School of Chemistry, University of Edinburgh, Edinburgh, UK EH9 3JJ.
Dalton Trans. 2010 Aug 7;39(29):6808-14. doi: 10.1039/c001584a. Epub 2010 Jun 4.
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 A) 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 A), 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 A), 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.
报告了一种形式为 [M(L(R))(2)N''] 的三价双（配体）配合物的相对稳定性研究，其中 M 为三价第 3 族、镧系和锕系阳离子，使用空间位阻要求高的 N-杂环卡宾配体 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)）。对于较小的 Y(III)阳离子（r(6-coord) = 1.040 A）和最小的 L(R)，R = (i)Pr，可以制备单、双和三（L(P)）配合物；[Y(L(P))(2)N'']和[Y(L(P))(3)]已被表征。对于较大的配体 L(M)和 L(D)，只能制备单（L(R)）配合物 [Y(L(M))N''(2)] 和 [Y(L(D))N''(2)]。对于较大的 Ce(III)（r(6-coord) = 1.15 A），可以制备单（L(R)）和双（L(R)）配合物 [Ce(L(M))N''(2)]、[Ce(L(D))N''(2)]、[Ce(L(M))(2)N'']和[Ce(L(D))(2)N'']；后两种配合物的结构表征证实了其高度的空间位阻。还分离出了新的配合物[U(L(M))N''(2)]。尽管 Ce(III)和 U(III)的半径非常相似（r(6-coord) = 1.165 A），但不能分离出[U(L(R))(2)N'']配合物；这是 4f 和 5f 金属系列之间差异的惊人展示。然而，如果使用较小的辅助配体，则可以很容易地分离出六配位、双配体 U(IV)配合物；[U(L(M))(2)I(2)]和[U(L(D))(2)I(2)]已被完全表征，包括结构。
