A combination of IR spectroelectrochemistry and DFT calculations has been used to demonstrate that the vinyl ligands in the complexes [Ru(CHdCHC 6 H 4 Me-4)Cl(CO)-(PMe 3 ) 3 ] and [{RuCl(CO)(PMe 3 ) 3 } 2 (μ-CHdCHC 6 H 4 CHd CH)] are redox noninnocent, and one-electron oxidation results in radical cations that are best described in terms of metal-stabilized organic radicals.

Examples of singly-metallated derivatives of 1,1'-bis(o-carborane) have been prepared and spectroscopically and structurally characterised. Metallation of [7-(1'-1',2'-closo-C2B10H11)-7,8-nido-C2B9H10](2-) with a {Ru(p-cymene)}(2+) fragment affords both the unisomerised species [1-(1'-1',2'-closo-C2B10H11)-3-(p-cymene)-3,1,2-closo-RuC2B9H10] (2) and the isomerised [8-(1'-1',2'-closo-C2B10H11)-2-(p-cymene)-2,1,8-closo-RuC2B9H10] (3), and 2 is easily transformed into 3 with mild heating. Metallation with a preformed {CoCp}(2+) fragment also affords a 3,1,2-MC2B9-1',2'-C2B10 product [1-(1'-1',2'-closo-C2B10H11)-3-Cp-3,1,2-closo-CoC2B9H10] (4), but if CoCl2/NaCp is used followed by oxidation the result is the 2,1,8-CoC2B9-1',2'-C2B10 species [8-(1'-1',2'-closo-C2B10H11)-2-Cp-2,1,8-closo-CoC2B9H10] (5). Compound 4 does not convert into 5 in refluxing toluene, but does do so if it is reduced and then reoxidised, perhaps highlighting the importance of the basicity of the metal fragment in the isomerisation of metallacarboranes. A computational study of 1,1'-bis(o-carborane) is in excellent agreement with a recently-determined precise crystallographic study and establishes that the {1',2'-closo-C2B10H11} fragment is electron-withdrawing compared to H.

In the title compound, the two {1,2-closo-C2B10H11} cages are linked across a centre of inversion with a C—C distance of 1.5339 (11) Å. By careful analysis of the structure, it is established that the non-linking cage C atom is equally disordered over cage vertices 2 and 3.

The dithia[3.3]paracyclophane-bridged bimetallic ruthenium alkynyl and vinyl complexes {Cp*(dppe)RuCC} 2 (μdithia[3.3]paracyclophane) (8) and {(PMe 3 ) 3 (CO)ClRuCH CH} 2 (μ-dithia[3.3]paracyclophane) (9) have been prepared and, in the case of 8, structurally characterized. Compounds 8 and 9 each undergo two consecutive one-electron-oxidation processes, with supporting investigations conducted using IR and UV/vis/near-IR spectroelectrochemical methods establishing the redox-noninnocent character of the dithia[3.3]paracyclophane bridge unit in both 8 and 9. Both [8] + and [9] + exhibit multiple transitions in the near-IR region, which have been assigned with the aid of DFT calculations to combinations of MLCT and intraligand transitions and transitions involving the donor sulfur atoms within the cyclophane scaffold to the partially occupied orbital located on the diethynyl-or divinylphenylene portion of the bridging cyclophane.

Doubly-deprotonated 1,1'-bis(o-carborane) reacts with [RuCl2(p-cymene)]2 to afford [Ru(κ3-2,2',3'-{1-(1'-1',2'-closo-C2B10H10)-1,2-closo-C2B10H10})(p-cymene)] (1) in which 1,1'-bis(o-carborane) acts as an X2-(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-(κ2-2,2'-{1-(1'-1',2'-closo-C2B10H10)-1,2-closo-C2B10H10})(p-cymene)(CO)] (2) with the 1,1'-bis(o-carborane)simply an X2(C,C') ligand. With PPh3 or dppe 1 yields [Ru(κ3-2,3',3-{1-(1'-1',2'-closo-C2B10H10)-1,2-closo-C2B10H10})(PPh3)2] (3) or [Ru(κ3-2,3',3-{1-(1'-1',2'-closo-C2B10H10)-1,2-closo-C2B10H10})(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 X2(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 PPh3 ligand is lost to afford [Ru(κ2-2,3'-{1-(1'-1',2'-closo-C2B10H10)-1,2-closo-C2B10H10})(CO)3(PPh3)](5), which exists as a 1 : 1 mixture of isomers, one having PPh3 trans to C2, the other trans to B3'. With MeCN the analogous product [Ru(κ2-2,3'-{1-(1'-1',2'-closo-C2B10H10)-1,2-closo-C2B10H10})(MeCN)3(PPh3)] (6) is formed as only the former isomer. With CO 4 affords [Ru(κ2-2,3'-{1-(1'-1',2'-closo-C2B10H10)-1,2-closo-C2B10H10})(CO)2(dppe)] (7), whilst with MeCN 4 yields [Ru(κ2-2,3'-{1-(1'-1',2'-closo-C2B10H10)-1,2-closo-C2B10H10})(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 CH2Cl2 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.