Aryl-containing chelates and amine debenzylation to afford 1,3-di-2-pyridyl-2-azaallyl (smif): structures of {kappa-C,N,N(py)(2)-(2-pyridylmethyl)(2)N(CH(2)(4-(t)Bu-phenyl-2-yl))}FeBr and (smif)CrN(TMS)(2).
Aryl-bromide ligand precursors have been prepared with the potential to afford tetradentate chelates (2-pyridylmethyl)(3-x)N(CH(2)-2-Aryl)(x) (x = 1, 2) containing metal-aryl linkages that promise to impart stronger fields about first row transition metals. Oxidative addition to Ni(COD)(2) afforded two diamagnetic Ni(II) complexes, {kappa-C,N,N(py)-(2-pyridylmethyl)N(CH(2)(4-(t)Bu-phenyl-2-yl))(CH(2)(4-(t)Bu-phenyl-2-Br))}NiBr (1-Ni) and {(kappa-C,N,N(py)(2)-(2-pyridylmethyl)(2)N(CH(2)(4-(t)Bu-phenyl-2-yl))}NiBr (2-Ni) in 96% and 67% yield, respectively. Extending these synthetic efforts to iron provided {kappa-C,N,N(py)(2)-(2-pyridylmethyl)(2)N(CH(2)(4-(t)Bu-phenyl-2-yl))}FeBr (2-Fe, X-ray) in 91% yield via reduction of an adduct, {kappa-N,N(py)(2)-(2-pyridylmethyl)(2)N(CH(2)(4-(t)Bu-phenyl-2-Br))}FeBr(2) (3-Fe). 5-Coordinate 2-Fe possessed a pseudo-tbp structure, and SQUID magnetometry showed it to be S = 2 with significant zero field splitting (ZFS). 2-Fe was initially prepared via oxidative addition to Fe{N(TMS)(2)}(2)(THF) upon disproportionation to "Fe(0)" and 2 Fe{N(TMS)(2)}(3), but when this approach was attempted with Cr{N(TMS)(2)}(2)(THF)(2), the azaallyl complex {kappa-N,N(py)(2)-1,3-dipyridyl-2-azaallyl}CrN(TMS)(2) ((smif)CrN(TMS)(2), 4-Cr, X-ray), formed instead (>50%) via amine debenzylation. An alternative route consisting of addition of 1,3-di-2-pyridyl-2-azapropene to Cr{N(TMS)(2)}(2)(THF)(2) afforded 4-Cr in 74% yield. Pseudo-square planar 4-Cr was also S = 2 (SQUID) with marked ZFS. The dipyridylazaallyl ligand "smif" imparts a remarkable optical density to 4-Cr via intraligand bands at 675 nm (epsilon approximately 15,000 M(-1)cm(-1)) and 396 nm (epsilon approximately 27,000 M(-1)cm(-1)). The effective fields of the chelate complexes are discussed, and a comparison of smif to isoelectronic NHC ligands is given.
Frazier
Brenda A
BA
Department of Chemistry & Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853, USA.
Wolczanski
Peter T
PT
Lobkovsky
Emil B
EB