Diastereoselective synthesis of new psi[(E)-CH=CMe]- and psi[(Z)-CH=CMe]-type alkene dipeptide isosteres by organocopper reagents and application to conformationally restricted cyclic RGD peptidomimetics

Diastereoselective synthesis of new psi[(E)-CH=CMe]- and psi[(Z)-CH=CMe]-type alkene dipeptide isosteres corresponding to dipeptides having one N-methylamino acid, and application to bioactive peptides, are described. In a key reaction introducing the chiral alpha-alkyl group of the isosteres, organocopper-mediated alkylation of syn-beta-methylated gamma-mesyloxy-alpha,beta-enoate 26a afforded E- and Z-isomers of anti-S(N)2' products in a solvent-dependent manner. The resulting two isosteres, D-Phe-psi[(E)-CH=CMe]-L-Val 27a and D-Phe-psi[(Z)-CH=CMe]-L-Val 28b, which corresponded to trans- and cis-conformers of D-Phe-L-MeVal, respectively, were utilized in a structure-activity relationship study on cyclic RGD peptides 1 and 2, in company with a psi[(E)-CH=CH]-type alkene dipeptide isostere, D-Phe-psi[(E)-CH=CH]-L-Val. The cyclic isostere-containing pseudopeptides 3, 4, and 40 were synthesized and biological activity against integrin alpha(V)beta(3) and alpha(IIb)beta(3) receptors were also evaluated.     

Diastereoselective synthesis of psi[(E)-CMe=CH]- and psi[(E)-CMe=CMe]- type dipeptide isosteres based on organocopper-mediated anti-S(N)2' reaction

[reaction: see text] A straightforward synthetic route for the synthesis of diastereomerically pure psi[(E)-CMe=CH]- and psi[(E)-CMe=CMe]-type dipeptide isosteres was developed on the basis of regio- and stereoselective anti-S(N)2' alkylation of 3-(N-Boc-5-methyl-4-substituted-oxazolidin-2-on-5-yl)acrylates with organocopper reagents.     

Ni[(EPiPr2)2N]2 complexes: stereoisomers (E = Se) and square-planar coordination (E = Te)

The reaction of ((i)Pr 2PE) 2NM.TMEDA (M = Li, E = Se; M = Na, E = Te) with NiBr 2.DME in THF affords Ni[(SeP (i)Pr 2) 2N] 2 as either square-planar (green) or tetrahedral (red) stereoisomers, depending on the recrystallization solvent; the Te analogue is obtained as the square-planar complex Ni[(TeP (i)Pr 2) 2N] 2.     

Self-assembly of gold(I) rings and reversible formation of organometallic [2]catenanes

The reaction of the digold(I) diacetylide [(AuCCCH2OC6H4)2CMe2] with diphosphane ligands can lead to formation of either macrocyclic ring complexes or [2]catenanes by self-assembly. This gives an easy route to rare organometallic [2]catenanes, and the effect of the diphosphane ligand on the selectivity of self-assembly is studied. With diphosphane ligands Ph2P(CH2)xPPh2, the simple ring complex [Au2[(CCCH2OC6H4)2CMe2](Ph2P(CH2)xPPh2)] is formed selectively when x = 2, but the [2]catenanes [Au2[(CCCH2OC6H4)2CMe2](Ph2P(CH2)xPPh2)]2 are formed when x = 4 or 5. When x = 3, a mixture of the simple ring and [2]catenane is formed, along with the "double-ring" complex, [Au4[(CCCH2OC6H4)2CMe2]2(Ph2P(CH2)3PPh2)2] and a "hexamer" Au2[(CCCH2OC6H4)2CMe2](Ph2P(CH2)3PPh2)]6] whose structure is not determined. A study of the equilibria between these complexes by solution NMR techniques gives insight into the energetics and mechanism of [2]catenane formation. When the oligomer [(AuCCCH2OC6H4)2CMe2] was treated with a mixture of two diphosphane ligands, or when two [2]catenane complexes [[Au2[(CCCH2OC6H4)2CMe2](diphosphane)]2] were allowed to equilibrate, only the symmetrical [2]catenanes were formed. The diphosphanes Ph2PCCPPh2, trans-[Ph2PCH=CHPPh2] and (Ph2PC5H4)2Fe give the corresponding ring complexes [Au2[(CCCH2OC6H4)2CMe2](diphosphane)], and the chiral, unsymmetrical diacetylide [Au2[(CCCH2OC6H4C(Me)(CH2CMe2)C6H3OCH2CC)] gives macrocyclic ring complexes with all diphosphane ligands Ph2P(CH2)xPPh2 (x = 2-5).     

