Organometallic Chemistry of Reactive Organic Compounds. 41. Metal-Induced Carbyne/Carbene Coupling with Buchner's Diazo Compound†

Wolfgang A. Herrmann, Manfred L. Ziegler, Orhan Serhadii

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Abstract

An example of a transition-metal-centered carbon-carbon coupling reaction between a carbyne and a carbene fragment has been encountered through an unexpected diazoalkane fragmentation process: Buchner's prototypal mercuriodiazoalkanes, bis[(alkoxycarbonyl)diazomethyl]mercury, Hg[C(=N2)C02R]2 (R = C2H5, 2a; t-C4H9, 2b), react with bromopentacarbonylmanganese, (CO)5 MnBr (1), in boiling diethyl ether to yield the previously described dinuclear μ-carbyne complexes of composition [(μ-CC02R)Mn(C0)4]2 (7a,b) as well as the mononuclear carbyne/carbene coupling products (C0)4MnC(C02R)=C(HgBr)C- (OR)=O (8a,b), the molecular structure of which latter compounds has been established by means of X-ray crystallography: space group C52h, (P21/c); a = 1468.9 (2) pm, b = 686.2 (5) pm, c = 1759.4 (3) pm, β = 91.04. Important bond parameters: HgBr = 242.9 (4) pm, C=C = 138 (4) pm, MnO = 207.4 (17) pm; ∠Br, Hg, C = 176.5 (8). The characteristic structural element is a five-membered metallacyclic frame that arises from [2 + 3] cycloaddition of the (bromomercurio)carbene |C(HgBr)CO2R upon the intermediate carbyne complex (C0)4Mn=CC02R. This novel mode of cyclization implies the formation of a carbon-carbon double bond between carbene and carbyne carbon atoms [cf. C(5)-C(6)]. From a formalistic point of view, compounds 8a and 8b might also be described as to result from homolytic trans addition (metal-lamercuration) of (CO)5MnHgBr across the triple bond of preformed acetylenedicarboxylates, R02CC=CC02R, with subsequent decarbonylation and concomitant cyclization of the vinyl-type derivative (CO)sMn C(C02R)=C(HgBr)C02R. This latter mechanistic alternative was, however, ruled out by negative parallel experiments using authentic (CO)5MnHgBr and the respective alkynes.

Original languageEnglish
Pages (from-to)958-962
Number of pages5
JournalOrganometallics
Volume2
Issue number8
DOIs
StatePublished - Aug 1983
Externally publishedYes

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