Synthesis, Structures, and Ring-Opening Polymerization Reactions of Substituted Cyclopentadienyl Complexes of Zinc

The reaction of 2 equiv of the new pyrrole-substituted cyclopentadienyl ligand cyclo-C4H4NSiMe2C5H5 ( 2a , CppyH) with Zn[N(SiMe3)2]2 gives the bis(cyclopentadienyl)zinc complex Zn(Cppy)2 ( 3a ). The reaction of 2a and the related derivatives cyclo-2,5-Me2C4H2NSiMe2C5H5 ( 2b , CppymeH) and 3,5-Me2C6H3CH2CMe2C5H5 ( 2c , CpmesH) with dibutylmagnesium gives the corresponding magnesocenes MgCpR2 ( 3a - c ). Prolonged heating of the appropriate cyclopentadiene with zinc dialkyls in toluene, or alternatively stirring with [XZnN(SiMe3)2]2 in toluene at 40 °C for 1 h, gives the monocyclopentadienyl zinc alkyl complexes CpRZnX ( 6a , CpR = Cppy, X = Me; 6c , CpR = Cpmes, X = Me; 7a , CpR = Cppy, X = Et; 7c , CpR = Cpmes, X = Et), which provide spectroscopic evidence for a Zn···(hetero)arene interaction. Addition of tetramethylethylenediamine (TMEDA) gives CpRZnX(TMEDA) ( 8a , b , X = Me; 9a - c , X = Et). The crystal structures of 8b and 9c show ?2-bound cyclopentadienyl ligands, with one long and one short Zn-C interaction. The reaction of 7c with B(C6F5)3 in toluene proceeds with alkyl/C6F5 exchange to give CpmesZn(C6F5) ( 10 ). Treatment of 9c with B(C6F5)3 in toluene results in an ionic product, [CpmesZn(TMEDA)]+[EtB(C6F5)3]- ( 11 ). On the other hand, the reaction of 9a with B(C6F5)3 in toluene or dichloromethane proceeds with ß-H abstraction, with concomitant loss of ethene, as well as both ethyl and cyclopentadienyl abstraction. Both 11 and 9a /B(C6F5)3 mixtures catalyze the polymerization of cyclohexene oxide and e-caprolactone