Multiple One-Electron Transfers in Bipyridine Complexes of Bis(phospholyl) Thulium

The synthesis of original neutral bis­(phospholyl) thulium complexes, Dtp₂Tm­(L), where L is tetramethylbiphosphinine (tmbp) and bipyridine (bipy), is reported. The electronic structures of these complexes have been investigated and it appears that, in both cases, an electron transfer occurs from the divalent metal to the ligand, a consequence of the strong reduction potential of the bis­(phospholyl) thulium fragment, Dtp₂Tm. When 1 equiv of bipyridine is added to the Dtp₂Tm­(tmbp) complex, another electron transfer occurs to form the Dtp₂Tm­(bipy) complex along with free tmbp ligand. Astonishingly, despite the apparent trivalent nature of the thulium center, the Dtp₂Tm­(bipy) complex is still reactive toward neutral bipyridine to form a new complex in which one phospholyl ligand is replaced by a bipyridine radical anion. An experimental kinetic analysis is reported to rationalize this unprecedented redox reaction with thulium and reveals an associative type of mechanism

Multiple One-Electron Transfers in Bipyridine Complexes of Bis(phospholyl) Thulium

The synthesis of original neutral bis­(phospholyl) thulium complexes, Dtp₂Tm­(L), where L is tetramethylbiphosphinine (tmbp) and bipyridine (bipy), is reported. The electronic structures of these complexes have been investigated and it appears that, in both cases, an electron transfer occurs from the divalent metal to the ligand, a consequence of the strong reduction potential of the bis­(phospholyl) thulium fragment, Dtp₂Tm. When 1 equiv of bipyridine is added to the Dtp₂Tm­(tmbp) complex, another electron transfer occurs to form the Dtp₂Tm­(bipy) complex along with free tmbp ligand. Astonishingly, despite the apparent trivalent nature of the thulium center, the Dtp₂Tm­(bipy) complex is still reactive toward neutral bipyridine to form a new complex in which one phospholyl ligand is replaced by a bipyridine radical anion. An experimental kinetic analysis is reported to rationalize this unprecedented redox reaction with thulium and reveals an associative type of mechanism

Reductive Disproportionation of CO₂ with Bulky Divalent Samarium Complexes

The base-free divalent samarium complex Cp^tt₂Sm (<b>1</b>; Cp^tt = 1,3-(^<i>t</i>Bu)₂(C₅H₃)) has been synthesized in diethyl ether by salt metathesis of SmI₂. Crystals of <b>1</b> suitable for X-ray study have been obtained by sublimation at 116 °C under reduced pressure. The dissolution of <b>1</b> in thf and pyridine solution leads to the solvent adducts Cp^tt₂Sm­(thf)₂ (<b>3</b>) and Cp^tt₂Sm­(py) (<b>4</b>), respectively, while drying <b>3</b> under reduced pressure yields Cp^ttSm­(thf) (<b>5</b>). The reaction of CO₂ with the base-free divalent samarium complexes Cp^tt₂Sm (<b>1</b>) and Cp^ttt₂Sm (<b>2</b>; Cp^ttt =1,2,4-(^<i>t</i>Bu)₃(C₅H₂)) leads to the clean formation of bridged carbonate samarium dimers [Cp^ttt₂Sm]₂(μ-CO₃) (<b>7</b>) and [Cp^tt₂Sm]₂(μ-CO₃) (<b>8</b>). This is indicative of the reductive disproportionation of CO₂ in both cases with release of CO. This contrasts with the formation of the oxalate-bridged samarium dimer reported from the reaction of CO₂ with the Cp*₂Sm­(thf)₂ complex. Otherwise, the reaction with CO does not proceed with the bulky complexes, while traces of O₂ have led to the formation of the original bridged peroxo samarium dimer [Cp^ttt₂Sm]₂(μ-O₂) (<b>6</b>). The mechanism for these reactions is studied herein by experiments and also by theoretical computations. The key result is that the different pathways are rather close in energy, which also explains why the nature of the final product, if only one is present, is difficult to <i>predict</i> a priori in this chemistry

Reductive Disproportionation of CO₂ with Bulky Divalent Samarium Complexes

The base-free divalent samarium complex Cp^tt₂Sm (<b>1</b>; Cp^tt = 1,3-(^<i>t</i>Bu)₂(C₅H₃)) has been synthesized in diethyl ether by salt metathesis of SmI₂. Crystals of <b>1</b> suitable for X-ray study have been obtained by sublimation at 116 °C under reduced pressure. The dissolution of <b>1</b> in thf and pyridine solution leads to the solvent adducts Cp^tt₂Sm­(thf)₂ (<b>3</b>) and Cp^tt₂Sm­(py) (<b>4</b>), respectively, while drying <b>3</b> under reduced pressure yields Cp^ttSm­(thf) (<b>5</b>). The reaction of CO₂ with the base-free divalent samarium complexes Cp^tt₂Sm (<b>1</b>) and Cp^ttt₂Sm (<b>2</b>; Cp^ttt =1,2,4-(^<i>t</i>Bu)₃(C₅H₂)) leads to the clean formation of bridged carbonate samarium dimers [Cp^ttt₂Sm]₂(μ-CO₃) (<b>7</b>) and [Cp^tt₂Sm]₂(μ-CO₃) (<b>8</b>). This is indicative of the reductive disproportionation of CO₂ in both cases with release of CO. This contrasts with the formation of the oxalate-bridged samarium dimer reported from the reaction of CO₂ with the Cp*₂Sm­(thf)₂ complex. Otherwise, the reaction with CO does not proceed with the bulky complexes, while traces of O₂ have led to the formation of the original bridged peroxo samarium dimer [Cp^ttt₂Sm]₂(μ-O₂) (<b>6</b>). The mechanism for these reactions is studied herein by experiments and also by theoretical computations. The key result is that the different pathways are rather close in energy, which also explains why the nature of the final product, if only one is present, is difficult to <i>predict</i> a priori in this chemistry