Asymmetric hydrogenation of an α-unsaturated carboxylic acid catalyzed by intact chiral transition metal carbonyl clusters - diastereomeric control of enantioselectivity.

Twenty clusters of the general formula [(µ-H)2Ru3(µ3-S)(CO)7(µ-P-P*)] (P-P* = chiral diphosphine of the ferrocene-based Walphos or Josiphos families) have been synthesised and characterised. The clusters have been tested as catalysts for asymmetric hydrogenation of tiglic acid [trans-2-methyl-2-butenoic acid]. The observed enantioselectivities and conversion rates strongly support catalysis by intact Ru3 clusters. A catalytic mechanism involving an active Ru3 catalyst generated by CO loss from [(µ-H)2Ru3(µ3-S)(CO)7(µ-P-P*)] has been investigated by DFT calculations.

Tetranuclear group 7/8 mixed-metal and open trinuclear group 7 metal carbonyl clusters bearing bridging 2-mercapto-1-methylimidazole ligands.

The reactivity of group 7 metal dinuclear carbonyl complexes [M(2)(CO)(6)(mu-SN(2)C(4)H(5))(2)] (1, M = Re; 2, M = Mn) toward group 8 metal trinuclear carbonyl clusters were examined. Reactions of 1 and 2 with [Os(3)(CO)(10)(NCMe)(2)] in refluxing benzene furnished the tetranuclear mixed-metal clusters [Os(3)Re(CO)(13)(mu(3)-SN(2)C(4)H(5))] (3) and [Os(3)Mn(CO)(13)(mu(3)-SN(2)C(4)H(5))] (4), respectively. Similar treatment of 1 and 2 with Ru(3)(CO)(12) yielded the ruthenium analogs [Ru(3)Re(CO)(13)(mu(3)-SN(2)C(4)H(5))] (5), and [Ru(3)Mn(CO)(13)(mu(3)-SN(2)C(4)H(5))] (6), but in the case of 2 a secondary product [Mn(3)(CO)(10)(mu-Cl)(mu(3)-SN(2)C(4)H(5))(2)] (7) was also formed. Compounds have a butterfly core of four metal atoms with the M (Mn or Re) at a wingtip of the butterfly and containing a noncrystallographic mirror plane of symmetry. This result provides a potential method for the synthesis of a series of new group 7/8 mixed metal complexes containing a bifunctional heterocyclic ligand. Compound 7 is a unique example of a 54-electron trimanganese complex having bridging 2-mercapto-1-methylimidazolate and chloride ligands. Interestingly, the reaction of 1 with Fe(3)(CO)(12) at 70-75 degrees C furnished the tri- and dirhenium complexes [Re(3)(CO)(10)(mu-H)(mu(3)-SN(2)C(4)H(5))(2)] (8) and [Re(2)(CO)(6)(N(2)C(4)H(5))(mu-SN(2)C(4)H(5))(2)] (9), respectively instead of the expected formation of the mixed-metal clusters. The former is an interesting example of a 52-electron trirhenium-hydridic complex containing bridging 2-mercapto-1-methylimidazolate ligand, while the latter can be viewed as a 1-methylimidazole adduct of 1 . No mixed Fe-Re complexes were produced in this reaction. The molecular structures of the new compounds and were established by single-crystal X-ray diffraction analyses and the DFT studies of compounds , and are reported.

Ruthenium and osmium carbonyl clusters incorporating stannylene and stannyl ligands.

The reaction of [Ru(3)(CO)(12)] with Ph(3)SnSPh in refluxing benzene furnished the bimetallic Ru-Sn compound [Ru(3)(CO)(8)(mu-SPh)(2)(mu(3)-SnPh(2))(SnPh(3))(2)] which consists of a SnPh(2) stannylene bonded to three Ru atoms to give a planar tetra-metal core, with two peripheral SnPh(3) ligands. The stannylene ligand forms a very short bond to one Ru atom [Sn-Ru 2.538(1) A] and very long bonds to the other two [Sn-Ru 3.074(1) A]. The germanium compound [Ru(3)(CO)(8)(mu-SPh)(2)(mu(3)-GePh(2))(GePh(3))(2)] was obtained from the reaction of [Ru(3)(CO)(12)] with Ph(3)GeSPh and has a similar structure to that of as evidenced by spectroscopic data. Treatment of [Os(3)(CO)(10)(MeCN)(2)] with Ph(3)SnSPh in refluxing benzene yielded the bimetallic Os-Sn compound [Os(3)(CO)(9)(mu-SPh)(mu(3)-SnPh(2))(MeCN)(eta(1)-C(6)H(5))] . Cluster has a superficially similar planar metal core, but with a different bonding mode with respect to that of . The Ph(2)Sn group is bonded most closely to Os(2) and Os(3) [2.786 and 2.748 A respectively] with a significantly longer bond to Os(1), 2.998 A indicating a weak back-donation to the Sn. The reaction of the bridging dppm compound [Ru(3)(CO)(10)(mu-dppm)] with Ph(3)SnSPh afforded [Ru(3)(CO)(6)(mu-dppm)(mu(3)-S)(mu(3)-SPh)(SnPh(3))] . Compound contains an open triangle of Ru atoms simultaneously capped by a sulfido and a PhS ligand on opposite sides of the cluster with a dppm ligand bridging one of the Ru-Ru edges and a Ph(3)Sn group occupying an axial position on the Ru atom not bridged by the dppm ligand.