Initiators of the Type Mo(NAr)(CHR‘)(OR‘ ‘)₂ for the Controlled Polymerization of Diethyldipropargylmalonate

The reaction between Mo(NAr)( trans -CHCH CHMe)[OCMe(CF 3 ) 2 ] 2 (quin) (Ar = 2,6- i -Pr 2 -C 6 H 3; quin = quinuclidine) and lithium tert -butoxide yields Mo(NAr)( trans -CHCH CHMe)(O- t -Bu) 2 (quin) ( 1 ). The achiral,syn isomer could be isolated and was shown in an X-ray study to be a trigonal bipyramid in which quinuclidine is coordinated trans to a syn butenylidene group. A base-free species ( 2 ) that contains a five-membered ring as part of a trienylidene unit could be obtained by treating Mo(NAr)(CHCMe 2 R)[OCMe(CF 3 ) 2 ] 2 (R = Me, Ph) with diethyl 3-(2-methylprop-1-enyl)-4-vinylcyclopent-3-ene-1,1-dicarboxylate ( B ) in pentane. The tert -butoxide analogue of 2 ( 3 ) was obtained straightforwardly and was shown in an X-ray study to be the syn alkylidene isomer. The reaction between 1-methylidene-5,5-bis(carboxyethyl)cyclohex-1-ene and Mo(NAr)(CHCMe 3 )[OCMe(CF 3 ) 2 ] 2 gave Mo(NAr)[1-methylidene-5,5-bis(carboxyethyl)cyclohex-1-ene)][OCMe(CF 3 ) 2 ] 2 ( 5a ), which could be treated with LiO- t -Bu to yield an analogous tert -butoxide species ( 5b ). An X-ray structure of a sample of 5b that retained 2 equiv of LiOCMe(CF 3 ) 2 showed it to be a dimeric species in which two Mo complexes were joined through a Li 4 O 4 heterocubane-type structure binding to one ester oxygen in each of the Mo species. Reactions between diethyldipropargylmalonate (DEDPM) and 1, 3, or 5b showed initiation to be smooth with k p / k i values less than 1 and to yield oligomers that were consistent with formation of polymers that contain largely five-membered rings. All reactions can be followed by proton NMR spectra of the alkylidene proton region, and all appear to be living polymerizations under the conditions employed. A Wittig-like reaction between diethyl 3-formyl-4-(2-methylprop-1-enyl)cyclopent-3-ene-1,1-dicarboxylate ( A ) and 2 yielded a symmetric pentaene ( C ) as an ivory-colored solid. The heptaene ( D ) and the nonaene ( E ) could be isolated from reactions between 1 equiv of DEDPM and 3 in CH 2 Cl 2 in the presence of 1 equiv of quinuclidine at −30 °C followed by quenching with aldehyde A .