-Selective Synthesis and Coordination Chemistry of Pyridine-Phosphaalkenes: Five Ligands Produce Four Distinct Types of Ru(II) Complexes.

Pyridine-phosphaalkene (PN) ligands were prepared in an -selective fashion using phospha-Wittig methodology. Treatment of these five ligands, varying only in their 6-substituent with RuCl(PPh), produced four distinct types of coordination complexes: pyridine-phosphaalkene-derived , cyclized , and six-coordinate and . Prolonged heating of in THF resulted in C-H activation of the Mes* group and cyclization to give featuring a bidentate pyridine-phospholane ligand bound to the metal center. Complex , also possessing a newly formed phospholane ring, contained a different spatial arrangement of donors to Ru(II) with an agostic Ru-H-C interaction serving as the sixth donor to the transition metal center. Ligands and Ru(II) complexes and were all characterized by X-ray crystallography. Six-coordinate featured a structure similar to , but with the CF substituent acting as a weakly bound sixth ligand to the Ru(II) center, as observed by P{H} andF NMR spectroscopy. The calculated structure of established that the closest Ru- - -F contact was at 2.978 Å.