[Cp2M] Metallocene Species Promoted Reductive Coupling of Cl2CPR: Synthesis, Structure, and Reactivity of the First 3,4-Dihalo-1,2-dihydro-1,2-diphosphetes

Early metallocene transition complexes [Cp 2 M] (M = Zr, Ti) react with C-dihalogenated phosphaalkenes R 2 NP CCl 2 [R 2 N = 2,2,6,6-tetramethyl- N -piperidyl (TMP), (Me 3 Si) 2 N] to give 3,4-dihalo-1,2-dihydro-1,2-diphosphetes (R 2 NPCCl) 2 . A single crystal X-ray determination of [(TMP)PCCl] 2 reveals an unprecedented stretched phosphorus−phosphorus bond (2.320(4) Å) due to a negative hyperconjugation between the nitrogen lone pairs of the amino groups and the antibonding σ* PP orbital. Experimental results, ab initio 6-31G(d,p)//MP2 calculations, and photoelectron analysis are consistent with a strong interaction of the π-HOMO of R 2 NP CCl 2 and the 2a 1 orbital of the metallocene [Cp 2 M] fragment as the first step in the formation of (R 2 NPCCl) 2 .