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)]

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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, PL, observed for both (1) and (2).