Monocarbollide Complexes of Rhodium

Abstract

The rhodium sandwich complexes [Rh(η6-arene)(η5-7-NHBut-7-CB10H10)] (arene = C6H5Me (2b), C6H3Me3-1,3,5 (3), MeC6H4C6H4Me-4,4‘ (4), [22](1,4)-C16H16 (5)) have been prepared from reactions between 1:1 mol mixtures of the arenes and [RhCl(PPh3)(η5-7-NH2But-7-CB10H10)] (1a) in CH2Cl2 in the presence of AgBF4. The crystal structures of 3 and 5 have been determined by X-ray diffraction confirming that in these species the rhodium is pentahapto coordinated on one side by the formally three-electron-donor 7-NHBut-7-CB10H10 and on the other in the hexahapto manner by a mesitylene molecule and one C6H4 ring of the cyclophane, respectively. The reaction between 4 and [Mo(CO)3(NCMe)3] in THF gave the dirhodium complex [Rh2(CO)2(η5-7-NH2But-7-CB10H10)2] (6), the structure of which has been established by X-ray diffraction. In the molecule two Rh(CO)(η5-7-NH2But-7-CB10H10) fragments are held together by a Rh−Rh bond which is spanned by two B−H⇀Rh two-electron three-center bonds employing in each CBBBB ring ligating a rhodium center a boron atom in one of the β-sites with respect to the carbon vertex. Reactions between 1a and tris(pyrazolyl)methane in the presence of TlPF6 and between 1a and K[HB(pzMe2-3,5)3] (HB(pzMe2-3,5)3 = hydrotris(3,5-dimethylpyrazolyl)borate) afforded respectively [Rh{HC(pz)3}(η5-7-NH2But-7-CB10H10)][PF2O2] (7) and [Rh{HB(pzMe2-3,5)3}(η5-7-NH2But-7-CB10H10)] (8). An X-ray diffraction study on 7 confirmed the pentahapto bonding of the charge-compensated 7-NH2But-7-CB10H10 ligand and the tridentate character of the tris(pyrazolyl)methane group and also established the anion as [PF2O2]- formed by hydrolysis of [PF6]-. The NMR data for the new compounds are reported and discussed.