Unpredictable cycloisomerization of 1,11-dien-6-ynes by a common cobalt catalyst

1,11-Dien-6-ynes undergo cycloisomerization in the presence of the cobalt catalytic system CoBr2/phosphine ligand/Zn/ZnI2 giving cyclohexene, diene or cyclopropane structures depending on the type of the phosphine ligand. This unpredictable behaviour suggests that, although the availability of the cobalt catalytic system is appealing, the development of well-defined catalysts is desirable for further progress

Catalytic utilization of converter gas – an industrial waste for the synthesis of pharmaceuticals

Converter gas is a large scale waste product that is usually burned to carbon dioxide and contributes to the world emission of greenhouse gases. Herein we demonstrate that instead of burning the converter gas can be used as a reducing agent in organic reactions to produce valuable pharmaceuticals and agrochemicals. In particular, amide-based selected drug molecules have been synthesized by a reaction of aromatic nitro compounds and carboxylic acids in the presence of converter gas. In addition, we showed that this gas can also be conveniently utilized to carryout classical reductive amination reaction.Web of Science14164350434

(Tetramethylcyclobutadiene)cobalt Complexes with Five-Electron Carbo- and Heterocyclic Ligands

Tetramethylcyclobutadiene(cyclopentadienyl)cobalt complexes Cb*Co(C5H4R) (Cb* = η4-C4Me4; R = H (5a), Me (5b), SiMe3 (5d), C(O)H (5f), and C(O)Me (5g)) were obtained by reaction of cyclopentadienide anions either with the (carbonyl)iodide complex Cb*Co(CO)2I (1) (method A) or with the more reactive acetonitrile complex [Cb*Co(MeCN)3]+ (2) (method B). Analogous compounds Cb*CoCp* (5c), Cb*Co(1,3-C5H3(SiMe3)2) (5e), and Cb*Co(η5-indenyl) (6) can be prepared only by method B. Treatment of 5f,g with NaBH4/AlCl3 or LiAlH4 affords the alkyl derivatives 5b and 5h (R = Et) or the alcohols 5i (R = CH2OH) and 5j (R = CH(OH)Me), respectively. The reaction of 1 with fluorene/AlCl3 yields complex [Cb*Co(η6-fluorene)]+ (8), which was deprotonated by KOBut to give Cb*Co(η6-fluorenyl) (9). Visible light irradiation of 9 induces η6→η5 haptotropic rearrangement to afford Cb*Co(η5-fluorenyl) (7). The pyrrolyl and phospholyl complexes Cb*Co(C4R4N) (R = H (10a), Me (10c)) and Cb*Co(C4R4P) (R = H (11a), Me (11c); R4 = H2Me2 (11b)) were obtained by reaction of 2 with the corresponding pyrrolide or phospholide anions. Improved procedures for the preparation of the starting materials 1 and 2 were developed. Using a one-pot procedure, the iodide 1 was obtained in high yield from 2-butyne and Co2(CO)8. Complex 2 was prepared by heating or irradiation of the toluene complex [Cb*Co(C6H5Me)]+ (4b) in acetonitrile. Structures of 5g, 6, and 11c were investigated by X-ray diffraction. Electrochemistry and joint UV−visible and EPR spectroelectrochemistry of complexes prepared were studied

Cyclobutadiene Metal Complexes: A New Class of Highly Selective Catalysts. An Application to Direct Reductive Amination

A catalyst of a new type, cyclobutadiene complex [(C₄Et₄)­Rh­(<i>p</i>-xylene)]­PF₆, was found to promote selective reductive amination in the presence of carbon monoxide under mild conditions (1–3 bar, 90 °C). The reaction demonstrated perfect compatibility with a wide range of functional groups prone to reduction by conventional reducing agents. The developed system represents the first systematic investigation of cyclobutadiene metal complexes as catalysts

Unprecedented steric deformation of ortho-carborane

The reduction and subsequent oxidation of meta-carboranes containing bulky groups attached to the cage C atoms affords sterically-crowded ortho-carboranes with unprecedentedly long C-C connectivities..</p

Cyclobutadiene Arene Complexes of Rhodium and Iridium

Reactions of [(C₂H₄)₂RhCl]₂ or [(coe)₂RhCl]₂ (coe = cyclooctene) with AgPF₆ and arenes, followed by addition of 3-hexyne, give the cyclobutadiene complexes [(C₄Et₄)­Rh­(arene)]⁺ in 40–65% yield (arene = <i>tert</i>-butylbenzene, <i>p</i>-xylene, mesitylene, 4-mesitylbutanoic acid). In the absence of arenes, the hexaethylbenzene complex [(C₄Et₄)­Rh­(C₆Et₆)]⁺ is formed in 70% yield as a result of cyclotrimerization of 3-hexyne in the coordination sphere of rhodium. Similar reaction of [(coe)₂IrCl]₂ with AgPF₆ and 3-hexyne leads to [(C₄Et₄)­Ir­(C₆Et₆)]⁺, which is apparently the first reported cyclobutadiene iridium complex. DFT calculations suggest that formation of the model cyclobutadiene complex [(C₄Me₄)­Rh­(C₆H₆)]⁺ from bis­(alkyne) intermediate [(C₂Me₂)₂Rh­(C₆H₆)]⁺ can proceed via a metallacycle transition state with a low energy barrier of 14.5 kcal mol^–1

Synthesis of 13-vertex dimetallacarboranes by electrophilic insertion into 12-vertex ruthenacarboranes

The electrophilic insertion of organometallic species into metallacarboranes was studied in detail for the model compound-the 12-vertex closo-ruthenacarborane anion [Cp∗Ru(C2B9H11)]- (1). Reactions of the anion 1 with the 12-electron cationic species [M(ring)]+ (M(ring) = RuCp, RuCp∗ and Co(C4Me4)) gave the 13-vertex closo-dimetallacarboranes Cp∗Ru(C2B9H11)M(ring). Similar reactions of the neutral ruthenacarborane Cp∗Ru(Me2S-C2B9H10) produce the cationic dimetallacarboranes [Cp∗Ru(Me2S-C2B9H10)M(ring)]+. The symmetrical 13-vertex diruthenacarboranes (C5R5)Ru(R2C2B9H9)Ru(C5R5) can be prepared by the direct reactions of Tl2[7,8-R2-7,8-C2B9H9] (R = H and Me) with two equivalents of [CpRu(MeCN)3]+ or [Cp∗RuCl]4. The insertions of the 14-electron cationic species [M(ring)]+ (M(ring) = NiCp, NiCp∗ and Co(C6Me6)) into 1 gave the 13-vertex dimetallacarboranes Cp∗Ru(C2B9H11)M(ring), which have a distorted framework with one open face. The structures of Cp∗Ru(C2B9H11)Co(C4Me4) and Cp∗Ru(C2B9H11)NiCp were established by X-ray diffraction. Some of the 13-vertex dimetallacarboranes have two electrons less than required by Wade's rules. This violation is explained by the absence of the appropriate pathway for the distortion of the framework