Synthesis and characterization of tetracarbonylpyrazinetrimethylphosphitetungsten(0) complexes

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Tezin Türü: Yüksek Lisans

Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Fen Edebiyat Fakültesi, Kimya Bölümü, Türkiye

Tezin Onay Tarihi: 2004

Öğrenci: FATMA ALPER

Eş Danışman: SAİM ÖZKAR, CEYHAN KAYRAN İŞÇİ

Özet:

In this study, the effect of a donor ligand on the stabilization of a carbonyl pyrazine tungsten complex was studied. The pentacarbonylpyrazinetungsten(0) complex could be formed from the photolysis of hexacarbonyltungsten(0) in the presence of pyrazine and could be isolated as crystalline solid. However, the complex was found to be unstable in solution, being converted to a bimetallic complex, (CO)5W(pyz)W(CO)5 and free pyrazine molecule. Two complexes exist in solution at equilibrium. The equilibrium constant could be determined by 1H-NMR spectroscopy and found to be 0.0396 at 25°C. To test whether the introduction of a second pyrazine ligand might provide stability for the carbonyl-pyrazine-tungsten complex, W(CO)4(pyz)2 was attempted to be synthesized. The cis-W(CO)4(pyz)2 complex could be generated from the thermal substitution reaction of cis-W(CO)4(piperidine)2 with excess pyrazine in dichloromethane. However, this complex could not be isolated because of the lack of stability. The complex could only be identified by IR spectroscopy in solution. To stabilize the pentacarbonylpyrazinetungsten(0) complex, trimethylphosphite was introduced to the complex as a donor ligand. For this purpose, cis-W(CO)4[P(OCH3)3](thf), photogenerated from W(CO)5[P(OCH3)3] in tetrahydrofuran (thf), was reacted with pyrazine. The replacement of tetrahydrofuran with pyrazine (pyz) yielded cis-W(CO)4[P(OCH3)3](pyz). The complex could be isolated from the reaction solution and characterized by means of IR, 1H-, 13C-, 31P-NMR, and Mass spectroscopies. The introduction of P(OCH3)3 has proved that a donor ligand will strengthen the metal-pyrazine bond and thus stabilizes the complex. As a result of this stabilization, the complex could be isolated as the first example of tungsten pyrazine complexes that contain a donor ligand.