Derivative chemistry of [UCl 2{B(pz) 4} 2]: stability of complexes containing the fragments [U{B(pz) 4} 2] and [U{HB(pz) 3} 2

Abstract

Uranium tetrachloride reacts with two equivalents of K[B(pz) 4] in THF affording [UCl 2{B(pz) 4} 2] ( 1) in 75% yield. Complex 1 is monomeric and crystallizes in the monoclinic space group C2/ c with cell parameters a=13.700(6), b=12.759(2), c=17.513(8) Å, β=101.37(2)°, V=3001(2) Å 3, Z=4. Derivatives [UCl(OR){B(pz) 4} 2] (R=C 2H 5 ( 2), t Bu ( 3), C 6H 4- o-OMe ( 4) and C 6H 2-2,4,6-Me 3 ( 5)), [U(O t Bu) 2{B(pz) 4} 2] ( 6), [U(S i Pr) 2{B(pz) 4} 2] ( 7) and [UCl(Me){B(pz) 4} 2] ( 8) were obtained by reacting 1 with sodium alkoxides, with NaS i Pr or with LiMe. X-ray crystallographic analysis of 5 and 7 shows that uranium is eight-coordinate by the two η 3-[B(pz) 4] ligands and by two monodentate coligands ( 5: crystallizes in the monoclinic space group C2/ c with cell parameters a=30.575(3), b=9.929(1), c=24.884(3) Å, β=90.59(1)°, V=7554(1) Å 3, Z=8; 7 crystallizes in the monoclinic space group C2/ c with cell parameters a=24.286(7), b=9.471(2), c=16.076(3) Å, β=96.44(3)°, V=3674(2) Å 3, Z=4). Extended Hückel molecular orbital (EHMO) calculations were used to get a better insight into the electronic properties of the ligand [B(pz) 4] and to get some explanation on the relative stability of complexes containing the fragments ‘[U{B(pz) 4} 2]’ and ‘[U{HB(pz) 3} 2]’.