Isocyano-triphenylene complexes of gold, copper, silver and platinum. Coordination features and mesomorphic behavior

Producción CientíficaStable organometallic complexes [AuX(CN-TriPh)] [X = Cl, C6F5, C6F4O-C10H21), C6F4O- (R)-2-octyl)], [(-4,4’-C6F4C6F4){Au(CN-TriPh)}2], [AuX(CN-TriPh)], [CuCl(CN-TriPh)], trans-[PtI2(CN-TriPh)2] and [Ag(CN-TriPh)2]BF4, bearing the previously unreported triphenylene-isocyanide ligand 1-isocyano-2,3,6,7,10,11-hexadodecyloxytriphenylene (CNTriPh), have been synthesized. The coordination features of the metal ion determine their thermal behavior. The free isocyanide ligand and all of the monomeric gold derivatives display enantiotropic mesomorphic behavior over a wide range of temperature (from 5 to 220 ºC), while the copper complex, with the same stoichiometry but not isostructural with the gold complexes, melts directly to an isotropic liquid. The bis-isocyanide platinum and silver complexes also melt directly to an isotropic liquid at low temperatures. In this case, the two trans coordinated isocyanide ligands, connected by a too short linker, cannot become coplanar, which prevents the formation of a mesogenic structure. On the contrary, in the dinuclear gold complex the two isocyanide trans ligands are, due to the long Au-C6F4-C6F4-Au bridge, sufficiently separated to become coplanar and this complex gives rise to a mesophase. The structures of the mesophases were determined by small-angle X-ray scattering. All materials prepared show a fluorescent emission centered on the triphenylene coreMinisterio de Economía, Industria y Competitividad (CTQ2014-52796-P)Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA302U13

The Amide Group as Modulator of Crystalline and Liquid Crystalline Structures in Isocyano-Alkylanilide Silver(I) Complexes

Silver­(I) complexes [AgX­(CNR] and [Ag­(CNR)₂]­X (X = anionic ligand), containing an amide-functionalized isocyanide, CNR = CN–C₆H₄–NHCOR, have been synthesized and their X-ray structures have been determined for [Ag­(X)­(CN–C₆H₄–NHCOCH₃)] (X = NO₃^–, CF₃SO₃^–) and [Ag­(CN–C₆H₄–NHCOCH₃)₂]­X (X = NO₃^–, CF₃SO₃^–, BF₄^–). All the crystal structures show a packing of polymeric chains formed through Ag–OC_amide interactions. These chains associate in layers through hydrogen bonds involving the amide group, and by further interactions of the metal ion with oxygen-donor moieties. Substitution of the Me group in the amide by a nonyl chain (R = C₉H₁₉) leads to neutral [Ag­(NO₃)­(CN–C₆H₄–NHCOC₉H₁₉)] and ionic [Ag­(CN–C₆H₄–NHCOC₉H₁₉)₂]­X (X = NO₃^–, CF₃SO₃^–, H₂₅C₁₂OSO₃^–, BF₄^–) mesomorphic complexes. All of them display smectic liquid crystalline phases compatible with the crystal structures found for the methyl derivatives, and FTIR/ATR spectroscopy confirms that the intermolecular interactions observed in the solid state are preserved in the mesophase

Olefin Insertion Versus Cross-Coupling in <i>trans</i>-[Pd(Ar)X(AsPh₃)₂] Complexes (X = I, F, CF₃) Treated with a Phosphine-EWOlefin Ligand to Induce Ar–X Coupling

Addition of the coupling promoter PEWO ligand 1-(Ph₂P),2-(CHCH–C­(O)­Ph)­C₆F₄ (PhPEWO-F) to precursors with the displaceable AsPh₃ ligand <i>trans</i>-[PdXAr­(AsPh₃)₂] (X = I, F, CF₃) fails to induce the pursued Ar–F or Ar–CF₃ coupling and results in formation of products of olefin insertion into the Pd–Ar bond for X = I, CF₃, and in Ar–Ar coupling for X = F. In the course of the processes, <i>trans</i>-[PdXAr­(PhPEWO-F)­(AsPh₃)] intermediates are observed for X = I, F, CF₃, with P-coordinated PhPEWO-F monodentate ligands and a dangling olefin group. For X = I, CF₃, subsequent insertion of the double bond into the Pd–Ar bond and O-coordination gives rise to complexes with a P,C,O-pincer system. The observed insertion rates suggest that the limiting step toward insertion is the trans to cis isomerization, while insertion itself is very fast. This is supported by the fast insertion observed when PhPEWO-F is added to <i>cis</i>-[Pd­(CF₃)­Ar­(3-F-py)₂]. The insertion mechanism in PhPEWO-F resembles the initial phase of the dearomative rearrangement mechanism reported for PdArBrL (L = dialkyl biaryl phosphine)

