Carlo Castellari

On the stabilization of five-coordinate trigonal-bipyramidal palladium(II) species. Crystal structure of (2,9-dimethyl-1,10-phenanthroline)methylchloropalladium(II)

Abstract The role of the steric requirements of the NN′ chelate ligand in the stabilization of trigonal-bipyramidal [Pd(NN′)(olefin)RX] complexes is discussed. The crystal structure of the precursor (2,9-dimethyl-1,10,phenanthroline)methylchloropalladium(II) (1a) has been determined. The molecule adopts a significantly distorted square-planar coordination geometry in order to accomodate the crowding in the coordination plane. The most significant distortions involves the coordinated methyl group and the dimethylphenanthroline molecule, whose mean plane lies out of the coordination plane by 39.3°. There is ready CO insertion into the PdMe bond of 1a to give an acyl derivative. The formation of a five-coordinate acyl derivative by subsequent uptake of an olefin also illustrates the importance of the steric effects of NN′ ligands.

A NEW ROUTE TO AMINOSUGARS FROM SUGAR NITRONES : SYNTHESIS OF 6-DEOXYNOJIRIMYCIN

Abstract The 1,3-addition of methylmagnesium chloride to dialdose derived nitrones 3 and 7 afforded N- benzylhydroxylamines 4 5 and 8 9 , respectively, in high yields. The stereoselectivity of the addition reaction was improved by the use of trimethylsilyl triflate. The NO bond reductive cleavages of N-benzylhydroxylamines took place in good yields and offered an easy access to N-benzylaminosugars. The potential of these aminosugars is demonstrated by the synthesis of glycosidase inhibitor 6-deoxynojirimycin 1a.

Synthesis and characterization of five-coordinate platinum(II) complexes [Pt(2,9-dimethyl-1,10-phenanthroline) (SnRnX3-n)X(olefin)] (X

Abstract Five-coordinate olefin complexes of platinum(II) of the general formula [Pt(2,9-Me2-1,10-phen)(SnRnX3-n)X(olefin)] have been synthesized through oxidative addition of organotin halides RnSnX4-n to three-coordinate platinum(O) complexes [Pt(2,9-Me2-1,10-phen)(olefin)]. The X-ray crystal structure of the title complex has been determined. This crystallizes in the monoclinic system, space group P21/n with a = 13.858(8), b = 13.730(6), c = 16.820(8) A, β = 102.44(5)°, and Z = 4. Refinement converged at R = 0.04 (Rw = 0.044). The geometry of the five-coordinate platinum complex is bipyramidal, with anionic ligands inapical positions and the olefinic double bond in the equatorial plane. Some general features of the addition process, and the structural and NMR properties of the complexes, are also discussed.

Lewis-acid promoted addition of 2-trimethylsilyloxyfuran to nitrones: Synthesis and absolute configuration of tetrahydro-2-benzyl-3-(1-benzyloxyethyl)-furo[2,3-d]isoxazol-5(2H)ones

Abstract A straightforward synthesis of tetrahydro-2-benzyl-3-(1-benzyloxyethyl)-furo[2,3-d]isoxazol-5(2H)ones is reported, based on the Lewis acid-catalysed addition of 2-trimethylsilyloxyfuran to the N-benzyl nitrone of (S)-lactaldehyde.

New cationic five-coordinate monoolefin hydrocarbyl complexes of platinum(II)

Abstract Cationic trigonal bipyramidal complexes of the type [PtRL(NN′)(olefin)]BF 4 with various hydrocarbyl (R), neutral monodentate (L), and bidentate nitrogen (NN′) ligands have been prepared and characterized by elemental analysis, conductivity measurements, and 1 H NMR spectroscopy. The coordination around Pt II is trigonal bipyramidal, with the olefin and the NN′ ligand in equatorial positions. The reversible loss of the olefin is markedly affected by the nature of the apical ligand L, which also influences stereochemical aspects, and by the steric requirements of NN′.

An investigation of the viscoelastic properties of molten polypropylene

Two series of polypropylene samples of different molecular weight, the first obtained directly from polymerization reactions and the second from controlled thermal degradation, were studied by dynamic testing in the melt state. Several viscoelastic parameters were determined, and correlated with weight-average molecular weightMw. It is found that theMw-dependence of the two series is rather different.

