Without Any Isomerizing Activity

See Table VIII. Titanium based catalysts dimerize ethylene to 1-butene and codimerize ethylene and 1-butene into mixed hexenes (probably for steric reasons titanium is unable to homodimerize 1-butene or other 

Tantalum complex D not only converts ethylene to 1-butene but selectively transforms all the a-olefins into a mixture of t,t or h,t dimers, depending on the size of the substituent (Table IX). 

Depending on the solvent Ni(PPR3)2(ethylene) catalyzes the dimerization of ethylene to 1-butene (chlorobenzene) or to cyclobutane (toluene). It is the only case of cyclodimer formation from an unstrained olefin (R. H. Grubbs). 

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