Rare‐Earth Amido and Borohydrido Complexes Supported by Tetradentate Amidinate Ligands: Synthesis, Structure, and Catalytic Activity in Polymerization of Cyclic Esters

Abstract

Amido [Bu t C(NC 6 H 4 -2-OMe) 2 ] 2 LnN(SiMe 3 ) 2 (Ln = Y (3), Nd (4)) and borohydrido complexes [Bu t C(NC 6 H 4 -2-OMe) 2 ] 2 LnBH 4 (Ln = Y (5), Nd (6)) coordinated by new amidinate ligand bearing two pendant anisolyl groups are synthesized. According to X-ray analysis in complexes 3 and 4 one amidinate ligand is coordinated to the Ln 3+ cation in a bidentate fashion (κ 2 -NN), while the second one is tetradentate (κ 4 -NNOO). At the same time in borohydrido neodymium complex 6 the amidin-[a] G. A. Razuvaev

Bis(alkyl) Sc and Y Complexes Supported by Tri‐ and Tetradentate Amidinate Ligands: Synthesis, Structure, and Catalytic Activity in α‐Olefin and Isoprene Polymerization

“…Available o‐anisidine was used as a platform for the synthesis of tri‐ ( 1 ) [9c] and tetradentate ( 2 ) [10] amidines bearing a pendant −C 6 H 4 −2‐OMe group in the side chain. Generally, two different synthetic approaches are successfully used for the preparation of bis(alkyl) rare‐earth complexes.…”

“…(1), [9c] (C 6 H 4 À 2-OMe) N=C(tBu)À NH(C 6 H 4 À 2-OMe) (2) [10] were prepared according to literature procedures. All other commercially available chemicals were used after appropriate purifications.…”

“…[23,24] The CÀ N interatomic distances in the amidinate group in complex 7 are within a narrow range of values (1.332(2), 1.343(2) Å), which indicates a delocalization of a negative charge within the NCN fragment. The YÀ O distance in 7 (2.445(2)-2.462(2) Å) are considerably shorter than the coordination bond between Y 3 + and oxygen atoms of the amido complex [(2-OMeÀ C 6 H 4 N) 2 C(tBu)] 2 YN(SiMe 3 ) 2 (2.594(2), 2.628(2) Å), [10] [9c] It is interesting to note that the amidinate and amide ligands in 7 are distorted much less compared to 5: the dihedral angles between the metallocycles YOCCN and YNCN in both ligands fall into the range of 168.1(2)-175.4(2)°.…”

“…The ternary systems including 4 demonstrate a modest stereoselectivity leading to the polymer samples with only slightly prevalent 3,4-regularity (up to 59-68 %), with no appreciable effects or understandable trends resulting from the activator (TB or HNB) introduced into the catalytic system (Table 3, entries 3, 4, 6, 7). However, the systems 5/borate/AliBu 3 allowed to reach 3,4-regularity up to 71-77 %, wherein no formation of 1,4-trans-units was observed (Table 3, entries 10,11,13,14). In contrast, the ternary systems including 6 allow to "switch" the stereoselectivity of isoprene polymerization (Table 3, entries 17,19) and to obtain polymers with high content of cis-1,4-units (86-96 %).…”

“…The polymeric samples obtained with ternary catalytic systems 6/ HNB/AliBu 3 and 6/TB/AliBu 3 showed monomodal GPC traces with broadened polydispersity values M w /M n (3.3-5.5). Ternary catalytic systems containing 4 and 5 enable the formation of PIPs with a reasonable molecular weight distribution (M w /M n = 1.6-2.9) and high molecular weights M n = 1164000-1637000 (Table 3, entries 3,4,6,10,11,13,14).…”