Limiting DAC input voltage from opp amp

I im trying to connect the out put of an opp amp to a ADC I2C chip PCF8591. I have tried limiting the voltage to the opp amp supply to 0-5v (with no limiting it can swing +-12) using a resister voltage divider but that effected the out put of the opp amp within the part I was trying to capture with the DAC. So now I am trying to use a zener diode in series with a resister to clip the output. I have it hooked my test up to a variable power supply but it is not behaving as I thort it would as seen in the simulation.

My problems are the voltage starts to get clipped be for the zener diode rating. 5v in gives me 4.3 out and 7.3v givs me 4.7 (what I wanted 5v to give me 4.7)

and the current goes into over load when the input exceeds the rating of the zener.

Any advice on this circuit or an alternative would be greatly appreciated

Thank you

Use two schottky diodes.
1) Input of ADC to ground to stop voltage at -0.35V.
2) Input of ADC to PCF8591 supply so the voltage can not get above supply by more than +0.35V.

Zener diodes do not have a sharp turn on voltage. A 5V diode with you 100k resistor will turn on early (4V).
Use 10k resistor or lower. You ADC may not work well with 100k ohms. It may want 2k. The data sheet will give this information.