Carbon-Carbon Coupling in Dinuclear Cycloaurated Complexes Containing Bridging 2-(Diphenylphosphino)phenyl or 2-(Diethylphosphino)phenyl. Role of the Axial Ligand and the Fine Balance between Gold(II)

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• 作者：Martin A. Bennett ; David C. R. Hockless ; A. David Rae ; Lee L. Welling ; and Anthony C. Willis
• 刊名：Organometallics
• 出版年：2001
• 出版时间：January 8, 2001
• 年：2001
• 卷：20
• 期：1
• 页码：79 - 87
• 全文大小：184K
• 年卷期：v.20,no.1(January 8, 2001)
• ISSN：1520-6041

文摘

Reactions of the homovalent bis(benzoato)digold(II) complexes [Au^II₂(O₂CPh)₂(r.gif">-2-C₆H₄PR₂)₂] (R = Ph (1a), Et (1b)) with the anions CH₃^-, C₆F₅^-, and SCN^- have been investigated.Dimethylmagnesium gives the stable heterovalent complexes [Au^I(r.gif">-2-C₆H₄PR₂)₂Au^III(CH₃)₂](R = Ph (2a), Et (2b)), whereas (pentafluorophenyl)lithium gives the homovalent complexes[Au^II₂(C₆F₅)₂(r.gif">-2-C₆H₄PR₂)₂] (R = Ph (3a), Et (3b)). On prolonged heating in toluene, thelatter rearrange to give predominantly dinuclear bis(pentafluorophenyl)digold(I) complexesof the corresponding (2,2'-biphenylyl)bis(tertiary phosphines) [Au^I₂(C₆F₅)₂(r.gif">-2,2'-R₂PC₆H₄C₆H₄PR₂)] (R = Ph (4a), Et (4b)), resulting from coupling of the C₆H₄PR₂ units. Minor productsof these rearrangements are the zwitterionic heterovalent complexes [(C₆F₅)₂Au^III(r.gif">-2-C₆H₄PR₂)₂Au^I] (R = Ph (5a), Et (5b)). The structure of 5a differs from that of 2a by rotation ofone of the bridging 2-C₆H₄PPh₂ groups through 180. Precursors to 4a/5a and 4b/5b havebeen detected by ³¹P NMR spectroscopy and tentatively assigned the heterovalent structures(C₆F₅)Au^I(r.gif">-2-R₂PC₆H₄)Au^III(C₆F₅)(rs/eta.gif" BORDER=0 >²-2-C₆H₄PR₂)] (R = Ph (6a), Et (6b)), in which one C₆H₄PR₂ group bridges the two gold atoms while the other binds as a bidentate chelate ligand togold(III). The S-bonded bis(thiocyanato) complexes [Au^II₂(SCN)₂(r.gif">-2-C₆H₄PR₂)₂] (R = Ph (8a),Et (8b)) formed from 1a or 1b and KSCN undergo C-C coupling more rapidly than theC₆F₅ compounds to give [Au^I₂(SCN)₂(r.gif">-2,2'-R₂PC₆H₄C₆H₄PR₂)] (R = Ph (10a), Et (10b)) viathe detectable heterovalent intermediates 9a or 9b, which are analogues of 6a and 6b. TheX-ray structures of complexes 2a, 3a, 4a, 4b, 5a, and 10b have been determined. The gold-gold separations in 2a, 3a, and 5a are respectively 2.8874(4), 2.6139(4), and 2.931(1)/2.921(1) Å (for independent molecules), the shorter distance in 3a corresponding to a covalentmetal-metal bond. In 4a and 10b the torsion about the central C-C bond of the biphenylbackbone results in a syn configuration for the Au-X (X = C₆F₅, SCN) fragments and aclose intramolecular aurophilic contact between the gold atoms (r(Au^...Au) = 3.0688(8) Å(4a), 3.0853(9) Å (10b)), whereas in 4b the Au-C₆F₅ units adopt an anti configuration relativeto the biphenyl fragment, leading to a nonbonding gold-gold separation of 5.3469(7) Å. Thedifferences in behavior of digold(II) complexes [Au₂X₂(r.gif">-2-C₆H₄PR₂)₂] as the axial anionicligand X is varied and the pathway of the intramolecular C-C coupling reaction arediscussed.