ADDITION OF PHOSPHANES TO THE C-ALPHA-ATO M OF ALLENYLIDENE(PENTACARBONYL)CHROMIUM AND REARRANGEMENT TO PHOSPHANE COMPLEXES

The allenylidene(pentacarbonyl)chromium complex (CO)(5)Cr[C=C=C(C(6)H( 4)NMe(2)-p)(2)] (1a) adds phosphines PR(3) at the C-alpha atom to give ylide complexes, (CO)(5)Cr-[C(PR(3))=C=C(C(6)H(4)NMe(2)-p)(2)] (PR(3) = PMe(3) (2), PHPh(2) (3), PH(2)Mes (7) (Mes = C(6)H(2)Me(3)-2,4,6)). At room temperature complex 3 slowly rearranges to the allenylphosphi ne complex (CO)(5)Cr-PPh(2)[CH=C=C (C(6)H(4)NMe(2)-p)(2)] (4). The str ucture of 4 was established by an X-ray structure analysis. The adduct 7 obtained from 1a and PH(2)Mes, however, could not be detected. It i mmediately isomerizes to the alkynylphosphine complex (CO)(5)Cr-PH(Mes )[C drop C-CH(C(6)H(4)NMe(2)-p)(2)] (8). At room temperature the ylide complex 5, formed by addition of PHPh(2) to the C(a)lpha atom of the allenylidene complex (CO)(5)Cr=C=C=C(o-C6H4)(2)O (1b), rearranges in C H2Cl2 in the presence of excess PHPh(2) to give a binuclear bisphosphi ne complex (6). 6 corresponds to the product of the chemo-, regio- and stereo-selective dimerization of the allenylphosphine complex analogo us to 4.