The syntheses and structures of derivatives of a novel uninegative bidentate ligand, the dimethylbis(2-pyridyl)-borate anion, (py) 2 BMe 2 -, are reported. Lithium dimethylbis(2-pyridyl)borate, Li(py) 2 BMe 2 , was prepared by adding a solution of bromodimethylborane to a solution of 2-lithiopyridine in a 1:2 molar ratio, respectively; subsequent hydrolysis afforded hydrogen dimethylbis(2-pyridyl)borate, H(py) 2 BMe 2 , in 44% yield. Reaction of Li(py) 2 BMe 2 with either bromodimethylborane or bromodiphenylborane afforded the corresponding tricyclic bis-(organo)boronium dimethylbis(2-pyridyl)borate species R 2 B(µ-py) 2 BMe 2 (R ) CH 3 , C 6 H 5 ) in approximately 90% yields. Reaction of H(py) 2 BMe 2 with anhydrous zinc(II) chloride or nickel(II) chloride hexahydrate in a 4:1 molar ratio gave the tetrahedral complex bis[dimethylbis(2-pyridyl)borato-N,N ′]zinc(II), Zn{(µ-py) 2 BMe 2 } 2 , or the square planar complex bis[dimethylbis(2-pyridyl)borato-N,N ′]nickel(II), Ni{(µ-py) 2 BMe 2 } 2 , respectively. H(py) 2 BMe 2 is monoclinic, P2 1 /m, with a ) 8.836 (2) Å, b ) 7.1825(5) Å, c ) 9.2789(11) Å, ) 99.81(2)°, V ) 580.29(13) Å 3 , and Z ) 2. Ph 2 B(µ-py) 2 BMe 2 is monoclinic, P2 1 /n, a ) 8.0334(12) Å, b ) 10.9169(9) Å, c ) 22.981(2) Å, ) 94.653(9)°, V ) 2008.8(4) Å 3 , and Z ) 4. Zn{(µ-py) 2 BMe 2 } 2 is monoclinic, Cc, with a ) 8.010(2) Å, b ) 31.256(3) Å, c ) 18.753(3) Å, ) 90.83(2)°, V ) 4694.8(13) Å 3 , and Z ) 8. Ni{(µ-py) 2 -BMe 2 } 2 is triclinic, P1 h, with a ) 7.675(2) Å, b ) 8.819(2) Å, c ) 9.459(2) Å, R ) 115.72(3)°, ) 96.89(3)°, γ ) 94.02(3)°, and Z ) 1.
ring at N and Cy and is presumed not to extend to the 4f orbital involved in electron transfer from Eu2+,25,26 for the latter undergoes a sign inversion on passage through the same plane. On this basis, through-space interaction between the ring and metal center may be taken to assume a more significant role in the Eu(II) reactions, and the different attenuation patterns noted for the two reductants may thus be linked (albeit tentatively) to differences in the symmetry character of the donor orbitals.Specific rates for reduction by V2+ (ky values) do not appear to be enhanced by the ligands used in this study. This lack of response cannot be reasonably attributed to the limit on inner-sphere rates imposed by sluggish substitution at the V(II) center,10,27 for a number of carboxylato derivatives of (N-H3)5Coni have been found to exhibit ky values several times those noted here.143,28 Instead, we suspect that the formal potential of V2+ (E°= -0.242 V)29 is not sufficiently negative (25) It is assumed here that the ligand environments about both Eu(II) and Eu(III) in our systems are approximately octahedral. The 4f orbital taken to be active in the electron transfer process is the antisymmetric fj3 orbital.26(26) See, for example: (a) H. G. Friedman, G. R. Choppin, and D. G.
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