Pop-the-cork strategy in synthetic utilization of imines: stabilization by complexation and activation via liberation of the ligated species

Treatment of trans-[PtCl(4)(RCN)(2)] (R = Me, Et) with ethanol allowed the isolation of trans-[PtCl(4)[E-NH[double bond]C(R)OEt](2)]. The latter were reduced selectively, by the ylide Ph(3)P[double bond]CHCO(2)Me, to trans-[PtCl(2)[E-NH[double bond]C(R)OEt](2)]. The complexed imino esters NH[double bond]C(R)OEt were liberated from the platinum(II) complexes by reaction with 2 equiv of 1,2-bis(diphenylphosphino)ethane (dppe) in chloroform; the cationic complex [Pt(dppe)(2)]Cl(2) precipitates almost quantitatively from the reaction mixture and can be easily separated by filtration to give a solution of NH[double bond]C(R)OEt with a known concentration of the imino ester. The imino esters efficiently couple with the coordinated nitriles in trans-[PtCl(4)(EtCN)(2)] to give, as the dominant product, [PtCl(4)[NH[double bond]C(Et)N[double bond]C(R)OEt](2)] containing a previously unknown linkage, i.e., ligated N-(1-imino-propyl)-alkylimidic acid ethyl esters. In addition to [PtCl(4)[NH[double bond]C(Et)N[double bond]C(Et)OEt](2)], another compound was generated as the minor product, i.e., [PtCl(4)(EtCN)[NH[double bond]C(Et)N[double bond]C(Et)OEt]], which was reduced to [PtCl(2)(EtCN)[NH[double bond]C(Et)N[double bond]C(Et)OEt]], and this complex was characterized by X-ray single-crystal diffraction. The platinum(IV) complexes [PtCl(4)[NH[double bond]C(Et)N[double bond]C(R)OEt](2)] are unstable toward hydrolysis and give EtOH and the acylamidine complexes trans-[PtCl(4)[Z-NH[double bond]C(Et)NHC(R)[double bond]O](2)], where the coordination to the Pt center results in the predominant stabilization of the imino tautomer NH[double bond]C(Et)NHC(R)[double bond]O over the other form, i.e., NH(2)C(Et)[double bond]NC(R)[double bond]O, which is the major one for free acylamidines. The structures of trans-[PtCl(4)[Z-NH[double bond]C(Et)NHC(R)[double bond]O](2)] (R = Me, Et) were determined by X-ray studies. The complexes [PtCl(4)[NH[double bond]C(Et)N[double bond]C(R)OEt](2)] were reduced to the appropriate platinum(II) compounds [PtCl(2)[NH[double bond]C(Et)N[double bond]C(R)OEt](2)], which, similarly to the appropriate Pt(IV) compounds, rapidly hydrolyze to yield the acylamidine complexes [PtCl(2)[NH[double bond]C(Et)NHC(R)[double bond]O](2)] and EtOH. The latter acylamidine compounds were also prepared by an alternative route upon reduction of the corresponding platinum(IV) complexes. Besides the first observation of the platinum(IV)-mediated nitrile-imine ester integration, this work demonstrates that the application of metal complexes gives new opportunities for the generation of a great variety of imines (sometimes unreachable in pure organic chemistry) in metal-mediated conversions of organonitriles, the "storage" of imino species in the complexed form, and their synthetic utilization after liberation.     

Reactions of Et(3)ZnLi with ketones: electronic and steric effects(1)

Toluene solutions of composition Et(3)ZnLi react rapidly with aldehydes and ketones to form addition products. Et(3)ZnNa and Et(3)ZnK solutions react readily with the same substrates although metalation, as well as addition, is significant with substrates having alpha-hydrogens. The Et(3)ZnM solutions react with 2-cyclohexenone to give mainly the 1,4-addition product. Relative rates of addition of Et(3)ZnLi to substituted acetophenones give a Hammett rho of 2.78. Addition of Et(3)ZnLi to acetophenone is slowed significantly by alpha and ortho methyl substituents; relative rates of addition to acetophenone, o-methylacetophenone, and tert-butyl phenyl ketone are 1.00, 0.012, and 0.003.     

Synthetic and structural studies on [Fe2(SR)2(CN)x(CO)6-x](x-) as active site models for Fe-only hydrogenases.

