Synthesis, experimental and theoretical characterization of palladium(II) and platinum(II) saccharinate complexes with 2-(2-pyridyl)benzimidazole

New palladium(II) and platinum(II) complexes of saccharinate (sac) with 2-(2-pyridyl)benzimidazole (pybim) have been synthesized and characterized by elemental analysis and spectroscopic techniques. From the experimental studies, these complexes were formulated as [Pd(pybim)(sac)2] (1), and [Pt(pybim)(sac)2]·4H2O (2). The ground-state geometries of both complexes were optimized using density functional theory (DFT) methods at the B3LYP level. A bidentate pybim ligand together with two N-coordinated sac ligands form the square-planar MN4 coordination geometry around the palladium(II) and platinum(II) ions. The calculated IR and UV-vis spectral data have been correlated to the experimental results. Thermal analysis data support the molecular structures of both complexes.     

Tuning the electronic structures of platinum(II) complexes with a cyclometalating aryldiamine ligand

Triflate salts of four platinum(II) pyridyl complexes with a mer-coordinating tridentate pincer ligand, pip(2)NCN(-) (pip(2)NCNH = 1,3-bis(piperidylmethyl)benzene), are reported: Pt(pip(2)NCN)(L)(+) (2, L = pyridine; 3, L = 4-phenylpyridine; 5, L = 2,6-pyridinedimethanol) and [(Pt(pip(2)NCN))(2)(micro-4,4'-bipyridine)](2+) (4). The complexes have been fully characterized by (1)H NMR spectroscopy, elemental analysis, and X-ray crystallography. Compound 2(CF(3)SO(3)(-)): triclinic, P1, a = 9.7518(6) A, b = 12.0132(8) A, c = 12.6718(9) A, alpha = 114.190(2) degrees, beta = 100.745(3) degrees, gamma = 103.545(2) degrees, V = 1247.95(14) A(3), Z = 2. Compound 3(CF(3)SO(3)(-)): monoclinic, P2(1)/c, a = 15.550(2) A, b = 9.7386(11) A, c = 18.965(3) A, beta = 92.559(7) degrees, V = 2869.1(6) A(3), Z = 4. Compound 4(CF(3)SO(3)(-))(2).1/2(CH(3))(2)CO: monoclinic, I2/a, a = 21.3316(5) A, b = 9.6526(2) A, c = 26.1800(6) A, beta = 96.4930(10) degrees, V = 5356.0(2) A(3), Z = 4. Compound 5(CF(3)SO(3)(-)).3/2CHCl(3): monoclinic, P2(1)/n, a = 17.1236(10) A, b = 9.3591(5) A, c = 21.3189(11) A, beta = 96.11(3) degrees, V = 3397.2(3) A(3), Z = 4. The accumulated data indicate that the phenyl group of pip(2)NCN(-) labilizes the trans pyridyl ligand. The electronic structures were investigated using cyclic voltammetry, as well as UV-visible absorption and emission spectroscopies. Red emission from 2 in rigid media originates from a lowest triplet ligand field excited state, whereas yellow-green emissions from 3 and 4 originate from a lowest pyridyl ligand-centered triplet pi-pi state, indicating that substitution of the pyridyl ligand results in a dramatic change in the orbital character of the emissive state.     

Synthesis, molecular structures, and chemistry of some new palladium(II) and platinum(II) complexes with pentafluorophenyl ligands

A series of palladium(II) and platinum(II) complexes possessing pentafluorophenyl ligands of the general formula [M(L-L)(C6F5)Cl][space](M = Pd 3; L-L=tmeda (N,N,N',N',-tetramethylethylenediamine) a; 1,2-bis(2,6-dimethylphenylimino)ethane) b; dmpe (1,2-bis(dimethylphosphino)ethane) c; dcpe (1,2-bis(dicyclohexylphosphino)ethane) d; Pt ; L-L=tmeda a; 1,2-bis[3,5-bis(trifluoromethyl)phenylimino]-1,2-dimethylethane b; dmpe c; dcpe d) were readily synthesized from the dimer [M(C6F5)(tht)(mu-Cl)2] (M=Pd 1b, Pt 2b; tht=tetrahydrothiophene) and the corresponding bidentate ligand. In the case of palladium, the corresponding iodo analogues (6a-c) were readily synthesized in a one-pot reaction from [Pd2(dba)3], iodopentafluorobenzene, and the appropriate ligand. The platinum complexes 4c-d were then converted to the water complexes [Pt(L-L)(C6F5)(OH2)]OTf (L-L =dmpe 7a; dcpe 7b)via reaction with AgOTf in the presence of water. Attempts to convert the palladium complexes 3c-d to the corresponding water complexes resulted in the disproportionation of the intermediate water complex to form [Pd(L-L)(C6F5)2] (L-L=dmpe 8) or [Pd(L-L)2][OTf]2(L-L=dcpe 9). Upon standing in solution for prolonged periods, complex 7a undergoes an identical disproportionation reaction to the Pd analogues to form [Pt(L-L)(C6F5)2] (L-L=dmpe 10). Complexes 4c and 4d were converted to the corresponding hydrides (11b-c, respectively) using two different hydride sources: 11a was formed by the reaction of with NaBH4 in refluxing THF, while 11b was synthesized in near quantitative yield using [Cp2ZrH2] in refluxing THF. Attempts to synthesize eta2-tetrafluorobenzyne complexes [Pt(L-L)(C6F4)] (L-L=dmpe, dcpe) from reaction of 11a-b with butyllithium were unsuccessful. The molecular structures of 3a,4a, 4c, 4d, 6b, 7a, 8, 11b and have been determined by X-ray crystallographic studies, and are discussed.     