Facile and selective aliphatic C-H bond activation at ambient temperatures initiated by Cp*W(NO)(CH2CMe3)(eta(3)-CH2CHCHMe)

Thermolysis of Cp*W(NO)(CH2CMe3)(eta(3)-CH2CHCHMe) (1) at ambient temperatures leads to the loss of neopentane and the formation of the eta(2)-diene intermediate, Cp*W(NO)(eta(2)-CH2=CHCH=CH2) (A), which has been isolated as its 18e PMe3 adduct. In the presence of linear alkanes, A effects C-H activations of the hydrocarbons exclusively at their terminal carbons and forms 18e Cp*W(NO)(n-alkyl)(eta(3)-CH2CHCHMe) complexes. Similarly, treatments of 1 with methylcyclohexane, chloropentane, diethyl ether, and triethylamine all lead to the corresponding terminal C-H activation products. Furthermore, a judicious choice of solvents permits the C-H activation of gaseous hydrocarbons (i.e., propane, ethane, and methane) at ambient temperatures under moderately elevated pressures. However, reactions between intermediate A and cyclohexene, acetone, 3-pentanone, and 2-butyne lead to coupling between the eta(2)-diene ligand and the site of unsaturation on the organic molecule. For example, Cp*W(NO)(eta(3),eta(1)-CH2CHCHCH2C(CH2CH3)2O) is formed exclusively in 3-pentanone. When the site of unsaturation is sufficiently sterically hindered, as in the case of 2,3-dimethyl-2-butene, C-H activation again becomes dominant, and so the C-H activation product, Cp*W(NO)(eta(1)-CH2CMe=CMe2)(eta(3)-CH2CHCHMe), is formed exclusively from the alkene and 1. All new complexes have been characterized by conventional spectroscopic and analytical methods, and the solid-state molecular structures of most of them have been established by X-ray crystallographic analyses. Finally, the newly formed alkyl ligands may be liberated from the tungsten centers in the product complexes by treatment with iodine. Thus, exposure of a CDCl3 solution of the n-pentyl allyl complex, Cp*W(NO)(n-C5H11)(eta(3)-CH2CHCHMe), to I2 at -60 degrees C produces n-C5H11I in moderate yields.     

Electro- and magnetocommunication in [5,5]ditrovacenyls, [(eta7-C7H7)V(eta5-C5H4-X-eta5-C5H4)V(eta7-C7H7)], mediated by the spacers X = (Z)-CH=CH-, (E)-CH=CH-, > C=CH2, -CH2CH2-, and -CH2-

Five new paramagnetic dinuclear complexes containing [5]trovacenyl groups, (eta7-C7H7)V(eta5-C5H4-), have been prepared and characterized, including by single-crystal X-ray diffraction. As intervening spacers, ethenediyl units in the geminal and vicinal (Z)- and (E)-bridging modes as well as methanediyl and ethanediyl units have been included with the aim of studying their propensity to transmit electric and magnetic information. It is found that redox splitting of consecutive electron-transfer steps is resolved for reduction (0-->1- -->2-) only, unsaturation of the C2 bridge not being requisite, since the -CH2CH2- spacer also gives rise to a small redox splitting. Magnetic communication is quantified in terms of the exchange coupling constant J, accessible from the EPR hyperfine pattern in solution and from magnetic susceptometry in the solid state. The results obtained from these methods generally differ; this fact is not surprising in view of conformational differences in the respective states of aggregation. It is concluded that orientation-dependent mechanisms of spin-spin interactions (pi-orbital overlap, hyperconjugation) contribute extensively although, as implied by sizeable J values for -CH2- and -C2H4- linked di[5]trovacenyl groups, coupling mediated by the sigma-orbital chain must also be considered.     

Reactivity of the inversely polarized phosphaalkenes RP=C(NMe2)2 (R = tBu, Me3Si, H) towards arylcarbene complexes [(CO)5M=C(oEt)Ar] (Ar= Ph, M = Cr, W; Ar = 2-MeC6H4, 2-MeOC6H4, M = W)

