Phosphinine Ligands Research Articles

Structure and Reactivity of Ag(I) Complexes Bearing Tridentate Phosphinine Ligands

Structure and reactivity of novel Ag(I) complexes with tridentate phosphinine (phosphabenzene) ligands are discussed in this article. An equilibrium between the dimer and the monomer was observed for the λ3-phosphinine Ag(I) complex in the solution state. The λ3-phosphinine Ag(I) complex can be oxidized by PhI(OAc)2 to afford λ5-phosphinine species, maintaining the coordination to the metal center. Photochemical properties of the Ag(I) complexes were also investigated, and the emission of the λ3-phosphinine Ag(I) complex showed solvatochromic behavior.

A dinuclear Rh(-i)/Rh(i) complex bridged by biphilic phosphinine ligands.

Bimetallic complexes have enabled precise control of catalysis by accumulating two discrete metal centres. In these complexes, bridging ligands are essential to combine multiple metals into one molecule. Among some bridging modes, an unsymmetric bridging mode will differentiate the electronic structures of the two metal centres. In this study, a dinuclear Rh(-i)/Rh(i) complex bridged by tridentate phosphine-phosphinine-phosphine ligands was prepared by reduction of the corresponding Rh(i) complex. Single-crystal X-ray analysis and DFT calculations suggest that the phosphinine ligands adopt an unsymmetric bridging mode wherein phosphinine accepts d-electrons from one Rh centre and, at the same time, donates lone pairs to the other Rh centre.

Copper(I) and Gold(I) Complexes of Aminofunctionalized Phosphinines: Synthesis and Structural Characterization

AbstractA series of novel 3‐N,N‐dimethylaminofunctionalized phosphinines were synthesized and structurally characterized. DFT calculations showed that these aromatic phosphorus heterocycles possess stronger π‐donor and σ‐donor properties compared to the parent phosphinine C5H5P. With CuBr ⋅ SMe2, the corresponding complexes of the type [(phosphinine)2CuBr]2are formed, which show the classical terminal σ‐coordination mode of the phosphorus donor towards the Cu(I) center. Upon reaction with AuCl ⋅ SMe2, mononuclear phosphinine‐Au(I)Cl complexes could be obtained and crystallographically characterized. Moreover, the presence of a SiMe3‐group and a donor‐functionality provide the possibility for post‐synthetic ligand modifications. With CuCl ⋅ SMe2the phosphinine‐based hydrochloride salts forms a rare Cu(I) complex with a Cu4Cl4‐core, that contains two pairs of differently coordinating phosphinine ligands.

Reactivity Studies of Phosphinines: The Selenation of Diphenyl-Phosphine Substituents and Formation of a Chelating Bis(Phosphinine) Palladium(II) Complex

Phosphinines and donor-substituted phosphinines are of recent interest due to their use in homogeneous catalysis. In this article, a Pd(II) bis(phosphinine) complex was characterised and phosphorus–selenium coupling constants were used to assess the donor properties of the diphenylphosphine substituents of phosphinine ligands to promote their further use in catalysis. The selenation of 2,5-bis(diphenylphosphino)-3,6-dimethylphosphinine (5) and 2-diphenylphosphino-3-methyl-6-trimethylsilylphosphinine (6) gave the corresponding phosphine selenides 8 and 9, respectively, leaving the phosphinine ring intact. Multinuclear NMR spectroscopy, mass spectrometry and single crystal X-ray diffraction confirmed the oxidation of all the diphenylphosphine substituents with 1JP-Se coupling constants determined to be similar to SePPh3, indicating that the phosphinine rings were electronically similar to phenyl substituents. Solutions of 6 were found to react with oxygen slowly to produce the phosphine oxide 10 along with other by-products. The reaction of [bis{3-methyl-6-(trimethylsilyl)phosphinine-2-yl}dimethylsilane] (4) with [PdCl2(COD)] gave the chelating dichloropalladium(II) complex, as determined by multinuclear NMR spectroscopy, mass spectrometry and an elemental analysis. The molecular structure of the intermediate 2 in the formation of 4,6-di(tert-butyl)-1,3,2-diazaphosphinine (3) was also determined, which confirmed the structure of the diazaphosphacycle P(Cl){N=C(tBu)CH=C(tBu)-N(H)}.

