Initiators of the type Mo(NAr)(CHR′)(OR")2 for the controlled polymerization of diethyldipropargylmalonate

The reaction between Mo(NAr)(trans-CHCH=CHMe)[OCMe(CF3)(2)](2)(quin) (Ar = 2,6-i-Pr-2-C6H3; 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)(CHCMe2R)-[OCMe(CF3)(2)](2) (R = Me, Ph) with diethyl 3-(2-methylprop-1-enyt)-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)(CHCMe3)[OCMe(CF3)(2)](2) gave Mo(NAr)[1-methylidene-5,5-bis(carboxyethyl)cyclohex-1-ene)] [OCMe(CF3)(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(CF3)(2) showed it to be a dimeric species in which two Mo complexes were joined through a Li4O4 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 CH2Cl2 in the presence of I equiv of quinuclidine at -30 degrees C followed by quenching with aldehyde A.