Reactivity studies of the zirconium-induced insertion of isonitriles into a 1-sila-3-zirconacyclobutane ring. Structural and chemical evidence of carbenium-like intermediates for the intramolecular 1,2-silyl shift and reductive coupling reactions

Efficient One‐Pot Synthesis of N‐Containing Heterocycles by Multicomponent Coupling of Silicon‐Tethered Diynes, Nitriles, and Isocyanides through Intramolecular Cyclization of IminoacylZr Intermediates

“…The chemical shift of the iminoacylZr carbon in 3 a was comparable with those found in Cp 2 ZrCl(C(N t Bu)C(Ph)C(PPh 2 )C≡CPh) (223.4 ppm)2a and Cp 2 ZrCl(C(N t Bu)CH 2 SiMePhC(Ph)CHPh) (228.77 ppm) 2o. The two imine carbons of the bis(iminoacyl)Zr moiety in 4 showed the respective singlets at δ =164.95 and 222.57 ppm in the 13 C NMR spectrum, which are consistent with the data for a reported bis(iminoacyl)Zr complex 3d. Compared with the mono(iminoacyl)Zr carbon in 3 a , the iminoacyl carbon in 4 (222.57 ppm) appeared to be shifted upfield in the 13 C NMR spectrum, probably owing to the electron‐withdrawing effect of the adjacent imino group.…”

“…Note that double-insertion of isocyanides into Zr À C bonds is rare, and this work represents an efficient preparation of bis(iminoacyl)ÀZr complexes. [3] These h 2 -iminoacylÀZr complexes 3 a, 3 b, 4, and 5 were all characterized by using 1 H NMR and 13 C NMR spectroscopy. The imine carbon atom neighboring the silicon in 3 a showed a singlet at d = 186.88 ppm, whereas the characteristic carbon of the h 2 -iminoacyl À Zr moiety displayed a singlet at d = 234.17 ppm in the 13 C NMR spectrum in [D 6 ]benzene, which is shifted down field.…”

“…The insertion of isocyanides into MÀC bonds is one of the powerful means for carbon chain construction, and has been utilized as a key step in organic synthesis. [1][2][3][4][5][6][7][8] The resulting h 2 -iminoacyl-metal intermediates in this process, such as h 2iminoacyl À Zr complexes, [2,3] can be conveniently converted to one-carbon elongated products such as imines, [7b] aldehydes, [7c-f] or nitriles [7g, h] through the cleavage of various chemical bonds, including Zr À C, C=N, and N-R bonds (Scheme 1 a). h 2 -IminoacylÀZr complexes also displayed other useful reactivities, including reductive elimination (Scheme 1 b), [2n] [1,2]-alkyl shift of nonacyl Zr À C bonds (Scheme 1 c), [4, 5f] and other types of rearrangements.…”

[η2-8-(tert-Butylimino)-1-naphthyl]bis(η5-cyclopentadienyl)titanium(IV)

“…A similar compound has been reported by Campora et al (1995) and a related compound with Zr by Berg & Petersen (1989).…”

η2‐Iminoacyl and η2‐Acyl Monocyclopentadienyl Tantalum Complexes Bearing Oxo and Oxo‐Borane Ligands

“…[1] For a given metal atom, the stability and further evolution of these compounds are determined by the nature of the ancillary ligands. Many reaction pathways may follow to give a broad variety of products: [1] (a) migratory insertion of a second alkyl or aryl group to give η 2 -imine or η 2 -ketene complexes; [2][3][4][5] (b) intra-or intermolecular coupling of iminoacyl or acyl units affording diaza-or dioxobutene complexes; [6,7] (c) transfer of the NR or O moieties to the metal centre; [8][9][10][11] (d) insertion of a second CNR [12][13][14][15][16] or CO [17] molecule into the new M-C bond formed after the first insertion process and (e) hydrogen migration. [18,19] We reported the results of our studies on the insertion reactions of CNR into the Ta-C(methyl) bond of monocyclopentadienyl complexes of the type [TaCp*Cl x Me 4-x ] [8][9][10] for which processes (a) and (c) were observed.…”