Thiotungstates containing the syn-[W2(O/S)2(μ-S)2] (E = O, S) and cuboidal [W2Cu2(μ3-S)4] cores

Reaction of [W^VIS₄]²⁻ with ethane-1,2-dithiol edtH₂ in the presence of the sulfide scavenger Cd²⁺ yielded the dinuclear tungstate syn-[{(edt)W^V(O/S)}₂(μ-S)₂]²⁻ (1), with the terminal S/O disordered over the two tungsten sites in the ratio 0.8:02. In the presence of thiocyanate, phosphine and CuI, the anionic cuboidal clusters of composition [{(SCN)₃W^V}₂{Cu^I(PPh₃)}₂(μ₃-S)₄]²⁻ (2) and (3, diphos = 1,2-bis(o-diphenylphosphinophenyl)ethane), and possibly via an intermediate [{(SCN)₃W^VS}₂(μ-S)₂]⁴⁻. The crystal and molecular structures of [Et₄N]₂1, [Et₄N]₂2 · H₂O and [Et₄N]₂3 · H₂O have been determined.     

A novel tetranuclear hydrogenphosphate-bridged Cu(II) cluster. Synthesis, structure, spectroscopy and magnetism of [Cu4(dpyam)4(μ4,η-HPO4)2(μ-X)2]X2(H2O)6 (X = Cl, Br)

Two novel tetranuclear compounds with an unprecedented mode of a hydrogenphosphato bridge, [Cu₄(dpyam)₄(μ₄,η³-HPO₄)₂(μ-X)₂]²⁺ (in which dpyam = di-2-pyridylamine and X = Cl (1), Br (2)) have been synthesised and characterised structurally and magnetically. The Cu(II) ions in the structures each display a square-pyramidal geometry, with two tridentate hydrogenphosphato groups bridging four copper atoms in a μ₄,η³ coordination mode which is rarely found in hydrogenphosphate metal compounds. Each (different) pair of Cu(II) ions is additionally bridged by halide ions, with relatively long Cu-X distances (2.551(3)-2.604(3) Å for 1 and 2.707(1)-2.766(2) Å for 2) and subsequently also a small Cu-X-Cu angle (65.7(1)° and 65.1(1)° for 1 and 61.6(1)° and 62.4(1) for 2) and a large Cu-X-Cu angle (95.5(1)° and 96.5(1)° for 1 and 91.1(1)° and 92.6(1)° for 2). Cu?Cu distances in the tetranuclear units varies from 2.802(3) to 5.232(3) Å for 1 and from 2.834(1) to5.233(1) Å in 2. The lattice structures are stabilised by extensive intermolecular hydrogen bonds. The magnetic susceptibility measurements down to 5 K revealed a weak ferromagnetic interaction between the outer pairs of Cu(II) ions which vary from 22 to 46 cm⁻¹ in 1 and 12 to 33 cm⁻¹ in 2 and a moderately strong antiferromagnetic interaction between the inner Cu(II) ions of −79 cm⁻¹ in 1 and −83 cm⁻¹ in 2, via the Cu-O-P-O-Cu pathway.     

A one-dimensional copper (II) coordination polymer [Cu3(ampym)2(μ1,1-N3)4(μ1,3-N3)2(dmf)2]n (ampym = 2-aminopyrimidine) containing both end-on and end-to-end azido bridges

A new polynuclear copper (II) complex, derived from the azido-bridging ligand and 2-aminopyrimidine, has been synthesized and its 3-D structure has been determined by X-ray diffraction methods at two different temperatures. The compound crystallizes in the triclinic system space group, with the central copper atom lying on an inversion centre. The crystal structure is built up by trinuclear units (each of them contains two double end-on azido bridges) linked through two azide ions in an end-to-end (EE) fashion, to yield the polymer chain [Cu₃(ampym)₂(μ_1,1-N₃)₄(μ_1,3-N₃)₂(dmf)₂]_n. Magnetic susceptibility measurement shows a ferromagnetic interaction above 30 K, whereas a weak anti-ferromagnetic interaction prevails in the range of 30-2 K.     

