Synthesis and reactivity of the rhodium monocarbollide complexes [1-NHCMe2-2-Cl-2-PPh3-closo-2,1-RhCB10H10] and [1-NH3-2-Cl-2-PPh3-closo-2,1-RhCB10H10]

The carborane 7-NHCMe2-nido-7-CB10H12 reacts with [RhCl(PPh3)3] in toluene at reflux temperatures to give the charge-compensated 16-electron Rh(III) complex [1-NHCMe2-2-Cl-2-PPh3-closo-2,1-RhCB10H10] (1) in good yield. The structure of this product was established by X-ray diffraction (XRD). Upon methanolysis 1 affords [1-NH3-2-Cl-2-PPh3-closo-2,1-RhCB10H10] (2), also a 16-electron charge-compensated Rh(III) complex. Some reactions of 2 were investigated. At room temperature, in the presence of Na2CO3, it reacts with acetic, methacrylic, and crotonic anhydrides to give the complexes [1,2-μ-{NHC(R)O}-2-PPh3-closo-2,1-RhCB10H10] [R=Me (3), CMeCH2 (4a), and (E)-CHCHMe (4b)], respectively. Benzoyl bromide with 2 and Na2CO3 yields [1,2-μ-{NHC(Ph)O}-2-PPh3-closo-2,1-RhCB10H10] (5). An XRD study of 4a established that the acyl group is coordinated to the rhodium through the oxygen. In the crystal molecules lie pair-wise linked by a BH⇀Rh bridge so that in one molecule the rhodium atom has a 16-electron valence shell and in the other an 18-electron configuration. However, in solution NMR studies reveal that only monomeric molecules occur. With CNBut in the presence of Na2CO3, compound 2 affords [1-NH2-2,2-(CNBut)2-2-PPh3-closo-2,1-RhCB10H10] (7), the structure of which was determined by XRD. The NMR parameters of the new compounds are reported and discussed.