(NEt(4))(2)[Fe(CN)(2)(CO)('S(3)')]: an iron thiolate complex modeling the [Fe(CN)(2)(CO)(S-Cys)(2)] site of [NiFe] hydrogenase centers

In the search for complexes modeling the [Fe(CN)(2)(CO)(cysteinate)(2)] cores of the active centers of [NiFe] hydrogenases, the complex (NEt(4))(2)[Fe(CN)(2)(CO)('S(3)')] (4) was found ('S(3)'(2-)=bis(2-mercaptophenyl)sulfide(2-)). Starting complex for the synthesis of 4 was [Fe(CO)(2)('S(3)')](2) (1). Complex 1 formed from [Fe(CO)(3)(PhCH=CHCOMe)] and neutral 'S(3)'-H(2). Reactions of 1 with PCy(3) or DPPE (1,2-bis(diphenylphosphino)ethane) yielded diastereoselectively [Fe(CO)(2)(PCy(3))('S(3)')] (2) and [Fe(CO)(dppe)('S(3)')] (3). The diastereoselective formation of 2 and 3 is rationalized by the trans influence of the 'S(3)'(2-) thiolate and thioether S atoms which act as pi donors and pi acceptors, respectively. The trans influence of the 'S(3)'(2-) sulfur donors also rationalizes the diastereoselective formation of the C(1) symmetrical anion of 4, when 1 is treated with four equivalents of NEt(4)CN. The molecular structures of 1, 3 x 0.5 C(7)H(8), and (AsPh(4))(2)[Fe(CN)(2)(CO)('S(3)')] x acetone (4 a x C(3)H(6)O) were determined by X-ray structure analyses. Complex 4 is the first complex that models the unusual 2:1 cyano/carbonyl and dithiolate coordination of the [NiFe] hydrogenase iron site. Complex 4 can be reversibly oxidized electrochemically; chemical oxidation of 4 by [Fe(Cp)(2)PF(6)], however, led to loss of the CO ligand and yielded only products, which could not be characterized. When dissolved in solvents of increasing proton activity (from CH(3)CN to buffered H(2)O), complex 4 exhibits drastic nu(CO) blue shifts of up to 44 cm(-1), and relatively small nu(CN) red shifts of approximately 10 cm(-1). The nu(CO) frequency of 4 in H(2)O (1973 cm(-1)) is higher than that of any hydrogenase state (1952 cm(-1)). In addition, the nu(CO) frequency shift of 4 in various solvents is larger than that of [NiFe] hydrogenase in its most reduced or oxidized state. These results demonstrate that complexes modeling properly the nu(CO) frequencies of [NiFe] hydrogenase probably need a [Ni(thiolate)(2)] unit. The results also demonstrate that the nu(CO) frequency of [Fe(CN)(2)(CO)(thiolate)(2)] complexes is more significantly shifted by changing the solvent than the nu(CO) frequency of [NiFe] hydrogenases by coupled-proton and electron-transfer reactions. The "iron-wheel" complex [Fe(6)[Fe('S(3)')(2)](6)] (6) resulting as a minor by-product from the recrystallization of 2 in boiling toluene could be characterized by X-ray structure analysis.     

The electronic structure of the tris(ethylene) complexes [M(C2H4)3] (M=Ni, Pd, and Pt): a combined experimental and theoretical study

In this article we analyze in detail the electronic properties of the D(3h)-symmetric tris(ethylene) complexes of nickel, palladium, and platinum ([M(C(2)H(4))(3)] M=Ni, Pd, Pt). In the case of [Pd(C(2)H(4))(3)] the analysis is based on new experimental IR and Raman spectra for the matrix-isolated molecules and in all cases on the results of quantum-chemical (DFT) calculations. The experimental spectra collected for [Pd(C(2)H(4))(3)] provide evidence for several previously unobserved vibrational modes, including the in-phase and out-of-phase nu(C-C) and delta(CH(2)) modes, and the in-phase nu(M-C) mode. Special consideration is given to possible inter-ligand interactions. The interaction force constant f(CC,CC) between two C(2)H(4) ligands can be directly estimated from the spectra, and its very small value (0.002 N m(-1)) indicates the absence of any significant inter-ligand interaction. An analysis of the topology of the theoretical electron density distribution, rho(r), and the corresponding Laplacian, nabla(2)rho(r), for [Pd(C(2)H(4))(3)] and its lighter and heavier homologues [Ni(C(2)H(4))(3)] and [Pt(C(2)H(4))(3)], respectively, is in full agreement with the conclusions drawn from the experimental results. The combined experimental and quantum-chemical results provide detailed insights in the electronic properties of these prototypical ethylene complexes.     