Dithiolate and diselenolate complexes [Pt2(μ-ECH2CHCHCH2E)(PPh3)4] (E = S, Se): Synthesis, characterisation and mass spectrometric formation of the dichalcogenide species [Pt2(μ-E2)(PPh3)4]

The reactions of [Pt₂(μ-E)₂(PPh₃)₄] (E = S, Se) with cis-1,4-dichlorobut-2-ene (cis-ClCH₂CHCHCH₂Cl) give the dichalcogenolate complexes [Pt₂(μ-ECH₂CHCHCH₂E)(PPh₃)₄]²⁺; an X-ray structure determination on the thiolate complex was carried out. The complexes give the expected dications in ESI mass spectra recorded at very low cone voltages, but at moderate cone voltages undergo facile fragmentation via a retro-Diels-Alder reaction and loss of 1,3-butadiene, giving the dichalcogenide species [Pt₂(μ-E₂)(PPh₃)₄]²⁺. Analogous species containing bidentate phosphine or arsine ligands have been previously generated electrochemically, and studied theoretically.     

The complexes with end-to-end dicyanamide bridges: syntheses, characterization and crystal structures of [Cu(μ1,5-dca)2(phen)]n and [Cd(μ1,5-dca)2(py)2]n (phen=phenanthroline; py=pyridine; dca=dicyanamide, N(CN)2 )

Two new dicyanamide (dicyanamide=[N(CN)₂]⁻, dca) bridged complexes, [Cu(μ_1,5-dca)₂(phen)]_n (1) and [Cd(μ_1,5-dca)₂(py)₂]_n (2) have been synthesized and their structures have been determined by X-ray crystallography diffraction. Complex 1 crystallizes in the monoclinic space group P2(1)/c with a=10.1502(3), b=10.9815(4), c=14.5839(4) Å and Z=4. The adjacent copper atoms are connected by single end-to-end dca bridges to form a chain structure along the b axis. The chains are linked via Cu?N weak interactions to give rise to a 2D layer structure, which furthermore into a 3D structure by the π-π interaction between aromatic rings of adjacent layers. Complex 2 crystallizes in the monoclinic space group C2/m with a=6.6849(10), b=17.476(2), c=13.231(2) Å and Z=4. The cadmium(II) center is six-coordinated with a distorted octahedral geometry, bounded to four N atoms of four dca ligands and two N atoms of two-chelated py ligands. Neighbor Cd(II) atoms are linked by the double end-to-end dca bridges to generate a chain structure, which result in a 2D layer structure through the π-π interactions between the adjacent chains with distances 3.641 Å. EPR and magnetic results of 1 suggest that the complex exhibits a weak ferromagnetic interaction through CuNCNCNCu pathways.     

Sulfide-bridged aggregates from the metalloligand [Pt2(μ-S)2(PPh3)4] and β-diketonate complexes of cobalt(II) and zinc(II)

Reaction of [Pt₂(μ-S)₂(PPh₃)₄] with a range of zinc(II) and cobalt(II) complexes ML₂, where L is a β-diketonate ligand CH₃COCHCOCH₃, PhCOCHCOPh, CF₃COCHCOTh (Th = 2-thienyl)] permits the synthesis of adducts [Pt₂(μ-S)₂(PPh₃)₄M(diketonate)]⁺, isolated as their salts in moderate yields. The cobalt and zinc acetylacetonate complexes were characterised by single-crystal X-ray diffraction studies, which reveal isomorphous structures, with tetrahedral heterometal centres.     

Low temperature matrix photochemistry of M2(CO)4(μ-S-t-Bu)2 and [M(CO)2Cl2] anions, where M = Rh and Ir

Photolysis of M₂(CO)₄(μ-S-t-Bu)₂, where M = Rh or Ir, in Nujol matrices at ca. 90 K results in simple CO loss to form a tricarbonyl intermediate analogous to that observed for Rh₂(CO)₄(μ-Cl)₂. Photolysis of the anions, [M(CO)₂Cl₂]¹⁻, where M = Rh or Ir, in inert ionic matrices at ca. 90 K, results in CO-loss to form an intermediate analogous to that formed by Rh(CO)₂(i-Pr₂HN)Cl. Finally, photolysis of trans-Ir(CO)(PMe₃)₂Cl in a Nujol matrix at ca. 90 K gives rise to a new species whose carbonyl band is shifted slightly down in energy as has been observed for trans-Rh(CO)(PMe₃)₂Cl. In all cases the iridium compounds behave similarly to the rhodium species although the photon energy for iridium photochemistry is typically above that of the rhodium compounds.     

