Formation of a Cationic Vinylimido Group upon C-H Activation of Nitriles by Trialkylamines in the Presence of TaCl5

Polarized Au(I)/Rh(I) bimetallic pairs cooperatively trigger ligand non-innocence and bond activation

The combination of molecular metallic fragments of contrasting Lewis character offers many possibilities for cooperative bond activation and for the disclosure of unusual reactivity. Here we provide a systematic investigation on the partnership of Lewis basic Rh(I) compounds of type [(η5-L)Rh(PR3)2] (η5-L = (C5Me5)- or (C9H7)-) with highly congested Lewis acidic Au(I) species. For the cyclopentadienyl Rh(I) compounds, we demonstrate the non-innocent role of the typically robust (C5Me5)- ligand through migration of a hydride to the Rh site and provide evidence for the direct implication of the gold fragment in this unusual bimetallic ligand activation event. This process competes with the formation of dinuclear Lewis adducts defined by a dative Rh → Au bond, with selectivity being under kinetic control and tunable by modifying the stereoelectronic and chelating properties of the phosphine ligands bound to the two metals. We provide a thorough computational study on the unusual Cp* non-innocent behavior and the divergent bimetallic pathways observed. The cooperative FLP-type reactivity of all bimetallic pairs has been investigated and computationally examined for the case of N-H bond activation in ammonia.

Differences in the Reactivity of Geminal Si-O-P and Al-O-P Frustrated Lewis Pairs

The new oxygen-bridged geminal Si/P Frustrated Lewis Pair (FLP) tBu2 P-O-Si(C2 F5 )3 (2) is able to reversibly bind carbon dioxide at ambient temperature. We compared its reactivity towards benzil, but-3-en-2-one, nitriles and phenylacetylene to that of the Al/P FLP tBu2 P-O-AlBis2 (Bis=-CH(SiMe3 )2 ) (1). When reacted with benzil, both, 1 and 2, form the 1,2-addition product, but in the Si/P FLP 2, the second carbonyl function additionally binds to the silicon atom. With but-3-en-2-one 2 forms the 1,2-addition product, while 1 binds in 1,4-position. The reaction with acetonitrile yielded an unexpected etheneimine adduct for both systems, while only 1 reacted with tert-butylnitrile. With benzonitrile and acrylonitrile, 2 showed reversible addition to the C≡N bond and 1 forms a stable adduct with benzonitrile. Solely 1 shows reactivity towards phenylacetylene affording a mixture of the CH deprotonation adduct tBu2 P(H)-O-AlBis2 (CCPh) and the FLP -C≡C 1,2-addition adduct under ring formation. All compounds were characterized by multinuclear NMR spectroscopy, XRD and elemental analysis.

Activation of Acetonitrile with (C2 F5 )3 PF2 and Amines

Acetonitrile is deprotonated by a combination of the strong Lewis acid (C₂ F₅ )₃ PF₂ and triethylamine. The resulting cyanomethyl function is bound to the phosphorus moiety, affording the highly stable salt [HNEt₃ ][P(C₂ F₅ )₃ F₂ (CH₂ CN)]. Salt metathesis reactions furnished the corresponding [Cu(MeCN)₂ ]⁺ and [Ag(MeCN)]⁺ derivatives in which the CH₂ CN substituent of the anion [P(C₂ F₅ )₃ F₂ (CH₂ CN)]^- coordinates to the metal. An investigation of the gas separation capability of the silver salt [Ag(MeCN)][P(C₂ F₅ )₃ F₂ (CH₂ CN)] shows an uptake of 1.7 equivalents of isobutene from a propane/isobutene mixture. The reaction of (C₂ F₅ )₃ PF₂ with acetonitrile and diethylamine furnishes [P(C₂ F₅ )₃ F₂ {NHC(CH₃ )NEt₂ }]-a phosphate featuring an amidine ligand which formally results from hydroamination of acetonitrile by HNEt₂ . Exchange of HNEt₂ with the primary amines H₂ NPh and H₂ NBu leads to comparable amidine salts that exhibit a solvent-dependent conformational isomerism.

Stable coordination complexes of α-diimines with Nb(v) and Ta(v) halides

Uncommon coordination compounds of high valent transition metal halides with N-aryl α-diimines have been obtained, without the need for reducing agents to quench the activation power of the metal centre.

Nucleophilic addition reactions to the ethylnitrilium derivative of nido-carborane 10-EtCN-7,8-C2B9H11

Stable imidates 10-EtC(OR)HN-7,8-C₂B₉H₁₁ and thioimidates 10-EtC(SR)HN-7,8-C₂B₉H₁₁ were synthesized via the reactions of a nitrilium derivative of nido-carborane 10-EtCN-7,8-C₂B₉H₁₁ with alcohols and thiols.

Activation of C-H Bonds of Alkyl- and Arylnitriles by the TaCl5-PPh3 Lewis Pair

A new pathway of activation of C-H bonds of alkyl- and arylnitriles by a cooperative action of TaCl₅ and PPh₃ under mild conditions is reported. Coordination of nitriles to the highly Lewis acidic Ta(V) center resulted in an activation of their aliphatic and aromatic C-H bonds, allowing nucleophilic attack and deprotonation by the relatively weak base PPh₃. The propensity of Ta(V) to form multiple bonds to nitrogen-containing ligands is an important driving force of the reaction as it led to a sequence of bond rearrangements and the emergence of, in the case of benzonitrile, a zwitterionic enediimido complex of Ta(V) through C═C double bond formation between two activated nitrile fragments. These transformations highlight the special role of the high-valent transition metal halide in substrate activation and distinguish the reactivity of the TaCl₅-PPh₃ system from both non-metal- and late transition metal-based frustrated Lewis pairs.

The reactions of α-amino acids and α-amino acid esters with high valent transition metal halides: synthesis of coordination complexes, activation processes and stabilization of α-ammonium acylchloride cations

We describe the synthesis of rare coordination compounds of early transition metals with α-amino acids and α-amino acid esters, the unusual C–C dimerization ofl-proline, and the stabilization of reactive α-ammonium acylchloride cations.