NHP)Cl]n with diverse N substituents. Characterisation by ESI‐MS and NMR spectroscopy revealed that N‐tBu‐ and N‐aryl‐substituted NHP precursors yield trimeric (n = 3) and dimeric (n = 2) products, respectively; the degree of aggregation is presumably controlled by the different steric requirements of the NHP moiety. A single‐crystal XRD study of a trimeric Pd complex confirmed the proposed constitution of the complexes with μ2‐bridging NHP and terminal chlorido ligands and allowed their metrical parameters to be analysed for the first time undisturbed by crystallographic disorder. Studies of ligand substitution and redistribution processes revealed that the complexes withstand exchange of the μ‐bridging NHP units but tolerate substitution of the terminal chlorido ligands by other strong nucleophiles (SCN–, I–) with conservation of the oligomeric framework. Attempts to replace chlorido by thiolato ligands led to the discovery of a reaction between a phosphenium metal thiolate [Pd(NHP)(SR)]3 and CH2Cl2 to give a formaldehyde dithioacetal H2C(SR)2 (R = benzyl). This reaction could be developed into a protocol for a C–S cross‐coupling reaction in the presence of a catalytic amount of the phosphenium complex.

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Section: Resultssupporting

confidence: 93%

Section: Resultsmentioning

confidence: 80%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Sterically Controlled Synthesis and Nucleophilic Substitution Reactions of Di‐ and Trimeric N‐Heterocyclic Phosphenium Metal(0) Halides

et al. 2014

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“…Both the unusual reaction pathway and the possibility to observe the reaction intermediate 8 are again to a large extent attributable to the strong prepolarization of the P-Cl bond in the starting chloro-NHP. A similar formation of a cation-captured Pd(0)-bromide was recently also observedduring the reaction of a P-bromo-NHP with tetrakis-triphenylphosphine palladium(0) 21. …”

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confidence: 76%

Diazaphospholenes:N-Heterocyclic Phosphines between Molecules and Lewis Pairs

Gudat

2010

Acc. Chem. Res.

134

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The interest in geometrically distorted or electronically polarized molecules is often motivated by the realization that unusual structures can engender unprecedented physical or chemical properties. 1,3,2-Diazaphospholenes are N-heterocyclic phosphines (NHPs) that have ring structures similar to N-heterocyclic carbenes (NHCs). Although NHPs were initially mainly of interest as precursors for carbene-analogous phosphenium cations, it was noted that they exhibit quite peculiar structural features and remarkable chemical behavior on their own. In this Account, we discuss both structure and chemistry in connection with the special bonding situation that is characterized by significant n(N)-σ*(P-X) hyperconjugation and induces a strong ionic polarization of the P-X bonds. This induced polarization is surprisingly maintained even when P and X have similar or like electronegativities (for example, X = H, P) and offers the possibility to design compounds with polarized homonuclear bonds. An exemption from the general pattern was only noted for some P-amino-NHPs in which reverse hyperconjugation weakens endocyclic P-N bonds and was predicted to facilitate ring fragmentation and formation of phosphinidenes. An important corollary of the P-X bond polarization in NHPs is a unique bond lengthening, which not only can be fine-tuned by adjusting intramolecular steric and electronic interactions but also responds to intermolecular influences and solvent effects. Insight from crystallographic, spectroscopic, and computational studies allows the development of concepts for controlled manipulation of the bonding, up to a point where P-X bonds are dominated by electrostatic interactions and species behave as Lewis pairs rather than covalent molecules. An appealing aspect lies in the fact that this P-X bond polarization induces reactivities that have hardly any precedence in phosphine chemistry. Examples include (i) reactions of P-hydrogen-substituted NHPs as hydride transfer reagents, (ii) metatheses and additions to multiple bonds (diphosphination) of phosphino-NHPs, which can be used to catalyze P-C cross-coupling reactions and to synthesize 1,2-bisphosphine ligands, (iii) cyclopentadienyl (Cp) transfer reactions of P-Cp-NHPs, and (iv) metal insertion into the P-X bonds of P-halogeno-NHPs. In many aspects, these reactions have potentially useful mechanistic or synthetic implications, and their future exploitation might help to convert NHPs from academically interesting species into useful reagents.

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Diazaphospholene Chemistry

Gudat¹

2018

Encyclopedia of Inorganic and Bioinorganic Chemistry

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Diazaphospholenes are N‐heterocyclic phosphines that can be derived from N‐heterocyclic carbenes by formally replacing the divalent carbon atom by a P–X unit consisting of a tervalent phosphorus atom and an exocyclic substituent X. This arrangement provides a very peculiar electronic structure that is characterized by an exceptionally strong hyperconjugation between delocalized π‐electrons in the ring and the σ*(P–X) orbital and results in a considerable ionic polarization of the exocyclic bond with a concomitant increase of negative partial charge on X. The effect persists even in unpolar P–X bonds and induces unprecedented chemical reactivity like a marked polarization of homonuclear bonds to phosphorus‐based substituents, which immensely facilitates bond activation reactions, and a reversal of the polarity (“Umpolung”) of the P–H bonds in secondary diazaphospholenes, which gives rise to a hydride behavior unprecedented for phosphines. The emerging exploitation of these features in diverse areas of synthetic chemistry sparked various applications of diazaphospholenes both as stoichiometric reagents and as organocatalysts. It is the aim of this article to give a comprehensive overview on the chemistry of diazaphospholenes, starting with a discussion of their specific electronic structure, and addressing their synthesis, principal reaction patterns, and applications as reagents in stoichiometric reactions and organocatalysts in metal‐free catalytic transformations. A concluding section will focus on ligand‐centered reactions of diazaphospholenes with exocyclic transition metal substituents (“metallo‐diazaphospholenes”) and their application in catalysis.

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A Cation-Captured Palladium(0) Anion: Synthesis, Structure, and Bonding of [PdBr(PPh₃)₂]⁻ Ligated by an N-Heterocyclic Phosphenium Cation

Cited by 54 publications

References 26 publications

Sterically Controlled Synthesis and Nucleophilic Substitution Reactions of Di‐ and Trimeric N‐Heterocyclic Phosphenium Metal(0) Halides

Sterically Controlled Synthesis and Nucleophilic Substitution Reactions of Di‐ and Trimeric N‐Heterocyclic Phosphenium Metal(0) Halides

Diazaphospholenes:N-Heterocyclic Phosphines between Molecules and Lewis Pairs

Diazaphospholene Chemistry

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