Synthesis and reactions with carbon dioxide of mono(sigma-alkynyl) titanocene(III) complexes Cp*Ti-2(C CR) (R = Me, t-Bu) and the corresponding "Ate" complexes [Cp*Ti-2(C CR)(2)Li(THF)(n)] (R = SiMe3, t-Bu, Ph)

The reactions of the titanium(III) Complex CP*2TiCl with lithium acetylides RC drop CLi depend strongly on the solvents used. In THF only the lithium tweezer compounds [CP*Ti-2(C drop CR)(2)Li(THF)(n)] (CP* = eta (5)-C5Me5; R = SiMe3, n = 1 (1); R = t-Bu, n = 1 (2); R = Ph, n 2 (3)), not the expecte d mono(Gr-alkynyl) titanocene(III) complexes, were obtained, whereas in n-h exane these complexes CP*Ti-2(C drop CR) were isolated for R = Me (4), t-Bu (5). The reaction of the complex [CP*Ti-2(C drop CSiMe3)(2)Li(THF)] (1) wi th carbon dioxide results in the titanafuranone 6, which presumably is form ed by insertion of carbon dioxide into the eta (2)-butadiyne complex CP*Ti- 2(eta (2)-Me3SiC drop CC drop CSiMe3). The complex [CP*Ti-2(C dropC-t-Bu)(2 )Li(THF)] (2) reacts with carbon dioxide to yield the permethyltitanocene c arboxylateCP*Ti-2(O2CC dropC-t-Bu) (7) via insertion into the sigma -acetyl ide bond of the in situ formed titanium(III) intermediate [CP*Ti-2-C dropC- t-Bu]. Compound 7 was also obtained in the reaction of the isolated titaniu m(III) complex CP*Ti-2-C dropC-t-Bu (5) with carbon dioxide. The interactio n Of [CP*Ti-2(C drop CPh)(2)Li(THF)(2)] (3) with carbon dioxide gives the s table bis(sigma -acetylide) permethyltitanocene CP*Ti-2(C drop CPh)(2) (8) without coupling of the sigma -acetylide groups (as found for 1) and withou t insertion into the sigma -acetylide bond (as found for 2). The syntheses and reactions of these compounds are compared to those of similar complexes of unsubstituted titanocene compounds. Complexes 1, 5, and 7 were investig ated by X-ray crystal structure analysis.