Dispersion Force Stabilized Two-Coordinate Transition Metal–Amido Complexes of the −N(SiMe₃)Dipp (Dipp = C₆H₃-2,6-Prⁱ₂) Ligand: Structural, Spectroscopic, Magnetic, and Computational Studies

Abstract

A series of high spin, two-coordinate first row transition metal-amido complexes, M{N(SiMe3)Dipp}2 {M = Fe (1), Co (2), or Ni (3); Dipp = C6H3-2,6-Pr(i)2} and a tetranuclear C-H activated chromium amide, [Cr{N(SiMe2CH2)Dipp}2Cr]2(THF) (4), were synthesized by reaction of their respective metal dihalides with 2 equiv of the lithium amide salt. They were characterized by X-ray crystallography, electronic and infrared spectroscopy, SQUID magnetic measurements, and computational methods. Contrary to steric considerations, the structures of 1-3 display planar eclipsed M{NSiC(ipso)}2 arrays and short M-N distances. DFT calculations, corrected for dispersion effects, show that dispersion interactions involving C-H-H-C moieties likely stabilize the structures by 21.1-29.4 kcal mol(-1), depending on the level of the calculations employed. SQUID measurements confirm high spin electron configurations for all the complexes and substantial orbital contributions for 1 and 2.

Measurement of Extreme Hyperfine Fields in Two-Coordinate High-Spin Fe2+ Complexes by Mössbauer Spectroscopy: Essentially Free-Ion Magnetism in the Solid State

“…6 It has been proposed that the shorter Fe−N distance in 1 might be due to attractive dispersion forces between the ligand substituents. 9 A comparison (Figure 4) of the internal magnetic field in 1 with that of iron in iron foil underlines the large effect produced by the linear twocoordination environment of the Fe 2+ ion in 1.…”

“…However, the position of NR 2 − [i.e., N(SiMe 3 )Dipp − ] in this series is probably anomalous, because of the shortening of the Fe−N bonds by dispersion forces as described above. 9 Instead, the internal fields observed in Fe{N(H)C 6 H 3 -2,6(C 6 H 2 -2,4,6-i Pr 3 ) 2 } 2 (130 T) 6 and Fe-(N t Bu 2 ) 2 (113 T), 5 as discussed above, are probably more representative of the fields normally produced by amido ligands. Given the lower symmetry of complex 2, the assumptions about the nonadmixed ground state (see eq 6, SI) do not necessarily apply to this system.…”

Synthesis, Structural, Spectroscopic, and Magnetic Characterization of Two-Coordinate Cobalt(II) Aryloxides with Bent or Linear Coordination

“…The fitted parameters given in the lower two portions of Table 3 are quite similar to those reported recently for the two-coordinate linear cobalt(II) complex, Co[N(SiMe 3 )Dipp] 2 (Dipp = C 6 H 3 -2,6-Pr i 2 ). 23 The L = 2 orbital contribution to the moment required to fit the χ M T of 1, 2a, and 2b indicates that the ordering of the cobalt(II) 3d orbitals is similar to the d z 2 < d xy ∼ d x 2 −y 2 < d xz ∼ d yz ordering obtained 15 by ab initio calculations for the 3d 7 electronic configuration of the two-coordinate linear iron(I) anionic complex, [Fe{C(SiMe 3 ) 3 } 2 ] − . In this case one of the three electrons in the virtually degenerate d xy and d x 2 −y 2 orbitals yields an L = 2 orbital contribution to the magnetic moment of the linear complexes 2a and 2b and the pseudotetrahedral 1 complexes.…”

A bis(amido) ligand set that supports two-coordinate chromium in the +1, +2, and +3 oxidation states

“…4–7 Interestingly, this silylamido ligand cannot be used to support a strictly two-coordinate chromium complex; attempts to synthesize Cr[N(SiMe 3 )DIPP] 2 led to C–H bond activation of the ligand and formation of a remarkable tetra-chromium complex containing bridging –CH 2 (SiMe 2 ) groups ( A , Figure 1). 6 Also, although the silylamido ligand –N(SiMe 2 Ph) 2 can be used to support a two-coordinate chromium complex in the solid state, the bis(THF) adduct of the complex is also isolated from the same reaction mixture ( B , Figure 1). 8 …”