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Reaction of (P)AuOTf [P=P(t‐Bu)₂o‐biphenyl] with indenyl‐ or 3‐methylindenyl lithium led to isolation of gold η¹‐indenyl complexes (P)Au(η¹‐inden‐1‐yl) (1 a) and (P)Au(η¹‐3‐methylinden‐1‐yl) (1 b), respectively, in >65 % yield. Whereas complex1 bis static, complex1 aundergoes facile, degenerate 1,3‐migration of gold about the indenyl ligand (ΔG^≠_153K=9.1±1.1 kcal/mol). Treatment of complexes1 aand1 bwith (P)AuNTf₂led to formation of the corresponding cationic bis(gold) indenyl complexestrans‐[(P)Au]₂(η¹,η¹‐inden‐1,3‐yl) (2 a) andtrans‐[(P)Au]₂(η¹,η²‐3‐methylinden‐1‐yl) (2 b), respectively, which were characterized spectroscopically and modeled computationally. Despite the absence of aurophilic stabilization in complexes2 aand2 b, the binding affinity of mono(gold) complex1 atoward exogenous (P)Au⁺exceed that of free indene by ~350‐fold and similarly the binding affinity of1 btoward exogenous (P)Au⁺exceed that of 3‐methylindene by ~50‐fold. The energy barrier for protodeauration of bis(gold) indenyl complex2 awith HOAc was ≥8 kcal/mol higher than for protodeauration of mono(gold) complex1 a.

 

Allosteric control of reaction thermodynamics is well understood, but the mechanisms by which changes in local geometries of receptor sites lower activation reaction barriers in electronically uncoupled, remote reaction moieties remain relatively unexplored. Here we report a molecular scaffold in which the rate of thermal E-to-Z isomerization of an alkene increases by a factor of as much as 10⁴in response to fast binding of a metal ion to a remote receptor site. A mechanochemical model of the olefin coupled to a compressive harmonic spring reproduces the observed acceleration quantitatively, adding the studied isomerization to the very few reactions demonstrated to be sensitive to extrinsic compressive force. The work validates experimentally the generalization of mechanochemical kinetics to compressive loads and demonstrates that the formalism of force-coupled reactivity offers a productive framework for the quantitative analysis of the molecular basis of allosteric control of reaction kinetics. Important differences in the effects of compressive vs. tensile force on the kinetic stabilities of molecules are discussed.

 

Treatment of the gold vinyl carbene/allylic cation complex ( E )-[(IPr)AuC(H)C(H)C(4-C 6 H 4 OMe) 2 ] + OTf − with sulfoxides at −95 °C formed the corresponding gold allyloxysulfonium complexes [(IPr)AuC(H)(OSR 2 )C(H)C(4-C 6 H 4 OMe) 2 ] + OTf − [R = Me, –(CH 2 ) 4 –, Ar] in ≥95 ± 5% NMR yield. Allyloxysulfonium gold complexes underwent elimination at or below room temperature to form 3,3-bis(4-methoxyphenyl)acrylaldehyde in ≥67% yield. 

Cationic gold vinyl carbene/allylic cation complexes of the form ( E )-[(L)AuC(H)C(H)CAr 2 ] + OTf − {L = IPr, Ar = Ph [( E )- 5a ], L = IPr, Ar = 4-C 6 H 4 OMe [( E )- 5b ], L = P( t -Bu) 2 o -biphenyl, Ar = 4-C 6 H 4 OMe [( E )- 5c ]} were generated in solution via Lewis acid-mediated ionization of the corresponding gold (γ-methoxy)vinyl complexes ( E )-(L)AuC(H)C(H)C(OMe)Ar 2 at or below −95 °C. Complexes ( E )- 5b and ( E )- 5c were fully characterized in solution employing multinuclear NMR spectroscopy, which established the predominant contribution of the aurated allylic cation resonance structure and the significant distribution of positive charge into the γ-anisyl rings. Complex ( E )- 5b reacted rapidly at −95 °C with neutral two-electron, hydride, and oxygen atom donors exclusively at the C1 position of the vinyl carbene moiety and with p -methoxystyrene to form the corresponding vinylcyclopropane. In the absence of nucleophile ( E )- 5a decomposed predominantly via intermolecular carbene dimerization whereas formation of 1-aryl-5-methoxy indene upon ionization of ( Z )-(IPr)AuC(H)C(H)C(OMe)(4-C 6 H 4 OMe) 2 [( Z )- 6b ] implicated an intramolecular Friedel–Crafts or electrocyclic Nazarov pathway for the decomposition of the unobserved vinyl carbene complex ( Z )-[(IPr)AuC(H)C(H)C(4-C 6 H 4 OMe) 2 ] + OTf − [( Z )- 5b ]. 

