Copolymerization of silyl vinyl ethers with olefins by (alpha-diimine)PdR+

This paper reports that (alpha-diimine)PdMe+ catalyzes the copolymerization of olefins and silyl vinyl ethers. The reactions of (alpha-diimine)PdMe+ (alpha-diimine = (2,6-iPr2-C6H3)N=CMe-CMe=N(2,6-iPr2-C6H3)) with excess vinyl ethers CH2=CHOR (1a-d: R = tBu (a), SiMe3 (b), SiPh3 (c), Ph (d)) in CH2Cl2 at 20 degrees C afford polymers for 1a (rapidly) and 1b (slowly) but not for 1c or 1d. The structures of poly(1a,b) indicate a cationic polymerization mechanism. The reaction of (alpha-diimine)PdMe+ with 1-2 equiv of 1a-d proceeds by sequential C=C pi-complexation to form (alpha-diimine)PdMe(CH2=CHOR)+ (2a-d), 1,2 insertion to form (alpha-diimine)Pd(CH2CHMeOR)+ (3a-d), reversible isomerization to (alpha-diimine)Pd(CMe2OR)+ (4a-d), beta-OR elimination to generate (alpha-diimine)Pd(OR)(CH2=CHMe)+ (not observed), and allylic C-H activation to yield (alpha-diimine)Pd(eta3-C3H5)+ (5) and ROH. The reaction of (alpha-diimine)PdMe+ with 1-hexene/1b and 1-hexene/1c mixtures in CH2Cl2 at 20 degrees C affords copolymers containing up to 20 mol % silyl vinyl ether. The copolymers were purified to be free of any -[CH2CHOSiR3]n- homopolymer. The copolymer structures are similar to that of homopoly(1-hexene) generated under the same conditions. The major comonomer units are CH3CH(OSiR3)CH2-, CH2(OSiR3)CH2- and -CH2CH(OSiR3)CH2-. The 1-hexene/CH2=CHOSiR3 copolymers can be desilylated to give 1-hexene/CH2=CHOH copolymers. The results of control experiments argue against cationic and radical mechanisms for the copolymerization, and an insertion/chain-walking mechanism is proposed.     

A symmetric oxyselenenylation of simple olefins using optically active selenobinaphthyls

Asymmetric trans-addition reactions of simple olefins have been performed by using optically active 2-selenobinaphthyls 1 , 2a–g. Introduction of an amide group at the 2′-position in the binaphthyl skeleton enhances considerably the diastereomeric excess (de) of the asymmetric methoxyselenenylation. In the case of trans-olefins, introduction of another chiral center in the amide group further enhances the de due to double stereodifferentiation between the (R)-binaphthyl skeleton and the chiral amide group introduced at the 2′-position in the binaphthyl skeleton. The use of chiral nucleophiles is also effective to enhance the de for symmetrical cis-olefins.     

Poly[2,4-bis(chloroamino)-6-vinyl-1,3,5-triazine] as a recyclable oxidizing agent of alcohols

A polymer containing dichlorotriazine moiety was prepared readily by the reaction of poly(2,4-diamino-6-vinyl-1,3,5-triazine) with tert-butyl hypochlorite. This polymer oxidizes various primary and secondary alcohols to the corresponding carbonyl compounds under mild conditions, while the reaction of the monomeric analogue N,N′-dichloroacetoguanamine with alcohols does not proceed. The polymer reagent can be handled easily and recycled for further use.