Solvent-Driven P–S vs P–C Bond Formation from a Diplatinum(III) Complex and Sulfur-Based Anions

The outcome of the reaction of the Pt­(III),Pt­(III) complex [(C₆F₅)₂Pt^III(μ-PPh₂)₂Pt^III(C₆F₅)₂]­(<i>Pt–Pt</i>) (<b>1</b>) with the S-based anions thiophenoxide (PhS^–), ethyl xanthogenate (EtOCS₂^–), 2-mercaptopyrimidinate (pymS^–), and 2-mercaptopyridinate (pyS^–) was found to be dependent on the reaction solvent. The reactions carried out in acetone led to the formation of [NⁿBu₄]­[(R_F)₂Pt^II(μ-PhS-PPh₂)­(μ-PPh₂)­Pt^II(R_F)₂] (<b>2</b>), [NⁿBu₄]­[(R_F)₂Pt^II(μ-EtOCS₂-PPh₂)­(μ-PPh₂)­Pt^II(R_F)₂] (<b>3</b>), [NⁿBu₄]­[(R_F)₂Pt^II(μ-pymS-PPh₂)­(μ-PPh₂)­Pt^II(R_F)₂] (<b>4</b>), and [NⁿBu₄]­[(R_F)₂Pt^II(μ-pyS–PPh₂)­(μ-PPh₂)­Pt^II(R_F)₂] (<b>5</b>), respectively (R_F = C₆F₅). Complexes <b>2</b>–<b>5</b> display new Ph₂P­(SL) ligands exhibiting a κ²-<i>P</i>,<i>S</i> bridging coordination mode, which is derived from a reductive elimination of a PPh₂ group and the S-based anion. Carrying out the reaction in dichloromethane afforded, in the cases of EtOCS₂^– and pymS^–, the monobridged complexes [NⁿBu₄]­[(PPh₂R_F)­(R_F)₂Pt^II(μ-PPh₂)­Pt^II(EtOCS₂)­(R_F)] (<b>6</b>) and [NⁿBu₄]­[(PPh₂R_F)­(R_F)₂Pt^II(μ-PPh₂)­Pt^II(pymS)­(R_F)] (<b>7</b>), respectively, which are derived from reductive elimination of a PPh₂ group with a pentafluorophenyl ring. The reaction of <b>1</b> with EtOCS₂K in acetonitrile yielded a mixture of <b>3</b> and <b>6</b> as a consequence of the concurrence of two processes: (a) the formation of <b>3</b> by a reaction that parallels the formation of <b>3</b> by <b>1</b> plus EtOCS₂K in acetone and (b) the transformation of <b>1</b> into the neutral complex [(PPh₂R_F)­(CH₃CN)­(R_F)­Pt^II(μ-PPh₂)­Pt^II(R_F)₂(CH₃CN)] (<b>8</b>), which, in turn, reacts with EtOCS₂K to give <b>6</b>. The <b>1</b> to <b>8</b> transformation was found to be fully reversible. In fact, dissolving <b>8</b> in acetone or dichloromethane afforded pure <b>1</b> after solvent evaporation or crystallization with <i>n</i>-hexane. The XRD structures of <b>2</b>–<b>4</b> and <b>6</b>–<b>8</b> were determined, and the behavior in solution of the new complexes is discussed

