Facilitating access to the most easily ionized molecule: An improved synthesis of the key intermediate, W2(hpp)4Cl2, and related compounds

F. Albert Cotton; James P. Donahue; Nadine E. Gruhn; Dennis L. Lichtenberger; Carlos A. Murillo; Daren J. Timmons; Laura O. Van Dorn; Dino Villagrán; Xiaoping Wang

doi:10.1021/ic0515709

Facilitating access to the most easily ionized molecule: An improved synthesis of the key intermediate, W₂(hpp)₄Cl₂, and related compounds

F. Albert Cotton, James P. Donahue, Nadine E. Gruhn, Dennis L. Lichtenberger, Carlos A. Murillo, Daren J. Timmons, Laura O. Van Dorn, Dino Villagrán, Xiaoping Wang

Chemistry and Biochemistry

Research output: Contribution to journal › Article › peer-review

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Abstract

A far superior synthesis is reported for W₂(hpp) ₄Cl₂, a key intermediate in the synthesis of the most easily ionized closed-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°C, the one-pot reaction of the air-stable and commercially available compounds W(CO)₆ and Hhpp in o-dichlorobenzene produces W₂(hpp)₄Cl₂ in multigram quantities with isolated yields of over 90%. At lower temperatures, the reaction can lead to other compounds such as W(Hhpp)₂(CO)₄ or W ₂(μ-CO)₂(μ-hpp)₂(η²-hpp) ₂, which are isolable in good purity depending upon the specific conditions employed. These compounds provide insight into the reaction pathway to W₂(hpp)₄Cl₂ and W₂(hpp) ₄. Two additional derivatives, W₂(hpp)₄X ₂ where X is PF₆^- or the anion tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (TFPB), have also been synthesized and structurally characterized. A comparison of the electrode potentials of W₂(μ-CO)₂(μ-hpp)₂(η ²-hpp)₂ and the di-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 stabilizing high oxidation states. A differential pulse voltammogram of W₂(hpp)₄(TFPB)₂ in THF shows two reduction processes with an E_1/2 of -0.97 V for the first and -1.81 V (vs Ag/AgCl) for the second. DFT calculations on the W ₂(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 W ₂(hpp)₄ are also reported and discussed.

Original language	English (US)
Pages (from-to)	201-213
Number of pages	13
Journal	Inorganic Chemistry
Volume	45
Issue number	1
DOIs	https://doi.org/10.1021/ic0515709
State	Published - Jan 9 2006

ASJC Scopus subject areas

Physical and Theoretical Chemistry
Inorganic Chemistry

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10.1021/ic0515709

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@article{8e0a26dcc8754dc491b9330732c61e1e,

title = "Facilitating access to the most easily ionized molecule: An improved synthesis of the key intermediate, W2(hpp)4Cl2, and related compounds",

abstract = "A far superior synthesis is reported for W2(hpp) 4Cl2, a key intermediate in the synthesis of the most easily ionized closed-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°C, the one-pot reaction of the air-stable and commercially available compounds W(CO)6 and Hhpp in o-dichlorobenzene produces W2(hpp)4Cl2 in multigram quantities with isolated yields of over 90%. At lower temperatures, the reaction can lead to other compounds such as W(Hhpp)2(CO)4 or W 2(μ-CO)2(μ-hpp)2(η2-hpp) 2, which are isolable in good purity depending upon the specific conditions employed. These compounds provide insight into the reaction pathway to W2(hpp)4Cl2 and W2(hpp) 4. Two additional derivatives, W2(hpp)4X 2 where X is PF6- or the anion tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (TFPB), have also been synthesized and structurally characterized. A comparison of the electrode potentials of W2(μ-CO)2(μ-hpp)2(η 2-hpp)2 and the di-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 stabilizing high oxidation states. A differential pulse voltammogram of W2(hpp)4(TFPB)2 in THF shows two reduction processes with an E1/2 of -0.97 V for the first and -1.81 V (vs Ag/AgCl) for the second. DFT calculations on the W 2(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 W 2(hpp)4 are also reported and discussed.",