Oxidative cleavage of tetraaryltetraphosphane-1,4-diides by nickel(II) and palladium(II): formation of unusual Ni(0) and Pd(0) diaryldiphosphene complexes

[Na(2)(thf)(4)(P(4)Mes(4))] (1) (Mes = 2,4,6-Me(3)C(6)H(2)) reacts with one equivalent of [NiCl(2)(PEt(3))(2)], [NiCl(2)(PMe(2)Ph)(2)], [PdCl(2)(PBu(n)(3))(2)] or [PdCl(2)(PMe(2)Ph)(2)] to give the corresponding nickel(0) and palladium(0) dimesityldiphosphene complexes [Ni(eta(2)-P(2)Mes(2))(PEt(3))(2)] (2), [Ni(eta(2)-P(2)Mes(2))(PMe(2)Ph)(2)] (3), [Pd(eta(2)-P(2)Mes(2))(PBu(n)(3))(2)] (4) and [Pd(eta(2)-P(2)Mes(2))(PMe(2)Ph)(2)] (5), respectively, via a redox reaction. The molecular structures of the diphosphene complexes 2-5 are described.     

The versatile reactivity of cyclo-(P5tBu4)- with complexes of the nickel triad

Na[cyclo-(P(5)tBu(4))] (1) reacts with [NiCl(2)(PEt(3))(2)] and [PdCl(2)(PMe(2)Ph)(2)] with elimination of tBuCl and formation of the corresponding metal(0) cyclopentaphosphene complexes [Ni{cyclo-(P(5)tBu(3))}(PEt(3))(2)] (2) and [Pd{cyclo-(P(5)tBu(3))}(PMe(2)Ph)(2)] (3). In contrast, complexes with the more labile triphenylphosphane ligand, such as [MCl(2)(PPh(3))(2)] (M=Ni, Pd), react with 1 with formation of [NiCl{cyclo-(P(5)tBu(4))}(PPh(3))] (4) and [Pd{cyclo-(P(5)tBu(4))}(2)] (5), respectively, in which the cyclo-(P(5)tBu(4)) ligand is intact. In the case of palladium, the cyclopentaphosphene complex [Pd{cyclo-(P(5)tBu(3))}(PPh(3))(2)] (6) in trace amounts is also formed. However, [Ni{cyclo-(P(5)tBu(4))}(2)] (7) is easily obtained by reaction of two equivalents of 1 and one equivalent of [NiCl(2)(bipy)] at room temperature. Complex 7 rearranges on heating in n-hexane or toluene to the previously unknown [Ni{cyclo-(P(5)tBu(4))PtBu}{cyclo-(P(4)tBu(3))}] (8), which presumably is formed via the intermediate [Ni{cyclo-(P(5)tBu(4))}{cyclo-(P(4)tBu(3))PtBu}], which, after an unexpected and unprecedented phosphanediide migration, gives 8, but always as an inseparable mixture with 7. In the reaction of 1 with [PtCl(2)(PPh(3))(2)], ring contraction and formation of [PtCl{cyclo-(P(4)tBu(3))PtBu}(PMe(2)Ph)] (9) is observed. Complexes 3-5 and 7-9 were characterised by (31)P NMR spectroscopy, and X-ray structures were obtained for 5-9.     

Structural and physical properties of the ferromagnetic tris-dithiooxalato compounds,A[M(II)Cr(III)(C(2)S(2)O(2))(3)], with A(+) = N(n-C(n)()H(2)(n)(+1))(4)(+) (n = 3-5) and P(C(6)H(5))(4)(+) and M(II) = Mn,Fe, Co,and Ni

The structural and magnetic properties of the tris-dithiooxalato salts, A[M(II)Cr(C(2)S(2)O(2))(3)], have been investigated with A(+) = PPh(4)(+), N(n-C(n)()H(2)(n)()(+1))(4)(+), with n = 3-5, where M(II) is Mn, Fe, Co, and Ni. With the exception of A[MnCr(C(2)S(2)O(2))(3)], all the salts are ferromagnets with Curie temperatures, T(c), between 5 and 16 K. In contrast to the corresponding oxalates which are ferromagnetic, the A[MnCr(C(2)S(2)O(2))(3)] compounds are paramagnetic above 2 K. Powder neutron diffraction studies of d(20)-PPh(4)[FeCr(C(2)S(2)O(2))(3)] indicate that no structural phase transitions occur between 2.4 and 285 K and that the coefficient of linear expansion is four times larger for the c-axis than for the a-axis. The crystal structure refined from powder neutron diffraction data confirms the honeycomb layer arrangement observed in the related bimetallic tris-oxalate salts. The M?ssbauer spectra reveal that the iron(II) in PPh(4)[FeCr(C(2)S(2)O(2))(3)] is coordinated mainly to six oxygen atoms of the dithiooxalato ligand but with a minor component of sulfur coordination that increases with aging of the sample; the iron(II) is high-spin in both cases. Powder neutron diffraction profiles of d(20)-PPh(4)[FeCr(C(2)S(2)O(2))(3)] below T(c) show magnetic intensity with a q = 0 propagation vector, confirming the presence of ferromagnetic order.     