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

The reaction of [NBu₄]­[(C₆F₅)₂Pt­(μ-PPh₂)₂Pt­(μ-PPh₂)₂Pt­(<i>O</i>,<i>O</i>-acac)] (48 VEC) with [HPPh₃]­[ClO₄] gives the 46 VEC unsaturated [(C₆F₅)₂Pt¹(μ-PPh₂)₂Pt²(μ-PPh₂)₂Pt³(PPh₃)]­(Pt²–Pt³) (<b>1</b>), a trinuclear compound endowed with a Pt–Pt bond. This compound displays amphiphilic behavior and reacts easily with nucleophiles L, yielding the saturated complexes [(C₆F₅)₂Pt^II(μ-PPh₂)₂Pt^II(μ-PPh₂)₂Pt^II(PPh₃)­L] [L = PPh₃ (<b>2</b>), py (<b>3</b>)]. The reaction with the electrophile [Ag­(OClO₃)­PPh₃] affords the adduct <b>1</b>·AgPPh₃, which evolves, even at low temperature, to a mixture in which [(C₆F₅)₂Pt^III(μ-PPh₂)₂Pt^III(μ-PPh₂)₂Pt^II(PPh₃)₂]²⁺(Pt^III–Pt^III) and <b>2</b> (plus silver metal) are present. The nucleophilic nature of <b>1</b> is also demonstrated through its reaction with <i>cis</i>-[Pt­(C₆F₅)₂(THF)₂], which results in the formation of [Pt₄(μ-PPh₂)₄(C₆F₅)₄(PPh₃)] (<b>4</b>). The structure and NMR features indicate that <b>1</b> can be better considered as a Pt^II–Pt^III–Pt^I complex instead of a Pt^II–Pt^II–Pt^II derivative. Theoretical calculations (density functional theory) on similar model compounds are in agreement with the assigned oxidation states of the metal centers. The strong intermetallic interactions resulting in a Pt²–Pt³ metal–metal bond and the respective bonding mechanism were verified by employing a multitude of computational techniques (natural bond order analysis, the Laplacian of the electron density, and localized orbital locator profiles)

Multinuclear Solid-State NMR and DFT Studies on Phosphanido-Bridged Diplatinum Complexes

Multinuclear (³¹P, ¹⁹⁵Pt, ¹⁹F) solid-state NMR experiments on (<i>n</i>Bu₄N)₂[(C₆F₅)₂Pt­(μ-PPh₂)₂Pt­(C₆F₅)₂] (<b>1</b>), [(C₆F₅)₂Pt­(μ-PPh₂)₂Pt­(C₆F₅)₂]­(<i>Pt–Pt</i>) (<b>2</b>), and <i>cis</i>-Pt­(C₆F₅)₂(PHPh₂)₂ (<b>3</b>) were carried out under cross-polarization/magic-angle-spinning conditions or with the cross-polarization/Carr–Purcell Meiboom–Gill pulse sequence. Analysis of the principal components of the ³¹P and ¹⁹⁵Pt chemical shift (CS) tensors of <b>1</b> and <b>2</b> reveals that the variations observed comparing the isotropic chemical shifts of <b>1</b> and <b>2</b>, commonly referred to as “ring effect”, are mainly due to changes in the principal components oriented along the direction perpendicular to the Pt₂P₂ plane. DFT calculations of ³¹P and ¹⁹⁵Pt CS tensors confirmed the tensor orientation proposed from experimental data and symmetry arguments and revealed that the different values of the isotropic shieldings stem from differences in the paramagnetic and spin–orbit contributions

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

The reaction of [NBu₄]­[(C₆F₅)₂Pt­(μ-PPh₂)₂Pt­(μ-PPh₂)₂Pt­(<i>O</i>,<i>O</i>-acac)] (48 VEC) with [HPPh₃]­[ClO₄] gives the 46 VEC unsaturated [(C₆F₅)₂Pt¹(μ-PPh₂)₂Pt²(μ-PPh₂)₂Pt³(PPh₃)]­(Pt²–Pt³) (<b>1</b>), a trinuclear compound endowed with a Pt–Pt bond. This compound displays amphiphilic behavior and reacts easily with nucleophiles L, yielding the saturated complexes [(C₆F₅)₂Pt^II(μ-PPh₂)₂Pt^II(μ-PPh₂)₂Pt^II(PPh₃)­L] [L = PPh₃ (<b>2</b>), py (<b>3</b>)]. The reaction with the electrophile [Ag­(OClO₃)­PPh₃] affords the adduct <b>1</b>·AgPPh₃, which evolves, even at low temperature, to a mixture in which [(C₆F₅)₂Pt^III(μ-PPh₂)₂Pt^III(μ-PPh₂)₂Pt^II(PPh₃)₂]²⁺(Pt^III–Pt^III) and <b>2</b> (plus silver metal) are present. The nucleophilic nature of <b>1</b> is also demonstrated through its reaction with <i>cis</i>-[Pt­(C₆F₅)₂(THF)₂], which results in the formation of [Pt₄(μ-PPh₂)₄(C₆F₅)₄(PPh₃)] (<b>4</b>). The structure and NMR features indicate that <b>1</b> can be better considered as a Pt^II–Pt^III–Pt^I complex instead of a Pt^II–Pt^II–Pt^II derivative. Theoretical calculations (density functional theory) on similar model compounds are in agreement with the assigned oxidation states of the metal centers. The strong intermetallic interactions resulting in a Pt²–Pt³ metal–metal bond and the respective bonding mechanism were verified by employing a multitude of computational techniques (natural bond order analysis, the Laplacian of the electron density, and localized orbital locator profiles)

