Oxidative Addition of Halogens to Homoleptic Perfluoromethyl or Perfluorophenyl Derivatives of Platinum(II): A Comparative Study.
The equilibrium geometries of the homoleptic perfluorinated organoplatinate(II) anions [Pt(CF3)(4)](2-) and [Pt(C6F5)(4)](2-) have been computed at the B3P86/LANL2DZ level of theory. Remarkably good agreement with the experimentally determined structures has been obtained by X-ray diffraction methods. The reactivity of [NBu4](2)[Pt(CF3)(4)] (1) towards halogens (Cl-2, Br-2, and I-2) has been investigated by using a combined experimental and theoretical approach. The perfluoromethyl derivative 1. has been found to undergo clean oxidative addition of the three halogens under investigation, giving rise to [NBu4](2)[trans-Pt(CF3)(4)X-2] (X = Cl (7), Br (10), I (13)) in a quantitative and stereoselective way. In the low-temperature reaction of the perfluorophenyl derivative [NBu4](2)[Pt(C6F5)(4)] (3) with Cl-2 or Br-2, the corresponding oxidative-addition products [NBu4](2)[trans-Pt (C6F5)(4)X-2] (X = Cl (14), Br (15)) can also be obtained. In the case in which X = Br and working in CHCl3 at -55 degrees C. it has been possible to detect the formation of an intermediate species to which we assign the formula [trans-Pt(C6F5)(4)Br(ClCHCl2)](-) (16). The solvento complex 16 is thermally unstable and prone to undergo reductive elimination Of C6F5-C6F5. In the presence of PhCN, complex [NBu4][trans-Pt(C6F5)(4)Br(NCPh)] (17) was isolated and structurally characterized. The reaction of 3 with I-2 gave no organoplatinum(IV) compound. Our comparative study reveals that the CF3 group is especially suited to stabilize organometallic compounds in high oxidation states. This ability can be attributed to a combination of factors: its hardness, its high group electronegativity, its small size, and its reluctance to undergo reductive elimination processes.