Phosphenium ions, not to be confused with phosphonium or phosphirenium, are divalent cations of phosphorus of the form [PR2]+. Phosphenium ions have long been proposed as reaction intermediates.
Phosphenium ions, not to be confused with phosphonium or phosphirenium, are divalent cations of phosphorus of the form [PR2]+. Phosphenium ions have long been proposed as reaction intermediates.
The first cyclic phosphenium compounds were reported in 1972 by Suzanne Fleming and coworkers. [1] Acyclic phosphenium compounds were synthesized by Fleming's thesis advisor Robert Parry in 1976. [2]
Several methods exist for the preparation of two-coordinate phosphorus ions. A common method involves halide abstraction from halophosphines: [3]
Protonolysis of tris(dimethylamino)phosphine affords the phosphenium salt: [4]
Weakly coordinating anions are desirable. Triflic acid is often used. [3]
N-heterocyclic phosphenium (NHP) have also been reported. [5] Reaction of PI3 with the α-diimine yields the NHP cation by reduction of the diimine and oxidation of iodine.
According to X-ray crystallography, [(i-Pr2N)2P]+ is nearly planar consistent with sp2-hybridized phosphorus center. [6] The planarity of the nitrogen center is consistent with the resonance of the lone pair of the nitrogen atom as a pi bond to the empty phosphorus 3p orbital perpendicular to the N−P−N plane. An idealized sp2 phosphorus center would expect an N−P−N angle of 120°. The tighter N−P−N angle observed in the crystal structure can be interpreted as the result of repulsion between the phosphorus lone pair with the bulky i-Pr2N ligands, as the P(NH
2)+
2 and PH+
2 molecules have bond angles closer to 110° and 90°, respectively. [3] [6]
Calculations also show that the analogy to carbenes is lessened by strongly π-donating substituents. With NH2 substituents, the phosphenium cation assumes allyl character. [7] Generalized Valence Bond (GVB) calculations of the phosphenium ions as having a singlet ground state, singlet-triplet separation increases with increasing electronegativity of the ligands. [3] [8] [9] The singlet-triplet separation for PH+
2 and PF+
2 were calculated to be 20.38 and 84.00 kcal/mol, respectively. Additionally, the triplet state of the phosphenium ion displays a greater bond angle at the phosphorus. For example, the calculated bond angle of the singlet state of PH+
2 is approximately 94° compared to 121.5° in the triplet state. Calculated bond lengths between the two states are not significantly impacted. [9]
Phosphenium is isoelectronic with singlet (Fisher) carbenes and are therefore expected to be Lewis acidic. Adducts are produced by combining [P(NMe2)2]+ and P(NMe2)3: [2]
Being electrophilic, they undergo C−H insertion reactions. [10]
Phosphenium intermediates are invoked as intermediates in the McCormack reaction, a method for the synthesis of organophosphorus heterocycles. An illustrative reaction involves phenyldichlorophosphine and isoprene: [11]
Isolated phosphenium salts undergo this reaction readily. [12]
There are few examples of reactions catalyzed by phosphenium. In 2018, Rei Kinjo and coworkers reported the hydroboration of pyridines by the NHP salt, 1,3,2-diazaphosphenium triflate. The NHP is proposed to act as a hydride transfer reagent in this reaction. [13]
![Structure of [(Et2N)2PFe(CO)4] as the AlCl
4 salt. CINLAM.svg](http://upload.wikimedia.org/wikipedia/commons/thumb/f/f4/CINLAM.svg/330px-CINLAM.svg.png)
Phosphenium ions serve as ligands in coordination chemistry. [2] [(R2N)2PFe(CO)4]+ was prepared by two methods: the first being the abstraction of a fluoride ion from (R2N)2(F)PFe(CO)4 by PF5. The second method is the direct substitution reaction of Fe(CO)5 by the phosphenium ion [P(NR2)]+. [14] Related complexes exist of the type Fe(CO)4L, where L = [(Me2N)2P]+, [(Et2N)2P]+, [(Me2N)(Cl)P]+, and [(en)P]+ (en = C2H4(NH2)2). [3]
N-heterocyclic phosphenium-transition metal complexes are anticipated due to their isoelectronicity to N-heterocyclic carbenes. In 2004, Martin Nieger and coworkers synthesized two Cobalt-NHP complexes. Experimental and computation analysis of the complexes confirmed the expected L→M σ donation and the M→L π backbonding, though the phosphenium was observed to have reduced σ donor ability. It was suggested that this is due to the greater s orbital-character of the phosphorus lone pair compared to the lone pair of the analogous carbene. [15] Additional studies of NHP ligands by Christine Thomas and coworkers in 2012, likened the phosphenium to nitrosyl. [16] Nitrosyl is well known for its redox non-innocence, coordinating in either a bent or linear geometry that possess different L–M bonding modes. It was observed that NHPs in complex with a transition metal may have either a planar or pyramidal geometry about the phosphorus, reminiscent of the linear versus bent geometries of nitrosyl. Highly electron-rich metal complexes were observed to have pyramidal phosphorus, while less electron-rich metals showed greater phosphenium character at the phosphorus. Pyramidal phosphorus indicates significant lone pair character at phosphorus, suggesting that the L→M σ donation and the M→L π backbonding interactions have been replaced with M→L σ donation, formally oxidizing the metal center by two electrons. [16]
