Iron(II) Complexes Containing the 1,2-Diphospholanoethane Ligand

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].