The self-assembly of M2(CO)10 (M = Mn, Re), oxamide ligands [H2L = N,N′-dibutyloxamide (dbo), N,N′-dibenzyloxamide (dbno)], and flexible bidentate linkers [L′ = 1,2-bis(4-pyridyl)ethane (bpe), 1,3-bis(4-pyridyl)propane (bpp)] afforded MnI- and ReI-based dinuclear metallacycles [(CO)3M(μ-η4-L)(μ-L′)M(CO)3] (1-6). The oxidative addition of oxamide ligands to the equatorial sites and the addition of flexible dipyridyl ligands to the axial sites of facial metal tricarbonyl cores resulted in the formation of dinuclear metallacycles under one-pot reaction conditions. Metallacycles 1-6 were characterized through elemental analysis, IR, UV/Vis, and NMR spectroscopy. The formation of dinuclear compounds 1 and 4 was ascertained by ESI mass spectrometry. The molecular structures of 2, 3, 5, and 6 were elucidated by single-crystal X-ray crystallographic methods, which revealed horse-stirrup-like dinuclear frameworks in which the metal centers are orthogonally connected by a bridging oxamide ligand through ON∩NO bis(chelation) and a flexible bidentate ligand through M-N coordination. The first one-step syntheses of self-assembled neutral MnI-based dinuclear metallastirrups containing bis(chelating) oxamide ligands and their rhenium analogues are reported herein. Copyright © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.