Syntheses and crystal structures of the first iridium complexes with m- and p-terphenyl (tp). {[Ir2(p-tp)(cod)2](BF4)2 · 2CH2Cl2}3 and [Ir(m-tp)(η-C5Me5)](BF4)2

Novel two iridium terphenyl complexes were prepared and their structures were characterized crystallographically. The reaction of [Ir(cod)₂]BF₄ with p-terphenyl (p-tp) in CH₂Cl₂ was carried out to afford dinuclear Ir(I) complex {[Ir₂(p-tp)(cod)₂](BF₄)₂ · 2CH₂Cl₂}₃ (cod=1,5-cyclooctadiene) (1 · 2CH₂Cl₂), whereas the reaction of the intermediate [Ir(η⁵-C₅Me₅)(Me₂CO)₃]³⁺ in Me₂CO with m-terphenyl (m-tp) was done to provide mononuclear Ir(III) complex [Ir(m-tp)(η⁵-C₅Me₅)](BF₄)₂ (2). In complex 1 · 2CH₂Cl₂, two Ir atoms are η⁶-coordinated to both sides of terminal benzene rings from the upper and lower sides in the p-tp ligand, while one Ir atom is η⁶-coordinated to one side of the terminal benzene ring in the m-tp ligand in complex 2. Each crystal structure describes the first coordination mode found in metal complexes with the m- and p-tp ligands.     

[Zn(phen)(O,N,O)(H2O)] and [Zn(phen)(O,N)(H2O)] with O,N,O?is?2,6-dipicolinate and N,O?is?l-threoninate: synthesis, characterization, and biomedical properties

Two ternary Zn(II) complexes, with 1,10-phenanthroline (phen) as the main ligand and a carboxylate-containing ligand [dipicolinate (dipico) or L-threoninate (L-Thr)] as the subsidiary ligand, were prepared and characterized by elemental analysis, Fourier transform IR, UV, and fluorescence spectroscopy, X-ray diffraction, molar conductivity, and electrospray ionization mass spectrometry. X-ray structure analysis shows that both [Zn(phen)(dipico)(H(2)O)]·H(2)O (1) and [Zn(phen)(L-Thr)(H(2)O)Cl]·2H(2)O (2) have octahedral geometry about the Zn(II) atom. Both complexes can inhibit topoisomerase I, and have better anticancer activity than cisplatin against nasopharyngeal cancer cell lines, HK1 and HONE-1, with concentrations causing 50?% inhibition of cell proliferation (IC(50)) in the low micromolar range. Complex 2 has the highest therapeutic index for HK1. Both Zn(II) complexes can induce cell death by apoptosis. Changing the subsidiary ligand in the Zn(II) complexes affects the UV-fluorescence spectral properties of the coordinated phen ligand, the binding affinity for some DNA sequences, nucleobase sequence-selective binding, the phase at which cell cycle progression was arrested for treated cancer cells, and their therapeutic index.     

Thallium(III) complexes of the metalloligands [Pt2(μ-S)2(PPh3)4] and [Pt2(μ-Se)2(PPh3)4]

Reactions of [Pt₂(μ-S)₂(PPh₃)₄] with the diarylthallium(III) bromides Ar₂TlBr [Ar = Ph and p-ClC₆H₄] in methanol gave good yields of the thallium(III) adducts [Pt₂(μ-S)₂(PPh₃)₄TlAr₂]⁺, isolated as their salts. The corresponding selenide complex [Pt₂(μ-Se)₂(PPh₃)₄TlPh₂]BPh₄ was similarly synthesised from [Pt₂(μ-Se)₂(PPh₃)₄], Ph₂TlBr and NaBPh₄. The reaction of [Pt₂(μ-S)₂(PPh₃)₄] with PhTlBr₂ gave [Pt₂(μ-S)₂(PPh₃)₄TlBrPh]⁺, while reaction with TlBr₃ gave the dibromothallium(III) adduct [Pt₂(μ-S)₂(PPh₃)₄TlBr₂]⁺[TlBr₄]⁻. The latter complex is a rare example of a thallium(III) dihalide complex stabilised solely by sulfur donor ligands. X-ray crystal structure determinations on the complexes [Pt₂(μ-S)₂(PPh₃)₄TlPh₂]BPh₄, [Pt₂(μ-S)₂(PPh₃)₄TlBrPh]BPh₄ and [Pt₂(μ-S)₂(PPh₃)₄TlBr₂][TlBr₄] reveal a greater interaction between the thallium(III) centre and the two sulfide ligands on stepwise replacement of Ph by Br, as indicated by shorter Tl-S and Pt?Tl distances, and an increasing S-Tl-S bond angle. Investigations of the ESI MS fragmentation behaviour of the thallium(III) complexes are reported.     

