Reactions of Tungsten(VI) Dialkyl Complexes with ^tBuNC:  Synthesis and Characterization of New Square Pyramidal and Trigonal Bipyramidal Tungsten(VI) Complexes

Abstract

The complexes [(TMS)2pda](NPh)WR2 ((TMS)2pda = o-(Me3SiN)2C6H4}2-; R = CH3 (1), CH2CMe3 (4)) react with tBuNC to form the octahedral monoadducts [(TMS)2pda](NPh)WR2(CNtBu) (1a and 4a). 1a is observed only at low temperature, while 4a can be isolated. Both 1a and 4a react with tBuNC to form the corresponding trigonal bipyramidal bis(η2-imino-acyl) species [(TMS)2pda](NPh)W[η2-(tBu)NCR]2 (R = CH3 (2), CH2CMe3 (5)), which have been isolated and characterized. Compound 2 isomerizes upon heating to the square pyramidal metallacycle [(TMS)2pda](NPh)W[(tBu)NC(CH3)C(CH3)N(tBu)] (3), which has been isolated as a red solid. X-ray crystal structures have been obtained for compounds 2 and 3. Crystals of 2 are orthorhombic, space group P212121, with a = 9.1175(3) Å, b = 17.9587(5) Å, c = 20.9435(6) Å, and Z = 4. Compound 2 has trigonal bipyramidal geometry with the imido N and one amido N in axial positions. Crystals of 3 are monoclinic, space group C2/c, with a = 35.1302(9) Å, b = 12.6459(2) Å, c = 16.2386(6) Å, β = 112.021(3)°, and Z = 8. 3 has distorted square pyramidal geometry with the imido moiety in the apical position.

Isocyanide insertion reactivity of dinuclear niobium and tantalum imido complexes: X-ray crystal structure of [{Nb(η5-C5H4SiMe3)(CH2Ph)2}2(μ-1,4-NC6H4N)]

“…This selective migration of the amide rather than the methyl group is in agreement with that previously reported for similar niobium and tantalum complexes [14]. However this behaviour is unusual, as shown in the reactivity of alkyl amide complexes of titanium [15], zirconium [16], tungsten [17], uranium [18], tantalum [19] and niobium [20], where the isocyanide insertion takes place at the M-C(alkyl) bond. The presence of the g 2 -iminocarbamoyl in 13 was confirmed by 13 C NMR spectroscopy.…”

C−C, C−S, and C−N Coupling versus Dealkylation Processes in the Cationic Tris(thiolato)dimolybdenum(III) Complexes [Mo2Cp2(μ-SMe)3L2]+ (L = xylNC, t-BuNC, CO, MeCN)

“…As suggested above, the closest parallel to the work reported in this part would appear to be the studies by Lippard et al of reductive coupling of isocyanide ligands in mononuclear seven-coordinate metal complexes . In particular, these authors have also postulated a cationic aminocarbyne complex as an intermediate in related coupling reactions, in accordance with many examples in the literature where electron-rich isocyanide complexes have been converted to aminocarbynes by electrophilic attack (H + ) at the nitrogen atom .…”

“…In particular, almost all the carbonylation reactions are intramolecular, while most of the insertions of isocyanides into metal−carbon bonds are, in contrast, intermolecular, in which the incoming ligand is the one inserted. Interestingly, almost all the examples of intramolecular coupling reactions between two isocyanides that have been investigated experimentally are induced in mononuclear transition-metal complexes by the carbon−carbon reductive coupling of adjacent ligands . Such reactions, which are reported in the literature, may be viewed formally as the addition of one electron and one proton to each of two isocyanide ligands, which then couple to one another.…”

Synthesis of Chelate-Supported Dialkyl and Alkylidene Complexes of Molybdenum(VI)

“…6 By using this chelating ligand, we achieved the syntheses of thermally stable, coordinatively unsaturated dialkyl species. 7 These complexes display insertion chemistry with alkyl isocyanides 8 and undergo β-hydride abstraction in the presence of Lewis bases. 9 In addition, the thermally stable neopentylidene com-plex W(NPh)(C(H)CMe 3 )(o-(Me 3 SiN) 2 C 6 H 4 )(PMe 3 ) was shown to catalyze the ROMP of norbornene and cyclooctene and catalyze the ADMET oligomerization of 1,9-decadiene.…”