[CP2M] METALLOCENE SPECIES PROMOTED REDUCTIVE COUPLING OF CL2C=PR - SYNTHESIS, STRUCTURE, AND REACTIVITY OF THE FIRST 3,4-DIHALO-1,2-DIHYDRO-1,2-DIPHOSPHETES

Early metallocene transition complexes [Cp2M] (M = Zr, Ti) react with C-dihalogenated phosphaalkenes R2NP=CCl2 [R2N = 2,2,6,6-tetramethyl-N- piperidyl (TMP), (Me3Si)(2)N] to give 3,4-dihalo-1,2-dihydro-1,2-dipho sphetes (R2NPCCl)(2). A single crystal X-ray determination of [(TMP)PC Cl](2) reveals an unprecedented stretched phosphorus-phosphorus bond ( 2.320(4) Angstrom) due to a negative hyperconjugation between the nitr ogen lone pairs of the amino groups and the antibonding sigma(PP) orb ital. Experimental results, ab initio 6-31G(d,p)//MP2 calculations, an d photoelectron analysis are consistent with a strong interaction of t he pi-HOMO of R2NP=CCl2 and the 2a(1) orbital of the metallocene [Cp2M ] fragment as the first step in the formation of (R2NPCCl)(2).