Synthesis, structural characterization, and photophysical properties of palladium and platinum(II) complexes containing 7,8-benzoquinolinate and various phosphine ligands

A series of mononuclear cyclometalated benzo[h]quinolinate platinum and palladium(II) complexes with phosphine ligands, namely, [M(bzq)ClL] (L=PPh2H, Pt 1, Pd 2; PPh2CCPh, Pt 3, Pd 4), [Pt(bzq)(PPh2H)(PPh2CCPh)]ClO4 5, [Pt(bzq)(PPh2C(Ph)=C(H)PPh2)]ClO4 6, and [Pt(bzq)(CCPh)(PPh2CCPh)] (7a, 7b), were synthesized. The X-ray crystal structures of 1, 6.CH3COCH3.1/2CH3(CH2)4CH3, and 7b.CH3COCH3 have been determined. In 1, the metalated carbon atom and the P atom are mutually cis, whereas in 7b they are trans located. For complex 6, C and N are crystallographically indistinguishable. Reaction of [Pt(bzq)(mu-Cl)]2 with PPh2H and excess of NEt3 leads to the phosphide-bridge platinum dimer [Pt(bzq)(mu-PPh2)]2 8 (X-ray). Moderate pi-pi intermolecular interactions and no evident Pt-Pt interactions are found in 1, 7b, and in 8. All of the complexes exhibit absorption bands at high energy due to the intraligand transitions (1IL pi --> pi) and absorptions at lower energy which are attributed to MLCT (5d) pi --> pi (CLambdaN) transition. Platinum complexes show strong luminescence in both solid state and frozen solutions. The influence of the coligands on the photophysics of the platinum complexes has been examined by absorption and emission spectroscopy.     

Organometallic building blocks with amino-substituted cyclopentadienyl and boratabenzene ligands for the synthesis of heterometallic complexes and clusters

A comparative study of the reactivity of isolobal rhenium and molybdenum carbonylmetallates containing a borole, in [Re(eta5-C4H4BPh)(CO)3]- (2), a boratanaphthalene, in [Mo(eta5-2,4-MeC9H6BMe)(CO)3]- (4a) and [Mo(eta5-2,4-MeC9H6BNi-Pr2)(CO)3]- (4b), a boratabenzene, in [Mo(eta5-3,5-Me2C5H3BNi-Pr2)(CO)3]- (6) or a dimethylaminocyclopentadienyl ligand, in [Mo(eta5-C5H4NMe2)(CO)3]- (7), toward palladium(II), gold(I), mercury(II) and platinum(II) complexes has allowed an evaluation of the role of these pi-bonded ligands on the structures and unprecedented coordination modes observed in the resulting metal-metal bonded, heterometallic complexes. The new metallate 6 was reacted with [AuCl(PPh3)], and with 1 or 2 equiv. HgCl2, which afforded the new heterodinuclear complexes [Au{Mo(eta5-3,5-Me2C5H3BNi-Pr2)(CO)3}(PPh3)] (Mo-Au) (10) and [Hg{Mo(eta5-3,5-Me2C5H3BNi-Pr2)(CO)3}Cl] (Hg-Mo) (11) and the heterometallic chain complex [Hg{Mo(eta5-3,5-Me2C5H3BNi-Pr2)(CO)3}2] (Mo-Hg-Mo) (12), respectively. Reactions of the new metallate 7 with HgCl2, trans-[PtCl2(CNt-Bu)2] and trans-[PtCl2(NCPh)2] yielded the heterodinuclear complex [Hg{Mo(eta5-C5H4NMe2)(CO)3}Cl] (Mo-Hg) (15), the heterotrinuclear chain complexes trans-[Pt{Mo(eta5-C5H4NMe2)(CO)3}2(CNt-Bu)2] (Mo-Pt-Mo) (16) and trans-[Pt{Mo(eta5-C5H4NMe2)(CO)3}2(NCPh)2] (Mo-Pt-Mo) (17), the mononuclear complex [Mo(eta5-C5H4NMe2)(CO)3Cl] (18), the lozenge-type cluster [Mo2Pt2(eta5-C5H4NMe2)2(CO)8] (19) and the heterodinuclear complex [[upper bond 1 start]Pt{Mo(eta5-C5H4N[upper bond 1 end]Me2)(CO)3}(NCPh)Cl](Mo-Pt) (20), respectively. The complexes 11, 16, 17.2THF, 18 and 20 have been structurally characterized by X-ray diffraction and 20 differs from all other compounds in that the dimethylaminocyclopentadienyl ligand forms a bridge between the metals.     

