Iodide Ligands Research Articles

A novel mixed-valence trinickel complex containing nickel(I), nickel(II) and iodonium moieties

The title complex, [{Ni(C 14H 28N 2S 2) 2}NiI 2] +I −·CH 3CN forms as a crystalline minor product in the oxidation of Ni(C 14H 28N 2S 2) with iodine. X-ray analysis reveals that the trinuclear monocations are racemic and consist of two neutral, square-planar Ni(II)N(amine) 2S(thiolate) 2 units bridged via the thiolate ligands by an unusual NiI 2 + group that can be described as containing Ni(I) and I(I) species. The Ni(I) atom is coordinated to two S(thiolate) ligands, an iodide ligand and an iodonium atom in an unusual distorted trigonal-pyramidal arrangement. The I(I) ion is coordinated to the remaining two S(thiolate) ligands [SIS=171.91(7)°] and to the Ni(I) ion [Ni(I)I(I)=3.0298(14) Å] to yield a T-shaped geometry. Pyramidal coordination at the four sulfur atoms gives each cation a U-shaped conformation in profile.

Synthesis, characterisation, crystal structures and reactivity of a series of ruthenium–cobalt mixed-metal nitrido carbonyl clusters with iodide ligands

Reaction of [Ru 3(μ-H) 2(CO) 9(μ 3-NOMe)] ( 1) with two equivalents of [Cp*Co(CO)I 2] (Cp*=η 5-C 5Me 5) in refluxing THF resulted in the isolation of four new heterometallic tetranuclear nitrido clusters, namely [Ru 3CoH(μ-H)(CO) 6(Cp*){μ-η 2-C(OMe)O}(μ 4-N)(μ-I) 2] ( 2), [Ru 3Co(μ-H) 2(CO) 6(Cp*){μ-η 2-C(OMe)O}(μ 4-N)I(μ-I)] ( 3), [Ru 3Co(μ-H) 2(CO) 6(Cp*){μ-η 2-C(OMe)O}(μ 4-N)I(μ-I)] ( 4) and [Ru 3Co(μ-H) 2(CO) 8(η 5-C 5Me 5)(μ 4-N)(μ-I)] ( 5), together with a triruthenium nitrene cluster [Ru 3(μ-H) 3(CO) 8(μ 3-NOMe)I] ( 6) in moderate yields. The first four clusters have either a chain ( 2) or a spiked triangle ( 3– 5) metal skeleton with the central nitrido atom capping all four metal atoms; alternatively, these four clusters can also be viewed as having a highly distorted butterfly arrangement. Clusters 2, 3 and 4 are isomers with different ligand dispositions. The hinge and an RuRu wing-edge are missing in 2, whereas a wing-edge is lost in each of 3 and 4 (RuRu) and 5 (RuCo). Opening up the hinge metal–metal bond has a significant effect upon the nitrido chemical shift in the 15N-NMR spectrum. Clusters 3 and 4 differ from each other in the coordination site of a terminal iodide ligand, and both clusters are inter-convertible under vigorous conditions. Cluster 6 is a trihydrido nitrene cluster with a terminal iodide ligand. 15N-NMR studies were performed in order to investigate the environment of the nitrogen atoms in these nitrido and nitrene clusters.

Copper(II) and nickel(II) complexes of binucleating macrocyclic bis(disulfide)tetramine ligands.

