Lanthanide/actinide differentiation with sterically encumbered N-heterocyclic carbene ligandsElectronic supplementary information (ESI) available: For additional synthetic characterising data (NMR spectroscopic) and X-ray crystallographic data in CIF and other electronic format see DOI: 10.1039/c001584a and online at ccdc.cam.ac.uk, reference numbers 763328-763331

• Main Authors: Arnold, Polly L, Turner, Zoë R, Germeroth, Anne I, Casely, Ian J, Bellabarba, Ronan, Tooze, Robert P
• Format: Article
• Language: English
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c001584a

A study is reported on the relative stability of trivalent bis (ligand) complexes of the form [M(L R ) 2 N′′] for trivalent group 3, lanthanide and actinide cations, using the sterically demanding N-heterocyclic carbene ligand L R = [OCMe 2 CH 2 {CNCH 2 CH 2 NR}] (R = i Pr L P , Mes L M , Dipp L D ; N′′ = N(SiMe 3 ) 2 ). For the small Y III cation (r 6-coord = 1.040 Å) and the smallest L R , R = i Pr, mono , bis , and tris (L P ) complexes can be made; [Y(L P ) 2 N′′] and [Y(L P ) 3 ] have been characterised. For the larger ligands, L M and L D , only the mono (L R ) complexes [Y(L M )N′′ 2 ] and [Y(L D )N′′ 2 ] can be made. For the larger Ce III (r 6-coord = 1.15 Å), mono (L R ) and bis (L R ) complexes [Ce(L M )N′′ 2 ], [Ce(L D )N′′ 2 ], [Ce(L M ) 2 N′′], and [Ce(L D ) 2 N′′] can be made; structural characterisation of the latter two confirm the high degree of steric congestion. The new complex [U(L M )N′′ 2 ] has also been isolated. Despite the very similar radii of Ce III and U III (r 6-coord = 1.165 Å), the complexes [U(L R ) 2 N′′] cannot be isolated; a surprising display of the difference between the 4f and 5f metal series. However, the six-coordinate, bis (ligand) U IV complexes can readily be isolated if smaller ancillary ligands are used; [U(L M ) 2 I 2 ] and [U(L D ) 2 I 2 ] have been fully, including structurally, characterised. Using sterically demanding N-heterocyclic carbene ligands L R , the organometallic bis (NHC) Ce III complexes [Ce(L R ) 2 N′′] (N′′ = N(SiMe 3 ) 2 ), are readily isolated. Despite the same size of Ce III and U III , the complexes [U(L R ) 2 N′′] cannot be isolated; a surprisingly dramatic display of the difference between the 4f and 5f metal series.