Treatment of ruthenabenzene [(C9H6NO)Ru{CC(PPh3)CHC(PPh3)CH}(C9H6NO)(PPh3)]Cl2 (1) with NaBH4 produces the first ruthenacyclohexa-1,4-diene [(C9H6NO)Ru{CC(PPh3)CH2C(PPh3)CH}(C9H6NO)(PPh3)]Cl (2), which was fully characterized. Under an oxygen atmosphere, complex 2 can easily convert to complex 1. DFT calculations were carried out to rationalize the high regioselectivity in the reaction of the ruthenabenene 1 with NaBH4 and the interconversion between 1 and 2.