Heterometallic Complexes by Transmetalation of Alkynyl Groups from Copper or Silver to Allyl Palladium Complexes: Demetalation Studies and Alkynyl Homocoupling

The reaction of [Pd­(η³-allyl)­ClL] (L = AsPh₃, PPh₃) with [M­(CCR)]_<i>n</i> (M = Cu, Ag; R = ⁿBu, Ph) leads to transmetalation of the alkynyl group from M to Pd. However, the group 11 metal stays η²-bound to the new Pd–alkynyl fragment and heterometallic Pd–M complexes are formed with different nuclearities depending on M: [{Pd­(η³-allyl)­(alkynyl)­L}­CuCl]₂ (<b>3</b>, <b>4</b>) or [{Pd­(η³-allyl)­(alkynyl)­L}₂AgCl] (<b>5</b>, <b>6</b>). The M-containing fragment can be eliminated to give the actual transmetalation complex [Pd­(η³-allyl)­(alkynyl)­L] by adding an excess of arsine or phosphine, whereas amines do not have this effect. Allyl–alkynyl reductive elimination is a slow process; therefore, complexes <b>3</b>–<b>6</b> cleanly decompose by dimerization (homocoupling) of the alkynyl group. In the decomposition process reversible alkynyl transmetalation from Pd to Cu has been observed

Heterometallic Complexes by Transmetalation of Alkynyl Groups from Copper or Silver to Allyl Palladium Complexes: Demetalation Studies and Alkynyl Homocoupling

The reaction of [Pd­(η³-allyl)­ClL] (L = AsPh₃, PPh₃) with [M­(CCR)]_<i>n</i> (M = Cu, Ag; R = ⁿBu, Ph) leads to transmetalation of the alkynyl group from M to Pd. However, the group 11 metal stays η²-bound to the new Pd–alkynyl fragment and heterometallic Pd–M complexes are formed with different nuclearities depending on M: [{Pd­(η³-allyl)­(alkynyl)­L}­CuCl]₂ (<b>3</b>, <b>4</b>) or [{Pd­(η³-allyl)­(alkynyl)­L}₂AgCl] (<b>5</b>, <b>6</b>). The M-containing fragment can be eliminated to give the actual transmetalation complex [Pd­(η³-allyl)­(alkynyl)­L] by adding an excess of arsine or phosphine, whereas amines do not have this effect. Allyl–alkynyl reductive elimination is a slow process; therefore, complexes <b>3</b>–<b>6</b> cleanly decompose by dimerization (homocoupling) of the alkynyl group. In the decomposition process reversible alkynyl transmetalation from Pd to Cu has been observed

Solvent-Induced Reduction of Palladium-Aryls, a Potential Interference in Pd Catalysis

The decomposition of the Pd-aryl complex (NBu₄)₂[Pd₂(μ-Br)₂Br₂(C₆F₅)₂] (<b>1</b>) to the reduction product C₆F₅H was checked in different solvents and conditions. <b>1</b> is not stable in N-alkyl amides (DMF, NMP, DMA), cyclohexanone, and diethers (1,4-dioxane, DME) at high temperatures (above 80 °C). Other solvents such as nitriles, THF, water, or toluene are safe, and no significant decomposition occurs. The solvent is the source of hydrogen, and the decomposition mechanisms have been identified by analyzing the reaction products coming from the solvent. β-H elimination involving the methyl group in a N-coordinated amide is the predominant pathway for amides. An O-coordinated diether undergoes β-H elimination and subsequent deprotonation of the resulting oxonium salt to give an enol ether. A palladium enolate from cyclohexanone leads to cyclohexenone, a reaction favored by the presence of a base. Oxygen strongly increases the extent of decomposition, and we propose this occurs by reoxidation of the Pd(0) species formed in the process and regeneration of active Pd­(II) complexes

Some Singular Features of Gold Catalysis: Protection of Gold(I) Catalysts by Substoichiometric Agents and Associated Phenomena

