Keywords: ab initio calculations . electrochemistry . lanthanide compounds [l] For a recent review on metallofullerenes. see:

The 1+1 reaction of the symmetrical dimers [ClP(m-N t Bu)] 2 1 and [H 2 NP(m-N t Bu)] 2 2 in thf-Et 3 N gives the tetrameric macrocycle [{P(m-N t Bu)} 2 NH] 4 3 (67%); consisting of four P 2 (m-N t Bu) 2 rings linked by endo N-H groups.

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Reaction of the imidotitanium complex [(κ 3 -N 2 Npy)Ti(dNtBu)(py)] (1) [N 2 Npy ) (2-C 5 H 4 N)C(Me)(CH 2 NSiMe 3 ) 2 ] with 2,6-xylylisocyanide led to double insertion of the isocyanide into the imidotitanium bond and yielded the four-membered titanacycle [(κ 3 -N 2 Npy)Ti-{N(tBu)C(dN-2,6-Me 2 C 6 H 3 )C(dN-2,6-C 6 H 3 Me 2 )}] (2), which was characterized by X-ray crystallography. While unreactive toward bulky arylisocyanides, 2 reacted with a whole seriesSingle-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 R to the NC group leads to a sequential coupling of 3 molar equiv of the isocyanide with the imido complex, yielding metal-bonded diaminodi-NCHRR′}] (R,R′ ) C 5 H 10 , 5a; CH 3 ,CH 3 , 5b; Ph,CH 3 , 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.