Synthesis, Structure, and Reactivity of a Gold Carbenoid Complex That Lacks Heteroatom Stabilization

Abstract

Hydride abstraction from the neutral gold cycloheptatrienyl complex [(P)Au(η(1)-C7H7)] (P=P(tBu)2(o-biphenyl)) with triphenylcarbenium tetrafluoroborate at -80 °C led to the isolation of the cationic gold cycloheptatrienylidene complex [(P)Au(η(1)-C7H6)](+) BF4(-) in 52% yield, which was characterized in solution and by single-crystal X-ray diffraction. This cycloheptatrienylidene complex represents the first example of a gold carbenoid complex that lacks conjugated heteroatom stabilization of the electron-deficient C1 carbon atom. The cycloheptatrienylidene ligand of this complex is reactive; it can be reduced by mild hydride donors, and converted to tropone in the presence of pyridine N-oxide.

Enhanced π‐Backdonation from Gold(I): Isolation of Original Carbonyl and Carbene Complexes

“…[14] In complex B, [13f,g, 14a] Gratifyingly, the [(DPCb)AuNTf 2 ] complex 3 was found to rapidly and cleanly react with diphenyldiazomethane at temperatures as low as À40 8C (Scheme 2). Complex 4 was isolated (93 % yield) as a dark violet solid.…”

A Nucleophilic Gold(III) Carbene Complex

“…[1] Thevery nature of the AuÀC carbene bond has also attracted considerable attention. Accordingly, p donation from the carbene substituents [4][5][6] or enhanced p backdonation from the Au center, [7] were recently distinguished as the main stabilization modes of the electrophilic carbene center ( Figure 1). Accordingly, p donation from the carbene substituents [4][5][6] or enhanced p backdonation from the Au center, [7] were recently distinguished as the main stabilization modes of the electrophilic carbene center ( Figure 1).…”

Synthesis and Characterization of a Gold Vinylidene Complex Lacking π‐Conjugated Heteroatoms

“…13 C-Spin saturation transfer analysis of [1,2-13 C 2 ]-3 at À90 8 8Cc onfirmed interconversion of the C1 and C2 vinylidene carbon atoms and established an energy barrier of DG°1 83K = 9.7 kcal mol À1 for this process.T he simplest mechanism that accounts for interconversion of the C1 and C2 vinylidene carbon atoms of 3 involves 1,2-silyl migration to generate the unobserved gold h 2 -disilacyclohexyne intermediate [(P)Au{h 2 -C K CSi(Me) 2 CH 2 CH 2 SiL (Me) 2 }] + B(C 6 F 5 ) 4 À (II; Scheme 4). [7,10] TheC 1a nd C2 vinylidene atoms of 3 undergo facile interconversion (DG°1 83K = 9.7 kcal mol À1 ), presumably via the gold p-disilacyclohexyne intermediate II. [23] In summary,w eh ave synthesized the gold (b,b-disilyl)vinylidene complex 3 by hydride abstraction/cyclization of neutral gold acetylide complex 2.C omplex 3 represents the first example of agold vinylidene complex and arare example of ag old carbene complex that lacks p-conjugated heteroatoms.…”

“…[4,5] Although the intermediacyo fg old carbenes in these transformations is generally accepted, there remains considerable debate regarding the electronic structure of the Au À C bond, [6][7][8][9] due in large part to the dearth of suitable model complexes for structural and/or spectroscopic interrogation. It is therefore significant that within the past year welldefined gold carbene complexes that 1) lack p-conjugated heteroatoms (A, B), [7,10] 2) displayalkylidene transfer behavior (C), [8] or 3) contain ac yclopropyl group at C1 (D) [9] have been reported (Scheme 1), which provide new insight into the electronic structure and behavior of gold carbene complexes. [11,12] Gold vinylidene complexes of the form [(L)Au=C=CR 2 ] + constitute ap articularly intriguing class of gold carbene complexes that have attracted considerable recent interest.…”