First examples of homogeneous catalytic cyclotrimerization and polymerization of phenylacetylene and copolymerization of phenylacetylene and norbonene with dinuclear complexes containing unbridged metal-metal quadruple bond

Article abstract of DOI:10.1135/cccc20031094

First examples of application of dinuclear complexes containing unbrigded metal-metal quadruple bond as catalysts in cyclotrimerization, oligomerization and polymerization of substituted acetylene are reported. The d⁴-d⁴ dinuclear co

Full text of DOI:10.1135/cccc20031094

1094
Mertis et al.:
FIRST EXAMPLES OF HOMOGENEOUS CATALYTIC CYCLOTRIMERIZATION
AND POLYMERIZATION OF PHENYLACETYLENE AND
COPOLYMERIZATION OF PHENYLACETYLENE AND NORBONENE
WITH DINUCLEAR COMPLEXES CONTAINING UNBRIDGED
METAL–METAL QUADRUPLE BOND
a
a
Konstantinos MERTISa1,*, Stavros ARBILIAS , Demos ARGYRIS ,
Nikos PSAROUDAKISa2, Jiří VOHLÍDAL , Olivier LAVASTRE and
b
c1
c2
Pierre H. DIXNEUF
a
University of Athens, Inorganic Chemistry Laboratory, Panepistimiopolis, 15701 Athens, Greece;
e-mail: cmertis@cc.uoa.gr, psaroudakis@chem.uoa.gr
Charles University, Department of Physical and Macromolecular Chemistry, Laboratory of
Specialty Polymers, Albertov 2030, CZ-12840 Prague 2, Czech Republic;
e-mail: vohlidal@natur.cuni.cz
1
2
b
c
Université de Rennes 1, Laboratoire de Chimie de Coordination et Catalyse, 35042 Rennes,
France; e-mail: lavastre@univ-rennes.fr, dixneuf@univ.rennes-1.fr
1
2
Received May 31, 2002
Accepted Decem ber 2, 2002
Dedicated to Professor F. A. Cotton for his discovery of the metal–metal quadruple bond.
First exam ples of application of din uclear com plexes con tain in g un brigded m etal–m etal qua-
druple bon d as catalysts in cyclotrim erization , oligom erization an d polym erization of substi-
tuted acetylen e are reported. Th e d4-d4 din uclear com plexes (Bu4N)2[Re2X8] (1) (1a, X = Cl;
1b, X = Br an d 1c, X = I) sh ow low activity an d th e com plex [Mo2Cl4(MeOH)2(PPh 3)2] (2)
m edium activity in cyclotrim erization an d oligom erization of ph en ylacetylen e (PA). In con -
trast, th e tun gsten -based d4-d4, com plex Na4[W2Cl8] (3) exh ibits h igh polym erization activ-
ity (polym er yield above 90%) an d ca 75% cis-selectivity in tetrah ydrofuran . Th e activity an d
cis-stereoselectivity of th ese sin gle-com pon en t catalysts decrease in th e order 3 >> 2 >> 1,
wh ich is proportion al to th e m etal–m etal quadruple bon d propen sity towards ligan d addi-
tion reaction s. Com plex 3 in duces m etath esis polym erization of n orborn en e (NBE) to
poly(cyclopen ten e-1,3-diylvin ylen e) with 82% cis-selectivity an d copolym erization of PA an d
NBE to alm ost all-cis h igh -m olecular-weigh t copolym er con tain in g cyclopen ten e-1,3-diyl-
vin ylen e un its, wh ich is free of lon ger sequen ces of both PA an d NBE un its. Th is suggests
th at also h om opolym erization of PA with 3 proceeds by th e m etath esis m ech an ism an d th at
th e PA/NBE copolym er structure is close to th e altern atin g on e.
Keyw ord s: Cyclotrim erization s; Din uclear com plexes; Metal–m etal quadruple bon d; Alken es;
Alkyn es; ROMP; Metath esis polym erization s; Sin gle-com pon en t catalysts; Rh en ium ; Tun g-
sten ; Molybden um .
