(eta(8)-cyclooctatetraene)(eta(4)-1,2- and -1,3-diphosphacyclobutadiene)titanium: Preparation, structure, and reactivity

The synthesis of the (eta(8)-cyclooctatetraene)(eta(4)-1,3- and -1,2-diphosphacyclobutadiene)titanium complexes 3a-c and 4a, b by cyclodimerization of the phosphaalkynes 2a-c [a: R = tBu, b: R = adamantyl (ad), and c: R = (iPr)(Me(3)Si)N] in the coordination sphere of the (eta(8)-cyclooctatetraene)titanium complex 1 is described. The molecular structures of 3a-c and 4a, b were determined by spectroscopic methods (P-31, H-1, and C-13 NMR). In the case of 3a and 4a, X-ray analyses were carried out. The increased reactivity of 4a compared to 3a was utilized to separate 3a from 4a. Displacement of the 1,2-diphosphete (isolated as its cyclodimer 5) from 3b was achieved by reaction with hexachlorethane.