Stepwise Degradation of Trifluoromethyl Platinum(II) Compounds

The action of moisture on the homoleptic organoplatinum(II) compound [NBu4]2[Pt(CF3)4] (1) gives rise to the carbonyl derivative [NBu4][Pt(CF3)3(CO)] (2), which is itself moisture stable. However, treatment of compound 2 with HCl(aq) results in the formation of [NBu4][cis‐Pt(CF3)2Cl(CO)] (3), which undergoes degradation of an additional CF3 group by further treatment with HCl(aq) in large excess, affording [NBu4][cis‐Pt(CF3)Cl2(CO)] (4). The carbonyl derivatives 2–4 are fairly stable species, in which the CO ligand, however, can be readily extruded by reaction with trimethylamine N‐oxide (ONMe3). Thus, compound 2 reacts with ONMe3 in the presence of a number of neutral or anionic ligands affording a series of singly or doubly charged derivatives with the general formulae [NBu4][Pt(CF3)3(L)] [L=CNtBu (5), PPh3 (6), P(o‐tolyl)3 (7), tht (8; tht=tetrahydrothiophene)] and [NBu4]2[Pt(CF3)3X] [X=Cl (9), Br (10), I (11)], respectively. Compound 2 also reacts with ONMe3 and pyridin‐2‐thiol (C5H5NS) giving rise to the five‐membered metallacyclic derivative [NBu4][Pt(CF3)2(CF2NC5H4S‐κC,κS)] (12), which can be viewed as a difluorocarbene species stabilized by intramolecular base coordination. On the other hand, treatment of compound 3 with ONMe3 in the presence of C5H5NS yields the four‐membered metallacyclic compound [NBu4][Pt(CF3)2(NC5H4S‐κN,κS)] (13). The geometries of the metallacycles in compounds 12 and 13 are compared. In the absence of any additional ligand, compound 3 undergoes dimerization producing the dinuclear species [NBu4]2[{Pt(CF3)2}2(μ‐Cl)2] (14). Halide ion in the latter compound with AgClO4 in THF yields the solvento compound cis‐[Pt(CF3)2(thf)2] (15). The highly labile character of the THF ligands in compound 15 makes this species a convenient synthon of the “cis‐Pt(CF3)2” unit. Step by step: Selective and stepwise degradation of CF3 groups in the homoleptic organoplatinum(II) derivative [NBu4]2[Pt(CF3)4] can be achieved by using increasingly harsher acidic conditions (Brønsted acids: H2O or HCl, see scheme). Indirect evidence for the intermediacy of the highly electrophilic [Pt]CF2 species has been attained through the isolation and structural characterization of a donor (L)‐stabilized [Pt]CF2⋅L compound.