Stepwise synthesis, structures, and reactivity of mono-, di-, and trimetallic metal complexes with a 6pi + 6pi quinonoid zwitterion

The benzoquinonemonoimine N,N'-dineopentyl-2-amino-5-alcoholate-1,4-benzoquinonemonoiminium [C(6)H(2)(NHCH(2)t-Bu)(2)(O)(2)] 6, which is a rare example of an organic zwitterion being more stable than its canonical form, is best described as constituted of two chemically connected but electronically not conjugated 6pi electron subunits. The two successive acidities of 6 allow the preparation of mono-, di-, and trimetallic complexes in which the control of the pi-system delocalization becomes possible. Reaction of 6 with NaOt-Bu results in monodeprotonation of one N-H function, and the isolated sodium salt 9, which is stable under N(2), reacts with chloride-bridged Pd(II) homodimetallic complexes, [AuCl(PPh(3))] or trans-[NiCl(Ph)(PPh(3))(2)], to afford the monometallic complexes 10-15 in which the pi-system is localized. A second in situ deprotonation of the remaining N-H amino function of 10 with NaH followed by reaction with [Pd(8-mq)(mu-Cl)](2) (8-mq = orthometalated 8-methylquinoline) affords the homodimetallic complex 17 in which the pi-system of the quinonoid ligand is delocalized between the two metal centers. Deprotonation of both N-H amino functions of the square-planar complex trans-[Ni(N,O)(2)] 15 with NaH and reaction with [Pd(8-mq)(mu-Cl)](2) affords the heterotrimetallic (Pd, Ni, Pd) complex 18 in which the pi-system of the two quinonoid ligands is delocalized between the three metal centers. The crystal structures of the monometallic complexes 10 and 13 and of the dipalladium complex 17 are reported and consequences of metal coordination discussed. Complex 15 was tested in catalytic ethylene oligomerization with AlEtCl(2) as cocatalyst.     

Three-component self-assembly of a series of triply interlocked Pd12 coordination prisms and their non-interlocked Pd6 analogues

Template-assisted formation of multicomponent Pd(6) coordination prisms and formation of their self-templated triply interlocked Pd(12) analogues in the absence of an external template have been established in a single step through Pd-N/Pd-O coordination. Treatment of cis-[Pd(en)(NO(3))(2)] with K(3) tma and linear pillar 4,4'-bpy (en=ethylenediamine, H(3) tma=benzene-1,3,5-tricarboxylic acid, 4,4'-bpy=4,4'-bipyridine) gave intercalated coordination cage [{Pd(en)}(6)(bpy)(3)(tma)(2)](2)[NO(3)](12) (1) exclusively, whereas the same reaction in the presence of H(3) tma as an aromatic guest gave a H(3) tma-encapsulating non-interlocked discrete Pd(6) molecular prism [{Pd(en)}(6)(bpy)(3)(tma)(2)(H(3)tma)(2)][NO(3)](6) (2). Though the same reaction using cis-[Pd(NO(3))(2)(pn)] (pn=propane-1,2-diamine) instead of cis-[Pd(en)(NO(3))(2)] gave triply interlocked coordination cage [{Pd(pn)}(6)(bpy)(3)(tma)(2)](2)[NO(3)](12) (3) along with non-interlocked Pd(6) analogue [{Pd(pn)}(6)(bpy)(3) (tma)(2)](NO(3))(6) (3'), and the presence of H(3) tma as a guest gave H(3) tma-encapsulating molecular prism [{Pd(pn)}(6)(bpy)(3)(tma)(2)(H(3) tma)(2)][NO(3)](6) (4) exclusively. In solution, the amount of 3' decreases as the temperature is decreased, and in the solid state 3 is the sole product. Notably, an analogous reaction using the relatively short pillar pz (pz=pyrazine) instead of 4,4'-bpy gave triply interlocked coordination cage [{Pd(pn)}(6) (pz)(3)(tma)(2)](2)[NO(3)](12) (5) as the single product. Interestingly, the same reaction using slightly more bulky cis-[Pd(NO(3))(2)(tmen)] (tmen=N,N,N',N'-tetramethylethylene diamine) instead of cis-[Pd(NO(3))(2)(pn)] gave non-interlocked [{Pd(tmen)}(6)(pz)(3)(tma)(2)][NO(3)](6) (6) exclusively. Complexes 1, 3, and 5 represent the first examples of template-free triply interlocked molecular prisms obtained through multicomponent self-assembly. Formation of the complexes was supported by IR and multinuclear NMR ((1)H and (13)C) spectroscopy. Formation of guest-encapsulating complexes (2 and 4) was confirmed by 2D DOSY and ROESY NMR spectroscopic analyses, whereas for complexes 1, 3, 5, and 6 single-crystal X-ray diffraction techniques unambiguously confirmed their formation. The gross geometries of H(3) tma-encapsulating complexes 2 and 4 were obtained by universal force field (UFF) simulations.     

