Template Synthesis of Iron(II) Complexes Containing Tridentate P−N−S, P−N−P, P−N−N, and Tetradentate P−N−N−P Ligands

Abstract

A series of mer-tridentate iron(II) complexes bearing P-N-S (3), P-N-P (4), and P-N-N (5) ligands have been prepared via the metal template effect in one pot involving air-stable phosphonium dimers [cyclo-(-PPh(2)CH(2)C(OH)H-)(2)](Br)(2) (1) and [cyclo-(-PCy(2)CH(2)C(OH)H-)(2)](Br)(2) (2), KOtBu, [Fe(H(2)O)(6)][BF(4)](2) and 2-aminothiolphenol (for 3), 2-(diphenylphosphino)ethylamine (for 4), and 2-(aminomethyl)pyridine (for 5). The new phosphonium dimer 2 was prepared via an S(N)2 reaction of PCy(2)H with BrCH(2)CH(OEt)(2). The complexes Fe{PR(2)CH(2)CH=N(2-C(6)H(4))S}(2)FeBr(2) (3a, R = Ph; 3b, R = Cy) are paramagnetic, and X-ray diffraction studies revealed that they are bimetallic, in which the S atoms of the bis-tridentate (PNS)(2)Fe unit bridge to a FeBr(2) fragment. Complexes [Fe(PR(2)CH(2)CH=NC(2)H(4)PPh(2))(NCMe)(3)]X(2) (4a, R = Ph; 4b, R = Cy; X(2) = FeBr(4) or (BF(4))(2)) form when 1 equiv of iron is reacted with PPh(2)CH(2)CH(2)NH(2) and 0.5 equiv of the appropriate phosphonium dimer. The evidence for P-N-P coordination is the large (2)J(PP) coupling constant in the (31)P {(1)H} NMR spectrum for the trans phosphorus nuclei. If 0.5 equiv of [Fe(H(2)O)(6)][BF(4)](2) were added in the synthesis, the complex trans-[Fe(NCMe)(2)(Ph(2)PC(2)H(4)NH(2))(2)][FeBr(4)] (4c) formed, and this has been characterized by X-ray diffraction. Complexes [Fe{PR(2)CH(2)CH=NCH(2)(2-C(5)H(4)N)}(2)](BPh(4))(2) (5) are bis-tridentate iron(II) complexes with pyridyl donors trans to the phosphine donors. Interestingly, addition of the diamines ethylenediamine, (1R,2R)-(-)-1,2-diaminocyclohexane, (1R,2R)-(-)-1,2-diphenylethylenediamine, or o-phenylenediamine, in the template synthesis with 2 led directly to tetradentate P-N-N-P iron(II) complexes trans-[Fe(NCMe)(2)(PCy(2)CH(2)CH=N-Q-N=CHCH(2)PCy(2)](BPh(4))(2) (Q = CH(2)CH(2), 6a; Q = (1R,2R)-cyclo-C(6)H(10), 6b; Q = (1R,2R)-CHPhCHPh, 6c; Q = C(6)H(4), 6d). In contrast, similar reactions under the same conditions with dimer 1 led to complexes mer-[Fe(P-N-N)(2)](2+) as reported previously. Complexes 6a and 6b have been characterized by X-ray diffraction and exhibited large P-Fe-P bond angles of 112.92(2) and 111.96(4) degrees, respectively.