Controlled radical polymerization of styrene in the presence of lithium molybdate(V) complexes and benzylic halides

Citation
Jam. Brandts et al., Controlled radical polymerization of styrene in the presence of lithium molybdate(V) complexes and benzylic halides, J ORGMET CH, 584(2), 1999, pp. 246-253
Citations number
25
Categorie Soggetti
Organic Chemistry/Polymer Science
Journal title
JOURNAL OF ORGANOMETALLIC CHEMISTRY
ISSN journal
0022328X → ACNP
Volume
584
Issue
2
Year of publication
1999
Pages
246 - 253
Database
ISI
SICI code
0022-328X(19990723)584:2<246:CRPOSI>2.0.ZU;2-X
Abstract
The new lithium molybdate(V) complexes [LiMo(NAr)(2)(C-N)R] (C-N = C6H4(CH2 NMe2)-2; R = (C-N) (5), Me (6) CH2SiMe3 (7), p-tolyl (8)), have been genera ted in situ from reaction of the corresponding molybdenum(V)) complexes [Mo (NAr)(2)(C-N>R] (C-N= C6H4(CH2NMe2)-2; R = (C-N) (1), Me (2), CH2SiMe3 (3), p-tolyl (4)) with n-BuLi. The nature of these radical anions was studied b y EPR spectroscopy. The spectra of toluene solutions of in situ prepared co mplexes 5-8 revealed the presence of two different paramagnetic species, i. e. a molybdenum compound with distinct g(iso)- and A(iso)-values and an uni dentified radical with a sometimes strong signal at g = 1.986 +/- 0.001, la cking any hyperfine coupling. Extended Huckel calculations on the crystal s tructure of 5 showed that the single electron occupies a molybdenum centere d orbital, merely d(x2-y2) in character. In situ prepared complexes 5-8 wer e successfully applied in the atom transfer radical polymerization (ATRP) o f styrene using benzyl chloride as the initiator. The efficiency of the ben zyl chloride initiator is rather poor (6-18%). Reaction of the lithium moly bdate(V) complex 5 with (alpha-chloroethyl)benzene and (alpha-bromoethyl)be nzene resulted in the formation of 1, LiCl and LiBr, respectively. The mole cular weights as well as the molecular weight distributions show that the c atalytic system, BzCl/5-8, catalyses styrene polymerization successfully bu t does not exercise much control over the polymerization reaction due to th e poor initiator efficiency of benzyl chloride and probably the extreme air -sensitivity of the lithium molybdate(V) compounds. The unidentified radica l (g = 1.986 +/- 0.001) is unable to initiate radical polymerization but po ssibly influences the ATRP activity. (C) 1999 Elsevier Science S.A. All rig hts reserved.