Pt(II)-promoted [2 + 3] cycloaddition of azide to cyanopyridines: convenient tool toward heterometallic structures

The [2 + 3] cycloaddition reactions (which are greatly accelerated by microwave irradiation) of the di(azido)platinum(II) compounds cis-[Pt(N(3))(2)(PPh(3))(2)] (1) with cyanopyridines NCR (2) (R = 4-, 3-, and 2-NC(5)H(4)) give the corresponding bis(pyridyltetrazolato) complexes trans-[Pt(N(4)CR)(2)(PPh(3))(2)] (3) [R = 4-NC(5)H(4) (3a), 3-NC(5)H(4) (3b), and 2-NC(5)H(4) (3c)]. Compound 3c has been characterized as the N(1)N(2)-bonded isomer in the solid state by X-ray crystallography and represents the first bis(tetrazolato) complex of this kind. Complexes 3a and 3b have been used as metallaligands to generate heteronuclear coordination polymers in the presence of copper nitrate. A one-dimensional supramolecular architecture was obtained as the exclusive product, {trans-[Pt(2)(N(4)CR)(4)(PPh(3))(4)Cu](n)(NO(3))(2n).nH(2)O (4.nH(2)O) (R = 4-NC(5)H(4)), when 3a was employed, whereas with 3b the heteronuclear square complex trans-[Pt(N(4)CR)(2)(PPh(3))(2)Cu(NO(3))(2)(H(2)O)](2) (5) (R = 3-NC(5)H(4)), composed of Pt/Cu ions, was obtained. All the isolated complexes were characterized by IR, elemental, and (for 3b, 3c, 4, and 5) X-ray structural analyses. Complexes 3 were additionally characterized by (1)H, (13)C, and (31)P {(1)H} NMR spectroscopies.     

Stannaborate transition metal chemistry: ligand properties, reactivity, and density functional theory calculations of platinum and palladium complexes

Three stannaborate complexes of platinum(II) and a novel stannoborate palladium(II) derivative have been prepared in excellent yield. The tin transition metal bond is formed through nucleophilic substitution and the resulting complexes [Bu3MeN] [trans-[(Et3P)2Pt(SnB11H11)H]] (6), [trans-[(Et3P)2Pt(SnB11H11)(CNtBu)]] (7), [Bu3MeN]2[trans-[(Et3P)2Pt(SnB11H11)2-(CNtBu)]] (8), and [Bu3MeN][(dppe)-Pd(SnB11H11)Me] (12) (dppe = 1,2-bis-(diphenylphosphanyl)ethane) were characterized by NMR spectroscopy and elemental analysis. In the cases of the zwitterion 7, the pentacoordinated complex 9, the palladium salt 12 and [(triphos)Pt(SnB11H11)] (10) (triphos = 1,1,1-tris(diphenylphosphanylmethyl)ethane), their solid-state structures are determined by X-ray crystal structure analyses. The trans influence of the [SnB11H11] ligand is evaluated from the results of the IR spectroscopy and X-ray crystallographic structures of complexes 6, 7, and 12. The dipole moment of the zwitterion 7 is calculated by density functional theory (DFT) methods. The alignment of the dipole moments of the polar molecules 7 and 12 in the solid state is discussed.     

