New tripodal N-heterocyclic carbene chelators for small molecule activation

A review. In an effort to develop new tripodal N-heterocyclic carbene (NHC) ligands for small mol. activation, two new classes of tripodal NHC ligands TIMER and TIMENR were synthesized. The C-anchored tris(carbene) ligand system TIMER (R = Me, t-Bu) forms bi- or polynuclear metal complexes. While the Me deriv. exclusively forms trinuclear 3:2 [(TIMEMe)2M3]3+ with Group 11 metal ions, the tert-Bu deriv. yields a dinuclear 2:2 [(TIMEt-Bu)2Cu2]2+ with Cu(I). The latter complex shows both normal and abnormal carbene binding modes and accordingly, is best formulated as a bis(carbene)alkenyl complex. The N-anchored tris(carbene) ligands TIMENR (R = alkyl, aryl) bind to a variety of 1st-row transition metal ions in 1:1 stoichiometry, affording monomeric complexes with a protected reactivity cavity at the coordinated metal center. Complexes of TIMENR with Cu(I)/(II), Ni(0)/(I), and Co(I)/(II)/(III) were synthesized. The Co(I) complexes with the aryl-substituted TIMENR (R = mesityl, xylyl) ligands show great potential for small mol. activation. These complexes activate, e.g., dioxygen to form Co(III) peroxo complexes that, upon reaction with electrophilic org. substrates, transfer an O atom. The Co(I) complexes are also precursors for terminal Co(III) imido complexes. These imido complexes undergo unprecedented intramol. imido insertion reactions to form Co(II) imine species. The mol. and electronic structures of some representative metal NHC complexes as well as the nature of the metal-carbene bond of these metal NHC complexes was elucidated by x-ray and DFT computational methods and are discussed briefly. In contrast to the common assumption that NHCs are pure sigma-donors, the authors' studies revealed non-negligible and even significant pi-backbonding in electron-rich metal NHC complexes. [on SciFinder (R)]


Published in:
Journal of Organometallic Chemistry, 690, 24-25, 5474-5484
Year:
2005
Keywords:
Pi bond (back-; prepn. of tripodal N-heterocyclic carbene ; chelators and prepn. ; structure and bonding of their transition-metal complexes ; for small mol. activation); Bond (carbon-metal; prepn. of ; tripodal N-heterocyclic carbene chelators and prepn. ; structure and bonding of their transition-metal complexes ; for small mol. activation); Transition metal complexes Role: ; CAT (Catalyst use) ; MSC (Miscellaneous) ; PRP (Properties) ; RCT (Reactant) ; SPN (Synthetic preparation) ; PREP (Preparation) ; USES (Uses) ; RACT (Reactant or reagent) (first-row; prepn. of tripodal ; N-heterocyclic carbene chelators and prepn. ; structure and bonding of their transition-metal complexes ; for small mol. activation); Ligands Role: PRP (Properties) ; RCT (Reactant) ; RACT (Reactant or reagent) (multidentate ; tripodal NHC; prepn. of tripodal N-heterocyclic carbene ; chelators and prepn. ; structure and bonding of their transition-metal complexes ; for small mol. activation); Heterocyclic compounds Role: CAT ; (Catalyst use) ; MSC (Miscellaneous) ; PRP (Properties) ; RCT (Reactant) ; SPN (Synthetic preparation) ; PREP (Preparation) ; USES (Uses) ; RACT (Reactant or reagent) (nitrogen ; five-membered ; transition-metal complexes; prepn. of tripodal ; N-heterocyclic carbene chelators and prepn. ; structure and bonding of their transition-metal complexes ; for small mol. activation); Molecular structure (of tripodal ; N-heterocyclic carbene complexes); Molecular structure ; (optimized; of tripodal N-heterocyclic carbene complexes); ; Coordination compounds Role: CAT (Catalyst use) ; MSC (Miscellaneous) ; PRP (Properties) ; RCT (Reactant) ; SPN (Synthetic preparation) ; PREP (Preparation) ; USES (Uses) ; RACT (Reactant or reagent) (polynuclear; prepn. of tripodal ; N-heterocyclic carbene chelators and prepn. ; structure and bonding of their transition-metal complexes ; for small mol. activation); Chelating agents; Density ; functional theory; Electronic structure; Insertion reaction ; (prepn. of tripodal N-heterocyclic carbene chelators and prepn. ; structure and bonding of their transition-metal complexes ; for small mol. activation); Carbene complexes; Group IB ; element complexes Role: CAT (Catalyst use) ; MSC (Miscellaneous) ; PRP (Properties) ; RCT (Reactant) ; SPN (Synthetic preparation) ; PREP (Preparation) ; USES (Uses) ; RACT (Reactant or reagent) (prepn. of tripodal ; N-heterocyclic carbene chelators and prepn. ; structure and bonding of their transition-metal complexes ; for small mol. activation); Molecules (small ; activation; prepn. of tripodal N-heterocyclic carbene ; chelators and prepn. ; structure and bonding of their transition-metal complexes ; for small mol. activation) ; review tripodal nitrogen heterocyclic carbene ligand small ; mol activation; copper complex tripodal nitrogen ; heterocyclic carbene prepn structure review; cobalt complex ; tripodal nitrogen heterocyclic carbene prepn structure ; review; transition metal complex tripodal NHC prepn ; structure DFT review
Note:
CAN 144:129018 29-0 Organometallic and Organometalloidal Compounds Department of Chemistry and Biochemistry,University of California, San Diego,La Jolla,CA,USA. Journal; General Review 0022-328X written in English. 7440-48-4DP (Cobalt); 7440-50-8DP (Copper) Role: CAT (Catalyst use), MSC (Miscellaneous), PRP (Properties), RCT (Reactant), SPN (Synthetic preparation), PREP (Preparation), USES (Uses), RACT (Reactant or reagent) (prepn. of tripodal N-heterocyclic carbene chelators and prepn., structure and bonding of their transition-metal complexes for small mol. activation)
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 Record created 2007-12-17, last modified 2018-07-07


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