22087-95-2Relevant academic research and scientific papers
An NMR Method for Distinguishing Classical from Nonclassical Structures in Transition-Metal Polyhydrides
Hamilton, Douglas G.,Crabtree, Robert H.
, p. 4126 - 4133 (1988)
A T1 method is described for distinguishing classical hydrides with terminal M-H bonds from nonclassical hydrides with H-H as well as M-H bonds.The method can still be used even where the hydrides are fluxional as is the case for transition-metal polyhydrides.The temperature dependence of the T1 shows a minimum for several cases studied.This allows the H-H distance in the H2 ligand to be estimated and the structural type determined.ReH7(PPh3)2 is shown to be nonclassical with the probable structure Re(H2)H5PPh3)2. - is shown to be classical and 2- seems to be classical, however.Other hydrides shown to be nonclassical are Re(H2)H5(dpe), FeH2(H2)L3, RuH2(H2)L3, and +; the Re examples are the first d2 and the Os example the first d4 dihydrogen complex.Complexes shown to be classical are the following: IrH5(PCy3)2, ReH5(PPh3)3, OsH4(Pp-tolyl3)3, MoH4(PMePh2)4, and, more surprisingly, +, H2Fe(CO)4, +, and WH6(PMe2Ph)3.Typical distance estimates (reff) obtained are the following: +, 1.04C Angstroem; ReH5(H2)(PPh3)2, 1.20C Angstroem; ReH5(H2)(dpe), 1.25C Angstroem; MoH4(PMePh2)4, 1.72C Angstroem, where C is a calibration constant (as yet undetermined but ca. 0.9).The ordering of the reff values observed seems to parallel the relative lability order of the complexes studied, the more labile species being associated whit shorter reff values.
An attractive Cis-effect of hydride on neighbor ligands: Experimental and theoretical studies on the structure and intramolecular rearrangements of Fe(H)2(η2-H2)(PEtPh2) 3
Van Der Sluys, Lori S.,Eckert, Juergen,Eisenstein, Odile,Hall, John H.,Huffman, John C.,Jackson, Sarah A.,Koetzle, Thomas F.,Kubas, Gregory J.,Vergamini, Phillip J.,Caulton, Kenneth G.
, p. 4831 - 4841 (2007/10/02)
The compound of formula FeH4(PEtPh2)3 has been established by neutron diffraction to possess the structure and linkage cis,mer-Fe(H)2(H)2(PEtPh2), and thus be generally similar in structure to cis,mer-Fe(H)2(N2)(PEtPh2)3, whose structure has been determined by X-ray diffraction. The Fe-hydride distances in Fe(H)2(H2)(PEtPh2)3 are 1.538 (7) ? (trans to H2) and 1.514 (6) ? (trans to PEtPh2), and the Fe-H (of H2) distances are 1.607 (8) and 1.576 (9) ?. The H-H distance in coordinated dihydrogen is 0.821 (10) ?, but the H-H bond adopts an orientation unique among structurally characterized octahedral H2 complexes; staggered with respect to the cis Fe-P and Fe-H axes. Vibrational frequencies of the Fe(H)2(H2) substructure have been measured by difference inelastic neutron scattering spectroscopy. Neutron scattering also reveals the low-frequency rotational tunneling splitting, allowing estimation of the height of the torsional barrier for coordinated H2 rotating about its midpoint (～ 1 kcal/mol). Molecular mechanics calculations predict a ground-state structure where the H-H bond eclipses the P-Fe-P direction. Extended Hückel calculations with conventional hydrogen parameters predict a structure where the H-H bond eclipses the P-Fe-P vector. However, if the hydridic character of the hydride center is considered in the calculations, the experimental conformation is found to be the most stable one. The extended Hückel results are analyzed to reveal the importance of a stabilizing overlap between the filled Fe-H σ orbital and the empty σ*H-H. This nascent H/H2 bond formation is proposed to facilitate the hydride/H2 fluxionality of Fe(H)2(H2)(PEtPh2)3, in part by avoiding an intermediate with four independent hydride ligands. Crystal data for Fe(H)2(H2)(PEtPh2)3 (27 K): a = 21.527 (5) ?, b = 11.753 (5) ?, c = 31.034 7) ?, β= 112.09 (1)°, and Z = 8 in space group C2/c. Crystal data for Fe(H)2(N2)(PEtPh2)3 (118 K): a = 18.355 (7) ?, b = 12.227 (3) ?, c = 19.273 (8) ?, β= 118.48 (1)°, and Z = 4 in space group P21/n.
