New Arylruthenium(II) Complexes of the P,C,P‘-Coordinating Terdentate Monoanionic Aryl Ligands [C6H2(CH2PPh2)2-2,6-R-4]- (PCP-R-4; R = Ph, H). Synthesis of 16-Electron Species [RuIIX(PCP-R-4)(PPh3)] (X = Cl, I, OTf) and Their Reactivity toward the Neutral Terdentate N-Donor Ligand 2,2‘:6‘,2‘‘-Terpyridine (terpy)

The synthesis and characterization of new, five-coordinate, diamagnetic, 16-electron arylruthenium(II) complexes [Ru II X{C 6 H 2 (CH 2 PPh 2 ) 2 -2,6-R-4}(PPh 3 )] ( 1, X = Cl, R = H; 2, X = Cl, R = Ph; 3, X = OSO 2 CF 3, R = H; 4, X = I, R = H) are described. These coordinatively unsaturated complexes contain a stable C aryl −Ru σ-bond resulting from pseudo meridional terdentate P, C, P‘ -bonding of the monoanionic {C 6 H 2 (CH 2 PPh 2 ) 2 -2,6-R-4} - ligand (general abbreviation PCP-R-4; for R = H and R = Ph, abbreviated as PCP and PCP-Ph, respectively) that also provides two P → Ru bonds. This bonding mode of the PCP-R-4 ligands adopted in complexes 1 − 4 means that these species are structurally closely related to the complexes [RuCl{C 6 H 2 (CH 2 NMe 2 ) 2 -2,6-R-4}(PPh 3 )] (R = H, Ph) in which there is terdentate N, C, N‘ -coordination. Complexes 1 and 2 were synthesized via cyclometalation reactions of the respective neutral diphosphine compounds C 6 H 3 (CH 2 PPh 2 ) 2 -2,6-R-4 (general abbreviation PC(H)P-R-4; for R = H and R = Ph, abbreviated as PC(H)P and PC(H)P-Ph, respectively) with [Ru II Cl 2 (PPh 3 ) 4 ]. The complex [Ru II (OTf)(PCP)(PPh 3 )], 3, prepared by reaction of 1 with AgOTf (OTf = OSO 2 CF 3 = triflate), has the triflate anion bound to ruthenium in noncoordinating solvents. On the NMR time scale complex 3 in solution exhibits temperature-dependent fluxionality that is associated with reversible changes of the complex stereochemistry. The triflate PCP complex 3 reacts cleanly with the neutral N-donor ligand 2,2‘:6‘,2‘‘-terpyridine (terpy) to afford [Ru II (PCP)(terpy)][OTf], 5 . However, whereas the reaction of terpy with the PCP-Ph complex 2 affords [Ru II (PCP-Ph)(terpy)]Cl, 6, its reaction with PCP chloro complex 1 generates a mixture of products. These reactivities of PCP and PCP-Ph complexes ( 1 − 3 ) toward terpy are compared and contrasted with those of related ruthenium complexes containing the monoanionic aryldiamine ligand {C 6 H 2 (CH 2 NMe 2 ) 2 -2,6-R-4} - (abbreviated as NCN-R-4).