Complex sentence: This in part due to the steric clash between the substituents, which adopt a trans configuration as the most stable conformation in the metallacyclobutane intermediate, to form the "E-" isomer.
Split into simpler sentences: This in part due to the steric clash between the substituents in the metallacyclobutane intermediate. The substituents adopt a trans configuration as the most stable conformation resulting in the formation of the "E-" isomer.