Facile Preparation of a Scandium Terminal Imido Complex Supported by a Phosphazene Ligand

The scandium bis­(alkyl) complex bearing the phosphazene ligand L¹Sc­(CH₂SiMe₃)₂ (<b>1</b>) (L¹ = N­(PPh₂NPh)₂) reacted with an equimolar amount of 2,6-diisopropylaniline to afford the corresponding mixed alkyl/anilido complex L¹Sc­[NHC₆H₃(^<i>i</i>Pr)₂]­(CH₂SiMe₃) (<b>2</b>). Under mild conditions (20 °C, 4 h or 0 °C, 12 h), complex <b>2</b> could be swiftly transformed to the terminal imido complex L¹ScN­[C₆H₃(^<i>i</i>Pr)₂]­(DMAP)₂ (<b>4</b>) in the presence of DMAP (DMAP = 4-<i>N,N</i>-dimethylaminopyridine). Correspondingly, treatment of the yttrium and lutetium bis­(alkyl) complexes L²Ln­(CH₂SiMe₃)₂ (L² = N­[Ph₂PNC₆H₃(^<i>i</i>Pr)₂]₂; Ln = Y (<b>7</b>), Lu (<b>8</b>)) with equimolar amounts of 2,6-diisopropylaniline gave the mixed alkyl/anilido complexes L²Ln­[NHC₆H₃(^<i>i</i>Pr)₂]­(CH₂SiMe₃) (Ln = Y (<b>9</b>), Lu (<b>10</b>)), which, however, underwent dealkylation of the Ln–CH₂SiMe₃ species at temperatures of 60 °C for <b>9</b> and 100 °C for <b>10</b> to afford bis­(anilido) complexes L²Ln­[NHC₆H₃(^<i>i</i>Pr)₂]₂ (Ln = Y (<b>11</b>), Lu (<b>12</b>)) as redistribution products. All these complexes have been characterized by ¹H, ¹³C­{¹H}, and ³¹P­{¹H} NMR spectroscopy and X-ray diffraction analyses, and clear structural insight into the behavior of an imido functionality on a lanthanide metal center was provided

Rare-Earth-Metal Complexes Bearing Phosphazene Ancillary Ligands: Structures and Catalysis toward Highly Trans-1,4-Selective (Co)Polymerizations of Conjugated Dienes

The bis-arylated phosphazene compounds [HN­(PPh₂NAr)₂] (Ar = phenyl (HL¹), 2,6-dimethylphenyl (HL²), 2,6-diisopropylphenyl (HL³)) and the imidodiphosphinate compound HN­(PPh₂O)₂ (HL⁴) have been prepared via the Staudinger reaction. Treatment of the neutral compounds HL¹, HL², and HL³ with Ln­(CH₂SiMe₃)₃(THF)₂ (Ln = Sc, Y, Lu) generated the solvent-free bis­(alkyl) complexes L¹Ln­(CH₂SiMe₃)₂ (Ln = Sc (<b>1a</b>), Y (<b>1b</b>), Lu (<b>1c</b>)), L²Sc­(CH₂SiMe₃)₂ (<b>2a</b>), L³Y­(CH₂SiMe₃)₂ (<b>3b</b>), and L³Lu­(CH₂SiMe₃)₂ (<b>3c</b>), respectively. The reaction between HL⁴ and Y­(CH₂SiMe₃)₃(THF)₂ gave the rare zwitterionic complex <b>4b</b>. Lithiation of the ligand HL¹ by <i>n</i>BuLi followed by a metathesis reaction with Nd­(BH₄)₃(THF)₃ afforded the corresponding complex L¹Nd­(BH₄)₂(THF)₂ (<b>5</b>). Complexes <b>1</b> upon incorporation of [Ph₃C]­[B­(C₆F₅)₄] and Al<i>i</i>Bu₃ led to ternary systems that initiated isoprene polymerization with high activities, among which complex <b>1a</b> was the first example of a scandium catalytic precursor providing trans-1,4-selectivity (90.0%), while the lutetium analogue <b>1c</b> had medium trans-1,4-selectivity (54.3%) and the yttrium complex <b>1b</b> exhibited high cis-1,4-selectivity (76.3%). The ternary system based on the zwitterion <b>4b</b> displayed the highest activity for the isoprene polymerization among these complexes and gave cis-1,4-regularity-enriched polyisoprene (70.6%). Highly stereospecific homopolymerizations of isoprene (trans-1,4-content: 97.0%) and butadiene (trans-1,4-content: 94.0%) were achieved by using the borohydrido complex <b>5</b> upon the activation of dibutylmagnesium. The copolymerization of isoprene and butadiene with <b>1a</b>/[Ph₃C]­[B­(C₆F₅)₄/Al<i>i</i>Bu₃] gave randomly arranged trans-1,4-regulated polybutadiene and polyisoprene sequences. The kinetics study displayed competitive polymerization rates of <i>r</i>_BD = 2.89 and <i>r</i>_IP = 0.41. The thermal behaviors of the (co)­polymers were investigated

