A very straightforward synthesis of (IPr)Pd(acac)Cl from two commercially available starting materials, Pd(acac)2 and IPr.HCl [acac = acetylacetonate; IPr = N,N'-bis(2,6-diisopropylphenyl)imidazol-2-ylidene], has been developed. The resulting complex, (IPr)Pd(acac)Cl (1), has proven to be a highly active PdII precatalyst in the Buchwald-Hartwig and the alpha-ketone arylation reactions. A wide range of substrates has been screened, including unactivated, sterically hindered, and heterocyclic aryl chlorides.

Simple routes to two new types of mononuclear cationic palladium phosphine acetate complexes featuring κ1- or κ2-carboxylates have been developed, and the resulting materials have been characterized by single-crystal X-ray diffraction. In acetonitrile the complex [(iPr3P)2Pd(κ2 O,O‘-OAc)]+ leads not to the independently prepared trans-[(iPr3P)2Pd(MeCN)(OAc)]+ but to reversible cyclometalation to form [(iPr3P)(MeCN)Pd(κ2 C,P-C(Me)2PiPr2)]+.

Two classes of cationic palladium(II) phosphine carboxylate complexes were isolated and characterized. Reactions of trans-[(R3P)2Pd(O2CR‘)2] (1) with [Li(OEt2)2.5][B(C6F5)4] in MeCN led to carboxylate abstraction and formation of trans-[(R3P)2Pd(O2CR‘)(MeCN)][B(C6F5)4] (2) in good to excellent yields. On the other hand, carboxylate abstraction reactions of 1 with [Me2(H)NPh][B(C6F5)4] or p-toluenesulfonic acid (HOTs·H2O) in CH2Cl2 furnished the palladium cations [(R3P)2Pd(κ2-O,O-O2CR‘)]+ (3). The reactions of 2 and 3 with Lewis bases were found to be different in some cases. For example, reactions of 2 with pyridine furnished the simple products of acetonitrile substitution, trans-[(R3P)2Pd(O2CR‘)(py)][B(C6F5)4]. In contrast, the reaction of 3e (R = iPr, R‘ = CH3) with CD3CN in the presence of excess sodium carbonate yielded a material derived from cyclometalation of one of the iPr arms of a iPr3P ligand. New complexes were characterized by elemental analyses and NMR (1H, 13C, and 31P) spectroscopic methods and in two cases by single-crystal X-ray structural methods.

The homoleptic organochromium(II) compound [Mg(THF) 6 ][Cr II (C 6 F 5 ) 4 ] (1) was obtained as an extremely air-sensitive solid by reaction of [CrCl 2 (THF)] with C 6 F 5 MgBr. The arylation of MnBr 2 under similar conditions proceeded with oxidation of the metal center to give [Mg-(THF) 6 ][Mn III (C 6 F 5 ) 4 ] 2 (2). The crystal structures of 1 and 2 (X-ray diffraction) contain the anions [Cr(C 6 F 5 ) 4 ] 2and [Mn(C 6 F 5 ) 4 ] -, respectively, both with approximate square-planar (SP-4) geometry around the metal center. In the solid state there is no sign of any covalent interaction or ion-pairing between these anions and the virtually octahedral (OC-6) [Mg-(THF) 6 ] 2+ cations. The average Mn III -C distance in 2, 2.068(4) Å, is slightly shorter than the mean Cr II -C bond length in 1, 2.158(6) Å, a fact that can be attributed mainly to the different oxidation states of the metal centers in each case. The use of 2 as an initiator itself and as a weakly coordinating anion in Pd-catalyzed polymerization processes of strained olefins has also been assayed.