THE INVESTIGATION OF CATALYTIC ACTIVITY OF COMPLEX 1,1,3-(PPH3)3-1-H-ISONIDO-1,2,4-RUC2B8H9 IN THE REACTIONS OF ALKENE CYCLEPROPANATION
It is known that exo-nido- and closo-ruthenacarboranes based on carborane nido-{C2B9} exhibit catalytic activity in the reactions of cyclopropanation of various olefins. These results show that further modification of the geometry of the carbon and / or the nature of substituents in the framework with preservation of the close environment in the coordination sphere of the metal can be the direction of effective search for more active and stereoselective systems. In this study we investigated the catalytic activity of 11-vertex dicarbon ruthenacarborane 1,1,3-(PPh3)3-1-H-isonido-1,2,4-RuC2B8H9 (1) in the reactions of alkenes cyclopropanation. During the study, new conditions for obtaining 1 with almost quantitative yield were selected, which is an important factor in the use of catalysts containing platinum group metals. During the reaction under heterogeneous conditions (methanol, K2CO3, triethylbenzylammonium chloride (TEBAC)), which are sometimes used in the synthesis of some organometallic compounds, the yield of the complex 1 increases from 86 to 99.5%, while in the absence of an interfacial transporter TEBAC reaction is not going. It is shown that under the action of ethyl diazoacetate (2) olefins, activated aromatic or unsaturated substituents, or with oxygen hetero-atom containing, cyclopropanate more efficiently than non-activated aliphatic terminal or internal olefins/diolefins. The latter can also be cyclopropanated, but the yields are lower, due to the competing reaction of the formation of carbene dimers. The advantage of activated olefins was revealed in a special experiment in which equal amounts of styrene and cyclooctene were taken: styrene was cyclopropanized 7-8 times faster. An experiment on comparative cyclopropanation was also performed with equimolar amounts of styrene and 4-X-styrene (X = OMe, Me and Cl) and a limited amount of 2. It was found that electron donor substituents increase the reaction rate, while electron acceptor substituents decrease. Regiospecificity reaction was studied on the example of isoprene. Cyclopropanation in this case mainly (85%) occurs on a more electron donor double bond, which confirms the electrophilic nature of ruthenium-carbene intermediate, although such intermediates were not recorded in the reaction conditions.