Reduction-oxidation properties of organo-transition metal complexes. Part 33. Ligand-vs. metal-based oxidation of cyano-bridged catecholatoruthenium–manganese carbonyl compounds: the X-ray crystal structure of cis-[(dppe)(Et3P)(OC)2Mn(µ-CN)Ru(CO)2(PPh3)(o-O2C6Cl4)]·CH2Cl2

The reactions of cis- or trans-[Mn(CN)(CO)2{P(OPh)3}(dppm)](dppm = Ph2PCH2PPh2) or cis-[Mn(CN)(CO)2(PEt3)(dppe)](dppe = Ph2PCH2CH2PPh2) with [{Ru(CO)2)(PPh3)(µ-o-O2C6Cl4)}2] give the heterobinuclear complexes cis- and trans-[(dppm){(PhO)3P}(OC)2Mn(µ-CN)Ru(CO)2(PPh3)(o-O2C6Cl4)]5 and 6 and cis-[(dppe)(Et3P)(OC)2Mn(µ-CN)Ru(CO)2(PPh3)(o-O2C6Cl4)]7. The X-ray crystal structure of 7 shows approximately octahedrally co-ordinated ruthenium and manganese centres linked by a µ-CN ligand C-bonded to Mn and N-bonded to Ru, the Ru–N–C–Mn system is slightly non-linear, with angles at C and N of 174.8(5) and 171.4(4)°, despite the formal sp hybridisation at these atoms. Complexes 5–7 undergo two sequential one-electron oxidations at a platinum electrode in CH2Cl2. Treatment with 1 equivalent of [NO][PF6] gives the monocations cis- and trans-[(dppm){(PhO)3P}(OC)2Mn(µ-CN)Ru(CO)2(PPh3)(o-O2C6Cl4)]+5+ and 6+ and cis-[(dppe)(Et3P)(OC)2Mn(µ-CN)Ru(CO)2(PPh3)(o-O2C6Cl4)]+7+ the voltammetry and IR and ESR spectra of which show electron removal from the catecholate ligand. The reaction of [{Ru(CO)2(PPh3)(µ-o-O2C6Cl4)}2] with trans-[Mn(CN)(CO)2{P(OPh)3}(dppm)]+ also gave 6+ but the analogus reaction with trans-[Mn(CN)(CO)2(PEt3)(dppe)]+ gave 7+. In both cases, intramolecular electron transfer from the O,O-chelate to MnII follows cyanide-bridge formation; in the second case this is accompanied by trans–cis isomerisation at the resulting manganese(I) centre. Subsequent oxidation of 5+–7+ occurs at the manganese(II) centre and is accompanied by cis–trans isomerisation. The reaction of the more electron-rich manganese(I) donor trans-[Mn(CN)(CO)(dppm)2] with [{Ru(CO)2(PPh3)(µ-o-O2C6Cl4)}2] gives trans-[(dppm)2(OC)Mn(µ-CN)Ru(CO)2(PPh3)(o-O2C6Cl4)]8 which also undergoes two one-electron oxidations. In this case, however, oxidation at MnI precedes that at the catecholate ligand; the manganese(II)-containing monocation 8+ is synthesised from 8 and [N2C6H4F-p]+ or directly from [{Ru(CO)2(PPh3)(µ-o-O2C6Cl4)}2] and trans-[Mn(CN)(CO)(dppm)2]+. Changes in v(CN)bridge appear to be diagnostic of oxidation at the C- or N-bonded centre of the binuclear complexes.