Crystal and molecular structures of {Cu(μ-CCPh)(triphos)}2 [triphos = (PPh2CH2)3CMe]

The binuclear complex {Cu(μ-CCPh)(triphos)}₂ [triphos = (PPh₂CH₂)₃CMe] has been obtained from a reaction between {Cu(CCPh)}_n and triphos. The two copper atoms are bridged unsymmetrically by two CCPh groups, each attached through one carbon only [Cu-C, 2.016(4) Å], the separation between the two coppers being 2.4663(8) Å. Only two of the three phosphorus atoms in each ligand are coordinated to copper [Cu-P(1,2) 2.281, 2.273(1) Å]. The observed structure may be rationalised using a recent theoretical study [C. Mealli, S.S.M.C. Godinho, M.J. Calhorda, Organometallics 20 (2001) 1734] and differs from that assumed for the rationalisation of its luminescence properties [V. Pawlowski, G. Knör, C. Lennartz, A. Vogler, Eur. J. Inorg. Chem. (2005) 3167].     

Synthesis and electrochemical aspects of group 14 iron complexes of the type (η-C5H5)Fe(L)2ER3, L2 = (CO)2, (Ph2P)2CH2; E = C, Si, Ge, Sn

The dicarbonyl and diphosphine complexes of the type (η⁵-C₅H₅)Fe(L)₂ER₃ (L₂ = (CO)₂ (a), (Ph₂P)₂CH₂ (b); ER₃ = CH₃ (1a/b); SiMe₃ (2a/b), GeMe₃ (3a/b), SnMe₃ (4a/b)) were synthesized and studied electrochemically. Cyclic voltammetric studies on the dicarbonyl complexes 1a-4a revealed one electron irreversible oxidation processes whereas the same processes for the chelating phosphine series 1b-4b were reversible. The E_ox values found for the series 1a-4a were in the narrow range 1.3-1.5 V and in the order Si > Sn ≈ Ge > C; those for 1b-4b (involving replacement of the excellent retrodative π-accepting CO ligands by the superior σ-donor and poorer π-accepting phosphines) have much lower oxidation potentials in the sequence Sn > Si ≈ Ge > C. This latter oxidation potential pattern relates directly to the solution ³¹P NMR chemical shift data illustrating that stronger donation lowers the E_ox for the complexes; however, simple understanding of the trend must await the results of a current DFT analysis of the systems.     

A cyclic osmastannyl complex, Os(κ(Sn,P)-SnMe2C6H4PPh2)(κ-S2CNMe2)(CO)(PPh3) derived from the osmastannol complex, Os(SnMe2OH)(κ-S2CNMe2)(CO)(PPh3)2

Treatment of the six-coordinate trimethylstannyl complex, Os(SnMe₃)(κ²-S₂CNMe₂)(CO)(PPh₃)₂ (1) with SnMe₂Cl₂ produces Os(SnMe₂Cl)(κ²-S₂CNMe₂)(CO)(PPh₃)₂ (2), which in turn reacts readily with hydroxide ion to give, Os(SnMe₂OH)(κ²-S₂CNMe₂)(CO)(PPh₃)₂ (3). The osmastannol complex 3 undergoes a reaction with 2 equivalents of ^tBuLi, in which one of the phenyl rings of a triphenylphosphine ligand is “ortho-stannylated”, without cleavage of the Os-Sn bond, to give the cyclic complex, Os(κ²(Sn,P)-SnMe₂C₆H₄PPh₂)(κ²-S₂CNMe₂)(CO)(PPh₃) (4). This novel cyclic complex is selectively functionalised at the tin atom by reaction with SnMe₂Cl₂ which exchanges one methyl group for chloride giving the diastereomeric mixture, Os(κ²(Sn,P)-SnMeClC₆H₄PPh₂)(κ²-S₂CNMe₂)(CO)(PPh₃) (5a/5b). Crystal structure determination reveals that both diastereomers occur in the unit cell. The mixture, 5a/5b, undergoes reaction with hydroxide ion to give the diastereomeric osmastannol complexes, Os(κ²(Sn,P)-SnMeOHC₆H₄PPh₂)(κ²-S₂CNMe₂)(CO)(PPh₃) (6a/6b) and with sodium borohydride to give the corresponding tin-hydride mixture, Os(κ²(Sn,P)-SnMeHC₆H₄PPh₂)(κ²-S₂CNMe₂)(CO)(PPh₃) (7a/7b). Crystal structure determinations for 2, 4, and 5a/5b have been obtained.     