Collect. Czech. Chem. Commun. (Vol. 68) (2003)
doi:10.1135/cccc20031094

Metal–Metal Quadruple Bond
1095
Din uclear com plexes con tain in g m etal–m etal m ultiple bon ds possess sev-
eral attractive properties, wh ich m ake th em poten tial catalysts for various
organ ic tran sform ation s. Most im portan tly, th e [M–M]n+ core can act as a
tem plate for coordin ation an d activation of organ ic substrates an d as an
electron reservoir for facile m ulti-electron redox processes accom pan ied by
in tercon version s between th e [M–M]n+ species of differen t bon d orders1,2
.
Metal–m etal quadruple bon ds were discovered 36 years ago3 an d sin ce
th at tim e m olybden um an d tun gsten com plexes carryin g carboxylate, allyl,
h alide an d n itrile ligan ds h ave been used as un i- or bicom pon en t h om oge-
n eous or h eterogen eous catalysts in h ydrogen ation of alken es an d alkyn es4,
m etath esis of acyclic olefin s5–7, rin g open in g m etath esis polym erization
(ROMP) of cyclic olefin s8–10 an d polym erization of cyclopen tadien e an d
dicyclopen tadien e11,12
Alth ough certain com plexes con tain in g form ally double an d triple
.
13
14
bon ds, e.g. [M2Cl6(th t)3] (wh ere M is Nb 13, Ta
or Mo
an d th t is
tetrah ydroth ioph en e) an d [M2(OR)6] (wh ere15 M is Mo an d R is isopropyl,
tert-butyl or n eopen tyl or wh ere16 M is W an d R is (t-Bu)Me2SiO-), are capa-
ble of cyclotrim erizin g an d polym erizin g alkyn es, th ere is very little in for-
m ation on an alogous reaction s in duced with com plexes con tain in g th e
m etal–m etal quadruple bon d17. Th e on ly kn own exam ples are th e h etero-
m etallic com plexes [Mo2(µ-OCOR)2{Al(µ-OR′)4}2] (wh ere R is Me, t-Bu, CF3
an d R′ is ph en yl or substituted ph en yl) or an alogous species gen erated in situ
from th e reaction of h om on uclear [MєM]4+ or h eterodin uclear [MєM′]4+
(M is Mo an d M′ is W) com plexes with various alkoxides or ph en oxides of
alum in ium an d titan ium , wh ich are capable of in ducin g th e m etath esis of
specific in tern al alkyn es18. Also, th e [MoєMo]4+ bridged com plexes such
as cis-[Mo2(OAc)2(µ-en )2(en )2]·(AcO–)2·en (en is eth ylen ediam in e) an d
[Mo2(Me2NCH2CH2NMe2 or Me2PCH2CH2PMe2)- (µ-OAc)4]n catalyze coupling,
oligom erization an d m etath esis of in tern al alkyn es RC≡CR′, wh ere R an d R′
is alkyl C1–C10 or aryl19.
In view of th e isolation an d structural ch aracterization of th e [MєM]4+
20
com plex [Mo2(en )4(µ-4-MeC6H4C≡CH)(µ-OAc)]·(AcO–)2·(en )2
an d also th e
facile addition s of alkyn es to th e Ta=Ta doubly an d W≡W triply bon ded h a-
lide com plexes [Ta2Cl4(µ-Cl)2(µ-th t)(th t)2]21,22 an d Na[W2Cl7(th f)5]23 yield-
in g th e m etallotetrah edran e derivatives [M2Cl4(µ-Cl)2(µ-RC≡CR′)(th f)2] (M
is Ta or W an d RC≡CR′ is MeC≡CMe, EtC≡CEt, HC≡CH or Ph C≡CH), we
h ave exam in ed th e reactivity of th e d4-d4 com plexes (Bu4N)2[Re2X8] (1) (1a,
X = Cl 24a; 1b, X = Br 24b or 1c, X = I 24c), [Mo2Cl4(MeOH)2(PPh 3)2]25 (2) an d
Na4[W2Cl8]26 (3) wh ich h ave un bridged m etal–m etal quadruple bon ds an d
th e σ2π4δ2 electron ic con figuration (see Ch art 1) towards ph en ylacetylen e
Collect. Czech. Chem. Commun. (Vol. 68) (2003)

1096
Mertis et al.:
as a represen tative of substituted acetylen e. Th e results of th ese experi-
m en ts are reported in th is paper (see Sch em e 1 an d Table I).
