C-C and C-N coupling reactions of an imidotitanium complex with isocyanides

Reaction of the imidotitanium complex [(kappa (3)-N(2)Npy)Ti(=NtBu)(py)] (1) [N(2)Npy = (2-C5H4N)C(Me)(CH2NSiMe3)(2)] with 2,6-xylylisocyanide led to double insertion of the isocyanide into the imidotitanium bond and yielded the four-membered titanacycle [(kappa (3)-N(2)Npy)Ti{N(tBu)C(=N-2,6-Me2C6H3)C(=N-2,6-C6H3Me2)}] (2), which was characterized by X-ray crystallography. While unreactive toward bulky arylisocyanides, 2 reacted with a whole series of isocyanides R-NC [R = Et, nBu, iPr, Cy, tBu, PhCH2, p-Tol, (R)-CH(CH3)Ph] to give the iminoketene complexes [(kappa (3)-N(2)Npy)Ti{N(tBu)C[N(2,6-Me2C6H3)]C(=C=NR)N(2,6-Me2C6H3)]-(R = Et, 3a; nBu, 3b; iPr, Sc; Cy, 3d; tBu, 3e; PhCH2, 3f; p-Tol, 3g; (R)-CH(CH3)Ph, 3h). Single-crystal X-ray structure analyses of 3d, 3f, and 3g were carried out, which established the coordination of an imidoylketeneimene fragment to the metal center. The reaction of 1 with alkyl isocyanides bearing H atoms or to the NC group leads to a sequential coupling of 3 molar equiv of the isocyanide with the imido complex, yielding metal-bonded diaminodihydropyrimidine derivatives [(kappa (3)-N(2)Npy)Ti{N(tBu)[-C=NCH(R)N(CH2R)CHC . NCH2R}] (R = H, 4a; CH3, 4b; C3H7, 4C; Ph, 4d) and [(kappa (3)-N(2)Npy)Ti{N(tBu)[-C=NCRR'N(CHRR')CHC-]NCHRR'}] (R,R' = C5H10, 5a; CH3,CH3, 5b; Ph,CH3, 5c). An X-ray diffraction study of 4a unambiguously established the structure of this type of organometallic complex. These products are thought to be formed in a reaction sequence involving intermediates that are analogous to the stable complexes 2 and 3a-h. The latter are then converted to the N;heterocycles via a diazahexatriene generated through a 1,5-sigmatropic H-shift and the subsequent cyclization to give the pyrimidine derivatives.