The mechanism of the intermolecular hydroamination of 3‐methylbuta‐1,2‐diene (1) withN‐methylaniline (2) catalyzed by (IPr)AuOTf has been studied by employing a combination of kinetic analysis, deuterium labelling studies, and in situ spectral analysis of catalytically active mixtures. The results of these and additional experiments are consistent with a mechanism for hydroamination involving reversible, endergonic displacement ofN‐methylaniline from [(IPr)Au(NHMePh)]⁺(4) by allene to form the cationic gold π‐C1,C2‐allene complex [(IPr)Au(η²‐H₂C=C=CMe₂)]⁺(I), which is in rapid, endergonic equilibrium with the regioisomeric π‐C2,C3‐allene complex [(IPr)Au(η²‐Me₂C=C=CH₂)]⁺(I′). Rapid and reversible outer‐sphere addition of2to the terminal allene carbon atom ofI′to form gold vinyl complex (IPr)Au[C(=CH₂)CMe₂NMePh] (II) is superimposed on the slower addition of2to the terminal allene carbon atom ofIto form gold vinyl complex (IPr)Au[C(=CMe₂)CH₂NMePh] (III). Selective protodeauration ofIIIreleasesN‐methyl‐N‐(3‐methylbut‐2‐en‐1‐yl)aniline (3 a) with regeneration of4. At high conversion, gold vinyl complexIIis competitively trapped by an (IPr)Au⁺fragment to form the cationic bis(gold) vinyl complex {[(IPr)Au]₂[C(=CH₂)CMe₂NMePh]}⁺(6).

 

Methoxide abstraction from gold acetylide complexes of the form (L)Au[η¹‐C≡CC(OMe)ArAr′] (L=IPr, P(^tBu)₂(ortho‐biphenyl); Ar/Ar′=C₆H₄X where X=H, Cl, Me, OMe) with trimethylsilyl trifluoromethanesulfonate (TMSOTf) at −78 °C resulted in the formation of the corresponding cationic gold diarylallenylidene complexes [(L)Au=C=C=CArAr′]⁺ OTf⁻in ≥85±5 % yield according to¹H NMR analysis.¹³C NMR and IR spectroscopic analysis of these complexes established the arene‐dependent delocalization of positive charge on both the C1 and C3 allenylidene carbon atoms. The diphenylallenylidene complex [(IPr)Au=C=C=CPh₂]⁺ OTf⁻reacted with heteroatom nucleophiles at the allenylidene C1 and/or C3 carbon atom.

 

Methoxide abstraction from gold acetylide complexes of the form (L)Au[η¹‐C≡CC(OMe)ArAr′] (L=IPr, P(^tBu)₂(ortho‐biphenyl); Ar/Ar′=C₆H₄X where X=H, Cl, Me, OMe) with trimethylsilyl trifluoromethanesulfonate (TMSOTf) at −78 °C resulted in the formation of the corresponding cationic gold diarylallenylidene complexes [(L)Au=C=C=CArAr′]⁺ OTf⁻in ≥85±5 % yield according to¹H NMR analysis.¹³C NMR and IR spectroscopic analysis of these complexes established the arene‐dependent delocalization of positive charge on both the C1 and C3 allenylidene carbon atoms. The diphenylallenylidene complex [(IPr)Au=C=C=CPh₂]⁺ OTf⁻reacted with heteroatom nucleophiles at the allenylidene C1 and/or C3 carbon atom.