TY - JOUR
T1 - Arylthiolate coordination and reactivity at pseudotetrahedral nickel(II) centers
T2 - Modulation by noncovalent interactions
AU - Chattopadhyay, Swarup
AU - Deb, Tapash
AU - Ma, Huaibo
AU - Petersen, Jeffrey L.
AU - Young, Victor G
AU - Jensen, Michael P.
PY - 2008/4/21
Y1 - 2008/4/21
N2 - Five new pseudotetrahedral nickel(II) arylthiolate complexes Tp R.MeNi-SR′ [(TpR,Me)- = 2,2,2-κ3-hydridotris(3-R,5-methylpyrazolyl)borate; R = Me, R′ = C6H5 (Ph), 2,4,6-C6H 2(CH3)3 (Mes); R = Ph, R′ = C 6H5 (Ph), 2,4,6-C6H2(CH 3)3 (Mes), and 2,6-C6H3(CH 3)2 (Xyl)] were prepared by metathesis reactions of known chloride complexes with sodium arylthiolate salts in THF. The new products were fully characterized. The effect of increasing bulk of substituents at the proximal 3-pyrazolyl and ortho-thiolate positions represented in this series was evident in spectroscopic studies (UV-vis-NIR, 1H NMR) of the product complexes. Increased steric contact induced red-shifting of nickel-thiolate ligand to metal charge transfer (LMCT) bands and enhanced contact shifts of arylthiolate protons with the paramagnetic (S = 1) nickel(II) ion. These spectroscopic effects arise from structural distortion of the nickel(II)-thiolate bond revealed by X-ray crystal structure determinations of the structural extremes of the series, TpMe,MeNi-SPh and Tp Ph,MeNi-SXyl. The distortion consists of a significantly increased tilting of the Ni-S bond from an ideal trigonal axis and increased linearity of the Ni-S-R angle that alters covalency of the Ni-S coordinate bond. Reactivity of the nickel-thiolate linkage toward electrophilic alkylation with Mel is also significantly affected, showing enhanced rates according to two distinct competing mechanisms, direct bimolecular alkylation of intact complex and rate-limiting unimolecular dissociation of free thiolate. Possible biochemical relevance of these observations to tetrahedral nickel(II) centers in metalloenzymes is considered.
AB - Five new pseudotetrahedral nickel(II) arylthiolate complexes Tp R.MeNi-SR′ [(TpR,Me)- = 2,2,2-κ3-hydridotris(3-R,5-methylpyrazolyl)borate; R = Me, R′ = C6H5 (Ph), 2,4,6-C6H 2(CH3)3 (Mes); R = Ph, R′ = C 6H5 (Ph), 2,4,6-C6H2(CH 3)3 (Mes), and 2,6-C6H3(CH 3)2 (Xyl)] were prepared by metathesis reactions of known chloride complexes with sodium arylthiolate salts in THF. The new products were fully characterized. The effect of increasing bulk of substituents at the proximal 3-pyrazolyl and ortho-thiolate positions represented in this series was evident in spectroscopic studies (UV-vis-NIR, 1H NMR) of the product complexes. Increased steric contact induced red-shifting of nickel-thiolate ligand to metal charge transfer (LMCT) bands and enhanced contact shifts of arylthiolate protons with the paramagnetic (S = 1) nickel(II) ion. These spectroscopic effects arise from structural distortion of the nickel(II)-thiolate bond revealed by X-ray crystal structure determinations of the structural extremes of the series, TpMe,MeNi-SPh and Tp Ph,MeNi-SXyl. The distortion consists of a significantly increased tilting of the Ni-S bond from an ideal trigonal axis and increased linearity of the Ni-S-R angle that alters covalency of the Ni-S coordinate bond. Reactivity of the nickel-thiolate linkage toward electrophilic alkylation with Mel is also significantly affected, showing enhanced rates according to two distinct competing mechanisms, direct bimolecular alkylation of intact complex and rate-limiting unimolecular dissociation of free thiolate. Possible biochemical relevance of these observations to tetrahedral nickel(II) centers in metalloenzymes is considered.
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U2 - 10.1021/ic702417w
DO - 10.1021/ic702417w
M3 - Article
C2 - 18345601
AN - SCOPUS:43149115386
SN - 0020-1669
VL - 47
SP - 3384
EP - 3392
JO - Inorganic Chemistry
JF - Inorganic Chemistry
IS - 8
ER -