[Reaction: see text]. Aryl and alkenyl tosylates are easily prepared, inexpensive and, thus, attractive for transition-metal-catalyzed couplings, but their reactivity is low. We report examples of mild, palladium-catalyzed coupling of aryl, alkenyl, and alkyl Grignard reagents with aryl and alkenyl tosylates. The resulting biaryls, vinylarenes, and alkylarenes were isolated in good to excellent yield. These couplings were conducted with a nearly equimolar ratio of the two reactants, and many examples were conducted at room temperature.

The use of Wilkinson's catalyst with diisopropylphosphinite ligands acting as cocatalysts allows the catalytic orthoarylation of phenols [Eq. (1)], a process that relies on a CH activation of a phenol that has been incorporated into the cocatalyst by transesterification.

The use of rhodium catalysts such as [RhCl(PPh3)3] or [[RhCl(COD)]2] with PiPr2(OAr) or P(NMe2)3 co-catalysts allows the ortho-selective intermolecular arylation of phenols. The reaction proceeds via orthometalation of P-OAr groups and then transesterification liberates the product phenol. When 2-substituted phenols are used as substrates, [RhCl(PPh3)3]/iPr2(OAr) mixtures are typically the catalysts of choice, whereas for substrates without 2-substitution [[RhCl(COD)]2]/P(NMe2)3 mixtures tend to give better results.

Bulky triarylphosphite ligands undergo facile orthometallation reactions with palladium and platinum precursors. The crystal structure of an example of the resultant palladacycles has been determined. The reactivity of some of the metallacycles with HCl, monodentate and bidentate phosphines and sodium diethyldithiocarbamate has been investigated, and the crystal structure of a diethyldithiocarbamate adduct of a palladacycle is presented. The palladacyclic complexes prove to be extremely active catalysts for the Suzuki coupling of aryl bromides with aryl boronic acids. They can also be used as catalysts for the coupling of alkylboronic acids. Meanwhile di- and trialkyl phosphine adducts of one of the palladacycles shows very high activity in the Suzuki coupling of aryl chlorides and can also be used to good effect for the Stille coupling of these substrates. The role of the phosphite ligand in the Suzuki coupling of aryl chlorides seems to be one of increasing catalyst longevity by stabilisation of the Pd(0) resting state.

The orthometalated complex [{Pd(μ-Cl){κ2-P,C-P(OC6H2-2,4-tBu2)(OC6H3-2,4-tBu2)2}}2] reacts with phenylboronic acid hydrate and K2CO3 in dimethylacetamide to give [Pd{κ2-P,C-μ2-O-P(O)(C6H2-2,4-tBu2)(C6H3-2,4-tBu2)(DMAc)}]. When the reaction is repeated in dimethylformamide 3,3‘,5,5‘-tetra-tert-butyl-2,2‘-biphenol is isolated. Both compounds have been characterized crystallographically. The reaction of palladium dichloride with PiPr2(OC6H4-4-Et) in 2-methoxyethanol followed by recrystallization in the presence of ethanol leads to the formation of trans-[PdCl2{PiPr2(OEt)}2], which was also characterized by crystallography. To determine whether related solvolytic processes have a bearing on catalytic activity, the performance of a range of catalysts with “hydrolyzed” and “nonhydrolyzed” ligands was assessed in the Suzuki coupling of aryl bromides. In some cases it was evident that hydrolysis plays a significant role on the catalytic activity; however, this depends not only on the ligand, but also on the combination of ligand and palladium precursor.