When the reaction was carried out using a co2free dmd solution in a n2 atmosphere ester 2 was formed in 40% yield, whereas in the presence of an. Further important insights into the bond situations in carbene complexes are provided by the. According to our calculations the addition of the alkyne molecule to the carbene complex takes place before co loss in the initial steps of the reaction. Fischer chromium carbene complexes as nucleophiles in palladiumcatalyzed allylic substitution reactions. Alkynylamino cr 0 and w 0 fischer carbenes undergo a cuaac reaction with a diverse range of di. Crosscoupling of ntosylhydrazones with chromium fischer carbene complexes under catalystfree conditions has been developed.
A kinetic study of the reactions of thiolate ions with three fischer type aryloxyphenyl carbene pentacarbonyl chromium 0 complexes in 50% mecn50% water vv is reported. Chromium fischer carbene complexes, cromerco5 have been utilized as a source of chromium carbonyls in the synthesis of chromium nhc complexes. Synthesis and properties of fischer carbene complexes of n. Synthesis of nitrogencontaining compounds using chromium. Transmetalation reactions from fischer carbene complexes. Unexpected reaction pathways and products are apparently not the exception for reactions of fischer carbenes, and full recognition of the. Request pdf synthesis of nitrogencontaining compounds using chromium fischer carbene complexes synthetic utility of the fischertype carbene complexes of chromium for the preparation of. Photolysis of chromium fischer carbene complexes has become an established synthetic method for the synthesis of a wide range of products including. New heterocyclization reactions with fischer carbene.
The photochemical reaction of vinylaziridines and vinylazetidines with chromium 0 and molybdenum0 fischer carbene complexes. Metal carbene complexes are often classified into two types. General annulation of fischer carbenes with alkynes and alkenes. This method is simple, versatile, and is suitable for the preparation of a diverse range of structures with a high level of symmetry. Oxidative decomplexation of chromium fischer carbene. According to these arguments, the bond order for the crc carbene bond is much smaller than for the chromiumc co bond in the same complex, but greater than the bond order in a single bond. In the ground state, a singlet carbene has a pair of electrons in a single orbital, whereas the triplet has two unpaired.
Fischer carbene complexes in organic synthesis ke chen 3. New reactivity modes of chromium0 fischer carbene complexes. Molecular structure and bond characterization of the. Alkyl chromium 0 carbene complexes typically undergo cycloadditions with alkynes to afford carbo or heterocyclic compounds.
Fischer carbene complex ketene acetal michael addition vinylidene complex rearrangement alkenyl fischer. Despite the undeniable synthetic value of the benzannulation reaction of aryl and alkenyl fischer carbene complexes, the details of its mechanism at the molecular. In fischertype chromiumcarbene complexes of the type co 5crdcxr, the electronic characteristics of the carbene substituents x and r control the electrophilicity of the complex and therefore have a great influence on its chemical reactivity. Schrock, are characterized by more nucleophilic carbene carbon centers, these species typically feature higher valent. Chromiumcopper exchange of fischer carbene complexes.
Through hydrolysis of the initially formed methyl eno carbenes for today. Baran group meeting fischer carbene complexes in organic. The chromium fischer carbene acted as a source of chromium carbonyls. Transition metal fischer carbene complexes have ample applications in chemistry owing to their attractive redox properties which are highly sensitive to the electronic effect of ligands eel and substituents. Wulff department of chemistry, michigan state university, east lansing, michigan 48824 received june 17, 2005.
In the presence of silica gel or base, the cyclohexadienone complex will suffer loss of the iron and aromatization to give 2. Anions formed by deprotonation of alkoxy and amino fischer carbene complexes of chromium and tungsten have been used as nucleophiles with. Synthesis of chromium nheterocyclic carbene complexes. Nucleophilic addition of chromium and tungsten carbene. Chromium carbene complexes in the synthesis of molecules. This leaves an electrophillic carbon because direct c m donation is only partly.
A carbene is a neutral divalent carbon species containing two electrons that are not shared with other atoms. Catalystfree crosscoupling of ntosylhydrazones with. Chromium fischer carbene complexes with trans, transdienyl substituents on the carbene carbon will react with diiron nonacarbonyl to give 2alkoxycyclohexa2,4dienone iron tricarbonyl complexes andor 2alkoxyphenols in excellent yields. We present a systematic investigation of the reduction potentials e0 of a large variety of fische. The computational data were compared with the available experimental data. The synthesis, characterization, and organometallic reactions of heteroatom stabilized. Carbene ligands b have a heteroatom substituent unlike alkylidenes a which usually have alkyl substituents on the alpha carbon atom. Fischer carbene complexes of chromium, molybdenum and tungsten. Fischer carbene complexes, particularly chromium and tungsten compounds, are highly valuable building blocks for the construction of complex organic molecules. Alkynyl fischer carbene complexes are excellent dienophile partners in the classic dielsalder reaction.
