A new type of catalyst for the syndiospecific polymerization of styrene, $Cp^*Ti(TEA)$ (TEA = N($CH_2CH_2O)_3$) was prepared by either the reaction of triethanolamine with $Cp^*TiCl_3$ in the presence of triethylamine or the reaction of (TEA)TiCl with $LiCp^*$. The former reaction route is more efficient in terms of yield and easy accessibility of a starting titanium compound. The X-ray structure of $Cp^*Ti(TEA)$ reveals that $Cp^*Ti(TEA)$ exists as monomeric form in the solid state and the Ti atom adopts essentially an $\eta^5$ bonding posture with Cp* ring and a tetradentate bonding mode with triethanolateamine ligand via a transannular interaction from the bridgehead N atom to Ti. The compound $Cp^*Ti(TEA)$ is air and thermally stable, and soluble in hydrocarbon solvents.
The catalytic system $Cp^*Ti(TEA)$/MMAO is more efficient than $Cp^*TiCl_3$/MMAO in producing highly syndiotactic polystyrene in terms of activity, conversion, stereospecificity, and Tm at all polymerization temperatures. $Cp^*Ti(TEA)$/MMAO catalytic system could conduct syndiospecific homopolymerization of styrene containing silyl-protected alcohol and tertiary amines as manifested by the preparation of syndiotactic polymers of 4- tert-butyldimethylsilyloxystyrene, 4-dimethylaminostyrene, and 4-diethylaminostyrene. Their solubility in organic polar solvents and the high thermal stability indicate that the advantages of the functionalization of the styrene, the preservation of the desirable physical property of the original polymer as well as the development of the new chemical property, were achieved. The chemical transformation of polymer gave a new syndiotactic polar polymer, poly(4-hydroxystyrene) which has never been obtained by traditional methods. In addition, the reaction of syndiotactic poly(4-diethylaminostyrene) with HCl afforded a new syndiotactic poly(4-diethylaminostyrene hydrochloride).
The half-sandwich metallocene catalyst for the polymerization of ethylene, $Cp^*M(TEA)$ (M = Ti, Zr, and Hf), was prepared by the reaction of triethanolamine with $Cp^*MCl_3$ in the presence of triethylamine. Unlike $Cp^*Ti(TEA)$, $Cp^*Zr(TEA)$, and $Cp^*Hf(TEA)$, the heavier congeners of the compound $Cp^*Ti(TEA)$, are air sensitive and thermally unstable. All catalyst systems $Cp^*M(TEA)$/MAO show fairly good activities in ethylene polymerization in the order of $Cp^*Ti(TEA)$/MAO ＞ $Cp^*Zr(TEA)$/MAO ≫ $Cp^*Hf(TEA)$/MAO. The catalytic activity of $Cp^*Zr(TEA)$/MAO in ethylene polymerization increases with the polymerization time and the molecular weight of polymer products is in the order of 2 x $10^{5}$.
In order to investigate the effect of the substituents in the cyclopentadienyl ligand of $Cp^*Ti(TEA)$, Cp'Ti(TEA) ($Cp'=C_5Me_5$, $C_5Me_4H$, $C_5Me_4Et$, $C_5Me_4Pr^i$, $C_5Me_4Ph$, $C_5Me_4Tol$) was prepared by the reaction of triethanolamine with $Cp'TiCl_3$ in the presence of triethylamine. The X-ray analysis reveals that Cp'Ti(TEA) exhibits a similar structural motif to that of $Cp^*Ti(TEA)$. All compounds, which are air and thermally stable, and soluble in hydrocarbon solvents, show very high catalytic activities for the syndiospecific polymerization of styrene in the presence of MMAO.
