I assumed "xxx" refers to the name of the clinic/hospital rather than the time. The time would be unnecessary as you have already said "Tomorrow morning". Remember that we don't put a space before a comma but we do put a space after one. Having said that, I would replace the comma with "and".
Tomorrow morning, my wife is having/will have an operation at [name of clinic] and I need to pick her up around lunchtime. Therefore, I would be very grateful if you would allow me to work from home tomorrow.