The reaction of the arylated Fischer carbene complexes [(CO)5M=C(OEt)Ar] (Ar=Ph; M = Cr, W; 2-MeC6H4; 2-MeOC6H; M = W) with the phosphaalkenes RP=C(NMe2), (R=tBu, SiMe3) afforded the novel phosphaalkene complexes [[RP=C(OEt)Ar]M(CO)5] in addition to the compounds [(RP=C(NMe2)2]M(CO)5]. Only in the case of the R = SiMe3 (E/Z) mixtures of the metathesis products were obtained. The bis(dimethylamino)methylene unit of the phosphaalkene precursor was incorporated in olefins of the type (Me2N)2C=C(OEt)(Ar). Treatment of [(CO)5W=C(OEt)(2-MeOC6H4)] with HP=C(NMe2)2 gave rise to the formation of an E/Z mixture of [[(Me2N)2CH-P=C(OEt)(2-MeOC6H4)]W(CO)5] the organophosphorus ligand of which formally results from a combination of the carbene ligand and the phosphanediyl [P-CH(NMe2)2]. The reactions reported here strongly depend on an inverse distribution of alpha-electron density in the phosphaalkene precursors (Pdelta Cdelta+), which renders these molecules powerfu] nucleophiles.     

Structural consequences of the one-electron reduction of d4 [Mo(CO)2(eta-PhC[triple bond]CPh)Tp']+ and the electronic structure of the d5 radicals [M(CO)L(eta-MeC[triple bond]CMe)Tp'] {L = CO and P(OCH2)3CEt}

Reduction of [M(CO)2(eta-RC[triple bond]CR')Tp']X {Tp' = hydrotris(3,5-dimethylpyrazolyl)borate, M = Mo, X = [PF6]-, R = R' = Ph, C6H4OMe-4 or Me; R = Ph, R' = H; M = W, X = [BF4]-, R = R' = Ph or Me; R = Ph, R' = H} with [Co(eta-C5H5)2] gave paramagnetic [M(CO)2(eta-RC[triple bond]CR')Tp'], characterised by IR and ESR spectroscopy. X-Ray structural studies on the redox pair [Mo(CO)2(eta-PhC[triple bond]CPh)Tp'] and [Mo(CO)2(eta-PhC[triple bond]CPh)Tp'][PF6] showed that oxidation is accompanied by a lengthening of the C[triple bond]C bond and shortening of the Mo-C(alkyne) bonds, consistent with removal of an electron from an orbital antibonding with respect to the Mo-alkyne bond, and with conversion of the alkyne from a three- to a four-electron donor. Reduction of [Mo(CO)(NCMe)(eta-MeC[triple bond]CMe)Tp'][PF6] with [Co(eta-C5H5)2] in CH2Cl2 gives [MoCl(CO)(eta-MeC[triple bond]CMe)Tp'], via nitrile substitution in [Mo(CO)(NCMe)(eta-MeC[triple bond]CMe)Tp'], whereas a similar reaction with [M(CO){P(OCH2)3CEt}(eta-MeC[triple bond]CMe)Tp']+ (M = Mo or W) gives the phosphite-containing radicals [M(CO){P(OCH2)3CEt}(eta-MeC[triple bond]CMe)Tp']. ESR spectroscopic studies and DFT calculations on [M(CO)L(eta-MeC[triple bond]CMe)Tp'] {M = Mo or W, L = CO or P(OCH2)3CEt} show the SOMO of the neutral d5 species (the LUMO of the d4 cations) to be largely d(yz) in character although much more delocalised in the W complexes. Non-coincidence effects between the g and metal hyperfine matrices in the Mo spectra indicate hybridisation of the metal d-orbitals in the SOMO, consistent with a rotation of the coordinated alkyne about the M-C2 axis.     

Synthesis and structures of heterocyclic azidogallanes [(CH3)ClGaN3]4 and [(CH3)BrGaN3]3 en route to [(CH3)HGaN3]x: an inorganic precursor to GaN

The synthesis of [(CH3)ClGaN3]4 (1) with a heterocyclic cyclooctane-like structure and [(CH3)BrGaN3]3 (2) with a trimeric structure has been demonstrated. X-ray structural determinations reveal that 1 and 2 consist of Ga4N4 eight-membered rings and Ga3N3 six-membered rings, respectively, in which the Ga atoms are bridged by the alpha nitrogens of the azide groups. [(CH3)ClGaN3]4 crystallizes in the tetragonal space group P42(1)c with a = 11.017(4) A, c = 8.699(7) A, and Z = 8. [(CH3)BrGaN3]3 crystallizes in the triclinic space group P1 with a = 8.1080(10) A, b = 9.9390(13) A, c = 10.4439(13) A, alpha = 86.069(3) degrees, beta = 86.771(3) degrees, gamma = 80.829(2) degrees, and Z = 6. The reaction of 1 and 2 with LiGaH4 yields [(CH3)HGaN3]x, which is a new low-temperature source of GaN.     

