Synthesis and Characterization of a New Thiophene-Bridged Diamidophosphine [NPN] Donor Set and Its Coordination Chemistry with Zirconium(IV): Unexpected Deprotonation−Lithiation Sequence with a Mesitylaminothiophene Precursor

The synthesis and characterization of the thiophene-bridged diamidophosphine proligand [NPN]SH2 (2) (where [NPN]SH2 = {[N-(2,4,6-Me3C6H2)(3-NH-SC4H2-2-)]2PPh}) along with several [NPN]SZrX2 (X = NMe2, Cl, I) complexes are presented. The ligand precursor [NPN]SH2 was prepared from N-(2,4,6-Me3C6H2)(3-NH-4-Br-SC4H2) (1), tBuLi, and PhPCl2 in Et2O in 50% yield; the stereochemistry of the ligand precursor was unexpected and likely resulted from a competitive bromine−lithium exchange and deprotonation sequence with the thiophene starting material 1 and tBuLi. A mechanism to rationalize the observed stereochemistry of the product is proposed following deuteration experiments. [NPN]SZr(NMe2)2 (8) can be prepared in 80% yield by the direct reaction of [NPN]SH2 and Zr(NMe2)4 in toluene. Both [NPN]SZrCl2 (9) and [NPN]SZrI2 (10) are prepared in high yield by the reaction of 8 with excess Me3SiCl or Me3SiI, respectively.