Synthesis, Characterization, and Reactivity of α-Ketoacyl Complexes of Platinum(II) and Palladium(II). Crystal Structures of trans-Pt(PPh3)2(Cl)(COCOPh) and cis-Pt(PPh3)2(COPh)(COOMe)

Article abstract of DOI:10.1021/ja00235a023

The α-ketoacyl chloro complexes, trans-M(PPh3)2(Cl)(COCOR) (M = Pt; R = Ph, 1a; R = p-FC6H4, 1b; R = p-ClC6H4, 1c; R = p-MeC6H4, 1d; R = Me, 1e.M = Pd: R = Ph, 2), were synthesized by the oxidative addition of the appropriate α-ketoacyl chloride with either Pt(PPh3)4 or Pd(PPh3)4.The crystal structure of 1a showed a square-planar geometry around the Pt with the carbonyl groups virtually coplanar and in an s-trans configuration.The above compounds were found to decompose thermally to the corresponding benzoyl compounds, trans-M(PPh3)2(Cl)(COR).A detailed kinetic study of the decarbonylation of 1a and 2 indicated the presence of two competing pathways, one of which involved the initial dissociation of a PPh3 ligand.The kinetic and thermodynamic parameters for the various steps in the mechanism were determined.For the decarbonylation of compounds 1a-d, a correlation was observed between the rate constant for the phosphine-independent pathway and ?_para.The cationic α-ketoacyl complexes, trans-Pt(PPh3)2(L)(COCOR)⁺BF4^- (R = Ph; L = CH3CN, 4a; L = CO, 4b; L = PPh3, 4c.R = Me; L = CH3CN, 4d), were prepared by Cl^- abstraction from the corresponding neutral compounds in the presence of an appropriate ligand.In the absence of any added ligand, the Cl^- abstraction from 1a resulted in rapid deinsertion of CO to form cis-Pt(PPh3)2(CO)(COPh)⁺ (5a) initially, which then slowly converted to the corresponding trans compound, 5b.The decarbonylation of 1a to the corresponding chloro benzoyl compound was catalyzed by the addition of 5b.The addition of OMe^- to 5a and 5b resulted in the formation of the acyl-alkoxycarbonyl complexes cis- and trans-Pt(PPh3)2(COPh)(COOMe), 6a and 6b, respectively.Similarly, trans-Pt(PPh3)2(COCOPh)(COOMe) (6d) was formed by the reaction of OMe^- with 4b.The crystal structure of 6a revealed a square-planar geometry around the Pt with the CoPh and COOMe groups lying in planes perpendicular to the plane of the molecule.