Phosphinimino-amino Magnesium Complexes: Synthesis and Catalysis of Heteroselective ROP of <i>rac</i>-Lactide

Alkane elimination reactions of phosphinimino-amine ligands HL^1–8 ((2,6-Me₂-C₆H₃NH)­C­(Ph)CHPPh₂(NAr) (Ar = C₆H₅ (HL¹); 2,6-Me₂-C₆H₃ (HL²); 2,6-Et₂-C₆H₃ (HL³); 2,6-^<i>i</i>Pr₂-C₆H₃ (HL⁴); 2-OMe-C₆H₄ (HL⁵); 2-Cl-C₆H₄ (HL⁶); 3-CF₃-C₆H₄ (HL⁷); 4-MeO-C₆H₄ (HL⁸)) with Mg^<i>n</i>Bu₂, respectively, afforded a series of phosphinimino-amine-based complexes L^1–8Mg^<i>n</i>Bu­(THF) (<b>1</b>–<b>8</b>) by releasing butane. Complexes <b>1</b>–<b>8</b> are phosphinimino-amine-ligated THF-solvated mono­(alkyl)­s, among which <b>1</b>–<b>4</b> adopt twisted tetrahedral geometries, whereas <b>5</b> contains a trigonal bipyramido geometry core. Complexes <b>1</b>–<b>8</b> all display high activity for the ring-opening polymerization of <i>rac</i>-lactide. The molecular weights of the resulting PLA are close to the theoretic values, and the molecular weight distributions are narrow. Moreover, these complexes show medium to high heteroselectivity, which, interestingly, increases with the decrease of the ligand steric hindrance; thus, complex <b>1</b>, bearing a less bulky ligand, exhibits a heteroselectivity of <i>P</i>_r = 0.98, the highest value of a magnesium-based initiator achieved to date. The kinetics study showed that the polymerization rate is first-order dependent on both monomer and initiator concentrations, and the overall rate equation is −d­[LA]/d<i>t</i> = 3.78 M^–1 s^–1 [LA]­[Mg]

Efficient and Heteroselective Heteroscorpionate Rare-Earth-Metal Zwitterionic Initiators for ROP of <i>rac</i>-Lactide: Role of σ‑Ligand

A series of oxophosphine (3,5-Me₂Pz)₂CHP­(R)₂O (Pz = pyrazole; R = ^<i>t</i>Bu (HL¹), Cy (HL²)) and iminophosphine (3,5-Me₂Pz)₂CHP­(R)₂NAr (R = Cy, Ar = Ph (HL³); R = Ph, Ar = Ph (HL⁴), Ar = 2,6-Me₂-phenyl (HL⁵)) heteroscorpionate ligands were synthesized. Abstraction of the methide proton of these ligands by rare-earth-metal tris­(alkyl)­s, Ln­(CH₂SiMe₃)₃(THF)₂, afforded the corresponding zwitterionic bis­(alkyl) complexes L^1–5Ln­(CH₂SiMe₃)₂(THF) (L¹, Ln = Y (<b>1a</b>), Lu (<b>1b</b>); L², Ln = Y (<b>2a</b>), Lu (<b>2b</b>); L³, Ln = Y (<b>3a</b>), Lu (<b>3b</b>); L⁴, Ln = Y (<b>4a</b>), Lu (<b>4b</b>); L⁵, Ln = Y (<b>5a</b>), Lu (<b>5b</b>), while metathesis reaction of the lithium salts of LiL³ and LiL⁴ with YCl₃(THF)₂ or YBr₃(THF)₂ followed by treatment with LiCH₂SiMe₃ and KN­(SiHMe₂)₂, respectively, afforded the first heteroscorpionate yttrium mixed halogen/alkyl or amido complexes L^3–4Y­(Cl)­(CH₂SiMe₃)­(THF) (L³ (<b>6a</b>), L⁴ (<b>7a</b>)), L^3–4Y­(Cl)­(N­(SiHMe₂)₂)­(THF) (L³(<b>8a</b>), L⁴ (<b>9a</b>)), L⁴Y­(Br)­(CH₂SiMe₃)­(THF) (<b>10a</b>), and L⁴Y­(Br)­(N­(SiHMe₂)₂)­(THF) (<b>11a</b>). The structures of these complexes were well-defined, and the molecular structures of <b>1a</b>, <b>2a</b>, <b>3b</b>, <b>4b</b>, <b>5a</b>, and <b>7a</b> were further characterized by single crystal X-ray diffraction analysis. Complexes <b>1</b>–<b>5</b> showed similar high activity toward the ROP of <i>rac</i>-LA at room temperature, and both the alkyl species participated in initiation, of which the lutetium complexes exhibited slightly higher selectivity than their yttrium analogues (<i>P</i>_r = 0.85–0.89 vs 0.80–0.84) despite the bulkiness of the ligands. Interestingly, the mixed halogen complexes <b>6a</b>–<b>11a</b> were single-site initiators, where the σ-halogen moiety remaining on the central metal showed, for the first time, facilitating the heteroselectivity up to <i>P</i>_r = 0.98. This result sheds new light on designing specifically selective catalytic precursors