Platinum(II) diimine complexes with halide/pseudohalide ligands and dangling trialkylamine or ammonium groups

A series of platinum(II) complexes with the formulas Pt(diimine)(pip(2)NCNH(2))(L)(2+) [pip(2)NCNH(2)(+) = 2,6-bis(piperidiniummethyl)phenyl cation; L = Cl, Br, I, NCS, OCN, and NO(2); diimine = 1,10-phenanthroline (phen), 5-nitro-1,10-phenanthroline (NO(2)phen), and 5,5'-ditrifluoromethyl-2,2'-bipyridine (dtfmbpy)] were prepared by the treatment of Pt(pip(2)NCN)Cl with a silver(I) salt followed by the addition of the diimine and halide/pseudohalide under acidic conditions. Crystallographic data as well as (1)H NMR spectra establish that the metal center is bonded to a bidentate phenanthroline and a monodentate halide/pseudohalide. The pip(2)NCNH(2)(+) ligand with protonated piperidyl groups is monodentate and bonded to the platinum through the phenyl ring. Structural and spectroscopic data indicate that the halide/pseudohalide group (L(-)) and the metal center in Pt(phen)(pip(2)NCNH(2))(L)(2+) behave as Br?nsted bases, forming intramolecular NH···L/NH···Pt interactions involving the piperidinium groups. A close examination of the 10 structures reported here reveals linear correlations between N-H···Pt/L angles and H···Pt/L distances. In most cases, the N-H bond is directed toward the Pt-L bond, thereby giving the appearance that the proton bridges the Pt and L groups. In contrast to observations for Pt(tpy)(pip(2)NCN)(+) (tpy = 2,2';6',2"-terpyridine), the electrochemical oxidation of deprotonated adducts, Pt(diimine)(L)(pip(2)NCN), is chemically and electrochemically irreversible.     

Synthesis and preliminary DNA-binding studies of diimineplatinum(II) complexes containing 3- or 4-pyridineboronic acid

A series of platinum(II) complexes of the type [Pt(NN)(pyB)2](NO3)2 (NN = bipy, phen; pyB = 3- or 4-pyridineboronic acid) were successfully prepared and fully characterised by 1D- and 2D-multinuclear NMR spectroscopy and ESI-MS. Using VT 1H NMR spectroscopy, rotational isomers for [Pt(NN)(3-pyB)2](NO3)2 were identified and the free energies of activation for rotation of 3-pyB about the Pt-N bond were determined to be DeltaG++310) = 69.2 +/- 0.1 kJ mol(-1) and DeltaG++(305) = 66.0 +/- 0.1 kJ mol(-1) for [Pt(bipy)(3-pyB)2](NO3)2 and [Pt(phen)(3-pyB)2](NO3)2, respectively. The 3- and 4-pyB ligands readily deboronate in boiling H2O to afford [Pt(NN)(py)2](NO3)2; the structure of [Pt(phen)(py)2](2+) (as its PF6- salt) was confirmed by X-ray crystallography. Preliminary thermal denaturation studies revealed only minimal interactions between [Pt(NN)(pyB)2](NO3)2 and calf-thymus DNA and is attributed to hydroxylation of the boronic acid groups at pH 7.4 to afford the corresponding zwitterionic boronate species. This was confirmed by means of variable pH 1H and 11B{1H} NMR spectroscopy.     

Acetate-Bridged Platinum(III) Complexes Derived from Cisplatin

Oxidation of the acetate-bridged half-lantern platinum(II) complex cis-[Pt(II)(NH(3))(2)(μ-OAc)(2)Pt(II)(NH(3))(2)](NO(3))(2), [1](NO(3))(2), with iodobenzene dichloride or bromine generates the halide-capped platinum(III) species cis-[XPt(III)(NH(3))(2)(μ-OAc)(2)Pt(III)(NH(3))(2)X](NO(3))(2), where X is Cl in [2](NO(3))(2) or Br in [3](NO(3))(2), respectively. These three complexes, characterized structurally by X-ray crystallography, feature short (≈2.6 ?) Pt-Pt separations, consistent with formation of a formal metal-metal bond upon oxidation. Elongated axial Pt-X distances occur, reflecting the strong trans influence of the metal-metal bond. The three structures are compared to those of other known dinuclear platinum complexes. A combination of (1)H, (13)C, (14)N, and (195)Pt NMR spectroscopy was used to characterize [1](2+)-[3](2+) in solution. All resonances shift downfield upon oxidation of [1](2+) to [2](2+) and [3](2+). For the platinum(III) complexes, the (14)N and (195)Pt resonances exhibit decreased line widths by comparison to those of [1](2+). Density functional theory calculations suggest that the decrease in the (14)N line width arises from a diminished electric field gradient at the (14)N nuclei in the higher valent compounds. The oxidation of [1](NO(3))(2) with the alternative oxidizing agent bis(trifluoroacetoxy)iodobenzene affords the novel tetranuclear complex cis-[(O(2)CCF(3))Pt(III)(NH(3))(2)(μ-OAc)(2)Pt(III)(NH(3))(μ-NH(2))](2)(NO(3))(4), [4](NO(3))(4), also characterized structurally by X-ray crystallography. In solution, this complex exists as a mixture of species, the identities of which are proposed.     

