Ways in which osocyanides are used in organic chemistry are examined. Chemoselectivity and bond-making processes in relation to MCRs are also reviewed.
This review is focused on the analysis of current data on new methods of alkenylation of arenes and heteroarenes with alkynes by transition metal catalyzed reactions, Bronsted/Lewis acid promoted ...transformations, and others. The synthetic potential, scope, limitations, and mechanistic problems of the alkenylation reactions are discussed. The insertion of an alkenyl group into aromatic and heteroaromatic rings by inter- or intramolecular ways provides a synthetic route to derivatives of styrene, stilbene, chalcone, cinnamic acid, various fused carbo- and heterocycles, etc.
This review highlights recent studies discovering unconventional halogen bonding (HaB) that involves positively charged metal centers. These centers provide their filled d‐orbitals for HaB, and thus ...behave as nucleophilic components toward the noncovalent interaction. This role of some electron‐rich transition metal centers can be considered an oxymoron in the sense that the metal is, in most cases, formally cationic; consequently, its electron donor function is unexpected. The importance of Ha⋅⋅⋅d‐M (Ha=halogen; M is Group 9 (Rh, Ir), 10 (Ni, Pd, Pt), or 11 (Cu, Au)) interactions in crystal engineering is emphasized by showing remarkable examples (reported and uncovered by our processing of the Cambridge Structural Database), where this Ha⋅⋅⋅d‐M directional interaction guides the formation of solid supramolecular assemblies of different dimensionalities.
Metal centers provide their filled d‐orbitals for halogen bonding, and behave as nucleophilic components toward the noncovalent interaction.
This review classifies and summarizes the past 10–15 years of advancements in the field of metal-involving (i.e., metal-mediated and metal-catalyzed) reactions of oximes. These reactions are diverse ...in nature and have been employed for syntheses of oxime-based metal complexes and cage-compounds, oxime functionalizations, and the preparation of new classes of organic species, in particular, a wide variety of heterocyclic systems spanning small 3-membered ring systems to macroheterocycles. This consideration gives a general outlook of reaction routes, mechanisms, and driving forces and underlines the potential of metal-involving conversions of oxime species for application in various fields of chemistry and draws attention to the emerging putative targets.
•Synthesis, properties, and identification of metal-free amidoximes.•Synthesis and structural features of amidoxime complexes.•Comparison of chemistry of amidoximes with that of conventional ...oximes.•Metal-mediated and metal-catalyzed reactions involving uncomplexed amidoximes.•Reactions of amidoxime ligands.
Although the versatile chemistry of conventional oximes has been extensively reviewed over the years in both the organic chemistry literature and the coordination chemistry literature, amidoximes, RC(NH2)NOH, have so far received substantially less attention. Taking into account the increased publication activity on the subject, we systematically review the data on the routes for preparation of amidoxime complexes, the coordination patterns of ligands, and the classification of metal-involving reactions of amidoxime species. This survey includes a comparison of the coordination chemistry and metal-involving reactions of amidoximes with those of conventional ketoximes and aldoximes.
Platinum(II) complexes exhibiting an expressed d z 2 -nucleophilicity of the positively charged metal centers, namely, Pt(ppy)(acac) (1; acacH is acetylacetone; ppyH is 2-Ph-pyridine) and ...Pt(ppy)(tmhd) (2; tmhdH is 2,2,6,6-tetramethylheptanedione-3,5), were cocrystallized with the chalcogen bond donors (4-NC5F4)2Ch (Ch = Se, Te) to form two isostructural cocrystals 1·1/2(4-NC5F4)2Ch, and 2·2/3(4-NC5F4)2Se and 2·(4-NC5F4)2Te. The X-ray data for these cocrystals and appropriate theoretical DFT calculations (PBE0-D3BJ) allowed the recognition of the metal-involving chalcogen bond, namely, Ch···d z 2-PtII (its energy spans from −7 to −12 kcal/mol). In 1·1/2(4-NC5F4)2Ch, Ch···d z 2 -PtII bonding is accompanied by the C···d z 2-PtII interaction, representing a three-center bifurcate, whereas in 2·(4-NC5F4)2Te the chalcogen bond Te···d z 2-PtII is purely two-centered and is stronger than that in 1·1/2(4-NC5F4)2Ch because of more efficient orbital overlap. The association of 2 with (4-NC5F4)2Te and the structure of the formed adduct in CDCl3 solutions was studied by using 1H, 13C, 19F, 195Pt, 125Te NMR, 19F–1H HOESY, and diffusion NMR methods. The 195Pt and 125Te NMR titration and the isothermal titration calorimetry results revealed a 1:1 association of 2 with (4-NC5F4)2Te.