Novel macrocyclic bis(disulfide)tetramine ligands and several Cu(II) and Ni(II) complexes of them with additional ligands have been synthesized by the oxidative coupling of linear tetradentate N2S2 tetramines with iodine. Facile demetalation of the Ni(II) oxidation products affords the free 20-membered macrocycles meso-9 and rac-9 and the 22-membered macrocycle 16, all of which are potentially octadentate N4S4 ligands. X-ray structure analyses reveal distinctly different conformations for the two isomers of 9; meso-9 shows a stepped conformation in profile with the disulfide groups corresponding to the rise of the step, whereas rac-9 exhibits a V conformation with the disulfide groups near the vertex of the V. No metal complexes of rac-9 have been isolated. Crystallographic studies of three Cu(II) complexes reveal that depending upon the size of the macrocyclic ligand and the nature of the additional ligands (I-, NCO-, and CH3CN), the Cu(II) coordination geometry shows considerable variation (plasticity), with substantial changes in the Cu(II)-disulfide bonding. Thus, a diiodide salt contains six-coordinate Cu(II) to which all four bridging disulfide sulfur atoms form strong equatorial bonds. In contrast, isocyanato complexes of the 20- and 22-membered macrocycles exhibit trigonal-bipyramidal Cu(II) and distorted cis-octahedral Cu(II) geometries, respectively, having only one and no short equatorially bound sulfur atoms. The coordination geometry of the latter complex can also be described as four-coordinate seesaw with two semicoordinated S(disulfide) ligands. Disulfide-->Cu(II) ligand-to-metal charge transfer absorptions of both isocyanato-containing Cu(II) species appear too weak to observe, probably because of poor overlap of the sulfur orbitals with the Cu(II) d-vacancy. The dual disulfide-bridged Ni(II) units of the crystallographically characterized octahedral Ni(II) complex of meso-9 with axial iodide and acetonitrile ligands promote substantial antiferromagnetic coupling (J = -13.0(2) cm-1).

Mono(pentamethylcyclopentadienyl)uranium(III) Complexes: Synthesis, Properties, and X-ray Structures of (η-C5Me5)UI2(THF)3, (η-C5Me5)UI2(py)3, and (η-C5Me5)U[N(SiMe3)2]2

The uranium(III) iodide complex UI3(THF)4 reacts cleanly at ambient temperature with 1 equiv of sodium and potassium pentamethylcyclopentadienide salts in tetrahydrofuran to form the mono-ring uranium(III) complex (η-C5Me5)UI2(THF)3 (1). Additionally, reaction of UI3(THF)4 with 2 equiv or more of K(C5Me5) in THF solution leads to the formation of the bis-ring adduct (η-C5Me5)2UI(THF) (2) in high yield. In the solid state 1 exhibits a pseudo-octahedral mer,trans ligand geometry with the C5Me5 ligand occupying one axial position. U−I bond lengths range from 3.161(1) to 3.179(1) Å, while U−O distances to the THF ligands lie in the range 2.496(8)−2.594(10) Å. 1 also provides a convenient entry into a variety of other mono-ring complexes of uranium(III). In the presence of excess pyridine, the coordinated THF ligands of 1 are readily displaced to form the tris(pyridine) adduct (η-C5Me5)UI2(py)3 (3), which exhibits a mer,trans ligand geometry in the solid state similar to that of 1. Metathesis of the iodide ligands in 1 with 2 equiv of KN(SiMe3)2 affords the bis(amido) complex (η-C5Me5)U[N(SiMe3)2]2 (4). An X-ray diffraction study of this molecule reveals that methyl groups from both amido ligands are involved in agostic interactions with the uranium(III) center.

Bis(2-ethyl-3-hydroxy-4-pyranonato)diiodotin(IV) acetonitrile solvate

In the title compound, [SnI 2 (C 7 H 7 O 3 ) 2 ].C 2 H 3 N, the ligand donor atoms are arranged around the Sn atom in a distorted octahedron, with the iodide ligands cis with respect to one another. The acetonitrile molecule of crystallization occupies interstitial positions in the structure.

Synthesis of Configurationally Stable, Optically Active Organocobalt Compounds

The transmetalation reaction between a series of ortho-lithiated tertiary amine derivatives (N∧C−Li) and [(η5-C5H5)CoI2]2 affords a series of cobaltacyclic compounds of the general form (η5-C5H5)Co(C∧N)I, in which the cobalt center is in a pseudotetrahedral environment. With optically active lithiated compounds, such as those obtained from (R)- or (S)-1-(dimethylamino)-1-phenylethane, the reaction forms a mixture of two diastereoisomers (RC,RCo)-12a, (RC,SCo)-12a‘ and (SC,RCo)-12b, (SC,SCo)-12b‘, respectively, of which the isomers 12a and 12b‘ are predominant, as they are formed with a de of 90%. 1H NMR studies indicate that the compounds are configurationally stable at the cobalt center. Reaction of these species with neutral ligands such as phosphines, phosphites, or isocyanides led to the formation of cationic complexes via substitution of the iodide ligand, this reaction occurring mainly with retention of configuration for the optically active species.

