Michael T. Mock
Published: 2008
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The use of FeCl 2 (THF) 1.5 lead to the synthesis of [PhTt tB u]FeCl that provided entry into new [PhTt tBu]FeX chemistry. [PhTt tBu]FeCl crystallizes as a five-coordinate chloride bridged dimer that is a high-spin ferrous complex with an S = 2 ground state. The metathetical reaction of [PhTt tBu]FeCl with the desired dialkylmagnesium reagent, R 2 Mg (R = Me, Et, Ph, Bn), in 1,4-dioxane/THF leads to the formation of high-spin, S = 2, electronically and coordinatively unsaturated four-coordinate organoiron(II) complexes of the type, [PhTt tBu]Fe(R) (R = Me, Et, Ph, Bn). Reaction of [PhTt tBu]Fe(R) (R = Me, Et, Ph) with CO yields the low-spin, S = 0, six-coordinate complexes [PhTt tBu]Fe(CO) 2 (R) (R = Me, Et, Ph). Carbonylation of [PhTt tBu]Fe(Bn) yields [PhTt tBu]Fe(CO) 2 (Bn) and the reduced monovalent species [PhTt tBu]Fe(CO) 2 . The reduction of [PhTt tBu]FeCl in the presence of a phosphine ligand, PMe 3 or PEt 3, yields the high-spin, S = 3/2, monovalent iron complexes, [PhTt tBu]Fe(PMe 3) or [PhTt tBu]Fe(PEt 3) in moderate yields. [PhTt tBu]Fe(PMe 3) reacts with CO producing the low-spin, S = 1/2, monovalent product [PhTt tBu]Fe(CO) 2 . X-ray crystallographic analysis confirms a five-coordinate, square pyramidal coordination geometry. [PhTt tBu]Fe(PMe 3) reacts with diphenylacetylene producing the high-spin, S = 3/2 product [PhTt tBu]Fe(PhC=CPh). X-ray crystallography confirms a five-coordinate, square pyramidal coordination geometry with PhC=CPh bound to the iron center in a symmetric, side-on eta 2 binding mode. [PhTt tBu]Fe(PMe 3) reacts with adamantyl azide producing the high-spin, S = 3/2 product, [kappa 2 -PhTt tBu]Fe(N 4 Ad 2). The dialkyltetraazadiene ligand exhibits nearly identical N-N bonds suggesting a delocalized ligand radical dialkyltetraazadiene resonance form. Efforts to model a catalytically inhibited form of COdH were performed by designing a simple Ni:Fe binuclear complex that provides the essential metal coordination spheres of the C-cluster active site. The scope of these studies was expanded to include a series of cyanide-bridged binuclear complexes, ('S 3 ')Ni-CN-M[Tp tBu] (M = Fe, Co, Ni, Zn). A similar coupling scheme was used to synthesize the copper(I) analogue, Et 4 N{('S 3 ')Ni-CN-Cu[Tp tBu]}. Two synthetic strategies were employed to investigate the formation of cyanide-bridged linkage isomers. The products of two different 13 CN labeled reactions intended to yield ('S 3 ')Ni-CN-Zn[Tp tBu] and ('S 3 ')Ni-NC-Zn[Tp tBu] were analyzed. Nearly identical infrared and 13 C NMR spectroscopic data provide additional evidence that ('S 3 ')Ni-CN-Zn[Tp tBu] is produced in both reactions.