Oxidative Addition of Halogens to Homoleptic Perfluoromethyl or Perfluorophenyl Derivatives of Platinum(II): A Comparative Study

Abstract

Chlorocarbon solvents (solv=CH(2)Cl(2), CHCl(3)) are suggested to play an active role in the oxidative addition of halogens, X(2) (X=Cl, Br, I), to homoleptic d(8) perfluoromethyl and -phenyl platinum(II) species [Pt(R(F))(4)](2-) (R(F)=CF(3), C(6)F(5)). The perfluoromethyl group, CF(3), has been found to be considerably less prone to undergo reductive elimination processes, and is, therefore, more suitable for stabilizing organoplatinum(IV) derivatives (see scheme).The equilibrium geometries of the homoleptic perfluorinated organoplatinate(II) anions [Pt(CF(3))(4)](2-) and [Pt(C(6)F(5))(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 [NBu(4)](2)[Pt(CF(3))(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 [NBu(4)](2)[trans-Pt(CF(3))(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 [NBu(4)](2)[Pt(C(6)F(5))(4)] (3) with Cl(2) or Br(2), the corresponding oxidative-addition products [NBu(4)](2)[trans-Pt(C(6)F(5))(4)X(2)] (X=Cl (14), Br (15)) can also be obtained. In the case in which X=Br and working in CHCl(3) at -55 degrees C, it has been possible to detect the formation of an intermediate species to which we assign the formula [trans-Pt(C(6)F(5))(4)Br(ClCHCl(2))](-) (16). The solvento complex 16 is thermally unstable and prone to undergo reductive elimination of C(6)F(5)--C(6)F(5). In the presence of PhCN, complex [NBu(4)][trans-Pt(C(6)F(5))(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 CF(3) 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.

Highly Trifluoromethylated Platinum Compounds

“…[18] We have recently reported [12] 2À has also been detected as a solution species by other authors. [19] A few chemical species with higher CF 3 content have been detected but not isolated in pure form.…”

“…[24] It would, therefore, be expected that the nucleophilic attack would take place at the positively charged iodine atom (Scheme 4a), much in analogy with our previous observations with halogen molecules (Scheme 4b). [12] [25] or even CF 3 À [26] (Scheme 4c). The fact that, once formed, compound 3 slowly dissociates the iodo ligand can be taken as evidence for PtÀI being the primary stable bond formed between the Pt center and the nC 4 F 9 I molecule.…”

“…[10] Different salts of the homoleptic anions [M II A C H T U N G T R E N N U N G (CF 3 ) 4 ] 2À (M II = Pd, Pt) [11,12] have been obtained by reaction of the suitable metal substrate with a nucleophilic trifluoromethylating agent-typically the five-coordinate organosilicate species [Me 3 SiA C H T U N G T R E N N U N G (CF 3 …”

Trapping a Difluorocarbene–Platinum Fragment by Base Coordination

“…The PtÀC(CF 3 ) bond lengths in 2' are insensitive to the transstanding ligand (CO vs. CF 3 ) [12] and do not appreciably differ from those observed in the precursor species 1 (average PtÀ C(CF 3 ) bond length 205.0(4) pm). [8] The n(CO) frequency in 2' is the highest within the [PtR 3 …”

“…This feature, together with the richness in reactivity made possible by the availability of d orbitals, makes them attractive as potential agents leading to C À F bond activation, [5] which is the reason why the chemistry of trifluoromethyl-transition-metal derivatives is receiving much current attention. [6,7] We have now observed that [NBu 4 ] 2 [Pt(CF 3 ) 4 ] (1) [8] undergoes a hydrolytic process to give the monocarbonyl derivative [NBu 4 ][Pt(CF 3 ) 3 (CO)] (2) in high yield (Scheme 2 B; for experimental details, see the Supporting Information). The reaction takes place under mild conditions and is effected simply by moisture.…”