Synthesis and reactivity of hydridotris(1-pyrazolyl)borate tungsten(VI) amido alkylidyne complexes

• Published in: Inorganica Chimica Acta 2003-03, Vol.345, p.103-112
• Main Authors: Doufou, Percy, Abboud, Khalil A., Boncella, James M.
• Format: Article
• Language: English
• Subjects: Acid catalyzed tautomerization; Acid induced cleavage; Alkylidyne complexes; Amido alkylidyne complexes; Tungsten(VI) complexes
• ISSN: 0020-1693; 1873-3255
• DOI: 10.1016/S0020-1693(02)01350-6

The synthesis of a series of tungsten(VI) amido alkylidyne complexes containing the chelating ligands Tp (hydridotris(1-pyrazolyl)borate) and Tp′ (hydridotris(3,5-dimethyl-1-pyrazolyl)borate) is described. Complexes of general formula, TpW(CC(CH 3) 3)(Cl)(NHR) [R=C 6H 5, 4-BrC 6H 4, 3,5-(CF 3) 2C 6H 3, H], ( 3– 6), were formed by reaction of TpW(CC(CH 3) 3)(Cl) 2 with the appropriate amide [M][NHR] (M=Li, K). In presence of excess [Li][NHPh], TpW(CC(CH 3) 3)(NHPh) 2 ( 7) was isolated. Sub-stoichiometric quantities of H 2O or HCl were found to catalyze the tautomerization of 3 to the corresponding imido alkylidene. Reaction of excess H 2O with 3 produced significant amounts of TpW(O)(CHC(CH 3) 3)(Cl) ( 10) and TpW(O)(CC(CH 3) 3)(Cl) ( 11) along with tautomerization. Attempted acid catalyzed tautomerizations of 4 and 5 with HCl resulted in loss of the amido ligands and recovery of TpW(CC(CH 3) 3)(Cl) 2. The complex Tp′W(CC(CH 3) 3)(Cl)(NHPh) ( 8), was synthesized by reaction of (CH 3) 3SiN(H)Ph with (DME)W(CC(CH 3) 3)(Cl) 3 followed by addition of KTp′. X-ray crystal structures have been obtained for compounds 7 and 8 and show that the amido groups are syn with respect to the neopentylidyne ligand probably due to the steric demands of the chelating Tp and Tp′ ligands. A series of amido alkylidyne complexes of the formula TpW(CC(CH 3) 3)(Cl)(NHR) [R=Ph, p-BrPh, 3,5-bis-(CF 3), H], ( 1– 4) have been synthesized. These complexes undergo acid catalyzed tautomerization to the alkyidyne complexes or acid induced cleavage of the WNHR bond.