Accessing the +IV Oxidation State in Molecular Complexes of Praseodymium

Abstract

Out of the 14 lanthanide (Ln) ions, molecular complexes of Ln(IV) were known only for cerium and more recently terbium. Here we demonstrate that the +IV oxidation state is also accessible for the large praseodymium (Pr) cation. The oxidation of the tetrakis(triphenysiloxide) Pr(III) ate complex, [KPr(OSiPh 3 ) 4 (THF) 3 ], 1-Pr Ph , with [N(C 6 H 4 Br) 3 ][SbCl 6 ], affords the Pr(IV) complex [Pr(OSiPh 3 ) 4 (MeCN) 2 ], 2-Pr Ph , which is stable once isolated. The solid state structure, UV−visible spectroscopy, magnetometry, and cyclic voltammetry data along with the DFT computations of the 2-Pr Ph complex unambiguously confirm the presence of Pr(IV).

Comparison of tetravalent cerium and terbium ions in a conserved, homoleptic imidophosphorane ligand field

“…This dramatic shift in the Tb 4+/3+ reduction potential in 2-Tb(PN*) and for the Ce 4+/3+ reduction potential in 2-Ce(PN*) noticeably demonstrates that such significant modulation of other lanthanide redox couples should be accessible from a thermodynamic perspective. 18 …”

“… 15 – 17 Mazzanti and co-workers have recently extended this chemistry to tetravalent praseodymium. 18 Our terbium system is prepared by the oxidation of a trivalent precursor, [K][Tb 3+ (NP(1,2-bis- t Bu-diamidoethane)(NEt 2 )) 4 ], 1-Tb(PN*) , to give a four coordinate complex, [Tb 4+ (NP(1,2-bis- t Bu-diamidoethane)(NEt 2 )) 4 ], 2-Tb(PN*) .…”

Cerium(iv) complexes with guanidinate ligands: intense colors and anomalous electronic structures

“…44 Remarkable lanthanide-ligand orbital mixing has also been spectroscopically determined in tetravalent lanthanide oxides, LnO 2 (Ln = Ce, Pr, and Tb) 45 , and Pr(IV) and Tb(IV) siloxide compounds. [46][47][48] Inspired by these findings, we are interested in developing and studying cerium(IV) complexes that show red-shifted absorption bands (> 650 nm). We postulate that cerium (IV) complexes with such low energy LMCT bands would have strong metal-ligand interactions, leading to unusual electronic structures.…”

A hydrolytically stable Ce(iv) complex of glutarimide-dioxime

“…1,2 To stabilize this high oxidation state, it is necessary to employ an electron-donating ligand that is resistant towards oxidation. [3][4][5][6][7][8] There are a variety of reported Ce(IV) complexes stabilized by different ligand frameworks, such as [ ) 3 N] 3− ; X = F, Cl, Br), [Ce( pyNO) 4 ] ( pyNO = 2-( t BuNO)pyridine), and others. [9][10][11][12][13] Glutarimide-dioxime (H 3 A, C 5 H 9 N 3 O 2 ), a compound reported to be useful for sequestering uranium from seawater, is considered here for stabilization of the cerium(IV) cation.…”