would trans hydride ligands on a metal complex be beneficial for a catalyst?

Effects on reaction rates

• Steric effectsstrain – Increasing the steric strain of thechelatebackbone in square planar complexes pushes the carbonyl and methyl groups closer together, increasing the reactivity of insertion reactions.

• Oxidation state – Oxidation of the metal tends to increase insertion reaction rates. The main rate-limiting step in the mechanism is the migration of the methyl group onto a carbonyl ligand, oxidizing the metal by imparting a greater partial positive charge on the acetyl carbon, and thus increasing the rate of reaction.

• Lewis acids– Lewis acids also increase the reaction rates, for reasons similar to metal oxidation increasing the positive charge on the carbon. Lewis acids bind to the CO oxygen and remove charge, increasing the electrophilicity of the carbon. This can increase the reaction rate by a factor of up to 10⁸, and the complex formed is stable enough that the reaction proceeds even without additional CO to bind to the metal.

• Electronegativityof the leaving group - Increasing the electronegativity of the leaving alkyl group stabilizes the metal-carbon bond interaction and thus increases theactivation energyrequired for migration, decreasing the reaction rate.

• Trans-effect– Ligands in an octahedral or square planar complex are known to influence the reactivity of the group to which they aretrans-. This ligand influence is often referred to as thetrans-influence, and it varies in intensity between ligands. A partial list oftrans-influencing ligands is as follows, from highesttrans-effect to lowest:aryl, alkyl > NR₃> PR₃> AsR₃> CO >Cl. Ligands with a greatertrans-influence impart greater electrophilicity to the active site. Increasing the electrophilicity of the CO group has been shown experimentally to greatly increase the reaction rate, while decreasing the electrophilicity of the methyl group slightly increases the reaction rate. This can be demonstrated by reacting a square planar [(PN)M(CO)(CH₃)] complex with CO, where PN is abidentatephosphorus- or nitrogen-bound ligand. This reaction proceeds in much greater yield when the methyl group istrans-P and the COtrans-N, owing to the highertrans-influence of the more electronegative nitrogen.