Synthesis and Magnetic Properties of Linear Two-coordinate Monomeric Diaryliron(II) Complexes Bearing Fused-ring Bulky “Rind” Groups

Abstract

Monomeric diaryliron(II) complexes, Fe(Rind) 2 , have been obtained by introducing fused-ring bulky "Rind" groups. For Fe(Eind) 2 , a significant orbital contribution of the Fe(II) ion due to the linear two-coordination has been determined by the highly effective magnetic moment (® eff = 5.82 ® B ) and the extraordinarily large internal hyperfine field (H n = ca. 140 T) in the Mössbauer spectrum. Variable-frequency out-of-phase ac susceptibility data demonstrate an effective spin-reversal barrier of U eff = 51.2(7) cm ¹1 associated with the single-ion magnet behavior. In contrast, a linear two-coordinate iron diaryl compound has not been researched and remains elusive.5 Although several homoleptic two-coordinate diaryliron(II) complexes, Fe(Ar) 2 , have been successfully isolated using sterically-encumbered aryl groups (Ar = C 6 H 2 -2,4,6-t Bu 3 , 6 C 6 H 3 -2,6-(C 6 H 2 -2,4,6-Me 3 ) 2 , 7 and C 6 H 3 -2,6-(C 6 H 3 -2,6-i Pr 2 ) 2 8 ), their effective magnetic moments (® eff = 4.825.18 ® B ) were similar to the spin-only value (spin-only behavior of an S = 2 corresponds ® eff = 4.90 ® B ), most likely due to the bent geometries at the Fe center [CFe C = 150.34(6)171.1(1)°]. Based on these studies, the metal coordination geometry is responsible for the main magnetic properties of the two-coordinate iron complexes. 9 We have studied the low-coordinate compounds of the maingroup elements 10 and transition metals 11 with newly developed bulky aryl groups based on a fused-ring 1,1,3,3,5,5,7,7-octa-Rsubstituted s-hydrindacene skeleton (Rind groups).12,13 As part of these investigations, we anticipated that the bulky rigid Rind groups might provide a stable linear two-coordinate complex of transition metals. Herein, we report the synthesis, structural characterization, and magnetic properties of a new class of organoiron(II) compounds, Fe(Rind) 2 , in which the iron atom is directly connected to the two bulky Rind groups.As shown in Scheme 1, a series of diaryliron(II) complexes, Fe(Rind) 2 (Rind = Eind, MEind, xMEind, and EMind), were straightforwardly synthesized via salt metathesis by the addition of 2 equiv of (Rind)Li, which were prepared by the reaction of (Rind)Br with n

Extreme g-Tensor Anisotropy and Its Insensitivity to Structural Distortions in a Family of Linear Two-Coordinate Ni(I) Bis-N-heterocyclic Carbene Complexes

“…Complexes with a 3d 8 configuration, in particular iron­(II), were among the first MX 2 complexes reported to show slow magnetic relaxation, and their electronic structure and magnetic anisotropy have been studied thoroughly. − It was shown by ab initio analysis that changes in the ligand environment have little effect on the 5 Δ ground state as the orbital contribution | M L | = 2 remains largely unquenched in all cases …”

Fused-Ring Bulky “Rind” Groups Producing New Possibilities in Elemento-Organic Chemistry

“…We have focused on the synthesis and magnetic properties of the Rind-substituted diorganoiron(II) compounds, Fe(Rind) 2 . 50 The treatment of FeCl 2 (thf ) 1.5 with 2 equiv of (Rind)Li has resulted in the formation of discrete molecules of Fe(Rind) 2 as an air-sensitive compound. Figure 17 shows the structure of Fe(EMind) 2 determined by X-ray crystallography, demonstrating the almost linear structure with CFeC = 178.0 (1) We have isolated some mixed diorganocopper(I) species by introducing the bulky Rind groups, as shown in Scheme 16.…”

Synthesis and Structural Characterization of Lithium and Titanium Complexes Bearing a Bulky Aryloxide Ligand Based on a Rigid Fused-Ring s-Hydrindacene Skeleton

“… The readily available Rind groups have several advantages over the existing bulky aryl groups, as represented by the versatility and size-controllability by the introduction of a variety of R-substituents at the four benzylic positions in the rigid s -hydrindacenyl skeleton. We have already found that the Rind groups can stabilize some reactive species of the main group elements as well as transition metals. − For example, recently we reported the synthesis of a size-selected gold cluster, Au 41 [S­(Eind)] 12 , and a redox-active [Fe 4 S 4 ] 3+ cluster, [Fe 4 S 4 {S­(Eind)} 4 ] − , using a bulky Rind-based thiol, (Eind)­SH.…”