The reaction of 1,1'-Li 2 [(2,2'-C 2 B 10 H 10 ) 2 ]w ith the cyclometallated gold(III) complex( C^N)AuCl 2 afforded the first examples of gold(III) dicarboranyl complexes. The reactivity of these complexes is subject to the trans-influence exerted by the dicarboranyl ligand,w hichi ss ubstantially weaker than that of non-carboranyl anionic C-ligands. In line with this, displacemento fc oordinated pyridine by chloride is only possible under forcing conditions. While treatment of (C^N)Au{(2,2'-C 2 B 10 H 10 ) 2 }( 2)w ith triflic acid leads to AuÀC rather than AuÀNb ond protonolysis, aqueous HBr cleaves the AuÀNb ond to give the pyridinium bromo complex 7.The trans-influence of as eries of ligands including dicarboranyl and bis(dicarboranyl) was assessed by meansofD FT calculations. The analysis demonstrated that it was not suffi-cient to rely exclusively on geometricd escriptors (calculated or experimental) when attempting to rank ligands fort heir trans influence. Complex( C^N)Au(C 2 B 10 H 11 ) 2 containing two non-chelating dicarboranyll igandsw as prepared similar to 2.I ts reaction with trifluoroacetic acida lso leads to AuÀN cleavage to give trans-(Hpy^C)Au(OAc F )(C 2 B 10 H 11 ) 2 (8). In crystals of 8 the pyridiniumN ÀHb ond points towards the metal centre, while in 7 it is bent away.T he possible contribution of gold(III)···HÀNh ydrogen bonding in these complexes was investigated by DFT calculations. The results show that, unlike the situation for platinum(II), there is no evidencef or an energeticallys ignificant contribution by hydrogen bonding in the case of gold(III).

Deprotonation of 1,1′-bis(ortho-carborane) with n BuLi in THF followed by reaction with [RuCl 2 (p-cymene)] 2 affords, in addition to the known compound [Ru(κ 3 -2,2′,3′-{1-(1′-closo-1′,2′-C 2 B 10 H 10 )-closo-1,2-C 2 B 10 H 10 )}(pcymene)] (I), a small amount of a new species, [Ru(κ 3 -2,2′,11′-{1-(7′-nido-7′,8′-C 2 B 9 H 11 )-closo-1,2-C 2 B 10 H 10 )}(p-cymene)] (1a), with two B-agostic B− H⇀Ru bonds, making the bis(carborane) unit a closo-nido-X(C)L 2 ligand, a previously unreported bonding mode. Similar species were also formed with arene = benzene (1b), mesitylene (1c), and hexamethylbenzene (1d), although in the last two cases the metallacarborane-carborane species [1-(1′-closo-1′,2′-C 2 B 10 H 11 )-3-(arene)-closo-3,1,2-RuC 2 B 9 H 10 )], 2c and 2d, were also isolated. With the bis(ortho-carborane) transfer reagent [Mg(κ 2 -2,2′-{1-(1′-closo-1′,2′-C 2 B 10 H 10 )-closo-1,2-C 2 B 10 H 10 )}(DME) 2 ], the target compounds [Ru(κ 3 -2,2′,3′-{1-(1′-closo-1′,2′-C 2 B 10 H 10 )-closo-1,2-C 2 B 10 H 10 )}(arene)], 4b and 4d, were prepared in reasonable-to-good yields, although for arene = benzene and mesitylene small amounts of the unique paramagnetic species [{Ru(arene)} 2 (μ-Cl)(μ-κ 4 -2,2′,3,3′-{1-(1′closo-1′,2′-C 2 B 10 H 9 )-closo-1,2-C 2 B 10 H 9 })], 3b and 3c, were also formed. In compounds 3, the bis(carborane) acts as a closocloso-X 4 (C,C′,B,B′) ligand to the Ru 2 unit. In I, 4b, and 4d, the B-agostic B−H⇀Ru bond is readily cleaved by MeCN, affording compounds [Ru(κ 2 -2,2′-{1-(1′-closo-1′,2′-C 2 B 10 H 10 )-closo-1,2-C 2 B 10 H 10 })(arene)(NCMe)] (5a, 5b, and 5d) and suggesting that I, 4b, and 4d could act as Lewis acid catalysts, which is subsequently shown to be the case for the Diels−Alder cycloaddition reactions between cyclopentadiene and methacrolein, ethylacrolein and E-crotonaldehyde. All new species were characterized by multinuclear NMR spectroscopy and 1a , 1c, 1d, 2c, 2d, 3b, 3c, 4b, 4d, 5a, 5b, and 5d were also characterized crystallographically.

The transformation of C,C′-bound bis(ortho-carborane) to C,B′-bound is reported for the first time.

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