Preparations of Metal Trichalcogenophosphonates from Organophosphonate Esters

A new method for the preparation of metal trichalcogenophosphonates is presented wherein organophosphonate esters are first reduced with LiAlH₄ and subsequently treated with an organometallic reagent and elemental sulfur or selenium to give the desired trichalcogenophosphonate complex. Using this synthetic protocol with ^<i>n</i>BuLi as the organometallic reagent, the lithium trithiophosphonate complexes [Li₂(S₃PCH₂Ph)­(THF)­(TMEDA)]₂ (<b>1</b>) and [Li₄(S₃P^<i>n</i>Pr)₂(TMEDA)₃]_∞ (<b>3</b>), where THF = tetrahydrofuran and TMEDA = <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetramethylethylenediamine, have been prepared. In both cases, the formation of byproducts is also evident, including, for <b>1</b>, the tetrathiohypodiphosphonate complex [(PhCH₂P­(S₂))₂Li₂(THF)₄] (<b>2</b>), which has been structurally characterized. Replacement of ^<i>n</i>BuLi with ^<i>n</i>Bu₂Mg as the metallating agent led to much cleaner products and improved yields, with the new trithio- and triselenoorganophosphonate complexes [Mg­(S₃PCH₂Ph)­(TMEDA)]₂ (<b>4</b>) and [Mg­(Se₃P^<i>n</i>Pr)­(TMEDA)]₂ (<b>5</b>) reported. All trichalcogenophosphonate complexes have been structurally characterized in the solid state: <b>1</b> adopts a dimer structure in which the [PhCH₂PS₃]^2– ligand exhibits a unique μ₃-η²,η²,η²-coordination mode; <b>3</b> is polymeric comprising of [Li₄(S₃P^<i>n</i>Pr)₂(TMEDA)₂] dimers linked via additional bridging bis­(monodentate) TMEDA molecules; <b>4</b> and <b>5</b> both adopt dimeric motifs with μ₂-η²,η² coordination of the magnesium centers

Preparations of Metal Trichalcogenophosphonates from Organophosphonate Esters

A new method for the preparation of metal trichalcogenophosphonates is presented wherein organophosphonate esters are first reduced with LiAlH₄ and subsequently treated with an organometallic reagent and elemental sulfur or selenium to give the desired trichalcogenophosphonate complex. Using this synthetic protocol with ^<i>n</i>BuLi as the organometallic reagent, the lithium trithiophosphonate complexes [Li₂(S₃PCH₂Ph)­(THF)­(TMEDA)]₂ (<b>1</b>) and [Li₄(S₃P^<i>n</i>Pr)₂(TMEDA)₃]_∞ (<b>3</b>), where THF = tetrahydrofuran and TMEDA = <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetramethylethylenediamine, have been prepared. In both cases, the formation of byproducts is also evident, including, for <b>1</b>, the tetrathiohypodiphosphonate complex [(PhCH₂P­(S₂))₂Li₂(THF)₄] (<b>2</b>), which has been structurally characterized. Replacement of ^<i>n</i>BuLi with ^<i>n</i>Bu₂Mg as the metallating agent led to much cleaner products and improved yields, with the new trithio- and triselenoorganophosphonate complexes [Mg­(S₃PCH₂Ph)­(TMEDA)]₂ (<b>4</b>) and [Mg­(Se₃P^<i>n</i>Pr)­(TMEDA)]₂ (<b>5</b>) reported. All trichalcogenophosphonate complexes have been structurally characterized in the solid state: <b>1</b> adopts a dimer structure in which the [PhCH₂PS₃]^2– ligand exhibits a unique μ₃-η²,η²,η²-coordination mode; <b>3</b> is polymeric comprising of [Li₄(S₃P^<i>n</i>Pr)₂(TMEDA)₂] dimers linked via additional bridging bis­(monodentate) TMEDA molecules; <b>4</b> and <b>5</b> both adopt dimeric motifs with μ₂-η²,η² coordination of the magnesium centers

Functionalized Organocuprates: Structures of Lithium and Magnesium Grignard 2-Methoxyphenylcuprates

Lithium and magnesium Grignard diorganocuprates incorporating the functionalized aryl group 2-methoxyphenyl have been prepared and structurally characterized in the solid state. [Cu₄Li₂(C₆H₄OMe-2)₆(THF)₂] (<b>2</b>) and [Cu­(C₆H₄OCH₃-2)₂Mg­(THF)₂X] (<b>3-X</b>; X = Cl, Br) all exhibit coordination of the s-block metal center by the methoxy oxygen, resulting in the formation of novel aggregates and favoring contact ion pair structures. In contrast, separate ion pair structures had previously been observed under similar conditions for nonfunctionalized arylcuprates. The magnesium organocuprates <b>3-Cl</b> and <b>3-Br</b> are of particular interest, being rare examples of structurally characterized Grignard-derived organocuprates and the first examples of functionalized Grignard organocuprates. All reported organocuprates undergo oxidative aryl coupling in the presence of O₂ or PhNO₂ to give 2,2′-dimethoxybiphenyl