A series of models for the active site (H-cluster) of the iron-only hydrogenase enzymes (Fe-only H2-ases) were prepared. Treatment of MeCN solutions of Fe2(SR)2(CO)6 with 2 equiv of Et4NCN gave [Fe2(SR)2(CN)2(CO)4](2-) compounds. IR spectra of the dicyanides feature four nu(CO) bands between 1965 and 1870 cm(-1) and two nu(CN) bands at 2077 and 2033 cm(-1). For alkyl derivatives, both diequatorial and axial-equatorial isomers were observed by NMR analysis. Also prepared were a series of dithiolate derivatives (Et4N)2[Fe2(SR)2(CN)2(CO)4], where (SR)2 = S(CH2)2S, S(CH2)3S. Reaction of Et4NCN with Fe2(S-t-Bu)2(CO)6 gave initially [Fe2(S-t-Bu)2(CN)2(CO)4](2-), which comproportionated to give [Fe2(S-t-Bu)2(CN)(CO)5](-). The mechanism of the CN(-)-for-CO substitution was probed as follows: (i) excess CN(-) with a 1:1 mixture of Fe2(SMe)2(CO)6 and Fe2(SC6H4Me)2(CO)6 gave no mixed thiolates, (ii) treatment of Fe2(S2C3H6)(CO)6 with Me3NO followed by Et4NCN gave (Et4N)[Fe2(S2C3H6)(CN)(CO)5], which is a well-behaved salt, (iii) treatment of Fe2(S2C3H6)(CO)6 with Et4NCN in the presence of excess PMe3 gave (Et4N)[Fe2(S2C3H6)(CN)(CO)4(PMe3)] much more rapidly than the reaction of PMe3 with (Et4N)[Fe2(S2C3H6)(CN)(CO)5], and (iv) a competition experiment showed that Et4NCN reacts with Fe2(S2C3H6)(CO)6 more rapidly than with (Et4N)[Fe2(S2C3H6)(CN)(CO)5]. Salts of [Fe2(SR)2(CN)2(CO)4](2-) (for (SR)2 = (SMe)2 and S2C2H4) and the monocyanides [Fe2(S2C3H6)(CN)(CO)5](-) and [Fe2(S-t-Bu)2(CN)(CO)5](-) were characterized crystallographically; in each case, the Fe-CO distances were approximately 10% shorter than the Fe-CN distances. The oxidation potentials for Fe2(S2C3H6)(CO)4L2 become milder for L = CO, followed by MeNC, PMe3, and CN(-); the range is approximately 1.3 V. In water,oxidation of [Fe2(S2C3H6)(CN)2(CO)4](2-) occurs irreversibly at -0.12 V (Ag/AgCl) and is coupled to a second oxidation.     

Reactions of [Et(4)N](3)[Sb{Fe(CO)(4)}(4)] with Alkyl Halides and Dihalides: Formation of the Alkyl- and the Dialkylantimony-Iron Carbonyl Complexes

The reactions of [Et(4)N](3)[Sb{Fe(CO)(4)}(4)] (1) with RX (R = Me, Et, n-Pr; X = I) in MeCN form the monoalkylated antimony complexes [Et(4)N](2)[RSb{Fe(CO)(4)}(3)] (R = Me, 2; R = Et, 4; R = n-Pr, 6) and the dialkylated antimony clusters [Et(4)N][R(2)Sb{Fe(CO)(4)}(2)] (R = Me, 3; R = Et, 5; R = n-Pr, 7), respectively. When [Et(4)N](3)[Sb{Fe(CO)(4)}(4)] reacts with i-PrI, only the monoalkylated antimony complex [Et(4)N](2)[i-PrSb{Fe(CO)(4)}(3)] (8) is obtained. The mixed dialkylantimony complex [Et(4)N][MeEtSb{Fe(CO)(4)}(2)] (9) also can be synthesized from the reaction of 2 with EtI. While the reaction with Br(CH(2))(2)Br produces [Et(4)N](2)[BrSb{Fe(CO)(4)}(3)] (10), treatment with Cl(CH(2))(3)Br forms the monoalkylated product [Et(4)N](2)[Cl(CH(2))(3)Sb{Fe(CO)(4)}(3)] (11) and a dialkylated novel antimony-iron complex [Et(4)N][{&mgr;-(CH(2))(3)}Sb{Fe(CO)(4)}(3)] (12). On the other hand, the reaction with Br(CH(2))(4)Br forms the monoalkylated antimony product and the dialkylated antimony complex [Et(4)N][{&mgr;-(CH(2))(4)}Sb{Fe(CO)(4)}(2)] (13). Complexes 2-13 are characterized by spectroscopic methods or/and X-ray analyses. On the basis of these analyses, the core of the monoalkyl clusters consists of a central antimony atom tetrahedrally bonded to one alkyl group and three Fe(CO)(4) fragments and the dialkyl products are structurally similar to the monoalkyl clusters, with the central antimony bonded to two alkyl groups and two Fe(CO)(4) moieties in each case. The dialkyl complex 3 crystallizes in the monoclinic space group P2(1)/c with a = 13.014(8) ?, b = 11.527(8) ?, c = 17.085(5) ?, beta = 105.04(3) degrees, V = 2475(2) ?(3), and Z = 4. Crystals of 12 are orthorhombic, of space group Pbca, with a = 14.791(4) ?, b = 15.555(4) ?, c = 27.118(8) ?, V = 6239(3) ?(3), and Z = 8. The anion of cluster 12 exhibits a central antimony atom bonded to three Fe(CO)(4) fragments with a -(CH(2))(3)- group bridging between the Sb atom and one Fe(CO)(4) fragment. This paper discusses the details of the reactions of [Et(4)N](3)[Sb{Fe(CO)(4)}(4)] with a series of alkyl halides and dihalides. These reactions basically proceed via a novel double-alkylation pathway, and this facile methodology can as well provide a convenient route to a series of alkylated antimony-iron carbonyl clusters.     