Efficient and Heteroselective Heteroscorpionate Rare-Earth-Metal Zwitterionic Initiators for ROP of <i>rac</i>-Lactide: Role of σ‑Ligand

A series of oxophosphine (3,5-Me₂Pz)₂CHP­(R)₂O (Pz = pyrazole; R = ^<i>t</i>Bu (HL¹), Cy (HL²)) and iminophosphine (3,5-Me₂Pz)₂CHP­(R)₂NAr (R = Cy, Ar = Ph (HL³); R = Ph, Ar = Ph (HL⁴), Ar = 2,6-Me₂-phenyl (HL⁵)) heteroscorpionate ligands were synthesized. Abstraction of the methide proton of these ligands by rare-earth-metal tris­(alkyl)­s, Ln­(CH₂SiMe₃)₃(THF)₂, afforded the corresponding zwitterionic bis­(alkyl) complexes L^1–5Ln­(CH₂SiMe₃)₂(THF) (L¹, Ln = Y (<b>1a</b>), Lu (<b>1b</b>); L², Ln = Y (<b>2a</b>), Lu (<b>2b</b>); L³, Ln = Y (<b>3a</b>), Lu (<b>3b</b>); L⁴, Ln = Y (<b>4a</b>), Lu (<b>4b</b>); L⁵, Ln = Y (<b>5a</b>), Lu (<b>5b</b>), while metathesis reaction of the lithium salts of LiL³ and LiL⁴ with YCl₃(THF)₂ or YBr₃(THF)₂ followed by treatment with LiCH₂SiMe₃ and KN­(SiHMe₂)₂, respectively, afforded the first heteroscorpionate yttrium mixed halogen/alkyl or amido complexes L^3–4Y­(Cl)­(CH₂SiMe₃)­(THF) (L³ (<b>6a</b>), L⁴ (<b>7a</b>)), L^3–4Y­(Cl)­(N­(SiHMe₂)₂)­(THF) (L³(<b>8a</b>), L⁴ (<b>9a</b>)), L⁴Y­(Br)­(CH₂SiMe₃)­(THF) (<b>10a</b>), and L⁴Y­(Br)­(N­(SiHMe₂)₂)­(THF) (<b>11a</b>). The structures of these complexes were well-defined, and the molecular structures of <b>1a</b>, <b>2a</b>, <b>3b</b>, <b>4b</b>, <b>5a</b>, and <b>7a</b> were further characterized by single crystal X-ray diffraction analysis. Complexes <b>1</b>–<b>5</b> showed similar high activity toward the ROP of <i>rac</i>-LA at room temperature, and both the alkyl species participated in initiation, of which the lutetium complexes exhibited slightly higher selectivity than their yttrium analogues (<i>P</i>_r = 0.85–0.89 vs 0.80–0.84) despite the bulkiness of the ligands. Interestingly, the mixed halogen complexes <b>6a</b>–<b>11a</b> were single-site initiators, where the σ-halogen moiety remaining on the central metal showed, for the first time, facilitating the heteroselectivity up to <i>P</i>_r = 0.98. This result sheds new light on designing specifically selective catalytic precursors