Functionalized Organocuprates: Structures of Lithium and Magnesium Grignard 2-Methoxyphenylcuprates

Lithium and magnesium Grignard diorganocuprates incorporating the functionalized aryl group 2-methoxyphenyl have been prepared and structurally characterized in the solid state. [Cu₄Li₂(C₆H₄OMe-2)₆(THF)₂] (<b>2</b>) and [Cu­(C₆H₄OCH₃-2)₂Mg­(THF)₂X] (<b>3-X</b>; X = Cl, Br) all exhibit coordination of the s-block metal center by the methoxy oxygen, resulting in the formation of novel aggregates and favoring contact ion pair structures. In contrast, separate ion pair structures had previously been observed under similar conditions for nonfunctionalized arylcuprates. The magnesium organocuprates <b>3-Cl</b> and <b>3-Br</b> are of particular interest, being rare examples of structurally characterized Grignard-derived organocuprates and the first examples of functionalized Grignard organocuprates. All reported organocuprates undergo oxidative aryl coupling in the presence of O₂ or PhNO₂ to give 2,2′-dimethoxybiphenyl

Mechanistic and Performance Studies on the Ligand-Promoted Ullmann Amination Reaction

Over the last two decades many different auxiliary ligand systems have been utilized in the copper-catalyzed Ullmann amination reaction. However, there has been little consensus on the relative merits of the varied ligands and the exact role they might play in the catalytic process. Accordingly, in this work some of the most commonly employed auxiliary ligands have been evaluated for C–N coupling using reaction progress kinetic analysis (RPKA) methodology. The results reveal not only the relative kinetic competencies of the different auxiliary ligands but also their markedly different influences on catalyst degradation rates. For the model Ullmann reaction between piperidine and iodobenzene using the soluble organic base bis­(tetra-<i>n</i>-butylphosphonium) malonate (TBPM) at room temperature, <i>N</i>-methylglycine was shown to give the best performance in terms of high catalytic rate of reaction and comparatively low catalyst deactivation rates. Further experimental and rate data indicate a common catalytic cycle for all auxiliary ligands studied, although additional off-cycle processes are observed for some of the ligands (notably phenanthroline). The ability of the auxiliary ligand, base (malonate dianion), and substrate (amine) to all act competitively as ligands for the copper center is also demonstrated. On the basis of these results an improved protocol for room-temperature copper-catalyzed C–N couplings is presented with 27 different examples reported

Mechanistic Studies on the Copper-Catalyzed N‑Arylation of Alkylamines Promoted by Organic Soluble Ionic Bases

Experimental studies on the mechanism of copper-catalyzed amination of aryl halides have been undertaken for the coupling of piperidine with iodobenzene using a Cu­(I) catalyst and the organic base tetrabutylphosphonium malonate (TBPM). The use of TBPM led to high reactivity and high conversion rates in the coupling reaction, as well as obviating any mass transfer effects. The often commonly employed O,O-chelating ligand 2-acetylcyclohexanone was surprisingly found to have a negligible effect on the reaction rate, and on the basis of NMR, calorimetric, and kinetic modeling studies, the malonate dianion in TBPM is instead postulated to act as an ancillary ligand in this system. Kinetic profiling using reaction progress kinetic analysis (RPKA) methods show the reaction rate to have a dependence on all of the reaction components in the concentration range studied, with first-order kinetics with respect to [amine], [aryl halide], and [Cu]_total. Unexpectedly, negative first-order kinetics in [TBPM] was observed. This negative rate dependence in [TBPM] can be explained by the formation of an off-cycle copper­(I) dimalonate species, which is also argued to undergo disproportionation and is thus responsible for catalyst deactivation. The key role of the amine in minimizing catalyst deactivation is also highlighted by the kinetic studies. An examination of the aryl halide activation mechanism using radical probes was undertaken, which is consistent with an oxidative addition pathway. On the basis of these findings, a more detailed mechanistic cycle for the C–N coupling is proposed, including catalyst deactivation pathways

Metal–Organic Frameworks Constructed from Group 1 Metals (Li, Na) and Silicon-Centered Linkers

A series of “light metal” metal–organic frameworks containing secondary building units (SBUs) based on Li⁺ and Na⁺ cations have been prepared using the silicon-centered linkers Me_<i>x</i>Si­(<i>p</i>-C₆H₄CO₂H)_4‑<i>x</i> (<i>x</i> = 2, 1, 0). The unipositive charge, small size, and oxophilic nature of the metal cations give rise to some unusual and unique SBUs, including a three-dimensional nodal structure built from sodium and oxygen ions when using the triacid linker (<i>x</i> = 1). The same linker with Li⁺ cations generated a chiral, helical SBU, formed from achiral starting materials. One-dimensional rod SBUs are observed for the diacid (<i>x</i> = 2) and tetra-acid (<i>x</i> = 0) linkers with both Li⁺ and Na⁺ cations, where the larger size of Na⁺ compared to Li⁺ leads to subtle differences in the constitution of the metal nodes