Chromium complexes pentacarbonyls

Structural analogues of the /]4-vinylketene E were isolated by Wulff, Rudler and Moser [15]. The enaminoketene complex 11 was obtained from an intramolecular reaction of the chromium pentacarbonyl carbene complex 10. The silyl vinylketene 13 was isolated from the reaction of the methoxy(phenyl)-carbene chromium complex 1 and a silyl-substituted phenylacetylene 12, and -in contrast to alkene carbene complex 7 - gave the benzannulation product 14 after heating to 165 °C in acetonitrile (Scheme 6). The last step of the benzannulation reaction is the tautomerisation of the /]4-cyclohexadienone F to afford the phenol product G. The existence of such an intermediate and its capacity to undergo a subsequent step was validated by Wulff, who synthesised an... 

Excellent diastereomeric ratios were achieved with terpene-derived auxiliaries. The pentacarbonyl[(-)-menthyloxycarbene]chromium complex 39 reacted with the sterically hindered 3,3-dimethylbut-l-yne to give tricarbonyl chromium naphthohydroquinone complex 40 in 81% de as the major diastereomer which was also characterised by X-ray analysis [41] (Scheme 25). Surprisingly, the application of other even more sterically demanding terpene auxiliaries or a variation of the alkyne did not improve the diastereomeric ratio [42]. 

The fact that pentacarbonyl carbene complexes react with enynes in a chemo-selective and regiospecific way at the alkyne functionality was successfully applied in the total synthesis of vitamins of the Kj and K2 series [58]. Oxidation of the intermediate tricarbonyl(dihydrovitamin K) chromium complexes with silver oxide afforded the desired naphthoquinone-based vitamin K compounds 65. Compared to customary strategies, the benzannulation reaction proved to be superior as it avoids conditions favouring (E)/(Z)-isomerisation within the allylic side chain. The basic representative vitamin K3 (menadione) 66 was synthesised in a straightforward manner from pentacarbonyl carbene complex 1 and propyne (Scheme 38). 

A chromium(O) pentacarbonyl-methylene chloride complex 131 was formed under irradiation, which reacted with an alkyne to form a vinylidene complex 132. Complex 132 further reacted with an imine or a dialkylcarbodimide to afford /3-lactams after decomplexation of chromium (Scheme 58).233... 

Arene(alkoxy)carbene chromium complexes react with aryl-, alkyl-, terminal, or internal alkynes in ethers or acetonitrile to yield 4-alkoxy-1-naphthols, with the sterically more demanding substituent of the alkyne (Rl Figure 2.24) ortho to the hydroxy group. Acceptor-substituted alkynes can also be used in this reaction (Entry 4, Table 2.17) [331]. Donor-substituted alkynes can however lead to the formation of other products [191,192]. Also (diarylcarbene)pentacarbonyl chromium complexes can react with alkynes to yield phenols [332]. 

It is also worthy to note that the pentacarbonyl-tungsten complex of the phosphirenylium cation (5) has been recently reported, but no X-ray structure has been obtained. B3LYP/6-311G(d) optimization of the presumed -Cr(CO)5 complex of 5 resulted in an 7 -form (Figure 1) when starting from the bound chromium complex. Such a structure is in complete accord with a delocalized electronic structure of the cation. 

The following procedure can be extended to prepare l-oxacyclopent-2-ylidene chromium complexes substituted in the 3 or 5 position.4 Thus the reaction of the anion of pentacarbonyl(l-methoxypropylidene)chromium(0) with ethylene oxide gives pentacarbonyl [dihydro-3-methyl-2(3//)-furylidene] chromium(O) [pentacarbonyl(3-methyl-l-oxacyclopent-2-ylidene)chromium(P)], and the reaction of the anion of pentacarbonyl(l-methoxyethylidene)chromium(0) with propylene oxide gives pentacarbonyl(dihydro-5-methyl-2(3//)-furanylidene)-chromium(O) [pentacarbonyl(5-methyl-l-oxacyclopent-2-ylidene)chromium(0)]. 

