Structure, Electrochemistry and Hydroformylation Catalytic Activity of the Bis(pyrazolylborato)rhodium(I) Complexes [RhBp(CO)P] [P = P(NC₄H₄)₃, PPh₃, PCy₃, P(C₆H₄OMe‐4)₃]

Abstract

Keywords: Rhodium / N ligands / Electrochemistry / X-ray diffraction / Hydroformylation − and a value of the Lever E L ligand parameter identical to that of the pyrazolate ligand (−0.24 V vs. NHE for each coordinating arm) is proposed for the bis-and tris(pyrazolyl)borate ligands, whereas P(C 6 H 4 OMe-4) 3 is also shown to have an identical E L value (0.69 V) to that of P(NC 4 H 4 ) 3 . An improved linear relationship

Characterization of Coordination Compounds by Electrochemical Parameters

“…Although typically applied only to hexacoordinate complexes, the model has been recently extended by the current author to square-planar tetracoordinate [28,64] and pentacoordinate [28] Rh I/II complexes; the former has also been studied by others [65] although with a smaller number of compounds. Extensions to particular Ru clusters, [66][67][68] sandwich and half-sandwich complexes, [15,16,69] and to reduction processes centred at ligands [15,16] have also been proposed.…”

“…Nevertheless, Equation (15) is valid for allenylidenes and alkynyls. [28,36,42] ( 15) E L values are already known for a wide variety of ligands, [13][14][15][16][28][29][30]36,41,57,64,[70][71][72][73][74][75] including an extensive list of recently estimated values by the current author [36] for many carbyne, carbene, vinylidene, allenylidene and alkynyl ligands. Examples are given in Table 1.…”

“…[13][14][15][16]36,56] ) have already been proposed for the following M n+1/n redox couples: M = Nb (n = 3, 4), [13] Ta (n = 4), [13] Cr (n = 0, 2), [13] Mo (n = 0, 1), [13] Tc (n = 1-3), [14] Re (n = 1-3), [14] Fe (n = 2, 3), [13,26,27] Ru (n = 2, 3), [13,71] Os (n = 2) [13] and Rh (n = 1). [28,64] Normally, the redox centres are six-coordinate, with the exception of the four-and five-coordinate Rh II/I , [28,64] and in particular the five-coordinate Fe III/II [13] and Mn II/III [13] cases. The parameters usually have been obtained in organic media, but different values are observed in water where solvation effects and the complex charge can play a relevant role, as observed for Cr III/II , [13] Fe III/II , [13] Ru III/II (2+/1+), [13] Ru III/II (1-/2-) [71,75] and Os III/II [13] systems.…”

“…-1.00 [10] 0.02 [13] -0.74 [30] -0.26 [30] Hydrotris(3,5-dimethylpyrazolyl)borate ---0.23 [64] [HB(Me 2 pz) 3 -] Bis(pyrazolyl)borate (H 2 Bpz 2 -) ---0.24 [64] Pyrazolate -1.14 [36] -0.24 [13] 2-Pyridinecarboxylate (2-pyCOO -)…”

Molybdenum Complexes Bearing the Tris(1‐pyrazolyl)methanesulfonate Ligand: Synthesis, Characterization and Electrochemical Behaviour

“…The more negative value (-0.53 V vs Fc/Fc + ) is reported [70] 3 ], [71] whereas that of 1 is intermediate, in accord with the order of the net electron-donor ability of the corresponding tripodal ligands. This is shown by the values of the electrochemical Lever parameter (E L ; the lower this value, the stronger the ligand electron-donor character) that parallel the above E ½ ox values of the complexes: E L = -0.23 V (Tp), [76] -0.09 V (Tpms) [27] and 0.14 V (Tpm). [77] In addition, the hydride complex [Mo(Tpms)H(CO) 3 ] (5) is oxidized at a higher potential (-0.44 V) relative to the following related hydride compounds, in the order: [Mo-(Cp)H(CO) 3 ] (-0.50 V) [78] Ͼ [Mo(Tp)H(CO) 3 ] (-0.53 V) [78] Ͼ [Mo(Tp*)H(CO) 3 ] (-0.59 V) [78] [Tp* = hydrotris(3,5-dimethylpyrazolyl)borate] Ͼ [Mo(Cp*)H(CO) 3 ] (-0.71 V) [78] (values are vs the ferrocene/ferrocenium redox couple).…”