Tris(pyrrolyl-α-methyl)amines that Sterically Protect a Trigonal Metal Site

Wampler, Keith M.; Schrock, Richard R.

doi:10.1021/ic701472y

Cited by 25 publications

(29 citation statements)

References 22 publications

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“…The Mo(1)-N(4) bond length (2.2630(12) Å) is similar to what is found in related triamidoamine ligand systems, and longer than Mo(1)-N(3) (1.9539(12) Å) and Mo(1)-N(2) (1.9688(12) Å. The Mo(1)-N(1) bond length (2.081 Å) is slightly longer than the Mo-N amido bonds and the average Mo(1)-N pyrrolyl bond length (2.007 Å) in a tris(pyrrolyl-α-methyl)amine molybdenum chloride complex,15 but approximately what is found for Mo-N pyrrolyl bonds in several molybdenum-η 1 -pyrrolyl complexes 18…”

Section: Resultsmentioning

confidence: 92%

Synthesis of DiamidoPyrrolyl Molybdenum Complexes Relevant to Reduction of Dinitrogen to Ammonia

2010

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A potentially useful trianionic ligand for the reduction of dinitrogen catalytically by molybdenum complexes is one in which one of the arms in a [(RNCH2CH2)3N]3− ligand is replaced by a 2-mesitylpyrrolyl-α-methyl arm, i.e., [(RNCH2CH2)2NCH2(2-MesitylPyrrolyl)]3− (R = C6F5, 3,5-Me2C6H3, or 3,5-t-Bu2C6H3). Compounds have been prepared that contain the ligand in which R = C6F5 ([C6F5N)2Pyr]3−); they include [(C6F5N)2Pyr]Mo(NMe2), [(C6F5N)2Pyr]MoCl, [(C6F5N)2Pyr]MoOTf, and [(C6F5N)2Pyr]MoN. Compounds that contain the ligand in which R = 3,5-t-Bu2C6H3 ([Art-BuN)2Pyr]3−) include {[(Art-BuN)2Pyr]Mo(N2)}Na(15-crown-5), {[(Art-Bu N)2Pyr]Mo(N2)}[NBu4], [(Art-Bu N)2Pyr]Mo(N2) (νNN = 2012 cm−1 in C6D6), {[(Art-Bu N)2Pyr]Mo(NH3)}BPh4, and [(Art-Bu N)2Pyr]Mo(CO). X-ray studies are reported for [(C6F5N)2Pyr]Mo(NMe2), [(C6F5N)2Pyr]MoCl, and [(Art-BuN)2Pyr]MoN. The [(Art-BuN)2Pyr]Mo(N2)0/− reversible couple is found at −1.96 V (in PhF versus Cp2Fe+/0), but the [(Art-BuN)2Pyr]Mo(N2)+/0 couple is irreversible. Reduction of {[(Art-BuN)2Pyr]Mo(NH3)}BPh4 under Ar at approximately −1.68 V at a scan rate of 900 mV/sec is not reversible. Ammonia in [(Art-BuN)2Pyr]Mo(NH3) can be substituted for dinitrogen in about 2 hours if 10 equivalents of BPh3 are present to trap the ammonia that is released. [(Art-BuN)2Pyr]Mo-N=NH is a key intermediate in the proposed catalytic reduction of dinitrogen that could not be prepared. Dinitrogen exchange studies in [(Art-BuN)2Pyr]Mo(N2) suggest that steric hindrance by the ligand may be insufficient to protect decomposition of [(Art-BuN)2Pyr]Mo-N=NH through a variety of pathways. Three attempts to reduce dinitrogen catalytically with [(Art-BuN)2Pyr]Mo(N) as a “catalyst” yielded an average of 1.02 ± 0.12 equivalents of NH3.

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Section: Resultsmentioning

confidence: 92%

Synthesis of DiamidoPyrrolyl Molybdenum Complexes Relevant to Reduction of Dinitrogen to Ammonia

2010

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“…The geometry around the five-coordinate molybdenum center is square pyramidal. Two diastereotopic resonances at δ 2.38 and 2.87 are observed for the methyl groups associated with the coordinated NMe 2 H moiety at 273 K, both of which are doublets from coupling to (16); N(1)-Mo(1)-N (2), 89.89 (12); N(5)-Mo(1)-N(6), 86.27 (19); N(1)-Mo(1)-N(6), 95.34 (16); N(2)-Mo(1)-N(5), 81.29(15), C(1)-P(1)-C(2), 98.20 (18); C(1)-P(1)-C(3), 101.13 (17); C(2)-P(1)-C(3), 101.39 (17). The phosphorus adopts an inverted stereochemistry relative to 2a and 2b, so that the phosphine would need to invert to coordinate the remaining arm.…”

Section: Synthesis Of Diamagnetic Molybdenum Nitridesmentioning

confidence: 99%

Diamagnetic molybdenum nitride complexes supported by diligating tripodal triamido-phosphine ligands as precursors to paramagnetic phosphine donors

Hatnean

Johnson

2015

Dalton Trans.

