Mössbauer effect, 13C NMR and IR study of the effect of bulky Cp substituents and CO substitution on the structure and bonding of mono- and dinuclear organoiron complexes

Spin States, Bonding and Magnetism in Mixed‐Valence Iron(0)‐Iron(II) Complexes**

“…Modelling the Mössbauer spectra indicated isomer shifts ( δ ) of 0.08±0.05 mm s −1 (|Δ E Q |=1.79±0.09 mm s −1 ) and 0.58±0.07 mm s −1 (|Δ E Q |=0.78±0.13 mm s −1 ). The former doublet is similar to those found in CpFe 0 (CO) 2 compounds, such as that in B ( δ 190 K =0.08 mm s −1 , |Δ E Q |=1.73 mm s −1 ) and has a smaller isomer shift than Fe II compounds with similar coordination environments, such as CpFe II (CO) 2 Cl (( δ 220 K =0.14 mm s −1 , |Δ E Q |=1.83 mm s −1 ), and smaller than the anion, K[CpFe 0 (CO) 2 ] (( δ 80 K =0.16 mm s −1 , |Δ E Q |=2.07 mm s −1 ) [18,22] . The other doublet is comparable to those for high‐spin three coordinate L c Fe II X species, for example L c FeCl ( δ 4.2 K =0.74 mm s −1 , |Δ E Q |=1.61 mm s −1 ) and L c FeCH 3 ( δ 4.2 K =0.48 mm s −1 , |Δ E Q |=1.74 mm s −1 ; L c =3,5‐bis(2,6‐diisopropylphenylimido)‐2,6‐dimethylheptyl) [23] .…”

“…The former doublet is similar to those found in CpFe 0 (CO)2 compounds, such as that in Ar′Fe-Fp (d 190 K = 0.08 mm s -1 , |DEQ| = 1.73 mm s -1 ) and has a smaller shift than Fe II compounds with similar coordination environments, such as CpFe II (CO)2Cl (d 220 K = 0.14 mm s -1 , |DEQ| = 1.83 mm s -1 ), and smaller than the anion, K[CpFe 0 (CO)2] (d 80 K = 0.16 mm s -1 , |DEQ| = 2.07 mm s -1 ). [18,22] The other doublet is comparable to values for high-spin three coordinate L c Fe II X species, for example L c FeCl (d 4.2 K = 0.74 mm s -1 , |DEQ| = 1.61 mm s -1 ) and L c FeCH3 (d 4.2 K = 0.48 mm s -1 , |DEQ| = 1.74 mm s -1 ) (L c = 3,5-bis(2,6-diisopropylphenylimido)-2,6-dimethylheptyl). [23] These data led to a working model for the complex that assigns the sites as being a low-spin Fe 0 (CpFe(CO)2) and a high-spin Fe II (LFe).…”

Two-Coordinate First Row Transition Metal Complexes with Short Unsupported Metal−Metal Bonds

“…12 and -1.35, respectively, clearly indicating an intramolecular electron transfer from Fe(1) to Fe(2). A similar effect was observed in 2, where natural charges for Mn(1) and Fe(1) of +1.18 and -1.34, respectively, were calculated.…”

“…11 Another signal (δ ) 0.08 mm/s, ∆E Q ) 1.73 mm/s at 190 K) was consistent with an Fe atom in an [(η 5 -C 5 H 5 )Fe(CO) 2 ] fragment. 12 In addition, a signal (δ ) 0.15 mm/s, ∆E Q ) 1.94 mm/s at 190 K) indicated the presence of some [(η 5 -C 5 H 5 )Fe(CO) 2 ] 2 dimer (literature value: δ ) 0.227(2) mm/s, ∆E Q ) 1.912(5) mm/s at 77 K), 12 whose presence could be due to disproportionation or oxidation of 1.…”

“…14a The coordination at Fe(1) deviates from linear geometry to afford a C(1)-Fe(1)-Fe(2) angle of 163.94( 12)°. This is similar to those observed in a number of mononuclear, two-coordinate iron species, such as Fe{N(SiMePh 2 ) 2 } 2 (169.0(1)°), 15 Fe{N(C 6 H 3 -2,6i Pr 2 )(CH 2 t Bu)} 2 (168.8(2)°), 16 Fe(NMesBMes 2 ) 2 (166.6(1)°, Mes ) 2,4,6-Me 3 C 6 H 2 ), 17 Fe(C 6 H 3 -2,6-Mes 2 ) 2 (164.44 (12), 171.06(12)°), 18 and FeAr′ 2 (159.34(6)°). 19 The Fe(1)-C(1) distance (2.022(4) Å) in 1 is similar to the Fe-C σ-bond lengths in [Ar′FeFeAr′] (2.028(4) and 2.048(4) Å), 8 Fe(C 6 H 3 -2,6-Mes 2 ) 2 (2.040(3) Å), 18 FeAr′ 2 (2.059(1) Å), 19 and (η 6 -C 6 H 6 )Fe(Ar*-3,5-i Pr 2 ) (2.029(4) Å).…”