C–H bond activation through steric crowding of normally inert ligands in the sterically crowded gadolinium and yttrium (C ₅ Me ₅ ) ₃ M complexes

Abstract

Synthesis of the sterically crowded Tris(pentamethylcyclopentadienyl) lanthanide complexes, (C 5Me5)3Ln, has demonstrated that organometallic complexes with unconventionally long metal ligand bond lengths can be isolated that provide options to develop new types of ligand reactivity based on steric crowding. Previously, the (C 5Me5)3M complexes were known only with the larger lanthanides, La-Sm. The synthesis of even more crowded complexes of the smaller metals Gd and Y is reported here. These complexes allow an evaluation of the size͞reactivity correlations previously limited to the larger metals and demonstrate a previously undescribed type of C 5Me5-based reaction, namely C-H bond activation. (C 5Me5)3Gd, was prepared from GdCl3 through (C 5Me5)2GdCl2K(THF)2, (C5Me5)2Gd(C3H5), and [(C5Me5)2Gd][BPh4] and structurally characterized by x-ray crystallography. Although Gd 3؉ is redox-inactive, (C5Me5)3Gd functions as a reducing agent in reactions with 1,3,5,7-cyclooctatetraene (COT) and triphenylphosphine selenide to make (C 5Me5)Gd(C8H8), [(C5Me5)2Gd]2Se2, and [(C 5Me5)2Gd]2Se depending on the stoichiometry used. When the analogous synthetic method was attempted with yttrium in arene solvents, the previously characterized (C 5Me5)2YR complexes (R‫؍‬C 6H5, CH2C6H5) were isolated instead, i.e., C-H bond activation of solvent occurred. To avoid this problem, (C 5Me5)3Y was synthesized in high yield from [(C 5Me5)2YH]2 and tetramethylfulvene in aliphatic solvents. Isolated (C 5Me5)3Y was found to metalate benzene and toluene with concomitant formation of C 5Me5H, a reaction contrary to the normal pK a values of these hydrocarbons. In this case, the normally inert (C 5Me5) 1؊ ligand engages in C-H bond activation due to the extreme steric crowding.sterically induced reduction ͉ lanthanide ͉ pentamethylcyclopentadienyl ͉ arene activation ͉ long-bond organometallics

Electronic structures of organometallic complexes of f elements LXXV

“…This finding may be easily explained by the shorter LneC distances of the Ln(C 5 Me 4 H) 3 [24e26] complexes compared to those of the corresponding LnCp * 3 compounds [11e14, 16]. However, this general trend does not hold for the Slater parameter F 2 and the spin-orbit coupling parameter z 4f .…”

“…The latter class of compounds is difficult to synthesize [11e16] and as yet, only small single crystals could be grown, which allowed (besides X-ray diffraction work, which found the space group P6 3 /m, with two molecules of somewhat distorted D 3h symmetry in the unit cell [11e14, 16], see Fig. SI-1) only luminescence anisotropy [17] (LA) and Raman spectroscopic (both vibrational [18] and electronic [19] polarization measurements [9,10]. The former complexes (Ln ¼ La, Ce, Pr, Nd, Sm, Eu, Gd, Tb), however, are commercially available [20] and they have good crystallizing properties.…”

Selective benzylic C–H activation of solvent toluene and m-xylene by an iron–tin cluster complex: Fe2(μ-)2(CO)8

“…Recent studies have shown that even some cyclopentadienyl complexes of Ytterium and Gadolinium can also activate C-H bonds, Eq. (3) [5]. The most common main group elements known to metalate arene rings are those of complexes containing Tl [6] and Pb [7].…”

Coordinative Chain Transfer Polymerization of Butadiene with Functionalized Aluminum Reagents

“…Addition of NdVs 3 (2;V s = versatate), [14] Cp* 2 Nd(allyl) [15] (3), or Cp* 2 Gd(allyl) [16] (4;O RTEP plots shown in Figure 2) to the reaction mixture is beneficial in that the hydroalumination reaction is enhanced, and the resulting product mixtures may directly be used for butadiene polymerization upon activation with [PhNMe 2 H + ]/[B(C 6 F 5 ) 4 À ]( 5;F igure 1, Scheme 2, and Table 1). Addition of NdVs 3 (2;V s = versatate), [14] Cp* 2 Nd(allyl) [15] (3), or Cp* 2 Gd(allyl) [16] (4;O RTEP plots shown in Figure 2) to the reaction mixture is beneficial in that the hydroalumination reaction is enhanced, and the resulting product mixtures may directly be used for butadiene polymerization upon activation with [PhNMe 2 H + ]/[B(C 6 F 5 ) 4 À ]( 5;F igure 1, Scheme 2, and Table 1).…”