Low coordinate lanthanide(ii) complexes supported by bulky guanidinato and amidinato ligands

Abstract

The preparation of a series of homoleptic, four-coordinate lanthanide(ii) complexes, [Ln(Priso)(2)] (Ln = Sm, Eu or Yb) incorporating the bulky guanidinate ligand Priso(-) ([(ArN)(2)CNPr(i)(2)](-), Ar = 2,6-diisopropylphenyl) is described. X-ray crystallography shows the complexes to be isostructural and to exhibit coordination geometries midway between tetrahedral and planar. Comparisons between the geometries of the complexes and those of the bulkier systems, [Ln(Giso)(2)] (Giso(-) = [(ArN)(2)CNCy(2)](-), Cy = cyclohexyl) are discussed. Attempts to prepare the less hindered amidinate complexes, [Ln(Piso)(2)] (Piso(-) = [(ArN)(2)CBu(t)](-)), were not successful, but did give rise to the heteroleptic complex, [(kappa(1)-N,eta(6)-Piso)Sm(THF)(mu-I)(2)Sm(kappa(1)-N,eta(6)-Piso)]. Whereas the amidinate ligands in this complex chelate the samarium centre in an kappa(1)-N,eta(6)-Ar-fashion, in the closely related complex, [{(kappa(2)-N,N'-Priso)Yb(THF)(mu-I)}(2)], the ytterbium atoms are kappa(2)-N,N'-chelated by the guanidinate ligand. The facility of the planar four-coordinate complex, [Sm(Giso)(2)], to act as a one-electron reducing agent towards a variety of unsaturated substrates has also been explored. The complex has been shown to selectively reductively couple CS(2), via a C-S bond formation, to give the samarium(iii) dimer, [(Giso)(2)Sm(mu-eta(2)-:eta(2)-S(2)CSCS)Sm(Giso)(2)].

Activation of Heteroallenes COxS2–x (x = 0–2): Experimental and Theoretical Evidence of the Synthetic Versatility of a Bulky Guanidinato SmII Complex

“…[18] This is the only example in Sm II chemistry where C-S bond formation between two CS 2 molecules is observed (Figure 1). …”

“…The experimental study was reported previously by Jones et al, and no tractable product could be extracted although a reaction was observed. [18] From a computational point of view, the reactivity of COS requires more work since the C-O and C-S bonds are not polarized in the same way (actually, opposite polarization) so that two key intermediates can exist, [(Giso) 2 Sm(μ-η:SC-η:O)Sm(Giso) 2 ] or [(Giso) 2 Sm-(μ-η:OC-η:S)Sm(Giso) 2 ]. From these two key intermediates, one has to investigate all reaction pathways that yield carbonate and oxalate derivatives.…”

“…[37] -such observations have previously been made for similar complexes. [18] Evans method susceptibility ([D 6 ]benzene, 298 K): 2.37 μ B . [38] CCDC 1435010 (for 3) contains the supplementary crystallographic data for this paper.…”

“…[11][12][13][14][15][16][17][18][19][20][21][22][23][24] The metal as well as the steric and electronic contributions of the ligands influence the way conversion of CO 2 will proceed. Another nonnegligible factor is the solvent employed.…”

C‐C‐Bindungsknüpfung durch reduktive Kupplung von CS2 an Uran zur Bildung von Tetrathiooxalat‐ und Ethylentetrathiolatkomplexen

“…[11,12] Kürzlich wurde über einen Sm II -Komplex berichtet, der durch reduktive CS 2 -Kupplung zum Komplex [(Giso) 2 Sm(m-h 2 :h 2 -S 2 CSCS)Sm(Giso) 2 ] (Giso = [(ArN) 2 CNCy 2 ], Ar = 2,6-Diisopropylphenyl, Cy = Cyclohexyl) führte. [22] Durch reduktive Kopf-Kopf-Kupplung (C-C-Bindungsknüpfung) von CS 2 konnten bislang nur Ethylentetrathiolat (C 2 S 4 4À ) [13,14,16,17] oder C 2 S 4 4À -artige Thiooxalatkomplexe [15] hergestellt werden. Verglichen mit der C-C-s-Bindung im Oxalat-Dianion C 2 O 4 2À ist die C-C-s-Bindung in C 2 S 4 relativ schwach.…”