Help with high side MOSFET driver IC configuration
Since I only need the high side output


It is OK to use only the high side output and use a freewheeling diode at the low side. But keep in mind that, a significant amount of losses in Buck Converter occurs on the freewheeling diode. If you use a MOSFET with sufficiently low Rds,on resistance on the low side too, there will be less losses.


  would it be sufficient to ground pins 3, 4 and LO


You must always connect the COM pin to the ground, because it is the GND pin of the IC. If you desire to use only high side, you should ground the pins LIN pin. But never ground the LO pin! It is an active output pin. It might be shorted and damage the IC. Even if it doesn't damage it, there may be a power loss on it.


  Do I still need to connect Vcc to the supply?


Yes, of course. Vcc is always needed for powering the internal circuitry of the IC, and for boot-strapping the high side.

My suggestions:


Don't use an electrolytic capacitor for C1. They don't respond fast in high frequency circuits. Use a ceramic or film capacitor of at least 10nF; preferably 100nF.
The rated reverse voltage of DBOOT must be more that VHIGH_SIDE - Vcc.
CBOOT should at least be around 100 times the input capacitance of the MOSFET (Ciss) to be driven, and should be a low ESR (e.g.; film) capacitor.
The peek current on DBOOT will be \$\dfrac{V_{cc}}{R_{BOOT}}\$. Choose RBOOT and DBOOT accordingly. Lower the value of RBOOT, faster the capacitor will charge. The power loss on RBOOT is independent of its value.
CBOOT will only see Vcc on it. No need to buy an high voltage capacitor for it. The high reverse voltage will be on DBOOT. Make sure its reverse voltage rating is higher than the high side MOSFET drain voltage.