Covalent and noncovalent interactions for [metal(dien)nucleobase](2+) complexes with L-tryptophan derivatives: formation of palladium-tryptophan species by nucleobase substitution under biologically relevant conditions

The interaction of the complexes [Pd(dien)(1-MeCyt)]2+ (2) and [Pd(dien)(9-EtGH)]2+ (3) with the amino acids L-tryptophan (Trp) and N-acetyltryptophan (N-AcTrp) was studied and compared with the previously studied platinum analogues [Pt(dien)(1-MeCyt)]2+ (4) and [Pt(dien)(9-EtGH)]2+ (5). Solid-state structures for 2 and 4 are reported. For the palladium complexes, the interaction is pH sensitive. Below pH 5, the noncovalent interaction with stacking between the aromatic amino acid residue and the metalated nucleobase was observed. Fluorescence quenching experiments indicated similar association constants for platinum and palladium derivatives 2-5. Unusual substitution of the model nucleobases 1-methylcytosine (1-MeCyt) and 9-ethylguanine (9-EtGH) by tryptophan was observed in the range of pH 5-11. The resulting species [Pd(dien)(Trp)]+ (6) and [Pd(dien)(N-AcTrp)]+ (7) were characterized using 1H NMR, 13C NMR, and ESI-MS spectroscopy with coordination indicated through the amino and deprotonated amido nitrogens, respectively. Complexes 6 and 7 were also obtained from a solution of [Pd(dien)Cl]+ (1) incubated with either Trp or N-AcTrp, respectively.     

Synthesis and characterization of amidate bridged dimeric and oligomeric platinum complexes having short platinum-platinum interactions

A number of pivalamidate bridged dinuclear [PtII2(RNH2)4(NHCOtBu)2]2+, [PtIII2LL (RNH2)4(NHCOtBu)2]n+ (2RNH2 = 2NH3, 1,2-ethylenediamine, 1,2-diaminocyclohexane; L, L' = NO3-, H2O, or ketonate), trinuclear [{PtII(dap)(NHCOtBu)2}2PdIII]3+ (dap = 1,2-diaminopropane), tetranuclear [{PtII2(NH3)2(DACH)(NHCOtBu)2}2]4+ (DACH = 1,2-diaminocyclohexane), pentanuclear [{Pt2(C5H7O)(NH3)2Cl2(NHCOtBu)2}2PtCl4], and hexanuclear [Pt2(NH3)2(en)(NHCOtBu)2Pt(NO2)4]2 platinum complexes containing Pt(II)-Pt(II), Pt(II)-Pt(III), Pt(II)-Pd(III), and Pt(III)-Pt(III) interactions have been prepared and structurally characterized. The Pt-Pt interactions are characteristic of covalent, dative, or orbital symmetric Pt-Pt bonds. The dimeric Pt(III) complexes are able to activate C-H bonds of ketones to afford ketonate platinum(III) complexes. The Pt-Pt bonds are either doubly amidate-bridged or ligand unsupported. Their distances are 2.99-3.22 A for Pt(II)-Pt(II), 2.59-2.72 A for Pt(III)-Pt(III), 2.98 A for Pt(II)-Pt(III), and 2.66 A for Pt(II)-Pd(III) bonds depending on the oxidation states of the two metals and the ancillary ligands.     

Structural investigations of palladium(II) and platinum(II) complexes of salicylhydroxamic acid

Complexes of salicylhydroxamic acid (shaH) with palladium(II) and platinum(II) were investigated. The synthesis of [Pt(sha)(2)] was attempted via a number of methods, and ultimately (1)H NMR investigations revealed that salicylhydroxamate would not coordinate to chloro complexes of platinum(II). However, [Pt(sha-H)(PPh(3))(2)] was successfully synthesized and the crystal structure determined (orthorhombic, space group Pca2(1) a = 17.9325(19) A, b = 11.3102(12) A, c = 18.2829(19) A, Z = 4, R = 0.0224). The sha binds via an [O,O] binding mode, in its hydroximate form. In contrast the palladium complex [Pd(sha)(2)] was readily synthesized and crystallized as [Pd(sha)(2)](DMF)(4) in the triclinic space group P(-)1,a = 7.066(1) A, b = 9.842(2) A, c = 12.385(2) A, alpha = 99.213(3)(o), beta = 90.669(3), gamma = 109.767(3)(o), Z = 1, R = 0.037. The unexpected [N,O'] binding mode of the salicylhydroxamate ligand in [Pd(sha)(2)] prompted investigation of the stability of a number of binding modes of salicylhydroxamic acid in [M(sha)(2)] (M = Pd, Pt) by density functional theory, using the B3LYP hybrid functional at the 6-311G* level of theory. Geometry optimizations were carried out for various binding modes of the ligands and their relative energies established. It was found that the [N,O'] mode gave the more stable complex, in accord with experimental observations. Stabilization of hydroxamate binding to platinum is evidently afforded by soft ligands lying trans to them.     

