A Very Short Uranium(IV)-Rhodium(I) Bond with Net Double-Dative Bonding Character

Abstract

Reaction of [U{C(SiMe₃ )(PPh₂ )}(BIPM)(μ-Cl)Li(TMEDA)(μ-TMEDA)_0.5 ]₂ (BIPM=C(PPh₂ NSiMe₃ )₂ ; TMEDA=Me₂ NCH₂ CH₂ NMe₂ ) with [Rh(μ-Cl)(COD)]₂ (COD=cyclooctadiene) affords the heterotrimetallic U^IV -Rh^I₂ complex [U(Cl)₂ {C(PPh₂ NSiMe₃ )(PPh[C₆ H₄ ]NSiMe₃ )}{Rh(COD)}{Rh(CH(SiMe₃ )(PPh₂ )}]. This complex has a very short uranium-rhodium distance, the shortest uranium-rhodium bond on record and the shortest actinide-transition metal bond in terms of formal shortness ratio. Quantum-chemical calculations reveal a remarkable RhI→→ U^IV net double dative bond interaction, involving Rh^I 4dz2 - and 4d_xy/xz -type donation into vacant U^IV 5f orbitals, resulting in a Wiberg/Nalewajski-Mrozek U-Rh bond order of 1.30/1.44, respectively. Despite being, formally, purely dative, the uranium-rhodium bonding interaction is the most substantial actinide-metal multiple bond yet prepared under conventional experimental conditions, as confirmed by structural, magnetic, and computational analyses.

Keywords: C−H activation; carbenes; metal-metal bonding; rhodium; uranium.