Shinya Miya

37. Propylene Polymerizations with Silylene-Bridged Metallocene Catalysts

New C 2 -symmetric silylene-bridged metallocene compounds, [Me 2 Si(R n -C 5 H 4-n )(R′ m -C 5 H 4-m )]MCl 2 (M=Zr, Hf; R n , R′ m =Me, t-Bu, 2,4-Me 2 , 2,3,5-Me 3 ), were synthesized together with C ° -symmetric compounds (M=Zr, Hf; R n =2,3,5-Me3, 2,4-Me 2 , 3,4-Me 2 , t-Bu, Me; R′ m =Me,H) for comparison and employed as the catalysts for isotactic polymerization of propylene in combination with methylaluminoxane. The C 2 -symmetric metallocenes bearing methyl groups at the 2- or 5-positions gave polymers of the highest melting point (160–163 °C) and stereoregularity ([mmmm]=97–99%).

Cobalt metallacycles. Part 16. X-Ray structures of 4-iminocobaltacyclobutene complexes

Three 4-iminocobaltacyclobutene complexes, [[graphic omitted](NC6H4Me-p)}(η5-C5H5)(PPh3)] have been analysed by single-crystal X-ray analyses. Crystals of (1)(R1= Ph, R2= CO2Me; CH2Cl2 solvate) are triclinic, space group P, with a= 12.381(3), b= 13.987(4), c= 11.209(4)A, α= 91.16(3), β= 103.30(2), γ= 77.14(2)°, Z= 2, and R= 0.066 for 3 055 reflections. Crystals of (2)(R′= Me, R2= CO2Me) are monoclinic, space group P21/c, with a= 12.062(5), b= 14.945(4), c= 17.817(5)A, β= 113.70(4)°, Z= 4, and R= 0.052 for 2 842 reflections. Crystals of (3)(R1= CO2Me, R2= Ph) are triclinic, space group P, with a= 12.271(6), b= 13.216(5), c= 10.833(4)A, α= 96.07(3), β= 98.77(4), γ= 102.23(3)°, Z= 2, and R= 0.048 for 4 324 reflections. The Co–C(R1) distance in these complexes depends on the bulkiness of the substituent R1, varying from 1.966(8)A for R1= Ph (1), to 1.931(5)A for R1= CO2Me (3), and to 1.908(7)A for R1= Me (2). In all cases the substituent of the imino group, C6H4Me-p, is located syn with respect to the metal. Treatment of (1) with methyl iodide gives a cationic complex which has been isolated as [[graphic omitted](NMeC6H4Me-p)}(η5-C5H5)(PPh3)]PF6(4). Crystals of (4) are triclinic, space group P, with a= 13.658(3), b= 14.142(2), c= 10.517(3)A, α= 94.42(2), β= 95.39(1), γ= 102.62(1)°, Z= 2, and R= 0.082 for 2 314 reflections. The methyl group originating from methyl iodide is bound to the imino nitrogen. Metallacyclobutadiene character in (4) is apparent from the shorter metal–carbon bonds and more averaged C–C distances than in the parent complex (1).

Cobalt metallacycles. Part 15. Regioselective formation and rearrangement of 4-iminocobaltacyclobutene complexes

The reaction of [Co(η5-C5H5)(PPh3)(R1CCR2)](1)(R1= H, Me, or Ph; R2= Ph, CO2Me, or CN) with isocyanides R3NC (R3= Ph, p-MeC6H4, or 2,6-Me2C6H3) gives the 1-(η5-cyclopentadienyl)-4 imino-1-(triphenylphosphine)cobaltacyclobutene complexes [[graphic omitted](NR3)}(η5-C5H5)(PPh3)](3). When (1) containing an unsymmetrical acetylene is used, the reaction is highly regioselective as only one of the two possible regioisomers has been detected. It has been concluded that the regioselectivity originates not from a steric effect but from an electronic requirement such that the acetylenic carbon with an electron-withdrawing substituent becomes the a carbon of the metallacycle. That this requirement leads to kinetically-controlled products has been demonstrated by thermal skeletal rearrangement of (3bi)(R1= Ph, R2= CO2Me) and (3ci)(R1= Ph, R2= CN) to [[graphic omitted](NC6H4Me-p)}(η5-C5H5)(PPh3)](8a)(R1= CO2Me, R2= Ph) and (8b)(R1= CN, R2= Ph), respectively. These regioselectivity observations have been rationalized by ab initio molecular orbital calculations. The imino configuration in these complexes is syn with respect to the metal and the substituent on the nitrogen. Methyl iodide reacts with (3bi) to give a PF6– salt of [[graphic omitted](NMeC6H4Me-p)}(η5-C5H5)(PPh3)]+(9a), where the methyl group is bonded to the nitrogen anti to the metal. In solution, (9a) isomerizes to (9b) at room temperature by rotation of the CN bond. Reactions of (3ai) with PhC2Ph, CO, CS2, and MeNCS have been studied.