Double-stranded W/Ag/S chain structure generated from [syn-(WO(NCS)(2))(2)(mu-S)(2)] building blocks

The dimeric W(V) complex [Et(4)N](4)[syn-(O=W(NCS)(3))(2)(mu-S)(2)], 1, prepared from [Et(4)N](2)[WS(4)], SCN(-), and Cd(2+), shows interesting reactivity patterns in that the thiocyanate trans to the oxo group can in part be replaced, initiated by Mn(2+), by dimethylformamide (DMF) to form [Et(4)N](2.5)[(O=W(NCS)(2.25)(DMF)(1.25))(2)(mu-S)(2)], 2. With Ag(+), 1 undergoes partial replacement of SCN(-) by DMF and coordinates to the silver ions to generate ([Et(4)N](2.5)[(W(2)O(2)(NCS)(2)(mu-S)(2))(mu-NCS)(2)(DMF)(Ag(0.5)(SCN))])(n), 3. Compound 3 constitutes a polymeric double-stranded chain, with normal bonding interactions [via W-(mu-NCS)-Ag] between the two strands, and moderate intrastrand [W-(mu-NCS).Ag] bonding. The crystal and molecular structures of the three compounds are described.     

Heterobimetallic Clusters of Copper(I) with Trithiotungstate and Trithiomolybdate. Synthesis and Characterization of the Octanuclear Clusters [Et(4)N](4)[M(4)Cu(4)S(12)O(4)] (M = Mo, W) and the Dodecanuclear Clusters [M(4)Cu(4)S(12)O(4)(CuTMEN)(4)] (M = Mo, W; TMEN = N,N,N',N'-Tetramethylethylenediamine)

Synthetic methods for [Et(4)N](4)[W(4)Cu(4)S(12)O(4)] (1), [Et(4)N](4)[Mo(4)Cu(4)S(12)O(4)] (2), [W(4)Cu(4)S(12)O(4)(CuTMEN)(4)] (3), and [Mo(4)Cu(4)S(12)O(4)(CuTMEN)(4)] (4) are described. [Et(4)N](2)[MS(4)], [Et(4)N](2)[MS(2)O(2)], Cu(NO(3))(2).3H(2)O, and KBH(4) (or Et(4)NBH(4)) were used as starting materials for the synthesis of 1 and 2. Compounds 3 and 4 were produced by reaction of [Et(4)N](2)[WOS(3)], Cu(NO(3))(2).3H(2)O, and TMEN and by reaction of [Me(4)N](2)[MO(2)O(2)S(8)], Cu(NO(3))(2).3H(2)O, and TMEN, respectively. Crystal structures of compounds 1-4 were determined. Compounds 1 and 2 crystallized in the monoclinic space group C2/c with a = 14.264(5) ?, b = 32.833(8) ?, c = 14.480(3) ?, beta = 118.66(2) degrees, V = 5950.8(5) ?(3), and Z = 4 for 1 and a = 14.288(5) ?, b = 32.937(10) ?, c = 14.490(3) ?, beta = 118.75(2) degrees, V = 5978.4(7) ?(3), and Z = 4 for 2. Compounds 3 and 4 crystallized in the trigonal space group P3(2)21 with a = 13.836(6) ?, c = 29.81(1) ?, V = 4942(4) ?(3), and Z = 3 for 3 and a = 13.756(9) ?, c = 29.80(2) ?, V = 4885(6) ?(3), and Z = 3 for 4. The cluster cores have approximate C(2v) symmetry. The anions of 1 and 2 may be viewed as consisting of two butterfly-type [CuMOS(3)Cu] fragments bridged by two [MOS(3)](2-) groups. Eight metal atoms in the anions are arranged in an approximate square configuration, with a Cu(4)M(4)S(12) ring structure. Compounds 3 and 4 can be considered to consist of one [M(4)Cu(4)S(12)O(4)](4-) (the anions of 1 and 2) unit capped by Cu(TMEN)(+) groups on each M atom; the Cu(TMEN)(+) groups extend alternately up and down around the Cu(4)M(4) square. The electronic spectra of the compounds are dominated by the internal transitions of the [MOS(3)](2-) moiety. (95)Mo NMR spectral data are investigated and compared with those of other compounds.     

