Low-field electrodynamics of polycrystalline ternary molybdenum chalcogenides

The penetration of very weak magnetic fields into the polycrystalline low-temperature superconductor SnMo₆S₈ is studied experimentally. The experimental results agree satisfactorily with the theory of the critical state in the framework of low-field electrodynamics. It is found that the critical current density in this case does not depend on the dc magnetic field. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 3, 184–188 (10 February 1999)     

New acyclic aminocarbene palladium(ii) complexes as convenient catalysts for the Sonogashira and Suzuki cross-coupling

A reaction of isocyanide complex cis-[PdCl₂(CNAr)₂] with hydrazones H₂N-N=CR¹R² proceeded at the carbon atom of one of the isocyanide groups and gave the corresponding diaminocarbene isocyanide palladium(ii) complexes. These complexes showed high catalytic activity in the Sonogashira and Suzuki cross-coupling reactions.     

Dramatically Enhanced Solubility of Halide‐Containing Organometallic Species in Diiodomethane: The Role of Solvent⋅⋅⋅Complex Halogen Bonding

In the current study, we evaluated the solubility of a number of organometallic species and showed that it is noticeably improved in diiodomethane when compared to other haloalkane solvents. The better solvation properties of CH₂I₂ were associated with the substantially better σ‐hole‐donating ability of this solvent, which results in the formation of uniquely strong solvent–(metal complex) halogen bonding. The strength of the halogen bonding is attenuated by the introduction of additional halogen atoms in the organometallic species owing to the competitive formation of more favourable intermolecular complex–complex halogen bonding. The exceptional solvation properties of diiodomethane and its inertness towards organometallic species make this solvent a good candidate for NMR studies, in particular, for the acquisition of spectra of insensitive spins.     

The metalla-Pinner reaction between Pt(IV)-bound nitriles and alkylated oxamic and oximic forms of hydroxamic acids

The nitrile ligands in the platinum(IV) complexes trans-[PtCl4(RCN)2] (R=Me, Et, CH2Ph) and cis/trans-[PtCl4(MeCN)(Me2SO)] are involved in a metalla-Pinner reaction with N-methylbenzohydroxamic acid (N-alkylated form of hydroxamic acid, hydroxamic form; F1), PhC(=O)N(Me)OH, to achieve the imino species [PtCl4[NH=C(R)ON(Me)C(=O)Ph]2 (1-3) and [PtCl4[NH=C(Me)ON(Me)C(=O)Ph](Me2SO)] (7), respectively. Treatment of trans-[PtCl4(RCN)2] (R=Me, Et) and cis/trans-[PtCl4(MeCN)(Me2SO)] with the O-alkylated form of a hydroxamic acid (hydroximic form), i.e. methyl 2,4,6-trimethylbenzohydroximate, 2,4,6-(Me3C6H2)C(OMe)=NOH (F2A), allows the isolation of [PtCl4[NH=C(R)ON=C(OMe)(2,4,6-Me3C6H2)]2] (5, 6) and [PtCl4[NH=C(Me)ON=C(OMe)(2,4,6-Me3C6H2)](Me2SO)] (8), correspondingly. In accord with the latter reaction, the coupling of nitriles in trans-[PtCl4(EtCN)2] with methyl benzohydroximate, PhC(OMe)=NOH (F2B), gives [PtCl4[NH=C(Et)ON=C(OMe)Ph]2] (4). The addition proceeds faster with the hydroximic F2, rather than with the hydroxamic form F1. The complexes 1-8 were characterized by C, H, N elemental analyses, FAB+ mass-spectrometry, IR, 1H and 13C[1H] NMR spectroscopies. The X-ray structure determinations have been performed for both hydroxamic and hydroximic complexes, i.e. 2 and 6, indicating that the imino ligands are mutually trans and they are in the E-configuration.     

Kinetic and mechanistic study of the Pt(II) versus Pt(IV) effect in the platinum-mediated nitrile-hydroxylamine coupling