Hydrolytic metal-mediated coupling of dialkylcyanamides at a Pt(IV) center giving a new family of diimino ligands

Addition of excess R(2)NCN to an aqueous solution of K(2)[PtCl(4)] led to the precipitation of [PtCl(2)(NCNR(2))(2)] (R(2) = Me(2) 1; Et(2) 2; C(5)H(10) 3; C(4)H(8)O, 4) in a cis/trans isomeric ratio which depends on temperature. Pure isomers cis-1-3 and trans-1-3 were separated by column chromatography on SiO(2), while trans-4 was obtained by recrystallization. Complexes cis-1-3 isomerize to trans-1-3 on heating in the solid phase at 110 degrees C; trans-1 has been characterized by X-ray crystallography. Chlorination of the platinum(II) complexes cis-1-3 and trans-1-4 gives the appropriate platinum(IV) complexes [PtCl(4)(NCNR(2))(2)] (cis-5-7 and trans-5-8). The compound cis-6 was also obtained by treatment of [PtCl(4)(NCMe)(2)] with neat Et(2)NCN. The platinum(IV) complex trans-[PtCl(4)(NCNMe(2))(2)] (trans-5) in a mixture of undried Et(2)O and CH(2)Cl(2) undergoes facile hydrolysis to give trans-[PtCl(4)[(H)=C(NMe(2))OH](2)] (9; X-ray structure has been determined). The hydrolysis went to another direction with the cis-[PtCl(4)(NCNR(2))(2)] (cis-5-7) which were converted to the metallacycles [PtCl(4)[NH=C(NR(2))OC(NR(2))=NH]] (11-13) due to the unprecedented hydrolytic coupling of the two adjacent dialkylcyanamide ligands giving a novel (for both coordination and organic chemistry) diimino linkage. Compounds 11-13 and also 14 (R(2) = C(4)H(8)O) were alternatively obtained by the reaction between cis-[PtCl(4)(MeCN)(2)] and neat undried NCNR(2). The structures of complexes 11, 13, and 14 were determined by X-ray single-crystal diffraction. All the platinum compounds were additionally characterized by elemental analyses, FAB mass-spectrometry, and IR and (1)H and (13)C[(1)H] NMR spectroscopies.     

Synthesis, carbohydrate- and DNA-binding studies of cationic 2,2':6',2'-terpyridineplatinum(II) complexes containing N- and S-donor boronic acid ligands

A series of platinum(II) complexes of the type [Pt(trpy)L](NO(3))(n) (L = 3- or 4-pyridineboronic acid (3- or 4-pyB, respectively), n = 2; HL = 4-mercaptophenylboronic acid (HmpB), n = 1; trpy = 2,2':6',2'-terpyridine) and [{Pt(trpy)}(2)(μ-pzB)](NO(3))(3) (HpzB = 4-pyrazoleboronic acid) were synthesized and fully characterized by means of multinuclear ((1)H, (13)C, (11)B, and (195)Pt) 1D- and 2D-NMR spectroscopy and elemental analysis. The triflate derivatives [Pt(trpy)(4-pyB)](OTf)(2) and [{Pt(trpy)}(2)(μ-pzB)](OTf)(3) were also prepared, and their molecular structures were confirmed by X-ray crystallography. Variable pH (1)H NMR spectroscopy showed that hydroxylation of the boronic acid group occurs in aqueous solution at pH > 5 and the pK(a) values for the complexes were determined. In buffered aqueous solution (pH 7.4), the complexes bind strongly to simple diols such as catechol and monosaccharides including D-fructose, D-ribose, D-sorbitol and D-mannitol, as determined by isothermal titration calorimetry (ITC). The equilibrium binding constants for these reactions were determined and were found to exceed those of organic boronic acids such as phenylboronic acid by an order of magnitude or greater, an effect that can be directly attributed to the cationic charge of the complexes. 2D-NMR methods (HSQC and HMBC) were used to elucidate the structures of the carbohydrate adducts [Pt(trpy)(3-pyB)]·D-fructose·NO(3) and [Pt(trpy)(4-pyB)]·D-fructose·NO(3) in aqueous solution. DNA-binding experiments with calf-thymus DNA (CT-DNA) indicate an avid DNA-binding interaction by the mononuclear complexes, as determined using thermal melting methods and ITC, but the behaviour of the dinuclear species [{Pt(trpy)}(2)(μ-pzB)](NO(3))(3) is complicated and could not be modeled adequately; higher ionic strength solutions and lower temperatures resulted in a similar DNA binding interaction to the mononuclear complexes. The presence of excess d-fructose did not significantly affect the binding of the platinum(II)-trpy complexes to CT-DNA.     

