Cobalt ketene complex

To show a metal-mediated coupling of a carbene with carbon monoxide, the isolation of the ketene complex Co2(CO)7(CH2=C=0) in 32% yield in the reaction of Co2(CO)8 with the carbene precursor CH2Br2 in the presence of Znat 20 °C for 2 days in TH F was taken into account. This cobalt ketene complex was found to catalyze the methoxycarbonylation or aminocarbonylation of a mixture of CH2Br2 and Zn under 5 bar carbon monoxide pressure at —40-20 °C in THF solution, yielding methyl acetate (385% based on C02(CO)7(CH2=C=O)) and N,N-diethylacetamide (184% based on Co2(CO)7(CH2=C=0)) using methanol and diethylamine as the additional reagents in the reaction, respectively [75]. 

Mukaiyama-type reaction of cobalt-alkyne complexes with ketene acetals gives the syn product exclusively, a reaction used as a key in a relay to bengamide E (Scheme 201). Total synthesis of blastomycinone utilizing a Mukaiyama-type reaction has been reported (Scheme 202). It is interesting to note the complete reversal of selectivity compared to the uncomplexed aldehyde (Scheme 203). 

Konno reported a detailed study of the reaction of fluorine-containing propargyl acetates under Nicholas conditions with a variety of nucleophiles. Allylstannanes and allylsilanes provided moderate yields of the desired products, while enamines, silyl enol ethers, and silyl ketene acetals furnished the target compounds with excellent efficiency. In one example, cobalt-alkyne complex 25 reacts with silyl ketene acetal 26 in the presence of trimethylsilyl triflate to yield, after cobalt decomplexation, ester 27. ... 

Ketene generator (K-1), 529 Lithium-alkylamine reduction (L-1), 580 Manipulation of a noxious solid with rubber gloves, a powder funnel, and a dust mask (N-3), 717 Mel-Temp apparatus (D-3), 243 Mercury seal for stirrer (G-3), 416 Model of the complex Coi(CO)g CuHaC— CCsHt (D-1) for construction of cobalt atoms, see L. F. Fieser, J- Chem. Ed., 42, 408 (1965), 111 Molecular sieve crystals (M-2), 704... 

Diastereoselective aldol reactions of propynals.4 The cobalt complex 1 of propynal reacts with O-silyl ketene 0,S-acetate (2) to form the syn aldol almost exclusively. 

Lewis-acid-promoted alkylations of silylenol ethers and silyl ketene acetals [195] with Co-complexed acetylenic acetals [196] and acetylenic aldehydes [197,198] (Scheme 4-56) also proceed with fair to excellent syn diastereoselectivity, in contrast to the low selectivity reactions of the free acetylenic derivatives [199, 200]. Reactions of the complexed aldehydes with lithium enolates are stereospecific, with (Z)-enolates giving syn selectivity and ( )-enolates anti selectivity [201]. The complementary stereoselectivity of the crossed aldol reactions of free and cobalt-complexed propynals with silyl ketene 0,S-acetals has been elaborated by Hanoaka exclusive syn selectivity is exhibited by the complexes and high anti selectivity is found with pro-... 

Diazo compounds react with cobalt(II)-porphyrins, including [Co (Pl)] to give complexed carbenes (Figure 4.12). These can then undergo carbonylation by addition of carbon monoxide, with in situ capture of the ketenes by nucleophiles, or with imines forming PTactams (Eqn (4.45)). ... 

Cobalt. - Crystal structures are reported for the phosphine substituted complex [Co2(C0)g(PMe3)2] and for the alkynyliron bridged species [Co2((t-PhCsCFp) (CO)g].240 studies of the radical anion [CO2(C0)2 (PF2)2NMe>3r indicate that the unpaired electron is in an intermetallic a molecular orbital mainly composed of cobalt orbitals.241 The coupling of alkylIdene with CO in complexes [Co2 /t-CHR)(jx-L)( -dppm)(CO)4] to yield ketenes has been studied under CO or S02. ... 

Numerous carbon nucleophiles participate in the Nicholas reaction the most popular are electron rich aromatics, enamines, enol ethers, ketene acetals, alkenes, allylsilanes, allylstannanes, and organoaluminum compounds. Upon completion of the substitution reaction, the cobalt complex can be oxidatively removed with E, Fe(III), or Ce(IV). Additional chemistry based on cobalt-complexed alkynes, like the Pauson-Khand reaction, can also be performed to further increase molecular complexity. 

---