Triamidoamine–Uranium(IV)‐Stabilized Terminal Parent Phosphide and Phosphinidene Complexes

Abstract

Terminal metal phosphinidene complexes (L n M = PR) are, despite continued interest, far less developed than their isolobal metal imide and alkylidene counterparts.[1] Although the first L n M=PR complex was reported over a quarter of a century ago, [2] sterically demanding R-groups are required, as M=PR linkages are reactive and require kinetic stabilization.[3] Certainly, free phosphinidenes (PR) are usually very reactive owing to their triplet ground states and unsaturated valence shells.[4] Although stabilization of a triplet PR group by a triplet metal fragment to generate a formal M=P bond is an attractive strategy, unlike the well-known L n M=NH and L n M=CH 2 linkages, [5] there has never been a structurally authenticated report of a d-/f-block metal-stabilized terminal parent phosphinidene L n M = PH, [6,7] and studies of such species are limited to computational investigations. [8] This paucity is underscored by a triplet-singlet energy gap of 22 kcal mol À1 for free PH, [4b] which has only been observed transiently in the gas phase or low temperature matrices. [4a, 9]

Triamidoamine uranium(IV)–arsenic complexes containing one-, two- and threefold U–As bonding interactions

“…The 1 H NMR spectrum of 3c spans the range +7 to −27 ppm, which is a similar range to the majority of resonances for 2c, consistent with the presence of uranium(IV). The AsH hydrogen atom could not be observed in the 1 H NMR spectrum, analogously to 3b, where the PH hydrogen atom resonance was not observed 43 . This is attributed to line-broadening arising from the close proximity of the AsH hydrogen atom to the paramagnetic uranium(IV) ion.…”

“…The calculated uranium MDC-q charges (2.42-2.74) are typical of Tren-uranium(IV) complexes 37,43 . The calculated arsenic MDC-q charges reflect the changes from formally mono-anionic arsenide (−0.51) to dianionic arsinidene (−0.89) to trianionic arsenido Supplementary Figs 8-11) reveal that the uranium(IV)-arsenic interactions are dominated by arsenic 4p orbitals and uranium 5f orbitals.…”

“…Spurred on by previous matrix isolation experiments 54,55 37,43 . From a main group perspective, these species represent fundamental, metal-stabilized parent p-block fragments that are predominantly found as transient intermediates in the gas-phase or low-temperature matrices.…”

“…Uranium is one actinide that is amenable to routine study, and uranium-ligand multiple-bond complexes have attracted attention because they would be expected to contain some covalency 13-15 . Recently, in addition to the numerous uranium-oxo derivatives, for example uranyl 16 , there have been advances in the synthesis, characterization and understanding of covalent, terminal uraniumcarbene [17][18][19][20][21][22] , -imido [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] , -nitride [38][39][40] , -phosphinidene [41][42][43] and heavier-chalcogenide 44,45 multiple bonds. Nevertheless, carbon, nitrogen and oxygen donor ligands dominate, and post-first-row donor ligands remain relatively rare and sharply decrease in number as the periodic table is descended.…”

“…Nevertheless, carbon, nitrogen and oxygen donor ligands dominate, and post-first-row donor ligands remain relatively rare and sharply decrease in number as the periodic table is descended. For example, where pnictide donor ligands are concerned, many uranium amido and imido complexes are known 16 , but only two terminal uranium phosphinidene complexes 42,43 and four uranium and thorium polyphosphides are known [46][47][48][49] . Indeed, given that uranium comes into contact with a wide range of elements in nuclear fuel cycles, it is surprising that there are no structurally authenticated molecular uranium-arsenic bonds of any type under ambient conditions 50,51 .…”