The selective cross McMurry couplings of diaryl or aryl ketones with various substituted ketones were achieved in 53-94% isolated yields. It is believed that the strong affinity of the substituents to the low-valent titanium surface plays an important role in regards to moderating selectivity. Through the introduction of such substituents followed by their removal post McMurry coupling, structurally similar ketones can be effectively cross-coupled.

The imidazolium ligand precursors [L1H1H2]Cl and [L2H1 2H2]Cl (H1 = NHCO, H2 = NCHN) for the potentially bidentate and pincer-type amido-NHC ligands were synthesized in 66−78% yields. Selective deprotonation of H2 in these salts with pyridine in the presence of palladium chloride resulted in the monodentate palladium(II) complexes Pd(L1H1)(py)Cl2 and Pd(L2H1 2)(py)Cl2. The use of K2CO3 in pyridine or DMF led to the double and triple deprotonations of the ligand precursors, giving the bis-bidentate and pincer-type palladium(II) complexes PdL1 2 and PdL2(py), respectively. Intriguingly, in certain cases, both the cis and the trans isomers of PdL1 2 were formed and isolated in pure forms. A theoretical study indicates that the trans-PdL1 2 is thermodynamically more stable than the cis isomer (ca. 5.8 kcal mol-1). All the new complexes are characterized by NMR (1D and 2D) and single-crystal X-ray diffraction studies. A systematic study of the new complexes in Suzuki coupling reactions revealed the following order of activities:  Pd(L1H1)(py)Cl2 > PdL2(py) > PdL1 2.

A new imidazolium salt, 1,3-bis(2-diphenylphosphanylethyl)-3H-imidazol-1-ium chloride (2), for the phosphine/N-heterocyclic carbene-based pincer ligand, PC(NHC)P, and its palladium complexes were reported. The complex, [Pd(PC(NHC)P)Cl]Cl (4), was prepared by the common route of silver carbene transfer reaction and a novel direct reaction between the ligand precursor, PC(NHC)P.HCl and PdCl(2) without the need of a base. Metathesis reactions of 4 with AgBF(4) in acetonitrile produced [Pd(PC(NHC)P)(CH(3)CN)](BF(4))(2) (5). The same reaction in the presence of excess pyridine gave [Pd(PC(NHC)P)(py)](BF(4))(2) (6). The X-ray structure determination on 4-6 revealed the chiral twisting of the central imidazole rings from the metal coordination plane. In solution, fast interconversion between left- and right-twisted forms occurs. The twisting reflects the weak pi-accepting property of the central NHC in PC(NHC)P. The uneven extent of twisting among the three complexes further implies the low rotational barrier about the Pd-NHC bond. Related theoretical computations confirm the small rotational energy barrier about the Pd-NHC bond (ca. 4 kcal/mol). Catalytic applications of 4 and 5 have shown that the complexes are modest catalysts in Suzuki coupling. The complexes were active catalysts in Heck coupling reactions with the dicationic complex 5 being more effective than the monocationic complex 4.

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A mild, stereoselective, and quick approach to accessing alkynyl and alkenyl C-glycosides via BF(3)·Et(2)O promoted coupling of organotrifluoroborates and glycosyl fluorides is reported. The application of this method was further demonstrated by the concise and efficient total synthesis of (+)-varitriol in only seven steps.