H
CH3
Cl
2-
4-
O
X
Re
X
X
Re
X
Cl
W
Cl
Cl
W
Cl
Ph3P
X
X
Cl
Cl
Cl
Mo
Mo
X
X
Cl
Cl
Cl
Cl
PPh3
O
H3C
H
1
3
1a, X = Cl
1b, X = Br
1c, X = I
2
CHART 1
Ph
Ph
Ph
Ph
C
CH
+
+
LnM MLn
Ph
Ph
Ph
Ph
n
SCHEME 1
TABLE I
Results of reaction s of PA with quadruply bon ded din uclear com plexes of Re, Mo an d W.
In itial con cen tration s: [1]0 = 7.35 m m ol/l, [PA]0 = 1.470 m ol/l; [2]0 = 2.14 m m ol/l, [PA]0
0.107 m ol/l; [3]0 = 2.88 m m ol/l, [PA]0 = 0.576 m ol/l
=
Yield, %
Reaction
tim e, h
Mn × 10–3
Catalyst
Solven t
T, °C
cyclo-
polym er
trim ers
(oligom ers)
1a
1,2-dich loroben zen e
THF
130
25
6
6
2.5
2.3
15
11
1.1
1.1
1a + EtAlCl2
(1 : 1)
1b
1c
2
toluen e
toluen e
CH3OH
THF
90
70
25
25
25
6
6
4
4
3
3.9
3.0
18
–
14
7
1.1
1.1
4.0
–
40
–
2
3
THF
7
91
140
Collect. Czech. Chem. Commun. (Vol. 68) (2003)

Metal–Metal Quadruple Bond
1097
EXPERIMENTAL
Materials
All operation s were perform ed un der pure argon usin g th e Sch len k tech n ique an d all sol-
ven ts an d reagen ts (from Aldrich ) were deoxygen ated before use by freeze-vacuum -th aw
cycles except for m eth an ol wh ich was degassed by purgin g with argon for 30 m in . Tetra-
h ydrofuran (THF) an d dieth yl eth er were distilled from Na/Ph 2CO, h exan e an d toluen e were
distilled from Na, CH2Cl2 an d 1,2-dich loroben zen e were distilled from CaH2, an d m eth an ol
was distilled from th e correspon din g m agn esium alkoxide. Ph en ylacetylen e (PA) an d
n orbon en e (NBE) were dried by stirrin g with CaH2 un der argon , distilled un der vacuum an d
stored in a dark place un der argon . Th e m etal–m etal quadruple-bon ded com plexes were pre-
24b
26
pared an d ch ecked for purity as referen ced earlier: 1a 24a, 1b
an d 1c 24c, 2 25, an d 3
.
