Tungsten complexes protonation

Schmidt reaction of ketones, 7, 530 from thienylnitrenes, 4, 820 tautomers, 7, 492 thermal reactions, 7, 503 transition metal complexes reactivity, 7, 28 tungsten complexes, 7, 523 UV spectra, 7, 501 X-ray analysis, 7, 494 1 H-Azepines conformation, 7, 492 cycloaddition reactions, 7, 520, 522 dimerization, 7, 508 H NMR, 7, 495 isomerization, 7, 519 metal complexes, 7, 512 photoaddition reactions with oxygen, 7, 523 protonation, 7, 509 ring contractions, 7, 506 sigmatropic rearrangements, 7, 506 stability, 7, 492 N-substituted mass spectra, 7, 501 rearrangements, 7, 504 synthesis, 7, 536-537... 

No intermediate tungsten complexes were observed in this reaction. The alcohol, sec-phenethylalcohol, is consumed at a rate which is much faster than that of its formation. It was shown separately to be converted to ethylbenzene (Eq. (23)) by HOTf and [Cp(CO)3WH]. This reaction presumably proceeds through loss of water from the protonated alcohol, followed by hydride transfer from [Cp(CO)3WH] to give ethylbenzene. 

The monoanionic tungsten complex W[S2C2Ph(p-MeOPh)]3 has been reported to catalyze formation of hydrogen from water, using free radicals derived from methyl viologen as the source of electrons (112). The catalytic cycle has been proposed to involve sequential electron and proton transfer. 

Dithioliumyl-diphenylphosphine tungsten complexes 495 were synthesized by protonation of the (dithioalkyl-carbonyl)diphenylphosphinotungsten complexes 494 with HBF4 (Equation 59) <20010M2604>. 

Reaction of the tungsten complex 167 with diphenylphosphine at elevated temperatures affords complex 168 [Eq. (140)] (76i). The same compound could be obtained by sequential addition of LiPPh2 and NH4Br. Formation of this product is surprising considering the ease with which some phospines induce carbyne-carbonyl coupling in complex 167 (see Section IV,F). The by-product 169 could possibly be derived from an intermediate ketenyl complex. Protonation of complex 168 in acetonitrile occurs at the former carbyne carbon to give the phosphine complex 170. 

The physical and solubility properties of the tungsten complex are similar to those of the molybdenum analog, except that it is less photosensitive. The HNMR spectrum at room temperature (toluene-tig) shows this complex to be stereochemically rigid, but at 60 °C, a binomial quintet is observed at d — 1.72 for the W—H protons ( ph = 31 Hz). 

Since many organometallics behave as Lewis bases due to electron-rich metals, protonation is a common reaction. For example, the tungsten hydride 3 undergoes reversible protonation at the metal, forming the water-soluble cationic hydride 4 (Eq. 5). In nickelocene 5, a 20e complex, protonation occurs at the jr-bonded cyclo-pentadienyl ligand the intermediate 6 has a stable, isolable counterpart in the fully methylated derivative. Consecutive loss of cyclopentadiene forms the cation 7, which adds to unchanged nickelocene forming the tripledecker sandwich 8 (Scheme 3). 

However, this work pre-dated the discovery of protonation of dinitrogen in the molybdenum and tungsten complexes and, once this had come to light, we turned our attention to the behaviour of isocyanides and alkynes at those sites that activated dinitrogen to reduction. For isocyanides, the first step was to bind these ligands in place of dinitrogen in the complexes trflns-[M(N2)2(dppe)2], which was done by a displacement reaction [Equation (23)]. ... 

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