Combination of magnetic susceptibility and electron paramagnetic resonance to monitor the 1D to 2D solid state transformation in flexible metal-organic frameworks of Co(II) and Zn(II) with 1,4-bis(triazol-1-ylmethyl)benzene

Two families of coordination polymers, {[M(btix)(2)(OH(2))(2)]·2NO(3)·2H(2)O}(n) [M = Co (1), Zn (2), Co-Zn (3); btix = 1,4-bis(triazol-1-ylmethyl)benzene] and {[M(btix)(2)(NO(3))(2)]}(n) [M = Co (4), Zn (5), Co-Zn (6)], have been synthesized and characterized. The two conformations of the ligand, syn and anti, lead to one-dimensional (1D) cationic chains or two-dimensional (2D) neutral grids. Extrusion of the water molecules of the 1D compounds results in an irreversible transformation into the 2D compounds, which involves a change in conformation of the btix ligands and a rearrangement in the metal environment with cleavage and reformation of covalent bonds. This structural transformation has been followed by electron paramagnetic resonance (EPR) and magnetic susceptibility measurements to monitor the minor modifications that the metal centers suffer.     

Metal-assisted ring-closing/opening process of a chiral tetrahydroquinazoline

The ring-chain tautomerism of a 2-aryl-1,2,3,4-tetrahydroquinazoline has been exploited to induce reversible changes in the aminal-imine equilibrium, as desired, by coordination of a suitable metal ion. This process was studied by NMR and UV-vis spectroscopies, X-ray crystallography, and molecular modeling approach. The results obtained show that the imine H(2)L(i) undergoes a selective ring-closing reaction upon complexation with Ni(2+). As a result, complexes of the type Ni(HL(a))(2) are obtained, whose chirality arises from the chiral ligand H(2)L(a) and the helicity of the structure. Hence, helical enantiomers form the following racemates: [Δ-C(R,R)N(S,S),Λ-C(S,S)N(R,R)]-Ni(HL(a))(2)·2HOAc and [Δ,Λ-C(S,R)N(R,S)]-Ni(HL(a))(2)·4MeOH. In contrast to the situation observed for Ni(2+), the cyclic tautomer of the ligand, H(2)L(a), undergoes a selective ring-opening reaction upon complex formation with Pd(2+), ultimately yielding Pd(HL(i))(2)·MeOH, in which the open-chain imine ligand is bidentate through the N,O donor set of the quinoline residue. Density functional theory calculations were conducted to provide insight into the different behavior of both coordinated metals (Ni(2+) and Pd(2+)) and to propose a mechanism for the metal-assisted opening/closing reaction of the tetrahydroquinazoline ring.     

Metal-metal interactions in heterobimetallic d8-d10 complexes. Structures and spectroscopic investigation of [M'M' '(mu-dcpm)2(CN)2]+ (M' = Pt,Pd; M' ' = Cu,Ag, Au) and related complexes by UV-vis absorption and resonance Raman spectroscopy and ab initio calculations