A hypervalent molecule (the phenomenon is sometimes colloquially known as expanded octet) is a molecule that contains one or more main group elements apparently bearing more than eight electrons in their valence shells. Phosphorus pentachloride (PCl5), sulfur hexafluoride (SF6), chlorine trifluoride (ClF3), the chlorite (ClO−
2) ion, and the triiodide (I−
3) ion are examples of hypervalent molecules.
The 3-center 4-electron (3c–4e) bond is a model used to explain bonding in certain hypervalent molecules such as tetratomic and hexatomic interhalogen compounds, sulfur tetrafluoride, the xenon fluorides, and the bifluoride ion. It is also known as the Pimentel–Rundle three-center model after the work published by George C. Pimentel in 1951, which built on concepts developed earlier by Robert E. Rundle for electron-deficient bonding. An extended version of this model is used to describe the whole class of hypervalent molecules such as phosphorus pentafluoride and sulfur hexafluoride as well as multi-center π-bonding such as ozone and sulfur trioxide.
Kenneth Norman Raymond is a bioinorganic and coordination chemist. He is Chancellor's Professor of Chemistry at University of California, Berkeley, Professor of the Graduate School, the Director of the Seaborg Center in the Chemical Sciences Division at Lawrence Berkeley National Laboratory, and the President and Chairman of Lumiphore.
Organogold chemistry is the study of compounds containing gold–carbon bonds. They are studied in academic research, but have not received widespread use otherwise. The dominant oxidation states for organogold compounds are I with coordination number 2 and a linear molecular geometry and III with CN = 4 and a square planar molecular geometry. The first organogold compound discovered was gold(I) carbide Au2C2, which was first prepared in 1900.
Metal carbon dioxide complexes are coordination complexes that contain carbon dioxide ligands. Aside from the fundamental interest in the coordination chemistry of simple molecules, studies in this field are motivated by the possibility that transition metals might catalyze useful transformations of CO2. This research is relevant both to organic synthesis and to the production of "solar fuels" that would avoid the use of petroleum-based fuels.
In chemistry, a boranylium ion is an inorganic cation with the chemical formula BR+
2, where R represents a non-specific substituent. Being electron-deficient, boranylium ions form adducts with Lewis bases. Boranylium ions have historical names that depend on the number of coordinated ligands:
Gregory S. Girolami is the William H. and Janet G. Lycan Professor of Chemistry at the University of Illinois at Urbana-Champaign. His research focuses on the synthesis, properties, and reactivity of new inorganic, organometallic, and solid state species. Girolami has been elected a fellow of the American Association for the Advancement of Science, the Royal Society of Chemistry, and the American Chemical Society.
The fluorosulfates or fluorosulfonates are a set of salts of fluorosulfuric acid with an ion formula SO3F−. The fluorosulfate anion can be treated as though it were a hydrogen sulfate anion with hydroxyl substituted by fluorine. The fluorosulfate ion has a low propensity to form complexes with metal cations. Since fluorine is similar in size to oxygen, the fluorosulfate ion is roughly tetrahedral and forms salts similar to those of the perchlorate ion. It is isoelectronic with hydrogen sulfate, HSO−
4. When an organic group is substituted for the anions, organic fluorosulfonates are formed.
David Markham Lemal is the Albert W. Smith Professor of Chemistry Emeritus and Research Professor of Chemistry at Dartmouth College. He received an A.B. degree (summa) from Amherst College in 1955 and a Ph.D. in Chemistry from Harvard University in 1959. At Harvard he worked with R. B. Woodward on deoxy sugars and a synthesis of the alkaloid yohimbine.