Stabilization of Cerium(IV) in the Presence of an Iodide Ligand: Remarkable Effects of Lewis Acidity on Valence State

The stability of the trivalent state in the lanthanides1 is exploited in the use of SmI2 as a reducing agent,2 and also in the use of [(NH4)2][Ce(NO3)6] (CAN) as an oxidizing agent.3 Cerium is the only lanthanide for which the tetravalent state is readily attained in solution, although in view of the high oxidizing potential of this ion [E°(CeIV/III): 1.7 V (1 M HClO4)] its stability in water must be due to kinetic factors.4 The organometallic chemistry of cerium(IV) is correspondingly sparse5 and it has recently been confirmed experimentally6 that cerocene [Ce(η8C8H8)2] and its analogues7 are best described as [Ce3+{(η8C8H8)2}], i.e. containing cerium(III). We note that in the actinide complexes of the triamidoamines8 [N(CH2CH2NR)3] (particularly the ligand with R ) SiMe2Bu, henceforth NN′3) the higher oxidation states in the metal are stabilized.9 Here we report that as a consequence of exceptionally high Lewis acidity at the metal, cerium(IV) triamidoamines are unusually stable to reduction, even in the presence of an iodide ligand. The solvent-base free trivalent complex [Ce(NN′3)] (1) was readily synthesized (Scheme 1) by a method similar to that which we have used to prepare the group 3 complexes,10 i.e. treatment of [CeCl3(THF)4] with [Li3(THF)3(NN′3)] in dry THF followed by sublimation in vacuo. This bright yellow-orange complex decomposes rapidly in air but is otherwise quite stable.12 The reaction of 1 as a solution in pentane with 0.5-1.5 equiv of chlorine led to an immediate color change to purple and deposition of large purple crystals of the fascinating mixed valence CeIII/IV complex [{Ce(NN′3)}2(μ-Cl)] (2). Similarly, reaction of 1 with bromine gave purple [{Ce(NN′3)}2(μ-Br)] (3). Most unexpectedly, however, the weakest oxidizing agent iodine gave the purple cerium(IV) iodide complex, [Ce(NN′3)I] (4). The molecular structures of 2 (Figure 1) and 313 are analogous to those of the uranium complex [{U(NN′3)}2(μ-Cl)] which we have synthesized by reduction of [U(NN′3)Cl] with potassium.9d The presence of a crystallographic inversion center that coincides with the apparent position of the halogen atoms in the structures of 2 and 3 requires that the two 3-fold symmetric (triamidoamine)cerium fragments are crystallographically equivalent. The anisotropic displacement ellipsoid for the Cl atom in 2 has its greatest amplitude along the Ce-Cl-Ce vector, i.e. at right angles to the expected maximum thermal libration. This is consistent with the presence in 2 and 3 of unsymmetric Ce-X f Ce bridges with the halogen atom disordered between two positions on the intermetallic axis. Although the molecular structure of the triamidoamine fragment in 4 (Figure 2) is unexceptional,9,10 the CeIV-I unit [3.1284(6) A] is without precedent. Known CeIII-I distances range from 3.157(1) A in [CeI3(HOPr)3] to 3.299(1) A in [Ce(η-C8H8)I(THF)3].

Platinum(II) complexes with the tridentate phosphino–thioether ligand bis(2-diphenylphosphinoethyl)sulfide, (PPh 2CH 2CH 2) 2S. X-ray crystal structures of [Pt{(PPh 2CH 2CH 2) 2S}Cl]ClO 4 and [Pt{(PPh 2CH 2CH 2) 2S}I

A series of new four coordinate Pt(II) complexes with the potentially tridentate chelate ligand bis(2-diphenylphosphinoethyl)sulfide (PSP) have been synthesized and characterized and the X-ray crystal stuctures of [Pt(PSP)Cl]ClO 4 and [Pt(PSP)I]I were determined. The spectroscopic data are consistent with the general formula [Pt(PSP)X] n+ with X=Cl −, Br −, I −, SCN −, CN −, thiourea or PPh 3 where all the three donor atoms in PSP are coordinated to platinum in all the complexes. Both the crystal structures show that the coordination sphere of the tridentate chelate system is strongly tetrahedrally distorted from a square planar geometry. The larger iodide ligand appears to cause a greater distortion. The potentially larger trans influence of iodide shows no effect on the structure of the, apparently, rigid Pt(PSP) moiety, whereas the trans influence of the chelating sulfur donor appears to be large which is reflected in unusually long platinum–halogen distances.

