Synthesis and crystal structures of dialkyl[1,1-bis(alkylchloroalanyl)organylmethyl]phosphine_•dialkylchloroalane(1/1) complexes

Abstract

Dialkyl[1,1-bis(alkylchloroalanyl)organylmethyl]phosphine•dialkylchloroalane(1/1) complexes (1a–1d) were synthesized and fully characterized. In 1a–1d, dative bonding between phosphorus or chlorine as a donor atom and aluminum as an acceptor atom results in a bicyclic system. The ³¹P{¹H} NMR spectra of all compounds dissolved in d₆-benzene indicate the presence of several isomers in solution. The ²⁷Al{¹H} NMR spectra of 1a–1d dissolved in d₆-benzene as well show very broad singlets between 177 and 140 ppm. For all compounds, crystal structures consist of two fused four- and five-membered rings. The 1λ³-phosphaalkyne reacts at the Al–C bond of the starting material, whereas the Al–Cl moiety remains intact. The heterocycle isolated is a molecular complex of the underlying insertion compound and a third equivalent of dialkylaluminum chloride. The four- and five-membered rings both contain two chlorine-bridged aluminum atoms, Al3 and Al1, slightly more symmetrical than that between Al1 and Al6. In the four-membered ring the two aluminum atoms Al1 and Al6 approach each other at an average distance of 289.1 pm which tallies with the element–element distance (286.3 pm) in aluminum metal.

Keywords:

• Chloroalane
• phospha-alkyne
• phosphine
• crystal structure
• bicyclic system

Acknowledgement

This paper is based on a one chapter of the Ph.D dissertation (ISBN 978-3-86186-549-0) of the first author and a part of his postdoctoral research work done in the laboratory of Professor Gerd Becker at Institut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany. First author wish to thanks Dr Ralph Löw for providing us the CIF file for structure 1a which belongs to his doctoral work in Professor Becker’s laboratory, and was deposited by him at the Institut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart under the supervision of Professor Gerd Becker.