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First, general formula (I) will be described. 

In general formula (I), each of Ru, R$_{12 }$and R$_{13 }$indepen› dently represents a hydrogen atom, an alkyl group, a monova› lent aliphatic hydrocarbon ring group, a halogen atom, a cyano group or an alkoxycarbonyl group. 

The alkyl group is an optionally substituted linear or branched alkyl group, preferably an optionally substituted alkyl group having 20 or less carbon atoms, such as a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, a hexyl group, a 2-ethyl› hexyl group, an octyl group or a dodecyl group. An alkyl group having 8 or less carbon atoms is more preferred. An alkyl group having 3 or less carbon atoms is most preferred. 

i, As the monovalent aliphatic hydrocarbon ring group, there can be mentioned an optionally substituted monocyclic or polycyclic aliphatic hydrocarbon ring group. An substituted monocyclic monovalent aliphatic hydrocarbon ring group having 3 to 8 carbon atoms, such as a cyclopropyl group, a cyclopentyl group or a cyclohexyl group, is pre› ferred. 

As preferred substituents that can be introduced in these groups, there can be mentioned a hydroxyl group; a halogen atom (fluorine, chlorine, bromine or iodine); a nitro group; a cyano group; an amido group; a sulfonamido group; any of the alkyl groups mentioned above with respect to R$_{11 }$to R$_{13}$; an alkoxy group, such as a methoxy group, an ethoxy group, a hydroxyethoxy group, a propoxy group, a hydroxypropoxy group or a butoxy group; an alkoxycarbonyl group, such as a methoxycarbonyl group or an ethoxycarbonyl group; an acyl group, such as a formyl group, an acetyl group or a benzoyl group; an acyloxy group, such as an acetoxy group or a butyryloxy group; and a carboxyl group. A hydroxyl group and a halogen atom are especially preferred. 

In general formula (I), each of Ru, R$_{12 }$and R$_{13 }$is prefer› ably a hydrogen atom, an alkyl group or a halogen atom. A hydrogen atom, a methyl group, an ethyl group, a trifluorom› ethyl group (-CF 3 ), a hydroxymethyl group (----CH $_{2}$---0H), a chloromethyl group (----CH$_{2}$----Cl) and a fluorine atom are especially preferred. 

X$_{11 }$ represents ---0-, -S-, -CO-, -S0$_{2}$-, -NR- (R represents a hydrogen atom or an alkyl group), a bivalent nitrogenous nonaromatic heterocyclic group or a group composed of a combination of these. 

With respect to -NR-, the alkyl group represented by R is an optionally substituted linear or branched alkyl group. Particular examples thereof are the same as those of the alkyl groups represented by R$_{1 }$ i, R$_{12 }$and R$_{13}$. R is most preferably a hydrogen atom, a methyl group or an ethyl group. 

The bivalent nitrogenous nonaromatic heterocyclic group refers to a preferably 3- to 8-membered nonaromatic hetero› cyclic group having at least one nitrogen atom. In particular, there can be mentioned, for example, bivalent connecting groups with the following structures. 

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X$_{11 }$ is preferably -0-, -CO-, -S0$_{2}$ -, -NR- (R represents a hydrogen atom or an alkyl group) or a group composed of a combination of these. X$_{11 }$ is most preferably -COO- or -CONR- (R represents a hydrogen atom or an alkyl group). 

L$_{11 }$ represents an alkylene group, an alkenylene group, a bivalent aliphatic hydrocarbon ring group or a group com› posed of a combination of two or more of these, provided that in the group composed of a combination, two or more groups combined together may be identical to or different from each other and may be linked to each other through, as a connecting group, ---0-, -S-, -CO-, -S0$_{2}$ -, -NR- (R rep› resents a hydrogen atom or an alkyl group), a bivalent nitrog› enous nonaromatic heterocyclic group, a bivalent aromatic ring group or a group composed of a combination of these. 

