Adrian Looney

Structural and spectroscopic studies on four-, five-, and six-coordinate complexes of zinc, copper, nickel, and cobalt: Structural models for the bicarbonate intermediate of the carbonic anhydrase catalytic cycle

The molecular structures and electronic spectra of a series of four-, five-, and six-coordinate complexes of cobalt, nickel, copper, and zinc, stabilized by tris(pyrazolyl)hydroborato ligands, have been determined. The structural variations that are observed for the series of nitrate and carbonate complexes reveal that the preference for bidentate coordination of these ligands increases across the series Zn < Co ⪡ Cu and Ni.

Poly(pyrazolyl)hydroborato and poly(pyrazolyl)methane aluminium alkyl derivatives

Abstract Bis- and tris(pyrazolyl)hydroborato aluminium methyl derivatives, {η 3 -HB(3,5- Me 2 pyz) 3 }Al(CH 3 ) 2 , {η 2 -HB(3-Bu t pyz) 3 }Al(CH 3 ) 2 and {η 2 -H 2 B(3-Bu t pyz) 2 }Al(CH 3 ) 2 have been prepared by metathesis of Al(CH 3 ) 3 with either K{HB(3,5-Me 2 pyz) 3 }, Tl{HB(3- Bu t pyz) 3 } or K{H 2 B(3-Bu t pyz) 2 }, respectively. In contrast to the formation of these 1 : 1 complexes, the isostructural but neutral ligand HC(pyz) 3 readily coordinates three equivalents of (CH 3 ) 3 Al giving {HC(pyz) 3 }[Al(CH 3 ) 3 ] 3 . 1 H NMR studies provide evidence for the formation of the mono- and bis-complexes {HC(pyz) 3 }[Al(CH 3 ) 3 ] and {HC(pyz) 3 } [Al(CH 3 ) 3 ] 2 as products of the reaction of HC(pyz) 3 with less than three equivalents of Al(CH 3 ) 3 . The aluminium-carbon bonds of {η 3 -HB(3,5-Me 2 pyz) 3 }Al(CH 3 ) 2 are readily cleaved by H 2 O to give {η 3 -HB(3,5-Me 2 pyz) 3 }Al(OH) 2 and CH 4 . However, the reaction of {η 3 -HB(3,5-Me 2 pyz) 3 }Al(CH 3 ) 2 with D 2 O gives CH 4 in addition to CH 3 D and thus demonstrates that a secondary process involving coupling of the aluminium-methyl ligand with one of the hydrogen atoms of the pyrazolyl methyl group must be competitive with the direct reaction of the aluminium-carbon bond with D 2 O. The complex {η 2 -H 2 B(3- Bu t pyz) 2 }Al(CH 3 ) 2 undergoes a unimolecular rearrangement of the bis(3-t-butylpyrazolyl)hydroborato ligand to give the more stable isomer, {η 2 -H 2 B(3-Bu t pyz)(5-Bu t pyz)} Al(CH 3 ) 2 . The kinetics of this rearrangement are first-order with the activation parameters Δ h ‡ = 34.5(8) kcal mol −1 and Δ s ‡ = 6(2) e.u. and the proposed mechanism consists of steps involving a 1,2-shift of the t-butylpyrazolyl group.

Tris(3-tert-butylpyrazolyl)hydroborato zinc hydride: synthesis, structure and reactivity of a monomeric zinc hydride derivative

The monomeric zinc hydride derivative {η3-HB(3-Butpz)3}ZnH has been synthesized by the reaction of ZnH2 with Tl{η3-HB(3-Butpz)3} and its reactivity investigated.

Tris(pyrazolyl)hydroboratozinc alkyl derivatives: direct comparison of the reactivity of Zn-C and Mg-C bonds

The monoalkyl zinc derivatives [η3-HB(3-Butpz)3]ZnR (3-Butpz = 3-C3N2ButH2; R = Me, Et) have been prepared by metathesis of R2Zn with Tl[HB(3-Butpz)3], and their reactivity compared with that of the isostructural magnesium alkyl derivatives.