In order to investigate the effect of substituents in the arms of the triethanolamine ligand on the polymerization behavior, a set of $Cp^*Ti$(N($CH_2CHR^1O$)($CH_2CHR^2O$) ($CH_2CHR^3O$)) ($R^1$=$R^2$=$R^3$=(S)-Me, (R)-Me, or (R)-Ph; $R^1$=H and $R^2$=$R^3$=(S)-Me or (R)-Me; $R^1$=$R^2$=H and $R^3$=(S)-Me or (R)-Me) was prepared by the reaction of homochiral trialkanolamine with $Cp^*TiCl_3$ in the presence of triethylamine. All compounds show very high catalytic activity for the syndiospecific polymerization of styrene in the presence of MMAO cocatalyst. In addition, they have the maximum catalytic activity at very high polymerization temperature of 90℃ and the resulting polymers have high Tm and syndiotacticity.
A new type of the half-sandwich metallocene catalysts for the polymerization of sPS and ethylene, $Cp^*MCl(DEA-R)$ (DEA = $(OCH_2CH_2)_2$N;R=Me, Zr, orHf; R=n-Bu, M=Ti) was prepared by the reaction of corresponding N-alkyl-N,N-diethanolamine with $Cp^*MCl_3$ in the presence of triethylamine. Unlike the compound $Cp^*Ti(TEA)$, all compounds are air-sensitive and thermally unstable. All catalyst systems show moderate activities in ethylene polymerization in the order of $Cp^*TiCl$(DEA-Me)/MMAO ＞ $Cp^*TiCl$(DEA-Bu)/MMAO ＞ $Cp^*ZrCl$(DEA-Me)/MMAO ≫ $Cp^*HfCl$(DEA-Me)/MMAO and fairly good activities in sPS polymerization in the order of $Cp^*TiCl$(DEA-Bu)/MAO ＞ $Cp^*TiCl$(DEA-Me)/MAO.
The group 4 metal complexes $[HB(pz^*)_3]MCl_3$ (M=Ti, Zr, and Hf) have been prepared by the reaction of $MCl_4$ with potassium hydrotris(3,5-dimethyl-1-pyrazoly)borate. These compounds are thermally stable but slightly air sensitive. Although methyl substituent of 3 position in pyrazolyl ring cause considerable steric crowding around the metal, the reaction of $[HB(pz^*)_3]MCl_3$ with triethanolamine (TEA) in the presence of NEt_3 yielded the corresponding[$HB(pz^*)_3$]M(TEA) which is air and thermally stable. In addition, the reaction of $CpZrCl_3$ with potassium hydrotris(3,5-dimethyl-1-pyrazoly)borate in toluene could give [$HB(pz^*)_3$]$CpZrCl_2$ which is isolobal to $Cp^*CpZrCl_2$ and a good candidate for PE catalyst.
A new type of the half-sandwich metallocene catalysts for the polymerization of sPS and ethylene, $Cp^*M$(trisilanolate-POSS) (trisilanolate-POSS = (O)$_3O_9Si_7(c-C_5H_9)_7$, M = Ti, Zr, and Hf), was prepared by the reactionof 1,3,5,7,9,11,14-heptacyclopentyltricyclo[7.3.3.1$^{5,11}$] heptasiloxane-\it endo\rm-3,7,14-triol (trisilanol-POSS) with $Cp^*MCl_3$ in the presence of triethylamine. $Cp^*Ti$(trisilanolate-POSS) is air- and thermally stable, which the heavier congeners of $Cp^*Ti$(trisilanolate-POSS), $Cp^*Zr$(trisilanolate-POSS) and Cp*Hf(trisilanolate-POSS), are slightly air sensitive. The catalytic system $Cp^*Ti$(trisilanolate-POSS)/MMAO shows fairly good activities in sPS polymerization. The catalytic systems $Cp^*Ti$(trisilanolate-POSS)/MMAO and Cp*Zr(trisilanolate-POSS)/MMAO in ethylene polymerization show good activities in the order of $Cp^*Zr$(trisilanolate-POSS)/MMAO ＞ $Cp^*Ti$(trisilanolate-POSS)/MMAO. The maximum activity of $Cp^*Ti$(trisilanolate-POSS)/MMAO and $Cp^*Zr(trisilanolate-POSS)/MMAO in the polymerization of ethylene is shown at 30℃ and 70℃, respectively.