When cyclopropylidenemethy](ethoxy)carbene chromium pentacarbonyl is treated with diphenylacetylene in THF, a mixture of products is obtained, from which only the tricarbonyl(5-ethoxy-6,7-diphenylbenzofuran)chromium complex could be isolated, in... 

The configuration of these complexes were established on the basis of IR and H-NMR spectra (62). When triphenylarsine was reacted with sulfoxonium ylide complex, pentacarbonyl triphenylarsonium ylide-chromium complex was obtained (95). 

An interesting situation exists in the deprotonation of the pentacarbonyl-(cyclobutenylidene)chromium complexes 51 and 52.110 These complexes are characterized by a strong... 

Pentaalkynylferrocenes, preparation, 6, 190 Pentaarylantimonys, in C-C bond formation, 9, 430 Pentaarylcyclopentadienyl compounds, with iron, 6, 159 Pentacarbaboranes, metal complexes, 3, 230-233 Pentacarbonyl(3-aminoallenylidene)chromium complexes, preparation, 5, 270... 

Pentacarbonylchromium, oxygen difluoride reaction, 5, 231 Pentacarbonyl[ethoxy(2-amnioethenyl)carbene]chromium complexes, preparation, 5, 270 Pentacarbonyliron... 

Dihydrobenzenes.2 Pyranylidene pentacarbonyl chromium complexes such as 1, prepared as shown, react with electron-rich alkenes, such as enol ethers, to form an adduct a, which extrudes Cr(CO)6 to provide dihydrobenzenes (2) in high yield. Attempted chromatography of 2 results in aromatization. 

Methanol, platinum complex, 26 135 tungsten complex, 26 45 Methyl, iridium complex, 26 118 manganese complex, 26 156 osmium complex, 27 206 rhenium complexes, 26 107 Methyl acetate, iron complex, 27 184 osmium complex, 27 204 Methyl benzoate, chromium complex, 26 32 Methylene, osmium complex, 27 206 Molybdate(l -), (acetato)pentacarbonyl-, M.-nitrido-bis(triphenylphosphorus) (I-h), 27 297... 

The transition metal complex pentacarbonyl(methoxyaiylcarbene)chromium(0) (65), gave selenoesters on treatment with elemental selenium. ... 

Fig. 6. "B-NMR data for 2-diethylboryl-5-methyl thiophene (a) and its pentacarbonyl-chromium complex (b). In the latter, donor-acceptor relationship between boron and the carbonyl group is postulated to account for its higher field nB shift (c).

Subsequently Jutzi allowed a ring diphosphirane to react with [Cr(CO)5THF] and obtained an // -diphosphirane pentacarbonyl chromium complex (Equation (21)) <92ZAAC(610)75>. 

The chromium complexes of alkoxy(styryl)carbenes frequently react with alkenes to give a mixture of products. Thus, pentacarbonyl[(4-methoxyphenyl)vinyl(methoxy)carbene] or [(2-... 

Pentacarbonyl[cyclopropylethynyl(ethoxy)carbene]chromium complex 19 reacted with cyclo-penta-1,3-diene to give a cyclopropyl-substituted carbene complex of norbornadiene 22, which was converted to the corresponding carboxylic acid 23 upon oxidation or to a 1,4-quinone-type derivative 24 after Dotz-type cyclization with phenylethyne. ... 

Similarly, the pentacarbonyl[(2-cyclopropyl-2-dimethylaminovinyl)ethoxycarbene]chromium complex 27, prepared from pentacarbonyl[cyclopropylethynyl(ethoxy)carbene]chromium 19 and dimethylamine (or other secondary amines), reacted with pent-l-yne or phenylethyne to give 1-propyl- or 1-phenyl-substituted 5-cyclopropyl-5-dimethylamino-3-ethoxycyclopenta-1,3-diene in 62-77% yield.With substituents other than cyclopropyl yields were drastically lower unless the reaction of the carbene complex was performed in pyridine or acetonitrile. 

