Organic Syntheses via Transition Metal Complexes. 118.¹ Retro-Fischer Reaction Induced by a β-Imino Functionality of (Alkyl,ethoxy)carbene Complexes (M = W, Cr):  Efficient Access to C-Enamino and N-Enamino Carbene Complexes

Abstract

Condensation of (ethoxy,methyl)carbene complexes (OC) 5 MdC(OEt)CH 3 1a,b (M ) W, Cr) with R,β-unsaturated secondary acid amides PhCHdCHC(dO)NHR 7a-c in the presence of POCl 3 /Et 3 N affords C-enamino carbene complexes (3Z)-3a-f () 4-NH-amino-1-metalla-1,3,5-hexatrienes). A fundamental change of the reaction course was induced by an R-substituent of the carbene complex 1. Thus, (n-butyl,ethoxy)carbene complex 1c under similar conditions yields N-enamino carbene complexes 8h-l instead of C-enamino carbene complexes (Scheme 2). Formation of compounds 8 involves an unprecedented retro-Fischer reaction, by which the C,C bond between the R-carbon atom and the carbene carbon atom is broken under the influence of a β-imino functionality.

Unexpected reactivity of pyridinium salts toward alkynyl Fischer complexes to produce oxo‐heterocycles

“…Another remarkable difference was observed with the metallic fragment [(CO) 5 M] of the alkynyl carbene, as suggested by a number of studies wherein reactivity is strongly influenced by this moiety . For this particular case, the results indicated a preference for tungsten over chromium complexes when comparing yields of the molecular scaffolds (Table , entries 1 and 8, M = Cr vs 2 and 9, M = W).…”

Preparing α,β-unsaturated Fischer-type carbene complexes via an unforeseen route

“…Instead the reaction yields three different compound classes as mentioned above and all of them only involve sulfenylation. 5 The formation of similar products, with deprotonated methoxycarbene complexes, albeit in very low yields, could also clearly be observed in 1 H and 13 C NMR spectra, but the yields were insufficient for isolation in pure form. The thioether complexes, (CO) 5 MS(CH 3 ) 2 , also formed in low yields as in the instance of the aminocarbene complexes.…”

The Effect of Remote Donor Substituents on the Properties of Alkoxy and Amino Fischer Carbene Complexes of Tungsten

“…The data for the present set of complexes should also be compared to the [W{CPh 2 }(CO) 5 ] benchmark system with its WÀ C1 bond length of 2.15(2) Å. [15] Further points of comparison are provided by the complexes [W{CN(allyl)CH 2 CH 2 N(allyl)}(CO) 5 ] (WÀ C1 = 2.266(3) Å), [16] [W{CN(Et)CMeCMeN(Et)}(CO) 5 ] (WÀ C1 = 2.275(8) Å) with an unsaturated NHC ligand, [14b] and the acyclic aminooxycarbene complex [W{C(OEt)N{C(CHCHPh) CH n Pr} i Pr}(CO) 5 ] (WÀ C1 = 2.297(8) Å)), [17] where steric congestion caused by the bulky amino substituent on the carbene carbon atom may also contribute to the bond lengthening.…”