Olefins are hydroformylated with syngas in the presence of a novel organo metallic complex catalyst to form the corresponding aldehydes at high reaction rates and improved selectivity of linear aldehydes over branched aldehydes.The novel catalyst comprises an organo metallic complex formed from a mixture of:(1) platinum (II) acetylacetonate;(2) a Group IVB metal halide; and(3) a bidentate tertiary ligand of the formula ##STR1## wherein Q is arsenic, antimony, or phosphorus; and R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are alkyl, alkoxyl, aryl, or aryloxyl groups, and may be the same or different.