X-ray structural and spectroscopic properties of a series of heterodinuclear d(8)-d(10) metal complexes [M'M' '(mu-dcpm)(2)(CN)(2)](+) containing d(8) Pt(II), Pd(II), or Ni(II) and d(10) Au(I), Ag(I), or Cu(I) ions with a dcpm bridging ligand have been studied (dcpm = bis(dicyclohexylphosphino)methane; M' = Pt, M' ' = Au 4, Ag 5, Cu, 6; M' ' = Au, M' = Pd 7, Ni 8). X-ray crystal analyses showed that the metal...metal distances in these heteronuclear metal complexes are shorter than the sum of van der Waals radii of the M' and M' ' atoms. The UV-vis absorption spectra of 4-6 display red-shifted intense absorption bands from the absorption spectra of the mononuclear trans-[Pt(phosphine)(2)(CN)(2)] and [M' '(phosphine)(2)](+) counterparts, attributable to metal-metal interactions. The resonance Raman spectra confirmed assignments of (1)[nd(sigma)-->(n + 1)p(sigma)] electronic transitions to the absorption bands at 317 and 331 nm in 4 and 6, respectively. The results of theoretical calculations at the MP2 level reveal an attractive interaction energy curve for the skewed [trans-Pt(PH(3))(2)(CN)(2)-Au(PH(3))(2)(+)] dimer. The interaction energy of Pt(II)-Au(I) was calculated to be ca. 0.45 ev.     

Synthesis, structure and magnetism of homodinuclear complexes of Co, Ni and Cu supported by a novel bitriazine scaffold

Btzn (1), an amine-functionalized bi(1,3,5-triazine) 4,4'-(NH(2))(2)-6,6'-(NHC(6)H(5))(2)-2,2'-(1,3,5-C(3)N(3))(2), is reported, and its coordination with Co, Ni and Cu is explored. Reactions of metal salts (2 equiv) with Btzn (1 equiv) result in dimeric species [(Btzn)Co(2)(NCS)(4)(EtOH)(2)(DMF)(2)], (2), [(Btzn)Ni(2)(η(1)-ONO(2))(2)(MeOH)(4)(DMF)(2)]·2[NO(3)], (3), [(Btzn)Cu(2)Cl(4)(DMF)(2)], (4), and [(Btzn)Cu(2)(η(2)-O(2)NO)(2)(OH(2))(2)(DMF)(2)]·2[NO(3)], (5). These complexes are the first examples of the coordination of transition metals with bi(1,3,5-triazine) ligands. Their structures display a bridging bis-bidentate coordination mode for Btzn. Variable-temperature magnetic susceptibility of the complexes reveals antiferromagnetic exchange between the spin carriers, with calculated exchange coupling values (J) of -4.7 cm(-1) for 3, -18.2 cm(-1) for 4, and -5.5 cm(-1) for 5. An in-depth evaluation of the metal geometry highlights the inefficient overlap of the magnetic d-orbitals through the bridging ligand, most likely leading to reduced delocalization and coupling.     

Di- and trinuclear complexes derived from hexakis(2-pyridyloxy)cyclotriphosphazene. Unusual P-O bond cleavage in the formation of [{(L'CuCl)2(Co(NO3)}Cl] (L' = N3P3(OC5H4N)5(O))

Hexakis(2-pyridyloxy)cyclotriphosphazene (L) is an efficient multisite coordination ligand which binds with transition metal ions to produce dinuclear (homo- and heterometallic) complexes [L(CuCl)(CoCl3)], [L(CuCl)(ZnCl3)], [L(CoCl)(ZnCl3)], and [L(ZnCl2)2]. In these dinuclear derivatives the cyclophosphazene ligand utilizes from five to six nitrogen coordination sites out of the maximum of nine available sites. Further, the spacer oxygen that separates the pyridyl moiety from the cyclophosphazene ring ensures minimum steric strain to the cyclophosphazene ring upon coordination. This is reflected in the near planarity of the cyclophosphazene ring in all the dinuclear derivatives. In the dinuclear heterobimetallic derivatives one of the metal ions [Cu(II) or Co(II)] is hexacoordinate and is bound by the cyclophosphazene in a eta5-gem-N5 mode. The other metal ion in these heterobimetallic derivatives [Co(II) or Zn(II)] is tetracoordinate and is bound in an eta(1)-N(1) fashion. In the homobimetallic derivative, [L(ZnCl2)2], one of the zinc ions is five-coordinate (eta3-nongem-N3), while the other zinc ion is tetracoordinate(eta2-gem-N2). The reaction of L with CuCl2 followed by Co(NO3)2.6H2O yields a trinuclear heterobimetallic complex [{(L'CuCl)2Co(NO3)}Cl] [L' = N3P3(OC5H4N)5(O)]. In the formation of this compound an unusual P-O bond cleavage involving one of the phosphorus-pyridyloxy bonds is observed. The molecular structure of [{(L'CuCl)2Co(NO3)}Cl] [L' = N3P3(OC5H4N)5(O)] reveals that each of the two the P-O-cleaved L' ligands is involved in binding to Cu(II) to generate the motif L'CuCl. Two such units are bridged by a Co(II) ion. The coordination environment around the bridging Co(II) ion contains four oxygen (two P-O units, one chelating nitrate) and two nitrogen atoms (pyridyloxy nitrogens).     

