Chiral Bora[1]ferrocenophanes: Syntheses,Mechanistic Insights,and Ring‐Opening Polymerizations

A series of new boron‐bridged [1]ferrocenophanes ([1]FCPs) was prepared by salt‐metathesis reactions between enantiomerically pure dilithioferrocenes and amino(dichloro)boranes (Et₂NBCl₂, iPr₂NBCl₂, or tBu(Me₃Si)NBCl₂). The dilithioferrocenes were prepared in situ by lithium–bromine exchange from the respective planar‐chiral dibromides (S_p,S_p)‐[1‐Br‐2‐(HR₂C)H₃C₅]₂Fe (R=Me or Et). In most of the cases, mixtures of the targeted [1]FCPs 4 and the unwanted 1,1′‐bis(boryl)ferrocenes 5 were formed. The product ratio depends on the bulkiness of the amino group, the speed of addition of the amino(dichloro)borane, the alkyl group on Cp rings, and in particular on the reaction temperature. The formation of strained [1]FCPs is strongly favored by increased reaction temperatures. Secondly, CHEt₂ groups at Cp rings favored the formation of the targeted [1]FCPs stronger than CHMe₂ groups. These discoveries open up new possibilities to further suppress the formation of unwanted byproducts by a careful choice of the reaction temperature and through tailoring the bulkiness of CHR₂ groups on ferrocene. Thermal ring‐opening polymerizations of selected boron‐bridged [1]FCPs gave metallopolymers with a M_w of 10 kDa (GPC).     

Bis(phosphinimino)methanide Borohydride Complexes of the Rare‐Earth Elements as Initiators for the Ring‐Opening Polymerization of ε‐Caprolactone: Combined Experimental and Computational Investigations

Rare‐earth‐metal borohydrides are known to be efficient catalysts for the polymerization of apolar and polar monomers. The bis‐borohydrides [{CH(PPh₂NSiMe₃)₂}La(BH₄)₂(THF)] and [{CH(PPh₂NSiMe₃)₂}Ln(BH₄)₂] (Ln=Y, Lu) have been synthesized by two different synthetic routes. The lanthanum and the lutetium complexes were prepared from [Ln(BH₄)₃(THF)₃] and K{CH(PPh₂NSiMe₃)₂}, whereas the yttrium analogue was obtained from in situ prepared [{CH(PPh₂NSiMe₃)₂}YCl₂]₂ and NaBH₄. All new compounds were characterized by standard analytical/spectroscopic techniques, and the solid‐state structures were established by single‐crystal X‐ray diffraction. The ring‐opening polymerization (ROP) of ε‐caprolactone initiated by [{CH(PPh₂NSiMe₃)₂}La(BH₄)₂(THF)] and [{CH(PPh₂NSiMe₃)₂}Ln(BH₄)₂] (Ln=Y, Lu) was studied. At 0 °C the molar mass distributions determined were the narrowest values (M?_w/M?_n=1.06–1.11) ever obtained for the ROP of ε‐caprolactone initiated by rare‐earth‐metal borohydride species. DFT investigations of the reaction mechanism indicate that this type of complex reacts in an unprecedented manner with the first B? H activation being achieved within two steps. This particularity has been attributed to the metallic fragment based on the natural bond order analysis.     

Ring‐opening polymerization of 1,3‐benzoxazines by p‐toluenesulfonates as thermally latent initiators

p‐Toluenesulfonic acid (TsOH) and several alkyl p‐toluenesulfonates, that is, methyl p‐toluenesulfonate (TsOMe), cyclohexyl p‐toluenesulfonate (TsOCH), and neopentyl p‐toluenesulfonate (TsONP), were evaluated as initiators for the ring‐opening polymerization of benzoxazines. TsOH and TsOMe were highly efficient initiators that induced the polymerization at 60 and 80 °C, respectively. In contrast, TsOCH and TsONP did not initiate the polymerization below 100 °C, while they induced the polymerization at elevated temperatures, 120 and 150 °C, respectively. When TsOCH was used as an initiator, the corresponding polymerization rate was comparable to that observed for the polymerization with using TsOH as an initiator. These results suggested that neutral TsOCH and TsONP can be regarded as “thermally latent initiators,” which underwent the thermal dissociation at the elevated temperatures to generate the corresponding alkyl cations and/or TsOH as the initiators of the polymerization. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Incorporation of ketone groups into poly(4‐hydroxystyrene)s main chain by radical copolymerization of 2,2‐diphenyl‐4‐methylene‐1,3‐dioxorane with O‐protected hydroxystyrenes and their photodegradable behavior

