Molybdenum Hydride and Dihydride Complexes Bearing Diphosphine Ligands with a Pendant Amine: Formation of Complexes with Bound Amines

Shaoguang Zhang, R. Morris Bullock

Research output: Contribution to journalArticle

10 Citations (Scopus)

Abstract

CpMo(CO)(PNP)H complexes (PNP = (R2PCH2)2NMe, R = Et or Ph) were synthesized by displacement of two CO ligands of CpMo(CO)3H by the PNP ligand; these complexes were characterized by IR and variable temperature 1H and 31P NMR spectroscopy. CpMo(CO)(PNP)H complexes are formed as mixture of cis- and trans-isomers. The structures of both cis-CpMo(CO)(PEtNMePEt)H and trans-CpMo(CO)(PPhNMePPh)H were determined by single crystal X-ray diffraction. Electrochemical oxidation of CpMo(CO)(PEtNMePEt)H and CpMo(CO)(PPhNMePPh)H in CH3CN are both irreversible at slow scan rates and quasireversible at higher scan rates, with E1/2 = -0.36 V (vs Cp2Fe+/0) for CpMo(CO)(PEtNMePEt)H and E1/2 = -0.18 V for CpMo(CO)(PPhNMePPh)H. Hydride abstraction from CpMo(CO)(PNP)H with [Ph3C]+[A]- (A = B(C6F5)4 or BArF4; [ArF = 3,5-bis(trifluoromethyl)phenyl]) afforded "tuck-in" [CpMo(CO)(κ3-PNP)]+ complexes that feature the amine bound to the metal. Displacement of the κ3 Mo-N bond by CD3CN gives [CpMo(CO)(PNP)(CD3CN)]+. The kinetics of this reaction were studied by 31P{1H} NMR spectroscopy for [CpMo(CO)(κ3-PEtNMePEt)]+, providing the activation parameters ΔH = 21.6 ± 2.8 kcal/mol, ΔS = -0.3 ± 9.8 cal/(mol K), Ea = 22.1 ± 2.8 kcal/mol. Protonation of CpMo(CO)(PEtNMePEt)H affords the Mo dihydride complex [CpMo(CO)(κ2-PEtNMePEt)(H)2]+, which loses H2 to generate [CpMo(CO)(κ3-PEtNMePEt)]+ at room temperature. Our results show that the pendant amine has a strong driving force to form stable "tuck-in" [CpMo(CO)(κ3-PNP)]+ complexes, and also promotes hydrogen elimination from [CpMo(CO)(PNP)(H)2]+ complexes by formation of a Mo-N dative bond. CpMo(CO)(dppp)H (dppp = 1,3-bis(diphenylphosphino)propane) was studied as a Mo diphosphine analogue without a pendant amine, and the product of protonation of this complex gives [CpMo(CO)(dppp)(H)2]+. (Chemical Equation Presented).

Original languageEnglish
Pages (from-to)6397-6409
Number of pages13
JournalInorganic Chemistry
Volume54
Issue number13
DOIs
Publication statusPublished - Jul 6 2015

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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