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.     

Synthesis and structural characterisation of group 10 metal(II) gallyl complexes: analogies with platinum diboration catalysts?

Reactions of the anionic gallium(i) heterocycle, [:Ga{[N(Ar)C(H)](2)}](-) (Ar = C(6)H(3)Pr(i)(2)-2,6), with a variety of mono- and bidentate phosphine, tmeda and 1,5-cyclooctadiene (COD) complexes of group 10 metal dichlorides are reported. In most cases, salt elimination occurs, affording either mono(gallyl) complexes, trans-[MCl{Ga{[N(Ar)C(H)](2)}}(PEt(3))(2)] (M = Ni or Pd) and cis-[PtCl{Ga{[N(Ar)C(H)](2)}}(L)] (L = R(2)PCH(2)CH(2)PR(2), R = Ph (dppe) or cyclohexyl (dcpe)), or bis(gallyl) complexes, trans-[M{Ga{[N(Ar)C(H)](2)}}(2)(PEt(3))(2)] (M = Ni, Pd or Pt), cis-[Pt{Ga{[N(Ar)C(H)](2)}}(2)(PEt(3))(2)], cis-[M{Ga{[N(Ar)C(H)](2)}}(2)(L)] (M = Ni, Pd or Pt; L = dppe, Ph(2)CH(2)PPh(2) (dppm), tmeda or COD). The crystallographic and spectroscopic data for the complexes show that the trans-influence of the gallium(i) heterocycle lies in the series, B(OR)(2) > H(-) > PR(3) approximately [:Ga{[N(Ar)C(H)](2)}](-) > Cl(-). Comparisons between the reactivity of one complex, [Pt{Ga{[N(Ar)C(H)](2)}}(2)(dppe)], with that of closely related platinum bis(boryl) complexes indicate that the gallyl complex is not effective for the catalytic or stoichiometric gallylation of alkenes or alkynes. The phosphaalkyne, Bu(t)C[triple bond, length as m-dash]P, does, however, insert into one gallyl ligand of the complex, leading to the novel, crystallographically characterised P,N-gallyl complex, [Pt{Ga{[N(Ar)C(H)](2)}}{Ga{PC(Bu(t))C(H)[N(Ar)]C(H)N(Ar)}}(dppe)]. An investigation into the mechanism of this insertion reaction has been undertaken.     

Organoplatinum complexes containing bis(diphenylphosphino)amine as ligand: uncommon case of N-H . . . I-Pt hydrogen bonding

The complex [PtMe(2)(dppa)], 1a, dppa = Ph(2)PNHPPh(2), which has previously been prepared as a mixture with the dimeric form [Pt(2)Me(4)(micro-dppa)(2)], was synthesized in pure form by the reaction of [PtCl(2)(dppa)] with MeLi. The aryl analogue [Pt(p-MeC(6)H(4))(2)(dppa)], 1b, was prepared by replacement of SMe(2) in cis-[Pt(p-MeC(6)H(4))(2)(SMe(2))(2)] with dppa. The reaction of the chelate complexes 1 with one equiv. of dppa afforded the complexes [PtR(2)(dppa-P)(2)], R=Me, 2a and R=p-MeC(6)H(4) 2b. The reaction of [PtR(2)(dppa)], 1, with neat MeI gave the organoplatinum(iv) complexes [PtR(2)MeI(dppa)], R=Me, 5a and R=p-MeC(6)H(4), 5b. The structure of 5a, determined by X-ray crystallography, indicated that the complex undergoes self-assembly by intermolecular N-H . . . I-Pt hydrogen bonding. MeI was also double oxidatively added to organodiplatinum(ii) complex cis,cis-[Me(2)Pt(micro-SMe(2))(micro-dppa)PtMe(2)], to give diorganoplatinum(iv) complex [Me(3)Pt(micro-dppa)(micro-I)(2)PtMe(3)], 4. The aryl analogue organodiplatinum(ii) complex cis,cis-[(p-MeC(6)H(4))(2)Pt(micro-SMe(2))(micro-dppa)Pt(p-MeC(6)H(4))(2)], 3b, was prepared by the reaction of cis-[Pt(p-MeC(6)H(4))(2)(SMe(2))(2)] with half equiv. of dppa, but 3b refused to react with MeI, probably because of the steric effects of the aryl ligands. The tetramethyl complex [PtMe(4)(dppa)], 6, was prepared either by reaction of 5a with MeLi or by replacement of SMe(2) in [Pt(2)Me(8)(micro-SMe(2))(2)] with dppa. All the complexes were fully characterized in solution by multinuclear NMR ((1)H, (13)C, (31)P and (195)Pt) methods and their coordination compared with that of the corresponding known dppm complexes.     

