Mikhail A. Kinzhalov

Difference in Energy between Two Distinct Types of Chalcogen Bonds Drives Regioisomerization of Binuclear (Diaminocarbene)PdII Complexes

The reaction of cis-[PdCl2(CNXyl)2] (Xyl = 2,6-Me2C6H3) with various 1,3-thiazol- and 1,3,4-thiadiazol-2-amines in chloroform gives a mixture of two regioisomeric binuclear diaminocarbene complexes. For 1,3-thiazol-2-amines the isomeric ratio depends on the reaction conditions and kinetically (KRs) or thermodynamically (TRs) controlled regioisomers were obtained at room temperature and on heating, respectively. In CHCl3 solutions, the isomers are subject to reversible isomerization accompanied by the cleavage of Pd-N and C-N bonds in the carbene fragment XylNCN(R)Xyl. Results of DFT calculations followed by the topological analysis of the electron density distribution within the formalism of Baders theory (AIM method) reveal that in CHCl3 solution the relative stability of the regioisomers (ΔGexp = 1.2 kcal/mol; ΔGcalcd = 3.2 kcal/mol) is determined by the energy difference between two types of the intramolecular chalcogen bonds, viz. S···Cl in KRs (2.8-3.0 kcal/mol) and S···N in TRs (4.6-5.3 kcal/mol). In the case of the 1,3,4-thiadiazol-2-amines, the regioisomers are formed in approximately equal amounts and, accordingly, the energy difference between these species is only 0.1 kcal/mol in terms of ΔGexp (ΔGcalcd = 2.1 kcal/mol). The regioisomers were characterized by elemental analyses (C, H, N), HRESI+-MS and FTIR, 1D (1H, 13C{1H}) and 2D (1H,1H-COSY, 1H,1H-NOESY, 1H,13C-HSQC, 1H,13C-HMBC) NMR spectroscopies, and structures of six complexes (three KRs and three TRs) were elucidated by single-crystal X-ray diffraction.

Metal-mediated coupling of a coordinated isocyanide and indazoles

A reaction between equimolar amounts of cis-[PdCl2(CNCy)2] (1) and indazole (HInd, 2) or 5-methylindazole (HInd(Me), 3) proceeded in refluxing CHCl3 for ca. 6 h affording the aminocarbene species cis-[PdCl2{C(Ind)=N(H)Cy}(CNCy)] (4) or cis-[PdCl2{C(Ind(Me))=N(H)Cy}(CNCy)] (5) in good (72-83%) isolated yields. Complexes 4 and 5 were characterized by elemental analyses (C, H, N), HR ESI(+)-MS, IR, and 1D ((1)H, (13)C{(1)H}) and 2D ((1)H,(1)H-COSY, (1)H,(13)C-HMQC/(1)H,(13)C-HSQC, (1)H,(13)C-HMBC) NMR spectroscopies, and complex 4 as well by X-ray diffraction. The observed coupling represents the first example of metal-mediated integration between any isocyanide and any aromatic heterocyclic system having an HN center.

Coupling of C-amino aza-substituted heterocycles with an isocyanide ligand in palladium(ii) complex

The reaction of cis-dichlorobis(2,6-xylylisocyanide)palladium(ii) with 2-aminopyrazine affords a binuclear palladium complex, in which one of the metal atoms is involved in the palladacyclic ligand. In the contrast, the coupling of isocyanide ligands in cis-dichlorobis-(2,6-xylylisocyanide)palladium(ii) with another C-amino aza-substituted heterocycle, viz.,4-acetyl-3-amino-5-methylpyrazole, gives a mononuclear cationic palladium diaminocarbene complex. Both compounds were characterized by elemental analysis, IR spectroscopy, 1H, 13C{1H}, DEPT90/DEPT135, and 1H,13C-HSQC/1H,13C-HMBC NMR spectroscopy, high-resolution electrospray ionization mass spectrometry, and X-ray diffraction.

Addition of N-nucleophiles to gold(iii)-bound isocyanides leading to short-lived gold(iii) acyclic diaminocarbene complexes

Reaction of [AuCl3(CNR1)] (R1 = Xyl, Cy, (S)-CHMePh) with amines unexpectedly proceeds via the redox pathway giving gold(I)–isocyanides and imines, while the addition of benzophenone hydrazone to the isocyanide ligand in [AuCl3(CNR1)] at RT leads to short-lived gold(III) acyclic diaminocarbene complexes [AuCl3{C(NHNCPh2)NHR1}].

