HeteroC4lradialene / 1,2-Diphosphetane / Butadiene, 2,3-bis(chlorophosphanyl)-1,2-Diphosphetane 4, the first "1,2-diphospha[4]radialene", has been prepared in 83% yield by the reductive coupling reaction of 2,3-bis(chloroisopropylphosphanyl)butadiene 3a with lith-ium in THF. The X-ray crystal structure of 4 was determined, and it shows that 4 is a highly strained 1,2-diphosphetane.
Carbon-phosphorus heterocycles possessing an endocyclic P -P bond have gained a continual interest in the last decades"]. 1,2-Diphosphetanes are accessible by [2 + 21 cycloaddition, on the one hand by head-to-head dimerization of suitably substituted phos-phaalkenesI2] and on the other hand by reaction of a transitionmetal-substituted diphosphene with electron-deficient alkenesC3].
Recently, we reported on the synthesis and reactivity of "phospha[3]radialenes" 114]. A fascination ring opening of 1 and 2 with dichloroorganophosphanes exclusively provided the corresponding 2,3-bis(chlorophosphanyl)butadiene 3I4]. In principle, 3 represents a building block in the synthesis of the 1,2-diphosphetane 4 which is accessible by reductive cyclization of 3 with an electropositive metal. However, it must be taken into account that a P-P bond can be cleaved by lithium in ethereal solvents[51.