The enhanced structural carborane effect

Further studies of the Enhanced Structural Carborane Effect: tricarbonylruthenium and related derivatives of benzocarborane, dihydrobenzocarborane and biphenylcarborane

“…Both the <C cage -Ru> and <C cage -B6> distances are significantly shorter [differences 0.042(3) and 0.015(4) Å, respectively] and the C1-C2 distance significantly longer [difference 0.036(4) Å] in compound 2 compared to compound 1 providing clear evidence for an Enhanced Structural Carborane Effect and implying some degree of aromaticity in the C 6 ring of 1; if the cage C p π orbitals in 1 are involved in an aromatic exopolyhedral ring they will be less involved in bonding to the Ru3 and B6 atoms. The same conclusion was reached when we compared molecular structures of I-Co and II-Co. 1 A colourless minor co-product, compound 3, was produced along with 2. Elemental analysis and mass spectrometry were consistent with only a dicarbonyl species.…”

“…1) as one pair, 3,4 and their {CoCp} derivatives [1,2-μ-(C 4 H 4 )-3-Cp-3,1,2-closo-CoC 2 B 9 H 9 ] (I-Co) and [1,2-μ-(C 4 H 6 )-3-Cp-3,1,2-closo-CoC 2 B 9 H 9 ] (II-Co) as the other. 1 Although the differences were small they were significantin the compounds with the {C 4 H 4 } tether the C cage -B/M3 and C cage -B6 distances were longer, and the C cage -C cage distances shorter, than those in the compounds with the {C 4 H 6 } tether, providing firm evidence for an ESCE.…”

“…We recently named the phenomenon whereby cage C atoms in metallacarboranes of the type 3,1,2-closo-MC 2 B 9 H 11 are less strongly bound to the metal atom than cage B atoms as the Structural Carborane Effect (SCE). 1 The origin of the SCE is that in a carborane ligand the C atoms contribute relatively little to the cage frontier molecular orbitals. 2 Although this effect was already very well-known, giving it this name allowed us subsequently to describe the Enhanced Structural Carborane Effect (ESCE).…”

“…2 Although this effect was already very well-known, giving it this name allowed us subsequently to describe the Enhanced Structural Carborane Effect (ESCE). 1 This arises when an exopolyhedral {C 4 H 4 } diene tethers the two carborane C atoms allowing the p π orbitals of the cage C atoms to participate in a pseudoaromatic C 6 ring at the expense of bonding to the metal atom. The effect is similar to the difference in metal-bonding of a Cp ligand and an indenyl ligandin the former the M-C interactions are equivalent but in the latter the ring junction C atoms are weaker bound to the metal atom since their p π orbitals are simultaneously part of two aromatic systems.…”

“…Found for 1 C 28.5, H 3.67%. 11 B{ 1 H} NMR, δ 5.4 (1B), −2.4 (1B), −6.3 (6B), −10.6 (1B) 1. H NMR, δ 6.99 (m, 2H, tether CH), 6.05 (m, 2H, tether CH).…”