A Cerium(IV)–Carbon Multiple Bond

Abstract

Straightforward access to a cerium(IV)-carbene complex was provided by one-electron oxidation of an anionic "ate" cerium(III)-carbene precursor, thereby avoiding decomposition reactions that plague oxidations of neutral cerium(III) compounds. The cerium(IV)-carbene complex is the first lanthanide(IV)-element multiple bond and involves a twofold bonding interaction of two electron pairs between cerium and carbon.

Covalent Uranium Carbene Chemistry

“…Investigations began with ascertaining whether the deprotonation of [U(BIPM TMS H)(O) 2 (Cl)(THF)] with a suitable base, such as benzyl sodium, would afford the uranyl carbene [U(BIPM TMS )(O) 2 (THF) n ] via elimination of sodium chloride and toluene, in an analogous fashion to rare-earth systems. [68,84,85] However, a uranyl carbene was not isolated, and instead the mixed valence dinuclear methanide U V -U VI complex [{U(BIPM TMS H) (O) 2 } 2 (l-Cl)], 50, was observed as the major reaction product, with the U V-U V -U VI trimetallic [{U(BIPM TMS H)(O) 2 } 3 (l 3 -Cl)], 51, also observed as a minor product (Scheme 19). [73] The formation of these complexes, which are the first examples of organometallic uranyl(V) complexes, was somewhat unexpected, given the straightforward preparation of 33, but it is in line with the reducing nature of alkali metal alkyls.…”

“…The reaction of 54 or 55 with benzaldehyde afforded conversion to the Wittig-type alkene product (H)(Ph)C = C(PPh 2 NDipp) 2 (66), analogously to the reactivity observed by 43-45. (68), respectively, with coordination of the ketone to the uranium center in the former and to the lithium center in the latter (Scheme 27). [64] It was reasoned that the occluded lithium chloride could be blocking the reactivity of the carbene; however, when the reactions were repeated utilizing the lithium chloride-free carbene 54, no reactivity was observed.…”

“…[64] It is of note that the preparation of [U(BIPM Mes H)(Cl) 3 (THF)] was straightforward, because related rare-earth {BIPM R H} -methanide complexes require more esoteric ligand transfer reagents. [65][66][67][68] Although this preparation could be achieved on a small scale, attempts to scale-up were capricious and it was reported that a more convenient synthetic route to 37 is from the reaction of [U(Cl) 4 (THF) 3 ] with half an equivalent of [{Li 2 (BIPM Mes )} 2 ] with elimination of two equivalents of LiCl. The U=C distance in 37 of 2.358(4) Å is shorter than the U=C distances in 36, as expected due to the decreased steric demands about uranium, and is in line with the analogous {SCS} 2-complexes 24 and 22.…”

Formation of a Ce(IV) Oxo Complex via Inner Sphere Nitrate Reduction

“…17 Also of note is the Ce(IV) methanediide complex, [Ce(BIPM TMS )(ODipp) 2 ] (BIPM TMS = C(PPh 2 NSiMe 3 ) 2 ; Dipp = C 6 H 3 -2,6-i Pr 2 ), reported by Liddle and co-workers. 18,19 This paucity of lanthanide examples has been rationalized by the mismatch in the energies of the metal and ligand frontier orbitals, which results in poor orbital overlap. [20][21][22] However, recent XAS studies have demonstrated that the 4f orbitals can participate in cerium-ligand bonding, at least for the Ce(IV) oxidation state, suggesting that some covalency within lanthanide-ligand bonding is possible.…”

Lanthanides and actinides: Annual survey of their organometallic chemistry covering the year 2013

“…cerium(IV)-carbene bond lengths in a BIPM TMS -bis(aryloxide) environment, the colorless Ce(BIPM TMS H)(ODipp) 2 (THF) has also been prepared from Ce(BIPM TMS H)I 2 (THF) and two equivalents of K(ODipp) (19% crystalline yield). The cerium(IV)-carbene distance in Ce(BIPM TMS )(ODipp) 2 was determined to be 2.441(5)Å, which is one of the shortest molecular cerium-carbon distances on record [14].…”