Cationic Scandium Allyl Complexes Bearing Mono(cyclopentadienyl) Ligands: Synthesis, Novel Structural Variety, and Olefin‐Polymerization Catalysis

Abstract

The one-pot salt-metathesis reaction of ScCl(3), cyclopentadienyl lithium salts, and allylmagnesium chlorides afforded with ease the corresponding base-free half-sandwich scandium di(eta(3)-allyl) complexes [(C(5)Me(4)SiMe(3))Sc(C(3)H(5))(2)] (1 a), [(C(5)Me(5))Sc(C(3)H(5))(2)] (1 b), and [(C(5)Me(5))Sc(2-MeC(3)H(4))(2)] (1 c) in high yields. Reaction of 1 a with 1 equivalent of [PhNMe(2)H][B(C(6)F(5))(4)] in toluene gave rapidly the N,N-dimethylaniline-coordinated cationic mono(eta(3)-allyl) complex [(C(5)Me(4)SiMe(3))Sc(eta(3)-C(3)H(5))(eta(6)-PhNMe(2))][B(C(6)F(5))(4)] (2). The similar reaction of 1 a with [Ph(3)C][B(C(6)F(5))(4)] yielded the analogous toluene-separated ion pair [(C(5)Me(4)SiMe(3))Sc(eta(3)-C(3)H(5))(eta(6)-PhMe)][B(C(6)F(5))(4)] (3). When [PhNMe(2)H][BPh(4)] was treated with 1 a, the contact ion pair [(C(5)Me(4)SiMe(3))Sc(eta(3)-C(3)H(5))( mu,eta(6)-Ph)BPh(3)] (4) was obtained. Recrystallization of 2, 3, and 4 in THF yielded the corresponding thf-separated ion pair complexes [(C(5)Me(4)SiMe(3))Sc(eta(3)-C(3)H(5))(thf)(2)][B(C(6)F(5))(4)] (5) and [(C(5)Me(4)SiMe(3))Sc(eta(3)-C(3)H(5))(thf)(2)][BPh(4)] (6). The N,N-dimethylaniline-coordinated cationic scandium allyl complex 2 and the toluene-coordinated analogue 3 showed high activity (activity: 3>2) toward the polymerization and copolymerization of isoprene and norbornene to afford random copolymers with a broad range of isoprene content (33-86 mol %). The tight ion pair 4 and the thf-coordinated complexes 5 and 6 showed no activity under the same conditions. These results offer unprecedented insight into the structure-activity relationship of a cationic metal polymerization-catalyst system.

Rare-Earth-Metal Allyl Complexes Supported by the [2-(N,N-Dimethylamino)ethyl]tetramethylcyclopentadienyl Ligand: Structural Characterization, Reactivity, and Isoprene Polymerization

“…The overall ligand arrangement is comparable with that of the N,N-dimethylanilinyl-substituted half-sandwich rare-earth complexes [(C 5 Me 4 C 6 H 4 -o-NMe 2 )Ln-(η 3 -C 3 H 5 ) 2 ] (Ln = Y, Lu). 24 The bond angles Ct 2 −Ln−Ct 3 involving the allyl centroids (1a, 108.40°; 1b, 108.64°; 1c, 108.12°) are smaller than in the nonfunctionalized rare-earth-metal bis(allyl) complexes [(C 5 Me 4 R)Sc(η 3 -C 3 H 5 ) 2 ] (R = SiMe 3 , 119.11°; R = Me, 115.09) 43 but somewhat elongated in comparison to [(C 5 Me 4 C 6 H 4 -o-NMe 2 )Ln(η 3 -C 3 H 5 ) 2 ] (Y, 106.9°; Lu, 106.0°). 24 Furthermore, the bite angles between the cyclopentadienyl centroid and the nitrogen atom Ct 1 −Ln−N (1a, 96.99°; 1b, 97.43°; 1c, 98.21°) are slightly wider than in the anilinyl-functionalized complexes (Y, 95.4°; Lu, 96.7°).…”

1,3-Diene Polymerization Mediated by Homoleptic Tetramethylaluminates of the Rare-Earth Metals

“…As a clear identification of the active species was not successful so far, due to the paramagnetic character of most of the lanthanide ions and the low tendency of the active species toward crystallization, active species elucidation remains challenging. A reasonable interpretation of this polymerization behavior seems to be that solvent [4,5,13,37], pre-reaction side products (e.g., Ph 3 CMe (A) and PhNMe 2 (B): Ln(III)-arene coordination) [38][39][40], or even anion coordination (e.g., via Ln(III)-F interactions) [41] come into play. Furthermore, dimerization might take place or a η 2 -to-η 3 coordination switch of the remaining tetramethylaluminate moiety, which tendency seems more pronounced for the larger lanthanides as found for the neutral precatalysts [4,10,12].…”

Half-Sandwich Rare Earth Metal Complexes as Novel Catalysts for Olefin Polymerization and Other Chemical Transformations

“…dimethylaniline (a co-product of the deprotonation reaction) is trapped to the metal center through coordination of the phenyl ring in an © 6 -fashion (Scheme 10). 10 This is the first example of a structurally characterized cationic metal complex that unambiguously shows an interaction between N,N-dimethylaniline and a metal center via the phenyl ring rather than via the amino group. 4 ], all of these complexes become active for the syndiospecific polymerization of styrene, with the activity being dependent on both the ion size of the central metals and the ancillary ligands.…”

“…The THF-free half-sandwich di-allyl scandium complex [Sc(© 3 -CH 2 CHCH 2 ) 2 (C 5 Me 4 SiMe 3 )] (3) has been prepared by the one-pot metathetical reactions of [ScCl 3 (thf) 3 ] with C 5 Me 4 SiMe 3 Li and allylmagnesium chloride in THF (Scheme 3). 10 The analogous half-sandwich rare earth metal dialkyl complexes bearing heteroatom-containing cyclopentadienyl groups such as azaborolyl (4), 11 pyrrolyl (5a), 12 and phospholyl (5b) 13 as ancillary ligands have also been obtained in similar ways (Scheme 4).…”