Two neutral and two cationic half-sandwich Os(II)-arene metallodendrimers, of general formula [DAB-PPI-{(eta(6)-p-cym)Os((C7H5NO)-kappa(2)-N,O)Cl}(n)] and [DAB-PPI-{(eta(6)-p-cym)Os((C6H5N2)-kappa(2)-N,N)Cl}(n)]PF6 (where n = 4 (G1) or 8 (G2)) have been synthesised. In addition, two cationic half-sandwich Os(II)-arene metallodendrimers, containing PTA (1,3,5-triaza-7-phosphatricyclo[3.3.1.1.] decane), of general formula [DAB-PPI-{(eta(6)-p-cym)Os((C7H5NO)-kappa(2)-N,O)PTA}(n)]PF6 are also reported. All complexes have been characterised using analytical (i.e. HR-ESI or EI mass spectrometry and elemental analysis) and spectroscopic (i.e. H-1, C-13{H-1} NMR and infrared) methods. Model mononuclear analogues have been prepared and their molecular structures determined by single-crystal X-ray crystallography. The cytotoxicity of the complexes were evaluated against the A2780 and A2780cisR human ovarian carcinoma cell lines and some display moderate activity. (C) 2013 Elsevier B. V. All rights reserved.