PdII-mediated integration of isocyanides and azide ions might proceed via formal 1,3-dipolar cycloaddition between RNC ligands and uncomplexed azide

Reaction between equimolar amounts of trans-[PdCl(PPh3)2(CNR)][BF4] (R = t-Bu 1, Xyl 2) and diisopropylammonium azide 3 gives the tetrazolate trans-[PdCl(PPh3)2(N4t-Bu)] (67%, 4) or trans-[PdCl(PPh3)2(N4Xyl)] (72%, 5) complexes. 4 and 5 were characterized by elemental analyses (C, H, N), HRESI+-MS, 1H and 13C{1H} NMR spectroscopies. In addition, the structure of 4 was elucidated by a single-crystal X-ray diffraction. DFT calculations showed that the mechanism for the formal cycloaddition (CA) of N3− to trans-[PdCl(PH3)2(CNMe)]+ is stepwise. The process is both kinetically and thermodynamically favorable and occurs via the formation of an acyclic NNNCN-intermediate. The second step of the formal CA, i.e. cyclization, is rate limiting. Despite the fact that the substitution of CNMe by the N3− ligand is slightly thermodynamically favorable, we were unable to find paths on the potential energy surface for hypothetical CA between uncomplexed isocyanide and palladium-bound azide. Thus, we believe that the experimentally observed palladium tetrazolate complexes are, in fact, generated from the negatively charged uncomplexed azide and the positively charged metal-bound isocyanide species, and this reaction path is favorable from the viewpoint of Coulomb attraction.

Crystal structure of cis-[PdCl2(CNMes)2]

The interaction between PdCl2(CH3CN)2 and 2,4,6-Me3C6H2NC (MesNC) proceeds with the substitution of acetonitrile ligands and leads to the synthesis of a cis-[PdCl2(MesNC)2] complex. The structure of this compound is determined by single crystal X-ray diffraction (XRD). The complex has a slightly distorted square-planar structure of the metal center with two cis-positioned isocyanide ligands. In both CN isocyanide moieties the triple bonds have lengths similar to the lengths of the respective bonds in other isocyanide complexes. In the structure, the cis-[PdCl2(MesNC)2] complexes are bound by weak С–H∙∙∙Cl hydrogen bonds and π-stacking interactions.

Halides Held by Bifurcated Chalcogen–Hydrogen Bonds. Effect of μ(S,N–H)Cl Contacts on Dimerization of Cl(carbene)PdII Species

The reaction of cis-[PdCl2(CNCy)2] (1) with thiazol-2-amines (2-10) leads to the C,N-chelated diaminocarbene-like complexes [PdCl{ C(N(H)4,5-R2-thiazol-2-yl)NHCy}(CNCy)] (11-14; 82-91%) in the case of 4,5-R2-thiazol-2-amines (R, R = H, H (2), Me, Me (3), -(CH2)4- (4)) and benzothiazol-2-amine (5) or gives the diaminocarbene species cis-[PdCl2{C(N(H)Cy)N(H)4-R-thiazol-2-yl}(CNCy)] (15-19; 73-93%) for the reaction with 4-aryl-substituted thiazol-2-amines (R = Ph (6), 4-MeC6H4 (7), 4-FC6H4 (8), 4-ClC6H4 (9), 3,4-F2C6H3 (10)). Inspection of the single-crystal X-ray diffraction data for 15-17 and 19 suggests that the structures of all these species exhibit previously unrecognized bifurcated chalcogen-hydrogen bonding μ(S,N-H)Cl and also PdII···PdII metallophilic interactions. These noncovalent interactions collectively connect two symmetrically located molecules of 15-17 and 19, resulting in their solid-state dimerization. The existence of the μ(S,N-H)Cl system and its strength (6-9 kcal/mol) were additionally verified/estimated by a Hirshfeld surface analysis and DFT calculations combined with a topological analysis of the electron density distribution within the formalism of Baders theory (AIM method) and NBO analysis. The observed noncovalent interactions are jointly responsible for the dimerization of 15-19 not only in the solid phase but also in CHCl3 solutions, as predicted theoretically by DFT calculations and confirmed experimentally by FTIR, HRESI-MS, 1H NMR, and diffusion coefficient NMR measurements. Available CCDC data were processed under the new moiety angle, and the observed μ(S,E-H)Cl systems were classified accordingly to E (E = N, O, C) type atoms.

