Contribution to the Chemistry of Metal Complexes with Stereogenic Metal Centers:  Diastereoselective Formation of Ruthenium Half-Sandwich Complexes

Abstract

The chiral half-sandwich complexes 3 and 4 are formed with high diastereoselectivities in the reaction of cyclopentadienides 2a,b, bearing tethered phosphaferrocene donor moieties with planar chirality, and [(PPh 3 ) 3 RuCl 2 ] in toluene at 90°C. The diastereoisomers of the Cp complex 3 are obtained in a 95:5 ratio, whereas for the Cp* derivative 4 only one isomer is detectable, the structure of which has been determined by X-ray diffraction. Substitution of the chloride ligand in 4 by other anionic (H -, I -) or neutral (H 2 , py) ligands proceeds stereospecifically in all cases. In contrast, conversion of the chlorides 3a,b (95:5) to the respective hydrides 9a,b proceeds with complete epimerization at Ru. In CHCl 3 the 1:1 mixture of hydrides 9a,b is reconverted to the chlorides to give a kinetically controlled 4:1 mixture of isomers 3a,b. Equilibration of this mixture in toluene at 90°C restores the original ratio of isomers of 95:5, which we therefore believe to reflect the thermodynamically controlled value. The cationic H 2 complex 7, generated via Cl abstraction from 4 in the presence of H 2 , was characterized to be a η 2 -dihydrogen complex by measuring the T 1 value of the coordinated H 2 ligand.

The Continuing Development of the Chemistry of Phospholes

“…Placement of electron-withdrawing groups on phosphorus in phospholes greatly increases their reactivity to dienophiles, presumably because they have reduced aromaticity as revealed by structural parameters [40] (Section 7). Thus, while 3,4-dimethyl-1-phenylphosphole does not undergo the Diels-Alder reaction with acrylonitrile, 1-cyano-3,4-dimethylphosphole reacts quantitatively at 80°C for 18 h to give a non-separable mixture of anti (147) and syn (148) cycloadducts (35% and 50%, respectively), along with 15% of an unidentified product. An alkoxy group on phosphorus greatly improved the cycloaddition reaction; the 1-isopropoxy phosphole 149 with acrylonitrile gave exclusively the anti isomer (150) after only 1 hr at 30°.…”

Phosphaalkene, phospholyl and phosphinine ligands: New tools in coordination chemistry and catalysis

“…is represented) [117]. A mixed anionic ligand featuring a phosphaferrocene moiety and cyclopentadienyl was also employed in the synthesis of the Ru(II) complex 114 in which the phosphaferrocene behaves as a pendant two electron donor ligand [118]. The first homoleptic complexes of these ligands were only synthesized in 1999.…”

Phosphorus Heterocycles: From Laboratory Curiosities to Ligands in Highly Efficient Catalysts

“…Chloride abstraction from 41 by TlPF 6 in an H 2 atmosphere occurred with the formation of the cationic dihydrogen complex 44 as one single diastereoisomer. A diastereoselective displacement of the H 2 ligand to afford 45 was observed in the reaction of 44 with pyridine, whereas the employment of NEt 3 as stronger base gave rise to diastereoselective deprotonation to give 43 (Scheme ) 36…”