Surprising Reactions of Iodo Pt(IV) and Pt(II) Complexes with Human Albumin: Detection of Cys34 Sulfenic Acid

cis-[PtCl2(NH3)2] is the anticancer drug cisplatin, but the iodide analogue cis-[PtI2(NH3)2] is inactive. This inactivity is usually attributed to the greater stability and lower reactivity of Pt−I bonds compared to Pt−Cl in aqueous solution. Interest in reactions of Pt(IV) complexes with thiols arises from the reductive activation of Pt(IV) anticancer drugs in blood plasma. Recently, we found (J. Am. Chem. Soc. 1998, 120, 8253−8254) that low Mr thiols react with Pt(IV)−I bonds of trans,cis-[Pt(en)(OH)2I2] via attack on the coordinated iodo ligand giving rise to reactive chelate-ring-opened Pt(II) ethylenediamine species. Here we report reactions of the Pt(II) and Pt(IV) complexes [Pt(en)I2] and trans,cis-[Pt(en)(OH)2I2] with the major thiol in blood plasma, Cys34 of the protein albumin (66 kDa). Unexpectedly, [Pt(en)I2] reacted more rapidly with albumin than the cisplatin analogue, [Pt(en)Cl2], and did not give products with Pt bound to Cys34. The Pt(IV) chloro analogue, trans,cis-[Pt(en)(OH)2Cl2], did not react at all with albumin. Reactions of trans,cis-[Pt(en)(OH)2I2] with the protein, via direct attack of an iodo ligand on Cys34, gave rise to a relatively stable sulfenic acid derivative, in contrast to reactions with low Mr thiols. Reactions of Pt complexes with thiols in proteins can therefore take a different course: albumin can exert control over the reactivity of Cys34 and stabilize activated derivatives such as the sulfenyl iodide and sulfenic acid. The reactivity of iodide ligands in Pt complexes is much higher than has been previously recognized, and it may be possible to incorporate them into drug design strategies.

Synthesis and characterization of a mixed-ring bis-cyclopentadienyl derivative of neodymium. X-ray crystal structures of ( η-C 5Me 5)NdI 2(py) 3 and ( η-C 5Me 5)( η-C 5H 4SiMe 3)NdI(py)

Reaction of neodymium metal with 1.5 equiv of elemental iodine in iso-propanol, followed by crystallization from THF, leads to isolation of NdI 3(THF) x ( 1). Compound 1 reacts with one equiv of KC 5Me 5 to produce the mono-pentamethylcyclopentadienyl derivative ( η-C 5Me 5)NdI 2(THF) 3 ( 2) in moderate yield. Treatment of 2 with an excess of pyridine in toluene leads to displacement of the THF ligands and formation of the tris-pyridine adduct ( η-C 5Me 5)NdI 2(py) 3 ( 3). Compound 3 reacts with one equiv of KC 5H 4SiMe 3 to yield the mixed-ring complex ( η-C 5Me 5)( η-C 5H 4SiMe 3)NdI(py) ( 4). Single crystal X-ray diffraction studies have been performed on complexes 3 and 4. ( η-C 5Me 5)NdI 2(py) 3 ( 3) adopts a pseudo-octahedral geometry in the solid state, with the cyclopentadienyl ligand occupying one coordination site, the three pyridine ligands in a mer-configuration, and the iodide ligands trans to one another. The Nd–I distance is 3.1603(5) Å, while Nd–N bond lengths to the pyridine ligands are 2.631(4) and 2.678(6) Å. The solid state structure of ( η-C 5Me 5)( η-C 5H 4SiMe 3)NdI(py) ( 4) features a typical bent metallocene Cp 2MX 2 geometry with Nd–I and Nd–N distances of 3.0664(4) and 2.555(4) Å, respectively.

Oxidative-Addition Reactions of Diiodine to Dinuclear Rhodium Pyrazolate Complexes.

