Formation of Metalloheterocycles by Addition of Heteroallenes to the Electron-Rich Carbonyl Complex

Article abstract of DOI:10.1021/ja00201a023

The reactions of (1) with a range of heteroallenes establish that four-membered metalloheterocycles can be formed by addition of heteroallenes to an electron-rich neutral carbonyl complex.Metallocycloimides > (2, R=CH3; 3, R=Ph) are formed by addition of methyl and phenyl isocyanate to 1, and the metallocycloacylamidine > (4) is formed by addition of diphenylcarbodiimide to 1.In surprising contrast, addition of phenyl isothiocyanate to 1 leads to formation of a four-membered metalloheterocycledetermined by single-crystal X-ray diffraction (R_W=3.77percent) to be the metallocyclothioacylamidine > (5).The complex crystallizes in the monoclinic space group P2₁/n with a=7.816(2) Angstroem, b=19.838(5) Angstroem, c=13.066(3) Angstroem, β=92.33(2)deg, d_calcd=1.81 g mL^-1, Z=4.It is proposed that initial S=C=NPh addition to 1 results in ring closure through S to give a metallocycle which eliminates COS (GC) to form an intermediate isonitrile complex.Addition of a second S=C=NPh with ring closure through N then leads to 5.There is a fine balance between ring closure through S and N in isothiocyanate addition to 1, and S=C=NCH3 forms predominantly the metallocycloacylthioamide > (8) in diethyl ether and a mixture of 8 (53percent) and the bis adduct > (9) (27percent) in pentane.