Mechanistic Studies for Pd(II)(O) Reduction Generating Pd(0) and HO: Formation of Pd(OH) as a Key Intermediate.

Molecular oxygen (O) remains to be an ideal yet underutilized feedstock for the oxidative transformation of organic substrates and renewable energy systems such as fuel cells. Palladium (Pd) has shown particular promise in enabling these applications. The present study describes a Pd-mediated O reduction to water via C-H activation of 9,10-dihydroanthracene (DHA) by a Pd(II) η-peroxo complex .

Aryl-fluoride reductive elimination from Pd(II): feasibility assessment from theory and experiment.

DFT methods were used to elucidate features of coordination environment of Pd(II) that could enable Ar-F reductive elimination as an elementary C-F bond-forming reaction potentially amenable to integration into catalytic cycles for synthesis of organofluorine compounds with benign stoichiometric sources of F(-). Three-coordinate T-shaped geometry of Pd(II)Ar(F)L (L = NHC, PR(3)) was shown to offer kinetics and thermodynamics of Ar-F elimination largely compatible with synthetic applications, whereas coordination of strong fourth ligands to Pd or association of hydrogen bond donors with F each caused pronounced stabilization of Pd(II) reactant and increased activation barrier beyond the practical range. Decreasing donor ability of L promotes elimination kinetics via increasing driving force and para-substituents on Ar exert a sizable SNAr-type TS effect.

Studies relevant to catalytic reduction of dinitrogen to ammonia by molybdenum triamidoamine complexes.

In this paper we explore several issues surrounding the catalytic reduction of dinitrogen by molybdenum compounds that contain the [(HIPTNCH2CH2)3N]3- ligand (where HIPT = 3,5-(2,4,6-i-Pr3C6H2)2C6H3). Four additional plausible intermediates in the catalytic dinitrogen reduction have now been crystallographically characterized; they are MoN= NH (Mo = [(HIPTNCH2CH2)3N]Mo), [Mo=NNH2][BAr'4] (Ar' = 3,5-(CF3)2C6H3), [Mo=NH][BAr'4], and Mo(NH3). We also have crystallographically characterized a 2,6-lutidine complex, Mo(2,6-Lut)+, which is formed upon treatment of MoH with [2,6-LutH][B(C6F5)4].

Molybdenum triamidoamine complexes that contain hexa-tert-butylterphenyl, hexamethylterphenyl, or p-bromohexaisopropylterphenyl substituents. An examination of some catalyst variations for the catalytic reduction of dinitrogen.

Three new tetramines, (ArNHCH(2)CH(2))(3)N, have been synthesized in which Ar = 3,5-(2,4,6-t-Bu(3)C(6)H(2))(2)C(6)H(3) (H(3)[HTBTN(3)N]), 3,5-(2,4,6-Me(3)C(6)H(2))(2)C(6)H(3) (H(3)[HMTN(3)N]), or 4-Br-3,5-(2,4,6-i-Pr(3)C(6)H(2))(2)C(6)H(2) (H(3)[pBrHIPTN(3)N]). The diarylated tetramine, [3,5-(2,4,6-t-Bu(3)C(6)H(2))(2)C(6)H(3)NHCH(2)CH(2)](2)NCH(2)CH(2)NH(2), has also been isolated, and the "hybrid" tetramine [3,5-(2,4,6-t-Bu(3)C(6)H(2))(2)C(6)H(3)NHCH(2)CH(2)](2)NCH(2)CH(2)NH(4-t-BuC(6)H(4)) has been prepared from it. Monochloride complexes, [(TerNCH(2)CH(2))(3)N]MoCl, have been prepared, as well as a selection of intermediates that would be expected in a catalytic dinitrogen reduction such as [(TerNCH(2)CH(2))(3)N]Mo[triple bond]N and [[(TerNCH(2)CH(2))(3)N]Mo(NH(3))][BAr'(4)] (Ter = HTBT, HMT, or pBrHIPT and Ar' = 3,5-(CF(3))(2)C(6)H(3))).

Catalytic reduction of dinitrogen to ammonia at a single molybdenum center.

Dinitrogen (N2) was reduced to ammonia at room temperature and 1 atmosphere with molybdenum catalysts that contain tetradentate [HIPTN3N]3- triamidoamine ligands (such as [HIPTN3N]Mo(N2), where [HIPTN3N]3- is [(3,5-(2,4,6-i-Pr3C6H2)2C6H3NCH2CH2)3N]3-) in heptane. Slow addition of the proton source [(2,6-lutidinium)(BAr'4), where Ar' is 3,5-(CF3)2C6H3]and reductant (decamethyl chromocene) was critical for achieving high efficiency ( approximately 66% in four turnovers). Numerous x-ray studies, along with isolation and characterization of six proposed intermediates in the catalytic reaction under noncatalytic conditions, suggest that N2 was reduced at a sterically protected, single molybdenum center that cycled from Mo(III) through Mo(VI) states.

Synthesis and reactions of molybdenum triamidoamine complexes containing hexaisopropylterphenyl substituents.

We have synthesized a triamidoamine ligand ([(RNCH(2)CH(2))(3)N](3)(-)) in which R is 3,5-(2,4,6-i-Pr(3)C(6)H(2))(2)C(6)H(3) (hexaisopropylterphenyl or HIPT). The reaction between MoCl(4)(THF)(2) and H(3)[HIPTN(3)N] in THF followed by 3.1 equiv of LiN(SiMe(3))(2) led to formation of orange [HIPTN(3)N]MoCl.

Reduction of dinitrogen to ammonia at a well-protected reaction site in a molybdenum triamidoamine complex.

We have synthesized a triamidoamine ligand ([(RNCH2CH2)3N]3-) in which R is 3,5-(2,4,6-i-Pr3C6H2)2C6H3 (HexaIsoPropylTerphenyl or HIPT). The reaction between MoCl4(THF)2 and H3[HIPTN3N] in THF followed by 3.1 equiv of LiN(SiMe3)2 led to formation of orange [HIPTN3N]MoCl.