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 = AsPh(3); 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(mu-carbanion)2] (carbanion = 2-C6F4PPh2 2, C6H3-5-F-2-PPh2 3, C6H3-6-F-2-PPh2 4) 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(mu-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 [XAu(I)(mu-P,C-carbanion)(kappa2-P,C-carbanion)Au(III)X] (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(mu-2-C6F4PPh2)2] (Y = OAc 14, ONO2 15, OBz 16, O2CCF3 17 and OTf 20), which do not isomerise to the corresponding gold(I)-gold(III) complexes [YAu(mu-2-C6F4PPh2)(kappa2-2-C6F4PPh2)AuY] on heating, though the latter [Y = OAc 35, ONO2 36, OBz 37, O2CCF3 38] 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, [Au(I)(mu-2-C6F4PPh2)2Au(III)(CH3)2] 19, in which both 2-C6F4PPh2 groups are bridging. In contrast, the corresponding reaction of 16 with C6F5Li gives a digold(II) complex [Au(II)2(C6F5)2(mu-2-C6F4PPh2)2] 18, which on heating isomerises to a gold(I)-gold(III) complex, [(C6F5)Au(I)(mu-2-C6F4PPh2)(kappa2-2-C6F4PPh2)Au(III)(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(mu-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(mu-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 ...

Preparation, Structure, and Reactivity of Dipalladium(I) Complexes Containing the Carbanion 2-C6F4PPh2: Coexistence of Distinct, Noninterconverting Head-to-Head [Dipalladium(0/II)] and Head-to-Tail [Dipalladium(I)] Species

“…A similar migration has been invoked as the first step of the rearrangement of the homovalent dihalodigold(II) complexes [Au 2 X 2 (μ-2-C 6 F 4 PPh 2 ) 2 ] (X = halide) to their heterovalent gold(I)−gold(III) isomers [XAu I (μ-2-Ph 2 PC 6 F 4 )-Au III X(κ 2 C,P-2-C 6 F 4 PPh 2 )]. 51 The sequence is completed by cleavage of the Pd(2)−P bond from the remaining μ-2-C 6 F 4 PPh 2 ligand, giving 15, and elimination of [Ph 4 P]I from Pd(2). Since the formation of metallic palladium is not observed, the fate of Pd(2) is unclear; however, in general agreement with the proposed course of the reaction, it has been reported that [PdI(Ph)(PPh 3 ) 2 ] eliminates [Ph 4 P]I on heating 52 and that the quaternization of PPh 3 by aryl bromides is catalyzed by [Pd(OAc) 2 ] in DMF, 53 a reaction that probably involves Pd(0).…”

Synthesis of dinuclear N-heterocyclic dicarbene Au(III)/Au(III) and Au(II)/Au(II) complexes via oxidative addition of chlorine or bromine to Au(I)/Au(I) species

“…This observation is somewhat surprising but in agreement with previous results on dinuclear gold complexes with o-metallated phosphines or phosphorous diylides. In these last cases 31 P NMR spectra and XPS analysis suggest a similar electron density on gold(II) and gold(III) centres [12,13].…”

Phosphorus‐Bearing Lithium Compounds in Modern Synthesis

“…The bidentate ligand 95 usually binds as a chelate group (κ 2 P,C) A or a bridging (μ 2 -P,C) moiety B. Ortho-metallated complexes A and B of Pt, Rh, Ir, and Au are well known. Transmetallation of a fluorinated derivative of 95 [R 1 = Ph, R 2 = (F) 4 ] with [AuCl(tht)] (tht, tetrahydrothiophene) affords the cycloaurated digold(I) complex 96 (coordination mode B) featuring two linearly coordinated Au(I) metal atoms bridged by the carbanionic ligands in a head-to-tail arrangement [40]. Complex 96 undergoes oxidative addition of Cl 2 by treatment with PhICl 2 to yield the dichlorodigold(II) species 97 showing a metal-metal bond.…”