Meth ods
NMR spectra (δ, ppm ) were recorded on a Varian Un ity Plus 300 in strum en t operatin g at fre-
quen cy 299.948 MHz for 1H an d 75.429 MHz for 13C NMR usin g sam ples dissolved in CDCl3
an d h exam eth yldisilan e (1%, v/v) for referen cin g 1H (δ +0.04 ppm ) spectra. 13C NMR spectra
were referen ced to th e solven t (δ +76.99 ppm ). Th e relaxation delay was set to 5 s. Sign als of
proton ated an d n on proton ated carbon s were distin guish ed by th e APT (attach ed proton
test) m eth od with th e J-m odulation period m in im ized by 13C an d 1H refocusin g pulses. IR
spectra were recorded on a Perkin –Elm er 883 IR spectrom eter. UV-VIS spectra were recorded
on a Hitach i U-2000 spectrom eter. Size exclusion ch rom atograph y (SEC) an alyses were m ade
on a TSP (Th erm o Separation Products, Florida, U.S.A.) ch rom atograph equipped with a UV
detector operatin g at 254 n m an d a series of two PL-gel colum n s (Mixed-B an d Mixed-C
(Polym er Laboratories Bristol, U.K.), THF eluen t, flow rate 0.7 m l/m in ) or, altern atively, on a
m odular in strum en t con sistin g of a Waters Model 510 pum p, a Waters Model U6K sam ple
in jector, a Waters Model 401 differen tial refractom eter an d a set of four µ-Styragel colum n s
with a porosity from 103 to 106 Å h oused in a th erm ostated box (THF, flow rate 1 m l/m in ).
Molecular weigh t averages relative to polystyren e stan dards are reported. A Varian Star
3400CX GC/MS/MS gas ch rom atograph equipped with a h igh -resolution capillary colum n
DB-5MS (30 m ) an d with a m ass spectrom etric detector Saturn 2000 was used for m on itor-
in g th e reaction s.
Procedures
All reaction s were carried out in Sch len ck tubes un der dry argon . Experim en ts with 1b an d
1c were perform ed in th e absen ce of ligh t. In a typical experim en t, a m easured volum e of
PA was added to th e catalyst suspen sion (1) or solution (2, 3) in an appropriate solven t an d
th e m ixture was allowed to react un der stirrin g at a required tem perature for a given tim e
(see Table I). Th e reaction progress was m on itored by GC-MS an d/or 1H NMR m eth ods. After
a ch osen reaction tim e, all volatiles were rem oved in vacuum , collected in a cold trap (liq-
uid N2) an d furth er an alyzed as above. Th e n on -volatile residue was extracted several tim es
with CH2Cl2 or THF, th e obtain ed extract was con cen trated to a m in im um volum e an d sep-
arated by ch rom atograph y on n eutral alum in a un der strictly an aerobic con dition s because
of poly(PA) (PPA) sen sitivity to m olecular oxygen 27–29. Th e followin g m obile ph ases were
used in th e ch rom atograph y: h exan e/dieth yl eth er for elution of PA cyclotrim ers, dieth yl
Collect. Czech. Chem. Commun. (Vol. 68) (2003)

1098
Mertis et al.:
eth er for elution of PA oligom ers an d THF for elution of PPA. Con trol experim en ts per-
form ed in th e absen ce of catalyst precursors h ave sh own n egligible oligom erization but n ei-
th er cyclotrim erization n or polym erization of PA. Th e reaction s of 3 with NBE an d a
m ixture of PA/NBE were carried out sim ilarly. Th e polym er in th e form er reaction was iso-
lated by precipitation in eth an ol acidified by a few drops of con cen trated HCl, wh ereas in
th e latter by precipitation in acidified m eth an ol. All polym ers were dried in vacuo at 30 °C.
