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Cyanide Ligand Basicities in Cp‘M(L) 2 CN Complexes (M = Ru, Fe). Correlation between Heats of Protonation and νCN

1998; American Chemical Society; Volume: 37; Issue: 8 Linguagem: Inglês

10.1021/ic971124o

1520-510X

Chip Nataro, Jiabi Chen, Robert J. Angelici,

Ferrocene Chemistry and Applications

Basicities of the cyanide ligands in a series of Cp'M(L)2CN complexes were investigated by measuring their heats of protonation (−ΔHCNH) by CF3SO3H in 1,2-dichloroethane solution at 25.0 °C to give Cp'M(L)2(CNH)+CF3SO3-, in which the N−H+ group is probably hydrogen-bonded to the CF3SO3- anion. Basicities (−ΔHCNH) of the CpRu(PR3)2CN complexes increase from 20.5 (PPh3) to 22.4 (PMe3) kcal/mol with increasing donor abilities of the phosphine ligands. Basicities of all the Cp'Ru(PR3)2CN complexes, where Cp' = Cp or Cp*, are linearly correlated with their νCN values; the nonphosphine complexes, CpRu(1,10-phen)CN and CpRu(COD)CN, do not follow the same correlation. For a large number of Cp'M(L)2CN complexes (M = Ru, Fe, L2 = mono- and bidentate phosphines, CO, 1,10-phen, and COD), their νCN values parallel νCN values of their protonated Cp'M(L)2(CNH)+ analogues. Also, 31P NMR chemical shifts of the unprotonated Cp'M(PR3)2CN and protonated CpM(PR3)2(CNH)+ complexes are linearly related. Despite the high basicity of Ru in Cp*Ru(PMe3)2Cl (30.2 kcal/mol), the CN- in Cp*Ru(PMe3)2CN (25.0 kcal/mol) is the site of protonation; factors that determine whether protonation occurs at the Ru or the CN- are discussed.