| http://www.w3.org/ns/prov#value | - yl ring which may be substituted, or derivative thereof which may be substituted; M is a Group 4, 5, or 6 transition metal, for example titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum and tungsten; R is a hydrocarbyl group or hydrocarboxy group having from one to 20 carbon atoms; X may be a halide, a hydride, an alkyl group, an alkenyl group or an arylalkyl group; a
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