Synthesis of [RuX(CO){η 2 ‐ C , N ‐C 6 H 4 C(H)=NC 6 H 4 ‐4‐NO 2 }(PPh 3 ) 2 ] (X = F, Cl, Br, I): Evidence of Non‐Conventional Ru−X Hydrogen Bonds Leading to Octahedral Coordination at the Halide Atom

Treatment of [RuCl(CO){η 2 ‐ C , N ‐C 6 H 4 C(H)=NC 6 H 4 ‐4‐NO 2 }(PPh 3 ) 2 ] ( 4‐Cl ) with Ag[BF 4 ] in acetone/CH 2 Cl 2 gives the cationic complex [Ru{O=C(CH 3 ) 2 }(CO){η 2 ‐ C , N ‐C 6 H 4 C(H)=NC 6 H 4 ‐4‐NO 2 }(PPh 3 ) 2 ][BF 4 ] (not isolated), which then reacts with NaX (X = F, Br, I) to afford the new compounds [RuX(CO){η 2 ‐ C , N ‐C 6 H 4 C(H)=NC 6 H 4 ‐4‐NO 2 }(PPh 3 ) 2 ] (X = F, Br, I) ( 4‐F , 4‐Br , and 4‐I ). All of the new compounds have been characterised by elemental analysis (C, H, and N), 1 H, 13 C{ 1 H}, 31 P{ 1 H} NMR spectroscopy and IR spectroscopy. The IR data support the hypothesis that the fluoride ligand is the strongest halogen π‐donor to the metal centre. In addition, the compounds 4‐Br· 1.5CHCl 3 , 4‐Cl· 1.5CHCl 3 , 4‐F· 2CDCl 3 , and 4‐I· 1.5CHCl 3 have been characterised by single‐crystal X‐ray diffraction studies; all show Ru−X ··· HCCl 3 interactions with the Ru−F interaction being the strongest. In addition, there is evidence for the presence of competing RuX ··· ClCHCl 2 (X = Cl, Br) interactions in compounds 4‐Br and 4‐Cl ; these appear to be charge transfer in nature. The generality of these interactions has been probed using searches of the Cambridge Crystallographic Database and the data obtained suggests that these interactions have some, but limited, precedence. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)