The reaction of Ph2P(O)(OSiMe3) with [(η5-C5H5)TiCl3] or [(η5-C5Me5)TaCl4] in dichloromethane yields the complexes [(η5-C5H5)TiCl2(µ-Ph2PO2)}2] (1) or [(η5-C5Me5)TaCl3(µ-Ph2PO2)}2] (2), respectively. Structural analysis of 1 and 2 by single-crystal X-ray diffraction revealed the presence of eight-membered metallacycles consisting of bridgingbidentate diphenylphosphinate groups between two metal centers.Key words: inorganic rings, phosphinate complexes, tantalum, titanium.