The nucleophilic addition of 3-(4-cyanopyridin-2-yl)-1,1-dimethylurea (1) to cis-Pt(CNXyl)2Cl2 (2) gave a new cyclometallated compound 3. It was characterized by NMR spectroscopy (1H, 13C, 195Pt) and ...high-resolution mass spectrometry, as well as crystallized to obtain two crystalline forms (3 and 3·2MeCN), whose structures were determined by X-ray diffraction. In the crystalline structure of 3, two conformers (3A and 3B) were identified, while the structure 3·2MeCN had only one conformer 3A. The conformers differed by orientation of the N,N-dimethylcarbamoyl moiety relative to the metallacycle plane. In both crystals 3 and 3·2MeCN, the molecules of the Pt(II) complex are associated into supramolecular dimers, either {3A}2 or {3B}2, via stacking interactions between the planes of two metal centers, which are additionally supported by hydrogen bonding. The theoretical consideration, utilizing a number of computational approaches, demonstrates that the C···dz2(Pt) interaction makes a significant contribution in the total stacking forces in the geometrically optimized dimer 3A2 and reveals the dz2(Pt)→π*(PyCN) charge transfer (CT). The presence of such CT process allowed for marking the C···Pt contact as a new example of a rare studied phenomenon, namely, tetrel bonding, in which the metal site acts as a Lewis base (an acceptor of noncovalent interaction).
The complex Ni(S2COEt)2 (1) and 1,4-diiodotertafluorobenzene (1,4-FIB) or 1,3,5-triiodotrifluorobenzene (1,3,5-FIB) were cocrystallized to form solid adducts 1·2(1,4-FIB) and 1·2(1,3,5-FIB), ...respectively; the structures of the adducts were studied by X-ray crystallography. The introduction of any one of the FIBs dramatically changed the supramolecular architecture of 1, and the structure-directing interactions changed from predominantly Ni···S semicoordination (in 1) to I···S halogen bonding between an FIB and the electron-donating S atoms of 1 (in the adducts). The semicoordination bond breaking and halogen bond making upon the interaction of 1 with the FIBs make the employed crystal engineering approach relevant (or even similar) to the molecular synthesis of metal species. The DFT study indicates that the strength of both types of interactions in the adducts are comparable (−3.0 to −4.9 kcal/mol and −4.3 to −4.9 kcal/mol) but very different in regard to their physical nature. If the electrostatics determine the I···S halogen bonds, the Ni···S semicoordination bonding is basically dominated by orbital effects.
2,3,5,6-Tetramethyl-1,4-diisocyanobenzene (1), 1,4-diisocyanobenzene (2), and 1,4-dicyanobenzene (3) were co-crystallized with 1,3,5-triiodotrifluorobenzene (1,3,5-FIB) to give three cocrystals, ...1·1,3,5-FIB, 2·2(1,3,5-FIB), and 3·2(1,3,5-FIB), which were studied by X-ray diffraction. A common feature of the three structures is the presence of I···Cisocyanide or I···Nnitrile halogen bonds (HaBs), which occurs between an iodine σ-hole and the isocyanide C-(or the nitrile N-) atom. The diisocyanide and dinitrile cocrystals 2·2(1,3,5-FIB) and 3·2(1,3,5-FIB) are isostructural, thus providing a basis for accurate comparison of the two types of noncovalent linkages of C≡N/N≡C groups in the composition of structurally similar entities and in one crystal environment. The bonding situation was studied by a set of theoretical methods. Diisocyanides are more nucleophilic than the dinitrile and they exhibit stronger binding to 1,3,5-FIB. In all structures, the HaBs are mostly determined by the electrostatic interactions, but the dispersion and induction components also provide a noticeable contribution and make the HaBs attractive. Charge transfer has a small contribution (<5%) to the HaB and it is higher for the diisocyanide than for the dinitrile systems. At the same time, diisocyanide and dinitrile structures exhibit typical electron-donor and π-acceptor properties in relation to the HaB donor.
The nitrosoguanidinate complexes Ni{NHdouble bond, length as m-dashC(NR
)NN(O)}
(R
= Me
1, (CH
)
O 2, (CH
)
3, (CH
)
4, (Me)Ph 5, Ph
6, (p-MeC
H
)
7) were obtained in low-to-moderate (12-26%) yields ...but reproducible yields in an unexpected metal-mediated reaction in MeOH between the nickel salt NiCl
·2H
O, N,N-disubstituted cyanamides NCNR
, and the amidoxime MeC(double bond, length as m-dashNOH)NH
. These complexes were formed along with a spectrum of cyanamide-oxime coupling products. The IR and X-ray data indicate the delocalization within the NNO and NCN systems of the nitrosoguanidinate ligand. This delocalization was additionally confirmed by inspection of Wiberg bond indices for the selected bonds. In the X-ray structure of 5, the rare metallophilic contacts NiNi between stacks of the square-planar complexes were detected and these non-covalent interactions were studied by non-relativistic and relativistic DFT calculations and topological analysis of the electron density distribution within the framework of Bader's theory (QTAIM method). The estimated strength of the NiNi interactions is 1.3-1.9 kcal mol
and they are mostly determined by crystal packing effects and weak attractive interactions between adjacent metal centers due to the overlapping of their d
and p
orbitals.
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