Dioxomolybdenum(VI) Complexes with New Enantiomerically Pure Amino Diol Ligands

(R)-Phenylglycinol is shown to be an efficient building block for the synthesis of chiral amino diols in pure diastereomeric form by epoxide ring-opening reactions. The reaction with rac-trans-stilbene oxide gives [HOCH2- (R)-PhCH]NH[(S)-PhCH-(R)-PhCHOH] [2(R)-3(R)-4(S)-HNO2H2] in 32% yield, which can be methylated at nitrogen to give enantiomerically pure [HOCH2-(R)-PhCH]NCH3[(S)-PhCH-(R)-PhCHOH] [2(R)-3(R)-4(S)- MeNO2H2]. These amino diol ligands have been used to prepare chiral dioxomolybdenyl complexes of the formula N(R)-2(R)-3(R)-4(S)-(HNO2)MoO2 (1) and N(R)-2(R)-3(R)-4(S)-(MeNO2)MoO2 (2). The absolute configuration at each stereocenter in the Mo(VI) complexes has been established by 1H NOESY spectroscopy. The configuration determined for 1 has been confirmed by an X-ray analysis. Crystal data: orthorhombic P212121, a ) 7.620(3), b ) 13.589(2), c ) 20.339(3) Å, Z ) 4, R ) 0.0336. The structure consists of a polymeric chain of N(R)-2(R)- 3(R)-4(S)-(HNO2)MoO2 molecules connected through unsymmetrical ModO f Mo bridges. Each metal center is coordinated in a distorted octahedral geometry by a cis dioxo unit and by two trans alkoxo atoms. The coordination polyhedron is completed by a nitrogen atom and by a bridging oxo oxygen atom from an adjacent molecule. Compound 2 catalyzes the oxidation of PPh3 to OPPh3 by DMSO through a mechanism that involves the intermediacy of a Mo(IV) species.