Diversity of Isomerization Patterns and Protolytic Forms in Aminocarbene Pd^II and Pt^II Complexes Formed upon Addition of N,N′-Diphenylguanidine to Metal-Activated Isocyanides

Abstract

Reaction of the palladium(II) and platinum(II) isocyanide complexes cis-[MCl 2 (CNR) 2 ] [M = Pd, R = C 6 H 3 (2,6-Me 2 ) (Xyl), 2-Cl-6-MeC 6 H 3 , cyclohexyl (Cy), t-Bu, C(Me) 2 CH 2 (Me) 3 (1,1,3,3-tetramethylbuth-1-yl abbreviated as tmbu); M = Pt, R = Xyl, 2-Cl-6-MeC 6 H 3 , Cy, t-Bu, and tmbu] with N,N′-diphenylguanidine (DPG) leads to DPG-derived metal-bound deprotonated acyclic diaminocarbene (ADC) species. This reaction occurs via a two-step process, involving the initial coupling of the guanidine with one of the isocyanides and leading to deprotonated monocarbene monochelated species, while the next addition grants the deprotonated bis-carbene bis-chelated metal compounds. DPG behaves as nucleophile, deprotonating base, and chelator. The addition of DPG proceeded with different regioselectivity depending on the metal center and, in a larger extent, on the substituent R in RNCs. The X-ray diffraction studies for the deprotonated mono-and bis-carbene complexes confirmed the regioisomerism of these species and allowed the identification of ADC protolytic forms stabilized in the solid-state. 1D ( 1 H and 13 C{ 1 H}) and 2D ( 1 H, 1 H-NOESY; 1 H, 15 N-HSQC; 1 H, 15 N-HMBC) solution NMR of the obtained systems demonstrated their configuration isomerism accompanied by prototropic tautomerism. Together, the solid-state and solution data provide an insight into the flexible character of ADC species.

Pyridine‐2(1H)‐thione as a Bifunctional Nucleophile in Reaction with PdII and PtII Aryl Isocyanide Complexes

“…The other one has a length of 1.242–1.271 Å, which is more consistent with the double C=N bond (1.260(1) Å) [27] . This situation was also observed earlier for complexes with azaheterocyclic thions in our previous work, [16] as well as for other deprotonated diaminocarbene complexes [28–30] . The distances between the sulfur and carbon atoms in the cyclometalated fragment are in the range 1.714(1)–1.717(1) Å and are greater than the values for the C=S double bond in the starting pyridinethione (1.692(2) Å) [31] .…”

“…[27] This situation was also observed earlier for complexes with azaheterocyclic thions in our previous work, [16] as well as for other deprotonated diaminocarbene complexes. [28][29][30] The distances between the sulfur and carbon atoms in the cyclometalated fragment are in the range 1.714(1)-1.717(1) Å and are greater than the values for the C=S double bond in the starting pyridinethione (1.692(2) Å). [31] Also, these distances exceed the CÀ S distances in similar complexes based on azole thiones (ca.…”

“…Taking into account the values of the bond lengths for single and double bonds CS (d(C−S)=1.75 Å, d(C=S)=1.64 Å), [32] it can be concluded that the sulfur atoms in cyclometalated fragment of complexes 4 b , 5 b , 6 b , and 7 are predominantly in thiol rather than thionic form. All other bond lengths are in the standard range for bonds of this type [28–30] …”

Metal‐(Acyclic Diaminocarbene) Complexes Demonstrate Nanomolar Antiproliferative Activity against Triple‐Negative Breast Cancer

“…X-Ray analysis of 3 and 7 reveals that the Pd II /Pt II adopts a square planar coordination geometry completed by two C,N-chelated diaminocarbene ligands (Figure 2 and S5.1); in the solid state, similar to the previously reported derivatives, [14] complexes exist as asymmetrically protonated species featuring an intramolecular bifurcated N•••H•••N hydrogen bond (H-bond), which is consistent with their 1 H NMR spectra in solutions (Figures S7.2 and S7.3 in SI).…”

Intra-/Intermolecular Bifurcated Chalcogen Bonding in Crystal Structure of Thiazole/Thiadiazole Derived Binuclear (Diaminocarbene)PdII Complexes

“…These results are accordingly discussed in the sections that follow. In the continuation of our projects focused on metal-mediated reactions of isocyanides [15,[58][59][60][61][62][63][64][65][66][67][68] and on non-covalent interactions [15,58,[69][70][71][72][73][74][75][76][77], we recently reported on the coupling between cis-[PdCl 2 (CNXyl) 2 ] (Xyl = 2,6-Me 2 C 6 H 4 ) and various thiazol-and thiadiazol-2-amines that leads to a mixture of two regioisomeric binuclear diaminocarbene complexes corresponding to kinetically (3a-d) or thermodynamically (4a-d) controlled regioisomers (Scheme 1). There is an equilibrium between these two species in CHCl 3 solutions that depends on the energy difference between two types of intramolecular CBs, viz.…”