TY - JOUR
T1 - 2,6-Bis(oxazolinyl)phenylnickel(II) bromide and 2,6-bis(ketimine) phenylnickel(II) bromide
T2 - Synthesis, structural features, and redox properties
AU - Stol, Marianne
AU - Snelders, Dennis J.M.
AU - Godbole, Meenal D.
AU - Havenith, Remco W.A.
AU - Haddleton, David
AU - Clarkson, Guy
AU - Lutz, Martin
AU - Spek, Anthony L.
AU - Van Klink, Gerard P.M.
AU - Van Koten, Gerard
PY - 2007/7/30
Y1 - 2007/7/30
N2 - 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 η3-mer-N,C,N′-bonded Phebox ligand but also [NiBr(R,R′-Phebox)(PEt3)2], 7, where the nickel center is η1-C bonded to the intra-annular Cipso 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, η3- 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 NiII-Phebox complexes, which excludes the (reversible) formation of a d7-Ni III-Phebox complex, a crucial condition for subsequent reactions. Cyclovoltammetry (CV) experiments ((n-Bu)4NBr as supporting electrolyte) showed no electrochemical waves between -1.00 and +1.50 V (Ag/AgCl reference electrode, (n-Bu)4NBr as supporting electrode). Theoretical calculations showed that the energy (Eox) 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).
AB - 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 η3-mer-N,C,N′-bonded Phebox ligand but also [NiBr(R,R′-Phebox)(PEt3)2], 7, where the nickel center is η1-C bonded to the intra-annular Cipso 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, η3- 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 NiII-Phebox complexes, which excludes the (reversible) formation of a d7-Ni III-Phebox complex, a crucial condition for subsequent reactions. Cyclovoltammetry (CV) experiments ((n-Bu)4NBr as supporting electrolyte) showed no electrochemical waves between -1.00 and +1.50 V (Ag/AgCl reference electrode, (n-Bu)4NBr as supporting electrode). Theoretical calculations showed that the energy (Eox) 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).
UR - http://www.scopus.com/inward/record.url?scp=34547773109&partnerID=8YFLogxK
U2 - 10.1021/om061055y
DO - 10.1021/om061055y
M3 - Article
AN - SCOPUS:34547773109
SN - 0276-7333
VL - 26
SP - 3985
EP - 3994
JO - Organometallics
JF - Organometallics
IS - 16
ER -