A process for the minimization of phosphonium ion ligand degradation products formed during reaction of a polyunsaturated olefin or an unconjugated functionalized olefin in the presence of a transition metal-triorganophosphine ligand complex catalyst to form as a product, by-product, or intermediate product a conjugated functionalized olefin having a carbon-carbon double bond conjugated to an .alpha.-electron-withdrawing group, such as, an .alpha.,.beta.-unsaturated aldehyde, ketone, ester, acid, or nitrile. The minimization process involves conducting the reaction under selected conditions of conversion, temperature, pressure, or a combination thereof; and/or by selecting a triorganophosphine ligand with a specified steric and/or electronic property. Further, a process for reversion of phosphonium ion ligand degradation product(s) back to useful triorganophosphine ligand(s), the reversion involving treating a reaction product fluid containing the degradation product(s) with an inert gas, hydrogen, synthesis gas, or a mixture thereof under conditions sufficient to regenerate the triorganophosphine ligand(s).