Synthesis of azetidinylidene complexes from [(CO)5M(CH2Cl2)], phenylacetylene and imines and oxidative decomplexation to give β-lactams

Photolysis of [M(CO)(6)] in CH2Cl2 gives [(CO)(5)M(CH2Cl2)]. Substitution of phenylacetylene for CH2Cl2 produces the thermolabile phenylacetylene complexes [(CO)(5)M(HC=CPh)] [M=Cr (1), Mo (2), W (3)]. Addition of N-alkyl benzylideneimines, RN=C(Ph)H, to solutions of 1-3 affords the 2-azetidin-1-ylidene complexes [(CO)(5)M=C-NR-C(Ph)H-C(Ph)H] [M = Cr, Mo, W; R = Et, i-Pr]. The reaction presumably proceeds 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 greater than or equal to 9). The reaction of 3 with dialkylcarbodimides, RN=C=NR (R=c-Hex, i-Pr), yields 3-imino-2-azetidinl-1-ylidene complexes, [(CO)(5)W=C-NR-C(=NR)-C(Ph)H]. By oxidative cleavage of the Cr=C bond in [(CO)(5)Cr=C-NR-C(Ph)H-C(Ph)H] the corresponding beta-lactams are obtained in high yields. (C) 1999 Elsevier Science S.A. All rights reserved.