Reaction of a heterotopic P,SAs ligand with group 10 metal(II) complexes: As-S bond cleavage and the formation of two unusual trinuclear structural isomers for Pd and Pt

The synthesis of the heterotopic P,SAs ligand, 1-Ph(2)AsSC(6)H(4)-2-PPh(2) (1) and its reaction with [PdCl(2)(cod)], [PtI(2)(cod)] (cod = 1,5-cyclooctadiene) and NiCl(2)·6H(2)O is reported. Cleavage of the As-S bond of 1 and coordination of the resulting phosphanylthiolato ligand (SC(6)H(4)-2-PPh(2))(-) (SC(6)H(4)-2-PPh(2) = P,S) was observed with formation of [M(P,S)(2)] (M = Ni, Pd, Pt). In the case of Pd and Pt, not only the mononuclear complexes [M(P,S)(2)] formed, but also the trimers of [MX(P,S)] ([MX{(μ-S-SC(6)H(4)-2-PPh(2))-κ(2)S,P}](3) [M = Pd, X = Cl (2) and M = Pt, X = I (4)]). Formation of 2 and 4 was preceded by the trinuclear isomeric intermediates [(cis-M{(μ-S-SC(6)H(4)-2-PPh(2))-κ(2)S,P}(2))-MX(2)-MX{(μ-S-SC(6)H(4)-2-PPh(2))-κ(2)S,P}] [M = Pd, X = Cl (3) and M = Pt, X = I (5)]. The crystal structures of 1-5 and a possible reaction mechanism that leads to 2 and 4 are presented.     

Neutral (bis-beta-diketonato) iron(III), cobalt(II), nickel(II), copper(II) and zinc(II) metallocycles: structural, electrochemical and solvent extraction studies

Neutral dimeric metallocyclic complexes of type [M(2)(L(1))(2)B(n)] (where M = cobalt(II), nickel(II) and zinc(II), L(1) is the doubly deprotonated form of a 1,3-aryl linked bis-beta-diketone ligand of type 1,3-bis(RC(O)CH(2)C(O))C(6)H(4) (R=Me, n-Pr, t-Bu) and B is pyridine (Py) or 4-ethylpyridine (EtPy)) have been synthesised, adding to similar complexes already reported for copper(II). New lipophilic ligand derivatives with R = octyl or nonyl were also prepared for use in solvent extraction experiments. Structural, electrochemical and solvent extraction investigations of selected metal complex systems from the above series are reported, with the X-ray structures of [Co(2)(L(1))(2)(Py)(4)] x 2.25CHCl(3) x 0.5H(2)O (R=Pr), [Co(2)(L(1))(2)(EtPy)(4)] (R=t-Bu), [Ni(2)(L(1))(2)(EtPy)(4)] (R=t-Bu), [Zn(2)(L(1))(2)(EtPy)(2)] (R=Me) and [Zn(2)(L(1))(2)(EtPy)(4)] (R=t-Bu) being presented. The electrochemistry of H(2)L(1) (R=t-Bu) and of [Fe(2)(L(1))(3)], [Co(2)(L(1))(2)(Py)(4)], [Ni(2)(L(1))(2)(Py)(4)], [Cu(2)(L(1))(2)] and [Zn(2)(L(1))(2)(Py)(2)] has been examined. Oxidative processes for the complexes are dominantly irreversible, but several examples of quasireversible behaviour were observed and support the assignment of an anodic process, seen between +1.0 and +1.6 V, as a metal-centred oxidation. The reduction processes for the respective metal complexes are not simple, and irreversible in most cases. Solvent extraction studies (water/chloroform) involving variable concentrations of metal, bis-beta-diketone and heterocyclic base have been performed for cobalt(II) and zinc(II) using a radiotracer technique to probe the stoichiometries of the extracted species in each case. Synergism was observed when 4-ethylpyridine was added to the bis-beta-diketone ligand in the chloroform phase. Competitive extraction studies show a clear uptake preference for copper(II) over cobalt(II), nickel(II), zinc(II) and cadmium(II).     