Yttrium Hydride Complex Bearing CpPN/Amidinate Heteroleptic Ligands: Synthesis, Structure, and Reactivity

The reaction of the yttrium dialkyls (C₅H₄–PPh₂N–C₆H₃^<i>i</i>Pr₂)­Y­(CH₂SiMe₃)₂(thf) (<b>1</b>) with an excess of <i>N</i>,<i>N′</i>-diisopropylcarbodiimide gave the yttrium monoalkyl complex (C₅H₄–PPh₂N–C₆H₃^<i>i</i>Pr₂)­Y­(CH₂SiMe₃)­[^<i>i</i>PrNC­(CH₂SiMe₃)–N^<i>i</i>Pr] (<b>2</b>). <b>2</b> subsequently reacted with 1 equiv of PhSiH₃ to generate the CpPN/amidinate heteroleptic yttrium hydride {(C₅H₄–PPh₂N–C₆H₃^<i>i</i>Pr₂)­Y­[^<i>i</i>PrNC­(CH₂SiMe₃)–N^<i>i</i>Pr]­(μ-H)}₂ (<b>3</b>). Hydride <b>3</b> showed good reactivity toward various substrates containing unsaturated C–C, C–N, and N–N bonds, such as azobenzene, <i>p</i>-tolyacetylene, 1,4-bis­(trimethylsilyl)-1,3-butanediyne, <i>N</i>,<i>N′</i>-diisopropylcarbodiimide, and 4-dimethylaminopyridine, affording the yttrium hydrazide complex <b>4</b> with a rare η²-Cp bonding mode, yttrium terminal alkynyl complex <b>5</b>, yttrium η³-propargyl complex <b>6</b>, yttrium amidinate complex <b>7</b>, and yttrium 2-hydro-4-dimethylaminopyridyl product <b>8</b>, respectively

Yttrium Hydride Complex Bearing CpPN/Amidinate Heteroleptic Ligands: Synthesis, Structure, and Reactivity

The reaction of the yttrium dialkyls (C₅H₄–PPh₂N–C₆H₃^<i>i</i>Pr₂)­Y­(CH₂SiMe₃)₂(thf) (<b>1</b>) with an excess of <i>N</i>,<i>N′</i>-diisopropylcarbodiimide gave the yttrium monoalkyl complex (C₅H₄–PPh₂N–C₆H₃^<i>i</i>Pr₂)­Y­(CH₂SiMe₃)­[^<i>i</i>PrNC­(CH₂SiMe₃)–N^<i>i</i>Pr] (<b>2</b>). <b>2</b> subsequently reacted with 1 equiv of PhSiH₃ to generate the CpPN/amidinate heteroleptic yttrium hydride {(C₅H₄–PPh₂N–C₆H₃^<i>i</i>Pr₂)­Y­[^<i>i</i>PrNC­(CH₂SiMe₃)–N^<i>i</i>Pr]­(μ-H)}₂ (<b>3</b>). Hydride <b>3</b> showed good reactivity toward various substrates containing unsaturated C–C, C–N, and N–N bonds, such as azobenzene, <i>p</i>-tolyacetylene, 1,4-bis­(trimethylsilyl)-1,3-butanediyne, <i>N</i>,<i>N′</i>-diisopropylcarbodiimide, and 4-dimethylaminopyridine, affording the yttrium hydrazide complex <b>4</b> with a rare η²-Cp bonding mode, yttrium terminal alkynyl complex <b>5</b>, yttrium η³-propargyl complex <b>6</b>, yttrium amidinate complex <b>7</b>, and yttrium 2-hydro-4-dimethylaminopyridyl product <b>8</b>, respectively

Phosphazene-Functionalized Cyclopentadienyl and Its Derivatives Ligated Rare-Earth Metal Alkyl Complexes: Synthesis, Structures, and Catalysis on Ethylene Polymerization

