Zerovalent Rhodium and Iridium Silatranes Featuring Two‐Center, Three‐Electron Polar σ Bonds

Abstract

Species with 2‐center, 3‐electron (2c/3e−) σ bonds are of interest owing to their fascinating electronic structures and potential for interesting reactivity patterns. Report here is the synthesis and characterization of a pair of zerovalent (d9) trigonal pyramidal Rh and Ir complexes that feature 2c/3e− σ bonds to the Si atom of a tripodal tris(phosphine)silatrane ligand. X‐ray diffraction, continuous wave and pulse electron paramagnetic resonance, density‐functional theory calculations, and reactivity studies have been used to characterize these electronically distinctive compounds. The data available highlight a 2c/3e− bonding framework with a σ*‐SOMO of metal 4‐ or 5dz2 parentage that is partially stabilized by significant mixing with Si (3pz) and metal (5‐ or 6pz) orbitals. Metal‐ligand covalency thus buffers the expected destabilization of transition‐metal (TM)‐silyl σ*‐orbitals by d–p mixing, affording well‐characterized examples of TM–main group, and hence polar, 2c/3e− σ “half‐bonds”.

Mononuclear Fe(I) and Fe(II) Acetylene Adducts and Their Reductive Protonation to Terminal Fe(IV) and Fe(V) Carbynes

“…32 By contrast, the comparatively small ΔEQ values observed for the (SiP3)Fecarbyne series reflects the additional presence of substantial electron density along the z-axis (parallel to the Fe≡C-R vector). Inspection of the molecular orbitals of the carbyne series shows that the nominally high-lying Fe-C σ*antibonding orbital is highly stabilized by mixing with Si(σ), 35 resulting in a heavily mixed orbital of a1 symmetry energetically below the filled, primarily nonbonding orbitals of d(xy) and d(x 2 -y 2 ) parentage (Figure 8). This observation bears relevance to a contributing resonance structure we have previously considered, with electron density being polarized between a cationic R3Si + anchor and a nominally reduced Fe center (Figure 9).…”

Three‐Coordinate Rhodium Complexes in Low Oxidation States

“…Afterwards, fully characterized d 9 ‐ML 4 and d 10 ‐ML 4 compounds with diphosphines, and mixed olefin‐phosphine ligands have been reported and extensively studied by Grützmacher (Scheme ) . They are typically tetracoordinate, thus following the 18‐electron rule, and display more or less distorted tetrahedral structures, except the distinctive trigonal pyramidal [K(thf) 3 ][P 3 Si Rh] [P 3 Si =tris( o ‐diisopropylphosphinophenyl)silylide . Those of Rh 0 have been characterized and many of them fully studied by EPR spectroscopy and DFT methods .…”

“…Si Rh] [P 3 Si = tris(o-diisopropylphosphinophenyl)silylide. [9] Those of Rh 0 have been characterizeda nd many of them fully studied by EPR spectroscopy and DFT methods. [10] Interestingly,t hey are all highly delocalized radicals,w ith the exception of one metal-centered radical, [Rh(trop 2 PPh)(PPh 3 )], [1(Rh) 58 %],w hich is in electromerice quilibrium with the delocalized radical.…”

“…Selectedbonddistances []a nd angles [8]: RhÀAu 2.5302(3), RhÀC1 2.073(2), RhÀCt1 2.018(2), RhÀCt2 2.021(2), C28ÀC29 1.434(3),C 32ÀC33 1.431(3), AuÀ P2 .2477 (7), C1-Rh-Ct1 114.96 (9), C1-Rh-Ct2 109.79 (9), Ct1-Rh-Ct2 134.86 (10), Rh-Au-P 163.13(2).C t1 and Ct2 are middle points of C28,29 and C32,C33,respectively.O nly CH carbonso fthe iPr groups are shownbyc larity.…”

A diradical based on odd-electron σ-bonds

“…The concept of the odd-electron σ-bond was first proposed by Pauling 8 , and species with these intriguing bonds have been recognized as important intermediates in chemistry and biochemistry [9][10][11][12][13][14][15][16][17][18][19][20][21] . A number of radicals with a one-electron [22][23][24][25] or three-electron σ-bond 12,[26][27][28][29][30][31][32] have been isolated and structurally studied (Fig. 1).…”