We are currently developing a 2-step sol-gel route to metal oxide / phosphonate hybrid materials, based on the non-hydrolytic condensation of a metal alkoxide with a phosphonic acid, followed by hydrolysis / condensation of the remaining alkoxy groups. Several molecular intermediates in this process were obtained by reaction of Ti(OiPr)4 with phosphonic acids RPO3H2(R = Me, Ph, tBu):[Ti4(OiPr)2(tBuPO3)]4(1),[Ti4(μ3-O)(OiPr)5(μ-OiPr)3(PhPO3)3]·DMSO (2), [Ti4(μ3-O)(OiPr)5(μ-OiPr)3(MePO3)3]·DMSO (3), [Ti4(μ3-O)(OiPr)5(μ-OiPr)3(tBuPO3)3]·DMSO (4), which were characterized by single crystal X-ray structure analysis and/or NMR spectroscopy. These compounds give information on the sol-gel chemistry in our process and are structural models for the final hybrid materials. In all cases the non-hydrolytic condensation is complete, and the phosphoryl oxygen is coordinated to a titanium atom. In addition, these clusters are soluble in common organic solvents and contain hydrolyzable alkoxy groups, which make them potential building blocks in the sol gel process. Accordingly, the use of cluster 2 as a single source precursor was investigated.