Electronic stability of metal-dihydrogen and polyhydrogen complexes

Abstract

with the latter reagents.20 In similar studies difluoroethylenes were major products of the C2H2 and F2 matrix photochemical reaction.7 Additional support for this assignment is obtained by comparing the absorptions of HFC=NF with those of gas-phase F2C=NF4 in Table II. The frequencies of three stretching modes of HF-C=NF showed the anticipated red shift from those of F2C=NF since an electron-withdrawing fluorine is replaced with an electron-donating hydrogen. Furthermore, these modes show deuterium shifts for interaction and mixing with H-C-N or D-C-N bending motions. In addition, theoretical calculations1•2 have shown the cis geometric isomer to be more stable than the trans isomer. Finally, the carbon-nitrogen bond was found again to possess double-bond character.Other Products. Additional weaker absorptions were identified in these samples that point to other minor reaction products. The two strongest bands of the F2CN free radical5 were detected here at 1734 and 1252 cm™1. Weak bands produced on annealing at 1778 and 1232 cm™1 exhibit deuterium shifts and are due to the addition of more than two F atoms to HCN. Finally, the sharp 1284-cm™1 band produced on annealing at the expense of F2CN was unshifted with DCN and observed in previous FCN studies,5 which suggests a higher (CN)(F)" species.(20) Andrews, L.; Lascóla, R. J. Am. Chem. Soc., in press. ConclusionsIn summary, hydrogen cyanide and fluorine were photolyzed to form a well-defined 1:1 hydrogen-bonded complex of the form FCN--HF in solid argon. The matrix v, and v] modes are quite similar with HCN--HF observations,9 which provides spectral evidence for the 1:1 product's being a cyanide nitrogen lone pair complex with a linear structure. Blue shifts were observed for all three FCN submolecule fundamentals in the complex. In addition, m-HFC=NF is formed during photolysis, and three predominantly bond stretching modes were observed. The primary photochemical reaction of HCN and F2 is probably fluorine addition to form excited HFCNF, which eliminates HF to give the FCN--HF complex or relaxes in the matrix cage. Similar yields of the C-F stretching bands at 1205 and 1107 cm™1 suggest that these two processes make major contributions to the overall reaction mechanism. Analogous C2H2 and F2 photolysis studies gave similar results.7 Sample annealing promoted single F atom addition to HCN, which produced HFC=N. Four infrared absorptions were observed for this free radical, which shifted appropriately for DFC=N. The carbon-nitrogen bonds for both fluorine addition products are found to have double-bond character by comparison to spectra of similar compounds.

Dihydrogen complexes as prototypes for the coordination chemistry of saturated molecules

“…7). The intermediate is a ''trihydrogen'' complex (91,92). Although not isolated, evidence exists for its intermediacy in facile H-atom exchange in ReH 2 (H 2 )(CO)(PR 3 ) 3 (93), which can be exceedingly fast even at Ϫ140°C in hydrido(H 2 ) complexes (94)(95)(96)(97)(98)(99).…”

Activation of Molecular Hydrogen

“…This process is facilitated by a cis interaction, that is, a weak hydrogen bonding like interaction between the H 2 and H ligands observable in the solid state. 3,8,67 The intermediate can be considered to be a "trihydrogen" (H 3 ) complex, 68,69 as exemplified by studies carried out on bis(cyclopentadienyl)Mo-type complexes. The ansa-bridged complexes [Me 2 X(C 5 …”

Chemical bonding of hydrogen molecules to transition metal complexes

“…5 show that this interaction is the first step towards formation of a transient H3 ligand which has often been proposed to be an intermediate in exchange of H2 and hydride. H3+ is a known mass-spectrometer molecule and its possible stabilization on a metal complex has been proposed [18] but thus far has not been observed. [C5(CH3)5]IrH3(L) (L= phosphine-type donor), in this temperature range which also has been determined to be a quantum mechanical process [19].…”