A ruthenium cis-dihydride with 2-phosphinophosphinine ligands catalyses the acceptorless dehydrogenation of benzyl alcohol.

The first ruthenium dihydride complex featuring a phosphinine ligand cis-[Ru(H)2(2-PPh2-3-Me-6-SiMe3-PC5H2)2] was synthesised exclusively as the cis-isomer. When formed in situ from the reaction of cis-[Ru(Cl)2(2-PPh2-3-Me-6-SiMe3-PC5H2)2] with two equivalents of Na[BHEt3], as demonstrated by 31P and 1H NMR spectroscopy, the catalysed acceptorless dehydrogenation of benzyl alcohol was observed leading to benzyl benzoate in up to 70% yield.

Phosphorus Analogues of [Ni(bpy)2]: Synthesis and Application in Carbon-Halogen Bond Activation.

The neutral, homoleptic pyridylphosphininenickel(0) complex [Ni(2-Py-4,6-Ph2-PC5H2)2] (1) has been obtained by reaction of the formal Ni(0) source [(IPr)Ni(H2C═CHSiMe3)2] with 2 equiv of 2-(2'-pyridyl)-4,6-diphenylphosphinine (L). Compound 1 can be oxidized both electrochemically and through the use of ferrocenium salts, to afford the corresponding Ni(I) complexes [1]BF4, [1(THF)]PF6, and [12](BArF4)2. The structures of these salts reveal an interesting dependence on the nature of the anion. While [1]BF4 and [1(THF)]PF6 show trigonal-bipyramidal coordination of Ni in the solid state, [12](BArF4)2 exists as a dinuclear Ni(I) complex and possesses a bridging phosphinine moiety in a rare μ2 mode. Reactions of 1 with halobenzenes highlight the noninnocent behavior of the aromatic phosphinine ligand, leading to the formation of oxidized Ni complexes but not to classical oxidative addition products. The reaction of 1 with bromobenzene affords the λ5 phosphinine 2 and the bipyramidal Ni(I) complex [1]Br, whereas a more unconventional oxidation product 3 is formed from the reaction of 1 and iodobenzene.

Facile C=O Bond Splitting of Carbon Dioxide Induced by Metal-Ligand Cooperativity in a Phosphinine Iron(0) Complex.

New iron complexes [Cp*FeL]− (1‐σ and 1‐π, Cp*=C5Me5) containing the chelating phosphinine ligand 2‐(2′‐pyridyl)‐4,6‐diphenylphosphinine (L) have been prepared, and found to undergo facile reaction with CO2 under ambient conditions. The outcome of this reaction depends on the coordination mode of the versatile ligand L. Interaction of CO2 with the isomer 1‐π, in which L binds to Fe through the phosphinine moiety in an η5 fashion, leads to the formation of 3‐π, in which CO2 has undergone electrophilic addition to the phosphinine group. In contrast, interaction with 1‐σ—in which L acts as a σ‐chelating [P,N] ligand—leads to product 3‐σ in which one C=O bond has been completely broken. Such CO2 cleavage reactions are extremely rare for late 3d metals, and this represents the first such example mediated by a single Fe centre.

Multidentate Phosphanyl Phosphinines: Synthesis and Properties.

With respect to the well-developed chemistry of pyridines, that of phosphinines is in its infancy. There are still challenges to be overcome with respect to the development of simple syntheses and the application of phosphinine derivatives. Here, we show that sodium phosphinin-2-olate is a valuable building block to prepare multidentate phosphinine ligands, which in turn can be employed for the preparation of metal complexes. These PdII and RhI complexes were fully characterized, including by NMR spectra and single-crystal X-ray diffraction studies, which clearly demonstrate that molecules R3-x P(O-phosphinine)x with one, two, and three phosphinines (x=1, 2, 3) can be tethered to a central phosphorus donor center to give bis-, tris-, and tetradentate ligands.