Formation of P–C Bond through Reductive Coupling between Bridging Phosphido and Benzoquinolinate Groups. Isolation of Complexes of the Pt(II)/Pt(IV)/Pt(II) Sequence

The rational synthesis of dinuclear asymmetric phosphanido derivatives of palladium and platinum­(II), [NBu₄]­[(R_F)₂M­(μ-PPh₂)₂M′(κ²,<i>N</i>,<i>C</i>-C₁₃H₈N)] (R_F = C₆F₅; M = M′ = Pt, <b>1</b>; M = Pt, M′ = Pd, <b>2</b>; M = Pd, M′ = Pt, <b>3</b>; M = M′ = Pd, <b>4</b>), is described. Addition of I₂ to <b>1</b>–<b>4</b> gives complexes [(R_F)₂M^II(μ-PPh₂)­(μ-I)­Pd^II{PPh₂(C₁₃H₈N)}] (M = M′ = Pt, <b>6</b>; M = Pt, M′ = Pd, <b>7</b>; M = M′ = Pd, <b>8</b>; M = Pd, M′ = Pt <b>10</b>) which contain the aminophosphane PPh₂(C₁₃H₈N) ligand formed through a Ph₂P/C^∧N reductive coupling on the mixed valence M­(II)–M′(IV) [NBu₄]­[(R_F)₂M^II(μ-PPh₂)₂M′^IV(κ²,<i>N</i>,<i>C</i>- C₁₃H₈N)­I₂] complexes, which were identified for M^II = Pd, M′^IV = Pt (<b>9</b>), and isolated for M^II = Pt, M′^IV = Pt (<b>5</b>). Complex <b>5</b> showed an unusual dynamic behavior consisting in the exchange of two phenyl groups bonded to different P atoms, as well as a “through space” spin–spin coupling between <i>ortho</i>-F atoms of the pentafluorophenyl rings

Oxidatively Induced P–O Bond Formation through Reductive Coupling between Phosphido and Acetylacetonate, 8‑Hydroxyquinolinate, and Picolinate Groups

