Abstract
Reaction of [U{C(SiMe(3) )(PPh(2) )}(BIPM)(μ-Cl)Li(TMEDA)(μ-TMEDA)(0.5) ](2) (BIPM=C(PPh(2) NSiMe(3) )(2) ; TMEDA=Me(2) NCH(2) CH(2) NMe(2) ) with [Rh(μ-Cl)(COD)](2) (COD=cyclooctadiene) affords the heterotrimetallic U(IV) -Rh(I)(2) complex [U(Cl)(2) {C(PPh(2) NSiMe(3) )(PPh[C(6) H(4) ]NSiMe(3) )}{Rh(COD)}{Rh(CH(SiMe(3) )(PPh(2) )}]. 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.