Palladium(II) and palladium(II)-silver(I) complexes with N-heterocyclic carbene and zwitterionic thiolate mixed ligands: synthesis, structural characterization and catalytic properties

The integration of a geometrically rigid Pd((II)), a coordinatively monotonous N-heterocyclic carbene 1,3-dimethylimidazoline-2-ylidene (IMe), and a flexible zwitterionic thiolate 4-(trimethylammonio) benzenethiolate (Tab) affords a class of Pd-IMe-Tab complexes with various nuclearities, namely, trans-[Pd(IMe)(2)(Tab)(2)](OTf)(2) (2, mononuclear), cis-[Pd(IMe)(2)(Tab)(2)](OTf)(Cl) (3a, mononuclear), cis[Pd(IMe)(2)(Tab)(2)](PF6)(2)center dot MeCN (3b center dot MeCN, mononuclear), [Pd-2(IMe)(4)(Tab)(2)](PF6)(4)center dot 2MeCN (4 center dot 2MeCN, dinuclear) and [Pd-4(IMe)(4)(Tab)(6)](OTf)(6)(Cl)(2) (5, tetranuclear). Further presence of Ag(I) in the assembly provides a heterometallic octanuclear cluster of [Pd4Ag4(IMe) (Tab)(10)](PF6)(12) (6). Compounds 2-6 are formed by the reaction of trans-Pd(IMe) Cl-2(2) (1) with various additional reagents via different reaction pathways. These compounds are characterized by means of FT-IR, H-1 and C-13 NMR, ESI-MS, elemental analysis and X-ray crystallography. Notably, the skeleton of compound 5 features a [Pd4S4] parallelogram wherein each of the four Pd((II)) centers bisects the edge defined by the S atoms. The main skeleton of compound 6 is an oval-shaped Pd4Ag4S10 unit, featuring an edge-fused norbornane-like (Pd2Ag4S6) framework appended by two additional PdS2 motifs at the polar positions. Compounds 5 and 6 also feature Pd...Pd (5), Pd...Ag and Ag...Ag (6) interactions. Compound 5 as a representative example is highly effective at catalyzing Suzuki-Miyaura couplings in water, highlighting the potential of applying these types of homoand heterometallic clusters as catalysts for organic transformations in environmentally benign media.