Methyl-and tert-butylphosphonic bis(N',N',N",N"-tetramethylguanidinide) 1 and 2 were allowed to react with various transition metal compounds. The resulting complexes were studied by IR spectroscopy, mass spectrometry and, in the case of 10, by NMR spectroscopy. In the case of the cornpounds 7-10 the metal was coordinated only via the imino nitrogen atoms of 2 (IR evidence). X-ray structure analyses were performed for [L1CoBr2], 5, L2Mn(acac), 6, L2CuC12 9, and L2PdC12 10 (L1 = 1, L2 = 2). In 5 L1 acts as an N,O bridging ligand, leading to tetrahedral coordination at Co and eightmembered (-Co-0-P-N-), rings. In 6 coordination by L2 is solely through the P=O group, occupying the apical site ot the square pyramidal (0,) geometry at Mn. In 9 and 10 L2 chelates the metal atom through two N atoms, leading to PN2M rings; the coordination geometry is distorted planar.