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Enantioselective Polymerization of 1 2-DiisocyanoarenesЧSynthesis of Optically Active Helical Poly(quinoxaline-2 3-diyl)s.

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(51 M Wilchek, E. A. Bayer, Trends Biochem. Sei. 1989, 14, 408-412.
[6] H. Sigel, E.xperienriu 1981, 37, 789-798.
[7] PnAO is an acronym used for this type ofligand. PnAO is the abbreviation
for the bifunctional derivative of propylenediamine dioxime.
[S] The product was pure by TLC (silica gel, CH,CN/25% NH, l O / i ,
R , = 0.18) and HPLC (C18, Bondapak 10 pm, 0.01 M ammonium acetate
(pH 7)/CH,CN 213). The ' 3 C and ' H N M R spectra as well as FAB mass
spectra were consistent with the proposed structure.
[9] S. Jurisson, E.O. Schlemper, D.E. Troutner, L. R. Canning, D.P.
Nowotnik, R. D. Neirinckx, fnorg. Chem. 1986, 25, 543-549.
[lo] I n a few patients the pretargeting approach was compared with the usual
direct application of a 99mTclabeled antibody. The pretargeting approach
showed the tumor very clearly with very little unspecific uptake and a good
tumorinontumor ratio, whereas the direct labeling showed high unspecific
uptake. The comparative study will be published elsewhere, but supplementary material is available on request.
Enantioselective Polymerization of
1,2-Diisocyanoarenes-Synthesis of Optically
Active, Helical Poly(quinoxaline-2,3-diyl)s
By Yoshihiko Ito,* Eiji Ihara, and Masahiro Murakami
The synthesis of an optically active polymer from an achiral monomer using a chiral catalyst is a significant challenge."] We now report an enantioselective polymerization
of 1,2-diisocyanoarenes induced by new chiral palladium
catalysts having helical conformations.
We reported recently that a new living polymerization of
1,2-diisocyanoarenes 1 was catalyzed by trans-bromo(methyl)bis(phosphine)palladium(lr) to give poly(quinoxaline-2J-diyl)s 3 with narrow molecular weight distributions.['] Noteworthy was that several of the propagating palladium(r1) complexes 2, which were still reactive in the
polymerization, were isolated and fully characterized.
The X-ray crystallographic study of pentamer 4, revealed
a helical structure (Fig.
This finding prompted us to
undertake a synthesis of optically active poly(quinoxa1ine2,3-diyl) 3, whose chirality emanates from the helical
Fig. 1. Structure of 4. CH,SiMe, groups and hydrogen atoms are omitted for
lar dichroism (CD) spectra of 5a and 5b showing large Cotton effects are nearly mirror images of each other and indicative of enantiomers with opposite helicities (Fig. 2 ) . After
removal of the chiral bis(phosphine)palladium(n) moiety
by the reaction with methylmagnesium bromide, 5 gave
quinque(quinoxaline-2,3-diyl)s 6, which have identical spec-
6b [a]o=-25
L'= PPh I[SI-2-rnethylbutylll
5b [a10 = + 2 3
troscopic properties["] and optical rotations in opposite directions; 6a [a], = + 25 (c = 0.1, CHCI,), 6b:[a], = - 25
(c = 0.1, CHCI,). The CD spectra of 6 a and 6b exhibit weak
Cotton effects. Based on these results, the two isomers 5a
and 5 b were assigned to the diastereomers which arise from
structure. Oligomerization of 1,2-diisocyano-3,6-di-p-tolylbenzene (4 equiv) catalyzed by tran~-bromobis[bis((S)-2methylbutyl)phenylphosphine]methylpalladium(~r) (1 equiv)
gave a mixture of oligo(S,8-di-p-tolylquinoxaline-2,3diyl)palhdium(Ii) complexes in quantitative yield. Gel permeation chromatography (GPC) on polystyrene allowed the
