UNUSUAL [2+2] CYCLOADDITION ADDUCTS OF AN IMIDOVANADIUM COMPLEX WITH ALKYNES AND ETHENE - CONVERSION TO ETA(3)-1-AZAALLYL AND ETHENYL COMPLEXES

2-Butyne displaces Et2O from (RNH)-(RN =)2V(OEt2) (3; R = t-Bu3Si) at 25-degrees-C to afford crystalline (RNH)(RN =)V{C(Me) = C(Me)N(R)} (5a), which undergoes ligand metalation to give complex 4a. Thermolysis Of (RNH)2(RN =) VMe (2a) in the presence of alkynes also yields (RNH) (RN=) V{eta1:eta3-CH2C(Me)2-Si(t-Bu)2)VC(R')CHR'} (R'= Me (4a), Et (4b)); the X-ray structure of 4b shows the first example of eta3-azaallyl coordination to a d0 transition metal. Ethene reacts reversibly with 3 to afford fluxional (RNH)(RN =)V{CH2-CH2N(R)} (7a), which slowly rearranges to (RNH)2-(RN =)V(CH = CH2) (6a), analogous to related complexes obtained from 2a and 1-alkenes at 80-degrees-C.