At the Edge of Stability: the Unexpected Isolation of an f-Element Triphenylphosphine Complex

Abstract

Abstract While PPh3 is a dominant ligand in transition-metal chemistry, it is completely absent in rare-earth and actinide structural chemistry. The open coordination site and high Lewis acidity of (CpSiMe3)3U are leveraged to generate the first structurally characterized PPh3 complex in these series. X-ray crystallography and variable-temperature nuclear magnetic resonance spectroscopy give insight into the structure and fluxional behavior of (CpSiMe3)3U–PPh3 (1). The U–P bonding energetics were experimentally determined to be endergonic at room temperature, partially rationalizing the absence of triphenylphosphine in f-element chemistry. The structural and dynamic properties of 1 were compared to an analogous phosphite complex, (CpSiMe3)3U–P(OCH2)3CEt (2), and the large discrepancies discussed in the context of π-bonding and steric interactions.