Selective C-H bond functionalization is a potentially valuable approach for synthesis in areas ranging from fuels and commodity chemicals to pharmaceuticals. 1 C-H activation studies in our laboratory have focused on models of the Shilov system, 2 particularly methylplatinum cations [(diimine)Pt II (Me)(solv)] + (2, diimine ) ArNdC(Me)-C(Me)dNAr; solv ) 2,2,2-trifluoroethanol (TFE), H 2 O). 3 These cations are able to activate a variety of R-H bonds to form [(diimine)Pt II (R)(solv)] + complexes (3), as shown in Scheme 1, because the H can be removed as methane. 4 Under some conditions double protonolysis of 1a generates dicationic platinum-(II) complex 4a, which can activate certain C-H bonds: those that are part of a benzylic or allylic system, or can otherwise form a chelate product (illustrated for the allylic case in Scheme 1). 5 These systems are limited because productive catalytic functionalization, as in the original Shilov system, requires activation by a metal complex that does not include a sacrificial organic group. An alternative, non-organometallic route to complexes of the general form [(diimine)M(solv) 2 ] 2+ involves metathesis of [(diimine)MCl 2 ] complexes with silver salts (in the presence of ∼1% water), which leads to the formation of dimeric bis(hydroxo)-bridged complexes for both palladium 6 and platinum. 7 No C-H activation reactions have been reported for these species, and in some oxidative functionalization schemes such dimers appear to be the thermodynamic "final resting places". 8 As water will usually be a byproduct of oxidative functionalization, aquo-or hydroxo-ligated complexes must not be dead ends.We here report that the air-and water-tolerant dimeric hydroxybridged dimers [(diimine)M(OH)] 2 2+ (M ) Pt, Pd), prepared and used without the intermediacy of any M-Me bond, are not necessarily resting states. In fact, they can effect not only stoichiometric activation of a variety of C-H bonds, but also catalytic conversion of cyclohexene to benzene, using dioxygen as the terminal oxidant, when the metal is palladium.Metathesis reactions of [(diimine)MCl 2 ] complexes 6 (M ) Pt) and 7 (M ) Pd) proceed as shown in Scheme 2. For platinum with the diimine ligands Ar ) 3,5-t-Bu 2 C 6 H 3 (6a) or 2,4,6-Me 3 C 6 H 2 (6b) mixtures of dimeric hydroxo-bridged (i) and monomeric bis(aquo) (ii) dications are formed initially, but the dimeric forms can be isolated cleanly. 9 In the case of palladium, the dimers 9ai 6 and 9bi could be cleanly isolated in low yield, while the monomeric bis-(aquo)dication 9aii was synthesized following a literature procedure. 6 8ai and 8aii equilibrate slowly in the presence of added aqueous HBF 4 (Scheme 3), as demonstrated by the dependence of speciation on [H + ] and temperature (K 1 ) 1.33(14) × 10 3 M -1 at 80 °C; ∆H°) 17(1) kcal/mol and ∆S°) 63(4) eu from 20 to 80 °C). 10 Platinum dimer 8ai reacts with cyclohexene in the presence of acid (delivered as BF 3 -TFE-d 3 , HBF 4 (aq), or 8aii) to yield

Tris(perfluoroalkyl)phosphines, of interest as tunable alternatives to the carbon monoxide ligand, can be synthesised by the nucleophile mediated reaction of perfluoroalkyltrimethylsilanes with triphenylphosphite; the method can be extended to diphosphines.

Simple chlorodiisopropylphosphine adducts of rhodium, either pre-formed or formed in situ, prove to be highly effective catalysts for the ortho-arylation of phenols.

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