1,4-Dihydrophosphinolines and their complexes with group 10 metals

Syntheses and characterizations of novel phosphaheterocycles, 1-phenyl-4,4-dimethyl-1,4-dihydrophosphinoline (2a) and 1-phenyl-2-bromo-4,4-dimethyl-1,4-dihydrophosphinoline (2b), and their complexes with Pd(II) and Pt(II) are described. Reduction of 1-phenyl-4,4-dimethyl-1,4-dihydrophosphinoline 1-oxide (1a) and 1-phenyl-2-bromo-4,4-dimethyl-1,4-dihydrophosphinoline 1-oxide (1b) using trichlorosilane in refluxing benzene gave the target phosphines in a yield of 83–87%. Reactions of phosphines with acetonitrile complexes of Pd(II) (3) and Pt(II) (4) yielded bis(phosphine) species [MCl2L2] (5–8). Complexes 5–8 were characterized by 1H, 13C, 31P, 195Pt NMR and HRMS. The structures of all these new complexes were determined with single crystal X-ray diffraction. The configuration of the complexes in a CDCl3 solution was investigated via comparing of 31P NMR data in solution and solid state.

Iridium(III)-catalysed cross-linking of polysiloxanes leading to the thermally resistant luminescent silicone rubbers

Cyclometallated iridium(III) complexes with 2-phenylpyridine [Ir(ppy)2(CNR)Cl] (ppy = (2-phenylpyridinato-C2,N), R = Xyl, Mes), [Ir(ppy)2(CNR)2](OTf) (R = Xyl, Mes), and fac-[Ir(ppy)3] catalyse the cross-linking of polysiloxanes exclusively at temperatures above 100 °C leading to luminescent rubbers.

Ligation-Enhanced π-Hole···π Interactions Involving Isocyanides: Effect of π-Hole···π Noncovalent Bonding on Conformational Stabilization of Acyclic Diaminocarbene Ligands

The reaction of cis-[PdCl2(CNXyl)2] (Xyl = 2,6-Me2C6H3) with the aminoazoles [1 H-imidazol-2-amine (1), 4 H-1,2,4-triazol-3-amine (2), 1 H-tetrazol-5-amine (3), 1 H-benzimidazol-2-amine (4), 1-alkyl-1 H-benzimidazol-2-amines, where alkyl = Me (5), Et (6)] in a 2:1 ratio in the presence of a base in CHCl3 at RT proceeds regioselectively and leads to the binuclear diaminocarbene complexes [(ClPdCNXyl)2{μ-C(N-azolyl)N(Xyl)C═NXyl}] (7-12; 73-91%). Compounds 7-12 were characterized by C, H, N elemental analyses, high-resolution ESI+-MS, Fourier transform infrared spectroscopy, 1D (1H, 13C) and 2D (1H,1H-COSY, 1H,1H-NOESY, 1H,13C-HSQC, 1H,13C-HMBC) NMR spectroscopies, and X-ray diffraction (XRDn). Inspection of the XRDn data and results of the Hirshfeld surface analysis suggest the presence in all six structures of intramolecular π-holeisocyanide···πarene interactions between the electrophilic C atom of the isocyanide moiety and the neighboring arene ring. These interactions also result in distortion of the Pd-C≡N-Xyl fragment from the linearity. Results of density functional theory calculations [M06/MWB28 (Pd) and 6-31G* (other atoms) level of theory] for model structures of 7-9 followed by the topological analysis of the electron density distribution within the framework of Baders theory (QTAIM method) reveal the presence of these weak interactions also in a CHCl3 solution, and their calculated strength is 1.9-2.2 kcal/mol. The natural bond orbital analysis of 7-9 revealed that π(C-C)Xyl → π*(C-N)isocyanide charge transfer (CT) takes place along with the intramolecular π-holeisocyanide···πarene interactions. The observed π(C-C)Xyl → π*(C-N)isocyanide CT is due to ligation of the isocyanide to the metal center, whereas in the cases of the uncomplexed p-CNC6H4NC and CNXyl species, the effects of CT are negligible. Available CCDC data were processed from the perspective of isocyanide-involving π-hole···π interactions, disclosed the role of metal coordination in the π-hole donor ability of isocyanides, and verified the π-holeisocyanide···πarene interaction effect on the stabilization of the in-conformation in metal-bound acyclic diaminocarbenes.