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The reaction of the ligand precursors P[CH2NHAr(R)]3 () with (Me2N)3Mo[triple bond, length as m-dash]N generated the complexes P(CH2NAr(R))3Mo[triple bond, length as m-dash]N (), where Ar(R) = 3,5-(CH3)2C6H3 (), Ph (), and 3,5-(CF3)2C6H3 (), with (Me2N)3Mo[triple bond, length as m-dash]N generated the complexes P(CH2NAr(R))3Mo[triple bond, length as m-dash]N (). Complex was obtained in poor yield, due to the formation of P(CH2N-3,5-(CF3)2C6H3)2(CH2NH-3,5-(CF3)2C6H3)(NMe2H)(NMe2)Mo[triple bond, length as m-dash]N () as the major product. Reaction of with VMes3THF generated the paramagnetic complexes P(CH2NAr(R))3Mo(μ-N)V(Mes)3 (). The reaction of with Ni(acac)2 generated the Ni(0) complexes Ni[P(CH2NAr(R))3Mo[triple bond, length as m-dash]N]4 () in poor yield. These complexes were synthesized in higher yields from the reaction of with Ni(COD)2, where COD = 1,5-cyclooctadiene. Reaction of either with V(Mes)3THF or with Ni(COD)2 generated the paramagnetic nonanuclear complex Ni[P(CH2NAr(R))3Mo(μ-N)VMes3]4 ().

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“…In an effort to prepared a suitable trianionic ligand in which the " amido " nitrogens will not be protonated readily when bound as a trianion to a metal, three substituted tris(pyrrolyl -α -methyl)amines (H 3 [Aryl 3 TPA]) (Aryl = 2,4,6 -C 6 H 2 Me 3 , 2,4,6 -C 6 H 2 ( i -Pr) 3 (Trip), or 3,5 -C 6 H 3 (CF 3 ) 2 ) were prepared [71] . An X -ray study of [Trip 3 TPA]MoCl shows it to be a distorted trigonal bipyramidal species in which the Mo -N and Mo -Cl bond lengths are in the expected range, and in which the 2,4,6 -triisopropylphenyl substituents surround and protect the apical chloride (Figure 2.4 ); other [Aryl 3 TPA]MoCl derivatives could not be prepared.…”

Section: Moh and Mo(h 2 )mentioning

confidence: 99%

Catalytic Reduction of Dinitrogen to Ammonia by Molybdenum

Schrock

2010

Catalysis Without Precious Metals

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IntroductionIn the 1960s it was fi rst recognized that dinitrogen is reduced to ammonia in the environment by a metalloenzyme, an FeMo nitrogenase [1 -5] . Although " alternative " nitrogenases have been discovered that do not contain Mo [6 -8] , the FeMo nitrogenase is the most accessible. The FeMo nitrogenase has been purifi ed, crystallized, and studied for several decades. It appears to be the most effi cient at reducing dinitrogen to ammonia, with only approximately one equivalent of dihydrogen being produced 1 -50 atm of dinitrogen. It has also been subjected to X -ray studies that have elicited additional discussion concerning the mechanism of dinitrogen reduction [9 -12] . However, no defi nitive conclusions have yet been reached.After the discovery of the fi rst dinitrogen complex ([Ru(NH 3 ) 5 (N 2 )] 2 + ) by Allen and Senoff [13] , reduction of dinitrogen to ammonia under mild conditions with an abiological catalyst seemed imminent [14 -21] . However, the problem proved to be a great deal more challenging than anticipated. Over a period of several decades, hundreds of man years were invested in attempting to demonstrate that it is possible to reduce dinitrogen abiologically and catalytically under mild conditions (25 ° C and 1 atm of N 2 ). Perhaps it was not fully appreciated how diffi cult reduction of dinitrogen to ammonia in solution with protons and electrons would be; dinitrogen is an extraordinarily stable molecule, and protons are reduced readily to dihydrogen, a reaction that itself may be catalyzed by transition metals. The only reaction in which dinitrogen is reduced catalytically (to an approximately 10 : 1 mixture of hydrazine and ammonia) under mild conditions was reported by Shilov [22] . That reaction also requires molybdenum and is catalytic with respect to it. The solvent is methanol and a relatively strong reducing agent such as sodium amalgam is required. Hydrazine is the primary product with ammonia being formed through a metal -catalyzed disproportionation of hydrazine to dinitrogen and ammonia, a reaction that is accomplished relatively readily by transition metals. Shilov proposed that dinitrogen is bound and reduced between two metal centers, although direct evidence was not provided.

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Tris(pyrrolyl-α-methyl)amines that Sterically Protect a Trigonal Metal Site

Cited by 25 publications

References 22 publications

Synthesis of DiamidoPyrrolyl Molybdenum Complexes Relevant to Reduction of Dinitrogen to Ammonia

Synthesis of DiamidoPyrrolyl Molybdenum Complexes Relevant to Reduction of Dinitrogen to Ammonia

Diamagnetic molybdenum nitride complexes supported by diligating tripodal triamido-phosphine ligands as precursors to paramagnetic phosphine donors

Catalytic Reduction of Dinitrogen to Ammonia by Molybdenum

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