A Resorcin[4]arene-Based Phosphite-Phosphine Ligand for the Branched-Selective Hydroformylation of Alkyl Alkenes.

Synthesis of a chelating phosphite-phosphine ligand from a tris(quinoxaline) extended resorcin[4]arene and its application in the rhodium-catalyzed hydroformylation of terminal alkyl alkenes are reported. Rhodium complexes are formed within the cavity of the macrocycle and branched-selective hydroformylation of 1-octene with a / ratio of 5.9 has been achieved at 60 °C under 1:1 H/CO (20 bar).

Copper(I) Catalysed Diboron(4) Reduction of Nitrous Oxide.

A process for the catalytic reduction of nitrous oxide using NHC-ligated copper(I) tert-butoxide precatalysts and Bpin as the reductant is reported. These reactions proceed under mild conditions via copper(I)-boryl intermediates which react with NO by facile O-atom insertion into the Cu-B bond and liberate N. Turnover numbers >800 can be achieved at 80 °C under 1 bar NO.

Synthetic and Mechanistic Studies into the Reductive Functionalization of Nitro Compounds Catalyzed by an Iron(salen) Complex.

We report on the use of a simple, bench-stable [Fe(salen)]-μ-oxo precatalyst in the reduction of nitro compounds. The reaction proceeds at room temperature across a range of substrates, including nitro aromatics and aliphatics. By changing the reducing agent from pinacol borane (HBpin) to phenyl silane (HSiPh), we can chemoselectively reduce nitro compounds while retaining carbonyl functionality.

Capture of mechanically interlocked molecules by rhodium-mediated terminal alkyne dimerisation.

The transition metal-mediated dimerisation of terminal alkynes is an attractive and atom-economic method for preparing conjugated 1,3-enynes. Using a phosphine-based macrocyclic pincer ligand, we demonstrate how this transformation can be extended to the synthesis of novel, hydrocarbon-based interlocked molecules: a rotaxane by 'active' metal template synthesis and a catenane by sequential 'active' and 'passive' metal template procedures.

The Complex Reactivity of [(salen)Fe](μ-O) with HBpin and Its Implications in Catalysis.

We report a detailed study into the method of precatalyst activation during alkyne cyclotrimerization. During these studies we have prepared a homologous series of Fe(III)-μ-oxo(salen) complexes and use a range of techniques including UV-vis, reaction monitoring studies, single crystal X-ray diffraction, NMR spectroscopy, and LIFDI mass spectrometry to provide experimental evidence for the nature of the on-cycle iron catalyst. These data infer the likelihood of ligand reduction, generating an iron(salan)-boryl complex as a key on-cycle intermediate.

Iridium complexes of an -trifluoromethylphenyl substituted PONOP pincer ligand.

The synthesis and iridium coordination chemistry of a new pyridine-based phosphinito pincer ligand 2,6-(ArPO)CHN (PONOP-Ar; Ar = 2-(CF)CH) are described, where the P-donors have -trifluoromethylphenyl substituents. The iridium(III) 2,2'-biphenyl (biph) derivative [Ir(PONOP-Ar)(biph)Cl] was obtained by reaction with [Ir(biph)(COD)Cl] (COD = 1,5-cyclooctadiene) and subsequent halide ion abstraction enabled isolation of [Ir(PONOP-Ar)(biph)] which features an Ir ← F-C bonding interaction in the solid state. Hydrogenolysis of the biphenyl ligand and formation of [Ir(PONOP-Ar)(H)] was achieved by prolonged reaction of [Ir(PONOP-Ar)(biph)] with dihydrogen.

Broken Promises? On the Continued Challenges Faced in Catalytic Hydrophosphination.

In this Perspective, we discuss what we perceive to be the continued challenges faced in catalytic hydrophosphination chemistry. Currently the literature is dominated by catalysts, many of which are highly effective, that generate the same phosphorus architectures, e.g.

Taming PH: State of the Art and Future Directions in Synthesis.

Appetite for reactions involving PH has grown in the past few years. This in part is due to the ability to generate PH cleanly and safely via digestion of cheap metal phosphides with acids, thus avoiding pressurized cylinders and specialized equipment. In this perspective we highlight current trends in forming new P-C/P-OC bonds with PH and discuss the challenges involved with selectivity and product separation encumbering these reactions.

Synthesis and reactivity of iridium complexes of a macrocyclic PNP pincer ligand.

Having recently reported on the synthesis and rhodium complexes of the novel macrocyclic pincer ligand PNP-14, which is derived from lutidine and features terminal phosphine donors trans-substituted with a tetradecamethylene linker (Dalton Trans., 2020, 49, 2077-2086 and Dalton Trans., 2020, 49, 16649-16652), we herein describe our findings critically examining the chemistry of iridium homologues.

Reactions of Rh(PNP) pincer complexes with terminal alkynes: homocoupling through a ring or not at all.

Through use of a bespoke macrocyclic variant, we demonstrate a novel approach for tuning the reactivity of rhodium PNP pincer complexes that enables formation of conjugated enynes from terminal alkynes, rather than vinylidene derivates. This concept is illustrated using tert-butylacetylene as the substrate and rationalised by a ring-induced switch in mechanism.

Synthesis and rhodium complexes of macrocyclic PNP and PONOP pincer ligands.

The synthesis of macrocyclic variants of commonly employed phosphine-based pincer ligands derived from lutidine (PNP-14) and 2,6-dihydroxypyridine (PONOP-14) is described, where the P-donors are trans-substituted with a tetradecamethylene linker. This was accomplished using an eight-step procedure involving borane protection, ring-closing olefin metathesis, chromatographic separation from the cis-substituted diastereomers, and borane deprotection. The rhodium coordination chemistry of these ligands has been explored, aided by the facile synthesis of 2,2'-biphenyl (biph) adducts [Rh(PNP-14)(biph)][BAr] and [Rh(PONOP-14)(biph)][BAr] (Ar = 3,5-(CF)CH).

Synthesis and Structural Dynamics of Five-Coordinate Rh(III) and Ir(III) PNP and PONOP Pincer Complexes.

The synthesis and characterization of a homologous series of five-coordinate rhodium(III) and iridium(III) complexes of PNP (2,6-( tBuPCH)CHN) and PONOP (2,6-( tBuPO)CHN) pincer ligands are described: [M(PNP)(biph)][BAr] (M = Rh, 1a; Ir, 1b; biph = 2,2'-biphenyl; Ar = 3,5-(CF)CH) and [M(PONOP)(biph)][BAr] (M = Rh, 2a; Ir, 2b). These complexes are structurally dynamic in solution, exhibiting pseudorotation of the biph ligand on the H NMR time scale (Δ G ca. 60 kJ mol) and, in the case of the flexible PNP complexes, undergoing interconversion between helical and puckered pincer ligand conformations (Δ G ca.

A convenient method for the generation of {Rh(PNP)} and {Rh(PONOP)} fragments: reversible formation of vinylidene derivatives.

The substitution reactions of [Rh(COD)2][BArF4] with PNP and PONOP pincer ligands 2,6-bis(di-tert-butylphosphinomethyl)pyridine and 2,6-bis(di-tert-butylphosphinito)pyridine in the weakly coordinating solvent 1,2-F2C6H4 are shown to be an operationally simple method for the generation of reactive formally 14 VE rhodium(i) adducts in solution. Application of this methodology enables synthesis of known adducts of CO, N2, H2, previously unknown water complexes, and novel vinylidene derivatives [Rh(pincer)(CCHR)][BArF4] (R = tBu, 3,5-tBu2C6H3), through reversible reactions with terminal alkynes.