RESULTS AND DISCUSSION
Rh en ium com plex 1a does n ot react with PA at room tem perature or by
refluxin g in CH2Cl2, CHCl3, CH3CN, C6H6, C6H5CH3 or THF. However in
1,2-Cl2C6H4 at 130 °C produces a yellow-brown reaction m ixture, from
wh ich colorless PA cyclotrim ers, 1,2,4-triph en ylben zen e (4a), 1,3,5-tri-
ph en ylben zen e (4b) an d yellow PA oligom ers (5) (n um ber-average m olecu-
lar weigh t Mn ≈ 1000) of trans-structure, can be isolated in low yield (4a an d
4b 2.5–3.9%, 5 7–15%). Th is oligom erization of PA is th e first partly suc-
cessful application of th e [Re2Cl8]2– ion as a polym erization catalyst. A weak
1
broad sign al at 3.8 ppm in th e H NMR spectrum of oligom er 6 suggests th e
presen ce of cycloh exadien e sequen ces30–32 in th e oligom er. Oligom er 6
1
sh ows th e followin g ch aracteristics: H NMR (CDCl3, 25 °C): 7.20 (broad,
≈6–7.7, 6 H, arom atic an d olefin ic trans-un its); 3.8 (broad weak sign al,
1
cycloh exadien e sequen ces). 13C-{ H} NMR: 125–133 (arom atic, olefin ic);
142 (weak, quatern ary carbon atom s). IR (KBr): ban ds at 692, 756, 912, 964,
1258, 1441 an d 1482 cm –1; absen ce of absorption ban ds ch aracteristic of
cis-un its at 740, 895 an d 1380 cm –1
.
Com plexes 1b an d 1c are sligh tly m ore reactive requirin g tem peratures of
90 an d 70 °C, respectively. Th e reactivity of 1a can be greatly en h an ced by
in troducin g a co-catalyst. Th us, addition of a two-m olar excess of AlEtCl2 to
th e green -blue solution of 1a in CH2Cl2 causes im m ediate precipitation of
an air sen sitive solid, sparin gly soluble in CH2Cl2 or THF. Th is after filtra-
tion reacts with PA in th e above m edia at room tem perature yieldin g th e
sam e products as 1a.
Th e alkali salts of th e [Mo2Cl8]4– an ion are in soluble in m ost com m on or-
gan ic solven ts an d salts with bulky organ ic cation s such as Ph 4P+ or Bu4N+
are un stable to be isolated. Th erefore, com plex 2 h as been em ployed in our
tests as a represen tative of th e Mo-based din uclear com plexes. Th is is stable
in MeOH but un stable in weakly coordin atin g solven ts (CH2Cl2, C6H6,
THF), in wh ich it polym erizes to an in soluble an d un reactive com poun d
25
h avin g th e form ula [Mo2Cl4(PPh 3)]n con tain in g Mo4 rectan gular un its as
tetram etal cyclobutadiyn es. Th e reaction of 2 with PA in MeOH proceeded
at room tem perature resultin g in a brown solution from wh ich cyclotrim ers
Collect. Czech. Chem. Commun. (Vol. 68) (2003)

Metal–Metal Quadruple Bond
1099
4a an d 4b (18% total) an d a yellow, low-m olecular-weigh t polym er (40%)
were isolated. Th e polym er den oted as PPA (2) is of irregular cis–trans struc-
ture accordin g to both NMR (broad sign als) an d IR spectra. 1H NMR
(CDCl3, 25 °C): 7.15 (stron g, arom atic an d olefin ic trans-un its); 6.70 (sh oul-
der, 2 H ortho arom atic in cis-un its); 5.80 (weak, 1 H, olefin ic cis-un its).
1
13C-{ H} NMR: 126, 128 (broad, stron g, arom atic, olefin ic); 142 (weak, qua-
tern ary carbon atom s). IR (KBr): absorption s at 740, 895, 1380 cm –1 are n ot
discern ible. Th e con ten t of cis-un its calculated from th e relative in ten sity of
th e sign al at 5.80 ppm is approxim ately 50%, sim ilar to th at observed for
33
34
substituted acetylen e polym ers prepared with MoCl5 or MoOCl4 based
catalysts.
Com plex 3 is un stable above –10 °C, th erefore PA was added to a THF so-
lution of 3 at –15 °C. Upon warm in g to th e room tem perature, th e origin al
brillian t blue solution becom es red-brown affordin g n early quan titatively
(91%), auburn to oran ge, prevailin gly cis (≈75% cis accordin g to both IR an d
1H NMR data), h igh -m olecular-weigh t (Mn = 140 000) polym er (den oted as
PPA (3)) an d a sm all am oun t of cyclotrim ers (7%). Spectroscopic data for
1
PPA (3): H NMR (CDCl3, 25 °C): 6.95 (stron g, 3 H, arom atic); 6.80 (sh oul-
der, 2 H, ortho arom atic in cis-un its); 5.84 (weak, 1 H, olefin ic in cis-un its).
