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The synthesis and crystal structure of cis-Fe(BPE5)2Cl2 (BPE5 = 1,2-diphospholanoethane), the first symmetrical cis-Fe(PP)2Cl2 (PP = bidentate phosphine), is reported (monoclinic, P21/n, a = 12.084(3) Å, b = 14.059(2) Å, c = 17.665(2) Å, β = 101.77(1)°, Z = 4). The overall structure and Fe−P and Fe−Cl bond lengths of cis-Fe(BPE5)2Cl2 more closely resemble those in Fe(PP3)Cl2 complexes (PP3 = tripodal, tetradentate phosphine ligand) than in other Fe(PP)2Cl2 complexes. In solution, cis-Fe(BPE5)2Cl2 exhibits temperature-dependent paramagnetic behavior due to reversible dissociation of chloride. The dissociation of chloride was exploited in the synthesis of Fe(BPE5)2X2 (X = Br, I) and [Fe(BPE5)2(L)(Cl)]+ (L = CO, PMe3). The crystal structure of [cis-Fe(BPE5)2(CO)(Cl)][BPh4] is reported (monoclinic, P21/a, a = 12.938(3) Å, b = 29.647(4) Å, c = 13.131(3) Å, β = 107.89(2)°, Z = 4). The relative chelation strength of BPE5 in Fe(PP)2Cl2 complexes is BPE5 ≈ DMPE > DEPE > DPrPE [DMPE = 1,2-bis(dimethylphoshino)ethane; DEPE = 1,2-bis(diethylphoshino)ethane; DPrPE = bis(di-n-propylphosphino)ethane].

The synthesis of two ethylene-bridged bidentate phosphines is described. 1,2-Bis(1-phospholano)ethane ((C(4)H(8))PCH(2)CH(2)P(C(4)H(8))) was synthesized by the stepwise addition of 2,2-dioxo-1,3,2-dioxathiepane to H(2)PCH(2)CH(2)PH(2). 1,2-Bis(1-phosphorinano)ethane ((C(5)H(10))PCH(2)CH(2)P(C(5)H(10))) was synthesized by the novel photochemical addition of 1,4-pentadiene to H(2)PCH(2)CH(2)PH(2). These bis(phosphines) form two-to-one complexes of the form Fe(PP)(2)Cl(2) when added to iron(II) chloride.

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