Transfer hydrogenation (TH) has historically been dominated by Meerwein–Ponndorf–Verley (MPV) reactions. However, with growing interest in amine–boranes, not least ammonia–borane (H3N⋅BH3), as potential hydrogen storage materials, these compounds have also started to emerge as an alternative reagent in TH reactions. In this Review we discuss TH chemistry using H3N⋅BH3 and their analogues (amine–boranes and metal amidoboranes) as sacrificial hydrogen donors. Three distinct pathways were considered: 1) classical TH, 2) nonclassical TH, and 3) hydrogenation. Simple experimental mechanistic probes can be employed to distinguish which pathway is operating and computational analysis can corroborate or discount mechanisms. We find that the pathway in operation can be perturbed by changing the temperature, solvent, amine–borane, or even the substrate used in the system, and subsequently assignment of the mechanism can become nontrivial.

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., anti-Markovnikov products from the reaction of activated alkenes and alkynes with diarylphosphines. We highlight the state of the art in stereoselective hydrophosphination and the scope and limitations of chemoselective hydrophosphination with primary phosphines and PH 3 . We also highlight the progress in the chemistry of the heavier homologues. In general, we have tried to emphasize what is missing from our hydrophosphination armament, with the aim of guiding future research targets.

Metal carbonyls are commonly employed probes for quantifying the donor properties of monodentate ligands. With a view to extending this methodology to mer-tridentate "pincer" ligands, the spectroscopic properties [ν(CO), δ 13C , 1 J RhC ] of rhodium(I) and rhodium(III) carbonyl complexes of the form [Rh(pincer)(CO)][BAr F 4 ] and [Rh(pincer)Cl 2 (CO)][BAr F 4 ] have been critically analysed for four pyridyl-based pincer ligands, with two flanking oxazoline (NNN), phosphine (PNP), or N-heterocyclic carbene (CNC) donors. Our investigations indicate that the carbonyl bands of the rhodium(I) complexes are the most [a]

Appetite for reactions involving PH 3 has grown in the past few years. This in part is due to the ability to generate PH 3 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 3 and discuss the challenges involved with selectivity and product separation encumbering these reactions. We highlight the reactivity of PH 3 with main group reagents, building on the early pioneering work with transition metal complexes and PH 3 . Additionally, we highlight the recent renewal of interest in alkali metal sources of H 2 P − which are proving to be useful synthons for chemistry across the periodic table. Such MPH 2 sources are being used to generate the desired products in a more controlled fashion and are allowing access to unexplored phosphorus-containing species.