The regioselective, platinum-catalysed hydroformylation of functionalized and non-functionalized olefins was chosen to demonstrate the great potential of room temperature liquid chlorostannate ionic liquids as solvents for homogeneous catalysis. The moderate Lewis-acidity of these ionic liquids allows the activation of the Pt-catalyst combined with tolerance of the functional groups in the substrate. Dissolved in chlorostannate ionic liquids, the Pt-catalyst shows enhanced stability and selectivity in the hydroformylation of methyl-3-pentenoate (M3P) compared to the identical reaction in conventional organic solvents. In the case of 1-octene hydroformylation, a biphasic reaction system could be realised using the chlorostannate ionic liquids as catalyst solvents. Besides the catalytic results, a method to determine the Lewis-acidity of chlorostannate ionic liquids by Sn-119 NMR is presented.