Stol, Marianne, Snelders, Dennis J. M., Godbole, Meenal D., Havenith, Remco W. A., Haddleton, David M., Clarkson, Guy J., Lutz, Martin, Spek, Anthony L., van Klink, Gerard P. M. and van Koten, Gerard (2007) 2,6-Bis(oxazolinyl)phenylnickel(II) bromide and 2,6-bis(ketimine)phenylnickel(II) bromide: synthesis, structural features, and redox properties. Organometallics, Vol.26 (No.16). pp. 3985-3994. ISSN 0276-7333

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Abstract

2,6-Bis(oxazolinyl)phenylnickel bromide complexes [NiBr(R,R'-Phebox)] (2) were synthesized via two synthetic routes (A and B). In route A, selective bis-ortho lithiation of [R,R'-PheboxBr], followed by a transmetalation reaction with [NiBr2(PEt3)(2)], yielded not only complexes 2 with an eta(3)-mer-N,C,N'-bonded Phebox ligand but also [NiBr(R,R'-Phebox)(PEt3)(2)], 7, where the nickel center is eta(1)-C bonded to the intra-annular C-ipso of the Phebox ligand. Coordination of two PEt3 ligands completes the square-planar coordination sphere of the Ni center in 7. When R = t-Bu, R' = H, only complex 7c was formed. Alternatively, when route B (oxidative addition with [Ni(cod)(2)], cod = cyclooctadiene) was followed, selective formation of complexes 2 was observed. X-ray crystal structures were obtained for [NiBr-(i-Pr,H-Phebox)] (2b) and [NiBr(bis(ketimine)phenyl)] (3). The Ni centers have square-planar geometries with a planar, eta(3)-mer-N,C,N' coordination of the terdentate ligand systems. Complexes 2 were found to be inactive as catalysts in the atom-transfer radical polymerization (ATRP) reaction of methyl methacrylate (MMA) and in the atom-transfer radical addition (ATRA, Kharasch addition) reaction of CCl4 to MMA. This is ascribed to the relatively high oxidation potential of Ni-II-Phebox complexes, which excludes the (reversible) formation of a d(7)-Ni-III-Phebox complex, a crucial condition for subsequent reactions. Cyclovoltammetry (CV) experiments ((n-Bu)(4)NBr as supporting electrolyte) showed no electrochemical waves between -1.00 and +1.50 V (Ag/AgCl reference electrode, (n-Bu)(4)NBr as supporting electrode). Theoretical calculations showed that the energy (E-ox) needed for the oxidation reaction occurring during the CV experiments is considerably higher for [NiBr(Me,Me-Phebox)] (1.87 eV) and [NiBr(bis(ketimine)phenyl)] (1.90 eV) than for [NiBr(NCN)] (1) (1.45 eV).

Item Type:	Journal Item
Subjects:	Q Science > QD Chemistry
Divisions:	Faculty of Science > Chemistry
Journal or Publication Title:	Organometallics
Publisher:	American Chemical Society
ISSN:	0276-7333
Date:	30 July 2007
Volume:	Vol.26
Number:	No.16
Number of Pages:	10
Page Range:	pp. 3985-3994
Identification Number:	10.1021/om061055y
Status:	Peer Reviewed
Publication Status:	Published
Access rights to Published version:	Restricted or Subscription Access
URI:	http://wrap.warwick.ac.uk/id/eprint/31668

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