Accessing Alkyl- and Alkenylcyclopentanes from Cr-Catalyzed Ethylene Oligomerization Using 2-Phosphinophosphinine Ligands

Desilylation of the 2-phosphinophosphinine 2-PPh2-3-Me-6-SiMe3-PC5H2 with HCl gave 2-PPh2-3-Me-PC5H3, demonstrating the late-stage modification of this bidentate heterocyclic ligand. Group 6 metal carbonyl complexes of these ligands showed κ2 binding and very small bite angles of 65.1–68.3°, and also demonstrated that the donor properties of 2-phosphinophosphinines can be tuned readily by the presence of the SiMe3 group, which gives a more π accepting phosphinine ligand. The properties of 2-phosphinophosphinines were compared to those of bidentate diphosphorus ligands computationally, contextualizing them in the ligand knowledge base for bidentate P,P donor ligands (LKB-PP), and were found to occupy an area of ligand space adjacent to Ar2PN(R)NAr2 ligands that have been successfully used in ethylene oligomerization reactions, but with well-separated properties in the second principal component. Testing 2-phosphinophosphinines in Cr-catalyzed ethylene oligomerization reactions showed key differences from s...

Synthesis and Photoluminescence Properties of CuI Complexes with Chelating Phosphinito Phosphinine Ligands

AbstractInvited for the cover of this issue are the groups of Hansjörg Grützmacher, ETH Zurich, Switzerland, and Zhongshu Li, Sun Yat‐Sen University, Guangzhou, China. The cover image shows the synthesis of dinuclear copper(I) halide complexes from a new diphenylphosphinite phosphinine as chelating ligand and simple CuI halides.

π-Rich σ(2)P-heterocycles: bent η(1)-P- and μ(2)-P-coordinated 1,3-benzazaphosphole copper(I) halide complexes.

The reaction of 1-neopentyl-1,3-benzazaphosphole 1 with CuCl, CuBr, or Cu(SMe2)Br in THF at room temperature provides sparingly soluble [Cu7(μ(2)-L6)(μ(2)-X7)](+)[CuX2](-) cluster complexes 2a,b (L indicates coordinated 1, a X = Cl, b X = Br), with loosely bound THF, in high yields. The conversions proceed via transient THF-soluble labile [(L2CuX)2] complexes. Separation before complete conversion, combined with suitable conditions for crystallization, allowed these intermediates to be trapped. Depending on the reactant ratios, crystals of the clusters or of dimeric L2CuX complexes were formed. The crystal structure analyses of 2a·4THF and the dimers 3b [{Cu(η(1)-L)2(μ(2)-Br)}2], 4b [{Cu(μ(2)-L)(η(1)-L)(κBr)}2], 5a·2MeOH, and 5b·2MeOH [{Cu(μ(2)-L)(η(1)-L)(κX···HOMe)}2] generally display μ(2)-P- and/or tilted η(1)-P-coordination, contrasting with the preference for the η(1)-P in-plane coordination mode of phosphinine ligands in their copper(I) halide complexes. DFT studies of geometry-optimized monomers LCuBr, L(CuBr)2, L2CuBr, and the dimers 3b and 4b, calculated at the ωB97xD/cc-PVDZ level, suggest that weak competing interactions with the solvent THF and the entropy factor of the dimerization result in lability and a subtle balance between the different complexes in solution, whereas the particular coordination observed in the crystals is attributable to conservation of the delocalized π-system in the ligand. The HOMO of 4b is composed of Cu d orbitals and the π-type HOMO of the bridging ligand. Interestingly, despite the rather short Cu···Cu interatomic separation (2.726 Ǻ), no bond critical point could be located in 4b, indicating the absence of weak cuprophilic interactions in this compound.

Gold(i) complexes with a phosphinine ligand: synthesis and structural characterization

The synthesis of two novel gold(I) complexes with a phosphinine ligand is reported. Reaction of a monodentate phosphinine ligand, 2,6-diphenyl-4-methylphosphorin (Lp; 1), with gold(I) molecular bricks leads to the preparation of two new mononuclear complexes with the general formulae [AuCl(Lp)] (2) and [Au(Lp)2](OTf) (3). The new compounds were spectroscopically characterized by infrared and NMR (1H, 13C and 31P). In addition, the molecular structure of [AuCl(Lp)] (2) was unequivocally ascertained by a single-crystal X-ray diffraction study. Furthermore the UV-Vis absorption and emission properties of these compounds were investigated. These complexes pave the way for the synthesis of a new class of phosphinine gold complexes displaying peculiar properties, which might hold promise as luminescent materials.

