Abstract

Abstract

Abstract

Abstract

Two structurally related bis(imidoylamidine or 1,3,5-triazapentadiene)nickel(II) compounds {Ni[HN=C(3-py)NC(3-py)=NH]₂}·H₂O·MeOH (1) and [Ni{HN=C(3-py)N(H)C(3-py)=NH}₂]Cl₂ (2) with symmetrical 3-pyridyl (3-py) substituents have been prepared by direct 2-butanone oxime mediated transformation of 3-cyanopyridine in the presence of Ni(MeCO₂)₂·4H₂O or NiCl₂·2H₂O, respectively. Compounds 1 and 2 have been characterized by elemental analyses, IR, ¹H and ¹³C{¹H} NMR spectroscopy, and FAB⁺ mass spectrometry, while their slow recrystallization in air from organic solvents revealed a high affinity for water and resulted in the formation of the derived compounds [Ni{HN=C(3-py)NC(3-py)=NH}₂]·6H₂O (1′) and [Ni{HN=C(3-py)N(H)_0.5C(3-py)=NH}₂]Cl·2H₂O (2′). Single-crystal X-ray diffraction analyses allowed the identification of discrete hexameric water or hybrid water–chloride clusters hosted by the crystal matrixes of 1′ and 2′, respectively. Both the (H₂O)₆ and [(H₂O)₄(Cl)₂]^2– clusters possess similar geometries and consist of cyclic planar tetranuclear (H₂O)₄ or [(H₂O)₂(Cl)₂]^2– cores with two dangling water molecules. These water associates occupy voids in the crystal cells and display extensive H-bonding interactions with monomeric nickel–organic units, thus playing a key role in the formation of 3D hydrogen-bonded supramolecular assemblies. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

The reaction between the nitrile oxides 2,4,6-R₃C₆H₂CNO (R = Me, OMe) and trans-[PdCl₂(RCN)₂], or RCN (R = Me, Et, CH₂CN, NMe₂, Ph) in the presence of PdCl₂, proceeded smoothly under mild conditions and allowed the isolation of the 1,2,4-oxadiazole complexes trans-[PdCl₂{N^a=C(R)-ON=C^b(C₆H₂R₃)(N^a–C^b)}₂] (1–8) in 40–85 % yields. In CH₂Cl₂, the reaction between 2,4,6-R₃C₆H₂CNO and [PdCl₂(MeCN)₂] furnishes [PdCl₂(ONCC₆H₂R₃)₂] (9 and 10), which are the first representatives of metal compounds where nitrile oxides act as ligands. The 1,2,4-oxadiazole complexes 1–8 were characterized by elemental analysis, FAB mass spectrometry, and IR, ¹H and ¹³C{¹H} NMR spectroscopy, while 2, 3, 7, and 8 were additionally characterized by X-ray crystallography. The liberation of the heterocyclic species from 1–8 was successfully performed by substitution reaction either with 1,2-bis(diphenylphosphanyl)ethane or with an excess amount of Na₂S·7H₂O in MeOH; the liberated 1,2,4-oxadiazoles (11–18) were characterized by positive-ion FAB mass spectrometry and ¹H and ¹³C{¹H} NMR spectroscopy. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Refluxing PdCl₂ with the ketoximes R¹R²C=NOH (R¹R² = MeMe, MeEt, C₅H₁₀) in RCN (R = Me, Et, nPr, Ph) for 2–3 h results in precipitation of the oxime complexes [PdCl₂(R¹R²C=NOH)₂], whereas further reflux of the reaction mixture for an additional 6–12 h leads to formation of the chelated species [PdCl₂{NH=C(R)ON=CR¹R²-κ²N}] (R/R¹R² = Me/MeMe 1; Et/MeMe 2; nPr/MeMe 3; Me/MeEt 4; Me/C₅H₁₀5; Ph/MeMe 6) by a Pd^II-mediated coupling between the oximes and the nitriles; complexes 1–6 were isolated in the solid state in 60–75 % yields. The reaction time could be drastically reduced, to 15–30 min, when the system was additionally irradiated with microwaves (100 W, about 60 °C). Compounds 1–6 can also be obtained without isolation of the intermediate oxime complexes either by refluxing for 8–15 h or by microwave irradiation (100 W, about 60 °C) for 15–30 min. The formulation of 1–6 is based upon satisfactory C, H, and N elemental analyses, FAB mass spectrometry, and IR, ¹H and ¹³C{¹H} NMR spectroscopy, while the structures of 1·(Me₂CO), 1·(CHCl₃), 2·(H₂O), and 6·½(H₂O) were determined by X-ray single-crystal diffraction. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

