Triphenylcyanoborate complexes of rhodium. A nitrogen-15 NMR study of [Rh(NCBPh(3))(PPh(3))(3)] and [Rh(CNBPh(3))(PPh(3))(3)] and their derivatives

The isomeric compounds [Rh(NCBPh(3))(PPh(3))(3)] (1) (prepared from [RhCl(PPh(3))(3)] and K[NCBPh(3)]) and [Rh(CNBPh(3))(PPh(3))(3)] (2) (prepared from [Rh(CN)(PPh(3))(3)] and BPh(3)) undergo ligand exchange with pyridine (py) to give cis-[Rh(NCBPh(3))(PPh(3))(2)(py)] and trans-[Rh(CNBPh(3))(PPh(3))(2)(PY)] and with L = ethylene (reversibly), carbon monoxide, and 2,6 xylyl isocyanide (XNC) to give trans-[Rh(X)(PPh(3))(2)(L)] (X = NCBPh(3), CNBPh(3)) and oxidative addition with hydrogen (reversibly) and triphenyltin hydride to give [Rh(X)(H)(2)(PPh(3))(3)] and [Rh(X)(H)(SnPh(3))(PPh(3))(2)], respectively; triphenylsilane combines with 1 (reversibly) but not with 2. By heating 1 to 100 degrees C in an inert solvent, the rearrangement of 1 to 2 is observed. Complex 1 in DMSO combines with oxygen to yield a product formulated as a sulfonium salt, although in CH2Cl2 it is unreactive toward oxygen unlike 2 which forms an O-2 adduct. In a solution of toluene containing pyridine or substituted pyridines in the presence of oxygen, 1 forms cis- [Rh(NCBPh(3))(O-2)(PPh(3))(2)(py)] while 2 loses B Ph(3) to give [Rh(CN)(O-2)(PPh(3))(2)(py)]. Hydrogen is bound reversibly by trans- [Rh(CNBPh(3))(PPh(3))(2)(py)] and irreversibly by cis- [Rh(NC B Ph(3))(PPh(3))(2)(py)]. A comparison of the properties of 1 and 2 and their derivatives shows the N-bonded isomers to be the more electrophilic and the N-B bond to be significantly more labile than the C-B bond. Nitrogen-15 NMR data are reported for complexes enriched to 99% in N-15.