This study deals with two striking phenomena: the complete protection against decomposition of hypothetically monocoordinated Au^I intermediates [AuL]Y (L = strongly coordinating ligand; Y^– = poorly coordinating anion) by addition of small substoichiometric amounts (5 mol % relative to Au) of not strongly coordinating ligands (e.g., AsPh₃) and the fact that, in contrast, strongly coordinating ligands cannot provide this substoichiometric protection. The two phenomena are explained considering that (i) the existence of real monocoordinated [AuL]Y is negligible in condensed phases and the kinetically efficient existing species are dicoordinated [AuL­(W)]­Y (W = any very weakly coordinating ligand existing in solution, including OH₂, the solvent, or the Y^– anion) and (ii) these [AuL­(W)]Y intermediates give rise to decomposition by a disproportionation mechanism, via polynuclear intermediates formed by associative oligomerization with release of some W ligands. It is also shown that very small concentrations of [AuL­(W)]Y are still catalytically efficient and can be stabilized by overstoichiometric adventitious water, so that full decomposition of the catalyst is hardly reached, although eventually the stabilized concentration can be kinetically inefficient for the catalysis. These results suggest that, in cases of gold catalysis requiring the use of a significant quantity of gold catalyst, the turnover numbers can be increased or the concentration of gold catalyst widely reduced, using substoichiometric protection properly tuned to the case

Cross Alkyl–Aryl versus Homo Aryl–Aryl Coupling in Palladium-Catalyzed Coupling of Alkyl–Gold(I) and Aryl–Halide

Experiments on palladium-catalyzed cross-coupling of [AuMe­(PPh₃)] with aryl iodides show that Ar–Ar homocoupling products are the main product or an abundant byproduct of the reaction. The percentage of cross-coupling product is higher for aryls with a larger σ_p Hammet parameter. The scrambling of organic groups via bimetallic intermediates explains the formation of these products. This scrambling can be observed and the activation energies partially quantified in some cases using as aryl C₆Cl₂F₃, which is relatively reluctant to coupling

The Negishi Catalysis: Full Study of the Complications in the Transmetalation Step and Consequences for the Coupling Products

In addition to the expected products, <i>trans-</i> and <i>cis</i>-[PdRfMe­(PPh₃)₂], the transmetalation between ZnMe₂ and <i>trans</i>-[PdRfCl­(PPh₃)₂] yields [PdMeCl­(PPh₃)₂] and ZnRfMe as the result of secondary transmetalation processes. ZnRfMe is also formed by reaction of <i>trans-</i> and <i>cis</i>-[PdRfMe­(PPh₃)₂] with ZnMe₂. The different competitive reaction mechanisms that participate in the transmetalations have been studied by experiments and by DFT calculations. The relative contribution of each reaction pathway in the formation of the unwanted product ZnRfMe has been measured. The effect of excess ligand (PPh₃) on the several transmetalations has been established

Organometallic Nucleophiles and Pd: What Makes ZnMe₂ Different? Is Au Like Zn?

The <i>cis</i>/<i>trans</i> isomerization of [PdMeAr­(PR₃)₂] complexes (Ar = C₆F₅, C₆F₃Cl₂) can take place spontaneously (via dissociation and topomerization, studied experimentally) or be catalyzed by ZnMe₂. The latter mechanism, studied by DFT methods, involves methyl exchange between Pd and Zn. The study of this catalyzed isomerization shows that, in contrast with the typical acidic behavior of Zn in ZnMeCl, Zn in ZnMe₂ (or, more exactly, the ZnMe bond) behaves as a strong basic center, able to attack the relatively high in energy acceptor orbital at Pd in fairly electron rich Pd complexes such as [PdArMeL₂] or [PdMe₂L₂]. This makes the two reagents very different in Negishi couplings. The catalyzed isomerization occurs via transmetalation; thus, both processes are connected. A comparison of the Pd/Zn intermediates and transition states with those found previously for Pd/Au transmetalations reveals very similar structures with intermetallic distances in the order of or noticeably shorter than the sum of the vdW radii, regardless of the nature of the metal (metallophilic Au or nonmetallophillic Zn). These short distances are associated with the involvement of the metals in 3c2e electron deficient bonds during R group transmetalation. In this respect, there is a remarkable similarity to the structurally known behavior of main-group electron-deficient compounds, which supports a unified view of the transmetalation processes