Reactivity and structural and physical studies of tetranuclear iron(III) clusters containing the [Fe4(mu3-O)2]8+ "butterfly" core: an FeIII4 cluster with an S = 1 ground state

The initial use of di-2-pyridyl ketone oxime [(py)2CNOH] in iron(III) carboxylate chemistry has yielded the tetranuclear complex [Fe4O2Cl2(O2CMe)2{(py)2CNO}4] (1). Compound 1 can be synthesized either by the 1:2:1 molar ratio reaction between Fe(III), MeCO2-, and (py)2CNOH (complex 1a) or by the 1:3 molar ratio reaction between [Fe3O(O2CMe)6(H2O)3]Cl and (py)2CNOH (complex 1b). The presence of N3- in both reaction mixtures has afforded the tetranuclear complex [Fe4O2(N3)2(O2CMe)2{(py)2CNO}4] (2), which can be alternatively synthesized by the reaction of 1 with N3-. Compound 1a crystallizes in the tetragonal space group /-4 with (at 25 degrees C) a = 35.06(2) A, b = 35.06(2) A, c = 13.255(6) A, V = 16293(2) A(3), and Z = 8. Compound 1b crystallizes in the monoclinic space group P2(1)/c with (at 25 degrees C) a = 22.577(7) A, b = 17.078(6) A, c = 17.394(6) A, beta = 93.50(1) degrees , V = 6694(4) A(3), and Z = 4. Compound 2 crystallizes in the triclinic space group P1 with (at 25 degrees C) a = 13.658(9) A, b = 15.815(9) A, c = 17.29(1) A, alpha = 97.08(3) degrees , beta = 98.55(3) degrees , gamma = 112.12(3) degrees , V = 3355(4) A(3), and Z = 2. The structures of 1 and 2 contain the [Fe4(mu3-O)2]8+ core comprising four Fe(III) ions in a "butterfly" disposition and two mu3-O2- ions, each bridging three Fe(III) ions forming the "wings" of the "butterfly". The M?ssbauer spectra of 1b and 2 consist of composite quadrupole-split doublets, with parameters typical for high-spin Fe(III) in octahedral environments. Magnetic susceptibility measurements on 1a revealed antiferromagnetic interactions between the S = 5/2 ferric ions, with best-fit parameters being J(wb) = -40.2 cm(-1) and J(bb) = -59.4 cm(-1) (H = -2SigmaJiJj) for wingtip-body and body-body interactions, respectively, yielding an S = 1 ground state. Both wingtip-body and body-body interactions are well determined.     

Dialkylaluminum hydrazides derived from free hydrazine N2H4. Molecular Structures of [(MeC)2AlN2H3]2 and [(MeC)2Al]4(N2H2)2

The reaction of di(tert-butyl)aluminum hydride with hydrazine N2H4 afforded the hydrazide (Me3C)2AlN2H3, 1, by the release of elemental hydrogen. Compound 1 is a dimer in solution and in the solid state and possesses a six-membered Al2N4 heterocycle in a twist conformation with two intact N-N bonds. Further reaction of 1 with an excess of HAl(CMe3)2 yielded the tricyclic aluminum and nitrogen rich Al4N4 compound [(Me3C)2AlN2H2]2[Al(CMe3)2]2, 2, in which each N-N bond of a central six-membered Al2N4 ring similar to that of 1 is side-on-coordinated to an Al(CMe3)2 group. The structure of 2 may be interpreted as a dimer of the dialuminum hydrazide (Me3C)2Al-NH-NH-Al(CMe3)2.     

Synthesis of Ru-Pt and Ru-Pd mixed-metal imido clusters from a diruthenium imido-methylene scaffold [(Cp*Ru)2(mu2-NPh)(mu2-CH2)

The diruthenium mu2-imido mu2-methylene complex [(Cp*Ru)2(mu2-NPh)(mu2-CH2)] serves as a bifunctional scaffold for cluster synthesis, producing a mu3-imido Ru2Pt cluster [(Cp*Ru)2(mu3-NPh)(mu2-CH2)Pt(PMe3)2] on treatment with [Pt(eta2-C2H4)(PMe3)2] and a mu3-methylidyne Ru4Pd2 cluster [(Cp*Ru)2(mu2-NPh)(mu3-CH)PdCl]2 with [PdMeCl(cod)].     

