Unsymmetrical Chelation of N-Thioether-Functionalized Bis(diphenylphosphino)amine-Type Ligands and Substituent Effects on the Nuclearity of Iron(II) Complexes: Structures, Magnetism, and Bonding

Abstract

Starting from the short-bite ligands N-thioether-functionalized bis(diphenylphosphino)amine-type (Ph2P)2N(CH2)3SMe (1) and (Ph2P)2N(p-C6H4)SMe (2), the Fe(II) complexes [FeCl2(1)]n (3), [FeCl2(2)]2 (4), [Fe(OAc)(1)2]PF6 (5), and [Fe(OAc)(2)2]PF6 (6) were synthesized and characterized by Fourier transform IR, mass spectrometry, elemental analysis, and also by X-ray diffraction for 3, 4, and 6. Complex 3 is a coordination polymer in which 1 acts as a P,P-pseudochelate and a (P,P),S-bridge, whereas 4 has a chlorido-bridged dinuclear structure in which 2 acts only as a P,P-pseudochelate. Since these complexes were obtained under strictly similar synthetic and crystallization conditions, these unexpected differences were ascribed to the different spacer between the nitrogen atom and the −SMe group. In both compounds, one Fe–P bond was found to be unusually long, and a theoretical analysis was performed to unravel the electronic or steric reasons for this difference. Density functional theory calculations were performed for a set of complexes of general formula [FeCl2(SR2){R21PN(R2)P′R23}] (R = H, Me; R1, R2, and R3 = H, Me, Ph), to understand the reasons for the significant deviation of the iron coordination sphere away from tetrahedral as well as from trigonal bipyramidal and the varying degree of unsymmetry of the two Fe–P bonds involving pseudochelating PN(R)P ligands. Electronic factors nicely explain the observed structures, and steric reasons were further ruled out by the structural analysis in the solid-state of the bis-chelated complex 6, which displays usual and equivalent Fe–P bond lengths. Magnetic susceptibility studies were performed to examine how the structural differences between 3 and 4 would affect the interactions between the iron centers, and it was concluded that 3 behaves as an isolated high-spin Fe(II) mononuclear complex, while significant intra- and intermolecular ferromagnetic interactions were evidenced for 4 at low temperatures. Complexes 3 and 4 were also tested in catalytic ethylene oligomerization but did not exhibit any significant activity under the studied conditions.

Functional Short-Bite Ligands: Synthesis, Coordination Chemistry, and Applications of N-Functionalized Bis(diaryl/dialkylphosphino)amine-type Ligands

“…Reactions between ligands 192 and 196 and FeCl 2 followed by recrystallization yielded complex 212 as a coordination polymer in which 192 acts simultaneously as a P,P-pseudochelate and a (P,P),S-bridge, while complex 213 has a chlorido-bridged dinuclear structure in which 196 acts only as a P,P-pseudochelate, as established by XRD analyses (Scheme and Table ). Since these complexes were obtained under strictly similar synthetic and crystallization conditions, the structural difference observed could only be ascribed to the different spacer between the N atom and the −SMe group. In both Fe­(II) complexes, one Fe–P bond was found to be unusually long [2.798(2) and 2.762(1) Å for 212 and 213 , respectively], and a theoretical analysis was performed [including a series of Fe complexes of general formula [FeCl 2 (SR 2 )­{R 2 1 PN­(R 2 )­PR 2 3 }] (R = H, Me; R 1 , R 2 , and R 3 = H, Me, Ph)] to unravel the electronic or steric reasons for this difference.…”

Zwitterionic Cobalt Complexes with Bis(diphenylphosphino)(N-thioether)amine Assembling Ligands: Structural, EPR, Magnetic, and Computational Studies

“…Further indications that subtle changes in ligand design can strongly affect the nature of the resulting coordination complexes were also provided by the reactions between FeCl 2 and ligand 1 or 2 (1:1 molar ratio) since they led, under strictly similar reaction conditions, to an infinite coordination polymer or a dinuclear complex, respectively . It was concluded that electronic factors accounted for the unusual unsymmetrical chelation of the iron center (Chart , bottom), raising the question of a possible lability of phosphorus donors in solution, which is relevant to catalyst behavior.…”

“…10 Further indications that subtle changes in ligand design can strongly affect the nature of the resulting coordination complexes were also provided by the reactions between FeCl 2 and ligand 1 or 2 (1:1 molar ratio) since they led, under strictly similar reaction conditions, to an infinite coordination polymer or a dinuclear complex, respectively. 11 It was concluded that electronic factors accounted for the unusual unsymmetrical chelation of the iron center (Chart 1, bottom), raising the question of a possible lability of phosphorus donors in solution, which is relevant to catalyst behavior. Whereas studies on the coordination chemistry of DPPA-type ligands have mostly focused on metals of groups 6, 10, and 11, Ru and Rh, 5,12 those on Fe and Co remain scarce, although these earth-abundant metals are of considerable current interest and display versatile coordination spheres (coordination numbers and geometries) associated with diverse chemical and physical properties.…”

Tetracarbonyl group 6B metal complexes of a N-(4-acetylphenyl)-N-(diphenylphosphino)amine ligand. Molecular structure of cis-[Cr(CO)4{4-CH3CO–C6H4-1-N(PPh2)2}]

“…Several bis(phosphino)amine ligands as well as their complexes have been studied in a wide range of catalytic processes [ 1 ], particularly in ethylene oligo/polymerization [ 11 ] and C–C cross coupling reactions [ 12 ]. These ligands are also used as assembling ligands for the formation of multinuclear complexes, due to the multiple donor atoms [ 13 ], and some of them and their derivatives have also found applications in surface and materials sciences [ 14 , 15 ]. Moreover, the chalcogenide forms of this type of ligands are also becoming increasingly important in view of their potential applications in catalysis [ 16 ].…”