Display omitted •Preparation of half-sandwich ruthenium allenylidene complexes.•Preparation of diazoalkane complexes of ruthenium.•The diazoalkane unit presents an important bending angle RuNN.•The metal-ligand overlap in the HOMO plays a role in the bending of the RuNN angle.•DFT studies corroborate the role of metal–ligand overlap in the HOMO and lower occupied orbitals to the acute character of the RuNN angle. Half-sandwich mixed phosphine-phosphinite ruthenium complexes RuCp’Cl(PPh3)L Cp’ = Cp (1), Cp* (2), and RuCp*ClL2 (3) were prepared by substitution of the triphenylphosphine by the phosphinite ligand PPh2OCH2Ph, L, on the parent complexes RuCp’Cl(PPh3)2. Allenylidene compounds Ru(η5-C5H5){CC = CPh2}(PPh3)LPF6 (4) and Ru(η5-C5Me5){CC = CPhR}(L)(L’)BPh4 L’ = PPh3(5), L (6); R = Ph (a), R = Me (b) were obtained by reaction of compounds 1–3 with the appropriate propargylic alcohols 1,1-diphenyl-2-propyn-1-ol, and 2-phenyl-3-butyn-2-ol. Diazoalkane complexes RuCp(N2CAr1Ar2)(PPh3)LPF6 Ar1 = Ar2 = Ph (7a), Ar1Ar2 = C12H8 (7b) and RuCp*{N2C(C12H8)}L2PF6 (8) were obtained by reaction of 1 or 3 with the corresponding diazoalkanes in the presence of NaPF6. Complexes were characterized by IR and NMR spectroscopy and, in the case of compounds 1 and 7a, by X-ray diffraction analysis.