Pd(II) and Pt(II) complexes of 2-(2'-pyridyl)-4,6-diphenylphosphinine: synthesis, structure, and reactivity

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.

Palladium(II) complexes of bis(diphosphene) with different coordination behaviors

Organophosphorus compounds possessing a P-P double-bond character are intriguing materials in coordination chemistry because it is possible to form a variety of coordination modes from the π-bond in addition to the lone pairs. We report herein the complexation of a new bidentate ligand, ethylene-tethered bis(binaphthyldiphosphene) (S,S)-2, with palladium(II) species. The reaction of (S,S)-2 with [Pd(π-allyl)(cod)](SbF₆) and PdCl₂(cod) afforded η¹/η¹-bis(diphosphene) complex 7 and η¹-diphosphene/η²-phosphanylphosphide complex 8, respectively. The latter was characterized by a chloride migration from the palladium atom to a phosphorus atom due to the high electron-accepting character of the PP moiety. Theoretical calculations revealed the migration process and nature of complex 8.

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)}.

Making Aromatic Phosphorus Heterocycles More Basic and Nucleophilic: Synthesis, Characterization and Reactivity of the First Phosphinine Selenide

The synthesis and isolation of a phosphinine selenide was achieved for the first time by reacting red selenium with 2,6-bis(trimethylsilyl)phosphinine. The rather large coupling constant of ¹ J_P,Se =883 Hz is in line with a P-Se bond of high s-character. The σ-electron donating Me₃ Si-substituents significantly increase the energy of the phosphorus lone pair and hence its basicity, making the heterocycle considerably more basic and nucleophilic than the unsubstituted phosphinine C₅ H₅ P, as confirmed by the calculated gas phase basicities. NBO calculations further reveal that the lone pairs of the selenium atom are stabilized through donor-acceptor interactions with antibonding orbitals of the aromatic ring. The novel phosphinine selenide shows a distinct reactivity towards hexafluoro-2-butyne, Au(I)Cl as well as ⁱ PrOH. Our results pave the way for new perspectives in the chemistry of phosphorus in low coordination.

Phosphinines versus mesoionic carbenes: a comparison of structurally related ligands in Au(i)-catalysis

Gold(i) complexes based on a 2,4,6-triarylphosphinine and a mesoionic carbene derivative have been prepared and characterized crystallographically. Although structurally related, both heterocycles differ significantly in their donor/acceptor properties. These opposed electronic characteristics have been exploited in Au(i)-catalyzed cycloisomerization reactions. For the conversion of the standard substrate dimethyl 2-(3-methylbut-2-enyl)-2-(prop-2-ynyl)malonate the results obtained for both Au-catalysts were found to be very similar and comparable to the ones reported in the literature for other carbene- or phosphorus(iii)-based Au(i)-complexes. In contrast, a clear difference between the catalytic systems was found for the cycloisomerization of the more challenging substrate N-2-propyn-1-ylbenzamide. A combination of the phosphinine-based complex and [AgSbF₆] or [Cu(OTf)₂] leads to a catalytic species, which is more active than the mesoionic carbene-based coordination compound. We attribute these differences to the stronger π-accepting ability of phosphinines in comparison to mesoionic carbenes. The here presented results show for the first time that phosphinines can be used efficiently as π-accepting ligands in Au(i)-catalyzed cycloisomerization reactions.

Substituent effects in pyridyl-functionalized pyrylium salts, pyridines and λ3,σ2-phosphinines: a fundamental and systematic study

A series of pyridyl-functionalized O⁺–, N–, and P– containing heterocycles have been prepared and investigated for substituent effects.

Two isomers of a bis(diphenylphosphino)phosphinine, and the synthesis and reactivity of Ru arene/Cp* phosphinophosphinine complexes

Two isomers of a bis(diphenylphosphino)phosphinine have been synthesised, and the Ru coordination chemistry of a 2-phosphinophosphinine extended to include reactions of H₂O across a PC double bond.

A ruthenium(ii) bis(phosphinophosphinine) complex as a precatalyst for transfer-hydrogenation and hydrogen-borrowing reactions

A Ru(ii) complex with 2-phosphinophosphinine ligands activated with KO^tBu catalyses the room temperature transfer hydrogenation of acetophenone and the hydrogen-borrowing reaction of MeOH/EtOH to the advanced biofuel isobutanol.

2-(2′-Pyridyl)-4,6-diphenylphosphinine versus 2-(2′-pyridyl)-4,6-diphenylpyridine: synthesis and characterization of novel Cr0, Mo0 and W0 carbonyl complexes containing chelating P,N and N,N ligands

Replacing nitrogen by phosphorus in otherwise similar structures changes the properties of the resulting compounds significantly due to the electronic differences that exist between these heteroatoms.

An unprecedented cyclometallated platinum(ii) complex incorporating a phosphinine co-ligand: synthesis and photoluminescence behaviour

The first luminescent platinum(ii) complex bearing phosphinine co-ligands with a long-lived emission from a phosphinine-localised triplet excited state is reported.