New phosphine-functionalized N-heterocyclic carbene ligand precursors (L 1 H • I and L 2 H • I) were prepared. The former compound contains a PPh 2 moiety, whereas the latter one has a more electrondonating PCy 2 group. A reaction of L 1 H • • • I with PdCl 2 in the presence of base afforded the complex PdL 1 ClI. An interconversion process between the two structural isomers of PdL 1 ClI was observed by variable-temperature NMR. The coalescence temperature (T c ) is at 368 K with the free energy of activation (∆G q ) found to be 68.9 kJ mol -1 . A similar reaction of L 2 H • I with PdCl 2 produced a mixture of PdL 2 ClI, PdL 2 Cl 2 , and PdL 2 I 2 . Unlike PdL 1 ClI, PdL 2 ClI undergoes a much faster exchange between the two structural isomers. Pure PdLI 2 (L ) L 1 and L 2 ) can be obtained by adding NaI in the reaction mixture to facilitate ligand exchange. [PdL(CH 3 CtN) 2 ](BF 4 ) 2 were also prepared straightforwardly by salt metathesis reactions. In total, seven new palladium complexes of L were structurally characterized, and in each of these structures an anagostic interaction exists between the palladium center and one of the diastereotopic methylene protons. The interaction also exists in solution, as evidenced by the downfield NMR shift of the proton. The new complexes PdLI 2 and [PdL(CH 3 CtN) 2 ](BF 4 ) 2 show mediocre activities in benchmark Suzuki coupling reactions under conventional and microwave heating. They are, however, highly promising in mediating direct arylation of phenyl halides and diphenylacetylene, affording 9-benzylidene-9H-fluorene in good yields.

A series of bis-bidentate nickel(II) complexes with bifunctional ligands of N-heterocyclic carbene and amido moieties were prepared from the ligand precursors, [L1H1H2]Cl and [L2H1 2H2]Cl (H1 = NHCO, H2 = NCHN), in 48−82% yields. The complexes NiL1 2 and Ni(L2H1)2 are stable in the air and toward moisture. They are characterized by NMR (1D and 2D) and single-crystal X-ray diffraction studies. According to the NMR, crystallographic, and PXRD studies, one of the NiL1 2 complexes undergoes an intriguing reversible solvent-induced cis/trans transformation process, producing the cis form with DMSO and trans with CHCl3. The exchange process is highly specific and can be explained by the higher polarity of cis-NiL1 2, which favors the polar DMSO solvent, whereas the less polar trans form due to cancellation of polarity from the trans disposition of ligands favors the less polar CHCl3 solvent. A DFT calculation is in support of the experimental findings. Unlike the previous reported palladium analogues, NiL1 2 and Ni(L2H1)2, in the presence of PPh3 as cocatalyst, are highly efficient in catalyzing the Suzuki cross-coupling reaction of aryl chlorides with phenylboronic acid. A 3 mol % of NiL1 2 (Ni:PPh3 = 1:2) was sufficient to mediate the formation of 4-methoxy-1,1‘-biphenyl from 4-chloroanisole in 95% yield in 12 h.

The new palladium complexes with NHC and phosphine ligands, cis-PdCl 2 (L 2 )(PPh 3 ) (2), cis-PdBr 2 (L 2 )(PPh 3 ) (3), and cis-PdCl 2 (L 3 )(PPh 3 ) (4) were prepared following a general protocol of a one pot reaction between PdCl 2 (COD), PPh 3 , and the ligand precursors LH 3 Y (Y=Cl, Br, BF 4 ) (L 2 = 1,3-dibenzylimidazolin-2-ylidene; L 3 =1,3-dibenzylimidazol-2-ylidene). The cis-PdCl 2 (L 3 )(PCy 3 ) complex (5) was prepared by the ligand substitution reaction between 4 and PCy 3 . The palladium complexes with NHC and pyridine complexes, trans-PdCl 2 (L)(py) (6: L = L 2 ; 7: L = L 3 ) were obtained by heating a mixture of PdCl 2 (COD) and LH 3 BF 4 in pyridine. A similar reaction condition using CH 3 CN as solvent with KO t Bu as base afforded cis-PdCl 2 (L 3 ) 2 (8). Complexes 2-8 were successfully characterized by X-ray crystallographic studies, among which, intriguingly, two polymorphs of 8 were obtained. Thermogravimetric analysis showed that the cis-PdX 2 (NHC)(PR 3 ) complexes are more thermally stable than the trans-PdCl 2 (NHC)(py) complexes. Together with the known cis-PdCl 2 (L 1 )(PCy 3 ) (1) (L 1 =1-benzyl-3-(N-phenylacetamido)imidazol-2-ylidene), they were screened for the direct arylation reaction between aryl halides and alkynes. The result indicate that the carbene/phosphine complexes 1-5 are superior precatalysts than 6-8 with higher activities than the commonly-used system of Pd(OAc) 2 /2PPh 3 .

The solid-state structure of an alkaline-earth metal complex reveals the formation of a remarkable supramolecular framework based on concurrent lone pair-pi, pi-pi, and pi-anion interactions whose stability has been investigated by density functional theory.