Addition of Nucleophiles to Phosphanido Derivatives of Pt(III): Formation of P–C, P–N, and P–O Bonds

Abstract

The reactivity of the dinuclear platinum(III) derivative [(R(F))2Pt(III)(μ-PPh2)2Pt(III)(R(F))2](Pt-Pt) (R(F) = C6F5) (1) toward OH(-), N3(-), and NCO(-) was studied. The coordination of these nucleophiles to a metal center evolves with reductive coupling or reductive elimination between a bridging diphenylphosphanido group and OH(-), N3(-), and NCO(-) or C6F5 groups and formation of P-O, P-N, or P-C bonds. The addition of OH(-) to 1 evolves with a reductive coupling with the incoming ligand, formation of a P-O bond, and the synthesis of [NBu4]2[(R(F))2Pt(II)(μ-OPPh2)(μ-PPh2)Pt(II)(R(F))2] (3). The addition of N3(-) takes place through two ways: (a) formation of the P-N bond and reductive elimination of PPh2N3 yielding [NBu4]2[(R(F))2Pt(II)(μ-N3)(μ-PPh2)Pt(II)(R(F))2] (4a) and (b) formation of the P-C bond and reductive coupling with one of the C6F5 groups yielding [NBu4][(R(F))2Pt(II)(μ-N3)(μ-PPh2)Pt(II)(R(F))(PPh2R(F))] (4b). Analogous behavior was shown in the addition of NCO(-) to 1 which afforded [NBu4]2[(R(F))2Pt(II)(μ-NCO)(μ-PPh2)Pt(II)(R(F))2] (5a) and [NBu4][(R(F))2Pt(II)(μ-NCO)(μ-PPh2)Pt(II)(R(F))(PPh2R(F))] (5b). In the reaction of the trinuclear complex [(R(F))2Pt(III)(μ-PPh2)2Pt(III)(μ-PPh2)2Pt(II)(R(F))2](Pt(III)-Pt(III)) (2) with OH(-) or N3(-), the coordination of the nucleophile takes place selectively at the central platinum(III) center, and the PPh2/OH(-) or PPh2/N3(-) reductive coupling yields the trinuclear [NBu4]2[(R(F))2Pt(II)(μ-Ph2PO)(μ-PPh2)Pt(II)(μ-PPh2)2Pt(II)(R(F))2] (6) and [NBu4][(R(F))2Pt(1)(μ3-Ph2PNPPh2)(μ-PPh2)Pt(2)(μ-PPh2)Pt(3)(R(F))2](Pt(2)-Pt(3)) (7). Complex 7 is fluxional in solution, and an equilibrium consisting of Pt-Pt bond migration was ascertained by (31)P EXSY experiments.

Synthesis and Reactivity of the Unsaturated Trinuclear Phosphanido Complex [(C6F5)2Pt(μ-PPh2)2Pt(μ-PPh2)2Pt(PPh3)]

“…In fact, while the chemical shift of Pt 1 is not greatly affected on passing from [(C 6 F 5 ) 2 Pt 1 (μ-PPh 2 ) 2 Pt 2 (μ-PPh 2 ) 2 Pt 3 (O,O-acac)] − (δ Pt 1 −3793) to the unsaturated 1 (δ Pt 1 −3712), the Pt 2 atom experienced a high shielding (from δ Pt 2 −3894 to δ Pt 2 −4720), which has already been observed upon Pt II to Pt III oxidation of phosphanido-bridged polynuclear complexes, 31 and the chemical shift of Pt 3 for 1 (δ Pt 3 −5228) is perfectly in the −5000 to −6000 ppm range of the known phosphanido-bridged Pt I complexes 2 (the chemical shift of Pt 3 in the precursor is δ Pt 3 −3159).…”

“…31 When protonation of A was carried out with [PPh 3 4 ] in a noncoordinating solvent, the pale-yellow color of the solution turned instantaneously red, and from the reaction mixture, the unsaturated trinuclear complex (46 VEC) 1 could be crystallized. The unsaturated nature of this complex requires that a Pt−Pt bond be formed.…”

“…The geometry around Pt (3) is identical with that found for phosphanidoplatinum(I) complexes bonded to terminal phosphanes (or phosphinites) and bridged by diorganophosphanides of the general formula [(PR 1 2 R 2 )Pt(μ-PR 3 2 ) 2 Pt(PR 4 2 R 5 )](Pt−Pt) (R 1 = R 2 = R 4 = R 5 = Me, R 3 = t Bu; R 1 = R 2 = R 4 = R 5 = Ph, R 3 = t Bu; 34 R 1 = R 4 = Me, R 2 = R 5 = OMe, R 3 = cyclo-C 6 H 11 ; 5 R 1 = R 2 = R 3 = R 4 = R 5 = Ph). 35 Considering that the geometry of Pt(2) is reminiscent of that of the known phosphanido-bridged Pt III atoms, i.e., Pt 1/2 in [(C 6 F 5 ) 2 Pt 1 (μ-PPh 2 ) 2 Pt 2 (C 6 F 5 ) 2 ](Pt−Pt), 10 [(C 6 F 5 ) 2 Pt 1 (μ-PPh 2 ) 2 Pt 2 (μ-PPh 2 ) 2 Pt 3 (O,O-acac)](Pt 1 −Pt 2 ) + , 31 and [(C 6 F 5 ) 2 Pt 1 (μ-PPh 2 ) 2 Pt 2 (μ-PPh 2 ) 2 Pt 3 (C 6 F 5 ) 2 ](Pt 1 −Pt 2 ), 36 On the other hand, the Pt 2 and Pt 3 signals of 1 (δ −4720 and −5228, respectively) were obtained by recording a 1 H− 195 Pt HMQC NMR spectrum (Figure 3), which was set to exploit the scalar coupling between the o-H of the phenyl rings and Pt atoms. Once the chemical shifts of each of the three 195 Pt signals were located, their fine structures were obtained by recording a 1D 195 Pt{ 1 H} NMR spectrum ( Figure S1 in the Supporting Information), which showed inter alia a coupling constant between Pt 2 and Pt 3 of 515 Hz.…”

“…In all likelihood, the saturated complexes 2 and 3 do not display M−M bonds as for [NBu 4 ][(C 6 F 5 ) 2 Pt(μ-PPh 2 ) 2 Pt(μ-PPh 2 ) 2 Pt(acac)]. 31 On the other hand, we have shown that in complex [(C 6 F 5 ) 2 Pt 1 (μ-PPh 2 ) 2 Pt 2 (PPh 3 )] (C) the μ-P−Pt 2 bond is electron-rich and reacts with electrophiles such as AgPPh 3 + , giving trinuclear complexes with the Pt−Ag bond. 39 This behavior is in full agreement with the hypothesis of the different oxidation states of Pt 1 (III) and Pt 2 (I), thus more electron-rich.…”

“…NMR spectra were recorded on a Bruker Avance 400 spectrometer with CFCl 3 , 85% H 3 PO 4 , and H 2 PtCl 6 as external references for 19 F, 31 P, and 195 Pt, respectively. Literature methods were used to prepare the starting materials [NBu 4 ][(C 6 F 5 ) 2 Pt(μ-PPh 2 ) 2 Pt(μ-PPh 2 ) 2 Pt(acac)] 31 and cis-[Pt(C 6 F 5 ) 2 (THF) 2 ]. 40 Safety Note.…”