@article {994,
	title = {Spectroscopic properties and quantum chemistry-based normal coordinate analysis (QCB-NCA) of a dinuclear tantalum complex exhibiting the novel side-on end-on bridging geometry of N-2: Correlations to electronic structure and reactivity},
	journal = {Journal of the American Chemical Society},
	volume = {126},
	number = {1},
	year = {2004},
	note = {ISI Document Delivery No.: 761ZMTimes Cited: 16Cited Reference Count: 40},
	month = {Jan},
	pages = {280-290},
	type = {Article},
	abstract = {The vibrational properties and the electronic structure of the side-on end-on N-2-bridged Ta complex ([NPN]Ta(mu-H))(2)(mu-eta(1):eta(2)-N-2) (1) (where [NPN] = (PhNSiMe2CH2)(2)PPh) are analyzed. Vibrational characterization of the Ta-2(mu-N-2)(mu-H)(2) core is based on resonance Raman and infrared spectroscopies evaluated with a novel quantum chemistry-based normal coordinate analysis (QCB-NCA). The N-N stretching frequency is found at 1165 cm(-1) exhibiting a N-15(2) isotope shift of -37 cm(-1). Four other modes of the Ta2N2H2 core are observed between 430 and 660 cm(-1). Two vibrations of the bridging hydrido ligands are also identified in the spectra. On the basis of experimental frequencies and the QCB-NCA procedure, the N-N force constant is determined to be 2.430 mdyn -Angstrom(-1). The Ta-N force constants are calculated to be 2.517 mdyn Angstrom(-1) for the Ta-eta(1)-N-2 bond and 1.291 and 0.917 mdyn Angstrom(-1) for the Ta-eta(2)-N-2 bonds, respectively. DFT calculations on 1 suggest that the bridging dinitrogen ligand carries a charge of -1.1, which is equally distributed over the two nitrogen atoms. However, orbital analysis reveals that the terminal nitrogen makes lower contributions to the pi orbitals and much higher contributions to the pi* orbitals of the N-2 ligand than the bridging nitrogen. This suggests that reactions of the dinitrogen ligand with electrophiles should preferentially occur at the terminal N atom, in agreement with experimental results.},
	keywords = {ACTIVATION, CLEAVAGE, DINITROGEN FIXATION, EFFECTIVE CORE POTENTIALS, FUNCTIONALIZATION, LIGAND, MOLECULAR CALCULATIONS, MOLYBDENUM, NITROGEN-FIXATION, REDUCTION PATHWAY},
	isbn = {0002-7863},
	url = {<Go to ISI>://000187945400064},
	author = {Studt, F. and MacKay, B. A. and Fryzuk,Michael D. and Tuczek, F.}
}
@article {5075,
	title = {New mode of coordination for the dinitrogen ligand: Formation, bonding, and reactivity of a tantalum complex with a bridging N-2 unit that is both side-on and end-on},
	journal = {Journal of the American Chemical Society},
	volume = {123},
	number = {17},
	year = {2001},
	note = {ISI Document Delivery No.: 428CCTimes Cited: 84Cited Reference Count: 91},
	month = {May},
	pages = {3960-3973},
	type = {Article},
	abstract = {The reaction of a mixture of 1 equiv of PhPH2 and 2 equiv of PhNHSiMe2CH2Cl with 4 equiv of (BuLi)-Li-n followed by the addition of THF generates the lithiated ligand precursor [NPN]Li-2. (TKF)2(where [NPN] = PhP(CH2SiMe2NPh)(2)). The reaction of [NPN]Li-2. (THF)(2) with TaMe3Cl2 produces [NPN]TaMe3, which reacts under HZ to yield the diamagnetic dinuclear Ta(IV! tetrahydride ([NPN]Ta)(2)(mu -H)4 This hydride reacts with N-2 with the loss of H-2 to produce ([NPN]Ta(mu -H))(2)(mu-eta (1):eta (2)-N-2), which was characterized both in solution and in the solid state, and contains strongly activated Nz bound in the unprecedented side-on end-on dinuclear bonding mode. A density functional theory calculation on the model complex [(H3P)(H2N)(2)Ta(mu -H)](2)-mu-eta (1):eta (2)-N-2) provides insight into the molecular orbital interactions involved in the side-on end-on bonding mode of dinitrogen. The reaction of ([NPN]Ta(mu -H))(2)(mu-eta (1):eta (2)-N-2) with propene