1
13C-{ H} NMR: 127, 128, 132 (stron g, arom atic an d olefin ic in trans-un its);
140, 143 (quatern ary carbon atom s). IR (KBr): ch aracteristic absorption s at
692, 738, 754, 801, 884, 910, 1024, 1068, 1329, 1387, 1438 an d 1484 cm –1
.
Th e product selectivity of 3 for cis-con figuration of m ain -ch ain double
bon ds stron gly con trasts with th at of WCl6-based catalysts, wh ich typically
provide h igh -trans-PPA 35
.
Th is n ew-class in itiators (2 an d 3) differ from th e relevan t un icom pon en t
h alide catalysts such as NbCl5 an d TaCl5 36,37, [MoCl3(th f)3]14, [M2Cl6(th t)3]
(wh ere M is Nb 13, Ta 13, Mo 14), wh ich exclusively cyclotrim erize PA to a
m ixture of th e 1,3,5- an d 1,2,4-isom ers. Th ey also differ from th e arch e-
typal h igh -valen t ch lorides MoCl5, WCl6 wh ich require activation by a
co-catalyst in order to produce PPA in com parable yields, but resem ble to
th e bin ary MoCl5 or WCl6/Ph 4Sn system s35 as for polym er yield an d m olec-
ular weigh t. It sh ould be n oted h ere th at th e observed en h an cem en t of th e
cis-stereoselectivity of 3 could be in duced by THF wh ich was used as solven t
for th is catalyst, sin ce 1,4-dioxan e in duces a sim ilar effect in polym eriza-
tion of various substituted acetylen es with WOCl4 an d WCl6 based cata-
lysts33–36
Th e observed catalyst activity can be well correlated with th e m etal–m etal
.
4+
4+
6+
quadruple bond reactivity, which decreases in the order W2 > Mo2 > Re2
.
Th e m ost active catalyst is derived from com plex 3, wh ich con tain s th e
Collect. Czech. Chem. Commun. (Vol. 68) (2003)

1100
Mertis et al.:
tun gsten –tun gsten quadruple bon d th at is kn own to be extrem ely reactive
in oxidation an d ligan d addition reaction s1. Th is en h an ced reactivity de-
4+
layed th e isolation of 3 an d th e developm en t of W2 ch em istry in gen eral
for n early two decades, but in con trast, wh en suitably exploited, it can pro-
vide robust catalysis in volvin g δ-bon ds38.
Th e com plexity of th e system an d m ultiplicity of path ways available
m akes difficult in obtain in g m ech an istic in form ation , especially on th e pri-
m ary step(s). Our efforts to isolate an d ch aracterize catalytically active,
yield-related in term ediates h ave n ot yet been successful. Th erefore, we de-
cided to obtain at least in form ation about propagation m ech an ism , i.e., to
solve th e question wh eth er th e polym erization of PA in duced by 3 proceeds
via m etath esis or in sertion m ech an ism . Th is in form ation can be obtain ed
in directly by exam in in g th e catalytic activity of 3 in th e rin g open in g m e-
tath esis polym erization of NBE an d in th e copolym erization of NBE an d PA.
