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

• Published in: Journal of organometallic chemistry 1997-06, Vol.538 (1), p.223-239
• Main Authors: Campello, M. Paula C., Calhorda, Maria José, Domingos, Ângela, Galvão, Adelino, Leal, João Paulo, Pires de Matos, A., Santos, Isabel
• Format: Article
• Language: English
• Subjects: Hydrocarbyl; Molecular orbital calculations; Poly(pyrazolyl)borates; Reactivity; Synthesis; Uranium
• ISSN: 0022-328X; 1872-8561
• DOI: 10.1016/S0022-328X(97)00078-8

The reaction of [UCl 2HB(pz) 3 2] ( 1) with lithium alkyls LiR (R = Me, CH 2SiMe 3, C 6H 4- o-CH 2NMe 2) in the 1:1 or 1:2 molar ratio affords the compounds [UCIRHB(pz) 3 2] (pz = C 3H 3N 2, R = Me ( 2), CH 2SiMe 3 ( 3), C 6H 4- o-CH 2NMe 2 ( 4)) and [UR 2HB(pz) 3 2] (R = Me ( 5), CH 2SiMe 3 ( 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) 2HB(pz) 3 2] ( 8). The alkoxide [U(OC 6H 4- o-OMe) 2HB(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(OCMe 2CH 2(C=O)Me)HB(pz) 3 2] ( 11) was obtained, due to the activation of α-CH bond of acetone; however, for 3 the reaction is not clean and a mixture of 11 and [UCl(OCMe 2CH 2SiMe 3)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 tBu)HB(pz) 3 2] and [U(O tBu) 2HB(pz) 3 2] respectively, while the insertion product [U(OCMe 2CH 2SiMe 3) 2HB(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 P1¯ with unit cell dimensions a = 12.295(2) Å, b = 12.640(2) Å, c = 13.994(2) Å, α = 76.10(1)°, β = 72.50(1)°, γ = 80.71(1)°, V = 2004(2) Å 3 and Z = 2. Recrystallization of a mixture containing [UCl(O tBu)HB(pz) 32] and 11 led to a decomposition product which has been characterized by X-ray structural analysis as [UCl(Hpz)(O tBu)(μ-O)B(μ-pz)(pz) 2] 2 ( 13): monoclinic P2 1/ n, a = 13.701(3) Å, b = 11.337(2) Å, c = 14.857(4) Å, β = 104.65(2)°, V = 2233(1) Å 3 and Z = 2. Extended Hückel molecular orbital calculations provided some information on the bonding capabilities of the [UHB(pz) 3 2] fragment compared to [U(C 5Me 5) 2] and on the vulnerability of the poly(pyrazolyl)borate ligands to nucleophilic attack.