The pyrazolato (Pz) rhodium(I) complexes [{Rh(&mgr;-Pz)(CO)(L)}(2)] (L = CNBu(t), P(OMe)(3), PMe(2)Ph, P(OPh)(3), P(p-tolyl)(3)) result from the reaction of [{Rh(&mgr;-Pz)(CO)(2)}(2)] with the appropriate L ligand in a trans:cis ratio ranging from 60:40 (L = CNBu(t)) to 95:5 (L = P(p-tolyl)(3)). The pure trans isomers add 1 molar equiv of diiodine to give the dirhodium(II) complexes [{Rh(&mgr;-Pz)(I)(CO)(L)}(2)] (L = CNBu(t) (6), P(OMe)(3) (7), PMe(2)Ph (8), P(OPh)(3) (9)). These complexes incorporate two iodide ligands trans to the rhodium-rhodium bond, as substantiated by the X-ray structure for 7, while the complex [(P{p-tolyl}(3))(CO)(I)Rh(&mgr;-Pz)(2)(&mgr;-CO)Rh(I)(P{p-tolyl}(3))] (10) contains a bridging ketonic CO ligand, due to the insertion of a terminal CO into the metal-metal bond. The metal-metal bond formation involves a 2e oxidation, since identical compounds (6-9) are obtained by oxidation with [Fe(Cp)(2)](PF(6)) followed by addition of potassium iodide. Further reactions of the dirhodium(II) complexes 6-9 with diiodine leading to the metal-metal rupture are electrophilic additions, as exemplified by the reactions with the positive iodine complex [I(Py)(2)](+). They start at the "endo site" (the metal-metal bond) if it is sterically accessible to the electrophile, to give directly the dirhodium(III) complexes [{Rh(&mgr;-Pz)(I)(CO)(L)}(2)(&mgr;-I)](+) (L = CNBu(t), CO). Otherwise, as for the complexes with P-donor ligands, abstraction of a iodide ligand trans to the metal-metal bond (the "exo site") occurs first, to give the dirhodium(II) cationic complexes [(PR(3))(CO)(I)Rh(&mgr;-Pz)(2)Rh(CO)(PR(3))](+) and triiodide. These react again with diiodine to give dirhodium(III) complexes [{Rh(&mgr;-Pz)(I)(CO)(PR(3))}(2)(&mgr;-I)](+) similar to those described above, but with triiodide or pentaiodide as counterion, as substantiated by the X-ray structure of [{Rh(&mgr;-Pz)(I)(CO)(PMe(2)Ph)}(2)(&mgr;-I)]I(5) (18). The diiridium(II) complexes [{Ir(&mgr;-Pz)(I)(CO)(PR(3))}(2)] (PR(3) = P(OPh)(3), PMe(2)Ph) also react with diiodine to give the cationic diiridium(III) complexes [{Ir(&mgr;-Pz)(I)(CO)(PR(3))}(2)(&mgr;-I)]I(3) through a reaction pathway involving the "exo site", while no reaction is observed for [{Ir(&mgr;-Pz)(I)(CO)(2)}(2)]. Finally, replacement of a carbonyl ligand in [{Rh(&mgr;-Pz)(I)(CO)(L)}(2)(&mgr;-I)](+) (L = CNBu(t), CO) by iodide gives the compounds [(CO)(L)(I)Rh(&mgr;-Pz)(2)(&mgr;-I)Rh(I)(2)(L)].

