ANIONIC, 4-COORDINATE, 10-ELECTRON BISMUTH COMPLEXES - ASPECTS OF SYNTHESIS, STRUCTURE AND BONDING

The reaction between [BiCl{Fe(CO)2(eta-C5H5)}2] 1 and 1 equivalent of [N(PPh3)2]Cl afforded the ionic complex [N(PPh3)2][BiCl2{Fe(CO)2(eta-C5H5)}2] 2. The [NMe4]+ salt, [NMe4][BiCl2{Fe(CO)2(eta-C5H5)}2] 3, was prepared similarly. An analogous bromide derivative, [PPh4][BiBr2{Fe(CO)2(eta-C5H5)}2] 4, was prepared from the reaction between [BiBr{Fe(CO)2(eta-C5H5)}2] 5 and [PPh4]Br. The reaction between [BiCl{Mo(CO)3(eta-C5H5)}2] 7 and 1 equivalent of [N(PPh3)2]Cl afforded the complex [N(PPh3)2][BiCl2(Mo(CO)3(eta-C5H5)}2] 8, that between [PPh3(CH2Ph)]Cl and 7 afforded [PPh3(CH2Ph)] [BiCl2(Mo(CO)3(eta-C5H5)}2] 9. In tetrahydrofuran (thf) solution some degree of dissociation of [Mo(CO)3(eta-C5H5)]- is observed for 8 and 9. The bromide complexes [PPh4][BiBr2{Mo(CO)3(eta-C5H5)}2] 10 and [NBun4][BiBr2{Mo(CO)3(eta-C5H5)}2] 11 were prepared from the reactions between [BiBr{Mo(CO)3(eta-C5H5)}2] 12 and 1 equivalent of [PPh4]Br and [NBun4]Br respectively. The tungsten complexes [N(PPh3)2][BiCl2{W(CO)3(eta-C5H5)}2] 13 and [PPh3(CH2Ph)][BiCl2{W(CO)3(eta-C5H5)}2] 14 were similarly prepared. Spectroscopic data for the complexes [N(PPh3)2][BiCl3(Mo(CO)3(eta-C5H5)}] 16 and [N(PPh3)2][BiCl3{W(CO)3(eta-C5H5)}] 17 are also presented. The structures of compounds 2,8,9 (as a thf solvate) and 13 were determined by X-ray crystallography. The structures of all of the compounds comprise a four-co-ordinate bismuth centre bonded to two chlorine atoms and two ML(n) fragments. The precise co-ordination geometries, however, vary from close to an idealised equatorially-vacant trigonal bipyramid (disphenoidal), 2 and 9, with axial chlorines and equatorial metal centres, to nearly tetrahedral, 8 and 13. These results are incorporated into a general discussion of the structures found for AB4E complexes, i.e. four-co-ordinate with ten valence electrons, and some ideas are advanced on possible electronic factors which determine the particular geometry adopted.