Metallkomplexe mit 1,2-Dithion-Liganden. III. Dithiooxamide als starke Donatoren oder Akzeptoren in Molybdäncarbonylkomplexen |
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| Authors: | H Tom Dieck Michael Form |
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| Abstract: | Metal Complexes with 1,2-Dithione Ligands. III. Dithiooxamides as Strong Donors or Acceptors in Molybdenum Carbonyl Complexes. Starting from substitution labile molybdenum carbonyl complexes L2Mo(CO)4, L3Mo(CO)3 and L2L2′Mo(CO)2 several new complex types with the C? C-twisted tetraalkyldithiooxamides (R4dto) and the planar N,N′-dialkyldithiooxamides (R2H2dto) such as (R4dto)Mo(CO)4 ( 8 – 11 ), (R2H2dto)Mo(CO)4 ( 12 – 18 ), (R2R2′dto)Mo(CO)3(P(C6H5)3) ( 27 – 31 ), (R2R2′dto)Mo(CO)2(PR3)2 ( 36 – 51 ) are described and compared with complexes of a cyclic dithiooxamide ( 62 – 64 ) and analogous complexes with thioamides R2NC(S)R′ ( 19 – 25 , 52 – 55 , 57 – 60 ). In Mo(CO)4 complexes, dithiooxamides display a rather strong donor character and are thus similar to simple thioamides, but the blue colour of the R2H2dto complexes indicates already low-lying acceptor levels. When passing from the Mo(CO)4 complexes via Mo(CO)3(PR3) complexes to the very electron rich Mo(CO)2(PR3)2 complexes, the i.r. and eletronic spectra indicate an unexpected and drastic change in ligand character. Dto ligands in the latter complex type turn out to be very strong acceptors, independent of the degree of N-alkylation. A conformational change, with twisted R2N? C bonds and a planar S? C? C? S skeleton (as in the dithiolene complexes), can account for all the peculiarities of the (dto)-dicarbonylbis(phosphine) complexes as compared to the “normal” thioamide complexes. Dithiooxamides can thus control the oxidation state of metals by a remote conformational change and possibly act as an electron reservoir in chemical reactions at the metal center. |
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