Routes to Ruthenium-Fluoro Cations of the Type [RuL2(CO)nF]+ (n=2,3; L = PR3, NHC): A Play-Off between Solvent, L and Weakly Coordinating Anion

Interaction of cis,cis,trans-[RuF2(CO)(2)(PPh3)(2)] (1a) with BF3 in acetonitrile affords the dicationic adduct [Ru(NCMe)(2)-(CO)(2)(PPh3)(2)](BF4)(B2F7) (2), which can be readily carbonylated to form [Ru(CO)(4)(PPh3)(2)](BF4)(2) (3). In contrast, reaction of 1a with BF3 in dichloromethane leads to the neutral ruthenium-fluoro species [RuF(FBF3)(CO)(2)(PPh3)(2)] (4); facile displacement of the bound FBF3 ligand in 4 occurs on treatment with CO or PPh3 to afford cationic [RuF(CO)(2)(L)(PPh3)(2)](BF4) [L = CO (5a), PPh3 (5b)]. On the other hand, reaction of 1a with PF5 in dichloromethane furnishes the coordinatively unsaturated 16-electron salt [RuF(CO)(2)(PPh3)(2)](PF6) (6). Metathesis of the PF6 anion in 6 with KB(Ar-F)(4) [ArF = 3,5-(CF3)(2)-C6H3] in dichloromethane results in rapid decomposition, while in the presence of CO solvent exchange (CH2Cl2) takes place to yield chloride-containing [RuCI(CO)(3)(PPh3)(2)]-[B(Ar-F)(4)] (7). Unexpectedly, 1a proved unreactive towards tris(pentafluorophenyl)borane in dichloromethane. However, by substituting the triphenylphosphane ligands in 1a with better donor phosphanes or with an N-heterocyclic carbene (NHC) [to give cis,cis,trans-[RuF2(CO)(2)(L)(2)] [L = PEt2Ph (1b), P(CCPh)Ph-2 (1c), IPr (1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) (1d)], fluoride abstraction could be achieved using B(C6F5)(3) to give 16-electron [RuF(CO)(2)(L)(2)][FB(C6F5)(3)] (L = PEt2Ph (8b), P(CCPh)Ph-2 (8c), IPr (8d)]. Carbonylation of 8d proceeds smoothly to generate the coordinatively saturated species [RuF(CO)(3)(IPr)(2)][FB(C6F5)(3)] (9) in high yield. Single crystal X-ray structures are presented for 2, 3, 5a/3, 7 and 9.