Reactions of hafnocene stannyl complexes with stannanes: implications for the mechanism of the metal-catalyzed dehydropolymerization of secondary stannanes

Abstract

Reactions of the hydrostannyl complexes CpCp ∗Hf(SnHMes 2)Cl ( 2 ), [Me 2C(C 5H 4) 2]Hf(SnHMes 2)NMe 2 ( 3 ) and CpCp ∗Hf(SnHMes 2)OMe ( 4 ) with Ph 2SnH 2 or n Bu 2SnH 2 afforded poly- and oligostannanes of varying molecular weights. The reaction of 2 with 1.2 equiv. of Ph 2SnH 2 produced the oligostannyl complexes CpCp ∗Hf(SnPh 2SnHMes 2)Cl ( 6 , 68%), CpCp ∗Hf(SnPh 2SnHPh 2)Cl ( 7 , 15%), and CpCp ∗Hf(SnPh 2SnPh 2SnHPh 2)Cl ( 8 , 7%), which may be intermediates in the dehydropolymerization process. Compounds 7 and 8 were observed in higher yields in the reaction of CpCp ∗Hf(H)Cl ( 1 ) with 2 equiv. of Ph 2SnH 2. Possible mechanisms for the formation of 6 , 7 , and 8 are discussed. Two trialkylstannyl complexes, CpCp ∗Hf(SnMe 3)Cl ( 11 ) and CpCp ∗Hf(Sn n Bu 3)Cl ( 12 ), were synthesized in good yields from the reaction of 1 with R 3SnH (R=Me, n Bu). When a solution of 11 was heated to 100 °C for 1 h, CpCp ∗Hf(SnMe 2SnMe 3)Cl ( 13 ) and CpCp ∗Hf(SnMe 2SnMe 2SnMe 3)Cl ( 14 ) were formed, probably via Me 2Sn insertion into Hf–Sn bonds. Based on the known influence of catalyst structure on the molecular weight of polystannanes, and the observations reported herein, it is proposed that the Sn–Sn bond-forming mechanism may involve R 2Sn insertions into M–Sn bonds.