Five-coordinate hydrido-complexes [PtX(H)(N,N-chelate)(olefin)] (X Cl, Br or I). Crystal structure of [PtCl(H)(2,9-Me2-1,1O-phenanthroline)(dimethyl maleate)]

Abstract The title compounds were obtained by oxidative addition of hydrogen halides to suitable [Pt( N,N -chelate) (olefin)] species. The properties of the ligands and of the electrophile which allow the isolation of stable products must meet very strict requirements. The crystal structure of [PtCl(H)(2,9-Me 2 -1,1O-phenanthroline) (dimethyl maleate)] was determined by single-crystal X-ray diffraction. Substitution, insertion, and elimination reactions were performed on one hydride complex.

Electrophilically promoted cyanide abstraction in diiron cyano(amino) alkylidene complexes: molecular structure of [Fe2(CO)2(η-C5H5)2(µ-CO){µ-CN(CH2)4CH2}][(OC)5WCNW(CO)5]

The reactions of the µ-cyano(amino)alkylidene complexes [Fe2(CO)2(cp)2(µ-CO){µ-C(CN)(NR2)}][cp η5-C5H5, NR2 [graphic omitted]H21a or NMe21b] with [W(CO)5(thf)](thf = tetrahydrofuran), MeSO3CF3 and HSO3CF3 electrophiles promotes µ-C–CN bond cleavage with formation of the corresponding [Fe2(CO)2(cp)2(µ-CO)(µ-CNR2)]+3. In the case of [W(CO)5(thf)] the unexpected salts [Fe2(CO)2(cp)2(µ-CO)(µ-CNR2)][(OC)5WCNW(CO)5] have been prepared and characterized by the crystal structure of 3a[NR2= [graphic omitted]H2]. The structure [monoclinic, space group P21/n,a= 11.196(3), b= 17.389(3), c= 17.938(3)A, β= 95.19(2)°, Z= 4, R= 0.032] contains ordered cations and anions. Distances of interest are Fe–µ-C(N) 1.875(6), C–N 1.280(8)A in the cation and W–C(N) 2.184(8), W–N(C) 2.187(7) and C–N 1.15(1)A in the anion, where the cyanide ligand symmetrically bridges two W(CO)5 units. Electrophilic addition to phosphorus in [Fe2(CO)2(cp)2(µ-CO){µ-C(CN)(PEt2)}]2 has been observed and the adduct [Fe2(CO)2(cp)2(µ-CO){µ-C(CN)[PEt2W(CO)5]}]4 spectroscopically characterized. The different reactivity of 1 and 2 with electrophilic reagents is attributed to the strong tendency to CN double-bond formation.

Synthesis, Chemical Characterization, and Molecular Structure of Au~8{Fe(CO)~4}~4(dppe)~2 and Au~6Cu~2{Fe(CO)~4}~4(dppe)~2

The new Au8{Fe(CO)4}4(P^P)2 and Au6Cu2{Fe(CO)4}4(P^P)2 (P^P=dppm, dppe) neutral cluster compounds were isolated in good yields by condensation of the [Au3{Fe(CO)4}2(P^P)]- anions with Au(SEt2)Cl and CuCl, respectively, and have been characterized by IR, NMR and microanalyses. The molecular structures of Au8{Fe(CO)4}4(dppe)2 and Au6Cu2{Fe(CO)4}4(dppe)2 have been determined by X-ray diffraction studies. Both molecules adopt a stereogeometry of the heavy atoms consisting of a triangulated and corrugated ribbon twisted around the elongation direction. Contrary to the expectations the latter displays the two copper atoms in the sites of highest connectivity. This implies that site exchange between copper and gold occurs during the synthesis.

Synthesis, molecular structure, and magnetic properties of [CuLNi(H2O)2LCu][ClO4]2·4H2O [H2L =N,N′-bis(3-amino-2,2-dimethylpropyl)oxamide] and its trinickel homologue

The compounds [MLNi(H2O)2LM][ClO4]2·4H2O [M = Cu or Ni; H2L =N,N′-bis(3-amino-2,2-dimethylpropyl)oxamide] were prepared and characterized by means of structural, magnetic and spectroscopic measurements. The crystals of both compounds are triclinic, space group P and Z= 2, with a= 12.080(1), b= 13.054(1), c= 14.775(2)A, α= 101.97(1), β= 90.82(1) and γ= 101.88(1)°, for M = Cu and a= 12.099(5), b= 13.060(4), c= 14.750(7)A, α= 101.98(3), β= 90.28(4) and γ= 102.25(3)° for M = Ni. The structural unit of both complexes consists of trinuclear dipositive cations, two perchlorate anions and four lattice water molecules. The central and terminal metal ions are antiferromagnetically coupled, J= 90(1) cm–1 in the case of M = Cu.