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

Heterotrimetallic compounds Mo2Ru­(dpa)4Cl2 (1) and W2Ru­(dpa)4Cl2 (2) 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 (1) and 2.39 Å (2), 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.