The dinuclear anionic complexes [NBu₄]­[(R_F)₂M^II(μ-PPh₂)₂M′^II(N^∧O)] (R_F = C₆F₅. N^∧O = 8-hydroxyquinolinate, hq; M = M′ = Pt <b>1</b>; Pd <b>2</b>; M = Pt, M′ = Pd, <b>3</b>. N^∧O = <i>o</i>-picolinate, pic; M = Pt, M′ = Pt, <b>4</b>; Pd, <b>5</b>) are synthesized from the tetranuclear [NBu₄]₂[{(R_F)₂Pt­(μ-PPh₂)₂M­(μ-Cl)}₂] by the elimination of the bridging Cl as AgCl in acetone, and coordination of the corresponding <i>N</i>,<i>O</i>-donor ligand (<b>1</b>, <b>4</b>, and <b>5</b>) or connecting the fragments “<i>cis</i>-[(R_F)₂M­(μ-PPh₂)₂]^2–” and “M′(N^∧O)” (<b>2</b> and <b>3</b>). The electrochemical oxidation of the anionic complexes <b>1</b>–<b>5</b> occurring under HRMS­(+) conditions gave the cations [(R_F)₂M­(μ-PPh₂)₂M′(N^∧O)]⁺, presumably endowed with a M­(III),M′(III) core. The oxidative addition of I₂ to the 8-hydroxyquinolinate complexes <b>1</b>–<b>3</b> triggers a reductive coupling between a PPh₂ bridging ligand and the <i>N</i>,<i>O</i>-donor chelate ligand with formation of a P–O bond and ends up in complexes of platinum­(II) or palladium­(II) of formula [(R_F)₂M^II(μ-I)­(μ-PPh₂)­M′^II(<i>P</i>,<i>N</i>-PPh₂hq)], M = M′ = Pt <b>7</b>, Pd <b>8</b>; M = Pt, M′ = Pd, <b>9</b>. Complexes <b>7</b>–<b>9</b> show a new Ph₂P-OC₉H₆N (Ph₂P-hq) ligand bonded to the metal center in a <i>P</i>,<i>N</i>-chelate mode. Analogously, the addition of I₂ to solutions of the <i>o</i>-picolinate complexes <b>4</b> and <b>5</b> causes the reductive coupling between a PPh₂ bridging ligand and the starting <i>N</i>,<i>O</i>-donor chelate ligand with formation of a P–O bond, forming Ph₂P-OC₆H₄NO (Ph₂P-pic). In these cases, the isolated derivatives [NBu₄]­[(Ph₂P-pic)­(R_F)­Pt^II(μ-I)­(μ-PPh₂)­M^II(R_F)­I] (M = Pt <b>10</b>, Pd <b>11</b>) are anionic, as a consequence of the coordination of the resulting new phosphane ligand (Ph₂P-pic) as monodentate <i>P</i>-donor, and a terminal iodo group to the M atom. The oxidative addition of I₂ to [NBu₄]­[(R_F)₂Pt^II(μ-PPh₂)₂Pt^II(acac)] (<b>6</b>) (acac = acetylacetonate) also results in a reductive coupling between the diphenylphosphanido and the acetylacetonate ligand with formation of a P–O bond and synthesis of the complex [NBu₄]­[(R_F)₂Pt^II(μ-I)­(μ-PPh₂)­Pt^II(Ph₂P-acac)­I] (<b>12</b>). The transformations of the starting complexes into the products containing the P–O ligands passes through mixed valence M­(II),M′(IV) intermediates which were detected, for M = M′ = Pt, by spectroscopic and spectrometric measurements

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

The reactivity of the dinuclear platinum­(III) derivative [(R_F)₂Pt^III(μ-PPh₂)₂­Pt^III(R_F)₂]<i>(Pt–Pt)</i> (R_F = C₆F₅) (<b>1</b>) 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 <b>1</b> 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] (<b>3</b>). 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] (<b>4a</b>) 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)] (<b>4b</b>). Analogous behavior was shown in the addition of NCO^– to <b>1</b> which afforded [NBu₄]₂[(R_F)₂Pt^II(μ-NCO)­(μ-PPh₂)­Pt^II(R_F)₂] (<b>5a</b>) and [NBu₄]­[(R_F)₂Pt^II(μ-NCO)­(μ-PPh₂)­Pt^II(R_F)­(PPh₂R_F)] (<b>5b</b>). In the reaction of the trinuclear complex [(R_F)₂Pt^III(μ-PPh₂)₂Pt^III(μ-PPh₂)₂­Pt^II(R_F)₂]<i>(Pt</i>^<i>III</i><i>–Pt</i>^<i>III</i><i>)</i> (<b>2</b>) 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] (<b>6</b>) and [NBu₄]­[(R_F)₂Pt¹(μ₃-Ph₂PNPPh₂)­(μ-PPh₂)­Pt²(μ-PPh₂)­Pt³(R_F)₂]<i>(Pt</i>^<i>2</i><i>–Pt</i>^<i>3</i><i>)</i> (<b>7</b>). Complex <b>7</b> is fluxional in solution, and an equilibrium consisting of Pt–Pt bond migration was ascertained by ³¹P EXSY experiments