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. 2010 Sep 28;43(18):7515-7522.
doi: 10.1021/ma101375v.

Z-Selective and Syndioselective Ring-Opening Metathesis Polymerization (ROMP) Initiated by MonoAryloxidePyrrolide (MAP) Catalysts

Margaret M Flook  1 , Laura C H Gerber, Galia T Debelouchina, Richard R Schrock
Affiliations

Z-Selective and Syndioselective Ring-Opening Metathesis Polymerization (ROMP) Initiated by MonoAryloxidePyrrolide (MAP) Catalysts

Margaret M Flook et al. Macromolecules. .

Abstract

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.

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Figures

Figure 1
Figure 1
Ad = 1-adamantyl, Ar = 2,6-i-Pr2C6H3, TRIP = 2,4,6-i-Pr3C6H2, Ar' = 2,6-Me2C6H3.
Figure 2
Figure 2
Partial 13C NMR spectra of polyMPCP samples prepared from 1, 2a, 2b, and 3a.
Figure 3
Figure 3
Partial 13C{1H} NMR spectra (CD2Cl2, 125 MHz) of polyMPCP synthesized at various temperatures (t = 6 h for runs at −78 °C, 0 °C, and 20 °C; t = 2 h for 46 °C and −20 °C; *residual toluene).
Figure 4
Figure 4
First order plot for the conversion of anti-4+1trans to syn-4+1trans at −30 °C.
Figure 5
Figure 5
1H NMR spectra at −60 °C of (top) syn-4 after irradiation at −78 °C in toluene-d8 with 360 nm light, and (bottom) after addition of MPCP (~0.1 equiv) to the mixture of syn-4 plus anti-4.
Figure 6
Figure 6
Decay of anti-4 to syn-4; k = 5.2(0.5) × 10−3 s−1 at −15 °C, 2.1(0.1) × 10−3 s−1 at −20 °C, 5.6(0.2) × 10−4 s−1 at −25 °C, 4.1(0.1) × 10−4 s−1 at −30 °C, and 1.9(0.1) × 10−4 s−1 at −35 °C.
Figure 7
Figure 7
Eyring plot for the decay of anti-4trans to syn-4trans. ΔH‡ = 19.9 ± 2 kcal/mol and ΔS‡ = 8 ± 2 eu.
See this image and copyright information in PMC

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