Transition-Metal Complexes of the Optically Active Cyclopentadienyl Ligand PinCp*: Crystal Structure of (SRe)-(η5-PinCp*)Re(NO)(PPh3)[CONHCH(CH3)C10H7]

Abstract

The synthesis of (η5‐PinCp*)Re(CO)3 [PinCp* = tetramethyl(pinanyl)cyclopentadienyl] is described. Successive substitution of two CO ligands by NO+ and PPh3 generates a 1:1 diastereomeric mixture of chiral‐at‐metal [(SRe)/(RRe)‐(PinCp*)Re(CO)(NO)(PPh3)]BF4. The diastereomers are converted with sodium methoxide into the derivative “esters” (SRe)/(RRe)‐(PinCp*)Re(COOCH3)(NO)(PPh3), and then with (+)‐(R)‐(1‐naphthylethyl)amine to the “amides” (SRe)/(RRe)‐(PinCp*)Re(NO)(PPh3)[CONHCH(CH3)C10H7] [(SRe)/(RRe) = 1:1]. Fractional crystallisation separates the (SRe) isomer with an optical purity of > 98%. The latter compound has been characterized by X‐ray structure analysis. By treating the (SRe)‐amide with CF3CO2H and NaBF4, (SRe)‐(PinCp*)Re(CH3)(NO)(PPh3) can be generated. Protolysis of this compound with HBF4/Et2O in CD2Cl2 at –78 °C leads to the solvent‐stabilized complex (SRe)‐[(PinCp*)Re(NO)(PPh3)(ClCD2Cl)]+BF4−. The thermal and configurational stability of this chiral Lewis acid is investigated at various temperatures. The syntheses of [PinCp*RhCl2]2, PinCp*TiCl3 and PinCp*M(CO)2(NO) (M = Mo, W) are also described. Starting with PinCp*M(CO)2(NO), the relatively stable 16‐VE complexes PinCp*MCl2(NO) and PinCp*W(CH2SiMe3)2(NO) are synthesized.

Improved Synthesis of [CpRRhCl2]2 Complexes

“…The pentamethylcyclopentadiene (Cp*) derivative is the most widely used for all of these applications. However, recent reports have shown that complexes bearing substituted cyclopentadienyl ligands exhibit enhanced reactivity and/or selectivity for many transformations. ,,, As such, the development of efficient, general, and high-yielding synthetic routes to [Cp R RhCl 2 ] 2 complexes is of high interest.…”

[Tc(NO)(Cp)(PPh3)Cl] and [Tc(NO)(Cp)(PPh3)(NCCH3)](PF6), and Their Reactions with Pyridine and Chalcogen Donors

“…The chemistry of the {Re(NO)(Cp)(PPh 3 )} + fragment has been comprehensively studied by John Gladysz et al and by some other groups, and the results have been published in more than a hundred papers [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 ]. The chlorido ligand of the chiral parent complex [Re(NO)(Cp)(PPh 3 )Cl] can readily be replaced by numerous inorganic and organic ligands.…”