110316-34-2Relevant academic research and scientific papers
Intramolecular Coupling of η2-Iminoacyl and η2-Acyl Fuctions af Group 4 and Group 5 Metal Centers: Structure and Spectroscopic Properties of the Resulting Enamidolate and Enediamide Complexes
Chamberlain, Linda R.,Durfee, Loren D.,Fanwick, Phillip E.,Kobriger, Lisa M.,Latesky, Stanley L.,et al.
, p. 6068 - 6076 (2007/10/02)
A series of group 4 and group 5 metal aryloxide compouds containing enamidolate or enediamide ligation have been prepared by the intramolecular coupling of η2-acyl and η2-iminoacyl functional groups.For the group 4 metal reaction of the mono-iminoacyl's (ArO)2M(η2-R'NCR)(R) (M = Ti, Ar = 2,6-diisopropylphenyl, R = CH2Ph; M = Zr, Ar = 2,6-di-tert-butylphenyl, R = CH2Ph) with carbon monoxide (700-1000 psi) leads directly to the corresponding enamidolate (I) with no evidence for the presumed intermediate mixed acyl, iminoacyl compound.However, the isolable bis η2-iminoacyl compounds (ArO)2M(η2-R'NCR)2 (M = Ti, Zr, Hf; ArO = 2,6-diisopropyl-, 2,6-diphenyl-,and 2,6-di-tert-butylphenyl; R = CH3, CH2Ph) only undergo intramolecular coupling to the corresponding enediamide derivatives (II) on thermolysis in hydrocarbon solvents.In contrast, attempts to prepare a bis η2-iminoacyl derivative of Ti(OAr-2,6-Ph2)2(η2-PhNCCH2SiMe3)(CH2SiMe3) (OAr-2,6Ph2 = 2,6-diphenylphenoxide) by addition of PhNC led only to the isolation of a tris-inserted, coupled complex Ti(OAr-2,6Ph2)2 (III) (R = CH2SiMe3) containig an enediamide chelate with an imine substituent on the carbon backbone.The tantalum bis η2-iminoacyl Ta(OAr-2,6Me2)3(η2-xyNCCH2Ph)2 undergoes the clean formation of the enediamide Ta(OAr-2,6Me2)3 (IV) on thermolysis at 110 deg C.Single-crystal X-ray diffraction studies on six compounds of types I, II, III, and IV have been carried out.In the enamidolate compounds Ti(OAr-2,6Pri2)2t> (Ia) and Zr(OAr-2,6-But2)2 (Ib) both molecules were found to contain a pseudotetrahedral geometry about the metal.The 5-membered metallacycle formed by the enamidolate chelate ring was found to be nonplanar with the metal atom lying out of the plane of the OC=CN backbone.Despite fold angles of 51.1 deg and 50.0 deg, respectively, solution NMR spectra indicated that inversion of the bent metallacycle was facile.For the related group 4 metal enediamide compounds Ti(OAr-2,6Pri2)2t> (IIc), Zr(OAr-2,6But2)2 (IId) and Ti(OAr-2,6Ph2)2 (III) (R = CH2SiMe3) a similar, nonplanar geometry for the chelate ring is observed.However, in this case a significant barrier (12-17 kcal mol-1) to inversion of the bent metallacycle ring is indicated by analysis of the temperature dependence of the 1H NMR spectra of compounds of type II and III.In contrast the compound Ta(OAr-2,6Me2)3 (IV) was found to contain an essentially planar metallacycle, the two nitrogen atoms of the enediamide chelate occupying one axial and one equatorial position about the 5-coordinate, trigonal-bipyramidal, metal atom.Structural parameters for all of the coupled products obtained in this study are totally consistant with them being viewed as containing enamidolate and enediamide ligands bound to TiIV, ZrIV, and TaV, d0-metal centers with little support for an alternate situation...
