Hydrocarbyl derivatives of [UCl2{HB(pz)(3)}(2)]: Synthesis, characterization and reactivity studies towards protic substrates and ketones

The reaction of [UCl2{HB(pz)(3)}(2)] (1) with lithium alkyls LiR (R = Me, CH2SiMe3, C6H4-o-CH2NMe2) in the 1:1 or 1:2 molar ratio affords the compounds [UCIR{HB(pz)(3)}(2)] (pt = C3H3N2, R = Me (2), CH2SiMe, (3), C6H4-o-CH2NMe2 (4)) and [UR2{HB(pz)(3)}(2)] (R = Me (5), CH2SiMe3 (6)) respectively in 60-80% yield. Complex 2 can also be obtained (60% yield) by redistribution at room temperature between the complexes 1 and 5. Compounds 2, 3 and 4 react with pzH providing [UCl(pz){HB(pz)(3)}(2)] (7) in almost quantitative yield and 5 and 6 react also with pzH leading to [U(pz)(2){HB(pz)(3)}(2)] (8). The alkoxide [U(OC6H4-o-OMe)(2){HB(pz)(3)}(2)](9) was synthesized by reacting 5 or 6 with guaiacol. By reacting the chlorohydrocarbyls 2, 3 or 4 with excess of acetone the aldolate [UCl(OCMe2CH2(C=O)Me){HB(pz)(3)}(2)] (11) was obtained, due to the activation of alpha-CH bond of acetone; however, for 3 the reaction is not clean and a mixture of 11 and [UCl(OCMe2CH2SiMe3){HB(Pz)(3)}(2)] (12) is always obtained. Stoichiometric amounts of acetone insert into the metal-carbon bonds of 2 and 5 yielding [UCl(O-t Bu){HB(pz)(3)}(2)] and [U((OBu)-Bu-t)(2){HB(pz)(3)}(2)] respectively, while the insertion product [U(OCMe2CH2SiMe3)(2){HB(pz)(3)}(2)] (10) can only be obtained when 6 reacts with excess of this substrate. 9 crystallizes from toluene/hexane in the triclinic space group P (1) over bar with unit cell dimensions a = 12.295(2)Angstrom, b = 12.640(2)Angstrom, c = 13.994(2)Angstrom, alpha = 76.10(1)degrees, beta = 72.50(1)degrees, gamma = 80.71(1)degrees, V = 2003(2)Angstrom and Z = 2. Recrystallization of a mixture containing [UCl((OBu)-Bu-t)HB(pz)(32)] and 11 led to a decomposition product which has been characterized by X-ray structural analysis as [UCl(Hpz)((OBu)-Bu-t)(mu-O)B(mu-pz)(pz)(2)](2) (13): monoclinic P2(1)/n, a = 13 701(3)Angstrom, b = 11.337(2) Angstrom, c = 14.857(4)Angstrom, beta = 104.65(2)degrees, V = 2233(1)Angstrom(3) and Z = 2. Extended Huckel molecular orbital calculations provided some information on the bonding capabilities of the [U{HB(pz)(3)}(2)] fragment compared to [U(C5Me5)(2)] and on the vulnerability of the poly(pyrazolyl)borate ligands to nucleophilic attack.