Preparation of propargyl hydroperoxides by regioselective oxidation of allenic zinc reagents with molecular oxygen

Treatment of allenic zinc reagents (R(1)R(2)C[double bond]C[double bond]C(R(3))ZnL), generated by the reaction of propargyl derivative (R(1)R(2)C(X)[triple bond](CH) with triorganozincates (R(3)(3)ZnLi), under oxygen atmosphere in the presence of ZnCl(2) and chlorotrimethylsilane afforded propargyl hydroperoxides (R(1)R(2)C(OOH)C[triple bond];CR(3)) regioselectively. In this reaction, the use of ZnCl(2) and chlorotrimethylsilane as additives is essential for the transformation of the initially generated allenic reagents to more reactive chlorozinc species.     

Initial example of a triangular single-molecule magnet from ligand-induced structural distortion of a [MnIII3O]7+ complex

The reaction of [Mn3O(O2CR)6(py)3](ClO4) (R = Me, Et) with methyl 2-pyridyl ketone oxime (mpkoH) in a 1:3 molar ratio in MeOH/MeCN leads to [Mn3O(O2CR)3(mpko)3](ClO4) in 80-90% isolated yield. Ferromagnetic exchange interactions between the three MnIII ions in the nonplanar [MnIII3O]7+ triangular core lead to a spin ground state of S = 6; single-crystal studies reveal the temperature and sweep rate dependent hysteresis loops expected for a single-molecule magnet.     

1,2-Distanna-closo-dodecaborate--a rare example of a 1,2-distannylene ligand in transition metal chemistry

The coordination chemistry of the novel bidentate tin ligand 1,2-distanna-closo-dodecaborate is illustrated for the first time by reactions with molybdenum, platinum and gold metal complexes. Up to three clusters coordinate two metal centers in close proximity. For all these metal complexes the typical μ-bridging coordination mode was observed exclusively. Furthermore, two cluster anions react with dichloromethane via substitution of the chloride ions. The carbon functionalized tin cluster [Et(4)N](2)[CH(2)(Sn(2)B(10)H(10))(2)] and the coordination complexes [Et(3)NMe](6)[Mo(2)(CO)(6)(Sn(2)B(10)H(10))(3)], [Et(3)NMe](2)[{HPt(PEt(3))(2)(Sn(2)B(10)H(10))}(2)], [Et(4)N](2)[{HPt(PPh(3))(2)(Sn(2)B(10)H(10))}(2)] and [{(TP)Au}(2)(Sn(2)B(10)H(10))] (TP = PhP(o-Ph(2)PC(6)H(4))(2)) are fully characterized by multinuclear NMR spectroscopy, elemental analyses and crystal structure analyses.     

Fragmentation of negative ions from carbohydrates: Part 2. Fragmentation of high-mannose N-linked glycans

[M + NO3]- And [M + (NO3)2]2- ions were produced by electrospray from neutral high-mannose ([Man](5-9)[GlcNAc]2, [Glc](1-3)[Man](4-9)[GlcNAc]2) N-linked glycans and their 2-aminobenzamide derivatives sprayed from methanol:water containing ammonium nitrate. Low energy collision-induced decomposition (CID) spectra of both types of ions were almost identical and dominated by cross-ring and C-type fragments, unlike the corresponding spectra of the positive ions that contained mainly B- and Y-type glycosidic fragments. This behavior could be rationalized by an initial proton abstraction from various hydroxy groups by the initially-formed anionic adduct. These negative ion spectra were more informative than the corresponding positive ion spectra and contained prominent ions that were diagnostic of structural features such as the composition of individual antennas that were not easily obtainable by other means. C-ions defined the sequence of the constituent monosaccharide residues. Detailed fragmentation mechanisms are proposed to account for many of the diagnostic ions.     