2
1
5
3
CH CH
6
7
3
4
n
SCHEME 2
Polym erization of NBE with 3 proceeds rath er slowly an d provides on ly
12% of poly(n orborn en e), PNBE, after 19 h of reaction . PNBE prepared h ad
Mn = 86 000 an d well resolved NMR spectra. Spectroscopic ch aracteristics of
PNBE: 1H NMR (CCl4, 25 °C): 5.25 (weak un resolved m , H6 an d H7 in
trans-un its); 5.11 (stron g m , H6 an d H7 in cis-un its); 2.70 (stron g s, H1 an d
H3 in cis-un its); 2.40 (weak s, H1 an d H3 in trans-un its); 0.85–1.90 (m ,
1
m ain sign als at 1.75, 1.3 an d 0.95, H4, H5 an d H2). 13C-{ H} NMR: 133.99
(very stron g, olefin ic carbon s C6 an d C7 in ccc triads); 133.21 w, 130.06 w
an d sh oulders at 134.08, 133.8, 133.28 (C6 an d C7 in oth er triads);
m ultiplet of carbon s C1 an d C3 (position , diad): 43.67 tc weak, 43.43 tt
weak, 38.88 cc stron g, 38.67 ct weak (all); m ultiplet of carbon C2 (position ,
diad): 42.88 cc stron g, 42.24 ct weak, 41.52 tt w; m ultiplet of carbon s C4
an d C5 (position , diad): 33.39 cc stron g, 33.18 ct weak, 32.61 tc weak, 32.42
tt weak. Sign al observed at 31.89 (weak) was n ot assign ed. Th e sign als as-
sign m en t was don e accordin g to literature data39. Con ten t of cis-un its in
th e polym er was determ in ed to be 82% wh en calculated from th e in ten sity
ratio of sign als at 5.12 (cis CH=CH) an d 5.25 (trans CH=CH) as well as th e
in ten sity ratio of sign als of C1 an d C3 carbon s at 2.73 (cis-un its) an d 2.38
ppm (trans-un its). 13C NMR spectrum sh ows h igh blockin ess of th e pre-
Collect. Czech. Chem. Commun. (Vol. 68) (2003)

Metal–Metal Quadruple Bond
1101
pared PNBE, wh ich is used to be ch aracterized by th e product rcrt, wh ere rc
an d rt are in ten sity ratios of sign als of given carbon s in diads com posed of
cis (c) an d trans (t) un its: rc = (cc)/(ct) an d rt = (tt)/(tc). If th e double bon d dis-
tribution is ran dom (Bern oullian ), rcrt = 1. Values of rcrt > 1 prove existen ce
of blocks of cis-un its an d trans-un its in a given polym er: th e h igh er is th e
value of th e product rcrt th e h igh er is th e blockin ess of given polym er39. We
foun d th e followin g values for PNBE prepared with 3: m ultiplet of carbon s
an d C3: rc = 7.4, rt = 1.3 an d rcrt = 9.6; m ultiplet of carbon C2 rc = 7.5, rt =
1.3 an d rcrt = 9.75. Th e average value rcrt 9.7 foun d for our polym er ran ges
to th e h igh est values of PNBE blockin ess ever observed39
.
Th e above results clearly in dicate th at com plex 3 in duces m etath esis
polym erization of NBE, wh ich suggests th at also polym erization of PA with
com plex 3 proceeds via m etath esis m ech an ism . To obtain furth er eviden ce
supportin g th is con clusion , we copolym erized PA an d NBE with com plex 3.
