The new family of Lewis base free hydrido complexes of rare‐earth metals supported by guanidinate ligands [{Ln{(Me3Si)2NC(NiPr)2}2(μ‐H)}2] (Ln=Y, Nd, Sm, Gd, Yb) was synthesized and structurally characterized. Single‐crystal X‐ray and solution NMR studies revealed that these complexes are dimeric in both solid state and in [D6]benzene. The dimeric hydrido complexes can adopt eclipsed (Nd, Sm, Gd) or staggered (Y, Yb, Lu) conformations depending on the metal‐atom size. Catalytic activity of these [{Ln{(Me3Si)2NC(NiPr)2}2(μ‐H)}2] complexes in the polymerization of ethylene, propylene, and styrene has been investigated. Complexes of Sm and Y have high catalytic activity in ethylene polymerization (1268 and 442 g mmol−1 atm−1 h−1, respectively).

Two new amidines that contain a pendant Lewis base in the side arm, 2-MeOC 6 H 4 NC(tBu)NH(2,6-R 2 C 6 H 3 ) (R = Me, iPr), were synthesized and successfully employed as tridentate ligands for the preparation of the dialkyl rare earth complexes [2-MeOC 6 H 4 NC(tBu)N(2,6-R 2 C 6 H 3 )]Ln(CH 2 SiMe 3 ) 2 (L) n {Ln = Y, Lu; R = Me, iPr; L = thf (n = 2), dme (n = 1)}. These ligands provided enhanced stability for the complexes. The X-ray structure determinations revealed that intramolecular coordination of the 2-MeOC 6 H 4 group is realized if a thf molecule is coordinated to the metal center (Ln = Y, Lu), which results in the coordination number of six. The treatment of complex [2-MeOC 6 H 4 NC(tBu)N(2,6-Me 2 C 6 H 3 )]Lu(CH 2 Si-Me 3 ) 2 (thf) with dme afforded a six-coordinate dme adduct in which the methoxy group of the amidinate ligand has drifted out from the metal coordination sphere. The reaction of [2-MeOC 6 H 4 NC(tBu)N(2,6-iPr 2 C 6 H 3 )]Y(CH 2 SiMe 3 ) 2 (thf) with[a] G. A. Razuvaev

2 ]Li in toluene at 65°C. The complexes were isolated after recrystallization from hexane in 66, 64, and 68 % yield, respectively. X-ray diffraction studies revealed that compounds 1-3 are heterodimetallic complexes that have two borohydride li-

Most likely a hydrid species is formed in the course of this reaction, which undergoes rapid C-H actiVation since 3 is formed from 2 directly about 500 times slower than in the presence of 1 equiV of PhSiH 3 . Molecular structures of complexes 2 and 3 haVe been confirmed by X-ray crystal structure analysis.Even after a lapse of twenty-five years since the pioneering works on the synthesis of the first molecular rare earth metal hydrido complexes, 1 these compounds still attract considerable attention 2 and remain one of the most promising classes of compounds for various catalytic applications. 3 Enhanced reactivity of hydrido complexes, which allows even C-F bond activation, 4 gives evidence of their high potential in stoichiometric reactions. Until very recently rare earth metal hydrides were represented exclusively by sandwich-2 and half-sandwichtype ("constrained geometry") 5 complexes. Remarkable progress has been made in this field, and the formerly challenging monomeric 4 and dihydrido 6 species became a reality. The hydride supported by benzamidinate ligands {[PhC(NSiMe 3 ) 2 ] 2 Y-(µ-H)} 2 7 synthesized by Teuben and co-workers in 1993 was the first and for a long time the sole example of a cyclopentadienyl-free rare earth metal hydrido complex. The recent advances in rare earth metal hydrido chemistry 8 are linked to application of novel types of coordination environments: bis-(silylamido)biphenyl, 9a calyx-tetrapyrrol, 9b,c salicylaldimine, 9d,e tris(pyrazolil)borate. 9f However, to date, "post-metallocene" hydrides still remain a rarity. Recently we reported the synthesis of the series of hydrido lanthanide complexes supported by bulky tetrasubstituted guanidinate ligands, which have demonstrated high catalytic activity in olefin polymerization. 10 Sterically demanding aminopyridinato ligands 11 were also successfully used as a suitable coordination environment for stabilization of monomeric lanthanide species. Both guanidinate and aminopyridinate frameworks have a common feature: a chelating monoanionic planar NCN moiety. In order to investigate the influence of ancillary ligation on the reactivity of the Y-H and Y-C bonds, we decided to employ the aminopyridinate ligation system for synthesis of alkyl and hydrido complexes. Herein we report on the exiting outcomes of the attempts to synthesize alkyl and hydrido yttrium complexes supported by the bulky aminopyridinate ligand system. Bulky 2,6-(diisopropylphenyl)-[6-(2,6-dimethylphenyl)pyridin-2-yl]amine (Ap′-H) (Scheme 1) 11a,b was used as the ligand For example see, hydrogenation: (a) Jeske, G.; Lauke, H.; Mauermann, H.; Schumann, H.; Marks, T. J. J. Am. Chem. Soc. 1985, 107, 8111-8118. (b) Conticello, V. P.; Brard, L.; Giardello, M. A.; Tsyji, Y.; Sabat, M.; Stern, C. L.; Marks, T. J. Lauke, H.; Mauermann, H.; Swepston, P. N.; Schumann, H.; Marks, T. J. (a) Trifonov, A. A.; Fedorova, E. A.; Fukin, G. K.; Bochkarev, M. N. Eur. J. Inorg. Chem. 2004, 4396-4401. (b) Trifonov, A. A.; Skvortsov, G. G.; Lyubov, D. M.; Skorodumova, N. A.; Fukin, G. K.; Bar...