TY - JOUR
T1 - Strengthening of N-H⋯Co hydrogen bonds upon increasing the basicity of the hydrogen bond acceptor (Co)
AU - Zhao, Dong
AU - Ladipo, Folami T.
AU - Braddock-Wilking, Janet
AU - Brammer, Lee
AU - Sherwood, Paul
PY - 1996/5/5
Y1 - 1996/5/5
N2 - Low temperature crystal structures of (DABCO)H+Co(CO)4- (1) and (DABCO)H+Co-(CO)3PPh3- (2) (DABCO = 1,4-diazabicyclooctane) indicate that both salts exhibit N-H⋯ Co hydrogen bonding. IR and NMR data indicate that these hydrogen bonded species persist in nonpolar solvents such as toluene, but exist as solvent separated ions in more polar solvents. Replacement of the axial CO ligand by PPh3 leads to a shortening of the N⋯Co separation in the solid state from 3.437(3) to 3.294(6) Å. This change is accompanied by an increase in the angle between the equatorial carbonyl ligands. Thus, the crystallographic results suggest a strengthening of the N-H⋯Co hydrogen bond upon increasing the basicity of the metal center, the first observation of this type in the solid state. This assertion is supported by variable-temperature 1H and 13C NMR data in toluene-d8 solution which, discussed in the light of ab initio calculations, indicate that the barrier to a fluxional process involving cleavage of the N-H⋯Co hydrogen bond is greater in 2 than in 1. The crystal structures of 1 and 2 have been determined by X-ray diffraction at 135(5) and 123(5) K, respectively [1 monoclinic, P21/n (No. 14), a = 8.728(2), b = 23.333(5), c = 12.146(2) Å, β= 95.74(2)°, V = 2461.1(9) Å3, Z = 8, R(F) = 0.043, Rw(F) = 0.043, S(F) = 1.21: 2 orthorhombic, Pca21 (No. 29), a = 16.084(8), b = 8.874(3), c = 17.312(3) Å, V = 2471(1) Å3, Z = 4, R(F) = 0.065, Rw(F) = 0.060, S(F) = 1.16].
AB - Low temperature crystal structures of (DABCO)H+Co(CO)4- (1) and (DABCO)H+Co-(CO)3PPh3- (2) (DABCO = 1,4-diazabicyclooctane) indicate that both salts exhibit N-H⋯ Co hydrogen bonding. IR and NMR data indicate that these hydrogen bonded species persist in nonpolar solvents such as toluene, but exist as solvent separated ions in more polar solvents. Replacement of the axial CO ligand by PPh3 leads to a shortening of the N⋯Co separation in the solid state from 3.437(3) to 3.294(6) Å. This change is accompanied by an increase in the angle between the equatorial carbonyl ligands. Thus, the crystallographic results suggest a strengthening of the N-H⋯Co hydrogen bond upon increasing the basicity of the metal center, the first observation of this type in the solid state. This assertion is supported by variable-temperature 1H and 13C NMR data in toluene-d8 solution which, discussed in the light of ab initio calculations, indicate that the barrier to a fluxional process involving cleavage of the N-H⋯Co hydrogen bond is greater in 2 than in 1. The crystal structures of 1 and 2 have been determined by X-ray diffraction at 135(5) and 123(5) K, respectively [1 monoclinic, P21/n (No. 14), a = 8.728(2), b = 23.333(5), c = 12.146(2) Å, β= 95.74(2)°, V = 2461.1(9) Å3, Z = 8, R(F) = 0.043, Rw(F) = 0.043, S(F) = 1.21: 2 orthorhombic, Pca21 (No. 29), a = 16.084(8), b = 8.874(3), c = 17.312(3) Å, V = 2471(1) Å3, Z = 4, R(F) = 0.065, Rw(F) = 0.060, S(F) = 1.16].
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U2 - 10.1021/om950777e
DO - 10.1021/om950777e
M3 - Article
AN - SCOPUS:0000610629
SN - 0276-7333
VL - 15
SP - 1441
EP - 1445
JO - Organometallics
JF - Organometallics
IS - 5
ER -