The catalytic oxidation of cis-2-butene and propylene with molecular oxygen in the presence of a well-defined surface coordination compound, (≡SiO)2Mo(═O)2, affords acetaldehyde. Using a cis-2-butene/O2 feed at 350–400 °C, the reaction yields a conversion of approximately 10% and an acetaldehyde selectivity of approximately 70%. This performance is maintained up to an experimental time of 20 h in a continuous flow reactor. The Mo(bis-oxo) surface compound was fully characterized by multiple spectroscopic techniques as well as surface microanalysis. The results from quantum mechanics calculations indicate that the reaction proceeds via [2 + 2] cycloaddition/cycloelimination steps with the formation of metalla-oxacyclobutane intermediates, analogous to the Chauvin mechanism in olefin metathesis.