Facilitating Access to the Most Easily Ionized Molecule: an Improved Synthesis of the Key Intermediate, W2(hpp)4Cl2, and Related Compounds
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- 作者：F. Albert Cotton ; James P. Donahue ; Nadine E. Gruhn ; Dennis L. Lichtenberger ; Carlos A. Murillo ; Daren J. Timmons ; Laura O. Van Dorn ; Dino Villagrá ; n ; and Xiaoping Wang
- 刊名：Inorganic Chemistry
- 出版年：2006
- 出版时间：January 9, 2006
- 年：2006
- 卷：45
- 期：1
- 页码：201 - 213
- 全文大小：382K
- 年卷期：v.45,no.1(January 9, 2006)
- ISSN：1520-510X
文摘
A far superior synthesis is reported for W2(hpp)4Cl2, a key intermediate in the synthesis of the most easily ionizedclosed-shell molecule W2(hpp)4 (hpp = the anion of the bicyclic guanidine compound 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine). At 200 
ntities/deg.gif">C, the one-pot reaction of the air-stable and commercially available compoundsW(CO)6 and Hhpp in o-dichlorobenzene produces W2(hpp)4Cl2 in multigram quantities with isolated yields of over90%. At lower temperatures, the reaction can lead to other compounds such as W(Hhpp)2(CO)4 or W2(ntities/mgr.gif">-CO)2(ntities/mgr.gif">-hpp)2(
2-hpp)2, which are isolable in good purity depending upon the specific conditions employed. These compoundsprovide insight into the reaction pathway to W2(hpp)4Cl2 and W2(hpp)4. Two additional derivatives, W2(hpp)4X2where X is PF6- or the anion tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (TFPB), have also been synthesizedand structurally characterized. A comparison of the electrode potentials of W2(ntities/mgr.gif">-CO)2(ntities/mgr.gif">-hpp)2(2-hpp)2 and thedi-p-anisylformamidinate analogue shows that oxidation of the hpp compound is significantly displaced (1.12 V)and shows that the bicyclic guanidinate ligand is considerably better than the formamidinate anion at stabilizinghigh oxidation states. A differential pulse voltammogram of W2(hpp)4(TFPB)2 in THF shows two reduction processeswith an E1/2 of -0.97 V for the first and -1.81 V (vs Ag/AgCl) for the second. DFT calculations on the W2(hpp)42+units in W2(hpp)4X2 compounds show that the metal-metal bonding orbitals are destabilized by the axial ligands,which accounts for significant variations in the W-W distances. The low-energy gas-phase ionizations of W2(hpp)4are also reported and discussed.
ntities/deg.gif">C, the one-pot reaction of the air-stable and commercially available compoundsW(CO)6 and Hhpp in o-dichlorobenzene produces W2(hpp)4Cl2 in multigram quantities with isolated yields of over90%. At lower temperatures, the reaction can lead to other compounds such as W(Hhpp)2(CO)4 or W2(ntities/mgr.gif">-CO)2(ntities/mgr.gif">-hpp)2(2-hpp)2, which are isolable in good purity depending upon the specific conditions employed. These compoundsprovide insight into the reaction pathway to W2(hpp)4Cl2 and W2(hpp)4. Two additional derivatives, W2(hpp)4X2where X is PF6- or the anion tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (TFPB), have also been synthesizedand structurally characterized. A comparison of the electrode potentials of W2(ntities/mgr.gif">-CO)2(ntities/mgr.gif">-hpp)2(2-hpp)2 and thedi-p-anisylformamidinate analogue shows that oxidation of the hpp compound is significantly displaced (1.12 V)and shows that the bicyclic guanidinate ligand is considerably better than the formamidinate anion at stabilizinghigh oxidation states. A differential pulse voltammogram of W2(hpp)4(TFPB)2 in THF shows two reduction processeswith an E1/2 of -0.97 V for the first and -1.81 V (vs Ag/AgCl) for the second. DFT calculations on the W2(hpp)42+units in W2(hpp)4X2 compounds show that the metal-metal bonding orbitals are destabilized by the axial ligands,which accounts for significant variations in the W-W distances. The low-energy gas-phase ionizations of W2(hpp)4are also reported and discussed.