Pyridine adducts of arylbismuth(III) halides

A range of bismuth trihalide and arylbismuth(III) halide complexes with pyridine ligands has been prepared and structurally characterised. The complex [BiI3(py)3] (py = pyridine) is octahedral with the iodide and pyridine ligands arranged in a mer configuration. A seven-co-ordinate complex [BiCl3(py)4] is also described. The compounds [BiCl2Ph(4-Mepy)2] (4-Mepy = 4-methylpyridine), [BiBr2Ph(4-Mepy)2], [BiBr2Ph(4-Butpy)2] (4-Butpy = 4-tert-butylpyridine) and [BiI2Ph(4-Butpy)2] all have a five-co-ordinate, square-based pyramidal bismuth centre in which the phenyl group occupies the apical position with two trans halides and two trans pyridine ligands residing in the basal plane. In the solid state these moieties are dimerised through a pair of weak asymmetric halide bridging interactions. The complexes [BiBr2Ph(py)2] and [BiI2Ph(4-Mepy)2] have similar monomeric units but in the former case these are weakly associated into polymeric chains rather than dimers whereas, for the latter, dimers are formed through a single bridging iodide. In the structure of the ionic compound [4-ButpyH][BiCl3Ph(4-Butpy)] the [BiCl3Ph(4-Butpy)]– anion is monomeric with a square-based pyramidal structure in which the phenyl group is in an apical site whilst the three chlorides and 4-Butpy ligand occupy the basal positions. An example of a diphenylbismuth halide complex is seen in the structure of [BiIPh2(4-Mepy)], the monomeric unit of which contains a four-co-ordinate bismuth centre with a geometry based on an equatorially vacant trigonal bipyramid in which the two phenyl groups are equatorial and the iodide and 4-methylpyridine ligand are axial. A weak association into polymeric chains occurs through long Bi· · ·I interactions approximately trans to one phenyl group. All compounds are discussed in terms of their structure and bonding and compared with related materials previously characterised.

Iodo(phthalocyaninato)vanadium(III)

A new vanadium phthalocyanine complex with the formula [VI(C32H16N8)], or PcVI (Pc=C32H16N8), has been obtained by the reaction of pure V powder with 1,2-dicyanobenzene under iodine vapour. The V atom is bonded to one apical iodide ligand and four Nisoindole atoms, and has a square pyramidal coordination geometry. The mean V—Nisoindole distance is 1.952 (3) A. The V—I bond is 2.6279 (8) A long and is tilted 1.7 (1)° to the normal of the plane formed by the four Nisoindole atoms. The phthalocyaninato ligand is saucer-shaped.

Radiation kills human peripheral T cells by a Fas-independent mechanism.

The mechanism by which radiation induces human peripheral T cell apoptosis is not known. We examined sequential changes in post-irradiated peripheral blood mononuclear cells (PBMC(S)) taken from normal volunteers, by using flow-cytometer and an anti-CD3 monoclonal antibody, annexin V, propidium iodide, anti-Fas antibody, and anti-Fas ligand antibody. After 5 or 10 Gy of irradiation with a 60Co radiation therapy unit, most of the human peripheral T cells showed positivity against annexin V in 15 h, and positivity against propidium iodide in 23 h after irradiation. On a microscopy-video system, approximately 80% of mononuclear cells revealed apoptotic changes in 24 h after irradiation. Because of its proposed role in activation-induced cytotoxicity, we also examined the Fas (CD95/Apo-1) pathway in killing T cells by irradiation. Irradiated PBMC, displayed no increase in surface Fas expression and caspase-3 activity relative to non-irradiated cells. In addition, the anti-Fas ligand failed to eliminate the apoptotic death of PBMC, after irradiation. These results suggest that irradiation induces direct apoptosis of T cells by a Fas-independent mechanism.

Halocarbonyl alkyne complexes of molybdenum (II) : crystal structures of [MoI2 (CO) (NCMe) (η2-RC2R) 2] (R=Me and Ph) and [MoI2 (CO) (5,6-Me2-1,10-phen) (η2-PhC2Ph)

Reaction of [MoXX′ (CO) 3 (NCMe) 2] with RC2R′ in CH2Cl2 at room temperature gave the bis (alkyne) complexes [MoXX′ (CO) (NCMe) (η2-RC2R′) 2] (X=X′=I, R=R′=Me; X=X′=Br, R=R′=Me, Ph; X′=I, X=Cl, Br, R=R′=Me, Ph) (1→7) in high yield. The molecular structures of [MoI2 (CO) (NCMe) (η2-RC2R) 2] (R=Me, Ph) have been determined by X-ray crystallography. The two structures are very similar, with the two alkyne ligands cis- and parallel to each other and trans- to the two iodo ligands. The carbon monoxide and acetonitrile ligands occupy the two axial sites. Treatment of [MoI2 (CO) (NCMe) (η2-RC2Ph) 2] with an equimolar amount of L∩L {for R=Ph, L∩L=5,6-Me2-1,10-phen, Ph2P (CH2) 2PPh2; for R=Me, L∩L=2,2′-bipy, Ph2P (CH2) nPPh2, n=1, 3, 4} yielded the mono (alkyne) complexes [MoI2 (CO) (L∩L) (η2-RC2Ph) ] (8→13) , which for L∩L=5,6-Me2-1,10-phen, R=Ph (8) was crystallogaphically characterised. The geometry around the molybdenum centre is essentially octahedral, with the phenanthroline ligand trans- to a carbonyl and an iodide ligand, with the alkyne and other iodide group in the axial sites. Reaction of [MoI2 (CO) (NCMe) (η2-MeC2Ph) 2] with two equivalents of NaS2CNMe2 in CH2Cl2 gave [Mo (CO) (S2CNMe2) 2 (η2-MeC2Ph) ] (14) .