A click approach to polymetallic chromium0 and tungsten. Chromiumtemplated benzannulation reactions university of. By preparing the chromium carbene complex from colabeled chromium hexacarbonyl, b. Fac and mer dppesubstituted fischer carbene complexes of. Pdf synthesis of chromium nheterocyclic carbene complexes using chromium fischer carbenes as a source of chromium carbonyls helmut sitzmann and young chung academia. Diaryl ethers using fischer chromium carbene mediated. Iron in the service of chromium the orthobenzannulation. In the presence of pd catalyst, it is demonstrated that a traditional cycloaddition pathway is completely altered.
Fischer, who reported the first example in 1964 and later won a nobel. Electrochemical illumination of thienyl and ferrocenyl. Reactions of alkenyl fischer carbene complexes with ketene. Two new chromiumcarbonylcarbene complexes journal of the. Ph causes a 81 1ppm downfield shift in the carbene carbon resonance while that same variation with the aminocarbene complexes causes only a 0.
Fischer carbene complex with alkenes is called the. Pdf low temperature carbene transfer from alkoxychromium. Schrock, is nucleophilic at the carbene carbon atom in an unpaired triplet state. Wulff michigan state university jacs 2005, 127, 1716217163. Control experiments show that trans,transdienyl chromium carbene complexes do not undergo conversion to 2alkoxyphenols in the absence of an iron source. The synthesis of heterobi and heterotrimetallic fischer carbene complexes of a h 6rc 6 h 5crco 3 fragment is reported for r nme 2 three different isomers of heterobimetallic complexes have been prepared under conditions of kinetic or thermodynamic control substitution of a co ligand at the carbene site grant access to wco 4 complexes with a chelate bonding of the heteroatom. The fischer carbenes can be modified by electronrich groups. Using the synthetic method, chromium complexes of various nhc ligands were isolated in reasonable. This protocol employs stable carbene complexes and reactive diazo compounds, which are in situ generated from ntosylhydrazones. Herein we wish to communicate our preliminary results for the synthesis of chromium nhc complexes via a reaction of chromium fischer carbenes with nhcs and an xray crystal structure of one of them. They are highly reactive and can give access to a range of biologically active compounds. Conjugated chromium fischer alkoxy carbene complex 1 is quantitatively transformed into a mixture of zvinyl ether 2 and eallyl ether 3 by nabh4 reduction in etoh scheme 7.
Transmetalation reactions from chromium0 fischer carbene complexes to late. Several fischer carbenes were synthesized and characterized, some simple and known and some novel. Pdcatalyzed crosscoupling of terminal alkynes with. Surprisingly, a chromium nhc complex was obtained as the sole chromium product. Heteroatom and substituent effects in chromium fischer carbene complexes we have carried out a. Goddard iii arthur amos noyes laboratory of chemrcal physrcs, cahorma instrtute of technology, pasadena, ca 91125, usa a.
An experimental and theoretical investigation of unstable. Carbene ligands possess a metalcarbon double bond and are closely related to alkylidenes. The formation of 2alkoxyphenols from dienyl chromium carbene complexes is a known process orthobenzannulation that only occurs with certain cis,transdienyl complexes. The orthobenzannulation of trans,transdienyl fischer carbene complexes yiqian lian and william d. Structure of pentacarbonylmethoxyphenylcarbenechromium0. Metalcentered oc5cr ch3 ome o c3h7 ph thf,10 5oc h o ch3 ome c h3 ph o o ch3 ome ch3 ph o 48 % 18 % j. The fischer carbenes named after ernst otto fischer feature strong.
Electrochemical study of chromium0 fischer carbene. The photochemical reaction of vinylaziridines and vinylazetidines with chromium0 and molybdenum0 fischer carbene complexes. For example, the attack of an amine on the electronpoor carbon atom of a fischer carbene results in the displacement of the or group to yield a new carbene me represents the. Addition of chromium hexacarbonyl to the organolithiums formed the acylpentacarbonyl chromate salt which was alkylated with meerwein salt, resulting in the fischer carbene and a byproduct, tetrabutyltin, which proved difficult to remove. These are sometimes called fischer carbenes in honor of e. Fischer carbene complexes in organic synthesis scripps. Low temperature carbene transfer from alkoxychromium0 fischer carbene complexes. When these two electrons have opposite spins, the carbene is designated a singlet carbene. Fischer carbenes reactivity of the carbene carbon is controlled by the bonding a fischer carbene is predominantly a. Thus, they react with 2azadienes to afford, after column chromatography, the corresponding pyridone derivatives in high yield scheme3 4. Request pdf electrochemical illumination of thienyl and ferrocenyl chromium0 fischer carbene complexes a series of ferrocenyl and thienyl mono and. The reaction course of the oxidative decomplexation of fischer carbene complexes with dioxiranes was examined. Fischer carbenes are typically electrophilic and are stabilized by a single.