Synthesis and structural characterization of Sm(II) and Yb(II) complexes containing sterically demanding, chelating secondary phosphide ligands

Metathesis between [(Me3Si)2CH)(C6H4-2-OMe)P]K and SmI2(THF)2 in THF yields [([Me3Si]2CH)(C6H4-2-OMe)P)2Sm(DME)(THF)] (1), after recrystallization. A similar reaction between [(Me3Si)2CH)(C6H3-2-OMe-3-Me)P]K and SmI2(THF)2 yields [([Me3Si]2CH)(C6H3-2-OMe-3-Me)P)2Sm(DME)].Et2O (2), while reaction between [(Me3Si)2CH)(C6H4-2-CH2NMe2)P]K and either SmI2(THF)2 or YbI2 yields the five-coordinate complex [([Me3Si]2CH)(C6H4-2-CH2NMe2)P)2Sm(THF)] (3) or the solvent-free complex [([Me3Si]2CH)(C6H4-2-CH2NMe2)P)2Yb] (4), respectively. X-ray crystallography shows that complex 2 adopts a distorted cis octahedral geometry, while complex 1 adopts a distorted pentagonal bipyramidal geometry (1, triclinic, P1, a = 11.0625(9) A, b = 15.924(6) A, c = 17.2104(14) A, alpha = 72.327(2) degrees, beta = 83.934(2) degrees, gamma = 79.556(2) degrees, Z = 2; 2, monoclinic, P2(1), a = 13.176(4) A, b = 13.080(4) A, c = 14.546(4) A, beta = 95.363(6) degrees, Z = 2). Complex 3 crystallizes as monomers with a square pyramidal geometry at Sm and exhibits short contacts between Sm and the ipso-carbon atoms of the ligands (3, monoclinic, C2/c, a = 14.9880(17) A, b = 13.0528(15) A, c = 24.330(3) A, beta = 104.507(2) degrees, Z = 4). Whereas preliminary X-ray crystallographic data for 4 indicate a monomeric structure in the solid state, variable-temperature 1H, 13C(1H), 31P(1H), and 171Yb NMR spectroscopies suggest that 4 undergoes an unusual dynamic process in solution, which is ascribed to a monomer-dimer equilibrium in which exchange of the bridging and terminal phosphide groups may be frozen out at low temperature.     

Stereoselective trimerization of [(S)R]-[(p-tolylsulfinyl)methyl]-p-quinols and p-quinamines

[reaction: see text] The asymmetric synthesis of pentacyclic derivatives was achieved in a single step starting from enantiopure [(S)R]-[(p-tolylsulfinyl)methyl]-p-quinols or the nitrogen analogue, through a domino sequence involving four conjugate additions in excellent yields. Eight new stereogenic centers were created in one step and in a highly diastereoselective manner.     

A Convenient Preparation of 2-(2-Arylidene)- and 2-(2-Polyhydroxyalkylidene)hydrazono-4-imidazolidinones with Various Heterocyclic Side Chain Substituents at Position 5 as Potential Antiviral and Antitumor Agents

A variety of novel 5-[( Z )-arylidene]-2-[(2-( E )-arylidene)hydrazono]-4-imidazolidinones 1a-c to 4a , b and 5-[( Z )-arylidene]-2-[(2-( E )-polyhydroxyalkylidene)hydrazono]-4-imidazolidinones 5a-c to 7a-c were prepared from the reaction of 5-[( Z )-arylidene]-2-methylmercaptohydantoins 8a-c with 2-( E )-arylidene hydrazones 13a-d and/or 2-( E )-monosaccharides hydrazones 16a-c . The linear structure, and not that of the angular isomer, has been selected for the products. This structure has been confirmed from a model study of the condensation of 5-[( Z )-2-thienylidene]-2-hydrazono-4-imidazolidinone 9a with benzaldehyde and D -galactose, respectively. The acetylation and benzoylation reactions of compounds 1-7 have been studied. All the new compounds were tested for their potential antiviral and antitumor activities.     

Synthesis and catalysis of di- and tetranuclear metal sandwich-type silicotungstates [(gamma-SiW10O36)2M2(mu-OH)2]10- and [(gamma-SiW10O36)2M4(mu4-O)(mu-OH)6]8- (M = Zr or Hf)

