Manganese 2-phosphinophosphinine precatalysts for methanol/ethanol upgrading to isobutanol

Two Mn-phosphinophosphinine complexes were synthesised from reaction of the proligand with [MnBr(CO)5] at 80 °C for 2 h; 2-diphenylphosphino-3-methyl-6-trimethylsilylphosphinine manganese tricarbonyl bromide (2TMS) and 2-diphenylphosphino-3-methyl-phosphinine manganese tricarbonyl bromide (2H). 31P{1H} NMR spectroscopy revealed characteristic chemical shifts for the phosphinine and phosphine donors bound to Mn (255.4 and 23.7 ppm for 2TMS; 234.2 and 24.8 ppm for 2H), and single crystal X-ray diffraction established the structure of the chelating complex 2TMS. Rapid reaction of both complexes with water was observed with 2TMS reacting to eventually yield a single product, syn-3TMS, from the syn-1,2-addition of water across the PC multiple bond on the bromide face, confirmed by X-ray diffraction for both an unsolvated and solvated structure, where MeOH was found to be H-bonding to the P-OH functionality. The reaction of 2R with dry methanol gave multiple products that were not in equilibrium with each other, and the molecular structure of one isomer was definitively established by X-ray diffraction as an unusual 1,4-addition product (1,4-4TMS). However, reaction of 2R with methanol in the presence of trace water showed that hydrolysis products 3R were formed preferentially. Both phosphinine complexes acted as pre-catalysts for the Guerbet upgrading of methanol/ethanol to isobutanol at 180 °C over 90 h, giving yields of isobutanol (based on moles of ethanol) of 22% for 2TMS and 27% for 2H. This is superior to known Mn dppm complexes [dppm = bis(diphenylphosphino)methane], including the 21% yield recorded for the best derivative [MnBr(κ2-PPh2C(H)PhPPh2)(CO)3] shown to date.

NIR-Emissive Chromium(0), Molybdenum(0), and Tungsten(0) Complexes in the Solid State at Room Temperature

The development of NIR emitters based on earth-abundant elements is an important goal in contemporary science. We present here Cr(0), Mo(0), and W(0) carbonyl complexes with a pyridyl-mesoionic carbene (MIC) based ligand. A detailed photophysical investigation shows that all the complexes exhibit dual emissions in the VIS and in the NIR region. The emissive excited states are assigned to two distinct triplet states by time-resolved emission and step-scan FTIR spectroscopy at variable temperature, supported by density functional theory. In particular, the NIR emissive triplet state exhibits unprecedented lifetimes of up to 600±10 ns and quantum yields reaching 1.7 ⋅ 10-4 at room temperature. These are the first examples of Cr(0), Mo(0) and W(0) complexes that emit in the NIR II region.

Facile Synthesis of a Stable Side-on Phosphinyne Complex by Redox Driven Intramolecular Cyclisation

Alkyne complexes with vicinal substitution by a Lewis acid and a Lewis base at the coordinated alkyne are prospective frustrated Lewis pairs exhibiting a particular mutual distance and, hence, a specific activation potential. In this contribution, investigations on the generation of a WII alkyne complex bearing a phosphine as Lewis base and a carbenium group as Lewis acid are presented. Independently on potential substrates added, an intramolecular cyclisation product was always isolated. A subsequent deprotonation step led to an unprecedented side-on λ5 -phosphinyne complex, which is interpreted as highly zwitterionic according to visible absorption spectroscopy supported by TD-DFT. Low-temperature 31 P NMR and EPR spectroscopic measurements combined with time-dependent IR-spectroscopic monitoring provided insights in the mechanism of the cyclisation reaction. Decomposition of the multicomponent IR spectra by multivariate curve resolution and a kinetic hard-modelling approach allowed the derivation of kinetic parameters. Assignment of the individual IR spectra to potential intermediates was provided by DFT calculations.

Making the unconventional μ2-P bridging binding mode more conventional in phosphinine complexes

As compared to the normal η¹-P σ-complexes or η⁶-phosphinine π-complexes, the rare μ²-P bridging binding mode of phosphinines can be tuned by employing electron donating substitute.

Phosphinines, as aromatic heterocycles, usually engage in coordination as η¹-P σ-complexes or η⁶-phosphinine π-complexes. The μ²-P bridging coordination mode is rarely observed. With the aim to study the effect of different electronic configurations of phosphinines on the coordination modes, a series of anionic phosphinin-2-olates and neutral phosphinin-2-ols were prepared with moderate to high yield. Then the coordination chemistry of these two series was studied in detail towards coinage metals (Au(i) and Cu(i)). It is observed that the anionic phosphinin-2-olates possess a higher tendency to take a bridging position between two metal centers compared to the neutral phosphinin-2-ols. Based on these experimental findings bolstered by DFT calculations, some insight is gained on how the unconventional μ²-P phosphinine bridging coordination mode can be made more conventional and used for the synthesis of polynuclear complexes.

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.