Synthesis and Hydrolysis of [Alkenyl(alkoxy)carbene]manganese Complexes: Evidence for a Transient Allylic Intermediate on the Way to α,β-Unsaturated Aldehydes

Abstract

A variety of alkenylcarbene complexes [Cp′(CO)2Mn=C(OEt)CH=CHR] (3) (Cp′ = η5‐MeC5H4) was obtained in a straightforward manner upon aldol condensation of [Cp′(CO)2Mn=C(OEt)CH3] (1) with aromatic and α,β‐unsaturated aldehydes RC(H)O (2). The reaction is totally stereoselective, giving (E)‐ or (all‐E)‐alkenylcarbenes only. The protonation of 3 at low temperature followed by reaction with water affords the α,β‐unsaturated aldehyde complexes [Cp′(CO)2Mn(η2‐RCH=CHCHO] (5), from which the aldehydes RC(H)=C(H)C(H)O (6) were displaced by acetonitrile. The intermediate aldehyde complexes are shown to result from the hydrolysis of a transient cationic π‐allyl species [Cp′(CO)2Mn(η3‐RCHCHC(OEt)H]+ ([4]+) formed upon protonation of 3.

Unusual C–H bond activation—aldol condensation of aromatic aldehydes with the methyl group of a carbene-like triosmium cluster

“…1 The synthetic potential of this type of reaction in organometallic chemistry is mainly related to Fischer carbene complexes, for which there are many important applications. 2- 7 In such cases, a general synthetic strategy consists of the generation of a carbanion in the αposition relative to the carbene carbon followed by nucleophilic attack of this species onto the carbonyl carbon of an aldehyde to form a new carbon-carbon bond. 2,3, 7 Here we report the condensation reactions of a series of aromatic aldehydes with the methyl group of the organic ligand in [HOs 3 (CO) 10 (η 1 :η 1 -OC 4 H 2 CCH 3 )] (1).…”

“…2- 7 In such cases, a general synthetic strategy consists of the generation of a carbanion in the αposition relative to the carbene carbon followed by nucleophilic attack of this species onto the carbonyl carbon of an aldehyde to form a new carbon-carbon bond. 2,3, 7 Here we report the condensation reactions of a series of aromatic aldehydes with the methyl group of the organic ligand in [HOs 3 (CO) 10 (η 1 :η 1 -OC 4 H 2 CCH 3 )] (1). 8 These condensations represent unusual examples of C-H bond activation in transition metal clusters and demonstrate a Fischer carbene reactivity pattern of the coordinated organic fragment.…”

Recent advances in the field of multicarbene and multimetal carbene complexes of the Fischer-type

“…94, Fig. 37) [11,158], the tethered biscarbene complexes (95) in Fig. 37 are two of the scarce examples with two cyclopentadienylcarbene moieties [139].…”

ChemInform Abstract: Organometallic Chemistry. Part 2. Transition Metals in Organic Synthesis: Stoichiometric Applications

“…For example, ferrocenecarbaldehyde (80) affords b-ferrocenylacrylaldehyde (81) in 75% yield, Scheme 21. 42 Aryl ketones are converted to arylfuranones by a three-step sequence involving a Mn(III) oxidation. Thus acenaphthone (82) affords naphthylbutenolide (83), via bromoacetoxyketone and phosphonate intermediates, in an overall yield of 43%, Scheme 22.…”