Hydrides, Halides, and Polymers: Some Unexpected Intermediates on the Routes to First-Row Transition Metal M{N(SiMe₃)₂}_n (n = 2, 3) Complexes

Abstract

The reaction of 2 equiv of LiN­(SiMe3)2·Et2O with TiCl3(NMe3)2 or VCl3(NMe3)2 afforded the dimeric, halide bridged complexes [Ti­(μ-Cl)­{N­(SiMe3)2}2]2 (1) or [V­(μ-Cl)­{N­(SiMe3)2}2]2 (2) in moderate yields. The reduction of titanium complex 1 with 3 equiv of 5% (wt) Na/NaCl gave the mixed metal titanium/sodium hydride cluster Ti2(μ-H)2{N­(SiMe3)2}3­{N­(SiMe3)­(SiMe2CH)}­(Na) (3), which was formed by activation of two C–H bonds at a single methyl group of one of the bis­(trimethylsilyl)­amide ligands. Attempts to form the analogous vanadium complex by reduction of 2 gave only intractable products. Treatment of Co­{N­(SiMe3)2}2 with 1 equiv of BrN­(SiMe3)2 (which was previously shown to give the unique three-coordinate cobalt­(III) trisamide Co­{N­(SiMe3)2}3) afforded the polymeric [(μ-Br)­Co­{μ-N­(SiMe3)­(SiMe2CH2CH2Me2Si)­(Me3Si)­μ-N}­Co­(μ-Br)]∞ (4) as a second product, which was shown by a structural analysis to possess a carbon–carbon bond formed between the two ligands. Attempts to isolate manganese and iron complexes analogous to 4 were unsuccessful. The role of bromine in these reactions was further studied by examining the reaction of 0.5 equiv of elemental bromine with [Mn­{N­(SiMe3)2}2]2 or [Co­{N­(SiMe3)2}2]2, which for manganese was shown to give the previously reported manganese trisamide Mn­{N­(SiMe3)2}3 but for cobalt gives the dimeric amide-bridged [Co­(Br)­{μ-N­(SiMe3)2}]2 (5).

Reassessment of N2 activation by low-valent Ti-amide complexes: a remarkable side-on bridged bis-N2 adduct is actually an arene adduct

“…The Ti III -N(TMS) 2 moiety has Ti-N lengths of 2.028(2) and 2.030(2) A which is consistent with Ti-N(TMS) 2 bond lengths in 18 other Ti III compounds (1.929(3) to 2.057(1) A). 25,26,[29][30][31][32][33][34][35][36][37] The Ti II -N(TMS) 2 bearing the (PhMe)K moiety has longer Ti-N(TMS) 2 bond lengths which range from 2.129(2) to 2.146(2) A which is expected for an ion with a lower oxidation state. A similar difference in Ti-N lengths is been found in mixed-valent Ti II / Ti III inverse sandwich 4.…”

“…However, reduction of [N(TMS) 2 ] 2 TiCl(THF) with only 1 equiv of KC 8 in pentane yielded the end-on bridged N 2 complex [(N(TMS) 2 ) 2 Ti(THF)] 2 (μ-η 1 :η 1 -N 2 )(10). Interestingly, further reaction of 10 with excess KC 8 did not result in significant formation of 8•THF.Selected bond distances from the solid-state structures of 8, 8•THF, 730 and 10 are reported in Table1. The Ti-N nitride distances in 8 and 8•THF have nearly identical bond metrical parameters despite containing an additional coordinated THF to each potassium cation in 8•THF.…”

Three-Coordinate Halide and Methyl Complexes of Chromium, Manganese, Iron, Cobalt, and Nickel Enabled by an Imidazolin-2-iminato Ligand

“…This is different from the typical dimeric metal complexes with the molecular formula (LMX) 2 (L is a monoanionic ligand), which has bridging halide ligands. The only known example of such a structure is the hexamethyldisilazide Co complex [Co­{μ 2 -N­(SiMe 3 ) 2 } 2 (Br)] 2 recently reported by Stennett and Power . Notable three- and four-coordinate dimeric examples with monodentate ligands are [M­(Ar i Pr6 )­(μ 2 -X)] 2 reported by the Power group and [M­{N­(SiR 3 )­(Ar*)}­(μ 2 -X)] 2 [R = CH 3 or Ph, Ar* = C 6 H 2 -2,6-{C­(H)­Ph 2 } 2 -4-CH 3 ] reported by Hicks and Jones .…”

Structural characterization of three hydride-bridged sodium aluminate compounds

“…There are 87 hits returned in the CSD when a search is carried out for the 'Na-HMDS' fragment; this reduces to 78 when only heterobimetallic compounds are considered and reduces to just two hits when 'H-Na-HMDS' is searched with one structure being a titanium-hydride compound (Stennett & Power, 2021), and the other a sodium-hydrido magnesiate (Liptrot et al, 2014). When the CSD is searched for 'Al-HMDS' it returns 78 results; when only heterobimetallic species are considered this reduces to 46 hits (with 10 of these involving alkali metals) and 29 hits are returned when the 'H-Al-HMDS' fragment is searched.…”