Reactin g an equim olar m ixture of PA an d NBE with 3, we ach ieved total
con version of both m on om ers with in 1 h of polym erization an d obtain ed a
yellowish rubbery copolym er poly(NBE-co-PA) (isolated yield 86%, Mn
=
19 000) an d, in addition , a low-m olecular-weigh t fraction isolated from th e
supern atan t after th e copolym er isolation . NMR ch aracteristics of
1
poly(NBE-co-PA): H NMR (CCCl3, 25 °C): 7.5–6.5 broad un resolved m ulti-
plet (arom atic protons); 5.35 m (very weak, H6 and H7 in trans-units); 5.21 m
(stron g, H6 an d H7 in cis-un its); 3.75 br s an d 3.42 br s (both related to PA
un its); 2.82 m (stron g, H1 an d H3 in cis-un its); 2.45 m (very weak, H1 an d
H3 in trans-un its); 0.85–2.00 m (m ain sign als at 1.75, 1.40 an d 1.02, H4, H5
1
an d H2). 13C-{ H} NMR: 141 an d 139.5 (quatern ary carbon s); 134.72,
134.09, 133.54 an d 132.99 (well resolved sign als of olefin ic carbon s in PA
un its an d C6 an d C7 of NBE un its); 130–125 (broad, un resolved, arom atic
carbon s in PA un its); 42.65 (m ultiplet with m axim a at 43.19, 42.96, 42.65,
42.42 an d 42.10, C1, C2 an d C3); 38.24 (quadruplet with m axim a at 39.43,
38.93, 38.24 an d 37.75, C1 an d C3); 33.19 (poorly resolved m ultiplet with
m axim a at 33.44, 33.19 an d 33.03, C4 an d C5). It sh ould be em ph asized
h ere th at resolved sign als ch aracteristic of olefin ic h ydrogen (5.84 ppm )
an d o-h ydrogen s of ph en yl rin g (6.85 ppm ) in PPA (3) are practically m iss-
in g in 1H NMR spectrum of poly(NBE-co-PA), wh ich proves absen ce of lon -
ger sequen ces of PA un its in th e copolym er. Also th e fin e structure of 13C
NMR spectrum of poly(PA-co-NBE) is differen t from th at of PNBE. Th ese ob-
servation s clearly in dicate th at th e polym er form ed is a real copolym er an d
1
th at its structure is close to th e altern atin g on e. High in ten sities of H NMR
sign als ch aracteristic of cis-NBE un its togeth er with very low in ten sity of all
sign als ch aracteristic of trans-NBE un its prove to an alm ost all-cis structure
Collect. Czech. Chem. Commun. (Vol. 68) (2003)

1102
Mertis et al.:
of poly(PA-co-NBE) prepared with 3. More detailed structure ch aracteriza-
tion of th is copolym er requires furth er in vestigation , wh ich is beyon d th e
scope of th is article. Neverth eless, it is clear th at th e polym er form ed in
com m on polym erization of PA an d NBE is a copolym er an d n ot a m ixture
of two h om opolym ers.
Th e yellow low-m olecular-weigh t fraction (14%) con tain s traces of cyclo-
trim ers 4 an d a copolym er in volvin g lon ger sequen ces of cis-PA un its an d,
m ost probably, isolated NBE un its. Th e presen ce of lon ger sequen ces of
cis-PA un its is eviden ced in 1H NMR: 6.6–6.8 (o-h ydrogen s of ben zen e rin g);
5.85 (olefin proton s in cis-un its). 13C NMR: 142.9, 139.4 (quatern ary car-
bon s); 131.4 (olefin ic proton s) an d broad sign al of arom atic proton s with
local m axim a at 128.6, 127.6 an d 127.2. Th e fin e structure of 13C NMR sig-
n als foun d for th is low-m olecular-weigh t fraction is practically iden tical
with th at foun d for poly(NBE-co-PA), wh ereas th e fin e structure foun d for
PNBE is m issin g. Th is proves th e absen ce of lon ger sequen ces of NBE un its.
Sum m arizin g th e above, it can be con cluded th at th e polym erization of
PA an d NBE as well as copolym erization of th ese m on om ers in duced with
tun gsten com plex 3 proceed via m etath esis m ech an ism . Furth er reactivity
studies an d attem pts to un derstan d th e m ech an ism of th ese reaction s an d
structure of th e above polym ers are in progress.
Financial support by the EU (contract No. ERBCHRXCT-930147), the Special Research Account of
Athens University, the Grant Agency of the Charles University (project No. 241/2002/B-CH), the
Grant Agency of the Czech Republic (project No. 202/00/1152) and the Ministry of Education, Youth
and Sports of the Czech Republic (project No. 1131000001) is gratefully acknowledged. Also, we
would like to thank the Industrial Chemistry Laboratory of Athens University for helpful support.
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