Heterometallic Multiple Bonding: Delocalized Three-Center σ and π Bonding in Chains of 4d and 5d Transition Metals

Heterotrimetallic compounds Mo₂Ru­(dpa)₄Cl₂ (<b>1</b>) and W₂Ru­(dpa)₄Cl₂ (<b>2</b>) are prepared by reactions of M₂(dpa)₄ (M = Mo or W; dpa = 2,2′-dipyridylamide) with [Ru­(CO)₃Cl₂]₂. Crystallographic studies reveal short Mo–Ru and W–Ru distances, 2.38 Å (<b>1</b>) and 2.39 Å (<b>2</b>), suggestive of delocalized Mo–Mo–Ru and W–W–Ru bonding. In contrast to the σ bonding found in the corresponding iron compounds, density functional theory calculations reveal both a three-center/two-electron σ bond and two three-center/four-electron π bonds in the M–M–Ru compounds