Issue 36, 2009

Synthesis and interconversions of digold(i), tetragold(i), digold(ii), gold(i)–gold(iii) and digold(iii) complexes of fluorine-substituted aryl carbanions

Abstract

Treatment of [AuXL] (X = Br, L = AsPh3; X = Cl, L = tht) with the lithium or trimethyltin derivatives of the carbanions [2-C6F4PPh2] and [C6H3-n-F-2-PPh2] (n = 5, 6) gives digold(I) complexes [Au2(μ-carbanion)2] (carbanion = 2-C6F4PPh22, C6H3-5-F-2-PPh23, C6H3-6-F-2-PPh24) which, like their 2-C6H4PPh2 counterpart, undergo oxidative addition with halogens X2 (X = Cl, Br, I) to give the corresponding, metal-metal bonded digold(II) complexes [Au2X2(μ-carbanion)2] (carbanion = 2-C6F4PPh2, X = Cl 5, Br 8, I 11; carbanion = C6H3-5-F-2-PPh2, X = Cl 6, Br 9, I 12; carbanion = C6H3-6-F-2-PPh2, X = Cl 7, Br 10, I 13). In the case of 2-C6F4PPh2 and C6H3-6-F-2-PPh2, the dihalodigold(II) complexes rearrange on heating to isomeric gold(I)–gold(III) complexes [XAuI(μ-P,C-carbanion)(κ2-P,C-carbanion)AuIIIX] (carbanion = 2-C6F4PPh2, X = Cl 25, Br 26, I 27; carbanion = C6H3-6-F-2-PPh2, X = Cl 28, Br 29, I 30), in which one of the carbanions chelates to the gold(III) atom. This isomerisation is similar to, but occurs more slowly than, that in the corresponding C6H3-6-Me-2-PPh2 system. The Au2X2 complexes 6, 9 and 12, on the other hand, rearrange on heating via C–C coupling to give digold(I) complexes of the corresponding 2,2′-biphenyldiylbis(diphenylphosphine), [Au2X2(2,2′-Ph2P-5-F-C6H3C6H3-5-F-PPh2)] (X = Cl 32, Br 33, I 34), this behaviour resembling that of the 2-C6H4PPh2 and C6H3-5-Me-2-PPh2 systems. Since the C–C coupling probably occurs via undetected gold(I)–gold(III) intermediates, the presence of a 6-fluoro substituent is evidently sufficient to suppress the reductive eliminations, possibly because of an electronic effect that strengthens the gold(III)-aryl bond. Anation of 5 or 8 gives the bis(oxyanion)digold(II) complexes [Au2Y2(μ-2-C6F4PPh2)2] (Y = OAc 14, ONO215, OBz 16, O2CCF317 and OTf 20), which do not isomerise to the corresponding gold(I)–gold(III) complexes [YAu(μ-2-C6F4PPh2)(κ2-2-C6F4PPh2)AuY] on heating, though the latter [Y = OAc 35, ONO236, OBz 37, O2CCF338] can be made by anation of 25–27. Reaction of the bis(benzoato)digold(II) complex 16 with dimethylzinc gives a dimethyl gold(I)–gold(III) complex, [AuI(μ-2-C6F4PPh2)2AuIII(CH3)2] 19, in which both 2-C6F4PPh2groups are bridging. In contrast, the corresponding reaction of 16 with C6F5Li gives a digold(II) complex [AuII2(C6F5)2(μ-2-C6F4PPh2)2] 18, which on heating isomerises to a gold(I)–gold(III) complex, [(C6F5)AuI(μ-2-C6F4PPh2)(κ2-2-C6F4PPh2)AuIII(C6F5)] 31, analogous to 25–27. The bis(triflato)digold(II) complex 20 is reduced by methanol or cyclohexanol in CH2Cl2 to a tetranuclear gold(I) complex [Au4(μ-2-C6F4PPh2)4] 21 in which the four carbanions bridge a square array of metal atoms, as shown by a single-crystal X-ray diffraction study. The corresponding tetramers [Au4(μ-C6H3-n-F-2-PPh2)4] (n = 5 22, 6 23) are formed as minor by-products in the preparation of dimers 3 and 4; the tetramers do not interconvert readily with, and are not in equilibrium with, the corresponding dimers 2–4. Addition of an excess of chlorine or bromine (X2) to the digold(II) complexes 5 and 8, and to their gold(I)–gold(III) isomers 25 and 26, gives isomeric digold(III) complexes [Au2X4(μ-2-C6F4PPh2)2] (X = Cl 39, Br 40) and [X3Au(μ-2-C6F4PPh2)AuX(κ2-2-C6F4PPh2)] (X = Cl 41, Br 42), respectively. The structures of the digold(I) complexes 2, 4 and 32, the digold(II) complexes 5–11 and 14–18, the gold(I)–gold(III) complexes 19, 25, 35 and 38, the tetragold(I) complexes 21 and 22, and the digold(III) complexes 41 and 42, have been determined by single-crystal X-ray diffraction. In the digold(II) (5d9–5d9) series, there is a systematic lengthening, and presumably weakening, of the Au–Au distance in the range 2.5012(4)–2.5885(2) Å with increasing trans-influence of the axial ligand, in the order X = ONO2 < O2CCF3 < OBz < Cl < Br < I < C6F5. The strength of the Au–Au interaction is probably the main factor that determines whether the digold(II) compounds isomerise to gold(I)–gold(III). The gold-gold separations in the digold(I) and gold(I)–gold(III) complexes are in the range 2.8–3.6 Å suggestive of aurophilic interactions, but these are probably absent in the digold(III) compounds (Au⋯Au separation ca. 5.8 Å). Attempted recrystallisation of complex 10 gave a trinuclear gold(II)–gold(II)–gold(I) complex, [Au3Br2(μ-C6H3-6-F-2-PPh2)3] 24, which consists of the expected digold(II) framework in which one of the axial bromide ligands has been replaced by a σ-carbon bonded (C6H3-6-F-2-PPh2)AuIBr fragment.

Graphical abstract: Synthesis and interconversions of digold(i), tetragold(i), digold(ii), gold(i)–gold(iii) and digold(iii) complexes of fluorine-substituted aryl carbanions

Supplementary files

Article information

Article type
Paper
Submitted
03 Apr 2009
Accepted
12 Jun 2009
First published
27 Jul 2009

Dalton Trans., 2009, 7537-7551

Synthesis and interconversions of digold(I), tetragold(I), digold(II), gold(I)–gold(III) and digold(III) complexes of fluorine-substituted aryl carbanions

M. A. Bennett, S. K. Bhargava, N. Mirzadeh, S. H. Privér, J. Wagler and A. C. Willis, Dalton Trans., 2009, 7537 DOI: 10.1039/B906769H

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements