Unusual addition of but-2-yne to a permethyltitanocene species

The [TiCl2(η5-C5Me5)2]/Mgexcess/tetrahydrofuran system reacts with but-2-yne in excess to give paramagnetic (η5:η1-1,2,3,4-tetramethyl-5-(2,3,4,5-tetramethylpenta-2,4-dien-1,5-diyl-κC5)cyclopentadienyl)(η5-pentamethylcyclopentadienyl)titanium(III) (1) as the main product. The crystal structure of 1 shows a minimum steric hindrance between the methylated cyclopentadienyl ligands and non-coplanar conjugated double bonds in the C5 tether.