Well-Defined Transition Metal Catalysts for Metathesis Polymerization - Late Transition Metal Polymerization Catalysis - page 182

5.2.5
Osmium-Based Initiators

Reaction of dineopentylosmium dioxide with 2 equiv. of Ta(CHR)(CH 2 R) 3 was
reported to result in the formation of osmium dineopentylbisneopentylidene
[269, 270]. I nterconversion of the two isomeric forms ( syn - anti and anti - anti )of
this compound was postulated to proceed via an osmium tris(neopentyl)neo-
pentylidene. So far, no reports on the ROMP activity of these complexes

have been given. Similar to OsCl 3 [271] and ( p -cymene)OsCl 2 P(c-H x ) 3 [272],

( -H) 2 Os 3 (CO) 10 was reported to be active in the ROMP of NBE to yield all cis-

poly-NBE [273].

5.3
Outlook

Future applications of both chiral molybdenum-based initiators currently investi-
gated by Schrock and Hoveyda and NHC-based Ru-carbenes will clearly be situ-
ated in the area of organic synthesis [274-279]. This is particularly true for their
heterogeneous analogues [193, 280-291]. From a realistic point of view, this poly-
merization technique will certainly not rival “traditional” polymerizations such as
Ziegler-Natta- or metallocene-based chemistry. Nevertheless, ROMP, alkyne or AD-
MET polymerization certainly already hold their place in the synthesis of specialty
polymers for both catalysis [291-293] and applications in materials [294] and life
sciences [295-298], the more so as these techniques are additionally applicable to
precipitation [299, 300], dispersion [301] and emulsion polymerization [302] as
well as to polymerizations in supercritical CO 2 [303]. Tandem syntheses including
consecutive ROMP [304], ADMET [305] or RCM [306] followed by catalytic hydro-
genation by an in situ transformed Ru-catalyst additionally strengthen metathesis
within the area of polymer synthesis. Once the problem of long-time stability of
ROMP and ADMET polymers under ambient conditions is solved, a tremendous
impact on polymer modification, in particular for polyolefins, can be expected.

5.4
References

1 G. Dall'Asta, G. Motroni, Eur. Polym. J.

1971 , 7 , 707-716.

5 R. R. Schrock, J. Am. Chem. Soc. 1974 ,

96 , 6796.

J.-L. Hérrison, Y. Chauvin, Makromol.
Chem. 1971 , 141 , 161-176.

R. R. Schrock, S.M. Rocklage, J.H.
Wengrovius, G. Rupprecht, J. Fell-
mann, J. Mol. Catal. A: Chem. 1980 , 8 ,
73.

2 6

T. J. Katz, S. J. Lee, N. Acton, Tetrahe-
dron Lett. 1976 , 47 , 4247-4250.

3

T. J. Katz, J. McGinnis, J. Am. Chem.
Soc. 1975 , 97 , 1592-1594.

R. R. Schrock, J. Organomet. Chem.
1986 , 300 , 249.

4 7