%0 Journal Article %1 Bruns.1995 %A Bruns, Wolfgang %A Kaim, Wolfgang %A Waldhoer, Eberhard %A Krejcik, Michael. %D 1995 %J Inorganic Chemistry %K carbonyl dinuclear electrochem molybdenum mononuclear phosphine phosphine;molybdenum redox redox;tungsten tungsten %N 3 %P 663--672 %R 10.1021/ic00107a021 %T Electronic Structure of the 16 Valence Electron Fragments M(CO)3(PR3)2 (M = Mo, W; R = iPr, Cy) in Their Complexes with H2, THF, and Three p-Conjugated Dinucleating Ligands: Electrochemistry and Spectroscopy of Different Oxidation States %V 34 %X Mononuclear trans,mer-(PR3)2(CO)3M(L) (M = Mo, W; R = iPr, Cy; L = THF, h2-H2) and dinuclear trans,mer-[(PR3)2(CO)3M]2(m-L) with the sym. bridging ligands m-L = pyrazine (pz), 4,4'-bipyridine (bp) and 3,6-bis(4-pyridyl)-1,2,4,5-tetrazine (4,4'-bptz) were studied by cyclic voltammetry and by IR, UV/visible/near-IR, and EPR spectroscopy. Oxidn. of the electron-rich and dissociatively labile (Mo \textgreater W) systems yields M(I) species, including stable (Kc \textgreater 106) mixed-valent d5/d6 cations [(PiPr3)2(CO)3M]2(pz)+. These mixed-valent complex ions exhibit complete delocalization on the vibrational time scale and show similar spectroscopic features as the structurally related Creutz-Taube ion [(H3N)5Ru]2(μ-pz)5+. Reversible two-electron oxidn. processes and thus no mixed-valent states were obsd. for the bp- and 4,4'-bptz-bridged ditungsten systems. Whereas the oxidn. of (PCy3)2(CO)3W(h2-H2) is irreversible with the assumed loss of a proton, the solvates (PR3)2(CO)3M(THF) are reversibly oxidized and reduced, the latter process requiring rather neg. potentials. In nonpolar solvents the neutral dinuclear complexes display very intense and strikingly narrow charge transfer bands in the near-IR region, suggesting very little geometrical change between ground and MLCT excited states. One-electron redn. of the dinuclear complexes produces EPR-detectable radical anion complexes which show the loss of one PR3 ligand per metal center, i.e. the preference for a 16 + d rather than an 18 + d valence electron configuration. The tungsten-centered oxidn. of (PR3)2(CO)3W(L) is facilitated in the order L = mpz+, pz, H2, 4,4'-bptz, bp, and THF, illustrating quant. the well-balanced s-donor and s*- or p*-acceptor characteristics of the H2 ligand. From the results of this study apparently the (PR3)2(CO)3M fragments are suited to bind H2 because of a very finely tuned combination of s-acceptor and fairly strong but not excessive p-donor characteristics, in addn. to the proper amt. of steric shielding. [on SciFinder(R)]

@article{Bruns.1995, abstract = {Mononuclear trans,mer-(PR3)2(CO)3M(L) (M = Mo, W; R = iPr, Cy; L = THF, \textgreek{h}2-H2) and dinuclear trans,mer-[(PR3)2(CO)3M]2(\textgreek{m}-L) with the sym. bridging ligands \textgreek{m}-L = pyrazine (pz), 4,4'-bipyridine (bp) and 3,6-bis(4-pyridyl)-1,2,4,5-tetrazine (4,4'-bptz) were studied by cyclic voltammetry and by IR, UV/visible/near-IR, and EPR spectroscopy. Oxidn. of the electron-rich and dissociatively labile (Mo {\textgreater} W) systems yields M(I) species, including stable (Kc {\textgreater} 106) mixed-valent d5/d6 cations {[(PiPr3)2(CO)3M]2(pz)}+. These mixed-valent complex ions exhibit complete delocalization on the vibrational time scale and show similar spectroscopic features as the structurally related Creutz-Taube ion {[(H3N)5Ru]2(μ-pz)}5+. Reversible two-electron oxidn. processes and thus no mixed-valent states were obsd. for the bp- and 4,4'-bptz-bridged ditungsten systems. Whereas the oxidn. of (PCy3)2(CO)3W(\textgreek{h}2-H2) is irreversible with the assumed loss of a proton, the solvates (PR3)2(CO)3M(THF) are reversibly oxidized and reduced, the latter process requiring rather neg. potentials. In nonpolar solvents the neutral dinuclear complexes display very intense and strikingly narrow charge transfer bands in the near-IR region, suggesting very little geometrical change between ground and MLCT excited states. One-electron redn. of the dinuclear complexes produces EPR-detectable radical anion complexes which show the loss of one PR3 ligand per metal center, i.e. the preference for a 16 + \textgreek{d} rather than an 18 + \textgreek{d} valence electron configuration. The tungsten-centered oxidn. of (PR3)2(CO)3W(L) is facilitated in the order L = mpz+, pz, H2, 4,4'-bptz, bp, and THF, illustrating quant. the well-balanced \textgreek{s}-donor and \textgreek{s}*- or \textgreek{p}*-acceptor characteristics of the H2 ligand. From the results of this study apparently the (PR3)2(CO)3M fragments are suited to bind H2 because of a very finely tuned combination of \textgreek{s}-acceptor and fairly strong but not excessive \textgreek{p}-donor characteristics, in addn. to the proper amt. of steric shielding. [on SciFinder(R)]}, added-at = {2022-06-15T11:26:56.000+0200}, author = {Bruns, Wolfgang and Kaim, Wolfgang and Waldhoer, Eberhard and Krejcik, Michael.}, biburl = {https://puma.ub.uni-stuttgart.de/bibtex/21516320099dda469aae674ac30f455cc/huebleriac}, doi = {10.1021/ic00107a021}, interhash = {ee16534744739108d0f9eb811f7b6c97}, intrahash = {1516320099dda469aae674ac30f455cc}, issn = {0020-1669}, journal = {Inorganic Chemistry}, keywords = {carbonyl dinuclear electrochem molybdenum mononuclear phosphine phosphine;molybdenum redox redox;tungsten tungsten}, number = 3, pages = {663--672}, timestamp = {2022-06-15T09:26:56.000+0200}, title = {Electronic Structure of the 16 Valence Electron Fragments M(CO)3(PR3)2 (M = Mo, W; R = iPr, Cy) in Their Complexes with H2, THF, and Three \textgreek{p}-Conjugated Dinucleating Ligands: Electrochemistry and Spectroscopy of Different Oxidation States}, volume = 34, year = 1995 }