Alternative Reaction Pathways in Domino Reactions of Hydrazinediidozirconium Complexes with Alkynes

• Published in: Chemistry : a European journal Vol. 18; no. 13; pp. 3925 - 3941
• Main Authors: Gehrmann, Thorsten, Scholl, Solveig A., Fillol, Julio Lloret, Wadepohl, Hubert, Gade, Lutz H.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 26.03.2012; WILEY‐VCH Verlag; Wiley; Wiley Subscription Services, Inc
• Subjects: Alkynes; Chemistry; Chemistry, Multidisciplinary; CN coupling; Derivatives; domino reactions; Equivalence; Formations; Indoles; Joining; Pathways; Physical Sciences; Roads; Science & Technology; zirconium; N-N BOND; MOLECULAR-ORBITAL METHODS; C-N; TITANIUM HYDRAZIDES; alkynes; ANTI-MARKOVNIKOV HYDROAMINATION; TERMINAL ALKYNES; C?N coupling; HYDRAZIDO COMPLEXES; ALPHA CYCLOADDITION; indoles; domino reactions; CATALYZED INTERMOLECULAR HYDROAMINATION; zirconium; POLARIZATION FUNCTIONS
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201103497

Reaction of [Zr{(NAr)2Npy}(NMe2)2] (Ar=3,5‐xylyl: 2 a, mesityl: 2 b) with one or two molar equivalents of 1,1‐diphenylhydrazine gave the mixed amido/hydrazido(1−) complex [Zr{(NMes)2Npy}(HNNPh2)(NMe2)] (3), the bis‐hydrazido complex [Zr{(NMes)2Npy}(HNNPh2)2] (4), and, in the presence of excess 4‐dimethylaminopyridine (DMAP), hexacoordinate hydrazinediidozirconium complexes [Zr{(NXyl)2Npy}(NN(Me)Ph)(dmap)2] (5) and [Zr{(NXyl)2Npy}(NNPh2)(dmap)2] (6). The reaction of one equivalent of the zirconium–hydrazinediide [Zr{(NTBS)2Npy}(NNPh2)(py)] (1) with disubstituted alkynes at RT for 16 h led to the formation of seven‐membered diazazirconacycles 7 a–7 e in high yields. Similar reactivity was observed by reacting bis‐amido complex 2 b with one molar equivalent of the corresponding alkyne and diphenylhydrazine. The formation of the seven‐membered zirconacycles implied a key coupling step that involved the alkyne and one of the aryl rings of the diphenylhydrazinediido ligand. In some cases, such as the reaction with 2‐butyne, the corresponding metallacycle was only obtained in modest yields (45 % for the reaction with 2‐butyne) and a second major product, vinylimido complex 9, was formed in almost equal amounts (42 %) by 1,2‐amination (formal insertion of the alkyne). The formation of compounds 7 a and 9 followed in part the same sequence of reaction steps and a key intermediate, an azirinido complex, represented a “bifurcation point” in the reaction network. Reaction of 1.2 equivalents of several diarylhydrazines and various substituted alkynes (1 equiv) at ambient temperature (or at 80 °C) in the presence of 10 mol % [Zr{(NXyl)2Npy}(NMe2)2] (2 a) gave the corresponding indole derivatives. On the other hand, the replacement of 1,1‐diarylhydrazines by 1‐methyl‐1‐phenyl hydrazine led to head‐to‐head cis‐1,3‐enynes in good yields. A fork in the road: Azirinidozirconium species A is the key intermediate for two reaction pathways in the metal‐catalyzed coupling of diarylhydrazines and alkynes. Electrophilic metal–azirinide attack at the ortho C atom (C) affords substituted indoles.