• Electronic Structure, Spectroscopic Properties, and Reactivity of Molybdenum and Tungsten Nitrido and Imido Complexes with Diphosphine Coligands: Influence of the trans Ligand
    K. Mersmann, A. Hauser, N. Lehnert and F. Tuczek
    Inorganic Chemistry, 45 (2006), p5044-5056
    DOI:10.1021/ic060141n | unige:3294 | Abstract | Article HTML | Article PDF
A series of molybdenum and tungsten nitrido, [M(N)(X)(diphos)2], and imido complexes, [M(NH)(X)(diphos)2)]Y, (M = Mo, W) with diphosphine coligands (diphos = dppe/depe), various trans ligands (X = N3-, Cl-, NCCH3) and different counterions (Y- = Cl-, BPh4-) is investigated. These compounds are studied by infrared and Raman spectroscopies; they are also studied with isotope-substitution and optical-absorption, as well as emission, spectroscopies. In the nitrido complexes with trans-azido and -chloro coligands, the metal−N stretch is found at about 980 cm-1; upon protonation, it is lowered to about 920 cm-1. The 1A11E (n → π*) electronic transition is observed for [Mo(N)(N3)(depe)2] at 398 nm and shows a progression in the metal−N stretch of 810 cm-1. The corresponding 3E → 1A (π* → n) emission band is observed at 542 nm, exhibiting a progression in the metal−N stretch of 980 cm-1. In the imido system [Mo(NH)(N3)(depe)2]BPh4, the n → π* transition is shifted to lower energy (518 nm) and markedly decreases in intensity. In the trans-nitrile complex [Mo(N)(NCCH3)(dppe)2]BPh4, the metal−N(nitrido) stretching frequency increases to 1016 cm-1. The n → π* transition now is found at 450 nm, shifting to 525 nm upon protonation. Most importantly, the reduction of this nitrido trans-nitrile complex is drastically facilitated compared to its counterparts with anionic trans-ligands (Epred = −1.5 V vs Fc+/Fc). On the other hand, the basicity of the nitrido group is decreased (pKa{[Mo(NH)(NCCH3)(dppe)2](BPh4)2} = 5). The implications of these findings with respect to the Chatt cycle are discussed.

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