2-Phenoxypyridyl dinucleating ligands for assembly of diiron(II) complexes: efficient reactivity with O(2) to form (mu-Oxo)diiron(III) units.
A series of 2-phenoxypyridyl and 2-phenoxyimino ligands, H(2)L(R,R') [2,2'-(5,5'-(1,2-phenylenebis(ethyne-2,1-diyl))bis(pyridine-5,2-diyl))diphenol, where R = H, Me, or t-Bu, and R' = H or Ph] and H(2)BIPS(Me,Ph) [(3,3'-(1E,1'E)-(3,3'-sulfonylbis(3,1-phenylene)bis(azan-1-yl-1-ylidene))bis(methan-1-yl-1-ylidene)bis(5-methylbiphenyl-2-ol)], were synthesized as platforms for nonheme diiron(II) protein model complexes. UV-vis spectrophotometric studies and preparative-scale reactions of L(R,R') or BIPS(Me,Ph), where L(R,R') and BIPS(Me,Ph) are the deprotonated forms of H(2)L(R,R') and H(2)BIPS(Me,Ph), respectively, with iron(II) revealed that the presence of sterically protective o-phenol substituents is necessary to obtain discrete dinuclear species. The reaction of L(Me,Ph) with iron(II) in tetrahydrofuran (THF) afforded the doubly bridged compound [Fe(2)(L(Me,Ph))(2)(THF)(3)] (1), which was characterized in the solid state by X-ray crystallography. A large internal cavity in this complex facilitates its rapid reaction with dioxygen, even at -50 degrees C, to produce the thermodynamically stable [Fe(2)(mu-O)(L(Me,Ph))(2)] (2) species. Reaction of (18)O(2) instead of (16)O(2) with 1 led to a shift in the Fe-O-Fe vibrational frequency from 833 to 798 cm(-1), confirming the presence of the (mu-oxo)diiron(III) core and molecular oxygen as the source of the bridging oxo group. The L(Me,Ph) ligand is robust toward oxidative decomposition and does not display any reversible redox activity.
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Loi H
LH
Do
Stephen J
SJ
Lippard
D007501:Iron / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D011725:Pyridines / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet
D008024:Ligands; D009942:Organometallic Compounds; D011725:Pyridines; D007501:Iron; C023666:pyridine; D010100:Oxygen