The methyltriphenylphosphonium methylcarbonate salt [Ph3PCH3][CH3OCO2], obtained directly by quaternarization of triphenylphosphine with dimethylcarbonate, is a latent ylide that promotes Wittig vinylation of aldehydes and ketones. Alkenes are obtained simply by mixing [Ph3PCH3][CH3OCO2] and the carbonyl and heating in a solvent (no base, no halides, and no inorganic byproducts). Deuterium exchange experiments and the particularly short anion-cation distance measured by XRD in [Ph3PCH3][CH3OCO2] allowed to explain the nature and reactivity of this species. Green chemistry metrics (atom economy, mass index, environmental factor) indicate that this vinylation procedure is more efficient than comparable ones. Deuterated [Ph3PCD3][CH3OCO2] promoted the synthesis of deuterated olefins.