Exhaustive chlorination of [B12H12]2- without chlorine gas and the use of [B12Cl12]2- as a Supporting anion in catalytic hydrodefluorination of aliphatic C-F bonds

The fully chlorinated closo-dodecaborate salt Cs(2)[B(12)Cl(12)] was prepared in high yield from Cs(2)[B(12)H(12)] and SO(2)Cl(2) in acetonitrile at refluxing temperature. [Ph(3)C](2)[B(12)Cl(12)] was obtained by simple metathesis reactions. Catalytic hydrodefluorination of benzotrifluoride sp(3) C-F bonds was accomplished using [Ph(3)C](2)[B(12)Cl(12)] as a precatalyst and Et(3)SiH as a stoichiometric reagent. Full consumption of the sp(3) C-F bonds in p-FC(6)H(4)CF(3) and C(6)F(5)CF(3) with a turnover number up to 2000 was achieved.     

Tautomerization of methyldiazene to formaldehyde-hydrazone in ruthenium and osmium complexes

Mixed-ligand hydrazine complexes [M(CO)(RNHNH2)P4](BPh4)2 (1, 2) [M = Ru, Os; R = H, CH3, C6H5; P = P(OEt)3] with carbonyl and triethyl phosphite were prepared by allowing hydride [MH(CO)P4]BPh4 species to react first with HBF4.Et2O and then with hydrazines. Depending on the nature of the hydrazine ligand, the oxidation of [M(CO)(RNHNH2)P4](BPh4)2 derivatives with Pb(OAc)4 at -30 C gives acetate [M(kappa1-OCOCH3)(CO)P4]BPh4 (3a), phenyldiazene [M(CO)(C6H5N=NH)P4](BPh4)2 (3c, 4c), and methyldiazene [M(CO)(CH3N=NH)P4](BPh4)2 (3b, 4b) derivatives. Methyldiazene complexes 3b and 4b undergo base-catalyzed tautomerization of the CH3N=NH ligand to formaldehyde-hydrazone NH2N=CH2, giving the [M(CO)(NH2N=CH2)P4](BPh4)2 (5, 6) derivatives. Complexes 5 and 6 were characterized spectroscopically and by the X-ray crystal structure determination of the [Ru(CO)(NH2N=CH2)[P(OEt)3]4](BPh4)2 (5) derivative. Acetone-hydrazone [M(CO)[NH2N=C(CH3)2]P4](BPh4)2 (7, 8) complexes were also prepared by allowing hydrazine [M(CO)(NH2NH2)P4](BPh4)2 derivatives to react with acetone.     

Self-assembly of D-penicillaminato M6M'8 (M = Ni(II), Pd(II), Pt(II); M' = Cu(I), Ag(I)) clusters and their organization into extended La(III)M6M'8 supramolecular structures

A series of chiral M(6)M'(8) cluster compounds having twelve free carboxylate groups, [M(6)M'(8)(D-pen-N,S)(12)X](5-) (M/M'/X = Pd(II)/Ag(I)/Cl(-) ([1](5-)), Pd(II)/Ag(I)/Br(-) ([2](5-)), Pd(II)/Ag(I)/I(-) ([3](5-)), Ni(II)/Ag(I)/Cl(-) ([4](5-)), Pt(II)/Ag(I)/Cl(-) ([5](5-)), Pd(II)/Cu(I)/Cl(-) ([6](5-)); D-H(2)pen = D-penicillamine), in which six cis-[M(D-pen-N,S)(2)](2-) square-planar units are bound to a [M'(8)X](7+) cubic core through sulfur-bridges, was synthesized by the reactions of cis-[M(D-pen-N,S)(2)](2-) with M' in water in the presence of halide ions. These M(6)M'(8) clusters readily reacted with La(3+) in aqueous buffer to form La(III)(2)M(6)M'(8) heterotrimetallic compounds, La(2)[1](CH(3)COO), La(2)[2](CH(3)COO), La(2)[3](CH(3)COO), La(2)[4](CH(3)COO), La(2)[5](CH(3)COO) and La(2)[6]Cl, in which the M(6)M'(8) cluster units are linked by La(3+) ions through carboxylate groups in a 1?:?2 ratio. While the La(III)(2)M(6)Ag(I)(8) compounds derived from [1](5-), [2](5-), [3](5-), [4](5-) and [5](5-) have a 1D helix supramolecular structure with a right-handedness, the La(III)(2)Pd(II)(6)Cu(I)(8) compound derived from [6](5-) has a 2D sheet-like structure with a triangular grid of the Pd(II)(6)Cu(I)(8) cluster units. When aqueous HCl was added to the reaction solution of [6](5-) and La(3+), another La(III)(2)Pd(II)(6)Cu(I)(8) heterotrimetallic compound, La(2)[6]Cl·HCl, in which the Pd(II)(6)Cu(I)(8) cluster units are linked by La(3+) ions to form a 2D structure with a rectangular grid, was produced. The solid-state structures of these La(III)(2)M(6)M'(8) compounds, determined by single-crystal X-ray crystallography, along with the spectroscopic properties of the M(6)M'(8) cluster compounds in solution, are described.     

