Hi Michael,
I would recommend you to use the periph_i2c example as base for your application, it is included in the LPCOpen package for the LPCXpreso LPC1347 board:
LPCOpen Software for LPC13XX|NXP
Here is a document that explains how to get started with LPCOpen:
https://community.nxp.com/docs/DOC-332667
Hope it helps!
Best Regards,
Carlos Mendoza
Technical Support Engineer