The development of N₂S₂ metal complexes as bidentate ligands for organometallic chemistry /
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| Format: | Thesis eBook |
| Language: | English |
| Published: |
[College Station, Tex.] :
[Texas A&M University],
[2007]
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| Online Access: | Link to OAK Trust copy |
| Abstract: | Electronic and steric parameters for square planar NiN₂S₂ complexes as bidentate, S-donor ligands have been established. According to the [nu](CO) stretching frequencies and associated computed Cotton-Kraihanzel force constants of (NiN₂S₂)W(CO)₄ adducts, a ranking of donor abilities and a comparison with classical bidentate ligands are as follows: Ni(ema)= > { [NiN₂S₂]⁰ } > bipy [asymp] phen > Ph₂PCH₂CH₂PPh₂ > Ph₂PCH₂PPh₂. In addition, we have demonstrated that the NiN₂S₂ ligands are hemilabile as evidenced from CO addition to (NiN₂S₂)W(CO)₄, which is in equilibrium with the resulting (NiN₂S₂)W(CO)₅ species (Keq = 2.8 M⁻¹, [delta]G° = -1.4 kJ/mole at 50°C). Complete NiN₂S₂ ligand displacement by CO-cleavage of the remaining W-S bond to form W(CO)₆ was not observed, indicating that the remaining W-S bond is considerably strengthened upon ring-opening. Several new cluster compounds based on the NiN₂S₂ ligands bound to Cu¹, Rh¹, Pd² and W⁰ are reported. Structural analysis of (NiN₂S₂)ML[pi] complexes show a unique structural feature defined by the dihedral angle formed by the intersection of NiN₂S₂/WS₂C₂ planes; placing the NiN₂S₂ ligand in closer proximity to one side of the reactive metal center. This unique orientational feature of the NiN₂S₂ ligands in the series of bimetallic compounds contrasts with classical diphosphine or diimine ligands. The "hinge angle" ranges in value from 136° as in the (Ni-1*)W(CO)₄ to 101° in the (Ni-1)Pd(CH₃)(Cl) complexes. The rigidity of the [mu]SR hinge of the nickeldithiolate ligands suggests that they might be suitable for stereochemical and regioselective substrate addition to catalytically active metals such as Rh¹ and Pd². The structural as well as functional similarities of the acetyl CoA synthase enzyme (ACS) and a palladium-metal based industrial type catalyst led to the preparation of a [(Ni-1)Pd(CH₃)]⁺ bimetallic complex. This complex facilitates CO and ethylene copolymerization to produce polyketone similar to conventional (diphosphine)Pd(X)₂ catalysts. However, the diphosphine ligands produce more efficient catalysts as the electron-rich character of the NiN₂S₂ ligand favors the resting state of the catalyst, [(Ni-1)Pd(C(O)CH₃)(CO)]⁺, over the reactive form (Ni-1)Pd(C(O)CH₃)([eta]²-C₂H₄)]⁺. An exploratory investigation with the Ni-Pd heterobimetallic showed that this complex also facilitated the C-S coupling reaction to form a thioester similar to the ACS enzyme. |
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| Item Description: | "Major Subject: Chemistry" Title from author supplied metadata (automated record created on Apr. 27, 2007.) Vita. Abstract. Electronic resource. |
| Format: | Mode of access: World Wide Web. System requirements: World Wide Web access and Adobe Acrobat Reader. |
| Bibliography: | Includes bibliographical references. |