Problems in Interfacing DUE with UNO through I2C?

Hardware Arduino Due
1

I need to interface DUE(master) with UNO(slave),there are 3 questions
1.How to reduce clock speed DUE is 84 MHz while uno is 16 MHz?
2.operating Voltage of DUE is 3.3 V while due is 5V(whether any external components needed) ?
3.why not normal wire library in this scenario not working?

2

You have already asked this question and got all the answers.
http://forum.arduino.cc/index.php?topic=270556.msg1907498#msg1907498