Tetraphenylborate Coordination Chemistry. Synthesis, Solid State and Solution Characterization, and Properties of {[(C2H4)2Rh(h6-Ph)]2BPh2}O3SCF3 and {[(C2H4)2Rh(h6-Ph)]3BPh}(O3SCF3)2: the First Examples of a Tetraphenylborate Anion Acting as a 12 or 18 e- Donor to Metal Centres

{[(C2H4)2Rh(η6-Ph)]2BPh2}O3SCF3 (3) and {[(C2H4)2Rh(η6-Ph)]3BPh}(O3SCF3)2 (4) have been synthesized by reaction of (C2H4)2Rh(η6-PhBPh3) with in situ generated Rh(C2H4)2(O3SCF3). 3 And 4 are the first examples of a tetraphenylborate anion bridging two and three metal centers, respectively. {[(C2H4)2Rh(η6-Ph)]2BPh2}O3SCF3 has been characterized in the solid state by x-ray diffraction (crystals of {[(C2H4)2Rh(η6-Ph)]2BPh2}O3SCF3 are monoclinic, spacegroup P2/n; a=13.050(1)A, b=14.805(2), c=19.736(4)A,beta=70.71(1)°, Z=4, V=3599 A3) and in solution by means of 1H and 13C NMR spectroscopy. Complex 3 shows, in solution, at room temperature, a complicated fluxional behavior involving the rotation of the coordinated ethylene molecules around the metal-olefin bond axis, the rotation of the (C2H4)2Rh fragments around the respective Rh-arene bond vector, and the interconversion of its enantiomeric forms upon rotation of the BPh4- Ph rings around the B-C bonds. The energy barrier at 301 K relative to the rotation of the olefin molecules is ΔG‡(301 K) = 57.7 kJ mol-1. Complex 4 has been characterized in solution by 1H NMR spectroscopy. In solution of poorly coordinating solvents it is partially dissociated into 3 and Rh(C2H4)2(O3SCF3). The dissociation is temperature dependent. The first example of a tetraphenylborate anion transfer between two metal centers is also described.