| Author |
Sivaev, Igor B. Rosair, Georgina M. Riley, Laura E. Welch, Alan J. Chan, Antony P. Y. Man, Wing Y. Ellis, David Taylor, James |
| Description |
Author Affiliation: Riley LE ( Institute of Chemical Sciences, Heriot-Watt University, Edinburgh, EH14 4AS UK. a.j.welch@hw.ac.uk.); Chan AP ( Institute of Chemical Sciences, Heriot-Watt University, Edinburgh, EH14 4AS UK. a.j.welch@hw.ac.uk.); Taylor J ( Institute of Chemical Sciences, Heriot-Watt University, Edinburgh, EH14 4AS UK. a.j.welch@hw.ac.uk.); Man WY ( Institute of Chemical Sciences, Heriot-Watt University, Edinburgh, EH14 4AS UK. a.j.welch@hw.ac.uk.); Ellis D ( Institute of Chemical Sciences, Heriot-Watt University, Edinburgh, EH14 4AS UK. a.j.welch@hw.ac.uk.); Rosair GM ( Institute of Chemical Sciences, Heriot-Watt University, Edinburgh, EH14 4AS UK. a.j.welch@hw.ac.uk.); Welch AJ ( Institute of Chemical Sciences, Heriot-Watt University, Edinburgh, EH14 4AS UK. a.j.welch@hw.ac.uk.); Sivaev IB ( A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 28 Vavilov Str., 119991, Moscow, Russia.) |
| Abstract |
Doubly-deprotonated 1,1′-bis(o-carborane) reacts with $[RuCl_{2}(p-cymene)]_{2}$ to afford $[Ru(κ^{3}-2,2′,3′-\{1-(1′-1′,2′-closo-C_{2}B_{10}H_{10})-1,2-closo-C_{2}B_{10}H_{10}\})(p-cymene)]$ (1) in which 1,1′-bis(o-carborane) acts as an $X_{2}(C,C′)L$ ligand where “L” is a B3′–H3′⇀Ru B-agostic interaction, fluctional over four BH units (3′, 6′, 3 and 6) at 298 K but partially arrested at 203 K (B3′ and B6′). This interaction is readily cleaved by CO affording $[Ru(κ^{2}-2,2′-\{1-(1′-1′,2′-closo-C_{2}B_{10}H_{10})-1,2-closo-C_{2}B_{10}H_{10}\})(p-cymene)(CO)]$ (2) with the 1,1′-bis(o-carborane) simply an $X_{2}(C,C′)$ ligand. With $PPh_{3}$ or dppe 1 yields $[Ru(κ^{3}-2,3′,3-\{1-(1′-1′,2′-closo-C_{2}B_{10}H_{10})-1,2-closo-C_{2}B_{10}H_{10}\})(PPh_{3})_{2}]$ (3) or $[Ru(κ^{3}-2,3′,3-\{1-(1′-1′,2′-closo-C_{2}B_{10}H_{10})-1,2-closo-C_{2}B_{10}H_{10}\})(dppe)]$ (4) via unusually facile loss of the η-(p-cymene) ligand. In 3 and 4 the 1,1′-bis(o-carborane) has unexpectedly transformed into an $X_{2}(C,B′)L$ ligand with “L” now a B3–H3⇀Ru B-agostic bond. Unlike in 1 the B-agostic bonding in 3 and 4 appears non-fluctional at 298 K. With CO the B-agostic interaction of 3 is cleaved and a $PPh_{3}$ ligand is lost to afford $[Ru(κ^{2}-2,3′-\{1-(1′-1′,2′-closo-C_{2}B_{10}H_{10})-1,2-closo-C_{2}B_{10}H_{10}\})(CO)_{3}(PPh_{3})]$ (5), which exists as a 1:1 mixture of isomers, one having $PPh_{3}trans$ to C2, the other trans to B3′. With MeCN the analogous product $[Ru(κ^{2}-2,3′-\{1-(1′-1′,2′-closo-C_{2}B_{10}H_{10})-1,2-closo-C_{2}B_{10}H_{10}\})(MeCN)_{3}(PPh_{3})]$ (6) is formed as only the former isomer. With CO 4 affords $[Ru(κ^{2}-2,3′-\{1-(1′-1′,2′-closo-C_{2}B_{10}H_{10})-1,2-closo-C_{2}B_{10}H_{10}\})(CO)_{2}(dppe)]$ (7), whilst with MeCN 4 yields $[Ru(κ^{2}-2,3′-\{1-(1′-1′,2′-closo-C_{2}B_{10}H_{10})-1,2-closo-C_{2}B_{10}H_{10}\})(MeCN)_{2}(dppe)]$ (8). In 5 and 6 the three common ligands (CO or MeCN) are meridional, whilst in 7 and 8 the two monodentate ligands are mutually trans. Compound 1 is an 18-e, 6-co-ordinate, species but with a labile B-agostic interaction and 3 and 4 are 16-e, formally 5-co-ordinate, species also including a B-agostic interaction, and thus all three have the potential to act as Lewis acid catalysts. A 1% loading of 1 catalyses the Diels–Alder cycloaddition of cyclopentadiene and methacrolein in $CH_{2}Cl_{2}$ with full conversion after 6 h at 298 K, affording the product with exo diastereoselectivity (de >77%). Compounds 1–8 are fully characterised spectroscopically and crystallographically. |
