TY - JOUR
T1 - Isolation of an Extremely Labile Dihydrogen Complex, Cr(CO)3(PPri3)2(H2), Containing the Shortest Ligated H-H Bond
AU - Kubas, Gregory J.
AU - Nelson, Janet E.
AU - Bryan, Jeffrey C.
AU - Eckert, Juergen
AU - Wisniewski, Linda
AU - Zilm, Kurt
PY - 1994/6/1
Y1 - 1994/6/1
N2 - First-row members of the group 6 series of transition metal dihydrogen complexes Cr(CO)3(PR3)2(η2-H2) (R = Cy, Pri) have been synthesized and examined by X-ray crystallography and NMR, infrared, and inelastic neutron scattering spectroscopies. The complexes completely dissociate H2 in solution to give Cr(CO)3(PR3)2, which contains an agostic C-H interaction. An X-ray structure of Cr(CO)3(PPri3)2(H2) showed a side-bonded dihydrogen ligand with H-H = 0.67(5) Å, and proton NMR of the HD isotopomer showed a J(HD) value of 35 Hz. Solid-state 1H NMR spectroscopy of the PCy3 complex indicated that the H-H separation is 0.85(1) Å, which is believed to be a more precise and accurate measure of this key parameter. The barrier to rotation of the η2-H2 has been recalculated to be 1.17(10) kcal/mol, as compared with 1.32(10) and 1.9(1) kcal/mol for the Mo and W analogues, based on H-H distances from solid-state NMR. Correlations of properties of the group 6 species indicate that the H2 → M σ-bonding strength appears to increase as Mo < Cr ~ W but that dπ → H2 σ* back-bonding increases down the group. It might be generally concluded that back-bonding is more of a factor than σ-bonding in influencing stability, H-H distance, and possibly overall bond strengths. Crystallographic data: space group P21/c, a = 13.457-(3) Å, b = 11.493(3) Å, c = 16.639(4) Å, β = 102.25(2)°, Z = 4, R = 3.32%.
AB - First-row members of the group 6 series of transition metal dihydrogen complexes Cr(CO)3(PR3)2(η2-H2) (R = Cy, Pri) have been synthesized and examined by X-ray crystallography and NMR, infrared, and inelastic neutron scattering spectroscopies. The complexes completely dissociate H2 in solution to give Cr(CO)3(PR3)2, which contains an agostic C-H interaction. An X-ray structure of Cr(CO)3(PPri3)2(H2) showed a side-bonded dihydrogen ligand with H-H = 0.67(5) Å, and proton NMR of the HD isotopomer showed a J(HD) value of 35 Hz. Solid-state 1H NMR spectroscopy of the PCy3 complex indicated that the H-H separation is 0.85(1) Å, which is believed to be a more precise and accurate measure of this key parameter. The barrier to rotation of the η2-H2 has been recalculated to be 1.17(10) kcal/mol, as compared with 1.32(10) and 1.9(1) kcal/mol for the Mo and W analogues, based on H-H distances from solid-state NMR. Correlations of properties of the group 6 species indicate that the H2 → M σ-bonding strength appears to increase as Mo < Cr ~ W but that dπ → H2 σ* back-bonding increases down the group. It might be generally concluded that back-bonding is more of a factor than σ-bonding in influencing stability, H-H distance, and possibly overall bond strengths. Crystallographic data: space group P21/c, a = 13.457-(3) Å, b = 11.493(3) Å, c = 16.639(4) Å, β = 102.25(2)°, Z = 4, R = 3.32%.
UR - http://www.scopus.com/inward/record.url?scp=0000145279&partnerID=8YFLogxK
U2 - 10.1021/ic00091a039
DO - 10.1021/ic00091a039
M3 - Article
AN - SCOPUS:0000145279
SN - 0020-1669
VL - 33
SP - 2954
EP - 2960
JO - Inorganic Chemistry
JF - Inorganic Chemistry
IS - 13
ER -