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¦ b - 3.90 (N-Me) [C6D"] 33
11 (R = Me) 1
CH3 Me7^' Zn-S- a TPP: - 0.35 (a), - 0.75 (b).
S | b - 3.86 (N-Me) [C6D6] 34
18 (R = Me) 1
TPP: 22.214.171.124-Tetraphcnylporphinato, EtioP: Etioporphyrinato-I.
Table 5. Activities of Aluminum and Zinc Porphyrins for Controlled
o' Si: Si-o'
M-X 11 12 13 14 15 16 17 18 19 20 21
Al-Cl 0 0 0 X X X X A ND X X
Al-OR 0 0 Sluggish 0 0 0 Î A 0 X X
Al-OAr 0 ND 0 X X ND ND ND ND X X
Al-CbCR 0 ND 0 X X ND ND ND ND X X
Al-SR ND ND ND ND ND ND ND A ND 0 0
Al-Enolate 0 0 ND 0 0 ND ND ND ND 0 0
Al-Alkyl Sluggish ND X X X ND ND ND ND slow 0
(irradiation) (irradiation) (irradii
Zn-Cl, 0->CR X ND X X X ND ND ND ND ND ND
Zn-OR, Zn-SR 0 ND ND ND ND ND ND 0 ND ND ND
Zn-Alky] X ND X X ND ND ND ND ND ND ND
O: Controlled polymerization, Ë: Polymerization with side reactions, X:
No polymerization. ND: not determined.
42 / Metalloporhpyrins as Catalysts
Figure 5. Polymerization of 1,2-epoxypropane (11, R = Me) initiated with
1-propanethiolate complex of zinc N-methyltetraphenylpor-phyrin (5g, R =
Pr) in CH2CI2 at 35 °C. Effect of visible light on polymerization.
resulting in an increase in the content of the crosspropagation sequence.
This is the first example of copolymerizability enhancement by visible
In contrast to zinc /V-substituted porphyrins (5), aluminum porphyrins
(1) are not able to polymerize episulfides (18) in a controlled fashion,
where the polymerization is accompanied by desulfurization, leading to
unsaturated units. On the other hand, the zinc complexes (5) are not
capable of initiating the polymerization of lactones (13-15). Therefore,
the reactivity of 5 as a polymerization initiator is much different from
that of aluminum porphyrins.
B. ADDITION POLYMERIZATION OF UNSATURATED MONOMERS
Organoaluminum porphyrins with axial alkyl groups (la, lb) are effective
for the living polymerization of unsaturated monomers such as acrylates
(20)21 and methacrylates
(21),22 whereas chloride, alcoholate, phenolate and carbox-ylate
complexes (lc-f) are totally inert for the polymerization of these
monomers.36 In contrast to the polymerization of polar vinyl monomers,
controlled polymerization of nonpolar vinyl monomers such as styrene with
aluminum porphyrins has been unsuccessful.
Polymerization of methacrylic esters (21), for example, with la is
initiated by a conjugate addition of the Al-Me bond of the initiator to
21, to give an aluminum enolate (32i) as the growing species (Scheme 5A),
which in the subsequent stage reacts with 21 to give a living polymer
with an enolate reactive end (32n) (Scheme 5B).22 After acidic work-up, a
narrow MWD poly(methyl methacrylate) is obtained (Scheme 5C). Typically,
to a CH2C12 solution (40 mL) of la (1 mmol) in a round-bottomed flask,