Cobalt(II)–porphyrin catalysis is a process in which a Co(II) porphyrin complex acts as a catalyst, inducing and accelerating a chemical reaction.
Parisa Mehrkhodavandi is a Canadian chemist and Professor of Chemistry at the University of British Columbia (UBC). Her research focuses on the design of new catalysts that can effect polymerization of sustainably sourced or biodegradable polymers.
Christopher "Kit" Colin Cummins is an American chemist currently the Henry Dreyfus Professor at Massachusetts Institute of Technology. He has made contributions to the coordination chemistry of transition metal nitrides, phosphides, and carbides.
Lawrence Que Jr. is a chemist who specializes in bioinorganic chemistry and is a Regents Professor at the University of Minnesota, Twin Cities. He received the 2017 American Chemical Society (ACS) Award in Inorganic Chemistry for his contributions to the field., and the 2008 ACS Alfred Bader Award in Bioinorganic Chemistry.
A lanthanocene is a type of metallocene compound that contains an element from the lanthanide series. The most common lanthanocene complexes contain two cyclopentadienyl anions and an X type ligand, usually hydride or alkyl ligand.
Julia A. Kovacs is an American chemist specializing in bioinorganic chemistry. She is Professor of Chemistry at the University of Washington. Her research involves synthesizing small-molecule mimics of the active sites of metalloproteins, in order to investigate how cysteinates influence the function of non-heme iron enzymes, and the mechanism of the oxygen-evolving complex (OEC).
Fluorosulfite is an ion with the formula SO2F−. The term is also used for compounds or salts containing this group. Fluorosulfite was discovered in 1953 by F Seel and H Meier.
Metal-ligand cooperativity (MLC) is a mode of reactivity in which a metal and ligand of a complex are both involved in the bond breaking or bond formation of a substrate during the course of a reaction. This ligand is an actor ligand rather than a spectator, and the reaction is generally only deemed to contain MLC if the actor ligand is doing more than leaving to provide an open coordination site. MLC is also referred to as "metal-ligand bifunctional catalysis." Note that MLC is not to be confused with cooperative binding.
Karsten Meyer is a German inorganic chemist and Chair of Inorganic and General Chemistry at the Friedrich-Alexander University of Erlangen-Nürnberg (FAU). His research involves the coordination chemistry of transition metals as well as uranium coordination chemistry, small molecule activation with these coordination complexes, and the synthesis of new chelating ligands. He is the 2017 recipient of the Elhuyar-Goldschmidt Award of the Spanish Royal Society of Chemistry, the Ludwig-Mond Award of the Royal Society of Chemistry, and the L.A. Chugaev Commemorative Medal of the Russian Academy of Sciences, among other awards. He also serves as an Associate Editor of the journal Organometallics since 2014.
Connie C. Lu is a Taiwanese-American inorganic chemist who is a Professor of Chemistry at the University of Minnesota, Twin Cities. Lu's research focuses on the synthesis of novel bimetallic coordination complexes, as well as metal-organic frameworks. These molecules and materials are investigated for the catalytic conversion of small molecules like as N2 and CO2 into value-added chemicals like ammonia and methanol. Lu is the recipient of multiple awards for her research, including the National Science Foundation CAREER Award and the Sloan Research Fellowship in 2013, and an Early Career Award from the University of Minnesota's Initiative for Renewable Energy and the Environment in 2010.
9-borafluorenes are a class of boron-containing heterocycles consisting of a tricyclic system with a central BC4 ring with two fused arene groups. 9-borafluorenes can be thought of as a borole with two fused arene rings, or as a trigonal planar boron atom with an empty p orbital bridging two biphenyl rings. However, 9-borafluorenes are generally less reactive than boroles due to less antiaromatic character and Lewis acidity. Containing highly conjugated π systems, 9-borafluorenes possess interesting photophysical properties. In addition, 9-borafluorenes are good Lewis acids. This combination of properties enables potential uses such as in light-emitting materials, solar cells, and sensors for some molecules.