Syntheses and characterization of iridium and rhodium ethylene complexes containing a doubly linked cyclopentadienyl ligand

The dimerization of 6,6-dimethylfulvene with Ni(cod)2 yields the 4,4,8,8-tetramethyl-3a,4,7a,8-tetrahydro-s-indacene isomer (1a). Heating a solution of 1a converts it to the 1,4,5,8 (1b) and 1,4,7,8 (1c) tetrahydro-s-indacene isomers. The activation energy for the isomerization is 23(1) kcal/mol. 1b and 1c can be deprotonated with n-BuLi and the reaction of the dianion with [ClIr(C2H4)2]2 gives two isomers, cis-[(η5-C5H3)(CMe2)Ir(C2H4)2]2 (cis-2) and trans-[(η5-C5H3)(CMe2)Ir(C2H4)2]2 (trans-2). Reaction of 1b and 1c with RhCl3 · xH2O in refluxing methanol yields a red-orange solid, which was consistent with the empirical formula, [(C5H3)(CMe2)RhCl2]n (3). Reaction of 3 with C2H4 in a Na2CO3/ethanol mixture afforded cis-[(η5-C5H3)(CMe2)Rh(C2H4)2]2 in 5% yield.