A theoretical study of the activity in Rh-catalysed hydroformylation: the origin of the enhanced activity of the π-acceptor phosphinine ligand

The factors governing the activity in Rh-catalyzed hydroformylation were investigated using DFT and QSAR methods.

Reactions of Pyridyl‐Functionalized, Chelating λ3‐Phosphinines in the Coordination Environment of RhIII and IrIII

Rh(III) and Ir(III) complexes based on the λ(3)-P,N hybrid ligand 2-(2'-pyridyl)-4,6-diphenylphosphinine (1) react selectively at the P=C double bond to chiral coordination compounds of the type [(1H⋅OH)Cp*MCl]Cl (2,3), which can be deprotonated with triethylamine to eliminate HCl. By using different bases, the pKa value of the P-OH group could be estimated. Whereas [(1H⋅O)Cp*IrCl] (4) is formed quantitatively upon treatment with NEt3, the corresponding rhodium compound [(1H⋅O)Cp*RhCl] (5) undergoes tautomerization upon formation of the λ(5)σ(4)-phosphinine rhodium(III) complex [(1⋅OH)Cp*RhCl] (6) as confirmed by single-crystal X-ray diffraction. Blocking the acidic P-OH functionality in 3 by introducing a P-OCH3 substituent leads directly to the λ(5)σ(4)-phosphinine iridium(III) complex (8) upon elimination of HCl. These new transformations in the coordination environment of Rh(III) and Ir(III) provide an easy and general access to new transition-metal complexes containing λ(5)σ(4)-phosphinine ligands.

New Low Coordination Phosphorus Heterocycles

With the aim of synthesizing novel functionalized derivatives of phosphinine (phosphabenzene), we investigated Diels-Alder approaches to 2-halophosphinines. The reaction of dienes such as 1-isopropenyl-1-cyclohexene and 1-vinylnaphthalene with Cl2P-CHCl2 and triethylamine gave 2-chlorophosphinines, but their substitution pattern was unsuitable for the synthesis of bidentate phosphinine ligands. However, the precursor Cl2P-CHl2 reacted with triethylamine in the presence of 1,3-butadiene or its 2,3-dimethyl derivative to furnish 2-iodophosphinines 5 which, directly or after formation of their pentacarbonyltungsten complexes, underwent a number of interesting functionalization reactions. Useful for reaction with a number of electrophiles were the organozinc reagent 4,5-dimethyl-2-iodozincophosphinine (26) which could be obtained directly from the corresponding 2-iodophosphinine 5b and zinc either in DMF or in THF/TMEDA, and the pentacarbonyltungsten coordinated 2-lithio derivative 36.

Solid-state 31P NMR characterisation of phosphinine-stabilised gold nanoparticles and a phosphinine-gold complex

Solid-State (31)P NMR studies reveal that phosphinine ligands employed for the stabilisation of gold nanoparticles react in part during the synthesis, and that the particles are stabilised by a mixture of intact phosphinine units together with several other surface-bound species. The spectral data of these species are characteristic for phosphine-type donors although unambiguous structure assignment was as yet unfeasible. The spectral data of surface-bound phosphinines were verified by comparison with the spectrum of an authentic complex [()AuCl]. The metal-bound phosphinines in both the complex and the nanoparticles prefer eta(1)(P)-coordination to a single metal atom, and the observation of splittings arising from coupling with (197)Au (I = 3/2) nuclei indicates that these ligands are not mobile. The fraction of intact phosphinines on the nanoparticles drops with decreasing steric protection although the observed product distribution shows no simple relation with substituent patterns.

Diphosphinine Derivatives of Terpyridine: A New Class of Neutral π‐Accepting PNP‐Pincer Ligands

The first diphosphinine analogue of terpyridine has been developed, which represents a new class of π-accepting neutral PNP-pincer ligands. Its electronic properties were evaluated by means of DFT calculations and the corresponding CuIBr complex was characterized crystallographically. The molecular structure revealed a distorted tetrahedral coordination geometry of the CuI center, due to an unusual coordination mode of the two phosphinine ligands (see graphic).