The di- and tetranuclear metal sandwich-type silicotungstates of Cs10[(gamma-SiW10O36)2{Zr(H2O)}2(mu-OH)2] x 18 H2O (Zr2, monoclinic, C2/c (No. 15), a = 25.3315(8) A, b = 22.6699(7) A, c = 18.5533(6) A, beta = 123.9000(12) degrees, V = 8843.3(5) A(3), Z = 4), Cs10[(gamma-SiW10O36)2{Hf(H2O)}2(mu-OH)2] x 17 H2O (Hf2, monoclinic, space group C2/c (No. 15), a = 25.3847(16) A, b = 22.6121(14) A, c = 18.8703(11) A, beta = 124.046(3) degrees, V = 8974.9(9) A(3), Z = 4), Cs8[(gamma-SiW10O36)2{Zr(H2O)}4(mu4-O)(mu-OH)6] x 26 H2O (Zr4, tetragonal, P4(1)2(1)2 (No. 92), a = 12.67370(10) A, c = 61.6213(8) A, V = 9897.78(17) A(3), Z = 4), and Cs8[(gamma-SiW10O36)2{Hf(H2O)}4(mu4-O)(mu-OH)6] x 23 H2O (Hf4, tetragonal, P4(1)2(1)2 (No. 92), a = 12.68130(10) A, c = 61.5483(9) A, V = 9897.91(18) A(3), Z = 4) were obtained as single crystals suitable for X-ray crystallographic analyses by the reaction of a dilacunary gamma-Keggin silicotungstate K8[gamma-SiW10O36] with ZrOCl2 x 8 H2O or HfOCl2 x 8 H2O. These dimeric polyoxometalates consisted of two [gamma-SiW10O36](8-) units sandwiching metal-oxygen clusters such as [M2(mu-OH)2](6+) and [M4(mu4-O)(mu-OH)6](8+) (M = Zr or Hf). The dinuclear zirconium and hafnium complexes Zr2 and Hf2 were isostructural. The equatorially placed two metal atoms in Zr2 and Hf2 were linked by two mu-OH ligands and each metal was bound to four oxygen atoms of two [gamma-SiW10O36](8-) units. The tertanuclear zirconium and hafnium complexes Zr4 and Hf4 were isostructural and consisted of the adamantanoid cages with a tetracoordinated oxygen atom in the middle, [M4(mu4-O)(mu-OH)6](8+) (M = Zr or Hf). Each metal atom in Zr4 and Hf4 was linked by three mu-OH ligands and bound to two oxygen atoms of the [gamma-SiW10O36](8-) unit. The tetra-nuclear zirconium and hafnium complexes showed catalytic activity for the intramolecular cyclization of (+)-citronellal to isopulegols without formation of byproducts resulting from etherification and dehydration. A lacunary silicotungstate [gamma-SiW10O34(H2O)2](4-) was inactive, and the isomer ratio of isopulegols in the presence of MOCl2 x 8 H2O (M = Zr or Hf) were much different from that in the presence of tetranuclear complexes, suggesting that the [M4(mu4-O)(mu-OH)6](8+) core incorporated into the POM frameworks acts as an active site for the present cyclization. On the other hand, the reaction hardly proceeded in the presence of dinuclear zirconium and hafnium complexes under the same conditions. The much less activity is possibly explained by the steric repulsion from the POM frameworks in the dinuclear complexes.     

Four-coordinate Mo(II) as (silox)2Mo(PMe3)2 and its W(IV) congener (silox)2HW(eta2-CH2PMe2)(PMe3) (silox = tBu3SiO)

The reduction of [( (t) Bu 3SiO) 2MoCl] 2 ( 2 2) provided the cyclometalated derivative, (silox) 2HMoMo(kappa-O,C-OSi (t) Bu 2CMe 2CH 2)(silox) ( 3), and alkylation of 2 2 with MeMgBr afforded [( (t) Bu 3SiO) 2MoCH 3] 2 ( 4 2). The hydrogenation of 4 2 was ineffective, but the reduction of 2 2 under H 2 generated [( (t) Bu 3SiO) 2MoH] 2 ( 5 2), and the addition of 2-butyne to 3 gave [(silox) 2Mo] 2(mu:eta (2)eta (2)-C 2Me 2) ( 6), thereby implicating the existence of [(silox) 2Mo] 2 ( 1 2). The addition of (silox)H to Mo(NMe 2) 4 led to (silox) 2Mo(NMe 2) 2 ( 7), but further elaboration of the core proved ineffective. The silanolysis of MoCl 5 afforded (silox) 2MoCl 4 ( 8) and (silox) 3MoCl 3 ( 9) as a mixture from which pure 8 could be isolated, and the addition of THF or PMe 3 resulted in derivatives of 9 as (silox) 2Cl 3MoL (L = THF, 10; PMe 3, 11). Reductions of 11 and (silox) 2WCl 4 ( 15) in the presence of excess PMe 3 provided (silox) 2Cl 2MPMe 3 (M = Mo, 12; W, 16) or (silox) 2HW(eta (2)-CH 2PMe 2)PMe 3 ( 14). While "(silox) 2W(PMe 3) 2" was unstable with respect to W(IV) as 14, a reduction of 12 led to the stable Mo(II) diphosphine, (silox) 2Mo(PMe 3) 2 ( 17). X-ray crystal structures of 10 (pseudo- O h ), 12 (square pyramidal), and 14 and 17 (distorted T d ) are reported. Calculations address the diamagnetism of 12 and 16, and the distortion of 17 and its stability to cyclometalation in contrast to 14.     

