@article {23411,
	title = {Side-on End-on Bound Dinitrogen: An Activated Bonding Mode That Facilitates Functionalizing Molecular Nitrogen},
	journal = {Accounts of Chemical Research},
	volume = {42},
	year = {2009},
	month = {Jan},
	pages = {127-133},
	type = {Review},
	abstract = {<p>Molecular nitrogen is the source of all of the nitrogen necessary to sustain life on this planet. How it is incorporated into the biosphere is complicated by its intrinsic inertness. For example, biological nitrogen fixation takes N-2 and converts it into ammonia using various nitrogenase enzymes, whereas industrial nitrogen fixation converts N-2 and H-2 to NH3 using heterogeneous iron or ruthenium surfaces. In both cases, the processes are energy-intensive. Is it possible to discover a homogeneous catalyst that can convert molecular nitrogen into higher-value organonitrogen compounds using a less energy-intensive pathway? If this could be achieved, it would be considered a major breakthrough in this area. In contrast to carbon monoxide, which is reactive and an important feedstock in many homogeneous catalytic reactions, the ischelectronic but inert N-2 molecule is a very poor ligand and not a common industrial feedstock, except for the above-mentioned industrial production of NH3. Because N-2 is readily available from the atmosphere and because nitrogen is an essential element for the biosphere, attempts to discover new processes involving this simple small molecule have occupied chemists for over a century. Since the first discovery of a dinitrogen complex in 1965, inorganic chemists have been key players in this area and have contributed much fundamental knowledge on structures, binding modes, and reactivity patterns. For the most part, the synthesis of dinitrogen complexes relies on the use of reducing agents to generate an electron-rich intermediate that can interact with this rather inert molecule. In this Account, a facile reaction of dinitrogen with a ditantalum tetrahydride species to generate the unusual side-on end-on bound N-2 moiety is described. This particular process is one of a growing number of new, milder ways to generate dinitrogen complexes. Furthermore, the resulting dinitrogen complex undergoes a number of reactions that expand the known patterns of reactivity for coordinated N-2. This Account reviews the reactions of ([NPN]Ta)(2)(mu-H)(2)(mu-eta(1):eta(2)-N-2), 2 (where NPN = PhP(CH2SiMe2NPh)(2)), with a variety of simple hydride reagents, E-H (where E-H = R2BH, R2AlH, RSiH3, and Cp2ZrCl(H)), each of which results in the cleavage of the N-N bond to form various functionalized imide and nitride moieties. This work is described in the context of a possible catalytic cycle that in principle could generate higher-value nitrogen-containing materials and regenerate the starting ditantalum tetrahydride. How this fails for each particular reagent is discussed and evaluated.</p>},
	keywords = {ammonia, CLEAVAGE, CONVERSION, COORDINATED N-2 LIGAND, H-2, HYDROSILYLATION, MOLYBDENUM, REACTIVITY, REDUCTION, TANTALUM COMPLEX},
	isbn = {0001-4842},
	author = {Fryzuk, MD}
}
@article {1573,
	title = {Inner-sphere two-electron reduction leads to cleavage and functionalization of coordinated dinitrogen},
	journal = {Proceedings of the National Academy of Sciences of the United States of America},
	volume = {103},
	number = {46},
	year = {2006},
	note = {ISI Document Delivery No.: 108OPTimes Cited: 14Cited Reference Count: 55Spencer, Liam P. MacKay, Bruce A. Patrick, Brian O. Fryzuk, Michael D.},
	month = {Nov},
	pages = {17094-17098},
	type = {Article},