Treatment of Ln­(CH₂SiMe₃)₃(thf)₂ (Ln = Sc, Y, and Lu) with 1 equiv of CpPN-type ligands C₅H₄PPh₂–NH–C₆H₃R₂ (R = Me, <b>L¹(Me)</b>; R = ^<i>i</i>Pr, <b>L¹(^<i>i</i>Pr)</b>) at room temperature readily generated the corresponding CpPN-type bis­(alkyl) complexes <b>1</b> and <b>2a</b>–<b>2c</b>. Addition of 3 equiv of LiCH₂SiMe₃ to a mixture of <b>L¹(^<i>i</i>Pr)</b> and LnCl₃(thf)₂ (Ln = Sm and Nd) also afforded the CpPN-type bis­(alkyl) complexes <b>2d</b> and <b>2e</b>. The Cp moiety bonds to the central metal in a classical η⁵ mode in all CpPN-type complexes <b>1</b> and <b>2</b>. In contrast, the Cp^MePN-type ligands C₅Me₄H–PPh₂N–C₆H₃R₂ (R = Me, <b>L²(Me)</b>; R = ^<i>i</i>Pr, <b>L²(^<i>i</i>Pr)</b>) behaved differently. <b>L²(Me)</b> did not react with Sc­(CH₂SiMe₃)₃(thf)₂. Similarly, <b>L²(^<i>i</i>Pr)</b> was also inert to Sc­(CH₂SiMe₃)₃(thf)₂ even at 50 °C. When the central metal was changed to yttrium, however, the equimolar reaction between Y­(CH₂SiMe₃)₃(thf)₂ and <b>L²(^<i>i</i>Pr)</b> in the presence of LiCl afforded two bis­(alkyl) complexes <b>3a</b> and <b>3b</b>. In the main product <b>3a</b>, [C₅HMe₃(η³-CH₂)–PPh₂N–C₆H₃^<i>i</i>Pr₂]­Y­(CH₂SiMe₃)₂(thf), the ligand bonds to the Y³⁺ ion in a rare η³-allyl/κ-N mode, whereas in <b>3b</b>, <b>(</b>C₅Me₄–PPh₂N–C₆H₃^<i>i</i>Pr₂)­Y­(CH₂SiMe₃)₂(LiCl)­(thf), the Cp ring coordinates to the Y³⁺ ion in an η⁵ mode, and a LiCl unit is located between the Y³⁺ ion and the nitrogen atom. When the central metal was changed to lutetium, a bis­(alkyl) complex <b>4a</b>, [C₅HMe₃(η³-CH₂)–PPh₂N–C₆H₃^<i>i</i>Pr₂]­Lu­(CH₂SiMe₃)₂(thf), and a bis­(alkyl) complex <b>4b</b>, (C₅Me₄–PPh₂N–C₆H₃^<i>i</i>Pr₂)­Lu­(CH₂SiMe₃)₂, were isolated. The protonolysis reaction of the IndPN-type ligands C₉H₇–PPh₂N–C₆H₃R₂ (R = Me, <b>L³(Me)</b>; R = Et, <b>L³(Et)</b>; R = ^<i>i</i>Pr, <b>L³(^<i>i</i>Pr)</b>) with Ln­(CH₂SiMe₃)₃(thf)₂ (Ln = Sc, Y, and Lu) generated the IndPN-type bis­(alkyl) complexes <b>5a</b>–<b>5c</b>, <b>6</b>, and <b>7a</b>–<b>7c</b>, selectively, where the Ind moiety tends to adopt an η³-bonding fashion. The more bulky FluPN-type ligands C₁₃H₉–PPh₂N–C₆H₄R (R = H, <b>L⁴(H)</b>; R = Me, <b>L⁴(Me)</b>) were treated with Ln­(CH₂SiMe₃)₃(thf)₂ (Ln = Sc and Lu) to afford the FluPN-type bis­(alkyl) complexes <b>8</b> and <b>9a</b> and <b>9b</b>, where the Flu moiety has a rare η¹-bonding mode. Complexes <b>1</b>–<b>9</b> were fully characterized by ¹H, ¹³C, and ³¹P NMR; X-ray; and elemental analyses. Upon activation with AlR₃ and [Ph₃C]­[B­(C₆F₅)₄], the scandium complexes showed good to high catalytic activity for ethylene polymerization. The effects of the sterics and electronics of the ligand, the loading and the type of AlR₃, the polymerization temperature, and the polymerization time on the catalytic activity were also discussed

Phosphazene-Functionalized Cyclopentadienyl and Its Derivatives Ligated Rare-Earth Metal Alkyl Complexes: Synthesis, Structures, and Catalysis on Ethylene Polymerization

