Monomeric oxoboranes have hitherto been detected only as short-lived species in gas-phase or low-temperature matrix experiments. Here, we report formation of the oxoboryl complex trans-[(Cy(3)P)(2)BrPt(B O)] (Cy being cyclohexyl) by means of reversible liberation of trimethylsilylbromide from the boron-bromine oxidative addition product of dibromo (trimethylsiloxy) borane and [Pt(PCy(3))(2)] in room-temperature toluene solution. The platinum complex is inert toward oligomerization, even under photolytic conditions and at elevated temperatures. The bromide was substituted by thiophenolate, and spectral parameters of both products as well as results of computational and x-ray diffraction studies are in agreement with the formulation of a triple bond between boron and oxygen. The boron-oxygen distance of 120.5(7) picometers shows a bond shortening of 7.2% as compared with a double bond, which is similar to the shortening observed in carbon-carbon analogs.