	abstract = {Activation of molecular nitrogen by transition metal complexes is an area of current interest as investigations using the inert N-2 molecule to produce higher-value organonitrogen compounds intensify. In an attempt to extend the addition of hydride reagents E-H (where E = BR2, AIR(2), and SiR3) to the dinitrogen complex ([NPN]Ta)(2)(mu-H)(2)(mu-eta(2):eta(2)-N-2) [1; where NPN = (PhNSiMe2CH2)(2)PPh], the reaction with zirconocene chlorohydride, [Cp2Zr(Cl)H](x), was examined. The crystalline product formed in 35\% yield was determined to be ([NP(N)N]Ta)(mu-H)(2)(mu-N)(Ta[NPN])(ZrCP2) (2) in which the coordinated N-2 has been cleaved to form a phosphinimide bridging between Ta and Zr and a triply bridging nitride. The mechanism of this reaction was examined to determine the fate of the chloride and hydricle ligands attached to Zr in the starting zirconocene reagent. Using the zirconocene dihydride dimer ([Cp2ZrH2](2)), a higher yield of 2 was obtained (76\%), and H-2 was also observed by H-1 NMR spectroscopy. To probe the origin of the eliminated H-2, the dideuterated dinitrogen complex ([NPN]Ta)(2)(tLID)(2)(mu-eta(1):n(2)-N-2) (d(2)-1) was allowed to react with ([CP2ZrH2](2)), which resulted in the formation of ([NP(N)N]Ta)(mu-D)(2)(mu-N)(Ta[NPN]) (ZrCP2), (d(2)-2), with no evidence of hydrogen for deuterium scrambling between the starting zirconocene dihydride and the ditantalum dinitrogen complex. Studies into the use of preformed Zr(II) and Ti(II) reagents were also performed. The proposed mechanism involves initial adduct formation that facilitates inner-sphere electron transfer to cleave the N-N bond to form a species with bridging nitrides, one of which is transformed by nucleophilic attack of a phosphine donor to generate the observed phosphinimide.},
	keywords = {BOND-CLEAVAGE, BRIDGING N-2 UNIT, CLEAVAGE, COMPLEXES, dinitrogen coordination, END-ON, METAL-COMPLEXES, MOLECULAR, MOLYBDENUM-IRON PROTEIN, NITROGEN, nitrogen fixation, nitrogen-nitrogen bond, PHOSPHINIMIDE COMPLEXES, SIDE-ON, TANTALUM COMPLEX, TUNGSTEN},
	isbn = {0027-8424},
	url = {<Go to ISI>://000242249400008},
	author = {Spencer, L. P. and MacKay, B. A. and Patrick, B. O. and Fryzuk,Michael D.}
}
@article {734,
	title = {Vanadium and niobium diamidophosphine complexes and their reactivity},
	journal = {Canadian Journal of Chemistry-Revue Canadienne De Chimie},
	volume = {81},
	number = {12},
	year = {2003},
	note = {ISI Document Delivery No.: 751CNTimes Cited: 7Cited Reference Count: 27},
	month = {Dec},
	pages = {1431-1437},
	type = {Article},
	abstract = {The tridentate ligand precursors R{\textquoteright}P(CH2SiMe2NR")(2) ((R{\textquoteright}R{\textquoteright}{\textquoteright})[NPN]: R{\textquoteright} = Cy, Ph; R" = Ph, Mes, Me) were prepared from metathesis reactions of a lithiated amine, chloro(chloromethyl)dimethylsilane, the appropriate 1degrees phosphine, and n-butyl lithium and were isolated as solvent adducts. Metathesis between (CyPh)[NPN]Li-2(OEt2), 2, and VCl3(THF)(3) afforded ((CyPh)[NPN]VCl)(2), 7, whose solid-state structure was established by X-ray crystallography. Reduction attempts of the ((R{\textquoteright}R{\textquoteright}{\textquoteright})[NPN]VCl)(2) species with KC8 incorporated molecular nitrogen but were complicated by imide formation and ligand decomposition. Metathesis of 2 with NbCl2Me3 afforded the highly unstable complex (CyPh)[NPN]NbMe3, 15. Attempts to hydrogenate this species were unsuccessful.},
	keywords = {3-COORDINATE MOLYBDENUM(III), BRIDGING N-2 UNIT, COORDINATION, COORDINATION CHEMISTRY, DINITROGEN COMPLEX, END-ON, FUNCTIONALIZATION, HYDROGENATION, LIGAND, METATHESIS, NIOBIUM, REDUCTION, REDUCTIVE CLEAVAGE, SIDE-ON, TANTALUM COMPLEX, VANADIUM},
	isbn = {0008-4042},
	url = {<Go to ISI>://000187035400001},
	author = {Shaver, M. P. and Thomson, R. K. and Patrick, B. O. and Fryzuk,Michael D.}
}
