Selective synthesis and formation mechanisms of trans- and cis-benzoyl(carbamoyl)platinum(II) complexes coordinated with tertiary phosphine ligands

Article abstract of DOI:10.1021/om00159a033

trans-Pt(COPh)Cl(PPh₃)₂ (1) reacts with secondary amines under CO pressure (10 atm) at room temperature to give cis-Pt(COPh)(CONR₂)(PPh₃)₂ complexes (NR₂ = NMe₂ (5a), N(CH₂)₄CH₂ (5b), N(CH₂)₃CH₂ (5c), NEt₂ (5d)) exclusively, while the same amines react with trans-[Pt(COPh)(CO)(PPh₃)₂]BF₄ (7) under a nitrogen atmosphere to afford trans-Pt(COPh) (CONR₂) (PPh₃)₂ complexes (NR₂ = NMe₂ = NMe₂ (6a), N(CH₂)₄CH₂ (6b), N(CH₂)₃CH₂ (6c), NEt₂ (6d)). The isomerization of the trans-benzoylcarbamoyl complexes (6a-d) to their cis isomers (5a-d) in a neat solvent is a slow process, but the isomerization is significantly accelerated by addition of amine and CO. On the other hand, benzoylplatinum complexes coordinated with compact and basic PMe₃ ligands, trans-Pt(COPh)Cl(PMe₃)₂ (2) and trans-[Pt(COPh)(acetone)(PMe₃)₂]BF₄ (4), give trans-Pt(COPh)(CONR₂)(PMe₃)₂ (9) exclusively on treatment with CO and the secondary amines. Complex 9 is inert to isomerization to its cis isomer. Formation pathways of irons- and cis-benzoyl(carbamoyl)platinum complexes and their trans-cis isomerization process are examined in detail, and a new type of isomerization pathway involving participation of added CO and amine is proposed.