With an imino substituent at the alkenyl terminus, a, -unsaturated pentacarbonyl(car-bene)chromium complexes 30 did not insert alkynes, but cyclized directly, even with cyclopropyl substituents present, to give 2//-pyrroles 31 in high yield. ... 

Pentacarbonyl(carbene)chromium complexes with a primary amino group at the alkenyl terminus 32, readily obtained by addition of ammonia to alkynyl-substituted complexes, initially rearranged upon heating to pentacarbonylchromium-coordinated 1-azabuta-l,3-dienes 33, which subsequently underwent [4 + 2] cycloaddition of an alkyne to give coordinated 4-ethoxy-1,4-dihydropyridines the corresponding pyridines, e.g. 34, were formed by 1,4-elimination of ethanol. ... 

When the arylcarbene(pentacarbonyl)chromium complex bears a (phenyl) alkyne at the orf/zo-position of the aryl group, an intramolecular alkyne-carbe-ne chelate (126) can be formed by low temperature photodecarbonylation. The tetracarbonylchromium chelate 126 obviously dimerizes and furnishes finally a densely functionalized centrosymmetric chrysene (127, see Scheme 58 [160a, d]). 

In an interesting and novel organometallic approach to monocyclic and bicyclic p-lactam synthesis, it has been shown that pentacarbonyl(methoxy-methyl)chromium complexes will add to imines under sunlight irradiation (Scheme 38). ... 

G. Simonneaux et al. (57) published the synthesis and complexation to ruthenium(II) and iron(in) m 5(9-tetraphenylporphyrins of two new fluorinated alkyl isocyanides, 2-monofluoroethyl isocyanide and 2,2,2-trifluoroethyl isocyanide. A new synthesis of trifluoromethyl isocyanide, pentafluoroethyl isocyanide and heptafluoropropyl isocyanide from R-N=Cp2 (R = CF3, C2F5, C3F7) using triphenyl phosphine has been reported (58). Geometries and HOMO and LUMO energies of fluorinated vinyl isocyanides have been calculated (59). Pentacarbonyl chromium complexes of both isomers of the first fluorinated diisocyanide, l,2-diisocyano-l,2,3,3,4,4-hexafluoro cyclobutane have been isolated from a [2+2] cycloaddition reaction of pentacarbonyl(trifluorovinyl isocyanide) chromium. The structure of the cis isomer has been elucidated by X-ray crystallography (60),... 

A recent study by Frenking [84] investigated in great detail the influence of the carbene substitutents X and R at a pentacarbonyl-chromium Fischer-type complex. The electronic characteristics of these substituents control the reac-... 

Catalytic cyclopropanation of alkenes has been reported by the use of diazoalkanes and electron-rich olefins in the presence of catalytic amounts of pentacarbonyl(rj2-ris-cyclooctene)chromium [23a,b] (Scheme 6) and by treatment of conjugated ene-yne ketone derivatives with different alkyl- and donor-substituted alkenes in the presence of a catalytic amount of pentacarbon-ylchromium tetrahydrofuran complex [23c]. These [2S+1C] cycloaddition reactions catalysed by a Cr(0) complex proceed at room temperature and involve the formation of a non-heteroatom-stabilised carbene complex as intermediate. 

Although most of the examples of [3S+2C] cycloaddition reactions with carbene complexes are referred to as 1,3-dipolar processes, we should include in this section another kind of non-dipolar transformation dealing with the reaction of pentacarbonyl(methoxymethylcarbene)chromium with a base followed by treatment with an epoxide in the presence of boron trifluoride. This reaction gives cyclic carbene complexes in a process that can be considered a [3S+2C] cycloaddition [44] (Scheme 14). 

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