Allenylidene complexes as synthons for preparation of hydroxylaminocarbene and isoxazolidinylidene complexes

The diarylallenylidene complexes (CO)(5)M=C=C=C(C(6)H(4)NMe(2)-p)(2) [M=W (1), Cr (2)] add N-alkyl-substituted hydroxylamines, RNH-OH, to form the hitherto unknown isoxazolidinylidene complexes (CO)(5)M=C-N(R)-O-C(C(6)H(4)NMe(2)-p)(2)-CH2 [M=W (3), Cr (4); R=Me (a), Bn (b), Pr-i (c), (c)Hex (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)(5)Cr=C[N(H)(c)Hex]C(H)=C(C(6)H(4)NMe(2)-p)(2)(E/Z-5)] be isolated. The reaction of 1 with the sterically strongly hindered N-alkyl-substituted hydroxylamine (t)BuNH-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)(5)W=C[N(H)(t)Bu]C(H)=C(C(6)H(4)NMe(2)-p)(2) (6) and E/Z-(CO)(5)W=C[N(H)p-Tol]C(H)=C(C6H4-NMe(2)-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, Me(2)N-OH, only the alkenyl(amino)carbene complex (CO)(5)W=C[NMe(2)]C(H)=C(C(6)H(4)NMe(2)-p)(2) (8) is isolated. Hence, formation of 3 and 4 must proceed by initial attack of the hydroxylamine N-atom at the C-alpha-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)(5)W=C[N(Me)OMe]C(H)=C(C(6)H(4)NMe(2)-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.