isolation of pentamer 5. Of note was that subsequent highly
resolved, preparative high-pressure liquid chromatography
(HPLC) permitted the separation of two isomers 5a and 5b
(3 :4), which were conformationally stable in solution. Circu-
Prof. Dr. Y Ito. E. Ihard, Dr. M. Murakami
Department of Synthetic Chemistry
Faculty of Engineering, Kyoto University
Yoshida. Kyoto 606 (Japan)
Angru. Chrm. Inr. Ed. Engl. 1992, 31, No. 11
Fig. 2. C D spectra of 5 a and 5 b in CH,CI,
VCH Verlagsgese~lscha~
mbH. W-6940 Wernheim. f992
1 SO9
20 min. The mixture was quenched with water and extracted with benzene. The
collected organic phases were dried, and the solvent was removed under vacuum to give trans-bis[bis{(S)-2-methylbutyl}phenylphosphine]hromo(methyl)palladium(ii) (57 mg, 81 pmol) in almost pure form. To this were added 1.2diisocyano-3,6-di-p-tolylbenzene(99 mg, 0.32 mmol) and THF ( 5 mL). The
mixture was stirred at room temperature for 12 h and then concentrated to
comafford a mixture of oligo(5,8-di-p-tolylquinoxaline-2,3-diyl)palladium(i1)
plexes quantitatively. Pentamer 5 (48 mg) was isolated by preparative GPC
(polystyrene, CHCI,). Two isomers 5 a and 5b were separated by preparative
HPLC on silica gel (hexane: Et0Ac:EtOH = 200:20:1). 5 a : UV (CH,CI,):
A,,, [nm] ( E ) = 263 (139000); [c& = - 343 (c = 0.7, CHCI,). 5 b:UV (CH,CI,):
A,, [nm] ( 6 ) = 263 (175000); [MI, = + 233 (c = 0.8, CHCI,).
8 a : A solution of 7 (31 mg, 0.10mmol) and 5 a (4.9 mg, 2.2pmol) in T H F
(6 mL) was stirred at room temperature for 36 h before MeMgBr (0.6 mmol,
2 M solution in ether) was added. After the reaction mixture had been stirred for
1h, water was added, and the mixture was extracted with CHCI,. Thecollected
organic phases were dried, and the solvent was removed under vacuum. Preparative GPC (polystyrene, CHCI,) afforded 8a. Yield: 27 mg (78%). UV
(CH,CI,): A,,, [nm] ( E ) = 287 (905000), 349 (345000).
8 b : Following the procedure for 8a, 7 (30.5 mg, 0.10mmol) and 5 b (4.9mg,
[nm] ( E ) = 288
2.2 pmol) provided 8 b. Yield: 28 mg (83 %). UV (CHJI,):
(912000), 349 (339000).
[a10 = +165
8b [a]o=-171
the combination of the helical secondary structure and the
chirality of the phosphine ligand.
We thought that the rigid and stable conformations of 5 a
and 5b might induce further polymerization of 1,Zdiisocyanoarenes with stereocontrol, resulting in the extension of
the helical chain. Indeed, enantioselective polymerization of
(7)t51 was accomplished with the diastereomerically pure palIadium(n) complex 5 a as a chiral initiator. After removal
of the chiral palladium(I1) moiety, optically active poly= f 1 6 5 ( c = 0.54, CHCI,),
(quinoxaline-2,3-diyI) 8a ([oI],,
M , = 11200 (vapor-pressure osmometry in CHCI,)) was obtained which showed a larger optical rotation and much
more distinct Cotton effects than 6 a (Fig. 3).r61Similarly, the
other diastereomer 5 b gave poly(quinoxaline-2,3-diyl) 8 b,
Fig. 3. CD spectra of 8 a and 8 b in CH,CI,
whose optical rotation is almost identical, but with the opposite sign ([& = - 171 (c = 0.56, CHCI,), Mn =10000 (vapor-pressure osmometry in CHCI,)). The C D spectrum of
8b is the complete mirror image of that of 8 a (Fig. 3). These
observations indicate that poly(quinoxaline-2,3-diyl)s 8a
and 8b have helical structures which are the mirror images of
each other.
1,2-Diisocyanoarenes: 1,2-Diisocyano-3,6-di-p-tolylbenzene
and 7 were prepared from the corresponding 1,2-diformamidoarenes by the procedure previously reported [7].
