[Bis(tetrahydrofuran–O)–bis(1,3–dialkyl–2–diphenylphosphanyl–1,3–diazaallyl)calcium] – Synthesis and Crystal Structures of Calcium Bis[phospha(III)guanidinates] and Investigations of Catalytic Activity

The reaction of (thf)₄Ca(PPh₂)₂] ( 1 ) with diisopropyl– and dicyclohexylcarbodiimides yields the phospha(III)guanidinates (thf)₂Ca{RNC(PPh₂)NR}₂] with R = isopropyl ( 2 ) and cyclohexyl ( 3 ). The metathesis reaction of K{RNC(PPh₂)NR} with anhydrous CaI₂ also allows the synthesis of these phospha(III)guanidinate complexes 2 and 3 . For 2 a cis arrangement is observed whereas 3 crystallizes as trans isomer. The phospha(III)guanidinates act as bidentate chelate bases with an average Ca–N distance of 242.5 pm. The C–P bond length between the PPh₂ fragment and the 1,3–diazaallyl unit is with values above 190 pm very large. The complexes 2 and 3 show a moderate catalytic activity in hydrophosphanylation reactions of dialkylcarbodiimides with diphenylphosphane.