The reaction between the nitrone p-MeC₆H₄CH=N(Me)O and trans-[PdCl₂(RCN)₂] (R = Ph, Me) in the corresponding RCN (or of the nitrone in neat RCN in the presence of PdCl₂) proceeds at 45 °C (R = Ph) or reflux (R = Me) for 1 d and allows the isolation of the Δ⁴-1,2,4-oxadiazoline complexes [PdCl₂{N^a=C(R)ON(Me)C^bH(C₆H₄Me-p)}₂(N^a–C^b)] (R = Ph 1; R = Me 2) in ca. 50 and ca. 15 % yields, respectively. The reaction time can be drastically reduced by focused microwave irradiation of the reaction mixture. In CH₂Cl₂ or acetone, this reaction proceeds in another direction to achieve the unstable nitrone complex [PdCl₂{ON(Me)=CH(C₆H₄Me-p)}₂] (3), which was characterized by electrospray mass spectrometry, IR and ¹H NMR spectroscopy. Complex 3 is the first representative of (nitrone)Pd^II compounds and is the key intermediate in at least two further reactions, i.e. cyclopalladation to give the dimeric complex [Pd₂(μ-Cl)₂{ON(Me)=C(H)C₆H₃Me-p}₂] (5; 30 % isolated yield) and deoxygenation of the nitrone to furnish the imine compound [PdCl₂{N(Me)=CH(C₆H₄Me-p)}₂] (4). The palladium complexes 1, 2, 4 and 5 were characterized by C, H, and N analyses, FAB-MS, IR, ¹H and ¹³C{¹H} spectroscopy, while 4 and 5 additionally by X-ray crystallography. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

The reaction of trans-[PtCl₄(EtCN)₂] and two equivalents of the formamides RR′NCHO (R/R′ = Me/Me, Me/H, tBu/H) in CH₂Cl₂ led to the formation of the compounds cis-[PtCl₄{(O=)CHNRR′}₂], two of which (R/R′ = Me/H, tBu/H) were characterized by X-ray single-crystal diffractometry, as well as by elemental analysis, FAB⁺-MS, and IR, ¹H, ¹³C and ¹⁹⁵Pt NMR spectroscopy (including NOE, HMQC and INEPT experiments). The X-ray structures and IR spectroscopic data indicate the coordination of the formamides through the O atom and significant contribution of the bipolar structure ⁻O−C(H)=⁺NHR in the resonance hybrid of the ligands. The complexes cis-[PtCl₄{(O=)CHNRR′}₂] represent the first example of (formamide)Pt^IV species and also a rare case of platinum(IV) complexes with neutral O-donor ligands.

The reaction of K₂[PtCl₄] and salicylaldoxime in an approximate 1:2 molar ratio in water resulted in the isolation of a mixture of four compounds from which [Pt(o-OC₆H₄CH=NOH)₂] (1) and [PtCl(OC₆H₄CH=NOH)(HOC₆H₄CH=NOH)] (2) were isolated, whereas the other two were shown to be unstable and decomposed both in solution and on SiO₂ during chromatography. Chlorination of 1 and 2 with Cl₂ resulted in the oxidative addition of chlorine to the platinum(II) center and in the chlorination of the benzene ring, giving the platinum(IV) complexes [PtCl₂(3,5,2-Cl,Cl,OC₆H₂CH=NOH)₂] (3) and [PtCl₃(3,5,2-Cl,Cl,OC₆H₂CH=NOH)(3,5,2-Cl,Cl,HOC₆H₂CH=NOH)] (5), respectively, containing commercially unavailable 3,5-dichloro-2-hydroxybenzaldehye oxime. Alternatively, treatment of 1 with NOCl resulted only in the oxidation of the platinum(II) center to furnish [PtCl₂(o-OC₆H₄CH=NOH)₂] (4), whereas the benzene rings of salicylaldoximato ligands remained intact. All complexes were characterized by C, H, N, Cl and Pt elemental analyses, FAB⁺ mass spectrometry, IR and ¹H, ¹³C{¹H} and ¹⁹⁵Pt NMR spectroscopy. Compounds 1, 3 and 5 were analyzed by X-ray crystallography. In 1, the salicylaldoximato ligands adopt a trans configuration and the hydrogen atoms of the OH groups are involved in intramolecular hydrogen bonding, forming five-membered rings. In 3, every molecule of the complex forms the repeating unit for a self-assembly that produces infinite one-dimensional polymeric chains directed along the z axis held by hydrogen bonds. The complex 5 represents the first example of a structurally characterized metal complex with a monodentate salicylaldoxime-type ligand, although the conventional bidentate N,O-coordination mode is a classical topic in coordination chemistry.

Heating of [RhCl₃(MeCN)₃] in benzyl cyanide at 100 °C gives the substitution product mer-[RhCl₃(PhCH₂CN)₃] (90% yield), whose recrystallization from an acetone/toluene mixture leads to formation of the toluene solvate mer-[RhCl₃(PhCH₂CN)₃]·1/2 C₆H₅Me. The crystal structure of the latter, determined by X-ray single-crystal diffractometry, shows an unusual self-assembly due to intermolecular CH···Cl hydrogen bonding with concomitant clathration of toluene. Diffusion of ammonia into a solution of mer-[RhCl₃(PhCH₂CN)₃] in neat benzyl cyanide brings about a facile rhodium(III)-assisted addition of NH₃ to the coordinated nitrile species to produce the amidine complex mer-[RhCl₃{PhCH₂C(NH₂)=NH}₃] (83% yield). Both starting material and the product were characterized by elemental analyses, FAB-MS, IR and ¹H and ¹³C{¹H} NMR spectroscopy. The crystal structure of mer-[RhCl₃{PhCH₂C(NH₂)=NH}₃] provides the first example of a rhodium(III) complex with a monodentate amidine ligand.