The paucity of boron-containing heteroalkene complexes prompted us to explore the coordination of phosphinoboranes. The complexes {[R2PB(C6F5)(2)]Pt(PPh3)(2)} (R = Cy, t-Bu) were obtained by ethylene displacement. Spectroscopic and crystallographic data indicated symmetric side-on coordination of the phosphinoborane to Pt. Thorough analysis of the bonding situation by computational means revealed important similarities but also significant differences between the phosphinoborane and ethylene complexes.