Synthesis and characterisation of [Pt2(μ-S)(μ-I)(PPh3)4] - A cationic iodo analogue of the metalloligand [Pt2(μ-S)2(PPh3)4]

Reaction of [Pt₂(μ-S)₂(PPh₃)₄] with a number of transition metal-iodo complexes leads to the formation of the cationic iodo analogue [Pt₂(μ-S)(μ-I)(PPh₃)₄]⁺, identified using electrospray ionisation mass spectrometry (ESI MS). Synthetic routes to this complex were developed, using the reaction of [Pt₂(μ-S)₂(PPh₃)₄] with either [PtI₂(PPh₃)₂] or elemental iodine. The complex was characterised by NMR spectroscopy, ESI MS and an X-ray structure determination, which reveals the presence of a planar, disordered {Pt₂SI}⁺ core. Monitoring the iodine reaction by ESI MS allows the identification of various iodine species, including the short-lived intermediate [Pt₂(μ-S)₂(PPh₃)₄I]⁺, which allows a mechanism for the reaction to be proposed.     

Chalcogenolato-bridged cyclometallated binuclear palladium complexes: Synthesis, spectroscopy, structures of [Pd2(μ-Cl)(μ-SMes)(C10H6NMe2-C,N)2] and [Pd2(μ-SePh)2(C10H6NMe2-C,N)2]

Reactions of orthometallated binuclear palladium complexes with NaER, obtained by NaBH₄ reduction of R₂E₂ in methanol, gave complexes, [Pd₂(μ-ER)₂(C^∩Y)₂] (HC^∩Y = N,N-dimethylbenzylamine (C₆H₅CH₂NMe₂), N,N-dimethylnaphthylamine (C₁₀H₇NMe₂), tri-o-tolylphosphine {P(tol-o)₃}; ER=SePh, SeMes, TePh, TeMes (Mes = 2,4,6-Me₃C₆H₂). Similar reactions of [Pd₂(μ-Cl)₂(C₁₀H₆NMe₂-C,N)₂] with Pb(SMes)₂ or MesSH in the presence of NaHCO₃ gave chloro/thiolato-bridged complex [Pd₂(μ-Cl)(μ-SMes)(C₁₀H₆NMe₂-C,N)₂]. The newly synthesized complexes were characterized by elemental analysis, UV-Vis, IR, NMR (¹H, ¹³C, ³¹P, ⁷⁷Se, ¹²⁵Te) spectroscopy. These complexes crystallized out preferentially in sym-cis configuration. A low energy charge transfer transition has been identified from chalcogenolate centers to an emptyπ^∗ orbital of cyclometallated ligand in absorption spectroscopy in these complexes. The structures of [Pd₂(μ-Cl)(μ-SMes)(C₁₀H₆NMe₂-C,N)₂] (1) and [Pd₂(μ-SePh)₂(C₁₀H₆NMe₂-C,N) ₂] (3) have been established by single crystal X-ray diffraction analyses. In the former, the two palladium atoms are held together by chloro and thiolato bridges whereas in the latter, the two phenylselenolato ligands bridge two palladium atoms. The pyrolysis of [Pd(μ-TeMes)(C₁₀H₆NMe₂-C,N)]₂ (10) in a furnace gave Pd₇Te₃ whereas thermolysis in TOPO afforded primarily PdTe₂.     

Platinum(II) halide complexes of PPh2(CFCF2) and PPh2(CClCF2). The synthesis and crystal structure of [PtI(μ-I){PPh2(CXCF2)}]2, (X = F, Cl); the first crystallographically characterised iodide-bridged platinum(II) phosphine dimers

The reactions of the fluorovinyl-substituted phosphines PPh₂(CFCF₂) and PPh₂(CClCF₂), with K₂PtX₄ (X = Br, I) have been investigated. The resulting complexes have been characterized by a combination of ¹⁹F and ³¹P{¹H} NMR, IR and Raman spectroscopy. The reactions of these phosphines with K₂PtBr₄ yield the monomeric complexes cis-[PtBr₂{PPh₂(CFCF₂)}₂] (1) and trans-[PtBr₂{PPh₂(CClCF₂)}₂] (2), respectively, whilst the reactions with K₂PtI₄ yield both the monomeric species trans-[PtI₂{PPh₂(CXCF₂)}₂], {X = F (3), Cl (4)}, and the dimeric species [PtI(μ-I){PPh₂(CXCF₂)}]₂, {X = F (5), Cl (6)}. The dimers 5 and 6 represent the first crystallographically characterised platinum(II) iodide-bridged phosphine complexes, and both adopt the symmetric-trans structure.     

