Carbenes carbonyl

The occurrence of stable carbene complexes of Groups VI and VII is well documented (87, 96, 202), but the 77-cyclopentadienyliron carbene carbonyl cations (103, 151) appear unstable. 

Ofele et al. found gronp 6 bis-carbene carbonyl complexes to be invariably chelating, but their wingtip group was limited to methyl [337]. 

Identically, triazole-based carbenes were found to be able to substitute CO, giving rise to mono- or disubstituted carbene carbonyl complexes (53) and (54) as a function of the reaction stoichiometry (Scheme 8). Reaction between M(CO)e and one equivalent of triazolylidene led to the formation of cis... 

It has been proposed that these carbyne-acyl rearrangements start with the protonation of the car-byne carbon atom to initially give a carbene complex. For the next step two different pathways have been proposed i) An intramolecular carbene carbonyl coupling to yield a 7C-ketene complex,... 

Figure 4.12 Ketene formation by cobalt ll)-porphyrin catalysed carbene carbonylation. Reprinted from Ref. 41 with permission from Wiiey VCH.

A new platinum(O) carbonyl complex has been prepared by the reaction of 3 equiv. of carbon monoxide with a carbene complex (Equation (1)). Not only does the carbon monoxide displace an existing ligand but coordinated GO is also attacked by the ligating nitrogens, with the siloxy group migrating to give the unusual tris-carbene carbonyl complex 1, where all the donor atoms are carbon. Yields are reported to be quantitative, and an X-ray structure has a short Pt-GO bond of 1.868(6) A with a GO stretch of 2,038 cm Further aspects of the synthesis of both 1 and its precursor are discussed in Sections 8.07.3.2.2 and 8.07.3.3. 

Very recently [54] a 2e reductirMi of V-heterocyclic carbene-carbonyl Mn(I) to Mn(—I) has been reported which occurs at the same potential (—1.35 V vs SCTE) instead of two consecutive potentials separated by a few hundred mV as shown for analogous MnBr(CO) t(2N 1). Such Mn complexes catalyse very selectively the CO2 to CO reduction with a faradaic efficiency of 34.6 %. 

In 1998, Liu et al. reported the preparation of carbene carbonyl- or biscar-bene-Pt complexes using a transfer reaction between W-complex and [(PhCN)2PtCl2]. On the other hand, the Cavell group proposed an oxidative addition of imidazolium salt to Pt complex to yield Pt -hydrido/NHC... 

Manganese carbonyl complexes LMn(CO)2(THF) (L=ti -CH3C5H4 or ti -CsHs) were found to be effective in the dediazotation of diazoalkanes and in the formation of stable manganese carbene carbonyl complexes. See for examples reactions 8.23 and 8.24 [47,48]. 

In the presence of a large excess of tetracarbonyl nickel and ethanol diphenyldiazo-methane, diazofiuorene, bis-(4-methoxyphenyl)diazomethane, and ethyl diazoacetate give carbonylation products trapped by ethanol and processed into the corresponding carboxylic acid in 74,38,26, and 8.5% isolated yields, respectively, which presumably arise from a nickel carbene carbonyl intermediate that releases a substituted ketene upon decomposition at 50-66 °C. In the absence of ethanol, by refluxing a solution of 1 mol diphenylketene with 6.4 mol tetracarbonyl nickel in diethylether 35% isolated yield of diphenylketene was observed [86]. The r -(C,C)-ketene complex of nickel (31) was isolated in 17% yield from the reaction of nickelacyclobutane (29) with carbon monoxide (3 bar) at 50 °C (reaction 8.54) [87]. Complex 29 is believed to be in equilibrium with the nickel-carbene-olefrn complex 30 [88]. The nickel-ketene complex 31 was also obtained either by direct reaction of Ni(PPh3)4 with ketene or by carbonylation of the nickel-carbene complexes presumably formed from the reaction of Ni(PPh3)4 and CH2Br2 in the presence of metallic zinc [89]. 

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