Isocyanide insertion into Au-H bonds: first gold iminoformyl complexes

Isocyanides insert into gold(III)-hydrogen bonds to give the first examples of gold iminoformyl complexes. The reaction is initiated by catalytic amounts of radicals; DFT calculations indicate that this is an equilibrium reaction driven forward by isocyanide in sufficient excess to trap the Au(II) intermediate

Formation of gold(III) alkyls from gold alkoxide complexes

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

Gold-Catalysed Heck Reaction: Fact or Fiction?

Two recent high-profile publications described the formation of Heck-type arylated alkenes catalysed by MeDalPhosAuCl / AgOTf (J. Am. Chem. Soc. 2023, 145, 8810) and their cyclisation to tetralines (Angew. Chem. Int. Ed. 2023, e202312786), claiming that these were the first demonstrations of alkene insertion into Au-aryl bonds, β-H elimination and chain-walking by Au-H cations under catalytic conditions. We show here that in fact this chemistry is a two-stage process. Only the first step, the production of an alkyl triflate ester as primary product by the well-known alkene heteroarylation sequence, involves gold. The subsequent formation of Heck-type olefins and their cyclisation to tetralines represent are classical H+-triggered carbocationic chemistry. These steps proceed in the absence of gold with identical results. Literature claims of new gold reactivity such as chain walking by the putative [LAuH]2+ dication have no basis in fact

Analysis of Stereochemistry Control in Homogeneous Olefin Polymerization Catalysis

We propose a new method, using statistical analysis, to quantify factors contributing to stereo- and regiocontrol in olefin polymerization catalysis and competing β-hydrogen transfer to monomer. The method has been applied to three rather different Zr-based catalysts: (<b>1</b>) <i>rac</i>-Me₂Si­(3-Me-C₅H₃)₂ZrR⁺, a representative of “standard” <i>ansa</i> metallocenes; (<b>2</b>) [2,2′-bis­(2-indenyl)­biphenyl]­ZrR⁺, a sterically congested and rather atypical metallocene; and (<b>3</b>) [1,2-(2-<i>O</i>-3-^<i>t</i>Bu-C₆H₃CH₂NMe)₂-C₂H₄]­ZrR⁺, an example of an octahedral “ONNO”-type catalyst. The analysis produces separate numeric values for repulsive ligand–chain, chain–monomer, and ligand–monomer interactions. For insertion in the Zr–^<i>i</i>Bu bond of <b>1</b> and <b>3</b>, the ordering is <i>syn</i> (∼2.3 kcal/mol) > ligand–chain (∼1.6) > ligand–monomer (∼1.3), while for more crowded system <b>2</b> the three interactions are all around 2.0–2.5 kcal/mol. Despite the non-negligible magnitude of the ligand–chain interaction, the standard Corradini model of stereocontrol was found to apply for all cases. Our results also indicate that the stereocontrol penalties are sensitive to the nature of the chain and the olefin and that extrapolation from H or Me “chains” to more realistic chains is not warranted

Mimicking Ziegler-Natta catalysts in homogeneous phase. Part 1. C2-Symmetric octahedral Zr(IV) complexes with tetradentate [ONNO]-type ligands

Propene polymn. was carried out in the presence of 2 of the title Zr complexes, giving isotactic site-controlled or weakly syndiotactic chain-end-controlled polymers via highly regioselective 1,2 primary monomer insertion. The two catalysts are believed to be good models of Ziegler-Natta active species, albeit with lower abs. rates of chain propagation and transfer

Gold-catalysed Heck reaction: Fact or fiction? Correspondence on “Unlocking the Chain Walking Process in Gold Catalysis”

Two recent high-profile publications reported the formation of Heck-type arylated alkenes catalysed by MeDalPhosAuCl / AgOTf (J. Am. Chem. Soc. 2023, 145, 8810) and their cyclisation to tetralines (Angew. Chem. Int. Ed. 2023, e202312786). It was claimed that these were the first demonstrations in gold catalysis of alkene insertion into Au-aryl bonds, β-H elimination and chain-walking by Au-H dications. We show here that in fact this chemistry is a two-stage process. Only the first step, the production of an alkyl triflate ester as the primary organic product by the well-known alkene heteroarylation sequence, involves gold. The subsequent formation of Heck-type olefins and their cyclisation to tetralines represent classical H+-triggered carbocationic chemistry. These steps proceed in the absence of gold with identical results. Literature claims of new gold reactivity such as chain walking by the putative [LAuH]2+ dication have no basis in fact