Formation of gold(III) alkyls from gold alkoxide complexes

Chambrier, Isabelle, Roşca, Dragoş-Adrian, Fernandez-Cestau, Julio, Hughes, David L., Budzelaar, Peter H. M. and Bochmann, Manfred ORCID: (2017) Formation of gold(III) alkyls from gold alkoxide complexes. Organometallics, 36 (7). 1358–1364. ISSN 0276-7333

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The gold(III) methoxide complex (C^N^C)AuOMe 1 reacts with tris(p-tolyl)phosphine in benzene at room temperature under O-abstraction to give methylgold product (C^N^C)AuMe 2 together with O=P(p-tol)3 {(C^N^C) = [2,6-(C6H3tBu-4)2¬pyridine]2 }. Calculations show that this reaction is energetically favourable (ΔG = 32.3 kcal mol 1). The side-products in this reaction, the Au(II) complex [Au(C^N^C)]2 3 and the phosphorane (p-tol)3P(OMe)2, suggest that at least two reaction pathways may operate, including one involving (C^N^C)Au• radicals. Attempts to model the reaction by DFT methods showed that PPh3 can approach 1 to give a near-linear Au-O-P arrangement, without phosphine coordination to gold. The analogous reaction of (C^N^C)AuOEt, on the other hand, gives exclusively a mixture of 3 and (p-tol)3P(OEt)2. Whereas the reaction of (C^N^C)AuOR (R = But, p-C6H4F) with P(p-tol)3 proceeds over a period of hours, compounds with R = CH2CF3 or CH(CF3)2 react almost instantaneously, to give 3 and O=P(p-tol)3. In chlorinated solvents, treatment of the alkoxides (C^N^C)AuOR with phosphines generates [(C^N^C)Au(PR3)]Cl, via Cl-abstraction from the solvent. Attempts to extend the synthesis of gold(III) alkoxides to allyl alcohols were unsuccessful; the reaction of (C^N^C)AuOH with an excess of CH2=CHCH2OH in toluene led instead to allyl alcohol isomerization to give a mixture of gold alkyls, (C^N^C)AuR′ (R′ = -CH2CH2CHO 10 and CH2CH(CH2OH)¬OCH2¬CH=CH2 11), while 2-methallyl alcohol affords R′ = CH2CH(Me)CHO 12. The crystal structure of 11 was determined. The formation of Au-C instead of the expected Au-O products is in line with the trend in metal-ligand bond dissociation energies for Au(III), M-H > M-C > M-O.

Item Type: Article
Faculty \ School: Faculty of Science > School of Chemistry
Depositing User: Pure Connector
Date Deposited: 18 Mar 2017 01:42
Last Modified: 22 Oct 2022 02:26
DOI: 10.1021/acs.organomet.7b00077

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