210817-10-0Relevant academic research and scientific papers
Five-coordinate platinum(II) alkyne complexes: Synthesis, ab initio calculations and crystal and molecular structure of [PtI2(Me2phen) (η2-PhC≡CPh)]·CHCl3
Fanizzi, Francesco Paolo,Natile, Giovanni,Lanfranchi, Maurizio,Tiripicchio, Antonio,Pacchioni, Gianfranco
, p. 500 - 509 (2008/10/08)
[PtX2(Me2phen)] complexes (1) (Me2phen = 2,9-dimethyl-1,10-phenanthroline; X = Br, 1y; I, 1z), having a highly distorted square-planar geometry, undergo alkynes uptake in chlorinated solvents to give the five-coordinate trigonal-bipyramidal species [PtX2(Me2phen)-(alkyne)] (2) (alkyne = ethyne, a; propyne, b; 2-butyne, c; 1-pentyne, d; phenylacetylene, e; methylphenylacetylene, f; diphenylacetylene, g). The equilibrium constants for formation (Kf) decrease in the order (I > Br) already observed for the analogous reaction with alkenes to give the [PtX2(Me2phen) (alkene)] complexes (3) (I > Br > Cl) although the differences in Kf values are much greater in the case of alkynes. In contrast, the number and bulk of substituents at the metal-coordinated carbons have practically no effect on the Kf of the alkyne complexes, while they greatly reduce the stability of the five-coordinate olefin compounds. Finally, the ΔG of activation for rotation around the Pt-alkyne bond calculated by variable temperature 1H NMR spectroscopy (71.5 ± 0.8 kJ mol-1 for 2zb) is considerably smaller than the value found for the corresponding five-coordinate propene complex (86.2 ± 0.8 kJ mol-1). The crystal and molecular structure of the chloroform solvate of [PtI2(Me2phen) (η2-PhC≡CPh)] (2zg·CHCl3) has been determined by X-ray diffraction methods. In the crystals two crystallographically independent complexes and chloroform molecules are present: space group Cmc21, a = 14.367(3), b = 15.529(3), c = 26.959(5) A, Z = 8, R = 0.0444. The average bending back of the phenyl groups with respect to the C≡C triple bond axis is 25(1)°. Spectroscopic and crystal data show that the conformation of the coordinated alkynes in these five-coordinate complexes is intermediate between those found for the trigonal Pt(0) and the square-planar Pt(II) alkyne complexes. Ab initio Hartree-Fock calculations and constrained space orbital variation analyses have shown that in the five-coordinate species ethylene exhibits better σ-donating and π-accepting properties than acetylene.
