The reaction of [Pt(PCy3)2] with Br2B-CH(SiMe3)2 resulted in generation of the first alkylideneboryl complex, trans-[Br(Cy3P)2Pt{B=CH(SiMe3)}], with concomitant elimination of Me3 SiBr. The trans bromide ligand of the alkylideneboryl complex was readily substituted by a methyl group upon treatment with methyllithium, leading to another alkylideneboryl complex, trans-[Me(Cy3P)2Pt{B=CH(SiMe3)}]. Various spectrochemical techniques, single-crystal X-ray crystallography, and quantum chemical calculations confirmed the formulation of a double bond between the boron and the carbon atom. The theoretical studies also provided evidence for the stronger trans influence of the alkylideneboryl ligand over iminoboryl and oxoboryl ligands.