Pyridine-phosphaalkene (PN) ligands 2a−e were prepared in an E-selective fashion using phospha-Wittig methodology. Treatment of these five ligands, varying only in their 6-substituent with RuCl 2 (PPh 3 ) 3 , produced four distinct types of coordination complexes: pyridine-phosphaalkenederived 3b,d, cyclized 4e, and six-coordinate 5a and 6c. Prolonged heating of 3b,d in THF resulted in C−H activation of the Mes* group and cyclization to give 4b,d featuring a bidentate pyridine-phospholane ligand bound to the metal center. Complex 5a, 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 2b,d,e and Ru(II) complexes 3b, 4b,e and 5a were all characterized by X-ray crystallography. Six-coordinate 6c featured a structure similar to 4b,d,e, but with the CF 3 substituent acting as a weakly bound sixth ligand to the Ru(II) center, as observed by 31 P{ 1 H} and 19 F NMR spectroscopy. The calculated structure of 6c established that the closest Ru---F contact was at 2.978 Å.
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