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

Abstract

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 Mn^II 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 Mn^I 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.