Oxidative nuclease activity of ferromagnetically coupled μ-hydroxo-μ-propionato copper(II) complexes [Cu3(L)2(μ-OH)2(μ-propionato)2] (L = N-(pyrid-2-ylmethyl)R-sulfonamidato, R = benzene, toluene, naphthalene)

Three doubly-bridged, trinuclear copper(II) compounds with hydroxo and carboxylato bridges, ^∞₁[Cu₃(L1)₂(μ-OH)₂(μ-propionato)₂](1), [Cu₃(L2)₂(μ-OH)₂(μ-propionato)₂(DMF)₂] (2) and ^∞₁{[Cu₃(L3)₂(μ-OH)₂(μ-propionato)₂]} [Cu₃(L3)₂(μ-OH)₂(μ-propionato)₂(DMF)₂]} (3) [HL1 = N-(pyrid-2-ylmethyl)benzenesulfonylamide, HL2 = N-(pyrid-2-ylmethyl)toluenesulfonylamide, HL3 = N-(pyrid-2-ylmethyl)naphthalenesulfonylamide], have been synthesized and characterized. 1 is built from [Cu₃(L1)₂(μ-OH)₂(μ-propionato)₂] clusters. Each unit contains three copper(II) with two different coordination environments: the terminal centers are square-base pyramidal whereas the central copper is square planar. 2 presents a similar square-base pyramidal geometry in the terminal centers, but the central copper is six-coordinate. 3 shows an unusual 1D coordination polymer comprised of two distinct building blocks: one similar to that found in 1 and the other similar to that found in 2. The magnetic susceptibility measurements (2-300 K) reveal a ferromagnetic interaction between the Cu(II) ions with J values of 76.0, 55.0, and 48.0 cm⁻¹ for 1, 2, and 3, respectively. Emission spectroscopy, thermal denaturation, viscosimetry and cyclic voltammetry show an interaction of the complexes with DNA through the sugar-phosphate backbone. All three Cu(II) complexes were found to be very efficient agents of plasmid DNA cleavage in the presence of ascorbato or mercaptopropionic acid. Both the kinetics and the mechanism of the cleavage reaction have also been examined.     

Further studies on the dialkylation chemistry of [Pt2(μ-S)2(PPh3)4] with activated alkyl halides RC(O)CH2X (X = Cl, Br)

Further studies have been carried out into the reactivity of [Pt₂(μ-S)₂(PPh₃)₄] towards a range of activated alkylating agents of the type RC(O)CH₂X (R = organic moiety, e.g. phenyl, pyrenyl; X = Cl, Br). Alkylation of both sulfide centers is observed for PhC(O)CH₂Br, 3-(bromoacetyl)coumarin [CouC(O)CH₂Br], and 1-(bromoacetyl)pyrene [PyrC(O)CH₂Br], giving dications [Pt₂{μ-SCH₂C(O)R}₂(PPh₃)₄]²⁺, isolated as their PF₆⁻ salts. The X-ray structure of [Pt₂{μ-SCH₂C(O)Ph}₂(PPh₃)₄](PF₆)₂ shows the presence of short Pt?O contacts. In contrast, the corresponding chloro compounds [typified by PhC(O)CH₂Cl] and imino analogues [e.g. PhC(NOH)CH₂Br] do not dialkylate [Pt₂(μ-S)₂(PPh₃)₄]. The ability of PhC(O)CH₂Br to dialkylate [Pt₂(μ-S)₂(PPh₃)₄] allows the synthesis of new mixed-alkyl dithiolate derivatives of the type [Pt₂{μ-SCH₂C(O)Ph}(μ-SR)(PPh₃)₄]²⁺ (R = Et or n-Bu), through alkylation of in situ-generated monoalkylated compounds [Pt₂(μ-S)(μ-SR)(PPh₃)₄]⁺ (from [Pt₂(μ-S)₂(PPh₃)₄] and excess RBr). In these heterodialkylated systems ligand replacement of PPh₃ occurs by the bromide ions in the reaction mixture forming monocations [Pt₂{μ-SCH₂C(O)Ph}(μ-SR)(PPh₃)₃Br]⁺. This ligand substitution can be easily suppressed by addition of PPh₃ to the reaction mixture. The complex [Pt₂{μ-SCH₂C(O)Ph}(μ-SBu)(PPh₃)₄]²⁺ was crystallographically characterized. X-ray crystal structures of the bromide-containing complexes [Pt₂{μ-SCH₂C(O)Ph}(μ-SR)(PPh₃)₃Br]⁺ (R = Et, Bu) are also reported. In both structures the coordinated bromide is trans to the SCH₂C(O)Ph ligand, which adopts an axial position, while the ethyl and butyl substituents adopt equatorial positions, in contrast to the structures of the dialkylated complexes [Pt₂{μ-SCH₂C(O)Ph}₂(PPh₃)₄]²⁺ and [Pt₂{μ-SCH₂C(O)Ph}(μ-SBu)(PPh₃)₄]²⁺ (and many other known analogues) where both alkyl groups adopt axial positions.     