author = "Cotton, {F. Albert} and Donahue, {James P.} and Gruhn, {Nadine E.} and Lichtenberger, {Dennis L.} and Murillo, {Carlos A.} and Timmons, {Daren J.} and {Van Dorn}, {Laura O.} and Dino Villagr{\'a}n and Xiaoping Wang",

year = "2006",

month = jan,

day = "9",

doi = "10.1021/ic0515709",

language = "English (US)",

volume = "45",

pages = "201--213",

journal = "Inorganic Chemistry",

issn = "0020-1669",

publisher = "American Chemical Society",

number = "1",

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TY - JOUR

T1 - Facilitating access to the most easily ionized molecule

T2 - An improved synthesis of the key intermediate, W2(hpp)4Cl2, and related compounds

AU - Cotton, F. Albert

AU - Donahue, James P.

AU - Gruhn, Nadine E.

AU - Lichtenberger, Dennis L.

AU - Murillo, Carlos A.

AU - Timmons, Daren J.

AU - Van Dorn, Laura O.

AU - Villagrán, Dino

AU - Wang, Xiaoping

PY - 2006/1/9

Y1 - 2006/1/9

N2 - A far superior synthesis is reported for W2(hpp) 4Cl2, a key intermediate in the synthesis of the most easily ionized closed-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°C, the one-pot reaction of the air-stable and commercially available compounds W(CO)6 and Hhpp in o-dichlorobenzene produces W2(hpp)4Cl2 in multigram quantities with isolated yields of over 90%. At lower temperatures, the reaction can lead to other compounds such as W(Hhpp)2(CO)4 or W 2(μ-CO)2(μ-hpp)2(η2-hpp) 2, which are isolable in good purity depending upon the specific conditions employed. These compounds provide insight into the reaction pathway to W2(hpp)4Cl2 and W2(hpp) 4. Two additional derivatives, W2(hpp)4X 2 where X is PF6- or the anion tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (TFPB), have also been synthesized and structurally characterized. A comparison of the electrode potentials of W2(μ-CO)2(μ-hpp)2(η 2-hpp)2 and the di-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 stabilizing high oxidation states. A differential pulse voltammogram of W2(hpp)4(TFPB)2 in THF shows two reduction processes with an E1/2 of -0.97 V for the first and -1.81 V (vs Ag/AgCl) for the second. DFT calculations on the W 2(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 W 2(hpp)4 are also reported and discussed.

AB - A far superior synthesis is reported for W2(hpp) 4Cl2, a key intermediate in the synthesis of the most easily ionized closed-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°C, the one-pot reaction of the air-stable and commercially available compounds W(CO)6 and Hhpp in o-dichlorobenzene produces W2(hpp)4Cl2 in multigram quantities with isolated yields of over 90%. At lower temperatures, the reaction can lead to other compounds such as W(Hhpp)2(CO)4 or W 2(μ-CO)2(μ-hpp)2(η2-hpp) 2, which are isolable in good purity depending upon the specific conditions employed. These compounds provide insight into the reaction pathway to W2(hpp)4Cl2 and W2(hpp) 4. Two additional derivatives, W2(hpp)4X 2 where X is PF6- or the anion tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (TFPB), have also been synthesized and structurally characterized. A comparison of the electrode potentials of W2(μ-CO)2(μ-hpp)2(η 2-hpp)2 and the di-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 stabilizing high oxidation states. A differential pulse voltammogram of W2(hpp)4(TFPB)2 in THF shows two reduction processes with an E1/2 of -0.97 V for the first and -1.81 V (vs Ag/AgCl) for the second. DFT calculations on the W 2(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 W 2(hpp)4 are also reported and discussed.

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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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CCDC 295664: Experimental Crystal Structure Determination

CCDC 295668: Experimental Crystal Structure Determination

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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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CCDC 295664: Experimental Crystal Structure Determination

CCDC 295668: Experimental Crystal Structure Determination

CCDC 295665: Experimental Crystal Structure Determination

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Facilitating access to the most easily ionized molecule: An improved synthesis of the key intermediate, W₂(hpp)₄Cl₂, and related compounds