2 Mn=C(OR*)Ph] (4aϪe) phanes afforded (S Mn )-[Cp(CO)(PR 3 )Mn=C(OR*)Ph] [PR 3 = P(OPh) 3 (8), P(OMe) 3 (9), P(OMe) 2 Ph (10), P(OMe)Ph 2 (11), were prepared by reaction of [Cp(CO) 2 Mn=C(OAc)Ph] (2) with HOR* [HOR* = 1,2:3,4-di-O-isopropylidene-D-galacto-PPh 3 (12), P(C 6 H 4 Cl-p) 3 ( )] with a de > 96%. Photolysis of (S)-4d in the presence of P(OMe) 3 gave (R Mn ,S)-9. Complex pyranose (3a), 2,3,4,6-tetra-O-acetyl-D-galactopyranose (3b), 2,3,4,6-tetra-O-acetyl-D-glucopyranose (3c), (S)-(3d) and (R)-(R)-14 [related to (R)-4d] was obtained from [Cp(CO) 2 Mn= C(OAc)Tol-p] and 3d. Replacement of CO by PR 3 in (R)-1,2-O-isopropylideneglycerol (3e)]. The replacement of a CO ligand with PTol 3 in 4aϪe proceeded diastereoselectively to 14 gave (S Mn ,R)-[Cp(CO)(PR 3 )Mn=C(OR*)Tol-p] [R = Tol-p (15), OMe (16), C 6 H 4 Cl-p ( )] with a de > 96%. In solution, give [Cp(CO)(PTol 3 )Mn=C(OR*)Ph] (5aϪe). The diastereoselectivity increased in the order a, b, c, d: de = 8% (5a), 33% the PTol 3 -substituted complex 5d is configurationally stable whereas the P(OMe) 3 complex 9 epimerizes slowly at room (5b), 70% (5c), > 96% (5d). For (R)-5d the isomer with the (S) configuration at manganese (S Mn ) was formed predomi-temperature in CH 2 Cl 2 , Et 2 O, and THF within about one week. nantly. For (S)-5d, only (R Mn ,S)-5d was detected (de > 96%). Photolysis of (R)-4d in the presence of phosphites or phos-Recently, we reported the synthesis of chiral complexes pure compounds of both configurations at the chiral meof manganese and rhenium. These complexes, of the type tal center.
[Cp(CO) 2 MϭC(OR*)RЈ] (M ϭ Mn, Re, OR* ϭ mannofu-Results and Discussion ranosyl, glucofuranosyl, fructopyranosyl, RЈ ϭ Ph, Tol), were obtained by addition of the monoanion of the corre-Successive reaction of the lithium benzoylmanganate 1 sponding protected carbohydrate to the cationic carbyne with TMEDA and acetyl bromide gave the thermolabile complexes [Cp(CO) 2 MϵCRЈ] ϩ . [4] acetoxy carbene complex 2 as described previously. [5] The Another route to chiral carbene complexes involves nureaction of 2 with partially protected carbohydrates that are cleophilic substitution by chiral alcoholates, such as (Ϫ)unprotected either in the 6-position [1,2:3,4-di-O-isopromentholate and borneolate, of the acetoxy substituent in pylidene--galactopyranose (3a)] or in the 1-position acetoxycarbene complexes of manganese [Cp(CO) 2 Mnϭ [2,3,4,6-tetra-O-acetyl--galactopyranose (3b) and 2,3,4,6-C(OAc)RЈ]. [5] [6] tetra-O-acetyl--glucopyranose (3c)] afforded the chiral-atligand dicarbonyl(cyclopentadienyl)[alkoxy(phenyl)carbene] Photolysis of the chiral carbohydratocarbene complexes in the presence of phosphanes or phosphites (L) afforded complexes 4aϪc in 40Ϫ66% yield (Scheme 1). The complexes (R)-and (S)-4d were obtained from the reaction of chiral-at-metal carbene complexes of the type [Cp(CO)(L)MϭC(OR*)RЈ]. The diastereomeric excess (de) 2 with the enantiomerically pure alcohols (S)-and (R)-1,2-O-isopropylideneglycerol, (S)-and (R)-3d. [7] ranged from 0 to 80% and depended on the nature of the