Umberto Casellato

Bio: Umberto Casellato is an academic researcher from University of Padua. The author has contributed to research in topics: Crystal structure & Triclinic crystal system. The author has an hindex of 21, co-authored 92 publications receiving 1267 citations. Previous affiliations of Umberto Casellato include National Research Council.

Reactivity of the [ReNR]3+ and [ReN]2+ cores toward bis(diphenylphosphino)amine and its derivatives. Synthesis and crystal structures

Abstract: The complexes fac-[Re(NMe)Cl3{NH(PPh2)2-P,P′}]1, [ReNCl{NH(PPh2)2-P,P′}2]X (X = Cl 2 or BPh42a), [Re(NMe) Cl2{N(XPPh2)2-X,X′}(PPh3)](X = 0 3, S 4 or Se 8), [Re(NMe)Cl{N(XPPh2)2-X,X′}2](X = S 5 or Se 9), [ReNCl{N(SPPh2)2-S,S′}(PPh3)]6, [ReN{N(XPPh2)2-X,X′)2](X = S 7 or Se 10) and trans-[ReOCl2{N(OPPh2)2-O,O′}(AsPh3)]11 were obtained by treatment of [Re(NMe)Cl3(PPh3)2], [ReNCl2(PPh3)2] or [ReOCl3(AsPh3)2] with the appropriate ligand under different experimental conditions. The structures of complexes 1, 2a and 6 were determined by X-ray crystallography. In 1 and 2a the Re atom is six-co-ordinate in a distorted octahedral configuration, whereas in 6 the Re atom is five-co-ordinate square pyramidal with the N atom in the apical position.

The Medicinal Applications of Imidazolium Carbene Metal Complexes

Abstract: Ofele and Wanzlick reported the synthesis of the first N-heterocyclic carbene (NHC) metal complexes in 1968.1,2 The isolation of the first free carbene by Arduengo in 1991 set the scene for an ever-growing interest and advancement in the field of N-heterocyclic carbene chemistry.3 Shortly thereafter, the use of these ligands in organometallic chemistry, particularly in catalysis dramatically increased.4,5 N-heterocyclic carbenes are neutral 2-electron donors, with an ability to bond to both hard and soft metals making them more versatile ligands than phosphines.6 As an added advantage, not only are NHCs easier to synthesize and functionalize than phosphines but they also form a stronger bond to metals and therefore form more stable metal complexes than metal phosphine complexes.7,8 The N-heterocyclic carbene ligands interact with metal centers primarily through strong σ-donation and to a lesser degree through π-backdonation (Figure 1).9,10 Figure 1 Orbital diagram of NHC bonding to metal center. Ghosh and coworkers11,12,13,14,15,16 as well as others17,18,19 took special interest in the exceptional stability of several metal-NHC complexes and conducted in depth analyses in order to gain better insights into the structure and bonding. In particular, the metal-ligand donor-acceptor interactions were inspected using the charge decomposition analysis (CDA). CDA is a tool used to quantitatively estimate the degree of NHC → metal σ-donation, designated by d, and NHC ← metal π-back donation, designated by b.20,21 Thus a higher d/b ratio emphasizes the ability of NHC to function as an effective σ-donor, whereas a lower d/b ratio highlights the greater NHC ← metal π-back donation. Interestingly, in the studies conducted by Ghosh, greater NHC ← metal π-back donation was observed in Pd-NHC complexes exhibiting lower d/b ratios ranging between 2.59 – 3.9913,14 and Au-NHC complexes with d/b ratios ranging between 5.23 – 5.8815,16 as compared to the Ag-NHC complexes with d/b ratios ranging between 7.8 – 12.6811,12,16. This observation could attest to why silver-NHC complexes are particularly better transmetallating agents. The newly emerging interest in the medicinal applications of stable metal NHCs led us to examine the few accounts available in the literature dealing with this area of research. This review will discuss in detail the medicinal applications of various transition metal-NHC complexes including silver, gold, rhodium, ruthenium, and palladium. The antimicrobial, antitumor, and resistance properties, along with proposed mechanisms of action to suppress the bacterial growth or proliferation of tumor cells will be discussed.

Anticancer and Antimicrobial Metallopharmaceutical Agents Based on Palladium, Gold, and Silver N-Heterocyclic Carbene Complexes

Abstract: Complete synthetic, structural, and biomedical studies of two Pd complexes as well as Au and Ag complexes of 1-benzyl-3-tert-butylimidazol-2-ylidene are reported. Specifically, trans-[1-benzyl-3-tert-butylimidazol-2-ylidene]Pd(pyridine)Cl2 (1a) was synthesized from the reaction of 1-benzyl-3-tert-butylimidazolium chloride (1) with PdCl2 in the presence of K2CO3 as a base. The other palladium complex, [1-benzyl-3-tert-butylimidazol-2-ylidene]2PdCl2 (1b), and a gold complex, [1-benzyl-3-tert-butylimidazol-2-ylidene]AuCl (1c), were synthesized by following a transmetallation route from the silver complex, [1-benzyl-3-tert-butylimidazol-2-ylidene]AgCl (1d), by treatment with (COD)PdCl2 and (SMe2)AuCl, respectively. The silver complex 1d in turn was synthesized by the reaction of 1 with Ag2O. The molecular structures of 1a−d have been determined by X-ray diffraction studies. Biomedical studies revealed that, while the palladium complexes 1a and 1b displayed potent anticancer activity, the gold (1c) and silver ...