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

<p>Dialkyl[1,1-bis(alkylchloroalanyl)organylmethyl]phosphine•dialkylchloroalane(1/1) complexes (<b>1a</b>–<b>1d</b>) were synthesized and fully characterized. In <b>1a</b>–<b>1d</b>, 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 <b>1a</b>–<b>1d</b> 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.</p