Systematic Investigation of the Molecular and Electronic Structure of Thorium and Uranium Phosphorus and Arsenic Complexes

Abstract

In continuing to examine the interaction of actinide-ligand bonds with soft donor ligands, a comparative investigation with phosphorus and arsenic was conducted. A reaction of (C 5 Me 5 ) 2 AnMe 2 , An = Th, U, with 2 equiv of H 2 AsMes, Mes = 2,4,6-Me 3 C 6 H 2 , forms the primary bis(arsenido) complexes, (C 5 Me 5 ) 2 An[As(H)Mes] 2 . Both exhibit thermal instability at room temperature, leading to the elimination of H 2 , and the formation of the diarsenido species, (C 5 Me 5 ) 2 An(η 2 -As 2 Mes 2 ). The analogous diphosphido complexes, (C 5 Me 5 ) 2 An(η 2 -P 2 Mes 2 ), could not be synthesized via the same route, even upon heating the bis(phosphido) species to 100 °C in toluene. However, they were accessible via the reaction of dimesityldiphosphane, MesP(H)P(H)Mes, with (C 5 Me 5 ) 2 AnMe 2 at 70 °C in toluene. When (C 5 Me 5 ) 2 AnMe 2 is reacted with 1 equiv of H 2 AsMes, the bridging μ 2 -arsinidiide complexes [(C 5 Me 5 ) 2 An] 2 (μ 2 -AsMes) 2 are formed. Upon reaction of (C 5 Me 5 ) 2 UMe 2 with 1 equiv of H 2 PMes, the phosphinidiide [(C 5 Me 5 ) 2 U(μ 2 -PMes)] 2 is isolated. However, the analogous thorium reaction leads to a phosphido and C−H bond activation of the methyl on the mesityl group, forming {(C 5 Me 5 ) 2 Th[P(H)(2,4-Me 2 C 6 H 2 -6-CH 2 )]} 2 . The reactivity of [(C 5 Me 5 ) 2 An(μ 2 -EMes)] 2 was investigated with OPPh 3 in an effort to produce terminal phosphinidene or arsinidene complexes. For E = As, An = U, a U(III) cation−anion pair [(C 5 Me 5 ) 2 U(η 2 -As 2 Mes 2 )][(C 5 Me 5 ) 2 U(OPPh 3 ) 2 ] is isolated. The reaction of [(C 5 Me 5 ) 2 Th(μ 2 -AsMes)] 2 with OPPh 3 does not result in a terminal arsinidene but, instead, eliminates PPh 3 to yield a bridging arsinidiide/oxo complex, [(C 5 Me 5 ) 2 Th] 2 (μ 2 -AsMes)(μ 2 -O). Finally, the combination of [(C 5 Me 5 ) 2 U(μ 2 -PMes)] 2 and OPPh 3 yields a terminal phosphinidene, (C 5 Me 5 ) 2 U(PMes)(OPPh 3 ), featuring a short U−P bond distance of 2.502(2) Å. Electrochemical measurements on the uranium pnictinidiide complexes demonstrate only a 0.04 V difference with phosphorus as a slightly better donor. Magnetic measurements on the uranium complexes show more excited-state mixing and therefore higher magnetic moments with the arsenic-containing compounds but no deviation from uncoupled U(IV) behavior. Finally, a quantum theory of atoms in molecules analysis shows highly polarized actinide-pnictogen bonds with similar bonding characteristics, supporting the electrochemical and magnetic measurements of similar bonding between actinide-phosphorus and actinide-arsenic bonds.

Formation and Reactivity with tBuCN of a Thorium Phosphinidiide through a Combined Experimental and Computational Analysis

“…The proposed product, as shown in Figure , should have two methyl resonances. Indeed, a resonance at 0.16 ppm can be attributed to the methylene coordinated to thorium, while a resonance at 0.43 ppm is consistent with other monomethyl thorium complexes. , The resonance at 1.92 ppm is assigned to the (C 5 Me 5 ) − resonance, which is one of the resonances we could not identify in the 1 H NMR spectrum of 2 …”

“…59,62 The resonance at 1.92 ppm is assigned to the (C 5 Me 5 ) − resonance, which is one of the resonances we could not identify in the 1 H NMR spectrum of 2. 41 Reactivity with t BuCN. The reactivity of 3 with 1 and 2 (or excess) equiv of t BuCN was investigated (Scheme 1).…”

“…Recently, in an attempt to make the bridging phosphinidiide [(C 5 Me 5 ) 2 Th­(μ-PMes)] 2 the reaction of (C 5 Me 5 ) 2 ThMe 2 with the less sterically crowded phosphine H 2 PMes (Mes = 2,4,6-Me 3 C 6 H 2 ) in a 1:1 stoichiometric ratio was conducted. However, the major product was a phosphido with a C–H bond activation of one of the methyl groups of the mesityl, [(C 5 Me 5 ) 2 Th­(μ 2 -P­(H)­(2,4-Me 2 C 6 H 2 -6-CH 2 ))] 2 ( 2 ; eq ).…”

Structural, Spectroscopic, and Computational Analysis of Heterometallic Thorium Phosphinidiide Complexes

“…Complexes containing metal–ligand multiple bonding continue to enhance our understanding of the molecular and electronic structures of the actinides . This is especially true of the pnictogen group, for which actinide–imido complexes have been studied for 3 decades, − while studies involving actinide–phosphinidene − or phosphinidiide − moieties are less studied but are becoming more common. In recent years, several examples of other actinide–main group bonds have been reported, with both thorium­(IV) and uranium­(VI) having diamagnetic ground states, affording bonding information by combining structural and spectroscopic techniques with density functional theory (DFT) calculations. − However, no such study has been conducted with f element–phosphorus bonds.…”

Backbonding in Thorium(IV) and Uranium(IV) Diarsenido Complexes with tBuNC and CO

“…Recently, we reported the diarsenido complexes, (C 5 Me 5 ) 2 An(η 2 -As 2 Mes 2 ), An=Th, U, which result from loss of H 2 from the bis(arsenido) complexes, (C 5 Me 5 ) 2 An[As(H)Mes] 2 . [17] The exploration of actinide complexes with phosphorus and arsenic ligands has produced unusual reactivity with substrates such as tBuNC and CO, [18][19][20][21] and we sought to examine this unique diarsenido moiety in more detail. Herein, we report the coordination of (C 5 Me 5 ) 2 An(η 2 -As 2 Mes 2 ) with the isoelectronic, unsaturated substrates tBuNC and CO.…”