X-ray Crystal Structure, ab Initio Calculations, and Reactivity of 1,3,2lambda(5)-Diazaphosphetes: A New Type of
Gilles Alcaraz1, Antoine Baceiredo, Martin Nieger
1Laboratoire de Chimie de Coordination du CNRS, 205, route de Narbonne, 31077 Toulouse Cédex, France, Institut für Anorganische Chemie der Universität Bonn, Gerhard-Domagk-Strasse 1, D-5300 Bonn 1, Germany, and Fakultät für Chemie der Universität, Postfach 10 01 31, D-33615 Bielefeld, Germany.
Abstract:
The structure of P,P-bis(diisopropylamino)-4-phenyl-1,3,2lambda(5)-diazaphosphete, 1a, has been determined by a single-crystal X-ray diffraction study (C(19)H(33)N(4)P, monoclinic system, space group P2(1), a = 9.482(1) Å, b = 11.374(3) Å, c = 9.668(2) Å, beta = 97.16(1) degrees, Z = 2). According to quantum chemical calculations at an RHF level of optimization utilizing the 6-31g(d,p) basis set, 1a has a zwitterionic structure with the negative charge delocalized on the NCN allylic fragment and the positive charge localized at the phosphorus. Heterocycle 1a reacts with water and benzaldehyde affording N-phosphoranylbenzamidine 3 (95% yield) and the expected aza-Wittig adduct 4 (85% yield), respectively. Addition of 1 equiv of methyl trifluoromethanesulfonate and of 2 equiv of BH(3).THF to 1a affords cyclic phosphonium salt 5 (94% yield) and the bis(borane) adduct 6a (90% yield), respectively. Dimethyl acetylenedicarboxylate slowly reacts with 1a giving rise to 1,3,4lambda(5)-diazaphosphinine, 9, in 70% yield. The X-ray crystal structures of products 2,3, and 6a are reported (2: C(26)H(38)N(5)P, monoclinic system, space group C2/c, a = 16.337(8) Å, b = 19.810(2) Å, c = 8.800(2) Å, beta = 117.68(2) degrees, Z = 4. 3: C(19)H(35)N(4)OP, orthorhombic system, space group P2(1)2(1)2(1), a = 9.090(1) Å, b = 12.955(2) Å, c = 17.860(3) Å, Z = 4. 6a: C(19)H(39)B(2)N(4)P, orthorhombic system, space group P2(1)2(1)2(1), a = 10.340(1) Å, b = 13.247(1) Å, c = 16.996(1) Å, Z = 4).
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