Synthesis of dinitroxylcis-diaminoplatinum(ii) complexes and their interaction with DNA

Dinitroxyl complexes of platinum,cis-PtII(APO)2X2, where APO is 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl, were obtained by either a direct reaction of APO with K2PtX4 (X=Cl or I) or a replacement of iodide ligands incis-PtII(APO)2I2 by nitrate and oxalate ligands. The interation of water-solublecis-PtII(APO)2(NO3)2 with, ox spleen DNA resulted in platinated DNA with a degree of modification (r)-7 times lower than that obtained withcis-PtII(NH3)2Cl2 (cisplatin). Melting pointT m, melting range ΔT, and the degree of hyperchromicity ΔH for platinated DNA showed that for equalr values, thecis-PtII(APO)2—DNA adducts increase heterogeneity in the DNA structure much more effectively than thecis-PtII(NH3)2—DNA adducts. Poor platinating activity, substantial disturbance of the DNA structure, as well as low toxicity and moderate antitumor activity ofcis-PtII(APO)2X2 complexes are probably explained by steric hindrances caused by two bulky APO ligands.

Diiodotetrakis[tris(dimethylamino)phosphine oxide-O]bismuth(III) Pentaiodide, [BiI2{OP(NMe2)3}4][I5

The title compound, [BiI2(C6H18N3OP)4][I5], contains the pseudo-octahedral BiIII cation [BiI2{OP(NMe2)3}4]+, which has crystallographic \overline{4} symmetry, and trans iodide ligands. The central iodine atom of the disordered [I5]− anion is also situated on a site of \overline{4} symmetry, and the atoms of this anion form an infinite three-dimensional network, resulting in a `cage' type structure. The cations are situated within the `cage' cavities.

Model reactions of a carbonylation catalyst: phosphite induced migratory CO insertion in [MeIr(CO) 2I 3] −

Carbonylation of the anionic iridium(III) methyl complex, [MeIr(CO) 2I 3] − ( 1) is an important step in the new iridium-based process for acetic acid manufacture. A model study of the migratory insertion reactions of 1 with P-donor ligands is reported. Complex 1 reacts with phosphites to give neutral acetyl complexes, [Ir(COMe)(CO)I 2L 2] (L = P(OPh) 3 ( 2), P(OMe) 3 ( 3)). Complex 2 has been isolated and fully characterised from the reaction of Ph 4As[MeIr(CO) 2I 3] with AgBF 4 and P(OPh) 3; comparison of spectroscopic properties suggests an analogous formulation for 3. IR and 31P NMR spectroscopy indicate initial formation of unstable isomers of 2 which isomerise to the thermodynamic product with trans phosphite ligands. Kinetic measurements for the reactions of 1 with phosphites in CH 2Cl 2 show first order dependence on [ 1], only when the reactions are carried out in the presence of excess iodide. The rates exhibit a saturation dependence on [ L] and are inhibited by iodide. The reactions are accelerated by addition of alcohols (e.g. 18× enhancement for L = P (OMe) 3 in 1:3 MeOH-CH 2Cl 2). A reaction mechanism is proposed which involves substitution of an iodide ligand by phosphite, prior to migratory CO insertion. The observed rate constants fit well to a rate law derived from this mechanism. Analysis of the kinetic data shows that k 1, the rate constant for iodide dissociation, is independent of L, but is increased by a factor of ∼18 on adding 25% MeOH to CH 2Cl 2. Activation parameters for the k 1 step are Δ H ≠ = 71 (±3) kJ mol −, Δ S ≠ = −81 (±9) J mol −1 K −1 in CH 2Cl 2 and Δ H ≠ = 60(±4) kJ mol −1, Δ S ≠ = −93(± 12) J mol −1 K −1 in 1:3 MeOH-CH 2Cl 2. Solvent assistance of the iodide dissociation step gives the observed rate enhancement in protic solvents. The mechanism is similar to that proposed for the carbonylation of 1.

