Neutral Methyl and Cationic Aluminum Complexes Supported by a trans-1,2-Cyclooctanediyl-Bridged [OSSO]-Type Bis(phenolato) Ligand: Synthesis, Structures, and Use in Catalysis for Propylene Oxide Polymerization

Abstract

Treatment of trans-1,2-cyclooctanediyl-bridged [OSSO]-type bis(phenolate) 1 with Me3Al in hexane led to the formation of methylaluminum 4 as colorless crystals. X-ray diffraction analysis of 4 revealed that the aluminum center adopts a distorted-trigonal-bipyramidal geometry which occupies the axial positions with one phenoxide oxygen and one sulfur atoms. The dealkylation reaction of 4 with 1 equiv of B(C6F5)3 in C6D6 afforded the novel cationic aluminum species 5 2+ as a dimeric structure, which was isolated in the form of a [MeB(C6F5)3]− salt. In the crystal structure of 5 2+, one aluminum atom has a distorted-trigonal-bipyramidal environment, in which phenoxide and μ-bridging oxygen atoms are located at two axial positions, whereas the other aluminum atom has a distorted-square-pyramidal geometry, which occupies the axial position with a nonbridged oxygen atom. The cationic species 5 2+ promoted the ring-opening polymerization (ROP) of propylene oxide to give an atactic polymer in 44% yield with a low molecular weight (M n = 2500) and a very narrow molecular weight distribution (PDI = 1.04).

Highly Active and Isospecific Styrene Polymerization Catalyzed by Zirconium Complexes Bearing Aryl-substituted [OSSO]-Type Bis(phenolate) Ligands

“…In the crystalline state, the zirconium center possesses a distorted octahedral geometry with cis -arranged two sulfur atoms and two benzyl groups, adopting a cis -α configuration as similar as the previously reported [OSSO]-type zirconium(IV) complexes [ 49 , 50 , 57 , 58 , 59 , 60 ]. One benzyl ligand of 9 is coordinated to the zirconium center by η 1 -mode with the Zr–C benzyl –C ipso angle of 124.3(2)°, whereas the other has an acute Zr–C benzyl –C ipso angle of 84.4(2)° consistent with the η 2 -coordination fashion as similarly as in the case of t Bu-substituted complex 5a ; the Zr-C ipso distance (2.592(3) Å) is extremely shortened compared with that in 5a (2.820(3) Å) [ 48 ], indicating that this η 2 -benzyl group in 9 is strongly bound to the metal than that in 5a due to the less steric hindrance around the zirconium center in 9 as expected. The Zr–S bond lengths in 9 (2.8073(7), 2.8148(11) Å) are comparable to those in 5a (2.8107(8), 2.7682(8) Å) [ 49 , 50 ] and [Zr{2,2′-(OC 6 H 2 -4,6-Br 2 ) 2 CH 2 SCH 2 CH 2 SCH 2 }(CH 2 Ph) 2 ] (2.7934(7), 2.7932(6) Å) [ 61 ].…”

“…Recently, we have succeeded in the development of an [OSSO]-type bis(phenolate) ligand ( 4 ) based on a trans -1,2-cyclooctanediyl platform and the preparation of several early-transition metal and aluminum complexes [ 43 , 44 , 45 , 46 , 47 , 48 ]. We have also found that zirconium(IV) and hafnium(IV) complexes 5 [ 49 , 50 ] and 6 [ 51 ] incorporating ligand 4 with activator could promote precisely isospecific polymerizations of α-olefins such as 1-hexene, 4-methyl-1-pentene, and propylene involving excellent activity ( Scheme 1 ).…”

Enantio‐ and Stereoselective Cyclopolymerization of Hexa‐1,5‐diene Catalyzed by Zirconium Complexes Possessing Optically Active Bis(phenolato) Ligands

“…Recently, we have reported the development of [OSSO]‐type bis(phenolate)s incorporating with a trans ‐1,2‐cyclooctanediyl platform and the complexation of the pre‐ligand 1 with several early‐transition metal and aluminum complexes; we have found that zirconium(IV) and hafnium(IV) complexes with activator could promote precisely isospecific polymerizations of α‐olefins such as 1‐hexene, 4‐methyl‐1‐pentene, and propylene involving excellent activity . Since our zirconium complexes having the pre‐ligand 1 adopt chiral C 2 ‐symmetric structures with a helical arrangement of the robust [OSSO]‐type ligand around the octahedral metal center even in solution, we considered that the optically active complexes should ensure an enantio‐ and stereoselective cyclopolymerization of non‐conjugated α,ω‐dienes.…”

Zirconium and Hafnium Complexes with Cycloheptane- or Cyclononane-Fused [OSSO]-Type Bis(phenolato) Ligands: Synthesis, Structure, and Highly Active 1-Hexene Polymerization and Ring-Size Effects of Fused Cycloalkanes on the Activity

“…The insoluble inorganic materials were removed by filtration. The solvent of the filtrate was removed in vacuo, and the residual solid was washed with hexane (2 mL) and dried in vacuo to give [C7]HfCl 2 (13; 1.09 g, 77%) as colorless crystals: mp 180−181 °C dec; Synthesis of [C7]Zr(Bn) 2 (14). To a solution of [C7]ZrCl 2 (12; 205 mg, 0.270 mmol) in Et 2 O (15 mL) at −78 °C was added PhCH 2 MgCl (1.0 M in Et 2 O, 0.60 mL, 0.60 mmol).…”

“…Table 1, entries 2, 5, and 7. In the glovebox, B(C 6 F 5 ) 3 (10.2 mg, 0.020 mmol) or (Ph 3 C)[B(C 6 F 5 ) 4 ] (18.4 mg, 0.020 mmol) was added to a solution of [C7]Zr(Bn) 2 (14) in toluene (20 mM, 1.0 mL, 0.020 mmol) or [C7]Hf(Bn) 2 (15) in toluene (20 mM, 1.0 mL, 0.020 mmol) at room temperature. After it was stirred for 5 min at 25 or 0 °C, the mixture was kept at that temperature, and 1-hexene (3.0 g, 35.6 mmol) was added.…”