Comparative bonding behavior of functional cyclopentadienyl ligands and boron-containing analogues in heterometallic complexes and clusters

The reactivity of isolobal molybdenum carbonylmetalates containing a 2-boratanaphthalene, [Mo(eta5-2,4-MeC9H6BMe)(CO)3]- (5a) and [Mo(eta5-2,4-MeC9H6BNi-Pr2)(CO)3]- (5b), a 1-boratabenzene, [Mo(eta5-3,5-Me2C5H3BNi-Pr2)(CO)3]- (8), or a functionalized cyclopentadienyl ligand, the new metalate [Mo(eta5-C5H4Ph)(CO)3]- (7) and [Mo(eta5-C5H4NMe2)(CO)3]- (9), toward palladium (I and II) or platinum (I and II) complexes, such as trans-[PdCl2(NCPh)2], [Pd2(NCMe)6](BF4)2, trans-[PtCl2(PEt3)2], and [N(n-Bu)4]2 [Pt2Cl4(CO)2], has been investigated, and this has allowed an evaluation of the influence of the pi-bonded ligands on the structures and unprecedented coordination modes observed in the resulting metal-metal-bonded heterometallic clusters. The new 58 CVE planar-triangulated centrosymmetric clusters, [Mo2Pd2(eta5-C5H4Ph)2(CO)6(PEt3)2] (11), [Mo2Pd2(eta5-2,4-MeC9H6BNi-Pr2)2(CO)6] (12), [Mo(2)Pd(2)(eta5-3,5-Me2C5H3BNi-Pr2)2(CO)6] (13), [Mo2Pd2(eta5-C5H4NMe2)2(CO)6(PEt3)2] (15), [Mo2Pt2(eta5-C5H4NMe2)2(CO)6(PEt3)2] (16), and [Mo2Pt2(eta5-C5H4NMe2)2(CO)8] (20), have been characterized by single-crystal X-ray diffraction. Their structural features were compared with those of the 54 CVE cluster [Re2Pd2(eta5-C4H4BPh)2(CO)6)] (4), previously obtained from the borole-containing metalate [Re(eta5-C4H4BPh)(CO)3]- (2), in which a 2e-3c B-C(ipso)-Pd interaction involving the pi-ring was observed. As an extension of what has been observed in 4, clusters 12 and 13 present a direct interaction of the boratanaphthalene (12) and the boratabenzene (13) ligands with palladium. In clusters 11, 15, 16, and 20, the pi-ring does not interact with the palladium (11 and 15) or platinum centers (16 and 20), which confers to these clusters a geometry very similar to that of [Mo2Pd2(eta5-C5H5)2(CO)6(PEt3)2] (3b). The carbonylmetalates [Mo(pi-ring)(CO)3]- are thus best viewed as formal four electron donors which bridge a dinuclear d9-d9 unit. The orientation of this building block in the clusters influences the shape of their metal cores and the bonding mode of the bridging carbonyl ligands. The crystal structure of new centrosymmetric complex [Mo(eta5-C5H4Ph)(CO)3]2 (10) was determined, and it revealed intramolecular contacts of 2.773(4) A between the carbon atoms of carbonyl groups across the metal-metal bond and intermolecular bifurcated interactions between the carbonyl oxygen atoms (2.938(4) and 3.029(4) A), as well as intermolecular C-H...pi(Ar)(C=C) interactions (2.334(3) and 2.786(4) A) involving the phenyl substituents.     

Effects of the intramolecular NH...S hydrogen bond in mononuclear platinum(II) and palladium(II) complexes with 2,2'-bipyridine and benzenethiol derivatives

A series of complexes, [M(bpy)(SAr)2] (M = platinum(II) or palladium(II), bpy = 2,2'-bipyridine, SAr = 2- or 4-(acylamino)benzenethiolate, or 2-(alkylcarbamoyl)benzenethiolate), were synthesized and characterized on the basis of 1H NMR, IR, and electrochemical properties. The structures of [Pt(bpy)(S-2-Ph3CCONHC6H4)2] (1) and [Pt(bpy)(S-2-t-BuNHCOC6H4)2] (3) were determined by X-ray analysis. The complexes have intramolecular NH...S hydrogen bonds between the amide NH group and the sulfur atom. A weak NH...S hydrogen bond in these complexes and [Pd(bpy)(S-2-Ph3CCONHC6H4)2] (4) is detected from the 1H NMR spectra and the IR spectra in chloroform and in the solid state. [Pt(bpy)(S-2-Ph3CCONHC6H4)2] (1) exhibits a remarkably high-energy-shifted lowest-energy band in UV-visible spectra and has a positively shifted oxidation potential. The blue-shift of 42 nm and the positive shift of +0.24 V, as compared to those of [Pt(bpy)(SC6H5)2), are due to the effect of the NH...S hydrogen bond.     