Synthesis, Structure, and Reactivity of Iodo-Functionalized Heterobimetallic Alkoxides of Tin(IV): X-ray Crystal Structures of [I2Sn{Al(OPri)4}2], [I2Sn{Ti(OPri)5}2], [I3Sn{Zr(OPri)5(PriOH)}], and [I2Sn{Mo(C5H5)(CO)3}2

A series of new iodide heterobimetallic isopropoxides [I2Sn{Al(OPri)4}2] (1), [I2Sn{Ti(OPri)5}2] (2), [I2Sn{Nb(OPri)6}2] (3), and [I3Sn{Zr(OPri)5(PriOH)}] (4) obtained on reacting SnI4 with stoichiometric amounts of alkali-metal reagents [KAl(OPri)4]n, [KTi(OPri)5]n, [KZr(OPri)5]n, and [KNb(OPri)6]n, respectively, is reported. The monomeric formulation and hexacoordination of tin proposed for 1−4, on the basis of microanalytical, cryoscopic, and multinuclear (1H, 13C, 27Al, and 119Sn) NMR spectral data, was established for 1, 2, and 4 by single-crystal X-ray diffraction analysis. The solid-state structures of 1 and 2 feature an approximately octahedral tin(IV) center bearing two terminal iodide ligands and two bidentate {Al(OPri)4}- and {Ti(OPri)5}- moieties, containing aluminum or titanium atoms in a distorted tetrahedral or trigonal-bipyramidal environment of OPri ligands, respectively. The crystal structure of 4 represents a bioctahedron formed by the face-sharing interaction of two slightly distorted ...

On the Configuration Resulting from Oxidative Addition of RX to Pd(PPh3)4 and the Mechanism of the cis-to-trans Isomerization of [PdRX(PPh3)2] Complexes (R = Aryl, X = Halide)

The oxidative addition of RI to Pd(0) and further cis-to-trans isomerization, which are involved in the Stille reaction and other Pd-catalyzed syntheses, have been studied. C6Cl2F3I (1, C6Cl2F3 = 3,5-dichlorotrifluorophenyl) adds to Pd(PPh3)4 in THF at room temperature giving cis-[Pd(C6Cl2F3)I(PPh3)2] (2), which could be isolated before isomerization to the more stable trans-[Pd(C6Cl2F3)I(PPh3)2] (3). A 19F NMR kinetic study of the isomerization of 2 in THF at 322.6 K reveals a first-order law riso = kiso[2], with kiso = f + g[2]0 + (h + i[2]0)/([PPh3] + j) (f = (1.66 ± 0.03) × 10-4 s-1, g = (2.5 ± 0.2) × 10-3 mol-1 L s-1, h = (1.3 ± 0.7) × 10-8 mol L-1 s-1, i = (4 ± 2) × 10-7 s-1, and j = (1.4 ± 0.7) × 10-5 mol L-1). A four-pathway mechanism accounts for these results: Two are assigned to the associative replacements of PPh3 coordinated to 2 by an iodide ligand of I−[Pd] (I−[Pd] = 2 or 3), both THF-assisted (coefficient h) or direct (coefficient i), leading to a monoiodide-bridged intermediate cis-{Pd(C6Cl2F3)I(PPh3)(μ-I)-[Pd]}. The later rearranges via terminal-for-bridging iodide exchange to trans-{Pd(C6Cl2F3)I(PPh3)(μ-I)]-[Pd]}, which is finally cleaved by PPh3 yielding complex 3. The other two concurrent pathways are assigned to the isomerization via two consecutive Berry pseudorotations in the pentacoordinated species derived from 2 by coordination of THF (coefficient f) or I−[Pd] (coefficient g). The apparent activation entropy associated with kiso is negative (ΔS⧧ = −21 ± 3 J K-1 mol-1), in agreement with the proposed bimolecular mechanisms.