Here we report the incorporation of ketone groups into poly(4‐hydroxystyrene)s main chain by radical copolymerization of O‐protected hydroxystyrenes such as 4‐ethoxyethoxystyrene and 4‐acetoxystyrene with 2,2‐diphenyl‐4‐methylene‐1,3‐dioxorane (DPMD) followed by removal of the protective groups and the photodegradable behavior of obtained copolymers. The copolymerization of O‐protected hydroxystyrenes with DPMD gave the corresponding copolymers bearing DMPD‐derived ketone groups in the main chain, of which content could be controlled by changing monomer feed ratio. The ethoxyethyl and acetyl groups of the obtained copolymers were completely removed under acidic and basic conditions, respectively, to afford poly(4‐hydroxystyrene)s having ketone moieties in the main chain. The molecular weights of these copolymers decreased under photoirradiation due to the Norrish‐type reactions of the ketone groups distributed in the main chain. These results demonstrate that poly(4‐hydroxystyrene)s having ketone groups in the main chain possess good photo‐scissibility. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis of end‐functionalized polyethers by phosphazene base‐catalyzed ring‐opening polymerization of 1,2‐butylene oxide and glycidyl ether

For the living ring‐opening polymerization (ROP) of epoxy monomers, the catalytic activity of organic superbases, tert‐butylimino‐tris(dimethylamino)phosphorane, 1‐tert‐butyl‐2,2,4,4,4‐pentakis(dimethylamino)‐2Λ⁵,4Λ⁵‐catenadi(phosphazene), 2,8,9‐triisobutyl‐2,5,8,9‐tetraaza‐1‐phosphabicyclo[3.3.3]undecane, and 1‐tert‐butyl‐4,4,4‐tris(dimethylamino)‐2,2‐bis[tris(dimethylamino)phosphoranylidenamino]‐2Λ⁵,4Λ⁵‐catenadi(phosphazene) (t‐Bu‐P₄), was confirmed. Among these superbases, only t‐Bu‐P₄ showed catalytic activity for the ROP of 1,2‐butylene oxide (BO) to afford poly(1,2‐butylene oxide) (PBO) with predicted molecular weight and narrow molecular weight distribution. The results of the kinetic, post‐polymerization experiments, and MALDI‐TOF MS measurement revealed that the t‐Bu‐P₄‐catalyzed ROP of BO proceeded in a living manner in which the alcohol acted as the initiator. This alcohol/t‐Bu‐P₄ system was applicable to the glycidol derivatives, such as benzyl glycidyl ether (BnGE) and t‐butyl glycidyl ether, to afford well‐defined protected polyglycidols. The α‐functionalized polyethers could be obtained using different functionalized initiators, such as 4‐vinylbenzyl alcohol, 5‐hexen‐1‐ol, and 6‐azide‐1‐hexanol. In addition, the well‐defined cyclic‐PBO and PBnGE were successfully synthesized using the combination of t‐Bu‐P₄‐catalyzed ROP and click cyclization. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

用三氟化硼引发体系制备聚丁二醇

分子量在3000以下特别是1000或2000的聚丁二醇(PTMG)是制备嵌段聚醚聚氨酯及嵌段聚醚聚醋弹性体的重要软段原料。用三氟化硼(BF_3)体系引发制备PTMG巳有报道,但尚难在工业上采用,主要是引发效率低。前已报道,BF_3-环氧氯丙烷(ECH)体系的引发效率比BF_3-环氧乙烷(EO)体系高2.5～6倍,比BF_3-环氧丙烷(PO)体系高2～3倍。本文用BF_3-ECH为引发体系,并用水为分子量调节剂制备分子量1000或2000的PTMG,测