Provided is a metallocene catalyst component for use in preparing isotactic polyolefins, which component has the general formula (I): R'' (CpR1R2R3) (Cp'R'n) MQ2 wherein Cp is a substituted cyclopentadienyl ring; Cp' is a substituted or unsubstituted fluorenyl ring; R'' is a structural bridge imparting stereorigidity to the component; R1 is a substituent on the cyclopentadienyl ring which is distal to the bridge, which distal substituent comprises a bulky group of the formula XR*3 in which X is chosen from Group IVA, and each R* is the same or different and chosen from hydrogen or hydrocarbyl of from 1 to 20 carbon atoms, R2 is a substituent on the cyclopentadienyl ring which is proximal to the bridge and positioned non-vicinal to the distal substituent, and is of the formula YR#3, in which Y is chosen from Group IVA, and each R# is the same or different and chosen from hydrogen or hydrocarbyl of 1 to 7 carbon atoms, R3 is a substituent on the cyclopentadienyl ring which is proximal to the bridge and is a hydrogen atom or is of the formula ZR$3, in which Z is chosen from Group IVA, and each R$ is the same or different and chosen from hydrogen or hydrocarbyl of 1 to 7 carbon atoms, each R'n is the same or different and is hydrocarbyl having 1 to 20 carbon atoms in which 0≤n≤8; M is a Group IVB transition metal or vanadium; and each Q is hydrocarbyl having 1 to 20 carbon atoms or is a halogen.