Article abstract of DOI:10.1016/0022-328X(95)05731-4

The diarylallenylidene complexes (CO)₅M=C=C=C(C₆H₄NMe₂-p)₂ [M = W (1), Cr (2)] add N-alkyl-substituted hydroxylamines, RNH-OH, to form the hitherto unknown isoxazolidinylidene complexes (CO)₅M=C-N(R)-O-C(C₆H₄NMe₂-p)₂-CH₂ [M = W (3), Cr (4); R = Me (a), Bn (b), ⁱPr (c), ^cHex (d)]. The structure of these heterocyclic carbene complexes is established by X-ray analysis of compound 3a. Only in the synthesis of 4d could by-products [E/Z-(CO)₅Cr=C[N(H)^cHex]C(H)=C(C₆H₄NMe₂-p)₂(E/Z-5)] be isolated. The reaction of 1 with the sterically strongly hindered N-alkyl-substituted hydroxylamine ^tBuNH-OH or with the only weakly nucleophilic N-aryl-substituted hydroxylamine p-TolNH-OH does not afford isoxazolidinylidene complexes. Instead the alkenyl(amino)carbene complexes (CO)₅W=C[N(H)^tBu]C(H)=C(C₆H₄NMe₂-p)₂ (6) and E/Z-(CO)₅W=C[N(H)p-Tol]C(H)=C(C₆H₄-NMe₂-p)₂ (E/Z-7) are formed by the addition of amines which arise via dismutation of the hydroxylamines. From the reaction of 1 with the N,N-disubstituted hydroxylamine, Me₂N-OH, only the alkenyl(amino)carbene complex (CO)₅W=C[NMe₂]C(H)=C(C₆H₄NMe₂-p)₂ (8) is isolated. Hence, formation of 3 and 4 must proceed by initial attack of the hydroxylamine N-atom at the C_α-atom of 1 and 2. Similarly, 1 also adds the N,O-disubstituted hydroxylamine MeNH-OMe to give the alkenyl(hydroxylamino)carbene complexes E-and Z-(CO)₅W=C[N(Me)OMe]C(H)=C(C₆H₄NMe₂-p)₂ (E-9 and Z-9) in the ratio E/Z = 1:3.2. Both conformers were investigated by X-ray analysis. On warming in solution, E-9 isomerizes to form Z-9.