TY - JOUR
T1 - Synthesis and interconversions of digold(i), tetragold(i), digold(ii), gold(i)-gold(iii) and digold(iii) complexes of fluorine-substituted aryl carbanions
AU - Bennett, Martin A.
AU - Bhargava, Suresh K.
AU - Mirzadeh, Nedaossadat
AU - Privér, Steven H.
AU - Wagler, Jörg
AU - Willis, Anthony C.
PY - 2009
Y1 - 2009
N2 - Treatment of [AuXL] (X = Br, L = AsPh3; X = Cl, L = tht) with the lithium or trimethyltin derivatives of the carbanions [2-C6F 4PPh2]- and [C6H3-n-F-2- PPh2]- (n = 5, 6) gives digold(i) complexes [Au 2(μ-carbanion)2] (carbanion = 2-C6F 4PPh22, C6H3-5-F-2-PPh23, C6H3-6-F-2-PPh24) which, like their 2-C 6H4PPh2 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-C6F4PPh 2, X = Cl 5, Br 8, I 11; carbanion = C6H 3-5-F-2-PPh2, X = Cl 6, Br 9, I 12; carbanion = C 6H3-6-F-2-PPh2, X = Cl 7, Br 10, I 13). In the case of 2-C6F4PPh2 and C6H 3-6-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 C 6H3-6-Me-2-PPh2 system. The Au 2X2 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), [Au2X 2(2,2′-Ph2P-5-F-C6H3C 6H3-5-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-C 6F4PPh2)2] (Y = OAc 14, ONO 215, OBz 16, O2CCF317 and OTf 20), which do not isomerise to the corresponding gold(i)-gold(iii) complexes [YAu(μ-2-C 6F4PPh2)(κ2-2-C 6F4PPh2)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(CH 3)2] 19, in which both 2-C6F 4PPh2 groups 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)Au I(μ-2-C6F4PPh2) (κ2-2-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 [Au 4(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 [Au 4(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-C6F4PPh 2)2] (X = Cl 39, Br 40) and [X3Au(μ-2-C 6F4PPh2)AuX(κ2-2-C 6F4PPh2)] (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) (5d 9-5d9) 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, [Au 3Br2(μ-C6H3-6-F-2-PPh 2)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)Au IBr fragment.
AB - Treatment of [AuXL] (X = Br, L = AsPh3; X = Cl, L = tht) with the lithium or trimethyltin derivatives of the carbanions [2-C6F 4PPh2]- and [C6H3-n-F-2- PPh2]- (n = 5, 6) gives digold(i) complexes [Au 2(μ-carbanion)2] (carbanion = 2-C6F 4PPh22, C6H3-5-F-2-PPh23, C6H3-6-F-2-PPh24) which, like their 2-C 6H4PPh2 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-C6F4PPh 2, X = Cl 5, Br 8, I 11; carbanion = C6H 3-5-F-2-PPh2, X = Cl 6, Br 9, I 12; carbanion = C 6H3-6-F-2-PPh2, X = Cl 7, Br 10, I 13). In the case of 2-C6F4PPh2 and C6H 3-6-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 C 6H3-6-Me-2-PPh2 system. The Au 2X2 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), [Au2X 2(2,2′-Ph2P-5-F-C6H3C 6H3-5-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-C 6F4PPh2)2] (Y = OAc 14, ONO 215, OBz 16, O2CCF317 and OTf 20), which do not isomerise to the corresponding gold(i)-gold(iii) complexes [YAu(μ-2-C 6F4PPh2)(κ2-2-C 6F4PPh2)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(CH 3)2] 19, in which both 2-C6F 4PPh2 groups 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)Au I(μ-2-C6F4PPh2) (κ2-2-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 [Au 4(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 [Au 4(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-C6F4PPh 2)2] (X = Cl 39, Br 40) and [X3Au(μ-2-C 6F4PPh2)AuX(κ2-2-C 6F4PPh2)] (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) (5d 9-5d9) 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, [Au 3Br2(μ-C6H3-6-F-2-PPh 2)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)Au IBr fragment.
UR - http://www.scopus.com/inward/record.url?scp=69949182738&partnerID=8YFLogxK
U2 - 10.1039/b906769h
DO - 10.1039/b906769h
M3 - Article
SN - 1477-9226
SP - 7537
EP - 7551
JO - Dalton Transactions
JF - Dalton Transactions
IS - 36
ER -