The oxidative isomerisation of cis,cis-dicarbonylmanganese(I) derivatives; isolation of the resulting trans-dicarbonylmanganese(II) complexes and the X-ray structure of cis,cis-[MnBr(CO)2{P(OPh)3}(Ph2PCH2PPh2)]

Abstract

The manganese(I) complexes cis,cis-[MnL(CO)₂{P(OPh)₃}(dppm)]^z[1; z= 0, L = Br, NCS, or CN; z=+1, L = pyridine (py), NCMe, CNMe, or P(OPh)₃; dppm = Ph₂PCH₂PPh₂], cis,cis-[Mn(CO)₂LL′(dppe)]⁺[L = P(OPh)₃, L′= py or NCMe; L = L′= P(OEt)₃; dppe = Ph₂PCH₂CH₂PPh₂], and cis-[Mn(CO)₂(dppm)₂]⁺ undergo oxidative isomerisation at a platinum electrode in CH₂Cl₂ to the trans-dicarbonylmanganese(II) analogues which are also formed directly by the reversible one-electron oxidation of trans-[MnL(CO)₂{P(OPh)₃}(dppm)]^z(2; z= 0, L = Br or CN; z=+1, L = CNMe) or trans-[Mn(CO)₂{P(OEt)₃}₂(dppe)]⁺. The low-spin manganese(II) complexes trans-[MnL(CO)₂{P(OPh)₃}(dppm)]^z(3; z=+1, L = Br or CN) have been prepared as crystalline [PF₆]^– salts by the chemical oxidation of (1; z= 0, L = Br or CN) with [NO][PF₆] and [N(C₆H₄Br-p)₃][PF₆] respectively, but excess [NO][PF₆] and (1; z= 0, L = CN) gave the hydrogen isocyanide complex (3; z=+2, L = CNH); the e.s.r. spectra of these species are reported. The stereochemistry of cis,cis-[MnBr(CO)₂{P(OPh)₃}(dppm)] has been determined by X-ray crystallography. The bromide ligand is trans to CO, and the manganese has a distorted octahedral co-ordination geometry with the largest distortions due to the restricted bite of the chelating dppm ligand [P–Mn–P 71.4(1)⁰]. The structure analysis has aided a brief discussion of the significance of the linear correlations between E⁰ and the ligand constant, P_L, observed for both (1) and (2).