Oxidation of [Ru(NH3)5isn](BF4)2 by hyochlorous acid and chlorine in aqueous acidic media

UV-vis stopped-flow studies of the reaction of [Ru(NH3)5isn](2+) (isn = isonicotinamide) with excess HOCl at 25 degrees C demonstrate that it proceeds in two time-resolved steps. In the first step [Ru(NH3)5isn](3+) is produced with the rate law -d[Ru(II)]/dt = 2(aK(h)[H(+)] + b[H(+)][Cl(-)] + c[Cl(-)])[HOCl](tot)[Ru(II)]/(K(h) + [H(+)][Cl(-)]). Here, K(h) is 1.3 x 10(-3) M(2) and corresponds to the equilibrium hydrolysis of Cl2, a is (8.34 +/- 0.19) x 10(3) M(-2) s(-1) and represents the acid-assisted reduction of HOCl, b is (4.04 +/- 0.13) x 10(4) M(-1) s(-1) and represents the reduction of Cl2, and c is (6.25 +/- 0.59) x 10(2) s(-1) and represents the Cl(-)-assisted reduction of HOCl. In the second step [Ru(NH3)5isn](3+) undergoes further oxidation to a mixture of products with the rate law -d[Ru(III)]/dt = e[Ru(III)][HOCl]/[H(+)] where e is (1.18 +/- 0.01) x 10(-2) s(-1). This step is assigned a mechanism with Cl(+) transfer from HOCl to [Ru(III)(NH3)4(NH2)isn](2+) occurring in the rate-limiting step. These results underline the resistance of HOCl to act as a simple outer-sphere one-electron oxidant.     

Redox state switching of transition metals by deprotonation of the tridentate ligand 2,6-bis(imidazol-2-yl)pyridine

The chemistry of the ligand 1, 2,6-bis(imidazol-2-yl)pyridine with manganese, cobalt, nickel and ruthenium has been investigated. The ligand binds as a meridional tridentate ligand as shown by the crystal structures of [Mn(1)2](CF3SO3)2 x Et2O and [Ru(1)2](PF6)2 x 2CH3CN x H2O. The coordinated ligand is deprotonated in mildly basic solution, and this leads to a drop in the metal M(III)/M(II) reduction potential for cobalt and ruthenium of roughly 1.3 V. The crystal structure of Na2(PPN)[Co(1 - 2H)2]2(OH) x MeOH x 2H2O confirms the deprotonation and shows sodium to bind to the deprotonated nitrogen atoms. No stabilisation of the M(III) oxidation state was observed for nickel and manganese.     

Coordinatively Unsaturated Derivatives of Group 6 Metal Carbonyls Containing the pi-Donating Ligand 3,5-Di-tert-butylcatecholate

The series of group 6 metal tricarbonyl derivatives of di-tert-butylcatecholate have been synthesized from the reactions of M(CO)(5)THF (M = Cr, Mo, W) with 2 equiv of [Et(4)N][3,5-(t)Bu(2)OC(6)H(2)OH]. Subsequent removal of the free catechol was achieved by the addition of NaOMe. The complexes were shown by X-ray crystallography to exhibit coordinatively unsaturated M degrees centers. These metal dianions which have formally 16e(-) configurations are stabilized by pi-donation from the oxygen atoms of the catecholate ligand. This is evident from the short M-O bond distances, e.g., for M = W, 2.059(6) ? vs 2.151(4) ? for a single bond. The structures of these five-coordinate dianions can be loosely defined as trigonal bipyramidal with the more electron-rich oxygen donor of the catecholate (ortho to the electron-releasing tert-butyl substituent) occupying an equatorial site as indicated by a shorter M-O bond length. The tungsten derivative was shown to reversibly react with CO or phosphines to afford the 18e(-), saturated complexes. Although the molybdenum tricarbonyl derivative reacts with CO to partially provide the tetracarbonyl complex, the analogous process involving chromium did not occur. That is, the formation of an O-->M pi bond vs an additional M-CO bond is favored for M = chromium. Complex 2, [Et(4)N](2)[W(CO)(4)DTBCat], crystallizes in the monoclinic space group P2(1)/c with a = 10.013(5) ?, b = 43.921(14) ?, c = 9.113(4) ?, beta = 115.76(3) degrees, V = 3609(3) ?(3), and d(calc) = 1.429 g/cm(3), for Z = 4. Complex 4, [Et(4)N](2)[Mo(CO)(3)DTBCat], crystallized in the monoclinic space group C2 with a = 18.255(7) ?, b = 8.596(3) ?, c = 22.369(7) ?, beta = 91.05(6) degrees, V = 3510(2) ?(3), and d(calc) = 1.251 g/cm(3), for Z = 4. Similarly, complex 5, [Et(4)N](2)[Cr(CO)(3)DTBCat], crystallized in the monoclinic space group C2 with a = 18.09(2) ?, b = 8.553(3) ?, c = 21.927(11) ?, beta = 91.09(8) degrees, V = 3393(4) ?(3), and d(calc) = 1.208 g/cm(3), for Z = 4.     

