Photolysis of [M(CO) 6] in CH 2Cl 2 gives [(CO) 5M(CH 2Cl 2)] (M=Cr, W). Replacement of CH 2Cl 2 by arylacetylene, HCCC 6H 4R- p (R=Me, H, Br), produces the thermolabile arylacetylene complexes [(CO) 5M(HCCC 6H 4R- p)]. Addition of N-phenyl benzylideneimines, PhN=C(C 6H 4R′- p)H (R′=Me, H, Cl), to solutions of these alkyne complexes affords alkenyl(amino)carbene complexes, [(CO) 5MC(NPhH)C(C 6H 4R- p)C(C 6H 4R′- p)H], and 2-azetidin-1-ylidene complexes, [(CO) 5M CNPhC(C 6H 4R′-p)HC (C 6H 4R- p)H]. The formation of the alkenyl(amino)carbene complexes is favored. The ratio alkenyl(amino)carbene/2-azetidin-1-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 CC 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 CC bond) are produced. The structure of the major isomer of the alkenyl(amino)carbene complex [(CO) 5WC(NPhH)C(C 6H 4Me- p)C(Ph)H] has been established by X-ray structural analysis.