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

Abstract

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].

Understanding the Relationship Between Kinetics and Thermodynamics in CO2Hydrogenation Catalysis

“…The BPE5 ligand was considered based on previous evidence from Field et al that dmpe and BPE5 should have similar chelation strengths. 80 We were unable to estimate thermodynamic properties for Co(BPE5) 2 + due to its insolubility in nitrile solvents. However, the catalytic turnover frequency of Co-(BPE5) 2 H was found to lie between those of Co(dmpe) 2 H and Co(dmpbz) 2 H, suggesting that the hydricity of Co(BPE5) 2 H is between that of Co(dmpe) 2 H (36.3 kcal mol −1 ) and Co-(dmpbz) 2 H (38.0 kcal mol −1 ).…”

“…The BPE5 ligand was considered based on previous evidence from Field et al that dmpe and BPE5 should have similar chelation strengths . We were unable to estimate thermodynamic properties for Co­(BPE5) 2 + due to its insolubility in nitrile solvents.…”

Synthesis of Monomeric Fe(II) and Ru(II) Complexes of Tetradentate Phosphines

“…25 The trans geometry in these compounds may limit their reactivity by suppressing processes that require cis-disposed valencies, although cis-iron(II) complexes of bidentate and meso isomers of linear tetradentate phosphines are also formed on occasion. 23,[25][26][27][28][29][30] Ligand modifications can introduce strain, as well as control the geometry and configuration of late metal polyphosphine complexes. One approach involves replacing the central ethylene unit in DPPEPE with a methylene to shorten the ligand backbone and provide the ligand Ph 2 PCH 2 CH 2 PPhCH 2 PPhCH 2 -CH 2 PPh 2 (DPPEPM, Chart 1).…”

Addition of Nitrogen-Containing Heteroallenes to Iron(II)-Hydrides

“…The relative stability of the Fe(PP) 2 X 2 complexes can be rationalized by the fine balance between steric and electronic factors. The substituted tertiary phosphines are crowded at the Fe(II) center, and depending on the bulk of the substituents on P and the nature of X ligands, Fe(PP) 2 X 2 complexes have been characterized with either trans stereochemistry, e.g., Fe(dmpe) 2 Cl 2 , Fe(dmpe) 2 HCl, Fe(dmpe) 2 (CCR) 2 , [Fe(dmpe) 2 (H 2 )H] + , cis stereochemistry, e.g., Fe(dmpe) 2 H 2 , , Fe(BPE5) 2 Cl 2 (BPE5 = 1,2-bisphospholanoethane), or as an equilibrating mixture of the two, e.g., Fe(dprpe) 2 Cl 2 (dprpe = 1,2-bisdi( n -propyl)phosphinoethane), Fe(dmpe) 2 (SR) 2 …”