Palladium(II) and platinum(II) complexes of 6-methyl-2-acetylpyridine 3-hexamethyleneiminylthiosemicarbazones: A structural and spectral study

The reaction of 6-methyl-2-acetylpyridine 3-hexamethyleneiminyl-thiosemicarbazone, H6MAchexim, with potassium tetrachloropalladate(II) and tetrachloroplantinate(II) in methanol afforded the complexes [Pd(6MAchexim)Cl] and [Pt(6MAchexim)Cl], respectively. The X-ray crystal structure determination of both shows that anions of H6MAchexim coordinate in a planar conformation to the central palladium(II) or platinum(II) via the pyridyl nitrogen, azomethine nitrogen and thiolato sulfur atoms. The complexes have also been characterized by spectroscopic techniques (IR, UV–VIS and ¹H NMR).     

Synthesis and properties of para-substituted NCN-pincer palladium and platinum complexes

A variety of para-substituted NCN-pincer palladium(II) and platinum(II) complexes [MX(NCN-Z)] (M=Pd(II), Pt(II); X=Cl, Br, I; NCN-Z=[2,6-(CH(2)NMe(2))(2)C(6)H(2)-4-Z](-); Z=NO(2), COOH, SO(3)H, PO(OEt)(2), PO(OH)(OEt), PO(OH)(2), CH(2)OH, SMe, NH(2)) were synthesised by routes involving substitution reactions, either prior to or, notably, after metalation of the ligand. The solubility of the pincer complexes is dominated by the nature of the para substituent Z, which renders several complexes water-soluble. The influence of the para substituent on the electronic properties of the metal centre was studied by (195)Pt NMR spectroscopy and DFT calculations. Both the (195)Pt chemical shift and the calculated natural population charge on platinum correlate linearly with the sigma(p) Hammett substituent constants, and thus the electronic properties of predesigned pincer complexes can be predicted. The sigma(p) value for the para-PtI group itself was determined to be -1.18 in methanol and -0.72 in water/methanol (1/1). Complexes substituted with protic functional groups (CH(2)OH, COOH) exist as dimers in the solid state due to intermolecular hydrogen-bonding interactions.     

Special effects of ortho-isopropylphenyl groups. Diastereoisomerism in platinum(II) and palladium(II) complexes of helically chiral PAr3 ligands

The coordination chemistry of the four phosphines, P{C6H3(o-CH3)(p-Z)}3 where Z = H (1a) or OMe (1b) and P{C6H3(o-CHMe2)(p-Z)}3 Z = H (1c) or OMe (1d) with platinum(II) and palladium(II) is reported. Mononuclear complexes trans-[PdCl2L2](L = 1a,b) and trans-[PtCl2L2](L = 1a-c) have been prepared and the crystal structures of trans-[PdCl2(1b)2] and trans-[PtCl2(1c)2] as their dichloromethane solvates have been determined. The structures show that in these complexes, the ligands adopt g+ g+ a conformations. Examination of the Cambridge Structural Database confirms this to be one of only two conformer types that tri-o-tolylphosphines adopt and the only viable conformer in 4 and 6 coordinate complexes. The binuclear complexes trans-[Pd2Cl4L2](L = 1c,d) are formed even when an excess of the bulky 1c,d is used in the synthesis and the crystal structure of trans-[Pd2Cl4(1c)2] as its chloroform solvate is reported. Reaction of [PtCl2(NCBu(t))2] with 1b-d in refluxing toluene gave the cycloplatinated species [Pt2Cl2(L - H)2] where L - H is phosphine 1b-d deprotonated at one of the ortho-methyl carbon atoms. Variable temperature 31P and 1H NMR spectroscopy reveals that all the complexes reported are fluxional. The processes are analysed in terms of restricted P-C and P-M rotations that give rise to diastereoisomeric rotamers because of the helically chiral orientations of the aryl substituents. For the complexes of the bulky ligands 1c,d, rotation about the P-C bond is slow on the NMR timescale even up to 75 degrees C. The crystal structure of the cyclometallated complex [Pt2Cl2(1d - H)2] has been determined.