Substituted N-picolylethylenediamines of the type (ArNHCH2CH2){(2-C5H4N)CH2}NR [R = Me, 4-CH2=CH(C6H4)CH2, (2-C5H4N)CH2] and their transition metal(II) halide complexes

Alkylation of (ArNHCH2CH2){(2-C5H4N)CH2}NH with RX [RX = MeI, 4-CH2=CH(C6H4)CH2Cl) and (2-C5H5N)CH2Cl] in the presence of base has allowed access to the sterically demanding multidentate nitrogen donor ligands, {(2,4,6-Me3C6H2)NHCH2CH2}{(2-C5H4N)CH2}NMe (L1), {(2,6-Me3C6H3)NHCH2CH2}{(2-C5H4N)CH2}NCH2(C6H4)-4-CH=CH2 (L2) and (ArNHCH2CH2){(2-C5H4N)CH2}2N (Ar = 2,4-Me2C6H3 L3a, 2,6-Me2C6H3 L3b) in moderate yield. L3 can also be prepared in higher yield by the reaction of (NH2CH2CH2){(2-C5H4N)CH2}2N with the corresponding aryl bromide in the presence of base and a palladium(0) catalyst. Treatment of L1 or L2 with MCl2 [MCl2 = CoCl2.6H2O or FeCl2(THF)1.5] in THF affords the high spin complexes [(L1)MCl2](M = Co 1a, Fe 1b) and [(L2)MCl2](M = Co 2a, Fe 2b) in good yield, respectively; the molecular structure of reveals a five-coordinate metal centre with bound in a facial fashion. The six-coordinate complexes, [(L3a)MCl2](M = Co 3a, Fe 3b, Mn 3c) are accessible on treatment of tripodal L3a with MCl2. In contrast, the reaction with the more sterically encumbered leads to the pseudo-five-coordinate species [(L3b)MCl2](M = Co 4a, Fe 4b) and, in the case of manganese, dimeric [(L3b)MnCl(mu-Cl)]2 (4c); in 4a and 4b the aryl-substituted amine arm forms a partial interaction with the metal centre while in 4c the arm is pendant. The single crystal X-ray structures of , 1a, 3b.MeCN, 3c.MeCN, 4b.MeCN and 4c are described as are the solution state properties of 3b and 4b.     

Cyano- and isocyanotris(trifluoromethyl)borates: syntheses, spectroscopic properties, and solid state structures of K[(CF3)3BCN] and K[(CF3)3BNC

A two step synthesis to the isocyanotris(trifluoromethyl)borate anion, [(CF3)3BNC]-, and its isomerization to the cyanotris(trifluoromethyl)borate anion, [(CF3)3BCN]-, at temperatures above 150 degrees C are presented. In the first step (CF3)3BNCH was obtained by reacting (CF3)3BCO with hydrogen cyanide followed by deprotonation of the HCN adduct with Li[N(SiMe3)2] in toluene. The thermal behavior of K[(CF3)3BNC] and K[(CF3)3BCN] were investigated by differential scanning calorimetry (DSC), and K[BF4] was identified as a major solid decomposition product. The enthalpy of the isocyanide-cyanide rearrangement, deltaH(iso) = -35 +/- 4 kJ mol(-1), was obtained from DSC measurements, and the activation energy, E(a) = 180 +/- 20 kJ mol(-1), from kinetic measurements. The isomerization was modeled as an intramolecular reaction employing DFT calculations at the B3LYP/6-311+G(d) level of theory yielding a reaction enthalpy of deltaH(iso) = -36.1 kJ mol(-1) and an activation energy of E(a) = 155.7 kJ mol(-1). The solid-state structures of K[(CF3)3BNC] and K[(CF3)3BCN] were determined by single-crystal X-ray diffraction. Both salts are isostructural and crystallize in the orthorhombic space group Pnma (no. 62). In the crystals the borate anions possess C(s) symmetry, while for the energetic minimum C3 symmetry is predicted by DFT calculations. The borate anions have been characterized by IR and Raman spectroscopy as well as by NMR spectroscopy. The assignment of the IR and Raman bands is supported by their calculated wavenumbers and intensities. The spectroscopic and structural properties of both borate anions are compared to the properties of the isoelectronic borane carbonyl (CF3)3BCO and the [B(CF3)4]- anion as well as to those of other related species.     

