Double Isocyanide Insertion and C,C-Coupling Reaction of [(C₅Me₄)SiMe₂(N-t-Bu)]ZrMe₂. Structural Characterization of the Two 1,4-Diaza-5-zirconacyclopentene Ring Conformations for [(C₅Me₄)SiMe₂(N-t-Bu)]Zr[N(R)C(Me)C(Me)N(R)] Complexes

Abstract

The reactions of 2 equiv of CNR (R = (a) tert-butyl, (b) 2,6-xylyl, (c) Me) with [(C5Me4)SiMe2(N-t-Bu)]ZrMe2, 1, proceed sequentially with isocyanide insertion into both Zr−C(methyl) bonds of this 14-electron complex to give the corresponding η2-iminoacyl Zr complexes [(C5Me4)SiMe2(N-t-Bu)]ZrMe[η2-C(Me)NR], 2, and [(C5Me4)SiMe2(N-t-Bu)]Zr[η2-C(Me)NR]2, 3. Subsequent thermolysis of 3 leads to C,C-coupling of the two η2-iminoacyl units and proceeds solely with formation of the enediamidate 4. Compounds 2a, 3a−c, and 4a−c have been observed and characterized by solution NMR measurements, and the molecular structures of 3a, 3b, 4a, and 4b have been confirmed by crystallographic methods. The nonplanar 1,4-diaza-5-zirconacyclopentene rings of 4a and 4b are folded by ca. 50° in opposite directions along the corresponding N···N line segment and adopt the prone and supine conformations, respectively. The activation parameters for the first-order intramolecular C,C-coupling reaction leading to the conversion of 3a → 4a are ΔH ⧧ = 24.6(2) kcal/mol and ΔS ⧧ = −11.3(7) eu and of 3b → 4b are ΔH ⧧ = 23.9(3) kcal/mol and ΔS ⧧ = −10.4(8) eu.

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.…”

Synthesis and reactivity of di(silylamido)cyclopentadienyl titanium and zirconium complexes

“…5) shows the titanium atom at the centre of a distorted pseudotetrahedral coordination with the five-membered TiN 2 C 2 ring of the dad ligand folded along the N(3)-N(4) axis providing the less favourable prone orientation observed for dad-Ti (dad = RN-CH@CH-NR) compounds in solution [31,32], forced by the bond to the pendant amido group, in contrast with the supine conformation reported for group 4 enediamido complexes [30][31][32][33].…”

“…Double insertion in the dialkyl derivative [Zr{g 5 -C 5 Me 4 (SiMe 2 -g-NtBu)}Me 2 ] afforded a pseudo-octahedral configuration [30] in which, one atom of the iminoacyl groups occupies the axial or the equatorial position, depending on the R substituent of the isocyanide. When R = tBu, one of the imido-N atoms is in the axial position trans to the cyclopentadienyl ring, whereas when R is a less sterically demanding group (2,6-Me 2 C 6 H 3 ), one of the imido-N fragments is located in the equatorial plane.…”

Zirconium and Hafnium Complexes with (Allylsilyl)(η‐amidosilyl)‐η5‐cyclopentadienyl Ligands: Synthesis, Structure and Reactivity

“…Therefore these insertion reactions were complete when toluene solutions of the dialkyl complexes 10-13 were treated with two equivalents of 2,6-xylyl isocyanide at room temperature to give the corresponding bis(iminoacyl) compounds [48] [M{η 5 2 Ph 17) which were isolated as red and orange oily products and identified by elemental analysis and NMR and infrared spectroscopy.…”