5:MeMgBr ( 2 mmol, 2~ solution in ether) was added to a solution of transhis[bis{ (S)-2-methylbutyl}phenylphosphine]dibromopalladium(rr) (66 mg,
86 pmol) in benzene ( 5 mL) cooled in an ice-water bath and then stirred for
Veriagsgesellschaft mbH W-6940 Weinhelm, 1992
CAS Registry numbers:
4, 144043-06-1;5a. 144071-96-5;6a, 144043-08-3;7 (homopolymer), 144043144043-09-4;
01-6; trans-BrPd(CH,)[P(Ph){(S)-CH,CH(CH,)CH,CH,},],,
[i] Examples of optically active helical polymers: polyisocyanide: P. C. J.
Kamer, R. J. M. Nolte, W. Drenth, J. Am. Chem. SOC.1988, 110, 6818;
poly(triarylmethylmethacry1ate): Y Okamoto, H. Mohri, T. Nakano, K.
Hatada, ibid. 1989,111,5952; polychloral: K. Ute, K. Hirose, H. Kashimoto, K. Hatada, 0. Vogl, ibid. 1991, 113, 6305; poly(p-pyrrole): P. Magnus,
W Danikiewicz, T. Katoh, J. C. Huffman, K. Folting, ibid. 1990,112,2465.
[2] Y Ito, E. Ihara, M. Murakami, M. Shiro, J. Am. Chem. SOC.1990,112,6446.
131 4: Monoclinic, P2,/a, a = 25.287(8), b = 24.423(8), c = 15.842(7) A,
/3 = 93.52(3)", V = 9766(3) A', 2 = 4, L(Cu,.) = 1.54178 A, Mac Science
MXC3 diffractometer. The structure was solved by direct methods and
Fourier synthesis (CRYSTAN program package). R = 0.068, R , = 0.080
for 8462 reflections [Fo > 4a(Fo)]. Further details of the crystal structure
investigation are available on request from the Director of the Cambridge
Crystallographic Data Centre, University Chemical Laboratory, Lensfield
Road, GB-Cambridge CB2 IEW (UK), on quoting the full journal citation.
[4] 6:UV (CH,CI,): AmBX [nm] ( E ) = 263 (73500) 321 (35500); MS:m/r 1572.7
[S] Compound 7 was used as a monomer to ensure higher solubility of the
resulting polymer in THE
[6] The CD bands (250 and 290 nm) were assigned to the helical chromophore
of 8 by quantum mechanical calculations[S] of the helical poly(quinoxa1ine2,3-diyl).
[7] Y. Ito, A. Ohnishi. H. Ohsaki, M. Murakami, Synlhesis 1988, 714.
[8] Theoretical CD curves for helical poly(quinoxaline-2,3-diyl) were computed
on the basis of the exciton theory (R. W. Woody, J. P d y m . Sci. Macromol.
Rev. 1977, 12, 181), on the model compound 2-butyl-5,6,7,8-tetramethylquinoxaline taking into account a n-n* transition at 252 nm polarized along the long axis of the molecule. Details of the CD spectral analysis
will be published in due course.
Triphosphatrisilacyclohexanes as Tridentate
Coronands in Cr and Mo Complexes: Activation
of Si-H in an Early Stage versus Phosphane
By Matthias Dries,* Michael Reisgys, and Hans Pritzkow
Dedicated to Professor Hermann Schildknecht
on the occasion of his 70th birthday
Only isolated examples of cyclic multidentate phosphane
ligands such as phospha crown ethers are known, and these
Experimental Procedure
Received: May 2, 1992 [ Z 5327 IE]
German version: Angew. Chem. 1992, 104, 1508
Dr. M. Dries, Dipl.-Chem. M. Reisgys, Dr. H. Pritzkow
Anorganisch-chemisches Institut der Universitat
Im Neuenheimer Feld 270, D-W-6900 Heidelberg (FRG)
This work was supported by the Deutsche Forschungsgemeinschaft. We
thank the referees for valuable tips.
0570-0833/92/1lll-1510 $ 3 50+.25/0
Angew Chem. Int Ed Engl 1992, 3f, No 11
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diyl, optically, helical, activ, quinoxalines, enantioselectivity, poly, diisocyanoarenesчsynthesis, polymerization
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