The metal-mediated coupling between coordinated EtCN in the platinum(II) and platinum(IV) complexes cis- and trans-[PtCl(2)(EtCN)(2)], trans-[PtCl(4)(EtCN)(2)], a mixture of cis/trans-[PtCl(4)(EtCN)(2)] or [Ph(3)PCH(2)Ph][PtCl(n)(EtCN)] (n = 3, 5), and dialkyl- and dibenzylhydroxylamines R(2)NOH (R = Me, Et, CH(2)Ph, CH(2)C(6)H(4)Cl-p) proceeds smoothly in CH(2)Cl(2) at 20-25 degrees C and the subsequent workup allowed the isolation of new imino species [PtCl(n){NH=C(Et)ONR(2)}(2)] (n = 2, R = Me, cis-1 and trans-1; Et, cis-2 and trans-2; CH(2)Ph, cis-3 and trans-3; CH(2)C(6)H(4)Cl-p, cis-4 and trans-4; n = 4, R = Me, trans-9; Et, trans-10; CH(2)Ph, trans-11; CH(2)C(6)H(4)Cl-p, trans-12) or [Ph(3)PCH(2)Ph][PtCl(n){NH=C(Et)ONR(2)}] (n = 3, R = Me, 5; Et, 6; CH(2)Ph, 7; CH(2)C(6)H(4)Cl-p, 8; n = 5, R = Me, 13; Et, 14; CH(2)Ph, 15; CH(2)C(6)H(4)Cl-p, 16) in excellent to good (95-80%) isolated yields. The reduction of the Pt(IV) complexes 9-16 with the ylide Ph(3)P=CHCO(2)Me allows the synthesis of Pt(II) species 1-8. The compounds 1-16 were characterized by elemental analyses (C, H, N), FAB-MS, IR, (1)H, (13)C{(1)H}, and (31)P{(1)H} NMR (the latter for the anionic type complexes 5-8 and 13-16) and by X-ray crystallography for the Pt(II) (cis-1, cis-2, and trans-4) and Pt(IV) (15) species. Kinetic studies of addition of R(2)NOH (R = CH(2)C(6)H(4)Cl-p) to complexes [Ph(3)PCH(2)Ph][Pt(II)Cl(3)(EtCN)] and [Ph(3)PCH(2)Ph][Pt(IV)Cl(5)(EtCN)] by the (1)H NMR technique revealed that both reactions are first order in (p-ClC(6)H(4)CH(2))(2)NOH and Pt(II) or Pt(IV) complex, the second-order rate constant k(2) being three orders of magnitude larger for the Pt(IV) complex. The reactions are intermolecular in nature as proved by the independence of k(2) on the concentrations of added EtC triple bond N and Cl(-). These data and the calculated values of Delta H++ and Delta S++ are consistent with the mechanism involving the rate-limiting nucleophilic attack of the oxygen of (p-ClC(6)H(4)CH(2))(2)NOH at the sp-carbon of the C triple bond N bond followed by a fast proton migration.     

Oxidation of Pt-bound bis-hydroxylamine as a novel route to unexplored dinitrosoalkane ligated species

The reaction of K 2[PtCl 4] and HO(H)NCMe 2CMe 2N(H)OH.H 2SO 4 ( BHA.H 2SO 4; 2) in a molar ratio 1:2 at 20-25 degrees C in water affords a mixture of [Pt(BHA) 2][PtCl 4] ( 5) and [Pt(BHA-H) 2] ( 6) ( BHA- H = anionic monodeprotonated form of BHA) which, upon heating at 80-85 degrees C for 12 h or on prolonged keeping at 20-25 degrees C for 2 weeks, is subject to a slow transformation giving [PtCl 2(BHA)] ( 7). The latter compound is also obtained from the reaction between K[PtCl 3(Me 2 SO)] and 2. The chlorination of [PtCl 2(BHA)] ( 7) in freshly distilled dry chloroform leads to the selective oxidation of one N(H)OH group yielding [PtCl 2{HO(H) NCMe 2CMe 2 N=O}] ( 13), while the chlorination in water produces the complex [PtCl 2(O= NCMe 2CMe 2 N=O)] ( 14) bearing the unexplored dinitrosoalkane species. Treatment of 14 with 2 equiv of 1,2-bis-(diphenylphosphino)ethane (dppe) in CH 2Cl 2 results in the liberation of the dinitrosoalkane ligand followed by its fast cyclization giving the alpha-dinitrone (3,3,4,4-tetramethyl-1,2-diazete-1,2-dioxide) in solution and the solid [Pt(dppe) 2](Cl) 2. The Pt (II) complexes with hydroxylamino ( intersection)oximes [PtCl 2{HO(H) NC(Me) 2C(R)= NOH}] (R = Me 8; R = Ph 9) upon their oxidation with Cl 2 in CHCl 3 afford the nitrosoalkane derivatives [PtCl 2{O= NCMe 2C(R)= NOH}] (R = Me 16; Ph 17), respectively, while the corresponding chlorination of the bis-chelates [Pt{HO(H) NCMe 2C(R)= NOH} 2] (R = Me 10; Ph 11) gives [Pt{O= NCMe 2C(R)= NO} 2] (R = Me 18; Ph 19). The formulation of 5- 19 is based on C, H, and N microanalyses, IR, 1D ( (1)H, (13)C{ (1)H}, (195)Pt) and 2D ( (1)H, (1)H-COSY, (1)H, (13)C-HSQC) NMR spectroscopies, and X-ray diffraction for five complexes ( 5, 7, and 12- 14).     

Anomalous behavior of linear and nonlinear longitudinal susceptibilities below T c in a weakly anisotropic CdCr2Se4 ferromagnet

Frequency dependences of the linear and nonlinear longitudinal dynamic susceptibilities of an almost isotropic cubic CdCr₂Se₄ ferromagnet were studied experimentally in the ordered phase. It was found that at frequencies above the two-magnon creation threshold the linear susceptibility decreases as χ₁∝ω^?0.28 with increasing frequency and the nonlinear susceptibility decreases as χ_n∝ω^?0.73, irrespective of n, where n is an odd number. The observed susceptibility anomalies are due to the dipolar forces that violate the conservation of total spin.     

Metal‐Mediated [2+3] Cycloaddition of Nitrones to Palladium‐Bound Isonitriles

[2+3] Cycloadditions! The metal‐mediated [2+3] cycloaddition of acyclic [^?O⁺N(R²)?(H)R³] and nonaromatic cyclic nitrones [^?O⁺N^a?CHCH₂CH₂C^bMe₂(N^a? C^b)] to palladium‐bound isonitriles cis‐[PdCl₂(C?NR)₂] proceeds under mild conditions to furnish novel heterocyclic carbene complexes, which then undergo N? O bond rupture to give imino complexes and free isocyanates (see scheme).