Synthesis, protonation and electrochemical properties of trinuclear NiFe2 complexes Fe2(CO)6(μ3-S)2[Ni(Ph2PCH2)2NR] (R = n-Bu, Ph) with an internal pendant nitrogen base as a proton relay

Two trinuclear NiFe₂ complexes Fe₂(CO)₆(μ₃-S)₂[Ni(Ph₂PCH₂)₂NR] (R = n-Bu, 1; Ph, 2) containing an internal base were prepared as biomimetic models for the active sites of FeFe and NiFe hydrogenases. Treatment of complex Fe₂(CO)₆(μ₃-S)₂[Ni(Ph₂PCH₂)₂N(n-Bu)] (1) with HOTf gave an N-protonated complex [Fe₂(CO)₆(μ₃-S)₂{Ni(Ph₂PCH₂)₂NH(n-Bu)}][OTf] ([1H][OTf]). The structures of complexes 1, 2 and [1H][OTf] were determined by X-ray crystallography, which shows that the proton held by the N atom of [1H][OTf] lies in an equatorial position. Cyclic voltammograms of complexes 1 and [1H][OTf] were studied and compared with that of Fe₂(CO)₆(μ₃-S)₂[Ni(dppe)].     

Study of Pt(II)-aromatic amines complexes of the types cis- and trans-Pt(amine)2I2, [Pt(amine)4]I2 and I(amine)Pt(μ-I)2Pt(amine)I

Pt(II) complexes of the types cis- and trans-Pt(amine)₂I₂ with amines containing a phenyl group were synthesized and studied mainly by IR and multinuclear (¹⁹⁵Pt, ¹H and ¹³C) magnetic resonance spectroscopies. The compounds are not very soluble. In ¹⁹⁵Pt NMR spectroscopy, the cis isomers were observed at slightly lower fields than the trans analogues (average Δδ = 11 ppm) in acetone. In ¹H NMR, the NH groups were also found at slightly lower fields in the cis isomers. The coupling constants ²J(¹⁹⁵Pt-¹HN) varied from 53 to 85 Hz and seem slightly smaller in the trans configuration. The ¹³C NMR spectra of most of the complexes were measured. No coupling constants J(¹⁹⁵Pt-¹³C) were detected due to the low solubility of the compounds. The cis isomers containing a phenyl group on the N atom could not be isolated except for Ph-NH₂ which was shown to be a mixture of isomers in acetone. The tetrasubstituted ionic compounds [Pt(amine)₄]I₂ for the less crowded ligands were also studied mainly by NMR spectroscopy in aqueous solution. The ¹⁹⁵Pt chemical shifts vary between −2855 and −2909 ppm. The coupling constants ³J(¹⁹⁵Pt-¹H) are about 40 Hz. The iodo-bridged dinuclear species I(amine)Pt(μ-I)₂Pt(amine)I were also synthesized and characterized. Two isomers are present in acetone solution for most of the compounds. Their δ(Pt) signals were observed at about −4000 ppm and their coupling constants ²J(¹⁹⁵Pt-¹HN) are around 69 Hz.