Synthesis and characterization of the dimercury(I)-linked compound [PPn]4[(Re7C(CO)21Hg)2]. Oxidative cleavage of the mercury-mercury bond leading to carbidoheptarhenate complexes of mercury(II), including [PPN][Re7C(CO)21Hg(S=C(NME2)2)

The reaction of [PPN](3)[Re(7)C(CO)(21)] with Hg(2)(NO(3))(2).2H(2)O in dichloromethane formed the complex [PPN](4)[(Re(7)C(CO)(21)Hg)(2)] ([PPN](4)[1]), isolated in 60% yield. Analogous salts of [1](4-) with [PPh(4)](+) and [NEt(4)](+) were also prepared. The crystal structure of [PPN](4)[1] showed that two carbidoheptarhenate cores are linked by a dimercury(I) unit (d(Hg-Hg) = 2.610(4) A), with each individual mercury atom face-bridging. Oxidative cleavage of the Hg-Hg bond in [1](4-) was effected by 4-bromophenyl disulfide to form [Re(7)C(CO)(21)HgSC(6)H(4)Br](2-) ([4](2-)), by I(2) to form [Re(7)C(CO)(21)HgI](2-) ([5](2-)), and by Br(2) to form [Re(7)C(CO)(21)HgBr](2-) ([6](2-)). Oxidation of [1](4-) by ferrocenium ion (2 equiv) in the presence of tetramethylthiourea resulted in the derivative [Re(7)C(CO)(21)HgSC(NMe(2))(2)](-) ([7](-)). The molecular structure of [PPN][7] was determined by X-ray crystallography. This is the first example of a carbidoheptarhenate-mercury complex with a neutral ligand on mercury, and ligand exchange was demonstrated by displacement with triethylphosphine. Complex [7](-) can also be prepared by protonating [Re(7)C(CO)(21)HgO(2)CCH(3)](2-) in the presence of tetramethylthiourea. Cyclic voltammetry data to calibrate and compare the redox properties of compounds [1](4-) and [7](-) have been measured.     

Homoleptic 12-coordinate lanthanoids with eta(2)-nitroso ligands

The complexes [Et(4)N](3)[Ln(eta(2)-dcnm)(6)] (Ln = La, Ce, Nd, Gd, dcnm = dicyanonitrosomethanide) have discrete N, O 12-coordination owing to symmetrical chelation of the nitroso donor groups.     

Direct addition of alcohols to organonitriles activated by ligation to a platinum(IV) center

