280748-05-2Relevant academic research and scientific papers
Addition of N-aryl imines to alkyne(pentacarbonyl)chromium and tungsten - A novel route to alkenyl(amino)carbene complexes
Abd-Elzaher, Mokhles M.,Froneck, Thomas,Roth, Gerhard,Gvozdev, Valentin,Fischer, Helmut
, p. 288 - 297 (2000)
Photolysis of [M(CO)6] in CH2Cl2 gives [(CO)5M(CH2Cl2)] (M = Cr, W). Replacement of CH2Cl2 by arylacetylene, HC≡CC6H 4R-p (R = Me, H, Br), produces the thermolabile arylacetylene complexes [(CO)5M(HC≡CC6H4R-p)]. Addition of N-phenyl benzylideneimines, PhN = C(C6H4 R′-p)H (R′ = Me, H, Cl), to solutions of these alkyne complexes affords alkenyl(amino)carbene complexes, [(CO)5M=C(NPhH)C (C6H4R-p))=C(C6H4R′-p))H], and 2-azetidin-1-ylidene complexes, [(CO)5M=C-NPh-C(C 6H4R′-p)H-C(C6H4R-p)H]. The formation of the alkenyl(amino)carbene complexes is favored. The ratio alkenyl(amino)carbene/2-azetidin-l-ylidene complex is 2.5-3 for M = W and 6.5-8 for M = Cr. Both types of complexes are obtained as mixtures of isomers. The 2-azetidin-1-ylidene complexes are very likely formed by cycloaddition of the imines to the C=C bond of vinylidene complexes resulting from tautomerization of the alkyne complexes. The cycloaddition is highly stereoselective. Predominantly, the syn isomer is obtained (syn/anti ≥ 9). In contrast, the alkenyl(amino)carbene complexes are presumably derived from the alkyne complexes via cycloaddition of the imines to the coordinated alkyne and subsequent 1,2-hydrogen shift and ring opening. Preferentially, the E isomers (where both aryl substituents are cis with respect to the C=C bond) are produced. The structure of the major isomer of the alkenyl(amino)carbene complex [(CO)5W=C(NPhH)C(C6 H4Me-p)=C(Ph)H] has been established by X-ray structural analysis.
