[Ru(benzene)(κ 2 P,N-3)][BPh4] (6). ), P1-Ru1-N2 62.62(6). Thermal ellipsoids were drawn at the 50% probability level. Attempts to generate a bidentate complex with ligand 2 via the terminal nitrogen by changing the temperature, solvent or using halide-extraction agents were unsuccessful. We reasoned this was not only due to the potentially weak binding of the nitrogen, but also the flanking steric bulk from the two ortho-methyl groups on the mesityl substituent, which would clash with the arene ring on the ruthenium on coordination. To circumvent this problem, we used azophosphine 3, which has a smaller steric profile around the terminal nitrogen atom. The analogous reaction of 3 with the [Ru(benzene)Cl2]2 dimer revealed a similar small downfield shift in the 31 P{ 1 H} NMR spectrum (107.7 ppm (3) to 111.9 ppm), indicative of κ 1 P coordination of the ligand (Scheme 3). This was corroborated by single crystal X-ray diffraction, and showed that the compound has the composition Ru(benzene)(κ 1 P-3)Cl2 (5) (Figure ), which is structurally similar to 4. Addition of NaBPh4 to the chlorobenzene solution of 5 gave a brown precipitate, and extraction into dichloromethane left a white precipitate (NaCl). The 31 P{ 1 H} NMR spectrum showed a significant upfield shift to 58.0 ppm. Single crystals suitable for analysis confirmed the bidentate nature of the ligand in the complex [Ru(benzene)(κ 2 P,N-3)Cl][BPh4] (6) (Figure ).