Synthesis of monocarbollide complexes of rhodium

The compounds [RhX(PPh(3))(3)] react with nido-7-NH(2)Bu(t)-7-CB10H12 in toluene to give the 16-electron complexes [RhX(PPh(3))(eta(5)-7-NH(2)Bu(t)-7-CB10H10)] (1a, X = Br; 1b, X = Cl). The structure of the zwitterionic molecule 1a was determined by X-ray crystallography. Crystals are monoclinic, space group P2(1)/c, with a 12.937(3) Angstrom, b = 18.101(4) Angstrom, c = 14.695(4) Angstrom, beta = 104.21(2)degrees, and Z = 4. The metal atom is coordinated on one side by Br and PPh(3) groups and on the other in the pentahapto manner by the open CBBBB face of the cage system. Reactions of the complexes with several donor molecules have been investigated. With CNBu(t), by changing the stoichiometry or work-up procedures either the 18-electron complexes [RhX(CNBu(t))(PPh(3))(eta(5)-7-NH(2)Bu(t)-7-CB10H10)] (2a, X = Br; 2b, X = Cl) or [Rh(CNBu(t))(2)(PPh(3))(eta(5)-7-NHBu(t)-7-CB10H10)] (3) are obtained, or the 16-electron complex [Rh(CNBu(t))(PPh(3))(eta(5)-7-NHBu(t)-7-CB10H10)] (4) is formed. Formation of 3 and 4, in which the rhodium atoms are ligated by a nido-7-NHBu(t)-7-CB10H10 cage, formally a 3 pi-electron donor, is unusual and results from loss of HX from the precursors 1. To establish firmly the nature of these species, their molecular structures were determined by X-ray crystallography. Crystals of 3 are monoclinic, space group P2(1)/c, with a 10.533(2) Angstrom, b = 19.110(4) Angstrom, c = 19.707(4) Angstrom, beta = 105.413(9)degrees, and Z = 4, while those of 4 are triclinic, space group <P(1)over bar>, with a = 9.840(3) Angstrom, b = 10.809(3) <Angtrom>, c = 17.287(3) Angstrom, alpha = 88.49(2)degrees, beta = 84.57(2)degrees, gamma = 69.809(14)degrees, and Z = 2. The two molecular structures are very similar: the rhodium atom is attached on one side via an eta(5)-bonding mode to the open face of the 7-NHBu(t)-7-CB10H10 cage and on the other by the PPh(3) ligand and one or two CNBu(t) molecules, respectively. The reactions between the compounds 1 and PEt(3), PMe(3), NC(5)H(4)Me-4, and tetrahydrofuran (thf) give the complexes [RhBr(PEt(3))(eta(5)-7-NH(2)Bu(t)-7-CB10H10)] (5), [RhCl(PMe(3))(2)(eta(5)-7-NH(2)Bu(t)-7-CB10H10)] (6), and [RhBr(L)(eta(5)-7-NH(2)Bu(t)-7-CB10H10)] (7a, L = NC(5)H(4)Me-4; 7b, L = thf), respectively. Prolonged refluxing of mixtures of [CoCl(PPh(3))(3)] and nido-7-NH(2)Bu(t)-7-CB10H12 in toluene gives the arene(carborane)-cobalt complex [Co(eta(6)-C(6)H(5)Me)(eta(5)-7-NHBUt-7-CB10H10)] (8), the structure of which was determined by X-ray diffraction. Crystals are monoclinic, space group P2(1)/c, with a = 16.332(5) Angstrom, b = 10.397(2) A, 22.186(6) Angstrom, beta = 102.94(2)degrees, and Z = 8. NMR data for the new compounds are reported and discussed in relation to their structures.