Patent ID: 6875721

Claim:
A soluble complex comprising a magnesium dihalide and an electron donor represented by the following formula (I) expressing the molar ratio between the magnesium dihalide and the electron donor: MgX 2 .[(R(OR′) n ] m (I) wherein MgX 2 is the magnesium dihalide and R(OR′)N is the electron donor, X is a halogen, R is an n-valent C 1 -C 20 aliphatic group, an n-valent C 7 -C 27 araliphatic group or an n-valent C 2 -C 22 acylic group, R′ is a C 1 -C 20 alkyl group or a C 7 -C 27 aralkyl group, n is a number from 1 to 6 and m is defined as a number 0.5≦m≦2.0.