C-C coupling reactions in the coordination sphere of rhodium(I) and rhodium(III): New routes for the di- and trimerization of terminal alkynes

The alkynyl(vinylidene)rhodium(I) complexes trans-[Rh(C[triple bond, length as m-dash]CR)(=C=CHR)(PiPr3)2] 2, 5, 6 react with CO by migratory insertion to give stereoselectively the butenynyl compounds trans-[Rh{eta1-(Z)-C(=CHR)C[triple bond, length as m-dash]CR}(CO)(PiPr3)2](Z)-7-9, of which (Z)-7 (R=Ph) and (Z)-8 (R=tBu) rearrange upon heating or UV irradiation to the (E) isomers. Similarly, trans-[Rh{eta1-C(=CH2)C[triple bond, length as m-dash]CPh}(CO)(PiPr3)2] 12 and trans-[Rh{eta1-(Z)-C(=CHCO2Me)C[triple bond, length as m-dash]CR}(CO)(PiPr3)2](Z)-15, (Z)-16 have been prepared. At room temperature, the corresponding "non-substituted" derivative trans-[Rh{eta1-C(=CH2)C[triple bond, length as m-dash]CH}(CO)(PiPr3)2] 18 is in equilibrium with the butatrienyl isomer trans-[Rh(eta1-CH=]C=C=CH2)(CO)(PiPr3)2] 19 that rearranges photochemically to the alkynyl complex trans-[Rh(C[triple bond, length as m-dash]CCH=CH2)(CO)(PiPr3)2] 20. Reactions of (Z)-7, (E)-7, (Z)-8 and (E)-8 with carboxylic acids R'CO2H (R'=CH3, CF3) yield either the butenyne (Z)- and/or (E)-RC[triple bond, length as m-dash]CCH=CHR or a mixture of the butenyne and the isomeric butatriene, the ratio of which depends on both R and R'. Treatment of 2 (R=Ph) with HCl at -40 degrees C affords five-coordinate [RhCl(C[triple bond, length as m-dash]CPh){(Z)-CH=CHPh}(PiPr3)2] 23, which at room temperature reacts by C-C coupling to give trans-[RhCl{eta2-(Z)-PhC[triple bond, length as m-dash]CCH=CHPh}(PiPr3)2](Z)-21. The related compound trans-[RhCl(eta2-HC[triple bond, length as m-dash]CCH=CH2)(PiPr3)2] 27, prepared from trans-[Rh(C[triple bond, length as m-dash]CH)(=C=CH2)(PiPr3)2] 17 and HCl, rearranges to the vinylvinylidene isomer trans-[RhCl(=C=CHCH=CH2)(PiPr3)2] 28. While stepwise reaction of 2with CF3CO2H yields, via alkynyl(vinyl)rhodium(III) intermediates (Z)-29 and (E)-29, the alkyne complexes trans-[Rh(kappa1-O2CCF3)(eta2-PhC[triple bond, length as m-dash]CCH=CHPh)(PiPr3)2](Z)-30 and (E)-30, from 2 and CH3CO2H the acetato derivative [Rh(kappa2-O2CCH3)(PiPr3)2] 33 and (Z)-PhC[triple bond, length as m-dash]CCH=]CHPh are obtained. From 6 (R=CO2Me) and HCl or HC[triple bond, length as m-dash]CCO2Me the chelate complexes [RhX(C[triple bond, length as m-dash]CCO2Me){kappa2(C,O)-CH=CHC(OMe)=O}(PiPr3)2] 34 (X=Cl) and 35 (X=C[triple bond, length as m-dash]CCO2Me) have been prepared. In contrast to the reactions of [Rh(kappa2-O2CCH3)(C[triple bond, length as m-dash]CE)(CH=CHE)(PiPr3)2] 37(E=CO2Me) with chloride sources which give, via intramolecular C-C coupling, four-coordinate trans-[RhCl{eta2-(E)-EC[triple bond, length as m-dash]CCH=CHE}(PiPr3)2](E)-36, treatment of 37with HC[triple bond, length as m-dash]CE affords, via insertion of the alkyne into the rhodium-vinyl bond, six-coordinate [Rh(kappa2-O2CCH3)(C[triple bond, length as m-dash]CE){eta1-(E,E)-C(=CHE)CH=CHE}(PiPr3)2] 38. The latter reacts with MgCl2 to yield trans-[RhCl{eta2-(E,E)-EC[triple bond, length as m-dash]CC(=CHE)CH=CHE}(PiPr3)2] 39, which, in the presence of CO, generates the substituted hexadienyne (E,E)-EC[triple bond, length as m-dash]CC(=CHE)CH=CHE 40.