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

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

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

Sulfur-Assisted Phenyl Migration from Phosphorus to Platinum in PtW₂ and PtMo₂ Clusters Containing Thioether-Functionalized Short-Bite Ligands of the Bis(diphenylphosphanyl)amine-Type

The reactivity of dichloroplatinum­(II) complexes containing thioether-functionalized bis­(diphenyl­phosphanyl)­amines of formula (Ph₂P)₂N­(CH₂)₂SR (R = (CH₂)₅CH₃, CH₂Ph) toward group 6 carbonylmetalates Na­[M­(CO)₃Cp] (M = Mo or W, Cp = cyclopentadienyl) was explored. Reactions with two or more equivalents of Na­[M­(CO)₃Cp] (M = Mo or W) afforded the trinuclear complexes of general formula [PtPh­{M­(CO)₃Cp}­{μ-<i>P</i>(Ph)­N­(CH₂CH₂<i>S</i>R)­(<i>P</i>Ph₂)-κ³<i>P</i>,<i>P</i>,<i>S</i>}­M­(CO)₂Cp] (<b>3</b> M = Mo, R = (CH₂)₅CH₃; <b>4</b> M = Mo, R = CH₂Ph; <b>9</b> M = W, R = (CH₂)₅CH₃; <b>10</b> M = W, R = CH₂Ph), the structure of which consists of a six-membered platinacycle condensed with a four-membered M–P–N–P cycle, together with small amounts of isomeric PtM₂ clusters [PtM₂(CO)₅Cp₂­{(Ph₂P)₂N­(CH₂CH₂SR)-κ²<i>P</i>,<i>P</i>}] (<b>5</b> M = Mo, R = (CH₂)₅CH₃; <b>6</b> M = Mo, R = CH₂Ph; <b>11</b> M = W, R = (CH₂)₅CH₃; <b>12</b> M = W, R = CH₂Ph) in which the ligand (Ph₂P)₂NR solely chelates the Pt atom or bridges an M–Pt bond as in [PtM₂(CO)₅Cp₂­{μ-(Ph₂P)₂N­(CH₂CH₂SR)-κ²<i>P</i>,<i>P</i>}] (<b>7</b> M = Mo, R = (CH₂)₅CH₃; <b>8</b> M = Mo, R = CH₂Ph; <b>13</b> M = W, R = (CH₂)₅CH₃; <b>14</b> M = W, R = CH₂Ph). The synthesis of the trinuclear complexes <b>3</b>, <b>4</b>, <b>9</b>, and <b>10</b> entails an unexpected P-phenyl bond cleavage reaction and phenyl migration onto Pt. When only 1 equiv of Na­[M­(CO)₃Cp] (M = Mo or W) was used, the heterodinuclear products of monosubstitution [PtCl­{M­(CO)₃Cp}­{Ph₂PN­(R)­PPh₂-<i>P</i>,<i>P</i>}] (<b>15</b> M = Mo, R = (CH₂)₅CH₃; <b>16</b> M = Mo, R = CH₂Ph; <b>17</b> M = W, R = (CH₂)₅CH₃; <b>18</b> M = W, R = CH₂Ph) were obtained, which are the precursors to the bicyclic products <b>3</b>, <b>4</b>, <b>9</b>, and <b>10</b>, respectively. Density functional calculations were performed to study the thermodynamics of the formation of all the new complexes, to evaluate the relative stabilities of the isomeric chelated and bridged forms, and to trace the mechanism of formation of the phosphanido-bridged products <b>3</b>, <b>4</b>, <b>9</b>, and <b>10</b>. It was concluded that Pt­(II) complexes containing a <i>thioether</i>-functionalized short-bite ligand, [PtCl₂{Ph₂P­N­(R)­PPh₂}], react with Na­[M­(CO)₃Cp] to yield first heterodinuclear Pt–M and then heterotrinuclear PtM₂ complexes resulting from the activation of a P–C bond in one of the PPh₂ groups and phenyl migration to Pt. The critical role of an intramolecular thioether group was demonstrated