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The reactivity of the cubane-type rare-earth methylidene complex [Cp′Lu(μ3-CH2)]4 ( 1, Cp′=C5Me4SiMe3) with various unsaturated electrophiles was investigated. The reaction of 1 with CO (1 atm) at room temperature gave the bis(ketene dianion)/dimethylidene complex [Cp′4Lu4(μ3-CH2)2(μ3,η2-O-CCH2)2] ( 2) in 86 % yield through the insertion of two molecules of CO into two of the four lutetium-methylidene units. In the reaction with the sterically demanding N, N-diisopropylcarbodiimide at 60 °C, only one of the four methylidene units in 1 reacted with one molecule of the carbodiimide substrate to give the mono(ethylene diamido)/trimethylidene complex [Cp′4Lu4(μ3-CH2)3{ iPrNC(=CH2)N iPr}] ( 3) in 83 % yield. Similarly, the reaction of 1 with phenyl isothiocyanate gave the ethylene amido thiolate/trimethylidene complex [Cp′4Lu4(μ3-CH2)3{PhNC(S)=CH2}] ( 4). In the case of phenyl isocyanate, two of the four methylidene units in 1 reacted with four molecules of the substrate at ambient temperature to give the malonodiimidate/dimethylidene complex [Cp′4Lu4(μ3-CH2)2{PhN=C(O)CH2(O)CNPh}2] ( 5) in 87 % yield. In this reaction, each of the two lutetium-methylidene bonds per methylidene unit inserted one molecule of phenyl isocyanate. All the products have been fully characterized by NMR spectroscopy, X-ray diffraction, and microelemental analyses. [ABSTRACT FROM AUTHOR]