Treatment of Ln­(CH₂SiMe₃)₃(thf)₂ (Ln = Sc, Y, and Lu) with 1 equiv of CpPN-type ligands C₅H₄PPh₂–NH–C₆H₃R₂ (R = Me, <b>L¹(Me)</b>; R = ^<i>i</i>Pr, <b>L¹(^<i>i</i>Pr)</b>) at room temperature readily generated the corresponding CpPN-type bis­(alkyl) complexes <b>1</b> and <b>2a</b>–<b>2c</b>. Addition of 3 equiv of LiCH₂SiMe₃ to a mixture of <b>L¹(^<i>i</i>Pr)</b> and LnCl₃(thf)₂ (Ln = Sm and Nd) also afforded the CpPN-type bis­(alkyl) complexes <b>2d</b> and <b>2e</b>. The Cp moiety bonds to the central metal in a classical η⁵ mode in all CpPN-type complexes <b>1</b> and <b>2</b>. In contrast, the Cp^MePN-type ligands C₅Me₄H–PPh₂N–C₆H₃R₂ (R = Me, <b>L²(Me)</b>; R = ^<i>i</i>Pr, <b>L²(^<i>i</i>Pr)</b>) behaved differently. <b>L²(Me)</b> did not react with Sc­(CH₂SiMe₃)₃(thf)₂. Similarly, <b>L²(^<i>i</i>Pr)</b> was also inert to Sc­(CH₂SiMe₃)₃(thf)₂ even at 50 °C. When the central metal was changed to yttrium, however, the equimolar reaction between Y­(CH₂SiMe₃)₃(thf)₂ and <b>L²(^<i>i</i>Pr)</b> in the presence of LiCl afforded two bis­(alkyl) complexes <b>3a</b> and <b>3b</b>. In the main product <b>3a</b>, [C₅HMe₃(η³-CH₂)–PPh₂N–C₆H₃^<i>i</i>Pr₂]­Y­(CH₂SiMe₃)₂(thf), the ligand bonds to the Y³⁺ ion in a rare η³-allyl/κ-N mode, whereas in <b>3b</b>, <b>(</b>C₅Me₄–PPh₂N–C₆H₃^<i>i</i>Pr₂)­Y­(CH₂SiMe₃)₂(LiCl)­(thf), the Cp ring coordinates to the Y³⁺ ion in an η⁵ mode, and a LiCl unit is located between the Y³⁺ ion and the nitrogen atom. When the central metal was changed to lutetium, a bis­(alkyl) complex <b>4a</b>, [C₅HMe₃(η³-CH₂)–PPh₂N–C₆H₃^<i>i</i>Pr₂]­Lu­(CH₂SiMe₃)₂(thf), and a bis­(alkyl) complex <b>4b</b>, (C₅Me₄–PPh₂N–C₆H₃^<i>i</i>Pr₂)­Lu­(CH₂SiMe₃)₂, were isolated. The protonolysis reaction of the IndPN-type ligands C₉H₇–PPh₂N–C₆H₃R₂ (R = Me, <b>L³(Me)</b>; R = Et, <b>L³(Et)</b>; R = ^<i>i</i>Pr, <b>L³(^<i>i</i>Pr)</b>) with Ln­(CH₂SiMe₃)₃(thf)₂ (Ln = Sc, Y, and Lu) generated the IndPN-type bis­(alkyl) complexes <b>5a</b>–<b>5c</b>, <b>6</b>, and <b>7a</b>–<b>7c</b>, selectively, where the Ind moiety tends to adopt an η³-bonding fashion. The more bulky FluPN-type ligands C₁₃H₉–PPh₂N–C₆H₄R (R = H, <b>L⁴(H)</b>; R = Me, <b>L⁴(Me)</b>) were treated with Ln­(CH₂SiMe₃)₃(thf)₂ (Ln = Sc and Lu) to afford the FluPN-type bis­(alkyl) complexes <b>8</b> and <b>9a</b> and <b>9b</b>, where the Flu moiety has a rare η¹-bonding mode. Complexes <b>1</b>–<b>9</b> were fully characterized by ¹H, ¹³C, and ³¹P NMR; X-ray; and elemental analyses. Upon activation with AlR₃ and [Ph₃C]­[B­(C₆F₅)₄], the scandium complexes showed good to high catalytic activity for ethylene polymerization. The effects of the sterics and electronics of the ligand, the loading and the type of AlR₃, the polymerization temperature, and the polymerization time on the catalytic activity were also discussed