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-(-PPh2CH2C-(OH)H-)(2)](Br)(2) (1) and [cyclo-(-PCy2CH2C(OH)H-)(2)](Br)(2) (2), KOtBu, [Fe(H2O)(6)][BF4](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 PCy2H with BrCH2CH(OEt)(2). The complexes Fe{PR2CH2CH=N(2-C6H4)S}(2)FeBr2 (3a, R=Ph; 3b, R=Cy) are paramagnetic, and X-ray diffraction studies revealed that they are bimelallic, in which the S atoms of the bis-tridentate (PNS)(2)Fe unit bridge to a FeBr2 fragment. Complexes [Fe(PR2CH2CH=NC2H4PPh2)(NCMe)(3)]X-2 (4a, R=Ph; 4b, R=Cy; X-2=FeBr4 or (BF4)(2)) form when 1 equiv of iron is reacted with PPh2CH2CH2NH2 and 0.5 equiv of the appropriate phosphonium dimer. The evidence for P-N-P coordination is the large (2)JPP coupling constant in the P-31 {H-1} NMR spectrum for the trans phosphorus nuclei. If 0.5 equiv of [Fe(H2O)(6)][BF4](2) were added in the synthesis, the complex trans-[Fe(NCMe)(2)(Ph2PC2H4NH2)(2)][FeBr4] (4c) formed, and this has been characterized by X-ray diffraction. Complexes [Fe{PR2CH2CH=NCH2(2-C5H4N)}(2)]-(BPh4)(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)(PCy2CH2CH N-Q-N=CHCH2PCy2](BPh4)(2) (Q = CH2CH2, 6a; Q = (1R,2R)-cyclo-C6H10, 6b; Q=(1R,2R)-CHPhCHPh, 6c; Q=C6H4, 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.