CATALYST FOR POLYOLEFIN PRODUCTION, CATALYST COMPOSITION CONTAINING THE SAME, AND PRODUCTION OF POLYOLEFIN

PROBLEM TO BE SOLVED: To provide a new catalyst for polyolefin production which comprises a transition metal containing tetrapyrazolyl borate and can give polyolefins without using methylaluminoxane or a boric ester. SOLUTION: This catalyst is represented by formula I (wherein C5 Rn H5-m is cyclopentadienyl; n is 0-5; R is a 1-6C alkyl, L is tetrapyrazolyl borate, hydrotrispyrazolyl borate or the like; M is a group 3A, 4A or 5A transition metal; a+n=m-2; X and Y are each a halogen or a ligand represented by ER R R ; E is group 5B or 6B element; and R to R are each a 1-6C alkyl, an aryl or R is null). It is exemplified by formula II or formula III (wherein η -C5 H5 is cyclopentadienyl; and C3 H3 N2 is pyrazolyl). This catalyst has an excellent activity and can give a highly transparent polyolefin having a high molecular weight and a narrow molecular weight distribution without using methylaluminoxane or a boric ester when combined with a cocatalyst comprising a trialkylaluminum.