Monomeric, Divalent Vanadium Bis(arylamido) Complexes: Linkage Isomerism and Reactivity

Abstract

Divalent complexes of vanadium were synthesized employing bulky silyl(aryl)amido ligands −N(Si i Pr 3 )DIPP and −N(Si t Bu 2 Me)DIPP (DIPP = 2,6-i Pr 2 C 6 H 3 ). Solid-state structural characterization revealed that although the ligand −N-(Si i Pr 3 )DIPP supports a monomeric, bis(amido) complex of vanadium, its constitutional isomer −N(Si t Bu 2 Me)DIPP affords a homoleptic complex in which the vanadium center is sandwiched between the arene rings, an unusual binding mode for arylamido ligands. Magnetometry studies indicate that V[N(Si i Pr 3 )DIPP] 2 and V[(η 5 -DIPP)N(Si t Bu 2 Me)] 2 have similar high-spin d 3 electron configurations. However, spectroscopic methods, including electron paramagnetic resonance, nuclear magnetic resonance, infrared, and UV−visible spectroscopies, in addition to cyclic voltammetry and reactivity studies, suggest that V[N(Si i Pr 3 )DIPP] 2 is stereochemically nonrigid in solution, while V[(η 5 -DIPP)N(Si t Bu 2 Me)] 2 is not. This nonrigidity explicitly impacts the reactivity of V[N(Si i Pr 3 )DIPP] 2 , which can be used to access both amido-bound and arene-bound complexes. Moreover, treatment of V[N(Si i Pr 3 )DIPP] 2 with single and multielectron oxidants reveals a range of transformations including an intramolecular sp 3 C−H bond activation.

On the Synthesis and Reduction of Trigonal Halido Bis(silylamido) Metalates of Chromium to Cobalt

“…Similarly, salt‐like compounds, such as KN(SiMe 3 ) 2 or KCH 2 Ph, form interesting at‐complexes (e. g. [KM(CH 2 Ph){N(SiMe 3 ) 2 } 2 ] or [KFe{N(SiMe 3 ) 2 } 3 ]), which evoke distinct reactivities [18,19] . In addition to hexamethyldisilazanides, metal(II) complexes with bulkier silyamide ligands (e. g. −N(SiMe 2 Ph) or −N(Dipp)SiR 3 ) (Dipp=2,6‐di‐ iso ‐propylphenyl) also found their use with a persistent quasilinear geometry [20–25] . In recent reports it was also shown that such divalent 3d‐metal silylamides can be reduced giving linear, monovalent complex anions [22,25–29] .…”

“…In addition to hexamethyldisilazanides, metal(II) complexes with bulkier silyamide ligands (e. g. −N(SiMe 2 Ph) or −N(Dipp)SiR 3 ) (Dipp=2,6‐di‐ iso ‐propylphenyl) also found their use with a persistent quasilinear geometry [20–25] . In recent reports it was also shown that such divalent 3d‐metal silylamides can be reduced giving linear, monovalent complex anions [22,25–29] . These were employed in bond activation and substrate reduction [19,24,27,29–34] .…”

Accessing cationic tetrylene-nickel(0) systems featuring donor–acceptor E–Ni triple bonds (E = Ge, Sn)

“…Curious as to the true importance of the chelating arm in these systems in forming reactive systems G and H , we sought to develop closely related systems utilising the monodentate bulky amide SiiP Dipp ( SiiP Dipp = [Dipp( i Pr 3 Si)N] − ). 13 Herein we report on the resulting cationic tetrylene nickel(0) complexes, [ SiiP DippE·Ni(PPh 3 ) 3 ] + (E = Ge ( 4 ) and Sn ( 5 )), which feature linear L-E–Ni bonding interactions which are best described as donor–acceptor E–M triple bonds. This gives clear evidence that the chelating phosphine arms in G and H do indeed lead to a reduced bond order in those compounds, thus amplifying their reactivity.…”

Two-Coordinate, Nonlinear Vanadium(II) and Chromium(II) Complexes of the Silylamide Ligand–N(SiMePh2)2: Characterization and Confirmation of Orbitally Quenched Magnetic Moments in Complexes with Sub-d5 Electron Configurations

“…Curie fits of SQUID magnetic measurements afforded magnetic moments of 3.36 (1) and 4.68 (2) µB, consistent with high-spin configurations. These values are lower than the spinonly values of 3.88 and 4.90 µB expected for d 3 and d 4 complexes, suggesting a significant unquenched orbital angular momentum contribution to the overall moment, which is lower as a result of the positive spinorbit coupling constants.Only four such complexes are known for vanadium (the first of which was not reported until 2013), 14,15 although several low-valent complexes of higher coordination at vanadium are known. 8,[15][16][17][18][19] Neutral twocoordinate complexes of chromium are more numerous, with ca.…”

“…-N(Si i Pr3)Dipp, Dipp = 2,6diisopropylphenyl). 15 Because of these difficulties, investigations of the chemistry and properties of two-coordinate openshell (d 1 -d 9 ) transition metal complexes have mainly focused on species in which the d-valence shell is at least half full (i.e. d 5 -d 9 ).…”