Urea–Boron Trihalide Adducts. I. The Boron Trifluoride Adduct of Tetramethylurea

Abstract

Evidence is presented that oxygen is the donor atom in the 1:1 adduct of tetramethylurea and boron trifluoride (TMU•BF3). Hydrogen fluoride, a common impurity in boron trifluoride, leads to the formation of [Formula: see text] as well as TMU•BF3. Exchange reactions among TMU, [Formula: see text]and TMU•BF3 are investigated briefly. The results of the present investigation are compared with the results of a previous study which indicated that nitrogen is the donor atom in BF3 adducts of some partially alkylated ureas.

Urea – boron trihalide adducts. IV. Ionic–covalent equilibria in the tetramethylthiourea–BF3 and tetramethylselenourea–BF3 systems and the influence of B2F7− formation

“…The TMSeU-BF3 system is very similar. These systems differ from the TMU-BF3 system (1,3) in that the donor-acceptor bond lifetime is much shorter. Exchange of adduct with excess T M T U is rapid on the proton nmr time scale and even at -90 OC no free-TMTU peak could be detected a t 6 3.01 when BF3 was present.…”

“…Our investigations of the 1 : 1 boron trifluoride adducts of tetramethylurea (TMU) and dialkylureas demonstrated that oxygen was the donor site (1,2). We also found that under appropriate conditions redistribution to give ionic adducts (TMU)2BFZf.BX4-takes place (3).…”

“…Boron trifluoride, methylene chloride, and the nmr reference compounds were purified as described previously (1). Deuterochloroform (Merck, Sharp and Dohme) and dichlorofluoromethane (Matheson) were trap-to-trap distilled under high vacuum, the initial cut being rejected.…”

Urea – boron trihalide adducts. V. Effects of acid strength on restricted rotation in adducts of tetramethylurea and 1,1-bis(dimethylamino)ethylene

“…This confirms that oxygen is the donor site. We now report 'H nmr studies of restricted rotation in the heavier boron trihalide adducts of TMU and in the oxygen-replaced analogue of TMU, 1, l-bis-(dirnethylamino)ethyle~le (2). The adducts of 2 show some additional interesting features.…”

“…Results and Discussion Although proton spectra of tetramethylurea (TMU, 1) or its BF3 adduct show no evidence of restricted rotation about the central C-N bonds down to -100 O C (2), restricted rotation has been detected in the TMU.SbC15 adduct (3) and in dialkylurea-BF3 adducts (4). This confirms that oxygen is the donor site.…”