Multimetallic Complexes and Functionalized Gold Nanoparticles Based on a Combination of d- and f-Elements

Abstract

The new DO3A-derived dithiocarbamate ligand, DO3A-(t)Bu-CS2K, is formed by treatment of the ammonium salt [DO3A-(t)Bu]HBr with K2CO3 and carbon disulfide. DO3A-(t)Bu-CS2K reacts with the ruthenium complexes cis-[RuCl2(dppm)2] and [Ru(CH═CHC6H4Me-4)Cl(CO)(BTD)(PPh3)2] (BTD = 2,1,3-benzothiadiazole) to yield [Ru(S2C-DO3A-(t)Bu)(dppm)2](+) and [Ru(CH═CHC6H4Me-4)(S2C-DO3A-(t)Bu)(CO)(PPh3)2], respectively. Similarly, the group 10 metal complexes [Pd(C,N-C6H4CH2NMe2)Cl]2 and [PtCl2(PPh3)2] form the dithiocarbamate compounds, [Pd(C,N-C6H4CH2NMe2)(S2C-DO3A-(t)Bu)] and [Pt(S2C-DO3A-(t)Bu)(PPh3)2](+), under the same conditions. The linear gold complexes [Au(S2C-DO3A-(t)Bu)(PR3)] are formed by reaction of [AuCl(PR3)] (R = Ph, Cy) with DO3A-(t)Bu-CS2K. However, on reaction with [AuCl(tht)] (tht = tetrahydrothiophene), the homoleptic digold complex [Au(S2C-DO3A-(t)Bu)]2 is formed. Further homoleptic examples, [M(S2C-DO3A-(t)Bu)2] (M = Ni, Cu) and [Co(S2C-DO3A-(t)Bu)3], are formed from treatment of NiCl2·6H2O, Cu(OAc)2, or Co(OAc)2, respectively, with DO3A-(t)Bu-CS2K. The molecular structure of [Ni(S2C-DO3A-(t)Bu)2] was determined crystallographically. The tert-butyl ester protecting groups of [M(S2C-DO3A-(t)Bu)2] (M = Ni, Cu) and [Co(S2C-DO3A-(t)Bu)3] are cleaved by trifluoroacetic acid to afford the carboxylic acid products, [M(S2C-DO3A)2] (M = Ni, Cu) and [Co(S2C-DO3A)3]. Complexation with Gd(III) salts yields trimetallic [M(S2C-DO3A-Gd)2] (M = Ni, Cu) and tetrametallic [Co(S2C-DO3A-Gd)3], with r(1) values of 11.5 (Co) and 11.0 (Cu) mM(-1) s(-1) per Gd center. DO3A-(t)Bu-CS2K can also be used to prepare gold nanoparticles, Au@S2C-DO3A-(t)Bu, by displacement of the surface units from citrate-stabilized nanoparticles. This material can be transformed into the carboxylic acid derivative Au@S2C-DO3A by treatment with trifluoroacetic acid. Complexation with Gd(OTf)3 or GdCl3 affords Au@S2C-DO3A-Gd with an r(1) value of 4.7 mM(-1) s(-1) per chelate and 1500 mM(-1) s(-1) per object.

Combined Magnetic Resonance Imaging and Photodynamic Therapy Using Polyfunctionalised Nanoparticles Bearing Robust Gadolinium Surface Units

“…This can be partly traced to the effect on the rotational correlation time, which increases when the assembly rotates slowly, leading to greatly increased relaxivity per Gd 3+ ion. In addition to this intrinsic enhancement, the presence of many gadolinium ions creates a multimeric effect on the relaxation of water protons due to the increased localised contrast agent concentration …”

“…In 2014, we reported the first example of dithiocarbamates being used to attach gadolinium units to GNPs for potential use in MRI . These materials (Figure b) showed promising relaxivities, however, the hexadentate coordination of the Gd 3+ ion ( q =3) undermined their application due to the potential for loss of the toxic gadolinium ions under physiological conditions.…”

Multimetallic Complexes Based on a Diphosphine-Dithiocarbamate “Janus” Ligand

“…The facial coordination in this complex was inferred previously from spectroscopic data, in contrast to the chromium analogue which is thought to adopt a mer-arrangement. 19 (9), as shown in Fig. 3: (1) …”

“…5a,b,6a Alternatively, addition of further metals to the system can be achieved through the preference of the new metal (e.g., lanthanide ions) for the harder oxygen and nitrogen donors of a macrocycle. 9 While bifunctional phosphine-thiol linkers have been used successfully to modify the surface of nanoparticles, 13 to our knowledge, no linker has been reported which bears both dithiocarbamate and diphosphine functionalities. Given the ubiquity of phosphine ligands in applications of transition metals, this linker was considered a promising route to multimetallic complexes with potential for roles in catalysis.…”

“…4c Our recent contributions in the this area have attempted to tap this potential through manipulation of the NR 2 substituents of dithiocarbamate ligands (e.g., coordination to other metals, [5][6][7] alkene metathesis, 8 ) in order to addressing applications such as d-f hybrids with potential for medical imaging. 9 For over a decade, renewed interest in dithiocarbamates has also focused on their use as surface units for capping gold nanoparticles. 10 Linked to this development, a number of reports have probed the potential of this method for placing metal units on the surface of gold nanoparticles.…”