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

Abstract

Photolysis of [M(CO)6] in CH2Cl2 gives [(CO)5M(CH2Cl2)]. Substitution of phenylacetylene for CH2Cl2 produces the thermolabile phenylacetylene complexes [(CO)5M(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)5MView the MathML source(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≥9). The reaction of 3 with dialkylcarbodimides, RNCNR (R=c-Hex, i-Pr), yields 3-imino-2-azetidin-1-ylidene complexes, [(CO)5WView the MathML source(Ph)H]. By oxidative cleavage of the CrC bond in [(CO)5CrView the MathML source(Ph)H] the corresponding β-lactams are obtained in high yields.