Raspberry PI, PCF8574AT, MPU6050, BMP180 i2c voltage difference?
I2c is an open collector bus. You could easily power the bus at 3.3V of the RPi, and it will be safe. But then the devices won't work. They expect a Voltage Input High of 0.7*VDD which is 0.7 * 5v  = 3.5V. No guarante that they will read the input from the RPi via the pull up resistor.

You will need an i2c voltage converter. Please search the site as there are hundred of questions explaining these circuits.