Flook Margaret M, Gerber Laura C H, Debelouchina Galia T, Schrock Richard R
Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139.
Macromolecules. 2010 Sep 28;43(18):7515-7522. doi: 10.1021/ma101375v.
We report the Z-selective and syndioselective polymerization of 2,3-bis(trifluoromethyl)bicyclo[2.2.1]hepta-2,5-diene (NBDF6) and 3-methyl-3-phenylcyclopropene (MPCP) by monoaryloxide monopyrrolide imido alkylidene (MAP) catalysts of Mo. The mechanism of polymerization with syn-Mo(NAd)(CHCMe(2)Ph)(Pyr)(OHIPT) (1; Ad = 1-adamantyl, OHIPT = O-2,6-(2,4,6-i-Pr(3)C(6)H(2))(2)C(6)H(3)) as the initiator is proposed to consist of addition of monomer to the syn initiator to yield a syn first insertion product and propagation via syn insertion products. In contrast, the mechanism of polymerization with syn-Mo(NAr)(CHCMe(2)Ph)(Pyr)(OTPP) (4; Ar = 2,6-i-Pr(2)C(6)H(3), OTPP = 2,3,5,6-Ph(4)C(6)H) as the initiator at -78 °C consists of addition of monomer to the syn initiator to yield an anti first insertion product and propagation via anti insertion products. Polymerizations of NBDF6 and MPCP at room temperature initiated by 4 led to polymers without a regular structure. We propose that the syndiotacticity of cis polymers is the consequence of the required inversion at the metal center with each insertion of monomer, i.e., stereogenic metal control of the polymer structure. We also propose that the two mechanisms for forming cis,syndiotactic polymers arise as a consequence of the relative steric bulk of the imido and phenoxide ligands.
我们报道了通过钼的单芳氧基单吡咯酰亚胺亚烷基（MAP）催化剂对2,3-双（三氟甲基）双环[2.2.1]庚-2,5-二烯（NBDF6）和3-甲基-3-苯基环丙烯（MPCP）进行Z-选择性和间同立构选择性聚合。提出以顺式-Mo(NAd)(CHCMe(2)Ph)(Pyr)(OHIPT)（1；Ad = 1-金刚烷基，OHIPT = O-2,6-(2,4,6-i-Pr(3)C(6)H(2))(2)C(6)H(3)）为引发剂的聚合机理包括单体加成到顺式引发剂上生成顺式第一插入产物，并通过顺式插入产物进行链增长。相比之下，以顺式-Mo(NAr)(CHCMe(2)Ph)(Pyr)(OTPP)（4；Ar = 2,6-i-Pr(2)C(6)H(3)，OTPP = 2,3,5,6-Ph(4)C(6)H）为引发剂在-78°C下的聚合机理包括单体加成到顺式引发剂上生成反式第一插入产物，并通过反式插入产物进行链增长。由4引发的NBDF6和MPCP在室温下的聚合得到了无规则结构的聚合物。我们提出顺式聚合物的间同立构规整性是由于每次单体插入时金属中心需要发生反转，即聚合物结构的立体化学金属控制。我们还提出形成顺式、间同立构聚合物的两种机理是由于酰亚胺和酚盐配体相对空间位阻的结果。