Experimental evidence for the noninnocence of o-aminothiophenolates: coordination chemistry of o-iminothionebenzosemiquinonate(1-) pi-radicals with Ni(II), Pd(II), Pt(II)

The ligand 2-mercapto-3,5-di-tert-butylaniline, H[L(AP)], an o-aminothiophenol, reacts with metal(II) salts of Ni and Pd in CH3CN or C2H5OH in the presence of NEt3 under strictly anaerobic conditions with formation of beige to yellow cis-[M(II)(L(AP))2] (M = Ni (1), Pd (2)) where (L(AP))1- represents the o-aminothiophenolate(1-) form. The crystal structure of cis-[Pd(II)(L(AP))2][HN(C2H5)3][CH3CO2] has been determined by X-ray crystallography. In the presence of air the same reaction produces dark blue solutions from which mixtures of the neutral complexes trans/cis-[M(II)(L(ISQ))2] (M = Ni (1a/1b), Pd (2a/2b), and Pt (3a/3b)) have been isolated as dark blue-black solid materials. By using HPLC the mixture of 3a/3b has been separated into pure samples of 3a and 3b, respectively; (L(ISQ))1- represents the o-iminothionebenzosemiquinonate(1-) pi-radical. The structures of 1a.dmf and 3a.CH2Cl2 have also been determined. All compounds are square-planar and diamagnetic. 1H NMR spectroscopy established the cis <==> trans equilibrium of 1a/1b, 2a/2b, and 3a/3b in CH2Cl2 solution where the isomerization rate is very fast for the Ni, intermediate for the Pd, and very slow for the Pt species. It is shown that the electronic structures of 1a/1b, 2a/2b, 3a, and 3b are best described as diradicals with a singlet ground state. The spectro- and electrochemistries of all complexes display the usual full electron transfer series where the monocation, the neutral species, the mono- and dianions have been spectroscopically characterized. X-band EPR spectra of the monocations [1a/1b]+ and [3a]+ support the assignment of an oxidation-state distribution as predominantly [M(II)(L(ISQ))(L(IBQ))]+ where (L(IBQ))0 represents the o-iminothionequinone level. In contrast, the EPR spectra of the monoanions [1a/1b]- and [3a]- indicate an [M(II)(L(ISQ))(L(AP)-H)]- distribution but with a significant contribution of the [M(I)(L(ISQ))(2)]- resonance hybrid; (L(AP)-H)2- represents the o-imidothiophenolato(2-) oxidation level. Analysis of the geometric features of 120 published structures of complexes containing ligands of the o-aminothiophenolate type show that high precision X-ray crystallography allows to discern the differing protonation and oxidation levels of these ligands. o-Aminothiophenolates are unequivocally shown to be noninnocent ligands; the (L(ISQ))1- radical form is quite prevalent in coordination compounds and the electronic structure of a number of published complexes must be reconsidered.     

Heteropolytopic arsanylarylthiolato ligands: cis-trans isomerism of nickel(II), palladium(II), and platinum(II) complexes of 1-AsPh2-2-SHC6H4

Heteropolytopic arsanylthiolato ligands 1-AsPh(2)-2-SHC(6)H(4) (AsSH), PhAs(2-SHC(6)H(4))(2) (AsS(2)H(2)), and As(2-SHC(6)H(4))(3) (AsS(3)H(3)) have been prepared by lithiation-electrophilic substitution procedures. The 2:1 reaction of AsSH with NiCl(2)·6H(2)O, Na(2)[PdCl(4)], and [PtI(2)(cod)] (cod = 1,5-cyclooctadiene) in the presence of NEt(3) afforded the square-planar complexes trans-[Ni{(AsS)-κ(2)S,As}(2)] (1), cis-[Pd{(AsS)-κ(2)S,As}(2)] (2), trans-[Pd{(AsS)-κ(2)S,As}(2)] (3), and cis-[Pt{(AsS)-κ(2)S,As}(2)] (4). In the cases of nickel and platinum, only one isomer was isolated. With palladium, initially the cis isomer 2 is formed and undergoes slow isomerization to the trans isomer 3 in solution. Small amounts of the trinuclear complex [{PtI(1-AsPh(2)-μ-2-S-C(6)H(4)-κ(2)S,As)}(3)] (5) are also formed besides the mononuclear platinum bis-chelate complex 4. Density functional theory calculations support a dissociative mechanism for the isomerization of the palladium(II) complexes.