A New Route to Phosphaalkene Chelate Complexes: SET Deoxygenation of Oxaphosphirane Complexes Followed by Intramolecular CO Substitution

Analysis of Non-innocence of Phosphaquinodimethane Ligands when Charge and Aromaticity Come into Play

Several phosphaquinodimethanes and their M(CO)5 complexes (M=Cr, Mo, W) and model derivatives have been theoretically investigated regarding the quest of non-innocence. Computed structural and electronic properties of the P-Me/NH2 substituted phosphaquinodimethanes and tungsten complexes revealed an interesting non-innocent ligand behaviour for the radical anion complexes with distonic ion character and a strong rearomatization of the middle phenyl ring. The latter was further probed taking also geometric aromaticity (HOMA) and quinoid distortion parameters (HOMQc) into account, as well as NICS(1). Furthermore, the effect of the P-substitution was investigated for real (or plausible) complexes and their free ligands focusing on the resulting aromaticity at the middle phenyl ring and vertical one-electron redox processes. The best picture of ligand engagement in redox changes was provided by representing NICS(1) values versus HOMA and the new geometric distortion parameter HOMQc8.

Versatile Coordination Modes of Triphospha-1,4-pentadiene-2,4-diamine

1,3,5-Triphospha-1,4-pentadiene-2,4-diamine reacts with [M(CO)₄L] (M = Mo, L = nbd (norbornadiene); M = W, L = 2 CH₃CN) to give the chelate complexes [M(CO)₄(PMes{C(NHCy)PMes}₂-κ P¹ ,P³)]. In contrast, an unusual intramolecular rearrangement occurred with [Cu(CH₃CN)₄]PF₆ leading to the dimeric copper(I) complex [Cu(CNCy){PHMesPMesC(NHCy)PMes-κ P¹ ,P³}]₂(PF₆)₂. The mechanism of the rearrangement was supported by quantum-mechanical calculations. The transition-metal complexes were characterized by multinuclear NMR spectroscopy, mass spectrometry, infrared spectroscopy, and X-ray crystallography.

Reactivity studies of an imine-functionalised phosphaalkene; unusual electrostatic and supramolecular stabilisation of a σ2λ3-phosphorus motif via hydrogen bonding

Protonation with strong acids at an imine over addition to a phosphaalkene; resulting adducts display hydrogen bonding.

Unconventional ionic ring-deconstruction pathways of a three-membered heterocycle

Two different ionic deconstruction reactions of the oxaphosphirane ring in I are reported. One is induced by base and involves displacement of the aldehyde unit forming II whilst acid-initiated extrusion of the ring-carbon with its substituents yielded III. Further insights into the latter ring-deconstruction were obtained by quantum chemical calculations.

Study on the Acid-Induced Ring-Expansion of an Oxaphosphirane Complex with an Electron-Withdrawing C-Substituent

A study on the acid-induced ring-expansion reaction of the first oxaphosphirane complexes bearing an electron-withdrawing C-substituent is described. The stereoselectively obtained 1,3,4-dioxaphospholane complexes 4a–c, representing the first examples of such fluorinated ligands, were unambiguously characterized by multinuclear NMR, elemental analysis, mass spectrometry, and single-crystal X-ray diffraction studies.

A novel route to C-unsubstituted 1,2-oxaphosphetane and 1,2-oxaphospholane complexes

The synthesis of 1,2-oxaphosphetane complexes 7 and 1,2-oxaphospholane complex 12 bearing only substituents at phosphorus is reported using the reaction of Li/Cl phosphinidenoid complex 2 with 2-iodoethanol or 3-bromo-propane-1-ol and the subsequent dehydrohalogenation using KHMDS.

Rearrangement and deoxygenation of 3,3-bis(2-pyridyl)oxaphosphirane complexes

The reaction of Li/Cl phosphinidenoid pentacarbonylmetal(0) complexes with bis(2-pyridyl)ketone led to overcrowded oxaphosphirane derivatives. They can undergo deoxygenation by Ti(iii) reagents or ring expansion via P–C cleavage followed by P–N cyclization.

Metal carbonyl complexes of phosphaamidines. Coordinative integrity detected in C-amino(λ3,σ2)-phosphaalkene isomers coordinated through n(P) HOMO−1 donor orbitals

L(Cr,Mo,W)(CO)₅coordination ofN,P-disubstituted phosphaamidines stabilizes molecules prone to isomerization. NMR spectra are consistent with the average mirror symmetry.

Electronic structure predictions of the properties of non-innocent P-ligands in group 6B transition metal complexes

Neutral group 6B (Cr, Mo, W) pentacarbonyl complexes M(CO)5-L possessing various P-ligands such as phosphines, phosphaalkenes, and phospha-quinomethanes can form radical cations and anions under redox conditions. There is significant interest in whether the radical site is localized on the metal or on a "non-innocent" ligand. Density functional theory was used to predict whether the radicals of the complexes behave as metal or ligand-centered radicals and whether these compounds could form in solution or as an ion pair with various oxidizing and reducing agents. The quinone-like ligands are predicted to be ligand centered radicals when they are anions and metal centered radicals when they are cations. The predicted reaction energies for single electron transfer (SET) reactions involving the quinone like ligands are negative or near thermoneutral for both radicals in polar solutions and as solid state ion pairs. The energetics of the SET reactions can be controlled by the nature of L, the nature of the oxidizing/reducing agent, and the solvent polarity. Such complexes could be used as flexible catalysts for single electron transfer reactions.