generates the end-on bound dinitrogen complex ([NPN]Ta(CH2CH2CH3))(2)(mu-eta (1):eta (1)-N-2), and the reaction of [NPN]Li-2. (THF)(2) with NbCl3-(DME) generates the end-on bound dinitrogen complex ([NPN]NbCl)(2)(mu-eta (1):eta (1)-N-2). These two end-on bound dinitrogen complexes provide evidence that the bridging hydride ligands are responsible for the unusual bonding mode of dinitrogen in ([NPN]Ta(mu -H))(2)(mu-eta (1):eta (2)-N-2). The dinitrogen moiety in the side-on end-on mode is amenable to functionalization; the reaction of ([NPN]Ta(mu -H))(2)(mu-eta (1):eta (2)-N-2) with PhCH2Br results in C-N bond formation to yield [NPN]Ta(mu-eta (1):eta (2)-N2CH2Ph)(mu -H)(2)TaBr[NPN]. Nitrogen-15 NMR spectral data an provided for all the tantalum-dinitrogen complexes and derivatives described.},
	keywords = {CHEMISTRY, CLEAVAGE, COMPOUND, CRYSTAL-STRUCTURE, MOLECULAR-STRUCTURES, NITROGEN-FIXATION, {ACTIVATION},
	isbn = {0002-7863},
	url = {<Go to ISI>://000168442700013},
	author = {Fryzuk,Michael D. and Johnson, S. A. and Patrick, B. O. and Albinati, A. and Mason, S. A. and Koetzle, T. F.}
}
@article {2801,
	title = {END-ON VERSUS SIDE-ON BONDING OF DINITROGEN TO DINUCLEAR EARLY TRANSITION-METAL COMPLEXES},
	journal = {Journal of the American Chemical Society},
	volume = {115},
	number = {7},
	year = {1993},
	note = {ISI Document Delivery No.: KW980Times Cited: 72Cited Reference Count: 55},
	month = {Apr},
	pages = {2782-2792},
	type = {Article},
	abstract = {{The preparation of a series of dinuclear complexes of zirconium and tantalum is presented in an effort to determine factors involved in the coordination mode of the bridging dinitrogen ligand. Reduction of ZrCl3[N(SiMe2-CH2PR2)2] (R = Pr(i) and B(t)) with Na/Hg under N2 generate the corresponding dinitrogen complexes {[(R2PCH2-SiMe2)2 SiMe2)2N]ZrCl}2(mu-eta2:eta2-N2); the X-ray crystal structure of the dark blue derivative having R = Pr(i) shows that the dinitrogen unit is bridging in a planar side-on bonding mode. The N-N bond distance is 1.548(7) angstrom, which is the longest such distance for any dinitrogen complex reported. Molecular orbital calculations on this molecule indicate that the N2 unit bonds in a side-on fashion due to the unavailability of one of the d orbitals on each zirconium that would normally be involved in a pi-bond with the antibonding pi*-orbitals of the N2 moiety. This particular zirconium d orbital is unavailable due to the ancillary tridentate ligand which positions the amide donor (and the chloride) to overlap effectively with this d orbital. The results of this MO study also show that the HOMO has delta-symmetry. When the related derivative Zr(eta5-C5H5)Cl2[N(SiMe2CH2PPri2)2] is reduced under N2, the corresponding dinuclear derivative {[(Pri2PCH2SiMe2)2N]Zr(eta5-C5H5)}2(mu-eta1:eta1-N2) has the bridging dinitrogen unit end-on. In this case, the MO analysis shows that the cyclopentadienyl ligand overlaps with that zirconium d orbital which could form the delta-molecular orbital of the side-on mode; as a result, the end-on form is generated. A similar argument can be used to rationalize the end-on binding mode of the dinitrogen unit in the related tantalum derivatives {[(Pri2PCH2SiMe2)2N]Ta=CHR}2(mu-eta1:eta1-N2) (R = Bu(t), Ph), since now the alkylidene unit effectively overlaps with the same d orbital Crystals of {[(Pri2PCH2-SiMe2)2N]ZrCl}(mu-eta2:eta2-N2)-CH3C6H5 are monoclinic},
	keywords = {ACTIVATION, CARBON BONDS, CHEMISTRY, MOLECULAR-STRUCTURE, N-2 LIGAND, NITROGEN-FIXATION, PHOSPHINE COMPLEXES, RAY CRYSTAL-STRUCTURE, TANTALUM COMPLEXES, X-RAY},
	isbn = {0002-7863},
	url = {<Go to ISI>://A1993KW98000028},
	author = {Fryzuk,Michael D. and Haddad, T. S. and Mylvaganam, M. and McConville, D. H. and Rettig, S. J.}
}