Treatment of trans-[PtCl(4)(RCN)(2)] (R = Me, Et) with R'OH (R' = Me, Et, n-Pr, i-Pr, n-Bu) at 45 degrees C in all cases allowed the isolation of the trans-[PtCl(4)[(E)-NH=C(R)OR'](2)] imino ester complexes, while the reaction between cis-[PtCl(4)(RCN)(2)] and the least sterically hindered alcohols (methanol and ethanol) results in the formation of cis-[PtCl(4)[(E)-NH=C(R)OR'](2)] (R/R' = Me/Me) or trans-[PtCl(4)[(E)-NH=C(Et)OR'](2)] (R' = Me, Et), the latter being formed via thermal isomerization (ROH, reflux, 3 h) of the initially formed corresponding cis isomers. The reaction between alcohols R'OH and cis-[PtCl(4)(RCN)(2)] (R = Me, R' = Et, n-Pr, i-Pr, n-Bu; R = Et; R' = n-Pr, i-Pr, n-Bu), exhibiting greater R/R' steric congestion, allowed the isolation of cis-[PtCl(4)[(E)-NH=C(R)OR'][(Z)-NH=C(R)OR']] as the major products. The alcoholysis reactions of poorly soluble [PtCl(4)(RCN)(2)] (R = CH(2)Ph, Ph) performed under heterogeneous conditions, directly in the appropriate alcohol and for a prolonged time and, for R = Ph, with heating led to trans-[PtCl(4)[(E)-NH=C(R)OR'](2)] (R = CH(2)Ph, R' = Me, Et, n-Pr, i-Pr; R = Ph, R' = Me) isolated in moderate yields. In all of the cases, in contrast to platinum(II) systems, addition of R'OH to the organonitrile platinum(IV) complexes occurs under mild conditions and does not require a base as a catalyst. The formed isomerically pure (imino ester)Pt(IV) complexes can be reduced selectively, by Ph(3)P=CHCO(2)Me, to the corresponding isomers of (imino ester)Pt(II) species, exhibiting antitumor activity, without change in configuration of the imino ester ligands. Furthemore, the imino esters NH=C(R)OR' can be liberated from both platinum(IV) and platinum(II) complexes [PtCl(n)[H=C(R)OR'](2)] (n = 2, 4) by reaction with 1,2-bis(diphenylphosphino)ethane and pyridine, respectively. All of the prepared compounds were characterized by elemental analyses (C, H, N), FAB mass spectrometry, IR, and (1)H, (13)C[(1)H], and (195)Pt (metal complexes) NMR spectroscopies; the E and Z configurations of the imino ester ligands in solution were determined by observation of the nuclear Overhauser effect. X-ray structure determinations were performed for trans-[PtCl(4)[(E)-NH=C(Me)OEt](2)] (2), trans-[PtCl(4)[(E)-NH=C(Et)OEt](2)] (10), trans-[PtCl(4)[(E)-NH=C(Et)OPr-i](2)] (11), trans-[PtCl(4)[(E)-NH=C(Et)OPr-n](2)] (12), and cis-[PtCl(4)[(E)-NH=C(Et)OMe](2)] (14). Ab initio calculations have shown that the EE isomers are the most stable ones for both platinum(II) and platinum(IV) complexes, whereas the most stable configurations for the ZZ isomers are less stable than the respective EZ isomers, indicating an increase of the stability on moving from the ZZ to the EE configurations which is more pronounced for the Pt(IV) complexes than for the Pt(II) species.     

Metallosupramolecular chemistry with bis(benzene-o-dithiolato) ligands

The bis(benzene-o-dithiol) ligands H(4)-1, H(4)-2, and H(4)-3 react with [Ti(OC(2)H(5))(4)] to give dinuclear triple-stranded helicates [Ti(2)L(3)](4)(-) (L = 1(4)(-), 2(4)(-), 3(4)(-)). NMR spectroscopic investigations revealed that the complex anions possess C(3) symmetry in solution. A crystal structure analysis for (PNP)(4)[Ti(2)(2)(3)] ((PNP)(4)[14]) confirmed the C(3) symmetry for the complex anion in the solid state. The complex anion in Li(PNP)(3)[Ti(2)(1)(3)] (Li(PNP)(3)[13]) does not exhibit C(3) symmetry in the solid state due to the formation of polymeric chains of lithium bridged complex anions. Complexes [13](4)(-) and [14](4)(-) were obtained as racemic mixtures of the Delta,Delta and Lambda,Lambda isomers. In contrast to that, complex (PNP)(4)[Ti(2)(3)(3)] ((PNP)(4)[15]) with the enantiomerically pure chiral ligand 3(4)(-) shows a strong Cotton effect in the CD spectrum, indicating that the chirality of the ligands leads to the formation of chiral metal centers. The o-phenylene diamine bridged bis(benzene-o-dithiol) ligand H(4)-4 reacts with Ti(4+) to give the dinuclear double-stranded complex Li(2)[Ti(2)(4)(2)(mu-OCH(3))(2)] containing two bridging methoxy ligands between the metal centers. The crystal structure analysis and the (1)H NMR spectrum of (Ph(4)As)(2)[Ti(2)(4)(2)(mu-OCH(3))(2)] ((Ph(4)As)(2)[(16]) reveal C(2) symmetry for the anion [Ti(2)(4)(2)(mu-OCH(3))(2)](2)(-). For a comparative study the dicatechol ligand H(4)-5, containing the same o-phenylene diamine bridging group as the bis(benzene-o-dithiol) ligands H(4)-4, was prepared and reacted with [TiO(acac)(2)] to give the dinuclear complex anion [Ti(2)(5)(2)(mu-OCH(3))(2)](2)(-). The molecular structure of (PNP)(2)[Ti(2)(5)(2)(mu-OCH(3))(2)] ((PNP)(2)[17]) contains a complex anion which is similar to [16](2)(-), with the exception that strong N-H...O hydrogen bonds are formed in complex anion [17](2)(-), while N-H...S hydrogen bonds are absent in complex anion [16](2)(-).