Trouble initiating I2C communication with MSP430g2553
The I²C data/clock lines require pull-up resistors.
Setting the P1REN bits without setting the corresponding P1OUT bits is likely to result in pull-down resistors.

Furthermore, the pull-up resistors must be strong enough to overcome the parasitic capacitances of your circuit fast enough; a typical value for 100 kHz is 10 kΩ. The G2553's built-in resistors can have up to 50 kΩ, so it would be a better idea to use external resistors, or to reduce the clock frequency.